Preparation and development of FeS2 Quantum Dots on SiO2 nanostructures immobilized in biopolymers and synthetic polymers as nanoparticles and nanofibers catalyst for antibiotic degradation.

PubMed

Gao, Wei; Razavi, Razieh; Fakhri, Ali

2018-07-15

The FeS 2 Quantum Dots (QDs) decorated SiO 2 nanostructure were prepared by hydrothermal synthesis method. Chitosan and polypyrrole as polymers were used for the immobilization process. The characteristic structure of prepared samples was analyzed using several techniques such as X-ray diffraction, scanning and transmittance electron microscopy, photoluminescence and UV-vis spectroscopy. The mean crystallite sizes of FeS 2 QDs/SiO 2 nanocomposites, FeS 2 QDs/SiO 2 -chitosan nanocomposites and FeS 2 QDs/SiO 2 -polypyrrole nanohybrids are 56.12, 76.38, and 83.24nm, respectively. The band gap energy of FeS 2 QDs/SiO 2 nanocomposites, FeS 2 QDs/SiO 2 -chitosan nanocomposites and FeS 2 QDs/SiO 2 -polypyrrole nanohybrids were found out to be 3.0, 2.8, and 2.7eV, respectively. The photocatalysis properties were investigated by degradation of ampicillin under UV light illumination. The effect of experimental variables, such as, pH and time, on photo-degradation efficiency was studied. The results show that the three prepared samples nanopowders under UV light was in pH3 at 60min. As it could be seen that the amount of ampicillin degradation was increased with the loading of FeS 2 QDs on SiO 2 and FeS 2 QDs/SiO 2 on chitosan nanoparticles and polypyrrole nanofiber. The antibacterial experiment was investigated under visible light illumination and the FeS 2 QDs/SiO 2 -chitosan nanocomposites and FeS 2 QDs/SiO 2 -polypyrrole nanohybrids demonstrate good antibacterial compared to FeS 2 QDs/SiO 2 nanocomposites. Copyright © 2018 Elsevier B.V. All rights reserved.

Opto-electronic properties of P-doped nc-Si-QD/a-SiC:H thin films as foundation layer for all-Si solar cells in superstrate configuration

NASA Astrophysics Data System (ADS)

Kar, Debjit; Das, Debajyoti

2016-07-01

With the advent of nc-Si solar cells having improved stability, the efficient growth of nc-Si i-layer of the top cell of an efficient all-Si solar cell in the superstrate configuration prefers nc-Si n-layer as its substrate. Accordingly, a wide band gap and high conducting nc-Si alloy material is a basic requirement at the n-layer. Present investigation deals with the development of phosphorous doped n-type nanocrystalline silicon quantum dots embedded in hydrogenated amorphous silicon carbide (nc-Si-QD/a-SiC:H) hetero-structure films, wherein the optical band gap can be widened by the presence of Si-C bonds in the amorphous matrix and the embedded high density tiny nc-Si-QDs could provide high electrical conductivity, particularly in P-doped condition. The nc-Si-QDs simultaneously facilitate further widening of the optical band gap by virtue of the associated quantum confinement effect. A complete investigation has been made on the electrical transport phenomena involving charge transfer by tunneling and thermionic emission prevailing in n-type nc-Si-QD/a-SiC:H thin films. Their correlation with different phases of the specific heterostructure has been carried out for detailed understanding of the material, in order to improve its device applicability. The n-type nc-Si-QD/a-SiC:H films exhibit a thermally activated electrical transport above room temperature and multi-phonon hopping (MPH) below room temperature, involving defects in the amorphous phase and the grain-boundary region. The n-type nc-Si-QD/a-SiC:H films grown at ˜300 °C, demonstrating wide optical gap ˜1.86-1.96 eV and corresponding high electrical conductivity ˜4.5 × 10-1-1.4 × 10-2 S cm-1, deserve to be an effective foundation layer for the top nc-Si sub-cell of all-Si solar cells in n-i-p structure with superstrate configuration.

Boron doped Si rich oxide/SiO{sub 2} and silicon rich nitride/SiN{sub x} bilayers on molybdenum-fused silica substrates for vertically structured Si quantum dot solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Ziyun, E-mail: z.lin@unsw.edu.au; Wu, Lingfeng; Jia, Xuguang

2015-07-28

Vertically structured Si quantum dots (QDs) solar cells with molybdenum (Mo) interlayer on quartz substrates would overcome current crowding effects found in mesa-structured cells. This study investigates the compatibility between boron (B) doped Si QDs bilayers and Mo-fused silica substrate. Both Si/SiO{sub 2} and Si/SiN{sub x} based QDs bilayers were studied. The material compatibility under high temperature treatment was assessed by examining Si crystallinity, microstress, thin film adhesion, and Mo oxidation. It was observed that the presence of Mo interlayer enhanced the Si QDs size confinement, crystalline fraction, and QDs size uniformity. The use of B doping was preferred comparedmore » to phosphine (PH{sub 3}) doping studied previously in terms of better surface and interface properties by reducing oxidized spots on the film. Though crack formation due to thermal mismatch after annealing remained, methods to overcome this problem were proposed in this paper. Schematic diagram to fabricate full vertical structured Si QDs solar cells was also suggested.« less

Analysis of temporal evolution of quantum dot surface chemistry by surface-enhanced Raman scattering.

PubMed

Doğan, İlker; Gresback, Ryan; Nozaki, Tomohiro; van de Sanden, Mauritius C M

2016-07-08

Temporal evolution of surface chemistry during oxidation of silicon quantum dot (Si-QD) surfaces were probed using surface-enhanced Raman scattering (SERS). A monolayer of hydrogen and chlorine terminated plasma-synthesized Si-QDs were spin-coated on silver oxide thin films. A clearly enhanced signal of surface modes, including Si-Clx and Si-Hx modes were observed from as-synthesized Si-QDs as a result of the plasmonic enhancement of the Raman signal at Si-QD/silver oxide interface. Upon oxidation, a gradual decrease of Si-Clx and Si-Hx modes, and an emergence of Si-Ox and Si-O-Hx modes have been observed. In addition, first, second and third transverse optical modes of Si-QDs were also observed in the SERS spectra, revealing information on the crystalline morphology of Si-QDs. An absence of any of the abovementioned spectral features, but only the first transverse optical mode of Si-QDs from thick Si-QD films validated that the spectral features observed from Si-QDs on silver oxide thin films are originated from the SERS effect. These results indicate that real-time SERS is a powerful diagnostic tool and a novel approach to probe the dynamic surface/interface chemistry of quantum dots, especially when they involve in oxidative, catalytic, and electrochemical surface/interface reactions.

Photocurrent enhancement of SiNW-FETs by integrating protein-shelled CdSe quantum dots

NASA Astrophysics Data System (ADS)

Moh, Sang Hyun; Kulkarni, Atul; San, Boi Hoa; Lee, Jeong Hun; Kim, Doyoun; Park, Kwang Su; Lee, Min Ho; Kim, Taesung; Kim, Kyeong Kyu

2016-01-01

We proposed a new strategy to increase the photoresponsivity of silicon NW field-effect transistors (FETs) by integrating CdSe quantum dots (QDs) using protein shells (PSs). CdSe QDs were synthesized using ClpP, a bacterial protease, as protein shells to control the size and stability of QD and to facilitate the mounting of QDs on SiNWs. The photocurrent of SiNW-FETs in response to light at a wavelength of 480 nm was enhanced by a factor of 6.5 after integrating CdSe QDs because of the coupling of the optical properties of SiNWs and QDs. As a result, the photoresponsivity to 480 nm light reached up to 3.1 × 106, the highest value compared to other SiNW-based devices in the visible light range.We proposed a new strategy to increase the photoresponsivity of silicon NW field-effect transistors (FETs) by integrating CdSe quantum dots (QDs) using protein shells (PSs). CdSe QDs were synthesized using ClpP, a bacterial protease, as protein shells to control the size and stability of QD and to facilitate the mounting of QDs on SiNWs. The photocurrent of SiNW-FETs in response to light at a wavelength of 480 nm was enhanced by a factor of 6.5 after integrating CdSe QDs because of the coupling of the optical properties of SiNWs and QDs. As a result, the photoresponsivity to 480 nm light reached up to 3.1 × 106, the highest value compared to other SiNW-based devices in the visible light range. Electronic supplementary information (ESI) available: Materials and methods. See DOI: 10.1039/c5nr07901b

Opto-electronic properties of P-doped nc-Si–QD/a-SiC:H thin films as foundation layer for all-Si solar cells in superstrate configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kar, Debjit; Das, Debajyoti, E-mail: erdd@iacs.res.in

2016-07-14

With the advent of nc-Si solar cells having improved stability, the efficient growth of nc-Si i-layer of the top cell of an efficient all-Si solar cell in the superstrate configuration prefers nc-Si n-layer as its substrate. Accordingly, a wide band gap and high conducting nc-Si alloy material is a basic requirement at the n-layer. Present investigation deals with the development of phosphorous doped n-type nanocrystalline silicon quantum dots embedded in hydrogenated amorphous silicon carbide (nc-Si–QD/a-SiC:H) hetero-structure films, wherein the optical band gap can be widened by the presence of Si–C bonds in the amorphous matrix and the embedded high densitymore » tiny nc-Si–QDs could provide high electrical conductivity, particularly in P-doped condition. The nc-Si–QDs simultaneously facilitate further widening of the optical band gap by virtue of the associated quantum confinement effect. A complete investigation has been made on the electrical transport phenomena involving charge transfer by tunneling and thermionic emission prevailing in n-type nc-Si–QD/a-SiC:H thin films. Their correlation with different phases of the specific heterostructure has been carried out for detailed understanding of the material, in order to improve its device applicability. The n-type nc-Si–QD/a-SiC:H films exhibit a thermally activated electrical transport above room temperature and multi-phonon hopping (MPH) below room temperature, involving defects in the amorphous phase and the grain-boundary region. The n-type nc-Si–QD/a-SiC:H films grown at ∼300 °C, demonstrating wide optical gap ∼1.86–1.96 eV and corresponding high electrical conductivity ∼4.5 × 10{sup −1}–1.4 × 10{sup −2} S cm{sup −1}, deserve to be an effective foundation layer for the top nc-Si sub-cell of all-Si solar cells in n-i-p structure with superstrate configuration.« less

Application of core-shell-structured CdTe@SiO2 quantum dots synthesized via a facile solution method for improving latent fingerprint detection

NASA Astrophysics Data System (ADS)

Gao, Feng; Han, Jiaxing; Lv, Caifeng; Wang, Qin; Zhang, Jun; Li, Qun; Bao, Liru; Li, Xin

2012-10-01

Fingerprint detection is important in criminal investigation. This paper reports a facile powder brushing technique for improving latent fingerprint detection using core-shell-structured CdTe@SiO2 quantum dots (QDs) as fluorescent labeling marks. Core-shell-structured CdTe@SiO2 QDs are prepared via a simple solution-based approach using NH2NH2·H2O as pH adjustor and stabilizer, and their application for improving latent fingerprint detection is explored. The obtained CdTe@SiO2 QDs show spherical shapes with well-defined core-shell structures encapsulating different amounts of QDs depending on the type of the pH adjustor and stabilizer. Moreover, the fluorescence of CdTe@SiO2 QDs is largely enhanced by surface modification of the SiO2 shell. The CdTe@SiO2 QDs overcome the oxidation problem of pure CdTe QDs in air, thus affording better variability with strong adhesive ability, better resolution, and bright emission colors for practical application in latent fingerprint detection. In comparison with the conventional fluorescence powders, silver powders, and others, the effectiveness of CdTe@SiO2 QD powders for detection of latent fingerprints present on a large variety of object surfaces is greatly improved. The synthesis method for CdTe@SiO2 QDs is simple, cheap, and easy for large-scale production, and thus offers many advantages in the practical application of fingerprint detection.

Surface chemistry and density distribution influence on visible luminescence of silicon quantum dots: an experimental and theoretical approach.

PubMed

Dutt, Ateet; Matsumoto, Yasuhiro; Santana-Rodríguez, G; Ramos, Estrella; Monroy, B Marel; Santoyo Salazar, J

2017-01-04

The impact of the surface reconstruction of the density distribution and photoluminescence of silicon quantum dots (QDs) embedded in a silicon oxide matrix (SiO x ) has been studied. Annealing treatments carried out on the as-deposited samples provoked the effusion of hydrogen species. Moreover, depending on the surrounding density and coalescence of QDs, they resulted in a change in the average size of the particles depending on the initial local environment. The shift in the luminescence spectra all over the visible region (blue, green and red) shows a strong dependence on the resultant change in the size and/or the passivation environment of QDs. Density functional theoretical (DFT) calculations support this fact and explain the possible electronic transitions (HOMO-LUMO gap) involved. Passivation in the presence of oxygen species lowers the band gap of Si 29 and Si 35 nanoclusters up to 1.7 eV, whereas, surface passivation in the environment of hydrogen species increases the band gap up to 4.4 eV. These results show a good agreement with the quantum confinement model described in this work and explain the shift in the luminescence all over the visible region. The results reported here offer vital insight into the mechanism of emission from silicon quantum dots which has been one of the most debated topics in the last two decades. QDs with multiple size distribution in different local environments (band gap) observed in this work could be used for the fabrication of light emission diodes (LEDs) or shift-conversion thin films in third generation efficient tandem solar cells for the maximum absorption of the solar spectrum in different wavelength regions.

Graphene and PbS quantum dot hybrid vertical phototransistor

NASA Astrophysics Data System (ADS)

Song, Xiaoxian; Zhang, Yating; Zhang, Haiting; Yu, Yu; Cao, Mingxuan; Che, Yongli; Dai, Haitao; Yang, Junbo; Ding, Xin; Yao, Jianquan

2017-04-01

A field-effect phototransistor based on a graphene and lead sulfide quantum dot (PbS QD) hybrid in which PbS QDs are embedded in a graphene matrix has been fabricated with a vertical architecture through a solution process. The n-type Si/SiO2 substrate (gate), Au/Ag nanowire transparent source electrode, active layer and Au drain electrode are vertically stacked in the device, which has a downscaled channel length of 250 nm. Photoinduced electrons in the PbS QDs leap into the conduction band and fill in the trap states, while the photoinduced holes left in the valence band transfer to the graphene and form the photocurrent under biases from which the photoconductive gain is evaluated. The graphene/QD-based vertical phototransistor shows a photoresponsivity of 2 × 103 A W-1, and specific detectivity up to 7 × 1012 Jones under 808 nm laser illumination with a light irradiance of 12 mW cm-2. The solution-processed vertical phototransistor provides a new facile method for optoelectronic device applications.

Enhanced photoluminescence of multilayer Ge quantum dots on Si(001) substrates by increased overgrowth temperature.

PubMed

Liu, Zhi; Cheng, Buwen; Hu, Weixuan; Su, Shaojian; Li, Chuanbo; Wang, Qiming

2012-07-11

Four-bilayer Ge quantum dots (QDs) with Si spacers were grown on Si(001) substrates by ultrahigh vacuum chemical vapor deposition. In three samples, all Ge QDs were grown at 520 °C, while Si spacers were grown at various temperatures (520 °C, 550 °C, and 580 °C). Enhancement and redshift of room temperature photoluminescence (PL) were observed from the samples in which Si spacers were grown at a higher temperature. The enhancement of PL is explained by higher effective electrons capturing in the larger size Ge QDs. Quantum confinement of the Ge QDs is responsible for the redshift of PL spectra. The Ge QDs' size and content were investigated by atomic force microscopy and Raman scattering measurements.

Light-emitting diodes based on colloidal silicon quantum dots

NASA Astrophysics Data System (ADS)

Zhao, Shuangyi; Liu, Xiangkai; Pi, Xiaodong; Yang, Deren

2018-06-01

Colloidal silicon quantum dots (Si QDs) hold great promise for the development of printed Si electronics. Given their novel electronic and optical properties, colloidal Si QDs have been intensively investigated for optoelectronic applications. Among all kinds of optoelectronic devices based on colloidal Si QDs, QD light-emitting diodes (LEDs) play an important role. It is encouraging that the performance of LEDs based on colloidal Si QDs has been significantly increasing in the past decade. In this review, we discuss the effects of the QD size, QD surface and device structure on the performance of colloidal Si-QD LEDs. The outlook on the further optimization of the device performance is presented at the end.

The curious case of exploding quantum dots: anomalous migration and growth behaviors of Ge under Si oxidation

PubMed Central

2013-01-01

We have previously demonstrated the unique migration behavior of Ge quantum dots (QDs) through Si3N4 layers during high-temperature oxidation. Penetration of these QDs into the underlying Si substrate however, leads to a completely different behavior: the Ge QDs ‘explode,’ regressing back almost to their origins as individual Ge nuclei as formed during the oxidation of the original nanopatterned SiGe structures used for their generation. A kinetics-based model is proposed to explain the anomalous migration behavior and morphology changes of the Ge QDs based on the Si flux generated during the oxidation of Si-containing layers. PMID:23618165

Enhanced photovoltaic property by forming p-i-n structures containing Si quantum dots/SiC multilayers

PubMed Central

2014-01-01

Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC multilayers prepared in a plasma-enhanced chemical vapor deposition system. The thickness of amorphous Si layer was designed to be 4 nm, and the thickness of amorphous SiC layer was kept at 2 nm. Transmission electron microscopy observation revealed the formation of Si QDs after 900°C annealing. The optical properties of the Si QDs/SiC multilayers were studied, and the optical band gap deduced from the optical absorption coefficient result is 1.48 eV. Moreover, the p-i-n structure with n-a-Si/i-(Si QDs/SiC multilayers)/p-Si was fabricated, and the carrier transportation mechanism was investigated. The p-i-n structure was used in a solar cell device. The cell had the open circuit voltage of 532 mV and the power conversion efficiency (PCE) of 6.28%. PACS 81.07.Ta; 78.67.Pt; 88.40.jj PMID:25489285

Protease sensing using nontoxic silicon quantum dots.

PubMed

Cheng, Xiaoyu; McVey, Benjamin F P; Robinson, Andrew B; Longatte, Guillaume; O'Mara, Peter B; Tan, Vincent T G; Thordarson, Pall; Tilley, Richard D; Gaus, Katharina; Justin Gooding, John

2017-08-01

Herein is presented a proof-of-concept study of protease sensing that combines nontoxic silicon quantum dots (SiQDs) with Förster resonance energy transfer (FRET). The SiQDs serve as the donor and an organic dye as the acceptor. The dye is covalently attached to the SiQDs using a peptide linker. Enzymatic cleavage of the peptide leads to changes in FRET efficiency. The combination of interfacial design and optical imaging presented in this work opens opportunities for use of nontoxic SiQDs relevant to intracellular sensing and imaging. (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

Dramatically enhanced self-assembly of GeSi quantum dots with superior photoluminescence induced by the substrate misorientation

NASA Astrophysics Data System (ADS)

Zhou, Tong; Zhong, Zhenyang

2014-02-01

A dramatically enhanced self-assembly of GeSi quantum dots (QDs) is disclosed on slightly miscut Si (001) substrates, leading to extremely dense QDs and even a growth mode transition. The inherent mechanism is addressed in combination of the thermodynamics and the growth kinetics both affected by steps on the vicinal surface. Moreover, temperature-dependent photoluminescence spectra from dense GeSi QDs on the miscut substrate demonstrate a rather strong peak persistent up to 300 K, which is attributed to the well confinement of excitons in the dense GeSi QDs due to the absence of the wetting layer on the miscut substrate.

Highly conducting and wide band gap phosphorous doped nc-Si–QD/a-SiC films as n-type window layers for solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kar, Debjit; Das, Debajyoti, E-mail: erdd@iacs.res.in

2016-05-23

Nano-crystalline silicon quantum dots (Si-QDs) embedded in the phosphorous doped amorphous silicon carbide (a-SiC) matrix has been successfully prepared at a low temperature (300 °C) by inductively coupled plasma assisted chemical vapor deposition (ICP-CVD) system from (SiH{sub 4} + CH{sub 4})-plasma with PH{sub 3} as the doping gas. The effect of PH{sub 3} flow rate on structural, optical and electrical properties of the films has been studied. Phosphorous doped nc-Si–QD/a-SiC films with high optical band gap (>1.9 eV) and superior conductivity (~10{sup −2} S cm{sup −1}) are obtained, which could be appropriately used as n-type window layers for nc-Si solarmore » cells in n-i-p configuration.« less

Conductive atomic force microscopy studies on the transformation of GeSi quantum dots to quantum rings.

PubMed

Zhang, S L; Xue, F; Wu, R; Cui, J; Jiang, Z M; Yang, X J

2009-04-01

Conductive atomic force microscopy has been employed to study the topography and conductance distribution of individual GeSi quantum dots (QDs) and quantum rings (QRs) during the transformation from QDs to QRs by depositing an Si capping layer on QDs. The current distribution changes significantly with the topographic transformation during the Si capping process. Without the capping layer, the QDs are dome-shaped and the conductance is higher at the ring region between the center and boundary than that at the center. After capping with 0.32 nm Si, the shape of the QDs changes to pyramidal and the current is higher at both the center and the arris. When the Si capping layer increases to 2 nm, QRs are formed and the current of individual QRs is higher at the rim than that at the central hole. By comparing the composition distributions obtained by scanning Auger microscopy and atomic force microscopy combined with selective chemical etching, the origin of the current distribution change is discussed.

Multilevel characteristics and memory mechanisms for nonvolatile memory devices based on CuInS{sub 2} quantum dot-polymethylmethacrylate nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Yang; Yun, Dong Yeol; Kim, Tae Whan, E-mail: twk@hanyang.ac.kr

2014-12-08

Nonvolatile memory devices based on CuInS{sub 2} (CIS) quantum dots (QDs) embedded in a polymethylmethacrylate (PMMA) layer were fabricated using spin-coating method. The memory window widths of the capacitance-voltage (C-V) curves for the Al/CIS QDs embedded in PMMA layer/p-Si devices were 0.3, 0.6, and 1.0 V for sweep voltages of ±3, ±5, and ±7 V, respectively. Capacitance-cycle data demonstrated that the charge-trapping capability of the devices with an ON/OFF ratio value of 2.81 × 10{sup −10} was maintained for 8 × 10{sup 3} cycles without significant degradation and that the extrapolation of the ON/OFF ratio value to 1 × 10{sup 6} cycles converged to 2.40 × 10{sup −10}, indicative ofmore » the good stability of the devices. The memory mechanisms for the devices are described on the basis of the C-V curves and the energy-band diagrams.« less

Spontaneous emission of semiconductor quantum dots in inverse opal SiO2 photonic crystals at different temperatures.

PubMed

Yang, Peng; Yang, Yingshu; Wang, Yinghui; Gao, Jiechao; Sui, Ning; Chi, Xiaochun; Zou, Lu; Zhang, Han-Zhuang

2016-02-01

The photoluminescence (PL) characteristics of CdSe quantum dots (QDs) infiltrated into inverse opal SiO2 photonic crystals (PCs) are systemically studied. The special porous structure of inverse opal PCs enhanced the thermal exchange rate between the CdSe QDs and their surrounding environment. Finally, inverse opal SiO2 PCs suppressed the nonlinear PL enhancement of CdSe QDs in PCs excited by a continuum laser and effectively modulated the PL characteristics of CdSe QDs in PCs at high temperatures in comparison with that of CdSe QDs out of PCs. The final results are of benefit in further understanding the role of inverse opal PCs on the PL characteristics of QDs. Copyright © 2015 John Wiley & Sons, Ltd.

Structural, morphological and optical properties of PEDOT:PSS/QDs nano-composite films prepared by spin-casting

NASA Astrophysics Data System (ADS)

Najeeb, Mansoor Ani; Abdullah, Shahino Mah; Aziz, Fakhra; Ahmad, Zubair; Rafique, Saqib; Wageh, S.; Al-Ghamdi, Ahmed A.; Sulaiman, Khaulah; Touati, Farid; Shakoor, R. A.; Al-Thani, N. J.

2016-09-01

This paper describes the structural, morphological and optical properties of the nano-composite of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and quantum dots (QDs). The ZnSe and CdSe QDs have been synthesized, with the aid of Mercaptoacetic acid (MAA), by a colloidal method with an average size of 5 to 7 nm. QDs have been embedded in PEDOT:PSS using a simple solution processing approach and has been deposited as thin films by spin coating technique. The QDs embedded PEDOT:PSS enhances the light absorption spectra of samples, prominently in terms of absorption intensity which may consequently improve sensitivity of the optoelectronic devices.

Resonant inelastic light scattering and photoluminescence in isolated nc-Si/SiO{sub 2} quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bairamov, F. B., E-mail: Bairamov@mail.ioffe.ru; Toporov, V. V.; Poloskin, E. D.

2013-05-15

Observation at the room temperature the spectra of the resonant inelastic light scattering by the spatially confined optical phonons as well as the excitonic luminescence caused by confinement effects in the ensemble of isolated quantum dots (QDs) nc-Si/SiO{sub 2} is reported. It is shown that the samples investigated are high purity and high crystalline perfection quality nc-Si/SiO{sub 2} QDs without amorphous phase {alpha}-Si and contaminants. Comparison between the experimental data obtained and phenomenological model of the strong space confinement of optical phonons revealed the need of the more accurate form of the weighted function for the confinement of optical phonons.more » It is shown that simultaneous detection of the inelastic light scattering by the confinement of phonons and the excitonic luminescence spectra by the confined electron-hole pairs in the nc-Si/SiO{sub 2} QDs allows selfconsistently to determine more accurate values of the diameter of the nc-Si/SiO{sub 2} QDs.« less

Freestanding silicon quantum dots: origin of red and blue luminescence.

PubMed

Gupta, Anoop; Wiggers, Hartmut

2011-02-04

In this paper, we studied the behavior of silicon quantum dots (Si-QDs) after etching and surface oxidation by means of photoluminescence (PL) measurements, Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance spectroscopy (EPR). We observed that etching of red luminescing Si-QDs with HF acid drastically reduces the concentration of defects and significantly enhances their PL intensity together with a small shift in the emission spectrum. Additionally, we observed the emergence of blue luminescence from Si-QDs during the re-oxidation of freshly etched particles. Our results indicate that the red emission is related to the quantum confinement effect, while the blue emission from Si-QDs is related to defect states at the newly formed silicon oxide surface.

Microscopic origin of the fast blue-green luminescence of chemically synthesized non-oxidized silicon quantum dots.

PubMed

Dohnalová, Kateřina; Fučíková, Anna; Umesh, Chinnaswamy P; Humpolíčková, Jana; Paulusse, Jos M J; Valenta, Jan; Zuilhof, Han; Hof, Martin; Gregorkiewicz, Tom

2012-10-22

The microscopic origin of the bright nanosecond blue-green photoluminescence (PL), frequently reported for synthesized organically terminated Si quantum dots (Si-QDs), has not been fully resolved, hampering potential applications of this interesting material. Here a comprehensive study of the PL from alkyl-terminated Si-QDs of 2-3 nm size, prepared by wet chemical synthesis is reported. Results obtained on the ensemble and those from the single nano-object level are compared, and they provide conclusive evidence that efficient and tunable emission arises due to radiative recombination of electron-hole pairs confined in the Si-QDs. This understanding paves the way towards applications of chemical synthesis for the development of Si-QDs with tunable sizes and bandgaps. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Near-infrared luminescent cubic silicon carbide nanocrystals for in vivo biomarker applications: an ab initio Study

NASA Astrophysics Data System (ADS)

Gali, Adam; Zólyomi, Viktor; Somogyi, Bálint

2013-03-01

Small molecule-sized fluorescent emitters are needed as probes to image and track the locations of targeted nano-sized objects with minimal perturbation, and are much sought-after to probe biomolecules in living cells. For in vivo biological imaging, fluorescent biomarkers have to meet the following stringent requirements: (i) they should be non-toxic and bioinert, (ii) their hydrodynamical size should be sufficiently small for clearance, (iii) they should be photo-stable. Furthermore, it is highly desirable that (iv) they have intense, stable emission in the near-infrared range, and (v) they can be produced in relatively large amount for biological studies. Here we report time-density functional calculations on SiC-based QDs in the aspect of in vivo biological imaging applications. We find that Si-vacancy, divacancy, as well as single metal dopants such as Vanadium (V), Molybdenum (Mo) and Tungsten (W) in molecule-sized (1-2 nm) SiC QDs emit light efficiently in the near-infrared range. Furthermore, their emission wavelength varies on the size of host SiC QDs at less extent than that of pristine SiC QDs, thus sharper emission spectrum is expected even in a disperse size distribution of these QDs. These fluorescent SiC QDs are paramagnetic in the ground state. EU FP7 DIAMANT (Grant No. 270197)

Photoluminescence Spectra From The Direct Energy Gap of a-SiQDs

NASA Astrophysics Data System (ADS)

Abdul-Ameer, Nidhal M.; Abdulrida, Moafak C.; Abdul-Hakeem, Shatha M.

2018-05-01

A theoretical model for radiative recombination in amorphous silicon quantum dots (a-SiQDs) was developed. In this model, for the first time, the coexistence of both spatial and quantum confinements were considered. Also, it is found that the photoluminescence exhibits significant size dependence in the range (1-4) nm of the quantum dots. a-SiQDs show visible light emission peak energies and high radiative quantum efficiency at room temperature,in contrast to bulk a-Si structures. The quantum efficiency is sensitive to any change in defect density (the volume nonradiative centers density and/or the surface nonradiative centers density) but, with small dots sizes, the quantum efficiency is insensitive to such defects. Our analysis shows that the photoluminescence intensity increases or decreases by the effect of radiative quantum efficiency. By controlling the size of a-SiQDs, we note that the energy of emission can be tuned. The blue shift is attributed to quantum confinement effect. Meanwhile, the spatial confinement effect is clearly observed in red shift in emission spectra. we found a good agreement with the experimental published data. Therefore, we assert that a-SiQDs material is a promising candidate for visible, tunable, and high performance devices of light emitting.

Direct growth of Ge quantum dots on a graphene/SiO2/Si structure using ion beam sputtering deposition.

PubMed

Zhang, Z; Wang, R F; Zhang, J; Li, H S; Zhang, J; Qiu, F; Yang, J; Wang, C; Yang, Y

2016-07-29

The growth of Ge quantum dots (QDs) using the ion beam sputtering deposition technique has been successfully conducted directly on single-layer graphene supported by SiO2/Si substrate. The results show that the morphology and size of Ge QDs on graphene can be modulated by tuning the Ge coverage. Charge transfer behavior, i.e. doping effect in graphene has been demonstrated at the interface of Ge/graphene. Compared with that of traditional Ge dots grown on Si substrate, the positions of both corresponding photoluminescence (PL) peaks of Ge QDs/graphene hybrid structure undergo a large red-shift, which can probably be attributed to the lack of atomic intermixing and the existence of surface states in this hybrid material. According to first-principles calculations, the Ge growth on the graphene should follow the so-called Volmer-Weber mode instead of the Stranski-Krastanow one which is observed generally in the traditional Ge QDs/Si system. The calculations also suggest that the interaction between Ge and graphene layer can be enhanced with the decrease of the Ge coverage. Our results may supply a prototype for fabricating novel optoelectronic devices based on a QDs/graphene hybrid nanostructure.

Quantum confinement effect in 6H-SiC quantum dots observed via plasmon-exciton coupling-induced defect-luminescence quenching

NASA Astrophysics Data System (ADS)

Guo, Xiaoxiao; Zhang, Yumeng; Fan, Baolu; Fan, Jiyang

2017-03-01

The quantum confinement effect is one of the crucial physical effects that discriminate a quantum material from its bulk material. It remains a mystery why the 6H-SiC quantum dots (QDs) do not exhibit an obvious quantum confinement effect. We study the photoluminescence of the coupled colloidal system of SiC QDs and Ag nanoparticles. The experimental result in conjunction with the theoretical calculation reveals that there is strong coupling between the localized electron-hole pair in the SiC QD and the localized surface plasmon in the Ag nanoparticle. It results in resonance energy transfer between them and resultant quenching of the blue surface-defect luminescence of the SiC QDs, leading to uncovering of a hidden near-UV emission band. This study shows that this emission band originates from the interband transition of the 6H-SiC QDs and it exhibits a remarkable quantum confinement effect.

Cd-free Cu-Zn-In-S/ZnS quantum dots@SiO2 multiple cores nanostructure: preparation and application for white LEDs

NASA Astrophysics Data System (ADS)

Jiang, Tongtong; Shen, Mohan; Dai, Peng; Wu, Mingzai; Yu, Xinxin; Li, Guang; Xu, Xiaoliang; Zeng, Haibo

2017-10-01

The work reports the fabrication of Cu doped Zn-In-S (CZIS) alloy quantum dots (QDs) using dodecanethiol and oleic acid as stabilizing ligands. With the increase of doped Cu element, the photoluminescence (PL) peak is monotonically red shifted. After coating ZnS shell, the PL quantum yield of CZIS QDs can reach 78%. Using reverse micelle microemulsion method, CZIS/ZnS QDs@SiO2 multi-core nanospheres were synthesized to improve the colloidal stability and avoid the aggregation of QDs. The obtained multi-core nanospheres were dispersed in curing adhesive, and applied as a color conversion layer in down converted light-emitting diodes. After encapsulation in curing adhesive, the newly designed LEDs show artifically regulated color coordinates with varying the weight ratio of green QDs and red QDs, and the concentrations of these two types of QDs. Moreover, natural white and warm white LEDs with correlated color temperature of 5287, 6732, 2731, and 3309 K can be achieved, which indicates that CZIS/ZnS QDs@SiO2 nanostructures are promising color conversion layer material for solid-state lighting application.

Characterization of CuCl quantum dots grown in NaCl single crystals via optical measurements, X-ray diffraction, and transmission electron microscopy

NASA Astrophysics Data System (ADS)

Miyajima, Kensuke; Akatsu, Tatsuro; Itoh, Ken

2018-05-01

We evaluated the crystal size, shape, and alignment of the lattice planes of CuCl quantum dots (QDs) embedded in NaCl single crystals by optical measurements, X-ray diffraction (XRD) patterns, and transmission electron microscopy (TEM). We obtained, for the first time, an XRD pattern and TEM images for CuCl QDs in NaCl crystals. The XRD pattern showed that the lattice planes of the CuCl QDs were parallel to those of the NaCl crystals. In addition, the size of the QDs was estimated from the diffraction width. It was apparent from the TEM images that almost all CuCl QDs were polygonal, although some cubic QDs were present. The mean size and size distribution of the QDs were also obtained. The dot size obtained from optical measurements, XRD, and TEM image were almost consistent. Our new findings can help to reveal the growth mechanism of semiconductor QDs embedded in a crystallite matrix. In addition, this work will play an important role in progressing the study of optical phenomena originating from assembled semiconductor QDs.

TiO2 activity enhancement through synergistic effect of photons localization of photonic crystals and the sensitization of CdS quantum dots

NASA Astrophysics Data System (ADS)

Li, Ping; Wang, Yuan; Wang, Ai-Jun; Chen, Sheng-Li

2017-02-01

In this work, the enhancement of TiO2 photocatalytic activity was studied through synergistic effect of the photons localization of photonic crystals and the sensitization of CdS quantum dots (CdS QDs). CdS QDs sensitized TiO2 membrane (denoted as CdS QDs/TiO2) was synthesized through doping the TiO2 membrane with CdS QDs by chemical bath deposition method (CBD). After TiO2 was sensitized with CdS QDs, the edge of light absorption of TiO2 was red-shifted to 470 nm and the light absorption in the range of 400 600 nm was higher than that of plain TiO2 membrane. Another type of composite membrane, CdS QDs/TiO2/SiO2 opal composite membrane was prepared by coupling SiO2 opal (a kind of photonic crystal) layer onto the CdS QDs/TiO2 membrane, and the photonic band gap of the SiO2 opal photonic crystal layer was deliberately planned at the electronic band gap of the CdS QDs. The photodegradation of gaseous CH3CHO (acetaldehyde) was used as probe reaction to test the photocatalytic activity of the as-prepared membranes, and the results showed that the CdS QDs sensitization can significantly improve the photocatalytic activity of TiO2 membrane under visible light irradiation, with the acetaldehyde degradation rate constant (k) on CdS QDs/TiO2 membranes being 1.59 times of that on plain TiO2 membranes. The acetaldehyde degradation rate constant on CdS QDs/TiO2/SiO2 opal composite membrane reached 4 times of that on plain TiO2 membrane. The photocatalytic activity of TiO2 membrane can be improved through synergistic effect of the photons localization of photonic crystals and the sensitization of CdS QDs.

Toward precise site-controlling of self-assembled Ge quantum dots on Si microdisks.

PubMed

Wang, Shuguang; Zhang, Ningning; Chen, Peizong; Wang, Liming; Yang, Xinju; Jiang, Zuimin; Zhong, Zhenyang

2018-08-24

A feasible route is developed toward precise site-controlling of quantum dots (QDs) at the microdisk periphery, where most microdisk cavity modes are located. The preferential growth of self-assembled Ge QDs at the periphery of Si microdisks is discovered. Moreover, both the height and linear density of Ge QDs can be controlled by tuning the amount of deposited Ge and the microdisk size. The inherent mechanisms of these unique features are discussed, taking into account both the growth kinetics and thermodynamics. By growing Ge on the innovative Si microdisks with small protrusions at the disk periphery, the positioning of Ge QDs at the periphery can be exactly predetermined. Such a precise site-controlling of Ge QDs at the periphery enables the location of the QD right at the field antinodes of the cavity mode of the Si microdisk, thereby achieving spatial matching between QD and cavity mode. These results open a promising door to realize the semiconductor QD-microdisk systems with both spectral and spatial matching between QDs and microdisk cavity modes, which will be the promising candidates for exploring the fundamental features of cavity quantum electrodynamics and the innovative optoelectronic devices based on strong light-matter interaction.

Single step deposition of an interacting layer of a perovskite matrix with embedded quantum dots

NASA Astrophysics Data System (ADS)

Ngo, Thi Tuyen; Suarez, Isaac; Sanchez, Rafael S.; Martinez-Pastor, Juan P.; Mora-Sero, Ivan

2016-07-01

Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and electroluminescence experiments. The radiative exciplex relaxation is centered in the near infrared region (NIR), ~1200 nm, which corresponds to lower energies than the corresponding band gap of both perovskite (PS) and QDs. Our approach allows the fabrication of multi-wavelength light emitting diodes (LEDs) based on a PS matrix with embedded QDs, which show considerably low turn-on potentials. The presence of the exciplex state of PS and QDs opens up a broad range of possibilities with important implications in both LEDs and solar cells.Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and electroluminescence experiments. The radiative exciplex relaxation is centered in the near infrared region (NIR), ~1200 nm, which corresponds to lower energies than the corresponding band gap of both perovskite (PS) and QDs. Our approach allows the fabrication of multi-wavelength light emitting diodes (LEDs) based on a PS matrix with embedded QDs, which show considerably low turn-on potentials. The presence of the exciplex state of PS and QDs opens up a broad range of possibilities with important implications in both LEDs and solar cells. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr04082a

Bioconjugation of luminescent silicon quantum dots to gadolinium ions for bioimaging applications

NASA Astrophysics Data System (ADS)

Erogbogbo, Folarin; Chang, Ching-Wen; May, Jasmine L.; Liu, Liwei; Kumar, Rajiv; Law, Wing-Cheung; Ding, Hong; Yong, Ken Tye; Roy, Indrajit; Sheshadri, Mukund; Swihart, Mark T.; Prasad, Paras N.

2012-08-01

Luminescent imaging agents and MRI contrast agents are desirable components in the rational design of multifunctional nanoconstructs for biological imaging applications. Luminescent biocompatible silicon quantum dots (SiQDs) and gadolinium chelates can be applied for fluorescence microscopy and MRI, respectively. Here, we report the first synthesis of a nanocomplex incorporating SiQDs and gadolinium ions (Gd3+) for biological applications. The nanoconstruct is composed of a PEGylated micelle, with hydrophobic SiQDs in its core, covalently bound to DOTA-chelated Gd3+. Dynamic light scattering reveals a radius of 85 nm for these nanoconstructs, which is consistent with the electron microscopy results depicting radii ranging from 25 to 60 nm. Cellular uptake of the probes verified that they maintain their optical properties within the intracellular environment. The magnetic resonance relaxivity of the nanoconstruct was 2.4 mM-1 s-1 (in terms of Gd3+ concentration), calculated to be around 6000 mM-1 s-1 per nanoconstruct. These desirable optical and relaxivity properties of the newly developed probe open the door for use of SiQDs in future multimodal applications such as tumour imaging.Luminescent imaging agents and MRI contrast agents are desirable components in the rational design of multifunctional nanoconstructs for biological imaging applications. Luminescent biocompatible silicon quantum dots (SiQDs) and gadolinium chelates can be applied for fluorescence microscopy and MRI, respectively. Here, we report the first synthesis of a nanocomplex incorporating SiQDs and gadolinium ions (Gd3+) for biological applications. The nanoconstruct is composed of a PEGylated micelle, with hydrophobic SiQDs in its core, covalently bound to DOTA-chelated Gd3+. Dynamic light scattering reveals a radius of 85 nm for these nanoconstructs, which is consistent with the electron microscopy results depicting radii ranging from 25 to 60 nm. Cellular uptake of the probes verified that they maintain their optical properties within the intracellular environment. The magnetic resonance relaxivity of the nanoconstruct was 2.4 mM-1 s-1 (in terms of Gd3+ concentration), calculated to be around 6000 mM-1 s-1 per nanoconstruct. These desirable optical and relaxivity properties of the newly developed probe open the door for use of SiQDs in future multimodal applications such as tumour imaging. Electronic supplementary information (ESI) available: SEM images of MSiQD-Gd3+, DLS plot of MSiQD-NH2, images of Gd3+-functionalized Si QDs micelles in water, plot of percentages of Gd3+ leaked from original sample, and determination of free Gd3+ in solutions of Gd chelates. See DOI: 10.1039/c2nr31002c

Droplet heteroepitaxy of zinc-blende vs. wurtzite GaN quantum dots

NASA Astrophysics Data System (ADS)

Reese, C.; Jeon, S.; Hill, T.; Jones, C.; Shusterman, S.; Yacoby, Y.; Clarke, R.; Deng, H.; Goldman, Rs

We have developed a GaN droplet heteroepitaxy process based upon plasma-assisted molecular-beam epitaxy. Using various surface treatments and Ga deposition parameters, we have demonstrated polycrystalline, zinc-blende (ZB), and wurtzite (WZ) GaN quantum dots (QDs) on Si(001), r-Al2O3, Si(111), and c-GaN substrates. For the polar substrates (i.e. Si(111) and c-GaN), high-resolution transmission electron microscopy and coherent Bragg rod analysis reveals the formation of coherent WZ GaN QDs with nitridation-temperature-dependent sizes and densities. For the non-polar substrates (i.e. Si(001) and r-Al2O3) , QDs with strong near-band photoluminescence emission are observed and ZB GaN QD growth on Si(001) is demonstrated for the first time.

Paramagnetic, silicon quantum dots for magnetic resonance and two-photon imaging of macrophages.

PubMed

Tu, Chuqiao; Ma, Xuchu; Pantazis, Periklis; Kauzlarich, Susan M; Louie, Angelique Y

2010-02-17

Quantum dots (QDs) are an attractive platform for building multimodality imaging probes, but the toxicity for typical cadmium QDs limits enthusiasm for their clinical use. Nontoxic, silicon QDs are more promising but tend to require short-wavelength excitations which are subject to tissue scattering and autofluorescence artifacts. Herein, we report the synthesis of paramagnetic, manganese-doped, silicon QDs (Si(Mn) QDs) and demonstrate that they are detectable by both MRI and near-infrared excited, two-photon imaging. The Si(Mn) QDs are coated with dextran sulfate to target them to scavenger receptors on macrophages, a biomarker of vulnerable plaques. TEM images show that isolated QDs have an average core diameter of 4.3 +/- 1.0 nm and the hydrodynamic diameters of coated nanoparticles range from 8.3 to 43 nm measured by dynamic light scattering (DLS). The Si(Mn) QDs have an r(1) relaxivity of 25.50 +/- 1.44 mM(-1) s(-1) and an r(2) relaxivity of 89.01 +/- 3.26 mM(-1) s(-1) (37 degrees C, 1.4 T). They emit strong fluorescence at 441 nm with a quantum yield of 8.1% in water. Cell studies show that the probes specifically accumulate in macrophages by a receptor-mediated process, are nontoxic to mammalian cells, and produce distinct contrast in both T(1)-weighted magnetic resonance and single- or two-photon excitation fluorescence images. These QDs have promising diagnostic potential as high macrophage density is associated with atherosclerotic plaques vulnerable to rupture.

Self-assembly and photoluminescence evolution of hydrophilic and hydrophobic quantum dots in sol–gel processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Ping, E-mail: mse_yangp@ujn.edu.cn; Matras-Postolek, Katarzyna; Song, Xueling

2015-10-15

Graphical abstract: Highly luminescent quantum dots (QDs) with tunable photoluminescence (PL) wavelength were assembled into various morphologies including chain, hollow spheres, fibers, and ring structures through sol–gel processes. The PL properties during assembly as investigated. - Highlights: • Highly luminescent quantum dots (QDs) were synthesized from several ligands. • The evolution of PL in self-assembly via sol–gel processes was investigated. • CdTe QDs were assembled into a chain by controlling hydrolysis and condensation reactions. • Hollow spheres, fibers, and ring structures were created via CdSe/ZnS QDs in sol–gel processes. - Abstract: Highly luminescent quantum dots (QDs) with tunable photoluminescence (PL)more » wavelength were synthesized from several ligands to investigate the PL evolution in QD self-assembly via sol–gel processes. After ligand exchange, CdTe QDs were assembled into a chain by controlling the hydrolysis and condensation reaction of 3-mercaptopropyl-trimethoxysilane. The chain was then coated with a SiO{sub 2} shell from tetraethyl orthosilicate (TEOS). Hollow spheres, fibers, and ring structures were created from CdSe/ZnS QDs via various sol–gel processes. CdTe QDs revealed red-shifted and narrowed PL spectrum after assembly compared with their initial one. In contrast, the red-shift of PL spectra of CdSe/ZnS QDs is small. By optimizing experimental conditions, SiO{sub 2} spheres with multiple CdSe/ZnS QDs were fabricated using TEOS and MPS. The QDs in these SiO{sub 2} spheres retained their initial PL properties. This result is useful for application because of their high stability and high PL efficiency of 33%.« less

Decoupling the effects of confinement and passivation on semiconductor quantum dots.

PubMed

Rudd, Roya; Hall, Colin; Murphy, Peter J; Reece, Peter J; Charrault, Eric; Evans, Drew

2016-07-20

Semiconductor (SC) quantum dots (QDs) have recently been fabricated by both chemical and plasma techniques for specific absorption and emission of light. Their optical properties are governed by the size of the QD and the chemistry of any passivation at their surface. Here, we decouple the effects of confinement and passivation by utilising DC magnetron sputtering to fabricate SC QDs in a perfluorinated polyether oil. Very high band gaps are observed for fluorinated QDs with increasing levels of quantum confinement (from 4.2 to 4.6 eV for Si, and 2.5 to 3 eV for Ge), with a shift down to 3.4 eV for Si when oxygen is introduced to the passivation layer. In contrast, the fluorinated Si QDs display a constant UV photoluminescence (3.8 eV) irrespective of size. This ability to tune the size and passivation independently opens a new opportunity to extending the use of simple semiconductor QDs.

Communication: Photoinduced carbon dioxide binding with surface-functionalized silicon quantum dots.

PubMed

Douglas-Gallardo, Oscar A; Sánchez, Cristián Gabriel; Vöhringer-Martinez, Esteban

2018-04-14

Nowadays, the search for efficient methods able to reduce the high atmospheric carbon dioxide concentration has turned into a very dynamic research area. Several environmental problems have been closely associated with the high atmospheric level of this greenhouse gas. Here, a novel system based on the use of surface-functionalized silicon quantum dots (sf-SiQDs) is theoretically proposed as a versatile device to bind carbon dioxide. Within this approach, carbon dioxide trapping is modulated by a photoinduced charge redistribution between the capping molecule and the silicon quantum dots (SiQDs). The chemical and electronic properties of the proposed SiQDs have been studied with a Density Functional Theory and Density Functional Tight-Binding (DFTB) approach along with a time-dependent model based on the DFTB framework. To the best of our knowledge, this is the first report that proposes and explores the potential application of a versatile and friendly device based on the use of sf-SiQDs for photochemically activated carbon dioxide fixation.

Communication: Photoinduced carbon dioxide binding with surface-functionalized silicon quantum dots

NASA Astrophysics Data System (ADS)

Douglas-Gallardo, Oscar A.; Sánchez, Cristián Gabriel; Vöhringer-Martinez, Esteban

2018-04-01

Nowadays, the search for efficient methods able to reduce the high atmospheric carbon dioxide concentration has turned into a very dynamic research area. Several environmental problems have been closely associated with the high atmospheric level of this greenhouse gas. Here, a novel system based on the use of surface-functionalized silicon quantum dots (sf-SiQDs) is theoretically proposed as a versatile device to bind carbon dioxide. Within this approach, carbon dioxide trapping is modulated by a photoinduced charge redistribution between the capping molecule and the silicon quantum dots (SiQDs). The chemical and electronic properties of the proposed SiQDs have been studied with a Density Functional Theory and Density Functional Tight-Binding (DFTB) approach along with a time-dependent model based on the DFTB framework. To the best of our knowledge, this is the first report that proposes and explores the potential application of a versatile and friendly device based on the use of sf-SiQDs for photochemically activated carbon dioxide fixation.

Paramagnetic, silicon quantum dots for magnetic resonance and two photon imaging of macrophages

PubMed Central

Tu, Chuqiao; Ma, Xuchu; Pantazis, Periklis; Kauzlarich, Susan M.; Louie, Angelique Y.

2010-01-01

Quantum dots (QDs) are an attractive platform for building multimodality imaging probes, but the toxicity for typical cadmium QDs limits enthusiasm for their clinical use. Nontoxic, silicon QDs are more promising but tend to require short wavelength excitations which are subject to tissue scattering and autofluorescence artifacts. Herein, we report the synthesis of paramagnetic, manganese-doped, silicon QDs ((SiMn QDs) and demonstrate that they are detectable by both MRI and near infrared excited, two-photon imaging. The SiMn QDs are coated with dextran sulfate to target them to scavenger receptors on macrophages, a biomarker of vulnerable plaques. TEM images show that isolated QDs have an average core diameter of 4.3 ± 1.0 nm and the hydrodynamic diameters of coated nanoparticles range from 8.3 to 43 nm measured by Dynamic Light Scattering (DLS). The SiMn QDs have an r1 relaxivity of 25.50 ± 1.44 mM−1s−1 and an r2 relaxivity of 89.01 ± 3.26 mM−1s−1 (37 °C, 1.4 T). They emit strong fluorescence at 441 nm with a quantum yield of 8.1% in water. Cell studies show that the probes specifically accumulate in macrophages by a receptor-mediated process, are nontoxic to mammalian cells, and produce distinct contrast in both T1-weighted magnetic resonance and single- or two-photon excitation fluorescence images. These QDs have promising diagnostic potential as high macrophage density is associated with atherosclerotic plaques vulnerable to rupture. PMID:20092250

Efficiency enhancement of blue light emitting diodes by eliminating V-defects from InGaN/GaN multiple quantum well structures through GaN capping layer control

NASA Astrophysics Data System (ADS)

Tsai, Sheng-Chieh; Li, Ming-Jui; Fang, Hsin-Chiao; Tu, Chia-Hao; Liu, Chuan-Pu

2018-05-01

A facile method for fabricating blue light-emitting diodes (B-LEDs) with small embedded quantum dots (QDs) and enhanced light emission is demonstrated by tuning the temperature of the growing GaN capping layer to eliminate V-defects. As the growth temperature increases from 770 °C to 840 °C, not only does the density of the V-defects reduce from 4.12 ∗ 108 #/cm2 nm to zero on a smooth surface, but the QDs also get smaller. Therefore, the growth mechanism of smaller QDs assisted by elimination of V-defects is discussed. Photoluminescence and electroluminescence results show that smaller embedded QDs can improve recombination efficiency, and thus achieve higher peak intensity with smaller peak broadening. Accordingly, the external quantum efficiency of the B-LEDs with smaller QDs is enhanced, leading to a 6.8% increase in light output power in lamp-form package LEDs.

The Interplay of Quantum Confinement and Hydrogenation in Amorphous Silicon Quantum Dots.

PubMed

Askari, Sadegh; Svrcek, Vladmir; Maguire, Paul; Mariotti, Davide

2015-12-22

Hydrogenation in amorphous silicon quantum dots (QDs) has a dramatic impact on the corresponding optical properties and band energy structure, leading to a quantum-confined composite material with unique characteristics. The synthesis of a-Si:H QDs is demonstrated with an atmospheric-pressure plasma process, which allows for accurate control of a highly chemically reactive non-equilibrium environment with temperatures well below the crystallization temperature of Si QDs. © 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of biocompatible SiO2 coated ZnO quantum dots for cell imaging

NASA Astrophysics Data System (ADS)

Zhang, Min; Wang, Qian; Chen, Haiyan; Gu, Yueqing

2014-09-01

Quantum dots (QDs) is a promising candidate for biomedical imaging. However, the bio-toxicity of traditional quantum dots obstructed their further application seriously. In this work, a simple solution growth method was utilized to synthesize ZnO QDs. However, their self-assemble feature makes them unstable in aqueous solution. Furthermore, (3-Aminopropyl) triethoxysilane was selected as a capping agent to stabilize ZnO QDs and then ZnO@SiO2 nanoparticles were obtained. They dispersed excellently in water and exhibited favorable fluorescence properties owing to the protection of silane. The biocompatability of ZnO@SiO2 nanoparticles was verified by MTT assy. The cell affinity studies demonstrated that ZnO@SiO2 nanoparticles could be uptaken by cells efficiently. Therefore, the as-prepared ZnO@SiO2 nanoparticles is a promising candidate for applications in cell imaging.

Thermo-optical characterization of cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots embedded in biocompatible materials.

PubMed

Pilla, Viviane; Alves, Leandro P; Iwazaki, Adalberto N; Andrade, Acácio A; Antunes, Andrea; Munin, Egberto

2013-09-01

Cadmium selenide/zinc sulfide (CdSe/ZnS) core-shell quantum dots (QDs) embedded in biocompatible materials were thermally and optically characterized with a thermal lens (TL) technique. Transient TL measurements were performed with a mode-mismatched, dual-beam (excitation and probe) configuration. A thermo-optical study of the CdSe/ZnS QDs was performed for different core diameters (3.5, 4.0, 5.2, and 6.6 nm) in aqueous solution and synthetic saliva, and three different core diameters (2.4, 2.9, and 4.1 nm) embedded in restorative dental resin (0.025% by mass). The thermal diffusivity results are characteristic of the biocompatible matrices. The radiative quantum efficiencies for aqueous solution and biofluid materials are dependent on the core size of the CdSe/ZnS core-shell QDs. The results obtained from the fluorescence spectral measurements for the biocompatible materials support the TL results.

Fluorescently labelled multiplex lateral flow immunoassay based on cadmium-free quantum dots.

PubMed

Beloglazova, Natalia V; Sobolev, Aleksander M; Tessier, Mickael D; Hens, Zeger; Goryacheva, Irina Yu; De Saeger, Sarah

2017-03-01

A sensitive tool for simultaneous qualitative detection of two mycotoxins based on use of non-cadmium quantum dots (QDs) is presented for the first time. QDs have proven themselves as promising fluorescent labels for biolabeling and chemical analysis. With an increasing global tendency to regulate and limit the use of hazardous elements, indium phosphide (InP) QDs are highlighted as environmentally-friendly alternatives to the highly efficient and well-studied, but potentially toxic Cd- and Pb-based QDs. Here, we developed water-soluble InP QDs-based fluorescent nanostructures. They consisted of core/shell InP/ZnS QDs enrobed in a silica shell that allowed the water solubility (QD@SiO 2 ). Then we applied the QD@SiO 2 as novel, silica shell-encapsulated fluorescent labels in immunoassays for rapid multiplexed screening. Two mycotoxins, zearalenone and deoxynivalenol, were simultaneously detected in maize and wheat, since the two QD@SiO 2 labelled conjugates emit at two different, individually detectable wavelengths. The cutoff values for the simultaneous determination were 50 and 500μgkg -1 for zearalenone and deoxynivalenol, respectively, in both maize and wheat. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was used to confirm the result. Copyright © 2017 Elsevier Inc. All rights reserved.

Multifunctional QD-based co-delivery of siRNA and doxorubicin to HeLa cells for reversal of multidrug resistance and real-time tracking.

PubMed

Li, Jin-Ming; Wang, Yuan-Yuan; Zhao, Mei-Xia; Tan, Cai-Ping; Li, Yi-Qun; Le, Xue-Yi; Ji, Liang-Nian; Mao, Zong-Wan

2012-03-01

Co-delivery of siRNA and chemotherapeutic agents has been developed to combat multidrug resistance in cancer therapy. Recently, we developed a series of quantum dots (QDs) functionalized by β-cyclodextrin (β-CD) coupled to amino acids, some of which can be used to facilitate the delivery of siRNA. In this study, two CdSe/ZnSe QDs modified with β-CD coupled to L-Arg or L-His were used to simultaneously deliver doxorubicin (Dox) and siRNA targeting the MDR1 gene to reverse the multidrug resistance of HeLa cells. In this co-delivery system, Dox was firstly encapsulated into the hydrophobic cavities of β-CD, resulting in bypass of P-glycoprotein (P-gp)-mediated drug efflux. After complex formation of the mdr1 siRNA with Dox-loaded QDs via electrostatic interaction, significant down-regulation of mdr1 mRNA levels and P-gp expression was achieved as shown by RT-PCR and Western blotting experiments, respectively. The number of apoptotic HeLa cells after treatment with the complexes substantially exceeded the number of apoptotic cells induced by free Dox only. The intrinsic fluorescence of the QDs provided an approach to track the system by laser confocal microscopy. These multifunctional QDs are promising vehicles for the co-delivery of nucleic acids and chemotherapeutics and for real-time tracking of treatment. Copyright © 2011 Elsevier Ltd. All rights reserved.

Highly efficient and stable blue-emitting CsPbBr3@SiO2 nanospheres through low temperature synthesis for nanoprinting and WLED.

PubMed

Shao, He; Bai, Xue; Pan, Gencai; Cui, Haining; Zhu, Jinyang; Zhai, Yue; Liu, Jingshi; Dong, Biao; Xu, Lin; Song, Hongwei

2018-07-13

Inorganic perovskite quantum dots (QDs) have attracted wide attention in display and solid-state lighting because of their easily tunable band-gaps and high photoluminescence quantum yields (PLQY) of green light emission. However, some drawbacks limit their practical applications, including the low PLQY of blue light emission and the instability in the moisture environment. In this work, efficient blue-light emitting CsPbBr 3 perovskite QDs with PLQY of 72% were developed through a bandgap engineering approach. The achieved blue-light emitting PLQY is much higher than the values acquired in the inorganic perovskite QDs in the literature. And the emission color of the as-prepared QDs can be facially tuned by only adjusting the reaction temperature. Further, the mono-dispersed perovskite QDs@SiO 2 composites were constructed benefiting from the low temperature synthesis. The optical performance of the QDs could be well persisted even in the moisture environment. Finally, the as-prepared QDs@SiO 2 composite was fabricated as the QD ink on the anti-counterfeit printing technology, from which the obtained pattern would emit varied color under UV lamp. And the as-prepared composites was also applied for fabricating WLED, with Commission Internationale de l'Eclairage (CIE) color coordinates of (0.33, 0.38) and power efficiency of 32.5 lm W -1 , demonstrating their promising potentials in solid-state lighting.

Highly efficient and stable blue-emitting CsPbBr3@SiO2 nanospheres through low temperature synthesis for nanoprinting and WLED

NASA Astrophysics Data System (ADS)

Shao, He; Bai, Xue; Pan, Gencai; Cui, Haining; Zhu, Jinyang; Zhai, Yue; Liu, Jingshi; Dong, Biao; Xu, Lin; Song, Hongwei

2018-07-01

Inorganic perovskite quantum dots (QDs) have attracted wide attention in display and solid-state lighting because of their easily tunable band-gaps and high photoluminescence quantum yields (PLQY) of green light emission. However, some drawbacks limit their practical applications, including the low PLQY of blue light emission and the instability in the moisture environment. In this work, efficient blue-light emitting CsPbBr3 perovskite QDs with PLQY of 72% were developed through a bandgap engineering approach. The achieved blue-light emitting PLQY is much higher than the values acquired in the inorganic perovskite QDs in the literature. And the emission color of the as-prepared QDs can be facially tuned by only adjusting the reaction temperature. Further, the mono-dispersed perovskite QDs@SiO2 composites were constructed benefiting from the low temperature synthesis. The optical performance of the QDs could be well persisted even in the moisture environment. Finally, the as-prepared QDs@SiO2 composite was fabricated as the QD ink on the anti-counterfeit printing technology, from which the obtained pattern would emit varied color under UV lamp. And the as-prepared composites was also applied for fabricating WLED, with Commission Internationale de l’Eclairage (CIE) color coordinates of (0.33, 0.38) and power efficiency of 32.5 lm W‑1, demonstrating their promising potentials in solid-state lighting.

A label-free silicon quantum dots-based photoluminescence sensor for ultrasensitive detection of pesticides.

PubMed

Yi, Yinhui; Zhu, Gangbing; Liu, Chang; Huang, Yan; Zhang, Youyu; Li, Haitao; Zhao, Jiangna; Yao, Shouzhuo

2013-12-03

Sensitive, rapid, and simple detection methods for the screening of extensively used organophosphorus pesticides and highly toxic nerve agents are in urgent demand. A novel label-free silicon quantum dots (SiQDs)-based sensor was designed for ultrasensitive detection of pesticides. This sensing strategy involves the reaction of acetylcholine chloride (ACh) with acetylcholinesterase (AChE) to form choline that is in turn catalytically oxidized by choline oxidase (ChOx) to produce betaine and H2O2 which can quench the photoluminescence (PL) of SiQDs. Upon the addition of pesticides, the activity of AChE is inhibited, leading to the decrease of the generated H2O2, and hence the PL of SiQDs increases. By measuring the increase in SiQDs PL, the inhibition efficiency of pesticide to AChE activity was evaluated. It was found that the inhibition efficiency was linearly dependent on the logarithm of the pesticides concentration. Consequently, pesticides, such as carbaryl, parathion, diazinon, and phorate, were determined with the SiQDs PL sensing method. The lowest detectable concentrations for carbaryl, parathion, diazinon, and phorate reached 7.25 × 10(-9), 3.25 × 10(-8), 6.76 × 10(-8), and 1.9 × 10(-7) g/L, respectively, which were much lower than those previously reported. The detecting results of pesticide residues in food samples via this method agree well with those from high-performance liquid chromatography. The simple strategy reported here should be suitable for on-site pesticides detection, especially in combination with other portable platforms.

Increased size selectivity of Si quantum dots on SiC at low substrate temperatures: An ion-assisted self-organization approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seo, D. H.; Das Arulsamy, A.; Rider, A. E.

A simple, effective, and innovative approach based on ion-assisted self-organization is proposed to synthesize size-selected Si quantum dots (QDs) on SiC substrates at low substrate temperatures. Using hybrid numerical simulations, the formation of Si QDs through a self-organization approach is investigated by taking into account two distinct cases of Si QD formation using the ionization energy approximation theory, which considers ionized in-fluxes containing Si{sup 3+} and Si{sup 1+} ions in the presence of a microscopic nonuniform electric field induced by a variable surface bias. The results show that the highest percentage of the surface coverage by 1 and 2 nmmore » size-selected QDs was achieved using a bias of -20 V and ions in the lowest charge state, namely, Si{sup 1+} ions in a low substrate temperature range (227-327 deg. C). As low substrate temperatures ({<=}500 deg. C) are desirable from a technological point of view, because (i) low-temperature deposition techniques are compatible with current thin-film Si-based solar cell fabrication and (ii) high processing temperatures can frequently cause damage to other components in electronic devices and destroy the tandem structure of Si QD-based third-generation solar cells, our results are highly relevant to the development of the third-generation all-Si tandem photovoltaic solar cells.« less

Increased size selectivity of Si quantum dots on SiC at low substrate temperatures: An ion-assisted self-organization approach

NASA Astrophysics Data System (ADS)

Seo, D. H.; Rider, A. E.; Das Arulsamy, A.; Levchenko, I.; Ostrikov, K.

2010-01-01

A simple, effective, and innovative approach based on ion-assisted self-organization is proposed to synthesize size-selected Si quantum dots (QDs) on SiC substrates at low substrate temperatures. Using hybrid numerical simulations, the formation of Si QDs through a self-organization approach is investigated by taking into account two distinct cases of Si QD formation using the ionization energy approximation theory, which considers ionized in-fluxes containing Si3+ and Si1+ ions in the presence of a microscopic nonuniform electric field induced by a variable surface bias. The results show that the highest percentage of the surface coverage by 1 and 2 nm size-selected QDs was achieved using a bias of -20 V and ions in the lowest charge state, namely, Si1+ ions in a low substrate temperature range (227-327 °C). As low substrate temperatures (≤500 °C) are desirable from a technological point of view, because (i) low-temperature deposition techniques are compatible with current thin-film Si-based solar cell fabrication and (ii) high processing temperatures can frequently cause damage to other components in electronic devices and destroy the tandem structure of Si QD-based third-generation solar cells, our results are highly relevant to the development of the third-generation all-Si tandem photovoltaic solar cells.

Miniband-related 1.4–1.8 μm luminescence of Ge/Si quantum dot superlattices

PubMed Central

Cirlin, GE; Tonkikh, AA; Zakharov, ND; Werner, P; Gösele, U; Tomm, JW; Elsaesser, T

2006-01-01

The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4–1.8 µm range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 µm.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xin, Yunzi; Nishio, Kazuyuki; Saitow, Ken-ichi, E-mail: saitow@hiroshima-u.ac.jp

A silicon (Si) quantum dot (QD)-based hybrid inorganic/organic light-emitting diode (LED) was fabricated via solution processing. This device exhibited white-blue electroluminescence at a low applied voltage of 6 V, with 78% of the effective emission obtained from the Si QDs. This hybrid LED produced current and optical power densities 280 and 350 times greater than those previously reported for such device. The superior performance of this hybrid device was obtained by both the prepared Si QDs and the optimized layer structure and thereby improving carrier migration through the hybrid LED and carrier recombination in the homogeneous Si QD layer.

Interface roughness mediated phonon relaxation rates in Si quantum dots.

NASA Astrophysics Data System (ADS)

Ferdous, Rifat; Hsueh, Yuling; Klimeck, Gerhard; Rahman, Rajib

2015-03-01

Si QDs are promising candidates for solid-state quantum computing due to long spin coherence times. However, the valley degeneracy in Si adds an additional degree of freedom to the electronic structure. Although the valley and orbital indices can be uniquely identified in an ideal Si QD, interface roughness mixes valley and orbital states in realistic dots. Such valley-orbit coupling can strongly influence T1 times in Si QDs. Recent experimental measurements of various relaxation rates differ from previous predictions of phonon relaxation in ideal Si QDs. To understand how roughness affects different relaxation rates, for example spin relaxation due to spin-valley coupling, which is a byproduct of spin-orbit and valley-orbit coupling, we need to understand the effect of valley-orbit coupling on valley relaxation first. Using a full-band atomistic tight-binding description for both the system's electron and electron-phonon hamiltonian, we analyze the effect of atomic-scale interface disorder on phonon induced valley relaxation and spin relaxation in a Si QD. We find that, the valley splitting dependence of valley relaxation rate governs the magnetic field dependence of spin relaxation rate. Our results help understand experimentally measured relaxation times.

GaAs quantum dots in a GaP nanowire photodetector

NASA Astrophysics Data System (ADS)

Kuyanov, P.; McNamee, S. A.; LaPierre, R. R.

2018-03-01

We report the structural, optical and electrical properties of GaAs quantum dots (QDs) embedded along GaP nanowires. The GaP nanowires contained p-i-n junctions with 15 consecutively grown GaAs QDs within the intrinsic region. The nanowires were grown by molecular beam epitaxy using the self-assisted vapor-liquid-solid process. The crystal structure of the NWs alternated between twinned ZB and WZ as the composition along the NW alternated between the GaP barriers and the GaAs QDs, respectively, leading to a polytypic structure with a periodic modulation of the NW sidewall facets. Photodetector devices containing QDs showed absorption beyond the bandgap of GaP in comparison to nanowires without QDs. Voltage-dependent measurements suggested a field emission process of carriers from the QDs.

Solar cells based on InP/GaP/Si structure

NASA Astrophysics Data System (ADS)

Kvitsiani, O.; Laperashvil, D.; Laperashvili, T.; Mikelashvili, V.

2016-10-01

Solar cells (SCs) based on III-V semiconductors are reviewed. Presented work emphases on the Solar Cells containing Quantum Dots (QDs) for next-generation photovoltaics. In this work the method of fabrication of InP QDs on III-V semiconductors is investigated. The original method of electrochemical deposition of metals: indium (In), gallium (Ga) and of alloys (InGa) on the surface of gallium phosphide (GaP), and mechanism of formation of InP QDs on GaP surface is presented. The possibilities of application of InP/GaP/Si structure as SC are discussed, and the challenges arising is also considered.

White LED based on CaAl2Si2O8:Eu2+ Mn2+ phosphor and CdS/ZnS quantum dots

NASA Astrophysics Data System (ADS)

Shen, Changyu; Zhong, Chuan; Hou, Qianglong; Li, Ke

2011-02-01

Core/shell CdS/ZnS quantum dots (QDs) with the emission wavelength of 610nm, was synthesized by thermal deposition using cadmium oxide and selenium as precursors in a hot lauric acid and hexadecylamine trioctylphosphine oxide hybrid. CaAl2Si2O8:Eu2+ Mn2+ phosphor was synthesized by high-temperature solid state reaction at 1290 °C for 2 hours under the H2 reducing atmosphere, and X-ray powder diffraction analysis confirmed the formation of it. It has two emission bands peaking at 420 nm and 580nm originated from the transition 5d to 4f of Eu2+ and 4T1-6A1 of Mn2+, respectively. Blends of CaAl2Si2O8:Eu2+,Mn2+ phosphor and CdS/ZnS QDs exhibited the prominent spectral evolution with an increasing content of QDs. A hybrid white LED, which combines a blue LED with the blend of CaAl2Si2O8:Eu2+ Mn2+ phosphor and QDs with a weight ratio of 2:1, with the CIE coordinate of (0.3183, 0.3036) and CRI of 85 was obtained.

Photoluminescence enhancement of silicon quantum dot monolayer by plasmonic substrate fabricated by nano-imprint lithography

NASA Astrophysics Data System (ADS)

Yanagawa, Hiroto; Inoue, Asuka; Sugimoto, Hiroshi; Shioi, Masahiko; Fujii, Minoru

2017-12-01

Near-field coupling between a silicon quantum dot (Si-QD) monolayer and a plasmonic substrate fabricated by nano-imprint lithography and having broad multiple resonances in the near-infrared (NIR) window of biological substances was studied by precisely controlling the QDs-substrate distance. A strong enhancement of the NIR photoluminescence (PL) of Si-QDs was observed. Detailed analyses of the PL and PL excitation spectra, the PL decay dynamics, and the reflectance spectra revealed that both the excitation cross-sections and the emission rates are enhanced by the surface plasmon resonances, thanks to the broad multiple resonances of the plasmonic substrate, and that the relative contribution of the two enhancement processes depends strongly on the excitation wavelength. Under excitation by short wavelength photons (405 nm), where enhancement of the excitation cross-section is not expected, the maximum enhancement was obtained when the QDs-substrate distance was around 30 nm. On the other hand, under long wavelength excitation (641 nm), where strong excitation cross-section enhancement is expected, the largest enhancement was obtained when the distance was minimum (around 1 nm). The achievement of efficient excitation of NIR luminescence of Si-QDs by long wavelength photons paves the way for the development of Si-QD-based fluorescence bio-sensing devices with a high bound-to-free ratio.

Interface-induced spin-orbit interaction in silicon quantum dots and prospects for scalability

NASA Astrophysics Data System (ADS)

Ferdous, Rifat; Chan, Kok W.; Veldhorst, Menno; Hwang, J. C. C.; Yang, C. H.; Sahasrabudhe, Harshad; Klimeck, Gerhard; Morello, Andrea; Dzurak, Andrew S.; Rahman, Rajib

2018-06-01

We identify the presence of monatomic steps at the Si/SiGe or Si /SiO2 interface as a dominant source of variations in the dephasing time of silicon (Si) quantum dot (QD) spin qubits. First, using atomistic tight-binding calculations we show that the g -factors and their Stark shifts undergo variations due to these steps. We compare our theoretical predictions with experiments on QDs at a Si /SiO2 interface, in which we observe significant differences in Stark shifts between QDs in two different samples. We also experimentally observe variations in the g -factors of one-electron and three-electron spin qubits realized in three neighboring QDs on the same sample, at a level consistent with our calculations. The dephasing times of these qubits also vary, most likely due to their varying sensitivity to charge noise, resulting from different interface conditions. More importantly, from our calculations we show that by employing the anisotropic nature of the spin-orbit interaction (SOI) in a Si QD, we can minimize and control these variations. Ultimately, we predict that the dephasing times of the Si QD spin qubits will be anisotropic and can be improved by at least an order of magnitude, by aligning the external dc magnetic field towards specific crystal directions, given other decoherence mechanisms do not dominate over charge noise.

Biocompatible silicon quantum dots by ultrasound-induced solution route

NASA Astrophysics Data System (ADS)

Lee, Soojin; Cho, Woon-Jo

2004-10-01

The water-soluble silicon quantum dots (QDs) of average diameter ~3 nm were prepared in organic solvent by ultrasound-induced solution route. This speedy rout produces the silicon QDs in the size range from 2 nm to 4 nm at room temperature and ambient pressure. The product yield of QDs was estimated to be higher than 60 % based on the initial NaSi weight. The surfaces of QDs were terminated with organic molecules including biocompatible ending groups (hydroxyl, amine and carboxyl) during simple preparation. Covalent attached molecules were characterized by FT-IR spectroscopy. These water-soluble passivation of QDs has just a little effect on the optical properties of original QDs.

Study on the Fabrication of Paint-Type Si Quantum Dot-Sensitized Solar Cells

NASA Astrophysics Data System (ADS)

Seo, Hyunwoong; Son, Min-Kyu; Kim, Hee-Je; Wang, Yuting; Uchida, Giichiro; Kamataki, Kunihiro; Itagaki, Naho; Koga, Kazunori; Shiratani, Masaharu

2013-10-01

Quantum dots (QDs) have attracted much attention with their quantum characteristics in the research field of photochemical solar cells. Si QD was introduced as one of alternatives to conventional QD materials. However, their large particles could not penetrate inside TiO2 layer. Therefore, this work proposed the paint-type Si QD-sensitized solar cell. Its heat durability was suitable for the fabrication of paint-type solar cell. Si QDs were fabricated by multihollow discharge plasma chemical vapor deposition and characterized. The paste type, sintering temperature, and Si ratio were controlled and analyzed for better performance. Finally, its performance was enhanced by ZnS surface modification and the whole process was much simplified without sensitizing process.

Static strain tuning of quantum dots embedded in a photonic wire

NASA Astrophysics Data System (ADS)

Tumanov, D.; Vaish, N.; Nguyen, H. A.; Curé, Y.; Gérard, J.-M.; Claudon, J.; Donatini, F.; Poizat, J.-Ph.

2018-03-01

We use strain to statically tune the semiconductor band gap of individual InAs quantum dots (QDs) embedded in a GaAs photonic wire featuring very efficient single photon collection. Thanks to the geometry of the structure, we are able to shift the QD excitonic transition by more than 25 meV by using nano-manipulators to apply the stress. Moreover, owing to the strong transverse strain gradient generated in the structure, we can relatively tune two QDs located in the wire waveguide and bring them in resonance, opening the way to the observation of collective effects such as superradiance.

Ligand-surface interactions and surface oxidation of colloidal PbSe quantum dots revealed by thin-film positron annihilation methods

NASA Astrophysics Data System (ADS)

Shi, Wenqin; Eijt, Stephan W. H.; Suchand Sandeep, C. S.; Siebbeles, Laurens D. A.; Houtepen, Arjan J.; Kinge, Sachin; Brück, Ekkes; Barbiellini, Bernardo; Bansil, Arun

2016-02-01

Positron Two Dimensional Angular Correlation of Annihilation Radiation (2D-ACAR) measurements reveal modifications of the electronic structure and composition at the surfaces of PbSe quantum dots (QDs), deposited as thin films, produced by various ligands containing either oxygen or nitrogen atoms. In particular, the 2D-ACAR measurements on thin films of colloidal PbSe QDs capped with oleic acid ligands yield an increased intensity in the electron momentum density (EMD) at high momenta compared to PbSe quantum dots capped with oleylamine. Moreover, the EMD of PbSe QDs is strongly affected by the small ethylenediamine ligands, since these molecules lead to small distances between QDs and favor neck formation between near neighbor QDs, inducing electronic coupling between neighboring QDs. The high sensitivity to the presence of oxygen atoms at the surface can be also exploited to monitor the surface oxidation of PbSe QDs upon exposure to air. Our study clearly demonstrates that positron annihilation spectroscopy applied to thin films can probe surface transformations of colloidal semiconductor QDs embedded in functional layers.

Tuning the structural and electronic properties of heterogeneous chalcogenide nanostructures

NASA Astrophysics Data System (ADS)

Giberti, Federico; Voros, Marton; Galli, Giulia

Heterogeneous nanostructures, such as quantum dots (QDs) embedded in solid matrices, are promising platforms for solar energy conversion. Unfortunately, there is scarce information on the structure of the interface between the dots and their embedding matrix, thus hampering the design of functional materials with desired optoelectronic properties. Here, we developed a hierarchical computational strategy to obtain realistic models of semiconductor QDs embedded in matrices using enhanced sampling classical molecular dynamics simulations and predicted their electronic structure using first-principles electronic structure methods. We investigated PbSe/CdSe systems which are promising materials for solar cell applications and found a favorable quasi-type-II band alignments both for PbSe QDs in CdSe matrices and for CdSe embedded in PbSe. However, in the former case, we found the presence of detrimental intra-gap states, while in the latter no defect states are present. Hence we predict that embedding CdSe in PbSe leads to a more efficient platform for solar energy conversion. In addition, we showed that the structure of CdSe QD and in turn its band gap might be tuned by applying pressure to the PbSe matrix, providing a way to engineer the properties of new functional materials. Work by F. Giberti was supported by MICCoM funded by the U.S. Department of Energy (DOE), DOE/BES 5J-30161-0010A; work by M. Voros was supported by the U.S. DOE, under Award DE-AC02-06CH11357.

Phonons in self-assembled Ge/Si structures

NASA Astrophysics Data System (ADS)

Milekhin, A. G.; Nikiforov, A. I.; Pchelyakov, O. P.; Schulze, S.; Zahn, D. R. T.

2002-03-01

We present the results of an investigation dealing with fundamental vibrations in periodical Ge/Si structures with small-size Ge quantum dots (QDs) performed using macro- and micro-Raman spectroscopy under resonant and off-resonant conditions. Samples with different number of repetition of Ge and Si layers contain Ge QDs with an average dot base size of 15 nm and a QD height of 2 nm. Periodic oscillations observed in the low-frequency region of the Raman spectra are assigned to folded LA phonons in the Ge QD superlattices. The measured phonon frequencies are in a good agreement with those calculated using the Rytov model. These oscillations are superimposed with a broad continuous emission originating from the whole acoustic dispersion branch due to a breaking up of translational invariance. The Raman spectra of the structure with single Ge QD layer reveal a series of peaks corresponding to LA phonons localized in the Si layer. Using the measured phonon frequencies and corresponding wave vectors the dispersion of the LA phonons in the Si is obtained. The longitudinal-acoustic wave velocity determined from the dispersion is 8365 ms-1 and in excellent agreement with that derived from the Brillouin study. In the optical phonon range, the LO and TO phonons localized in Ge QDs are observed. The position of the LO Ge phonons shifts downwards with increasing excitation energy (from 2.5 to 2.7 eV) indicating the presence of a QD size distribution in Ge dot superlattices. Raman scattering from Ge QDs is size-selectively enhanced by the resonance of the exciting laser energy and the confined excitonic states.

