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Sample records for semiconductor nanocrystals inmicrofluidic

  1. Synthesis and Manipulation of Semiconductor Nanocrystals inMicrofluidic Reactors

    SciTech Connect

    Chan, Emory Ming-Yue

    2006-01-01

    Microfluidic reactors are investigated as a mechanism tocontrol the growth of semiconductor nanocrystals and characterize thestructural evolution of colloidal quantum dots. Due to their shortdiffusion lengths, low thermal masses, and predictable fluid dynamics,microfluidic devices can be used to quickly and reproducibly alterreaction conditions such as concentration, temperature, and reactiontime, while allowing for rapid reagent mixing and productcharacterization. These features are particularly useful for colloidalnanocrystal reactions, which scale poorly and are difficult to controland characterize in bulk fluids. To demonstrate the capabilities ofnanoparticle microreactors, a size series of spherical CdSe nanocrystalswas synthesized at high temperature in a continuous-flow, microfabricatedglass reactor. Nanocrystal diameters are reproducibly controlled bysystematically altering reaction parameters such as the temperature,concentration, and reaction time. Microreactors with finer control overtemperature and reagent mixing were designed to synthesize nanoparticlesof different shapes, such as rods, tetrapods, and hollow shells. The twomajor challenges observed with continuous flow reactors are thedeposition of particles on channel walls and the broad distribution ofresidence times that result from laminar flow. To alleviate theseproblems, I designed and fabricated liquid-liquid segmented flowmicroreactors in which the reaction precursors are encapsulated inflowing droplets suspended in an immiscible carrier fluid. The synthesisof CdSe nanocrystals in such microreactors exhibited reduced depositionand residence time distributions while enabling the rapid screening aseries of samples isolated in nL droplets. Microfluidic reactors werealso designed to modify the composition of existing nanocrystals andcharacterize the kinetics of such reactions. The millisecond kinetics ofthe CdSe-to-Ag2Se nanocrystal cation exchange reaction are measured insitu with micro

  2. Electronic spectra of semiconductor nanocrystals

    SciTech Connect

    Alivisatos, A.P.

    1993-12-31

    Semiconductor nanocrystals smaller than the bulk exciton show substantial quantum confinement effects. Recent experiments including Stark effect, resonance Raman, valence band photoemission, and near edge X-ray adsorption will be used to put together a picture of the nanocrystal electronic states.

  3. Semiconductor Nanocrystals for Biological Imaging

    SciTech Connect

    Fu, Aihua; Gu, Weiwei; Larabell, Carolyn; Alivisatos, A. Paul

    2005-06-28

    Conventional organic fluorophores suffer from poor photo stability, narrow absorption spectra and broad emission feature. Semiconductor nanocrystals, on the other hand, are highly photo-stable with broad absorption spectra and narrow size-tunable emission spectra. Recent advances in the synthesis of these materials have resulted in bright, sensitive, extremely photo-stable and biocompatible semiconductor fluorophores. Commercial availability facilitates their application in a variety of unprecedented biological experiments, including multiplexed cellular imaging, long-term in vitro and in vivo labeling, deep tissue structure mapping and single particle investigation of dynamic cellular processes. Semiconductor nanocrystals are one of the first examples of nanotechnology enabling a new class of biomedical applications.

  4. Semiconductor nanocrystal-based phagokinetic tracking

    DOEpatents

    Alivisatos, A Paul; Larabell, Carolyn A; Parak, Wolfgang J; Le Gros, Mark; Boudreau, Rosanne

    2014-11-18

    Methods for determining metabolic properties of living cells through the uptake of semiconductor nanocrystals by cells. Generally the methods require a layer of neutral or hydrophilic semiconductor nanocrystals and a layer of cells seeded onto a culture surface and changes in the layer of semiconductor nanocrystals are detected. The observed changes made to the layer of semiconductor nanocrystals can be correlated to such metabolic properties as metastatic potential, cell motility or migration.

  5. Photoemission studies of semiconductor nanocrystals

    SciTech Connect

    Hamad, K. S.; Roth, R.; Alivisatos, A. P.

    1997-04-01

    Semiconductor nanocrystals have been the focus of much attention in the last ten years due predominantly to their size dependent optical properties. Namely, the band gap of nanocrystals exhibits a shift to higher energy with decreasing size due to quantum confinement effects. Research in this field has employed primarily optical techniques to study nanocrystals, and in this respect this system has been investigated extensively. In addition, one is able to synthesize monodisperse, crystalline particles of CdS, CdSe, Si, InP, InAs, as well as CdS/HgS/CdS and CdSe/CdS composites. However, optical spectroscopies have proven ambiguous in determining the degree to which electronic excitations are interior or surface admixtures or giving a complete picture of the density of states. Photoemission is a useful technique for understanding the electronic structure of nanocrystals and the effects of quantum confinement, chemical environments of the nanocrystals, and surface coverages. Of particular interest to the authors is the surface composition and structure of these particles, for they have found that much of the behavior of nanocrystals is governed by their surface. Previously, the authors had performed x-ray photoelectron spectroscopy (XPS) on CdSe nanocrystals. XPS has proven to be a powerful tool in that it allows one to determine the composition of the nanocrystal surface.

  6. Core/Shell semiconductor nanocrystals.

    PubMed

    Reiss, Peter; Protière, Myriam; Li, Liang

    2009-02-01

    Colloidal core/shell nanocrystals contain at least two semiconductor materials in an onionlike structure. The possibility to tune the basic optical properties of the core nanocrystals, for example, their fluorescence wavelength, quantum yield, and lifetime, by growing an epitaxial-type shell of another semiconductor has fueled significant progress on the chemical synthesis of these systems. In such core/shell nanocrystals, the shell provides a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo-oxidation. The shell further provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. This effect is a fundamental prerequisite for the use of nanocrystals in applications such as biological labeling and light-emitting devices, which rely on their emission properties. Focusing on recent advances, this Review discusses the fundamental properties and synthesis methods of core/shell and core/multiple shell structures of II-VI, IV-VI, and III-V semiconductors.

  7. Semiconductor Nanocrystal Photonics

    DTIC Science & Technology

    2005-08-31

    Hahn, H. Du, and T. D. Krauss, "Photoluminescence enhancement of colloidal semiconductor quantum dots embedded in a monolithic microcavity," Appl... DBRs ). The colloidal NC suspension was spun-coat into a 95-nm thick layer in the center of the cavity and then the other layers forming the top DBR

  8. Semiconductor-nanocrystal/conjugated polymer thin films

    DOEpatents

    Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

    2014-06-17

    The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

  9. Semiconductor-nanocrystal/conjugated polymer thin films

    DOEpatents

    Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

    2010-08-17

    The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

  10. Quantum theory of electroabsorption in semiconductor nanocrystals.

    PubMed

    Tepliakov, Nikita V; Leonov, Mikhail Yu; Baranov, Alexander V; Fedorov, Anatoly V; Rukhlenko, Ivan D

    2016-01-25

    We develop a simple quantum-mechanical theory of interband absorption by semiconductor nanocrystals exposed to a dc electric field. The theory is based on the model of noninteracting electrons and holes in an infinitely deep quantum well and describes all the major features of electroabsorption, including the Stark effect, the Franz-Keldysh effect, and the field-induced spectral broadening. It is applicable to nanocrystals of different shapes and dimensions (quantum dots, nanorods, and nanoplatelets), and will prove useful in modeling and design of electrooptical devices based on ensembles of semiconductor nanocrystals.

  11. Phase transitions and doping in semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Sahu, Ayaskanta

    Colloidal semiconductor nanocrystals are a promising technological material because their size-dependent optical and electronic properties can be exploited for a diverse range of applications such as light-emitting diodes, bio-labels, transistors, and solar cells. For many of these applications, electrical current needs to be transported through the devices. However, while their solution processability makes these colloidal nanocrystals attractive candidates for device applications, the bulky surfactants that render these nanocrystals dispersible in common solvents block electrical current. Thus, in order to realize the full potential of colloidal semiconductor nanocrystals in the next-generation of solid-state devices, methods must be devised to make conductive films from these nanocrystals. One way to achieve this would be to add minute amounts of foreign impurity atoms (dopants) to increase their conductivity. Electronic doping in nanocrystals is still very much in its infancy with limited understanding of the underlying mechanisms that govern the doping process. This thesis introduces an innovative synthesis of doped nanocrystals and aims at expanding the fundamental understanding of charge transport in these doped nanocrystal films. The list of semiconductor nanocrystals that can be doped is large, and if one combines that with available dopants, an even larger set of materials with interesting properties and applications can be generated. In addition to doping, another promising route to increase conductivity in nanocrystal films is to use nanocrystals with high ionic conductivities. This thesis also examines this possibility by studying new phases of mixed ionic and electronic conductors at the nanoscale. Such a versatile approach may open new pathways for interesting fundamental research, and also lay the foundation for the creation of novel materials with important applications. In addition to their size-dependence, the intentional incorporation of

  12. Developing New Nanoprobes from Semiconductor Nanocrystals

    SciTech Connect

    Fu, Aihua

    2006-01-01

    In recent years, semiconductor nanocrystal quantum dots havegarnered the spotlight as an important new class of biological labelingtool. Withoptical properties superior to conventional organicfluorophores from many aspects, such as high photostability andmultiplexing capability, quantum dots have been applied in a variety ofadvanced imaging applications. This dissertation research goes along withlarge amount of research efforts in this field, while focusing on thedesign and development of new nanoprobes from semiconductor nanocrystalsthat are aimed for useful imaging or sensing applications not possiblewith quantum dots alone. Specifically speaking, two strategies have beenapplied. In one, we have taken advantage of the increasing capability ofmanipulating the shape of semiconductor nanocrystals by developingsemiconductor quantum rods as fluorescent biological labels. In theother, we have assembled quantum dots and gold nanocrystals into discretenanostructures using DNA. The background information and synthesis,surface manipulation, property characterization and applications of thesenew nanoprobes in a few biological experiments are detailed in thedissertation.

  13. Photoluminescent semiconductor nanocrystals for fingerprint detection.

    PubMed

    Menzel, E R; Savoy, S M; Ulvick, S J; Cheng, K H; Murdock, R H; Sudduth, M R

    2000-05-01

    The concept of utilizing photoluminescent semiconductor nanocrystals for latent fingerprint detection, especially in concert with phase-resolved imaging for background fluorescence suppression, is reduced to practice with CdS nanocrystals that are capped with dioctyl sulfosuccinate. The nanocrystals are dissolved in heptane or hexane and are applied in much the same way as staining with fluorescent dye, on articles that have been pre-fumed with cyanoacrylate ester and also on the sticky side of electrical tape without pre-fuming. Since CdS can form a photoluminescent nanocomposite with dendrimers, a feasibility examination of dendrimer tagging of fingerprints has also been conducted.

  14. Composition-tunable alloyed semiconductor nanocrystals.

    PubMed

    Regulacio, Michelle D; Han, Ming-Yong

    2010-05-18

    The ability to engineer the band gap energy of semiconductor nanocrystals has led to the development of nanomaterials with many new exciting properties and applications. Band gap engineering has thus proven to be an effective tool in the design of new nanocrystal-based semiconductor devices. As reported in numerous publications over the last three decades, tuning the size of nanocrystalline semiconductors is one way of adjusting the band gap energy. On the other hand, research on band gap engineering via control of nanocrystal composition, which is achieved by adjusting the constituent stoichiometries of alloyed semiconductors, is still in its infancy. In this Account, we summarize recent research on colloidal alloyed semiconductor nanocrystals that exhibit novel composition-tunable properties. Alloying of two semiconductors at the nanometer scale produces materials that display properties distinct not only from the properties of their bulk counterparts but also from those of their parent semiconductors. As a result, alloyed nanocrystals possess additional properties that are composition-dependent aside from the properties that emerge due to quantum confinement effects. For example, although the size-dependent emission wavelength of the widely studied CdSe nanocrystals can be continuously tuned to cover almost the entire visible spectrum, the near-infrared (NIR) region is far outside its spectral range. By contrast, certain alloy compositions of nanocrystalline CdSe(x)Te(1-x), an alloy of CdSe and CdTe, can efficiently emit light in the NIR spectral window. These NIR-emitting nanocrystals are potentially useful in several biomedical applications. In addition, highly stable nanocrystals formed by alloying CdSe with ZnSe (i.e., Zn(x)Cd(1-x)Se) emit blue light with excellent efficiency, a property seldom achieved by the parent binary systems. As a result, these materials can be used in short-wavelength optoelectronic devices. In the future, we foresee new discoveries

  15. Extracting hot carriers from photoexcited semiconductor nanocrystals

    SciTech Connect

    Zhu, Xiaoyang

    2014-12-10

    This research program addresses a fundamental question related to the use of nanomaterials in solar energy -- namely, whether semiconductor nanocrystals (NCs) can help surpass the efficiency limits, the so-called “Shockley-Queisser” limit, in conventional solar cells. In these cells, absorption of photons with energies above the semiconductor bandgap generates “hot” charge carriers that quickly “cool” to the band edges before they can be utilized to do work; this sets the solar cell efficiency at a limit of ~31%. If instead, all of the energy of the hot carriers could be captured, solar-to-electric power conversion efficiencies could be increased, theoretically, to as high as 66%. A potential route to capture this energy is to utilize semiconductor nanocrystals. In these materials, the quasi-continuous conduction and valence bands of the bulk semiconductor become discretized due to confinement of the charge carriers. Consequently, the energy spacing between the electronic levels can be much larger than the highest phonon frequency of the lattice, creating a “phonon bottleneck” wherein hot-carrier relaxation is possible via slower multiphonon emission. For example, hot-electron lifetimes as long as ~1 ns have been observed in NCs grown by molecular beam epitaxy. In colloidal NCs, long lifetimes have been demonstrated through careful design of the nanocrystal interfaces. Due to their ability to slow electronic relaxation, semiconductor NCs can in principle enable extraction of hot carriers before they cool to the band edges, leading to more efficient solar cells.

  16. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, A. Paul

    2010-04-13

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  17. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlam, Michael C; Alivisatos, A. Paul

    2014-03-25

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit tight of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  18. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    SciTech Connect

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, Paul A.

    2015-11-10

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit tight of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  19. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C; Alivisatos, A. Paul

    2014-02-11

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  20. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, A. Paul

    2011-09-27

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  1. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, A. Paul

    2005-03-08

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  2. Electronic displays using optically pumped luminescent semiconductor nanocrystals

    DOEpatents

    Weiss, Shimon; Schlamp, Michael C.; Alivisatos, A. Paul

    2015-06-23

    A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

  3. Exciton polarizability in semiconductor nanocrystals.

    PubMed

    Wang, Feng; Shan, Jie; Islam, Mohammad A; Herman, Irving P; Bonn, Mischa; Heinz, Tony F

    2006-11-01

    The response of charge to externally applied electric fields is an important basic property of any material system, as well as one critical for many applications. Here, we examine the behaviour and dynamics of charges fully confined on the nanometre length scale. This is accomplished using CdSe nanocrystals of controlled radius (1-2.5 nm) as prototype quantum systems. Individual electron-hole pairs are created at room temperature within these structures by photoexcitation and are probed by terahertz (THz) electromagnetic pulses. The electronic response is found to be instantaneous even for THz frequencies, in contrast to the behaviour reported in related measurements for larger nanocrystals and nanocrystal assemblies. The measured polarizability of an electron-hole pair (exciton) amounts to approximately 10(4) A(3) and scales approximately as the fourth power of the nanocrystal radius. This size dependence and the instantaneous response reflect the presence of well-separated electronic energy levels induced in the system by strong quantum-confinement effects.

  4. The structure and morphology of semiconductor nanocrystals

    SciTech Connect

    Kadavanich, Andreas V.

    1997-11-01

    Colloidal semiconductor nanocrystals were studied using High Resolution Transmission Electron Microscopy (HRTEM). Organically capped nanocrystals were found to have faceted shapes consistent with Wulff polyhedra after the effects of capping ligands on surface energies were taken into account. The basic shape thus derived for wurtzite (WZ) structure CdSe nanocrystals capped by tri-octyl phosphine oxide (TOPO) was a truncated hexagonal prism, elongated alone the <001> axis with (100) and (002) facets. This structure has C{sub 3v} point group symmetry. The main defect in this structure is a stacking fault (a single layer of zinc blende type stacking), which does not significantly affect the shape (does not alter the point group).

  5. Charge transport in semiconductor nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

    Mentzel, Tamar Shoshana

    In this thesis, we study charge transport in arrays of semiconductor nanocrystal quantum dots. Nanocrystals are synthesized in solution, and an organic ligand on the surface of the nanocrystal creates a potential barrier that confines charges in the nanocrystal. Optical absorption measurements reveal discrete electronic energy levels in the nanocrystals resulting from quantum confinement. When nanocrystals are deposited on a surface, they self-assemble into a close-packed array forming a nanocrystal solid. We report electrical transport measurements of a PbSe nanocrystal solid that serves as the channel of an inverted field-effect transistor. We measure the conductance as a function of temperature, source-drain bias and. gate voltage. The data indicates that holes are the majority carriers; the Fermi energy lies in impurity states in the bandgap of the nanocrystal; and charges hop between the highest occupied valence state in the nanocrystals (the 1S h states). At low source-drain voltages, the activation energy for hopping is given by the energy required to generate holes in the 1Sh state plus activation over barriers resulting from site disorder. The barriers from site disorder are eliminated with a sufficiently high source-drain bias. From the gate effect, we extract the Thomas-Fermi screening length and a density of states that is consistent with the estimated value. We consider variable-range hopping as an alternative model, and find no self-consistent evidence for it. Next, we employ charge sensing as an alternative to current measurements for studying transport in materials with localized sites. A narrow-channel MOSFET serves as a charge sensor because its conductance is sensitive to potential fluctuations in the nearby environment caused by the motion of charge. In particular, it is sensitive to the fluctuation of single electrons at the silicon-oxide interface within the MOSFET. We pattern a strip of amorphous germanium within 100 nm of the transistor. The

  6. Synthesis and applications of heterostructured semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Khon, Elena

    Semiconductor nanocrystals (NCs) have been of great interest to researchers for several decades due to their unique optoelectronic properties. These nanoparticles are widely used for a variety of different applications. However, there are many unresolved issues that lower the efficiency and/or stability of devices which incorporate these NCs. Our research is dedicated to addressing these issues by identifying potential problems and resolving them, improving existing systems, generating new synthetic strategies, and/or building new devices. The general strategies for the synthesis of different nanocrystals were established in this work, one of which is the colloidal growth of gold domains onto CdS semiconductor nanocrystals. Control of shape and size was achieved simply by adjusting the temperature and the time of the reaction. Depending on the exact morphology of Au and CdS domains, fabricated nano-composites can undergo evaporation-induced self-assembly onto a substrate, which is very useful for building devices. CdS/Au heterostructures can assemble in two different ways: through end-to-end coupling of Au domains, resulting in the formation of one-dimensional chains; and via side-by-side packing of CdS nanorods, leading to the onset of two-dimensional superlattices. We investigated the nature of exciton-plasmon interactions in Au-tipped CdS nanorods using femtosecond transient absorption spectroscopy. The study demonstrated that the key optoelectronic properties of electrically coupled metal and semiconductor domains are significantly different from those observed in systems with weak inter-domain coupling. In particular, strongly-coupled nanocomposites promote mixing of electronic states at semiconductor-metal domain interfaces, which causes a significant suppression of both plasmon and exciton carrier excitations. Colloidal QDs are starting to replace organic molecules in many different applications, such as organic light emmiting diods (OLEDs), due to their

  7. Multiexciton fluorescence from semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Fisher, Brent; Caruge, Jean-Michel; Chan, Yin-Thai; Halpert, Jonathan; Bawendi, Moungi G.

    2005-11-01

    We use transient photoluminescence to spectrally resolve the emission from 1, 2, and 3 electron-hole pairs states in CdSe colloidal nanocrystals with radii ranging between 2.3 and 5.2 nm. Temporally and spectrally resolved multiexciton emission from single NCs is also observed. The observation of multiexciton emission enables new experiments and potential applications at both the single NC level and using ensembles of NCs. First we discuss the use of single CdSe(CdZnS) core(shell) colloidal NCs (spheres and rods) to generate triggered photon pair emission at room temperature, with specific ordering of the pair's constituent photons. Second, we incorporate CdSe/ZnS core-shell nanocrystals into a TiO 2 host matrix and observe simultaneous two-state amplified spontaneous emission and lasing from both multiexcitonic transitions (1S 3/2-1S e and 1P 3/2-1P e) in a surface-emitting distributed feedback CdSe NC laser. From our data we deduce radiative lifetimes, quantum yields, stimulated emission gain, and power dependencies for the multiexciton transitions.

  8. Photocatalytic Solar Fuel Generation on Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Feldmann, Jochen

    2015-03-01

    I will review our scientific work on photocatalytic solar fuel generation utilizing colloidal semiconductor nanocrystals decorated with catalytic metal clusters. In particular, nanocrystals made of CdS, TiO2 and organo-metal halide perovskites will be discussed. Key issues are the role of hole scavangers (M. Berr et al., Appl. Phys. Lett. 100, 223903 (2012)), the size and density of catalytic clusters (M. Berr et al.: Appl. Phys. Lett. 97, 093108 (2010) and Nano Letters 12, 5903 (2012) , and dependencies on external parameters such as pH (T. Simon et al., Nature Mat. 13, 1013 (2014)). Financially supported by the Bavarian Research Cluster ``Solar Technologies Go Hybrid: SolTech''.