Optical excitations dynamics at hetero-interfaces fullerene/quantum dots

NASA Astrophysics Data System (ADS)

Righetto, Marcello; Privitera, Alberto; Franco, Lorenzo; Bozio, Renato

2017-08-01

Embedding Semiconductor Quantum Dots (QDs) into hybrid organic-inorganic solar cell holds promises for improving photovoltaic performances. Thanks to their strong coupling with electro-magnetic radiation field, QDs represent paradigmatic photon absorbers. Nevertheless, the quest for suitable charge separating hetero-interfaces is still an open challenge. Within this framework, the excited state interactions between QDs and fullerene derivatives are of great interest for ternary solar cells (polymer:QDs:fullerene). In this work, we investigated the exciton dynamics of core/shell CdSe/CdS QDs both in solution and in blends with fullerene derivative (PCBM). By means of transient optical techniques, we aimed to unveil the dynamics of the QDs-PCBM interaction. Indeed, the observed excited state depopulation of QDs in blends is compatible with an excited state interaction living on picosecond timescale. Through electron paramagnetic resonance, we delved into the nature of this interaction, identifying the presence of charge separated states. The concurrence of these observations suggest a fast electron transfer process, where QDs act as donors and PCBM molecules as acceptors, followed by effective charge separation. Therefore, our experimental results indicate the QDs-PCBM heterointerface as suitable exciton separating interface, paving the way for possible applications in photovoltaics.

Fabrication and characterization of multi-layer InAs/InGaAs quantum dot p-i-n GaAs solar cells grown on silicon substrates

NASA Astrophysics Data System (ADS)

Omri, M.; Sayari, A.; Sfaxi, L.

2018-01-01

This paper reports on InAs/InGaAs quantum dot solar cells (QDSCs) deposited by molecular beam epitaxy (MBE) on (001) n-type silicon ( n-Si) substrates. In-situ RHEED measurements show that InAs/InGaAs QDs SC has a high crystalline structure. The dislocation density in the active layer of the InAs/InGaAs QDSC and the lattice mismatch in the GaAs layer can be reduced by using an Si rough surface buffer layer (RSi). To show the effect of the QD layers, a reference SC with the same p-i-n structure as the InAs/InGaAs QDSC, but without InAs QDs, is also grown. The two SCs were studied by sepectroscopic ellipsometry (SE), in the 1-6 eV photon energy range, photoluminescence and photocurrent measurements. The optical constants of the two devices are determined in the photon energy range 1-6 eV from the SE data. The dominant features in the dielectric function spectra at 3 and 4.5 eV are attributed, respectively, to the E 1 and E 2 critical point structures of GaAs and InAs. The low-temperature photoluminescence spectrum of the InAs/InGaAs QDSC shows ground-state emissions, respectively, from the relatively small QDs near 1081 nm and from the large QDs near 1126 nm. Photocurrent measurements confirm the improved absorption performance (up to 1200 nm) of the InAs QDs SC which is ascribed to the optical absorption from the InAs/InGaAs QDs and the Si substrate as demonstrated by SE and photoluminescence measurements.

Ion beam processing and characterization of advanced optical materials

NASA Astrophysics Data System (ADS)

Zhu, Jie

Ion beams have been extensively applied for materials modification and characterization. In this dissertation, I will focus on the applications of ion beams for advanced optical materials. The first part of my work addresses the effects of 1.0 MeV proton irradiation on photoluminescence (PL) properties of self-assembled InAs QDs. Compared to the QDs grown in a GaAs thin film, the QDs embedded in an AlAs/GaAs superlattice structure exhibits much higher photoluminescence degradation resistance to proton irradiation. Proton irradiation combined with thermal annealing results in significant blueshifts in PL spectra of QDs embedded in GaAs, suggesting enhanced atomic intermixing in the QD systems due to point defects introduced by ion irradiation. In the second part of my work, ion channeling combined with Rutherford backscattering is applied to investigate In-Ga atomic intermixing processes in the proton irradiated InAs QD system. Ion channeling along the growth (<100>) direction shows evidence of In atoms with small displacement from the atomic row, which gives direct signature of QD lattice structures, allowing us to monitor atomic intermixing between In and Ga. Based on the channeling data, a model for In-Ga atomic intermixing in InAs/GaAs QD system is proposed, in which In-Ga atomic intermixing can take place along both the growth direction and the lateral direction in the QD layer. The third part of my dissertation is the elemental mapping of silica-based optical cross section using micron-ion-beam imaging techniques. This work is intended to examine the thermal stability of Ge-doped fiber cores in high-temperature environments. Our measurements show that Ge completely diffuses out of the core region following thermal annealing at 1000°C. This indicates that silica-based optical fibers cannot be used for applications at extreme high temperatures. The final part is the study of the effects of various wet treatment on GaN surface, which is a necessary step during the GaN device fabrication. In our work, the HCL treatment has reduced the Ga concentration on the surface for N type GaN. However, for samples with lower concentration of Si doping or P type GaN samples, this effect does not occur.

Lifetimes of the Vibrational States of DNA Molecules in Functionalized Complexes of Semiconductor Quantum Dots

NASA Astrophysics Data System (ADS)

Bayramov, F. B.; Poloskin, E. D.; Chernev, A. L.; Toporov, V. V.; Dubina, M. V.; Sprung, C.; Lipsanen, H. K.; Bairamov, B. Kh.

2018-01-01

Results of studying nanocrystalline nc-Si/SiO2 quantum dots (QDs) functionalized by short oligonucleotides show that complexes of isolated crystalline semiconductor QDs are unique objects for detecting the manifestation of new quantum confinement phenomena. It is established that narrow lines observed in high-resolution spectra of inelastic light scattering can be used for determining the characteristic time scale of vibrational excitations of separate nucleotide molecules and for studying structural-dynamic properties of fast oscillatory processes in biomacromolecules.

Enhanced emission of quantum dots embedded within the high-index dielectric regions of photonic crystal slabs

DOE Office of Scientific and Technical Information (OSTI.GOV)

See, Gloria G.; Naughton, Matt S.; Kenis, Paul J. A.

2016-04-25

We demonstrate a method for combining sputtered TiO{sub 2} deposition with liquid phase dip-coating of a quantum dot (QD) layer that enables precise depth placement of QD emitters within a high-index dielectric film, using a photonic crystal (PC) slab resonator to demonstrate enhanced emission from the QDs when they are located at a specific depth within the film. The depth of the QDs within the PC is found to modulate the resonant wavelength of the PC as well as the emission enhancement efficiency, as the semiconducting material embedded within the dielectric changes its spatial overlap with the resonant mode.

In Situ Crystallization Synthesis of CsPbBr3 Perovskite Quantum Dot-Embedded Glasses with Improved Stability for Solid-State Lighting and Random Upconverted Lasing.

PubMed

Yuan, Shuo; Chen, Daqin; Li, Xinyue; Zhong, Jiasong; Xu, Xuhui

2018-06-06

All-inorganic cesium lead bromide CsPbBr 3 perovskite quantum dots (QDs) are emerging as potential candidates for their applications in optoelectronic devices but they suffer from poor long-term stability due to their high sensitivity to UV irradiation, heat, and especially to moisture. Although great advances in improving stability of perovskite QDs have been achieved by surface modification or encapsulation in polymer and silica, they are not sufficiently refrained from external environment due to nondense structures of these protective layers. In this work, in situ nanocrystallization strategy is developed to directly grow CsPbBr 3 QDs among a specially designed TeO 2 -based glass matrix. As a result, QD-embedded glass shows typical bright green emission assigned to exciton recombination radiation and significant improvement of photon/thermal stability and water resistance due to the effective protecting role of dense structural glass. Particularly, ∼90% of emission intensity is even remained after immersing QD-embedded glass in water up to 120 h, enabling them to find promising applications in white-light-emitting device with superior color stability and low-threshold random upconverted laser under ambient air condition.

Large-area ordered Ge-Si compound quantum dot molecules on dot-patterned Si (001) substrates

NASA Astrophysics Data System (ADS)

Lei, Hui; Zhou, Tong; Wang, Shuguang; Fan, Yongliang; Zhong, Zhenyang

2014-08-01

We report on the formation of large-area ordered Ge-Si compound quantum dot molecules (CQDMs) in a combination of nanosphere lithography and self-assembly. Truncated-pyramid-like Si dots with {11n} facets are readily formed, which are spatially ordered in a large area with controlled period and size. Each Si dot induces four self-assembled Ge-rich dots at its base edges that can be fourfold symmetric along <110> directions. A model based on surface chemical potential accounts well for these phenomena. Our results disclose the critical effect of surface curvature on the diffusion and the aggregation of Ge adatoms and shed new light on the unique features and the inherent mechanism of self-assembled QDs on patterned substrates. Such a configuration of one Si QD surrounded by fourfold symmetric Ge-rich QDs can be seen as a CQDM with unique features, which will have potential applications in novel devices.

Multifunctional Nanocomposites for Breast Cancer Imaging and Therapy

DTIC Science & Technology

2008-07-01

compounds, because of the low stability of the thiolate -capped PbS QDs at physiological pH values. The following approach, consisting of 3 phases, was...syntheses employed amphiphilic polymers to stabilize CdSe/ZnS QDs, or phospholipids micelles to stabilize Si QDs, or used ligand exchange followed...attached per surface. However, it is very difficult to estimate the exact amount within the large G6- polymer of MW= 69,351 without measuring the 800 or

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Mahesh; Roul, Basanta; Central Research Laboratory, Bharat Electronics, Bangalore-560013

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

Voltage-Dependent Charge Storage in Cladded Zn0.56Cd0.44Se Quantum Dot MOS Capacitors for Multibit Memory Applications

NASA Astrophysics Data System (ADS)

Khan, J.; Lingalugari, M.; Al-Amoody, F.; Jain, F.

2013-11-01

As conventional memories approach scaling limitations, new storage methods must be utilized to increase Si yield and produce higher on-chip memory density. Use of II-VI Zn0.56Cd0.44Se quantum dots (QDs) is compatible with epitaxial gate insulators such as ZnS-ZnMgS. Voltage-dependent charging effects in cladded Zn0.56Cd0.44Se QDs are presented in a conventional metal-oxide-semiconductor capacitor structure. Charge storage capabilities in Si and ZnMgS QDs have been reported by various researchers; this work is focused on II-VI material Zn0.56Cd0.44Se QDs nucleated using photoassisted microwave plasma metalorganic chemical vapor deposition. Using capacitance-voltage hysteresis characterization, the multistep charging and discharging capabilities of the QDs at room temperature are presented. Three charging states are presented within a 10 V charging voltage range. These characteristics exemplify discrete charge states in the QD layer, perfect for multibit, QD-functionalized high-density memory applications. Multiple charge states with low operating voltage provide device characteristics that can be used for multibit storage by allowing varying charges to be stored in a QD layer based on the applied "write" voltage.

Structure and optical properties of Ge/Si quantum dots formed by driving the evolution of Ge thin films via thermal annealing

NASA Astrophysics Data System (ADS)

Shu, Qijiang; Yang, Jie; Chi, Qingbin; Sun, Tao; Wang, Chong; Yang, Yu

2018-04-01

Ge/Si quantum dots (QDs) are fabricated by driving the transformation of a Ge thin film-deposited using the direct current (DC) magnetron sputtering technique by controlling the subsequent in situ annealing processes. The experimental results indicate that, with the increase in annealing temperature, the volume of Ge QDs increases monotonically, while the QD density initially increases then decreases. The maximal QD density can reach 1.1 × 1011 cm‑2 after a 10 min annealing at 650 °C. The Ge–Ge peak of Ge QDs obtained by Raman spectroscopy initially undergoes a blue shift and then a red shift with increasing annealing temperature. This behavior results from the competition between the dislocation and the strain relaxation in QDs. Concurrently, a series of photoelectric detectors are fabricated to evaluate the photoelectric performance of these annealed Ge QD samples. A high-photoelectricity response is demonstrated in the QD sample annealed at 650 °C. Our results pave a promising way for whole-silicon-material optical-electronic integration based on a simple and practicable fabrication method.

Toxicity evaluation of hydrophilic CdTe quantum dots and CdTe@SiO2 nanoparticles in mice.

PubMed

Sadaf, Asma; Zeshan, Basit; Wang, Zhuyuan; Zhang, Ruohu; Xu, Shuhong; Wang, Chunlei; Cui, Yiping

2012-11-01

Quantum dots have drawn tremendous attention in the field of in vitro and small animal in vivo fluorescence imaging in the last decade. However, concerns over the cytotoxicity of their heavy metal constituents have limited their use in clinical applications. Here, we report our comparative studies on the toxicities of quantum dots (QDs) and silica coated CdTe nanoparticles (NPs) to mice after intravenous injection. The blood cells analysis showed significant increased level of white blood cells (WBCs) in groups treated with CdTe QDs as compared to the control while red blood cells (RBCs) and platelet counts were normal in treated as well as control groups. The concentration of biochemical markers of hepatic damage, alanine amino transferase (ALT) and aspartate aminotransferase (AST) were in the normal range in all the groups. However, renal function analyses of mice showed significantly increased in the concentration of blood urea nitrogen (BUN) and creatinine (CREA) in mice treated with CdTe QDs while remained within normal ranges in both the CdTe@SiO2 NPs and control group. The results of histopathology showed that the CdTe QDs caused mild nephrotoxicity while other organs were normal and no abnormalities were detected in control and CdTe@SiO2 treated group. These findings suggest that the nephrotoxicity could be minimized by silica coating which would be useful for many biomedical applications.

Bandgap Tuning of Silicon Quantum Dots by Surface Functionalization with Conjugated Organic Groups.

PubMed

Zhou, Tianlei; Anderson, Ryan T; Li, Huashan; Bell, Jacob; Yang, Yongan; Gorman, Brian P; Pylypenko, Svitlana; Lusk, Mark T; Sellinger, Alan

2015-06-10

The quantum confinement and enhanced optical properties of silicon quantum dots (SiQDs) make them attractive as an inexpensive and nontoxic material for a variety of applications such as light emitting technologies (lighting, displays, sensors) and photovoltaics. However, experimental demonstration of these properties and practical application into optoelectronic devices have been limited as SiQDs are generally passivated with covalently bound insulating alkyl chains that limit charge transport. In this work, we show that strategically designed triphenylamine-based surface ligands covalently bonded to the SiQD surface using conjugated vinyl connectivity results in a 70 nm red-shifted photoluminescence relative to their decyl-capped control counterparts. This suggests that electron density from the SiQD is delocalized into the surface ligands to effectively create a larger hybrid QD with possible macroscopic charge transport properties.

Electronic properties of single Ge/Si quantum dot grown by ion beam sputtering deposition.

PubMed

Wang, C; Ke, S Y; Yang, J; Hu, W D; Qiu, F; Wang, R F; Yang, Y

2015-03-13

The dependence of the electronic properties of a single Ge/Si quantum dot (QD) grown by the ion-beam sputtering deposition technique on growth temperature and QD diameter is investigated by conductive atomic force microscopy (CAFM). The Si-Ge intermixing effect is demonstrated to be important for the current distribution of single QDs. The current staircase induced by the Coulomb blockade effect is observed at higher growth temperatures (>700 °C) due to the formation of an additional barrier between dislocated QDs and Si substrate for the resonant tunneling of holes. According to the proposed single-hole-tunneling model, the fact that the intermixing effect is observed to increase as the incoherent QD size decreases may explain the increase in the starting voltage of the current staircase and the decrease in the current step width.

Synthesis and characterization of ZnS@Fe3O4 fluorescent-magnetic bifunctional nanospheres

NASA Astrophysics Data System (ADS)

Koc, Kenan; Karakus, Baris; Rajar, Kausar; Alveroglu, Esra

2017-10-01

Herein, we synthesized and characterized fluorescent and super paramagnetic ZnS@Fe3O4 nanospheres. First, (3-mercaptopropyl) trimethoxysilane (MPS) capped ZnS quantum dots (QDs) and SiO2 coated Fe3O4 nanoparticles were synthesized separately by using solution growth and co-precipitation techniques. After synthesis and characterization of these two nanoparticles, they were conglutinated together in a nano sized sphere. The QDs were attached to the surface of the Fe3O4 nanoparticles by Sisbnd Osbnd Si bonds and so Sisbnd Osbnd Si bonds created a SiO2 network around the nanoparticles during the formation of the ZnS@Fe3O4 nanospheres. The synthesized MPS capped ZnS fluorescent QDs, SiO2 coated magnetite super paramagnetic nanoparticles and ZnS@Fe3O4 fluorescent-magnetic bifunctional nanospheres were characterized by using UV-Vis Absorption Spectroscopy, Fluorescence Spectroscopy, X-ray analysis, Vibrating Sample Magnetometer analysis, Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy, Scanning Electron Microscope and Energy-dispersive X-ray spectroscopy. ZnS@Fe3O4 bifunctional nanospheres were shown to retain the magnetic properties of magnetite, while exhibiting the luminescent optical properties of ZnS nanoparticles. The combination of fluorescent and magnetic behaviors of nano composites make them useful for potential applications in the field of bio-medical and environmental.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raja, Shilpa N.; Zherebetskyy, Danylo; Wu, Siva

Nanoscale stress-sensing can be used across fields ranging from detection of incipient cracks in structural mechanics to monitoring forces in biological tissues. We demonstrate how tetrapod quantum dots (tQDs) embedded in block copolymers act as sensors of tensile/compressive stress. Remarkably, tQDs can detect their own composite dispersion and mechanical properties with a switch in optomechanical response when tQDs are in direct contact. Using experimental characterizations, atomistic simulations and finite-element analyses, we show that under tensile stress, densely packed tQDs exhibit a photoluminescence peak shifted to higher energies ("blue-shift") due to volumetric compressive stress in their core; loosely packed tQDs exhibitmore » a peak shifted to lower energies ("red-shift") from tensile stress in the core. The stress shifts result from the tQD's unique branched morphology in which the CdS arms act as antennas that amplify the stress in the CdSe core. Our nanocomposites exhibit excellent cyclability and scalability with no degraded properties of the host polymer. Colloidal tQDs allow sensing in many materials to potentially enable autoresponsive, smart structural nanocomposites that self-predict upcoming fracture.« less

Enhanced electrochemiluminescence quenching of CdS:Mn nanocrystals by CdTe QDs-doped silica nanoparticles for ultrasensitive detection of thrombin.

PubMed

Shan, Yun; Xu, Jing-Juan; Chen, Hong-Yuan

2011-07-01

This work reports an aptasensor for ultrasensitive detection of thrombin based on remarkably efficient energy-transfer induced electrochemiluminescence (ECL) quenching from CdS:Mn nanocrystals (NCs) film to CdTe QDs-doped silica nanoparticles (CdTe/SiO(2) NPs). CdTe/SiO(2) NPs were synthesized via the Stöber method and showed black bodies' strong absorption in a wide spectral range without excitonic emission, which made them excellent ECL quenchers. Within the effective distance of energy scavenging, the ECL quenching efficiency was dependent on the number of CdTe QDs doped into the silica NPs. Using ca. 200 CdTe QDs doped silica NPs on average of 40 nm in diameter as ECL quenching labels, attomolar detection of thrombin was successfully realized. The protein detection involves a competition binding event, based on thrombin replacing CdTe/SiO(2) NPs labeled probing DNA which is hybridized with capturing aptamer immobilized on a CdS:Mn NCs film modified glassy carbon electrode surface by specific aptamer-protein affinity interactions. It results in the displacement of ECL quenching labels from CdS:Mn NCs film and concomitant ECL signal recovery. Owing to the high-content CdTe QDs in silica NP, the increment of ECL intensity (ΔI(ECL)) and the concentration of thrombin showed a double logarithmic linear correlation in the range of 5.0 aM∼5.0 fM with a detection limit of 1aM. And, the aptasensor hardly responded to antibody, bovine serum albumin (BSA), haemoglobin (Hb) and lysozyme, showing good detection selectivity for thrombin. This long-distance energy scavenging could have a promising application perspective in the detection of biological recognition events on a molecular level.

Factors influencing epitaxial growth of three-dimensional Ge quantum dot crystals on pit-patterned Si substrate.

PubMed

Ma, Y J; Zhong, Z; Yang, X J; Fan, Y L; Jiang, Z M

2013-01-11

We investigated the molecular beam epitaxy growth of three-dimensional (3D) Ge quantum dot crystals (QDCs) on periodically pit-patterned Si substrates. A series of factors influencing the growth of QDCs were investigated in detail and the optimized growth conditions were found. The growth of the Si buffer layer and the first quantum dot (QD) layer play a key role in the growth of QDCs. The pit facet inclination angle decreased with increasing buffer layer thickness, and its optimized value was found to be around 21°, ensuring that all the QDs in the first layer nucleate within the pits. A large Ge deposition amount in the first QD layer favors strain build-up by QDs, size uniformity of QDs and hence periodicity of the strain distribution; a thin Si spacer layer favors strain correlation along the growth direction; both effects contribute to the vertical ordering of the QDCs. Results obtained by atomic force microscopy and cross-sectional transmission electron microscopy showed that 3D ordering was achieved in the Ge QDCs with the highest ever areal dot density of 1.2 × 10(10) cm(-2), and that the lateral and the vertical interdot spacing were ~10 and ~2.5 nm, respectively.

Direct conversion of hydride- to siloxane-terminated silicon quantum dots

DOE PAGES

Anderson, Ryan T.; Zang, Xiaoning; Fernando, Roshan; ...

2016-10-20

Here, peripheral surface functionalization of hydride-terminated silicon quantum dots (SiQD) is necessary in order to minimize their oxidation/aggregation and allow for solution processability. Historically thermal hydrosilylation addition of alkenes and alkynes across the Si-H surface to form Si-C bonds has been the primary method to achieve this. Here we demonstrate a mild alternative approach to functionalize hydride-terminated SiQDs using bulky silanols in the presence of free-radical initiators to form stable siloxane (~Si-O-SiR 3) surfaces with hydrogen gas as a byproduct. This offers an alternative to existing methods of forming siloxane surfaces that require corrosive Si-Cl based chemistry with HCl byproducts.more » A 52 nm blue shift in the photoluminescent spectra of siloxane versus alkyl-functionalized SiQDs is observed that we explain using computational theory. Model compound synthesis of silane and silsesquioxane analogues is used to optimize surface chemistry and elucidate reaction mechanisms. Thorough characterization on the extent of siloxane surface coverage is provided using FTIR and XPS. As a result, TEM is used to demonstrate SiQD size and integrity after surface chemistry and product isolation.« less

Emission Properties from ZnO Quantum Dots Dispersed in SiO2 Matrix

NASA Astrophysics Data System (ADS)

Panigrahi, Shrabani; Basak, Durga

2011-07-01

Dispersion of ZnO quantum dots in SiO2 matrix has been achieved in two techniques based on StÖber method to form ZnO QDs-SiO2 nanocomposites. Sample A is formed with random dispersion by adding tetraethyl orthosilicate (TEOS) to an ethanolic solution of ZnO nanoparticles and sample B is formed with a chain-like ordered dispersion by adding ZnO nanoparticles to an already hydrolyzed ethanolic TEOS solution. The photoluminescence spectra of the as-grown nanocomposites show strong emission in the ultraviolet region. When annealed at higher temperature, depending on the sample type, these show strong red or white emission. Interestingly, when the excitation is removed, the orderly dispersed ZnO QDs-SiO2 composite shows a very bright blue fluorescence visible by naked eyes for few seconds indicating their promise for display applications.

Size tunability and optical properties of CdSe quantum dots for various growth conditions

NASA Astrophysics Data System (ADS)

Ko, Eun Yee; Lee, Joo In; Jeon, Ju-Won; Lee, In Hwan; Shin, Yong Hyeon; Han, Il Ki

2013-01-01

We report the optical properties of CdSe quantum dots (QDs) synthesized under various growth conditions, such as growth temperature, growth time, ligand ratio, and Cd:Se ratio of the precursors. As the growth temperature and time was increased, the peaks of the photoluminescence (PL) spectra were a red shifted, indicating that the size of QDs increased. Different ligand ratios and Cd:Se ratios of the precursors played important roles in determining the QDs size. From the PL spectra and the transmission electron microscopy image, the size distribution, as well as the size of CdSe QDs, could be controlled by using the growth conditions. The temperature-dependent PL of CdSe QDs dropped and dried on Si substrates was measured at temperatures from 15 K to 290 K. With increasing temperature, the red shift of the QDs was about 35 meV, which is noticeably smaller than that of bulk CdSe (˜100 meV). The influence of the temperature on the optical properties of colloidal CdSe QDs is important for an application to various devices.

Detection of nitroaromatics in the solid, solution, and vapor phases using silicon quantum dot sensors

NASA Astrophysics Data System (ADS)

Nguyen, An; Gonzalez, Christina M.; Sinelnikov, Regina; Newman, W.; Sun, Sarah; Lockwood, Ross; Veinot, Jonathan G. C.; Meldrum, Al

2016-03-01

Silicon quantum dots (Si-QDs) represent a well-known QD fluorophore that can emit throughout the visible spectrum depending on the interface structure and surface functional group. Detection of nitroaromatic compounds by monitoring the luminescence response of the sensor material (typically fluorescent polymers) currently forms the basis of new explosives sensing technologies. Freestanding silicon QDs may represent a benign alternative with a high degree of chemical and physical versatility. Here, we investigate dodecyl and amine-terminated Si-QD luminescence response to the presence of nitrobenzene and dinitrotoluene (DNT) in various solid, solution, and vapor forms. For dinitrotoluene vapor the 3σ detection limit was 6 ppb for monomer-terminated QDs. For nitroaromatics dissolved in toluene the detection limit was on the order of 400 nM, corresponding to ∼100 pg of material distributed over ∼1 cm2 on the sensor surface. Solid traces of nitroaromatics were also easily detectable via a simple ‘touch test’. The samples showed minimal interference effects from common contaminants such as water, ethanol, and acetonitrile. The sensor can be as simple and inexpensive as a small circle of filter paper dipped into a QD solution, with a single vial of QDs able to make hundreds of these sensors. Additionally, a trial fiber-optic sensor device was tested by applying the QDs to one end of a 2 × 2 fiber coupler and exposing them to controlled DNT vapor. Finally, the quenching mechanism was explored via luminescence dynamics measurements and is different for blue (amine) and red (dodecyl) fluorescent silicon QDs.

Modification of emission photon statistics from single quantum dots using metal/SiO2 core/shell nanostructures.

PubMed

Naiki, Hiroyuki; Oikawa, Hidetoshi; Masuo, Sadahiro

2017-04-12

Emission photon statistics, i.e., single-photon and multi-photon emissions, of isolated QDs is required for tailoring optoelectronic applications. In this article, we demonstrate that the emission photon statistics can be modified by the control of the spectral overlap of the QDs with the localized surface plasmon resonance (LSPR) of the metal nanoparticle (metal NP) and by the distance between the QD and the metal NP. Moreover, the contribution to the modification of the emission photon statistics, which is the excitation and emission enhancements and the quenching generated by the spectral overlap and the distance, is elucidated. By fabricating well-defined SiO 2 -coated AgNPs and AuNPs (metal/SiO 2 ), the spectral overlap originated from the metal species of Ag and Au and the distance constituted by the thickness of the SiO 2 shell are controlled. The probability of single-photon emission of single QD was increased by the enhancement of the excitation rate via adjusting the distance using Ag/SiO 2 while the single-photon emission was converted to multi-photon emission by the effect of exciton quenching at a short distance and a small spectral overlap. By contrast, the probability of multi-photon emission was increased by enhancement of the multi-photon emission rate and the quenching via the spectral overlap using Au/SiO 2 . These results indicated the fundamental finding to control emission photon statistics in single QDs by controlling the spectral overlap and the distance, and understand the interaction of plasmonic nanostructures and single QD systems.

Modification of Light Emission in Si-Rich Silicon Nitride Films Versus Stoichiometry and Excitation Light Energy

NASA Astrophysics Data System (ADS)

Torchynska, T.; Khomenkova, L.; Slaoui, A.

2018-04-01

Si-rich SiN x films with different stoichiometry were grown on Si substrate by plasma-enhanced chemical vapor deposition. The Si content was varied by changing the NH3/SiH4 gas flow ratio from 0.45 up to 1.0. Conventional furnace annealing at 1100°C for 30 min was applied to produce the Si quantum dots (QDs) in the SiN x films. Spectroscopic ellipsometry was used to determine the refractive index of the SiN x films that allowed estimating the film's stoichiometry. Fourier transform infrared spectroscopy has been also used to confirm the stoichiometry and microstructure. Photoluminescence (PL) spectra of Si-rich SiN x films are complex. A non-monotonous variation of the different PL peaks versus Si excess contents testifies to the competition of different radiative channels. The analysis of PL spectra, measured at the different excitation light energies and variable temperatures, has revealed that the PL bands with the peaks within the range 2.1-3.0 eV are related to the carrier recombination via radiative native defects in the SiN x host. Simultaneously, the PL bands with the peaks at 1.5-2.0 eV are caused by the exciton recombination in the Si QDs of different sizes. The way to control the SiN x emission is discussed.

Modification of Light Emission in Si-Rich Silicon Nitride Films Versus Stoichiometry and Excitation Light Energy

NASA Astrophysics Data System (ADS)

Torchynska, T.; Khomenkova, L.; Slaoui, A.

2018-07-01

Si-rich SiN x films with different stoichiometry were grown on Si substrate by plasma-enhanced chemical vapor deposition. The Si content was varied by changing the NH3/SiH4 gas flow ratio from 0.45 up to 1.0. Conventional furnace annealing at 1100°C for 30 min was applied to produce the Si quantum dots (QDs) in the SiN x films. Spectroscopic ellipsometry was used to determine the refractive index of the SiN x films that allowed estimating the film's stoichiometry. Fourier transform infrared spectroscopy has been also used to confirm the stoichiometry and microstructure. Photoluminescence (PL) spectra of Si-rich SiN x films are complex. A non-monotonous variation of the different PL peaks versus Si excess contents testifies to the competition of different radiative channels. The analysis of PL spectra, measured at the different excitation light energies and variable temperatures, has revealed that the PL bands with the peaks within the range 2.1-3.0 eV are related to the carrier recombination via radiative native defects in the SiN x host. Simultaneously, the PL bands with the peaks at 1.5-2.0 eV are caused by the exciton recombination in the Si QDs of different sizes. The way to control the SiN x emission is discussed.

Anisotropic Exciton Rabi Oscillation in Single Telecommunication-Band Quantum Dot

NASA Astrophysics Data System (ADS)

Miyazawa, Toshiyuki; Nakaoka, Toshihiro; Watanabe, Katsuyuki; Kumagai, Naoto; Yokoyama, Naoki; Arakawa, Yasuhiko

2010-06-01

Anisotropic Rabi oscillation in the exciton state in a single InAs/GaAs quantum dot (QD) was demonstrated in the telecommunication-band by selecting two orthogonal polarization angles of the excitation laser. Our InAs QDs were embedded in an intrinsic layer of an n-i-Schottky diode, which provides an electric field to extract photoexcited carriers from QDs. Owing to the potential anisotropy of QDs, the fine structure splitting (FSS) energy in the exciton state in single InAs QDs was ˜110 µeV, measured by polarization-resolved photocurrent spectroscopy. The ratio between two different Rabi frequencies, which reflect anisotropic dipole moments of two orthogonal exciton states, was estimated to be ˜1.2. This demonstrates that the selective control of two orthogonal polarized exciton states is a promising technique for exciton-based-quantum information devices compatible with fiber optics.

Anisotropic Exciton Rabi Oscillation in Single Telecommunication-Band Quantum Dot

NASA Astrophysics Data System (ADS)

Toshiyuki Miyazawa,; Toshihiro Nakaoka,; Katsuyuki Watanabe,; Naoto Kumagai,; Naoki Yokoyama,; Yasuhiko Arakawa,

2010-06-01

Anisotropic Rabi oscillation in the exciton state in a single InAs/GaAs quantum dot (QD) was demonstrated in the telecommunication-band by selecting two orthogonal polarization angles of the excitation laser. Our InAs QDs were embedded in an intrinsic layer of an n-i-Schottky diode, which provides an electric field to extract photoexcited carriers from QDs. Owing to the potential anisotropy of QDs, the fine structure splitting (FSS) energy in the exciton state in single InAs QDs was ˜110 μeV, measured by polarization-resolved photocurrent spectroscopy. The ratio between two different Rabi frequencies, which reflect anisotropic dipole moments of two orthogonal exciton states, was estimated to be ˜1.2. This demonstrates that the selective control of two orthogonal polarized exciton states is a promising technique for exciton-based-quantum information devices compatible with fiber optics.

Design, Implementation and Characterization of a Quantum-Dot-Based Volumetric Display

NASA Astrophysics Data System (ADS)

Hirayama, Ryuji; Naruse, Makoto; Nakayama, Hirotaka; Tate, Naoya; Shiraki, Atsushi; Kakue, Takashi; Shimobaba, Tomoyoshi; Ohtsu, Motoichi; Ito, Tomoyoshi

2015-02-01

In this study, we propose and experimentally demonstrate a volumetric display system based on quantum dots (QDs) embedded in a polymer substrate. Unlike conventional volumetric displays, our system does not require electrical wiring; thus, the heretofore unavoidable issue of occlusion is resolved because irradiation by external light supplies the energy to the light-emitting voxels formed by the QDs. By exploiting the intrinsic attributes of the QDs, the system offers ultrahigh definition and a wide range of colours for volumetric displays. In this paper, we discuss the design, implementation and characterization of the proposed volumetric display's first prototype. We developed an 8 × 8 × 8 display comprising two types of QDs. This display provides multicolour three-type two-dimensional patterns when viewed from different angles. The QD-based volumetric display provides a new way to represent images and could be applied in leisure and advertising industries, among others.

Design, implementation and characterization of a quantum-dot-based volumetric display.

PubMed

Hirayama, Ryuji; Naruse, Makoto; Nakayama, Hirotaka; Tate, Naoya; Shiraki, Atsushi; Kakue, Takashi; Shimobaba, Tomoyoshi; Ohtsu, Motoichi; Ito, Tomoyoshi

2015-02-16

In this study, we propose and experimentally demonstrate a volumetric display system based on quantum dots (QDs) embedded in a polymer substrate. Unlike conventional volumetric displays, our system does not require electrical wiring; thus, the heretofore unavoidable issue of occlusion is resolved because irradiation by external light supplies the energy to the light-emitting voxels formed by the QDs. By exploiting the intrinsic attributes of the QDs, the system offers ultrahigh definition and a wide range of colours for volumetric displays. In this paper, we discuss the design, implementation and characterization of the proposed volumetric display's first prototype. We developed an 8 × 8 × 8 display comprising two types of QDs. This display provides multicolour three-type two-dimensional patterns when viewed from different angles. The QD-based volumetric display provides a new way to represent images and could be applied in leisure and advertising industries, among others.

Mechanisms of Local Stress Sensing in Multifunctional Polymer Films Using Fluorescent Tetrapod Nanocrystals

DOE PAGES

Raja, Shilpa N.; Zherebetskyy, Danylo; Wu, Siva; ...

2016-07-13

Nanoscale stress-sensing can be used across fields ranging from detection of incipient cracks in structural mechanics to monitoring forces in biological tissues. We demonstrate how tetrapod quantum dots (tQDs) embedded in block copolymers act as sensors of tensile/compressive stress. Remarkably, tQDs can detect their own composite dispersion and mechanical properties with a switch in optomechanical response when tQDs are in direct contact. Using experimental characterizations, atomistic simulations and finite-element analyses, we show that under tensile stress, densely packed tQDs exhibit a photoluminescence peak shifted to higher energies ("blue-shift") due to volumetric compressive stress in their core; loosely packed tQDs exhibitmore » a peak shifted to lower energies ("red-shift") from tensile stress in the core. The stress shifts result from the tQD's unique branched morphology in which the CdS arms act as antennas that amplify the stress in the CdSe core. Our nanocomposites exhibit excellent cyclability and scalability with no degraded properties of the host polymer. Colloidal tQDs allow sensing in many materials to potentially enable autoresponsive, smart structural nanocomposites that self-predict upcoming fracture.« less

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

NASA Astrophysics Data System (ADS)

Alireza, Samavati; Othaman, Z.; K. Ghoshal, S.; K. Mustafa, M.

2015-02-01

The influences of thermal annealing on the structural and optical features of radio frequency (rf) magnetron sputtered self-assembled Ge quantum dots (QDs) on Si (100) are investigated. Preferentially oriented structures of Ge along the (220) and (111) directions together with peak shift and reduced strain (4.9% to 2.7%) due to post-annealing at 650 °C are discerned from x-ray differaction (XRD) measurement. Atomic force microscopy (AFM) images for both pre-annealed and post-annealed (650 °C) samples reveal pyramidal-shaped QDs (density ˜ 0.26× 1011 cm-2) and dome-shape morphologies with relatively high density ˜ 0.92 × 1011 cm-2, respectively. This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity. The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role. The observed red-shift ˜ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing, and is related to the effect of quantum confinement. Furthermore, the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge dots. Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart. An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes. A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established. Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated. Project supported by Ibnu Sina Institute for Fundamental Science Study, Universiti Teknologi Malaysia through Vote Q.J130000.2526.02H94, O5 and Postdoctoral Research Grant.

Single layer of Ge quantum dots in HfO2 for floating gate memory capacitors.

PubMed

Lepadatu, A M; Palade, C; Slav, A; Maraloiu, A V; Lazanu, S; Stoica, T; Logofatu, C; Teodorescu, V S; Ciurea, M L

2017-04-28

High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO 2 were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO 2 /floating gate of single layer of Ge QDs in HfO 2 /tunnel HfO 2 /p-Si wafers. Both Ge and HfO 2 are nanostructured by RTA at moderate temperatures of 600-700 °C. By nanostructuring at 600 °C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 × 10 15 m -2 is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO 2 nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO 2 NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO 2 NCs boundaries, while another part of the Ge atoms is present inside the HfO 2 lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8 ± 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO 2 , distanced from the Si substrate by the tunnel oxide layer with a precise thickness.

Detection of malachite green in fish based on magnetic fluorescent probe of CdTe QDs/nano-Fe3O4@MIPs

NASA Astrophysics Data System (ADS)

Wu, Le; Lin, Zheng-Zhong; Zeng, Jun; Zhong, Hui-Ping; Chen, Xiao-Mei; Huang, Zhi-Yong

2018-05-01

A magnetic fluorescent probe of CdTe QDs/nano-Fe3O4@MIPs was prepared using CdTe QDs and Fe3O4 nanoparticles as co-nucleus and molecularly imprinted polymers (MIPs) as specific recognition sites based on a reverse microemulsion method. With the specific enrichment and magnetic separation properties, the probe of CdTe QDs/nano-Fe3O4@MIPs was used to detect malachite green (MG) in fish samples. The TEM analysis showed that the particles of CdTe QDs/nano-Fe3O4@MIPs were spherical with average diameter around 53 nm, and a core-shell structure was well-shaped with several Fe3O4 nanoparticles and CdTe QDs embedded in each of the microsphere. Quick separation of the probes from solutions could be realized with a magnet, indicating the excellent magnetic property of CdTe QDs/nano-Fe3O4@MIPs. The probe exhibited high specific adsorption towards MG and excellent fluorescence emission at λem 598 nm. The fluorescence of CdTe QDs/nano-Fe3O4@MIPs could be linearly quenched by MG at the concentrations from 0.025 to 1.5 μmol L-1. The detection limit was 0.014 μmol L-1. The average recovery of spiked MG in fish samples was 105.2%. The result demonstrated that the as-prepared CdTe QDs/nano-Fe3O4@MIPs could be used as a probe to the detection of trace MG in fish samples.

Electrical transport in transverse direction through silicon carbon alloy multilayers containing regular size silicon quantum dots

NASA Astrophysics Data System (ADS)

Mandal, Aparajita; Kole, Arindam; Dasgupta, Arup; Chaudhuri, Partha

2016-11-01

Electrical transport in the transverse direction has been studied through a series of hydrogenated silicon carbon alloy multilayers (SiC-MLs) deposited by plasma enhanced chemical vapor deposition method. Each SiC-ML consists of 30 cycles of the alternating layers of a nearly amorphous silicon carbide (a-SiC:H) and a microcrystalline silicon carbide (μc-SiC:H) that contains high density of silicon quantum dots (Si-QDs). A detailed investigation by cross sectional TEM reveals preferential growth of densely packed Si-QDs of regular sizes ∼4.8 nm in diameter in a vertically aligned columnar structure within the SiC-ML. More than six orders of magnitude increase in transverse current through the SiC-ML structure were observed for decrease in the a-SiC:H layer thickness from 13 nm to 2 nm. The electrical transport mechanism was established to be a combination of grain boundary or band tail hopping and Frenkel-Poole (F-P) type conduction depending on the temperature and externally applied voltage ranges. Evaluation of trap concentration within the multilayer structures from the fitted room temperature current voltage characteristics by F-P function shows reduction up-to two orders of magnitude indicating an improvement in the short range order in the a-SiC:H matrix for decrease in the thickness of a-SiC:H layer.

Structural studies of n-type nc-Si-QD thin films for nc-Si solar cells

NASA Astrophysics Data System (ADS)

Das, Debajyoti; Kar, Debjit

2017-12-01

A wide optical gap nanocrystalline silicon (nc-Si) dielectric material is a basic requirement at the n-type window layer of nc-Si solar cells in thin film n-i-p structure on glass substrates. Taking advantage of the high atomic-H density inherent to the planar inductively coupled low-pressure (SiH4 + CH4)-plasma, development of an analogous material in P-doped nc-Si-QD/a-SiC:H network has been tried. Incorporation of C in the Si-network extracted from the CH4 widens the optical band gap; however, at enhanced PH3-dilution of the plasma spontaneous miniaturization of the nc-Si-QDs below the dimension of Bohr radius (∼4.5 nm) further enhances the band gap by virtue of the quantum size effect. At increased flow rate of PH3, dopant induced continuous amorphization of the intrinsic crystalline network is counterbalanced by the further crystallization promoted by the supplementary atomic-H extracted from PH3 (1% in H2) in the plasma, eventually holding a moderately high degree of crystallinity. The n-type wide band gap (∼1.93 eV) window layer with nc-Si-QDs in adequate volume fraction (∼52%) could furthermore be instrumental as an effective seed layer for advancing sequential crystallization in the i-layer of nc-Si solar cells with n-i-p structure in superstrate configuration.

Highly luminescent silica-coated CdS/CdSe/CdS nanoparticles with strong chemical robustness and excellent thermal stability

NASA Astrophysics Data System (ADS)

Wang, Nianfang; Koh, Sungjun; Jeong, Byeong Guk; Lee, Dongkyu; Kim, Whi Dong; Park, Kyoungwon; Nam, Min Ki; Lee, Kangha; Kim, Yewon; Lee, Baek-Hee; Lee, Kangtaek; Bae, Wan Ki; Lee, Doh C.

2017-05-01

We present facile synthesis of bright CdS/CdSe/CdS@SiO2 nanoparticles with 72% of quantum yields (QYs) retaining ca 80% of the original QYs. The main innovative point is the utilization of the highly luminescent CdS/CdSe/CdS seed/spherical quantum well/shell (SQW) as silica coating seeds. The significance of inorganic semiconductor shell passivation and structure design of quantum dots (QDs) for obtaining bright QD@SiO2 is demonstrated by applying silica encapsulation via reverse microemulsion method to three kinds of QDs with different structure: CdSe core and 2 nm CdS shell (CdSe/CdS-thin); CdSe core and 6 nm CdS shell (CdSe/CdS-thick); and CdS core, CdSe intermediate shell and 5 nm CdS outer shell (CdS/CdSe/CdS-SQW). Silica encapsulation inevitably results in lower photoluminescence quantum yield (PL QY) than pristine QDs due to formation of surface defects. However, the retaining ratio of pristine QY is different in the three silica coated samples; for example, CdSe/CdS-thin/SiO2 shows the lowest retaining ratio (36%) while the retaining ratio of pristine PL QY in CdSe/CdS-thick/SiO2 and SQW/SiO2 is over 80% and SQW/SiO2 shows the highest resulting PL QY. Thick outermost CdS shell isolates the excitons from the defects at surface, making PL QY relatively insensitive to silica encapsulation. The bright SiO2-coated SQW sample shows robustness against harsh conditions, such as acid etching and thermal annealing. The high luminescence and long-term stability highlights the potential of using the SQW/SiO2 nanoparticles in bio-labeling or display applications.

Impact of distributions on the archetypes and prototypes in heterogeneous nanoparticle ensembles.

PubMed

Fernandez, Michael; Wilson, Hugh F; Barnard, Amanda S

2017-01-05

The magnitude and complexity of the structural and functional data available on nanomaterials requires data analytics, statistical analysis and information technology to drive discovery. We demonstrate that multivariate statistical analysis can recognise the sets of truly significant nanostructures and their most relevant properties in heterogeneous ensembles with different probability distributions. The prototypical and archetypal nanostructures of five virtual ensembles of Si quantum dots (SiQDs) with Boltzmann, frequency, normal, Poisson and random distributions are identified using clustering and archetypal analysis, where we find that their diversity is defined by size and shape, regardless of the type of distribution. At the complex hull of the SiQD ensembles, simple configuration archetypes can efficiently describe a large number of SiQDs, whereas more complex shapes are needed to represent the average ordering of the ensembles. This approach provides a route towards the characterisation of computationally intractable virtual nanomaterial spaces, which can convert big data into smart data, and significantly reduce the workload to simulate experimentally relevant virtual samples.

Effect of core quantum-dot size on power-conversion-efficiency for silicon solar-cells implementing energy-down-shift using CdSe/ZnS core/shell quantum dots.

PubMed

Baek, Seung-Wook; Shim, Jae-Hyoung; Seung, Hyun-Min; Lee, Gon-Sub; Hong, Jin-Pyo; Lee, Kwang-Sup; Park, Jea-Gun

2014-11-07

Silicon solar cells mainly absorb visible light, although the sun emits ultraviolet (UV), visible, and infrared light. Because the surface reflectance of a textured surface with SiNX film on a silicon solar cell in the UV wavelength region (250-450 nm) is higher than ∼27%, silicon solar-cells cannot effectively convert UV light into photo-voltaic power. We implemented the concept of energy-down-shift using CdSe/ZnS core/shell quantum-dots (QDs) on p-type silicon solar-cells to absorb more UV light. CdSe/ZnS core/shell QDs demonstrated clear evidence of energy-down-shift, which absorbed UV light and emitted green-light photoluminescence signals at a wavelength of 542 nm. The implementation of 0.2 wt% (8.8 nm QDs layer) green-light emitting CdSe/ZnS core/shell QDs reduced the surface reflectance of the textured surface with SiNX film on a silicon solar-cell from 27% to 15% and enhanced the external quantum efficiency (EQE) of silicon solar-cells to around 30% in the UV wavelength region, thereby enhancing the power conversion efficiency (PCE) for p-type silicon solar-cells by 5.5%.

Surface-initiated ring-opening metathesis polymerization (SI-ROMP) to attach a tethered organic corona onto CdSe/ZnS core/shell quantum dots

PubMed Central

Vatansever, Fatma; Hamblin, Michael R.

2016-01-01

Core–shell CdSe/ZnS quantum dots (QDs) are useful as tunable photostable fluorophores for multiple applications in industry, biology, and medicine. However, to achieve the optimum optical properties, the surface of the QDs must be passivated to remove charged sites that might bind extraneous substances and allow aggregation. Here we describe a method of growing an organic polymer corona onto the QD surface using the bottom-up approach of surface-initiated ring-opening metathesis polymerization (SI-ROMP) with Grubbs catalyst. CdSe/ZnS QDs were first coated with mercaptopropionic acid by displacing the original trioctylphosphine oxide layer, and then reacted with 7-octenyl dimethyl chlorosilane. The resulting octenyl double bonds allowed the attachment of ruthenium alkylidene groups as a catalyst. A subsequent metathesis reaction with strained bicyclic monomers (norbornene-dicarbonyl chloride (NDC), and a mixture of NDC and norbornenylethylisobutyl-polyhedral oligomeric silsesquioxane (norbornoPOSS)) allowed the construction of tethered organic homo-polymer or co-polymer layers onto the QD. Compounds were characterized by FT-IR, 1H-NMR, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy. Atomic force microscopy showed that the coated QDs were separate and non-aggregated with a range of diameter of 48–53 nm. PMID:28360819

Nanodiamonds and silicon quantum dots: ultrastable and biocompatible luminescent nanoprobes for long-term bioimaging.

PubMed

Montalti, M; Cantelli, A; Battistelli, G

2015-07-21

Fluorescence bioimaging is a powerful, versatile, method for investigating, both in vivo and in vitro, the complex structures and functions of living organisms in real time and space, also using super-resolution techniques. Being poorly invasive, fluorescence bioimaging is suitable for long-term observation of biological processes. Long-term detection is partially prevented by photobleaching of organic fluorescent probes. Semiconductor quantum dots, in contrast, are ultrastable, fluorescent contrast agents detectable even at the single nanoparticle level. Emission color of quantum dots is size dependent and nanoprobes emitting in the near infrared (NIR) region are ideal for low back-ground in vivo imaging. Biocompatibility of nanoparticles, containing toxic elements, is debated. Recent safety concerns enforced the search for alternative ultrastable luminescent nanoprobes. Most recent results demonstrated that optimized silicon quantum dots (Si QDs) and fluorescent nanodiamonds (FNDs) show almost no photobleaching in a physiological environment. Moreover in vitro and in vivo toxicity studies demonstrated their unique biocompatibility. Si QDs and FNDs are hence ideal diagnostic tools and promising non-toxic vectors for the delivery of therapeutic cargos. Most relevant examples of applications of Si QDs and FNDs to long-term bioimaging are discussed in this review comparing the toxicity and the stability of different nanoprobes.

Synthesis of surface molecular imprinting polymer on SiO2-coated CdTe quantum dots as sensor for selective detection of sulfadimidine

NASA Astrophysics Data System (ADS)

Zhou, Zhiping; Ying, Haiqin; Liu, Yanyan; Xu, Wanzhen; Yang, Yanfei; Luan, Yu; Lu, Yi; Liu, Tianshu; Yu, Shui; Yang, Wenming

2017-05-01

This paper demonstrates a facile method to synthesize surface molecular imprinting polymer (MIP) on SiO2-coated CdTe QDs for selective detection of sulfadimidine (SM2). The fluorescent MIP sensor was prepared using cadmium telluride quantum dots (CdTe QDs) as the material of fluorescent signal readout, sulfadimidine as template molecule, 3-aminopropyltriethoxysilane (APTES) as functional monomer and tetraethyloxysilane (TEOS) as cross-linking agent. The CdTe cores were embed in the silicon shells by a sol-gel reaction and then the molecular imprinting layers were immobilized on the surface of the SiO2-coated CdTe QDs. Under the optimized conditions, the relative fluorescent intensity weakened in a linear way with the increasing concentration of sulfadimidine in the range of 10-60 μmol L-1. The practical application of the fluorescent MIP sensor was evaluated by means of analyzing sulfadimidine in the real milk samples. The recoveries were at the range of 90.3-99.6% and the relative standard deviation (RSD) ranged from 1.9 to 3.1%, which indicates the successful synthesis of the fluorescent MIP sensor. This sensor provides an alternative solution for selective determination of sulfadimidine from real milk samples.

Photoluminescence enhancement through vertical stacking of defect-engineered Ge on Si quantum dots

NASA Astrophysics Data System (ADS)

Groiss, Heiko; Spindlberger, Lukas; Oberhumer, Peter; Schäffler, Friedrich; Fromherz, Thomas; Grydlik, Martyna; Brehm, Moritz

2017-02-01

In this work, we show that the room-temperature photoluminescence intensity from Ge ion-bombarded (GIB) epitaxial Ge on Si quantum dots (QD) can be improved by their vertical stacking. We stress that the growth of GIB-QD multilayers is more demanding compared to all-crystalline epitaxial QDs, as a consequence of local amorphous regions within the GIB-QDs required during their genesis. We show that in spite of those amorphous regions, for accurately chosen growth temperatures of the Si spacer layers separating the GIB-QD layers, multiple GIB-QD layers can be stacked without detrimental break-down of epitaxial growth. Compared to a single GIB-QD layer, we observe a 650% increase in PL intensity for an eleven-layer GIB-QD stack, indicating that such multilayers are promising candidates as gain material for all-group-IV nano-photonic lasers.

High color rendering index of remote-type white LEDs with multi-layered quantum dot-phosphor films and short-wavelength pass dichroic filters

NASA Astrophysics Data System (ADS)

Yoon, Hee Chang; Oh, Ji Hye; Do, Young Rag

2014-09-01

This paper introduces high color rendering index (CRI) white light-emitting diodes (W-LEDs) coated with red emitting (Sr,Ca)AlSiN3:Eu phosphors and yellowish-green emitting AgIn5S8/ZnS (AIS/ZS) quantum dots (QDs) on glass or a short-wavelength pass dichroic filter (SPDF), which transmit blue wavelength regions and reflect yellow wavelength regions. The red emitting (Sr,Ca)AlSiN3:Eu phosphor film is coated on glass and a SPDF using a screen printing method, and then the yellowish-green emitting AIS/ZS QDs are coated on the red phosphor (Sr,Ca)AlSiN3:Eu film-coated glass and SPDF using the electrospray (e-spray) method.To fabricate the red phosphor film, the optimum amount of phosphor is dispersed in a silicon binder to form a red phosphor paste. The AIS/ZS QDs are mixed with dimethylformamide (DMF), toluene, and poly(methyl methacrylate) (PMMA) for the e-spray coating. The substrates are spin-coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to fabricate a conductive surface. The CRI of the white LEDs is improved through inserting the red phosphor film between the QD layer and the glass substrate. Furthermore, the light intensities of the multi-layered phosphor films are enhanced through changing the glass substrate to the SPDF. The correlated color temperatures (CCTs) vary as a function of the phosphor concentration in the phosphor paste. The optical properties of the yellowish-green AIS/ZS QDs and red (Sr,Ca)AlSiN3:Eu phosphors are characterized using photoluminescence (PL), and the multi-layered QD-phosphor films are measured using electroluminescence (EL) with an InGaN blue LED (λmax = 450 nm) at 60 mA.

An ultrasensitive SiO2-encapsulated alloyed CdZnSeS quantum dot-molecular beacon nanobiosensor for norovirus.

PubMed

Adegoke, Oluwasesan; Seo, Min-Woong; Kato, Tatsuya; Kawahito, Shoji; Park, Enoch Y

2016-12-15

Ultrasensitive, rapid and selective diagnostic probes are urgently needed to overcome the limitations of traditional probes for norovirus (NV). Here, we report the detection of NV genogroup II via nucleic acid hybridization technology using a quantum dot (QD)-conjugated molecular beacon (MB) probe. To boost the sensitivity of the MB assay system, an ultrasensitive QD fluorophore with unique optical properties was synthesized, characterized and exploited as a fluorescence signal generator. Alloyed thioglycolic (TGA)-capped CdZnSeS QDs with a high photoluminescence (PL) quantum yield (QY) value of 92% were synthesized, and a modified silanization method was employed to encapsulate the thiol-capped QDs in a silica layer. The resulting highly luminescent alloyed SiO2-coated CdZnSeS QDs had a remarkable PL QY value of 98%. Transmission electron microscopy and dynamic light scattering confirmed the monodispersity of the alloyed nanocrystals, and zeta potential analysis confirmed their colloidal stability. Powder X-ray diffraction and PL lifetime measurements confirmed the surface modification of the QDs. The alloyed TGA-capped and SiO2-coated CdZnSeS QD-conjugated MB bioprobes detected extremely low concentrations of NV RNA. Ultrasensitive detection of low concentrations of NV RNA with a limit of detection (LOD) of 8.2copies/mL in human serum and a LOD of 9.3 copies/mL in buffer was achieved using the SiO2-coated CdZnSeS QD-MB probes, an increase in sensitivity of 3-fold compared with the detection limit for NV RNA using TGA-capped CdZnSeS QD-MBs. The additional merits of our detection system are rapidity, specificity and improved sensitivity over conventional molecular test probes. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Synthesis, properties, and formation mechanism of Mn-doped Zn 2 SiO 4 nanowires and associated heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Haiqing; Moronta, Dominic; Li, Luyao

In this study, we have put forth a facile hydrothermal approach to synthesize an array of one-dimensional (1D) Mn-doped Zn 2SiO 4 nanostructures. Specifically, we have probed and correlated the effects of controllable reaction parameters such as the pH and Mn dopant concentrations with the resulting crystal structures and morphologies of the products obtained. Based upon our results, we find that careful tuning of the pH versus the Mn dopant level gives rise to opposite trends with respect to the overall size of the resulting one-dimensional nanostructures. Significantly, we have highlighted the role of the Mn dopant ion concentration asmore » a potentially generalizable reaction parameter in solution-based synthesis for controlling morphology and hence, the observed optical behavior. Indeed, such a strategy can be potentially generalized to systems such as but not limited to Mn-doped ZnS, CdS, and CdSe quantum dots (QD), which, to the best of our knowledge, denote promising candidates for a variety of optoelectronic applications. Specifically, we have carefully optimized the synthesis conditions in order to generate a series of chemically well-defined Mn-doped Zn 2SiO 4 not only possessing Mn concentrations ranging from 3% to 8% but also characterized by highly crystalline, monodisperse wire-like motifs measuring ~30 nm in diameter and ~700 nm in length. Optically, the photoluminescence signals associated with the 1D series yielded a volcano-shaped relationship between PL intensities and the Mn dopant level. In additional experiments, we have immobilized CdSe quantum dots (QDs) onto the external surfaces of our as-synthesized Mn-doped Zn 2SiO 4 nanowires, in order to form novel composite heterostructures. The optical properties of the CdSe QD–Mn:Zn 2SiO 4 heterostructures have been subsequently examined. Our results have demonstrated the likely co-existence of both energy transfer and charge transfer phenomena between the two constituent components of our as-prepared composites. Specifically, when both components are photoexcited, both energy transfer and charge transfer were found to plausibly occur, albeit in opposite directions. When the CdSe QDs are excited alone for example, charge transfer probably takes place from the CdSe QDs to the dopant Mn 2+ ions. We believe that our as-processed heterostructures are therefore promising as a tunable light-harvesting motif. Essentially, these materials have broadened the effective light absorption range for optical ‘accessibility’, not only through their incorporation of dopant-tunable Zn 2SiO 4 possessing complementary absorption properties to those of the QDs but also through their integration of CdSe QDs with size-tailorable optical behavior.« less

Synthesis, properties, and formation mechanism of Mn-doped Zn 2 SiO 4 nanowires and associated heterostructures

DOE PAGES

Liu, Haiqing; Moronta, Dominic; Li, Luyao; ...

2018-03-28

In this study, we have put forth a facile hydrothermal approach to synthesize an array of one-dimensional (1D) Mn-doped Zn 2SiO 4 nanostructures. Specifically, we have probed and correlated the effects of controllable reaction parameters such as the pH and Mn dopant concentrations with the resulting crystal structures and morphologies of the products obtained. Based upon our results, we find that careful tuning of the pH versus the Mn dopant level gives rise to opposite trends with respect to the overall size of the resulting one-dimensional nanostructures. Significantly, we have highlighted the role of the Mn dopant ion concentration asmore » a potentially generalizable reaction parameter in solution-based synthesis for controlling morphology and hence, the observed optical behavior. Indeed, such a strategy can be potentially generalized to systems such as but not limited to Mn-doped ZnS, CdS, and CdSe quantum dots (QD), which, to the best of our knowledge, denote promising candidates for a variety of optoelectronic applications. Specifically, we have carefully optimized the synthesis conditions in order to generate a series of chemically well-defined Mn-doped Zn 2SiO 4 not only possessing Mn concentrations ranging from 3% to 8% but also characterized by highly crystalline, monodisperse wire-like motifs measuring ~30 nm in diameter and ~700 nm in length. Optically, the photoluminescence signals associated with the 1D series yielded a volcano-shaped relationship between PL intensities and the Mn dopant level. In additional experiments, we have immobilized CdSe quantum dots (QDs) onto the external surfaces of our as-synthesized Mn-doped Zn 2SiO 4 nanowires, in order to form novel composite heterostructures. The optical properties of the CdSe QD–Mn:Zn 2SiO 4 heterostructures have been subsequently examined. Our results have demonstrated the likely co-existence of both energy transfer and charge transfer phenomena between the two constituent components of our as-prepared composites. Specifically, when both components are photoexcited, both energy transfer and charge transfer were found to plausibly occur, albeit in opposite directions. When the CdSe QDs are excited alone for example, charge transfer probably takes place from the CdSe QDs to the dopant Mn 2+ ions. We believe that our as-processed heterostructures are therefore promising as a tunable light-harvesting motif. Essentially, these materials have broadened the effective light absorption range for optical ‘accessibility’, not only through their incorporation of dopant-tunable Zn 2SiO 4 possessing complementary absorption properties to those of the QDs but also through their integration of CdSe QDs with size-tailorable optical behavior.« less

Tailoring of quantum dot emission efficiency by localized surface plasmon polaritons in self-organized mesoscopic rings.

PubMed

Margapoti, Emanuela; Gentili, Denis; Amelia, Matteo; Credi, Alberto; Morandi, Vittorio; Cavallini, Massimiliano

2014-01-21

We report on the tailoring of quantum dot (QD) emission efficiency by localized surface plasmon polaritons in self-organized mesoscopic rings. Ag nanoparticles (NPs) with CdSe QDs embedded in a polymeric matrix are spatially organised in mesoscopic rings and coupled in a tuneable fashion by breath figure formation. The mean distance between NPs and QDs and consequently the intensity of QD photoluminescence, which is enhanced by the coupling of surface plasmons and excitons, are tuned by acting on the NP concentration.

A novel strategy towards designing a CdSe quantum dot-metallohydrogel composite material.

PubMed

Chatterjee, Sayantan; Maitra, Uday

2016-08-11

We have described here an efficient method to disperse hydrophobic CdSe quantum dots (QDs) in an aqueous phase using cetyltrimethylammonium bromide (CTAB) micelles without any surface ligand exchange. The water soluble QDs were then embedded in 3D self assembled fibrillar networks (SAFINs) of a hydrogel showing homogeneous dispersibility as evidenced from optical and electron microscopic techniques. The photophysical studies of the hydrogel-QD composite are reported for the first time. These composite materials may have potential applications in biology, optoelectronics, sensors, non-linear optics and materials science.

STM images of carbon-nanotube quantum dots: Seeing a Wigner molecule of correlated electrons

NASA Astrophysics Data System (ADS)

Secchi, Andrea; Rontani, Massimo

2011-03-01

The paradigm of few-electron complexes in quantum dots (QDs) relies on the idea that the lowest quantized levels are filled according to Pauli's exclusion principle. If Coulomb repulsion is sufficiently strong to overcome the kinetic energy cost of localization, a different scenario is predicted: a ``Wigner'' molecule (WM) forms, made of electrons frozen in space according to a geometrical pattern. Despite considerable experimental effort, evidence of the WM in semiconductor QDs has been elusive so far. Here we demonstrate theoretically that WMs occur in gate-defined QDs embedded in typical semiconducting carbon nanotubes (CNTs). The unambiguous signatures of the WM state must be searched in the scanning tunneling microscopy (STM) images of the electrons. Through exact diagonalisation (ED) calculations, we unveil the inherent features of the electron molecular states. We show that, like nuclei in a usual molecule, electrons have localized wave functions and hence negligible exchange interactions. ED results for single and double QDs provide a simple interpretation for transport experiments in ultraclean CNTs.

Detection of malachite green in fish based on magnetic fluorescent probe of CdTe QDs/nano-Fe3O4@MIPs.

PubMed

Wu, Le; Lin, Zheng-Zhong; Zeng, Jun; Zhong, Hui-Ping; Chen, Xiao-Mei; Huang, Zhi-Yong

2018-05-05

A magnetic fluorescent probe of CdTe QDs/nano-Fe 3 O 4 @MIPs was prepared using CdTe QDs and Fe 3 O 4 nanoparticles as co-nucleus and molecularly imprinted polymers (MIPs) as specific recognition sites based on a reverse microemulsion method. With the specific enrichment and magnetic separation properties, the probe of CdTe QDs/nano-Fe 3 O 4 @MIPs was used to detect malachite green (MG) in fish samples. The TEM analysis showed that the particles of CdTe QDs/nano-Fe 3 O 4 @MIPs were spherical with average diameter around 53nm, and a core-shell structure was well-shaped with several Fe 3 O 4 nanoparticles and CdTe QDs embedded in each of the microsphere. Quick separation of the probes from solutions could be realized with a magnet, indicating the excellent magnetic property of CdTe QDs/nano-Fe 3 O 4 @MIPs. The probe exhibited high specific adsorption towards MG and excellent fluorescence emission at λ em 598nm. The fluorescence of CdTe QDs/nano-Fe 3 O 4 @MIPs could be linearly quenched by MG at the concentrations from 0.025 to 1.5μmolL -1 . The detection limit was 0.014μmolL -1 . The average recovery of spiked MG in fish samples was 105.2%. The result demonstrated that the as-prepared CdTe QDs/nano-Fe 3 O 4 @MIPs could be used as a probe to the detection of trace MG in fish samples. Copyright © 2018 Elsevier B.V. All rights reserved.

Investigation of photoconductivity of individual InAs/GaAs(001) quantum dots by Scanning Near-field Optical Microscopy

NASA Astrophysics Data System (ADS)

Filatov, D. O.; Kazantseva, I. A.; Baidus', N. V.; Gorshkov, A. P.; Mishkin, V. P.

2017-10-01

The spatial distribution of the photocurrent in the input window plane of a GaAs-based p-i-n photodiode with embedded self-assembled InAs quantum dots (QDs) has been studied with the photoexcitation through a Scanning Near-field Optical Microscope (SNOM) probe at the emission wavelength greater than the intrinsic absorption edge of the host material (GaAs). The inhomogeneities related to the interband absorption in the individual InAs/GaAs(001) QDs have been observed in the photocurrent SNOM images. Thus, the possibility of imaging the individual InAs/GaAs(001) QDs in the photocurrent SNOM images with the lateral spatial resolution ˜ 100 nm (of the same order of magnitude as the SNOM probe aperture size) has been demonstrated.

Low-threshold indium gallium nitride quantum dot microcavity lasers

NASA Astrophysics Data System (ADS)

Woolf, Alexander J.

Gallium nitride (GaN) microcavities with embedded optical emitters have long been sought after as visible light sources as well as platforms for cavity quantum electrodynamics (cavity QED) experiments. Specifically, materials containing indium gallium nitride (InGaN) quantum dots (QDs) offer an outstanding platform to study light matter interactions and realize practical devices, such as on-chip light emitting diodes and nanolasers. Inherent advantages of nitride-based microcavities include low surface recombination velocities, enhanced room-temperature performance (due to their high exciton binding energy, as high as 67 meV for InGaN QDs), and emission wavelengths in the blue region of the visible spectrum. In spite of these advantages, several challenges must be overcome in order to capitalize on the potential of this material system. Such diffculties include the processing of GaN into high-quality devices due to the chemical inertness of the material, low material quality as a result of strain-induced defects, reduced carrier recombination effciencies due to internal fields, and a lack of characterization of the InGaN QDs themselves due to the diffculty of their growth and therefore lack of development relative to other semiconductor QDs. In this thesis we seek to understand and address such issues by investigating the interaction of light coupled to InGaN QDs via a GaN microcavity resonator. Such coupling led us to the demonstration of the first InGaN QD microcavity laser, whose performance offers insights into the properties and current limitations of the nitride materials and their emitters. This work is organized into three main sections. Part I outlines the key advantages and challenges regarding indium gallium nitride (InGaN) emitters embedded within gallium nitride (GaN) optical microcavities. Previous work is also discussed which establishes context for the work presented here. Part II includes the fundamentals related to laser operation, including the derivation and analysis of the laser rate equations. A thorough examination of the rate equations serves as a natural motivation for QDs and high-quality factor low-modal volume resonators as an optimal laser gain medium and cavity, respectively. The combination of the two theoretically yields the most efficient semiconductor laser device possible. Part III describes in detail the design, growth, fabrication and characterization of the first InGaN QD microcavity laser. Additional experiments are also conducted in order to conclusively prove that the InGaN QDs serve as the gain medium and facilitate laser oscillation within the microdisk cavities. Part III continues with work related towards the development of the next generation of nitride light emitting devices. This includes the realization of photonic crystal cavity (PCC) fragmented quantum well (FQW) lasers that exhibit record low lasing thresholds of 9.1 muJ/cm2, comparable to the best devices in other III-V material systems. Part III also discusses cavity QED experiments on InGaN QDs embedded within GaN PCCs in order to quantify the degree of light-matter interaction. The lack of experimental evidence for weak or strong coupling, in the form of the Purcell Effect or cavity-mode anti-crossing respectively, naturally motivates the question of what mechanism is limiting the device performance. Part III concludes with cathodoluminesence and tapered fiber measurements in order to identify the limiting factor towards achieving strong coupling between InGaN QDs and GaN microcavities.

Novel hybrid structure silica/CdTe/molecularly imprinted polymer: synthesis, specific recognition, and quantitative fluorescence detection of bovine hemoglobin.

PubMed

Li, Dong-Yan; He, Xi-Wen; Chen, Yang; Li, Wen-You; Zhang, Yu-Kui

2013-12-11

This work presented a novel strategy for the synthesis of the hybrid structure silica/CdTe/molecularly imprinted polymer (Si-NP/CdTe/MIP) to recognize and detect the template bovine hemoglobin (BHb). First, amino-functionalized silica nanoparticles (Si-NP) and carboxyl-terminated CdTe quantum dots (QDs) were assembled into composite nanoparticles (Si-NP/CdTe) using the EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride) chemistry. Next, Si-NP/CdTe/MIP was synthesized by anchoring molecularly imprinted polymer (MIP) layer on the surface of Si-NP/CdTe through the sol-gel technique and surface imprinting technique. The hybrid structure possessed the selectivity of molecular imprinting technique and the sensitivity of CdTe QDs as well as well-defined morphology. The binding experiment and fluorescence method demonstrated its special recognition performance toward the template BHb. Under the optimized conditions, the fluorescence intensity of the Si-NP/CdTe/MIP decreased linearly with the increase of BHb in the concentration range 0.02-2.1 μM, and the detection limit was 9.4 nM. Moreover, the reusability and reproducibility and the successful applications in practical samples indicated the synthesis of Si-NP/CdTe/MIP provided an alternative solution for special recognition and determination of protein from real samples.

Enhancing the Performance of Perovskite Solar Cells by Hybridizing SnS Quantum Dots with CH3 NH3 PbI3.

PubMed

Han, Jianhua; Yin, Xuewen; Nan, Hui; Zhou, Yu; Yao, Zhibo; Li, Jianbao; Oron, Dan; Lin, Hong

2017-08-01

The combination of perovskite solar cells and quantum dot solar cells has significant potential due to the complementary nature of the two constituent materials. In this study, solar cells (SCs) with a hybrid CH 3 NH 3 PbI 3 /SnS quantum dots (QDs) absorber layer are fabricated by a facile and universal in situ crystallization method, enabling easy embedding of the QDs in perovskite layer. Compared with SCs based on CH 3 NH 3 PbI 3 , SCs using CH 3 NH 3 PbI 3 /SnS QDs hybrid films as absorber achieves a 25% enhancement in efficiency, giving rise to an efficiency of 16.8%. The performance improvement can be attributed to the improved crystallinity of the absorber, enhanced photo-induced carriers' separation and transport within the absorber layer, and improved incident light utilization. The generality of the methods used in this work paves a universal pathway for preparing other perovskite/QDs hybrid materials and the synthesis of entire nontoxic perovskite/QDs hybrid structure. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Single photon sources with single semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Shan, Guang-Cun; Yin, Zhang-Qi; Shek, Chan Hung; Huang, Wei

2014-04-01

In this contribution, we briefly recall the basic concepts of quantum optics and properties of semiconductor quantum dot (QD) which are necessary to the understanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantum emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as optical properties of the QDs. We then review the localization of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and performances in terms of strong coupling regime, efficiency, directionality, and polarization control. Furthermore, we will discuss the recent progress on the fabrication of single photon sources, and various approaches for embedding single QDs into microcavities or photonic crystal nanocavities and show how to extend the wavelength range. We focus in particular on new generations of electrically driven QD single photon source leading to high repetition rates, strong coupling regime, and high collection efficiencies at elevated temperature operation. Besides, new developments of room temperature single photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for practical single-photon sources are also discussed.

Plasmonically enhanced electromotive force of narrow bandgap PbS QD-based photovoltaics.

PubMed

Li, Xiaowei; McNaughter, Paul D; O'Brien, Paul; Minamimoto, Hiro; Murakoshi, Kei

2018-05-30

Electromotive force of photovoltaics is a key to define the output power density of photovoltaics. Multiple exciton generation (MEG) exhibited by semiconductor quantum dots (QDs) has great potential to enhance photovoltaic performance owing to the ability to generate more than one electron-hole pairs when absorbing a single photon. However, even in MEG-based photovoltaics, limitation of modifying the electromotive force exists due to the intrinsic electrochemical potential of the conduction band-edges of QDs. Here we report a pronouncedly improved photovoltaic performance by constructing a PbS QD-sensitized electrode that comprises plasmon-active Au nanoparticles embedded in a titanium dioxide thin film. Significant enhancement on electromotive force is characterized by the onset potential of photocurrent generation using MEG-effective PbS QDs with a narrow bandgap energy (Eg = 0.9 eV). By coupling with localized surface plasmon resonance (LSPR), such QDs exhibit improved photoresponses and the highest output power density over the other QDs with larger bandgap energies (Eg = 1.1 and 1.7 eV) under visible light irradiation. The wavelength-dependent onset potential and the output power density suggest effective electron injection owing to the enhanced density of electrons excited by energy overlapping between MEG and LSPR.

Efficient Visible Photoluminescence from Self-Assembled Ge QDs Embedded in Silica Matrix

NASA Astrophysics Data System (ADS)

Samavati, Alireza; Samavati, Zahra; Ismail, A. F.; Othman, M. H. D.; Rahman, M. A.; Zulhairun, A. K.

2017-06-01

Not Available Supported by the Advanced Membrane Technology Research Center of the Universities Teknologi Malaysia under Grant No R.J130000.7609.4C112, the Postdoctoral Grant, and the Frontier Materials Research Alliance.

Photovoltaic devices based on quantum dot functionalized nanowire arrays embedded in an organic matrix

NASA Astrophysics Data System (ADS)

Kung, Patrick; Harris, Nicholas; Shen, Gang; Wilbert, David S.; Baughman, William; Balci, Soner; Dawahre, Nabil; Butler, Lee; Rivera, Elmer; Nikles, David; Kim, Seongsin M.

2012-01-01

Quantum dot (QD) functionalized nanowire arrays are attractive structures for low cost high efficiency solar cells. QDs have the potential for higher quantum efficiency, increased stability and lifetime compared to traditional dyes, as well as the potential for multiple electron generation per photon. Nanowire array scaffolds constitute efficient, low resistance electron transport pathways which minimize the hopping mechanism in the charge transport process of quantum dot solar cells. However, the use of liquid electrolytes as a hole transport medium within such scaffold device structures have led to significant degradation of the QDs. In this work, we first present the synthesis uniform single crystalline ZnO nanowire arrays and their functionalization with InP/ZnS core-shell quantum dots. The structures are characterized using electron microscopy, optical absorption, photoluminescence and Raman spectroscopy. Complementing photoluminescence, transmission electron microanalysis is used to reveal the successful QD attachment process and the atomistic interface between the ZnO and the QD. Energy dispersive spectroscopy reveals the co-localized presence of indium, phosphorus, and sulphur, suggestive of the core-shell nature of the QDs. The functionalized nanowire arrays are subsequently embedded in a poly-3(hexylthiophene) hole transport matrix with a high degree of polymer infiltration to complete the device structure prior to measurement.

Core-Shell Zn x Cd1- x Se/Zn y Cd1- y Se Quantum Dots for Nonvolatile Memory and Electroluminescent Device Applications

NASA Astrophysics Data System (ADS)

Al-Amoody, Fuad; Suarez, Ernesto; Rodriguez, Angel; Heller, E.; Huang, Wenli; Jain, F.

2011-08-01

This paper presents a floating quantum dot (QD) gate nonvolatile memory device using high-energy-gap Zn y Cd1- y Se-cladded Zn x Cd1- x Se quantum dots ( y > x) with tunneling layers comprising nearly lattice-matched semiconductors (e.g., ZnS/ZnMgS) on Si channels. Also presented is the fabrication of an electroluminescent (EL) device with embedded cladded ZnCdSe quantum dots. These ZnCdSe quantum dots were embedded between indium tin oxide (ITO) on glass and a top Schottky metal electrode deposited on a thin CsF barrier. These QDs, which were nucleated in a photo-assisted microwave plasma (PMP) metalorganic chemical vapor deposition (MOCVD) reactor, were grown between the source and drain regions on a p-type silicon substrate of the nonvolatile memory device. The composition of QD cladding, which relates to the value of y in Zn y Cd1- y Se, was engineered by the intensity of ultraviolet light, which controlled the incorporation of zinc in ZnCdSe. The QD quality is comparable to those deposited by other methods. Characteristics and modeling of the II-VI quantum dots as well as two diverse types of devices are presented in this paper.

Exploring ultrafast dynamics of excitons and multiexcitons in "giant" nanocrystal quantum dots

NASA Astrophysics Data System (ADS)

Sampat, Siddharth

In this work, we have performed extensive time resolved photoluminescence (PL) studies to further the understanding of charge dynamics in semiconductor nanocrystal quantum dots (QDs). Recent developments in QD synthesis have introduced a new set of QD known as "giant" quantum dots (gQDs) that consist of a CdSe core coated with up to 19 monolayers of a CdS shell. The thick shell layer is grown using a SILAR method resulting in a defect free, alloyed CdSe/CdS interface. This has been attributed to gQDs exhibiting excellent optical properties such as high excitonic quantum yield (QY), prolonged photostability and inhibition of flourescence intermittency ("blinking"), which is regularly observed in conventional QDs. In gQDs, however, owing to unique fabrication methods and material selection, the Auger process is strongly suppressed resulting in efficient radiative recombination of photogenerated excitons as well as high PL QY of charged excitonic and multiexcitonic species. We perform extensive single gQDs studies that establish the role played by gQD shell thickness and core size in governing their optical properties. It is found that both the core and shell dimensions can be tuned in order to achieve the smallest gQDs with the highest vii Auger suppression resulting in photostable dots with high QYs. Next, we perform a study of multiexcitonic species in gQDs that are encapsulated in an insulating SiO2shell. These silica-coated gQDs exhibit strong PL from charged excitons, biexcitons as well as triexcitons. This observation has led to an accurate description of excitonic and multiexcitonic behavior which is modeled using a statistical scaling approach. As a demonstration of the practical applicability of gQDs, energy transfer of excitons as well as multiexcitons to different substrates is studied. Finally, a back gated silicon nanomembrane FET device is discussed that exhibits a large photocurrent increase when sensitized with QDs.