  9. Scaling of multiexciton lifetimes in semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Klimov, V. I.; McGuire, J. A.; Schaller, R. D.; Rupasov, V. I.

    2008-05-01

    Ultrafast multiexciton decay via Auger recombination is a major impediment for prospective applications of semiconductor nanocrystals (NCs) in lasing and solar cells enabled by carrier multiplication. One important unexplored aspect of Auger recombination is the scaling of multiexciton lifetimes with the number of excitons per NC. To address this question, we analyze multiexciton dynamics in PbSe and CdSe NCs. We observe that these two systems show a distinct difference in scaling of multiexciton lifetimes, which can be explained in terms of a difference in symmetries of high-order multiexcitons resulting from significant disparity in degeneracies of the lowest-energy quantized states.

  10. Enantioselective cellular uptake of chiral semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Martynenko, I. V.; Kuznetsova, V. A.; Litvinov, I. K.; Orlova, A. O.; Maslov, V. G.; Fedorov, A. V.; Dubavik, A.; Purcell-Milton, F.; Gun'ko, Yu K.; Baranov, A. V.

    2016-02-01

    The influence of the chirality of semiconductor nanocrystals, CdSe/ZnS quantum dots (QDs) capped with L- and D-cysteine, on the efficiency of their uptake by living Ehrlich Ascite carcinoma cells is studied by spectral- and time-resolved fluorescence microspectroscopy. We report an evident enantioselective process where cellular uptake of the L-Cys QDs is almost twice as effective as that of the D-Cys QDs. This finding paves the way for the creation of novel approaches to control the biological properties and behavior of nanomaterials in living cells.

  11. Enantioselective cellular uptake of chiral semiconductor nanocrystals.

    PubMed

    Martynenko, I V; Kuznetsova, V A; Litvinov, I K; Orlova, A O; Maslov, V G; Fedorov, A V; Dubavik, A; Purcell-Milton, F; Gun'ko, Yu K; Baranov, A V

    2016-02-19

    The influence of the chirality of semiconductor nanocrystals, CdSe/ZnS quantum dots (QDs) capped with L- and D-cysteine, on the efficiency of their uptake by living Ehrlich Ascite carcinoma cells is studied by spectral- and time-resolved fluorescence microspectroscopy. We report an evident enantioselective process where cellular uptake of the L-Cys QDs is almost twice as effective as that of the D-Cys QDs. This finding paves the way for the creation of novel approaches to control the biological properties and behavior of nanomaterials in living cells.

  12. Semiconductor nanocrystals for novel optical applications

    NASA Astrophysics Data System (ADS)

    Moon, Jong-Sik

    Inspired by the promise of enhanced spectral response, photorefractive polymeric composites photosensitized with semiconductor nanocrystals have emerged as an important class of materials. Here, we report on the photosensitization of photorefractive polymeric composites at visible wavelengths through the inclusion of narrow band-gap semiconductor nanocrystals composed of PbS. Through this approach, internal diffraction efficiencies in excess of 82%, two-beam-coupling gain coefficients in excess of 211 cm-1, and response times 34 ms have been observed, representing some of the best figures-of-merit reported on this class of materials. In addition to providing efficient photosensitization, however, extensive studies of these hybrid composites have indicated that the inclusion of nanocrystals also provides an enhancement in the charge-carrier mobility and subsequent reduction in the photorefractive response time. Through this approach with PbS as charge-carrier, unprecedented response times of 399 micros were observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency and with internal diffraction efficiencies of 72% and two- beam-coupling gain coefficients of 500 cm-1 being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of the enhanced charge mobility without the accompaniment of superfluous traps. Finally, water soluble InP/ZnS and CdSe/ZnS quantum dots interacted with CPP and Herceptin to apply them as a bio-maker. Both of quantum dots showed the excellent potential for use in biomedical imaging and drug delivery applications. It is anticipated that these approaches can play a significant role in the eventual commercialization of these classes of materials.

  13. Doped semiconductor nanocrystal based fluorescent cellular imaging probes

    NASA Astrophysics Data System (ADS)

    Maity, Amit Ranjan; Palmal, Sharbari; Basiruddin, Sk; Karan, Niladri Sekhar; Sarkar, Suresh; Pradhan, Narayan; Jana, Nikhil R.

    2013-05-01

    Doped semiconductor nanocrystals such as Mn doped ZnS, Mn doped ZnSe and Cu doped InZnS, are considered as new classes of fluorescent biological probes with low toxicity. Although the synthesis in high quality of such nanomaterials is now well established, transforming them into functional fluorescent probes remains a challenge. Here we report a fluorescent cellular imaging probe made of high quality doped semiconductor nanocrystals. We have identified two different coating approaches suitable for transforming the as synthesized hydrophobic doped semiconductor nanocrystals into water-soluble functional nanoparticles. Following these approaches we have synthesized TAT-peptide- and folate-functionalized nanoparticles of 10-80 nm hydrodynamic diameter and used them as a fluorescent cell label. The results shows that doped semiconductor nanocrystals can be an attractive alternative for conventional cadmium based quantum dots with low toxicity.Doped semiconductor nanocrystals such as Mn doped ZnS, Mn doped ZnSe and Cu doped InZnS, are considered as new classes of fluorescent biological probes with low toxicity. Although the synthesis in high quality of such nanomaterials is now well established, transforming them into functional fluorescent probes remains a challenge. Here we report a fluorescent cellular imaging probe made of high quality doped semiconductor nanocrystals. We have identified two different coating approaches suitable for transforming the as synthesized hydrophobic doped semiconductor nanocrystals into water-soluble functional nanoparticles. Following these approaches we have synthesized TAT-peptide- and folate-functionalized nanoparticles of 10-80 nm hydrodynamic diameter and used them as a fluorescent cell label. The results shows that doped semiconductor nanocrystals can be an attractive alternative for conventional cadmium based quantum dots with low toxicity. Electronic supplementary information available: Characterization details of coating and

  14. Spectroscopy of intraband optical transitions in anisotropic semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Turkov, Vadim K.; Baimuratov, Anvar S.; Rukhlenko, Ivan D.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2013-09-01

    We propose a new type of optical spectroscopy of anisotropic semiconductor nanocrystals, which is based on the welldeveloped stationary pump-probe technique, where the pump and probe fields are absorbed upon, respectively, interband and intraband transitions of the nanocrystals' electronic subsystem. We develop a general theory of intraband absorption based on the density matrix formalism. This theory can be applied to study degenerate eigenstates of electrons in semiconductor nanocrystals of different shapes and dimentions. We demonstrate that the angular dependence of intraband absorption by nonspherical nanocrystals enables investigating their shape and orientation, as well as the symmetry of quantum states excited by the probe field and selection rules of electronic transitions.

  15. Luminescent Colloidal Semiconductor Nanocrystals Containing Copper: Synthesis, Photophysics, and Applications.

    PubMed

    Knowles, Kathryn E; Hartstein, Kimberly H; Kilburn, Troy B; Marchioro, Arianna; Nelson, Heidi D; Whitham, Patrick J; Gamelin, Daniel R

    2016-09-28

    Copper-doped semiconductors are classic phosphor materials that have been used in a variety of applications for many decades. Colloidal copper-doped semiconductor nanocrystals have recently attracted a great deal of interest because they combine the solution processability and spectral tunability of colloidal nanocrystals with the unique photoluminescence properties of copper-doped semiconductor phosphors. Although ternary and quaternary semiconductors containing copper, such as CuInS2 and Cu2ZnSnS4, have been studied primarily in the context of their photovoltaic applications, when synthesized as colloidal nanocrystals, these materials have photoluminescence properties that are remarkably similar to those of copper-doped semiconductor nanocrystals. This review focuses on the luminescent properties of colloidal copper-doped, copper-based, and related copper-containing semiconductor nanocrystals. Fundamental investigations into the luminescence of copper-containing colloidal nanocrystals are reviewed in the context of the well-established luminescence mechanisms of bulk copper-doped semiconductors and copper(I) molecular coordination complexes. The use of colloidal copper-containing nanocrystals in applications that take advantage of their luminescent properties, such as bioimaging, solid-state lighting, and luminescent solar concentrators, is also discussed.

  16. Process for forming shaped group III-V semiconductor nanocrystals, and product formed using process

    DOEpatents

    Alivisatos, A. Paul; Peng, Xiaogang; Manna, Liberato

    2001-01-01

    A process for the formation of shaped Group III-V semiconductor nanocrystals comprises contacting the semiconductor nanocrystal precursors with a liquid media comprising a binary mixture of phosphorus-containing organic surfactants capable of promoting the growth of either spherical semiconductor nanocrystals or rod-like semiconductor nanocrystals, whereby the shape of the semiconductor nanocrystals formed in said binary mixture of surfactants is controlled by adjusting the ratio of the surfactants in the binary mixture.

  17. Process for forming shaped group II-VI semiconductor nanocrystals, and product formed using process

    DOEpatents

    Alivisatos, A. Paul; Peng, Xiaogang; Manna, Liberato

    2001-01-01

    A process for the formation of shaped Group II-VI semiconductor nanocrystals comprises contacting the semiconductor nanocrystal precursors with a liquid media comprising a binary mixture of phosphorus-containing organic surfactants capable of promoting the growth of either spherical semiconductor nanocrystals or rod-like semiconductor nanocrystals, whereby the shape of the semiconductor nanocrystals formed in said binary mixture of surfactants is controlled by adjusting the ratio of the surfactants in the binary mixture.

  18. Doped semiconductor nanocrystal based fluorescent cellular imaging probes.

    PubMed

    Maity, Amit Ranjan; Palmal, Sharbari; Basiruddin, S K; Karan, Niladri Sekhar; Sarkar, Suresh; Pradhan, Narayan; Jana, Nikhil R

    2013-06-21

    Doped semiconductor nanocrystals such as Mn doped ZnS, Mn doped ZnSe and Cu doped InZnS, are considered as new classes of fluorescent biological probes with low toxicity. Although the synthesis in high quality of such nanomaterials is now well established, transforming them into functional fluorescent probes remains a challenge. Here we report a fluorescent cellular imaging probe made of high quality doped semiconductor nanocrystals. We have identified two different coating approaches suitable for transforming the as synthesized hydrophobic doped semiconductor nanocrystals into water-soluble functional nanoparticles. Following these approaches we have synthesized TAT-peptide- and folate-functionalized nanoparticles of 10-80 nm hydrodynamic diameter and used them as a fluorescent cell label. The results shows that doped semiconductor nanocrystals can be an attractive alternative for conventional cadmium based quantum dots with low toxicity.

  19. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    2008-01-01

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) an affinity molecule linked to the semiconductor nanocrystal. The semiconductor nanocrystal is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. Exposure of the semiconductor nanocrystal to excitation energy will excite the semiconductor nanocrystal causing the emission of electromagnetic radiation. Further described are processes for respectively: making the luminescent semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  20. Controlled Chemical Doping of Semiconductor Nanocrystals Using Redox Buffers

    SciTech Connect

    Engel, Jesse H.; Surendranath, Yogesh; Alivisatos, Paul

    2013-07-20

    Semiconductor nanocrystal solids are attractive materials for active layers in next-generation optoelectronic devices; however, their efficient implementation has been impeded by the lack of precise control over dopant concentrations. Herein we demonstrate a chemical strategy for the controlled doping of nanocrystal solids under equilibrium conditions. Exposing lead selenide nanocrystal thin films to solutions containing varying proportions of decamethylferrocene and decamethylferrocenium incrementally and reversibly increased the carrier concentration in the solid by 2 orders of magnitude from their native values. This application of redox buffers for controlled doping provides a new method for the precise control of the majority carrier concentration in porous semiconductor thin films.

  1. Nonlinear optical properties of semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Ricard, Gianpiero Banfi Vittorio Degiorgio Daniel

    1998-05-01

    This review is devoted to the description of recent experimental results concerning the nonlinear optical properties of semiconductor-doped glasses SDGs with particular emphasis on the regime in which the energy of the incident photon is smaller than the energy gap. A considerable theoretical and experimental effort has been devoted in the last 10years to the fundamental aspects of quantumconfined structures, which have properties somewhat intermediate between the bulk crystals and atoms or molecules. From this point of view, SDGs represent an easily available test system, and optical techniques have been a major diagnostic tool. Luminescence and absorption spectroscopy were extensively used to characterize the electronic states. The experiments aimed at the measurement of the real and imaginary parts of the third-order optical susceptibility of SDGs below the bandgap are described in some detail, and the results obtained with different techniques are compared. Besides the intrinsic fast nonlinearity due to bound electrons, SDGs may present a larger but much slower nonlinearity due to the free carriers generated by two-photon absorption. This implies that experiments have to be properly designed for separation of the two effects. In this article we stress the importance of a detailed structural characterization of the samples. Knowledge of the volume fraction occupied by the nanocrystals is necessary in order to derive from the experimental data the intrinsic nonlinearity and to compare it with the bulk nonlinearity. We discuss recent experiments in which the dependence of the intrinsic nonlinearity on the crystal size is derived by performing, on the samples, measurements of the real part and imaginary part of the nonlinear optical susceptibility and measurements of crystal size and volume fraction. Structural characterization is of interest also for a better understanding of the physical processes underlying the growth of crystallites in SDGs. The average size of

  2. Radiative decay rates of impurity states in semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2015-10-01

    Doped semiconductor nanocrystals is a versatile material base for contemporary photonics and optoelectronics devices. Here, for the first time to the best of our knowledge, we theoretically calculate the radiative decay rates of the lowest-energy states of donor impurity in spherical nanocrystals made of four widely used semiconductors: ZnS, CdSe, Ge, and GaAs. The decay rates were shown to vary significantly with the nanocrystal radius, increasing by almost three orders of magnitude when the radius is reduced from 15 to 5 nm. Our results suggest that spontaneous emission may dominate the decay of impurity states at low temperatures, and should be taken into account in the design of advanced materials and devices based on doped semiconductor nanocrystals.

  3. Charge-tunable quantum plasmons in colloidal semiconductor nanocrystals.

    PubMed

    Schimpf, Alina M; Thakkar, Niket; Gunthardt, Carolyn E; Masiello, David J; Gamelin, Daniel R

    2014-01-28

    Nanomaterials exhibiting plasmonic optical responses are impacting sensing, information processing, catalysis, solar, and photonics technologies. Recent advances have expanded the portfolio of plasmonic nanostructures into doped semiconductor nanocrystals, which allow dynamic manipulation of carrier densities. Once interpreted as intraband single-electron transitions, the infrared absorption of doped semiconductor nanocrystals is now commonly attributed to localized surface plasmon resonances and analyzed using the classical Drude model to determine carrier densities. Here, we show that the experimental plasmon resonance energies of photodoped ZnO nanocrystals with controlled sizes and carrier densities diverge from classical Drude model predictions at small sizes, revealing quantum plasmons in these nanocrystals. A Lorentz oscillator model more adequately describes the data and illustrates a closer link between plasmon resonances and single-electron transitions in semiconductors than in metals, highlighting a fundamental contrast between these two classes of plasmonic materials.

  4. Radiative decay rates of impurity states in semiconductor nanocrystals

    SciTech Connect

    Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2015-10-15

    Doped semiconductor nanocrystals is a versatile material base for contemporary photonics and optoelectronics devices. Here, for the first time to the best of our knowledge, we theoretically calculate the radiative decay rates of the lowest-energy states of donor impurity in spherical nanocrystals made of four widely used semiconductors: ZnS, CdSe, Ge, and GaAs. The decay rates were shown to vary significantly with the nanocrystal radius, increasing by almost three orders of magnitude when the radius is reduced from 15 to 5 nm. Our results suggest that spontaneous emission may dominate the decay of impurity states at low temperatures, and should be taken into account in the design of advanced materials and devices based on doped semiconductor nanocrystals.

  5. Synthesis of Doped Semiconductor Nanocrystals and Conductive Coatings

    NASA Astrophysics Data System (ADS)

    Wills, Andrew Wilke

    Semiconductor nanocrystals are an intriguing class of materials because of their size-tunable properties. This makes them promising for future optoelectronic devices such as solar cells and light emitting diodes. Realization of these devices, however, requires precise control of the flow of electricity through the particles. In bulk semiconductors, this is achieved by using materials with few unintentional defects, then intentionally adding particular defects or dopants to alter the semiconductor's electronic properties. In contrast, the addition of electrically active dopants has scarcely been demonstrated in semiconductor nanocrystals, and charge transport is hindered by the barrier of electron hopping between particles. The goal of this thesis, therefore, is to discover new methods to control charge transport in nanocrystals. It divides into three major thrusts: 1) the investigation of the doping process in semiconductor nanocrystals, 2) the invention of new synthetic methods to incorporate electrically active dopants into semiconductor nanocrystals, and 3) the invention of a new nanocrystal surface coating that aids processing of nanocrystals into devices but can be removed to enhance charge transport between particles. The first objective is achieved by the comparison of four different precursors that have been used to dope Mn into nanocrystals. Experiments show that dimethylmanganese incorporates efficiently into ZnSe nanocrystals while other precursors are less efficient and sometimes lower the quality of the nanocrystals produced. The second goal is met by the application of a core-shell synthetic strategy to the incorporation of non-isovalent impurities (Al and In) into CdSe nanocrystals. By separating the three steps of nucleation, dopant binding, and growth, each step can be optimized so that doping is achieved and high quality particles are produced. Detailed characterization shows dopant incorporation and local environment, while transistor

  6. Plasma-produced nanocrystals enable new insights in semiconductor physics

    NASA Astrophysics Data System (ADS)

    Greenberg, Benjamin; Robinson, Zachary; Gorynski, Claudia; Voigt, Bryan; Francis, Lorraine; Aydil, Eray; Kortshagen, Uwe

    2016-09-01

    The transition from semiconducting (insulating) to metallic behavior is a central problem of semiconductor physics. In bulk semiconductors, this insulator-to-metal transition is described by the well-known Mott criterion. However, in films of semiconductor nanocrystals the Mott criterion fails completely. Recent progress in the nonthermal plasma synthesis of films of highly doped silicon nanocrystals has contributed to the development of a new theory that presents a consistent analog to the Mott criterion for nanocrystal materials. Here, we study films of nonthermal plasma produced zinc oxide (ZnO) nanocrystals to in detail investigate the insulator-to-metal transition. We produce high-purity monodisperse ZnO nanocrystals in a nonthermal plasma and form dense films via supersonic impact deposition. We then modulate the free carrier density, n, and nanocrystal contact facet radius, ρ, via xenon-flashlamp intense pulsed light annealing, which induces necking between the clean surfaces of adjacent nanocrystals. Preliminary electrical measurements indicate that the electron mobility can be finely tuned and that the films cross the insulator-to-metal transition for sufficiently high n and ρ. This work was supported by the MRSEC program of the U.S. National Science Foundation under grant DMR-1420013.

  7. Metal-insulator transition in films of doped semiconductor nanocrystals.

    PubMed

    Chen, Ting; Reich, K V; Kramer, Nicolaas J; Fu, Han; Kortshagen, Uwe R; Shklovskii, B I

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.

  8. Optical activity of semiconductor nanocrystals with ionic impurities

    NASA Astrophysics Data System (ADS)

    Tepliakov, N. V.; Baimuratov, A. S.; Gun'ko, Yu. K.; Baranov, A. V.; Fedorov, A. V.; Rukhlenko, I. D.

    2017-01-01

    The strength of the enantioselective interaction of chiral semiconductor nanocrystals with circularly polarized light can be varied over a wide range, which finds a series of important applications in modern nanophotonics. As a rule, this interaction is relatively weak, because the dimension of nanocrystals is much smaller than the wavelength of the optical radiation, and the optical activity of nanocrystals is rather low. In this work, we show theoretically that, by applying ion doping, one can significantly enhance the optical activity of nanocrystals and to vary its magnitude over a wide range of values and over a wide range of frequencies. We show that, by precisely arranging impurities inside nanocrystals, one can optimize the rotatory strengths of intraband transitions, making them 100 times stronger than typical rotatory strengths of small chiral molecules.

  9. Ab initio Theory of Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Wang, Lin-Wang

    2007-03-01

    With blooming experimental synthesis of various nanostructures out of many semiconductor materials, there is an urgent need to calculate the electronic structures and optical properties of these nanosystems based on reliable ab initio methods. Unfortunately, due to the O(N^3) scaling of the conventional ab initio calculation methods based on the density functional theory (DFT), and the >1000 atom sizes of the most experimental nanosystems, the direct applications of these conventional ab intio methods are often difficult. Here we will present the calculated results using our O(N) scaling charge patching method (CPM) [1,2] to nanosystems up to 10,000 atoms. The CPM yields the charge density of a nanosystem by patching the charge motifs generated from small prototype systems. The CPM electron/hole eigen energies differ from the directly calculated results by only ˜10-20 meV. We will present the optical band gaps of quantum dots and wires, quantum rods, quantum dot/quantum well, and quantum dots doped with impurities. Besides good agreements with experimental measurements, we will demonstrate why it is important to perform ab initio calculations, in contrast with the continuum model k.p calculations. We will show the effects of surface polarization potentials and the internal electric fields. Finally, a linear scaling 3 dimensional fragment (LS3DF) method will be discussed. The LS3DF method can be used to calculate the total energy and atomic forces of a large nanosystem, with the results practically the same as the direct DFT method. Our work demonstrates that, with the help of supercomputers, it is now feasible to calculate the electronic structures and optical properties of >10,000 atom nanocrystals with ab initio accuracy. [1] L.W. Wang, Phys. Rev. Lett. 88, 256402 (2002). [2] J. Li, L.W. Wang, Phys. Rev. B 72, 125325 (2005).

  10. Diorganyl dichalcogenides as useful synthons for colloidal semiconductor nanocrystals.

    PubMed

    Brutchey, Richard L

    2015-11-17

    The ability to synthesize colloidal semiconductor nanocrystals in a well-controlled manner (i.e., with fine control over size, shape, size dispersion, and composition) has been mastered over the past 15 years. Much of this success stems from careful studies of precursor conversion and nanocrystal growth with respect to phosphine chalcogenide precursors for the synthesis of metal chalcogenide nanocrystals. Despite the high level of success that has been achieved with phosphine chalcogenides, there has been a longstanding interest in exploring alternate chalcogenide precursors because of issues associated with phosphine chalcogenide cost, purity, toxicity, etc. This has resulted in a large body of literature on the use of sulfur and selenium dissolved in octadecene or amines, thio- and selenoureas, and silyl chalcogenides as alternate chalcogenide precursors for metal chalcogenide nanocrystal synthesis. In this Account, emerging work on the use of diorganyl dichalcogenides (R-E-E-R, where E = S, Se, or Te and R = alkyl, allyl, benzyl, or aryl) as alternate chalcogenide precursors for the synthesis of metal chalcogenide nanocrystals is summarized. Among the benefits of these dichalcogenide synthons are the following: (i) they represent the first and only common precursor type that can function as chalcogen transfer reagents for each of the group VI elements (i.e., to make metal oxide, metal sulfide, metal selenide, and metal telluride nanocrystals); (ii) they possess relatively weak E-E bonds that can be readily cleaved under mild thermolytic or photolytic conditions; and (iii) the organic substituents can be tuned to affect the reactivity. These combined attributes have allowed dichalcogenide precursors to be employed for a wide range of metal chalcogenide nanocrystal syntheses, including those for In2S3, SnxGe1-xSe, SnTe, Cu2-xSySe1-y, ZnSe, CdS, CdSe, MoSe2, WSe2, BiSe, and CuFeS2. Interestingly, a number of metastable phases of compositionally complex

  11. Entropy-driven formation of binary semiconductor-nanocrystal superlattices.

    PubMed

    Evers, Wiel H; De Nijs, Bart; Filion, Laura; Castillo, Sonja; Dijkstra, Marjolein; Vanmaekelbergh, Daniel

    2010-10-13

    One of the main reasons for the current interest in colloidal nanocrystals is their propensity to form superlattices, systems in which (different) nanocrystals are in close contact in a well-ordered three-dimensional (3D) geometry resulting in novel material properties. However, the principles underlying the formation of binary nanocrystal superlattices are not well understood. Here, we present a study of the driving forces for the formation of binary nanocrystal superlattices by comparing the formed structures with full free energy calculations. The nature (metallic or semiconducting) and the size-ratio of the two nanocrystals are varied systematically. With semiconductor nanocrystals, self-organization at high temperature leads to superlattices (AlB(2), NaZn(13), MgZn(2)) in accordance with the phase diagrams for binary hard-sphere mixtures; hence entropy increase is the dominant driving force. A slight change of the conditions results in structures that are energetically stabilized. This study provides rules for the rational design of 3D nanostructured binary semiconductors, materials with promises in thermoelectrics and photovoltaics and which cannot be reached by any other technology.

  12. Photoluminescence from semiconductor cadmium selenide nanocrystals

    NASA Astrophysics Data System (ADS)

    Nazzal, Amjad Yousef

    In this dissertation, the photoluminescence (PL) emission properties from different CdSe nanocrystals (NCs) dispersed in polymer thin films were investigated. The PL spectroscopy was used as a probing tool to study core and surface-related emission properties of the CdSe NCs under investigation. The results found in these studies are promising from the point of view of fundamental understanding as well as the possible employments of the emission properties of CdSe NCs in certain technological applications. The studies presented in this dissertation include the following: (i) PL polarization spectroscopy of single CdSe NCs was performed on a system of colloidal CdSe quantum rods (QRs). Our experimental measurements suggest a strong polarization dependence of both excitation and emission, and confirm the unique linear dipole in the QRs along the long axis of the rod, i.e. the c axis of wurtzite structure, which is in agreement with the previous theoretical predictions. These results are very important because it represents an experimental test to the available theoretical models used in exploring the rich electronic spectra of these NC systems. These results also show the importance of the shape anisotropy on the electronic spectrum of NCs. (ii) Environmental effects on the PL from highly luminescent bare-core CdSe and core/shell CdSe/ZnS NCs were systematically investigated under different atmospheric environments and photo-irradiation conditions. In this study, the PL was used as a probe to detect changes in the electronic spectrum of the NCs due to photo-induced interactions on the surface of the NCs with the local surrounding atmosphere. Such studies are very important to provide a good understanding of the optimum operational conditions for emission applications of NCs in solid-state devices and also give a simple way of studying the surface of the NCs indirectly by investigating the surface interactions with different molecular systems and their effects on the

  13. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    SciTech Connect

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul A.

    2016-12-27

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  14. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    SciTech Connect

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2014-01-28

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  15. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2011-12-06

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  16. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2012-10-16

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  17. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon [Pinole, CA; Bruchez, Marcel [Newark, CA; Alivisatos, Paul [Oakland, CA

    2011-12-06

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  18. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    SciTech Connect

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2012-10-16

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  19. Methods of use of semiconductor nanocrystal probes for treating a material

    DOEpatents

    Weiss, Shimon; Bruchez, Marcel; Alivisatos, Paul

    2007-04-27

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  20. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    2006-09-05

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. subsequent exposure to excitation energy will excite the semiconductor nanocrystal in the probe causing the emission of electromagnetic radiation. Further described are processes for respectively: making the luminescent semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  1. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    2004-03-02

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. Subsequent exposure to excitation energy will excite the semiconductor nanocrystal in the probe, causing the emission of electromagnetic radiation. Further described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  2. Semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon [Pinole, CA; Bruchez, Marcel [Newark, CA; Alivisatos, Paul [Oakland, CA

    2011-12-20

    A semiconductor nanocrystal compound and probe are described. The compound is capable of linking to one or more affinity molecules. The compound comprises (1) one or more semiconductor nanocrystals capable of, in response to exposure to a first energy, providing a second energy, and (2) one or more linking agents, having a first portion linked to the one or more semiconductor nanocrystals and a second portion capable of linking to one or more affinity molecules. One or more semiconductor nanocrystal compounds are linked to one or more affinity molecules to form a semiconductor nanocrystal probe capable of bonding with one or more detectable substances in a material being analyzed, and capable of, in response to exposure to a first energy, providing a second energy. Also described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and treating materials with the probe.

  3. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    2005-08-09

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. Subsequent exposure to excitation energy will excite the semiconductor nanocrystal in the probe causing the emission of electromagnetic radiation. Further described are processes for respectively: making the luminescent semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  4. Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    2002-01-01

    A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. Subsequent exposure to excitation energy will excite the semiconductor nanocrystal in he probe, causing the emission of electromagnetic radiation. Further described are processes for respectively: making the semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

  5. Apparent Versus True Carrier Multiplication Yields in Semiconductor Nanocrystals

    SciTech Connect

    McGuire, John A.; Sykora, Milan; Joo, Jin; Pietryga, Jeffrey M.; Klimov, Victor I.

    2010-05-11

    Generation of multiple electron-hole pairs (excitons) by single photons, known as carrier multiplication (CM), has the potential to appreciably improve the performance of solar photovoltaics. In semiconductor nanocrystals, this effect usually has been detected using a distinct dynamical signature of multiexcitons associated with their fast Auger recombination. Here, we show that uncontrolled photocharging of the nanocrystal core can lead to exaggeration of the Auger decay component and, as a result, significant deviations of the apparent CM efficiencies from their true values. Specifically, we observe that for the same sample, apparent multiexciton yields can differ by a factor of ~3 depending on whether the nanocrystal solution is static or stirred. We show that this discrepancy is consistent with photoinduced charging of the nanocrystals in static solutions, the effect of which is minimized in the stirred case where the charged nanocrystals are swept from the excitation volume between sequential excitation pulses. Using side-by-side measurements of CM efficiencies and nanocrystal charging, we show that the CM results obtained under static conditions converge to the values measured for stirred solutions after we accurately account for the effects of photocharging. This study helps to clarify the recent controversy over CM in nanocrystals and highlights some of the issues that must be carefully considered in spectroscopic studies of this process.

  6. Coupling of Surface Plasmons and Semiconductor Nanocrystals for Nanophotonics Applications

    NASA Astrophysics Data System (ADS)

    Jayanti, Sriharsha V.

    The goal of this thesis is to engineer the interaction between surface plasmons and semiconductor nanocrystals for nanophotonic applications. Plasmonic metals support surface plasmon polaritons, hybrid photon and electron waves that propagate along a metal-dielectric interface. Unlike photons, surface plasmons can be confined in sub-diffraction geometries. This has two important consequences: 1) optical devices can be designed at the nanoscale, and 2) the high density of electromagnetic fields allows study of enhanced light-matter interactions. Surface plasmons have been exploited to demonstrate components of optoelectronic circuits, optical antennas, surface enhanced spectroscopy, enhanced fluorescence from fluorophores, and nanolasers. Despite the advances, surface plasmon losses limit their propagation lengths to tens of micrometers in the visible wavelengths, hindering many applications. Recently, the template-stripping approach was shown to fabricate metal films that exhibit larger grains and smoother surface, reducing the grain boundary and roughness scattering. To further improve the plasmonic properties, we investigate the importance of deposition conditions in the template-stripping approach. We provide insight and recipes to enhance the plasmonic performance of the most commonly used metals in the ultraviolet, visible, and near-infrared. We also explore the potential of low temperatures to improve the performance of metal films, where the electron-electron and electron-phonon scattering should be reduced. This sets a limit on the minimum loss metals can exhibit. Using this knowledge, we study the optical properties of quantum-confined semiconductor nanocrystals near metal structures. Semiconductor nanocrystals have many attractive characteristics that make them suitable for solid-state lighting and solar cells among others. Specifically, CdSe nanocrystals have been heavily studied for their large absorption and emission cross-sections, size dependent

  7. Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

    SciTech Connect

    Sachleben, Joseph Robert

    1993-09-01

    Semiconductor nanocrystals, small biomolecules, and 13C enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution 1H and 13C liquid state spectra of thiophenol ligands on the nanocrystal surfaces. The surface coverage by thiophenol was found to be low, being 5.6 and 26% for nanocrystal radii of 11.8 and 19.2 Å. Internal motion is estimated to be slow with a correlation time > 10-8 s-1. The surface thiophenol ligands react to form a dithiophenol when the nanocrystals were subjected to O2 and ultraviolet. A method for measuring 14N-1H J-couplings is demonstrated on pyridine and the peptide oxytocin; selective 2D T1 and T2 experiments are presented for measuring relaxation times in crowded spectra with overlapping peaks in 1D, but relaxation effects interfere. Possibility of carbon-carbon cross relaxation in 13C enriched solids is demonstrated by experiments on zinc acetate and L-alanine.

  8. Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

    NASA Astrophysics Data System (ADS)

    Sachleben, J. R.

    1993-09-01

    Semiconductor nanocrystals, small biomolecules, and C-13 enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution H-1 and C-13 liquid state spectra of thiophenol ligands on the nanocrystal surfaces. The surface coverage by thiophenol was found to be low, being 5.6 and 26% for nanocrystal radii of 11.8 and 19.2 angstrom. Internal motion is estimated to be slow with a correlation time greater than 10(exp -8) s(exp -1). The surface thiophenol ligands react to form a dithiophenol when the nanocrystals were subjected to O2 and ultraviolet. A method for measuring (N-14)-(H-1) J-couplings is demonstrated on pyridine and the peptide oxytocin; selective 2D T(sub 1) and T(sub 2) experiments are presented for measuring relaxation times in crowded spectra with overlapping peaks in 1D, but relaxation effects interfere. Possibility of carbon-carbon cross relaxation in C-13 enriched solids is demonstrated by experiments on zinc acetate and L-alanine.

  9. Semiconductor Nanocrystals-Based White Light Emitting Diodes

    SciTech Connect

    Dai, Quanqin; Hu, Michael Z.; Duty, Chad E

    2010-01-01

    In response to the demands for energy and the concerns of global warming and climate change, energy efficient and environmentally friendly solid state lighting, such as white light emitting diodes (WLEDs), is considered to be the most promising and suitable light source. Because of their small size, high efficiency, and long lifetime, WLEDs based on colloidal semiconductor nanocrystals (or quantum dots) are emerging as a completely new technology platform for the development of flat-panel displays and solid state lighting, exhibiting the potential to replace the conventionally used incandescent and fluorescent lamps. This replacement could cut the ever-increasing energy consumption, solve the problem of rapidly depleting fossil fuel reserves, and improve the quality of the global environment. In this review, we highlight the recent progress in semiconductor nanocrystals-based WLEDs, compare different approaches for generating white light, and discuss the benefits and challenges of the solid state lighting technology.

  10. Semiconductor-Nanocrystals-Based White Light-Emitting Diodes

    SciTech Connect

    Dai, Quanqin; Duty, Chad E; Hu, Michael Z.

    2010-01-01

    In response to the demands for energy and the concerns of global warming and climate change, energy efficient and environmentally friendly solid-state lighting, such as white lightemitting diodes (WLEDs), is considered to be the most promising and suitable light source. Because of their small size, high efficiency, and long lifetime, WLEDs based on colloidal semiconductor nanocrystals (or quantum dots) are emerging as a completely new technology platform for the development of flat-panel displays and solid-state lighting, exhibiting the potential to replace the conventionally used incandescent and fluorescent lamps. This replacement can cut the ever-increasing level of energy consumption, solve the problem of rapidly depleting fossil fuel reserves, and improve the quality of the global environment. In this review, the recent progress in semiconductor-nanocrystals-based WLEDs is highlighted, the different approaches for generating white light are compared, and the benefits and challenges of the solid-state lighting technology are discussed.

  11. Recent advances in biocompatible semiconductor nanocrystals for immunobiological applications.

    PubMed

    Nanda, Sitansu Sekhar; Kim, Min Jik; Kim, Kwangmeyung; Papaefthymiou, Georgia C; Selvan, Subramanian Tamil; Yi, Dong Kee

    2017-08-25

    Quantum confinement in inorganic semiconductor nanocrystals produces brightly luminescent nanoparticles endowed with unique photo-physical properties, such as tunable optical properties. These have found widespread applications in nanotechnology. The ability to render such nanostructures biocompatible, while maintaining their tunable radiation in the visible range of the electromagnetic spectrum, renders them appropriate for bio-applications. Promising in vitro and in vivo diagnostic applications have been demonstrated, such as fluorescence-based detection of biological interactions, single molecule tracking, multiplexing and immunoassaying. In particular, these fluorescent inorganic semiconductor nanocrystals, generally known as quantum dots, have the potential of remarkable immunobiological applications. This review focuses on the current status of biocompatible quantum dots and their applications in immunobiology - immunosensing, immunofluorescent imaging and immunotherapy. Copyright © 2017 Elsevier B.V. All rights reserved.

  12. Modeling photoinduced fluorescence enhancement in semiconductor nanocrystal arrays

    NASA Astrophysics Data System (ADS)

    Maenosono, Shinya

    2003-07-01

    Photoinduced fluorescence enhancement (PFE) in semiconductor nanocrystal (NC) arrays is modeled based on the rate equations for ground-state, excited-state and photoionized NCs in the array. The photoionization process is broken down into fast and slow ionization processes, which are expected to relate to blinking and darkening phenomena, respectively. Consequently, PFE behavior is found to change drastically, as it depends on both the intrinsic properties of NCs, and on external conditions, such as surface-capping molecules and atmosphere.

  13. Galvanic displacement of metals on semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Johnson, Melanie; Kelly, Joel A.; Henderson, Eric J.; Veinot, Jonathan G. C.

    2009-11-01

    We report the galvanic displacement (GD) of germanium from germanium nanocrystals (Ge-NCs) with silver. The Ge-NCs are synthesized by reductive thermal processing of germanium suboxide sol-gel prepolymers. Thermal processing yields size-controlled oxide-embedded Ge-NCs, which are liberated by dissolution of the germanium oxide matrix in water. Subsequent exposure of the freestanding Ge-NCs to aqueous solutions of AgNO3 leads to deposition of silver nanostructures by GD. The resulting metal structures were analyzed by XRD, XPS, TEM and EDX, confirming deposition of elemental silver in a variety of shapes and sizes.

  14. Controlled assembly and electronics in semiconductor nanocrystal-based devices

    NASA Astrophysics Data System (ADS)

    Drndic, Marija

    2006-03-01

    I will discuss the assembly of semiconductor nanocrystals (CdSe and PbSe) into electronic devices and the basic mechanisms of charge transport in nanocrystal arrays [1-4]. Spherical CdSe nanocrystals show robust memory effects that can be exploited for memory applications [1]. Nanocrystal memory can be erased electrically or optically and is rewritable. In PbSe nanocrystal arrays, as the interdot coupling is increased, the system evolves from an insulating regime dominated by Coulomb blockade to a semiconducting regime, where hopping conduction is the dominant transport mechanism [2]. Two-dimensional CdSe nanorod arrays show striking and anomalous transport properties, including strong and reproducible non-linearities and current oscillations with dc-voltage [4]. I will also discuss imaging of the charge transport in nanocrystal-based electronic devices. Nanocrystal arrays were investigated using electrostatic force microscopy (EFM) and transmission electron microscopy (TEM) [3]. Changes in lattice and transport properties upon annealing in vacuum were revealed. Local charge transport was directly imaged by EFM and correlated to nanopatterns observed with TEM. This work shows how charge transport in complex nanocrystal networks can be identified with nm resolution [3]. This work was supported by the ONR grant N000140410489, the NSF grants DMR-0449553 and MRSEC DMR00-79909, and the ACS PRF grant 41256-G10. References:1) Fischbein M. D. and Drndic M., ``CdSe nanocrystal quantum-dot memory,'' Applied Physics Letters, 86 (19), 193106, 2005.2) H. E. Romero and Drndic M., ``Coulomb blockade and hopping conduction in PbSe quantum dots,'' Physical Review Letters 95, 156801, 2005.3) Hu Z., Fischbein M. D. and Drndic M., ``Local charge transport in two-dimensional PbSe nanocrystal arrays studied by electrostatic force microscopy",'' Nano Letters 5 (7), 1463, 2005.4) Romero H.E., Calusine G. and Drndic M., ``Current oscillations, switching and hysteresis in CdSe nanorod

  15. Preparation of III-V semiconductor nanocrystals

    DOEpatents

    Alivisatos, A.P.; Olshavsky, M.A.

    1996-04-09

    Nanometer-scale crystals of III-V semiconductors are disclosed. They are prepared by reacting a group III metal source with a group V anion source in a liquid phase at elevated temperature in the presence of a crystallite growth terminator such as pyridine or quinoline. 4 figs.

  16. Preparation of III-V semiconductor nanocrystals

    DOEpatents

    Alivisatos, A. Paul; Olshavsky, Michael A.

    1996-01-01

    Nanometer-scale crystals of III-V semiconductors are disclosed, They are prepared by reacting a group III metal source with a group V anion source in a liquid phase at elevated temperature in the presence of a crystallite growth terminator such as pyridine or quinoline.

  17. Amphiphilic self-assembly of semiconductor nanocrystals with heterogeneous compositions

    NASA Astrophysics Data System (ADS)

    Taniguchi, Yuki; Takishita, Takao; Kobayashi, Yusei; Arai, Noriyoshi; Kawai, Tsuyoshi; Nakashima, Takuya

    2017-06-01

    We describe herein that amphiphilic semiconductor nanocrystals (NCs) self-assembled into network structures with heterogeneous compositions. The semiconductor nanorods and tetrapods were subjected to ligand exchange with short-chained water-soluble thiolates, giving an amphiphilic surface pattern with a hydrophilic wall and hydrophobic tips. The amphiphilic NCs self-assembled through hydrophobic effects between tip-surfaces in water. The hydrophobic effect-facilitated self-assembly of NCs was well reproduced by a dissipative particle dynamics simulation. The amphiphilic self-assembly of NCs was demonstrated regardless of NC-shapes and compositions to give semiconductor NC-network structures with heterogeneous compositions. The tandem connection of luminescent core/shell nanorods demonstrated energy transfer between the nanorods in the self-assembly. Contribution to the Focus Issue Self-assemblies of Inorganic and Organic Nanomaterials edited by Marie-Paule Pileni.