GaAs metal-oxide-semiconductor based non-volatile flash memory devices with InAs quantum dots as charge storage nodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Islam, Sk Masiul, E-mail: masiulelt@gmail.com; Chowdhury, Sisir; Sarkar, Krishnendu

2015-06-24

Ultra-thin InP passivated GaAs metal-oxide-semiconductor based non-volatile flash memory devices were fabricated using InAs quantum dots (QDs) as charge storing elements by metal organic chemical vapor deposition technique to study the efficacy of the QDs as charge storage elements. The grown QDs were embedded between two high-k dielectric such as HfO{sub 2} and ZrO{sub 2}, which were used for tunneling and control oxide layers, respectively. The size and density of the QDs were found to be 5 nm and 1.8×10{sup 11} cm{sup −2}, respectively. The device with a structure Metal/ZrO{sub 2}/InAs QDs/HfO{sub 2}/GaAs/Metal shows maximum memory window equivalent to 6.87 V. Themore » device also exhibits low leakage current density of the order of 10{sup −6} A/cm{sup 2} and reasonably good charge retention characteristics. The low value of leakage current in the fabricated memory device is attributed to the Coulomb blockade effect influenced by quantum confinement as well as reduction of interface trap states by ultra-thin InP passivation on GaAs prior to HfO{sub 2} deposition.« less

Magnetically engineered SnO2 quantum dots as a bimodal agent for optical and magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Dutta, Dipa; Gupta, Jagriti; Thakur, Dinbandhu; Bahadur, Dhirendra

2017-12-01

Combining more than one imaging technique into a single system can outweigh the limitations of conventional imaging techniques. Pairing optically active quantum dots (QDs) with superparamagnetic MRI agent is an adorable way to develop probes for bimodal imaging. Tiny SnO2 quantum dot embedded iron oxide (IO) nanocomposite (SQD-IO) is synthesized. This combines the superparamagnetic property of IO nanoparticles (NPs) and special optical properties of SnO2 QDs, and is explored as a bimodal imaging agent. Morphological studies of the nanocomposite reveal that 3 nm tiny SnO2 QDs are embedded in ~30 nm γ-Fe2O3 NPs. The SQD-IO preserves the intrinsic superparamagnetic behaviour of its constituent IO NPs with a magnetization ~21.4 emu g-1 measured at an applied field of 20k Oe. The emission colour of the nanocomposite is tuned by simply varying the excitation wavelength. The centre of the emission band shifts from 570 to 600 nm as the excitation alters from 488 to 535 nm. The cytotoxicity assessment indicates that the nanocomposite is suitable for its in vitro use. Transverse proton relaxivity (141 mM-1 s-1) of the nanocomposite is higher than the widely used negative contrast agent Feridex (R2  =  98.3 mM-1 s-1). The confocal laser scanning microscope images give evidence of the cellular uptake behaviour of SQD-IO in HeLa cells and it is seen that QDs retain their optical properties within the intracellular environment. The high R2 value for MRI and the tunable florescence images of HeLa cells essentially establish SQD-IO as a potential probe for bimodal imaging.

Selective collection and detection of MCF-7 breast cancer cells using aptamer-functionalized magnetic beads and quantum dots based nano-bio-probes.

PubMed

Hua, Xin; Zhou, Zhenxian; Yuan, Liang; Liu, Songqin

2013-07-25

A novel strategy for selective collection and detection of breast cancer cells (MCF-7) based on aptamer-cell interaction was developed. Mucin 1 protein (MUC1) aptamer (Apt1) was covalently conjugated to magnetic beads to capture MCF-7 cell through affinity interaction between Apt1 and MUC1 protein that overexpressed on the surface of MCF-7 cells. Meanwhile, a nano-bio-probe was constructed by coupling of nucleolin aptamer AS1411 (Apt2) to CdTe quantum dots (QDs) which were homogeneously coated on the surfaces of monodispersed silica nanoparticles (SiO2 NPs). The nano-bio-probe displayed similar optical and electrochemical performances to free CdTe QDs, and remained high affinity to nucleolin overexpressed cells through the interaction between AS1411 and nucleolin protein. Photoluminescence (PL) and square-wave voltammetric (SWV) assays were used to quantitatively detect MCF-7 cells. Improved selectivity was obtained by using these two aptamers together as recognition elements simultaneously, compared to using any single aptamer. Based on the signal amplification of QDs coated silica nanoparticles (QDs/SiO2), the detection sensitivity was enhanced and a detection limit of 201 and 85 cells mL(-1) by PL and SWV method were achieved, respectively. The proposed strategy could be extended to detect other cells, and showed potential applications in cell imaging and drug delivery. Copyright © 2013 Elsevier B.V. All rights reserved.

Structural properties of templated Ge quantum dot arrays: impact of growth and pre-pattern parameters

NASA Astrophysics Data System (ADS)

Tempeler, J.; Danylyuk, S.; Brose, S.; Loosen, P.; Juschkin, L.

2018-07-01

In this study we analyze the impact of process and growth parameters on the structural properties of germanium (Ge) quantum dot (QD) arrays. The arrays were deposited by molecular-beam epitaxy on pre-patterned silicon (Si) substrates. Periodic arrays of pits with diameters between 120 and 20 nm and pitches ranging from 200 nm down to 40 nm were etched into the substrate prior to growth. The structural perfection of the two-dimensional QD arrays was evaluated based on SEM images. The impact of two processing steps on the directed self-assembly of Ge QD arrays is investigated. First, a thin Si buffer layer grown on a pre-patterned substrate reshapes the pre-pattern pits and determines the nucleation and initial shape of the QDs. Subsequently, the deposition parameters of the Ge define the overall shape and uniformity of the QDs. In particular, the growth temperature and the deposition rate are relevant and need to be optimized according to the design of the pre-pattern. Applying this knowledge, we are able to fabricate regular arrays of pyramid shaped QDs with dot densities up to 7.2 × 1010 cm‑2.

Structural properties of templated Ge quantum dot arrays: impact of growth and pre-pattern parameters.

PubMed

Tempeler, J; Danylyuk, S; Brose, S; Loosen, P; Juschkin, L

2018-07-06

In this study we analyze the impact of process and growth parameters on the structural properties of germanium (Ge) quantum dot (QD) arrays. The arrays were deposited by molecular-beam epitaxy on pre-patterned silicon (Si) substrates. Periodic arrays of pits with diameters between 120 and 20 nm and pitches ranging from 200 nm down to 40 nm were etched into the substrate prior to growth. The structural perfection of the two-dimensional QD arrays was evaluated based on SEM images. The impact of two processing steps on the directed self-assembly of Ge QD arrays is investigated. First, a thin Si buffer layer grown on a pre-patterned substrate reshapes the pre-pattern pits and determines the nucleation and initial shape of the QDs. Subsequently, the deposition parameters of the Ge define the overall shape and uniformity of the QDs. In particular, the growth temperature and the deposition rate are relevant and need to be optimized according to the design of the pre-pattern. Applying this knowledge, we are able to fabricate regular arrays of pyramid shaped QDs with dot densities up to 7.2 × 10 10 cm -2 .

A molecularly imprinted dual-emission carbon dot-quantum dot mesoporous hybrid for ratiometric determination of anti-inflammatory drug celecoxib

NASA Astrophysics Data System (ADS)

Amjadi, Mohammad; Jalili, Roghayeh

2018-02-01

We report on a ratiometric fluorescent sensor based on dual-emission molecularly imprinted mesoporous silica embedded with carbon dots and CdTe quantum dots (mMIP@CDs/QDs) for celecoxib (CLX) as target molecule. The fluorescence of the embedded CDs is insensitive to the analyte while the green emissive QDs are selectively quenched by it. This effect is much stronger for the MIP than for the non-imprinted polymer, which indicates a good recognition ability of the mesoporous MIP. The hybrid sensor also exhibited good selectivity to CLX over other substances. The ratio of the intensity at two wavelengths (F550/F440) proportionally decreased with the increasing of CLX concentration in the range of 0.08-0.90 μM. A detection limit as low as 57 nM was achieved. Experimental results testified that this sensor was highly sensitive and selective for the detection of CLX in human serum samples.

Growth and characterization of InSb on (1 0 0) Si for mid-infrared application

NASA Astrophysics Data System (ADS)

Jia, Bo Wen; Tan, Kian Hua; Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt

2018-05-01

Monolithic integration of InSb on (1 0 0) Si is a practical approach to realizing on-chip mid-infrared photonic devices. An InSb layer was grown on a (1 0 0) Si substrate using an AlSb/GaSb buffer containing InSb quantum dots (QDs). The growth process for the buffer involved the growth of GaSb on Si using an interfacial misfit array, followed by InSb QDs on AlSb to decrease the density of microtwins. InSb layers were separately grown on AlSb and GaSb surfaces to compare the effect of different interfacial misfit arrays. The samples were characterized using transmission electron microscopy and X-ray diffraction to determine the structural properties of the buffer and InSb layers. The InSb on the AlSb sample exhibited higher crystal quality than the InSb on GaSb sample due to a more favorable arrangement of interfacial misfit dislocations. Hall measurements of unintentionally doped InSb layers demonstrated a higher carrier mobility in the InSb on the AlSb sample than in InSb on GaSb. Growing InSb on AlSb also improved the photoresponsivity of InSb as a photoconductor on Si.

Blinking suppression of CdTe quantum dots on epitaxial graphene and the analysis with Marcus electron transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirose, Takuya; Tamai, Naoto, E-mail: tamai@kwansei.ac.jp; Kutsuma, Yasunori

We have prepared epitaxial graphene by a Si sublimation method from 4H-SiC. Single-particle spectroscopy of CdTe quantum dots (QDs) on epitaxial graphene covered with polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) showed the suppression of luminescence blinking and ∼10 times decreased luminescence intensity as compared with those on a glass. The electronic coupling constant, H{sub 01}, between CdTe QDs and graphene was calculated to be (3.3 ± 0.4) × 10{sup 2 }cm{sup −1} in PVP and (3.7 ± 0.8) × 10{sup 2 }cm{sup −1} in PEG based on Marcus theory of electron transfer and Tang-Marcus model of blinking with statistical distribution.

Correlation between size distribution and luminescence properties of spool-shaped InAs quantum dots

NASA Astrophysics Data System (ADS)

Xie, H.; Prioli, R.; Torelly, G.; Liu, H.; Fischer, A. M.; Jakomin, R.; Mourão, R.; Kawabata, R.; Pires, M. P.; Souza, P. L.; Ponce, F. A.

2017-05-01

InAs QDs embedded in an AlGaAs matrix have been produced by MOVPE with a partial capping and annealing technique to achieve controllable QD energy levels that could be useful for solar cell applications. The resulted spool-shaped QDs are around 5 nm in height and have a log-normal diameter distribution, which is observed by TEM to range from 5 to 15 nm. Two photoluminescence peaks associated with QD emission are attributed to the ground and the first excited states transitions. The luminescence peak width is correlated with the distribution of QD diameters through the diameter dependent QD energy levels.

Purple-bacterial photosynthetic reaction centers and quantum-dot hybrid-assemblies in lecithin liposomes and thin films.

PubMed

Lukashev, Eugeny P; Knox, Petr P; Gorokhov, Vladimir V; Grishanova, Nadezda P; Seifullina, Nuranija Kh; Krikunova, Maria; Lokstein, Heiko; Paschenko, Vladimir Z

2016-11-01

Quantum dots (QDs) absorb ultraviolet and long-wavelength visible light energy much more efficiently than natural bacterial light-harvesting proteins and can transfer the excitation energy to photosynthetic reaction centers (RCs). Inclusion of RCs combined with QDs as antennae into liposomes opens new opportunities for using such hybrid systems as a basis for artificial energy-transforming devices that potentially can operate with greater efficiency and stability than devices based only on biological components or inorganic components alone. RCs from Rhodobacter sphaeroides and QDs (CdSe/ZnS with hydrophilic covering) were embedded in lecithin liposomes by extrusion of a solution of multilayer lipid vesicles through a polycarbonate membrane or by dialysis of lipids and proteins dispersed with excess detergent. The efficiency of RC and QD interaction within the liposomes was estimated using fluorescence excitation spectra of the photoactive bacteriochlorophyll of the RCs and by measuring the fluorescence decay kinetics of the QDs. The functional activity of the RCs in hybrid complexes was fully maintained, and their stability was even increased. The efficiency of energy transfer between QDs and RCs and conditions of long-term stability of function of such hybrid complexes in film preparations were investigated as well. It was found that dry films containing RCs and QDs, maintained at atmospheric humidity, are capable of maintaining their functional activity for at least some months as judged by measurements of their spectral characteristics, efficiency of energy transfer from QDs to RCs and RC electron transport activity. Addition of trehalose to the films increases the stability further, especially for films maintained at low humidity. These stable hybrid film structures are promising for further studies towards developing new phototransformation devices for biotechnological applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Surface modification of ZnO quantum dots by organosilanes and oleic acid with enhanced luminescence for potential biological application

NASA Astrophysics Data System (ADS)

Rissi, Nathalia Cristina; Hammer, Peter; Aparecida Chiavacci, Leila

2017-01-01

Luminescent ZnO-QDs is a promising candidate for biological application, especially due to their low toxicity. Nevertheless, colloidal ZnO-QDs prepared by sol-gel route are unstable in water and incompatible with lipophilic systems, hindering their application in biology and medicine. To tackle the problem, this study reports three different strategies for surface modification of ZnO-QDs by: (i) hydrophilic (3-glycidyloxypropyl) trimethoxysilane (GPTMS), (ii) hydrophobic hexadecyltrimethoxysilane (HTMS) and then by (iii) oleic acid (OA) and HTMS bilayer. Capped ZnO-QDs by GPTMS and HTMS were performed by hydrolysis and condensation reactions under basic catalysis, leading to the formation of siloxane layer, involving strong interaction between the silanes with hydroxylated surface of ZnO, thereby creating a covalent bond—ZnO-O-Si. Alternatively, OA and HTMS were employed as hydrophobic agent to form a bilayer barrier surrounding the nanoparticles (NPs). Capped ZnO-QDS were analyzed by techniques including: Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction and transmission electron microscopy, as well as the monitoring of excitonic peak of ZnO by UV-vis absorption spectroscopy. Photoluminescence measurements confirmed the importance of capping agents. Bare ZnO-QDs powder showed lowest photoluminescence intensity and displacement to yellow region when compared with ZnO-QDs capped, which present a higher photoluminescence in the green region. The above results can be related to changes of the concentration of oxygen vacancies (V o) and also by increased presence of surface defect density. Silane capping represents the best choice for high stability and photoluminescence enhancement of ZnO-QDs.

Silicon Quantum Dot Nanoparticles with Antifouling Coatings for Immunostaining on Live Cancer Cells.

PubMed

Tu, Chang-Ching; Chen, Kuang-Po; Yang, Tsu-An; Chou, Min-Yuan; Lin, Lih Y; Li, Yaw-Kuen

2016-06-08

Fluorescent silicon quantum dots (SiQDs) have shown a great potential as antiphotobleaching, nontoxic and biodegradable labels for various in vitro and in vivo applications. However, fabricating SiQDs with high water-solubility and high photoluminescence quantum yield (PLQY) remains a challenge. Furthermore, for targeted imaging, their surface chemistry has to be capable of conjugating to antibodies, as well as sufficiently antifouling. Herein, antibody-conjugated SiQD nanoparticles (SiQD-NPs) with antifouling coatings composed of bovine serum albumin (BSA) and polyethylene glycol (PEG) are demonstrated for immunostaining on live cancer cells. The monodisperse SiQD-NPs of diameter about 130 nm are synthesized by a novel top-down method, including electrochemical etching, photochemical hydrosilylation, high energy ball milling, and "selective-etching" in HNO3 and HF. Subsequently, the BSA and PEG are covalently grafted on to the SiQD-NP surface through presynthesized chemical linkers, resulting in a stable, hydrophilic, and antifouling organic capping layer with isothiocyanates as the terminal functional groups for facile conjugation to the antibodies. The in vitro cell viability assay reveals that the BSA-coated SiQD-NPs had exceptional biocompatibility, with minimal cytotoxicity at concentration up to 1600 μg mL(-1). Under 365 nm excitation, the SiQD-NP colloid emits bright reddish photoluminescence with PLQY = 45-55% in organic solvent and 5-10% in aqueous buffer. Finally, through confocal fluorescent imaging and flow cytometry analysis, the anti-HER2 conjugated SiQD-NPs show obvious specific binding to the HER2-overexpressing SKOV3 cells and negligible nonspecific binding to the HER2-nonexpressing CHO cells. Under similar experimental conditions, the immunofluorescence results obtained with the SiQD-NPs are comparable to those using conventional fluorescein isothiocyanate (FITC).

Electronic and optical properties of GaN/AlN quantum dots on Si(111) subject to in-plane uniaxial stresses and variable excitation

NASA Astrophysics Data System (ADS)

Moshe, O.; Rich, D. H.; Birner, S.; Povolotskyi, M.; Damilano, B.; Massies, J.

2010-10-01

We have studied the excitation- and polarization-dependent optical properties of GaN/AlN self-assembled quantum dots (QDs) grown on Si(111) substrates. Ensembles of QDs were subject to various external stress configurations that resulted from the thermal expansion coefficient mismatch between the GaN/AlN layers and the Si(111) substrate and ranged from in-plane uniaxial stress, primarily along the ⟨112¯0⟩ directions, to in-plane biaxial stress, having magnitudes ranging from 20-30 kbar. Limited regions of uniaxial stress were obtained by exploiting naturally occurring microcracks that form during the postgrowth cooling. These microcracks act as stressors in order to create the highly localized regions of uniaxial stress. The local strain tensors for such QDs, which are subject to an interfacial stress perturbation, have been determined by modeling the dependence of the QD excitonic transition energy on the interfacial stress. Cathodoluminescence (CL) measurements of the excitonic transitions exhibit an in-plane linear polarization anisotropy in close proximity to microcracks. The polarization anisotropy is strongly dependent on the sample temperature and the electron beam excitation conditions used to excite the QD ensemble. Localized CL spectroscopy of the QDs exhibits emissions from both the ground and excited states, whose relative contributions depend on the level of excitation and temperature. Experimental results indicate that the polarization anisotropy vanishes at high temperatures (˜300 K) with an increasing excitation of the QDs, while the anisotropy decreases more slowly with excitation at low temperatures (˜60 K). A theoretical modeling of the effect of carrier filling on the polarization anisotropy and the excitonic transition energy was performed, as based on three-dimensional self-consistent solutions of the Schrödinger and Poisson equations using the 6×6 kṡp and effective mass methods for calculations of the e-h wave functions and electron and hole quasi-Fermi levels for varying levels of state filling. We attribute carrier filling and a thermal excitation of holes into higher energy QD hole states during excitation to account for the observed gradual decrease in the polarization anisotropy with an increasing electron-hole pair excitation density at T =300 K.

Exploration of CdTe quantum dots as mesoscale pressure sensors via time-resolved shock-compression photoluminescent emission spectroscopy

NASA Astrophysics Data System (ADS)

Kang, Zhitao; Banishev, Alexandr A.; Lee, Gyuhyon; Scripka, David A.; Breidenich, Jennifer; Xiao, Pan; Christensen, James; Zhou, Min; Summers, Christopher J.; Dlott, Dana D.; Thadhani, Naresh N.

2016-07-01

The nanometer size of CdTe quantum dots (QDs) and their unique optical properties, including size-tunable narrow photoluminescent emission, broad absorption, fast photoluminescence decay, and negligible light scattering, are ideal features for spectrally tagging the shock response of localized regions in highly heterogeneous materials such as particulate media. In this work, the time-resolved laser-excited photoluminescence response of QDs to shock-compression was investigated to explore their utilization as mesoscale sensors for pressure measurements and in situ diagnostics during shock loading experiments. Laser-driven shock-compression experiments with steady-state shock pressures ranging from 2.0 to 13 GPa were performed on nanocomposite films of CdTe QDs dispersed in a soft polyvinyl alcohol polymer matrix and in a hard inorganic sodium silicate glass matrix. Time-resolved photoluminescent emission spectroscopy was used to correlate photoluminescence changes with the history of shock pressure and the dynamics of the matrix material surrounding the QDs. The results revealed pressure-induced blueshifts in emitted wavelength, decreases in photoluminescent emission intensity, reductions in peak width, and matrix-dependent response times. Data obtained for these QD response characteristics serve as indicators for their use as possible time-resolved diagnostics of the dynamic shock-compression response of matrix materials in which such QDs are embedded as in situ sensors.

Exploration of CdTe quantum dots as mesoscale pressure sensors via time-resolved shock-compression photoluminescent emission spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Zhitao; School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245; Banishev, Alexandr A.

The nanometer size of CdTe quantum dots (QDs) and their unique optical properties, including size-tunable narrow photoluminescent emission, broad absorption, fast photoluminescence decay, and negligible light scattering, are ideal features for spectrally tagging the shock response of localized regions in highly heterogeneous materials such as particulate media. In this work, the time-resolved laser-excited photoluminescence response of QDs to shock-compression was investigated to explore their utilization as mesoscale sensors for pressure measurements and in situ diagnostics during shock loading experiments. Laser-driven shock-compression experiments with steady-state shock pressures ranging from 2.0 to 13 GPa were performed on nanocomposite films of CdTe QDs dispersedmore » in a soft polyvinyl alcohol polymer matrix and in a hard inorganic sodium silicate glass matrix. Time-resolved photoluminescent emission spectroscopy was used to correlate photoluminescence changes with the history of shock pressure and the dynamics of the matrix material surrounding the QDs. The results revealed pressure-induced blueshifts in emitted wavelength, decreases in photoluminescent emission intensity, reductions in peak width, and matrix-dependent response times. Data obtained for these QD response characteristics serve as indicators for their use as possible time-resolved diagnostics of the dynamic shock-compression response of matrix materials in which such QDs are embedded as in situ sensors.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuruma, K.; Takamiya, D.; Ota, Y.

We demonstrate precise and quick detection of the positions of quantum dots (QDs) embedded in two-dimensional photonic crystal nanocavities. We apply this technique to investigate the QD position dependence of the optical coupling between the QD and the nanocavity. We use a scanning electron microscope (SEM) operating at a low acceleration voltage to detect surface bumps induced by the QDs buried underneath. This enables QD detection with a sub-10 nm precision. We then experimentally measure the vacuum Rabi spectra to extract the optical coupling strengths (gs) between single QDs and cavities, and compare them to the values estimated by a combinationmore » of the SEM-measured QD positions and electromagnetic cavity field simulations. We found a highly linear relationship between the local cavity field intensities and the QD-cavity gs, suggesting the validity of the point dipole approximation used in the estimation of the gs. The estimation using SEM has a small standard deviation of ±6.2%, which potentially enables the high accuracy prediction of g prior to optical measurements. Our technique will play a key role for deeply understanding the interaction between QDs and photonic nanostructures and for advancing QD-based cavity quantum electrodynamics.« less

Reduction in aggregation and energy transfer of quantum dots incorporated in polystyrene beads by kinetic entrapment due to cross-linking during polymerization.

PubMed

Vaidya, Shyam V; Couzis, Alex; Maldarelli, Charles

2015-03-17

We report the development of barcoded polystyrene microbeads, approximately 50 μm in diameter, which are encoded by incorporating multicolored semiconductor fluorescent nanocrystals (quantum dots or QDs) within the microbeads and using the emission spectrum of the embedded QDs as a spectral label. The polymer/nanocrystal bead composites are formed by polymerizing emulsified liquid droplets of styrene monomer and QDs suspended in an immiscible continuous phase (suspension polymerization). We focus specifically on the effect of divinylbenzene (DVB) added to cross-link the linearly growing styrene polymer chains and the effect of this cross-linking on the state of aggregation of the nanocrystals in the composite. Aggregated states of multicolor QDs give rise to nonradiative resonance energy transfer (RET) which distorts the emission label from a spectrum recorded in a reference solvent in which the nanocrystals are well dispersed and unaggregated. A simple barcode is chosen of a mixture of QDs emitting at 560 (yellow) and 620 nm (red). We find that for linear chain growth (no DVB), the QDs aggregate as is evident from the emission spectrum and the QD distribution as seen from confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) images. Increasing the extent of cross-linking by the addition of DVB is shown to significantly decrease the aggregation and provide a clear label. We suggest that in the absence of cross-linking, linearly growing polymer chains, through enthalpic and entropic effects, drive the nanocrystals into inclusions, while cross-linking kinetically entraps the particle and prevents their aggregation.

Flux-dependent anti-crossing of resonances in parallel non-coupled double quantum dots

NASA Astrophysics Data System (ADS)

Joe, Yong S.; Hedin, Eric R.; Kim, Jiseok

2008-08-01

We present novel resonant phenomena through parallel non-coupled double quantum dots (QDs) embedded in each arm of an Aharonov-Bohm (AB) ring with magnetic flux passing through its center. The electron transmission through this AB ring with each QD formed by two short-range potential barriers is calculated using a scattering matrix at each junction and a transfer matrix in each arm. We show that as the magnetic flux modulates, a distortion of the grid-like square transmission occurs and an anti-crossing of the resonances appears. Hence, the modulation of magnetic flux in this system can have an equivalent effect to the control of inter-dot coupling between the two QDs.

Luminescent manganese-doped CsPbCl3 perovskite quantum dots

NASA Astrophysics Data System (ADS)

Lin, Chun Che; Xu, Kun Yuan; Wang, Da; Meijerink, Andries

2017-04-01

Nanocrystalline cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I) form an exciting new class of semiconductor materials showing quantum confinement. The emission color can be tuned over the full visible spectral region making them promising for light‒emitting applications. Further control over the optical and magnetic properties of quantum dots (QDs) can be achieved through doping of transition metal (TM) ions such as Mn2+ or Co2+. Here we demonstrate how, following QD synthesis in the presence of a Mn‒precursor, dropwise addition of silicon tetrachloride (SiCl4) to the QDs in toluene results in the formation of Mn‒doped CsPbCl3 QDs showing bright orange Mn2+ emission around 600 nm. Evidence for successful doping is provided by excitation spectra of the Mn2+ emission, with all features of the CsPbCl3 QD absorption spectrum and a decrease of the 410 nm excitonic emission life time with increasing Mn‒concentration, giving evidence for enhanced exciton to Mn2+ energy transfer. As a doping mechanism we propose a combination of surface etching and reconstruction and diffusion doping. The presently reported approach provides a promising avenue for doping TM ions into perovskites QDs enabling a wider control over optical and magnetic properties for this new class of QDs.

Luminescent manganese-doped CsPbCl3 perovskite quantum dots.

PubMed

Lin, Chun Che; Xu, Kun Yuan; Wang, Da; Meijerink, Andries

2017-04-12

Nanocrystalline cesium lead halide perovskites (CsPbX 3 , X = Cl, Br, and I) form an exciting new class of semiconductor materials showing quantum confinement. The emission color can be tuned over the full visible spectral region making them promising for light‒emitting applications. Further control over the optical and magnetic properties of quantum dots (QDs) can be achieved through doping of transition metal (TM) ions such as Mn 2+ or Co 2+ . Here we demonstrate how, following QD synthesis in the presence of a Mn‒precursor, dropwise addition of silicon tetrachloride (SiCl 4 ) to the QDs in toluene results in the formation of Mn‒doped CsPbCl 3 QDs showing bright orange Mn 2+ emission around 600 nm. Evidence for successful doping is provided by excitation spectra of the Mn 2+ emission, with all features of the CsPbCl 3 QD absorption spectrum and a decrease of the 410 nm excitonic emission life time with increasing Mn‒concentration, giving evidence for enhanced exciton to Mn 2+ energy transfer. As a doping mechanism we propose a combination of surface etching and reconstruction and diffusion doping. The presently reported approach provides a promising avenue for doping TM ions into perovskites QDs enabling a wider control over optical and magnetic properties for this new class of QDs.

Silicon quantum dots embedded in a SiO2 matrix: From structural study to carrier transport properties

NASA Astrophysics Data System (ADS)

Garcia-Castello, Nuria; Illera, Sergio; Guerra, Roberto; Prades, Joan Daniel; Ossicini, Stefano; Cirera, Albert

2013-08-01

We study the details of electronic transport related to the atomistic structure of silicon quantum dots embedded in a silicon dioxide matrix using ab initio calculations of the density of states. Several structural and composition features of quantum dots (QDs), such as diameter and amorphization level, are studied and correlated with transport under transfer Hamiltonian formalism. The current is strongly dependent on the QD density of states and on the conduction gap, both dependent on the dot diameter. In particular, as size increases, the available states inside the QD increase, while the QD band gap decreases due to relaxation of quantum confinement. Both effects contribute to increasing the current with the dot size. Besides, valence band offset between the band edges of the QD and the silica, and conduction band offset in a minor grade, increases with the QD diameter up to the theoretical value corresponding to planar heterostructures, thus decreasing the tunneling transmission probability and hence the total current. We discuss the influence of these parameters on electron and hole transport, evidencing a correlation between the electron (hole) barrier value and the electron (hole) current, and obtaining a general enhancement of the electron (hole) transport for larger (smaller) QD. Finally, we show that crystalline and amorphous structures exhibit enhanced probability of hole and electron current, respectively.

Submonolayer Quantum Dot Infrared Photodetector

NASA Technical Reports Server (NTRS)

Ting, David Z.; Bandara, Sumith V.; Gunapala, Sarath D.; Chang, Yia-Chang

2010-01-01

A method has been developed for inserting submonolayer (SML) quantum dots (QDs) or SML QD stacks, instead of conventional Stranski-Krastanov (S-K) QDs, into the active region of intersubband photodetectors. A typical configuration would be InAs SML QDs embedded in thin layers of GaAs, surrounded by AlGaAs barriers. Here, the GaAs and the AlGaAs have nearly the same lattice constant, while InAs has a larger lattice constant. In QD infrared photodetector, the important quantization directions are in the plane perpendicular to the normal incidence radiation. In-plane quantization is what enables the absorption of normal incidence radiation. The height of the S-K QD controls the positions of the quantized energy levels, but is not critically important to the desired normal incidence absorption properties. The SML QD or SML QD stack configurations give more control of the structure grown, retains normal incidence absorption properties, and decreases the strain build-up to allow thicker active layers for higher quantum efficiency.

Misfit-guided self-organization of anticorrelated Ge quantum dot arrays on Si nanowires.

PubMed

Kwon, Soonshin; Chen, Zack C Y; Kim, Ji-Hun; Xiang, Jie

2012-09-12

Misfit-strain guided growth of periodic quantum dot (QD) arrays in planar thin film epitaxy has been a popular nanostructure fabrication method. Engineering misfit-guided QD growth on a nanoscale substrate such as the small curvature surface of a nanowire represents a new approach to self-organized nanostructure preparation. Perhaps more profoundly, the periodic stress underlying each QD and the resulting modulation of electro-optical properties inside the nanowire backbone promise to provide a new platform for novel mechano-electronic, thermoelectronic, and optoelectronic devices. Herein, we report a first experimental demonstration of self-organized and self-limited growth of coherent, periodic Ge QDs on a one-dimensional Si nanowire substrate. Systematic characterizations reveal several distinctively different modes of Ge QD ordering on the Si nanowire substrate depending on the core diameter. In particular, Ge QD arrays on Si nanowires of around 20 nm diameter predominantly exhibit an anticorrelated pattern whose wavelength agrees with theoretical predictions. The correlated pattern can be attributed to propagation and correlation of misfit strain across the diameter of the thin nanowire substrate. The QD array growth is self-limited as the wavelength of the QDs remains unchanged even after prolonged Ge deposition. Furthermore, we demonstrate a direct kinetic transformation from a uniform Ge shell layer to discrete QD arrays by a postgrowth annealing process.

Tin oxide quantum dots embedded iron oxide composite as efficient lead sensor

NASA Astrophysics Data System (ADS)

Dutta, Dipa; Bahadur, Dhirendra

2018-04-01

SnO2 quantum dots (QDs) embedded iron oxide (IO) nanocomposite is fabricated and explored as a capable sensor for lead detection. Square wave anodic stripping voltammetry (SWASV) and amperometry have been used to explore the proposed sensor's response towards lead detection. The modified electrode shows linear current response for concentration of lead ranging from 99 nM to 6.6 µM with limit of detection 0.42 µM (34 ppb). Amperometry shows a detection limit as low as 0.18 nM (0.015 ppb); which is far below the permissible limit of lead in drinking water by World Health Organization. This proposed sensor shows linear current response (R2 = 0.98) for the lead concentration ranging from 133 × 10-9 to 4.4 × 10-6M. It also exhibits rapid response time of 12 sec with an ultra high sensitivity of 5.5 µA/nM. These detection properties promise the use of SnO2 QDs -IO composite for detection of lead in environmental sample with great ease.

Development of ingan quantum dots by the Stranski-Krastanov method and droplet heteroepitaxy

NASA Astrophysics Data System (ADS)

Woodward, Jeffrey Michael

The development of InGaN quantum dots (QDs) is both scienti?cally challenging and promising for applications in visible spectrum LEDs, lasers, detectors, electroabsorption modulators and photovoltaics. Such QDs are typically grown using the Stranski-Krastanov (SK) growth mode, in which accumulated in-plane compressive strain induces a transition from 2D to 3D growth. This method has a number of inherent limitations, including the unavoidable formation of a 2D wetting layer and the di?culty of controlling the composition, areal density, and size of the dots. In this research, I have developed InGaN QDs by two methods using a plasma-assisted molecular beam epitaxy reactor. In the ?rst method, InGaN QDs were formed by SK growth mode on (0001) GaN/sapphire. In the second, I have addressed the limitations of the SK growth of InGaN QDs by developing a novel alternative method, which was utilized to grow on both (0001) GaN/sapphire and AlN/sapphire. This method relies upon the ability to form thermodynamically stable In-Ga liquid solutions throughout the entire compositional range at relatively low temperatures. Upon simultaneous or sequential deposition of In and Ga on a substrate, the adatoms form a liquid solution, whose composition is controlled by the ratio of the fluxes of the two constituents FIn/(FIn+FGa ). Depending on the interfacial free energy between the liquid deposit and substrate, the liquid deposit and vapor, and the vapor and substrate, the liquid deposit forms Inx-Ga1- x nano-droplets on the substrate. These nano-droplets convert into InxGa1-xN QDs upon exposure to nitrogen RF plasma. InGaN QDs produced by both methods were investigated in-situ by reflection high-energy electron diffraction and ex-situ by atomic force microscopy, field emission scanning electron microscopy, transmission electron microscopy, high resolution x-ray diffraction, and grazing incidence small angle x-ray scattering. The optical activity and device potential of the QDs were investigated by photoluminescence measurements and the formation and evaluation of PIN devices (in which the intrinsic region contains QDs embedded within a higher bandgap matrix). InGaN QDs with areal densities ranging from 109 to 1011 cm -2 and diameters ranging from 11 to 39 nm were achieved.

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors.

PubMed

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L; Banyai, Douglas; Savaikar, Madhusudan A; Jaszczak, John A; Yap, Yoke Khin

2016-02-05

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (in-situ STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.

Strain-tuning of the optical properties of semiconductor nanomaterials by integration onto piezoelectric actuators

NASA Astrophysics Data System (ADS)

Martín-Sánchez, Javier; Trotta, Rinaldo; Mariscal, Antonio; Serna, Rosalía; Piredda, Giovanni; Stroj, Sandra; Edlinger, Johannes; Schimpf, Christian; Aberl, Johannes; Lettner, Thomas; Wildmann, Johannes; Huang, Huiying; Yuan, Xueyong; Ziss, Dorian; Stangl, Julian; Rastelli, Armando

2018-01-01

The tailoring of the physical properties of semiconductor nanomaterials by strain has been gaining increasing attention over the last years for a wide range of applications such as electronics, optoelectronics and photonics. The ability to introduce deliberate strain fields with controlled magnitude and in a reversible manner is essential for fundamental studies of novel materials and may lead to the realization of advanced multi-functional devices. A prominent approach consists in the integration of active nanomaterials, in thin epitaxial films or embedded within carrier nanomembranes, onto Pb(Mg1/3Nb2/3)O3-PbTiO3-based piezoelectric actuators, which convert electrical signals into mechanical deformation (strain). In this review, we mainly focus on recent advances in strain-tunable properties of self-assembled InAs quantum dots (QDs) embedded in semiconductor nanomembranes and photonic structures. Additionally, recent works on other nanomaterials like rare-earth and metal-ion doped thin films, graphene and MoS2 or WSe2 semiconductor two-dimensional materials are also reviewed. For the sake of completeness, a comprehensive comparison between different procedures employed throughout the literature to fabricate such hybrid piezoelectric-semiconductor devices is presented. It is shown that unprocessed piezoelectric substrates (monolithic actuators) allow to obtain a certain degree of control over the nanomaterials’ emission properties such as their emission energy, fine-structure-splitting in self-assembled InAs QDs and semiconductor 2D materials, upconversion phenomena in BaTiO3 thin films or piezotronic effects in ZnS:Mn films and InAs QDs. Very recently, a novel class of micro-machined piezoelectric actuators have been demonstrated for a full control of in-plane stress fields in nanomembranes, which enables producing energy-tunable sources of polarization-entangled photons in arbitrary QDs. Future research directions and prospects are discussed.

Switchable electrochemiluminescence aptasensor coupled with resonance energy transfer for selective attomolar detection of Hg2+ via CdTe@CdS/dendrimer probe and Au nanoparticle quencher.

PubMed

Babamiri, Bahareh; Salimi, Abdollah; Hallaj, Rahman

2018-04-15

In the present study, an ultrasensitive electrochemiluminescence (ECL) aptasensing assay for selective detection of Hg 2+ was designed. In this electrochemiluminescence resonance energy transfer (ECL-RET) approach, Fe 3 O 4 @SiO 2 /dendrimers/QDs exhibited amplified ECL emissions (switch "on" state) and with the hybridization between T-rich ssDNA(S 1 ) immobilized on the Fe 3 O 4 @SiO 2 /dendrimers/QDs and AuNPs modified with complementary aptamer (AuNPs-S 2 ), the ECL of QDs nanocomposites was efficiently quenched (switch "off" state). In the presence of Hg 2+ ions, formation of strong and stable T-Hg 2+ -T complex led to the release of the AuNPs-S 2 from double-stranded DNA(dsDNA) and the recovery of the ECL signal of QDs (second signal switch "on" state). Under optimal conditions, Hg 2+ can be detected in a wide linear range from 20aM to 2µM with a very low detection limit of 2aM. The proposed ECL aptasensor showed high selectivity for Hg 2+ determination compared to other environmentally relevant metal ions at concentration ratio more than 1000 times. The aptasensor was used for detection Hg 2+ ions from samples of tap waters, carp and saltwater fishes with satisfactory results. The aptasensor exhibited high sensitivity, wide linear response (11 orders of magnitude), excellent reproducibility and stability. The proposed aptasensor will be a promising candidate for facile and rapid determination of Hg 2＋ in environmental and fishery samples. Copyright © 2017 Elsevier B.V. All rights reserved.

Observations on Si-based micro-clusters embedded in TaN thin film deposited by co-sputtering with oxygen contamination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Young Mi; Jung, Min-Sang; Choi, Duck-Kyun, E-mail: duck@hanyang.ac.kr, E-mail: mcjung@oist.jp

2015-08-15

Using scanning electron microscopy (SEM) and high-resolution x-ray photoelectron spectroscopy with the synchrotron radiation we investigated Si-based micro-clusters embedded in TaSiN thin films having oxygen contamination. TaSiN thin films were deposited by co-sputtering on fixed or rotated substrates and with various power conditions of TaN and Si targets. Three types of embedded micro-clusters with the chemical states of pure Si, SiO{sub x}-capped Si, and SiO{sub 2}-capped Si were observed and analyzed using SEM and Si 2p and Ta 4f core-level spectra were derived. Their different resistivities are presumably due to the different chemical states and densities of Si-based micro-clusters.

White lighting device from composite films embedded with hydrophilic Cu(In, Ga)S2/ZnS and hydrophobic InP/ZnS quantum dots

NASA Astrophysics Data System (ADS)

Kim, Jong-Hoon; Yang, Heesun

2014-06-01

Two types of non-Cd quantum dots (QDs)—In/Ga ratio-varied, green-to-greenish-yellow fluorescence-tuned Cu-In-Ga-S (CIGS) alloy ones, and red-emitting InP ones—are synthesized for use as down-converters in conjunction with a blue light-emitting diode (LED). Among a series of Ga-rich CI1-xGxS/ZnS core/shell QDs (x = 0.7, 0.8, and 0.9), CI0.2G0.8S/ZnS QD is chosen for the hydrophobic-to-hydrophilic surface modification via an in-situ ligand exchange and then embedded in a water-soluble polyvinyl alcohol (PVA). This free-standing composite film is utilized as a down-converter for the fabrication of a remote-type white QD-LED, but the resulting bi-colored device exhibits a cool white light with a limited color rendering index property. To improve white light qualities, another QD-polymer film of hydrophobic red InP/ZnS QD-embedding polyvinylpyrrolidone is sequentially stacked onto the CI0.2G0.8S/ZnS QD-PVA film, producing a unique dual color-emitting, flexible and transparent bilayered composite film. Tri-colored white QD-LED integrated with the bilayered QD film possesses an exceptional color rendering property through reinforcing a red spectral component and balancing a white spectral distribution.

White lighting device from composite films embedded with hydrophilic Cu(In, Ga)S2/ZnS and hydrophobic InP/ZnS quantum dots.

PubMed

Kim, Jong-Hoon; Yang, Heesun

2014-06-06

Two types of non-Cd quantum dots (QDs)-In/Ga ratio-varied, green-to-greenish-yellow fluorescence-tuned Cu-In-Ga-S (CIGS) alloy ones, and red-emitting InP ones-are synthesized for use as down-converters in conjunction with a blue light-emitting diode (LED). Among a series of Ga-rich CI1-xGxS/ZnS core/shell QDs (x = 0.7, 0.8, and 0.9), CI0.2G0.8S/ZnS QD is chosen for the hydrophobic-to-hydrophilic surface modification via an in-situ ligand exchange and then embedded in a water-soluble polyvinyl alcohol (PVA). This free-standing composite film is utilized as a down-converter for the fabrication of a remote-type white QD-LED, but the resulting bi-colored device exhibits a cool white light with a limited color rendering index property. To improve white light qualities, another QD-polymer film of hydrophobic red InP/ZnS QD-embedding polyvinylpyrrolidone is sequentially stacked onto the CI0.2G0.8S/ZnS QD-PVA film, producing a unique dual color-emitting, flexible and transparent bilayered composite film. Tri-colored white QD-LED integrated with the bilayered QD film possesses an exceptional color rendering property through reinforcing a red spectral component and balancing a white spectral distribution.

Increasing the quantum efficiency of GaAs solar cells by embedding InAs quantum dots

NASA Astrophysics Data System (ADS)

Salii, R. A.; Mintairov, S. A.; Nadtochiy, A. M.; Payusov, A. S.; Brunkov, P. N.; Shvarts, M. Z.; Kalyuzhnyy, N. A.

2016-11-01

Development of Metalorganic Vapor Phase Epitaxy (MOVPE) technology of InAs quantum dots (QDs) in GaAs for photovoltaic applications is presented. The growth peculiarities in InAs-GaAs lattice-mismatched system were considered. The photoluminescence (PL) intensity dependences on different growth parameters were obtained. The multimodal distribution of QDs by sizes was found using AFM and PL methods. GaAs solar cell nanoheterostructures with imbedded QD arrays were designed and obtained. Ones have been demonstrated a significant increase of quantum efficiency and photogenerated current of QD solar cells due to photo effect in InAs QD array (0.59 mA/cm2 for AM1.5D and 82 mA/cm2 for AM0).

Compact quantum dot-antibody conjugates for FRET immunoassays with subnanomolar detection limits

NASA Astrophysics Data System (ADS)

Mattera, Lucia; Bhuckory, Shashi; Wegner, K. David; Qiu, Xue; Agnese, Fabio; Lincheneau, Christophe; Senden, Tim; Djurado, David; Charbonnière, Loïc J.; Hildebrandt, Niko; Reiss, Peter

2016-05-01

A novel two-step approach for quantum dot (QD) functionalization and bioconjugation is presented, which yields ultra-compact, stable, and highly luminescent antibody-QD conjugates suitable for use in FRET immunoassays. Hydrophobic InPZnS/ZnSe/ZnS (emission wavelength: 530 nm), CdSe/ZnS (605 nm), and CdSeTe/ZnS (705 nm) QDs were surface functionalized with zwitterionic penicillamine, enabling aqueous phase transfer under conservation of the photoluminescence properties. Post-functionalization with a heterobifunctional crosslinker, containing a lipoic acid group and a maleimide function, enabled the subsequent coupling to sulfhydryl groups of proteins. This was demonstrated by QD conjugation with fragmented antibodies (F(ab)). The obtained F(ab)-QD conjugates range among the smallest antibody-functionalized nanoprobes ever reported, with a hydrodynamic diameter <13 nm, PL quantum yield up to 66% at 705 nm, and colloidal stability of several months in various buffers. They were applied as FRET acceptors in homogeneous, time-gated immunoassays using Tb-antibodies as FRET donors, both coupled by an immunological sandwich complex between the two antibodies and a PSA (prostate specific antigen) biomarker. The advantages of the compact surface coating for FRET could be demonstrated by an 6.2 and 2.5 fold improvement of the limit of detection (LOD) for PSA compared to commercially available hydrophilic QDs emitting at 605 and 705 nm, respectively. While the commercial QDs contain identical inorganic cores responsible for their fluorescence, they are coated with a comparably thick amphiphilic polymer layer leading to much larger hydrodynamic diameters (>26 nm without biomolecules). The LODs of 0.8 and 3.7 ng mL-1 obtained in 50 μL serum samples are below the clinical cut-off level of PSA (4 ng mL-1) and demonstrate their direct applicability in clinical diagnostics.A novel two-step approach for quantum dot (QD) functionalization and bioconjugation is presented, which yields ultra-compact, stable, and highly luminescent antibody-QD conjugates suitable for use in FRET immunoassays. Hydrophobic InPZnS/ZnSe/ZnS (emission wavelength: 530 nm), CdSe/ZnS (605 nm), and CdSeTe/ZnS (705 nm) QDs were surface functionalized with zwitterionic penicillamine, enabling aqueous phase transfer under conservation of the photoluminescence properties. Post-functionalization with a heterobifunctional crosslinker, containing a lipoic acid group and a maleimide function, enabled the subsequent coupling to sulfhydryl groups of proteins. This was demonstrated by QD conjugation with fragmented antibodies (F(ab)). The obtained F(ab)-QD conjugates range among the smallest antibody-functionalized nanoprobes ever reported, with a hydrodynamic diameter <13 nm, PL quantum yield up to 66% at 705 nm, and colloidal stability of several months in various buffers. They were applied as FRET acceptors in homogeneous, time-gated immunoassays using Tb-antibodies as FRET donors, both coupled by an immunological sandwich complex between the two antibodies and a PSA (prostate specific antigen) biomarker. The advantages of the compact surface coating for FRET could be demonstrated by an 6.2 and 2.5 fold improvement of the limit of detection (LOD) for PSA compared to commercially available hydrophilic QDs emitting at 605 and 705 nm, respectively. While the commercial QDs contain identical inorganic cores responsible for their fluorescence, they are coated with a comparably thick amphiphilic polymer layer leading to much larger hydrodynamic diameters (>26 nm without biomolecules). The LODs of 0.8 and 3.7 ng mL-1 obtained in 50 μL serum samples are below the clinical cut-off level of PSA (4 ng mL-1) and demonstrate their direct applicability in clinical diagnostics. Electronic supplementary information (ESI) available: SI-1: UV-vis/PL spectra; SI-2: TEM images; SI-3: DLS; SI-4: gel electrophoresis; SI-5: FTIR spectra; SI-6: overlap between QD absorption spectra and area-normalized Tb emission; SI-7: photographs of the samples; and optical characterization of QD-F(ab) conjugates (Table S1). See DOI: 10.1039/c6nr03261c

Efficient Fluorescence Resonance Energy Transfer between Quantum Dots and Gold Nanoparticles Based on Porous Silicon Photonic Crystal for DNA Detection.

PubMed

Zhang, Hongyan; Lv, Jie; Jia, Zhenhong

2017-05-10

A novel assembled biosensor was prepared for detecting 16S rRNA, a small-size persistent specific for Actinobacteria. The mechanism of the porous silicon (PS) photonic crystal biosensor is based on the fluorescence resonance energy transfer (FRET) between quantum dots (QDs) and gold nanoparticles (AuNPs) through DNA hybridization, where QDs act as an emission donor and AuNPs serve as a fluorescence quencher. Results showed that the photoluminescence (PL) intensity of PS photonic crystal was drastically increased when the QDs-conjugated probe DNA was adhered to the PS layer by surface modification using a standard cross-link chemistry method. The PL intensity of QDs was decreased when the addition of AuNPs-conjugated complementary 16S rRNA was dropped onto QDs-conjugated PS. Based on the analysis of different target DNA concentration, it was found that the decrease of the PL intensity showed a good linear relationship with complementary DNA concentration in a range from 0.25 to 10 μM, and the detection limit was 328.7 nM. Such an optical FRET biosensor functions on PS-based photonic crystal for DNA detection that differs from the traditional FRET, which is used only in liquid. This method will benefit the development of a new optical FRET label-free biosensor on Si substrate and has great potential in biochips based on integrated optical devices.

Luminescent manganese-doped CsPbCl3 perovskite quantum dots

PubMed Central

Lin, Chun Che; Xu, Kun Yuan; Wang, Da; Meijerink, Andries

2017-01-01

Nanocrystalline cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I) form an exciting new class of semiconductor materials showing quantum confinement. The emission color can be tuned over the full visible spectral region making them promising for light‒emitting applications. Further control over the optical and magnetic properties of quantum dots (QDs) can be achieved through doping of transition metal (TM) ions such as Mn2+ or Co2+. Here we demonstrate how, following QD synthesis in the presence of a Mn‒precursor, dropwise addition of silicon tetrachloride (SiCl4) to the QDs in toluene results in the formation of Mn‒doped CsPbCl3 QDs showing bright orange Mn2+ emission around 600 nm. Evidence for successful doping is provided by excitation spectra of the Mn2+ emission, with all features of the CsPbCl3 QD absorption spectrum and a decrease of the 410 nm excitonic emission life time with increasing Mn‒concentration, giving evidence for enhanced exciton to Mn2+ energy transfer. As a doping mechanism we propose a combination of surface etching and reconstruction and diffusion doping. The presently reported approach provides a promising avenue for doping TM ions into perovskites QDs enabling a wider control over optical and magnetic properties for this new class of QDs. PMID:28401894

Misfit-guided self-organization of anti-correlated Ge quantum dot arrays on Si nanowires

PubMed Central

Kwon, Soonshin; Chen, Zack C.Y.; Kim, Ji-Hun; Xiang, Jie

2012-01-01

Misfit-strain guided growth of periodic quantum dot (QD) arrays in planar thin film epitaxy has been a popular nanostructure fabrication method. Engineering misfit-guided QD growth on a nanoscale substrate such as the small curvature surface of a nanowire represents a new approach to self-organized nanostructure preparation. Perhaps more profoundly, the periodic stress underlying each QD and the resulting modulation of electro-optical properties inside the nanowire backbone promise to provide a new platform for novel mechano-electronic, thermoelectronic, and optoelectronic devices. Herein, we report a first experimental demonstration of self-organized and self-limited growth of coherent, periodic Ge QDs on a one dimensional Si nanowire substrate. Systematic characterizations reveal several distinctively different modes of Ge QD ordering on the Si nanowire substrate depending on the core diameter. In particular, Ge QD arrays on Si nanowires of around 20 nm diameter predominantly exhibit an anti-correlated pattern whose wavelength agrees with theoretical predictions. The correlated pattern can be attributed to propagation and correlation of misfit strain across the diameter of the thin nanowire substrate. The QD array growth is self-limited as the wavelength of the QDs remains unchanged even after prolonged Ge deposition. Furthermore, we demonstrate a direct kinetic transformation from a uniform Ge shell layer to discrete QD arrays by a post-growth annealing process. PMID:22889063

Interplay between Switching Driven by the Tunneling Current and Atomic Force of a Bistable Four-Atom Si Quantum Dot.

PubMed

Yamazaki, Shiro; Maeda, Keisuke; Sugimoto, Yoshiaki; Abe, Masayuki; Zobač, Vladimír; Pou, Pablo; Rodrigo, Lucia; Mutombo, Pingo; Pérez, Ruben; Jelínek, Pavel; Morita, Seizo

2015-07-08

We assemble bistable silicon quantum dots consisting of four buckled atoms (Si4-QD) using atom manipulation. We demonstrate two competing atom switching mechanisms, downward switching induced by tunneling current of scanning tunneling microscopy (STM) and opposite upward switching induced by atomic force of atomic force microscopy (AFM). Simultaneous application of competing current and force allows us to tune switching direction continuously. Assembly of the few-atom Si-QDs and controlling their states using versatile combined AFM/STM will contribute to further miniaturization of nanodevices.

Nonvolatile Memories Using Quantum Dot (QD) Floating Gates Assembled on II-VI Tunnel Insulators

NASA Astrophysics Data System (ADS)

Suarez, E.; Gogna, M.; Al-Amoody, F.; Karmakar, S.; Ayers, J.; Heller, E.; Jain, F.

2010-07-01

This paper presents preliminary data on quantum dot gate nonvolatile memories using nearly lattice-matched ZnS/Zn0.95Mg0.05S/ZnS tunnel insulators. The GeO x -cladded Ge and SiO x -cladded Si quantum dots (QDs) are self-assembled site-specifically on the II-VI insulator grown epitaxially over the Si channel (formed between the source and drain region). The pseudomorphic II-VI stack serves both as a tunnel insulator and a high- κ dielectric. The effect of Mg incorporation in ZnMgS is also investigated. For the control gate insulator, we have used Si3N4 and SiO2 layers grown by plasma- enhanced chemical vapor deposition.

Enhanced Emission of Quantum System in Si-Ge Nanolayer Structure.

PubMed

Huang, Zhong-Mei; Huang, Wei-Qi; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke

2016-12-01

It is very interesting that the enhanced peaks near 1150 and 1550 nm are observed in the photoluminescence (PL) spectra in the quantum system of Si-Ge nanolayer structure, which have the emission characteristics of a three-level system with quantum dots (QDs) pumping and emission of quasi-direct-gap band, in our experiment. In the preparing process of Si-Ge nanolayer structure by using a pulsed laser deposition method, it is discovered that the nanocrystals of Si and Ge grow in the (100) and (111) directions after annealing or electron beam irradiation. The enhanced PL peaks with multi-longitudinal-mode are measured at room temperature in the super-lattice of Si-Ge nanolayer quantum system on SOI.

Wigner molecules in carbon-nanotube quantum dots

NASA Astrophysics Data System (ADS)

Rontani, Massimo; Secchi, Andrea

2010-03-01

The paradigm of few-electron complexes in quantum dots (QDs) relies on the ``particle-in-a-box'' idea that lowest-energy orbitals are filled according to Pauli's exclusion principle. If Coulomb repulsion is sufficiently strong to overcome the kinetic energy cost of localization, a different scenario is predicted: a ``Wigner'' molecule (WM) forms, made of electrons frozen in space according to a geometrical pattern. Despite considerable experimental effort, evidence of the WM in semiconductor QDs has been elusive so far. Here we demonstrate theoretically that WMs occur in gate-defined QDs embedded in typical semiconducting carbon nanotubes (CNTs). Their signatures must be searched ---and indeed have already been observed [Deshpande and Bockrath, Nature Phys. 4, 314 (2008)] --- in tunneling spectra. Through exact diagonalisation (ED) calculations, we unveil the inherent features of the electron molecular states. We show that, like nuclei in a usual molecule, electrons have localized wave functions and hence negligible exchange interactions. The molecular excitations are vibrations around the equilibrium positions of electrons. ED results are well reproduced by an ansatz vibrational wave function, which provides a simple theoretical model for transport experiments in ultraclean CNTs.

Broadband light sources based on InAs/InGaAs metamorphic quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seravalli, L.; Trevisi, G.; Frigeri, P.

We propose a design for a semiconductor structure emitting broadband light in the infrared, based on InAs quantum dots (QDs) embedded into a metamorphic step-graded In{sub x}Ga{sub 1−x}As buffer. We developed a model to calculate the metamorphic QD energy levels based on the realistic QD parameters and on the strain-dependent material properties; we validated the results of simulations by comparison with the experimental values. On this basis, we designed a p-i-n heterostructure with a graded index profile toward the realization of an electrically pumped guided wave device. This has been done by adding layers where QDs are embedded in In{submore » x}Al{sub y}Ga{sub 1−x−y}As layers, to obtain a symmetric structure from a band profile point of view. To assess the room temperature electro-luminescence emission spectrum under realistic electrical injection conditions, we performed device-level simulations based on a coupled drift-diffusion and QD rate equation model. On the basis of the device simulation results, we conclude that the present proposal is a viable option to realize broadband light-emitting devices.« less

Assembly of P3HT/CdSe nanowire networks in an insulating polymer host.

PubMed

Heo, Kyuyoung; Miesch, Caroline; Na, Jun-Hee; Emrick, Todd; Hayward, Ryan C

2018-06-27

Nanoparticles may act as compatibilizing agents for blending of immiscible polymers, leading to changes in blend morphology through a variety of mechanisms including interfacial adsorption, aggregation, and nucleation of polymer crystals. Herein, we report an approach to define highly structured donor/acceptor networks based on poly(3-hexylthiophene) (P3HT) and CdSe quantum dots (QDs) by demixing from an insulating polystyrene (PS) matrix. The incorporation of QDs led to laterally phase-separated co-continuous structures with sub-micrometer dimensions, and promoted crystallization of P3HT, yielding highly interconnected P3HT/QD hybrid nanowires embedded in the polymer matrix. These nanohybrid materials formed by controlling phase separation, interfacial activity, and crystallization within ternary donor/acceptor/insulator blends, offer attractive morphologies for potential use in optoelectronics.

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

PubMed Central

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L.; Banyai, Douglas; Savaikar, Madhusudan A.; Jaszczak, John A.; Yap, Yoke Khin

2016-01-01

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (in-situ STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending. PMID:26846587

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

DOE PAGES

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; ...

2016-02-05

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under variousmore » bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (insitu STM-TEM). Ultimately, as suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.« less

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under variousmore » bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (insitu STM-TEM). Ultimately, as suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.« less

Delivery and reveal of localization of upconversion luminescent microparticles and quantum dots in the skin in vivo by fractional laser microablation, multimodal imaging, and optical clearing

NASA Astrophysics Data System (ADS)

Volkova, Elena K.; Yanina, Irina Yu; Genina, Elina A.; Bashkatov, Alexey N.; Konyukhova, Julia G.; Popov, Alexey P.; Speranskaya, Elena S.; Bucharskaya, Alla B.; Navolokin, Nikita A.; Goryacheva, Irina Yu.; Kochubey, Vyacheslav I.; Sukhorukov, Gleb B.; Meglinski, Igor V.; Tuchin, Valery V.

2018-02-01

Delivery and spatial localization of upconversion luminescent microparticles [Y2O3:Yb, Er] (mean size ˜1.6 μm) and quantum dots (QDs) (CuInS2/ZnS nanoparticles coated with polyethylene glycol-based amphiphilic polymer, mean size ˜20 nm) inside rat skin was studied in vivo using a multimodal optical imaging approach. The particles were embedded into the skin dermis to the depth from 300 to 500 μm through microchannels performed by fractional laser microablation. Low-frequency ultrasound was applied to enhance penetration of the particles into the skin. Visualization of the particles was revealed using a combination of luminescent spectroscopy, optical coherence tomography, confocal microscopy, and histochemical analysis. Optical clearing was used to enhance the image contrast of the luminescent signal from the particles. It was demonstrated that the penetration depth of particles depends on their size, resulting in a different detection time interval (days) of the luminescent signal from microparticles and QDs inside the rat skin in vivo. We show that luminescent signal from the upconversion microparticles and QDs was detected after the particle delivery into the rat skin in vivo during eighth and fourth days, respectively. We hypothesize that the upconversion microparticles have created a long-time depot localized in the laser-created channels, as the QDs spread over the surrounding tissues.

Effective surface passivation of multi-shelled InP quantum dots through a simple complexing with titanium species

NASA Astrophysics Data System (ADS)

Jo, Jung-Ho; Kim, Min-Seok; Han, Chang-Yeol; Jang, Eun-Pyo; Do, Young Rag; Yang, Heesun

2018-01-01

Fluorescent efficiency of various visible quantum dots (QDs) has been incessantly improved to meet industrially high standard mainly through the advance in core/shell heterostructural design, however, their stability against degradable environments appears still lacking. The most viable strategy to cope with this issue was to exploit chemically inert oxide phases to passivate QD surface in the form of either individual overcoating or matrix embedding. Herein, we report a simple but effective means to passivate QD surface by complexing its organic ligands with a metal alkoxide of titanium isopropoxide (Ti(i-PrO)4). For this, highly efficient red-emitting InP QDs with a multi-shell structure of ZnSeS intermediate plus ZnS outer shell are first synthesized and then the surface of resulting InP/ZnSeS/ZnS QDs is in-situ decorated with Ti(i-PrO)4. The presence of Tisbnd O species from Ti(i-PrO)4 on QD surface is verified by x-ray photoelectron and Fourier transform infrared spectroscopic analyses. Two comparative dispersions of pristine versus Ti(i-PrO)4-complexed QDs are exposed for certain periods of time to UV photon and heat and their temporal changes in photoluminescence are monitored, resulting in a huge improvement in QD stability from the latter ones through Ti(i-PrO)4-mediated better surface passivation.

CdSe/CdS semiconductor quantum rods as robust fluorescent probes for paraffin-embedded tissue imaging.

PubMed

Zacheo, Antonella; Quarta, Alessandra; Mangoni, Antonella; Pompa, Pier Paolo; Mastria, Rosanna; Capogrossi, Maurizio C; Rinaldi, Ross; Pellegrino, Teresa

2011-09-01

Immunofluorescence techniques on formalin fixed paraffin-embedded sections allow for the evaluation of the expression and spatial distribution of specific markers in patient tissue specimens or for monitoring the fate of labeled cells after in vivo injection. This technique suffers however from the auto-fluorescence background signal of the embedded tissue that eventually confounds the analysis. Here we show that rod-like semiconductor nanocrystals (QRs), intramuscularly injected in living mice, could be clearly detected by confocal microscopy in formalin fixed paraffin-embedded tissue sections. Despite the low amount of QRs amount injected (25 picomoles), these were clearly visible after 24 h in the muscle sections and their fluorescence signal was stronger than that of CdSe/ZnS quantum dots (QDs) similarly functionalized and in the case of QRs only, the signal lasted even after 21 days after the injection. © 2011 IEEE

Environmental release of core–shell semiconductor nanocrystals from free-standing polymer nanocomposite films†

PubMed Central

Pillai, Karthik V.; Gray, Patrick J.; Tien, Chun-Chieh; Bleher, Reiner; Sung, Li-Piin

2016-01-01

Concomitant with the development of polymer nanocomposite (PNC) technologies across numerous industries is an expanding awareness of the uncertainty with which engineered nanoparticles embedded within these materials may be released into the external environment, particularly liquid media. Recently there has been an interest in evaluating potential exposure to nanoscale fillers from PNCs, but existing studies often rely upon uncharacterized, poor quality, or proprietary materials, creating a barrier to making general mechanistic conclusions about release phenomena. In this study we employed semiconductor nanoparticles (quantum dots, QDs) as model nanofillers to quantify potential release into liquid media under specific environmental conditions. QDs of two sizes were incorporated into low-density polyethylene by melt compounding and the mixtures were extruded as free-standing fluorescent films. These films were subjected to tests under conditions intended to accelerate potential release of embedded particles or dissolved residuals into liquid environments. Using inductively-coupled plasma mass spectrometry and laser scanning confocal microscopy, it was found that the acidity of the external medium, exposure time, and small differences in particle size (on the order of a few nm) all play pivotal roles in release kinetics. Particle dissolution was found to play a major if not dominant role in the release process. This paper also presents the first evidence that internally embedded nanoparticles contribute to the mass transfer, an observation made possible via the use of a model system that was deliberately designed to probe the complex relationships between nanoparticle-enabled plastics and the environment. PMID:27529026

Efficient Fluorescence Resonance Energy Transfer between Quantum Dots and Gold Nanoparticles Based on Porous Silicon Photonic Crystal for DNA Detection

PubMed Central

Zhang, Hongyan; Lv, Jie; Jia, Zhenhong

2017-01-01

A novel assembled biosensor was prepared for detecting 16S rRNA, a small-size persistent specific for Actinobacteria. The mechanism of the porous silicon (PS) photonic crystal biosensor is based on the fluorescence resonance energy transfer (FRET) between quantum dots (QDs) and gold nanoparticles (AuNPs) through DNA hybridization, where QDs act as an emission donor and AuNPs serve as a fluorescence quencher. Results showed that the photoluminescence (PL) intensity of PS photonic crystal was drastically increased when the QDs-conjugated probe DNA was adhered to the PS layer by surface modification using a standard cross-link chemistry method. The PL intensity of QDs was decreased when the addition of AuNPs-conjugated complementary 16S rRNA was dropped onto QDs-conjugated PS. Based on the analysis of different target DNA concentration, it was found that the decrease of the PL intensity showed a good linear relationship with complementary DNA concentration in a range from 0.25 to 10 μM, and the detection limit was 328.7 nM. Such an optical FRET biosensor functions on PS-based photonic crystal for DNA detection that differs from the traditional FRET, which is used only in liquid. This method will benefit the development of a new optical FRET label-free biosensor on Si substrate and has great potential in biochips based on integrated optical devices. PMID:28489033

MOCVD Growth of III-V Photodetectors and Light Emitters for Integration of Optoelectronic Devices on Si substrates

NASA Astrophysics Data System (ADS)

Geng, Yu

With the increase of clock speed and wiring density in integrated circuits, inter-chip and intra-chip interconnects through conventional electrical wires encounter increasing difficulties because of the large power loss and bandwidth limitation. Optical interconnects have been proposed as an alternative to copper-based interconnects and are under intense study due to their large data capacity, high data quality and low power consumption. III-V compound semiconductors offer high intrinsic electron mobility, small effective electron mass and direct bandgap, which make this material system advantageous for high-speed optoelectronic devices. The integration of III-V optoelectronic devices on Si substrates will provide the combined advantage of a high level of integration and large volume production of Si-based electronic circuitry with the superior electrical and optical performance of III-V components, paving the way to a new generation of hybrid integrated circuits. In this thesis, the direct heteroepitaxy of photodetectors (PDs) and light emitters using metal-organic chemical vapor deposition for the integration of photonic devices on Si substrates were studied. First we studied the selective-area growth of InP/GaAs on patterned Si substrates for PDs. To overcome the loading effect, a multi-temperature composite growth technique for GaAs was developed. By decreasing various defects such as dislocations and anti-phase domains, the GaAs and InP buffer layers are with good crystalline quality and the PDs show high speed and low dark current performance both at the edge and center of the large growth well. Then the growth and fabrication of GaAs/AlGaAs QW lasers were studied. Ellipsometry was used to calibrate the Al composition of AlGaAs. Thick p and n type AlGaAs with a mirrorlike surface were grown by high V/III ratio and high temperature. The GaAs/AlGaAs broad area QW laser was successfully grown and fabricated on GaAs substrate and showed a pulsed lasing result with a threshold current density of about 800 A/cm2. For the integration of lasers on Si substrate, quantum dot (QD) lasers were studied. A flow-and-stop process of TBA was used to grow InAs QDs with the in-situ monitor EpiRas. QDs with a PL wavelength of ˜1.3 mum were grown on GaAs and Si substrates. To decrease the PL degradation problem caused by the contaminations from AlGaAs, an InGaAs insertion layer was inserted in between the AlGaAs and QDs region. Microdisk and a-Si waveguide lasers are designed and fabricated.

Hot spots based gold nanostar@SiO2@CdSe/ZnS quantum dots complex with strong fluorescence enhancement

NASA Astrophysics Data System (ADS)

Shan, Feng; Su, Dan; Li, Wei; Hu, Wei; Zhang, Tong

2018-02-01

In this paper, a novel gold nanostar (NS)@SiO2@CdSe/ZnS quantum dots (QDs) complex with plasmon-enhanced fluorescence synthesized using a step-by-step surface linkage method was presented. The gold NS was synthesized by the seed growth method. The synthesized gold NS with the apexes structure has a hot-spot effect due to the strong electric field distributed at its sharp apexes, which leads to a plasmon resonance enhancement. Because the distance between QDs and metal nanostructures can be precisely controlled by this method, the relationship between enhancement and distance was revealed. The thickness of SiO2 shell was also optimized and the optimum distance of about 21 nm was obtained. The highest fluorescence enhancement of 4.8-fold accompanied by a minimum fluorescence lifetime of 2.3 ns were achieved. This strong enhancement comes from the hot spots distributed at the sharp tip of our constructed nanostructure. Through the finite element method, we calculated the field distribution on the surface of NS and found that gold NS with the sharpest apexes exhibited the highest field enhancement, which matches well with our experiment result. This complex shows tremendous potential applications for liquid-dependent biometric imaging systems.

An optical fiber glass containing PbSe quantum dots

NASA Astrophysics Data System (ADS)

Cheng, Cheng; Jiang, Huilü; Ma, Dewei; Cheng, Xiaoyu

2011-09-01

An optical fiber material, sodium-aluminum-borosilicate glass doped with PbSe quantum dots (QDs) is synthesized by a high-temperature melting method. Crystallization, size distribution and absorption-photoluminescence (PL) of this material are observed by XRD, TEM, and spectrometer respectively. The obtained results indicate that the glass contains QDs in diameter of 6-13 nm depending on the heat-treatment temperature and with a higher doped concentration than those available. It shows an enhanced PL, widened FWHM (275-808 nm), obvious Stokes shift (20-110 nm), with the PL peak wavelength located within 1676-2757 nm depending on the size of QD. The glass is fabricated into an optical fiber in diameter of 10-70 μm and length of 1 m, with pliability and ductility similar to usual SiO 2 fibers. It can be easily fused and spliced with SiO 2 fibers due to a small difference of melting point between them. Characterized by high doped concentration and broad FWHM, this study suggests that the glass can be applied to designing novel broadband fiber amplifiers working in C-L waveband.

Confinement of gigahertz sound and light in Tamm plasmon resonators

NASA Astrophysics Data System (ADS)

Villafañe, V.; Bruchhausen, A. E.; Jusserand, B.; Senellart, P.; Lemaître, A.; Fainstein, A.

2015-10-01

We demonstrate theoretically and by pump-probe picosecond acoustics experiments the simultaneous confinement of light and gigahertz sound in Tamm plasmon resonators, formed by depositing a thin layer of Au onto a GaAs/AlGaAs Bragg reflector. The cavity has InGaAs quantum dots (QDs) embedded at the maximum of the confined optical field in the first GaAs layer. The different sound generation and detection mechanisms are theoretically analyzed. It is shown that the Au layer absorption and the resonant excitation of the QDs are the more efficient light-sound transducers for the coupling of near-infrared light with the confined acoustic modes, while the displacement of the interfaces is the main back-action mechanism at these energies. The prospects for the compact realization of optomechanical resonators based on Tamm plasmon cavities are discussed.

Delivery and reveal of localization of upconversion luminescent microparticles and quantum dots in the skin in vivo by fractional laser microablation, multimodal imaging, and optical clearing.

PubMed

Volkova, Elena K; Yanina, Irina Yu; Genina, Elina A; Bashkatov, Alexey N; Konyukhova, Julia G; Popov, Alexey P; Speranskaya, Elena S; Bucharskaya, Alla B; Navolokin, Nikita A; Goryacheva, Irina Yu; Kochubey, Vyacheslav I; Sukhorukov, Gleb B; Meglinski, Igor V; Tuchin, Valery V

2018-02-01

Delivery and spatial localization of upconversion luminescent microparticles [Y2O3:Yb, Er] (mean size ∼1.6  μm) and quantum dots (QDs) (CuInS2/ZnS nanoparticles coated with polyethylene glycol-based amphiphilic polymer, mean size ∼20  nm) inside rat skin was studied in vivo using a multimodal optical imaging approach. The particles were embedded into the skin dermis to the depth from 300 to 500  μm through microchannels performed by fractional laser microablation. Low-frequency ultrasound was applied to enhance penetration of the particles into the skin. Visualization of the particles was revealed using a combination of luminescent spectroscopy, optical coherence tomography, confocal microscopy, and histochemical analysis. Optical clearing was used to enhance the image contrast of the luminescent signal from the particles. It was demonstrated that the penetration depth of particles depends on their size, resulting in a different detection time interval (days) of the luminescent signal from microparticles and QDs inside the rat skin in vivo. We show that luminescent signal from the upconversion microparticles and QDs was detected after the particle delivery into the rat skin in vivo during eighth and fourth days, respectively. We hypothesize that the upconversion microparticles have created a long-time depot localized in the laser-created channels, as the QDs spread over the surrounding tissues. (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

Measurement of Valley Kondo Effect in a Si/SiGe Quantum Dot

NASA Astrophysics Data System (ADS)

Yuan, Mingyun; Yang, Zhen; Tang, Chunyang; Rimberg, A. J.; Joynt, R.; Savage, D. E.; Lagally, M. G.; Eriksson, M. A.

2013-03-01

The Kondo effect in Si/SiGe QDs can be enriched by the valley degree of freedom in Si. We have observed resonances showing temperature dependence characteristic of the Kondo effect in two consecutive Coulomb diamonds. These resonances exhibit unusual magnetic field dependence that we interpret as arising from Kondo screening of the valley degree of freedom. In one diamond two Kondo peaks due to screening of the valley index exist at zero magnetic field, revealing a zero-field valley splitting of Δ ~ 0.28 meV. In a non-zero magnetic field the peaks broaden and coalesce due to Zeeman splitting. In the other diamond, a single resonance at zero bias persists without Zeeman splitting for non-zero magnetic field, a phenomenon characteristic of valley non-conservation in tunneling. This research is supported by the NSA and ARO.

Homo-endotaxial one-dimensional Si nanostructures

DOE PAGES

Song, Jiaming; Hudak, Bethany M.; Sims, Hunter; ...

2017-11-29

One-dimensional (1D) nanostructures are highly sought after, both for their novel electronic properties as well as for their improved functionality. However, due to their nanoscale dimensions, these properties are significantly affected by the environment in which they are embedded. Here in this paper, we report on the creation of 1D homo-endotaxial Si nanostructures, i.e. 1D Si nanostructures with a lattice structure that is uniquely different from the Si diamond lattice in which they are embedded. We use scanning tunneling microscopy and spectroscopy, scanning transmission electron microscopy, density functional theory, and conductive atomic force microscopy to elucidate their formation and properties.more » Depending on kinetic constraints during growth, they can be prepared as endotaxial 1D Si nanostructures completely embedded in crystalline Si, or underneath a stripe of amorphous Si containing a large concentration of Bi atoms. Lastly, these homo-endotaxial 1D Si nanostructures have the potential to be useful components in nanoelectronic devices based on the technologically mature Si platform.« less

Fluorescence growth of self-polymerized fluorescence polydopamine for ratiometric visual detection of DA.

PubMed

Yu, Miao; Lu, Yang; Tan, Zhenjiang

2017-06-01

In this work, a novel and facile ratiometric fluorescence probe was prepared for the visual detection of dopamine (DA). In this detection system, red-emission CdTe@SiO 2 (r-QDs@SiO 2 ) was used as steady core of the probe and inverse microemulsion method was applied to synthesize uniform r-QDs@SiO 2 , this step could protect CdTe from contacting with human skin directly. Polydopamine (PDA) acted as response signal to detect DA, a very handy method which just combined polyethyleneimine (PEI) with DA together to synthesize PDA, this way for synthesis of PDA was much time-saving and non-toxic than any other methods. Differently from traditional analysis processes, the products of this experiment were also the analysis substances in final. Under optimum measurement conditions, the dual-emission ratiometric fluorescence probe was used for detections of DA in a concentration ranged from 10μM to 80μM with a detection limit of 0.12μM, with addition of DA the color of the probe changed from red to green watched by naked eyes. In addition, the developed probe was also used for detections of DA in human serum samples successfully. This study provides a simple, time-saving and non-toxic approach for detections of DA without the requirement of complex equipment. Copyright © 2017 Elsevier B.V. All rights reserved.

Evaluation of insertion characteristics of less invasive Si optoneural probe with embedded optical fiber

NASA Astrophysics Data System (ADS)

Morikawa, Takumi; Harashima, Takuya; Kino, Hisashi; Fukushima, Takafumi; Tanaka, Tetsu

2017-04-01

A less invasive Si optoneural probe with an embedded optical fiber was proposed and successfully fabricated. The diameter of the optical fiber was completely controlled by hydrogen fluoride etching, and the thinned optical fiber can propagate light without any leakage. This optical fiber was embedded in a trench formed inside a probe shank, which causes less damage to tissues. In addition, it was confirmed that the optical fiber embedded in the probe shank successfully irradiated light to optically stimulate gene transfected neurons. The electrochemical impedance of the probe did not change despite the light irradiation. Furthermore, probe insertion characteristics were evaluated in detail and less invasive insertion was clearly indicated for the Si optoneural probe with the embedded optical fiber compared with conventional optical neural probes. This neural probe with the embedded optical fiber can be used as a simple and easy tool for optogenetics and brain science.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Jiaming; Hudak, Bethany M.; Sims, Hunter

One-dimensional (1D) nanostructures are highly sought after, both for their novel electronic properties as well as for their improved functionality. However, due to their nanoscale dimensions, these properties are significantly affected by the environment in which they are embedded. Here in this paper, we report on the creation of 1D homo-endotaxial Si nanostructures, i.e. 1D Si nanostructures with a lattice structure that is uniquely different from the Si diamond lattice in which they are embedded. We use scanning tunneling microscopy and spectroscopy, scanning transmission electron microscopy, density functional theory, and conductive atomic force microscopy to elucidate their formation and properties.more » Depending on kinetic constraints during growth, they can be prepared as endotaxial 1D Si nanostructures completely embedded in crystalline Si, or underneath a stripe of amorphous Si containing a large concentration of Bi atoms. Lastly, these homo-endotaxial 1D Si nanostructures have the potential to be useful components in nanoelectronic devices based on the technologically mature Si platform.« less

Composite films of highly ordered Si nanowires embedded in SiGe0.3 for thermoelectric applications

NASA Astrophysics Data System (ADS)

Kikuchi, Akiou; Yao, Akifumi; Mori, Isamu; Ono, Takahito; Samukawa, Seiji

2017-10-01

We fabricated a high-density array of silicon nanowires (SiNWs) with a diameter of 10 nm embedded in silicon germanium (SiGe0.3) to give a composite thin film for thermoelectric device applications. The SiNW array was first fabricated by bio-template mask and neutral beam etching techniques. The SiNW array was then embedded in SiGe0.3 by thermal chemical vapor deposition. The cross-plane thermal conductivity of the SiNW-SiGe0.3 composite film with a thickness of 100 nm was 3.5 ± 0.3 W/mK in the temperature range of 300-350 K. Moreover, the temperature dependences of the in-plane electrical conductivity and in-plane Seebeck coefficient of the SiNW-SiGe0.3 composite were evaluated. The fabricated SiNW-SiGe0.3 composite film displayed a maximum power factor of 1 × 103 W/m K2 (a Seebeck coefficient of 4.8 × 103 μV/K and an electrical conductivity of 4.4 × 103 S/m) at 873 K. The present high-density SiNW array structure represents a new route to realize practical thermoelectric devices using mature Si processes without any rare metals.