  18. Two-Photon-Pumped Perovskite Semiconductor Nanocrystal Lasers.

    PubMed

    Xu, Yanqing; Chen, Qi; Zhang, Chunfeng; Wang, Rui; Wu, Hua; Zhang, Xiaoyu; Xing, Guichuan; Yu, William W; Wang, Xiaoyong; Zhang, Yu; Xiao, Min

    2016-03-23

    Two-photon-pumped lasers have been regarded as a promising strategy to achieve frequency up-conversion for situations where the condition of phase matching required by conventional approaches cannot be fulfilled. However, their practical applications have been hindered by the lack of materials holding both efficient two-photon absorption and ease of achieving population inversion. Here, we show that this challenge can be tackled by employing colloidal nanocrystals of perovskite semiconductors. We observe highly efficient two-photon absorption (with a cross section of 2.7 × 10(6) GM) in toluene solutions of CsPbBr3 nanocrystals that can excite large optical gain (>500 cm(-1)) in thin films. We have succeeded in demonstrating stable two-photon-pumped lasing at a remarkable low threshold by coupling CsPbBr3 nanocrystals with microtubule resonators. Our findings suggest perovskite nanocrystals can be used as excellent gain medium for high-performance frequency-up-conversion lasers toward practical applications.

  19. Synthesis and manipulation of semiconductor nanocrystals in microfluidic reactors

    NASA Astrophysics Data System (ADS)

    Chan, Emory Ming-Yue

    Microfluidic reactors are investigated as a mechanism to control the growth of semiconductor nanocrystals and characterize the structural evolution of colloidal quantum dots. Due to their short diffusion lengths, low thermal masses, and predictable fluid dynamics, microfluidic devices can be used to quickly and reproducibly alter reaction conditions such as concentration, temperature, and reaction time, while allowing for rapid reagent mixing and product characterization. These features are particularly useful for colloidal nanocrystal reactions, which scale poorly and are difficult to control and characterize in bulk fluids. To demonstrate the capabilities of nanoparticle microreactors, a size series of spherical CdSe nanocrystals was synthesized at high temperature in a continuous-flow, microfabricated glass reactor. Nanocrystal diameters are reproducibly controlled by systematically altering reaction parameters such as the temperature, concentration, and reaction time. Microreactors with finer control over temperature and reagent mixing were designed to synthesize nanoparticles of different shapes, such as rods, tetrapods, and hollow shells. The two major challenges observed with continuous flow reactors are the deposition of particles on channel walls and the broad distribution of residence times that result from laminar flow. To alleviate these problems, I designed and fabricated liquid-liquid segmented flow microreactors in which the reaction precursors are encapsulated in flowing droplets suspended in an immiscible carrier fluid. The synthesis of CdSe nanocrystals in such microreactors exhibited reduced deposition and residence time distributions while enabling the rapid screening a series of samples isolated in nL droplets. Microfluidic reactors were also designed to modify the composition of existing nanocrystals and characterize the kinetics of such reactions. The millisecond kinetics of the CdSe-to-Ag2Se nanocrystal cation exchange reaction are measured

  20. Recent Advances in Understanding Delayed Photoluminescence in Colloidal Semiconductor Nanocrystals.

    PubMed

    Marchioro, Arianna

    2017-02-22

    Colloidal semiconductor nanocrystals display remarkably bright, strongly size-dependent photoluminescence properties. Following photoexcitation of these materials, temporary charge carrier separation can occur where one or both charge carriers are trapped. Charge detrapping can reform the emissive state on long time scales up to seconds, causing delayed luminescence. This delayed luminescence has not yet been thoroughly explored, and appears to be closely associated with a phenomenon observed at the single particle level, i.e. photoluminescence intermittency (blinking). Here, some of our recent work on the delayed luminescence properties of nanocrystals of different chemical composition is reviewed. These results provide insight into the mechanism of carrier detrapping, and are discussed in the context of photoluminescence blinking.

  1. Organo Luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

    DOEpatents

    Weiss, Shimon; Bruchez, Jr., Marcel; Alivisatos, Paul

    1999-01-01

    A luminescent semiconductor nanocrystal compound is described which is capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation (luminescing) in a narrow wavelength band and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation--when excited by an electromagnetic radiation source (of narrow or broad bandwidth) or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The luminescent semiconductor nanocrystal compound is linked to an affinity molecule to form an organo luminescent semiconductor nanocrystal probe capable of bonding with a detectable substance in a material being analyzed, and capable of emitting electromagnetic radiation in a narrow wavelength band and/or absorbing, scattering, or diffracting energy when excited by an electromagnetic radiation source (of narrow or broad bandwidth) or a particle beam. The probe is stable to repeated exposure to light in the presence of oxygen and/or other radicals. Further described is a process for making the luminescent semiconductor nanocrystal compound and for making the organo luminescent semiconductor nanocrystal probe comprising the luminescent semiconductor nanocrystal compound linked to an affinity molecule capable of bonding to a detectable substance. A process is also described for using the probe to determine the presence of a detectable substance in a material.

  2. Building Structural Complexity in Semiconductor Nanocrystals through Chemical Transformations

    SciTech Connect

    Sadtler, Bryce F

    2009-05-01

    Methods are presented for synthesizing nanocrystal heterostructures comprised of two semiconductor materials epitaxially attached within individual nanostructures. The chemical transformation of cation exchange, where the cations within the lattice of an ionic nanocrystal are replaced with a different metal ion species, is used to alter the chemical composition at specific regions ofa nanocrystal. Partial cation exchange was performed in cadmium sulfide (CdS) nanorods of well-defined size and shape to examine the spatial organization of materials within the resulting nanocrystal heterostructures. The selectivity for cation exchange to take place at different facets of the nanocrystal plays an important role in determining the resulting morphology of the binary heterostructure. The exchange of copper (I) (Cu+) cations in CdS nanorods occurs preferentially at the ends of the nanorods. Theoretical modeling of epitaxial attachments between different facets of CdS and Cu2S indicate that the selectivity for cation exchange at the ends of the nanorods is a result of the low formation energy of the interfaces produced. During silver (I) (Ag+) cation exchange in CdS nanorods, non-selective nucleation of silver sulfide (Ag2S), followed by partial phase segregation leads to significant changes in the spatial arrangement of CdS and Ag2S regions at the exchange reaction proceeds through the nanocrystal. A well-ordered striped pattern of alternating CdS and Ag2S segments is found at intermediate fractions of exchange. The forces mediating this spontaneous process are a combination of Ostwald ripening to reduce the interfacial area along with a strain-induced repulsive interaction between Ag2S segments. To elucidate why Cu+ and Ag+ cation exchange with CdS nanorods produce different morphologies, models for epitaxial attachments between various facets of CdS with Cu2S or

  3. Controlling Carrier Dynamics using Quantum-Confined Semiconductor Nanocrystals

    SciTech Connect

    Beard, Matthew C.; Klimov, Victor I.

    2016-06-01

    The articles included in this special issue of Chemical Physics explore the use of quantum-confined semiconductor nanocrystals to control the flow of energy and/or charge. Colloidal quantum-confined semiconductor nanostructures are an emerging class of functional materials being developed for novel opto-electronic applications. In the last few years numerous examples in the literature have emerged where novel nanostructures have been tailored such as to achieve a specific function thus moving the field from the stage of discovery of novel behaviors to that of control of nanostructure properties. In addition to the internal structure of the NCs their assemblies can be tailored to achieve emergent properties and add additional control parameters that determine the final opto-electronic properties. These principles are explored via variations in shape, size, surface ligands, heterostructuring, morphology, composition, and assemblies and are demonstrated through measurements of excited state processes, such as Auger recombination; photoluminescence; charge separation and charge transport.

  4. Mapping the exciton diffusion in semiconductor nanocrystal solids.

    PubMed

    Kholmicheva, Natalia; Moroz, Pavel; Bastola, Ebin; Razgoniaeva, Natalia; Bocanegra, Jesus; Shaughnessy, Martin; Porach, Zack; Khon, Dmitriy; Zamkov, Mikhail

    2015-03-24

    Colloidal nanocrystal solids represent an emerging class of functional materials that hold strong promise for device applications. The macroscopic properties of these disordered assemblies are determined by complex trajectories of exciton diffusion processes, which are still poorly understood. Owing to the lack of theoretical insight, experimental strategies for probing the exciton dynamics in quantum dot solids are in great demand. Here, we develop an experimental technique for mapping the motion of excitons in semiconductor nanocrystal films with a subdiffraction spatial sensitivity and a picosecond temporal resolution. This was accomplished by doping PbS nanocrystal solids with metal nanoparticles that force the exciton dissociation at known distances from their birth. The optical signature of the exciton motion was then inferred from the changes in the emission lifetime, which was mapped to the location of exciton quenching sites. By correlating the metal-metal interparticle distance in the film with corresponding changes in the emission lifetime, we could obtain important transport characteristics, including the exciton diffusion length, the number of predissociation hops, the rate of interparticle energy transfer, and the exciton diffusivity. The benefits of this approach to device applications were demonstrated through the use of two representative film morphologies featuring weak and strong interparticle coupling.

  5. Engineered semiconductor nanocrystals with enhanced carrier multiplication yields

    NASA Astrophysics Data System (ADS)

    Klimov, Victor

    2014-03-01

    Carrier multiplication (CM) is a process whereby absorption of a single photon results in multiple electron-hole pairs (excitons). This process could benefit a number of solar-energy conversion technologies, most notably photocatalysis and photovoltaics. This presentation overviews recent progress in understanding the CM process in semiconductor nanocrystals, motivated by an outstanding challenge in this field - the lack of capability to predict the CM performance of nanocrystals based on their known photophysical properties or documented parameters of parental bulk solids. Here, we present a possible solution to this problem by showing that, using biexciton Auger lifetimes and intraband relaxation rates inferred from ultrafast spectroscopic studies, we can rationalize relative changes in CM yields as a function of nanocrystal composition, size and shape. Further, guided by this model, we demonstrate a two-fold enhancement in multiexciton yields in PbSe nanorods vs. quantum dots attributed to enhanced Coulomb interactions. We also explore the control of competing intra-band cooling for increasing multiexciton production. Specifically, we design a new type of hetero-structured PbSe/CdSe quantum dots with reduced rates of intra-band relaxation and demonstrate a four-fold boost in the multiexciton yield. These studies provide useful guidelines for future efforts to achieve the ultimate, energy-conservation-defined CM efficiencies.

  6. Plasmonic doped semiconductor nanocrystals: Properties, fabrication, applications and perspectives

    NASA Astrophysics Data System (ADS)

    Kriegel, Ilka; Scotognella, Francesco; Manna, Liberato

    2017-02-01

    Degenerately doped semiconductor nanocrystals (NCs) are of recent interest to the NC community due to their tunable localized surface plasmon resonances (LSPRs) in the near infrared (NIR). The high level of doping in such materials with carrier densities in the range of 1021cm-3 leads to degeneracy of the doping levels and intense plasmonic absorption in the NIR. The lower carrier density in degenerately doped semiconductor NCs compared to noble metals enables LSPR tuning over a wide spectral range, since even a minor change of the carrier density strongly affects the spectral position of the LSPR. Two classes of degenerate semiconductors are most relevant in this respect: impurity doped semiconductors, such as metal oxides, and vacancy doped semiconductors, such as copper chalcogenides. In the latter it is the density of copper vacancies that controls the carrier concentration, while in the former the introduction of impurity atoms adds carriers to the system. LSPR tuning in vacancy doped semiconductor NCs such as copper chalcogenides occurs by chemically controlling the copper vacancy density. This goes in hand with complex structural modifications of the copper chalcogenide crystal lattice. In contrast the LSPR of degenerately doped metal oxide NCs is modified by varying the doping concentration or by the choice of host and dopant atoms, but also through the addition of capacitive charge carriers to the conduction band of the metal oxide upon post-synthetic treatments, such as by electrochemical- or photodoping. The NIR LSPRs and the option of their spectral fine-tuning make accessible important new features, such as the controlled coupling of the LSPR to other physical signatures or the enhancement of optical signals in the NIR, sensing application by LSPR tracking, energy production from the NIR plasmon resonance or bio-medical applications in the biological window. In this review we highlight the recent advances in the synthesis of various different plasmonic

  7. X-ray and photoelectron spectroscopy of the structure, reactivity, and electronic structure of semiconductor nanocrystals

    SciTech Connect

    Hamad, Kimberly Sue

    2000-01-01

    Semiconductor nanocrystals are a system which has been the focus of interest due to their size dependent properties and their possible use in technological applications. Many chemical and physical properties vary systematically with the size of the nanocrystal and thus their study enables the investigation of scaling laws. Due to the increasing surface to volume ratio as size is decreased, the surfaces of nanocrystals are expected to have a large influence on their electronic, thermodynamic, and chemical behavior. In spite of their importance, nanocrystal surfaces are still relatively uncharacterized in terms of their structure, electronic properties, bonding, and reactivity. Investigation of nanocrystal surfaces is currently limited by what techniques to use, and which methods are suitable for nanocrystals is still being determined. This work presents experiments using x-ray and electronic spectroscopies to explore the structure, reactivity, and electronic properties of semiconductor (CdSe, InAs) nanocrystals and how they vary with size. Specifically, x-ray absorption near edge spectroscopy (XANES) in conjunction with multiple scattering simulations affords information about the structural disorder present at the surface of the nanocrystal. X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) probe the electronic structure in terms of hole screening, and also give information about band lineups when the nanocrystal is placed in electric contact with a substrate. XPS of the core levels of the nanocrystal as a function of photo-oxidation time yields kinetic data on the oxidation reaction occurring at the surface of the nanocrystal.

  8. Sol-gel derived precursors to Group 14 semiconductor nanocrystals - Convenient materials for enabling nanocrystal-based applications

    NASA Astrophysics Data System (ADS)

    Veinot, Jonathan G. C.; Henderson, Eric J.; Hessel, Colin M.

    2009-11-01

    Semiconductor nanocrystals are intriguing because of their electronic, optical, and chemical characteristics. Silicon nanocrystals (Si-NCs) of sub-5 nm dimension are of particular interest due to their intense photoluminescent response and the promise of linking silicon photonics and electronics. Other related nanomaterials of technological importance include SiC and Ge. The following contribution describes key experimental findings pertaining to synthetic methodology, investigation of nanodomain formation and growth, as determined by X-ray powder diffraction (XRD) and photoluminescence (PL) spectroscopy for a series of sol-gel derived prepolymers suitable for preparing Group 14 based nanocrystal containing composites.

  9. Theoretical investigation of magnetic and optical properties of semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Proshchenko, Vitaly

    This thesis presents the theoretical investigation of physical properties of pure and transition metal doped semiconductor nanostructures. First we study optical and energy (the density of states) spectra for Cd mSem clusters of various sizes and shapes, such as spheres, cubes, nanorods, and nanotubes. This work requires a careful computational analysis where a proper exchange-correlation functional has to be chosen to fit the experimental data. The next part of the thesis deals with the magnetic properties of manganese doped CdSe, ZnSe, ZnS, and CdS quantum dots (QDs). We theoretically explain the effect of dual luminescence and show that in the case with CdSe quantum dots the luminescence becomes tunable by a QD size. We also study the concentration dependence of magnetic order and optical transitions in Mn doped CdSe nanocrystals. Room temperature d0 ferromagnetism is studied in ZnS quantum dots and nanowires in Chapter 4. To find the magnetization of the medium and large size nanocrystals we introduce the surface-bulk (SB) model. We show that the condensation of Zn vacancies into a single droplet takes place which leads to the week d0 ferromagnetism in ZnS nanocrystals. In the last Chapter we study electronic, optical, and charge transport properties of two new holey 2D materials, ELH-g-C2N-H and ELH-g-C2N-Br with hydrogen and bromine side-groups, respectively. Since the two 2D crystals under study have not been synthesized yet, we provide the stability analysis and prove that the calculated crystal structures correspond to the global energy minimum criterion.

  10. Biexciton quantum yield of single semiconductor nanocrystals from photon statistics

    PubMed Central

    Nair, Gautham; Zhao, Jing; Bawendi, Moungi G

    2012-01-01

    Biexciton properties strongly affect the usability of a light emitter in quantum photon sources and lasers but are difficult to measure for single fluorophores at room temperature due to luminescence intermittency and bleaching at the high excitation fluences usually required. Here, we observe the biexciton (BX) to exciton (X) to ground photoluminescence cascade of single colloidal semiconductor nanocrystals (NCs) under weak excitation in a g(2) photon correlation measurement and show that the normalized amplitude of the cascade feature is equal to the ratio of the BX to X fluorescence quantum yields. This imposes a limit on the attainable depth of photon antibunching and provides a robust means to study single emitter biexciton physics. In NC samples, we show that the BX quantum yield is considerably inhomogeneous, consistent with the defect sensitivity expected of the Auger nonradiative recombination mechanism. The method can be extended to study X,BX spectral and polarization correlations. PMID:21288042

  11. Water-soluble semiconductor nanocrystals cap exchanged with metalated ligands.

    PubMed

    Liu, Di; Snee, Preston T

    2011-01-25

    We report a novel method for cap exchange of emissive semiconductor nanocrystals (NCs) using thiol functional ligands metalated with zinc. Utilizing this method, the NCs can be several times brighter and much more resistant to precipitation compared to control samples. This method has been applied using a variety of caps such as dihydrolipoic acid and cysteine. Our data suggest that the improved properties of the metalated cap exchanged NCs are due to a ligand metathesis process occurring at the NC surface where the zinc complex reacts with NC surface bound ligands, gently removing them and replacing them with another cap. Overall, the use of metalated ligands helps resolve many long-standing issues concerning the application of small cap exchanged NCs for biological imaging.

  12. Simplistic attachment and multispectral imaging with semiconductor nanocrystals.

    PubMed

    Jennings, Travis L; Triulzi, Robert C; Tao, Guoliang; St Louis, Zachary E; Becker-Catania, Sara G

    2011-01-01

    Advances in spectral deconvolution technologies are rapidly enabling researchers to replace or enhance traditional epifluorescence microscopes with instruments capable of detecting numerous markers simultaneously in a multiplexed fashion. While significantly expediting sample throughput and elucidating sample information, this technology is limited by the spectral width of common fluorescence reporters. Semiconductor nanocrystals (NC's) are very bright, narrow band fluorescence emitters with great potential for multiplexed fluorescence detection, however the availability of NC's with facile attachment chemistries to targeting molecules has been a severe limitation to the advancement of NC technology in applications such as immunocytochemistry and immunohistochemistry. Here we report the development of simple, yet novel attachment chemistries for antibodies onto NC's and demonstrate how spectral deconvolution technology enables the multiplexed detection of 5 distinct NC-antibody conjugates with fluorescence emission wavelengths separated by as little as 20 nm.

  13. Simplistic Attachment and Multispectral Imaging with Semiconductor Nanocrystals

    PubMed Central

    Jennings, Travis L.; Triulzi, Robert C.; Tao, Guoliang; St. Louis, Zachary E.; Becker-Catania, Sara G.

    2011-01-01

    Advances in spectral deconvolution technologies are rapidly enabling researchers to replace or enhance traditional epifluorescence microscopes with instruments capable of detecting numerous markers simultaneously in a multiplexed fashion. While significantly expediting sample throughput and elucidating sample information, this technology is limited by the spectral width of common fluorescence reporters. Semiconductor nanocrystals (NC’s) are very bright, narrow band fluorescence emitters with great potential for multiplexed fluorescence detection, however the availability of NC’s with facile attachment chemistries to targeting molecules has been a severe limitation to the advancement of NC technology in applications such as immunocytochemistry and immunohistochemistry. Here we report the development of simple, yet novel attachment chemistries for antibodies onto NC’s and demonstrate how spectral deconvolution technology enables the multiplexed detection of 5 distinct NC-antibody conjugates with fluorescence emission wavelengths separated by as little as 20 nm. PMID:22346658

  14. Biexciton quantum yield of single semiconductor nanocrystals from photon statistics.

    PubMed

    Nair, Gautham; Zhao, Jing; Bawendi, Moungi G

    2011-03-09

    Biexciton properties strongly affect the usability of a light emitter in quantum photon sources and lasers but are difficult to measure for single fluorophores at room temperature due to luminescence intermittency and bleaching at the high excitation fluences usually required. Here, we observe the biexciton (BX) to exciton (X) to ground photoluminescence cascade of single colloidal semiconductor nanocrystals (NCs) under weak excitation in a g((2)) photon correlation measurement and show that the normalized amplitude of the cascade feature is equal to the ratio of the BX to X fluorescence quantum yields. This imposes a limit on the attainable depth of photon antibunching and provides a robust means to study single emitter biexciton physics. In NC samples, we show that the BX quantum yield is considerably inhomogeneous, consistent with the defect sensitivity expected of the Auger nonradiative recombination mechanism. The method can be extended to study X,BX spectral and polarization correlations.

  15. Facts and artifacts in the blinking statistics of semiconductor nanocrystals.

    PubMed

    Crouch, Catherine H; Sauter, Orion; Wu, Xiaohua; Purcell, Robert; Querner, Claudia; Drndic, Marija; Pelton, Matthew

    2010-05-12

    Since its initial discovery just over a decade ago, blinking of semiconductor nanocrystals has typically been described in terms of probability distributions for durations of bright, or "on," states and dark, or "off," states. These distributions are obtained by binning photon counts in order to construct a time series for emission intensity and then applying a threshold to distinguish on states from off states. By examining experimental data from CdSe/ZnS core/shell nanocrystals and by simulating this data according to a simple, two-state blinking model, we find that the apparent truncated power-law distributions of on times can depend significantly on the choices of binning time and threshold. For example, increasing the binning time by a factor of 10 can double the apparent truncation time and change the apparent power-law exponent by 30%, even though the binning time is only 3% of the truncation time. Our findings indicate that stringent experimental conditions are needed to accurately determine blinking-time probability distributions. Similar considerations should apply to any phenomenon characterized by time series data that displays telegraph noise.

  16. Synthetic Strategies for Semiconductor Nanocrystals Expressing Localized Surface Plasmon Resonance.

    PubMed

    Niezgoda, J Scott; Rosenthal, Sandra J

    2016-03-03

    The field of semiconductor plasmonics has grown rapidly since its outset, only roughly six years ago, and now includes many crystalline substances ranging from GeTe to wide-bandgap transition-metal oxides. One byproduct of this proliferation is the sea of differing synthetic methods to realize localized surface plasmon resonances (LSPRs) based on the studied material. Strategies vary widely from material to material, but all have the common goal of introducing extremely high carrier densities to the semiconductor system. This doping results in tunable, size-quantized, and on/off-switchable LSPR modes, which are a complete departure from traditional metal-nanoparticle-based plasmon resonances. This Minireview will provide an overview of the current state of nanocrystal and quantum-dot plasmonics and the physical basis thereof, however its main purpose is to summarize the methods for realizing LSPRs in the various syntheses and systems that have been reported to date. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Hybrid photovoltaics based on semiconductor nanocrystals and amorphous silicon.

    PubMed

    Sun, Baoquan; Findikoglu, Alp T; Sykora, Milan; Werder, Donald J; Klimov, Victor I

    2009-03-01

    Semiconductor nanocrystals (NCs) are promising materials for applications in photovoltaic (PV) structures that could benefit from size-controlled tunability of absorption spectra, the ease of realization of various tandem architectures, and, perhaps, increased conversion efficiency in the ultraviolet region through carrier multiplication. The first practical step toward utilization of the unique properties of NCs in PV technologies could be through their integration into traditional silicon-based solar cells. Here, we demonstrate an example of such hybrid PV structures that combine colloidal NCs with amorphous silicon. In these structures, NCs and silicon are electronically coupled, and the regime of this coupling can be tuned by altering the alignment of NC energy states with regard to silicon band edges. For example, using wide-gap CdSe NCs we demonstrate a photoresponse which is exclusively due to the NCs. On the other hand, in devices comprising narrow-gap PbS NCs, both the NCs and silicon contribute to photocurrent, which results in PV response extending from the visible to the near-infrared region. The hybrid silicon/PbS NC solar cells show external quantum efficiencies of approximately 7% at infrared energies and 50% in the visible and a power conversion efficiency of up to 0.9%. This work demonstrates the feasibility of hybrid PV devices that combine advantages of mature silicon fabrication technologies with the unique electronic properties of semiconductor NCs.

  18. A novel approach for the fabrication of all-inorganic nanocrystal solids: Semiconductor matrix encapsulated nanocrystal arrays

    NASA Astrophysics Data System (ADS)

    Moroz, Pavel

    Growing fossil fuels consumption compels researchers to find new alternative pathways to produce energy. Along with new materials for the conversion of different types of energy into electricity innovative methods for efficient processing of energy sources are also introduced. The main criteria for the success of such materials and methods are the low cost and compelling performance. Among different types of materials semiconductor nanocrystals are considered as promising candidates for the role of the efficient and cheap absorbers for solar energy applications. In addition to the anticipated cost reduction, the integration of nanocrystals (NC) into device architectures is inspired by the possibility of tuning the energy of electrical charges in NCs via nanoparticle size. However, the stability of nanocrystals in photovoltaic devices is limited by the stability of organic ligands which passivate the surface of semiconductors to preserve quantum confinement. The present work introduces a new strategy for low-temperature processing of colloidal nanocrystals into all-inorganic films: semiconductor matrix encapsulated nanocrystal arrays (SMENA). This methodology goes beyond the traditional ligand-interlinking scheme and relies on the encapsulation of morphologically-defined nanocrystal arrays into a matrix of a wide-band gap semiconductor, which preserves optoelectronic properties of individual nanoparticles. Fabricated solids exhibit excellent thermal stability, which is attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces. The main characteristics and properties of these solids were investigated and compared with ones of traditionally fabricated nanocrystal films using standard spectroscopic, optoelectronic and electronic techniques. As a proof of concept, we. We also characterized electron transport phenomena in different types of nanocrystal films using all-optical approach. By measuring excited carrier lifetimes in either ligand-linked or

  19. Ion beam synthesis and optical properties of semiconductor nanocrystals and quantum dots

    SciTech Connect

    Zhu, J.G.; White, C.W.; Withrow, S.P.

    1996-11-01

    Nanocrystals of semiconductor materials have been fabricated in SiO{sub 2} by ion implantation and subsequent thermal annealing. Strong red photoluminescence (PL) peaked around 750 nm has been observed in samples containing Si nanocrystals in SiO{sub 2}. The Si nanocrystals in the samples with optimized PL intensities are a few nanometers in diameter. Difference in the absorption bandgap energies and the PL peak energies are discussed. Significant influence of implantation sequence on the formation of compound semiconductor nanocrystals are demonstrated with the GaAs in the SiO{sub 2} system. Optical absorption measurements show that Ga particles have already formed in the as-implanted stage if Ga is implanted first. A single surface phonon mode has been observed in the infrared reflectance measurement from samples containing GaAs nanocrystals.

  20. Gas-phase synthesis of semiconductor nanocrystals and its applications

    NASA Astrophysics Data System (ADS)

    Mandal, Rajib

    Luminescent nanomaterials is a newly emerging field that provides challenges not only to fundamental research but also to innovative technology in several areas such as electronics, photonics, nanotechnology, display, lighting, biomedical engineering and environmental control. These nanomaterials come in various forms, shapes and comprises of semiconductors, metals, oxides, and inorganic and organic polymers. Most importantly, these luminescent nanomaterials can have different properties owing to their size as compared to their bulk counterparts. Here we describe the use of plasmas in synthesis, modification, and deposition of semiconductor nanomaterials for luminescence applications. Nanocrystalline silicon is widely known as an efficient and tunable optical emitter and is attracting great interest for applications in several areas. To date, however, luminescent silicon nanocrystals (NCs) have been used exclusively in traditional rigid devices. For the field to advance towards new and versatile applications for nanocrystal-based devices, there is a need to investigate whether these NCs can be used in flexible and stretchable devices. We show how the optical and structural/morphological properties of plasma-synthesized silicon nanocrystals (Si NCs) change when they are deposited on stretchable substrates made of polydimethylsiloxane (PDMS). Synthesis of these NCs was performed in a nonthermal, low-pressure gas phase plasma reactor. To our knowledge, this is the first demonstration of direct deposition of NCs onto stretchable substrates. Additionally, in order to prevent oxidation and enhance the luminescence properties, a silicon nitride shell was grown around Si NCs. We have demonstrated surface nitridation of Si NCs in a single step process using non?thermal plasma in several schemes including a novel dual-plasma synthesis/shell growth process. These coated NCs exhibit SiNx shells with composition depending on process parameters. While measurements including

  1. Plasmas for controlling the synthesis of semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Anthony, Rebecca

    2014-10-01

    Recently, nonthermal plasma synthesis of opto-electronically active semiconductor nanomaterials has attracted interest. The plasma reactor is especially attractive for synthesis of some earth-abundant and nontoxic semiconductor nanocrystals (NCs), such as silicon and gallium nitride. These materials, with high melting temperatures, are more challenging to grow using the liquid-phase techniques that are successful for other materials, such as II-VI NCs. Here, plasma synthesis of high-quality NCs from these materials will be discussed, including investigations on controlling the NCs' light emission properties via physical changes in the NCs brought about by altering the plasma parameters. For example, nanoparticle crystallinity may be controlled by altering the power supplied to the plasma reactor, which has been revealed to influence both the density of atomic hydrogen and the ion density in the plasma. In addition, the surfaces of NCs (which have been shown to be crucial in determining NC luminescence properties) can be altered utilizing reactions that take place in the plasma after NC growth is finished. The features of the plasma reactor provide unique and selective control over the properties of NCs, and also allow for deposition of dense films of NCs directly from the gas-phase, in complete avoidance of liquid-phase methods. These features - crystallization of environmentally benign materials, capacity to control NC surfaces via plasma-intiated reactions, and direct deposition of these materials onto device substrates - unite in a method for ``green'' processing of nanomaterials. Future directions for utilizing plasma reactors for nanomaterials synthesis and processing will also be discussed.

  2. Molecular Chemistry to the Fore: New Insights into the Fascinating World of Photoactive Colloidal Semiconductor Nanocrystals

    SciTech Connect

    Vela-Becerra, Javier

    2013-02-01

    Colloidal semiconductor nanocrystals possess unique properties that are unmatched by other chromophores such as organic dyes or transition-metal complexes. These versatile building blocks have generated much scientific interest and found applications in bioimaging, tracking, lighting, lasing, photovoltaics, photocatalysis, thermoelectrics, and spintronics. Despite these advances, important challenges remain, notably how to produce semiconductor nanostructures with predetermined architecture, how to produce metastable semiconductor nanostructures that are hard to isolate by conventional syntheses, and how to control the degree of surface loading or valence per nanocrystal. Molecular chemists are very familiar with these issues and can use their expertise to help solve these challenges. In this Perspective, we present our group’s recent work on bottom-up molecular control of nanoscale composition and morphology, low-temperature photochemical routes to semiconductor heterostructures and metastable phases, solar-to-chemical energy conversion with semiconductor-based photocatalysts, and controlled surface modification of colloidal semiconductors that bypasses ligand exchange.

  3. Engineering of Semiconductor Nanocrystals for Light Emitting Applications

    PubMed Central

    Todescato, Francesco; Fortunati, Ilaria; Minotto, Alessandro; Signorini, Raffaella; Jasieniak, Jacek J.; Bozio, Renato

    2016-01-01

    Semiconductor nanocrystals are rapidly spreading into the display and lighting markets. Compared with liquid crystal and organic LED displays, nanocrystalline quantum dots (QDs) provide highly saturated colors, wide color gamut, resolution, rapid response time, optical efficiency, durability and low cost. This remarkable progress has been made possible by the rapid advances in the synthesis of colloidal QDs and by the progress in understanding the intriguing new physics exhibited by these nanoparticles. In this review, we provide support to the idea that suitably engineered core/graded-shell QDs exhibit exceptionally favorable optical properties, photoluminescence and optical gain, while keeping the synthesis facile and producing QDs well suited for light emitting applications. Solid-state laser emitters can greatly profit from QDs as efficient gain materials. Progress towards fabricating low threshold, solution processed DFB lasers that are optically pumped using one- and two-photon absorption is reviewed. In the field of display technologies, the exploitation of the exceptional photoluminescence properties of QDs for LCD backlighting has already advanced to commercial levels. The next big challenge is to develop the electroluminescence properties of QD to a similar state. We present an overview of QLED devices and of the great perspectives for next generation display and lighting technologies. PMID:28773794

  4. Effect of surface modification on semiconductor nanocrystal fluorescence lifetime.

    PubMed

    Ruedas-Rama, Maria J; Orte, Angel; Hall, Elizabeth A H; Alvarez-Pez, Jose M; Talavera, Eva M

    2011-04-04

    Semiconductor nanocrystals, namely, quantum dots (QDs), present a set of unique photoluminescence properties, which has led to increased interest in using them as advantageous alternatives to conventional organic dyes. Many applications of QDs involve surface modification to enhance the solubility or biocompatibility of the QDs. One of the least exploited properties of QDs is the very long photoluminescence lifetime that usually has complex kinetics owing to the effect of quantum confinement. Herein, we describe the effect of different surface modifications on the photoluminescence decay kinetics of QDs. The different surface modifications were carefully chosen to provide lipophilic or water-soluble QDs with either positive or negative surface net charges. We also survey the effect on the QD lifetime of several ligands that interact with the QD surface, such as organic chromophores or fluorescent proteins. The results obtained demonstrate that time-resolved fluorescence is a useful tool for QD-based sensing to set the basis for the development of time-resolved-based nanosensors.

  5. Response of semiconductor nanocrystals to extremely energetic excitation.

    PubMed

    Padilha, Lazaro A; Bae, Wan K; Klimov, Victor I; Pietryga, Jeffrey M; Schaller, Richard D

    2013-03-13

    Using a combination of transient photoluminescence and transient cathodoluminescence (trCL) we, for the first time, identify and quantify the distribution of electronic excitations in colloidal semiconductor nanocrystals (NCs) under high-energy excitation. Specifically, we compare the temporally and spectrally resolved radiative recombination produced following excitation with 3.1 eV, subpicosecond photon pulses, or with ionizing radiation in the form of 20 keV picosecond electron pulses. Using this approach, we derive excitation branching ratios produced in the scenario of energetic excitation of NCs typical of X-ray, neutron, or gamma-ray detectors. Resultant trCL spectra and dynamics for CdSe NCs indicate that all observable emission can be attributed to recombination between states within the quantum-confined nanostructure with particularly significant yields of trions and multiexcitons produced by carrier multiplication. Our observations offer direct insight into the transduction of atomic excitation into quantum-confined states within NCs, explain that the root cause of poor performance in previous scintillation studies arises from efficient nonradiative Auger recombination, and suggest routes for improved detector materials.

  6. Structure-Dependent Spin Polarization in Polymorphic CdS:Y Semiconductor Nanocrystals.

    PubMed

    Wang, Pan; Xiao, Bingxin; Zhao, Rui; Ma, Yanzhang; Zhang, Mingzhe

    2016-03-01

    Searching for the polymorphic semiconductor nanocrystals would provide precise and insightful structure-spin polarization correlations and meaningful guidance for designing and synthesizing high spin-polarized spintronic materials. Herein, the high spin polarization is achieved in polymorphic CdS:Y semiconductor nanocrystals. The high-pressure polymorph of rock-salt CdS:Y nanocrystals has been recovered at ambient conditions synthesized by the wurtzite CdS:Y nanocrystals as starting material under 5.2 GPa and 300 °C conditions. The rock-salt CdS:Y polymorph displays more robust room-temperature ferromagnetism than wurtzite sample, which can reach the ferromagnetic level of conventional semiconductors doped with magnetic transition-metal ions, mainly due to the significantly enhanced spin configuration and defect states. Therefore, crystal structure directly governs the spin configuration, which determines the degree of spin polarization. This work can provide experimental and theoretical methods for designing the high spin-polarized semiconductor nanocrystals, which is important for applications in semiconductor spintronics.

  7. Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials.

    PubMed

    Reiss, Peter; Carrière, Marie; Lincheneau, Christophe; Vaure, Louis; Tamang, Sudarsan

    2016-09-28

    We review the synthesis of semiconductor nanocrystals/colloidal quantum dots in organic solvents with special emphasis on earth-abundant and toxic heavy metal free compounds. Following the Introduction, section 2 defines the terms related to the toxicity of nanocrystals and gives a comprehensive overview on toxicity studies concerning all types of quantum dots. Section 3 aims at providing the reader with the basic concepts of nanocrystal synthesis. It starts with the concepts currently used to describe the nucleation and growth of monodisperse particles and next takes a closer look at the chemistry of the inorganic core and its interactions with surface ligands. Section 4 reviews in more detail the synthesis of different families of semiconductor nanocrystals, namely elemental group IV compounds (carbon nanodots, Si, Ge), III-V compounds (e.g., InP, InAs), and binary and multinary metal chalcogenides. Finally, the authors' view on the perspectives in this field is given.

  8. Nanocrystal structures

    DOEpatents

    Eisler, Hans J.; Sundar, Vikram C.; Walsh, Michael E.; Klimov, Victor I.; Bawendi, Moungi G.; Smith, Henry I.

    2006-12-19

    A structure including a grating and a semiconductor nanocrystal layer on the grating, can be a laser. The semiconductor nanocrystal layer can include a plurality of semiconductor nanocrystals including a Group II–VI compound, the nanocrystals being distributed in a metal oxide matrix. The grating can have a periodicity from 200 nm to 500 nm.

  9. Nanocrystal structures

    DOEpatents

    Eisler, Hans J [Stoneham, MA; Sundar, Vikram C [Stoneham, MA; Walsh, Michael E [Everett, MA; Klimov, Victor I [Los Alamos, NM; Bawendi, Moungi G [Cambridge, MA; Smith, Henry I [Sudbury, MA

    2008-12-30

    A structure including a grating and a semiconductor nanocrystal layer on the grating, can be a laser. The semiconductor nanocrystal layer can include a plurality of semiconductor nanocrystals including a Group II-VI compound, the nanocrystals being distributed in a metal oxide matrix. The grating can have a periodicity from 200 nm to 500 nm.

  10. Effective optical Faraday rotations of semiconductor EuS nanocrystals with paramagnetic transition-metal ions.

    PubMed

    Hasegawa, Yasuchika; Maeda, Masashi; Nakanishi, Takayuki; Doi, Yoshihiro; Hinatsu, Yukio; Fujita, Koji; Tanaka, Katsuhisa; Koizumi, Hitoshi; Fushimi, Koji

    2013-02-20

    Novel EuS nanocrystals containing paramagnetic Mn(II), Co(II), or Fe(II) ions have been reported as advanced semiconductor materials with effective optical rotation under a magnetic field, Faraday rotation. EuS nanocrystals with transition-metal ions, EuS:M nanocrystals, were prepared by the reduction of the Eu(III) dithiocarbamate complex tetraphenylphosphonium tetrakis(diethyldithiocarbamate)europium(III) with transition-metal complexes at 300 °C. The EuS:M nanocrystals thus prepared were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroanalysis (ICP-AES), and a superconducting quantum interference device (SQUID) magnetometer. Enhanced Faraday rotations of the EuS:M nanocrystals were observed around 550 nm, and their enhanced spin polarization was estimated using electron paramagnetic resonance (EPR) measurements. In this report, the magneto-optical relationship between the Faraday rotation efficiency and spin polarization is discussed.

  11. Semiconductor Nanocrystals Hybridized with Functional Ligands: New Composite Materials with Tunable Properties

    PubMed Central

    McDowell, Matthew; Wright, Ashley E.; Hammer, Nathan I.

    2010-01-01

    Semiconductor nanocrystals hybridized with functional ligands represent an important new class of composite nanomaterials. The development of these new nanoscale building blocks has intensified over the past few years and offer significant advantages in a wide array of applications. Functional ligands allow for incorporation of nanocrystals into areas where their unique photophysics can be exploited. Energy and charge transfer between the ligands and the nanocrystal also result in enhanced physical properties that can be tuned by the choice of ligand architecture. Here, progress in the development and applications involving this new class of composite materials will be discussed.

  12. Photosensitizer methylene blue-semiconductor nanocrystals hybrid system for photodynamic therapy.

    PubMed

    Rakovich, Aliaksandra; Rakovich, Tatsiana; Kelly, Vincent; Lesnyak, Vladimir; Eychmüller, Alexander; Rakovich, Yury P; Donegan, John F

    2010-04-01

    In this work we report on the development of novel hybrid material with enhanced photodynamic properties based on methylene blue and CdTe nanocrystals. Absorption spectroscopy, visible photoluminescence spectroscopy and fluorescence lifetime imaging of this system reveal efficient charge transfer between nanocrystals and the methylene blue dye. Near infra-red photoluminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were also performed, they point towards an improvement in the cell kill efficiency for the methylene blue-semiconductor nanocrystals hybrid system.

  13. Mechanisms of fluorescence blinking in semiconductor nanocrystal quantum dots.

    PubMed

    Tang, Jau; Marcus, R A

    2005-08-01

    The light-induced spectral diffusion and fluorescence intermittency (blinking) of semiconductor nanocrystal quantum dots are investigated theoretically using a diffusion-controlled electron-transfer (DCET) model, where a light-induced one-dimensional diffusion process in energy space is considered. Unlike the conventional electron-transfer reactions with simple exponential kinetics, the model naturally leads to a power-law statistics for the intermittency. We formulate a possible explanation for the spectral broadening and its proportionality to the light energy density, the -32 power law for the blinking statistics of the fluorescence intermittency, the breakdown of the power-law behavior with a bending tail for the "light" periods, a lack of bending tail for the "dark" periods (but would eventually appear at later times), and the dependence of the bending tail on light intensity and temperature. This DCET model predicts a critical time t(c) (a function of the electronic coupling strength and other quantities), such that for times shorter than t(c) the exponent for the power law is -12 instead of -32. Quantitative analyses are made of the experimental data on spectral diffusion and on the asymmetric blinking statistics for the "on" and "off" events. Causes for deviation of the exponent from the ideal value of -32 are also discussed. Several fundamental properties are determined from the present experimental data, the diffusion correlation time, the Stokes shift, and a combination of other molecular-based quantities. Specific experiments are suggested to test the model further, extract other molecular properties, and elucidate more details of the light-induced charge-transfer dynamics in quantum dots.