Controlled formation of GeSi nanostructures on pillar-patterned Si substrate

NASA Astrophysics Data System (ADS)

Zhou, Tong; Zeng, Ceng; Fan, Yongliang; Jiang, Zuimin; Xia, Jinsong; Zhong, Zhenyang; Fudan University Team; Huazhong University of Science; Technology Collaboration

2015-03-01

GeSi quantum nanostructures (QNs) have potential applications in optoelectronic devices due to their unique properties and compatibility with the sophisticated Si technology. However, the disadvantages of poor quantum efficiency of the GeSi QNs on flat Si (001) substrates hinder their optoelectronic applications. Today, numerous growth strategies have been proposed to control the formation of GeSi QNs in hope of improving the optoelectronic performances. One of the ways is to fabricate GeSi QNs on patterned substrates, where the GeSi QNs can be greatly manipulated in aspects of size, shape, composition, orientation and arrangement. Here, self-assembled GeSi QNs on periodic Si (001) sub-micro pillars (SPMs) are systematically studied. By controlling the growth conditions and the diameters of the SPMs, different GeSi QNs, including circularly arranged quantum dots (QDs), quantum rings (QRs), and quantum dot molecules (QDMs), are realized at the top edge of SMPs. Meanwhile, fourfold symmetric GeSi QDMs can be also obtained at the base edges of the SPMs. The promising features of self-assembled GeSi QNs are explained in terms of the surface chemical potential, which disclose the critical effect of surface morphology on the diffusion and the aggregation of Ge adatoms.

Silica coating of PbS quantum dots and their position control using a nanohole on Si substrate

NASA Astrophysics Data System (ADS)

Mukai, Kohki; Okumura, Isao; Nishizaki, Yuta; Yamashita, Shuzo; Niwa, Keisuke

2018-04-01

We succeeded in controlling the apparent size of a colloidal PbS quantum dot (QD) in the range of 20 to 140 nm by coating with silica and trapping the coated QDs in a nanohole prepared by scanning probe microscope lithography. Photoluminescence intensity was improved by controlling the process of adding the silica source material of tetraethoxysilane for the coating. Nanoholes of different sizes were formed on a single substrate by scanning probe oxidation with the combination of SF6 dry etching and KOH wet etching. QDs having an arbitrary energy structure can be arranged at an arbitrary position on the semiconductor substrate using this technique, which will aid in the fabrication of future nanosize solid devices such as quantum information circuits.

Characterization of the Structural and Optical Properties of III-V Semiconductor Materials for Solar Cell Applications

NASA Astrophysics Data System (ADS)

Xie, Hongen

The work contained in this dissertation is focused on the structural and optical properties of III-V semiconductor structures for solar cell applications. By using transmission electron microscopy, many of their structural properties have been investigated, including morphology, defects, and strain relaxation. The optical properties of the semiconductor structures have been studied by photoluminescence and cathodoluminescence. Part of this work is focused on InAs quantum dots (QDs) embedded in AlGaAs matrices. This QD system is important for the realization of intermediate-band solar cells, which has three light absorption paths for high efficiency photovoltaics. The suppression of plastic strain relaxation in the QDs shows a significant improvement of the optoelectronic properties. A partial capping followed by a thermal annealing step is used to achieve spool-shaped QDs with a uniform height following the thickness of the capping layer. This step keeps the height of the QDs below a critical value that is required for plastic relaxation. The spool-shaped QDs exhibit two photoluminescence peaks that are attributed to ground and excited state transitions. The luminescence peak width is associated with the QD diameter distribution. An InAs cover layer formed during annealing is found responsible for the loss of the confinement of the excited states in smaller QDs. The second part of this work is focused on the investigation of the In xGa1-xN thin films having different bandgaps for double-junction solar cells. InxGa1-xN films with x ≤ 0.15 were grown by metal organic chemical vapor deposition. The defects in films with different indium contents have been studied. Their effect on the optical properties of the film have been investigated by cathodoluminescence. InxGa 1-xN films with indium contents higher than 20% were grown by molecular beam epitaxy. The strain relaxation in the films has been measured from electron diffraction patterns taken in cross-sectional TEM specimens. Moire fringes in some of the films reveal interfacial strain relaxation that is explained by a critical thickness model.

Mechanical behavior enhancement of ZnO nanowire by embedding different nanowires

NASA Astrophysics Data System (ADS)

Vazinishayan, Ali; Yang, Shuming; Lambada, Dasaradha Rao; Wang, Yiming

2018-06-01

In this work, we employed commercial finite element modeling (FEM) software package ABAQUS to analyze mechanical properties of ZnO nanowire before and after embedding with different kinds of nanowires, having different materials and cross-section models such as Au (circular), Ag (pentagonal) and Si (rectangular) using three point bending technique. The length and diameter of the ZnO nanowire were measured to be 12,280 nm and 103.2 nm, respectively. In addition, Au, Ag and Si nanowires were considered to have the length of 12,280 nm and the diameter of 27 nm. It was found that after embedding Si nanowire with rectangular cross-section into the ZnO nanowire, the distribution of Von Misses stresses criterion, displacement and strain were decreased than the other nanowires embedded. The highest stiffness, the elastic deformation and the high strength against brittle failure have been made by Si nanowire comparison to the Au and Ag nanowires, respectively.

Chip-scale white flip-chip light-emitting diode containing indium phosphide/zinc selenide quantum dots

NASA Astrophysics Data System (ADS)

Fan, Bingfeng; Yan, Linchao; Lao, Yuqin; Ma, Yanfei; Chen, Zimin; Ma, Xuejin; Zhuo, Yi; Pei, Yanli; Wang, Gang

2017-08-01

A method for preparing a quantum dot (QD)-white light-emitting diode (WLED) is reported. Holes were etched in the SiO2 layer deposited on the sapphire substrate of the flip-chip LED by inductively coupled plasma, and these holes were then filled with QDs. An ultraviolet-curable resin was then spin-coated on top of the QD-containing SiO2 layer, and the resin was cured to act as a protecting layer. The reflective sidewall structure minimized sidelight leakage. The fabrication of the QD-WLED is simple in preparation and compatible with traditional LED processes, which was the minimum size of the WLED chip-scale integrated package. InP/ZnS core-shell QDs were used as the converter in the WLED. A blue light-emitting diode with a flip-chip structure was used as the excitation source. The QD-WLED exhibited color temperatures from 5900 to 6400 K and Commission Internationale De L'Elcairage color coordinates from (0.315, 0.325) to (0.325, 0.317), under drive currents from 100 to 400 mA. The QD-WLED exhibited stable optoelectronic properties.

Investigation of carrier dynamics in InAs/GaAsSb quantum dots with different silicon delta-doping levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ban, Keun-Yong; Kim, Yeongho; Kuciauskas, Darius

2016-11-10

The optical properties of InAs quantum dots (QDs) embedded in a GaAsSb matrix with different delta (d)-doping levels of 0, 2, 4, and 6 electrons per dot (e-/dot), incorporated to control the occupation of QD electronic states, are studied by photoluminescence (PL) spectroscopy. The time-resolved PL data taken at 10 K reveal that the increase of δ-doping density from 2 to 6 e -/dot decreases the recombination lifetime of carriers at ground states of the QDs from 996 ± 36 to 792 ± 19 ps, respectively. Furthermore, the carrier lifetime of the sample with 4 e -/dot is found tomore » increase at a slower rate than that of the undoped sample as temperature increases above 70 K. An Arrhenius plot of the temperature dependent PL intensity indicates that the thermal activation energy of electrons in the QDs, required for carrier escape from the dot ground state to continuum state, is increased when the d-doping density is high enough (>4 e -/dot). These results are attributed to the enhanced Coulomb interaction of electrons provided by the d-doping, leading to reduced thermal quenching of the PL.« less

Origin of White Electroluminescence in Graphene Quantum Dots Embedded Host/Guest Polymer Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Kyu Kim, Jung; Bae, Sukang; Yi, Yeonjin; Jin Park, Myung; Jin Kim, Sang; Myoung, Nosoung; Lee, Chang-Lyoul; Hee Hong, Byung; Hyeok Park, Jong

2015-06-01

Polymer light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nano-material without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions.

Origin of White Electroluminescence in Graphene Quantum Dots Embedded Host/Guest Polymer Light Emitting Diodes.

PubMed

Kyu Kim, Jung; Bae, Sukang; Yi, Yeonjin; Jin Park, Myung; Jin Kim, Sang; Myoung, NoSoung; Lee, Chang-Lyoul; Hee Hong, Byung; Hyeok Park, Jong

2015-06-11

Polymer light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nano-material without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions.

Flexible Memristive Devices Based on InP/ZnSe/ZnS Core-Multishell Quantum Dot Nanocomposites.

PubMed

Kim, Do Hyeong; Wu, Chaoxing; Park, Dong Hyun; Kim, Woo Kyum; Seo, Hae Woon; Kim, Sang Wook; Kim, Tae Whan

2018-05-02

The effects of the ZnS shell layer on the memory performances of flexible memristive devices based on quantum dots (QDs) with an InP/ZnSe/ZnS core-multishell structure embedded in a poly(methylmethacrylate) layer were investigated. The on/off ratios of the devices based on QDs with an InP/ZnSe core-shell structure and with an InP/ZnSe/ZnS core-multishell structure were approximately 4.2 × 10 2 and 8.5 × 10 3 , respectively, indicative of enhanced charge storage capability in the latter. After bending, the memory characteristics of the memristive devices based on QDs with the InP/ZnSe/ZnS structure were similar to those before bending. In addition, those devices maintained the same on/off ratios for retention time of 1 × 10 4 s, and the number of endurance cycles was above 1 × 10 2 . The reset voltages ranged from -2.3 to -3.1 V, and the set voltages ranged from 1.3 to 2.1 V, indicative of reliable electrical characteristics. Furthermore, the possible operating mechanisms of the devices are presented on the basis of the electron trapping and release mode.

Effect of uniaxial stress on the polarization of light emitted from GaN/AlN quantum dots grown on Si(111)

NASA Astrophysics Data System (ADS)

Moshe, O.; Rich, D. H.; Damilano, B.; Massies, J.

2008-04-01

Cathodoluminescence (CL) measurements of the ground-state excitonic transition of vertically stacked GaN/AlN quantum dots (QDs) exhibited an in-plane linear polarization anisotropy in close proximity to microcracks. Microcracks form as a result of a mismatch of the thermal expansion coefficient between the GaN/AlN layers and the Si(111) substrate. In close proximity to the cracks, the layers are found to be under uniaxial tensile stress, whereas the film is under biaxial tensile stress for distances greater than ˜3μm from the cracks. The microcracks serve as an excellent stressor through which the strain tensor of the GaN/AlN QDs can be reproducibly modified for studies of strain-induced changes in the optical and electronic properties by using a spatially resolved probe, such as with CL. Changes in the optical properties of the QDs are attributed to stress-dependent variations of the band edges and the electric field along [0001], which is caused by charge polarization. Such changes in the field will subsequently affect the oscillator strength between electrons and holes. Three-dimensional 6×6 kṡp calculations of the QD electron and hole wave functions and eigenstates were performed to examine the influence of biaxial and uniaxial tensile stresses on the polarization-dependent momentum matrix element in varying proximity to the microcracks. The model reveals that a change from biaxial to uniaxial stress alters the admixture of px and py characters of the band edges and the ground-state hole wave function, changes the shape and direction of elongation of the hole isosurfaces, and accounts well for the subsequent anisotropy in the polarization dependent optical transitions.

Large-area (over 50 cm × 50 cm) freestanding films of colloidal InP/ZnS quantum dots.

PubMed

Mutlugun, Evren; Hernandez-Martinez, Pedro Ludwig; Eroglu, Cuneyt; Coskun, Yasemin; Erdem, Talha; Sharma, Vijay K; Unal, Emre; Panda, Subhendu K; Hickey, Stephen G; Gaponik, Nikolai; Eychmüller, Alexander; Demir, Hilmi Volkan

2012-08-08

We propose and demonstrate the fabrication of flexible, freestanding films of InP/ZnS quantum dots (QDs) using fatty acid ligands across very large areas (greater than 50 cm × 50 cm), which have been developed for remote phosphor applications in solid-state lighting. Embedded in a poly(methyl methacrylate) matrix, although the formation of stand-alone films using other QDs commonly capped with trioctylphosphine oxide (TOPO) and oleic acid is not efficient, employing myristic acid as ligand in the synthesis of these QDs, which imparts a strongly hydrophobic character to the thin film, enables film formation and ease of removal even on surprisingly large areas, thereby avoiding the need for ligand exchange. When pumped by a blue LED, these Cd-free QD films allow for high color rendering, warm white light generation with a color rendering index of 89.30 and a correlated color temperature of 2298 K. In the composite film, the temperature-dependent emission kinetics and energy transfer dynamics among different-sized InP/ZnS QDs are investigated and a model is proposed. High levels of energy transfer efficiency (up to 80%) and strong donor lifetime modification (from 18 to 4 ns) are achieved. The suppression of the nonradiative channels is observed when the hybrid film is cooled to cryogenic temperatures. The lifetime changes of the donor and acceptor InP/ZnS QDs in the film as a result of the energy transfer are explained well by our theoretical model based on the exciton-exciton interactions among the dots and are in excellent agreement with the experimental results. The understanding of these excitonic interactions is essential to facilitate improvements in the fabrication of photometrically high quality nanophosphors. The ability to make such large-area, flexible, freestanding Cd-free QD films pave the way for environmentally friendly phosphor applications including flexible, surface-emitting light engines.

Defect reduction of SiNx embedded m-plane GaN grown by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Woo, Seohwi; Kim, Minho; So, Byeongchan; Yoo, Geunho; Jang, Jongjin; Lee, Kyuseung; Nam, Okhyun

2014-12-01

Nonpolar (1 0 -1 0) m-plane GaN has been grown on m-plane sapphire substrates by hydride vapor phase epitaxy (HVPE). We studied the defect reduction of m-GaN with embedded SiNx interlayers deposited by ex-situ metal organic chemical vapor deposition (MOCVD). The full-width at half-maximum values of the X-ray rocking curves for m-GaN with embedded SiNx along [1 1 -2 0]GaN and [0 0 0 1]GaN were reduced to 528 and 1427 arcs, respectively, as compared with the respective values of 947 and 3170 arcs, of m-GaN without SiNx. Cross-section transmission electron microscopy revealed that the basal stacking fault density was decreased by approximately one order to 5×104 cm-1 due to the defect blocking of the embedded SiNx. As a result, the near band edge emission intensities of the room-temperature and low-temperature photoluminescence showed approximately two-fold and four-fold improvement, respectively.

Two-dimensionally grown single-crystal silicon nanosheets with tunable visible-light emissions.

PubMed

Kim, Sung Wook; Lee, Jaejun; Sung, Ji Ho; Seo, Dong-jae; Kim, Ilsoo; Jo, Moon-Ho; Kwon, Byoung Wook; Choi, Won Kook; Choi, Heon-Jin

2014-07-22

Since the discovery of graphene, growth of two-dimensional (2D) nanomaterials has greatly attracted attention. However, spontaneous growth of atomic two-dimensional (2D) materials is limitedly permitted for several layered-structure crystals, such as graphene, MoS2, and h-BN, and otherwise it is notoriously difficult. Here we report the gas-phase 2D growth of silicon (Si), that is cubic in symmetry, via dendritic growth and an interdendritic filling mechanism and to form Si nanosheets (SiNSs) of 1 to 13 nm in thickness. Thin SiNSs show strong thickness-dependent photoluminescence in visible range including red, green, and blue (RGB) emissions with the associated band gap energies ranging from 1.6 to 3.2 eV; these emission energies were greater than those from Si quantum dots (SiQDs) of the similar sizes. We also demonstrated that electrically driven white, as well as blue, emission in a conventional organic light-emitting diode (OLED) geometry with the SiNS assembly as the active emitting layers. Tunable light emissions in visible range in our observations suggest practical implications for novel 2D Si nanophotonics.

Adsorption of quantum dots onto polymer and Gemini surfactant films: a quartz crystal microbalance study.

PubMed

Alejo, T; Merchán, M D; Velázquez, M M

2014-08-26

We used quartz crystal microbalance with dissipation to study the mechanical properties, the kinetics of adsorption, and the amount of CdSe quantum dots (QDs) adsorbed onto a SiO2 sensor, referred as bare sensor, onto the sensor modified with a film of the polymer poly(maleic anhydride-alt-1-octadecene), PMAO, or with a film of the Gemini surfactant ethyl-bis(dimethyl octadecyl ammonium bromide), abbreviated as 18-2-18. Results showed that when the sensor is coated with polymer or surfactant molecules, the coverage increases compared with that obtained for the bare sensor. On the other hand, rheological properties and kinetics of adsorption of QDs are driven by QD nanoparticles. Thus, the QD films present elastic behavior, and the elasticity values are independent of the molecule used as coating and similar to the elasticity value obtained for QDs films on the bare sensor. The QD adsorption is a two-step mechanism in which the fastest process is attributed to the QD adsorption onto the solid substrate and the slowest one is ascribed to rearrangement movements of the nanoparticles adsorbed at the surface.

Tapping the potential of trioctylphosphine (TOP) in the realization of highly luminescent blue-emitting colloidal indium phosphide (InP) quantum dots

NASA Astrophysics Data System (ADS)

Singh, Akanksha; Chawla, Parul; Jain, Shefali; Sharma, Shailesh Narain

2017-06-01

In this work, extremely small blue emitting colloidal InP-based quantum dots (size 2-5 nm) have been synthesized using trioctylphosphine (TOP) as a source of phosphorus. The method reported here is unconventional, quite rapid ( 90 min), more viable, less expensive and relatively greener as compared to other conventional methods that employ tristrimethylsilyylphosphine(P(SiMe3)3) which is scarce, expensive, flammable, highly toxic and even banned in a few countries. Highly luminescent InP QDs having bluish-green emission (λ 490 nm) can be synthesized using this method without resorting to any post-synthesis etching to tune the emission to the blue region. Besides being the source of phosphorus and the particle size regulating agent, the efficacy of TOP is further realized during synthesis via its reduction of indium salt, which aids in the formation of indium metal and then subsequently in the development of InP QDs. The PL intensity of as-synthesized InP QDs is further enhanced by growing a shell of wide band gap material, i.e. ZnS resulting in a concurrent increment in quantum yield from 25% to 38% respectively.

Enhancement of the Si p-n diode NIR photoresponse by embedding β-FeSi2 nanocrystallites.

PubMed

Shevlyagin, A V; Goroshko, D L; Chusovitin, E A; Galkin, K N; Galkin, N G; Gutakovskii, A K

2015-10-05

By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p(+)-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3-4 and 15-20 nm, and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2%, and a specific detectivity of 1.2 × 10(9) cm × Hz(1/2)/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2.

Fabrication of Si heterojunction solar cells using P-doped Si nanocrystals embedded in SiNx films as emitters

PubMed Central

2013-01-01

Si heterojunction solar cells were fabricated on p-type single-crystal Si (sc-Si) substrates using phosphorus-doped Si nanocrystals (Si-NCs) embedded in SiNx (Si-NCs/SiNx) films as emitters. The Si-NCs were formed by post-annealing of silicon-rich silicon nitride films deposited by electron cyclotron resonance chemical vapor deposition. We investigate the influence of the N/Si ratio in the Si-NCs/SiNx films on their electrical and optical properties, as well as the photovoltaic properties of the fabricated heterojunction devices. Increasing the nitrogen content enhances the optical gap E04 while deteriorating the electrical conductivity of the Si-NCs/SiNx film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device. These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiNx film as a mixture of a high-transparency SiNx phase and a low-resistivity Si-NC phase. A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell. PMID:24188725

Lectin-carbohydrate recognition mechanism of Plasmodium berghei in the midgut of malaria vector Anopheles stephensi using quantum dot as a new approach.

PubMed

Basseri, Hamid R; Javazm, Mahdi Salari; Farivar, Leila; Abai, Mohammad R

2016-04-01

Potential targets of Plasmodium ookinetes at the mosquito midgut walls were investigated in relation to interfering malarial transmission. In this study, the essential application of Quantum Dots (QDs) was used to examine the interaction between Plasmodium berghei ookinetes and the Anopheles stephensi midgut, based on lectin-carbohydrate recognition. Two significant lectins were utilized to determine this interaction. Two QDs, cadmium telluride (CdTe)/CdS and cadmium selenide (CdSe)/CdS, were employed in staining Plasmodium ookinete to study its interaction in the midgut of the mosquito vector in vivo. Concurrently, two lectins, wheat germ agglutinin (WGA) and concanavalin A (Con A), were inadvertently exploited to mask lectin binding sites between ookinetes and mosquito midgut cells. The numbers of ookinetes in both lumen and epithelial cells were eventually counted, following adequate preparation of wax sections extracted from whole midgut, and subsequent examination using a differential interference contrast a fluorescence microscopic technique. Interestingly, we detected that neither of the QDs mutated ookinete invasion into the midgut cells of the investigated mosquitoes. QD staining of ookinetes remained permanent despite the effective embedding procedure. The massive binding potency of ookinetes to midgut cells of the cross-examined mosquitoes undoubtedly revealed that Con A did not interrupt ookinete penetration into the midgut wall. In contrast, WGA inhibited ookinete invasion into the midgut cells. The results proved that QD nanoparticles are biocompatible, non-toxic to P. berghei and stable to photobleaching. The QDs staining, which was successfully implemented for ookinete labelling, is a simple and effective tool which plays a crucial role in bioimaging including the study of parasite-vector interactions. Copyright © 2016 Elsevier B.V. All rights reserved.

Excitonic lasing of strain-free InP(As) quantum dots in AlInAs microdisk

NASA Astrophysics Data System (ADS)

Lebedev, D. V.; Kulagina, M. M.; Troshkov, S. I.; Vlasov, A. S.; Davydov, V. Y.; Smirnov, A. N.; Bogdanov, A. A.; Merz, J. L.; Kapaldo, J.; Gocalinska, A.; Juska, G.; Moroni, S. T.; Pelucchi, E.; Barettin, D.; Rouvimov, S.; Mintairov, A. M.

2017-03-01

Formation, emission, and lasing properties of strain-free InP(As)/AlInAs quantum dots (QDs) embedded in AlInAs microdisk (MD) cavity were investigated using transmission electron microscopy and photoluminescence (PL) techniques. In MD structures, the QDs have the nano-pan-cake shape with the height of ˜2 nm, the lateral size of 20-50 nm, and the density of ˜5 × 109 cm-2. Their emission observed at ˜940 nm revealed strong temperature quenching, which points to exciton decomposition. It also showed unexpected type-I character, indicating In-As intermixing as confirmed by band structure calculations. We observed lasing of InP(As) QD excitons into whispering gallery modes in MD having the diameter of ˜3.2 μm and providing a free spectral range of ˜27 nm and quality factors up to Q˜13 000. Threshold of ˜50 W/cm2 and spontaneous emission coupling coefficient of ˜0.2 were measured for this MD-QD system.

Exciton dynamics in a site-controlled quantum dot coupled to a photonic crystal cavity

NASA Astrophysics Data System (ADS)

Jarlov, C.; Lyasota, A.; Ferrier, L.; Gallo, P.; Dwir, B.; Rudra, A.; Kapon, E.

2015-11-01

Exciton and cavity mode (CM) dynamics in site-controlled pyramidal quantum dots (QDs), integrated with linear photonic crystal membrane cavities, are investigated for a range of temperatures and photo-excitation power levels. The absence of spurious multi-excitonic effects, normally observed in similar structures based on self-assembled QDs, permits the observation of effects intrinsic to two-level systems embedded in a solid state matrix and interacting with optical cavity modes. The coupled exciton and CM dynamics follow the same trend, indicating that the CM is fed only by the exciton transition. The Purcell reduction of the QD and CM decay times is reproduced well by a theoretical model that includes exciton linewidth broadening and temperature dependent non-radiative processes, from which we extract a Purcell factor of 17 ± 5. For excitation powers above QD saturation, we show the influence of quantum wire barrier states at short delay time, and demonstrate the absence of multiexcitonic background emission.

Tuning Optoelectronic Properties of the Graphene-Based Quantum Dots C16- xSi xH10 Family.

PubMed

Ramadan, F-Z; Ouarrad, H; Drissi, L B

2018-06-07

The electronic and optical properties of graphene-based quantum dots (QDs) are investigated using DFT and many-body perturbation theory. Formation energy, hardeness and electrophilicity show that all structures, from pyrene to silicene QD passing through 15 CSi QD configurations, are energetically and chemically stable. It is also found that they are reactive which implies their favorable character for the possible electronic transport and conductivity. The electronic and optical properties are very sensitive to the number and position of the substituted silicon atoms as well as the directions of the light polarization. Moreover, quantum confinement effects make the exciton binding energy of CSi quantum dots larger than those of their higher dimensional allotropes such as silicene, graphene, and SiC sheet and nanotube. It is also higher those of other shapes of quantum dots like hexagonal graphene QDs and can be tailored from the ultraviolet region to the visible one. The values of the singlet-triplet splitting determined for the X- and Y-light polarized indicate that all configurations have a high fluorescence quantum yield compared to the yield of typical semiconductors, which makes them very promising for various applications such as the light-emitting diode material and nanomedicine.

Efficient fluorescence energy transfer system between CdTe-doped silica nanoparticles and gold nanoparticles for turn-on fluorescence detection of melamine.

PubMed

Gao, Feng; Ye, Qingqing; Cui, Peng; Zhang, Lu

2012-05-09

We here report an efficient and enhanced fluorescence energy transfer system between confined quantum dots (QDs) by entrapping CdTe into the mesoporous silica shell (CdTe@SiO₂) as donors and gold nanoparticles (AuNPs) as acceptors. At pH 6.50, the CdTe@SiO₂-AuNPs assemblies coalesce to form larger clusters due to charge neutralization, leading to the fluorescence quenching of CdTe@SiO₂ as a result of energy transfer. As compared with the energy transfer system between unconfined CdTe and AuNPs, the maximum fluorescence quenching efficiency of the proposed system is improved by about 27.0%, and the quenching constant, K(sv), is increased by about 2.4-fold. The enhanced quenching effect largely turns off the fluorescence of CdTe@SiO₂ and provides an optimal "off-state" for sensitive "turn-on" assay. In the present study, upon addition of melamine, the weak fluorescence system of CdTe@SiO₂-AuNPs is enhanced due to the strong interactions between the amino group of melamine and the gold nanoparticles via covalent bond, leading to the release of AuNPs from the surfaces of CdTe@SiO₂; thus, its fluorescence is restored. A "turn-on" fluorimetric method for the detection of melamine is proposed based on the restored fluorescence of the system. Under the optimal conditions, the fluorescence enhanced efficiency shows a linear function against the melamine concentrations ranging from 7.5 × 10⁻⁹ to 3.5 × 10⁻⁷ M (i.e., 1.0-44 ppb). The analytical sensitivity is improved by about 50%, and the detection limit is decreased by 5.0-fold, as compared with the analytical results using the CdTe-AuNPs system. Moreover, the proposed method was successfully applied to the determination of melamine in real samples with excellent recoveries in the range from 97.4 to 104.1%. Such a fluorescence energy transfer system between confined QDs and AuNPs may pave a new way for designing chemo/biosensing.

Evaluation of resistive switching properties of Si-rich oxide embedded with Ti nanodots by applying constant voltage and current

NASA Astrophysics Data System (ADS)

Ohta, Akio; Kato, Yusuke; Ikeda, Mitsuhisa; Makihara, Katsunori; Miyazaki, Seiichi

2018-06-01

We have studied the resistive switching behaviors of electron beam (EB) evaporated Si-rich oxide (SiO x ) sandwiched between Ni electrodes by applying a constant voltage and current. Additionally, the impact of Ti nanodots (NDs) embedded into SiO x on resistive switching behaviors was investigated because it is expected that NDs can trigger the formation of a conductive filament path in SiO x . The resistive switching behaviors of SiO x show that the response time during resistance switching was decreased by increasing the applied constant current or constant voltage. It was found that Ti-NDs in SiO x enhance the conductive filament path formation owing to electric field concentration by Ti-NDs.

Enhancement of the Si p-n diode NIR photoresponse by embedding β-FeSi2 nanocrystallites

PubMed Central

Shevlyagin, A. V.; Goroshko, D. L.; Chusovitin, E. A.; Galkin, K. N.; Galkin, N. G.; Gutakovskii, A. K.

2015-01-01

By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p+-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3–4 and 15–20 nm, and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2%, and a specific detectivity of 1.2 × 109 cm × Hz1/2/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2. PMID:26434582

A molecular imprinting-based turn-on Ratiometric fluorescence sensor for highly selective and sensitive detection of 2,4-dichlorophenoxyacetic acid (2,4-D).

PubMed

Wang, Xiaoyan; Yu, Jialuo; Wu, Xiaqing; Fu, Junqing; Kang, Qi; Shen, Dazhong; Li, Jinhua; Chen, Lingxin

2016-07-15

A novel molecular imprinting-based turn-on ratiometric fluorescence sensor was constructed via a facile sol-gel polymerization for detection of 2,4-dichlorophenoxyacetic acid (2,4-D) on the basis of photoinduced electron transfer (PET) by using nitrobenzoxadiazole (NBD) as detection signal source and quantum dots (QDs) as reference signal source. With the presence and increase of 2,4-D, the amine groups on the surface of QDs@SiO2 could bind with 2,4-D and thereby the NBD fluorescence intensities could be significantly enhanced since the PET process was inhibited, while the QDs maintained constant intensities. Accordingly, the ratio of the dual-emission intensities of green NBD and red QDs could be utilized for turn-on fluorescent detection of 2,4-D, along with continuous color changes from orange-red to green readily observed by the naked eye. The as-prepared fluorescence sensor obtained high sensitivity with a low detection limit of 0.14μM within 5min, and distinguished recognition selectivity for 2,4-D over its analogs. Moreover, the sensor was successfully applied to determine 2,4-D in real water samples, and high recoveries at three spiking levels of 2,4-D ranged from 95.0% to 110.1% with precisions below 4.5%. The simple, rapid and reliable visual sensing strategy would not only provide potential applications for high selective ultratrace analysis of complicated matrices, but also greatly enrich the research connotations of molecularly imprinted sensors. Copyright © 2016 Elsevier B.V. All rights reserved.

Exchange bias of Ni nanoparticles embedded in an antiferromagnetic IrMn matrix.

PubMed

Kuerbanjiang, Balati; Wiedwald, Ulf; Haering, Felix; Biskupek, Johannes; Kaiser, Ute; Ziemann, Paul; Herr, Ulrich

2013-11-15

The magnetic properties of Ni nanoparticles (Ni-NPs) embedded in an antiferromagnetic IrMn matrix were investigated. The Ni-NPs of 8.4 nm mean diameter were synthesized by inert gas aggregation. In a second processing step, the Ni-NPs were in situ embedded in IrMn films or SiOx films under ultrahigh vacuum (UHV) conditions. Findings showed that Ni-NPs embedded in IrMn have an exchange bias field HEB = 821 Oe at 10 K, and 50 Oe at 300 K. The extracted value of the exchange energy density is 0.06 mJ m(-2) at 10 K, which is in good accordance with the results from multilayered thin film systems. The Ni-NPs embedded in SiOx did not show exchange bias. As expected for this particle size, they are superparamagnetic at T = 300 K. A direct comparison of the Ni-NPs embedded in IrMn or SiOx reveals an increase of the blocking temperature from 210 K to around 400 K. The coercivity of the Ni-NPs exchange coupled to the IrMn matrix at 10 K is 8 times larger than the value for Ni-NPs embedded in SiOx. We studied time-dependent remanent magnetization at different temperatures. The relaxation behavior is described by a magnetic viscosity model which reflects a rather flat distribution of energy barriers. Furthermore, we investigated the effects of different field cooling processes on the magnetic properties of the embedded Ni-NPs. Exchange bias values fit to model calculations which correlate the contribution of the antiferromagnetic IrMn matrix to its grain size.

Ge nanocrystals embedded in ultrathin Si3N4 multilayers with SiO2 barriers

NASA Astrophysics Data System (ADS)

Bahariqushchi, R.; Gundogdu, Sinan; Aydinli, A.

2017-04-01

Multilayers of germanium nanocrystals (NCs) embedded in thin films of silicon nitride matrix separated with SiO2 barriers have been fabricated using plasma enhanced chemical vapor deposition (PECVD). SiGeN/SiO2 alternating bilayers have been grown on quartz and Si substrates followed by post annealing in Ar ambient from 600 to 900 °C. High resolution transmission electron microscopy (HRTEM) as well as Raman spectroscopy show good crystallinity of Ge confined to SiGeN layers in samples annealed at 900 °C. Strong compressive stress for SiGeN/SiO2 structures were observed through Raman spectroscopy. Size, as well as NC-NC distance were controlled along the growth direction for multilayer samples by varying the thickness of bilayers. Visible photoluminescence (PL) at 2.3 and 3.1 eV with NC size dependent intensity is observed and possible origin of PL is discussed.

Infrared absorption and admittance spectroscopy of Ge quantum dots on a strained SiGe layer

NASA Astrophysics Data System (ADS)

Yakimov, A. I.; Nikiforov, A. I.; Timofeev, V. A.; Dvurechenskii, A. V.

2011-12-01

A combined infrared absorption and admittance spectroscopy is carried out in examining the energy level structure and the hole emission process in self-assembled Ge quantum dots (QDs) placed on a strained Si0.65Ge0.35 quantum well (QW), which, in turn, is incorporated in a Si matrix. In the midinfrared spectral range, the dots exhibit three dominant absorption bands peaked at 130, 250 and 390 meV. By a comparison between absorption measurements and six-band {\\bf k}\\;{\\bm \\cdot}\\;{\\bf p} calculations, the long-wave (~130 meV) resonance is attributed to a transition from the QD hole ground state to the two-dimensional heavy-hole states confined in the Si0.65Ge0.35 layer. The mid-wave absorption band around 390 meV is ascribed to a transition from the QD hole ground state to the three-dimensional continuum states of the Si matrix. An equivalent absorption cross section for these two types of transitions is determined to be 1.2 × 10-15 cm2 and 1.2 × 10-16 cm2, respectively. The origin of the transmission minimum around 250 meV is more ambiguous. We tentatively propose that it can be due to transition either from the highest heavy-hole subband of the Si0.65Ge0.35 QW to continuum states above the Si barrier or from the dot states to the light-hole and split-off subbands of the Si0.65Ge0.35 layer. The photoinduced bleaching of the near-infrared absorption is detected under interband optical excitation of undoped samples. This finding is explained by blocking the interband transitions inside the dots due to the state filling effect. By using the admittance spectroscopy, the mechanism of hole escape from QDs in the presence of an ac vertical electric field is identified. A thermally activated emission from the QD ground state into the two-dimensional states of the Si0.65Ge0.35 well is observed. From the temperature- and frequency-dependent measurements the QD hole ground state is determined to be located ~160 meV below the heavy-hole subband of the Si0.65Ge0.35 layer in good agreement with the results obtained by infrared absorption spectroscopy and six-band {\\bf k}\\;{\\bm \\cdot}\\;{\\bf p} theory. The information acquired from our experimental observations is valuable for feasible device applications.

Light trapping in a-Si/c-Si heterojunction solar cells by embedded ITO nanoparticles at rear surface

NASA Astrophysics Data System (ADS)

Dhar, Sukanta; Mandal, Sourav; Mitra, Suchismita; Ghosh, Hemanta; Mukherjee, Sampad; Banerjee, Chandan; Saha, Hiranmoy; Barua, A. K.

2017-12-01

The advantages of the amorphous silicon (a-Si)/crystalline silicon (c-Si) hetero junction technology are low temperature (<200 °C) processing and fewer process steps to fabricate the device. In this work, we used indium tin oxide (ITO) nanoparticles embedded in amorphous silicon material at the rear side of the crystalline wafer. The nanoparticles were embedded in silicon to have higher scattering efficiency, as has been established by simulation studies. It has been shown that significant photocurrent enhancements (32.8 mA cm-2 to 35.1 mA cm-2) are achieved because of high scattering and coupling efficiency of the embedded nanoparticles into the silicon device, leading to an increase in efficiency from 13.74% to 15.22%. In addition, we have observed a small increase in open circuit voltage. This may be due to the surface passivation during the ITO nanoparticle formation with hydrogen plasma treatment. We also support our experimental results by simulation, with the help of a commercial finite-difference time-domain (FDTD) software solution.

Modified spontaneous emission of silicon nanocrystals embedded in artificial opals

NASA Astrophysics Data System (ADS)

Janda, Petr; Valenta, Jan; Rehspringer, Jean-Luc; Mafouana, Rodrigue R.; Linnros, Jan; Elliman, Robert G.

2007-10-01

Si nanocrystals (NCs) were embedded in synthetic silica opals by means of Si-ion implantation or opal impregnation with porous-Si suspensions. In both types of sample photoluminescence (PL) is strongly Bragg-reflection attenuated (up to 75%) at the frequency of the opal stop-band in a direction perpendicular to the (1 1 1) face of the perfect hcp opal structure. Time-resolved PL shows a rich distribution of decay rates, which contains both shorter and longer decay components compared with the ordinary stretched exponential decay of Si NCs. This effect reflects changes in the spontaneous emission rate of Si NCs due to variations in the local density of states of real opal containing defects.

Surface Control of Actuated Hybrid Space Mirrors

DTIC Science & Technology

2010-10-01

precision Nanolaminate foil facesheet and Silicon Carbide ( SiC ) substrate embedded with electroactive ceramic actuators. Wavefront sensors are used to...integrate precision Nanolaminate foil facesheet with Silicon Carbide ( SiC ) substrate equipped with embedded electroactive ceramic actuators...IAC-10.C2.5.8 SURFACE CONTROL OF ACTUATED HYBRID SPACE MIRRORS Brij. N. Agrawal Naval Postgraduate School, Monterey, CA, 93943, agrawal

Magnetic domain interactions of Fe3O4 nanoparticles embedded in a SiO2 matrix.

PubMed

Fuentes-García, J A; Diaz-Cano, A I; Guillen-Cervantes, A; Santoyo-Salazar, J

2018-03-23

Currently, superparamagnetic functionalized systems of magnetite (Fe 3 O 4 ) nanoparticles (NPs) are promising options for applications in hyperthermia therapy, drug delivery and diagnosis. Fe 3 O 4 NPs below 20 nm have stable single domains (SSD), which can be oriented by magnetic field application. Dispersion of Fe 3 O 4 NPs in silicon dioxide (SiO 2 ) matrix allows local SSD response with uniaxial anisotropy and orientation to easy axis, 90° <001> or 180° <111>. A successful, easy methodology to produce Fe 3 O 4 NPs (6-17 nm) has been used with the Stöber modification. NPs were embedded in amorphous and biocompatible SiO 2 matrix by mechanical stirring in citrate and tetraethyl orthosilicate (TEOS). Fe 3 O 4 NPs dispersion was sampled in the range of 2-12 h to observe the SiO 2 matrix formation as time function. TEM characterization identified optimal conditions at 4 h stirring for separation of SSD Fe 3 O 4 in SiO 2 matrix. Low magnetization (M s ) of 0.001 emu and a coercivity (H c ) of 24.75 Oe indicate that the embedded SSD Fe 3 O 4 in amorphous SiO 2 reduces the M s by a diamagnetic barrier. Magnetic force microscopy (MFM) showed SSD Fe 3 O 4 of 1.2 nm on average embedded in SiO 2 matrix with uniaxial anisotropy response according to Fe 3+ and Fe 2+ electron spin coupling and rotation by intrinsic Neél contribution.

Spatially confined synthesis of SiOx nano-rod with size-controlled Si quantum dots in nano-porous anodic aluminum oxide membrane.

PubMed

Pai, Yi-Hao; Lin, Gong-Ru

2011-01-17

By depositing Si-rich SiOx nano-rod in nano-porous anodic aluminum oxide (AAO) membrane using PECVD, the spatially confined synthesis of Si quantum-dots (Si-QDs) with ultra-bright photoluminescence spectra are demonstrated after low-temperature annealing. Spatially confined SiOx nano-rod in nano-porous AAO membrane greatly increases the density of nucleated positions for Si-QD precursors, which essentially impedes the route of thermally diffused Si atoms and confines the degree of atomic self-aggregation. The diffusion controlled growth mechanism is employed to determine the activation energy of 6.284 kJ mole(-1) and diffusion length of 2.84 nm for SiO1.5 nano-rod in nano-porous AAO membrane. HRTEM results verify that the reduced geometric dimension of the SiOx host matrix effectively constrain the buried Si-QD size at even lower annealing temperature. The spatially confined synthesis of Si-QD essentially contributes the intense PL with its spectral linewidth shrinking from 210 to 140 nm and its peak intensity enhancing by two orders of magnitude, corresponding to the reduction on both the average Si-QD size and its standard deviation from 2.6 to 2.0 nm and from 25% to 12.5%, respectively. The red-shifted PL wavelength of the Si-QD reveals an inverse exponential trend with increasing temperature of annealing, which is in good agree with the Si-QD size simulation via the atomic diffusion theory.

Magnetism from Fe2O3 nanoparticles embedded in amorphous SiO2 matrix

NASA Astrophysics Data System (ADS)

Sendil Kumar, A.; Bhatnagar, Anil K.

2018-02-01

Fe2O3 nanoparticles are embedded in amorphous SiO2 matrix by coprecipitation method with varying concentrations. Conditions are optimized to get almost monodispersed Fe2O3 nanoparticles with high chemical stability. Microstructure of synthesized nanoparticles is well characterized and found that Fe2O3 is in nanocrystalline form and embedded uniformly in amorphous SiO2 matrix. Enhanced surface reactivity is found for nanoparticles which influences physical properties of the SiO2 supported Fe2O3 system due to adsorption. In oxide nanoparticles, significant number of defect sites at the surface is expected but when supported medium such as SiO2 it reduces this defect concentration. Field- and temperature-dependent magnetisation studies on these samples show superparamagnetic behaviour. Superparamagnetic behaviour is seen in all the concentration systems but the coercivity observed in the lower concentration systems is found to be anomalous compared to that of higher concentrations. The observed magnetic behaviour comes from either unsaturated bond existing due to the absence of anions at the surface of nanoparticles or reconstruction of atomic orbitals taking place at interface of Fe2O3-SiO2 system.

Strong visible electroluminescence from silicon nanocrystals embedded in a silicon carbide film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huh, Chul, E-mail: chuh@etri.re.kr; Kim, Tae-Youb; Ahn, Chang-Geun

2015-05-25

We report the strong visible light emission from silicon (Si) nanocrystals (NCs) embedded in a Si carbide (SiC) film. Compared to Si NC light-emitting diode (LED) by employing the Si nitride (SiN{sub x}) film as a surrounding matrix, the turn-on voltage of the Si NC LED with the SiC film was significantly decreased by 4 V. This was attributed to a smaller barrier height for injecting the electrons into the Si NCs due to a smaller band gap of SiC film than a SiN{sub x} film. The electroluminescence spectra increases with increasing forward voltage, indicating that the electrons are efficiently injectedmore » into the Si NCs in the SiC film. The light output power shows a linear increase with increasing forward voltage. The light emission originated from the Si NCs in a SiC film was quite uniform. The power efficiency of the Si NC LED with the SiC film was 1.56 times larger than that of the Si NC LED with the SiN{sub x} film. The Si NCs in a SiC film show unique advantages and are a promising candidate for application in optical devices.« less

Ultra-high sensitive substrates for surface enhanced Raman scattering, made of 3 nm gold nanoparticles embedded on SiO2 nanospheres

NASA Astrophysics Data System (ADS)

Phatangare, A. B.; Dhole, S. D.; Dahiwale, S. S.; Bhoraskar, V. N.

2018-05-01

The surface properties of substrates made of 3 nm gold nanoparticles embedded on SiO2 nanospheres enabled fingerprint detection of thiabendazole (TBZ), crystal violet (CV) and 4-Aminothiophenol (4-ATP) at an ultralow concentration of ∼10-18 M by surface enhanced Raman spectroscopy (SERS). Gold nanoparticles of an average size of ∼3 nm were synthesized and simultaneously embedded on SiO2 nanospheres by the electron irradiation method. The substrates made from the 3 nm gold nanoparticles embedded on SiO2 nanospheres were successfully used for recording fingerprint SERS spectra of TBZ, CV and 4-ATP over a wide range of concentrations from 10-6 M to 10-18 M using 785 nm laser. The unique features of these substrates are roughness near the surface due to the inherent structural defects of 3 nm gold nanoparticles, nanogaps of ≤ 1 nm between the embedded nanoparticles and their high number. These produced an abundance of nanocavities which act as active centers of hot-spots and provided a high electric field at the reporter molecules and thus an enhancement factor required to record the SERS spectra at ultra low concentration of 10-18 M. The SERS spectra recorded by the substrates of 4 nm and 6 nm gold nanoparticles are discussed.

Fabrication of multilayered Ge nanocrystals embedded in SiO xGeN y films

NASA Astrophysics Data System (ADS)

Gao, Fei; Green, Martin A.; Conibeer, Gavin; Cho, Eun-Chel; Huang, Yidan; Perez-Wurfl, Ivan; Flynn, Chris

2008-09-01

Multilayered Ge nanocrystals embedded in SiO xGeN y films have been fabricated on Si substrate by a (Ge + SiO 2)/SiO xGeN y superlattice approach, using a rf magnetron sputtering technique with a Ge + SiO 2 composite target and subsequent thermal annealing in N 2 ambient at 750 °C for 30 min. X-ray diffraction (XRD) measurement indicated the formation of Ge nanocrystals with an average size estimated to be 5.4 nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode downward shifted to 299.4 cm -1, which was caused by quantum confinement of phonons in the Ge nanocrystals. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (Ge + SiO 2) layers. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the 'Z' growth direction.

Local Schottky contacts of embedded Ag nanoparticles in Al2O3/SiNx:H stacks on Si: a design to enhance field effect passivation of Si junctions.

PubMed

Ibrahim Elmi, Omar; Cristini-Robbe, Odile; Chen, Minyu; Wei, Bin; Bernard, Rémy; Okada, Etienne; Yarekha, Dmitri A; Ouendi, Saliha; Portier, Xavier; Gourbilleau, Fabrice; Xu, Tao; Stievenard, Didier

2018-04-26

This paper describes an original design leading to the field effect passivation of Si n+-p junctions. Ordered Ag nanoparticle (Ag-NP) arrays with optimal size and coverage fabricated by means of nanosphere lithography and thermal evaporation, were embedded in ultrathin-Al2O3/SiNx:H stacks on the top of implanted Si n+-p junctions, to achieve effective surface passivation. One way to characterize surface passivation is to use photocurrent, sensitive to recombination centers. We evidenced an improvement of photocurrent by a factor of 5 with the presence of Ag nanoparticles. Finite-difference time-domain (FDTD) simulations combining with semi-quantitative calculations demonstrated that such gain was mainly due to the enhanced field effect passivation through the depleted region associated with the Ag-NPs/Si Schottky contacts. © 2018 IOP Publishing Ltd.

Design, Fabrication, Characterization and Modeling of Integrated Functional Materials

DTIC Science & Technology

2010-10-19

ribbons: A relationship between the soft magnetic properties and GMI effect has been established in Co69Fe4.5R1.5Si10B15 (R = Ni, Al , Cr) amorphous... deposition . A strain compression-relaxation mechanism has been proposed in order to explain the structure- property relationships in the CFO-PZT bilayer...being pursued. The new Laser Assisted Spray process chamber for co- deposition of QDs and polymer films is shown in Fig. 55. Fig. 55

Optical design of endoscopic shape-tracker using quantum dots embedded in fiber bundles

NASA Astrophysics Data System (ADS)

Eisenstein, Jessica; Gavalis, Robb; Wong, Peter Y.; Cao, Caroline G. L.

2009-08-01

Colonoscopy is the current gold standard for colon cancer screening and diagnosis. However, the near-blind navigation process employed during colonoscopy results in endoscopist disorientation and scope looping, leading to missed detection of tumors, incorrect localization, and pain for the patient. A fiber optic bend sensor, which would fit into the working channel of a colonoscope, is developed to aid navigation through the colon during colonoscopy. The bend sensor is comprised of a bundle of seven fibers doped with quantum dots (QDs). Each fiber within the bundle contains a unique region made up of three zones with differently-colored QDs, spaced 120° apart circumferentially on the fiber. During bending at the QD region, light lost from the fiber's core is coupled into one of the QD zones, inducing fluorescence of the corresponding color whose intensity is proportional to the degree of bending. A complementary metal oxide semiconductor camera is used to obtain an image of the fluorescing end faces of the fiber bundle. The location of the fiber within the bundle, the color of fluorescence, and the fluorescence intensity are used to determine the bundle's bending location, direction, and degree of curvature, respectively. Preliminary results obtained using a single fiber with three QD zones and a seven-fiber bundle containing one active fiber with two QDs (180° apart) demonstrate the feasibility of the concept. Further developments on fiber orientation during bundling and the design of a graphical user interface to communicate bending information are also discussed.

Poly(N-isopropylacrylamide)-coated thermo-responsive nanoparticles for controlled delivery of sulfonated Zn-phthalocyanine in Chinese hamster ovary cells in vitro and zebra fish in vivo

NASA Astrophysics Data System (ADS)

He, Jia; Chen, Ji-Yao; Wang, Pu; Wang, Pei-Nan; Guo, Jia; Yang, Wu-Li; Wang, Chang-Chun; Peng, Qian

2007-10-01

Poly(N-isopropylacrylamide) (PNIPAM)-coated Fe3O4@SiO2@CdTe multifunctional nanoparticles with photoluminescent (PL), thermosensitive and magnetic properties, were investigated as carriers to deliver water-soluble, fluorescent sulfonated Zn-phthalocyanine (ZnPcS), a photosensitizing drug for photodynamic therapy of cancer, in Chinese hamster ovary (CHO) cells in vitro and zebra fish in vivo. PNIPAM is a well-known thermo-responsive polymer with a volume phase transition temperature. This property allows it to be swollen in water at temperatures lower than 32-34 °C to take up ZnPcS and shrunken to expel the drug at higher temperatures. Since the PL band of CdTe quantum dots (QDs) as indicators for the nanoparticles is at 585 nm and the emission band of ZnPcS is at 680 nm, it is possible to study the temperature-dependent release of ZnPcS from the nanoparticles by fluorescence measurements. ZnPcS was embedded in the PNIPAM of the nanoparticles at 25 °C in phosphate buffered saline (PBS) solution and released at 37 °C, measured with a spectrophotometer. When CHO cells had been incubated with the ZnPcS-loaded nanoparticles at 27 °C, a similar intracellular localization pattern of CdTe QDs and ZnPcS was seen by multichannel measurements in confocal laser scanning microscopy (CLSM), but a diffuse pattern of only ZnPcS fluorescence was detected in the cytoplasm of the cells at 37 °C, indicating a release of ZnPcS from the nanoparticles. Similar results were also found in the intestinal tract of zebra fish in vivo after intake of the nanoparticles. Since the nanoparticles contain magnetic (Fe3O4) material, the nanoparticles could also be manipulated to change their location in the intestinal tract of the zebra fish with an external magnetic field gradient of 300 G mm-1. The results presented suggest that such multifunctional nanoparticles may have combined potential for temperature-dependent drug delivery, QD photodetection and magnetic manipulation in diagnosis and therapy of diseases.

Indium Growth and Island Height Control on Si Submonolayer Phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jizhou

2009-01-01

Nanotechnology refers any technique that involves about object with nanoscale (10 -9 m) or even smaller. It has become more and more important in recently years and has changed our world dramatically. Most of modern electronic devices today should thanks to the miniaturizing driven by development of nanotechnology. Recent years, more and more governments are investing huge amount of money in research related to nanotechnology. There are two major reasons that nanostructure is so fascinate. The first one is the miniaturizing. It is obvious that if we can make products smaller without losing the features, we can save the costmore » and increase the performance dramatically. For an example, the first computer in the world, ENIAC, which occupied several rooms, is less powerful than the cheapest calculator today. Today's chips with sizes of less than half an inch contain millions of basic units. All these should thank to the development of nanotechnology. The other reason is that when we come to nanoscale, there are many new effects due to the quantum effect which can't be found in large systems. For an example, quantum dots (QDs) are systems which sizes are below 1μm(10 -6m) and restricted in three dimensions. There are many interesting quantum effects in QDs, including discrete energy levels, and interdot coupling. Due to these properties and their small sizes, QDs have varies potential applications such as quantum computing, probe, light emitting device, solar cells, and laser. To meet the requirement of the nanoelectrical applications, the QDs must be grown highly uniformly because their property is highly dependent on their sizes. The major methods to grow uniform QDs include epitaxial, and lithograph. Lithography is a process to make patterns on a thin film by selectively removing certain parts of the film. Using this method, people have good control over size, location and spacing of QDs. For an example, the Extreme ultraviolet lithography (EUVL) have a wave length of 13.4 nm so it can curve on the surface of an sample to make structure as small as the order of 10 nm. however, lithograph usually causes permanent damages to the surface and in many cases the QDs are damaged during the lithograph and therefore result in high percentage of defects. Quantum size effect has attracted more and more interests in surface science due to many of its effects. One of its effects is the height preference in film growing and the resulting possibility of uniformly sized self-assemble nanostructure. The experiment of Pb islands on In 4x1 phase shows that both the height and the width can be controlled by proper growth conditions, which expands the growth dimensions from 1 to 2. This discover leads us to study the In/Pb interface. In Ch.3, we found that the Pb islands growing on In 4x1-Si(111) surface which have uniform height due to QSE and uniform width due to the constriction of In 4x1 lattice have unexpected stability. These islands are stable in even RT, unlike usual nanostructures on Pb/Si surface which are stable only at low temperature. Since similar structures are usually grown at low temperature, this discovery makes the grown structures closer to technological applications. It also shows the unusual of In/Pb interface. Then we studied the In islands grown on Pb-α-√3x√3-Si(111) phase in Ch.4. These islands have fcc structure in the first few layers, and then convert to bct structure. The In fcc islands have sharp height preference due to QSE like Pb islands. However, the preferred height is different (7 layer for Pb on Si 7x7 and 4 layer for Pb on In 4x1), due to the difference of interface. The In islands structure prefers to be bct than fcc with coverage increase. It is quantitatively supported by first-principle calculation. Unexpectedly, the In islands grown on various of In interfaces didn't show QSE effects and phase transition from fcc and bct structures as on the Pb-α interface (Ch.6). In g(s) curve there is no clear oscillations in the g(s) curve as the In on Pb-α phase. This may be due to the extra mobility of In atoms, which causes the In bct islands to grow too fast to be observed in diffraction or STM (Ch.5). From these experiments we can see the importance of Pb-α phase in growth of In islands. It is the best interface to grow In islands in the phases we have experimented. Recent experiments show that the Existence of Pb will decrease the diffusion speed of In. In Ch.6 we have shown that In atoms diffusion is so fast that the bct spots are not visible in diffraction. But when we put some Pb onto the In surface, we can see the bct spots, although very weak. So Pb should play an role in slowing down the indium atoms diffusion. The interaction of Pb and In may play a role, but it is still not fully understood. So the general conclusion of this thesis is that In/Pb interface has extraordinary properties and may have potential in self-assembling growth.« less

Trapping time of excitons in Si nanocrystals embedded in a SiO2 matrix

NASA Astrophysics Data System (ADS)

de Jong, E. M. L. D.; de Boer, W. D. A. M.; Yassievich, I. N.; Gregorkiewicz, T.

2017-05-01

Silicon (Si) nanocrystals (NCs) are of great interest for many applications, ranging from photovoltaics to optoelectonics. The photoluminescence quantum yield of Si NCs dispersed in SiO2 is limited, suggesting the existence of very efficient processes of nonradiative recombination, among which the formation of a self-trapped exciton state on the surface of the NC. In order to improve the external quantum efficiency of these systems, the carrier relaxation and recombination need to be understood more thoroughly. For that purpose, we perform transient-induced absorption spectroscopy on Si NCs embedded in a SiO2 matrix over a broad probe range for NCs of average sizes from 2.5 to 5.5 nm. The self-trapping of free excitons on surface-related states is experimentally and theoretically discussed and found to be dependent on the NC size. These results offer more insight into the self-trapped exciton state and are important to increase the optical performance of Si NCs.

GaAs/GaP quantum dots: Ensemble of direct and indirect heterostructures with room temperature optical emission

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dadgostar, S.; Mogilatenko, A.; Masselink, W. T.

2016-03-07

We describe the optical emission and the carrier dynamics of an ensemble of self-assembled GaAs quantum dots embedded in GaP(001). The QD formation is driven by the 3.6% lattice mismatch between GaAs and GaP in the Stranski-Krastanow mode after deposition of more than 1.2 monolayers of GaAs. The quantum dots have an areal density between 6 and 7.6 × 10{sup 10} per cm{sup −2} and multimodal size distribution. The luminescence spectra show two peaks in the range of 1.7 and 2.1 eV. The samples with larger quantum dots have red emission and show less thermal quenching compared with the samples with smaller QDs.more » The large QDs luminescence up to room temperature. We attribute the high energy emission to indirect carrier recombination in the thin quantum wells or small strained quantum dots, whereas the low energy red emission is due to the direct electron-hole recombination in the relaxed quantum dots.« less

Quantum dot-containing polymer particles with thermosensitive fluorescence.

PubMed

Generalova, Alla N; Oleinikov, Vladimir A; Sukhanova, Alyona; Artemyev, Mikhail V; Zubov, Vitaly P; Nabiev, Igor

2013-01-15

Composite polymer particles consisting of a solid poly(acrolein-co-styrene) core and a poly(N-vinylcaprolactam) (PVCL) polymer shell doped with CdSe/ZnS semiconductor quantum dots (QDs) were fabricated. The temperature response of the composite particles was observed as a decrease in their hydrodynamic diameter upon heating above the lower critical solution temperature of the thermosensitive PVCL polymer. Embedding QDs in the PVCL shell yields particles whose fluorescence is sensitive to temperature changes. This sensitivity was determined by the dependence of the QD fluorescence intensity on the distances between them in the PVCL shell, which reversibly change as a result of the temperature-driven conformational changes in the polymer. The QD-containing thermosensitive particles were assembled with protein molecules in such a way that they retained their thermosensitive properties, including the completely reversible temperature dependence of their fluorescence response. The composite particles developed can be used as local temperature sensors, as carriers for biomolecules, as well as in biosensing and various bioassays employing optical detection schemes. Copyright © 2012 Elsevier B.V. All rights reserved.

Clinically compatible flexible wide-field multi-color fluorescence endoscopy with a porcine colon model

PubMed Central

Oh, Gyugnseok; Park, Youngrong; Yoo, Su Woong; Hwang, Soonjoo; Chin-Yu, Alexey V. Dan; Ryu, Yeon-Mi; Kim, Sang-Yeob; Do, Eun-Ju; Kim, Ki Hean; Kim, Sungjee; Myung, Seung-Jae; Chung, Euiheon

2017-01-01

Early detection of structural or molecular changes in dysplastic epithelial tissues is crucial for cancer screening and surveillance. Multi-targeting molecular endoscopic fluorescence imaging may improve noninvasive detection of precancerous lesions in the colon. Here, we report the first clinically compatible, wide-field-of-view, multi-color fluorescence endoscopy with a leached fiber bundle scope using a porcine model. A porcine colon model that resembles the human colon is used for the detection of surrogate tumors composed of multiple biocompatible fluorophores (FITC, ICG, and heavy metal-free quantum dots (hfQDs)). With an ex vivo porcine colon tumor model, molecular imaging with hfQDs conjugated with MMP14 antibody was achieved by spraying molecular probes on a mucosa layer that contains xenograft tumors. With an in vivo porcine colon embedded with surrogate tumors, target-to-background ratios of 3.36 ± 0.43, 2.70 ± 0.72, and 2.10 ± 0.13 were achieved for FITC, ICG, and hfQD probes, respectively. This promising endoscopic technology with molecular contrast shows the capacity to reveal hidden tumors and guide treatment strategy decisions. PMID:28270983

Defect characterization of proton irradiated GaAs pn-junction diodes with layers of InAs quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sato, Shin-ichiro, E-mail: sato.shinichiro@jaea.go.jp; Optoelectronics and Radiation Effects Branch, U.S. Naval Research Laboratory, Washington, DC 20375; Schmieder, Kenneth J.

2016-05-14

In order to expand the technology of III-V semiconductor devices with quantum structures to both terrestrial and space use, radiation induced defects as well as native defects generated in the quantum structures should be clarified. Electrically active defects in GaAs p{sup +}n diodes with embedded ten layers of InAs quantum dots (QDs) are investigated using Deep Level Transient Fourier Spectroscopy. Both majority carrier (electron) and minority carrier (hole) traps are characterized. In the devices of this study, GaP layers are embedded in between the QD layers to offset the compressive stress introduced during growth of InAs QDs. Devices are irradiatedmore » with high energy protons for three different fluences at room temperature in order to characterize radiation induced defects. Seven majority electron traps and one minority hole trap are found after proton irradiation. It is shown that four electron traps induced by proton irradiation increase in proportion to the fluence, whereas the EL2 trap, which appears before irradiation, is not affected by irradiation. These defects correspond to electron traps previously identified in GaAs. In addition, a 0.53 eV electron trap and a 0.14 eV hole trap are found in the QD layers before proton irradiation. It is shown that these native traps are also unaffected by irradiation. The nature of the 0.14 eV hole trap is thought to be Ga-vacancies in the GaP strain balancing layers.« less

Embedded Si/Graphene Composite Fabricated by Magnesium-Thermal Reduction as Anode Material for Lithium-Ion Batteries

NASA Astrophysics Data System (ADS)

Zhu, Jiangliu; Ren, Yurong; Yang, Bo; Chen, Wenkai; Ding, Jianning

2017-12-01

Embedded Si/graphene composite was fabricated by a novel method, which was in situ generated SiO2 particles on graphene sheets followed by magnesium-thermal reduction. The tetraethyl orthosilicate (TEOS) and flake graphite was used as original materials. On the one hand, the unique structure of as-obtained composite accommodated the large volume change to some extent. Simultaneously, it enhanced electronic conductivity during Li-ion insertion/extraction. The MR-Si/G composite is used as the anode material for lithium ion batteries, which shows high reversible capacity and ascendant cycling stability reach to 950 mAh·g-1 at a current density of 50 mA·g-1 after 60 cycles. These may be conducive to the further advancement of Si-based composite anode design.

Photoluminescence properties of arsenic and boron doped Si3N4 nanocrystal embedded in SiN x O y matrix

NASA Astrophysics Data System (ADS)

Puglia, Denise; Sombrio, Guilherme; dos Reis, Roberto; Boudinov, Henri

2018-03-01

Photoluminescence emission of Si3N4 nanocrystals embedded in SiN x O y matrices was investigated. Nanocrystals were grown by annealing of silicon oxynitride films deposited by sputtering, passivated in forming gas atmosphere and implanted with boron and arsenic. Emission energy was tuned from green to ultraviolet by changing the composition of SiN x O y matrices. Structural characterization of the nanocrystals was performed by Transmission Electron Microscopy. Photoluminescence at room and low temperatures was analyzed and the results suggest that light emission originates in the interface between the nanocrystals and the matrix. The highest photoluminescence intensity at room temperature was achieved by arsenic doped silicon oxynitride films deposited with an excess of nitrogen.

Ultrastable Quantum Dot Composite Films under Severe Environments.

PubMed

Yang, Zunxian; Zhang, Yuxiang; Liu, Jiahui; Ai, Jingwei; Lai, Shouqiang; Zhao, Zhiwei; Ye, Bingqing; Ruan, Yushuai; Guo, Tailiang; Yu, Xuebin; Chen, Gengxu; Lin, Yuanyuan; Xu, Sheng

2018-05-09

Semiconductor quantum dots (QDs) have attracted extensive attention because of their remarkable optical and electrical characteristics. However, the practical application of QDs and further the QD composite films have greatly been hindered mainly owing to their essential drawbacks of extreme unstability under oxygen and water environments. Herein, one simple method has been employed to enhance enormously the stability of Cd x Zn 1- x Se y S 1- y QD composite films by a combination of Cd x Zn 1- x Se y S 1- y QDs and poly(vinylidene) fluoride (PVDF), which is characteristic of closely arranged molecular chains and strong hydrogen bonds. There are many particular advantages in using QD/PVDF composite films such as easy processing, low cost, large-area fabrication, and especially extreme stability even in the boiling water for more than 240 min. By employing K 2 SiF 6 :Mn 4+ as a red phosphor, a prototype white light-emitting diode (WLED) with color coordinates of (0.3307, 0.3387), T c of 5568 K, and color gamut 112.1NTSC(1931)% at 20 mA has been fabricated, and there is little variation under different excitation currents, indicating that the QD/PVDF composite films fabricated by this simple blade-coating process make them ideal candidates for liquid-crystal display backlight utilization via assembling a WLED on a large scale owing to its ultrahigh stability under severe environments.

An ultra-sensitive impedimetric immunosensor for detection of the serum oncomarker CA-125 in ovarian cancer patients

NASA Astrophysics Data System (ADS)

Johari-Ahar, M.; Rashidi, M. R.; Barar, J.; Aghaie, M.; Mohammadnejad, D.; Ramazani, A.; Karami, P.; Coukos, G.; Omidi, Y.

2015-02-01

Effective treatment of ovarian cancer depends upon the early detection of the malignancy. Here, we report on the development of a new nanostructured immunosensor for early detection of cancer antigen 125 (CA-125). A gold electrode was modified with mercaptopropionic acid (MPA), and then consecutively conjugated with silica coated gold nanoparticles (AuNP@SiO2), CdSe quantum dots (QDs) and anti-CA-125 monoclonal antibody (mAb). The engineered MPA|AuNP@SiO2|QD|mAb immunosensor was characterised using transmission electron microscopy (TEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Successive conjugation of AuNP@SiO2, CdSe QD and anti-CA-125 mAb onto the gold electrode resulted in sensitive detection of CA-125 with a limit of detection (LOD) of 0.0016 U mL-1 and a linear detection range (LDR) of 0-0.1 U mL-1. Based on the high sensitivity and specificity of the immunosensor, we propose this highly stable and reproducible biosensor for the early detection of CA-125.Effective treatment of ovarian cancer depends upon the early detection of the malignancy. Here, we report on the development of a new nanostructured immunosensor for early detection of cancer antigen 125 (CA-125). A gold electrode was modified with mercaptopropionic acid (MPA), and then consecutively conjugated with silica coated gold nanoparticles (AuNP@SiO2), CdSe quantum dots (QDs) and anti-CA-125 monoclonal antibody (mAb). The engineered MPA|AuNP@SiO2|QD|mAb immunosensor was characterised using transmission electron microscopy (TEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Successive conjugation of AuNP@SiO2, CdSe QD and anti-CA-125 mAb onto the gold electrode resulted in sensitive detection of CA-125 with a limit of detection (LOD) of 0.0016 U mL-1 and a linear detection range (LDR) of 0-0.1 U mL-1. Based on the high sensitivity and specificity of the immunosensor, we propose this highly stable and reproducible biosensor for the early detection of CA-125. Electronic supplementary information (ESI) available: Additional materials including Figures and discussion as described in the text. See DOI: 10.1039/c4nr06687a

Uncooled infrared photon detection concepts and devices

NASA Astrophysics Data System (ADS)

Piyankarage, Viraj Vishwakantha Jayaweera

This work describes infrared (IR) photon detector techniques based on novel semiconductor device concepts and detector designs. The aim of the investigation was to examine alternative IR detection concepts with a view to resolve some of the issues of existing IR detectors such as operating temperature and response range. Systems were fabricated to demonstrate the following IR detection concepts and determine detector parameters: (i) Near-infrared (NIR) detection based on dye-sensitization of nanostructured semiconductors, (ii) Displacement currents in semiconductor quantum dots (QDs) embedded dielectric media, (iii) Split-off band transitions in GaAs/AlGaAs heterojunction interfacial workfunction internal photoemission (HEIWIP) detectors. A far-infrared detector based on GaSb homojunction interfacial workfunction internal photoemission (HIWIP) structure is also discussed. Device concepts, detector structures, and experimental results discussed in the text are summarized below. Dye-sensitized (DS) detector structures consisting of n-TiO 2/Dye/p-CuSCN heterostructures with several IR-sensitive dyes showed response peaks at 808, 812, 858, 866, 876, and 1056 nm at room temperature. The peak specific-detectivity (D*) was 9.5x1010 cm Hz-1/2 W-1 at 812 nm at room temperature. Radiation induced carrier generation alters the electronic polarizability of QDs provided the quenching of excitation is suppressed by separation of the QDs. A device constructed to illustrate this concept by embedding PbS QDs in paraffin wax showed a peak D* of 3x108 cm Hz 1/2 W-1 at ˜540 nm at ambient temperature. A typical HEIWIP/HIWIP detector structures consist of single (or multiple) period(s) of doped emitter(s) and undoped barrier(s) which are sandwiched between two highly doped contact layers. A p-GaAs/AlGaAs HEIWIP structure showed enhanced absorption in NIR range due to heavy/light-hole band to split-off band transitions and leading to the development of GaAs based uncooled sensors for IR detection in the 2--5 microm wavelength range with a peak D* of 6.8x105 cm Hz1/2 W-1. A HIWIP detector based on p-GaSb/GaSb showed a free carrier response threshold wavelength at 97 microm (˜3 THz) with a peak D* of 5.7x1011 cm Hz1/2 W-1 at 36 microm and 4.9 K. In this detector, a bolometric type response in the 97--200 microm (3--1.5 THz) range was also observed. INDEX WORDS: Infrared detectors, Photon detection, NIR detectors, THz detectors, Uncooled detectors, Dye-sensitized, IR dye, Quantum dot, Split-off band, GaSb, GaAs, AlGaAs, TiO2, CuSCN, PbS, Homojunction, Heterojunction, Workfunction, Photoemission, Displacement currents, 1/f noise.

Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study

PubMed Central

2013-01-01

We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO2 matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO2 thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO2 matrix. PMID:24314071

Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study.

PubMed

Pita, Kantisara; Baudin, Pierre; Vu, Quang Vinh; Aad, Roy; Couteau, Christophe; Lérondel, Gilles

2013-12-06

We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO2 matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO2 thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO2 matrix.

Broadband and wide-angle light harvesting by ultra-thin silicon solar cells with partially embedded dielectric spheres.

PubMed

Yang, Zhenhai; Shang, Aixue; Qin, Linling; Zhan, Yaohui; Zhang, Cheng; Gao, Pingqi; Ye, Jichun; Li, Xiaofeng

2016-04-01

We propose a design of crystalline silicon thin-film solar cells (c-Si TFSCs, 2 μm-thick) configured with partially embedded dielectric spheres on the light-injecting side. The intrinsic light trapping and photoconversion are simulated by the complete optoelectronic simulation. It shows that the embedding depth of the spheres provides an effective way to modulate and significantly enhance the optical absorption. Compared to the conventional planar and front sphere systems, the optimized partially embedded sphere design enables a broadband, wide-angle, and strong optical absorption and efficient carrier transportation. Optoelectronic simulation predicts that a 2 μm-thick c-Si TFSC with half-embedded spheres shows an increment of more than 10  mA/cm² in short-circuit current density and an enhancement ratio of more than 56% in light-conversion efficiency, compared to the conventional planar counterparts.

High performance SONOS flash memory with in-situ silicon nanocrystals embedded in silicon nitride charge trapping layer

NASA Astrophysics Data System (ADS)

Lim, Jae-Gab; Yang, Seung-Dong; Yun, Ho-Jin; Jung, Jun-Kyo; Park, Jung-Hyun; Lim, Chan; Cho, Gyu-seok; Park, Seong-gye; Huh, Chul; Lee, Hi-Deok; Lee, Ga-Won

2018-02-01

In this paper, SONOS-type flash memory device with highly improved charge-trapping efficiency is suggested by using silicon nanocrystals (Si-NCs) embedded in silicon nitride (SiNX) charge trapping layer. The Si-NCs were in-situ grown by PECVD without additional post annealing process. The fabricated device shows high program/erase speed and retention property which is suitable for multi-level cell (MLC) application. Excellent performance and reliability for MLC are demonstrated with large memory window of ∼8.5 V and superior retention characteristics of 7% charge loss for 10 years. High resolution transmission electron microscopy image confirms the Si-NC formation and the size is around 1-2 nm which can be verified again in X-ray photoelectron spectroscopy (XPS) where pure Si bonds increase. Besides, XPS analysis implies that more nitrogen atoms make stable bonds at the regular lattice point. Photoluminescence spectra results also illustrate that Si-NCs formation in SiNx is an effective method to form deep trap states.

Location and Electronic Nature of Phosphorus in the Si Nanocrystal − SiO2 System

PubMed Central

König, Dirk; Gutsch, Sebastian; Gnaser, Hubert; Wahl, Michael; Kopnarski, Michael; Göttlicher, Jörg; Steininger, Ralph; Zacharias, Margit; Hiller, Daniel

2015-01-01

Up to now, no consensus exists about the electronic nature of phosphorus (P) as donor for SiO2-embedded silicon nanocrystals (SiNCs). Here, we report on hybrid density functional theory (h-DFT) calculations of P in the SiNC/SiO2 system matching our experimental findings. Relevant P configurations within SiNCs, at SiNC surfaces, within the sub-oxide interface shell and in the SiO2 matrix were evaluated. Atom probe tomography (APT) and its statistical evaluation provide detailed spatial P distributions. For the first time, we obtain ionisation states of P atoms in the SiNC/SiO2 system at room temperature using X-ray absorption near edge structure (XANES) spectroscopy, eliminating structural artefacts due to sputtering as occurring in XPS. K energies of P in SiO2 and SiNC/SiO2 superlattices (SLs) were calibrated with non-degenerate P-doped Si wafers. results confirm measured core level energies, connecting and explaining XANES spectra with h-DFT electronic structures. While P can diffuse into SiNCs and predominantly resides on interstitial sites, its ionization probability is extremely low, rendering P unsuitable for introducing electrons into SiNCs embedded in SiO2. Increased sample conductivity and photoluminescence (PL) quenching previously assigned to ionized P donors originate from deep defect levels due to P. PMID:25997696

Embedded Si/Graphene Composite Fabricated by Magnesium-Thermal Reduction as Anode Material for Lithium-Ion Batteries.

PubMed

Zhu, Jiangliu; Ren, Yurong; Yang, Bo; Chen, Wenkai; Ding, Jianning

2017-12-16

Embedded Si/graphene composite was fabricated by a novel method, which was in situ generated SiO 2 particles on graphene sheets followed by magnesium-thermal reduction. The tetraethyl orthosilicate (TEOS) and flake graphite was used as original materials. On the one hand, the unique structure of as-obtained composite accommodated the large volume change to some extent. Simultaneously, it enhanced electronic conductivity during Li-ion insertion/extraction. The MR-Si/G composite is used as the anode material for lithium ion batteries, which shows high reversible capacity and ascendant cycling stability reach to 950 mAh·g -1 at a current density of 50 mA·g -1 after 60 cycles. These may be conducive to the further advancement of Si-based composite anode design.

Atomistic simulation of the thermal conductivity in amorphous SiO2 matrix/Ge nanocrystal composites

NASA Astrophysics Data System (ADS)

Kuryliuk, Vasyl V.; Korotchenkov, Oleg A.

2017-04-01

We use nonequilibrium molecular dynamics computer simulations with the Tersoff potential aiming to provide a comprehensive picture of the thermal conductivity of amorphous SiO2 (a-SiO2) matrix with embedded Ge nanocrystals (nc-Ge). The modelling predicts the a-SiO2 matrix thermal conductivity in a temperature range of 50 < T < 500 K yielding a fair agreement with experiment at around room temperature. It is worth noticing that the predicted room-temperature thermal conductivity in a-SiO2 is in very good agreement with the experimental result, which is in marked contrast with the thermal conductivity calculated employing the widely used van Beest-Kramer-van Santen (BKS) potential. We show that the thermal conductivity of composite nc-Ge/a-SiO2 systems decreases steadily with increasing the volume fraction of Ge inclusions, indicative of enhanced interface scattering of phonons imposed by embedded Ge nanocrystals. We also observe that increasing the volume fractions above a certain threshold value results in a progressively increased thermal conductivity of the nanocomposite, which can be explained by increasing volume fraction of a better thermally conducting Ge. Finally, non-equilibrium molecular dynamics simulations with the Tersoff potential are promising for computing the thermal conductivity of nanocomposites based on amorphous SiO2 and can be readily scaled to more complex composite structures with embedded nanoparticles, which thus help design nanocomposites with desired thermal properties.

Time-dependent pH sensing phenomena using CdSe/ZnS quantum dots in EIS structure.

PubMed

Kumar, Pankaj; Maikap, Siddheswar; Prakash, Amit; Tien, Ta-Chang

2014-04-12

Time-dependent pH sensing phenomena of the core-shell CdSe/ZnS quantum dot (QD) sensors in EIS (electrolyte insulator semiconductor) structure have been investigated for the first time. The quantum dots are immobilized by chaperonin GroEL protein, which are observed by both atomic force microscope and scanning electron microscope. The diameter of one QD is approximately 6.5 nm. The QDs are not oxidized over a long time and core-shell CdSe/ZnS are confirmed by X-ray photon spectroscopy. The sensors are studied for sensing of hydrogen ions concentration in different buffer solutions at broad pH range of 2 to 12. The QD sensors show improved sensitivity (38 to 55 mV/pH) as compared to bare SiO2 sensor (36 to 23 mV/pH) with time period of 0 to 24 months, owing to the reduction of defects in the QDs. Therefore, the differential sensitivity of the QD sensors with respect to the bare SiO2 sensors is improved from 2 to 32 mV/pH for the time period of 0 to 24 months. After 24 months, the sensitivity of the QD sensors is close to ideal Nernstian response with good linearity of 99.96%. Stability and repeatability of the QD sensors show low drift (10 mV for 10 cycles) as well as small hysteresis characteristics (<10 mV). This QD sensor is very useful for future human disease diagnostics.

Photovoltaic Properties and Ultrafast Plasmon Relaxation Dynamics of Diamond-Like Carbon Nanocomposite Films with Embedded Ag Nanoparticles.

PubMed

Meškinis, Šarūnas; Peckus, Domantas; Vasiliauskas, Andrius; Čiegis, Arvydas; Gudaitis, Rimantas; Tamulevičius, Tomas; Yaremchuk, Iryna; Tamulevičius, Sigitas

2017-12-01

Ultrafast relaxation dynamics of diamond-like carbon (DLC) films with embedded Ag nanoparticles (DLC:Ag) and photovoltaic properties of heterojunctions consisting of DLC:Ag and crystalline silicon (DLC:Ag/Si) were investigated by means of transient absorption (TAS) spectroscopy and photovoltaic measurements. The heterojunctions using both p type and n type silicon were studied. It was found that TAS spectra of DLC:Ag films were dependent on the used excitation wavelength. At wavelengths where Ag nanoparticles absorbed light most intensively, only DLC signal was registered. This result is in good accordance with an increase of the DLC:Ag/Si heterojunction short circuit current and open circuit voltage with the excitation wavelength in the photovoltaic measurements. The dependence of the TAS spectra of DLC:Ag films and photovoltaic properties of DLC:Ag/Si heterostructures on the excitation wavelength was explained as a result of trapping of the photoexcited hot charge carriers in DLC matrix. The negative photovoltaic effect was observed for DLC:Ag/p-Si heterostructures and positive ("conventional") for DLC:Ag/n-Si ones. It was explained by the excitation of hot plasmonic holes in the Ag nanoparticles embedded into DLC matrix. Some decrease of DLC:Ag/Si heterostructures photovoltage as well as photocurrent with DLC:Ag film thickness was observed, indicating role of the interface in the charge transfer process of photocarriers excited in Ag nanoparticles.