  14. New aspects of carrier multiplication in semiconductor nanocrystals.

    PubMed

    McGuire, John A; Joo, Jin; Pietryga, Jeffrey M; Schaller, Richard D; Klimov, Victor I

    2008-12-01

    One consequence of strong spatial confinement of electronic wave functions in semiconductor nanocrystals (NCs) is a significant enhancement in carrier-carrier Coulomb interactions. This effect leads to a number of novel physical phenomena including ultrafast decay of multiple electron-hole pairs (multiexcitons) by Auger recombination and high-efficiency generation of mutiexcitons by single photons via carrier multiplication (CM). Significant recent interest in multiexciton phenomena in NCs has been stimulated by studies of NC lasing, as well as potential applications of CM in solar-energy conversion. The focus of this Account is on CM. In this process, the kinetic energy of a "hot" electron (or a "hot" hole) does not dissipate as heat but is, instead, transferred via the Coulomb interaction to the valence-band electron, exciting it across the energy gap. Because of restrictions imposed by energy and translational-momentum conservation, as well as rapid energy loss due to phonon emission, CM is inefficient in bulk semiconductors, particularly at energies relevant to solar energy conversion. On the other hand, the CM efficiency can potentially be enhanced in zero-dimensional NCs because of factors such as a wide separation between discrete electronic states, which inhibits phonon emission ("phonon bottleneck"), enhanced Coulomb interactions, and relaxation in translational-momentum conservation. Here, we investigate CM in PbSe NCs by applying time-resolved photoluminescence and transient absorption. Both techniques show clear signatures of CM with efficiencies that are in good agreement with each other. NCs of the same energy gap show moderate batch-to-batch variations (within approximately 30%) in apparent multiexciton yields and larger variations (more than a factor of 3) due to differences in sample conditions (stirred vs static solutions). These results indicate that NC surface properties may affect the CM process. They also point toward potential interference

  15. Hydrogen-Bonded Organic Semiconductor Micro- And Nanocrystals: From Colloidal Syntheses to (Opto-)Electronic Devices

    PubMed Central

    2014-01-01

    Organic pigments such as indigos, quinacridones, and phthalocyanines are widely produced industrially as colorants for everyday products as various as cosmetics and printing inks. Herein we introduce a general procedure to transform commercially available insoluble microcrystalline pigment powders into colloidal solutions of variously sized and shaped semiconductor micro- and nanocrystals. The synthesis is based on the transformation of the pigments into soluble dyes by introducing transient protecting groups on the secondary amine moieties, followed by controlled deprotection in solution. Three deprotection methods are demonstrated: thermal cleavage, acid-catalyzed deprotection, and amine-induced deprotection. During these processes, ligands are introduced to afford colloidal stability and to provide dedicated surface functionality and for size and shape control. The resulting micro- and nanocrystals exhibit a wide range of optical absorption and photoluminescence over spectral regions from the visible to the near-infrared. Due to excellent colloidal solubility offered by the ligands, the achieved organic nanocrystals are suitable for solution processing of (opto)electronic devices. As examples, phthalocyanine nanowire transistors as well as quinacridone nanocrystal photodetectors, with photoresponsivity values by far outperforming those of vacuum deposited reference samples, are demonstrated. The high responsivity is enabled by photoinduced charge transfer between the nanocrystals and the directly attached electron-accepting vitamin B2 ligands. The semiconducting nanocrystals described here offer a cheap, nontoxic, and environmentally friendly alternative to inorganic nanocrystals as well as a new paradigm for obtaining organic semiconductor materials from commercial colorants. PMID:25253644

  16. The interplay of shape and crystalline anisotropies in plasmonic semiconductor nanocrystals

    DOE PAGES

    Kim, Jongwook; Agrawal, Ankit; Krieg, Franziska; ...

    2016-05-16

    Doped semiconductor nanocrystals are an emerging class of materials hosting localized surface plasmon resonance (LSPR) over a wide optical range. Studies so far have focused on tuning LSPR frequency by controlling the dopant and carrier concentrations in diverse semiconductor materials. However, the influence of anisotropic nanocrystal shape and of intrinsic crystal structure on LSPR remain poorly explored. Here, we illustrate how these two factors collaborate to determine LSPR characteristics in hexagonal cesium-doped tungsten oxide nanocrystals. The effect of shape anisotropy is systematically analyzed via synthetic control of nanocrystal aspect ratio (AR), from disks to nanorods. We demonstrate the dominant influencemore » of crystalline anisotropy, which uniquely causes strong LSPR band-splitting into two distinct peaks with comparable intensities. Modeling typically used to rationalize particle shape effects is refined by taking into account the anisotropic dielectric function due to crystalline anisotropy, thus fully accounting for the AR-dependent evolution of multiband LSPR spectra. Furthermore, this new insight into LSPR of semiconductor nanocrystals provides a novel strategy for an exquisite tuning of LSPR line shape.« less

  17. The Interplay of Shape and Crystalline Anisotropies in Plasmonic Semiconductor Nanocrystals.

    PubMed

    Kim, Jongwook; Agrawal, Ankit; Krieg, Franziska; Bergerud, Amy; Milliron, Delia J

    2016-06-08

    Doped semiconductor nanocrystals are an emerging class of materials hosting localized surface plasmon resonance (LSPR) over a wide optical range. Studies so far have focused on tuning LSPR frequency by controlling the dopant and carrier concentrations in diverse semiconductor materials. However, the influence of anisotropic nanocrystal shape and of intrinsic crystal structure on LSPR remain poorly explored. Here, we illustrate how these two factors collaborate to determine LSPR characteristics in hexagonal cesium-doped tungsten oxide nanocrystals. The effect of shape anisotropy is systematically analyzed via synthetic control of nanocrystal aspect ratio (AR), from disks to nanorods. We demonstrate the dominant influence of crystalline anisotropy, which uniquely causes strong LSPR band-splitting into two distinct peaks with comparable intensities. Modeling typically used to rationalize particle shape effects is refined by taking into account the anisotropic dielectric function due to crystalline anisotropy, thus fully accounting for the AR-dependent evolution of multiband LSPR spectra. This new insight into LSPR of semiconductor nanocrystals provides a novel strategy for an exquisite tuning of LSPR line shape.

  18. Self-assembly and alignment of semiconductor nanoparticles on cellulose nanocrystals

    Treesearch

    Sonal Padalkar; Jeff R. Capadona; Stuart J. Rowan; Christoph Weder; Robert J. Moon; Lia A. Stanciu

    2011-01-01

    The synthesis of cadmium sulfide (CdS), zinc sulfide (ZnS), and lead sulfide (PbS) nanoparticle chains on cellulose nanocrystal (CNC) templates can be accomplished by the reaction of the precursor salts. The use of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), was critical for the synthesis of well-defined semiconductor nanoparticle chains on the...

  19. Development of a novel microfluidic reactor for highly controlled synthesis of semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Winterton, Jeffrey D.

    Despite numerous advancements in the understanding of the unique properties of semiconductor nanocrystals, challenges associated with current production strategies have prevented these materials from finding widespread application. Current batch-wise synthesis methods offer only limited ability to probe the processes occurring during the formation of individual nanocrystals and no synthesis method yet exists that is capable of achieving widespread production of nanocrystals. Microfluidic reaction systems present an attractive alternative to conventional synthesis techniques because they afford greater control over local reaction environments than is possible in conventional batch-wise methods, and could ultimately increase production capabilities through massive parallelization. Here, the unique challenges associated with microfluidic synthesis of semiconductor nanocrystals are discussed, along with a presentation of an innovative microfluidic reactor concept that directly addresses the limitations of conventional microfluidic reaction systems for this purpose. The reactor discussed here features a droplet-based two-phase flow design that eliminates the dispersion-induced broadening of the particle size distribution that is characteristic of other microfluidic designs. The flow channels in the design are arranged to spiral in and out of novel reaction coin structures that are designed to allow the thermal profile of the reactor to be tailored to the specific requirements of nanocrystal synthesis operations. A simplified prototype reactor has been constructed and tested to demonstrate the feasibility of the reactor concept. Broader impacts of the design concept with respect to the ability to permit unprecedented control over the size distribution of the particles are discussed.

  20. Chemical and thermodynamic control of the surface of semiconductor nanocrystals for designer white light emitters.

    PubMed

    Krause, Michael M; Mooney, Jonathan; Kambhampati, Patanjali

    2013-07-23

    Small CdSe semiconductor nanocrystals with diameters below 2 nm are thought to emit white light due to random surface defects which result in a broad distribution of midgap emitting states, thereby preventing rational design of small nanocrystal white light emitters. We perform temperature dependent photoluminescence experiments before and after ligand exchange and electron transfer simulations to reveal a very simple microscopic picture of the origin of the white light. These experiments and simulations reveal that these small nanocrystals can be physically modeled in precisely the same way as normal-sized semiconductor nanocrystals; differences in their emission spectra arise from their surface thermodynamics. The white light emission is thus a consequence of the thermodynamic relationship between a core excitonic state and an optically bright surface state with good quantum yield. By virtue of this understanding of the surface and the manner in which it is coupled to the core excitonic states of these nanocrystals, we show both chemical and thermodynamic control of the photoluminescence spectra. We find that using both temperature and appropriate choice in ligands, one can rationally control the spectra so as to engineer the surface to target color rendering coordinates for displays and white light emitters.

  1. Conjugated polymers/semiconductor nanocrystals hybrid materials--preparation, electrical transport properties and applications.

    PubMed

    Reiss, Peter; Couderc, Elsa; De Girolamo, Julia; Pron, Adam

    2011-02-01

    This critical review discusses specific preparation and characterization methods applied to hybrid materials consisting of π-conjugated polymers (or oligomers) and semiconductor nanocrystals. These materials are of great importance in the quickly growing field of hybrid organic/inorganic electronics since they can serve as active components of photovoltaic cells, light emitting diodes, photodetectors and other devices. The electronic energy levels of the organic and inorganic components of the hybrid can be tuned individually and thin hybrid films can be processed using low cost solution based techniques. However, the interface between the hybrid components and the morphology of the hybrid directly influences the generation, separation and transport of charge carriers and those parameters are not easy to control. Therefore a large variety of different approaches for assembling the building blocks--conjugated polymers and semiconductor nanocrystals--has been developed. They range from their simple blending through various grafting procedures to methods exploiting specific non-covalent interactions between both components, induced by their tailor-made functionalization. In the first part of this review, we discuss the preparation of the building blocks (nanocrystals and polymers) and the strategies for their assembly into hybrid materials' thin films. In the second part, we focus on the charge carriers' generation and their transport within the hybrids. Finally, we summarize the performances of solar cells using conjugated polymer/semiconductor nanocrystals hybrids and give perspectives for future developments.

  2. Interfused semiconductor nanocrystals: brilliant blue photoluminescence and electroluminescence.

    PubMed

    Jun, Shinae; Jang, Eunjoo

    2005-09-28

    We describe a method for producing blue light-emitting interfused CdSe//ZnS (QE up to 60%) nanocrystals and report the good performance of an electroluminescent device which uses them (external quantum efficiency approximately 1.5 cd A(-1)).

  3. Fluorescence of semiconductor nanocrystals coupled to optical Tamm cavities

    NASA Astrophysics Data System (ADS)

    Feng, Fu; Pascale Senellart Team; Benoit Dubertret Team; Agnes Maitre Team

    We describe here the photoluminescence properties of a layer of colloidal CdSe/CdS fluorescent nanocrystals embedded in such a Tamm cavity. Spectral and angular analysis of fluorescence shows that the nanocrystals emission is into the Tamm states ; the emission dispersion relation for disks of various diameters shows the effect of the Tamm states lateral confinement. We also combined spatial and angular emission analysis and showed that the direction of emission is not the same for different points on a disk: emission from the left (resp. right) portion of the cavity is directed mostly in the left (resp. right) direction, in agreement with our numerical simulations. Our measurement scheme constitutes a probe of the Tamm state electric field phase gradient inside the cavity. Spatial and K space resolved spectroscopy.

  4. Role of mid-gap states in charge transport and photoconductivity in semiconductor nanocrystal films

    SciTech Connect

    Nagpal, Prashant; Klimov, Victor I.

    2011-09-27

    Colloidal semiconductor nanocrystals have attracted significant interest for applications in solution-processable devices such as light-emitting diodes and solar cells. However, a poor understanding of charge transport in nanocrystal assemblies, specifically the relation between electrical conductance in dark and under light illumination, hinders their technological applicability. Here we simultaneously address the issues of 'dark' transport and photoconductivity in films of PbS nanocrystals, by incorporating them into optical field-effect transistors in which the channel conductance is controlled by both gate voltage and incident radiation. Spectrally resolved photoresponses of these devices reveal a weakly conductive mid-gap band that is responsible for charge transport in dark. The mechanism for conductance, however, changes under illumination when it becomes dominated by band-edge quantized states. In this case, the mid-gap band still has an important role as its occupancy (tuned by the gate voltage) controls the dynamics of band-edge charges.

  5. Semiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers

    DOEpatents

    Alivisatos, A. Paul; Colvin, Vicki L.

    1998-01-01

    Methods are described for attaching semiconductor nanocrystals to solid inorganic surfaces, using self-assembled bifunctional organic monolayers as bridge compounds. Two different techniques are presented. One relies on the formation of self-assembled monolayers on these surfaces. When exposed to solutions of nanocrystals, these bridge compounds bind the crystals and anchor them to the surface. The second technique attaches nanocrystals already coated with bridge compounds to the surfaces. Analyses indicate the presence of quantum confined clusters on the surfaces at the nanolayer level. These materials allow electron spectroscopies to be completed on condensed phase clusters, and represent a first step towards synthesis of an organized assembly of clusters. These new products are also disclosed.

  6. Semiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers

    DOEpatents

    Alivisatos, A.P.; Colvin, V.L.

    1998-05-12

    Methods are described for attaching semiconductor nanocrystals to solid inorganic surfaces, using self-assembled bifunctional organic monolayers as bridge compounds. Two different techniques are presented. One relies on the formation of self-assembled monolayers on these surfaces. When exposed to solutions of nanocrystals, these bridge compounds bind the crystals and anchor them to the surface. The second technique attaches nanocrystals already coated with bridge compounds to the surfaces. Analyses indicate the presence of quantum confined clusters on the surfaces at the nanolayer level. These materials allow electron spectroscopies to be completed on condensed phase clusters, and represent a first step towards synthesis of an organized assembly of clusters. These new products are also disclosed. 10 figs.

  7. Role of mid-gap states in charge transport and photoconductivity in semiconductor nanocrystal films

    PubMed Central

    Nagpal, Prashant; Klimov, Victor I.

    2011-01-01

    Colloidal semiconductor nanocrystals have attracted significant interest for applications in solution-processable devices such as light-emitting diodes and solar cells. However, a poor understanding of charge transport in nanocrystal assemblies, specifically the relation between electrical conductance in dark and under light illumination, hinders their technological applicability. Here we simultaneously address the issues of 'dark' transport and photoconductivity in films of PbS nanocrystals, by incorporating them into optical field-effect transistors in which the channel conductance is controlled by both gate voltage and incident radiation. Spectrally resolved photoresponses of these devices reveal a weakly conductive mid-gap band that is responsible for charge transport in dark. The mechanism for conductance, however, changes under illumination when it becomes dominated by band-edge quantized states. In this case, the mid-gap band still has an important role as its occupancy (tuned by the gate voltage) controls the dynamics of band-edge charges. PMID:21952220

  8. Coherent Superposition of Multi - Exciton Complexes in Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Shabaev, Andrew

    2005-03-01

    Very efficient multi-exciton generation has been recently observed in nanocrystals where an optically excited electron-hole pair with an energy greater than the bandgap (Eg) produces one or more additional electron-hole pairs [1,2]. We present a theory of multiple exciton generation in nanocrystals. We have shown that very efficient and fast exciton generation in nanocrystals occurs by the optical excitation of a coherent superposition of multi-exciton states by a single photon. This model explains ultrafast dynamics of optical bleaching that arises from state filling including quantum beats between the multi-exciton states. We have also shown that although highly efficient multiple exciton generation begins at photon energy 3Eg, the threshold of multiple exciton generation is 2Eg not, 3Eg as was suggested previously. 1. R. Schaller and V. Klimov, Phys. Rev. Lett. 92, 186601 (2004). 2. R. J. Ellingson, M. C. Beard, P. Yu, O. I. Micic, A. J. Nozik, A. Shabaev, and Al. L. Efros, submitted.

  9. A new method to fabricate size-selected compound semiconductor nanocrystals: aerotaxy

    NASA Astrophysics Data System (ADS)

    Deppert, Knut; Bovin, Jan-Olov; Malm, Jan-Olle; Samuelson, Lars

    1996-11-01

    A new method of fabrication is proposed to produce compound semiconductor nanocrystals with very narrow size distribution. It utilizes the formation of an aerosol of ultrafine group-III particles and their self-limited reaction with a group-V containing precursor at elevated temperatures. Since the new material grows in a self-organized fashion within the aerosol phase we call this process aerotaxy. GaAs nanocrystals, of approximate diameter 10 nm, have been produced by this method employing the reaction of Ga particles with arsine. The size of the final GaAs particle is self-limited by the size of the introduced size-selected Ga particle. This size can be tuned carefully. Transmission electron microscopy images exhibit good crystallinity of the particles. The kinetics of the transformation of Ga particles into GaAs nanocrystals depend on temperature and arsine flow. The starting temperature of this conversion was found to be as low as 200°C, which may be the result of a very high {V}/{III} ratio. Studies on the variation of particle diameter with the conditions of formation have indicated activation energies for different process steps. Our approach opens the possibility to produce large quantities of size-selected nanocrystals of compound semiconductors.

  10. Luminescence, Plasmonic and Magnetic Properties of Doped Semiconductor Nanocrystals: Current Developments and Future Prospects.

    PubMed

    Pradhan, Narayan; Adhikari, Samrat Das; Nag, Angshuman; Sarma, D D

    2017-02-02

    Introducing few atoms of impurities or dopants in semiconductor nanocrystals can drastically alter the existing or even introduce new properties. For example, mid-gap states created by doping tremendously affect photocatalytic activities and surface controlled redox reactions, generate new emission centres, show thermometric optical switching, make suitable FRET donors by enhancing the excited state lifetime and also create localized surface plasmon resonance induced low energy absorption. In addition, researchers have more recently started focusing their attention on doped nanocrystals as an important and alternative material for solar energy conversion in order to meet the current demand for renewable energy. Moreover, electrical as well as magnetic properties of the host are also strongly altered on doping. These dopant-induced beneficial changes in material properties suggest that doped nanocrystals with proper selections of dopant-host pairs may be helpful for generating designer materials for a wide range of current technological needs. Such exciting properties related to various aspects of doping a variety of semiconductor nanocrystals are summarized and reported in this mini review.

  11. Synthesis and photo-darkening/photo-brightening of blue emitting doped semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Sarkar, Suresh; Guria, Amit K.; Patra, Biplab K.; Pradhan, Narayan

    2014-03-01

    By programming the synthetic reaction chemistry, stable blue emitting Cu(i) or Ag(i) doped Al(iii) co-doped ZnS (Al,Cu:ZnS or Al,Ag:ZnS) semiconductor nanocrystals are designed. Further, the photostability of the obtained intense blue-violet emission is studied, and the effects of doping/co-doping are correlated. Finally, it is revealed that the strong binding surface ligand 1-dodecanethiol and Al(iii) co-doping play pivotal roles in achieving such stable blue emitting doped nanocrystals.By programming the synthetic reaction chemistry, stable blue emitting Cu(i) or Ag(i) doped Al(iii) co-doped ZnS (Al,Cu:ZnS or Al,Ag:ZnS) semiconductor nanocrystals are designed. Further, the photostability of the obtained intense blue-violet emission is studied, and the effects of doping/co-doping are correlated. Finally, it is revealed that the strong binding surface ligand 1-dodecanethiol and Al(iii) co-doping play pivotal roles in achieving such stable blue emitting doped nanocrystals. Electronic supplementary information available: Detail of synthesis and supporting figures. See DOI: 10.1039/c3nr06048a

  12. 3D imaging of semiconductor colloid nanocrystals: on the way to nanodiagnostics of track membranes

    NASA Astrophysics Data System (ADS)

    Kulyk, S. I.; Eremchev, I. Y.; Gorshelev, A. A.; Naumov, A. V.; Zagorsky, D. L.; Kotova, S. P.; Volostnikov, V. G.; Vorontsov, E. N.

    2016-12-01

    The work concerns the feasibility of 3D optical diagnostic of porous media with subdifraction spatial resolution via epi-luminescence microscopy of single semiconductor colloid nanocrystals (quantum dots, QD) CdSe/ZnS used as emitting labels/nanoprobes. The nanoprecise reconstruction of axial coordinate is provided by double helix technique of point spread function transformation (DH-PSF). The results of QD localization in polycarbonate track membrane (TM) is presented.