Photovoltaic Properties and Ultrafast Plasmon Relaxation Dynamics of Diamond-Like Carbon Nanocomposite Films with Embedded Ag Nanoparticles

NASA Astrophysics Data System (ADS)

Meškinis, Šarūnas; Peckus, Domantas; Vasiliauskas, Andrius; Čiegis, Arvydas; Gudaitis, Rimantas; Tamulevičius, Tomas; Yaremchuk, Iryna; Tamulevičius, Sigitas

2017-04-01

Ultrafast relaxation dynamics of diamond-like carbon (DLC) films with embedded Ag nanoparticles (DLC:Ag) and photovoltaic properties of heterojunctions consisting of DLC:Ag and crystalline silicon (DLC:Ag/Si) were investigated by means of transient absorption (TAS) spectroscopy and photovoltaic measurements. The heterojunctions using both p type and n type silicon were studied. It was found that TAS spectra of DLC:Ag films were dependent on the used excitation wavelength. At wavelengths where Ag nanoparticles absorbed light most intensively, only DLC signal was registered. This result is in good accordance with an increase of the DLC:Ag/Si heterojunction short circuit current and open circuit voltage with the excitation wavelength in the photovoltaic measurements. The dependence of the TAS spectra of DLC:Ag films and photovoltaic properties of DLC:Ag/Si heterostructures on the excitation wavelength was explained as a result of trapping of the photoexcited hot charge carriers in DLC matrix. The negative photovoltaic effect was observed for DLC:Ag/p-Si heterostructures and positive ("conventional") for DLC:Ag/n-Si ones. It was explained by the excitation of hot plasmonic holes in the Ag nanoparticles embedded into DLC matrix. Some decrease of DLC:Ag/Si heterostructures photovoltage as well as photocurrent with DLC:Ag film thickness was observed, indicating role of the interface in the charge transfer process of photocarriers excited in Ag nanoparticles.

A modified Embedded-Atom Method interatomic potential for uranium-silicide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beeler, Benjamin; Baskes, Michael; Andersson, David

Uranium-silicide (U-Si) fuels are being pursued as a possible accident tolerant fuel (ATF). This uranium alloy fuel bene ts from higher thermal conductivity and higher ssile density compared to uranium dioxide (UO 2). In order to perform engineering scale nuclear fuel performance simulations, the material properties of the fuel must be known. Currently, the experimental data available for U-Si fuels is rather limited. Thus, multiscale modeling e orts are underway to address this gap in knowledge. In this study, a semi-empirical modi ed Embedded-Atom Method (MEAM) potential is presented for the description of the U-Si system. The potential is ttedmore » to the formation energy, defect energies and structural properties of U 3Si 2. The primary phase of interest (U 3Si 2) is accurately described over a wide temperature range and displays good behavior under irradiation and with free surfaces. The potential can also describe a variety of U-Si phases across the composition spectrum.« less

A modified Embedded-Atom Method interatomic potential for uranium-silicide

DOE PAGES

Beeler, Benjamin; Baskes, Michael; Andersson, David; ...

2017-08-18

Uranium-silicide (U-Si) fuels are being pursued as a possible accident tolerant fuel (ATF). This uranium alloy fuel bene ts from higher thermal conductivity and higher ssile density compared to uranium dioxide (UO 2). In order to perform engineering scale nuclear fuel performance simulations, the material properties of the fuel must be known. Currently, the experimental data available for U-Si fuels is rather limited. Thus, multiscale modeling e orts are underway to address this gap in knowledge. In this study, a semi-empirical modi ed Embedded-Atom Method (MEAM) potential is presented for the description of the U-Si system. The potential is ttedmore » to the formation energy, defect energies and structural properties of U 3Si 2. The primary phase of interest (U 3Si 2) is accurately described over a wide temperature range and displays good behavior under irradiation and with free surfaces. The potential can also describe a variety of U-Si phases across the composition spectrum.« less

A modified Embedded-Atom Method interatomic potential for uranium-silicide

NASA Astrophysics Data System (ADS)

Beeler, Benjamin; Baskes, Michael; Andersson, David; Cooper, Michael W. D.; Zhang, Yongfeng

2017-11-01

Uranium-silicide (U-Si) fuels are being pursued as a possible accident tolerant fuel (ATF). This uranium alloy fuel benefits from higher thermal conductivity and higher fissile density compared to uranium dioxide (UO2). In order to perform engineering scale nuclear fuel performance simulations, the material properties of the fuel must be known. Currently, the experimental data available for U-Si fuels is rather limited. Thus, multiscale modeling efforts are underway to address this gap in knowledge. In this study, a semi-empirical modified Embedded-Atom Method (MEAM) potential is presented for the description of the U-Si system. The potential is fitted to the formation energy, defect energies and structural properties of U3Si2. The primary phase of interest (U3Si2) is accurately described over a wide temperature range and displays good behavior under irradiation and with free surfaces. The potential can also describe a variety of U-Si phases across the composition spectrum.

Nanocomposites of phosphonic-acid-functionalized polyethylenes with inorganic quantum dots.

PubMed

Rünzi, Thomas; Baier, Moritz C; Negele, Carla; Krumova, Marina; Mecking, Stefan

2015-01-01

Insertion of diethyl vinyl phosphonates and free vinyl phosphonic acid, respectively, into [(P^O)Pd(Me)(dmso)] ((P^O) = κ(2)-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) (1-dmso) occurs in a 2,1- as well as 1,2-fashion, to form a four-and a five-membered chelate [(P^O)Pd{κ(2)-C,O-CH(P(O)(OR)2)CH2CH3}] and [(P^O)Pd{κ(2)-C,O-CH2CH(P(O)(OR)2)CH3}] (R = H, Et). No decomposition or other reactions of 1 by free phosphonic acid moieties occur. Copolymerization in a pressure reactor by 1-dmso yields linear random poly(ethylene-co-diethyl vinyl phosphonate) and poly(ethylene-co-vinyl phosphonic acid). In these copolymerizations, reversible coordination of the phosphonate moieties of free monomer as well as chelate formation by incorporated monomer retards chain growth as also evidenced by relative binding studies of diethyl phosphonate towards 1. Post-polymerization emulsification of poly(ethylene-co-vinyl phosphonic acid) together with CdSe/CdS quantum dots (QDs) yields submicron (ca. 50 nm from dynamic light scattering (DLS) and transmission electron microscopy (TEM)) polymer particles with the QDs embedded in the functionalized polyethylene in a nonaggregated fashion. This embedding benefits the fluorescence behavior in terms of continuous emission and life-time as revealed by wide-field fluorescence measurements. These composite particle dispersions are employed as a ″masterbatch" together with an aqueous high density polyethylene (HDPE) dispersion to generate thin films (by spin-coating) and bulk materials (from the melt), respectively, in which the inorganic nanoparticles remain highly disperse. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spatially resolved In and As distributions in InGaAs/GaP and InGaAs/GaAs quantum dot systems.

PubMed

Shen, J; Song, Y; Lee, M L; Cha, J J

2014-11-21

InGaAs quantum dots (QDs) on GaP are promising for monolithic integration of optoelectronics with Si technology. To understand and improve the optical properties of InGaAs/GaP QD systems, detailed measurements of the QD atomic structure as well as the spatial distributions of each element at high resolution are crucial. This is because the QD band structure, band alignment, and optical properties are determined by the atomic structure and elemental composition. Here, we directly measure the inhomogeneous distributions of In and As in InGaAs QDs grown on GaAs and GaP substrates at the nanoscale using energy dispersive x-ray spectral mapping in a scanning transmission electron microscope. We find that the In distribution is broader on GaP than on GaAs, and as a result, the QDs appear to be In-poor using a GaP matrix. Our findings challenge some of the assumptions made for the concentrations and distributions of In within InGaAs/GaAs or InGaAs/GaP QD systems and provide detailed structural and elemental information to modify the current band structure understanding. In particular, the findings of In deficiency and inhomogeneous distribution in InGaAs/GaP QD systems help to explain photoluminescence spectral differences between InGaAs/GaAs and InGaAs/GaP QD systems.

Low-power nanophotonics: material and device technology

NASA Astrophysics Data System (ADS)

Thylén, Lars; Holmstrom, Petter; Wosinski, Lech; Lourdudoss, Sebastian

2013-05-01

Development in photonics for communications and interconnects pose increasing requirements on reduction of footprint, power dissipation and cost, as well as increased bandwidth. Nanophotonics integrated photonics has been viewed as a solution to this, capitalizing on development in nanotechnology and an increased understanding of light matter interaction on the nanoscale. The latter can be exemplified by plasmonics and low dimensional semiconductors such as quantum dots (QDs). In this scenario the development of improved electrooptic materials is of great importance, the electrooptic polymers being an example, since they potentially offer superior properties for optical phase modulators in terms of power and integratability. Phase modulators are essential for e.g. the rapidly developing advanced modulation formats, since phase modulation basically can generate any type of modulation. The electrooptic polymers, in combination with plasmonics nanoparticle array waveguides or nanostructured hybrid plasmonic media can give extremely compact and low power dissipation modulators. Low-dimensional semiconductors, e.g. in the shape of QDs, can be employed for modulation or switching functions, offering possibilities for scaling to 2 or 3 dimensions for advanced switching functions. In both the high field confinement plasmonics and QDs, the nanosizing is due to nearfield interactions, albeit being of different physical origin in the two cases. Epitaxial integration of III-V structures on Si plays an important role in developing high-performance light sources on silicon, eventually integrated with silicon electronics. A brief remark on all-optical vs. electronically controlled optical switching systems is also given.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Loginova, Y.F.; Dezhurov, S.V.; Zherdeva, V.V.

Highlights: Black-Right-Pointing-Pointer New QDs coated with combination of polythiol ligands and silica shell were synthesized. Black-Right-Pointing-Pointer We examine the QDs stability in digestive tract of mice after per os administration. Black-Right-Pointing-Pointer The polymer/silica shell prevents QDs degradation and fluorescence quenching in vivo. -- Abstract: CdSe-core, ZnS-capped semiconductor quantum dots (QDs) are of great potential for biomedical applications. However, applications in the gastrointestinal tract for in vivo imaging and therapeutic purposes are hampered by their sensitivity to acidic environments and potential toxicity. Here we report the use of coatings with a combination of polythiol ligands and silica shell (QDs PolyT-APS) tomore » stabilize QDs fluorescence under acidic conditions. We demonstrated the stability of water-soluble QDs PolyT-APS both in vitro, in strong acidic solutions, and in vivo. The biodistribution, stability and photoluminescence properties of QDs in the gastrointestinal tract of mice after per os administration were assessed. We demonstrated that QDs coated with current traditional materials - mercapto compounds (QDs MPA) and pendant thiol group (QDs PolyT) - are not capable of protecting QDs from chemically induced degradation and surface modification. Polythiol ligands and silica shell quantum dots (QDs PolyT-APS) are suitable for biological and biomedical applications in the gastrointestinal tract.« less

Properties of nanocrystalline Si layers embedded in structure of solar cell

NASA Astrophysics Data System (ADS)

Jurečka, Stanislav; Imamura, Kentaro; Matsumoto, Taketoshi; Kobayashi, Hikaru

2017-12-01

Suppression of spectral reflectance from the surface of solar cell is necessary for achieving a high energy conversion efficiency. We developed a simple method for forming nanocrystalline layers with ultralow reflectance in a broad range of wavelengths. The method is based on metal assisted etching of the silicon surface. In this work, we prepared Si solar cell structures with embedded nanocrystalline layers. The microstructure of embedded layer depends on the etching conditions. We examined the microstructure of the etched layers by a transmission electron microscope and analysed the experimental images by statistical and Fourier methods. The obtained results provide information on the applied treatment operations and can be used to optimize the solar cell forming procedure.

Dual switchable CRET-induced luminescence of CdSe/ZnS quantum dots (QDs) by the hemin/G-quadruplex-bridged aggregation and deaggregation of two-sized QDs.

PubMed

Hu, Lianzhe; Liu, Xiaoqing; Cecconello, Alessandro; Willner, Itamar

2014-10-08

The hemin/G-quadruplex-catalyzed generation of chemiluminescence through the oxidation of luminol by H2O2 stimulates the chemiluminescence resonance energy transfer (CRET) to CdSe/ZnS quantum dots (QDs), resulting in the luminescence of the QDs. By the cyclic K(+)-ion-induced formation of the hemin/G-quadruplex linked to the QDs, and the separation of the G-quadruplex in the presence of 18-crown-6-ether, the ON-OFF switchable CRET-induced luminescence of the QDs is demonstrated. QDs were modified with nucleic acids consisting of the G-quadruplex subunits sequences and of programmed domains that can be cross-linked through hybridization, using an auxiliary scaffold. In the presence of K(+)-ions, the QDs aggregate through the cooperative stabilization of K(+)-ion-stabilized G-quadruplex bridges and duplex domains between the auxiliary scaffold and the nucleic acids associated with the QDs. In the presence of 18-crown-6-ether, the K(+)-ions are eliminated from the G-quadruplex units, leading to the separation of the aggregated QDs. By the cyclic treatment of the QDs with K(+)-ions/18-crown-6-ether, the reversible aggregation/deaggregation of the QDs is demonstrated. The incorporation of hemin into the K(+)-ion-stabilized G-quadruplex leads to the ON-OFF switchable CRET-stimulated luminescence of the QDs. By the mixing of appropriately modified two-sized QDs, emitting at 540 and 610 nm, the dual ON-OFF activation of the luminescence of the QDs is demonstrated.

Gadolinium embedded iron oxide nanoclusters as T1-T2 dual-modal MRI-visible vectors for safe and efficient siRNA delivery

NASA Astrophysics Data System (ADS)

Wang, Xiaoyong; Zhou, Zijian; Wang, Zhiyong; Xue, Yunxin; Zeng, Yun; Gao, Jinhao; Zhu, Lei; Zhang, Xianzhong; Liu, Gang; Chen, Xiaoyuan

2013-08-01

This report illustrates a new strategy of designing a T1-T2 dual-modal magnetic resonance imaging (MRI)-visible vector for siRNA delivery and MRI. Hydrophobic gadolinium embedded iron oxide (GdIO) nanocrystals are self-assembled into nanoclusters in the water phase with the help of stearic acid modified low molecular weight polyethylenimine (stPEI). The resulting water-dispersible GdIO-stPEI nanoclusters possess good stability, monodispersity with narrow size distribution and competitive T1-T2 dual-modal MR imaging properties. The nanocomposite system is capable of binding and delivering siRNA for knockdown of a gene of interest while maintaining its magnetic properties and biocompatibility. This new gadolinium embedded iron oxide nanocluster provides an important platform for safe and efficient gene delivery with non-invasive T1-T2 dual-modal MRI monitoring capability.This report illustrates a new strategy of designing a T1-T2 dual-modal magnetic resonance imaging (MRI)-visible vector for siRNA delivery and MRI. Hydrophobic gadolinium embedded iron oxide (GdIO) nanocrystals are self-assembled into nanoclusters in the water phase with the help of stearic acid modified low molecular weight polyethylenimine (stPEI). The resulting water-dispersible GdIO-stPEI nanoclusters possess good stability, monodispersity with narrow size distribution and competitive T1-T2 dual-modal MR imaging properties. The nanocomposite system is capable of binding and delivering siRNA for knockdown of a gene of interest while maintaining its magnetic properties and biocompatibility. This new gadolinium embedded iron oxide nanocluster provides an important platform for safe and efficient gene delivery with non-invasive T1-T2 dual-modal MRI monitoring capability. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02797j

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pina-Hernandez, Carlos; Koshelev, Alexander; Dhuey, Scott

A novel method to realizing printed active photonic devices was developed using nanoimprint lithography (NIL), combining a printable high-refractive index material and colloidal CdSe/CdS quantum dots (QDs) for applications in the visible region. Active media QDs were applied in two different ways: embedded inside a printable high-refractive index matrix to form an active printable hybrid nanocomposite, and used as a uniform coating on top of printed photonic devices. As a proof-of-demonstration for printed active photonic devices, two-dimensional (2-D) photonic crystals as well as 1D and 2D photonic nanocavities were successfully fabricated following a simple reverse-nanoimprint process. We observed enhanced photoluminescencemore » from the 2D photonic crystal and the 1D nanocavities. Outstandingly, the process presented in this study is fully compatible with large-scale manufacturing where the patterning areas are only limited by the size of the corresponding mold. This work shows that the integration of active media and functional materials is a promising approach to the realization of integrated photonics for visible light using high throughput technologies. We believe that this work represents a powerful and cost-effective route for the development of numerous nanophotonic structures and devices that will lead to the emergence of new applications.« less

Quantum dot-like emitters formed due to alloy fluctuations in GaNAs-based nanowires.

NASA Astrophysics Data System (ADS)

Buyanova, Irina; Jansson, M.; Filippov, S.; Stehr, J.; Palisaitis, J.; Persson, P.; Ishikawa, F.; Chen, Weimin

Group III-V semiconductor nanowires with embedded quantum dots (QDs) are currently attracting increasing attention as a highly attractive platform for a variety of advanced applications ranging from third generation photovoltaics to quantum information technologies. In this work, we show that local fluctuations in N composition inside coaxial GaAs/GaNAs nanowires induces three-dimensional confining potentials equivalent to that for QDs thus forming optically active and highly localized states inside the GaNAs shell. Principal quantization axis of these states is concluded to mainly coincide with the nanowire axis, based on the strong polarization of the detected emission orthogonal to the nanowire axis revealed from polarization-resolved micro-photoluminescence studies. This is partly attributed to a predominantly uniaxial tensile strain field in the GaNAs shell caused by lattice mismatch with the GaAs core. GaNAs alloys can, therefore, be used as an active material in hybrid QD-NW structures utilized for fabrication of nanoscale polarized-light sources that are efficient within the near-infrared spectral range. Financial support by the Swedish Energy Agency (Grant # P40119-1) and the Swedish Research Council (Grant # 2015-05532) is greatly appreciated.

pH-responsive drug release and real-time fluorescence detection of porous silica nanoparticles.

PubMed

Zhang, Xu; Wang, Yamin; Zhao, Yanbao; Sun, Lei

2017-08-01

In this work, pH-sensitive "dual-switch" porous silica (pSiO 2 ) nanoparticles (NPs) were constructed for drug delivery. Poly(acrylic acid) (PAA) was grafting onto the internal and external surfaces of amino groups functionalized porous silica (pSiO 2 -NH 2 ) NPs by the amidation between the amino groups and the carboxyl groups of PAA for pH triggered drug release. The resultant pSiO 2 /PAA NPs have an average diameter of 50-60nm and high specific surface area (914m 2 ·g -1 ). To improve the loading capacity, ZnO quantum dots (QDs) were used to block the partial pores of pSiO 2 /PAA and the loading capacity reached to 28% for methotrexate (MTX) model drug. The in vitro cellular cytotoxicity test and a hemolysis assay demonstrated that the pSiO 2 /PAA/ZnO NPs were highly biocompatible and suitable to utilize as drug carriers. The MTX-loaded pSiO 2 /PAA/ZnO NPs displayed more efficient cytotoxic to HepG2 cells than free MTX. The pSiO 2 /PAA/ZnO NPs displayed low premature, pH-responsive release and pH-dependent fluorescence. Moreover, pH-dependent fluorescence enables to trace MTX release behavior. Copyright © 2017 Elsevier B.V. All rights reserved.

Si Nanocrystal-Embedded SiO x nanofoils: Two-Dimensional Nanotechnology-Enabled High Performance Li Storage Materials.

PubMed

Yoo, Hyundong; Park, Eunjun; Bae, Juhye; Lee, Jaewoo; Chung, Dong Jae; Jo, Yong Nam; Park, Min-Sik; Kim, Jung Ho; Dou, Shi Xue; Kim, Young-Jun; Kim, Hansu

2018-05-02

Silicon (Si) based materials are highly desirable to replace currently used graphite anode for lithium ion batteries. Nevertheless, its usage is still a big challenge due to poor battery performance and scale-up issue. In addition, two-dimensional (2D) architectures, which remain unresolved so far, would give them more interesting and unexpected properties. Herein, we report a facile, cost-effective, and scalable approach to synthesize Si nanocrystals embedded 2D SiO x nanofoils for next-generation lithium ion batteries through a solution-evaporation-induced interfacial sol-gel reaction of hydrogen silsesquioxane (HSiO 1.5 , HSQ). The unique nature of the thus-prepared centimeter scale 2D nanofoil with a large surface area enables ultrafast Li + insertion and extraction, with a reversible capacity of more than 650 mAh g -1 , even at a high current density of 50 C (50 A g -1 ). Moreover, the 2D nanostructured Si/SiO x nanofoils show excellent cycling performance up to 200 cycles and maintain their initial dimensional stability. This superior performance stems from the peculiar nanoarchitecture of 2D Si/SiO x nanofoils, which provides short diffusion paths for lithium ions and abundant free space to effectively accommodate the huge volume changes of Si during cycling.

Adhesion of CdTe quantum dots on model membranes and internalization into RBL-2H3 cells.

PubMed

Zhang, Mengmeng; Wei, Xiaoran; Ding, Lei; Hu, Jingtian; Jiang, Wei

2017-06-01

Quantum dots (QDs) have attracted broad attention due to their special optical properties and promising prospect in medical and biological applications. However, the process of QDs on cell membrane is worth further investigations because such process may lead to harmful effects on organisms and also important for QD application. In this study, adhesion of amino- and carboxyl-coated CdTe QDs (A-QDs and C-QDs) on cell membrane and the subsequent internalization are studied using a series of endocytosis-free model membranes, including giant and small unilamellar vesicles, supported lipid bilayers and giant plasma membrane vesicles (GPMVs). The adhered QD amounts on model membranes are quantified by a quartz crystal microbalance. The CdTe QD adhesion on model membranes is governed by electrostatic forces. Positively charged A-QDs adhere on GPMV surface and passively penetrate the plasma membrane via endocytosis-free mechanism, but negatively charged C-QDs cannot. Rat basophilic leukemia (RBL-2H3) cells are exposed to CdTe QDs to monitor the QD internalization process. Both A- and C-QDs are internalized by RBL-2H3 cells mainly via endocytosis. CdTe QDs do not accumulate on the plasma membrane of living cells due to the fast endocytosis and the weakened electrostatic attraction in biological medium, resulting in low chance of passive penetration. The suspended cells after trypsin digestion take more QDs than the adherent cells. A-QDs cause lower cell viability than C-QDs, probably because the approach of positively charged QDs to cells is favored and the smaller aggregates of A-QDs. Copyright © 2017 Elsevier Ltd. All rights reserved.

Suggested Interactivity: Seeking Perceived Affordances for Information Visualization.

PubMed

Boy, Jeremy; Eveillard, Louis; Detienne, Françoise; Fekete, Jean-Daniel

2016-01-01

In this article, we investigate methods for suggesting the interactivity of online visualizations embedded with text. We first assess the need for such methods by conducting three initial experiments on Amazon's Mechanical Turk. We then present a design space for Suggested Interactivity (i. e., visual cues used as perceived affordances-SI), based on a survey of 382 HTML5 and visualization websites. Finally, we assess the effectiveness of three SI cues we designed for suggesting the interactivity of bar charts embedded with text. Our results show that only one cue (SI3) was successful in inciting participants to interact with the visualizations, and we hypothesize this is because this particular cue provided feedforward.

Charge transport in quantum dot organic solar cells with Si quantum dots sandwiched between poly(3-hexylthiophene) (P3HT) absorber and bathocuproine (BCP) transport layers

NASA Astrophysics Data System (ADS)

Verma, Upendra Kumar; Kumar, Brijesh

2017-10-01

We have modeled a multilayer quantum dot organic solar cell that explores the current-voltage characteristic of the solar cell whose characteristics can be tuned by varying the fabrication parameters of the quantum dots (QDs). The modeled device consists of a hole transport layer (HTL) which doubles up as photon absorbing layer, several quantum dot layers, and an electron transport layer (ETL). The conduction of charge carriers in HTL and ETL has been modeled by the drift-diffusion transport mechanism. The conduction and recombination in the quantum dot layers are described by a system of coupled rate equations incorporating tunneling and bimolecular recombination. Analysis of QD-solar cells shows improved device performance compared to the similar bilayer and trilayer device structures without QDs. Keeping other design parameters constant, solar cell characteristics can be controlled by the quantum dot layers. Bimolecular recombination coefficient of quantum dots is a prime factor which controls the open circuit voltage (VOC) without any significant reduction in short circuit current (JSC).

Anti-inflammatory and in-vitro antibacterial activities of Traditional Chinese Medicine Formula Qingdaisan.

PubMed

Zhao, Xinghua; He, Xin; Zhong, Xiuhui

2016-12-05

Qingdaisan (Formulated Indigo powder, QDS) are widely used for treatment of aphtha, sore throat and bleeding gums in China. The aim of the study is to evaluate the anti-inflammatory, antibacterial and dental ulcer therapeutic effects of QDS. Dimethylbenzene-induced ear edema test and cotton pellet-induced granuloma test were used to evaluate anti-inflammatory activities of QDS on acute and chronic inflammatory. The healing time and local pathologic changes were used to assess the therapeutic effects of QDS on dental ulcer. The antibacterial activities of each component and the whole formulation of QDS were determined by agar well diffusion assay. High-dose and low-dose QDS were tested in this experiment and Gui Lin Watermelon Frost Powder (GLWFP) was used as positive control. Oral treatment with QDS significantly accelerated the healing of ulcerative lesions induced by phenol injury. The dental ulcers of high-dose QDS group were all healed within 6 days. It was shorter than those of low-dose QDS group and GLWFP group. Less quantity of inflammatory cells and plenty fibroblasts were observed in pathological section of QDS groups. QDS also exhibited significant anti-inflammatory activity both in acute and chronic animal models. Although some of the components exhibited antibacterial activities, the whole formulation of QDS didn't show any significant antibacterial activity in vitro. The study showed that QDS has obviously anti-inflammatory activity for both acute and chronic inflammatory, also has a remarkable effect for healing dental ulcer caused by phenol. QDS didn't have antibacterial activity to selected strains in vitro.

High-Efficiency All-Solution-Processed Light-Emitting Diodes Based on Anisotropic Colloidal Heterostructures with Polar Polymer Injecting Layers.

PubMed

Castelli, Andrea; Meinardi, Francesco; Pasini, Mariacecilia; Galeotti, Francesco; Pinchetti, Valerio; Lorenzon, Monica; Manna, Liberato; Moreels, Iwan; Giovanella, Umberto; Brovelli, Sergio

2015-08-12

Colloidal quantum dots (QDs) are emerging as true candidates for light-emitting diodes with ultrasaturated colors. Here, we combine CdSe/CdS dot-in-rod heterostructures and polar/polyelectrolytic conjugated polymers to demonstrate the first example of fully solution-based quantum dot light-emitting diodes (QD-LEDs) incorporating all-organic injection/transport layers with high brightness, very limited roll-off and external quantum efficiency as high as 6.1%, which is 20 times higher than the record QD-LEDs with all-solution-processed organic interlayers and exceeds by over 200% QD-LEDs embedding vacuum-deposited organic molecules.

Embedded Metal Electrode for Organic-Inorganic Hybrid Nanowire Solar Cells.

PubMed

Um, Han-Don; Choi, Deokjae; Choi, Ahreum; Seo, Ji Hoon; Seo, Kwanyong

2017-06-27

We demonstrate here an embedded metal electrode for highly efficient organic-inorganic hybrid nanowire solar cells. The electrode proposed here is an effective alternative to the conventional bus and finger electrode which leads to a localized short circuit at a direct Si/metal contact and has a poor collection efficiency due to a nonoptimized electrode design. In our design, a Ag/SiO 2 electrode is embedded into a Si substrate while being positioned between Si nanowire arrays underneath poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), facilitating suppressed recombination at the Si/Ag interface and notable improvements in the fabrication reproducibility. With an optimized microgrid electrode, our 1 cm 2 hybrid solar cells exhibit a power conversion efficiency of up to 16.1% with an open-circuit voltage of 607 mV and a short circuit current density of 34.0 mA/cm 2 . This power conversion efficiency is more than twice as high as that of solar cells using a conventional electrode (8.0%). The microgrid electrode significantly minimizes the optical and electrical losses. This reproducibly yields a superior quantum efficiency of 99% at the main solar spectrum wavelength of 600 nm. In particular, our solar cells exhibit a significant increase in the fill factor of 78.3% compared to that of a conventional electrode (61.4%); this is because of the drastic reduction in the metal/contact resistance of the 1 μm-thick Ag electrode. Hence, the use of our embedded microgrid electrode in the construction of an ideal carrier collection path presents an opportunity in the development of highly efficient organic-inorganic hybrid solar cells.

Strain-driven growth of GaAs(111) quantum dots with low fine structure splitting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yerino, Christopher D.; Jung, Daehwan; Lee, Minjoo Larry, E-mail: minjoo.lee@yale.edu

2014-12-22

Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting (FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSSmore » with a median value of 7.6 μeV, due to the high symmetry of the (111) QDs. Tensile self-assembly thus offers a simple route to symmetric (111) QDs for entangled photon emitters.« less

Developmental toxicity of CdTe QDs in zebrafish embryos and larvae

NASA Astrophysics Data System (ADS)

Duan, Junchao; Yu, Yongbo; Li, Yang; Yu, Yang; Li, Yanbo; Huang, Peili; Zhou, Xianqing; Peng, Shuangqing; Sun, Zhiwei

2013-07-01

Quantum dots (QDs) have widely been used in biomedical and biotechnological applications. However, few studies focus on the assessing toxicity of QDs exposure in vivo. In this study, zebrafish embryos were treated with CdTe QDs (4 nm) during 4-96 h post-fertilization (hpf). Mortality, hatching rate, malformation, heart rate, and QDs uptake were detected. We also measured the larval behavior to analyze whether QDs had persistent effects on larvae locomotor activity at 144 hpf. The results showed that as the exposure dosages increased, the hatching rate and heart rate of zebrafish embryos were decreased, while the mortality increased. Exposure to QDs caused embryonic malformations, including head malformation, pericardial edema, yolk sac edema, bent spine, and yolk not depleted. QDs fluorescence was mainly localized in the intestines region. The larval behavior testing showed that the total swimming distance was decreased in a dose-dependent manner. The lowest dose (2.5 nM QDs) produced substantial hyperactivity while the higher doses groups (5, 10, and 20 nM QDs) elicited remarkably hypoactivity in dark periods. In summary, the data of this article indicated that QDs caused embryonic developmental toxicity, resulted in persistent effects on larval behavior.

Doxorubicin-conjugated D-glucosamine- and folate- bi-functionalised InP/ZnS quantum dots for cancer cells imaging and therapy.

PubMed

Ranjbar-Navazi, Zahra; Eskandani, Morteza; Johari-Ahar, Mohammad; Nemati, Ali; Akbari, Hamid; Davaran, Soudabeh; Omidi, Yadollah

2018-03-01

Nanoscaled quantum dots (QDs), with unique optical properties have been used for the development of theranostics. Here, InP/ZnS QDs were synthesised and functionalised with folate (QD-FA), D-glucosamine (QD-GA) or both (QD-FA-GA). The bi-functionalised QDs were further conjugated with doxorubicin (QD-FA-GA-DOX). Optimum Indium to fatty acid (In:MA) ratio was 1:3.5. Transmission electron microscopy (TEM) micrographs revealed spherical morphology for the QDs (11 nm). Energy-dispersive spectroscopy (EDS) spectrum confirmed the chemical composition of the QDs. MTT analysis in the OVCAR-3 cells treated with bare QDs, QD-FA, QD-GA, QD-FA-GA and QD-FA-GA-DOX (0.2 mg/mL of QDs) after 24 h indicated low toxicity for the bare QDs and functionalised QDs (about 80-90% cell viability). QD-FA-GA-DOX nanoparticles elicited toxicity in the cells. Cellular uptake of the engineered QDs were investigated in both folate receptor (FR)-positive OVCAR-3 cells and FR-negative A549 cells using fluorescence microscopy and FACS flow cytometry. The FA-functionalised QDs showed significantly higher uptake in the FR-positive OVCAR-3 cells, nonetheless the GA-functionalised QDs resulted in an indiscriminate uptake in both cell lines. In conclusion, our findings indicated that DOX-conjugated FA-armed QDs can be used as theranostics for simultaneous imaging and therapy of cancer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kong Lingmin; Feng Zhechuan; Wu Zhengyun

Four types of self-assembled InAs/GaAs quantum dots (QDs) were grown by molecular beam epitaxy and studied via temperature-dependent and time-resolved photoluminescence (PL) spectroscopy measurements. A thin InGaAs stain reducing layer (SRL) is adopted which extends the emission wavelength to 1.3 mum and the influence of strain on QDs is investigated. The SRL releases the strain between the wetting layer and QDs, and enlarges the size of QDs, as shown by atomic force microscopy measurements. As the thickness of InAs layer decreases to 1.7 ML, the QDs with the SRL are chained to strings and the density of QDs increases significantly,more » which leads to an abnormal redshift of 1.3 mum PL peak at room temperature. PL peaks of InAs QDs with the SRL show redshift compared with the QDs directly deposited on GaAs matrix. The dependences of PL lifetime on the QD size, density and temperature (T) are systematically studied. It is observed that the PL lifetime of QDs is insensitive to T below 50 K. Beyond 50 K, increases and then drops at higher temperature, with a peak at T{sub C}, which was determined by the SRL and the thickness of InAs. We have also observed an obvious PL spectral redshift of the QDs with 1.7 ML InAs coverage on SRL at low T as the measuring time delays. The PL lifetime of QDs with the SRL is smaller than that of QDs without the SRL. The QDs with different densities have different PL lifetime dependence on the QDs size. These observations can be explained by the competition between the carrier redistribution and thermal emission.« less

Hydrodynamic size-dependent cellular uptake of aqueous QDs probed by fluorescence correlation spectroscopy.

PubMed

Dong, Chaoqing; Irudayaraj, Joseph

2012-10-11

Aqueous quantum dots (QDs) directly synthesized with various thiol ligands have been investigated as imaging probes in living cells. However, the effect of the surface chemistry of these ligands on QDs' cellular uptakes and their intracellular fate remains poorly understood. In this work, four CdTe QDs were directly synthesized under aqueous conditions using four different thiols as stabilizers and their interactions with cells were investigated. Fluorescence correlation spectroscopy (FCS), X-ray photoelectron spectroscopy (XPS), and zeta potential measurements on QDs primarily show that the surface structure of these QDs is highly dependent on the thiol ligands used in the preparation of QDs' precursors, including its layer thicknesses, densities, and surface charges. Subsequently, FCS integrated with the maximum-entropy-method-based FCS (MEMFCS) was used to investigate the concentration distribution and dynamics of these QDs in living A-427 cells. Our findings indicate that QDs' surface characteristics affect cell membrane adsorption and subsequent internalization. More critically, we show that the cellular uptake of aqueous QDs is dependent on their hydrodynamic diameter and might have the potential to escape trapped environments to accumulate in the cytoplasm.

Non-blinking (Zn)CuInS/ZnS Quantum Dots Prepared by In Situ Interfacial Alloying Approach

PubMed Central

Zhang, Aidi; Dong, Chaoqing; Li, Liang; Yin, Jinjin; Liu, Heng; Huang, Xiangyi; Ren, Jicun

2015-01-01

Semiconductor quantum dots (QDs) are very important optical nanomaterials with a wide range of potential applications. However, blinking behavior of single QD is an intrinsic drawback for some biological and photoelectric applications based on single-particle emission. Herein we present a rational strategy for fabrication of non-blinking (Zn)CuInS/ZnS QDs in organic phase through in situ interfacial alloying approach. This new strategy includes three steps: synthesis of CuInS QDs, eliminating the interior traps of QDs by forming graded (Zn)CuInS alloyed QDs, modifying the surface traps of QDs by introducing ZnS shells onto (Zn)CuInS QDs using alkylthiols as sulfur source and surface ligands. The suppressed blinking mechanism was mainly attributed to modifying QDs traps from interior to exterior via a step-by-step modification. Non-blinking QDs show high quantum yield, symmetric emission spectra and excellent crystallinity, and will enable applications from biology to optoelectronics that were previously hindered by blinking behavior of traditional QDs. PMID:26458511

Efficiency improvement of InGaN light emitting diodes with embedded self-assembled SiO2 nanosphere arrays

NASA Astrophysics Data System (ADS)

Zhang, Yonghui; Wei, Tongbo; Wang, Junxi; Fan, Chao; Chen, Yu; Hu, Qiang; Li, Jinmin

2014-05-01

In this study, the periodic SiO2 nanosphere nanopatterned sapphire substrate (SiO2-NPSS) was made using self-assembled SiO2 nanosphere monolayer template and inductively coupled plasma (ICP) etching. And the self-assembled SiO2 nanosphere monolayer was directly embedded into the GaN/sapphire interface by nanoscale epitaxial lateral overgrowth (NELOG). For comparison, a common nanopatterned sapphire substrate (C-NPSS) was also made through dry etching with the SiO2 nanospheres used as the mask. Compared with LEDs grown on C-NPSS and flat sapphire substrate (FSS), the external quantum efficiency of LEDs with SiO2 nanopheres (SiO2-NPSS) was increased by 30.7% and 81.9% under a driving current 350 mA. The SiO2-NPSS not only improved the crystalline quality of GaN but also enhanced the light extraction efficiency (LEE) of LED. And the SiO2-NPSS LED also showed more light in vertical direction and more uniform light distribution. By finite-difference time-domain (FDTD) simulation, we confirmed that more light could be reflected from the GaN/SiO2 interface than the GaN/sapphire interface because the refractive index of SiO2 was lower than that of sapphire. Therefore, LED grown on the SiO2-NPSS showed superior light extraction efficiency compared to that on C-NPSS.

DFT/TD-DFT study on the electronic and spectroscopic properties of hollow cubic and hollow spherical (ZnO) m quantum dots interacting with CO, NO2 and SO3 molecules

NASA Astrophysics Data System (ADS)

Gopalakrishnan, Sankarasubramanian; Shankar, Ramasamy; Kolandaivel, Ponmalai

2018-03-01

Hollow spherical (HS) and hollow cubic (HC) (ZnO) m quantum dots (QDs) were constructed and optimized using density functional theory (DFT) method. CO, NO2 and SO3 molecules were used to interact with the HC and HS (ZnO) m QDs at the centre and on the surface of the QDs. The changes in the electronic energy levels of HC and HS (ZnO) m QDs due to the interactions of CO, NO2 and SO3 molecules have been studied. The electronic and spectroscopic properties, such as density of states, HOMO-LUMO energy gap, absorption spectra, IR and Raman spectra of HC and HS (ZnO) m QDs have been studied using DFT and Time dependent-DFT (TD-DFT) methods. The interaction energy values show that the SO3 molecule has strongly interacted with HC and HS (ZnO) m QDs than the CO and NO2 molecules. The results of the density of states show that the HC QDs have peaks that are very close to each other, whereas the same is found to be broad in the HS QDs. The HOMO-LUMO energy gap is more for the HS QDs than the HC QDs, and also it gets decreased, when the NO2 and SO3 molecules interact at the centre of the HC and HS (ZnO) m QDs. The blue and red shifts were observed in the absorption spectra of HS and HC QDs. The natural transition orbital (NTO) plot reveals that the interaction of the molecules on the surface of the QDs reduce the chance of electron-hole recombination; hence the energy gap increases for NO2 and SO3 molecular interactions on the surface of the HC and HS (ZnO) m QDs. The vibrational assignments have been made for HC and HS QDs interacting with CO, NO2 and SO3 molecules.

CdTe quantum dots: aqueous phase synthesis, stability studies and protein conjugation for development of biosensors

NASA Astrophysics Data System (ADS)

Borse, Vivek; Sadawana, Mayur; Srivastava, Rohit

2016-04-01

Synthesis of quantum dots (QDs) in aqueous medium is advantageous as compared to the organic solvent mediated synthesis, as the aqueous synthesis is less toxic, reagent effective, easily reproducible and importantly, synthesized QDs have biological compatibility. The QDs should be aqueous in nature for use in cell imaging, drug labeling, tracking and delivery. Structural modifications are necessary to enable their use in biosensing application. In this work, mercaptopropionic acid capped cadmium telluride QDs (MPA-CdTe QDs) were synthesized by hydrothermal method and characterized by various techniques. Water and various biochemical buffers were used to study the fluorescence intensity stability of the QDs at different physicochemical conditions. QDs stored in 4° C showed excellent stability of fluorescence intensity values as compared to the samples stored at room temperature. Staphylococcal protein A (SPA) was conjugated with the QDs (SPA-QDs) and characterized using UV and fluorescence spectroscopy, zeta potential, HRTEM, FTIR, and AFM. Blue shift was observed in the fluorescence emission spectra that may be due to reduction in the surface charge as carboxyl groups on QDs were replaced by amino groups of SPA. This SPA conjugated to QDs enables binding of the C-terminal of antibodies on its surface allowing N-terminal binding site remain free to bind with antigenic biomarkers. Thus, the biosensor i.e. antibody bound on SPA-QDs would bind to the antigenic biomarkers in sample and the detection system could be developed. As QDs have better fluorescence properties than organic dyes, this biosensor will provide high sensitivity and quantitative capability in diagnostics.

Time-dependent pH sensing phenomena using CdSe/ZnS quantum dots in EIS structure

PubMed Central

2014-01-01

Time-dependent pH sensing phenomena of the core-shell CdSe/ZnS quantum dot (QD) sensors in EIS (electrolyte insulator semiconductor) structure have been investigated for the first time. The quantum dots are immobilized by chaperonin GroEL protein, which are observed by both atomic force microscope and scanning electron microscope. The diameter of one QD is approximately 6.5 nm. The QDs are not oxidized over a long time and core-shell CdSe/ZnS are confirmed by X-ray photon spectroscopy. The sensors are studied for sensing of hydrogen ions concentration in different buffer solutions at broad pH range of 2 to 12. The QD sensors show improved sensitivity (38 to 55 mV/pH) as compared to bare SiO2 sensor (36 to 23 mV/pH) with time period of 0 to 24 months, owing to the reduction of defects in the QDs. Therefore, the differential sensitivity of the QD sensors with respect to the bare SiO2 sensors is improved from 2 to 32 mV/pH for the time period of 0 to 24 months. After 24 months, the sensitivity of the QD sensors is close to ideal Nernstian response with good linearity of 99.96%. Stability and repeatability of the QD sensors show low drift (10 mV for 10 cycles) as well as small hysteresis characteristics (<10 mV). This QD sensor is very useful for future human disease diagnostics. PMID:24725352

The influence of surface coating on the properties of water-soluble CdSe and CdSe/ZnS quantum dots

NASA Astrophysics Data System (ADS)

Coto-García, Ana María; Fernández-Argüelles, María T.; Costa-Fernández, José M.; Sanz-Medel, Alfredo; Valledor, Marta; Campo, Juan C.; Ferrero, Francisco J.

2013-01-01

It is well-known that ligands coating the surface of luminescent semiconductor nanocrystals (quantum dots [QDs]) play an important role in the preparation, stability and physical properties of the colloidal QDs in both organic and aqueous media. Here we report on the synthesis and characterization of core (CdSe QDs) and core-shell structured QDs (CdSe/ZnS QDs), both of them stabilized in aqueous medium through different mechanisms of modification of their surface chemistry. The approaches evaluated for QDs transfer to aqueous media were ligand exchange and polymer coating. Experiments were performed using two typical thioalkyl acids as ligands, namely mercaptoacetic acid (QDs-MAA) and 2-mercaptoethanesulphonic acid (QDs-MES), and an amphiphilic polymer (PQDs) based on poly(maleic anhydride) functional groups. The effects of pH (buffer solution), illumination and the presence of ions in the QD environment on the spectroscopic properties of the different synthesized QDs are reported. The stability of the prepared QDs has been comparatively evaluated aimed to elucidate which surface chemistry provides the suitable properties to be employed as fluorescence labels in distinct types of applications. The experimental results and conclusions will be useful for the development of sensitive sensors or assays adopting QDs as fluorescence labels.

Amorphous Ge quantum dots embedded in crystalline Si: ab initio results.

PubMed

Laubscher, M; Küfner, S; Kroll, P; Bechstedt, F

2015-10-14

We study amorphous Ge quantum dots embedded in a crystalline Si matrix through structure modeling and simulation using ab initio density functional theory including spin-orbit interaction and quasiparticle effects. Three models are generated by replacing a spherical region within diamond Si by Ge atoms and creating a disordered bond network with appropriate density inside the Ge quantum dot. After total-energy optimisations of the atomic geometry we compute the electronic and optical properties. We find three major effects: (i) the resulting nanostructures adopt a type-I heterostructure character; (ii) the lowest optical transitions occur only within the Ge quantum dots, and do not involve or cross the Ge-Si interface. (iii) for larger amorphous Ge quantum dots, with diameters of about 2.0 and 2.7 nm, absorption peaks appear in the mid-infrared spectral region. These are promising candidates for intense luminescence at photon energies below the gap energy of bulk Ge.

Investigation of Embedded Si/C System Exposed to a Hybrid Reaction of Centrifugal-Assisted Thermite Method

PubMed Central

Mahmoodian, Reza; Yahya, Rosiyah; Dabbagh, Ali; Hamdi, Mohd; Hassan, Mohsen A.

2015-01-01

A novel method is proposed to study the behavior and phase formation of a Si+C compacted pellet under centrifugal acceleration in a hybrid reaction. Si+C as elemental mixture in the form of a pellet is embedded in a centrifugal tube. The pellet assembly and tube are exposed to the sudden thermal energy of a thermite reaction resulted in a hybrid reaction. The hybrid reaction of thermite and Si+C produced unique phases. X-ray diffraction pattern (XRD) as well as microstructural and elemental analyses are then investigated. XRD pattern showed formation of materials with possible electronic and magnetic properties. The cooling rate and the molten particle viscosity mathematical model of the process are meant to assist in understanding the physical and chemical phenomena took place during and after reaction. The results analysis revealed that up to 85% of materials converted into secondary products as ceramics-matrix composite. PMID:26641651

Investigation of Embedded Si/C System Exposed to a Hybrid Reaction of Centrifugal-Assisted Thermite Method.

PubMed

Mahmoodian, Reza; Yahya, Rosiyah; Dabbagh, Ali; Hamdi, Mohd; Hassan, Mohsen A

2015-01-01

A novel method is proposed to study the behavior and phase formation of a Si+C compacted pellet under centrifugal acceleration in a hybrid reaction. Si+C as elemental mixture in the form of a pellet is embedded in a centrifugal tube. The pellet assembly and tube are exposed to the sudden thermal energy of a thermite reaction resulted in a hybrid reaction. The hybrid reaction of thermite and Si+C produced unique phases. X-ray diffraction pattern (XRD) as well as microstructural and elemental analyses are then investigated. XRD pattern showed formation of materials with possible electronic and magnetic properties. The cooling rate and the molten particle viscosity mathematical model of the process are meant to assist in understanding the physical and chemical phenomena took place during and after reaction. The results analysis revealed that up to 85% of materials converted into secondary products as ceramics-matrix composite.

Soft magnetic properties of nanocrystalline FeRuGaSi-Hf alloy films and head characteristics for the embedded thin film tape head

NASA Astrophysics Data System (ADS)

Ohmori, H.; Shoji, M.; Kobayashi, T.; Yamamoto, T.; Sugiyama, Y.; Hayashi, K.; Hono, K.

1996-04-01

The Hf-added FeRuGaSi alloy film has an amorphous structure in the as-deposited state and becomes nanocrystalline after annealing. Due to this structure change from crystalline to amorphous by the addition of Hf, soft magnetic degradation of the film deposited on the slant grooved substrate, which is necessary for the sophisticated embedded thin film (ETF) head structure, is greatly suppressed and the undesirable film stress is relieved. The FeRuGaSi-Hf alloy film has higher resistivity and permeability at high frequencies than those of sendust film, and the read/write characteristics of this alloy film show better performance than sendust film.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murray, E.; Floether, F. F.; Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE

Fundamental to integrated photonic quantum computing is an on-chip method for routing and modulating quantum light emission. We demonstrate a hybrid integration platform consisting of arbitrarily designed waveguide circuits and single-photon sources. InAs quantum dots (QD) embedded in GaAs are bonded to a SiON waveguide chip such that the QD emission is coupled to the waveguide mode. The waveguides are SiON core embedded in a SiO{sub 2} cladding. A tuneable Mach Zehnder interferometer (MZI) modulates the emission between two output ports and can act as a path-encoded qubit preparation device. The single-photon nature of the emission was verified using themore » on-chip MZI as a beamsplitter in a Hanbury Brown and Twiss measurement.« less

Antibacterial potential of rutin conjugated with thioglycolic acid capped cadmium telluride quantum dots (TGA-CdTe QDs)

NASA Astrophysics Data System (ADS)

Ananth, Devanesan Arul; Rameshkumar, Angappan; Jeyadevi, Ramachandran; Jagadeeswari, Sivanadanam; Nagarajan, Natarajan; Renganathan, Rajalingam; Sivasudha, Thilagar

2015-03-01

Quantum dots not only act as nanocarrier but also act as stable and resistant natural fluorescent bio markers used in various in vitro and in vivo photolabelling and biological applications. In this study, the antimicrobial potential of TGA-CdTe QDs and commercial phenolics (rutin and caffeine) were investigated against Escherichiacoli. UV absorbance and fluorescence quenching study of TGA-CdTe QDs with rutin and caffeine complex was measured by spectroscopic technique. QDs-rutin conjugate exhibited excellent quenching property due to the -OH groups present in the rutin structure. But the same time caffeine has not conjugated with QDs because of lacking of -OH group in its structure. Photolabelling of E. coli with QDs-rutin and QDs-caffeine complex was analyzed by fluorescent microscopic method. Microbe E. coli cell membrane damage was assessed by atomic force (AFM) and confocal microscopy. Based on the results obtained, it is suggested that QDs-rutin conjugate enhance the antimicrobial activity more than the treatment with QDs, rutin and caffeine alone.

Structural, optical and photovoltaic properties of co-doped CdTe QDs for quantum dots sensitized solar cells

NASA Astrophysics Data System (ADS)

Ayyaswamy, Arivarasan; Ganapathy, Sasikala; Alsalme, Ali; Alghamdi, Abdulaziz; Ramasamy, Jayavel

2015-12-01

Zinc and sulfur alloyed CdTe quantum dots (QDs) sensitized TiO2 photoelectrodes have been fabricated for quantum dots sensitized solar cells. Alloyed CdTe QDs were prepared in aqueous phase using mercaptosuccinic acid (MSA) as a capping agent. The influence of co-doping on the structural property of CdTe QDs was studied by XRD analysis. The enhanced optical absorption of alloyed CdTe QDs was studied using UV-vis absorption and fluorescence emission spectra. The capping of MSA molecules over CdTe QDs was confirmed by the FTIR and XPS analyses. Thermogravimetric analysis confirms that the prepared QDs were thermally stable up to 600 °C. The photovoltaic performance of alloyed CdTe QDs sensitized TiO2 photoelectrodes were studied using J-V characteristics under the illumination of light with 1 Sun intensity. These results show the highest photo conversion efficiency of η = 1.21%-5% Zn & S alloyed CdTe QDs.

Synthesis and exploitation of InP/ZnS quantum dots for bioimaging

NASA Astrophysics Data System (ADS)

Massadeh, Salam; Xu, Shu; Nann, Thomas

2009-02-01

Nano- and cytotoxicity becomes increasingly more important with an increasing number of potential bio-medical applications for semiconductor Quantum Dots (QDs). Therefore, the frequently used CdSe-based QDs are unsuitable per-se, since cadmium is a highly toxic heavy metal and may leach out of QDs. Cadmium-free QDs have not been available for a long time, because the synthesis of e.g. monodisperes and highly crystalline InP QDs caused many problems. We report on the synthesis of InP/ZnS QDs with optical properties similar to those displayed by typical CdSe/ZnS QDs. A major break-through has been reached by addition of zinc ions into the reaction mixture. Furthermore, the transfer of the InP/ZnS QDs to water and their exploitation for bioanalytical applications are reported. It is shown that InP/ZnS QDs can be used to replace CdSe-based ones for almost any bio-medical application.

The toxicity and invasive effects of QDs on mung bean development

NASA Astrophysics Data System (ADS)

Zhai, Peng; Wang, Xiaomei; Wang, Ruhua; Huang, Xuan; Feng, Gang; Lin, Guimiao; Chen, Qiang; Xu, Gaixia; Chen, Danni

2014-09-01

Objective: Nowadays, the nanomaterials have been applied in every aspects of our life, including cosmetics, fresh-keeping, antisepsis and medicines. However, we know little about the toxic effects of nanoparticles towards plants. In this thesis, we synthesized quantum dots (QDs), and then toxicity and invasive effects of QDs for mung beans were investigated. Methods: We synthesised red CdTe QDs in water sphase with L-Cystein stabilizers, then prepared different concentration of QDs solution to cultivate mung bean plant, the radical length of mung beans was measured after four days every day, after 7 days, the distribution of QDs in mung bean plant was recorded under the microscopic. Results: The result showed the QDs inhibited the growth of mung beans, the higher the concentration of QDs was, the greater the inhibition effect was. After 7 days, the radicle average lengths of mung beans in different concentrations of QDs solution - blank 0.1μmol/L 0.2μmol/L 0.5 μmol/L 1 μmol/L - were 19.350+/- 0.427, 14.050+/- 0.879, 10.525+/- 0.554, 7.250+/- 0.522, 7.650+/- 0.229. The QDs mostly adhered onto the root surface and hairs. Conclusion: In conclusion, the QDs synthesized with L-cystein have effects on the growth of mung beans. However, it is necessary to do more experiments to confirm the mechanism of the toxicity effect of QDs on plants.

Targeting and retention enhancement of quantum dots decorated with amino acids in an invertebrate model organism

NASA Astrophysics Data System (ADS)

Xing, Rui; Chen, Xue-Dong; Zhou, Yan-Feng; Zhang, Jue; Su, Yuan-Yuan; Qiu, Jian-Feng; Sima, Yang-Hu; Zhang, Ke-Qin; He, Yao; Xu, Shi-Qing

2016-01-01

The use of quantum dots (QDs) in biological imaging applications and targeted drug delivery is expected to increase. However, the efficiency of QDs in drug targeting needs to be improved. Here, we show that amino acids linked to CdTe QDs significantly increased the targeted transfer efficiency and biological safety in the invertebrate model Bombyx mori. Compared with bare QDs530, the transfer efficiency of Ala- and Gly-conjugated QDs (QDs530-Ala and QDs530-Gly) in circulatory system increased by 2.6 ± 0.3 and 1.5 ± 0.3 times, and increased by 7.8 ± 0.9 and 2.9 ± 0.2 times in target tissue silk glands, respectively, after 24 h of QDs exposure. Meanwhile, the amount of conjugated QDs decreased by (68.4 ± 4.4)% and (46.7 ± 9.1)% in the non-target tissue fat body, and the speed at which they entered non-target circulating blood cells significantly decreased. The resultant QDs530-Ala revealed a better structural integrity in tissues and a longer retention time in hemolymph than that of QDs530 after exposure via the dorsal vessel. On the other hand, QDs530-Ala significantly reduced the toxicity to hemocytes, silk gland, and fat body, and reduced the amount of reactive oxygen species (ROS) in tissues.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, Sang Hoon; Kim, Jae Hwan; Yi, Sang Min

Quantum dots (QDs) are rapidly emerging as an important class of nanoparticles (NPs) with potential applications in medicine. However, little is known about penetration of QDs through human skin. This study investigated skin penetration of QDs in both in vivo and in vitro human skin. Using the tape stripping method, this study demonstrates for the first time that QDs can actually penetrate through the stratum corneum (SC) of human skin. Transmission electron microscope (TEM) and energy diverse X-ray (EDX) analysis showed accumulation of QDs in the SC of a human skin equivalent model (HSEM) after dermal exposure to QDs. Thesemore » findings suggest possible transdermal absorption of QDs after dermal exposure over a relatively long period of time.« less

Control of Electronic Structures and Phonon Dynamics in Quantum Dot Superlattices by Manipulation of Interior Nanospace.

PubMed

Chang, I-Ya; Kim, DaeGwi; Hyeon-Deuk, Kim

2016-07-20

Quantum dot (QD) superlattices, periodically ordered array structures of QDs, are expected to provide novel photo-optical functions due to their resonant couplings between adjacent QDs. Here, we computationally demonstrated that electronic structures and phonon dynamics of a QD superlattice can be effectively and selectively controlled by manipulating its interior nanospace, where quantum resonance between neighboring QDs appears, rather than by changing component QD size, shape, compositions, etc. A simple H-passivated Si QD was examined to constitute one-, two-, and three-dimensional QD superlattices, and thermally fluctuating band energies and phonon modes were simulated by finite-temperature ab initio molecular dynamics (MD) simulations. The QD superlattice exhibited a decrease in the band gap energy enhanced by thermal modulations and also exhibited selective extraction of charge carriers out of the component QD, indicating its advantage as a promising platform for implementation in solar cells. Our dynamical phonon analyses based on the ab initio MD simulations revealed that THz-frequency phonon modes were created by an inter-QD crystalline lattice formed in the QD superlattice, which can contribute to low energy thermoelectric conversion and will be useful for direct observation of the dimension-dependent superlattice. Further, we found that crystalline and ligand-originated phonon modes inside each component QD can be independently controlled by asymmetry of the superlattice and by restriction of the interior nanospace, respectively. Taking into account the thermal effects at the finite temperature, we proposed guiding principles for designing efficient and space-saving QD superlattices to develop functional photovoltaic and thermoelectric devices.

Fluorescence Quenching of CdSe/ZnS Quantum Dots by Using Black Hole Quencher Molecules Intermediated With Peptide for Biosensing Application.

PubMed

Pillai, Sreenadh Sasidharan; Yukawa, Hiroshi; Onoshima, Daisuke; Biju, Vasudevanpillai; Baba, Yoshinobu

2015-12-17

Quantum dots (QDs) have recently been investigated as fluorescent probes for detecting a very small number of biomolecules and live cells; however, the establishment of molecular imaging technology with on-off control of QD fluorescence remains to be established. Here we have achieved the fluorescence off state of QDs with the conjugation of black hole quencher (BHQ) molecules intermediated with peptide by using streptavidin-QDs585 and biotin-pep-BHQ-1. The fluorescence of streptavidin-QDs585 was decreased by the addition of biotin-pep-BHQ-1 in a dose-dependent manner. It has been suggested that the decrease in QDs585 fluorescence occurred through a Förster resonance energy transfer (FRET) mechanism from the analysis of fluorescence intensity and lifetime of streptavidin-QDs585 and QDs585-pep-BHQ-1. QDs585 fluorescence could be quenched by more than 60% efficiency in this system. The sequence of intermediate peptide (pep) was GPLGVRGK, which can be cleaved by matrix metalloproteinases (MMPs) produced by cancer cells. QDs585-pep-BHQ-1 is thus expected to detect the MMP production by the recovery of QDs585 fluorescence as a new bioanalytical agent for molecular imaging.

Spectroscopic investigations on the effect of N-Acetyl-L-cysteine-Capped CdTe Quantum Dots on catalase

NASA Astrophysics Data System (ADS)

Sun, Haoyu; Yang, Bingjun; Cui, Erqian; Liu, Rutao

2014-11-01

Quantum dots (QDs) are recognized as some of the most promising semiconductor nanocrystals in biomedical applications. However, the potential toxicity of QDs has aroused wide public concern. Catalase (CAT) is a common enzyme in animal and plant tissues. For the potential application of QDs in vivo, it is important to investigate the interaction of QDs with CAT. In this work, the effect of N-Acetyl-L-cysteine-Capped CdTe Quantum Dots with fluorescence emission peak at 612 nm (QDs-612) on CAT was investigated by fluorescence, synchronous fluorescence, fluorescence lifetime, ultraviolet-visible (UV-vis) absorption and circular dichroism (CD) techniques. Binding of QDs-612 to CAT caused static quenching of the fluorescence, the change of the secondary structure of CAT and the alteration of the microenvironment of tryptophan residues. The association constants K were determined to be K288K = 7.98 × 105 L mol-1 and K298K = 7.21 × 105 L mol-1. The interaction between QDs-612 and CAT was spontaneous with 1:1 stoichiometry approximately. The CAT activity was also inhibited for the bound QDs-612. This work provides direct evidence about enzyme toxicity of QDs-612 to CAT in vitro and establishes a new strategy to investigate the interaction between enzyme and QDs at a molecular level, which is helpful for clarifying the bioactivities of QDs in vivo.

Systematical investigation of in vitro interaction of InP/ZnS quantum dots with human serum albumin by multispectroscopic approach.

PubMed

Huang, Shan; Qiu, Hangna; Liu, Yi; Huang, Chusheng; Sheng, Jiarong; Cui, Jianguo; Su, Wei; Xiao, Qi

2016-12-01

Cadmium-free quantum dots (QDs) have attracted great attention in biological and biomedical applications due to their less content of toxic metals, but their potential toxicity investigations on molecular biology level are rarely involved. Since few studies have addressed whether InP/ZnS QDs could bind and alter the structure and function of human serum albumin (HSA), in vitro interaction between InP/ZnS QDs and HSA was systematically characterized by multispectroscopic approaches. InP/ZnS QDs could quench the intrinsic fluorescence of HSA via static mode. The binding site of InP/ZnS QDs was mainly located at subdomain IIA of HSA. Some thermodynamic parameters suggested that InP/ZnS QDs interacted with HSA mainly through electrostatic interactions. As further revealed by three-dimensional spectrometry, FT-IR spectrometry and circular dichroism technique, InP/ZnS QDs caused more global and local conformational change of HSA than CdSe/ZnS QDs, which illustrated the stronger binding interaction and higher potential toxicity of InP/ZnS QDs on biological function of HSA. Our results offer insights into the in vitro binding mechanism of InP/ZnS QDs with HSA and provide important information for possible toxicity risk of these cadmium-free QDs to human health. Copyright © 2016 Elsevier B.V. All rights reserved.

Synthesis and characterization of P-doped amorphous and nanocrystalline Si

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jialing; Ganguly, Shreyashi; Sen, Sabyasachi

Intentional impurity doping lies at the heart of the silicon technology. The dopants provide electrons or holes as necessary carriers of the electron current and can significantly modify the electric, optical and magnetic properties of the semiconductors. P-doped amorphous Si (a-Si) was prepared by a solid state and solution metathesis reaction of a P-doped Zintl phase precursor, NaSi 0.99P 0.01, with an excess of NH 4X (X = Br, I). After the salt byproduct was removed from the solid state reaction, the a-Si material was annealed at 600 °C under vacuum for 2 h, resulting in P-doped nanocrystalline Si (nc-Si)more » material embedded in a-Si matrix. The product from the solution reaction also shows a combination of nc-Si embedded in a-Si; however, it was fully converted to nc-Si after annealing under argon at 650 °C for 30 min. Powder X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) show the amorphous nature of the P-doped Si material before the annealing and the nanocrystallinity after the annealing. Fourier Transform Infrared (FTIR) spectroscopy shows that the P-doped Si material surface is partially capped by H and O or with solvent. Finally, electron microprobe wavelength dispersive spectroscopy (WDS) as well as energy dispersive spectroscopy (EDS) confirm the presence of P in the Si material. 29Si and 31P solid state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy data provide the evidence of P doping into the Si structure with the P concentration of approximately 0.07 at.%.« less

Semiconductor Quantum Dots for Bioimaging and Biodiagnostic Applications

NASA Astrophysics Data System (ADS)

Kairdolf, Brad A.; Smith, Andrew M.; Stokes, Todd H.; Wang, May D.; Young, Andrew N.; Nie, Shuming

2013-06-01

Semiconductor quantum dots (QDs) are light-emitting particles on the nanometer scale that have emerged as a new class of fluorescent labels for chemical analysis, molecular imaging, and biomedical diagnostics. Compared with traditional fluorescent probes, QDs have unique optical and electronic properties such as size-tunable light emission, narrow and symmetric emission spectra, and broad absorption spectra that enable the simultaneous excitation of multiple fluorescence colors. QDs are also considerably brighter and more resistant to photobleaching than are organic dyes and fluorescent proteins. These properties are well suited for dynamic imaging at the single-molecule level and for multiplexed biomedical diagnostics at ultrahigh sensitivity. Here, we discuss the fundamental properties of QDs; the development of next-generation QDs; and their applications in bioanalytical chemistry, dynamic cellular imaging, and medical diagnostics. For in vivo and clinical imaging, the potential toxicity of QDs remains a major concern. However, the toxic nature of cadmium-containing QDs is no longer a factor for in vitro diagnostics, so the use of multicolor QDs for molecular diagnostics and pathology is probably the most important and clinically relevant application for semiconductor QDs in the immediate future.

Semiconductor quantum dots for bioimaging and biodiagnostic applications.

PubMed

Kairdolf, Brad A; Smith, Andrew M; Stokes, Todd H; Wang, May D; Young, Andrew N; Nie, Shuming

2013-01-01

Semiconductor quantum dots (QDs) are light-emitting particles on the nanometer scale that have emerged as a new class of fluorescent labels for chemical analysis, molecular imaging, and biomedical diagnostics. Compared with traditional fluorescent probes, QDs have unique optical and electronic properties such as size-tunable light emission, narrow and symmetric emission spectra, and broad absorption spectra that enable the simultaneous excitation of multiple fluorescence colors. QDs are also considerably brighter and more resistant to photobleaching than are organic dyes and fluorescent proteins. These properties are well suited for dynamic imaging at the single-molecule level and for multiplexed biomedical diagnostics at ultrahigh sensitivity. Here, we discuss the fundamental properties of QDs; the development of next-generation QDs; and their applications in bioanalytical chemistry, dynamic cellular imaging, and medical diagnostics. For in vivo and clinical imaging, the potential toxicity of QDs remains a major concern. However, the toxic nature of cadmium-containing QDs is no longer a factor for in vitro diagnostics, so the use of multicolor QDs for molecular diagnostics and pathology is probably the most important and clinically relevant application for semiconductor QDs in the immediate future.

Semiconductor Quantum Dots for Bioimaging and Biodiagnostic Applications

PubMed Central

Kairdolf, Brad A.; Smith, Andrew M.; Stokes, Todd H.; Wang, May D.; Young, Andrew N.; Nie, Shuming

2013-01-01

Semiconductor quantum dots (QDs) are light-emitting particles on the nanometer scale that have emerged as a new class of fluorescent labels for chemical analysis, molecular imaging, and biomedical diagnostics. Compared with traditional fluorescent probes, QDs have unique optical and electronic properties such as size-tunable light emission, narrow and symmetric emission spectra, and broad absorption spectra that enable the simultaneous excitation of multiple fluorescence colors. QDs are also considerably brighter and more resistant to photobleaching than are organic dyes and fluorescent proteins. These properties are well suited for dynamic imaging at the single-molecule level and for multiplexed biomedical diagnostics at ultrahigh sensitivity. Here, we discuss the fundamental properties of QDs; the development of next-generation QDs; and their applications in bioanalytical chemistry, dynamic cellular imaging, and medical diagnostics. For in vivo and clinical imaging, the potential toxicity of QDs remains a major concern. However, the toxic nature of cadmium-containing QDs is no longer a factor for in vitro diagnostics, so the use of multicolor QDs for molecular diagnostics and pathology is probably the most important and clinically relevant application for semiconductor QDs in the immediate future. PMID:23527547

Surface Passivation of CdSe Quantum Dots in All Inorganic Amorphous Solid by Forming Cd1-xZnxSe Shell.

PubMed

Xia, Mengling; Liu, Chao; Zhao, Zhiyong; Wang, Jing; Lin, Changgui; Xu, Yinsheng; Heo, Jong; Dai, Shixun; Han, Jianjun; Zhao, Xiujian

2017-02-07

CdSe quantum dots (QDs) doped glasses have been widely investigated for optical filters, LED color converter and other optical emitters. Unlike CdSe QDs in solution, it is difficult to passivate the surface defects of CdSe QDs in glass matrix, which strongly suppress its intrinsic emission. In this study, surface passivation of CdSe quantum dots (QDs) by Cd 1-x Zn x Se shell in silicate glass was reported. An increase in the Se/Cd ratio can lead to the partial passivation of the surface states and appearance of the intrinsic emission of CdSe QDs. Optimizing the heat-treatment condition promotes the incorporation of Zn into CdSe QDs and results in the quenching of the defect emission. Formation of CdSe/Cd 1-x Zn x Se core/graded shell QDs is evidenced by the experimental results of TEM and Raman spectroscopy. Realization of the surface passivation and intrinsic emission of II-VI QDs may facilitate the wide applications of QDs doped all inorganic amorphous materials.

Erbium Doped Quantum Dot and Si:O and Plasmon Resonance Enabled Quantum Dot Nanoscale Lasers

DTIC Science & Technology

2009-08-31

electroluminescence has to be coupled with a high-Q cavity for lasing. Alq3 PEDOT:PSS ITO — • MEHPPV +PbSe QDs . • •A iz^————— Gold (Au...PEDOT:PSS on the ITO anode and Alq3 /Ca/Al cathode. The inset is a SEM image of the L3 defect photonic crystal microcavity in silicon. Outer air holes at...consisting of tris(8-hydroxyquinoline)aluminum ( Alq3 ), calcium, and aluminum. The device heterostructure is schematically shown in Fig. 5(a). The ITO

Thermally Stable Silver Nanowires-Embedding Metal Oxide for Schottky Junction Solar Cells.

PubMed

Kim, Hong-Sik; Patel, Malkeshkumar; Park, Hyeong-Ho; Ray, Abhijit; Jeong, Chaehwan; Kim, Joondong

2016-04-06

Thermally stable silver nanowires (AgNWs)-embedding metal oxide was applied for Schottky junction solar cells without an intentional doping process in Si. A large scale (100 mm(2)) Schottky solar cell showed a power conversion efficiency of 6.1% under standard illumination, and 8.3% under diffused illumination conditions which is the highest efficiency for AgNWs-involved Schottky junction Si solar cells. Indium-tin-oxide (ITO)-capped AgNWs showed excellent thermal stability with no deformation at 500 °C. The top ITO layer grew in a cylindrical shape along the AgNWs, forming a teardrop shape. The design of ITO/AgNWs/ITO layers is optically beneficial because the AgNWs generate plasmonic photons, due to the AgNWs. Electrical investigations were performed by Mott-Schottky and impedance spectroscopy to reveal the formation of a single space charge region at the interface between Si and AgNWs-embedding ITO layer. We propose a route to design the thermally stable AgNWs for photoelectric device applications with investigation of the optical and electrical aspects.

Single-photon sources based on InAs/GaAs QDs for solar cell

NASA Astrophysics Data System (ADS)

Jia, Wei; Liu, Zhi; Wang, Xunchun

2013-08-01

We have grown InAs/GaAs quantum dots (QDs) by droplet epitaxy for application in single photon sources. This growth method enables the formation of QDs without strain, with emission wavelengths of around 1.3μm within the optimal detection range of cost effective silicon detector, and with reduced surface density of several tens to a few QDs per μm2 for easier isolation of single QDs. The optical properties of QDs were envisaged by exciton and biexciton emission peaks identified from power dependent and time-resolved micro-photoluminescence (μ-PL) measurements.

Low-toxic Mn-doped ZnSe@ZnS quantum dots conjugated with nano-hydroxyapatite for cell imaging

NASA Astrophysics Data System (ADS)

Zhou, Ronghui; Li, Mei; Wang, Shanling; Wu, Peng; Wu, Lan; Hou, Xiandeng

2014-11-01

Fluorescent bio-imaging has received significant attention in a myriad of research disciplines, and QDs are playing an increasingly important role in these areas. Doped QDs, an important alternative to conventional heavy metal-containing QDs are employed for biomedical applications. However, since QDs are exogenous substances to the biological environment, the biocompatibility of QDs is expected to be challenging in some cases. Herein, nano fluorine-doped hydroxyapatite (FAp, a well-known biocompatible material) was introduced to endow biocompatibility to Cd-free Mn-doped ZnSe@ZnS QDs. Thus, a nano-FAp-QD conjugate was developed and the biocompatibility, as well as potential cell imaging application, was investigated. To construct the proposed conjugate, Cd-free highly luminescent Mn-doped ZnSe@ZnS QDs and monodispersed nano-FAp were first prepared in high-temperature organic media. For facilitating the conjugation, hydrophobic nano-FAp was made water soluble via o-phosphoethanolamine (PEA) coating, which further provides conjugating sites for QDs to anchor. Cytotoxicity studies indicated the developed conjugate indeed possesses good compatibility and low toxicity to cells. The nano-FAp-QDs conjugate was successfully employed for cancer cell staining for at least 24 h, demonstrating the potential usefulness of this material in future biomedical research.Fluorescent bio-imaging has received significant attention in a myriad of research disciplines, and QDs are playing an increasingly important role in these areas. Doped QDs, an important alternative to conventional heavy metal-containing QDs are employed for biomedical applications. However, since QDs are exogenous substances to the biological environment, the biocompatibility of QDs is expected to be challenging in some cases. Herein, nano fluorine-doped hydroxyapatite (FAp, a well-known biocompatible material) was introduced to endow biocompatibility to Cd-free Mn-doped ZnSe@ZnS QDs. Thus, a nano-FAp-QD conjugate was developed and the biocompatibility, as well as potential cell imaging application, was investigated. To construct the proposed conjugate, Cd-free highly luminescent Mn-doped ZnSe@ZnS QDs and monodispersed nano-FAp were first prepared in high-temperature organic media. For facilitating the conjugation, hydrophobic nano-FAp was made water soluble via o-phosphoethanolamine (PEA) coating, which further provides conjugating sites for QDs to anchor. Cytotoxicity studies indicated the developed conjugate indeed possesses good compatibility and low toxicity to cells. The nano-FAp-QDs conjugate was successfully employed for cancer cell staining for at least 24 h, demonstrating the potential usefulness of this material in future biomedical research. Electronic supplementary information (ESI) available: Experimental details. See DOI: 10.1039/c4nr04473h

Schottky junction interfacial properties at high temperature: A case of AgNWs embedded metal oxide/p-Si

NASA Astrophysics Data System (ADS)

Mahala, Pramila; Patel, Malkeshkumar; Gupta, Navneet; Kim, Joondong; Lee, Byung Ha

2018-05-01

Studying the performance limiting parameters of the Schottky device is an urgent issue, which are addressed herein by thermally stable silver nanowire (AgNW) embedded metal oxide/p-Si Schottky device. Temperature and bias dependent junction interfacial properties of AgNW-ITO/Si Schottky photoelectric device are reported. The current-voltage-temperature (I-V-T), capacitance-voltage-temperature (C-V-T) and impedance analysis have been carried out in the high-temperature region. The ideality factor and barrier height of Schottky junction are assessed using I-V-T characteristics and thermionic emission, to reveal the decrease of ideality factor and increase of barrier height by the increasing of temperature. The extracted values of laterally homogeneous Schottky (ϕb) and ideality factor (n) are approximately 0.73 eV and 1.58, respectively. Series resistance (Rs) assessed using Cheung's method and found that it decreases with the increase of temperature. A linear response of Rs of AgNW-ITO/Si Schottky junction is observed with respect to change in forward bias, i.e. dRS/dV from 0 to 0.7 V is in the range of 36.12-36.43 Ω with a rate of 1.44 Ω/V. Impedance spectroscopy is used to study the effect of bias voltage and temperature on intrinsic Schottky properties which are responsible for photoconversion efficiency. These systematic analyses are useful for the AgNWs-embedding Si solar cells or photoelectrochemical cells.

Wide emission-tunable CdTeSe/ZnSe/ZnS core–shell quantum dots and their conjugation with E. coli O-157

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Haifeng; Zhou, Guangjun, E-mail: gjzhou@sdu.edu.cn; Zhou, Juan

2015-05-15

Highlights: • QDs with variety morphology were obtained via an injection controlled process. • 3-D PL spectra of core–shell QDs show different excitation wavelength dependence. • The PL intensity of QDs with ZnSe transition layer increases dramatically. • Core–shell QDs were processed into aqueous phase and conjugated with E. coli O-157. - Abstract: Wide emission-tunable and different morphological alloyed CdTeSe quantum dots (QDs), CdTeSe/ZnS and CdTeSe/ZnSe/ZnS core–shell QDs were successfully synthesized via an injection controlled process. The effect of injection procedure and reaction temperature were systematically discussed and the growth mechanism was proposed. Most efficient PL wavelength was correlated withmore » reaction time and temperature. The 3-D PL spectra of spherical bare CdTeSe and core–shell QDs with different passivation showed different excitation wavelength dependency. The PL intensity of CdTeSe/ZnSe/ZnS core–shell QDs increased greatly in comparison with that of CdTeSe and CdTeSe/ZnSe QDs. ZnSe transition layer played an important role in improving the PL intensity by providing a smoothened interface and gradient band offsets. The core–shell QDs were transferred into aqueous phase and successfully conjugated with Escherichia coli O-157. The proposed phase-transfer and bio-labeling strategy may be applicable to various QDs with different compositions.« less

An analysis of the specificity of defects embedded into (1 0 0) and (1 1 1) faceted CVD diamond microcrystals grown on Si and Mo substrates by using E/H field discharge

NASA Astrophysics Data System (ADS)

Nasieka, Iurii; Strelchuk, Victor; Naseka, Victor; Stubrov, Yuriy; Dudnik, Stanislav; Gritsina, Vasiliy; Opalev, Oleg; Koshevoy, Konstantin; Strel'nitskij, Vladimir; Tkach, Vasyl; Boyko, Mykola; Antypov, Ievgen

2018-06-01

The PE CVD method with magnetic field discharge stabilization was applied for the growth of arrays of freestanding diamond grains (island films) as well as continuous films on Mo and Si substrates with (1 1 1) and (1 0 0) faceted microcrystals, respectively. Raman, SEM, XRD and PL methods were used for search of the specific features of defects embedded into (1 0 0) and (1 1 1) faceted grains. The main characteristic differences in the defect states of the diamond island films grown on Si and Mo substrates with (1 0 0) and (1 1 1) faceted diamond microcrystals were discussed on the base of the experimental data.

Misalignment tolerant efficient inverse taper coupler for silicon waveguide

NASA Astrophysics Data System (ADS)

Wang, Peng; Michael, Aron; Kwok, Chee Yee; Chen, Ssu-Han

2015-12-01

This paper describes an efficient fiber to submicron silicon waveguide coupling based on an inversely tapered silicon waveguide embedded in a SiO2 waveguide that is suspended in air. The inverse taper waveguide consist of a 50um long and 240nm thick silicon that linearly taper in width from 500nm to 120nm, which is embedded in SiO2. The SiO2 waveguide is 6um wide and 10um long. The simulation results show that the coupling loss of this new approach is 2.7dB including the interface loss at the input and output. The tolerance to fiber misalignment at the input of the coupler is 2um in both horizontal and vertical directions for only 1.5dB additional loss.

Nanometer scale fabrication and optical response of InGaN/GaN quantum disks

NASA Astrophysics Data System (ADS)

Lai, Yi-Chun; Higo, Akio; Kiba, Takayuki; Thomas, Cedric; Chen, Shula; Lee, Chang Yong; Tanikawa, Tomoyuki; Kuboya, Shigeyuki; Katayama, Ryuji; Shojiki, Kanako; Takayama, Junichi; Yamashita, Ichiro; Murayama, Akihiro; Chi, Gou-Chung; Yu, Peichen; Samukawa, Seiji

2016-10-01

In this work, we demonstrate homogeneously distributed In0.3Ga0.7N/GaN quantum disks (QDs), with an average diameter below 10 nm and a high density of 2.1 × 1011 cm-2, embedded in 20 nm tall nanopillars. The scalable top-down fabrication process involves the use of self-assembled ferritin bio-templates as the etch mask, spin coated on top of a strained In0.3Ga0.7N/GaN single quantum well (SQW) structure, followed by a neutral beam etch (NBE) method. The small dimensions of the iron cores inside ferritin and nearly damage-free process enabled by the NBE jointly contribute to the observation of photoluminescence (PL) from strain-relaxed In0.3Ga0.7N/GaN QDs at 6 K. The large blueshift of the peak wavelength by over 70 nm manifests a strong reduction of the quantum-confined Stark effect (QCSE) within the QD structure, which also agrees well with the theoretical prediction using a 3D Schrödinger equation solver. The current results hence pave the way towards the realization of large-scale III-N quantum structures using the combination of bio-templates and NBE, which is vital for the development of next-generation lighting and communication devices.

Construction of optical glucose nanobiosensor with high sensitivity and selectivity at physiological pH on the basis of organic-inorganic hybrid microgels.

PubMed

Wu, Weitai; Zhou, Ting; Aiello, Michael; Zhou, Shuiqin

2010-08-15

A new class of optical glucose nanobiosensors with high sensitivity and selectivity at physiological pH is described. To construct these glucose nanobiosensors, the fluorescent CdS quantum dots (QDs), serving as the optical code, were incorporated into the glucose-sensitive poly(N-isopropylacrylamide-acrylamide-2-acrylamidomethyl-5-fluorophenylboronic acid) copolymer microgels, via both in situ growth method and "breathing in" method, respectively. The polymeric gel can adapt to surrounding glucose concentrations, and regulate the fluorescence of the embedded QDs, converting biochemical signals into optical signals. The gradual swelling of the gel would lead to the quenching of the fluorescence at the elevated glucose concentrations. The hybrid microgels displayed high selectivity to glucose over the potential primary interferents of lactate and human serum albumin in the physiologically important glucose concentration range. The stability, reversibility, and sensitivity of the organic-inorganic hybrid microgel-based biosensors were also systematically studied. These general properties of our nanobiosensors are well tunable under appropriate tailor on the hybrid microgels, in particular, simply through the change in the crosslinking degree of the microgels. The optical glucose nanobiosensors based on the organic-inorganic hybrid microgels have shown the potential for a third generation fluorescent biosensor. Copyright 2010 Elsevier B.V. All rights reserved.

Nanoimprinted High-Refractive Index Active Photonic Nanostructures Based on Quantum Dots for Visible Light

DOE PAGES

Pina-Hernandez, Carlos; Koshelev, Alexander; Dhuey, Scott; ...

2017-12-15

A novel method to realizing printed active photonic devices was developed using nanoimprint lithography (NIL), combining a printable high-refractive index material and colloidal CdSe/CdS quantum dots (QDs) for applications in the visible region. Active media QDs were applied in two different ways: embedded inside a printable high-refractive index matrix to form an active printable hybrid nanocomposite, and used as a uniform coating on top of printed photonic devices. As a proof-of-demonstration for printed active photonic devices, two-dimensional (2-D) photonic crystals as well as 1D and 2D photonic nanocavities were successfully fabricated following a simple reverse-nanoimprint process. We observed enhanced photoluminescencemore » from the 2D photonic crystal and the 1D nanocavities. Outstandingly, the process presented in this study is fully compatible with large-scale manufacturing where the patterning areas are only limited by the size of the corresponding mold. This work shows that the integration of active media and functional materials is a promising approach to the realization of integrated photonics for visible light using high throughput technologies. We believe that this work represents a powerful and cost-effective route for the development of numerous nanophotonic structures and devices that will lead to the emergence of new applications.« less

Facile synthesis of mercaptosuccinic acid-capped CdTe/CdS/ZnS core/double shell quantum dots with improved cell viability on different cancer cells and normal cells

NASA Astrophysics Data System (ADS)

Parani, Sundararajan; Bupesh, Giridharan; Manikandan, Elayaperumal; Pandian, Kannaiyan; Oluwafemi, Oluwatobi Samuel

2016-11-01

Water-soluble, mercaptosuccinic acid (MSA)-capped CdTe/CdS/ZnS core/double shell quantum dots (QDs) were prepared by successive growth of CdS and ZnS shells on the as-synthesized CdTe/CdSthin core/shell quantum dots. The formation of core/double shell structured QDs was investigated by ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectroscopy, PL decay studies, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The core/double shell QDs exhibited good photoluminescence quantum yield (PLQY) which is 70% higher than that of the parent core/shell QDs, and they are stable for months. The average particle size of the core/double shell QDs was ˜3 nm as calculated from the transmission electron microscope (TEM) images. The cytotoxicity of the QDs was evaluated on a variety of cancer cells such as HeLa, MCF-7, A549, and normal Vero cells by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell viability assay. The results showed that core/double shell QDs were less toxic to the cells when compared to the parent core/shell QDs. MCF-7 cells showed proliferation on incubation with QDs, and this is attributed to the metalloestrogenic activity of cadmium ions released from QDs. The core/double shell CdTe/CdS/ZnS (CSS) QDs were conjugated with transferrin and successfully employed for the biolabeling and fluorescent imaging of HeLa cells. These core/double shell QDs are highly promising fluorescent probe for cancer cell labeling and imaging applications.

Synthesis, biological targeting and photophysics of quantum dots

NASA Astrophysics Data System (ADS)

Clarke, Samuel Jon

Quantum dots (QDs) are inorganic nanoparticles that have exceptional optical properties. Currently, QDs have failed to reach their potential as fluorescent probes in live cells, due to the nontrivial requirements for biological interfacing. The goal of this thesis is to address technical hurdles related to the reproducible synthesis of QDs, strategies for the specific targeting of QDs to biological cells and to understanding and exploitation of the photophysical properties. High quality QDs of varying composition (CdSe, CdTe and core/shell CdSe/ZnS) were synthesized with an organometallic method. To prepare biocompatible QDs, three strategies were used. The simplest strategy used small mercaptocarboxylic acids, while performance improvements were realized with engineered-peptide and lipid-micelle coatings. For specific biological targeting of the QDs, conjugation strategies were devised to attach biomolecules, while spectroscopic characterization methods were developed to assess conjugation efficiencies. To target gram-negative bacterial cells, an electrostatic self-assembly method was used to attach an antibiotic selective for this class of bacteria, polymyxin B. To target dopamine neurotransmitter receptor, a covalent conjugation method was used to attach dopamine, the endogenous ligand for that receptor. It was shown that dopamine molecule enabled electron transfer to QDs and the photophysics was studied in detail. A novel conjugation and targeting strategy was explored to enable the selective binding of QDs to polyhistidine epitopes on membrane proteins. Epifluorescence microscopy was used to evaluate the biological activity of the three QD probes. Combined, they add to the QD 'toolkit' for live-cell imaging. Finally, due to its negative implications in biological imaging, the fluorescent intermittency (blinking) of CdTe QDs was investigated. It was shown that mercaptocarboxylic acids contribute to the blinking suppression of the QDs, results that may aid in the design of nonblinking QDs. Overall, these findings should be useful in the future design of QDs for biological imaging and biosensing applications.

Fluorescent quantum dot hydrophilization with PAMAM dendrimer

NASA Astrophysics Data System (ADS)

Potapkin, Dmitry V.; Geißler, Daniel; Resch-Genger, Ute; Goryacheva, Irina Yu.

2016-05-01

Polyamidoamine (PAMAM) dendrimers were used to produce CdSe core/multi-shell fluorescent quantum dots (QDs) which are colloidally stable in aqueous solutions. The size, charge, and optical properties of QDs functionalized with the 4th (G4) and 5th (G5) generation of PAMAM were compared with amphiphilic polymer-covered QDs and used as criteria for the evaluation of the suitability of both water solubilization methods. As revealed by dynamic and electrophoretic light scattering (DLS and ELS), the hydrodynamic sizes of the QDs varied from 30 to 65 nm depending on QD type and dendrimer generation, with all QDs displaying highly positive surface charges, i.e., zeta potentials of around +50 mV in water. PAMAM functionalization yielded stable core/multi-shell QDs with photoluminescence quantum yields ( Φ) of up to 45 %. These dendrimer-covered QDs showed a smaller decrease in their Φ upon phase transfer compared with QDs made water soluble via encapsulation with amphiphilic brush polymer bearing polyoxyethylene/polyoxypropylene chains.

Studying the influence of substrate conductivity on the optoelectronic properties of quantum dots langmuir monolayer

NASA Astrophysics Data System (ADS)

Al-Alwani, Ammar J.; Chumakov, A. S.; Begletsova, N. N.; Shinkarenko, O. A.; Markin, A. V.; Gorbachev, I. A.; Bratashov, D. N.; Gavrikov, M. V.; Venig, S. B.; Glukhovskoy, E. G.

2018-04-01

The formation of CdSe quantum dots (QDs) monolayers was studied by Langmuir Blodgett method. The fluorescence (PL) spectra of QD monolayers were investigated at different substrate type (glass, silicon and ITO glass) and the influence of graphene sheets layer (as a conductive surface) on the QDs properties has also been studied. The optoelectronic properties of QDs can be tuned by deposition of insulating nano-size layers of the liquid crystal between QDs and conductive substrate. The monolayer of QDs transferred on conductive surface (glass with ITO) has lowest intensity of PL spectra due to quenching effect. The PL intensity of QDs could be tuned by using various type of substrates or/and by transformed high conductive layer. Also the photooxidation processes of CdSe QDs monolayer on the solid surface can be controlled by selection of suitable substrate. The current-voltage (I–V) characteristics of QDs thin film on ITO surface was studied using scanning tunneling microscope (STM).

Highly efficient multifunctional MnSe/ZnSeS quantum dots for biomedical applications

NASA Astrophysics Data System (ADS)

Armijo, Leisha M.; Akins, Brian A.; Plumley, John B.; Rivera, Antonio C.; Withers, Nathan J.; Cook, Nathaniel C.; Smolyakov, Gennady A.; Huber, Dale L.; Smyth, Hugh D. C.; Osińki, Marek

2013-03-01

Colloidal quantum dots (QDs) are of interest for a variety of biomedical applications, including bioimaging, drug targeting, and photodynamic therapy. However, a significant limitation is that highly efficient photoluminescent QDs available commercially contain cadmium. Recent research has focused on cadmium-free QDs, which are anticipated to exhibit significantly lower cytotoxicity. Previous work has focused on InP and ZnO as alternative semiconductor materials for QDs. However, these nanoparticles have been shown to be cytotoxic. Recently, we have synthesized high quantum efficiency (exceeding 90%), color tunable MnSe/ZnSeS nanoparticles, as potentially attractive QDs for biomedical applications. Additionally, the manganese imparts magnetic properties on the QDs, which are important for magnetic field-guided transport, hyperthermia, and potentially magnetic resonance imaging (MRI). The QDs can be further biofunctionalized via conjugation to a ligand or a biomarker of disease, allowing combination of drug delivery with visual verification and colocalization due to the color tunability of the QDs.

Half-life of {sup 221}Fr in Si and Au at 4 K and at millikelvin temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wauters, F.; Breitenfeldt, M.; De Leebeeck, V.

2010-12-15

The half-life of the {alpha}-decaying nucleus {sup 221}Fr was determined in different environments, that is, embedded in Si at 4 K, and embedded in Au at 4 K and about 20 mK. No differences in half-life for these different conditions were observed within 0.1%. Furthermore, we quote a value for the absolute half-life of {sup 221}Fr of t{sub 1/2}=286.1(10) s that is of comparable precision to the most precise value available in the literature.

NIR-light-induced surface-enhanced Raman scattering for detection and photothermal/photodynamic therapy of cancer cells using methylene blue-embedded gold nanorod@SiO2 nanocomposites

PubMed Central

Seo, Sun-Hwa; Kim, Bo-Mi; Joe, Ara; Han, Hyo-Won; Chen, Xiaoyuan; Cheng, Zhen; Jang, Eue-Soon

2015-01-01

Methylene blue-loaded gold nanorod@SiO2 (MB-GNR@SiO2) core@shell nanoparticles are synthesized for use in cancer imaging and photothermal/photodynamic dual therapy. For the preparation of GNR@SiO2 nanoparticles, we found that the silica coating rate of hexadecylcetyltrimethylammonium bromide (CTAB)-capped GNRs is much slower than that of PEGylated GNRs due to the densely coated CTAB bilayer. Encapsulated MB molecules have both monomer and dimer forms that result in an increase in the photosensitizing effect through different photochemical pathways. As a consequence of the excellent plasmonic properties of GNRs at near-infrared (NIR) light, the embedded MB molecules showed NIR light-induced SERS performance with a Raman enhancement factor of 3.0 × 1010, which is enough for the detection of a single cancer cell. Moreover, the MB-GNR@SiO2 nanoparticles exhibit a synergistic effect of photodynamic and photothermal therapies of cancer under single-wavelength NIR laser irradiation. PMID:24424205

NIR-light-induced surface-enhanced Raman scattering for detection and photothermal/photodynamic therapy of cancer cells using methylene blue-embedded gold nanorod@SiO2 nanocomposites.

PubMed

Seo, Sun-Hwa; Kim, Bo-Mi; Joe, Ara; Han, Hyo-Won; Chen, Xiaoyuan; Cheng, Zhen; Jang, Eue-Soon

2014-03-01

Methylene blue-loaded gold nanorod@SiO2 (MB-GNR@SiO2) core@shell nanoparticles are synthesized for use in cancer imaging and photothermal/photodynamic dual therapy. For the preparation of GNR@SiO2 nanoparticles, we found that the silica coating rate of hexadecylcetyltrimethylammonium bromide (CTAB)-capped GNRs is much slower than that of PEGylated GNRs due to the densely coated CTAB bilayer. Encapsulated MB molecules have both monomer and dimer forms that result in an increase in the photosensitizing effect through different photochemical pathways. As a consequence of the excellent plasmonic properties of GNRs at near-infrared (NIR) light, the embedded MB molecules showed NIR light-induced SERS performance with a Raman enhancement factor of 3.0 × 10(10), which is enough for the detection of a single cancer cell. Moreover, the MB-GNR@SiO2 nanoparticles exhibit a synergistic effect of photodynamic and photothermal therapies of cancer under single-wavelength NIR laser irradiation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Characterization of Silicon Nanoparticles Formed from a Fluidized Bed Reactor and Their Incorporation onto Metal-Coated Carbon Fibers

NASA Astrophysics Data System (ADS)

Zbib, Mohamad B.; Sahaym, Uttara; Bahr, David F.

2014-01-01

Enhancing the light trapping using nonwoven arrays of fibers has the potential to improve the photocurrent of silicon solar cells. In this work, amorphous and crystalline Si nanopowders (30-300 nm) were embedded in carbon fibers and fixed in place with electrodeposited nickel. Scanning and transmission electron microscopy techniques have been used to study the morphology of the Si particles and their interactions with the coatings. Two types of nanoparticles are identified, homogeneous nucleated particles (amorphous particles with some crystalline regions) and attrition particles (mostly crystalline products formed from fracture of particles as they grow in a fluidized bed reactor). Using the Brunauer-Emmett-Teller (BET) technique, the surface area and the pore diameter of these agglomerated Si nanoparticles were calculated to be 6.4 m2/g and 9.8 nm, respectively. After embedding the Si particles into the carbon matrix with the metal coatings, the electrical resistivity decreases, suggesting it is possible to enhance the light extraction of silicon solar cells using Si nanoparticles.

Controllable Self-Assembly of Micro-Nanostructured Si-Embedded Graphite/Graphene Composite Anode for High-Performance Li-Ion Batteries.

PubMed

Lin, Ning; Xu, Tianjun; Li, Tieqiang; Han, Ying; Qian, Yitai

2017-11-15

Si-containing graphite-based composites are considered as promising high-capacity anodes for lithium-ion batteries (LIBs). Here, a controllable and scalable self-assembly strategy is developed to produce micro-nanostructured graphite/Si/reduced graphene oxides composite (SGG). The self-assembly procedure is realized by the hydrogen bond interaction between acylamino-modified graphite and graphene oxides (GO); Si nanoparticles are in situ embedded between graphite and GO sheets uniformly. This architecture is able to overcome the incompatibility between Si nanoparticles and microsized graphite. Accordingly, the as-prepared SGG anode (Si 8 wt %) delivers a reversible Li-storage capacity of 572 mAh g -1 at 0.2 C, 502.2 mAh g -1 after 600 cycles at 0.8 C with a retention of 92%, and a capacity retention of 64% even at 10 C. The impressive electrochemical properties are ascribed to the stable architecture and three-dimensional conductive network constructed by graphite and graphene sheets, which can accommodate the huge volume change of Si, keep the conductive contact and structural integrity, and suppress side reactions with electrolyte. Additionally, the full-cell (LiFePO 4 cathode/SGG anode) delivers a specific capacity of 550 mAh g -1 with a working potential beyond 3.0 V.

Gold nanoparticles deposited on linker-free silicon substrate and embedded in aluminum Schottky contact.

PubMed

Gorji, Mohammad Saleh; Razak, Khairunisak Abdul; Cheong, Kuan Yew

2013-10-15

Given the enormous importance of Au nanoparticles (NPs) deposition on Si substrates as the precursor for various applications, we present an alternative approach to deposit Au NPs on linker-free n- and p-type Si substrates. It is demonstrated that, all conditions being similar, there is a significant difference between densities of the deposited NPs on both substrates. The Zeta-potential and polarity of charges surrounding the hydroxylamine reduced seeded growth Au NPs, are determined by a Zetasizer. To investigate the surface properties of Si substrates, contact angle measurement is performed. Field-emission scanning electron microscope is then utilized to distinguish the NPs density on the substrates. Finally, Al/Si Schottky barrier diodes with embedded Au NPs are fabricated, and their structural and electrical characteristics are further evaluated using an energy-filtered transmission electron microscope and current-voltage measurements, respectively. The results reveal that the density of NPs is significantly higher on n-type Si substrate and consequently has more pronounced effects on the electrical characteristics of the diode. It is concluded that protonation of Si-OH group on Si surface in low pH is responsible for the immobilization of Au NPs, which eventually contributes to the lowering of barrier height and enhances the electrical characteristics. Copyright © 2013 Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mumin, Md Abdul, E-mail: pcharpentier@eng.uwo.ca; Akhter, Kazi Farida, E-mail: pcharpentier@eng.uwo.ca; Charpentier, Paul A., E-mail: pcharpentier@eng.uwo.ca

Semiconductor nanocrystals (NCs) (also known as quantum dots, QDs) have attracted immense attention for their size-tunable optical properties that makes them impressive candidates for solar cells, light emitting devices, lasers, as well as biomedical imaging. However monodispersity, high and consistent photoluminescence, photostability, and biocompatibility are still major challenges. This work focuses on optimizing the photophysical properties and biocompatibility of QDs by forming core-shell nanostructures and their encapsulation by a carrier. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm sizes were synthesized using a facile approach based on pyrolysis of the single molecule precursors. After capping the CdS QDsmore » with a thin layer of ZnS to reduce toxicity, the photoluminescence and photostability of the core-shell QDs was significantly enhanced. To make both the bare and core/shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interaction. This encapsulation enhanced the quantum yield and photostability compared to the bare QDs by providing much stronger resistance to oxidation and Oswald ripening of QDs. Encapsulation also improved biocompatibility of QDs that was evaluated with human umbilical vein endothelial cell lines (HUVEC)« less

Combination of Cation Exchange and Quantized Ostwald Ripening for Controlling Size Distribution of Lead Chalcogenide Quantum Dots

DOE PAGES

Zhang, Changwang; Xia, Yong; Zhang, Zhiming; ...

2017-03-22

A new strategy for narrowing the size distribution of colloidal quantum dots (QDs) was developed by combining cation exchange and quantized Ostwald ripening. Medium-sized reactant CdS(e) QDs were subjected to cation exchange to form the target PbS(e) QDs, and then small reactant CdS(e) QDs were added which were converted to small PbS(e) dots via cation exchange. The small-sized ensemble of PbS(e) QDs dissolved completely rapidly and released a large amount of monomers, promoting the growth and size-focusing of the medium-sized ensemble of PbS(e) QDs. The addition of small reactant QDs can be repeated to continuously reduce the size distribution. Themore » new method was applied to synthesize PbSe and PbS QDs with extremely narrow size distributions and as a bonus they have hybrid surface passivation. In conclusion, the size distribution of prepared PbSe and PbS QDs are as low as 3.6% and 4.3%, respectively, leading to hexagonal close packing in monolayer and highly ordered three-dimensional superlattice.« less

Continuous Purification of Colloidal Quantum Dots in Large-Scale Using Porous Electrodes in Flow Channel.

PubMed

Lim, Hosub; Woo, Ju Young; Lee, Doh C; Lee, Jinkee; Jeong, Sohee; Kim, Duckjong

2017-02-27

Colloidal quantum dots (QDs) afford huge potential in numerous applications owing to their excellent optical and electronic properties. After the synthesis of QDs, separating QDs from unreacted impurities in large scale is one of the biggest issues to achieve scalable and high performance optoelectronic applications. Thus far, however, continuous purification method, which is essential for mass production, has rarely been reported. In this study, we developed a new continuous purification process that is suitable to the mass production of high-quality QDs. As-synthesized QDs are driven by electrophoresis in a flow channel and captured by porous electrodes and finally separated from the unreacted impurities. Nuclear magnetic resonance and ultraviolet/visible/near-infrared absorption spectroscopic data clearly showed that the impurities were efficiently removed from QDs with the purification yield, defined as the ratio of the mass of purified QDs to that of QDs in the crude solution, up to 87%. Also, we could successfully predict the purification yield depending on purification conditions with a simple theoretical model. The proposed large-scale purification process could be an important cornerstone for the mass production and industrial use of high-quality QDs.

Continuous Purification of Colloidal Quantum Dots in Large-Scale Using Porous Electrodes in Flow Channel

NASA Astrophysics Data System (ADS)

Lim, Hosub; Woo, Ju Young; Lee, Doh Chang; Lee, Jinkee; Jeong, Sohee; Kim, Duckjong

2017-11-01

Colloidal Quantum dots (QDs) afford huge potential in numerous applications owing to their excellent optical and electronic properties. After the synthesis of QDs, separating QDs from unreacted impurities in large scale is one of the biggest issues to achieve scalable and high performance optoelectronic applications. Thus far, however, continuous purification method, which is essential for mass production, has rarely been reported. In this study, we developed a new continuous purification process that is suitable to the mass production of high-quality QDs. As-synthesized QDs are driven by electrophoresis in a flow channel and captured by porous electrodes and finally separated from the unreacted impurities. Nuclear magnetic resonance and ultraviolet/visible/near-infrared absorption spectroscopic data clearly showed that the impurities were efficiently removed from QDs with the purification yield, defined as the ratio of the mass of purified QDs to that of QDs in the crude solution, up to 87%. Also, we could successfully predict the purification yield depending on purification conditions with a simple theoretical model. The proposed large-scale purification process could be an important cornerstone for the mass production and industrial use of high-quality QDs.

Combination of Cation Exchange and Quantized Ostwald Ripening for Controlling Size Distribution of Lead Chalcogenide Quantum Dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Changwang; Xia, Yong; Zhang, Zhiming

A new strategy for narrowing the size distribution of colloidal quantum dots (QDs) was developed by combining cation exchange and quantized Ostwald ripening. Medium-sized reactant CdS(e) QDs were subjected to cation exchange to form the target PbS(e) QDs, and then small reactant CdS(e) QDs were added which were converted to small PbS(e) dots via cation exchange. The small-sized ensemble of PbS(e) QDs dissolved completely rapidly and released a large amount of monomers, promoting the growth and size-focusing of the medium-sized ensemble of PbS(e) QDs. The addition of small reactant QDs can be repeated to continuously reduce the size distribution. Themore » new method was applied to synthesize PbSe and PbS QDs with extremely narrow size distributions and as a bonus they have hybrid surface passivation. In conclusion, the size distribution of prepared PbSe and PbS QDs are as low as 3.6% and 4.3%, respectively, leading to hexagonal close packing in monolayer and highly ordered three-dimensional superlattice.« less

Coating of Quantum Dots strongly defines their effect on lysosomal health and autophagy.

PubMed

Peynshaert, Karen; Soenen, Stefaan J; Manshian, Bella B; Doak, Shareen H; Braeckmans, Kevin; De Smedt, Stefaan C; Remaut, Katrien

2017-01-15

In the last decade the interest in autophagy got an incredible boost and the phenomenon quickly turned into an extensive research field. Interestingly, dysfunction of this cytoplasmic clearance system has been proposed to lie at the root of multiple diseases including cancer. We therefore consider it crucial from a toxicological point of view to investigate if nanomaterials that are developed for biomedical applications interfere with this cellular process. Here, we study the highly promising 'gradient alloyed' Quantum Dots (QDs) that differ from conventional ones by their gradient core composition which allows for better fluorescent properties. We carefully examined the toxicity of two identical gradient alloyed QDs, differing only in their surface coatings, namely 3-mercaptopropionic (MPA) acid and polyethylene glycol (PEG). Next to more conventional toxicological endpoints like cytotoxicity and oxidative stress, we examined the influence of these QDs on the autophagy pathway. Our study shows that the cellular effects induced by QDs on HeLa cells were strongly dictated by the surface coat of the otherwise identical particles. MPA-coated QDs proved to be highly biocompatible as a result of lysosomal activation and ROS reduction, two cellular responses that help the cell to cope with nanomaterial-induced stress. In contrast, PEGylated QDs were significantly more toxic due to increased ROS production and lysosomal impairment. This impairment next results in autophagy dysfunction which likely adds to their toxic effects. Taken together, our study shows that coating QDs with MPA is a better strategy than PEGylation for long term cell tracking with minimal cytotoxicity. Gradient alloyed Quantum Dots (GA-QDs) are highly promising nanomaterials for biomedical imaging seeing they exhibit supremely fluorescent properties over conventional QDs. The translation of these novel QDs to the clinic requires a detailed toxicological examination, though the data on this is very limited. We therefore applied a systematic approach to examine the toxicity of GA-QDs coated with two commonly applied surface ligands, this while focusing on the autophagy pathway. The impact of QDs on this pathway is of importance since it has been connected with various diseases, including cancer. Our data accentuates that the coating defines the impact on autophagy and therefore the toxicity induced by QDs on cells: while MPA coated QDs were highly biocompatible, PEGylated QDs were toxic. Copyright © 2016 Acta Materialia Inc. All rights reserved.

Effects of quantum dots on the ROS amount of liver cancer stem cells.

PubMed

Li, Kunmeng; Xia, Chunhui; Wang, Baiqi; Chen, Hetao; Wang, Tong; He, Qian; Cao, Hailong; Wang, Yu

2017-07-01

Liver cancer (LC) is a serious disease that threatens human lives. LC has a high recurrence rate and poor prognosis. LC stem cells (LCSCs) play critical roles in these processes. However, the mechanism remains unclear. Reactive oxygen species (ROS) can be used to determine cell apoptosis and proliferation. However, studies of the effects of exogenous nanomaterials on LCSC ROS changes are rarely reported. In this work, quantum dots (QDs) were prepared using a hydrothermal method, and QDs were further modified with polyethylene glycol (PEG) and bovine serum albumin (BSA) using a chemical approach. The effects of QDs, PEG-modified QDs (PEG@QDs) and BSA-modified QDs (BSA@QDs) on the amounts of ROS in liver cancer PLC/PRF/5 (PLC) cells and liver cancer stem cells (LCSCs) were principally investigated. The results showed that when the concentration of QDs, PEG@QDs, and BSA@QDs were 10nM and 90nM, the ROS amount in PLC cells increased by approximately 2- to 5-fold. However, when the concentrations of these nanomaterials were 10nM and 90nM, ROS levels in LCSCs were reduced by approximately 50%. This critical path potentially leads to drug resistance and recurrence of LC. This work provides an important indication for further study of LC drug resistance and recurrence. Copyright © 2017 Elsevier B.V. All rights reserved.

Electrostatically driven resonance energy transfer in "cationic" biocompatible indium phosphide quantum dots.

PubMed

Devatha, Gayathri; Roy, Soumendu; Rao, Anish; Mallick, Abhik; Basu, Sudipta; Pillai, Pramod P

2017-05-01

Indium Phosphide Quantum Dots (InP QDs) have emerged as an alternative to toxic metal ion based QDs in nanobiotechnology. The ability to generate cationic surface charge, without compromising stability and biocompatibility, is essential in realizing the full potential of InP QDs in biological applications. We have addressed this challenge by developing a place exchange protocol for the preparation of cationic InP/ZnS QDs. The quaternary ammonium group provides the much required permanent positive charge and stability to InP/ZnS QDs in biofluids. The two important properties of QDs, namely bioimaging and light induced resonance energy transfer, are successfully demonstrated in cationic InP/ZnS QDs. The low cytotoxicity and stable photoluminescence of cationic InP/ZnS QDs inside cells make them ideal candidates as optical probes for cellular imaging. An efficient resonance energy transfer ( E ∼ 60%) is observed, under physiological conditions, between the cationic InP/ZnS QD donor and anionic dye acceptor. A large bimolecular quenching constant along with a linear Stern-Volmer plot confirms the formation of a strong ground state complex between the cationic InP/ZnS QDs and the anionic dye. Control experiments prove the role of electrostatic attraction in driving the light induced interactions, which can rightfully form the basis for future nano-bio studies between cationic InP/ZnS QDs and anionic biomolecules.

Probing into hybrid organic-molecule and InAs quantum-dots nanosystem with multistacked dots-in-a-well units

NASA Astrophysics Data System (ADS)

Chen, Miaoxiang; Kobashi, Kazufumi

2012-09-01

Hybridizing air-stable organic-molecules with advanced III-V semiconductor quantum-dots (QDs) structures can be utilized to create a new generation of biochemical sensing devices. In order to enhance their optical performances, the active regions in these QDs structures commonly consist of multistacked dots-in-a-well (DWELL) units. The effects of grafted molecules on the performances of the QDs structures with multistacked DWELLs, however, still remain unclear. Here, we show the significant improvements in the optical properties of InAs QDs in a hybrid nanosystem obtained by grafting biocompatible diazonium salt compound (amine donor) atop InAs QDs structure. Since its interface between the QDs structure and molecular monolayer retains an uncontaminated and non-oxidized condition, the nanosystem is an ideal platform to study the intrinsic properties of charge-carrier transport inside the system. Because of the complexity of the energy-levels in the QDs structure due to the existing surface QDs and DWELLs, selective excitation wavelengths (400, 633, and 885 nm, respectively) with different photo-energies are used to exactly analyze the complete charging mechanism in these QDs. A clear view of charge-carrier transfer inside the nanosystem is revealed by employing photoluminescence technique under selective-wavelength excitations. The present work provides new quantitative evidences for exploiting inorganic QDs applications in complex biological systems.

Plasmonic properties of Ag nanoparticles embedded in GeO2-SiO2 matrix by atom beam sputtering.

PubMed

Mohapatra, Satyabrata

2016-02-07

Nanocomposite thin films containing Ag nanoparticles embedded in the GeO2-SiO2 matrix were synthesized by the atom beam co-sputtering technique. The structural, optical and plasmonic properties and the chemical composition of the nanocomposite thin films were studied by transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX), UV-visible absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). UV-visible absorption studies on Ag-SiO2 nanocomposites revealed the presence of a strong localized surface plasmon resonance (LSPR) peak characteristic of Ag nanoparticles at 413 nm, which showed a blue shift of 26 nm (413 to 387 nm) along with a significant broadening and drastic decrease in intensity with the incorporation of 16 at% of Ge into the SiO2 matrix. TEM studies on Ag-GeO2-SiO2 nanocomposite thin films confirmed the presence of Ag nanoparticles with an average size of 3.8 nm in addition to their aggregates with an average size of 16.2 nm. Thermal annealing in air resulted in strong enhancement in the intensity of the LSPR peak, which showed a regular red shift of 51 nm (from 387 to 438 nm) with the increase in annealing temperature up to 500 °C. XPS studies showed that annealing in air resulted in oxidation of excess Ge atoms in the nanocomposite into GeO2. Our work demonstrates the possibility of controllably tuning the LSPR of Ag nanoparticles embedded in the GeO2-SiO2 matrix by single-step thermal annealing, which is interesting for optical applications.

Simplified design of thin-film polarizing beam splitter using embedded symmetric trilayer stack.

PubMed

Azzam, R M A

2011-07-01

An analytically tractable design procedure is presented for a polarizing beam splitter (PBS) that uses frustrated total internal reflection and optical tunneling by a symmetric LHL trilayer thin-film stack embedded in a high-index prism. Considerable simplification arises when the refractive index of the high-index center layer H matches the refractive index of the prism and its thickness is quarter-wave. This leads to a cube design in which zero reflection for the p polarization is achieved at a 45° angle of incidence independent of the thicknesses of the identical symmetric low-index tunnel layers L and L. Arbitrarily high reflectance for the s polarization is obtained at subwavelength thicknesses of the tunnel layers. This is illustrated by an IR Si-cube PBS that uses an embedded ZnS-Si-ZnS trilayer stack.

High-quality quantum-dot-based full-color display technology by pulsed spray method

NASA Astrophysics Data System (ADS)

Chen, Kuo-Ju; Chen, Hsin-Chu; Tsai, Kai-An; Lin, Chien-Chung; Tsai, Hsin-Han; Chien, Shih-Hsuan; Cheng, Bo-Siao; Hsu, Yung-Jung; Shih, Min-Hsiung; Kuo, Hao-Chung

2013-03-01

We fabricated the colloidal quantum-dot light-emitting diodes (QDLEDs) with the HfO2/SiO2-distributed Bragg reflector (DBR) structure using a pulsed spray coating method. Moreover, pixelated RGB arrays, 2-in. wafer-scale white light emission, and an integrated small footprint white light device were demonstrated. The experimental results showed that the intensity of red, blue, and green (RGB) emissions exhibited considerable enhancement because of the high reflectivity in the UV region by the DBR structure, which subsequently increased the use in the UV optical pumping of RGB QDs. In this experiment, a pulsed spray coating method was crucial in providing uniform RGB layers, and the polydimethylsiloxane (PDMS) film was used as the interface layer between each RGB color to avoid crosscontamination and self-assembly of QDs. Furthermore, the chromaticity coordinates of QDLEDs with the DBR structure remained constant under various pumping powers in the large area sample, whereas a larger shift toward high color temperatures was observed in the integrated device. The resulting color gamut of the proposed QDLEDs covered an area 1.2 times larger than that of the NTSC standard, which is favorable for the next generation of high-quality display technology.

Cadmium telluride quantum dots induce apoptosis in human breast cancer cell lines.

PubMed

Naderi, Saeed; Zare, Hakimeh; Taghavinia, Nima; Irajizad, Azam; Aghaei, Mahmoud; Panjehpour, Mojtaba

2018-05-01

Semiconductor quantum dots (QDs), especially those containing cadmium, have undergone marked improvements and are now widely used nanomaterials in applicable biological fields. However, great concerns exist regarding their toxicity in biomedical applications. Because of the lack of sufficient data regarding the toxicity mechanism of QDs, this study aimed to evaluate the cytotoxicity of three types of QDs: CdTe QDs, high yield CdTe QDs, and CdTe/CdS core/shell QDs on two human breast cancer cell lines MDA-MB468 and MCF-7. The breast cancer cells were treated with different concentrations of QDs, and cell viability was evaluated via MTT assay. Hoechst staining was applied for observation of morphological changes due to apoptosis. Apoptotic DNA fragmentation was visualized by the agarose gel electrophoresis assay. Flow cytometric annexin V/propidium iodide (PI) measurement was used for apoptosis detection. A significant decrease in cell viability was observed after QDs treatment ( p < 0.05). Apoptotic bodies and chromatin condensation was observed by Hoechst staining. DNA fragmentation assay demonstrated a DNA ladder profile in the exposed cells and also annexin V/PI flow cytometry confirmed apoptosis in a dose-dependent manner. Our results revealed that CdTe, high yield CdTe, and CdTe/CdS core/shell QDs induce apoptosis in breast cancer cell lines in a dose-dependent manner. This study would help realizing the underlying cytotoxicity mechanism, at least partly, of CdTe QDs and may provide information for the development of nanotoxicology and safe use of biological applications of QDs.

Origin of Photovoltage Enhancement via Interfacial Modification with Silver Nanoparticles Embedded in an a-SiC:H p-Type Layer in a-Si:H Solar Cells.

PubMed

Li, Tiantian; Zhang, Qixing; Ni, Jian; Huang, Qian; Zhang, Dekun; Li, Baozhang; Wei, Changchun; Yan, Baojie; Zhao, Ying; Zhang, Xiaodan

2017-03-29

We used silver nanoparticles (Ag-NPs) embedded in the p-type semiconductor layer of hydrogenated amorphous silicon (a-Si:H) solar cells in the Schottky barrier contact design to modify the interface between aluminum-doped ZnO (ZnO:Al, AZO) and p-type hydrogenated amorphous silicon carbide (p-a-SiC:H) without plasmonic absorption. The high work function of the Ag-NPs provided a good channel for the transport of photogenerated holes. A p-type nanocrystalline SiC:H layer was used to compensate for the real surface defects and voids on the surface of Ag-NPs to reduce recombination at the AZO/p-type layer interface, which then enhanced the photovoltage of single-junction a-Si:H solar cells to values as high as 1.01 V. The Ag-NPs were around 10 nm in diameter and thermally stable in the p-type a-SiC:H film at the solar-cell process temperature. We will also show that a wide range of photovoltages between 1.01 and 2.89 V could be obtained with single-, double-, and triple-junction solar cells based on the single-junction a-Si:H solar cells with tunable high photovoltage. These solar cells are suitable photocathodes for solar water-splitting applications.

Highly selective luminescent nanostructures for mitochondrial imaging and targeting

NASA Astrophysics Data System (ADS)

Fanizza, E.; Iacobazzi, R. M.; Laquintana, V.; Valente, G.; Caliandro, G.; Striccoli, M.; Agostiano, A.; Cutrignelli, A.; Lopedota, A.; Curri, M. L.; Franco, M.; Depalo, N.; Denora, N.

2016-02-01

Here a luminescent hybrid nanostructure based on functionalized quantum dots (QDs) is used as a fluorescent imaging agent able to target selectively mitochondria thanks to the molecular recognition of the translocator protein (TSPO). The selective targeting of such an 18 kDa protein mainly located in the outer mitochondrial membrane and overexpressed in several pathological states including neurodegenerative diseases and cancers may provide valuable information for the early diagnosis and therapy of human disorders. In particular, the rational design of amino functionalized luminescent silica coated QD nanoparticles (QD@SiO2 NPs) provides a versatile nanoplatform to anchor a potent and selective TSPO ligand, characterized by a 2-phenyl-imidazo[1,2-a]pyridine acetamide structure along with a derivatizable carboxylic end group, useful to conjugate the TSPO ligand and achieve TSPO-QD@SiO2 NPs by means of a covalent amide bond. The colloidal stability and optical properties of the proposed nanomaterials are comprehensively investigated and their potential as mitochondrial imaging agents is fully assessed. Sub-cellular fractionation, together with confocal laser scanning fluorescence microscopy and co-localization analysis of targeted TSPO-QD@SiO2 NPs in C6 glioma cells overexpressing the TSPO, proves the great potential of these multifunctional nanosystems as in vitro selective mitochondrial imaging agents.Here a luminescent hybrid nanostructure based on functionalized quantum dots (QDs) is used as a fluorescent imaging agent able to target selectively mitochondria thanks to the molecular recognition of the translocator protein (TSPO). The selective targeting of such an 18 kDa protein mainly located in the outer mitochondrial membrane and overexpressed in several pathological states including neurodegenerative diseases and cancers may provide valuable information for the early diagnosis and therapy of human disorders. In particular, the rational design of amino functionalized luminescent silica coated QD nanoparticles (QD@SiO2 NPs) provides a versatile nanoplatform to anchor a potent and selective TSPO ligand, characterized by a 2-phenyl-imidazo[1,2-a]pyridine acetamide structure along with a derivatizable carboxylic end group, useful to conjugate the TSPO ligand and achieve TSPO-QD@SiO2 NPs by means of a covalent amide bond. The colloidal stability and optical properties of the proposed nanomaterials are comprehensively investigated and their potential as mitochondrial imaging agents is fully assessed. Sub-cellular fractionation, together with confocal laser scanning fluorescence microscopy and co-localization analysis of targeted TSPO-QD@SiO2 NPs in C6 glioma cells overexpressing the TSPO, proves the great potential of these multifunctional nanosystems as in vitro selective mitochondrial imaging agents. Electronic supplementary information (ESI) available: Additional TEM micrographs, fluorescence and UV-Vis absorbance spectra of silica coated QD nanoparticles and TSPO ligand. See DOI: 10.1039/c5nr08139d

Silver nanoparticle deposition on inverse opal SiO2 films embedded in protective polypropylene micropits for SERS applications

NASA Astrophysics Data System (ADS)

Ammosova, Lena; Ankudze, Bright; Philip, Anish; Jiang, Yu; Pakkanen, Tuula T.; Pakkanen, Tapani A.

2018-01-01

Common methods to fabricate surface enhanced Raman scattering (SERS) substrates with controlled micro-nanohierarchy are often complex and expensive. In this study, we demonstrate a simple and cost effective method to fabricate SERS substrates with complex geometries. Microworking robot structuration is used to pattern a polypropylene (PP) substrate with micropits, facilitating protective microenvironment for brittle SiO2 inverse opal (IO) structure. Hierarchical SiO2 IO patterns were obtained using polystyrene (PS) spheres as a sacrificial template, and were selectively embedded into the hydrophilized PP micropits. The same microworking robot technique was subsequently used to deposit silver nanoparticle ink into the SiO2 IO cavities. The fabricated multi-level micro-nanohierarchy surface was studied to enhance Raman scattering of the 4-aminothiophenol (4-ATP) analyte molecule. The results show that the SERS performance of the micro-nanohierarchical substrate increases significantly the Raman scattering intensity compared to substrates with structured 2D surface geometries.

Synthesis of carbon-based quantum dots from starch extracts: Optical investigations.

PubMed

Al-Douri, Y; Badi, N; Voon, C H

2018-03-01

Carbon-based quantum dots (C-QDs) were synthesized through microwave-assisted carbonization of an aqueous starch suspension mediated by sulphuric and phosphoric acids. The as-prepared C-QDs showed blue, green and yellow luminescence without the addition of any surface-passivating agent. The C-QDs were further analyzed by UV-vis spectroscopy to measure the optical response of the organic compound. The energy gaps revealed narrow sizing of C-QDs in the semiconductor range. The optical refractive index and dielectric constant were investigated. The C-QDs size distribution was characterized. The results suggested an easy route to the large scale production of C-QDs materials. Copyright © 2017 John Wiley & Sons, Ltd.

Stable CdS QDs with intense broadband photoluminescence and high quantum yields

NASA Astrophysics Data System (ADS)

Mandal, Abhijit; Saha, Jony; De, Goutam

2011-11-01

Aqueous synthesis of CdS quantum dots (QDs) using thiolactic acid (TLA) as a capping agent was reported. These QDs exhibited excellent colloidal and photostability over a span of 2 years and showed intense broadband and almost white photoluminescence suitable for solid state lighting devices. The photoluminescence (PL) property of the aqueous CdS QDs is optimized by adjusting various processing parameters. The highest quantum yield (QY) achieved for TLA capped CdS QDs of average size 3.5 nm was ˜50%. Luminescence lifetime measurements of CdS-TLA QDs indicated longer lifetimes and a larger contribution of the surface-related emission, indicating removal of quenching defects.

Synthesis and characterization of colloidal ZnTe nanocrystals and ZnTe/ZnSe quantum dots

NASA Astrophysics Data System (ADS)

Gonzales, Gavin P.; Alas, Gema; Senthil, Arjun; Withers, Nathan J.; Minetos, Christina; Sandoval, Alejandro; Ivanov, Sergei A.; Smolyakov, Gennady A.; Huber, Dale L.; Osiński, Marek

2018-02-01

Quantum dots (QDs) emitting in the visible are of interest for many biomedical applications, including bioimaging, biosensing, drug targeting, and photodynamic therapy. However, a significant limitation is that QDs typically contain cadmium, which makes prospects for their FDA approval very unlikely. Previous work has focused on InP and ZnO as alternative semiconductor materials for QDs. However, these nanoparticles have also been shown to be cytotoxic. High-efficiency luminescent ZnTe-based QDs could be a reasonable alternative to Cd-containing QDs. In this paper, we present preliminary results of our recent studies of ZnTe-based QDs, including their synthesis, structural characterization, and optical properties.

Photoluminescence of ZnS-SiO2:Ce Thin Films Deposited by Magnetron Sputtering

NASA Astrophysics Data System (ADS)

Mizuno, Masao

2011-12-01

Photoluminescent emissions of zinc sulfide-silica-cerium thin films deposited by magnetron sputtering were observed. The films consisted of ZnS nanocrystals embedded in amorphous SiO2 matrices. ZnS-SiO2:Ce films exhibited photoluminescence even without postannealing. Their emission spectra showed broad patterns in the visible range; the emitted colors depended on film composition.

Silicon waveguide optical switch with embedded phase change material.

PubMed

Miller, Kevin J; Hallman, Kent A; Haglund, Richard F; Weiss, Sharon M

2017-10-30

Phase-change materials (PCMs) have emerged as promising active elements in silicon (Si) photonic systems. In this work, we design, fabricate, and characterize a hybrid Si-PCM optical switch. By integrating vanadium dioxide (a PCM) within a Si photonic waveguide, in a non-resonant geometry, we achieve ~10 dB broadband optical contrast with a PCM length of 500 nm using thermal actuation.

The interactions between CdSe quantum dots and yeast Saccharomyces cerevisiae: adhesion of quantum dots to the cell surface and the protection effect of ZnS shell.

PubMed

Mei, Jie; Yang, Li-Yun; Lai, Lu; Xu, Zi-Qiang; Wang, Can; Zhao, Jie; Jin, Jian-Cheng; Jiang, Feng-Lei; Liu, Yi

2014-10-01

The interactions between quantum dots (QDs) and biological systems have attracted increasing attention due to concerns on possible toxicity of the nanoscale materials. The biological effects of CdSe QDs and CdSe/ZnS QDs with nearly identical hydrodynamic size on Saccharomyces cerevisiae were investigated via microcalorimetric, spectroscopic and microscopic methods, demonstrating a toxic order CdSe>CdSe/ZnS QDs. CdSe QDs damaged yeast cell wall and reduced the mitochondrial membrane potential. Noteworthy, adhesion of QDs to the yeast cell surface renders this work a good example of interaction site at cell surface, and the epitaxial coating of ZnS could greatly reduce the toxicity of Cd-containing QDs. These results will contribute to the safety evaluation of quantum dots, and provide valuable information for design of nanomaterials. Copyright © 2014 Elsevier Ltd. All rights reserved.

Surface Stabilized InP/GaP/ZnS Quantum Dots with Mg Ions for WLED Application.

PubMed

Park, Joong Pill; Kim, Sang-Wook

2016-05-01

One of the most highlighted cadmium-free quantum dots (QDs), InP-based QDs, have improved their optical properties. However, InP-based QDs have some practical drawbacks, for example, stability, compared with CdSe-based QDs. Poor stability of InP-based QDs yields critical problems, such as agglomeration and photoluminescence quenching in light emitting diode (LED). It has to be solved for applications and most research has focused on thick outer shells as an effective solution. We introduced magnesium cations for improving stability of InP-based QDs. We applied very small amounts of Mg cations as surface stabilizers, as a result, stability of QDs is clearly improved. Then, QD based LED chips also yield improved values including RA of 84.4, CCT of 3799 K, and luminous efficiency of 129.57 Im/W, which are highly improved data compared with our previous results.

2d distribution mapping of quantum dots injected onto filtration paper by laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Škarková, Pavlína; Novotný, Karel; Lubal, Přemysl; Jebavá, Alžběta; Pořízka, Pavel; Klus, Jakub; Farka, Zdeněk; Hrdlička, Aleš; Kaiser, Jozef

2017-05-01

In this study, the feasibility of Quantum dots (QDs) 2D distribution mapping on the substrate by Laser-Induced Breakdown Spectroscopy (LIBS) was examined. The major objective of this study was to describe phenomena occurring after applying aqueous solutions of QDs onto filtration paper. Especially, the influence of pH and presence of Cu2 + cations in QDs solutions on LIBS signal was investigated. Cadmium Telluride QDs (CdTe QDs) were prepared by formation of nanosized semiconductor particles in so called ;one-pot; synthesis. CdTe QDs were capped by glutathione or by 3-mercaptopropionic acid. The technique described in this work allows detection of QDs injected on the selected substrate - filtration paper. Results obtained from LIBS experiments were collated with a comparative method, fluorescence microscopy, which showed variations in the distribution of QDs on the substrate surface and possibilities for quenching. Due to the immediate signal response, relatively simple instrumentation and automatization possibility, LIBS offers promising and fast alternative to other techniques, as it is able to detect also nanoparticles with no visible luminescence.

Synthesis of CdTe quantum dot-conjugated CC49 and their application for in vitro imaging of gastric adenocarcinoma cells

NASA Astrophysics Data System (ADS)

Zhang, Yun-Peng; Sun, Peng; Zhang, Xu-Rui; Yang, Wu-Li; Si, Cheng-Shuai

2013-06-01

The purpose of this experiment was to investigate the visible imaging of gastric adenocarcinoma cells in vitro by targeting tumor-associated glycoprotein 72 (TAG-72) with near-infrared quantum dots (QDs). QDs with an emission wavelength of about 550 to 780 nm were conjugated to CC49 monoclonal antibodies against TAG-72, resulting in a probe named as CC49-QDs. A gastric adenocarcinoma cell line (MGC80-3) expressing high levels of TAG-72 was cultured for fluorescence imaging, and a gastric epithelial cell line (GES-1) was used for the negative control group. Transmission electron microscopy indicated that the average diameter of CC49-QDs was 0.2 nm higher compared with that of the primary QDs. Also, fluorescence spectrum analysis indicated that the CC49-QDs did not have different optical properties compared to the primary QDs. Immunohistochemical examination and in vitro fluorescence imaging of the tumors showed that the CC49-QDs probe could bind TAG-72 expressed on MGC80-3 cells.

Potential effect of CuInS2/ZnS core-shell quantum dots on P3HT/PEDOT:PSS heterostructure based solar cell

NASA Astrophysics Data System (ADS)

Jindal, Shikha; Giripunje, S. M.

2018-07-01

Nanostructured quantum dots (QDs) are quite promising in the solar cell application due to quantum confinement effect. QDs possess multiple exciton generation and large surface area. The environment friendly CuInS2/ZnS core-shell QDs were prepared by solvothermal method. Thus, the 3 nm average sized CuInS2/ZnS QDs were employed in the bulk heterojunction device and the active blend layer consisting of the P3HT and CuInS2/ZnS QDs was investigated. The energy level information of CuInS2/ZnS QDs as an electron acceptor was explored by ultra violet photoelectron spectroscopy. Bulk heterojunction hybrid device of ITO/PEDOT:PSS/P3HT: (CuInS2/ZnS QDs)/ZnO/Ag was designed by spin coating approach and its electrical characterization was investigated by solar simulator. Current density - voltage characteristics shows the enhancement in power conversion efficiency with increasing concentration of CuInS2/ZnS QDs in bulk heterojunction device.

Luminescent ZnO quantum dots as an efficient sensor for free chlorine detection in water.

PubMed

Singh, Kulvinder; Mehta, S K

2016-04-21

Highly luminescent ZnO quantum dots (QDs) synthesized via a simple and facile route are used for the preparation of an optical sensor for the detection of free chlorine. The concentration of free chlorine greatly affects the PL emission of the ZnO QDs at 525 nm. Since hypochlorite gains electrons with high efficiency, it takes electrons from the oxygen vacancies of ZnO QDs, which gives rise to defect emission in ZnO QDs. UV-vis data analysis shows that free chlorine does not affect the optical absorption spectra of ZnO QDs. The optical sensing of free chlorine using ZnO QDs has several advantages, like quick response time, good selectivity and of course high sensitivity. The pH has very little effect on the PL emission of ZnO QDs. It does not interfere in the sensing mechanism for free chlorine. After 60 s, the response of the ZnO QDs remains stable. The present sensor shows high selectivity with respect to various common cations, as well as anions.

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source.

PubMed

Byun, Ho-June; Song, Woo-Seuk; Yang, Heesun

2011-06-10

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180 °C for 24 h by using a P source of P(N(CH(3))(2))(3). The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source

NASA Astrophysics Data System (ADS)

Byun, Ho-June; Song, Woo-Seuk; Yang, Heesun

2011-06-01

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180 °C for 24 h by using a P source of P(N(CH3)2)3. The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.

Improved Ionic Diffusion through the Mesoporous Carbon Skin on Silicon Nanoparticles Embedded in Carbon for Ultrafast Lithium Storage.

PubMed

An, Geon-Hyoung; Kim, Hyeonjin; Ahn, Hyo-Jin

2018-02-21

Because of their combined effects of outstanding mechanical stability, high electrical conductivity, and high theoretical capacity, silicon (Si) nanoparticles embedded in carbon are a promising candidate as electrode material for practical utilization in Li-ion batteries (LIBs) to replace the conventional graphite. However, because of the poor ionic diffusion of electrode materials, the low-grade ultrafast cycling performance at high current densities remains a considerable challenge. In the present study, seeking to improve the ionic diffusion, we propose a novel design of mesoporous carbon skin on the Si nanoparticles embedded in carbon by hydrothermal reaction, poly(methyl methacrylate) coating process, and carbonization. The resultant electrode offers a high specific discharge capacity with excellent cycling stability (1140 mA h g -1 at 100 mA g -1 after 100 cycles), superb high-rate performance (969 mA h g -1 at 2000 mA g -1 ), and outstanding ultrafast cycling stability (532 mA h g -1 at 2000 mA g -1 after 500 cycles). The battery performances are surpassing the previously reported results for carbon and Si composite-based electrodes on LIBs. Therefore, this novel approach provides multiple benefits in terms of the effective accommodation of large volume expansions of the Si nanoparticles, a shorter Li-ion diffusion pathway, and stable electrochemical conditions from a faster ionic diffusion during cycling.

A novel ultrasensitive carboxymethyl chitosan-quantum dot-based fluorescence "turn on-off" nanosensor for lysozyme detection.

PubMed

Song, Yu; Li, Yang; Liu, Ziping; Liu, Linlin; Wang, Xinyan; Su, Xingguang; Ma, Qiang

2014-11-15

In this work, we developed an ultrasensitive "turn on-off" fluorescence nanosensor for lysozyme (Lyz) detection. The novel nanosensor was constructed with the carboxymethyl chitosan modified CdTe quantum dots (CMCS-QDs). Firstly, the CMCS-QDs were fabricated via the electrostatic interaction between amino groups in CMCS polymeric chains and carboxyl groups on the surface of QDs. In the fluorescence "turn-on" step, the strong binding ability between Zn(2+) and CMCS on the surface of QDs can enhance the photoluminescence intensity (PL) of QDs. In the following fluorescence "turn-off" step, the N-acetyl-glucosamine (NAG) section along the CMCS chains was hydrolyzed by Lyz. As a result, Zn(2+) was released from the surface of QDs, and the Lyz-QDs complexes were formed to quench the QDs PL. Under the optimal conditions, there was a good linear relationship between the PL of QDs and the Lyz concentration (0.1-1.2 ng/mL) with the detection limit of 0.031 ng/mL. The developed method was ultrasensitive, highly selective and fast. It has been successfully employed in the detection of Lyz in the serum with satisfactory results. Copyright © 2014 Elsevier B.V. All rights reserved.

Fluorescence alteration of MPA capped CdSe quantum dots by spontaneous biomarker protein adsorption.

PubMed

Rowley, Amber; Parks, Tegan; Parks, Kaden; Medley, Kyle; Cordner, Alex; Yu, Ming

2018-05-23

Quantum dots (QDs) have significant potentials in biomedical applications of bioimaging and biosensing. Spontaneous adsorption of proteins on QDs surface is a common phenomenon, which occurred to serum proteins in biological samples, and has been observed to enhance QDs fluorescence. In this study, fluorescence alteration of 3-mercaptopropionic acid (MPA) capped CdSe quantum dots by four individual biomarker proteins was investigated. By monitoring the fluorescence emission of QDs, the biomarker protein adsorbed spontaneously on QDs surface was recognized and quantified. When alpha fetoprotein (AFP) or heat shock protein 90 alpha (HSP90α) were present, the QDs became brighter. The presence of cytochrome C (CytoC) or lysozyme (Lyz) made the QDs dimmer first, and then brighter. Within 5 min response time all four biomarker proteins were detected individually with the estimated detection limit in the range of 1-10 ng/mL and good linear dynamic ranges. The results suggested that the fluorescence of QDs was responsive to not only serum proteins but also biomarker proteins. The fluorescence response was able to correlate quantitatively with the amount of biomarker proteins in relatively low concentrations. These results provide more information to understand QDs and support their applications in biomedical fields. Copyright © 2018. Published by Elsevier Inc.

Composition-dependent trap distributions in CdSe and InP quantum dots probed using photoluminescence blinking dynamics.

PubMed

Chung, Heejae; Cho, Kyung-Sang; Koh, Weon-Kyu; Kim, Dongho; Kim, Jiwon

2016-07-21

Although Group II-VI quantum dots (QDs) have attracted much attention due to their wide range of applications in QD-based devices, the presence of toxic ions in II-VI QDs raises environmental concerns. To fulfill the demands of nontoxic QDs, synthetic routes for III-V QDs have been developed. However, only a few comparative analyses on optical properties of III-V QDs have been performed. In this study, the composition-related energetic trap distributions have been explored by using three different types of core/multishell QDs: CdSe-CdS (CdSe/CdS/ZnS), InP-ZnSe (InP/ZnSe/ZnS), and InP-GaP (InP/GaP/ZnS). It was shown that CdSe-CdS QDs have much larger trap densities than InP-shell QDs at higher energy states (at least 1Eg (band gap energy) above the lowest conduction band edge) based on probability density plots and Auger ionization efficiencies which are determined by analyses of photoluminescence blinking dynamics. This result suggests that the composition of encapsulated QDs is closely associated with the charge trapping processes, and also provides an insight into the development of more environmentally friendly QD-based devices.

Interaction of insulin with colloidal ZnS quantum dots functionalized by various surface capping agents.

PubMed

Hosseinzadeh, Ghader; Maghari, Ali; Farniya, Seyed Morteza Famil; Keihan, Amir Homayoun; Moosavi-Movahedi, Ali A

2017-08-01

Interaction of quantum dots (QDs) and proteins strongly influenced by the surface characteristics of the QDs at the protein-QD interface. For a precise control of these surface-related interactions, it is necessary to improve our understanding in this field. In this regard, in the present work, the interaction between the insulin and differently functionalized ZnS quantum dots (QDs) were studied. The ZnS QDs were functionalized with various functional groups of hydroxyl (OH), carboxyl (COOH), amine (NH 2 ), and amino acid (COOH and NH 2 ). The effect of surface hydrophobicity was also studied by changing the alkyl-chain lengths of mercaptocarboxylic acid capping agents. The interaction between insulin and the ZnS QDs were investigated by fluorescence quenching, synchronous fluorescence, circular dichroism (CD), and thermal aggregation techniques. The results reveal that among the studied QDs, mercaptosuccinic acid functionalized QDs has the strongest interaction (∆G ° =-51.50kJ/mol at 310K) with insulin, mercaptoethanol functionalized QDs destabilize insulin by increasing the beta-sheet contents, and only cysteine functionalized QDs improves the insulin stability by increasing the alpha-helix contents of the protein, and. Our results also indicate that by increasing the alkyl-chain length of capping agents, due to an increase in hydrophobicity of the QDs surface, the beta-sheet contents of insulin increase which results in the enhancement of insulin instability. Copyright © 2017 Elsevier B.V. All rights reserved.

"Use of acidophilic bacteria of the genus Acidithiobacillus to biosynthesize CdS fluorescent nanoparticles (quantum dots) with high tolerance to acidic pH".

PubMed

Ulloa, G; Collao, B; Araneda, M; Escobar, B; Álvarez, S; Bravo, D; Pérez-Donoso, J M

2016-12-01

The use of bacterial cells to produce fluorescent semiconductor nanoparticles (quantum dots, QDs) represents a green alternative with promising economic potential. In the present work, we report for the first time the biosynthesis of CdS QDs by acidophilic bacteria of the Acidithiobacillus genus. CdS QDs were obtained by exposing A. ferrooxidans, A. thiooxidans and A. caldus cells to sublethal Cd 2+ concentrations in the presence of cysteine and glutathione. The fluorescence of cadmium-exposed cells moves from green to red with incubation time, a characteristic property of QDs associated with nanocrystals growth. Biosynthesized nanoparticles (NPs) display an absorption peak at 360nm and a broad emission spectra between 450 and 650nm when excited at 370nm, both characteristic of CdS QDs. Average sizes of 6 and 10nm were determined for green and red NPs, respectively. The importance of cysteine and glutathione on QDs biosynthesis in Acidithiobacillus was related with the generation of H 2 S. Interestingly, QDs produced by acidophilic bacteria display high tolerance to acidic pH. Absorbance and fluorescence properties of QDs was not affected at pH 2.0, a condition that totally inhibits the fluorescence of QDs produced chemically or biosynthesized by mesophilic bacteria (stable until pH 4.5-5.0). Results presented here constitute the first report of the generation of QDs with improved properties by using extremophile microorganisms. Copyright © 2016 Elsevier Inc. All rights reserved.

High fluorescent water soluble CdTe quantum dots—a promising system for light harvesting applications

NASA Astrophysics Data System (ADS)

de Sa, Arsenio; Moura, Isabel; Abreu, Ana S.; Oliveira, Manuel; Ferreira, Miguel F.; Machado, Ana V.

2017-05-01

The entrapment of quantum dots (QDs) in the inner part of micelles formed by surfactant polymers is a powerful methodology to prepare stable and photoluminescent core nanoparticles with enhanced optical properties. These features are crucial for the application of QDs in the design of hybrid assemblies for light harvesting applications, where energy transfer processes are required. The present work was focused on the synthesis of a surfactant homopolymer, poly (acrylic acid) (PAA) macroRAFT, to be used as a stabilizer of hydrophobic cadmium telluride (CdTe) QDs in aqueous solution. PAA macroRAFT was synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization in a single chemical reaction. Its micelles were used to entangle and entrap hydrophobic CdTe QDs, with different molar ratio of polymer and QDs. The morphology and optical properties of the entrapped QDs were determined. The results showed that PAA macroRAFT is able to form micelles with a critical micelle concentration of 2.08 mg/mL. It was also noticed that the molar ratio of polymer and QDs have high influence on the QDs' morphology and their optical properties. The QDs' photoluminescence quantum yield was enhanced approximately 23% upon their entrapment in PAA macroRAFT micelles, using 60 equivalents of polymer. Moreover, while in solution, QDs are well-dispersed, having a 3.5 nm diameter, upon being entrapped in the micelles, tend to form clusters with a size around 100 nm.

Synthesis of Colloidal Quantum Dots Coated with Mercaptosuccinic Acid for Early Detection and Therapeutics of Oral Cancers

NASA Astrophysics Data System (ADS)

Jocelin, G.; Arivarasan, A.; Ganesan, M.; Prasad, N. Rajendra; Sasikala, G.

2016-04-01

Quantum dots (QDs) are gaining widespread recognition for its luminescence behavior and unique photo physical properties as a bio-marker and inorganic fluorophore. In spite of such rampant advantages, its application is clinically hampered depending on the surface coating decreasing its luminescence efficiency. The present study reports preparation of CdTe QDs capped with biologically active thiol based material, mercaptosuccinic acid (MSA) for diagnosis of oral cancer (KB) cells by acting as a fluorophore marking targeted tumor cells and at the same time exhibiting certain cytotoxic effects. Synthesized MSA coated CdTe QDs is spherical in shape with an average particle size of 3-5nm. In vitro, the rapid uptake of MSA CdTe QDs in oral cancer cell lines were assessed through fluorescence microscopy. Further, this study evaluates the therapeutic efficiency of MSA CdTe QDs in human oral cancer cell lines using MTT analysis. MSA CdTe QDs exhibit significant cytotoxicity in oral cancer cells in a dose dependent manner with low IC50 when compared with other raw CdTe QDs. MSA CdTe QDs were also treated with human lymphocytes (normal cells) to assess and compare the toxicity profile of QDs in normal and oral tumors. The results of our present study strengthen our hypothesis of using MSA CdTe QDs as detector for tracking and fluorescence imaging of oral cancer cells and exhibiting sufficient cytotoxicity in them.

High-Bandgap Silicon Nanocrystal Solar Cells: Device Fabrication, Characterization, and Modeling

NASA Astrophysics Data System (ADS)

Löper, Philipp; Canino, Mariaconcetta; Schnabel, Manuel; Summonte, Caterina; Janz, Stefan; Zacharias, Margit

Silicon nanocrystals (Si NCs) embedded in Si-based dielectrics provide a Si-based high-bandgap material (1.7 eV) and enable the construction of crystalline Si tandem solar cells. This chapter focusses on Si NC embedded in silicon carbide, because silicon carbide offers electrical conduction through the matrix material. The material development is reviewed, and optical modeling is introduced as a powerful method to monitor the four material components, amorphous and crystalline silicon as well as amorphous and crystalline silicon carbide. In the second part of this chapter, recent device developments for the photovoltaic characterization of Si NCs are examined. The controlled growth of Si NCs involves high-temperature annealing which deteriorates the properties of any previously established selective contacts. A membrane-based device is presented to overcome these limitations. In this approach, the formation of both selective contacts is carried out after high-temperature annealing and is therefore not affected by the latter. We examine p-i-n solar cells with an intrinsic region made of Si NCs embedded in silicon carbide. Device failure due to damaged insulation layers is analyzed by light beam-induced current measurements. An optical model of the device is presented for improving the cell current. A characterization scheme for Si NC p-i-n solar cells is presented which aims at determining the fundamental transport and recombination properties, i.e., the effective mobility lifetime product, of the nanocrystal layer at device level. For this means, an illumination-dependent analysis of Si NC p-i-n solar cells is carried out within the framework of the constant field approximation. The analysis builds on an optical device model, which is used to assess the photogenerated current in each of the device layers. Illumination-dependent current-voltage curves are modelled with a voltage-dependent current collection function with only two free parameters, and excellent agreement is found between theory and experiment. An effective mobility lifetime product of 10-10 cm2/V is derived and confirmed independently from an alternative method. The procedure discussed in this chapter is proposed as a characterization scheme for further material development, providing an optimization parameter (the effective mobility lifetime product) relevant for the photovoltaic performance of Si NC films.

NIR-Emitting Alloyed CdTeSe QDs and Organic Dye Assemblies: A Nontoxic, Stable, and Efficient FRET System.

PubMed

Ramírez-Herrera, Doris E; Rodríguez-Velázquez, Eustolia; Alatorre-Meda, Manuel; Paraguay-Delgado, Francisco; Tirado-Guízar, Antonio; Taboada, Pablo; Pina-Luis, Georgina

2018-04-11

In the present work, we synthesize Near Infrared (NIR)-emitting alloyed mercaptopropionic acid (MPA)-capped CdTeSe quantum dots (QDs) in a single-step one-hour process, without the use of an inert atmosphere or any pyrophoric ligands. The quantum dots are water soluble, non-toxic, and highly photostable and have high quantum yields (QYs) up to 84%. The alloyed MPA-capped CdTeSe QDs exhibit a red-shifted emission, whose color can be tuned between visible and NIR regions (608-750 nm) by controlling the Te:Se molar ratio in the precursor mixtures and/or changing the time reaction. The MPA-capped QDs were characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and zeta potential measurements. Photostability studies were performed by irradiating the QDs with a high-power xenon lamp. The ternary MPA-CdTeSe QDs showed greater photostability than the corresponding binary MPA-CdTe QDs. We report the Förster resonance energy transfer (FRET) from the MPA-capped CdTeSe QDs as energy donors and Cyanine5 NHS-ester (Cy5) dye as an energy acceptor with efficiency ( E ) up to 95%. The distance between the QDs and dye ( r ), the Förster distance ( R ₀), and the binding constant ( K ) are reported. Additionally, cytocompatibility and cell internalization experiments conducted on human cancer cells (HeLa) cells revealed that alloyed MPA-capped CdTeSe QDs are more cytocompatible than MPA-capped CdTe QDs and are capable of ordering homogeneously all over the cytoplasm, which allows their use as potential safe, green donors for biological FRET applications.

Biocompatible water soluble quantum dots as new biophotonic tools for hematologic cells: applications for flow cell cytometry

NASA Astrophysics Data System (ADS)

Lira, Rafael B.; de Sales Neto, Antonio T.; Carvalho, Kilmara K. H. G.; Leite, Elisa S.; Brasil, Aluizio G., Jr.; Azevedo, Denise P. L.; Cabral Filho, Paulo E.; Cavalcanti, Mariana B.; Amaral, Ademir J.; Farias, Patricía M. A.; Santos, Beate S.; Fontes, Adriana

2010-02-01

Quantum dots (QDs) are a promising class of fluorescent probes that can be conjugated to a variety of specific cell antibodies. For this reason, simple, cheap and reproducible routes of QDśs syntheses are the main goal of many researches in this field. The main objective of this work was to demonstrate the ability of QDs as biolabels for flow cell cytometry analysis. We have synthesized biocompatible water soluble CdS/Cd(OH)2 and CdTe/CdS QDs and applied them as fluorescent labels of hematologic cells. CdTe/CdS QDs was prepared using using a simple aqueous route with mercaptoacetic acid and mercaptopropionic acid as stabilizing agents. The resulting CdTe/CdS QDs can target biological membrane proteins and can also be internalized by cells. We applied the CdTe/CdS QDs as biolabels of human lymphocytes and compared the results obtained for lymphocytes treated and non-treated with permeabilizing agents for cell membranes. Permeabilized cells present higher fluorescence pattern than non permeabilized ones. We associated antibody A to the CdS/Cd(OH)2 QDs to label type A red blood cell (RBC). In this case, the O erythrocytes were used as the negative control. The results demonstrate that QDs were successfully functionalized with antibody A. There was a specific binding of QDs-antibody A to RBC membrane antigen only for A RBCs. We have also monitored QDs-hematologic cell interaction by using fluorescence microscopy. Our method shows that QDs can be conjugated to a variety of specific cell antibodies and can become a potential, highly efficient and low cost diagnostic tool for flow cell cytometry, very compatible with the lasers and filters used in this kind of equipments.

Photo-stability and time-resolved photoluminescence study of colloidal CdSe/ZnS quantum dots passivated in Al{sub 2}O{sub 3} using atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Chih-Yi; Mao, Ming-Hua, E-mail: mhmao@ntu.edu.tw; Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan

2016-08-28

We report photo-stability enhancement of colloidal CdSe/ZnS quantum dots (QDs) passivated in Al{sub 2}O{sub 3} thin film using the atomic layer deposition (ALD) technique. 62% of the original peak photoluminescence (PL) intensity remained after ALD. The photo-oxidation and photo-induced fluorescence enhancement effects of both the unpassivated and passivated QDs were studied under various conditions, including different excitation sources, power densities, and environment. The unpassivated QDs showed rapid PL degradation under high excitation due to strong photo-oxidation in air while the PL intensity of Al{sub 2}O{sub 3} passivated QDs was found to remain stable. Furthermore, recombination dynamics of the unpassivated andmore » passivated QDs were investigated by time-resolved measurements. The average lifetime of the unpassivated QDs decreases with laser irradiation time due to photo-oxidation. Photo-oxidation creates surface defects which reduces the QD emission intensity and enhances the non-radiative recombination rate. From the comparison of PL decay profiles of the unpassivated and passivated QDs, photo-oxidation-induced surface defects unexpectedly also reduce the radiative recombination rate. The ALD passivation of Al{sub 2}O{sub 3} protects QDs from photo-oxidation and therefore avoids the reduction of radiative recombination rate. Our experimental results demonstrated that passivation of colloidal QDs by ALD is a promising method to well encapsulate QDs to prevent gas permeation and to enhance photo-stability, including the PL intensity and carrier lifetime in air. This is essential for the applications of colloidal QDs in light-emitting devices.« less

NIR-Emitting Alloyed CdTeSe QDs and Organic Dye Assemblies: A Nontoxic, Stable, and Efficient FRET System

PubMed Central

Ramírez-Herrera, Doris E.; Rodríguez-Velázquez, Eustolia; Alatorre-Meda, Manuel; Paraguay-Delgado, Francisco; Tirado-Guízar, Antonio; Taboada, Pablo; Pina-Luis, Georgina

2018-01-01

In the present work, we synthesize Near Infrared (NIR)-emitting alloyed mercaptopropionic acid (MPA)-capped CdTeSe quantum dots (QDs) in a single-step one-hour process, without the use of an inert atmosphere or any pyrophoric ligands. The quantum dots are water soluble, non-toxic, and highly photostable and have high quantum yields (QYs) up to 84%. The alloyed MPA-capped CdTeSe QDs exhibit a red-shifted emission, whose color can be tuned between visible and NIR regions (608–750 nm) by controlling the Te:Se molar ratio in the precursor mixtures and/or changing the time reaction. The MPA-capped QDs were characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and zeta potential measurements. Photostability studies were performed by irradiating the QDs with a high-power xenon lamp. The ternary MPA-CdTeSe QDs showed greater photostability than the corresponding binary MPA-CdTe QDs. We report the Förster resonance energy transfer (FRET) from the MPA-capped CdTeSe QDs as energy donors and Cyanine5 NHS-ester (Cy5) dye as an energy acceptor with efficiency (E) up to 95%. The distance between the QDs and dye (r), the Förster distance (R0), and the binding constant (K) are reported. Additionally, cytocompatibility and cell internalization experiments conducted on human cancer cells (HeLa) cells revealed that alloyed MPA-capped CdTeSe QDs are more cytocompatible than MPA-capped CdTe QDs and are capable of ordering homogeneously all over the cytoplasm, which allows their use as potential safe, green donors for biological FRET applications. PMID:29641435

Electrostatically driven resonance energy transfer in “cationic” biocompatible indium phosphide quantum dots† †Electronic supplementary information (ESI) available: Detailed experimental methods, the synthesis and characterization of QDs, bioimaging, stability studies, control experiments, and the calculation of various parameters involved in the resonance energy transfer process etc. See DOI: 10.1039/c7sc00592j Click here for additional data file.

PubMed Central

Devatha, Gayathri; Roy, Soumendu; Rao, Anish; Mallick, Abhik; Basu, Sudipta

2017-01-01

Indium Phosphide Quantum Dots (InP QDs) have emerged as an alternative to toxic metal ion based QDs in nanobiotechnology. The ability to generate cationic surface charge, without compromising stability and biocompatibility, is essential in realizing the full potential of InP QDs in biological applications. We have addressed this challenge by developing a place exchange protocol for the preparation of cationic InP/ZnS QDs. The quaternary ammonium group provides the much required permanent positive charge and stability to InP/ZnS QDs in biofluids. The two important properties of QDs, namely bioimaging and light induced resonance energy transfer, are successfully demonstrated in cationic InP/ZnS QDs. The low cytotoxicity and stable photoluminescence of cationic InP/ZnS QDs inside cells make them ideal candidates as optical probes for cellular imaging. An efficient resonance energy transfer (E ∼ 60%) is observed, under physiological conditions, between the cationic InP/ZnS QD donor and anionic dye acceptor. A large bimolecular quenching constant along with a linear Stern–Volmer plot confirms the formation of a strong ground state complex between the cationic InP/ZnS QDs and the anionic dye. Control experiments prove the role of electrostatic attraction in driving the light induced interactions, which can rightfully form the basis for future nano-bio studies between cationic InP/ZnS QDs and anionic biomolecules. PMID:28626557

Imaging heterostructured quantum dots in cultured cells with epifluorescence and transmission electron microscopy

PubMed Central

Rivera, Erin M.; Provencio, Casilda Trujillo; Steinbruck, Andrea; Rastogi, Pawan; Dennis, Allison; Hollingsworth, Jennifer; Serrano, Elba

2011-01-01

Quantum dots (QDs) are semiconductor nanocrystals with extensive imaging and diagnostic capabilities, including the potential for single molecule tracking. Commercially available QDs offer distinct advantages over organic fluorophores, such as increased photostability and tunable emission spectra, but their cadmium selenide (CdSe) core raises toxicity concerns. For this reason, replacements for CdSe-based QDs have been sought that can offer equivalent optical properties. The spectral range, brightness and stability of InP QDs may comprise such a solution. To this end, LANL/CINT personnel fabricated moderately thick-shell novel InP QDs that retain brightness and emission over time in an aqueous environment. We are interested in evaluating how the composition and surface properties of these novel QDs affect their entry and sequestration within the cell. Here we use epifluorescence and transmission electron microscopy (TEM) to evaluate the structural properties of cultured Xenopus kidney cells (A6; ATCC) that were exposed either to commercially available CdSe QDs (Qtracker® 565, Invitrogen) or to heterostructured InP QDs (LANL). Epifluorescence imaging permitted assessment of the general morphology of cells labeled with fluorescent molecular probes (Alexa Fluor® ® phalloidin; Hoechst 33342), and the prevalence of QD association with cells. In contrast, TEM offered unique advantages for viewing electron dense QDs at higher resolution with regard to subcellular sequestration and compartmentalization. Preliminary results show that in the absence of targeting moieties, InP QDs (200 nM) can passively enter cells and sequester nonspecifically in cytosolic regions whereas commercially available targeted QDs principally associate with membranous structures within the cell. Supported by: NIH 5R01GM084702. PMID:21808662

Degradation of aqueous synthesized CdTe/ZnS quantum dots in mice: differential blood kinetics and biodistribution of cadmium and tellurium

PubMed Central

2013-01-01

Background Quantum dots (QDs) have been used as novel fluorescent nanoprobes for various bioapplications. The degradation of QDs, and consequent release of free cadmium ions, have been suggested to be the causes of their overall toxicity. However, in contrast to sufficient investigations regarding the biological fate of QDs, a paucity of studies have reported their chemical fate in vivo. Therefore, the overall aim of our study was to understand the chemical fate of QDs in vivo and explore analytical techniques or methods that could be used to define the chemical fate of QDs in vivo. Methods Male ICR mice were administered a single intravenous dose (0.2 μmol/kg) of aqueous synthesized CdTe/ZnS aqQDs. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to simultaneously measure the concentrations of cadmium (Cd) and tellurium (Te) in the blood and tissues over the course of a 28 day period. We compared the blood kinetic parameters and biodistributions of Cd and Te, and used the molar ratio of Cd:Te as a marker for QDs degradation. Results Cd and Te display different blood kinetics and biodistribution profiles. The Cd:Te ratio in the blood did not vary significantly within the first hour compared with intact CdTe/ZnS aqQDs. The Cd:Te ratio decreased gradually over time from the 6 h time point on. Cd accumulated in the liver, kidneys, and spleen. Te was distributed primarily to the kidneys. Sharp time-dependent increases in the Cd:Te ratio were found in liver tissues. Conclusions QDs can undergo degradation in vivo. In vitro, QDs are chemically stable and do not elicit the same biological responses or consequences as they do in vivo. Our methods might provide valuable information regarding the degradation of QDs in vivo and may enable the design and development of QDs for biological and biomedical applications. PMID:23915017

Degradation of aqueous synthesized CdTe/ZnS quantum dots in mice: differential blood kinetics and biodistribution of cadmium and tellurium.