  13. 3D imaging of semiconductor colloid nanocrystals: on the way to nanodiagnostics of track membranes

    NASA Astrophysics Data System (ADS)

    Kulyk, S. I.; Eremchev, I. Y.; Gorshelev, A. A.; Naumov, A. V.; Zagorsky, D. L.; Kotova, S. P.; Volostnikov, V. G.; Vorontsov, E. N.

    2017-01-01

    The work concerns the feasibility of 3D optical diagnostic of porous media with subdifraction spatial resolution via epi-luminescence microscopy of single semiconductor colloid nanocrystals (quantum dots, QD) CdSe/ZnS used as emitting labels/nanoprobes. The nanoprecise reconstruction of axial coordinate is provided by double helix technique of point spread function transformation (DH-PSF). The results of QD localization in polycarbonate track membrane (TM) is presented.

  14. Manipulating the growth of aqueous semiconductor nanocrystals through amine-promoted kinetic process.

    PubMed

    Han, Jishu; Zhang, Hao; Sun, Haizhu; Zhou, Ding; Yang, Bai

    2010-01-14

    In the conventional procedure of the preparation of aqueous semiconductor nanocrystals (NCs), the growth of NCs was mainly through the thermodynamics-favored Ostwald ripening process. It required additional energy to promote NC growth, such as reflux, hydrothermal method, microwave irradiation, and sonochemical synthesis. Energy-promoted growth usually led to the decomposition of mercapto-ligands and therewith decreased the quality of NCs. Consequently, in this study, the growth of aqueous semiconductor NCs was designed through an amine-promoted kinetic process, which efficiently shortened the growth duration and avoided the decomposition of ligands, thus providing a universal method for preparing various aqueous binary and ternary NCs.

  15. Photophysical Properties of II-VI Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Gong, Ke

    As it is well known, semiconductor nanocrystals (also called quantum dots, QDs) are being actively pursued for use in many different types of luminescent optical materials. These materials include the active media for luminescence downconversion in artificial lighting, lasers, luminescent solar concentrators and many other applications. Chapter 1 gives general introduction of QDs, which describe the basic physical properties and optical properties. Based on the experimental spectroscopic study, a semiquantitative method-effective mass model is employed to give theoretical prediction and guide. The following chapters will talks about several topics respectively. A predictive understanding of the radiative lifetimes is therefore a starting point for the understanding of the use of QDs for these applications. Absorption intensities and radiative lifetimes are fundamental properties of any luminescent material. Meantime, achievement of high efficiency with high working temperature and heterostructure fabrication with manipulation of lattice strain are not easy and need systematic investigation. To make accurate connections between extinction coefficients and radiative recombination rates, chapter 2 will consider three closely related aspects of the size dependent spectroscopy of II-VI QDs. First, it will consider the existing literature on cadmium selenide (CdSe) QD absorption spectra and extinction coefficients. From these results and fine structure considerations Boltzmann weighted radiative lifetimes are calculated. These lifetimes are compared to values measured on very high quality CdSe and CdSe coated with zinc selenide (ZnSe) shells. Second, analogous literature data are analyzed for cadmium telluride (CdTe) nanocrystals and compared to lifetimes measured for very high quality QDs. Furthermore, studies of the absorption and excitation spectra and measured radiative lifetimes for CdTe/CdSe Type-II core/shell QDs are reported. These results are also analyzed in

  16. Quantifying energy transfer in semiconductor nanocrystals using coherent phonon manipulation and ultrafast spectroscopy (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Spann, Bryan T.; Xu, Xianfan

    2015-10-01

    One potential way to increase photovoltaic efficiency is to take advantage of hot-carriers. Nanocrystal based solar cells aim to take advantage of hot-carrier capture to boost device performance. The crucial parameter for gauging a given nanocrystal material for this application is the electron-phonon coupling. The electron-phonon coupling will dictate the thermalization time of hot-carriers. In this study we demonstrate a method of quantifying the electron-phonon coupling in semiconductor nanocrystals. By employing ultrafast transient absorption spectroscopy with temporal pulse shaping, we manipulate coherent phonons in CdTe_{1-x}Se_{x} nanocrystals to quantify the efficiency of the electron-phonon coupling. The Raman active longitudinal optical phonon (LO) modes were excited and probed as a function of time. Using a temporal pulse shaper, we were able to control pump pulse pairs to coherently excite and cancel coherent phonons in the CdTe_{1-x}Se_{x} nanocrystals, and estimate the relative amount of optical energy that is coupled to the coherent CdSe LO mode which is the dominant thermalization pathway for the hot-electrons in this system.

  17. Synthesis and characterization of metal chalcogenide semiconductor nanocrystals using dialkyl dichalcogenide precursors

    NASA Astrophysics Data System (ADS)

    Norako, Michelle E.

    Metastable semiconductor nanocrystals have been shown to possess new and interesting properties that are highly reliant upon their synthetic reaction parameters. A versatile method for a relatively low temperature synthesis of metastable metal chalcogenide nanocrystals using dialkyl dichalcogenides as the chalcogen source has been developed. These precursors decompose in solution to promote the growth of kinetically controlled nanoscale products. Monodisperse metastable copper indium sulfide (CuInS2) nanocrystal were synthesized using di­tert­butyl disulfide as the sulfur source at 180 °C. In a similar fashion, metastable wurtzite copper indium selenide (CuInSe2) and metastable wurtzite copper tin selenide (CTSe) were synthesized and characterized for the first time. This method was further expanded to synthesize Cu2GeSe 3, Cu2SnS3, Ni0.95Se, CuSbS2, and PbS also using dialkyl dichalcogenide precursors. To further study these products, the nanocrystal growth mechanism was explored for the dichalcogenide­mediated synthesis of wz­CuInS2 and the potential applicability of the wurtzite CTSe nanocrystals as a photovoltaic material was assessed.

  18. Benefitting from Dopant Loss and Ostwald Ripening in Mn Doping of II-VI Semiconductor Nanocrystals.

    PubMed

    Zhai, You; Shim, Moonsub

    2015-12-01

    Annealing or growth at high temperatures for an extended period of time is considered detrimental for most synthetic strategies for high-quality Mn-doped II-VI semiconductor nanocrystals. It can lead to the broadening of size distribution and, more importantly, to the loss of dopants. Here, we examine how ripening can be beneficial to doping in a simple "heat-up" approach, where high dopant concentrations can be achieved. We discuss the interplay of the loss of dopants, Ostwald ripening, and the clustering of Mn near the surface during nanocrystal growth. Smaller nanocrystals in a reaction batch, on average, exhibit higher undesirable band-edge photoluminescence (PL) and lower desirable dopant PL. The optimization of dopant loss and the removal of such smaller undesirable nanocrystals through Ostwald ripening along with surface exchange/passivation to remove Mn clustering lead to high Mn PL quantum yields (45 to 55 %) for ZnSxSe1-x, ZnS, CdS, and CdSxSe1-x host nanocrystals. These results provide an improved understanding of the doping process in a simple and potentially scalable synthetic strategy for achieving "pure" and bright dopant emission.

  19. Benefitting from Dopant Loss and Ostwald Ripening in Mn Doping of II-VI Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Zhai, You; Shim, Moonsub

    2015-10-01

    Annealing or growth at high temperatures for an extended period of time is considered detrimental for most synthetic strategies for high-quality Mn-doped II-VI semiconductor nanocrystals. It can lead to the broadening of size distribution and, more importantly, to the loss of dopants. Here, we examine how ripening can be beneficial to doping in a simple "heat-up" approach, where high dopant concentrations can be achieved. We discuss the interplay of the loss of dopants, Ostwald ripening, and the clustering of Mn near the surface during nanocrystal growth. Smaller nanocrystals in a reaction batch, on average, exhibit higher undesirable band-edge photoluminescence (PL) and lower desirable dopant PL. The optimization of dopant loss and the removal of such smaller undesirable nanocrystals through Ostwald ripening along with surface exchange/passivation to remove Mn clustering lead to high Mn PL quantum yields (45 to 55 %) for ZnSxSe1-x, ZnS, CdS, and CdSxSe1-x host nanocrystals. These results provide an improved understanding of the doping process in a simple and potentially scalable synthetic strategy for achieving "pure" and bright dopant emission.

  20. Electroluminescent devices formed using semiconductor nanocrystals as an electron transport media and method of making such electroluminescent devices

    DOEpatents

    Alivisatos, A. Paul; Colvin, Vickie

    1996-01-01

    An electroluminescent device is described, as well as a method of making same, wherein the device is characterized by a semiconductor nanocrystal electron transport layer capable of emitting visible light in response to a voltage applied to the device. The wavelength of the light emitted by the device may be changed by changing either the size or the type of semiconductor nanocrystals used in forming the electron transport layer. In a preferred embodiment the device is further characterized by the capability of emitting visible light of varying wavelengths in response to changes in the voltage applied to the device. The device comprises a hole processing structure capable of injecting and transporting holes, and usually comprising a hole injecting layer and a hole transporting layer; an electron transport layer in contact with the hole processing structure and comprising one or more layers of semiconductor nanocrystals; and an electron injecting layer in contact with the electron transport layer for injecting electrons into the electron transport layer. The capability of emitting visible light of various wavelengths is principally based on the variations in voltage applied thereto, but the type of semiconductor nanocrystals used and the size of the semiconductor nanocrystals in the layers of semiconductor nanometer crystals may also play a role in color change, in combination with the change in voltage.

  1. Enhanced semiconductor nanocrystal conductance via solution grown contacts.

    PubMed

    Sheldon, Matthew T; Trudeau, Paul-Emile; Mokari, Taleb; Wang, Lin-Wang; Alivisatos, A Paul

    2009-11-01

    We report a 100000-fold increase in the conductance of individual CdSe nanorods when they are electrically contacted via direct solution phase growth of Au tips on the nanorod ends. Ensemble UV-vis and X-ray photoelectron spectroscopies indicate this enhancement does not result from alloying of the nanorod. Rather, low temperature tunneling and high temperature (250-400 K) thermionic emission across the junction at the Au contact reveal a 75% lower interface barrier to conduction compared to a control sample. We correlate this barrier lowering with the electronic structure at the Au-CdSe interface. Our results emphasize the importance of a nanocrystal surface structure for robust device performance and the advantage of this contact method.

  2. Charged two-exciton emission from a single semiconductor nanocrystal

    SciTech Connect

    Hu, Fengrui; Zhang, Qiang; Zhang, Chunfeng; Wang, Xiaoyong; Xiao, Min

    2015-03-30

    Here, we study the photoluminescence (PL) time trajectories of single CdSe/ZnS nanocrystals (NCs) as a function of the laser excitation power. At the low laser power, the PL intensity of a single NC switches between the “on” and “off” levels arising from the neutral and positively charged single excitons, respectively. With the increasing laser power, an intermediate “grey” level is formed due to the optical emission from a charged multiexciton state composed of two excitons and an extra electron. Both the inter-photon correlation and the PL decay measurements demonstrate that lifetime-indistinguishable photon pairs are emitted from this negatively charged two-exciton state.

  3. Enhanced Semiconductor Nanocrystal Conductance via Solution Grown Contacts

    SciTech Connect

    Sheldon, Matthew T.; Trudeau, Paul-Emile; Mokari, Taleb; Wang, Lin-Wang; Alivisatos, A. Paul

    2009-08-19

    We report a 100,000-fold increase in the conductance of individual CdSe nanorods when they are electrically contacted via direct solution phase growth of Au tips on the nanorod ends. Ensemble UV-Vis and X-Ray photoelectron spectroscopy indicate this enhancement does not result from alloying of the nanorod. Rather, low temperature tunneling and high temperature (250-400 K) thermionic emission across the junction at the Au contact reveal a 75percent lower interface barrier to conduction compared to a control sample. We correlate this barrier lowering with the electronic structure at the Au-CdSe interface. Our results emphasize the importance of nanocrystal surface structure for robust device performance and the advantage of this contact method.

  4. 1/f noise in semiconductor and metal nanocrystal solids

    SciTech Connect

    Liu, Heng Lhuillier, Emmanuel Guyot-Sionnest, Philippe

    2014-04-21

    Electrical 1/f noise is measured in thin films of CdSe, CdSe/CdS, ZnO, HgTe quantum dots and Au nanocrystals. The 1/f noise, normalized per nanoparticle, shows no systematic dependence on the nanoparticle material and the coupling material. However, over 10 orders of magnitude, it correlates well with the nearest neighbor conductance suggesting some universal magnitude of the 1/f noise in these granular conductors. In the hopping regime, the main mechanism of 1/f noise is determined to be mobility fluctuated. In the metallic regime obtained with gold nanoparticle films, the noise drops to a similar level as bulk gold films and with a similar temperature dependence.

  5. Structural transformations in II-VI semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Ricolleau, C.; Audinet, L.; Gandais, M.; Gacoin, T.

    Colloidal CdS and CdS/ZnS nanostructures were obtained by nucleation and growth in colloidal solution. Their mean sizes range between 3 and 10 nm. The structural properties were studied by the use of high-resolution transmission electron microscopy (HRTEM). Phase transition between the metastable cubic blende-type structure and the stable hexagonal wurtzite-type structure was evidenced to be a function of the size of the CdS clusters. The mechanism of the transition involving stacking faults was determined by the heating of CdS clusters at 200 °C for 30 h. Results concerning structural relations between CdS and ZnS that occur during the epitaxial growth of ZnS on the CdS nanocrystals showed the existence of the hexagonal structure of ZnS, which is the high-temperature phase of ZnS.

  6. Multicolor light-emitting diodes based on semiconductor nanocrystals encapsulated in GaN charge injection layers.

    PubMed

    Mueller, Alexander H; Petruska, Melissa A; Achermann, Marc; Werder, Donald J; Akhadov, Elshan A; Koleske, Daniel D; Hoffbauer, Mark A; Klimov, Victor I

    2005-06-01

    Numerous technologies including solid-state lighting, displays, and traffic signals can benefit from efficient, color-selectable light sources that are driven electrically. Semiconductor nanocrystals are attractive types of chromophores that combine size-controlled emission colors and high emission efficiencies with excellent photostability and chemical flexibility. Applications of nanocrystals in light-emitting technologies, however, have been significantly hindered by difficulties in achieving direct electrical injection of carriers. Here we report the first successful demonstration of electroluminescence from an all-inorganic, nanocrystal-based architecture in which semiconductor nanocrystals are incorporated into a p-n junction formed from GaN injection layers. The critical step in the fabrication of these nanocrystal/GaN hybrid structures is the use of a novel deposition technique, energetic neutral atom beam lithography/epitaxy, that allows for the encapsulation of nanocrystals within a GaN matrix without adversely affecting either the nanocrystal integrity or its luminescence properties. We demonstrate electroluminescence (injection efficiencies of at least 1%) in both single- and two-color regimes using structures comprising either a single monolayer or a bilayer of nanocrystals.

  7. Multilayer hybrid LEDs based on colloidal inorganic semiconductors nanocrystal and PIN technology

    NASA Astrophysics Data System (ADS)

    Rizzo, Aurora; Mazzeo, Marco; Gigli, Giuseppe

    2008-04-01

    Light emitting devices (LEDs) based on colloidal semiconductor nanocrystals represent a matter of technological interest for the development of flat panel display and lighting systems. The appealing features of these materials are the high fluorescence efficiency, narrow ban edge emission, potential chemical stability, and tunable light emission across the visible spectrum. However the integration of these materials in the very promising PIN technology is still challenging due to the lack of an appropriate QD deposition technique. So far only wet deposition methods such as spin-coating and drop-casting have been exploited to realize QD thin film. Moreover QD thermal evaporation is not possible because of their high molecular weight. In this scenario we developed a dry, simple, and inexpensive deposition technique to transfer semiconductor QDs on organic semiconductor materials. We exploited this technique to fabricated an organic/inorganic hybrid red emitting device whit a doped hole transport layer.

  8. Interfacing nanocarbons with organic and inorganic semiconductors: from nanocrystals/quantum dots to extended tetrathiafulvalenes.

    PubMed

    Katsukis, Georgios; Romero-Nieto, Carlos; Malig, Jenny; Ehli, Christian; Guldi, Dirk M

    2012-08-14

    There is no doubt that the outstanding optical and electronic properties that low-dimensional carbon-based nanomaterials exhibit call for their implementation into optoelectronic devices. However, to harvest the enormous potential of these nanocarbons it is essential to probe them in multifunctional electron donor-acceptor systems, placing particular attention on the interactions between electron donors/electron acceptors and nanocarbons. This feature article outlines challenges and recent breakthroughs in the area of interfacing organic and inorganic semiconductors with low-dimensional nanocarbons that range from fullerenes (0D) and carbon nanotubes (1D) to graphene (2D). In the context of organic semiconductors, we focus on aromatic macrocycles and extended tetrathiafulvalenes, and CdTe nanocrystals/quantum dots represent the inorganic semiconductors. Particular emphasis is placed on designing and probing solar energy conversion nanohybrids.

  9. Active photonic devices based on colloidal semiconductor nanocrystals and organometallic halide perovskites

    NASA Astrophysics Data System (ADS)

    Suárez Alvarez, Isaac

    2016-10-01

    Semiconductor nanocrystals have arisen as outstanding materials to develop a new generation of optoelectronic devices. Their fabrication under simple and low cost colloidal chemistry methods results in cheap nanostructures able to provide a wide range of optical functionalities. Their attractive optical properties include a high absorption cross section below the band gap, a high quantum yield emission at room temperature, or the capability of tuning the band-gap with the size or the base material. In addition, their solution process nature enables an easy integration on several substrates and photonic structures. As a consequence, these nanoparticles have been extensively proposed to develop several photonic applications, such as detection of light, optical gain, generation of light or sensing. This manuscript reviews the great effort undertaken by the scientific community to construct active photonic devices based on these nanoparticles. The conditions to demonstrate stimulated emission are carefully studied by comparing the dependence of the optical properties of the nanocrystals with their size, shape and composition. In addition, this paper describes the design of different photonic architectures (waveguides and cavities) to enhance the generation of photoluminescence, and hence to reduce the threshold of optical gain. Finally, semiconductor nanocrystals are compared to organometallic halide perovskites, as this novel material has emerged as an alternative to colloidal nanoparticles.

  10. Carrier multiplication in semiconductor nanocrystals detected by energy transfer to organic dye molecules

    PubMed Central

    Xiao, Jun; Wang, Ying; Hua, Zheng; Wang, Xiaoyong; Zhang, Chunfeng; Xiao, Min

    2012-01-01

    Carrier multiplication describes an interesting optical phenomenon in semiconductors whereby more than one electron-hole pair, or exciton, can be simultaneously generated upon absorption of a single high-energy photon. So far, it has been highly debated whether the carrier multiplication efficiency is enhanced in semiconductor nanocrystals as compared with their bulk counterpart. The controversy arises from the fact that the ultrafast optical methods currently used need to correctly account for the false contribution of charged excitons to the carrier multiplication signals. Here we show that this charged exciton issue can be resolved in an energy transfer system, where biexcitons generated in the donor nanocrystals are transferred to the acceptor dyes, leading to an enhanced fluorescence from the latter. With the biexciton Auger and energy transfer lifetime measurements, an average carrier multiplication efficiency of ~17.1% can be roughly estimated in CdSe nanocrystals when the excitation photon energy is ~2.46 times of their energy gap. PMID:23132020

  11. Broadband up-conversion at subsolar irradiance: triplet-triplet annihilation boosted by fluorescent semiconductor nanocrystals.

    PubMed

    Monguzzi, A; Braga, D; Gandini, M; Holmberg, V C; Kim, D K; Sahu, A; Norris, D J; Meinardi, F

    2014-11-12

    Conventional solar cells exhibit limited efficiencies in part due to their inability to absorb the entire solar spectrum. Sub-band-gap photons are typically lost but could be captured if a material that performs up-conversion, which shifts photon energies higher, is coupled to the device. Recently, molecular chromophores that undergo triplet-triplet annihilation (TTA) have shown promise for efficient up-conversion at low irradiance, suitable for some types of solar cells. However, the molecular systems that have shown the highest up-conversion efficiency to date are ill suited to broadband light harvesting, reducing their applicability. Here we overcome this limitation by combining an organic TTA system with highly fluorescent CdSe semiconductor nanocrystals. Because of their broadband absorption and spectrally narrow, size-tunable fluorescence, the nanocrystals absorb the radiation lost by the TTA chromophores, returning this energy to the up-converter. The resulting nanocrystal-boosted system shows a doubled light-harvesting ability, which allows a green-to-blue conversion efficiency of ∼12.5% under 0.5 suns of incoherent excitation. This record efficiency at subsolar irradiance demonstrates that boosting the TTA by light-emitting nanocrystals can potentially provide a general route for up-conversion for different photovoltaic and photocatalytic applications.

  12. A novel continuous microfluidic reactor design for the controlled production of high-quality semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Winterton, Jeffrey D.; Myers, David R.; Lippmann, Julian M.; Pisano, Albert P.; Doyle, Fiona M.

    2008-08-01

    An innovative microfluidic reactor concept for the production of high quality semiconductor nanocrystals is presented. The reactor features a droplet-based, two phase flow design that eliminates the dispersion-induced broadening of the particle size distribution that is characteristic of other microfluidic designs. The flow channels in the design are arranged to spiral in and out of novel reaction coin structures that are designed to allow the thermal profile of the reactor to be tailored to the requirements of specific nanocrystal synthesis operations. A simplified prototype reactor has been constructed and tested to demonstrate the feasibility of the reactor concept. Broader impacts of the design concept with respect to the ability to permit unprecedented control over the size distribution of the particles are discussed.