PubMed

Liu, Na; Mu, Ying; Chen, Yi; Sun, Hubo; Han, Sihai; Wang, Mengmeng; Wang, Hui; Li, Yanbo; Xu, Qian; Huang, Peili; Sun, Zhiwei

2013-08-06

Quantum dots (QDs) have been used as novel fluorescent nanoprobes for various bioapplications. The degradation of QDs, and consequent release of free cadmium ions, have been suggested to be the causes of their overall toxicity. However, in contrast to sufficient investigations regarding the biological fate of QDs, a paucity of studies have reported their chemical fate in vivo. Therefore, the overall aim of our study was to understand the chemical fate of QDs in vivo and explore analytical techniques or methods that could be used to define the chemical fate of QDs in vivo. Male ICR mice were administered a single intravenous dose (0.2 μmol/kg) of aqueous synthesized CdTe/ZnS aqQDs. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to simultaneously measure the concentrations of cadmium (Cd) and tellurium (Te) in the blood and tissues over the course of a 28 day period. We compared the blood kinetic parameters and biodistributions of Cd and Te, and used the molar ratio of Cd:Te as a marker for QDs degradation. Cd and Te display different blood kinetics and biodistribution profiles. The Cd:Te ratio in the blood did not vary significantly within the first hour compared with intact CdTe/ZnS aqQDs. The Cd:Te ratio decreased gradually over time from the 6 h time point on. Cd accumulated in the liver, kidneys, and spleen. Te was distributed primarily to the kidneys. Sharp time-dependent increases in the Cd:Te ratio were found in liver tissues. QDs can undergo degradation in vivo. In vitro, QDs are chemically stable and do not elicit the same biological responses or consequences as they do in vivo. Our methods might provide valuable information regarding the degradation of QDs in vivo and may enable the design and development of QDs for biological and biomedical applications.

Sponge-like Si-SiO2 nanocomposite—Morphology studies of spinodally decomposed silicon-rich oxide

NASA Astrophysics Data System (ADS)

Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.; Mikolajick, T.

2013-09-01

Sponge-like Si nanostructures embedded in SiO2 were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.

Suppressed blinking behavior of CdSe/CdS QDs by polymer coating

NASA Astrophysics Data System (ADS)

Zhang, Aidi; Bian, Yannan; Wang, Jinjie; Chen, Kuiyong; Dong, Chaoqing; Ren, Jicun

2016-02-01

Semiconductor quantum dots (QDs) are very important fluorescent nanocrystals with excellent optical properties. However, QDs, at the single-particle level, show severe fluorescence intermittency (or blinking) on a wide time scale from milliseconds to minutes, which limits certain optical and biological applications. Generally, blinking behavior of QDs strongly depends on their surface state and surrounding environment. Therefore, current blinking suppression approaches are mostly focused on the introduction of an inorganic shell and organic small molecule compounds. In this study, we described a ``bottom up'' approach for the synthesis of CdSe/CdS/polymer core/shell/shell QDs via the in situ one-pot polymerization approach in order to control the blinking behavior of QDs. Three monomers (dithiothreitol (DTT), phenylenediamine (PDA), and hexamethylenediamine (HDA)) were respectively used to polymerize with hexachlorocyclotriphosphazene (HCCP), and then the polyphosphazene polymers were obtained with cyclotriphosphazene as the basic macromolecular backbone. By regulating the molar ratios of the activated comonomers, we can control the blinking behavior of CdSe/CdS/polymer QDs. Under the optimal conditions, the percentage of ``non-blinking'' CdSe/CdS/polymer QDs (the ``on time'' fraction > 99% of the overall observation time) was up to 78%. The suppression mechanism was attributed to the efficient passivation of QD surface traps by the sulfhydryl or phenyl groups in the polyphosphazene polymers.Semiconductor quantum dots (QDs) are very important fluorescent nanocrystals with excellent optical properties. However, QDs, at the single-particle level, show severe fluorescence intermittency (or blinking) on a wide time scale from milliseconds to minutes, which limits certain optical and biological applications. Generally, blinking behavior of QDs strongly depends on their surface state and surrounding environment. Therefore, current blinking suppression approaches are mostly focused on the introduction of an inorganic shell and organic small molecule compounds. In this study, we described a ``bottom up'' approach for the synthesis of CdSe/CdS/polymer core/shell/shell QDs via the in situ one-pot polymerization approach in order to control the blinking behavior of QDs. Three monomers (dithiothreitol (DTT), phenylenediamine (PDA), and hexamethylenediamine (HDA)) were respectively used to polymerize with hexachlorocyclotriphosphazene (HCCP), and then the polyphosphazene polymers were obtained with cyclotriphosphazene as the basic macromolecular backbone. By regulating the molar ratios of the activated comonomers, we can control the blinking behavior of CdSe/CdS/polymer QDs. Under the optimal conditions, the percentage of ``non-blinking'' CdSe/CdS/polymer QDs (the ``on time'' fraction > 99% of the overall observation time) was up to 78%. The suppression mechanism was attributed to the efficient passivation of QD surface traps by the sulfhydryl or phenyl groups in the polyphosphazene polymers. Electronic supplementary information (ESI) available: Synthesis and characterization of QDs, FTIR analysis, particle distribution, PL decays, TGA data and power-law distribution of QDs. See DOI: 10.1039/c5nr08504g

The Developmental Toxicity of Complex Silica-Embedded Nickel Nanoparticles Is Determined by Their Physicochemical Properties

PubMed Central

Mahoney, Sharlee; Najera, Michelle; Bai, Qing; Burton, Edward A.; Veser, Götz

2016-01-01

Complex engineered nanomaterials (CENs) are a rapidly developing class of structurally and compositionally complex materials that are expected to dominate the next generation of functional nanomaterials. The development of methods enabling rapid assessment of the toxicity risk associated with this type of nanomaterial is therefore critically important. We evaluated the toxicity of three differently structured nickel-silica nanomaterials as prototypical CENs: simple, surface-deposited Ni-SiO2 and hollow and non-hollow core-shell Ni@SiO2 materials (i.e., ~1–2 nm Ni nanoparticles embedded into porous silica shells with and without a central cavity, respectively). Zebrafish embryos were exposed to these CENs, and morphological (survival and malformations) and physiological (larval motility) endpoints were coupled with thorough characterization of physiochemical characteristics (including agglomeration, settling and nickel ion dissolution) to determine how toxicity differed between these CENs and equivalent quantities of Ni2+ salt (based on total Ni). Exposure to Ni2+ ions strongly compromised zebrafish larva viability, and surviving larvae showed severe malformations. In contrast, exposure to the equivalent amount of Ni CEN did not result in these abnormalities. Interestingly, exposure to Ni-SiO2 and hollow Ni@SiO2 provoked abnormalities of zebrafish larval motor function, indicating developmental toxicity, while non-hollow Ni@SiO2 showed no toxicity. Correlating these observations with physicochemical characterization of the CENs suggests that the toxicity of the Ni-SiO2 and hollow Ni@SiO2 material may result partly from an increased effective exposure at the bottom of the well due to rapid settling. Overall, our data suggest that embedding nickel NPs in a porous silica matrix may be a straightforward way to mitigate their toxicity without compromising their functional properties. At the same time, our results also indicate that it is critical to consider modification of the effective exposure when comparing different nanomaterial configurations, because effective exposure might influence NP toxicity more than specific “nano-chemistry” effects. PMID:27031643

Interface induced spin-orbit interaction in silicon quantum dots and prospects of scalability

NASA Astrophysics Data System (ADS)

Ferdous, Rifat; Wai, Kok; Veldhorst, Menno; Hwang, Jason; Yang, Henry; Klimeck, Gerhard; Dzurak, Andrew; Rahman, Rajib

A scalable quantum computing architecture requires reproducibility over key qubit properties, like resonance frequency, coherence time etc. Randomness in these properties would necessitate individual knowledge of each qubit in a quantum computer. Spin qubits hosted in Silicon (Si) quantum dots (QD) is promising as a potential building block for a large-scale quantum computer, because of their longer coherence times. The Stark shift of the electron g-factor in these QDs has been used to selectively address multiple qubits. From atomistic tight-binding studies we investigated the effect of interface non-ideality on the Stark shift of the g-factor in a Si QD. We find that based on the location of a monoatomic step at the interface with respect to the dot center both the sign and magnitude of the Stark shift change. Thus the presence of interface steps in these devices will cause variability in electron g-factor and its Stark shift based on the location of the qubit. This behavior will also cause varying sensitivity to charge noise from one qubit to another, which will randomize the dephasing times T2*. This predicted device-to-device variability is experimentally observed recently in three qubits fabricated at a Si/Si02 interface, which validates the issues discussed.

Nanoengineering of an Si/MnGe quantum dot superlattice for high Curie-temperature ferromagnetism.

PubMed

Nie, Tianxiao; Kou, Xufeng; Tang, Jianshi; Fan, Yabin; Lee, Shengwei; He, Qinglin; Chang, Li-Te; Murata, Koichi; Gen, Yin; Wang, Kang L

2017-03-02

The realization and application of spintronic devices would be dramatically advanced if room-temperature ferromagnetism could be integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Herein, we report the observation of such a system - an Si/MnGe superlattice with quantum dots well aligned in the vertical direction successfully grown by molecular beam epitaxy. Such a unique system could take full advantage of the type-II energy band structure of the Si/Ge heterostructure, which could trap the holes inside MnGe QDs, significantly enhancing the hole-mediated ferromagnetism. Magnetic measurements indeed found that the superlattice structure exhibited a Curie temperature of above 400 K. Furthermore, zero-field cooling and field cooling curves could confirm the absence of ferromagnetic compounds, such as Ge 8 Mn 11 (T c ∼ 270 K) and Ge 3 Mn 5 (T c ∼ 296 K) in our system. Magnetotransport measurement revealed a clear magnetoresistance transition from negative to positive and a pronounced anomalous Hall effect. Such a unique Si/MnGe superlattice sets a new stage for strengthening ferromagnetism due to the enhanced hole-mediation by quantum confinement, which can be exploited for realizing the room-temperature Ge-based spin field-effect transistors in the future.

Enhancement of β-phase in PVDF films embedded with ferromagnetic Gd 5Si 4 nanoparticles for piezoelectric energy harvesting

DOE PAGES

Harstad, Shane; D’Souza, Noel; Soin, Navneet; ...

2017-01-04

Self-polarized Gd5Si4-polyvinylidene fluoride (PVDF) nanocomposite films have been synthesized via a facile phase-inversion technique. For the 5 wt% Gd 5Si 4-PVDF films, the enhancement of the piezoelectric β-phase and crystallinity are confirmed using Fourier transform infrared (FTIR) spectroscopy (phase fraction, FβFβ, of 81% as compared to 49% for pristine PVDF) and differential scanning calorimetry (crystallinity, ΔXcΔXc, of 58% as compared to 46% for pristine PVDF), respectively. The Gd5Si4 magnetic nanoparticles, prepared using high-energy ball milling were characterized using Dynamic Light Scattering and Vibrating Sample Magnetometry (VSM) to reveal a particle size of ~470 nm with a high magnetization of 11more » emu/g. The VSM analysis of free-standing Gd5Si4-PVDF films revealed that while the pristine PVDF membrane shows weak diamagnetic behavior, the Gd5Si4-PVDF films loaded at 2.5 wt% and 5 wt% Gd 5Si 4 show enhanced ferromagnetic behavior with paramagnetic contribution from Gd5Si3 phase. The interfacial interactions between Gd5Si4 and PVDF results in the preferential crystallization of the β-phase as confirmed via the shift in the CH 2 asymmetric and symmetric stretching vibrations in the FTIR. These results confirm the magnetic Gd 5Si 4 nanoparticles embedded in the PVDF membrane lead to an increased β-phase fraction, which paves the way for future efficient energy harvesting applications using a combination of magnetic and piezoelectric effects.« less

A room-temperature-operated Si LED with β-FeSi2 nanocrystals in the active layer: μW emission power at 1.5 μm

NASA Astrophysics Data System (ADS)

Shevlyagin, A. V.; Goroshko, D. L.; Chusovitin, E. A.; Balagan, S. A.; Dotsenko, S. A.; Galkin, K. N.; Galkin, N. G.; Shamirzaev, T. S.; Gutakovskii, A. K.; Latyshev, A. V.; Iinuma, M.; Terai, Y.

2017-03-01

This article describes the development of an Si-based light-emitting diode with β-FeSi2 nanocrystals embedded in the active layer. Favorable epitaxial conditions allow us to obtain a direct band gap type-I band alignment Si/β-FeSi2 nanocrystals/Si heterostructure with optical transition at a wavelength range of 1500-1550 nm at room temperature. Transmission electron microscopy data reveal strained, defect-free β-FeSi2 nanocrystals of diameter 6 and 25 nm embedded in the Si matrix. Intense electroluminescence was observed at a pumping current density as low as 0.7 A/cm2. The device reached an optical emission power of up to 25 μW at 9 A/cm2 with an external quantum efficiency of 0.009%. Watt-Ampere characteristic linearity suggests that the optical power margin of the light-emitting diode has not been exhausted. Band structure calculations explain the luminescence as being mainly due to radiative recombination in the large β-FeSi2 nanocrystals resulting from the realization of an indirect-to-direct band gap electronic configuration transformation arising from a favorable deformation of nanocrystals. The direct band gap structure and the measured short decay time of the luminescence of several tens of ns give rise to a fast operation speed for the device. Thus a method for developing a silicon-based photonic integrated circuit, combining complementary metal-oxide-semiconductor technology functionality and near-infrared light emission, is reported here.

Enhancement of 𝜷-phase in PVDF films embedded with ferromagnetic Gd5Si4 nanoparticles for piezoelectric energy harvesting

NASA Astrophysics Data System (ADS)

Harstad, Shane; D'Souza, Noel; Soin, Navneet; El-Gendy, Ahmed A.; Gupta, Shalabh; Pecharsky, Vitalij K.; Shah, Tahir; Siores, Elias; Hadimani, Ravi L.

2017-05-01

Self-polarized Gd5Si4-polyvinylidene fluoride (PVDF) nanocomposite films have been synthesized via a facile phase-inversion technique. For the 5 wt% Gd5Si4-PVDF films, the enhancement of the piezoelectric β-phase and crystallinity are confirmed using Fourier transform infrared (FTIR) spectroscopy (phase fraction, Fβ, of 81% as compared to 49% for pristine PVDF) and differential scanning calorimetry (crystallinity, Δ Xc , of 58% as compared to 46% for pristine PVDF), respectively. The Gd5Si4 magnetic nanoparticles, prepared using high-energy ball milling were characterized using Dynamic Light Scattering and Vibrating Sample Magnetometry (VSM) to reveal a particle size of ˜470 nm with a high magnetization of 11 emu/g. The VSM analysis of free-standing Gd5Si4-PVDF films revealed that while the pristine PVDF membrane shows weak diamagnetic behavior, the Gd5Si4-PVDF films loaded at 2.5 wt% and 5 wt% Gd5Si4 show enhanced ferromagnetic behavior with paramagnetic contribution from Gd5Si3 phase. The interfacial interactions between Gd5Si4 and PVDF results in the preferential crystallization of the β-phase as confirmed via the shift in the CH2 asymmetric and symmetric stretching vibrations in the FTIR. These results confirm the magnetic Gd5Si4 nanoparticles embedded in the PVDF membrane lead to an increased β-phase fraction, which paves the way for future efficient energy harvesting applications using a combination of magnetic and piezoelectric effects.

Enhancement of β-phase in PVDF films embedded with ferromagnetic Gd 5Si 4 nanoparticles for piezoelectric energy harvesting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harstad, Shane; D’Souza, Noel; Soin, Navneet

Self-polarized Gd5Si4-polyvinylidene fluoride (PVDF) nanocomposite films have been synthesized via a facile phase-inversion technique. For the 5 wt% Gd 5Si 4-PVDF films, the enhancement of the piezoelectric β-phase and crystallinity are confirmed using Fourier transform infrared (FTIR) spectroscopy (phase fraction, FβFβ, of 81% as compared to 49% for pristine PVDF) and differential scanning calorimetry (crystallinity, ΔXcΔXc, of 58% as compared to 46% for pristine PVDF), respectively. The Gd5Si4 magnetic nanoparticles, prepared using high-energy ball milling were characterized using Dynamic Light Scattering and Vibrating Sample Magnetometry (VSM) to reveal a particle size of ~470 nm with a high magnetization of 11more » emu/g. The VSM analysis of free-standing Gd5Si4-PVDF films revealed that while the pristine PVDF membrane shows weak diamagnetic behavior, the Gd5Si4-PVDF films loaded at 2.5 wt% and 5 wt% Gd 5Si 4 show enhanced ferromagnetic behavior with paramagnetic contribution from Gd5Si3 phase. The interfacial interactions between Gd5Si4 and PVDF results in the preferential crystallization of the β-phase as confirmed via the shift in the CH 2 asymmetric and symmetric stretching vibrations in the FTIR. These results confirm the magnetic Gd 5Si 4 nanoparticles embedded in the PVDF membrane lead to an increased β-phase fraction, which paves the way for future efficient energy harvesting applications using a combination of magnetic and piezoelectric effects.« less

The structures and electronic properties of zigzag silicene nanoribbons with periodically embedded with four- and eight-membered rings

NASA Astrophysics Data System (ADS)

Tan, Guiping; Lu, Junzhe; Zhu, Hengjiang; Li, Fangfang; Ma, Miaomiao; Wang, Xiaoning

2018-07-01

Using density functional theory (DFT), we have studied the structure of a zigzag silicene nanoribbons (SiNRs) with periodically embedded with four- and eight-membered rings, and studied their electronic properties by calculating its band structures and density of states (DOS). The results showed that the zigzag SiNRs have a sp2 hybridization, in addition, the band gap gradually decreased with the increase of the width by layer, and gradually changed from semiconductor properties to metal properties. The existence of vacancy defects increased the band gap and energies, but their positions could not change the structure and the electronic properties.

A 16-ch module for thermal neutron detection using ZnS:6LiF scintillator with embedded WLS fibers coupled to SiPMs and its dedicated readout electronics

NASA Astrophysics Data System (ADS)

Mosset, J.-B.; Stoykov, A.; Greuter, U.; Gromov, A.; Hildebrandt, M.; Panzner, T.; Schlumpf, N.

2017-02-01

A scalable 16-ch thermal neutron detection system has been developed in the framework of the upgrade of a neutron diffractometer. The detector is based on a ZnS:6LiF scintillator with embedded WLS fibers which are read out with SiPMs. In this paper, we present the 16-ch module, the dedicated readout electronics, a direct comparison between the performance of the diffractometer obtained with the current 3He detector and with the 16-ch detection module, and the channel-to-channel uniformity.

Facet-embedded thin-film III-V edge-emitting lasers integrated with SU-8 waveguides on silicon.

PubMed

Palit, Sabarni; Kirch, Jeremy; Huang, Mengyuan; Mawst, Luke; Jokerst, Nan Marie

2010-10-15

A thin-film InGaAs/GaAs edge-emitting single-quantum-well laser has been integrated with a tapered multimode SU-8 waveguide onto an Si substrate. The SU-8 waveguide is passively aligned to the laser using mask-based photolithography, mimicking electrical interconnection in Si complementary metal-oxide semiconductor, and overlaps one facet of the thin-film laser for coupling power from the laser to the waveguide. Injected threshold current densities of 260A/cm(2) are measured with the reduced reflectivity of the embedded laser facet while improving single mode coupling efficiency, which is theoretically simulated to be 77%.

Low-energy ion beam synthesis of Ag endotaxial nanostructures in silicon

NASA Astrophysics Data System (ADS)

Nagarajappa, Kiran; Guha, Puspendu; Thirumurugan, Arun; Satyam, Parlapalli V.; Bhatta, Umananda M.

2018-06-01

Coherently, embedded metal nanostructures (endotaxial) are known to have potential applications concerning the areas of plasmonics, optoelectronics and thermoelectronics. Incorporating appropriate concentrations of metal atoms into crystalline silicon is critical for these applications. Therefore, choosing proper dose of low-energy ions, instead of depositing thin film as a source of metal atoms, helps in avoiding surplus concentration of metal atoms that diffuses into the silicon crystal. In this work, 30 keV silver negative ions are implanted into a SiO x /Si(100) at two different fluences: 1 × 1015 and 2.5 × 1015 Ag- ions/cm2. Later, the samples are annealed at 700 °C for 1 h in Ar atmosphere. Embedded silver nanostructures have been characterized using planar and cross-sectional TEM (XTEM) analysis. Planar TEM analysis shows the formation of mostly rectangular silver nanostructures following the fourfold symmetry of the substrate. XTEM analysis confirms the formation of prism-shaped silver nanostructures embedded inside crystalline silicon. Endotaxial nature of the embedded crystals has been discussed using selected area electron diffraction analysis.

Integration of Si-CMOS embedded photo detector array and mixed signal processing system with embedded optical waveguide input

NASA Astrophysics Data System (ADS)

Kim, Daeik D.; Thomas, Mikkel A.; Brooke, Martin A.; Jokerst, Nan M.

2004-06-01

Arrays of embedded bipolar junction transistor (BJT) photo detectors (PD) and a parallel mixed-signal processing system were fabricated as a silicon complementary metal oxide semiconductor (Si-CMOS) circuit for the integration optical sensors on the surface of the chip. The circuit was fabricated with AMI 1.5um n-well CMOS process and the embedded PNP BJT PD has a pixel size of 8um by 8um. BJT PD was chosen to take advantage of its higher gain amplification of photo current than that of PiN type detectors since the target application is a low-speed and high-sensitivity sensor. The photo current generated by BJT PD is manipulated by mixed-signal processing system, which consists of parallel first order low-pass delta-sigma oversampling analog-to-digital converters (ADC). There are 8 parallel ADCs on the chip and a group of 8 BJT PDs are selected with CMOS switches. An array of PD is composed of three or six groups of PDs depending on the number of rows.

Characterization of phthalocyanine functionalized quantum dots by dynamic light scattering, laser Doppler, and capillary electrophoresis.

PubMed

Ramírez-García, Gonzalo; Oluwole, David O; Nxele, Siphesihle Robin; d'Orlyé, Fanny; Nyokong, Tebello; Bedioui, Fethi; Varenne, Anne

2017-02-01

In this work, we characterized different phtalocyanine-capped core/shell/shell quantum dots (QDs) in terms of stability, ζ-potential, and size at various pH and ionic strengths, by means of capillary electrophoresis (CE), and compared these results to the ones obtained by laser Doppler electrophoresis (LDE) and dynamic light scattering (DLS). The effect of the phthalocyanine metallic center (Zn, Al, or In), the number (one or four), and nature of substituents (carboxyphenoxy- or sulfonated-) of functionalization on the phthalocyanine physicochemical properties were evaluated. Whereas QDs capped with zinc mono-carboxyphenoxy-phtalocyanine (ZnMCPPc-QDs) remained aggregated in the whole analyzed pH range, even at low ionic strength, QDs capped with zinc tetracarboxyphenoxy phtalocyanine (ZnTPPc-QDs) were easily dispersed in buffers at pH equal to or higher than 7.4. QDs capped with aluminum tetrasulfonated phthalocyanine (AlTSPPc-QDs) and indium tetracarboxyphenoxy phthalocyanines (InTCPPc-QDs) were stable in aqueous suspension only at pH higher than 9.0 due to the presence of functional groups bound to the metallic center of the phthalocyanine. The ζ-potential values determined by CE for all the samples decreased when ionic strength increased, being well correlated with the aggregation of the nanoconjugates at elevated salt concentrations. The use of electrokinetic methodologies has provided insights into the colloidal stability of the photosensitizer-functionalized QDs in physiological relevant solutions and thereby, its usefulness for improving their design and applications for photodynamic therapy. Graphical Abstract Schematic illustration of the phthalocyanine capped QDs nanoconjugates and the capillary electrophoresis methods applied for size and ζ-potential characterization.

Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties

NASA Astrophysics Data System (ADS)

Mumin, Md Abdul; Xu, William Z.; Charpentier, Paul A.

2015-08-01

The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica-encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core-shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (˜65%) and photostability compared to the bare QDs. Both the encapsulated bare and core-shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (˜90%) and decreased UV transmission (˜75%).

Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties.

PubMed

Mumin, Md Abdul; Xu, William Z; Charpentier, Paul A

2015-08-07

The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica-encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core-shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (∼65%) and photostability compared to the bare QDs. Both the encapsulated bare and core-shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (∼90%) and decreased UV transmission (∼75%).

The Reproductive Toxicity of CdSe/ZnS Quantum Dots on the in vivo Ovarian Function and in vitro Fertilization

PubMed Central

Xu, Gaixia; Lin, Guimiao; Lin, Suxia; Wu, Na; Deng, Yueyue; Feng, Gang; Chen, Qiang; Qu, Junle; Chen, Danni; Chen, Siping; Niu, Hanben; Mei, Shujiang; Yong, Ken-Tye; Wang, Xiaomei

2016-01-01

Despite the usefulness of quantum dots (QDs) in biomedicine and optoelectronics, their toxicity risks remain a major obstacle for clinical usages. Hence, we studied the reproductive toxicity of CdSe/ZnS QDs on two aspects, (i) in vivo ovarian functions and (ii) in vitro fertilization process. The body weight, estrous cycles, biodistribution of QDs, and oocyte maturation are evaluated on female mice treated with QDs. The mRNA level of the follicle-stimulating hormone receptor (FSHr) and luteinizing hormone receptor (LHr) in ovaries are assayed. Then, the matured cumulus-oocyte-complexes are harvested to co-culture with in vitro capacitated sperms, and the in vitro fertilization is performed. The result revealed that QDs are found in the ovaries, but no changes are detected on the behavior and estrous cycle on the female mice. The mRNA downregulations of FSHr and LHr are observed and the number of matured oocytes has shown a significant decrease when the QDs dosage was above 1.0 pmol/day. Additionally, we found the presence of QDs has reduced the in vitro fertilization success rate. This study highly suggests that the exposure of CdSe/ZnS QDs to female mice can cause adverse effects to the ovary functions and such QDs may have limited applications in clinical usage. PMID:27876896

The Reproductive Toxicity of CdSe/ZnS Quantum Dots on the in vivo Ovarian Function and in vitro Fertilization.

PubMed

Xu, Gaixia; Lin, Guimiao; Lin, Suxia; Wu, Na; Deng, Yueyue; Feng, Gang; Chen, Qiang; Qu, Junle; Chen, Danni; Chen, Siping; Niu, Hanben; Mei, Shujiang; Yong, Ken-Tye; Wang, Xiaomei

2016-11-23

Despite the usefulness of quantum dots (QDs) in biomedicine and optoelectronics, their toxicity risks remain a major obstacle for clinical usages. Hence, we studied the reproductive toxicity of CdSe/ZnS QDs on two aspects, (i) in vivo ovarian functions and (ii) in vitro fertilization process. The body weight, estrous cycles, biodistribution of QDs, and oocyte maturation are evaluated on female mice treated with QDs. The mRNA level of the follicle-stimulating hormone receptor (FSHr) and luteinizing hormone receptor (LHr) in ovaries are assayed. Then, the matured cumulus-oocyte-complexes are harvested to co-culture with in vitro capacitated sperms, and the in vitro fertilization is performed. The result revealed that QDs are found in the ovaries, but no changes are detected on the behavior and estrous cycle on the female mice. The mRNA downregulations of FSHr and LHr are observed and the number of matured oocytes has shown a significant decrease when the QDs dosage was above 1.0 pmol/day. Additionally, we found the presence of QDs has reduced the in vitro fertilization success rate. This study highly suggests that the exposure of CdSe/ZnS QDs to female mice can cause adverse effects to the ovary functions and such QDs may have limited applications in clinical usage.

Inhibition of autophagy contributes to the toxicity of cadmium telluride quantum dots in Saccharomyces cerevisiae.

PubMed

Fan, Junpeng; Shao, Ming; Lai, Lu; Liu, Yi; Xie, Zhixiong

2016-01-01

Cadmium telluride quantum dots (CdTe QDs) are used as near-infrared probes in biologic and medical applications, but their cytological effects and mechanism of potential toxicity are still unclear. In this study, we evaluated the toxicity of CdTe QDs of different sizes and investigated their mechanism of toxicity in the yeast Saccharomyces cerevisiae. A growth inhibition assay revealed that orange-emitting CdTe (O-CdTe) QDs (half inhibitory concentration [IC50] =59.44±12.02 nmol/L) were more toxic than green-emitting CdTe QDs (IC50 =186.61±19.74 nmol/L) to S. cerevisiae. Further studies on toxicity mechanisms using a transmission electron microscope and green fluorescent protein tagged Atg8 processing assay revealed that O-CdTe QDs could partially inhibit autophagy at a late stage, which differs from the results reported in mammalian cells. Moreover, autophagy inhibited at a late stage by O-CdTe QDs could be partially recovered by enhancing autophagy with rapamycin (an autophagy activator), combined with an increased number of living cells. These results indicate that inhibition of autophagy acts as a toxicity mechanism of CdTe QDs in S. cerevisiae. This work reports a novel toxicity mechanism of CdTe QDs in yeast and provides valuable information on the effect of CdTe QDs on the processes of living cells.

Development and characterization of silk fibroin coated quantum dots

NASA Astrophysics Data System (ADS)

Nathwani, B. B.; Needham, C.; Mathur, A. B.; Meissner, K. E.

2008-02-01

Recent progress in the field of semiconductor nanocrystals or Quantum Dots (QDs) has seen them find wider acceptance as a tool in biomedical research labs. As produced, high quality QDs, synthesized by high temperature organometallic synthesis, are coated with a hydrophobic ligand. Therefore, they must be further processed to be soluble in water and to be made biocompatible. To accomplish this, the QDs are generally coated with a synthetic polymer (eg. block copolymers) or the hydrophobic surface ligands exchanged with hydrophilic material (eg. thiols). Advances in this area have enabled the QDs to experience a smooth transition from being simple inorganic fluorophores to being smart sensors, which can identify specific cell marker proteins and help in diagnosis of diseases such as cancer. In order to improve the biocompatibility and utility of the QDs, we report the development of a procedure to coat QDs with silk fibroin, a fibrous crystalline protein extracted from Bombyx Mori silkworm. Following the coating process, we characterize the size, quantum yield and two-photon absorption cross section of the silk coated QDs. Additionally, the results of biocompatibility studies carried out to compare the properties of these QD-silks with conventional QDs are presented. These natural polymer coatings on QDs could enhance the intracellular delivery and enable the use of these nanocrystals as an imaging tool for studying subcellular machinery at the molecular level.

Ligand-Asymmetric Janus Quantum Dots for Efficient Blue-Quantum Dot Light-Emitting Diodes.

PubMed

Cho, Ikjun; Jung, Heeyoung; Jeong, Byeong Guk; Hahm, Donghyo; Chang, Jun Hyuk; Lee, Taesoo; Char, Kookheon; Lee, Doh C; Lim, Jaehoon; Lee, Changhee; Cho, Jinhan; Bae, Wan Ki

2018-06-19

We present ligand-asymmetric Janus quantum dots (QDs) to improve the device performance of quantum dot light-emitting diodes (QLEDs). Specifically, we devise blue QLEDs incorporating blue QDs with asymmetrically modified ligands, in which the bottom ligand of QDs in contact with ZnO electron-transport layer serves as a robust adhesive layer and an effective electron-blocking layer and the top ligand ensures uniform deposition of organic hole transport layers with enhanced hole injection properties. Suppressed electron overflow by the bottom ligand and stimulated hole injection enabled by the top ligand contribute synergistically to boost the balance of charge injection in blue QDs and therefore the device performance of blue QLEDs. As an ultimate achievement, the blue QLED adopting ligand-asymmetric QDs displays 2-fold enhancement in peak external quantum efficiency (EQE = 3.23%) compared to the case of QDs with native ligands (oleic acid) (peak EQE = 1.49%). The present study demonstrates an integrated strategy to control over the charge injection properties into QDs via ligand engineering that enables enhancement of the device performance of blue QLEDs and thus promises successful realization of white light-emitting devices using QDs.

Direct generation of linearly polarized single photons with a deterministic axis in quantum dots

NASA Astrophysics Data System (ADS)

Wang, Tong; Puchtler, Tim J.; Patra, Saroj K.; Zhu, Tongtong; Ali, Muhammad; Badcock, Tom J.; Ding, Tao; Oliver, Rachel A.; Schulz, Stefan; Taylor, Robert A.

2017-07-01

We report the direct generation of linearly polarized single photons with a deterministic polarization axis in self-assembled quantum dots (QDs), achieved by the use of non-polar InGaN without complex device geometry engineering. Here, we present a comprehensive investigation of the polarization properties of these QDs and their origin with statistically significant experimental data and rigorous k·p modeling. The experimental study of 180 individual QDs allows us to compute an average polarization degree of 0.90, with a standard deviation of only 0.08. When coupled with theoretical insights, we show that these QDs are highly insensitive to size differences, shape anisotropies, and material content variations. Furthermore, 91% of the studied QDs exhibit a polarization axis along the crystal [1-100] axis, with the other 9% polarized orthogonal to this direction. These features give non-polar InGaN QDs unique advantages in polarization control over other materials, such as conventional polar nitride, InAs, or CdSe QDs. Hence, the ability to generate single photons with polarization control makes non-polar InGaN QDs highly attractive for quantum cryptography protocols.

Charge Transport between Coupling Colloidal Perovskite Quantum Dots Assisted by Functional Conjugated Ligands.

PubMed

Dai, Jinfei; Xi, Jun; Li, Lu; Zhao, JingFeng; Shi, Yifei; Zhang, Wenwen; Ran, Chenxin; Jiao, Bo; Hou, Xun; Duan, Xinhua; Wu, Zhaoxin

2018-05-14

Long alkyl-chain capping ligands are indispensable for preparing stable colloidal quantum dots. However, its insulating feature blocks efficient carrier transport among QDs, leading to inferior performance in light-emitting diodes (LEDs). The trade-off between conductivity and colloidal stability of QDs has now been overcome. Methylamine lead bromide (MAPbBr 3 ) QDs with a conjugated alkyl-amine, 3-phenyl-2-propen-1-amine (PPA), as ligands were prepared. Owing to electron cloud overlapping and the delocalization effect of conjugated molecules, the conductivity and carrier mobility of PPA-QDs films increased almost 22 times over that of OA-QD films without compromising colloidal stability and photoluminescence. PPA-QDs LEDs exhibit a maximum current efficiency of 9.08 cd A -1 , which is 8 times of that of OA-QDs LEDs (1.14 cd A -1 ). This work provides critical solution for the poor conductivity of QDs in applications of energy-related devices. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nano interface potential influences in CdTe quantum dots and biolabeling

NASA Astrophysics Data System (ADS)

Kanagasubbulakshmi, S.; Kadirvelu, K.

2018-05-01

Nano interface influences in physiochemical properties of quantum dots (QDs) are the challenging approach to tailor its surface functionalities. In this study, a set of polar and non-polar solvents were selected to analyze the influences in solvent-based dynamic radius and surface potential of QDs. From the nano interface chemistry of polar and non-polar solvents, an appropriate mechanism of precipitation and hydrophobic ligand exchange strategy were elucidated by correlating Henry's equation. Further, the in vitro cytotoxic potential and antimicrobial activity of QDs were assessed to perform biolabeling. From the observations, an appropriate dosage of QDs was fixed to label the animal ((RAW 264.7 cell lines) and bacterial cells (Escherichia coli) for effective cell attachment. Biolabeling was achieved by tailoring nano interface chemistry of QDs without additional support of biomolecules. Bacterial cell wall-based interaction of QDs was evaluated using SEM and EDAX analysis. Thus, provided clear insights into the nano interface chemistry in the development of highly photostable QDs will be helpful in biomedical applications.

Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with quantum dots

NASA Astrophysics Data System (ADS)

Bastos-Arrieta, Julio; Muñoz, Jose; Stenbock-Fermor, Anja; Muñoz, Maria; Muraviev, Dmitri N.; Céspedes, Francisco; Tsarkova, Larisa A.; Baeza, Mireia

2016-04-01

Intermatrix Synthesis (IMS) technique has proven to be a valid methodology for the in situ incorporation of quantum dots (QDs) in a wide range of nanostructured surfaces for the preparation of advanced hybrid-nanomaterials. In this sense, this communication reports the recent advances in the application of IMS for the synthesis of CdS-QDs with favourable distribution on sulfonated polyetherether ketone (SPEEK) membrane thin films (TFs), multiwall carbon nanotubes (MWCNTs) and nanodiamonds (NDs). The synthetic route takes advantage of the ion exchange functionality of the reactive surfaces for the loading of the QDs precursor and consequent QDs appearance by precipitation. The benefits of such modified nanomaterials were studied using CdS-QDs@MWCNTs hybrid-nanomaterials. CdS-QDs@MWCNTs has been used as conducting filler for the preparation of electrochemical nanocomposite sensors, which present electrocatalytic properties. Finally, the optical properties of the QDs contained on MWCNTs could allow a new procedure for the analytical detection of nanostructured carbon allotropes in water.

Effect of Chemicals on Morphology and Luminescence of CdSe Quantum Dots.

PubMed

Zhang, Xiao; Li, Xiaoyu; Zhang, Ruili; Yang, Ping

2015-04-01

CdSe quantum dots (QDs) with several morphologies were fabricated using various reaction sys- tems. In a trioctylamine (TOA) and octadecylphosphonic acid (ODPA) system, yellow-emitting (a photoluminescence (PL) peak wavelength of 583 nm) CdSe QDs revealed rod morphology and nar- row size distribution. When ODPA was replaced by tetradecylphosphonic acid (TDPA), red-emitting CdSe rods (a PL peak wavelength of 653 nm) with broad size distribution were fabricated. This is ascribed that the short carbon chain accelerated the growth of CdSe QDs. As a result, the use of ODPA resulted in CdSe QDs with high PL efficiency (3.1%). Furthermore, cubic-like CdSe QDs were created in a stearic acid (SA) and octadecene (ODE) reaction system. The PL efficiency of the QDs is low (0.2%). When hexadecylamine (HDA) was added in such SA and ODE reaction system, spherical CdSe QDs with narrow size distribution and high PL efficiency (3.4%) were prepared.

One-step instant synthesis of protein-conjugated quantum dots at room temperature.

PubMed

He, Xuewen; Gao, Li; Ma, Nan

2013-10-02

We present a new general facile strategy for the preparation of protein-functionalized QDs in a single step at ambient conditions. We demonstrated that highly luminescent red to near-infrared (NIR) protein-functionalized QDs could be synthesized at room temperature in one second through a one-pot reaction that proceeds in aqueous solution. Herein protein-functionalized QDs were successfully constructed for a variety of proteins with a wide range of molecular weights and isoelectric points. The as-prepared protein-conjugated QDs exhibited high quantum yield, high photostabiliy and colloidal stability, and high functionalization efficiency. Importantly, the proteins attached to the QDs maintain their biological activities and are capable of catalyzing reactions and biotargeting. In particular, the as-prepared transferrin-QDs could be used to label cancer cells with high specificity. Moreover, we demonstrated that this synthetic strategy could be extended to prepare QDs functionalized with folic acids and peptides, which were also successfully applied to cancer cell imaging.

Highly Enhanced Fluorescence of CdSeTe Quantum Dots Coated with Polyanilines via In-Situ Polymerization and Cell Imaging Application.

PubMed

Xue, Jingjing; Chen, Xinyi; Liu, Shanglin; Zheng, Fenfen; He, Li; Li, Lingling; Zhu, Jun-Jie

2015-09-02

The polyaniline (PAN)-coated CdSeTe quantum dots (QDs) were prepared by in situ polymerization of aniline on the surface of CdSeTe QDs. The PAN-coated CdSeTe QDs has a tremendously enhanced fluorescence (∼40 times) and improved biocompatibility compared to the uncoated CdSeTe QDs. The fluorescence intensity of the PAN-coated CdSeTe QDs can be adjusted by controlling the construction parameters of the PAN shell. The kinetics of the in situ controllable polymerization process was studied by varying the temperature, and the apparent activation energy of polymerization was estimated. With the same method, a series of the PAN derivatives were also tested to coat the CdSeTe QDs in this study. All the QDs showed a significant enhancement of the fluorescence intensity and better biocompatibility. The significantly enhanced fluorescence can provide highly amplified signal for luminescence-based cell imaging.

Bacterial Interactions with CdSe Quantum Dots

NASA Astrophysics Data System (ADS)

Holden, P.; Nadeau, J. L.; Kumar, A.; Clarke, S.; Priester, J. H.; Stucky, G. D.

2007-12-01

Cadmium selenide quantum dots (QDs) are semiconductor nanoparticles that are manufactured for biomedical imaging, photovoltaics, and other applications. While metallic nanoparticles can be made biotically by bacteria and fungi, and thus occur in nature, the fate of either natural or engineered QDs and relationships to nanoparticle size, conjugate and biotic conditions are mostly unknown. Working with several different bacterial strains and QDs of different sizes and conjugate chemistries, including QDs synthesized by a Fusarium fungal strain, we show that QDs can enter cells through specfic receptor-mediated processes, that QDs are broken down by bacteria during cell association, and that toxicity to cells is much like that imposed by Cd(II) ions. The mechanisms of entry and toxicity are not fully understood, but preliminary evidence suggests that electron transfer between cells and QDs occurs. Also, cell membranes are compromised, indicating oxidative stress is occurring. Results with planktonic and biofilm bacteria are similar, but differently, biofilms tend to accumulate Cd(II) associated with QD treatments.

Photoluminescence investigation of type-II GaSb/GaAs quantum dots grown by liquid phase epitaxy

NASA Astrophysics Data System (ADS)

Wang, Yang; Hu, Shuhong; Xie, Hao; Lin, Hongyu; lu, Hongbo; Wang, Chao; Sun, Yan; Dai, Ning

2018-06-01

GaSb quantum dots (QDs) with an areal density of ∼1 × 1010 cm-2 are successfully grown by the modified (rapid slider) liquid phase epitaxy technique. The morphology of the QDs has been investigated by scanning electron microscope (SEM) and atom force microscope (AFM). The power-dependence and temperature-dependence photoluminescence (PL) spectra have been studied. The bright room-temperature PL suggests a good luminescence quality of GaSb QDs/GaAs matrix system. The type-II alignment of the GaSb QDs/GaAs matrix system is verified by the blue-shift of the QDs peak with the increase of excitation power. From the temperature-dependence PL spectra, the activation energy of QDs is determined to be 111 meV.

Multifunctional quantum dots-based cancer diagnostics and stem cell therapeutics for regenerative medicine.

PubMed

Onoshima, Daisuke; Yukawa, Hiroshi; Baba, Yoshinobu

2015-12-01

A field of recent diagnostics and therapeutics has been advanced with quantum dots (QDs). QDs have developed into new formats of biomolecular sensing to push the limits of detection in biology and medicine. QDs can be also utilized as bio-probes or labels for biological imaging of living cells and tissues. More recently, QDs has been demonstrated to construct a multifunctional nanoplatform, where the QDs serve not only as an imaging agent, but also a nanoscaffold for diagnostic and therapeutic modalities. This review highlights the promising applications of multi-functionalized QDs as advanced nanosensors for diagnosing cancer and as innovative fluorescence probes for in vitro or in vivo stem cell imaging in regenerative medicine. Copyright © 2015 Elsevier B.V. All rights reserved.

Are quantum dots toxic? Exploring the discrepancy between cell culture and animal studies.

PubMed

Tsoi, Kim M; Dai, Qin; Alman, Benjamin A; Chan, Warren C W

2013-03-19

Despite significant interest in developing quantum dots (QDs) for biomedical applications, many researchers are convinced that QDs will never be used for treating patients because of their potential toxicity. The perception that QDs are toxic is rooted in two assumptions. Cadmium-containing QDs can kill cells in culture. Many researchers then assume that because QDs are toxic to cells, they must be toxic to humans. In addition, many researchers classify QDs as a homogeneous group of materials. Therefore, if CdSe QDs are harmful, they extrapolate this result to all QDs. Though unsubstantiated, these assumptions continue to drive QD research. When dosing is physiologically appropriate, QD toxicity has not been demonstrated in animal models. In addition, QDs are not uniform: each design is a unique combination of physicochemical properties that influence biological activity and toxicity. In this Account, we summarize key findings from in vitro and in vivo studies, explore the causes of the discrepancy in QD toxicological data, and provide our view of the future direction of the field. In vitro and in vivo QD studies have advanced our knowledge of cellular transport kinetics, mechanisms of QD toxicity, and biodistribution following animal injection. Cell culture experiments have shown that QDs undergo design-dependent intracellular localization and they can cause cytotoxicity by releasing free cadmium into solution and by generating free radical species. In animal experiments, QDs preferentially enter the liver and spleen following intravascular injection, undergo minimal excretion if larger than 6 nm, and appear to be safe to the animal. In vitro and in vivo studies show an apparent discrepancy with regard to toxicity. Dosing provides one explanation for these findings. Under culture conditions, a cell experiences a constant QD dose, but the in vivo QD concentration can vary, and the organ-specific dose may not be high enough to induce detectable toxicity. Because QDs are retained within animals, long-term toxicity may be a problem but has not been established. Future QD toxicity studies should be standardized and systematized because methodological variability in the current body of literature makes it difficult to compare and contrast results. We advocate the following steps for consistent, comparable toxicology data: (a) standardize dose metrics, (b) characterize QD uptake concentration, (c) identify in vitro models that reflect the cells QDs interact with in vivo, and (d) use multiple assays to determine sublethal toxicity and biocompatibility. Finally, we should ask more specific toxicological questions. For example: "At what dose are 5 nm CdSe QDs that are stabilized with mercaptoacetic acid and conjugated to the antibody herceptin toxic to HeLa cells?" rather than "Are QDs toxic?" QDs are still a long way from realizing their potential as a medical technology. Modifying the current QD toxicological research paradigm, investigating toxicity in a case-by-case manner, and improving study quality are important steps in identifying a QD formulation that is safe for human use.

Self-assembled inorganic clusters of semiconducting quantum dots for effective solar hydrogen evolution.

PubMed

Gao, Yu-Ji; Yang, Yichen; Li, Xu-Bing; Wu, Hao-Lin; Meng, Shu-Lin; Wang, Yang; Guo, Qing; Huang, Mao-Yong; Tung, Chen-Ho; Wu, Li-Zhu

2018-05-08

Owing to promoted electron-hole separation, the catalytic activity of semiconducting quantum dots (QDs) towards solar hydrogen (H2) production has been significantly enhanced by forming self-assembled clusters with ZnSe QDs made ex situ. Taking advantage of the favored interparticle hole transfer to ZnSe QDs, the rate of solar H2 evolution of CdSe QDs can be increased to ∼30 000 μmol h-1 g-1 with ascorbic acid as the sacrificial reagent, ∼150-fold higher than that of bare CdSe QDs clusters under the same conditions.

Growth of boron doped hydrogenated nanocrystalline cubic silicon carbide (3C-SiC) films by Hot Wire-CVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pawbake, Amit; Tata Institute of Fundamental Research, Colaba, Mumbai 400 005; Mayabadi, Azam

Highlights: • Boron doped nc-3C-SiC films prepared by HW-CVD using SiH{sub 4}/CH{sub 4}/B{sub 2}H{sub 6}. • 3C-Si-C films have preferred orientation in (1 1 1) direction. • Introduction of boron into SiC matrix retard the crystallanity in the film structure. • Film large number of SiC nanocrystallites embedded in the a-Si matrix. • Band gap values, E{sub Tauc} and E{sub 04} (E{sub 04} > E{sub Tauc}) decreases with increase in B{sub 2}H{sub 6} flow rate. - Abstract: Boron doped nanocrystalline cubic silicon carbide (3C-SiC) films have been prepared by HW-CVD using silane (SiH{sub 4})/methane (CH{sub 4})/diborane (B{sub 2}H{sub 6}) gasmore » mixture. The influence of boron doping on structural, optical, morphological and electrical properties have been investigated. The formation of 3C-SiC films have been confirmed by low angle XRD, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FTIR) spectroscopy and high resolution-transmission electron microscopy (HR-TEM) analysis whereas effective boron doping in nc-3C-SiC have been confirmed by conductivity, charge carrier activation energy, and Hall measurements. Raman spectroscopy and HR-TEM analysis revealed that introduction of boron into the SiC matrix retards the crystallanity in the film structure. The field emission scanning electron microscopy (FE-SEM) and non contact atomic force microscopy (NC-AFM) results signify that 3C-SiC film contain well resolved, large number of silicon carbide (SiC) nanocrystallites embedded in the a-Si matrix having rms surface roughness ∼1.64 nm. Hydrogen content in doped films are found smaller than that of un-doped films. Optical band gap values, E{sub Tauc} and E{sub 04} decreases with increase in B{sub 2}H{sub 6} flow rate.« less

The alkyl amines effect on the optical properties of inorganic perovskite quantum dot

NASA Astrophysics Data System (ADS)

Yang, Ya-Zhu; Chung, Shu-Ru

2017-08-01

Perovskite quantum dots (P-QDs) is a new kind of optoelectronic materials in recent years. Compared with organic perovskite QDs (MAPbX3), inorganic perovskite QDs (CsPbX3) have a better stability. Inorganic P-QDs can be prepared at low temperature. Those novel QDs can be applied in solar cells, light-emitting diodes (LEDs), display, and biolables. Typical synthesis process to prepare CsPbX3 QDs is used oleic acid (OA) and cesium carbonate (Cs2CO3) to form Cs-oleate complex first. Moreover, the oleylamine (OLA) and octadecene (ODE) are used as capping agents. Cs-oleate complex then reacts with PbX2 to form CsPbX3 QDs (reacts for 5 s). As we know that the CsPbBr3 QDs emits green light, and its emission wavelength can be tuned by adding Cland Iions to replace Brion. However, the reaction rate of CsPbX3 QDs is fast, and it is not easy to control the emission wavelength by particle size. In this study, we use the saturated alkyl amines with difference of carbon chain length such as dodecylamine (DDA), hexadecylamine (HDA), and octadecylamine (ODA) to prepare CsPbBr3 QDs. The result shows that the emission spectra for all samples range from 489 (ODA) to 514 nm (DDA), the full width at half-maximum (FWHM) is between 23 to 28 nm, the surface morphologies of all samples are nearly spherical, and the quantum yields (QYs) are higher up to 130 % (compared with R6G and the excitation wavelength is 450 nm). Based on emission spectra we can find that the emission peaks are fixed even under different excitation wavelength, imply that the particle size distribution of QDs is uniform. Moreover, the emission wavelength blue shifts with increasing carbon chain length of amines. The stability of alkyl amine-capped CsPbBr3 QDs is good, especially for DDA-capped sample. We also find that a small emission peak around 462 nm can be only observed for DDA-capped sample. Furthermore, this small peak also can be observed even prolong the reaction time to 10 min. The emission wavelengths of CsPbBr3 QDs can be controlled by carbon chain length of alkyl amines. The small FWHM and high QYs of CsPbBr3 QDs meaning that it is benefit to enhance the color gamut of display.

A composite material with CeO2-ZrO2 nanocrystallines embedded in SiO2 matrices and its enhanced thermal stability and oxygen storage capacity

NASA Astrophysics Data System (ADS)

Yang, Runnong; Liu, Yumei; Yu, Lin; Zhao, Xiangyun; Yang, Xiaobo; Sun, Ming; Luo, Junyin; Fan, Qun; Xiao, Jianming; Zhao, Yuzhong

2018-06-01

A simple hydrothermal procedure is introduced, which leads to the successful synthesis of a new composite material with fine CeO2-ZrO2 nanocrystallites embedded in amorphous and porous SiO2 matrices. The composite material possesses an extraordinary high thermal stability. After being calcined at 1000 °C, it retains CeO2-ZrO2 nanocrystallites of the size around 5 nm, a BET-specific surface area of 165 m2/g, and an oxygen storage capacity of 468 μmol/g. No phase segregation for CeO2-ZrO2 nanocrystallites is detected and the SiO2 matrices remain not crystallized. The composite material shows a great potential as a support of three-way catalyst, as evidenced in catalytic tests with supported Pt.

Enhanced Materials Based on Submonolayer Type-II Quantum Dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamargo, Maria C; Kuskovsky, Igor L.; Meriles, Carlos

2017-04-15

We have investigated a nanostructured material known as sub-monolayer type-II QDs, made from wide bandgap II-VI semiconductors. Our goal is to understand and exploit their tunable optical and electrical properties by taking advantage of the type-II band alignment and quantum confinement effects. Type-II ZnTe quantum dots (QDs) in a ZnSe host are particularly interesting because of their relatively large valence band and conduction band offsets. In the current award we have developed new materials based on sub-monolayer type-II QDs that may be advantageous for photovoltaic and spintronics applications. We have also expanded the structural characterization of these materials by refiningmore » the X-ray diffraction methodologies needed to investigate them. In particular, we have 1) demonstrated ZnCdTe/ZnCdSe type-II QDs materials that have ideal properties for the development of novel high efficiency “intermediate band solar cells”, 2) we developed a comprehensive approach to describe and model the growth of these ultra-small type-II QDs, 3) analysis of the evolution of the photoluminescence (PL) emission, combined with other characterization probes allowed us to predict the size and density of the QDs as a function of the growth conditions, 4) we developed and implemented novel sophisticated X-ray diffraction techniques from which accurate size and shape of the buried type-II QDs could be extracted, 5) a correlation of the shape anisotropy with polarization dependent PL was observed, confirming the QDs detailed shape and providing insight about the effects of this shape anisotropy on the physical properties of the type-II QD systems, and 6) a detailed “time-resolved Kerr rotation” investigation has led to the demonstration of enhanced electron spin lifetimes for the samples with large densities of type-II QDs and an understanding of the interplay between the QDs and Te-isoelectroic centers, a defect that forms in the spacer layers that separate the QDs.« less

Transport and release of colloidal 3-mercaptopropionic acid-coated CdSe–CdS/ZnS core-multishell quantum dots in human umbilical vein endothelial cells

PubMed Central

Fontana, Jacopo M; Yin, Huijuan; Chen, Yun; Florez, Ricardo; Brismar, Hjalmar; Fu, Ying

2017-01-01

Colloidal semiconductor quantum dots (QDs) have been extensively researched and developed for biomedical applications, including drug delivery and biosensing assays. Hence, it is pivotal to understand their behavior in terms of intracellular transport and toxicological effects. In this study, we focused on 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots (3MPA-QDs) converted from the as-grown octadecylamine-coated quantum dots (ODA-QDs) and their direct and dynamic interactions with human umbilical vein endothelial cells (HUVECs). Live cell imaging using confocal fluorescence microscopy showed that 3MPA-QDs first attached to and subsequently aggregated on HUVEC plasma membrane ~25 min after QD deposition. The aggregated QDs started being internalized at ~2 h and reached their highest internalization degree at ~24 h. They were released from HUVECs after ~48 h. During the 48 h period, the HUVECs responded normally to external stimulations, grew, proliferated and wound healed without any perceptible apoptosis. Furthermore, 1) 3MPA-QDs were internalized in newly formed LysoTracker-stained early endosomes; 2) adenosine 5′-triphosphate-induced [Ca2+]i modulation caused a transient decrease in the fluorescence of 3MPA-QDs that were attached to the plasma membrane but a transient increase in the internalized 3MPA-QDs; and 3) fluorescence signal modulations of co-stained LysoTracker and QDs induced by the lysosomotropic agent Gly-Phe-β-naphthylamide were spatially co-localized and temporally synchronized. Our findings suggest that 3MPA-QDs converted from ODA-QDs are a potential nontoxic fluorescent probe for future use in clinical applications. Moreover, the photophysical strategy and techniques reported in this work are easily applicable to study of direct interactions between other nanoparticles and live cells; contributing to awareness and implementation of the safe applications of nanoparticles. PMID:29270011

Transport and release of colloidal 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots in human umbilical vein endothelial cells.

PubMed

Fontana, Jacopo M; Yin, Huijuan; Chen, Yun; Florez, Ricardo; Brismar, Hjalmar; Fu, Ying

2017-01-01

Colloidal semiconductor quantum dots (QDs) have been extensively researched and developed for biomedical applications, including drug delivery and biosensing assays. Hence, it is pivotal to understand their behavior in terms of intracellular transport and toxicological effects. In this study, we focused on 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots (3MPA-QDs) converted from the as-grown octadecylamine-coated quantum dots (ODA-QDs) and their direct and dynamic interactions with human umbilical vein endothelial cells (HUVECs). Live cell imaging using confocal fluorescence microscopy showed that 3MPA-QDs first attached to and subsequently aggregated on HUVEC plasma membrane ~25 min after QD deposition. The aggregated QDs started being internalized at ~2 h and reached their highest internalization degree at ~24 h. They were released from HUVECs after ~48 h. During the 48 h period, the HUVECs responded normally to external stimulations, grew, proliferated and wound healed without any perceptible apoptosis. Furthermore, 1) 3MPA-QDs were internalized in newly formed LysoTracker-stained early endosomes; 2) adenosine 5'-triphosphate-induced [Ca 2+ ] i modulation caused a transient decrease in the fluorescence of 3MPA-QDs that were attached to the plasma membrane but a transient increase in the internalized 3MPA-QDs; and 3) fluorescence signal modulations of co-stained LysoTracker and QDs induced by the lysosomotropic agent Gly-Phe-β-naphthylamide were spatially co-localized and temporally synchronized. Our findings suggest that 3MPA-QDs converted from ODA-QDs are a potential nontoxic fluorescent probe for future use in clinical applications. Moreover, the photophysical strategy and techniques reported in this work are easily applicable to study of direct interactions between other nanoparticles and live cells; contributing to awareness and implementation of the safe applications of nanoparticles.

Biosensing of matrix metalloproteinase activity with Cd-free quantum dots

NASA Astrophysics Data System (ADS)

Plumley, John Bryan

Quantum dots (QDs) have become attractive in the biomedical field on account of their superior optical properties and stability, in comparison to traditional fluorophores. QDs also have properties which make them ideal for complex in vivo conditions. However, toxicity has been a chief concern in the eventual implementation of QDs for in vivo applications such as biosensing and tumor imaging. Commercially available QDs contain a notoriously noxious Cd component and therefore continuous research has gone into developing QDs without toxic heavy metals, generally Cd, that would still yield comparable performance in terms of their optical properties. Nonetheless, even in the case of Cd-free QDs, toxicity should be evaluated on a case by case basis, as other properties such as size, coating, stability, and charge can affect toxicity of nanomaterials as well, making it a very complex issue. With the high promise of QDs in the field of biomedical development as a motivation, this work strives to develop the efficient and repeatable synthesis of Cd-free QDs with high stability and luminescence, with proven low toxicity, and the ability to detect active matrix metalloproteinase (MMP) in a biosensing system, designed to identify direct biomarkers for pathological conditions, which in turn would enable early disease diagnosis and better treatment development. In this work, highly luminescent ZnSe:Mn/ZnS QDs have been synthesized, characterized, and modified with peptides with a bioconjugation procedure that utilized thiol-metal affinity. Experiments aiming at MMP detection were conducted using the peptide/QD conjugates. In addition, the ApoTox-Glo(TM) Triplex assay was utilized to evaluate cytotoxicity, and a safe concentration below 0.125 microM was identified for peptide-coated ZnSe:Mn/ZnS QDs in water. Finally, in contribution to developing an in vivo fiberoptic system for sensing MMP activity, the QDs were successfully tethered to silica and MMP detection was demonstrated with the peptide/QD conjugates.

Interaction of carboxylated CdSe/ZnS quantum dots with fish embryos: Towards understanding of nanoparticles toxicity.

PubMed

Rotomskis, Ričardas; Jurgelėnė, Živilė; Stankevičius, Mantas; Stankevičiūtė, Milda; Kazlauskienė, Nijolė; Jokšas, Kęstutis; Montvydienė, Danguolė; Kulvietis, Vytautas; Karabanovas, Vitalijus

2018-09-01

Due to colloidal instability even with protective coatings, nanoparticles tend to aggregate in complex environments and possibly interact with biota. In this study, visualization of quantum dots (QDs) interaction with rainbow trout (Oncorhynchus mykiss) embryos was performed. Studies on zebrafish (Danio rerio) and pearl gourami (Trichogaster leerii) embryos have shown that QDs interact with embryos in a general manner and their affects are independent on the type of the embryo. It was demonstrated that carboxylated CdSe/ZnS QDs (4 nM) were aggregating in accumulation media and formed agglomerates on the surface of fish embryos under 1-12 days incubation in deep-well water. Detailed analysis of QDs distribution on fish embryos surface and investigation of the penetration of QDs through embryo's membrane showed that the chorion protects embryos from the penetration through the chorion and the accumulation of nanoparticles inside the embryos. Confocal microscopy and spectroscopy studies on rainbow trout embryos demonstrated that QDs cause chorion damage, due to QDs aggregation on the surface of chorion, even the formation of the agglomerates at the outer part of the embryos and/or with the mucus were detected. Aggregation of QDs and formation of agglomerates on the outer part of the embryo's membrane caused the intervention of the aggregates to the chorion and even partially destroyed the embryo's chorion. The incorporation of QDs in chorion was confirmed by two methods: in living embryos from a 3D reconstruction view, and in slices of embryos from a histology view. The damage of chorion integrity might have adverse effects on embryonic development. Moreover, for the first time the toxic effect of QDs was separated from the heavy metal toxicity, which is most commonly discussed in the literature to the toxicity of the QDs. Copyright © 2018 Elsevier B.V. All rights reserved.

Preparation of water soluble L-arginine capped CdSe/ZnS QDs and their interaction with synthetic DNA: Picosecond-resolved FRET study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giri, Anupam; Goswami, Nirmal; Lemmens, Peter

2012-08-15

Graphical abstract: Förster resonance energy transfer (FRET) studies on the interaction of water soluble arginine-capped CdSe/ZnS QDs with ethidium bromide (EB) labeled synthetic dodecamer DNA. Highlights: ► We have solubilized CdSe/ZnS QD in water replacing their TOPO ligand by L-arginine. ► We have studied arginine@QD–DNA interaction using FRET technique. ► Arginine@QDs act as energy donor and ethidium bromide-DNA acts as energy acceptor. ► We have applied a kinetic model to understand the kinetics of energy transfer. ► Circular dichroism studies revealed negligible perturbation in the DNA B-form in the arg@QD-DNA complex. -- Abstract: We have exchanged TOPO (trioctylphosphine oxide) ligandmore » of CdSe/ZnS core/shell quantum dots (QDs) with an amino acid L-arginine (Arg) at the toluene/water interface and eventually rendered the QDs from toluene to aqueous phase. We have studied the interaction of the water soluble Arg-capped QDs (energy donor) with ethidium (EB) labeled synthetic dodecamer DNA (energy acceptor) using picoseconds resolved Förster resonance energy transfer (FRET) technique. Furthermore, we have applied a model developed by M. Tachiya to understand the kinetics of energy transfer and the distribution of acceptor (EB-DNA) molecules around the donor QDs. Circular dichroism (CD) studies revealed a negligible perturbation in the native B-form structure of the DNA upon interaction with Arg-capped QDs. The melting and the rehybridization pathways of the DNA attached to the QDs have been monitored by the CD which reveals hydrogen bonding is the associative mechanism for interaction between Arg-capped QDs and DNA.« less

Photophysics of Thermally-Assisted Photobleaching in "Giant" Quantum Dots Revealed in Single Nanocrystals.

PubMed

Orfield, Noah J; Majumder, Somak; McBride, James R; Yik-Ching Koh, Faith; Singh, Ajay; Bouquin, Sarah J; Casson, Joanna L; Johnson, Alex D; Sun, Liuyang; Li, Xiaoqin; Shih, Chih-Kang; Rosenthal, Sandra J; Hollingsworth, Jennifer A; Htoon, Han

2018-05-07

Quantum dots (QDs) are steadily being implemented as down-conversion phosphors in market-ready display products to enhance color rendering, brightness, and energy efficiency. However, for adequate longevity, QDs must be encased in a protective barrier that separates them from ambient oxygen and humidity, and device architectures are designed to avoid significant heating of the QDs as well as direct contact between the QDs and the excitation source. In order to increase the utility of QDs in display technologies and to extend their usefulness to more demanding applications as, for example, alternative phosphors for solid-state lighting (SSL), QDs must retain their photoluminescence emission properties over extended periods of time under conditions of high temperature and high light flux. Doing so would simplify the fabrication costs for QD display technologies and enable QDs to be used as down-conversion materials in light-emitting diodes for SSL, where direct-on-chip configurations expose the emitters to temperatures approaching 100 °C and to photon fluxes from 0.1 W/mm 2 to potentially 10 W/mm 2 . Here, we investigate the photobleaching processes of single QDs exposed to controlled temperature and photon flux. In particular, we investigate two types of room-temperature-stable core/thick-shell QDs, known as "giant" QDs for which shell growth is conducted using either a standard layer-by-layer technique or by a continuous injection method. We determine the mechanistic pathways responsible for thermally-assisted photodegradation, distinguishing effects of hot-carrier trapping and QD charging. The findings presented here will assist in the further development of advanced QD heterostructures for maximum device lifetime stability.

Quantum dot transport in soil, plants, and insects.

PubMed

Al-Salim, Najeh; Barraclough, Emma; Burgess, Elisabeth; Clothier, Brent; Deurer, Markus; Green, Steve; Malone, Louise; Weir, Graham

2011-08-01

Environmental risk assessment of nanomaterials requires information not only on their toxicity to non-target organisms, but also on their potential exposure pathways. Here we report on the transport and fate of quantum dots (QDs) in the total environment: from soils, through their uptake into plants, to their passage through insects following ingestion. Our QDs are nanoparticles with an average particle size of 6.5 nm. Breakthrough curves obtained with CdTe/mercaptopropionic acid QDs applied to columns of top soil from a New Zealand organic apple orchard, a Hastings silt loam, showed there to be preferential flow through the soil's macropores. Yet the effluent recovery of QDs was just 60%, even after several pore volumes, indicating that about 40% of the influent QDs were filtered and retained by the soil column via some unknown exchange/adsorption/sequestration mechanism. Glycine-, mercaptosuccinic acid-, cysteine-, and amine-conjugated CdSe/ZnS QDs were visibly transported to a limited extent in the vasculature of ryegrass (Lolium perenne), onion (Allium cepa) and chrysanthemum (Chrysanthemum sp.) plants when cut stems were placed in aqueous QD solutions. However, they were not seen to be taken up at all by rooted whole plants of ryegrass, onion, or Arabidopsis thaliana placed in these solutions. Leafroller (Lepidoptera: Tortricidae) larvae fed with these QDs for two or four days, showed fluorescence along the entire gut, in their frass (larval feces), and, at a lower intensity, in their haemolymph. Fluorescent QDs were also observed and elevated cadmium levels detected inside the bodies of adult moths that had been fed QDs as larvae. These results suggest that exposure scenarios for QDs in the total environment could be quite complex and variable in each environmental domain. Copyright © 2011 Elsevier B.V. All rights reserved.

Blocking the Formation of Zn2+/Dye Complexes in Dye-Sensitized Solar Cells by Inserting CdS Quantum Dots into Sandwich Layer

NASA Astrophysics Data System (ADS)

Sun, Yunfei; Liu, Chunling; Yang, Lili; Wei, Maobin; Lv, Shiquan; Sui, Yingrui; Cao, Jian; Chen, Gang; Yang, Jinghai

2018-06-01

ZnO NRAs are grown on ITO substrates by a simple chemical method. CdS QDs were deposited on ZnO NRAs by SILAR. N719 was synthesized by dipping method. J-V analysis indicates that by inserting a layer of CdS QDs, the conversion efficiency of DSSCs was improved obviously. The device with CdS QDs shows the higher conversion efficiency due to the three reasons: (1) CdS QDs enhanced adsorption spectra of DSSCs in the visible region; (2) CdS QDs block the formation of Zn2+/dye complex, it is beneficial for electros transport from dye to ZnO photoanode. It is the key to obtain higher conversion efficiency; (3) FRET dynamics exists by the introduction of CdS QDs.

Chiral Responsive Liquid Quantum Dots.

PubMed

Zhang, Jin; Ma, Junkai; Shi, Fangdan; Tian, Demei; Li, Haibing

2017-08-01

How to convert the weak chiral-interaction into the macroscopic properties of materials remains a huge challenge. Here, this study develops highly fluorescent, selectively chiral-responsive liquid quantum dots (liquid QDs) based on the hydrophobic interaction between the chiral chains and the oleic acid-stabilized QDs, which have been designated as (S)-1810-QDs. The fluorescence spectrum and liquidity of thermal control demonstrate the fluorescence properties and the fluidic behavior of (S)-1810-QDs in the solvent-free state. Especially, (S)-1810-QDs exhibit a highly chiral-selective response toward (1R, 2S)-2-amino-1,2-diphenyl ethanol. It is anticipated that this study will facilitate the construction of smart chiral fluidic sensors. More importantly, (S)-1810-QDs can become an attractive material for chiral separation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Biomimetic, Mild Chemical Synthesis of CdTe-GSH Quantum Dots with Improved Biocompatibility

PubMed Central

Pérez-Donoso, José M.; Monrás, Juan P.; Bravo, Denisse; Aguirre, Adam; Quest, Andrew F.; Osorio-Román, Igor O.; Aroca, Ricardo F.; Chasteen, Thomas G.; Vásquez, Claudio C.

2012-01-01

Multiple applications of nanotechnology, especially those involving highly fluorescent nanoparticles (NPs) or quantum dots (QDs) have stimulated the research to develop simple, rapid and environmentally friendly protocols for synthesizing NPs exhibiting novel properties and increased biocompatibility. In this study, a simple protocol for the chemical synthesis of glutathione (GSH)-capped CdTe QDs (CdTe-GSH) resembling conditions found in biological systems is described. Using only CdCl2, K2TeO3 and GSH, highly fluorescent QDs were obtained under pH, temperature, buffer and oxygen conditions that allow microorganisms growth. These CdTe-GSH NPs displayed similar size, chemical composition, absorbance and fluorescence spectra and quantum yields as QDs synthesized using more complicated and expensive methods. CdTe QDs were not freely incorporated into eukaryotic cells thus favoring their biocompatibility and potential applications in biomedicine. In addition, NPs entry was facilitated by lipofectamine, resulting in intracellular fluorescence and a slight increase in cell death by necrosis. Toxicity of the as prepared CdTe QDs was lower than that observed with QDs produced by other chemical methods, probably as consequence of decreased levels of Cd+2 and higher amounts of GSH. We present here the simplest, fast and economical method for CdTe QDs synthesis described to date. Also, this biomimetic protocol favors NPs biocompatibility and helps to establish the basis for the development of new, “greener” methods to synthesize cadmium-containing QDs. PMID:22292028

Aggregation, sedimentation, dissolution and bioavailability of ...

EPA Pesticide Factsheets

Due to increasing use in flat screen applications, solar cells, ink–jet printing, and medical devices, cadmium-based quantum dots (QDs) are among the fastest growing classes of engineered nanomaterial. These wide-ranging consumer product applications and end of use disposal issues assure that QDs will eventually enter the marine environment. In an effort to understand the fate and transport of CdSe QDs in estuarine systems, the aggregation, sedimentation, dissolution, and bioavailability of CdSe QDs in seawater was investigated. The size of CdSe QDs increased from 40-60 nm to >1 mm within one hour once introduced to seawater, and the diffusion-limited aggregation led to highly polydispersed aggregates with loose structures. As a result, the sedimentation rate of CdSe QD aggregates in seawater was measured to be 4-10 mm/day, which was slow considering their relatively large size. Humic acid (HA), as a model natural organic matter, further increased the size and polydispersity of CdSe QDs, and slowed their sedimentation accordingly. Given the effect of light on CdSe QDs, natural sunlight and light filters were employed to simulate the photic conditions at different water depths in an estuarine system. It was observed that light played a vital role in promoting the dissolution of CdSe QDs and the release of dissolved Cd. The ZnS shell surrounding the CdSe core also significantly hindered the degradation of CdSe QDs into their ionic components. With sufficient

Atomic Structure of Intrinsic and Electron-Irradiation-Induced Defects in MoTe2

PubMed Central

2018-01-01

Studying the atomic structure of intrinsic defects in two-dimensional transition-metal dichalcogenides is difficult since they damage quickly under the intense electron irradiation in transmission electron microscopy (TEM). However, this can also lead to insights into the creation of defects and their atom-scale dynamics. We first show that MoTe2 monolayers without protection indeed quickly degrade during scanning TEM (STEM) imaging, and discuss the observed atomic-level dynamics, including a transformation from the 1H phase into 1T′, 3-fold rotationally symmetric defects, and the migration of line defects between two 1H grains with a 60° misorientation. We then analyze the atomic structure of MoTe2 encapsulated between two graphene sheets to mitigate damage, finding the as-prepared material to contain an unexpectedly large concentration of defects. These include similar point defects (or quantum dots, QDs) as those created in the nonencapsulated material and two different types of line defects (or quantum wires, QWs) that can be transformed from one to the other under electron irradiation. Our density functional theory simulations indicate that the QDs and QWs embedded in MoTe2 introduce new midgap states into the semiconducting material and may thus be used to control its electronic and optical properties. Finally, the edge of the encapsulated material appears amorphous, possibly due to the pressure caused by the encapsulation. PMID:29503509

Profiling the Local Seebeck Coefficient of InAs-GaAs Quantum Dots Using Scanning Thermoelectric Microscopy

NASA Astrophysics Data System (ADS)

Lin, Yen-Hsiang; Walrath, Jenna; Huang, Simon; Goldman, Rachel

2014-03-01

Thermoelectric (TE) devices offer a method of recovering waste heat through solid state conversion of heat to electricity. However, the typical efficiencies of TE devices are 5-10% which constitutes a barrier to wide spread use. There have recently been a number of reports of an increase in the bulk thermopower due to nanostructuring. In addition to our recent report of enhanced thermopower for GaAs embedded with indium nanocrystals, a theoretical study by Mahan and Sofo suggested that the best thermoelectric materials have a delta function density of states. Quantum dots fit ideally into such a picture. To date, the influence of nanostructuring on the electronic LDOS and thermopower has been studied using spatially averaged measurements; a nanoscale investigation of the effects of nanostructures on thermopower has yet to be presented. To investigate the link between dimensionality and TE properties, we are examining structures ranging from QDs to bulk-like layers, comparing SThEM measurements of the local Seebeck coefficient, S, with STS measurements of the local density of states (LDOS). STM, STS, and SThEM performed on InAs quantum dots (QDs) grown on GaAs. SThEM reveals enhanced S-values near the QD edge; STS reveals band-bending at the QD/GaAs interface, suggesting that the S enhancement is due to interfacial charge accumulation.

Enhancing the thermal dissipation of a light-converting composite for quantum dot-based white light-emitting diodes through electrospinning nanofibers

NASA Astrophysics Data System (ADS)

Zheng, Huai; Lei, Xiang; Cheng, Ting; Liu, Sheng; Zeng, Xiaoliang; Sun, Rong

2017-06-01

Quantum dots (QDs) have been developed as one of the most promising light-converting materials for white light-emitting diodes (LEDs). In current QD-based LED packaging structures, composites of QDs and polymers are used as light-converting layers. However, the ultralow thermal conductivity of such composites seriously hinders the dissipation of QD-generating heat. In this paper, we demonstrate a method to enhance the thermal dissipation of QD-polymer composites through electrospinning polymer nanofibers. QD-polymer films embedded by electrospun nanofibers were prepared. Benefitting from aligned polymer chains in the electrospun nanofibers, the through-panel and in-panel thermal conductivities of the proposed QD-polymer film increased by 39.9% and 423.1%, respectively, compared to traditional QD-polymer film. The proposed and traditional QD-polymer films were both packaged on chip on board (CoB) LEDs for experimental comparison. Compared to traditional QD-polymer film, the luminous flux and luminous efficiency of the LEDs were increased by up to 51.8% and 42.9% by the proposed QD-polymer film under a current of 800 mA, respectively. With an increase in the driving current from 20-800 mA, the correlated color temperature (CCT) variation decreased by 72.7%. The maximum temperatures in the QD-polymer films were reduced from 419 K-411 K under a driving current of 200 mA.

High-performance PbS quantum dot vertical field-effect phototransistor using graphene as a transparent electrode

NASA Astrophysics Data System (ADS)

Che, Yongli; Zhang, Yating; Cao, Xiaolong; Song, Xiaoxian; Zhang, Haiting; Cao, Mingxuan; Dai, Haitao; Yang, Junbo; Zhang, Guizhong; Yao, Jianquan

2016-12-01

Solution processed photoactive PbS quantum dots (QDs) were used as channel in high-performance near-infrared vertical field-effect phototransistor (VFEpT) where monolayer graphene embedded as transparent electrode. In this vertical architecture, the PbS QD channel was sandwiched and naturally protected between the drain and source electrodes, which made the device ultrashort channel length (110 nm) simply the thickness of the channel layer. The VFEpT exhibited ambipolar operation with high mobilities of μe = 3.5 cm2/V s in n-channel operation and μh = 3.3 cm2/V s in p-channel operation at low operation voltages. By using the photoactive PbS QDs as channel material, the VFEpT exhibited good photoresponse properties with a responsivity of 4.2 × 102 A/W, an external quantum efficiency of 6.4 × 104% and a photodetectivity of 2.1 × 109 Jones at the light irradiance of 36 mW/cm2. Additionally, the VFEpT showed excellent on/off switching with good stability and reproducibility and fast response speed with a short rise time of 12 ms in n-channel operation and 10.6 ms in p-channel operation. These high mobilities, good photoresponse properties and simplistic fabrication of our VFEpTs provided a facile route to the high-performance inorganic photodetectors.

Eu-doped ZnO-HfO2 hybrid nanocrystal-embedded low-loss glass-ceramic waveguides

NASA Astrophysics Data System (ADS)

Ghosh, Subhabrata; N, Shivakiran Bhaktha B.

2016-03-01

We report on the sol-gel fabrication, using a dip-coating technique, of low-loss Eu-doped 70SiO2 -(30-x) HfO2-xZnO (x = 2, 5, 7 and 10 mol%) ternary glass-ceramic planar waveguides. Transmission electron microscopy and grazing incident x-ray diffraction experiments confirm the controlled growth of hybrid nanocrystals with an average size of 3 nm-25 nm, composed of ZnO encapsulated by a thin layer of nanocrystalline HfO2, with an increase of ZnO concentration from x = 2 mol% to 10 mol% in the SiO2-HfO2 composite matrix. The effect of crystallization on the local environment of Eu ions, doped in the ZnO-HfO2 hybrid nanocrystal-embedded glass-ceramic matrix, is studied using photoluminescence spectra, wherein an intense mixed-valence state (divalent as well as trivalent) emission of Eu ions is observed. The existence of Eu2+ and Eu3+ in the SiO2-HfO2-ZnO ternary matrix is confirmed by x-ray photoelectron spectroscopy. Importantly, the Eu{}2+,3+-doped ternary waveguides exhibit low propagation losses (0.3 ± 0.2 dB cm-1 at 632.8 nm) and optical transparency in the visible region of the electromagnetic spectrum, which makes ZnO-HfO2 nanocrystal-embedded SiO2-HfO2-ZnO waveguides a viable candidate for the development of on-chip, active, integrated optical devices.

Immune cells tracing using quantum dots

NASA Astrophysics Data System (ADS)

Hoshino, Akiyoshi; Fujioka, Kouki; Kawamura, Yuki I.; Toyama-Sorimachi, Noriko; Yasuhara, Masato; Dohi, Taeko; Yamamoto, Kenji

2006-02-01

Fluorescent nanoparticles, such as nanocrystal quantum dots (QDs), have potential to be applied to molecular biology and bioimaging, since some nanocrystals emit higher and longer lasting fluorescence than conventional organic probes do. Here we report an example of labeling immune cells by QDs. We collected splenic CD4 + T-lymphocyte and peritoneal macrophages from mice. Then cells were labeled with QDs. QDs are incorporated into the T-lymphocyte and macrophages immediately after addition and located in the cytoplasm via endocytosis pathway. The fluorescence of QDs held in the endosomes was easily detected for more than a week. In addition, T-lymphocytes labeled with QDs were stable and cell proliferation or cytokine production including IL-2 and IFN-γ was not affected. When QD-labeled T-lymphocytes were adoptively transferred intravenously to mice, they remained in the peripheral blood and spleen up to a week. Using QD-labeled peritoneal macrophages, we studied cell traffic during inflammation on viscera in peritoneum cavity. QD-labeled macrophages were transplanted into the peritoneum of the mouse, and colitis was induced by intracolonic injection of a hapten, trinitrobenzensulfonic acid. With the aid of stong signals of QDs, we found that macrophage accumuled on the inflammation site of the colon. These results suggested that fluorescent probes of QDs might be useful as bioimaging tools for tracing target cells in vivo.

Comparative studies of biological activity of cadmium-based quantum dots with different surface modifications

NASA Astrophysics Data System (ADS)

Kalinowska, D.; Grabowska-Jadach, I.; Drozd, M.; Pietrzak, M.

2018-05-01

This paper presents a modification of the surface of CdS/ZnS and CdSe x S1-x /ZnS quantum dots (QDs) with 3-mercaptopropionic and 6-mercaptohexanoic acid. The obtained QDs were characterized using TEM, DLS, UV-Vis, and fluorescence spectroscopy. Flow cytometry was applied to evaluate the cytotoxicity of QDs and examine the type of death caused by the tested nanoparticles. In addition, the generation of reactive oxygen species after incubation of the tested cells with CdSe x S1-x /ZnS-MPA and CdSe x S1-x /ZnS-MHA QDs was evaluated. The study was conducted on three cell lines: adherent (A549 and MRC-5) and suspension ones (K562). The conducted research demonstrated that the tested nanoparticles exhibit concentration-dependent toxicity. It was observed that the surface modification influences the toxicity level of the examined QDs, and modification of their surface with the use of the ligand of longer carbon chain (MHA) reduces the toxicity in comparison with QDs-MPA. It was also found that all tested QDs caused the death of cells in the course of necrosis. Based on obtained results, it was concluded that the cytotoxicity of QDs is to a large extent related to reactive oxygen species (ROS) generation.

Surface tuning laser desorption/ionization mass spectrometry (STLDI-MS) for the analysis of small molecules using quantum dots.

PubMed

Abdelhamid, Hani Nasser; Chen, Zhen-Yu; Wu, Hui-Fen

2017-08-01

In most applications of quantum dots (QDs) for surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS), one side of QDs is supported by a solid substrate (stainless - steel plate), whereas the other side is in contact with the target analytes. Therefore, the surface capping agent of QDs is a key parameter for laser desorption/ionization mass spectrometry (LDI-MS). Cadmium telluride quantum dots (CdTe QDs) modified with different capping agents are synthesized, characterized, and applied for surface tuning laser desorption/ionization mass spectrometry (STLDI-MS). Data shows that CdTe quantum dot modified cysteine (cys@CdTe QDs) has an absorption that matches with the wavelength of the N 2 laser (337 nm). The synergistic effect of large surface area and absorption of the laser irradiation of cys@CdTe QDs enhances the LDI-MS process for small - molecule analysis, including α-, β-, and γ-cyclodextrin, gramicidin D, perylene, pyrene, and triphenylphosphine. Cys@CdTe QDs are also applied using Al foils as substrates. Aluminum foil combined with cys@CdTe QDs enhances the ionization efficiency and is cheap compared to traditional matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) with a stainless - steel plate.

Ultrasensitive detection of amifostine and alkaline phosphatase based on the growth of CdS quantum dots.

PubMed

Na, Weidan; Liu, Siyu; Liu, Xiaotong; Su, Xingguang

2015-11-01

In this study, we reported a simple and sensitive fluorescence nanosensor for rapid detection of amifostine and alkaline phosphatase (ALP). The novel nanosensor was based on the fluorescence "turn on-off" of CdS quantum dots (QDs). Firstly, Cd(2+) cation could react with S(2-) anion to generate fluorescent CdS QDs in the presence of amifostine. The fluorescence (FL) intensity of amifostine-capped CdS QDs (Amifostine-CdS QDs) was increased with the increasing amounts of amifostine, and could be used for amifostine detection. However, amifostine could be converted to 2-(3-aminopropylamino) ethanethiol (WR1065) in the presence of ALP based on the dephosphorylation of ALP. Under the optimum conditions, the affinity of WR1065 to CdS QDs was weaker than that of amifostine. Therefore the new generation of WR1065-CdS QDs would reduce the FL intensity with the increase of ALP concentration, and the fluorescence of CdS QDs was turn off. The metabolic process of amifostine in the presence of alkaline phosphatase could be also studied via the change of FL intensity of CdS QDs. The present method was cost-effective, convenient, and does not require any complicated synthetic procedures. Copyright © 2015 Elsevier B.V. All rights reserved.

Functionalized near-infrared quantum dots for in vivo tumor vasculature imaging

NASA Astrophysics Data System (ADS)

Hu, Rui; Yong, Ken-Tye; Roy, Indrajit; Ding, Hong; Law, Wing-Cheung; Cai, Hongxing; Zhang, Xihe; Vathy, Lisa A.; Bergey, Earl J.; Prasad, Paras N.

2010-04-01

In this paper, we report the use of near-infrared (NIR)-emitting alloyed quantum dots (QDs) as efficient optical probes for high contrast in vivo imaging of tumors. Alloyed CdTe1 - xSex/CdS QDs were prepared in the non-aqueous phase using the hot colloidal synthesis approach. Water dispersion of the QDs were accomplished by their encapsulation within polyethyleneglycol (PEG)-grafted phospholipid micelles. For tumor-specific delivery in vivo, the micelle-encapsulated QDs were conjugated with the cyclic arginine-glycine-aspartic acid (cRGD) peptide, which targets the αvβ3 integrins overexpressed in the angiogenic tumor vasculatures. Using in vivo NIR optical imaging of mice bearing pancreatic cancer xenografts, implanted both subcutaneously and orthotopically, we have demonstrated that systemically delivered cRGD-conjugated QDs, but not the unconjugated ones, can efficiently target and label the tumors with high signal-to-noise ratio. Histopathological analysis of major organs of the treated mice showed no evidence of systemic toxicity associated with these QDs. These experiments suggest that cRGD-conjugated NIR QDs can serve as safe and efficient probes for optical bioimaging of tumors in vivo. Furthermore, by co-encapsulating these QDs and anticancer drugs within these micelles, we have demonstrated a promising theranostic, nanosized platform for both cancer imaging and therapy.

Micelle-templated composite quantum dots for super-resolution imaging.

PubMed

Xu, Jianquan; Fan, Qirui; Mahajan, Kalpesh D; Ruan, Gang; Herrington, Andrew; Tehrani, Kayvan F; Kner, Peter; Winter, Jessica O

2014-05-16

Quantum dots (QDs) have tremendous potential for biomedical imaging, including super-resolution techniques that permit imaging below the diffraction limit. However, most QDs are produced via organic methods, and hence require surface treatment to render them water-soluble for biological applications. Previously, we reported a micelle-templating method that yields nanocomposites containing multiple core/shell ZnS-CdSe QDs within the same nanocarrier, increasing overall particle brightness and virtually eliminating QD blinking. Here, this technique is extended to the encapsulation of Mn-doped ZnSe QDs (Mn-ZnSe QDs), which have potential applications in super-resolution imaging as a result of the introduction of Mn(2+) dopant energy levels. The size, shape and fluorescence characteristics of these doped QD-micelles were compared to those of micelles created using core/shell ZnS-CdSe QDs (ZnS-CdSe QD-micelles). Additionally, the stability of both types of particles to photo-oxidation was investigated. Compared to commercial QDs, micelle-templated QDs demonstrated superior fluorescence intensity, higher signal-to-noise ratios, and greater stability against photo-oxidization,while reducing blinking. Additionally, the fluorescence of doped QD-micelles could be modulated from a bright 'on' state to a dark 'off' state, with a modulation depth of up to 76%, suggesting the potential of doped QD-micelles for applications in super-resolution imaging.

Visual and sensitive fluorescent sensing for ultratrace mercury ions by perovskite quantum dots.

PubMed

Lu, Li-Qiang; Tan, Tian; Tian, Xi-Ke; Li, Yong; Deng, Pan

2017-09-15

Mercury ions sensing is an important issue for human health and environmental safety. A novel fluorescence nanosensor was designed for rapid visual detection of ultratrace mercury ions (Hg 2+ ) by using CH 3 NH 3 PbBr 3 perovskite quantum dots (QDs) based on the surface ion-exchange mechanism. The synthesized CH 3 NH 3 PbBr 3 QDs can emitt intense green fluorescence with high quantum yield of 50.28%, and can be applied for Hg 2+ sensing with the detection limit of 0.124 nM (24.87 ppt) in the range of 0 nM-100 nM. Furthermore, the interfering metal ions have no any influence on the fluorescence intensity of QDs, showing the perovskite QDs possess the high selectivity and sensitivity for Hg 2+ detection. The sensing mechanism of perovskite QDs for Hg 2+ is has also been investigated by XPS, EDX studies, showing Pb 2+ on the surface of perovskite QDs has been partially replaced by Hg 2+ . Spot plate test shows that the perovskite QDs can also be used for visual detection of Hg 2+ . Our research indicated the perovskite QDs are promising candidates for the visual fluorescence detection of environmental micropollutants. Copyright © 2017 Elsevier B.V. All rights reserved.

SERS-Based Flavonoid Detection Using Ethylenediamine-β-Cyclodextrin as a Capturing Ligand

PubMed Central

Choi, Jae Min; Hahm, Eunil; Park, Kyeonghui; Jeong, Daham; Rho, Won-Yeop; Kim, Jaehi; Jeong, Dae Hong; Lee, Yoon-Sik; Jhang, Sung Ho; Chung, Hyun Jong; Cho, Eunae; Yu, Jae-Hyuk; Jun, Bong-Hyun; Jung, Seunho

2017-01-01

Ethylenediamine-modified β-cyclodextrin (Et-β-CD) was immobilized on aggregated silver nanoparticle (NP)-embedded silica NPs (SiO2@Ag@Et-β-CD NPs) for the effective detection of flavonoids. Silica NPs were used as the template for embedding silver NPs to create hot spots and enhance surface-enhanced Raman scattering (SERS) signals. Et-β-CD was immobilized on Ag NPs to capture flavonoids via host-guest inclusion complex formation, as indicated by enhanced ultraviolet absorption spectra. The resulting SiO2@Ag@Et-β-CD NPs were used as the SERS substrate for detecting flavonoids, such as hesperetin, naringenin, quercetin, and luteolin. In particular, luteolin was detected more strongly in the linear range 10−7 to 10−3 M than various organic molecules, namely ethylene glycol, β-estradiol, isopropyl alcohol, naphthalene, and toluene. In addition, the SERS signal for luteolin captured by the SiO2@Ag@Et-β-CD NPs remained even after repeated washing. These results indicated that the SiO2@Ag@Et-β-CD NPs can be used as a rapid, sensitive, and selective sensor for flavonoids. PMID:28336842

Silver nanoparticles embedded mesoporous SiO2 nanosphere: an effective anticandidal agent against Candida albicans 077

NASA Astrophysics Data System (ADS)

Qasim, M.; Singh, Braj R.; Naqvi, A. H.; Paik, P.; Das, D.

2015-07-01

Candida albicans is a diploid fungus that causes common infections such as denture stomatitis, thrush, urinary tract infections, etc. Immunocompromised patients can become severely infected by this fungus. Development of an effective anticandidal agent against this pathogenic fungus, therefore, will be very useful for practical application. In this work, Ag-embedded mesoporous silica nanoparticles (mSiO2@AgNPs) have successfully been synthesized and their anticandidal activities against C. albicans have been studied. The mSiO2@AgNPs nanoparticles (d ˜ 400 nm) were designed using pre-synthesized Ag nanoparticles and tetraethyl orthosilicate (TEOS) as a precursor for SiO2 in the presence of cetyltrimethyl ammonium bromide (CTAB) as an easily removable soft template. A simple, cost-effective, and environmentally friendly approach has been adopted to synthesize silver (Ag) nanoparticles using silver nitrate and leaf extract of Azadirachta indica. The mesopores, with size-equivalent diameter of the micelles (d = 4-6 nm), were generated on the SiO2 surface by calcination after removal of the CTAB template. The morphology and surface structure of mSiO2@AgNPs were characterized through x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), particle size analysis (PSA), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller (BET) and high-resolution transmission electron microscopy (HRTEM). The HRTEM micrograph reveals the well-ordered mesoporous structure of the SiO2 sphere. The antifungal activities of mSiO2@AgNPs on the C. albicans cell have been studied through microscopy and are seen to increase with increasing dose of mSiO2@AgNPs, suggesting mSiO2@AgNPs to be a potential antifungal agent for C. albicans 077.

Scanning tunneling spectroscopy of molecular thin films and semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Gaan, Sandeep

Work presented in this thesis mostly deals with nano-scale study of electronic properties of organic semiconducting molecules using pentacene (Pn) as a model system and compared with various SiC surfaces to gain more insight into physical processes at nano-scale. In addition, InAs quantum dots (QDs) in a GaAs matrix are studied to probe electronic states of individual QDs. Scanning tunneling microscopy (STM) and spectroscopy (STS) are the primary experimental techniques used to probe local electronic properties on the nano-scale. Vacuum sublimated Pn thin films were deposited onto SiC substrates for STM/STS experiments. STM studies show high quality ordered Pn films. Atomic force microscopy (AFM) images reveal dendritic growth pattern of these films. Local density of states (LDOS) measurements using STS reveals a HOMO-LUMO bandgap. In order to study charge transport properties of Pn films, different amount of charge were injected into the sample by systematically changing the tip-sample separation. Saturation of the tunnel current was observed at positive sample voltages (LUMO states). This effect was attributed to a transport/space charge limitation in tunnel current by treating it as a situation analogous to charge injection into insulators which gives rise to space charge limited current (also previously observed in the case of organic semiconductors). Using a simple model we were able to derive a hopping rate that characterizes nano-scale transport in Pn films at least in the vicinity of the STM probe-tip. We have studied effect of transport limitation in the tunnel current for various semiconductor surfaces. In order to probe surfaces of varying conductivities, we have used Si-rich SiC surfaces such as 3x3 and 3x3 -R30° (both Mott-Hubbard insulators) as well as a highly conducting C-rich graphene surface, and compared those results with the data obtained from Pn. We observe variation of the decay constant kappa (which characterizes the tunneling process) on these surfaces of varying conductivities. The graphene surface shows no transport limitation in the tunnel current, as evidenced by only small changes in kappa as a function of tunnel current for these surfaces. This result is in sharp contrast to the case of Pn where kappa rapidly decays to zero with increasing tunnel current due to transport/space charge limited effects in the semiconductor. Thus, the change is kappa value in STM experiments is reflective of non-ideal behavior of the tunneling. As a specific case of transport limitation on the nano-scale we have also studied InAs QDs grown in a GaAs matrix. We observe that the occupation of discrete quantized states in the dots with electrons has a significant effect on tunneling spectra. When the QD state is occupied by an electron the potential in the dot is modified such that this state does not contribute to the tunnel current. The state then remains "invisible" in the tunneling spectra. Only in presence of transport channels in the vicinity of the dots can the electron localized in the QD state leak out to the substrate, and only then does the state appears in the spectrum. In our experiments these transport channels arise from steps which form as a result of in situ cleaving process for cross-sectional STM (XSTM) measurements.

Photogenerated carriers transport behaviors in L-cysteine capped ZnSe core-shell quantum dots

NASA Astrophysics Data System (ADS)

Shan, Qingsong; Li, Kuiying; Xue, Zhenjie; Lin, Yingying; Yin, Hua; Zhu, Ruiping

2016-02-01

The photoexcited carrier transport behavior of zinc selenide (ZnSe) quantum dots (QDs) with core-shell structure is studied because of their unique photoelectronic characteristics. The surface photovoltaic (SPV) properties of self-assembled ZnSe/ZnS/L-Cys core-shell QDs were probed via electric field induced surface photovoltage and transient photovoltage (TPV) measurements supplemented by Fourier transform infrared, laser Raman, absorption, and photoluminescence spectroscopies. The ZnSe QDs displayed p-type SPV characteristics with a broader stronger SPV response over the whole ultraviolet-to-near-infrared range compared with those of other core-shell QDs in the same group. The relationship between the SPV phase value of the QDs and external bias was revealed in their SPV phase spectrum. The wide transient photovoltage response region from 3.3 × 10-8 to 2 × 10-3 s was closely related to the long diffusion distance of photoexcited free charge carriers in the interfacial space-charge region of the QDs. The strong SPV response corresponding to the ZnSe core mainly originated from an obvious quantum tunneling effect in the QDs.

A highly selective and simple fluorescent sensor for mercury (II) ion detection based on cysteamine-capped CdTe quantum dots synthesized by the reflux method.

PubMed

Ding, Xiaojie; Qu, Lingbo; Yang, Ran; Zhou, Yuchen; Li, Jianjun

2015-06-01

Cysteamine (CA)-capped CdTe quantum dots (QDs) (CA-CdTe QDs) were prepared by the reflux method and utilized as an efficient nano-sized fluorescent sensor to detect mercury (II) ions (Hg(2+) ). Under optimum conditions, the fluorescence quenching effect of CA-CdTe QDs was linear at Hg(2+) concentrations in the range of 6.0-450 nmol/L. The detection limit was calculated to be 4.0 nmol/L according to the 3σ IUPAC criteria. The influence of 10-fold Pb(2+) , Cu(2+) and Ag(+) on the determination of Hg(2+) was < 7% (superior to other reports based on crude QDs). Furthermore, the detection sensitivity and selectivity were much improved relative to a sensor based on the CA-CdTe QDs probe, which was prepared using a one-pot synthetic method. This CA-CdTe QDs sensor system represents a new feasibility to improve the detection performance of a QDs sensor by changing the synthesis method. Copyright © 2014 John Wiley & Sons, Ltd.

Streptavidin-conjugated CdSe/ZnS quantum dots impaired synaptic plasticity and spatial memory process

NASA Astrophysics Data System (ADS)

Gao, Xiaoyan; Tang, Mingliang; Li, Zhifeng; Zha, Yingying; Cheng, Guosheng; Yin, Shuting; Chen, Jutao; Ruan, Di-yun; Chen, Lin; Wang, Ming

2013-04-01

Studies reported that quantum dots (QDs), as a novel probe, demonstrated a promising future for in vivo imaging, but also showed potential toxicity. This study is mainly to investigate in vivo response in the central nervous system (CNS) after exposure to QDs in a rat model of synaptic plasticity and spatial memory. Adult rats were exposed to streptavidin-conjugated CdSe/ZnS QDs (Qdots 525, purchased from Molecular Probes Inc.) by intraperitoneal injection for 7 days, followed by behavioral, electrophysiological, and biochemical examinations. The electrophysiological results show that input/output ( I/ O) functions were increased, while the peak of paired-pulse reaction and long-term potentiation were decreased after QDs insult, indicating synaptic transmission was enhanced and synaptic plasticity in the hippocampus was impaired. Meanwhile, behavioral experiments provide the evidence that QDs could impair rats' spatial memory process. All the results present evidences of interference of synaptic transmission and plasticity in rat hippocampal dentate gyrus area by QDs insult and suggest potential adverse issues which should be considered in QDs applications.

Exploitation of inimitable properties of CuInS2 quantum dots for energy conversion in bulk heterojunction hybrid solar cell

NASA Astrophysics Data System (ADS)

Jindal, Shikha; Giripunje, Sushama M.

2017-11-01

Quantum dots (QDs) are the suitable material for solar cell devices owing to its distinctive optical, electrical and electronic properties. Currently, the most efficient devices have employed the toxic QDs which cause destructive impact on environment. In the present article, we have used environment benign CuInS2 QDs as an acceptor material in bulk heterojunction device of P3HT and QDs. The energy level positions corroborated from UPS spectra substantiates the acceptor property of CuInS2. We scrutinized the hybrid solar cell by tailoring the acceptor content in active layer. The increased acceptor content intensifies the performance of device. The enhancement in photovoltaic parameters is mainly due to the fast dissociation and extraction of photogenerated excitons which occurs with the larger wt% of acceptor QDs. Current density-voltage characteristics describes the greater V oc and I sc in the 60 wt% CuInS2 QDs based solar cell as compared to the low wt% of QDs in the active layer.

Fabrication of quantum dot/silica core-shell particles immobilizing Au nanoparticles and their dual imaging functions

NASA Astrophysics Data System (ADS)

Kobayashi, Yoshio; Matsudo, Hiromu; Li, Ting-ting; Shibuya, Kyosuke; Kubota, Yohsuke; Oikawa, Takahiro; Nakagawa, Tomohiko; Gonda, Kohsuke

2016-03-01

The present work proposes preparation methods for quantum dot/silica (QD/SiO2) core-shell particles that immobilize Au nanoparticles (QD/SiO2/Au). A colloid solution of QD/SiO2 core-shell particles with an average size of 47.0 ± 6.1 nm was prepared by a sol-gel reaction of tetraethyl orthosilicate in the presence of the QDs with an average size of 10.3 ± 2.1 nm. A colloid solution of Au nanoparticles with an average size of 17.9 ± 1.3 nm was prepared by reducing Au3+ ions with sodium citrate in water at 80 °C. Introduction of amino groups to QD/SiO2 particle surfaces was performed using (3-aminopropyl)-triethoxysilane (QD/SiO2-NH2). The QD/SiO2/Au particles were fabricated by mixing the Au particle colloid solution and the QD/SiO2-NH2 particle colloid solution. Values of radiant efficiency and computed tomography for the QD/SiO2/Au particle colloid solution were 2.23 × 107 (p/s/cm2/sr)/(μW/cm2) at a QD concentration of 8 × 10-7 M and 1180 ± 314 Hounsfield units and an Au concentration of 5.4 × 10-2 M. The QD/SiO2/Au particle colloid solution was injected into a mouse chest wall. Fluorescence emitted from the colloid solution could be detected on the skin covering the chest wall. The colloid solution could also be X-ray-imaged in the chest wall. Consequently, the QD/SiO2/Au particle colloid solution was found to have dual functions, i.e., fluorescence emission and X-ray absorption in vivo, which makes the colloid solution suitable to function as a contrast agent for dual imaging processes.

A rapid and universal bacteria-counting approach using CdSe/ZnS/SiO2 composite nanoparticles as fluorescence probe.

PubMed

Fu, Xin; Huang, Kelong; Liu, Suqin

2010-02-01

In this paper, a rapid, simple, and sensitive method was described for detection of the total bacterial count using SiO(2)-coated CdSe/ZnS quantum dots (QDs) as a fluorescence marker that covalently coupled with bacteria using glutaraldehyde as the crosslinker. Highly luminescent CdSe/ZnS were prepared by applying cadmium oxide and zinc stearate as precursors instead of pyrophoric organometallic precursors. A reverse-microemulsion technique was used to synthesize CdSe/ZnS/SiO(2) composite nanoparticles with a SiO(2) surface coating. Our results showed that CdSe/ZnS/SiO(2) composite nanoparticles prepared with this method possessed highly luminescent, biologically functional, and monodispersive characteristics, and could successfully be covalently conjugated with the bacteria. As a demonstration, it was found that the method had higher sensitivity and could count bacteria in 3 x 10(2) CFU/mL, lower than the conventional plate counting and organic dye-based method. A linear relationship of the fluorescence peak intensity (Y) and the total bacterial count (X) was established in the range of 3 x 10(2)-10(7) CFU/mL using the equation Y = 374.82X-938.27 (R = 0.99574). The results of the determination for the total count of bacteria in seven real samples were identical with the conventional plate count method, and the standard deviation was satisfactory.

Mn-doped Ge self-assembled quantum dots via dewetting of thin films

NASA Astrophysics Data System (ADS)

Aouassa, Mansour; Jadli, Imen; Bandyopadhyay, Anup; Kim, Sung Kyu; Karaman, Ibrahim; Lee, Jeong Yong

2017-03-01

In this study, we demonstrate an original elaboration route for producing a Mn-doped Ge self-assembled quantum dots on SiO2 thin layer for MOS structure. These magnetic quantum dots are elaborated using dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing at high temperature of an amorphous Ge:Mn (Mn: 40%) nanolayer deposed at very low temperature by high-precision Solid Source Molecular Beam Epitaxy on SiO2 thin film. The size of quantum dots is controlled with nanometer scale precision by varying the nominal thickness of amorphous film initially deposed. The magnetic properties of the quantum-dots layer have been investigated by superconducting quantum interference device (SQUID) magnetometry. Atomic force microscopy (AFM), x-ray energy dispersive spectroscopy (XEDS) and transmission electron microscopy (TEM) were used to examine the nanostructure of these materials. Obtained results indicate that GeMn QDs are crystalline, monodisperse and exhibit a ferromagnetic behavior with a Curie temperature (TC) above room temperature. They could be integrated into spintronic technology.

New insights into the nanostructure of innovative thin film solar cells gained by positron annihilation spectroscopy

NASA Astrophysics Data System (ADS)

Eijt, S. W. H.; Shi, W.; Mannheim, A.; Butterling, M.; Schut, H.; Egger, W.; Dickmann, M.; Hugenschmidt, C.; Shakeri, B.; Meulenberg, R. W.; Callewaert, V.; Saniz, R.; Partoens, B.; Barbiellini, B.; Bansil, A.; Melskens, J.; Zeman, M.; Smets, A. H. M.; Kulbak, M.; Hodes, G.; Cahen, D.; Brück, E.

2017-01-01

Recent studies showed that positron annihilation methods can provide key insights into the nanostructure and electronic structure of thin film solar cells. In this study, positron annihilation lifetime spectroscopy (PALS) is applied to investigate CdSe quantum dot (QD) light absorbing layers, providing evidence of positron trapping at the surfaces of the QDs. This enables one to monitor their surface composition and electronic structure. Further, 2D-Angular Correlation of Annihilation Radiation (2D-ACAR) is used to investigate the nanostructure of divacancies in photovoltaic-high-quality a-Si:H films. The collected momentum distributions were converted by Fourier transformation to the direct space representation of the electron-positron autocorrelation function. The evolution of the size of the divacancies as a function of hydrogen dilution during deposition of a-Si:H thin films was examined. Finally, we present a first positron Doppler Broadening of Annihilation Radiation (DBAR) study of the emerging class of highly efficient thin film solar cells based on perovskites.

Recognition-Mediated Assembly of Quantum Dot Polymer Conjugates with Controlled Morphology

PubMed Central

Nandwana, Vikas; Subramani, Chandramouleeswaran; Eymur, Serkan; Yeh, Yi-Cheun; Tonga, Gulen Yesilbag; Tonga, Murat; Jeong, Youngdo; Yang, Boqian; Barnes, Michael D.; Cooke, Graeme; Rotello, Vincent M.

2011-01-01

We have demonstrated a polymer mediated “bricks and mortar” method for the self-assembly of quantum dots (QDs). This strategy allows QDs to self-assemble into structured aggregates using complementary three-point hydrogen bonding. The resulting nanocomposites have distinct morphologies and inter-particle distances based on the ratio between QDs and polymer. Time resolved photoluminescence measurements showed that the optical properties of the QDs were retained after self-assembly. PMID:22016664

Structural control of InP/ZnS core/shell quantum dots enables high-quality white LEDs.

PubMed

Kumar, Baskaran Ganesh; Sadeghi, Sadra; Melikov, Rustamzhon; Aria, Mohammad Mohammadi; Jalali, Houman Bahmani; Ow-Yang, Cleva W; Nizamoglu, Sedat

2018-08-24

Herein, we demonstrate that the structural and optical control of InP-based quantum dots (QDs) can lead to high-performance light-emitting diodes (LEDs). Zinc sulphide (ZnS) shells passivate the InP QD core and increase the quantum yield in green-emitting QDs by 13-fold and red-emitting QDs by 8-fold. The optimised QDs are integrated in the liquid state to eliminate aggregation-induced emission quenching and we fabricated white LEDs with a warm, neutral and cool-white appearance by the down-conversion mechanism. The QD-functionalized white LEDs achieve luminous efficiency (LE) up to 14.7 lm W -1 and colour-rendering index up to 80. The structural and optical control of InP/ZnS core/shell QDs enable 23-fold enhancement in LE of white LEDs compared to ones containing only QDs of InP core.

Design and development of novel linker for PbS quantum dots/TiO₂ mesoscopic solar cell.

PubMed

Etgar, Lioz; Park, Jinhyung; Barolo, Claudia; Nazeeruddin, Md K; Viscardi, Guido; Graetzel, Michael

2011-09-01

A novel bifunctional linker molecule, bis(4-mercaptophenyl)phosphinic acid, is designed to be used in a QDs solar cells. The linker anchors to TiO(2) mesoporous film through the phosphinic acid functional group and to the PbS QDs through the two thiol groups. The way of attachment of this new linker molecule in a photovoltaic PbS QDs/TiO(2) mesoporous device was studied by FTIR measurements. The photovoltaic performance of this new linker in a heterojunction PbS QDs solar cell show high V(oc) relative to QDs based solar cells, which will allow to receive high power conversion efficiency using this novel designed linker. This novel bifunctional linker molecule should pave the way for enhancing binding strength, and efficiency of QDs solar cells compared to the state-of-the-art linkers.

Fabrication and characterization of physically defined quantum dots on a boron-doped silicon-on-insulator substrate

NASA Astrophysics Data System (ADS)

Mizoguchi, Seiya; Shimatani, Naoki; Kobayashi, Mizuki; Makino, Takaomi; Yamaoka, Yu; Kodera, Tetsuo

2018-04-01

We study hole transport properties in physically defined p-type silicon quantum dots (QDs) on a heavily doped silicon-on-insulator (SOI) substrate. We observe Coulomb diamonds using single QDs and estimate the charging energy as ∼1.6 meV. We obtain the charge stability diagram of double QDs using single QDs as a charge sensor. This is the first demonstration of charge sensing in p-type heavily doped silicon QDs. For future time-resolved measurements, we apply radio-frequency reflectometry using impedance matching of LC circuits to the device. We observe the resonance and estimate the capacitance as ∼0.12 pF from the resonant frequency. This value is smaller than that of the devices with top gates on nondoped SOI substrate. This indicates that high-frequency signals can be applied efficiently to p-type silicon QDs without top gates.

Attaching quantum dots to HER2 specific phage antibodies

NASA Astrophysics Data System (ADS)

Chu, Viet Ha; Nghiem, Thi Ha Lien; Huyen La, Thi; Dieu Thuy Ung, Thi; Huan Le, Quang; Thuan Tong, Kim; Liem Nguyen, Quang; Nhung Tran, Hong

2010-06-01

This work presents the results of the attachment of Qdot 655 ITKTM amino (PEG) quantum dots (QDs) (Invitrogen) and CdTe QDs (provided by Institute of Materials Science, VAST) to HER2 (Human Epidermal growth factor Receptor 2) specific phage antibodies (Abs) (provided by Institute of Biotechnology, VAST) in solution. The QDs were attached to the phage display specific HER2 Abs to form a complex QD-Ab. The QDs and complex QD-Ab were characterized by UV-VIS spectroscopy, transmission electron microscopy (TEM) and fluorescence microscopy. The fluorescence images show the QDs conjugated to the phage. Due to the QDs attaching to the surface, the phage dimensions were amplified, so its shape could be observed by optical microscopy. The complex QD-Ab was stable and lasted for a month. The results illustrate the value of the HER2 phage-QD complex as a cancer detection platform.

In vivo biodistribution and behavior of CdTe/ZnS quantum dots.

PubMed

Zhao, Yan; Zhang, Yue; Qin, Gaofeng; Cheng, Jinjun; Zeng, Wenhao; Liu, Shuchen; Kong, Hui; Wang, Xueqian; Wang, Qingguo; Qu, Huihua

2017-01-01

The unique features of quantum dots (QDs) make them desirable fluorescent tags for cell and developmental biology applications that require long-term, multitarget, and highly sensitive imaging. In this work, we imaged fluorescent cadmium telluride/zinc sulfide (CdTe/ZnS) QDs in organs, tissues, and cells, and analyzed the mechanism of their lymphatic uptake and cellular distribution. We observed that the fluorescent CdTe/ZnS QDs were internalized by lymph nodes in four cell lines from different tissue sources. We obtained the fluorescence intensity-QD concentrations curve by quantitative analysis. Our results demonstrate that cells containing QDs can complete mitosis normally and that distribution of QDs was uniform across cell types and involved the vesicular transport system, including the endoplasmic reticulum. This capacity for CdTe/ZnS QD targeting provides insights into the applicability and limitations of fluorescent QDs for imaging biological specimens.

Multicolor quantum dot-encoded microspheres for the fluoroimmunoassays of chicken newcastle disease and goat pox virus.

PubMed

Yuan, Pingfan; Ma, Qiang; Meng, Rizeng; Wang, Chao; Dou, Wenchao; Wang, Guannan; Su, Xingguang

2009-05-01

Semiconductor nanocrystals (or quantum dots, QDs) have the potential to overcome some of the limitations encountered by traditional fluorophores in fluorescence labeling applications. The unique spectroscopic properties of QDs make them hold immense promise as versatile labels for biological applications. In this work, we employ the layer-by-layer (LbL) method for the construction of bio-functional multicolor QD-encoded microspheres. Polystyrene microspheres with diameter of 3 microm were used as templates for the deposition of different sized CdTe QDs/polyelectrolyte multilayers. Two different antigens, Chicken newcastle disease (CND) antigen and goat pox virus (GPV) antigen, were conjugated to two kinds of biofunctional multicolor microspheres with different optical encoding. The multicolor microspheres can capture corresponding antibodies labeled with QDs, QDs-CND antibody and QDs-GPV antibody in the fluoroimmunoassays. The microspheres can be distinguished from each other based on their optical encoding.

Pulsed laser induced optical nonlinearities in undoped, copper doped and chromium doped CdS quantum dots

NASA Astrophysics Data System (ADS)

Sharma, Dimple; Malik, B. P.; Gaur, Arun

2015-04-01

Quantum dots (QDs) of CdS, Cu doped and Cr doped CdS were synthesized through chemical co- precipitation method. The synthesized QDs have been characterized by x-ray diffraction, ultraviolet visible absorption spectroscopy. The diameters of QDs were calculated using Debye-Scherrer’s formula and Brus equation. They are found to be in 3.5-3.8 nm range. The nonlinear properties has been studied by the open and closed aperture Z-scan technique using frequency double Nd:YAG laser. The nonlinear refractive index (n2), nonlinear absorption coefficient (β), third order nonlinear susceptibilities (χ3) of QDs has been calculated. It has been found that the values of nonlinear parameters are higher for doped QDs than undoped CdS QDs. Hence they can be regarded as potential material for the development of optoelectronics and photonics devices.

Implications of orbital hybridization on the electronic properties of doped quantum dots: the case of Cu:CdSe

NASA Astrophysics Data System (ADS)

Wright, Joshua T.; Forsythe, Kyle; Hutchins, Jamie; Meulenberg, Robert W.

2016-04-01

This paper investigates how chemical dopants affect the electronic properties of CdSe quantum dots (QDs) and why a model that incorporates the concepts of orbital hybridization must be used to understand these properties. Extended X-ray absorption fine structure spectroscopy measurements show that copper dopants in CdSe QDs occur primarily through a statistical doping mechanism. Ultraviolet photoemission spectroscopy (UPS) experiments provide a detailed insight on the valence band (VB) structure of doped and undoped QDs. Using UPS measurements, we are able to observe photoemission from the Cu d-levels above VB maximum of the QDs which allows a complete picture of the energy band landscape of these materials. This information provides insights into many of the physical properties of doped QDs, including the highly debated near-infrared photoluminescence in Cu doped CdSe QDs. We show that all our results point to a common theme of orbital hybridization in Cu doped CdSe QDs which leads to optically and electronically active states below the conduction band minimum. Our model is supported from current-voltage measurements of doped and undoped materials, which exhibit Schottky to Ohmic behavior with Cu doping, suggestive of a tuning of the lowest energy states near the Fermi level.This paper investigates how chemical dopants affect the electronic properties of CdSe quantum dots (QDs) and why a model that incorporates the concepts of orbital hybridization must be used to understand these properties. Extended X-ray absorption fine structure spectroscopy measurements show that copper dopants in CdSe QDs occur primarily through a statistical doping mechanism. Ultraviolet photoemission spectroscopy (UPS) experiments provide a detailed insight on the valence band (VB) structure of doped and undoped QDs. Using UPS measurements, we are able to observe photoemission from the Cu d-levels above VB maximum of the QDs which allows a complete picture of the energy band landscape of these materials. This information provides insights into many of the physical properties of doped QDs, including the highly debated near-infrared photoluminescence in Cu doped CdSe QDs. We show that all our results point to a common theme of orbital hybridization in Cu doped CdSe QDs which leads to optically and electronically active states below the conduction band minimum. Our model is supported from current-voltage measurements of doped and undoped materials, which exhibit Schottky to Ohmic behavior with Cu doping, suggestive of a tuning of the lowest energy states near the Fermi level. Electronic supplementary information (ESI) available: Thermogravimetric analysis and X-ray photoelectron spectroscopy of QD films. See DOI: 10.1039/C6NR00494F

In Situ Generation and Consumption of H2O2 by Bienzyme-Quantum Dots Bioconjugates for Improved Chemiluminescence Resonance Energy Transfer.

PubMed

Xu, Shuxia; Li, Xianming; Li, Chaobi; Li, Jialin; Zhang, Xinfeng; Wu, Peng; Hou, Xiandeng

2016-06-21

Exploration of quantum dots (QDs) as energy acceptors revolutionizes the current chemiluminescence resonance energy transfer (CRET), since QDs possess large Stokes shifts and high luminescence efficiency. However, the strong and high concentration of oxidant (typically H2O2) needed for luminol chemiluminescence (CL) reaction could cause oxidative quenching to QDs, thereby decreasing the CRET performance. Here we proposed the use of bienzyme-QDs bioconjugate as the energy acceptor for improved CRET sensing. Two enzymes, one for H2O2 generation (oxidase) and another for H2O2 consumption (horseradish peroxidase, HRP), were bioconjugated onto the surface of QDs. The bienzyme allowed fast in situ cascaded H2O2 generation and consumption, thus alleviating fluorescence quenching of QDs. The nanosized QDs accommodate the two enzymes in a nanometric range, and the CL reaction was confined on the surface of QDs accordingly, thereby amplifying the CL reaction rate and improving CRET efficiency. As a result, CRET efficiency of 30-38% was obtained; the highest CRET efficiency by far was obtained using QDs as the energy acceptor. The proposed CRET system could be explored for ultrasensitive sensing of various oxidase substrates (here exemplified with cholesterol, glucose, and benzylamine), allowing for quantitative measurement of a spectrum of metabolites with high sensitivity and specificity. Limits of detection (LOD, 3σ) for cholesterol, glucose, and benzylamine were found to be 0.8, 3.4, and 10 nM, respectively. Furthermore, multiparametric blood analysis (glucose and cholesterol) is demonstrated.

Phase transformation in SiOx/SiO₂ multilayers for optoelectronics and microelectronics applications.

PubMed

Roussel, M; Talbot, E; Pratibha Nalini, R; Gourbilleau, F; Pareige, P

2013-09-01

Due to the quantum confinement, silicon nanoclusters (Si-ncs) embedded in a dielectric matrix are of prime interest for new optoelectronics and microelectronics applications. In this context, SiO(x)/SiO₂ multilayers have been prepared by magnetron sputtering and subsequently annealed to induce phase separation and Si clusters growth. The aim of this paper is to study phase separation processes and formation of nanoclusters in SiO(x)/SiO₂ multilayers by atom probe tomography. Influences of the silicon supersaturation, annealing temperature and SiO(x) and SiO₂ layer thicknesses on the final microstructure have been investigated. It is shown that supersaturation directly determines phase separation regime between nucleation/classical growth and spinodal decomposition. Annealing temperature controls size of the particles and interface with the surrounding matrix. Layer thicknesses directly control Si-nc shapes from spherical to spinodal-like structures. Copyright © 2012 Elsevier B.V. All rights reserved.

Transmission electron microscopy study of the formation of epitaxial CoSi2/Si (111) by a room-temperature codeposition technique

NASA Technical Reports Server (NTRS)

D'Anterroches, Cecile; Yakupoglu, H. Nejat; Lin, T. L.; Fathauer, R. W.; Grunthaner, P. J.

1988-01-01

Co and Si have been codeposited on Si (111) substrates near room temperature in a stoichiometric 1:2 ratio in a molecular beam epitaxy system. Annealing of these deposits yields high-quality single-crystal CoSi2 layers. Transmission electron microscopy has been used to examine as-deposited layers and layers annealed at 300, 500, and 600 C. Single-crystal epitaxial grains of CoSi2 embedded in a matrix of amorphous Co/Si are observed in as-deposited samples, while the layer is predominantly single-crystal, inhomogeneously strained CoSi2 at 300 C. At 600 C, a homogeneously strained single-crystal layer with a high density of pinholes is observed. In contrast to other solid phase epitaxy techniques used to grow CoSi2 on Si (111), no intermediate silicide phases are observed prior to the formation of CoSi2.

TiO{sub 2} flower-like nanostructures decorated with CdS/PbS nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trenczek-Zajac, Anita, E-mail: anita.trenczek-zajac@agh.edu.pl; Kusior, Anna; Lacz, Agnieszka

Highlights: • TiO{sub 2} flower-like nanostructures were prepared with the use of Ti foil and 30% H{sub 2}O{sub 2}. • QDs of CdS and PbS were deposited using the SILAR method. • The SILAR method makes it possible to control the size of QDs. • Band gap energy of CdS was found to be 2.35 eV. • Sensitization of TiO{sub 2} with CdS or PbS improves the photoelectrochemical properties. - Abstract: Flower-like nanostructures of TiO{sub 2} were prepared by immersing Ti foil in 30% H{sub 2}O{sub 2} at 80 °C for times varying from 15 to 240 min. Upon annealingmore » at 450 °C in an Ar atmosphere, the received amorphous samples crystallized in an anatase structure with rutile as a minority phase. SEM images revealed that partially formed flowers were present at the surface of the prepared samples as early as after 15 min of immersion. The size of the individual flowers increased from 400–800 nm after 15 min of reaction to 2.5–6.0 μm after 240 min. It was also found that surface is very rough and surface development is considerable. After 45 min of immersion, the nanoflowers were sensitized with CdS and PbS quantum dots (QDs-CdS/QDs-PbS) deposited using the SILAR method from water- and methanol-based precursor solutions at different concentrations (0.001–0.1 M). QDs-CdS crystallized in the hawleyite structure, while QDs-PbS in the galena form. SEM analysis showed the tendency of quantum dots to agglomerate at high concentrations of the precursor in water-based solutions. QDs obtained from methanol-based solutions were uniformly distributed. The produced QDs-PbS were smaller than QDs-CdS. Based on the optical reflectance spectra, the band-gap energies of TiO{sub 2} nanostructures with and without QDs were calculated to be 3.32 eV for flower-like TiO{sub 2} nanostructures and 2.35 eV for QDs-CdS. The photoelectrochemical behaviour of nanoflowers was found to improve significantly after the deposition of QDs-CdS.« less

Deposition of thin silicon layers on transferred large area graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lupina, Grzegorz, E-mail: lupina@ihp-microelectronics.com; Kitzmann, Julia; Lukosius, Mindaugas

2013-12-23

Physical vapor deposition of Si onto transferred graphene is investigated. At elevated temperatures, Si nucleates preferably on wrinkles and multilayer graphene islands. In some cases, however, Si can be quasi-selectively grown only on the monolayer graphene regions while the multilayer islands remain uncovered. Experimental insights and ab initio calculations show that variations in the removal efficiency of carbon residuals after the transfer process can be responsible for this behavior. Low-temperature Si seed layer results in improved wetting and enables homogeneous growth. This is an important step towards realization of electronic devices in which graphene is embedded between two Si layers.

Improved optical properties of InAs quantum dots for intermediate band solar cells by suppression of misfit strain relaxation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, H.; School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287-6106; Prioli, R.

The properties of InAs quantum dots (QDs) have been studied for application in intermediate band solar cells. It is found that suppression of plastic relaxation in the QDs has a significant effect on the optoelectronic properties. Partial capping plus annealing is shown to be effective in controlling the height of the QDs and in suppressing plastic relaxation. A force balancing model is used to explain the relationship between plastic relaxation and QD height. A strong luminescence has been observed from strained QDs, indicating the presence of localized states in the desired energy range. No luminescence has been observed from plasticallymore » relaxed QDs.« less

Erythorbic acid promoted formation of CdS QDs in a tube-in-tube micro-channel reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Yan; Tan, Jiawei; Wang, Jiexin

2014-12-15

Erythorbic acid assistant synthesis of CdS quantum dots (QDs) was conducted by homogeneous mixing of two continuous liquids in a high-throughput microporous tube-in-tube micro-channel reactor (MTMCR) at room temperature. The effects of the micropore size of the MTMCR, liquid flow rate, mixing time and reactant concentration on the size and size distribution of CdS QDs were investigated. It was found that the size and size distribution of CdS QDs could be tuned in the MTMCR. A combination of erythorbic acid promoted formation technique with the MTMCR may be a promising pathway for controllable mass production of QDs.

Ensemble and single particle photophysical properties (two-photon excitation, anisotropy, FRET, lifetime, spectral conversion) of commercial quantum dots in solution and in live cells.

PubMed

Grecco, H E; Lidke, K A; Heintzmann, R; Lidke, D S; Spagnuolo, C; Martinez, O E; Jares-Erijman, E A; Jovin, T M

2004-11-01

In this work, we characterized streptavidin-conjugated quantum dots (QDs) manufactured by Quantum Dot Corporation. We present data on: (1) two-photon excitation; (2) fluorescence lifetimes; (3) ensemble and single QD emission anisotropy; (4) QDs as donors for Forster resonance energy transfer (FRET); and (5) spectral conversion of QDs exposed to high-intensity illumination. We also demonstrate the utility of QDs for (1) imaging the binding and uptake of biotinylated transferrin on living cells, and (2) resolving by fluorescence lifetime imaging microscopy (FLIM) signals originating from QDs from those of spatially and spectrally overlapping visible fluorescent proteins (VFPs). (c) 2005 Wiley-Liss, Inc.

Preparation and Characterization of InP/Poly(methyl methacrylate) Nanocomposite Films.

PubMed

Kwon, Younghoon; Kim, Jongsung

2017-04-01

Quantum dots (QDs) are nanocrystalline semiconductors with many unusual optical properties. They exhibit very high fluorescence intensities and possess exceptional stability against photo-bleaching. In this study, we report the preparation of InP QDs-poly(methyl methacrylate) (PMMA) hybrids by fabricating QDs via a thermal decomposition reaction, followed by radical polymerization. The InP QDs were synthesized using indium(III) chloride and tris(dimethylamino)phosphine. Flexible composite films were obtained by radical polymerization using methyl methacrylate (MMA) as the monomer and 2,2′-azobis(2-methylpropionitrile) (AIBN) as a radical initiator. The PL intensity of the QDs was lowered upon composite formation with PMMA. However, the composites exhibited higher thermal stability than pure PMMA.

Stress-Engineered Quantum Dots for Multispectral Infra-Red Detector Arrays

DTIC Science & Technology

2006-06-30

moment in self-assembled InAs/GaAs(001) QDs. Simultaneously, the interband dipole moment is also determined [publication 25]. 10. Observed temperature... dependence of intraband transition induced dipole moment in self-assembled InAs/GaAs(001) QDs [unpublished]. 11. Utilized cathodoluminescence...001) QDs than that of GaAs capped InAs/GaAs(0O1) QDs [publications 8, 11]. 12. Studied the substrate orientation dependence of the formation of InSb

Tailoring folic acid and methotrexate-attributed quantum dots for integrated cancer cell imaging and therapy

NASA Astrophysics Data System (ADS)

Fahmi, Mochamad Zakki; Chang, Jia-Yaw

2016-03-01

Potential application of folic acid and methotrexate-attributed AgInS2-ZnS quantum dots on both detection and therapeutic of cancer cell were intensively investigated on this study. In the initial step, the bright luminescent of QDs, with % QY up to 55.3, were synthesized with one-pot two-step process resulting narrow particle distribution and successfully transferred to water phase without significant effect on optical properties. The water-soluble AgInS2-ZnS quantum dots (QDs) encapsulated with oleylamine have been successfully prepared by ultrasonication assisting. Several aspect including QDs characterization, pH stability, ionic strength, and bonding properties were investigated to reach desired condition of water-soluble AgInS2-ZnS QDs. Folic acid was further conjugated to QDs for HeLa and MCF7 cancer cell imaging to performs the targeting capability. Moreover, folic acid is efficiently internalized into cell through the receptor-mediated endocytosis even when conjugated with a wide variety of molecules. Confocal imaging characterization further informs folic acid-conjugated AgInS2-ZnS QDs could most specific targeted to the human cervical (HeLa) cells. The therapeutic feature of QDs on HeLa cancer cell was conjugated by attributing methotrexate on the QDs, instead of folic acid, and the design could improve on inhibiting the cancer cell viability as well as its fluorescent intensity.

Effect of antimony incorporation on the density, shape, and luminescence of InAs quantum dots

NASA Astrophysics Data System (ADS)

Chen, J. F.; Chiang, C. H.; Wu, Y. H.; Chang, L.; Chi, J. Y.

2008-07-01

This work investigates the surfactant effect on exposed and buried InAs quantum dots (QDs) by incorporating Sb into the QD layers with various Sb beam equivalent pressures (BEPs). Secondary ion mass spectroscopy shows the presence of Sb in the exposed and buried QD layers with the Sb intensity in the exposed layer substantially exceeding that in the buried layer. Incorporating Sb can reduce the density of the exposed QDs by more than two orders of magnitude. However, a high Sb BEP yields a surface morphology with a regular periodic structure of ellipsoid terraces. A good room-temperature photoluminescence (PL) at ˜1600 nm from the exposed QDs is observed, suggesting that the Sb incorporation probably improves the emission efficiency by reducing the surface recombination velocity at the surface of the exposed QDs. Increasing Sb BEP causes a blueshift of the emission from the exposed QDs due to a reduction in the dot height as suggested by atomic force microscopy. Increasing Sb BEP can also blueshift the ˜1300 nm emission from the buried QDs by decreasing the dot height. However, a high Sb BEP yields a quantum well-like PL feature formed by the clustering of the buried QDs into an undulated planar layer. These results indicate a marked Sb surfactant effect that can be used to control the density, shape, and luminescence of the exposed and buried QDs.

Enhanced oxidation stability of quasi core-shell alloyed CdSeS quantum dots prepared through aqueous microwave synthesis technique.

PubMed

Zhan, Hong-Ju; Zhou, Pei-Jiang; Ma, Rong; Liu, Xi-Jing; He, Yu-Ning; Zhou, Chuan-Yun

2014-01-01

Quasi core shell alloyed CdSeS quantum dots (QDs) have been prepared through a facile aqueous-phase route employing microwave irradiation technique. The optical spectroscopy and structure characterization evidenced the quasi core shell alloyed structures of CdSeS QDs. The X-ray diffraction patterns of the obtained CdSeS QDs displayed peak positions very close to those of bulk cubic CdS crystal structures and the result of X-ray photoelectron spectroscopy data re-confirmed the thick CdS shell on the CdSe core. The TEM images and HRTEM images of the CdSeS QDs ascertained the well-defined spherical particles and a relatively narrow size distribution. On the basis, the stability of the obtained QDs in an oxidative environment was also discussed using etching reaction by H2O2. The experiments result showed the as-prepared QDs present high tolerance towards H2O2, obviously superior to the commonly used CdTe QDs and core-shell CdTe/CdS QDs, which was attributed to the unique quasi core-shell CdSeS crystal structure and the small lattice mismatch between CdSe and CdS semiconductor materials. This assay provided insight to obtain high stable crystal structured semiconductor nanocrystals in the design and synthesis process.

Interactions between photoexcited NIR emitting CdHgTe quantum dots and graphene oxide

NASA Astrophysics Data System (ADS)

Jagtap, Amardeep M.; Varade, Vaibhav; Konkena, Bharathi; Ramesh, K. P.; Chatterjee, Abhijit; Banerjee, Arup; Pendyala, Naresh Babu; Koteswara Rao, K. S. R.

2016-02-01

Hydrothermally grown mercury cadmium telluride quantum dots (CdHgTe QDs) are decorated on graphene oxide (GO) sheets through physisorption. The structural change of GO through partial reduction of oxygen functional groups is observed with X-ray photoelectron spectroscopy in GO-QDs composites. Raman spectroscopy provides relatively a small change (˜1.1 times) in D/G ratio of band intensity and red shift in G band from 1606 cm-1 to 1594 cm-1 in GO-CdHgTe QDs (2.6 nm) composites, which indicates structural modification of GO network. Steady state and time resolved photoluminescence (PL) spectroscopy shows the electronic interactions between photoexcited near infrared emitting CdHgTe QDs and GO. Another interesting observation is PL quenching in the presence of GO, and it is quite effective in the case of smaller size QDs (2.6 nm) compared to the larger size QDs (4.2 nm). Thus, the observed PL quenching is attributed to the photogenerated electron transfer from QDs to GO. The photoexcited electron transfer rate decreases from 2.2 × 109 to 1.5 × 108 s-1 with increasing particle size from 2.6 to 4.2 nm. Photoconductivity measurements on QDs-GO composite devices show nearly 3 fold increase in the current density under photo-illumination, which is a promising aspect for solar energy conversion and other optoelectronic applications.

Structure, strain, and composition profiling of InAs/GaAs(211)B quantum dot superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Florini, N.; Dimitrakopulos, G. P.; Kioseoglou, J.

2016-01-21

The morphology, nanostructure, and strain properties of InAs quantum dots (QDs) grown on GaAs(211)B, uncapped or buried, are explored by transmission electron microscopy and related quantitative techniques. Besides the built-in piezoelectric field, other differences of (211) growth compared to (100)-oriented growth are discussed in terms of the (211) surface non-singularity, leading to anisotropic shape of the QDs and local chemical inhomogeneity of the wetting layer. The shape of the uncapped QDs was precisely defined as truncated pyramidal, elongated along the 〈111〉 direction, and bounded by the (110), (100), and (213) facets. Local strain measurements showed that large surface QDs weremore » almost unstrained due to plastic relaxation, exhibiting small residual elastic strain at the interface that gradually diminished toward their apex. Conversely, buried QDs were pseudomorphically grown on GaAs. By postulating a plane stress state, we have established a systematic increase of the local strain from the base toward the apex region of the QDs. Using Vegard's law, their chemical composition profiles were calculated, revealing an indium content gradient along the growth direction and compositional variants among different QDs. Photoluminescence measurements showed variations in emission energy between the QDs and consistency with a graded In-content, which complied with the quantitative strain analysis.« less

CdTe/CdSe quantum dots improve the binding affinities between α-amylase and polyphenols.

PubMed

Ni, Xiaoling

2012-03-01

People exposed to engineered nanomaterials have potential health risks associated. Human α-amylase is one of the key enzymes in the digestive system. There are few reports about the influence of quantum dots (QDs) on the digestive enzymes and their inhibition system. This work focused on the toxic effect of CdTe/CdSe QDs on the interactions between α-amylase and its natural inhibitors. Thirty-six dietary polyphenols, natural α-amylase inhibitors from food, were studied for their affinities for α-amylase in the absence and presence of CdTe/CdSe QDs by a fluorescence quenching method. The magnitudes of apparent binding constants of polyphenols for α-amylase were almost in the range of 10(5)-10(7) L mol(-1) in the presence of CdTe/CdSe QDs, which were higher than the magnitudes of apparent binding constants in the absence of CdTe/CdSe QDs (10(4)-10(6) L mol(-1)). CdTe/CdSe QDs obviously improved the affinities of dietary polyphenols for α-amylase up to 389.04 times. It is possible that the binding interaction between polyphenols and α-amylase in the presence of CdTe/CdSe QDs was mainly caused by electrostatic interactions. QDs significantly influence the digestive enzymes and their inhibition system. This journal is © The Royal Society of Chemistry 2012

Polarized emission from CsPbX3 perovskite quantum dots

NASA Astrophysics Data System (ADS)

Wang, Dan; Wu, Dan; Dong, Di; Chen, Wei; Hao, Junjie; Qin, Jing; Xu, Bing; Wang, Kai; Sun, Xiaowei

2016-06-01

Compared to organic/inorganic hybrid perovskites, full inorganic perovskite quantum dots (QDs) exhibit higher stability. In this study, full inorganic CsPbX3 (X = Br, I and mixed halide systems Br/I) perovskite QDs have been synthesized and interestingly, these QDs showed highly polarized photoluminescence which is systematically studied for the first time. Furthermore, the polarization of CsPbI3 was as high as 0.36 in hexane and 0.40 as a film. The CsPbX3 perovskite QDs with high polarization properties indicate that they possess great potential for application in new generation displays with wide colour gamut and low power consumption.Compared to organic/inorganic hybrid perovskites, full inorganic perovskite quantum dots (QDs) exhibit higher stability. In this study, full inorganic CsPbX3 (X = Br, I and mixed halide systems Br/I) perovskite QDs have been synthesized and interestingly, these QDs showed highly polarized photoluminescence which is systematically studied for the first time. Furthermore, the polarization of CsPbI3 was as high as 0.36 in hexane and 0.40 as a film. The CsPbX3 perovskite QDs with high polarization properties indicate that they possess great potential for application in new generation displays with wide colour gamut and low power consumption. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01915c

Phototoxicity free quantum dot-based niosome formulation for controlled drug release and its monitoring

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Kang, T. W.; Bala, Suman; Kamboj, Sunil; Jeon, H. C.

2018-04-01

A novel niosomes-based system composed of Hypromellose (HPMC) functionalized fluorescent, biocompatible ZnS:Mn quantum dots (QDs), and anti-HIV drug Tenofovir disoproxil fumarate (TDF) was designed. An appropriate ratio of surfactant Sorbitan Monostearate (SPAN-60) and cholesterol was used to obtain an optimal entrapment efficiency. Initially, after observing the successful interaction of HPMC with SPAN-60, the noisome formulation including (QDs + drug) and HPMC-coated QDs was synthesized by a wet chemical route and characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM) and Selected Electron Diffraction (SAED). Secondly, (QDs + drug) loaded niosome formulations were studied by varying the ratio of SPAN-60 and cholesterol. Multiple studies were done to characterize the shape, size, viscosity, colloidal stability, and entrapment efficiency of (QDs + drug) loaded niosomes. Lastly, pH-dependent (QDs + drug) release profiles were studied by a spectroscopic technique considering the pH of the human gastrointestinal region to obtain the formulation stability of (QDs + drug) release from the niosome vesicles. These studies also include pH-dependent photo-stability measurements based on laser-induced multiphoton excitation technique in the Infrared region. The multiphoton time-resolved studies were completed to avoid the UV induced phototoxicity in the drug delivery modules. Current studies on the formulation of niosomes-based (QDs + drug) system laid a foundation to make a complete phototoxicity free system for tracking controlled drug release and its imaging.

Solvothermal synthesis of InP quantum dots and their enhanced luminescent efficiency by post-synthetic treatments.

PubMed

Byun, Ho-June; Lee, Ju Chul; Yang, Heesun

2011-03-01

InP quantum dots (QDs) were solvothermally synthesized by using a greener phosphorus source of P(N(CH(3))(2))(3) instead of highly toxic P(TMS)(3) widely used, and subsequently subjected to a size-sorting processing. While as-grown QDs showed an undetectably low emission intensity, post-synthetic treatments such as photo-etching, photo-radiation, and photo-assisted ZnS shell coating gave rise to a substantial increase in emission efficiency due to the effective removal and passivation of surface states. The emission efficiency of the photo-etched QDs was further enhanced by a consecutive UV photo-radiation, attributable to the photo-oxidation at QD surface. Furthermore, a relatively thick ZnS shell on the surface of InP QDs that were surface-modified with hydrophilic ligands beforehand was photochemically generated in an aqueous solution at room temperature. The resulting InP/ZnS core/shell QDs, emitting from blue to red wavelengths, were more efficient than the above photo-treated InP QDs, and their luminescent properties (emission bandwidth and quantum yield) were comparable to those of InP QDs synthesized with P(TMS)(3). Structural, size, and compositional analyses on InP/ZnS QDs were also conducted to elucidate their core/shell structure. Copyright © 2010 Elsevier Inc. All rights reserved.

SU-C-201-01: Core/shell and Multishell Colloidal Quantum Dots Nanodosimeters Behaviour Under Repeated MV and KV Irradiations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delage, M; Cloutier, E; Lecavalier, M

2016-06-15

Purpose: This study intends to characterize the energy dependence of the effect of radiation damage on CdSe multi-shell (MS) (CdS/CdZnS/ZnS) and CdSe core/shell (CS)(ZnS) cQDs. It also aims to investigate irregularities resulting of pauses between subsequent irradiations. Methods: Radioluminescence (RL) measurements were performed with a CCD camera as dose was cumulated by the cQDs (up to 10 kGy), for beam energies 120 kVp, 220 kVp and 6 MV. Repeated expositions of 1999 MU were cumulated. Pauses between subsequent irradiations were varied from 2 to 50 minutes. cQDs photoluminescence (PL) and RL spectral stability was tracked by quantifying the position andmore » FWHM of the luminescence peak. Results: Both types of cQDs showed a clear energy dependence of the RL signal decrease between the kV and the MV beams. For 1.2 kGy of dose cumulated, MS cQDs had 92% of the initial signal left at 6 MV compared to 98% at 120 kVp. The same was observed for CS cQDs: 87% at 6 MV vs 94% at 120 kVp. MS cQDs were found to have a systematic (though small, ∼1%) RL intensity recovery for pauses of 15 minutes or more, while CS cQDs maintain a stable loss regardless of the pause duration. PL and RL spectral measurements revealed a good stability (< 1% variation of the peak position and FWHM) for both types of cQDs. Conclusion: In all, both MS and CS cQDs have a sufficient resistance to large doses of radiation for standard radiation therapy and imaging. Since this resistance is better for lower energy, the utilization of cQDs could be optimized for low energy applications (e.g. theragnostic applications for small animal studies and others). Finally, the ionizing radiation damage mechanisms for this new type of nano-scintillator still have to be identified properly.« less

Formation of SiGe nanocrystals embedded in Al2O3 for the application of write-once-read-many-times memory

NASA Astrophysics Data System (ADS)

Wu, Min-Lin; Wu, Yung-Hsien; Lin, Chia-Chun; Chen, Lun-Lun

2012-10-01

The structure of SiGe nanocrystals embedded in Al2O3 formed by sequential deposition of Al2O3/Si/Ge/Al2O3 and a subsequent annealing was confirmed by transmission electron microscopy and energy dispersive spectroscopy (EDS), and its application for write-once-read-many-times (WORM) memory devices was explored in this study. By applying a -10 V pulse for 1 s, a large amount of holes injected from Si substrate are stored in the nanocrystals and consequently, the current at +1.5 V increases by a factor of 104 as compared to that of the initial state. Even with a smaller -5 V pulse for 1 μs, a sufficiently large current ratio of 36 can still be obtained, verifying the low power operation. Since holes are stored in nanocrystals which are isolated from Si substrate by Al2O3 with good integrity and correspond to a large valence band offset with respect to Al2O3, desirable read endurance up to 105 cycles and excellent retention over 100 yr are achieved. Combining these promising characteristics, WORM memory devices are appropriate for high-performance archival storage applications.

Plasmonic and metallic optical properties of Au/SiO2 metal-insulator films

NASA Astrophysics Data System (ADS)

Battie, Yann; En Naciri, Aotmane; Vergnat, Michel

2017-12-01

In this paper, the optical properties and the growth mechanism of Au/SiO2 metal-insulator films (MIFs) are investigated by combining ellipsometry and transmission electron microscopy. The ellipsometric measurements, analyzed by using effective medium theories, show that the growth mechanism involves a Volmer-Weber growth mode while the morphology and the optical properties of Au/SiO2 MIFs are directly related to the percolation of the Au nanostructures. Indeed, below the percolation threshold of Au, the MIFs consist of ellipsoidal Au inclusions embedded in a SiO2 matrix. These insulating films present anisotropic plasmonic properties, attributed to the asymmetric interactions between nanaoparticles (NPs), which can be modeled according to the interacted shape distributed nanoparticle effective medium theory. At the percolation threshold of Au, an insulator-to-metal transition is observed. The MIFs simultaneously exhibit plasmonic and metallic optical properties, which can be described by the Bruggeman theory. The density of free electrons increases and the MIFs become more and more conductive as the Au volume fraction increases. We also demonstrate that for a high Au volume fraction, Bruggeman and Maxwell Garnett theories converge toward the same results, suggesting that the film is composed of isolated SiO2 inclusion embedded in a gold matrix.

White light emitting device based on single-phase CdS quantum dots.

PubMed

Li, Feng; Nie, Chao; You, Lai; Jin, Xiao; Zhang, Qin; Qin, Yuancheng; Zhao, Feng; Song, Yinglin; Chen, Zhongping; Li, Qinghua

2018-05-18

White light emitting diodes (WLEDs) based on quantum dots (QDs) are emerging as robust candidates for white light sources, however they are suffering from the problem of energy loss resulting from the re-absorption and self-absorption among the employed QDs of different peak wavelengths. It still remains a challenging task to construct WLEDs based on single-phase QD emitters. Here, CdS QDs with short synthesis times are introduced to the fabrication of WLEDs. With a short synthesis time, on one hand, CdS QDs with a small diameter with blue emission can be obtained. On the other hand, surface reconstruction barely has time to occur, and the surface is likely defect-ridden, which enables the existence of a broad emission covering the range of green, yellow and red regions. This is essential for the white light emission of CdS QDs, and is very important for WLED applications. The temporal evolution of the PL spectra for CdS QDs was obtained to investigate the influence of growth time on the luminescent properties. The CdS QDs with a growth time of 0.5 min exhibited a colour rendering index (CRI) of 79.5 and a correlated colour temperature (CCT) of 6238 K. With increasing reaction time, the colour coordinates of the CdS QDs will move away from the white light region in the CIE 1931 chromaticity diagram. By integrating the as prepared white light emission CdS QDs with a violet GaN chip, WLEDs were fabricated. The fabricated WLEDs exhibited a CRI of 87.9 and a CCT of 4619 K, which satisfy the demand of general illumination. The luminous flux and the luminous efficiency of the fabricated WLEDs, being less advanced than current commercial white light sources, can be further improved, meaning there is a need for much more in-depth studies on white light emission CdS QDs.

White light emitting device based on single-phase CdS quantum dots

NASA Astrophysics Data System (ADS)

Li, Feng; Nie, Chao; You, Lai; Jin, Xiao; Zhang, Qin; Qin, Yuancheng; Zhao, Feng; Song, Yinglin; Chen, Zhongping; Li, Qinghua

2018-05-01

White light emitting diodes (WLEDs) based on quantum dots (QDs) are emerging as robust candidates for white light sources, however they are suffering from the problem of energy loss resulting from the re-absorption and self-absorption among the employed QDs of different peak wavelengths. It still remains a challenging task to construct WLEDs based on single-phase QD emitters. Here, CdS QDs with short synthesis times are introduced to the fabrication of WLEDs. With a short synthesis time, on one hand, CdS QDs with a small diameter with blue emission can be obtained. On the other hand, surface reconstruction barely has time to occur, and the surface is likely defect-ridden, which enables the existence of a broad emission covering the range of green, yellow and red regions. This is essential for the white light emission of CdS QDs, and is very important for WLED applications. The temporal evolution of the PL spectra for CdS QDs was obtained to investigate the influence of growth time on the luminescent properties. The CdS QDs with a growth time of 0.5 min exhibited a colour rendering index (CRI) of 79.5 and a correlated colour temperature (CCT) of 6238 K. With increasing reaction time, the colour coordinates of the CdS QDs will move away from the white light region in the CIE 1931 chromaticity diagram. By integrating the as prepared white light emission CdS QDs with a violet GaN chip, WLEDs were fabricated. The fabricated WLEDs exhibited a CRI of 87.9 and a CCT of 4619 K, which satisfy the demand of general illumination. The luminous flux and the luminous efficiency of the fabricated WLEDs, being less advanced than current commercial white light sources, can be further improved, meaning there is a need for much more in-depth studies on white light emission CdS QDs.

ABC transporters affect the elimination and toxicity of CdTe quantum dots in liver and kidney cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Mingli; Yin, Huancai; Bai, Pengli

This paper aimed to investigate the role of adenosine triphosphate-binding cassette (ABC) transporters on the efflux and the toxicity of nanoparticles in liver and kidney cells. In this study, we synthesized CdTe quantum dots (QDs) that were monodispersed and emitted green fluorescence (maximum peak at 530 nm). Such QDs tended to accumulate in human hepatocellular carcinoma cells (HepG2), human kidney cells 2 (HK-2), and Madin-Darby canine kidney (MDCK) cells, and cause significant toxicity in all the three cell lines. Using specific inhibitors and inducers of P-glycoprotein (Pgp) and multidrug resistance associated proteins (Mrps), the cellular accumulation and subsequent toxicity ofmore » QDs in HepG2 and HK-2 cells were significantly affected, while only slight changes appeared in MDCK cells, corresponding well with the functional expressions of ABC transporters in cells. Moreover, treatment of QDs caused concentration- and time- dependent induction of ABC transporters in HepG2 and HK-2 cells, but such phenomenon was barely found in MDCK cells. Furthermore, the effects of CdTe QDs on ABC transporters were found to be greater than those of CdCl{sub 2} at equivalent concentrations of cadmium, indicating that the effects of QDs should be a combination of free Cd{sup 2+} and specific properties of QDs. Overall, these results indicated a strong dependence between the functional expressions of ABC transporters and the efflux of QDs, which could be an important reason for the modulation of QDs toxicity by ABC transporters. - Highlights: • ABC transporters contributed actively to the cellular efflux of CdTe quantum dots. • ABC transporters affected the cellular toxicity of CdTe quantum dots. • Treatment of CdTe quantum dots induced the gene expression of ABC transporters. • Free Cd{sup 2+} should be partially involved in the effects of QDs on ABC transporters. • Cellular efflux of quantum dots could be an important modulator for its toxicity.« less

Synthesis and Characterizations of Pb-modified CdSe Aqueous Quantum Dots and Their Applications in Quantum Dot-Sensitized Solar Cells

NASA Astrophysics Data System (ADS)

Lu, Cheng-Hsin

Quantum Dots (QDs) are semiconductor nanocrystals with typical size ranges around 1-20 nm. They exhibit distinctive size-dependent photoluminescence (PL) properties due to the quantum confinement effect. QDs have great potentials in display, lighting, lasing, bioimaging, fluorescent label, sensor, photodetector, and photovoltaic applications, and have been widely studied in the past decades. Cadmium selenide (CdSe) QDs have been synthesized using an environmentally friendly, aqueous method under low temperature. While traditional QDs synthesized by hot injection method using organic solvent generally exhibit edge-state emission with narrow peaks, aqueous quantum dots (AQDs) tend to have trap-state emissions with broad peaks. The objective of this thesis is to investigate how Pb modifications in CdSe AQDs synthesis can affect the optoelectronic properties of the QDs and how these modifications affect their corresponding photovoltaic performance in quantum dot-sensitized solar cell (QDSSC) applications. Lead (Pb) precursor has been introduced either during the synthesis or after the synthesis of CdSe AQDs forming either Pb-doped or Pb-coated CdSe QDs, respectively. Pb-doped CdSe QDs exhibit red-shift in both absorption and emission spectra while Pb-coated CdSe QDs exhibit blue-shift in both absorption and emission spectra along with the generation of more surface defects. Although blue-shifted absorption indicating a narrower absorption range and the surface defects providing undesired recombination pathways are detrimental to solar cell performance, however surprisingly, we found that QDSSCs made from Pb-coated CdSe QDs actually had better solar cell performance than that made from Pb-doped CdSe QDs. We attributed this finding to a protection/passivation layer formed in-situ when the coated Pb react with the iodide/triiodide electrolyte during solar cell operation resulting in QDSSCs with better charge injection and stability.

Protein-directed synthesis of Mn-doped ZnS quantum dots: a dual-channel biosensor for two proteins.

PubMed

Wu, Peng; Zhao, Ting; Tian, Yunfei; Wu, Lan; Hou, Xiandeng

2013-06-03

Proteins typically have nanoscale dimensions and multiple binding sites with inorganic ions, which facilitates the templated synthesis of nanoparticles to yield nanoparticle-protein hybrids with tailored functionality, water solubility, and tunable frameworks with well-defined structure. In this work, we report a protein-templated synthesis of Mn-doped ZnS quantum dots (QDs) by exploring bovine serum albumin (BSA) as the template. The obtained Mn-doped ZnS QDs give phosphorescence emission centered at 590 nm, with a decay time of about 1.9 ms. A dual-channel sensing system for two different proteins was developed through integration of the optical responses (phosphorescence emission and resonant light scattering (RLS)) of Mn-doped ZnS QDs and recognition of them by surface BSA phosphorescent sensing of trypsin and RLS sensing of lysozyme. Trypsin can digest BSA and remove BSA from the surface of Mn-doped ZnS QDs, thus quenching the phosphorescence of QDs, whereas lysozyme can assemble with BSA to lead to aggregation of QDs and enhanced RLS intensity. The detection limits for trypsin and lysozyme were 40 and 3 nM, respectively. The selectivity of the respective channel for trypsin and lysozyme was evaluated with a series of other proteins. Unlike other protein sensors based on nanobioconjugates, the proposed dual-channel sensor employs only one type of QDs but can detect two different proteins. Further, we found the RLS of QDs can also be useful for studying the BSA-lysozyme binding stoichiometry, which has not been reported in the literature. These successful biosensor applications clearly demonstrate that BSA not only serves as a template for growth of Mn-doped ZnS QDs, but also impacts the QDs for selective recognition of analyte proteins. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of Shell Thickness on the Performance of NiO-Based All-Inorganic Quantum Dot Light-Emitting Diodes.

PubMed

Wang, Ting; Zhu, Bingyan; Wang, Shuangpeng; Yuan, Qilin; Zhang, Han; Kang, Zhihui; Wang, Rong; Zhang, Hanzhuang; Ji, Wenyu

2018-05-02

The effect of shell thickness on the performance of all-inorganic quantum dot light-emitting diodes (QLEDs) is explored by employing a series of green quantum dots (QDs) (Zn x Cd 1- x Se/ZnS core/shell QDs with different ZnS shell thicknesses) as the emitters. ZnO nanoparticles and sol-gel NiO are employed as the electron and hole transport materials, respectively. Time-resolved and steady-state photoluminescence results indicate that positive charging processes might occur for the QDs deposited on NiO, which results in emission quenching of QDs and poor device performance. The thick shell outside the core in QDs not only largely suppresses the QD emission quenching but also effectively preserves the excitons in QDs from dissociation of electron-hole pairs when they are subjected to an electric field. The peak efficiency of 4.2 cd/A and maximum luminance of 4205 cd/m 2 are achieved for the device based on QDs with the thickest shells (∼4.2 nm). We anticipate that these results will spur progress toward the design and realization of efficient all-inorganic QLEDs as a platform for the QD-based full-colored displays.

AgInS2 quantum dots for the detection of trinitrotoluene

NASA Astrophysics Data System (ADS)

Baca, Alfred J.; Meylemans, Heather A.; Baldwin, Lawrence; Cambrea, Lee R.; Feng, Ji; Yin, Yadong; Roberts, M. Joseph

2017-01-01

AgInS2 (AIS) quantum dots (QDs) were synthesized via a thermal decomposition reaction with dodecylamine as the ligand to help stabilize the QDs. This reaction procedure is relatively easy to implement, scalable to large batches (up to hundreds of milligrams of QDs are produced), and a convenient method for the synthesis of chalcogenide QDs. Metal powders of AgNO3 and In(NO3)3, were used as the metal precursors while diethyldithiocarbamate was used as the sulfur source. The AIS QDs were characterized via transmission electron microscopy, atomic force microscopy, and energy dispersive x-ray spectroscopy. As an application for these less toxic nanomaterials, we demonstrate the selective detection of Trinitrotoluene (TNT) at concentrations as low as 6 micromolar (μM) and without the functionalization of a ligand that is specifically designed to interact with TNT molecules. We also demonstrate a simple approach to patterning the AIS QDs onto filter paper, for the detection of TNT molecules by eye. Collectively, the ease of the synthesis of the less toxic AIS QDs, and the ability to detect TNT molecules by eye suggest an attractive route to highly sensitive and portable substrates for environmental monitoring, chemical warfare agent detection, and other applications.

Impact of CdSe/ZnS quantum dots on the development of zebrafish embryos

NASA Astrophysics Data System (ADS)

Lei, Yong; Xiao, Qi; Huang, Shan; Xu, Wansu; Zhang, Zhe; He, Zhike; Liu, Yi; Deng, Fengjiao

2011-12-01

Due to their unique fluorescent characteristics, quantum dots (QDs) have been successfully applied in the fields of biotechnology and medicine, but there is very limited information regarding their biodistribution and chronic toxicity in vivo. In this article, the biological behavior and toxic effects of mercaptoacetic acid-CdSe/ZnS QDs (MAA-QDs) in developing zebrafish embryos were investigated by in vivo tests. The MAA-QDs were introduced into zebrafish through microinjection at early stage. The results showed that the MAA-QDs at certain concentrations influenced the survival of zebrafish embryos, but treated embryos without developmental defects were also observed. MAA-QDs injected into the cytoplasm at the one-cell stage were allocated to progeny blastoderm cells during proliferation and almost never entered the yolk. The formation of notochord and primordial germ cells with normal morphologies was detected in the treated embryos by whole-mount in situ hybridization. Furthermore, traces of the element cadmium were mainly discovered in the tissue of liver and kidney of 3-month-old-treated zebrafish by quantitative assessment with inductively coupled plasma mass spectrometry. Thus, we hypothesized that low concentration MAA-QDs have chronic toxicities when they were delivered into zebrafish organs.

Reduced Carrier Recombination in PbS - CuInS2 Quantum Dot Solar Cells

PubMed Central

Sun, Zhenhua; Sitbon, Gary; Pons, Thomas; Bakulin, Artem A.; Chen, Zhuoying

2015-01-01

Energy loss due to carrier recombination is among the major factors limiting the performance of TiO2/PbS colloidal quantum dot (QD) heterojunction solar cells. In this work, enhanced photocurrent is achieved by incorporating another type of hole-transporting QDs, Zn-doped CuInS2 (Zn-CIS) QDs into the PbS QD matrix. Binary QD solar cells exhibit a reduced charge recombination associated with the spatial charge separation between these two types of QDs. A ~30% increase in short-circuit current density and a ~20% increase in power conversion efficiency are observed in binary QD solar cells compared to cells built from PbS QDs only. In agreement with the charge transfer process identified through ultrafast pump/probe spectroscopy between these two QD components, transient photovoltage characteristics of single-component and binary QDs solar cells reveal longer carrier recombination time constants associated with the incorporation of Zn-CIS QDs. This work presents a straightforward, solution-processed method based on the incorporation of another QDs in the PbS QD matrix to control the carrier dynamics in colloidal QD materials and enhance solar cell performance. PMID:26024021

Cyto-molecular Tuning of Quantum Dots

NASA Astrophysics Data System (ADS)

Lee, Bong; Suresh, Sindhuja; Ekpenyong, Andrew

Quantum dots (QDs) are semiconductor nanoparticles composed of groups II-VI or III-V elements, with physical dimensions smaller than the exciton Bohr radius, and between 1-10 nm. Their applications and promising myriad applications in photovoltaic cells, biomedical imaging, targeted drug delivery, quantum computing, etc, have led to much research on their interactions with other systems. For biological systems, research has focused on biocompatibility and cytotoxicity of QDs in the context of imaging/therapy. However, there is a paucity of work on how biological systems might be used to tune QDs. Here, we hypothesize that the photo-electronic properties of QDs can be tuned by biological macromolecules following controlled changes in cellular activities. Using CdSe/ZnS core-shell QDs, we perform spectroscopic analysis of optically excited colloidal QDs with and without promyelocytic HL60 cells. Preliminary results show shifts in the emission spectra of the colloidal dispersions with and without cells. We will present results for activated HL60-derived cells where specific macromolecules produced by these cells perturb the electric dipole moments of the excited QDs and the associated electric fields, in ways that constitute what we describe as cyto-molecular tuning. Startup funds from the College of Arts and Sciences, Creighton University (to AEE).