  13. A facile and green preparation of high-quality CdTe semiconductor nanocrystals at room temperature

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Shen, Qihui; Yu, Dongdong; Shi, Weiguang; Li, Jixue; Zhou, Jianguang; Liu, Xiaoyang

    2008-06-01

    One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth of semiconductor nanocrystals (cadmium telluride) instead of additional energy, which was applied to the synthesis of high-quality CdTe nanocrystals at room temperature and ambient conditions within several hours. Under this mild condition the mercapto stabilizers were not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrow and uniform distribution over the largest possible range. The CdTe nanocrystals (photoluminescence emission range of 530-660 nm) synthesized in this way had very good spectral properties; for instance, they showed high photoluminescence quantum yield of up to 60%. Furthermore, we have succeeded in detecting the living Borrelia burgdorferi of Lyme disease by its photoluminescence image using CdTe nanocrystals.

  14. Semiconductor Nanocrystals as Light Harvesters in Solar Cells

    PubMed Central

    Etgar, Lioz

    2013-01-01

    Photovoltaic cells use semiconductors to convert sunlight into electrical current and are regarded as a key technology for a sustainable energy supply. Quantum dot-based solar cells have shown great potential as next generation, high performance, low-cost photovoltaics due to the outstanding optoelectronic properties of quantum dots and their multiple exciton generation (MEG) capability. This review focuses on QDs as light harvesters in solar cells, including different structures of QD-based solar cells, such as QD heterojunction solar cells, QD-Schottky solar cells, QD-sensitized solar cells and the recent development in organic-inorganic perovskite heterojunction solar cells. Mechanisms, procedures, advantages, disadvantages and the latest results obtained in the field are described. To summarize, a future perspective is offered. PMID:28809318

  15. Semiconductor Nanocrystals as Light Harvesters in Solar Cells.

    PubMed

    Etgar, Lioz

    2013-02-04

    Photovoltaic cells use semiconductors to convert sunlight into electrical current and are regarded as a key technology for a sustainable energy supply. Quantum dot-based solar cells have shown great potential as next generation, high performance, low-cost photovoltaics due to the outstanding optoelectronic properties of quantum dots and their multiple exciton generation (MEG) capability. This review focuses on QDs as light harvesters in solar cells, including different structures of QD-based solar cells, such as QD heterojunction solar cells, QD-Schottky solar cells, QD-sensitized solar cells and the recent development in organic-inorganic perovskite heterojunction solar cells. Mechanisms, procedures, advantages, disadvantages and the latest results obtained in the field are described. To summarize, a future perspective is offered.

  16. Rational design of the gram-scale synthesis of nearly monodisperse semiconductor nanocrystals

    PubMed Central

    2011-01-01

    We address two aspects of general interest for the chemical synthesis of colloidal semiconductor nanocrystals: (1) the rational design of the synthesis protocol aiming at the optimization of the reaction parameters in a minimum number of experiments; (2) the transfer of the procedure to the gram scale, while maintaining a low size distribution and maximizing the reaction yield. Concerning the first point, the design-of-experiment (DOE) method has been applied to the synthesis of colloidal CdSe nanocrystals. We demonstrate that 16 experiments, analyzed by means of a Taguchi L16 table, are sufficient to optimize the reaction parameters for controlling the mean size of the nanocrystals in a large range while keeping the size distribution narrow (5-10%). The DOE method strongly reduces the number of experiments necessary for the optimization as compared to trial-and-error approaches. Furthermore, the Taguchi table analysis reveals the degree of influence of each reaction parameter investigated (e.g., the nature and concentration of reagents, the solvent, the reaction temperature) and indicates the interactions between them. On the basis of these results, the synthesis has been scaled up by a factor of 20. Using a 2-L batch reactor combined with a high-throughput peristaltic pump, different-sized samples of CdSe nanocrystals with yields of 2-3 g per synthesis have been produced without sacrificing the narrow size distribution. In a similar setup, the gram-scale synthesis of CdSe/CdS/ZnS core/shell/shell nanocrystals exhibiting a fluorescence quantum yield of 81% and excellent resistance of the photoluminescence in presence of a fluorescent quencher (aromatic thiol) has been achieved. PACS: 81.20.Ka, 81.07.Bc, 78.67.Bf PMID:21791060

  17. Rational design of the gram-scale synthesis of nearly monodisperse semiconductor nanocrystals.

    PubMed

    Protière, Myriam; Nerambourg, Nicolas; Renard, Olivier; Reiss, Peter

    2011-07-26

    We address two aspects of general interest for the chemical synthesis of colloidal semiconductor nanocrystals: (1) the rational design of the synthesis protocol aiming at the optimization of the reaction parameters in a minimum number of experiments; (2) the transfer of the procedure to the gram scale, while maintaining a low size distribution and maximizing the reaction yield. Concerning the first point, the design-of-experiment (DOE) method has been applied to the synthesis of colloidal CdSe nanocrystals. We demonstrate that 16 experiments, analyzed by means of a Taguchi L16 table, are sufficient to optimize the reaction parameters for controlling the mean size of the nanocrystals in a large range while keeping the size distribution narrow (5-10%). The DOE method strongly reduces the number of experiments necessary for the optimization as compared to trial-and-error approaches. Furthermore, the Taguchi table analysis reveals the degree of influence of each reaction parameter investigated (e.g., the nature and concentration of reagents, the solvent, the reaction temperature) and indicates the interactions between them. On the basis of these results, the synthesis has been scaled up by a factor of 20. Using a 2-L batch reactor combined with a high-throughput peristaltic pump, different-sized samples of CdSe nanocrystals with yields of 2-3 g per synthesis have been produced without sacrificing the narrow size distribution. In a similar setup, the gram-scale synthesis of CdSe/CdS/ZnS core/shell/shell nanocrystals exhibiting a fluorescence quantum yield of 81% and excellent resistance of the photoluminescence in presence of a fluorescent quencher (aromatic thiol) has been achieved.PACS: 81.20.Ka, 81.07.Bc, 78.67.Bf.

  18. Rational design of the gram-scale synthesis of nearly monodisperse semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Protière, Myriam; Nerambourg, Nicolas; Renard, Olivier; Reiss, Peter

    2011-07-01

    We address two aspects of general interest for the chemical synthesis of colloidal semiconductor nanocrystals: (1) the rational design of the synthesis protocol aiming at the optimization of the reaction parameters in a minimum number of experiments; (2) the transfer of the procedure to the gram scale, while maintaining a low size distribution and maximizing the reaction yield. Concerning the first point, the design-of-experiment (DOE) method has been applied to the synthesis of colloidal CdSe nanocrystals. We demonstrate that 16 experiments, analyzed by means of a Taguchi L16 table, are sufficient to optimize the reaction parameters for controlling the mean size of the nanocrystals in a large range while keeping the size distribution narrow (5-10%). The DOE method strongly reduces the number of experiments necessary for the optimization as compared to trial-and-error approaches. Furthermore, the Taguchi table analysis reveals the degree of influence of each reaction parameter investigated (e.g., the nature and concentration of reagents, the solvent, the reaction temperature) and indicates the interactions between them. On the basis of these results, the synthesis has been scaled up by a factor of 20. Using a 2-L batch reactor combined with a high-throughput peristaltic pump, different-sized samples of CdSe nanocrystals with yields of 2-3 g per synthesis have been produced without sacrificing the narrow size distribution. In a similar setup, the gram-scale synthesis of CdSe/CdS/ZnS core/shell/shell nanocrystals exhibiting a fluorescence quantum yield of 81% and excellent resistance of the photoluminescence in presence of a fluorescent quencher (aromatic thiol) has been achieved. PACS: 81.20.Ka, 81.07.Bc, 78.67.Bf

  19. Highly fluorescent semiconductor core shell CdTe CdS nanocrystals for monitoring living yeast cells activity

    NASA Astrophysics Data System (ADS)

    de Farias, P. M. A.; Santos, B. S.; Menezes, F. D.; Brasil, A. G., Jr.; Ferreira, R.; Motta, M. A.; Castro-Neto, A. G.; Vieira, A. A. S.; Silva, D. C. N.; Fontes, A.; Cesar, C. L.

    2007-12-01

    Fluorescent semiconductor nanocrystals in quantum confinement regime (quantum dots) present several well-known features which make them very useful tools for biological labeling purposes. Low photobleaching rates, high chemical stability and active surface allowing conjugation to living cells explain the success of this labeling procedure over the commonly used fluorescent dyes. In this paper we report the results obtained with highly fluorescent core shell CdTe CdS (diameter=3 7 nm) colloidal nanocrystals synthesized in aqueous medium and conjugated to glucose molecules. The conjugated nanocrystals were incubated with living yeast cells, in order to investigate their glucose up-take activity in real time, by confocal microscopy analysis.

  20. Resonance energy transfer in conjugates of semiconductor nanocrystals and organic dye molecules

    NASA Astrophysics Data System (ADS)

    Artemyev, Mikhail

    2012-01-01

    I analyze the efficiency of Förster resonance energy transfer (FRET) in luminescent donor-acceptor complexes based on conjugates of CdSe/ZnS quantum dots and nanorods and the luminescent dyes. Semiconductor nanocrystals serve either as FRET donors or acceptors. Experimentally observed reduced FRET efficiency in complexes of nanorods and dye molecules as compared to quantum dots are found to be attributable to a distance-limited energy transfer rate in case of point-like dye dipoles and extended nanorod dipole.

  1. Modeling the antireflective properties of composite materials based on semiconductor filamentary nanocrystals

    NASA Astrophysics Data System (ADS)

    Gorai, L. I.; Buravlev, A. D.; Ponyaev, S. A.

    2015-07-01

    The feasibility of application of films of composite materials based on semiconductor filamentary nanocrystals (FNCs) to suppress the reflection of electromagnetic radiation in the radiofrequency range is demonstrated for the first time with the use of the effective medium theory (EMT). It is shown that the reflec- tion coefficients of single- and double-layer models may be reduced several-fold and by as much as two orders of magnitude, respectively, in a wide range of parameters. The agreement of the EMT data with the results of rigorous calculations allows one to apply the zeroth-order EMT in the analysis and synthesis of antireflective composite materials based on FNCs.

  2. The colloidal chemistry synthesis and electron microscopy characterization of shape-controlled metal and semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Biacchi, Adam J.

    Solution methods of materials synthesis have found application in a variety of fields due to the diversity of products accessible, facility of process scalability, and the ease of tuning their properties through prudent selection of reaction conditions. Control of experimental variables during the formation of colloidally stable nanoscale solids within a liquid matrix allows for tailoring of the particles' characteristics, including shape, size, composition, and surface chemistry. In this dissertation, I will discuss how the manipulation of reaction chemistries can be used to synthesize shape-controlled metal and semiconductor colloidal nanocrystals. Further, I will elaborate on the mechanisms by which these particles form from molecular precursors and describe how their properties can differ from their bulk analogues through extensive characterization, especially using transmission electron microscopy. These studies contribute to the continued development of chemical routes to nanocrystals and their application as functional materials. First, I will review recent advances in the synthesis and characterization of shape-controlled nanocrystals, as well as highlight their promising applicability in a number of emerging technologies. These principles will then be leveraged to the specific case of catalytically-active rhodium nanocrystals, which can be synthesized with morphological and dimensional control using a polyol solution-mediated strategy. I describe an innovative shape-controlled synthesis to monodisperse colloidal rhodium icosahedra, cubes, triangular plates, and octahedra using this route. Additionally, new insights into the important role of the polyol reducing solvent on the synthesis of these nanocrystals are revealed, and how these might be exploited to engender superior reaction control and novel products. Next, I will describe how a crystallization mechanism was established for the synthesis of numerous morphologies of noble metal nanocrystals. I

  3. Hybrid Solar Cells with Prescribed Nanoscale Morphologies Based onHyperbranched Semiconductor Nanocrystals

    SciTech Connect

    Gur, Ilan; Fromer, Neil A.; Chen, Chih-Ping; Kanaras, AntoniosG.; Alivisatos, A. Paul

    2006-09-09

    In recent years, the search to develop large-area solar cells at low cost has led to research on photovoltaic (PV) systems based on nanocomposites containing conjugated polymers. These composite films can be synthesized and processed at lower costs and with greater versatility than the solid state inorganic semiconductors that comprise today's solar cells. However, the best nanocomposite solar cells are based on a complex architecture, consisting of a fine blend of interpenetrating and percolating donor and acceptor materials. Cell performance is strongly dependent on blend morphology, and solution-based fabrication techniques often result in uncontrolled and irreproducible blends, whose composite morphologies are difficult to characterize accurately. Here we incorporate 3-dimensional hyper-branched colloidal semiconductor nanocrystals in solution-processed hybrid organic-inorganic solar cells, yielding reproducible and controlled nanoscale morphology.

  4. DNA-templated semiconductor nanocrystal growth for controlled DNA packing and gene delivery.

    PubMed

    Gao, Li; Ma, Nan

    2012-01-24

    DNA-templated semiconductor nanocrystal (SNC) growth represents a facile means to generate bioactive hybrid nanostructures by directly integrating DNA molecules and luminescent SNCs together via a one-step synthesis, which has been applied to biosensing and cell imaging. In this study we for the first time demonstrated that DNA-templated CdS SNC growth could also be used to rationally tune the structures and activities of large DNA molecules. We explored the synergistic effects of nanocrystal growth on the sizes and charges of DNA molecules and demonstrate that the CdS growth-induced DNA packing could be used as a smart gene delivery system. Herein we used DNA plasmids encoding intact enhanced green fluorescence protein (EGFP) genes as templates to grow CdS SNCs and found that the stepwise growth of CdS nanocrystals can spontaneously induce DNA condensation and negative charge shielding in a synergistic manner. The condensed DNA plasmids exhibited efficient cellular uptake and a relative gene transfection efficiency of 32%. The transfection efficiency can be further doubled in the presence of chloroquine. We elucidated that the gene transfection and expression is controlled by reversible DNA packing, where ligand exchange of DNA with intracellular glutathione molecules plays a critical role in the recovery of DNA plasmids for gene expression. © 2011 American Chemical Society

  5. The More Exotic Shapes of Semiconductor Nanocrystals: Emerging Applications in Bioimaging

    PubMed Central

    Lim, Sung Jun; Smith, Andrew; Nie, Shuming

    2014-01-01

    Semiconductor nanocrystals are tiny fluorescent particles that have recently made a major impact in the biological and medical sciences by enabling high-sensitivity imaging of biomolecules, cells, and tissues. Spherical quantum dots are the prototypical material for these applications but recent synthetic advances have led to a diverse range of nanostructures with controllable sizes, shapes, and materials combinations that offer new dimensions of optical and structural tunability. Uniform anisotropic shapes with linearly polarized light emission allow optical imaging of particle orientation, planar structures have large flexible surfaces and ultra-narrow electronic transitions, and compact nanoparticles have enhanced diffusion in crowded biological environments. These properties are providing unique opportunities to probe basic biological processes, cellular structures, and organismal physiology. PMID:24982823

  6. Getting across the plasma membrane and beyond: intracellular uses of colloidal semiconductor nanocrystals.

    PubMed

    Luccardini, Camilla; Yakovlev, Aleksey; Gaillard, Stéphane; van 't Hoff, Marcel; Alberola, Alicia Piera; Mallet, Jean-Maurice; Parak, Wolfgang J; Feltz, Anne; Oheim, Martin

    2007-01-01

    Semiconductor nanocrystals (NCs) are increasingly being used as photoluminescen markers in biological imaging. Their brightness, large Stokes shift, and high photostability compared to organic fluorophores permit the exploration of biological phenomena at the single-molecule scale with superior temporal resolution and spatial precision. NCs have predominantly been used as extracellular markers for tagging and tracking membrane proteins. Successful internalization and intracellular labelling with NCs have been demonstrated for both fixed immunolabelled and live cells. However, the precise localization and subcellular compartment labelled are less clear. Generally, live cell studies are limited by the requirement of fairly invasive protocols for loading NCs and the relatively large size of NCs compared to the cellular machinery, along with the subsequent sequestration of NCs in endosomal/lysosomal compartments. For long-period observation the potential cytotoxicity of cytoplasmically loaded NCs must be evaluated. This review focuses on the challenges of intracellular uses of NCs.

  7. Extended storage of multiple excitons in trap states of semiconductor nanocrystals

    SciTech Connect

    Xu, Qinfeng; Huang, Xiangnan; Hua, Zheng; Zhang, Chunfeng; Wang, Xiaoyong; Hu, Lian; Du, Lingxiao; Wu, Huizhen; Xiao, Min

    2016-02-29

    Owing to the Auger recombination effect, multiple excitons (MEs) in semiconductor nanocrystals (NCs) are dissipated nonradiatively at the sub-nanosecond time scale, which sets a stringent limit on the time window within which one can operate with them. Here, we show that this issue can be resolved by utilizing an intrinsic energy transfer system in CdSe NCs, where MEs created in the donor quantized states can be effectively extracted to the acceptor trap states. This was evidenced by the step-like increase in the intensity and the apparent decrease in the rise time of the trap-state photoluminescence with the elevated laser excitation power. With the radiative lifetime being tens of nanoseconds for the trap states, extended storage of MEs has been achieved and marks a crucial step towards flexible manipulations of their optoelectronic properties.

  8. Charge Blinking Statistics of Semiconductor Nanocrystals Revealed by Carbon Nanotube Single Charge Sensors.

    PubMed

    Zbydniewska, Ewa; Duzynska, Anna; Popoff, Michka; Hourlier, Djamila; Lenfant, Stéphane; Judek, Jaroslaw; Zdrojek, Mariusz; Mélin, Thierry

    2015-10-14

    We demonstrate the relation between the optical blinking of colloidal semiconductor nanocrystals (NCs) and their electrical charge blinking for which we provide the first experimental observation of power-law statistics. To show this, we harness the performance of CdSe/ZnS NCs coupled with carbon nanotube field-effect transistors (CNTFETs), which act as single charge-sensitive electrometers with submillisecond time resolution, at room temperature. A random telegraph signal (RTS) associated with the NC single-trap charging is observed and exhibits power-law temporal statistics (τ(-α), with α in the range of ∼1-3), and a Lorentzian current noise power spectrum with a well-defined 1/f(2) corner. The spectroscopic analysis of the NC-CNTFET devices is consistent with the charging of NC defect states with a charging energy of Ec ≥ 200 meV. These results pave the way for a deeper understanding of the physics and technology of nanocrystal-based optoelectronic devices.

  9. General low-temperature reaction pathway from precursors to monomers before nucleation of compound semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Yu, Kui; Liu, Xiangyang; Qi, Ting; Yang, Huaqing; Whitfield, Dennis M.; Y. Chen, Queena; Huisman, Erik J. C.; Hu, Changwei

    2016-08-01

    Little is known about the molecular pathway to monomers of semiconductor nanocrystals. Here we report a general reaction pathway, which is based on hydrogen-mediated ligand loss for the precursor conversion to `monomers' at low temperature before nucleation. We apply 31P nuclear magnetic resonance spectroscopy to monitor the key phosphorous-containing products that evolve from MXn+E=PPh2H+HY mixtures, where MXn, E=PPh2H, and HY are metal precursors, chalcogenide precursors, and additives, respectively. Surprisingly, the phosphorous-containing products detected can be categorized into two groups, Ph2P-Y and Ph2P(E)-Y. On the basis of our experimental and theoretical results, we propose two competing pathways to the formation of M2En monomers, each of which is accompanied by one of the two products. Our study unravels the pathway of precursor evolution into M2En monomers, the stoichiometry of which directly correlates with the atomic composition of the final compound nanocrystals.

  10. Semiconductor nanocrystal-aptamer bioconjugate probes for specific prostate carcinoma cell targeting

    NASA Astrophysics Data System (ADS)

    Shieh, Felice; Lavery, Laura; Chu, Chitai T.; Richards-Kortum, Rebecca; Ellington, Andrew D.; Korgel, Brian A.

    2005-04-01

    Cancer of the prostate affects approximately 1 in 11 men. Current early screening for prostate cancer utilizes digital rectal examinations to detect anomalies in the prostate gland and blood test screenings for upregulated levels of prostate specific antigen (PSA). Many of these tests are invasive and can often be inconclusive as PSA levels may be heightened due to benign factors. Prostate specific membrane antigen (PSMA), a well-characterized integral membrane protein, is expressed in virtually all prostate cancers and often correlates with cancer aggressiveness. Therefore, it may be used as an indicator of cancer growth and metastases. PSMA-specific antibodies have been identified and conjugated to fluorescent markers for cancer cell targeting; however, both the antibodies and markers possess significant limitations in their pharmaceutical and diagnostic value. Here we report the use of semiconductor nanocrystals bioconjugated to PSMA-specific aptamer recognition molecules for prostate carcinoma cell targeting. The nanocrystal/aptamer bioconjugates are small biocompatible probes with the potential for color-tunability for multicolor imaging. Ongoing in vitro and in vivo research seeks to introduce these nanoparticle bioconjugates into medical diagnostics.

  11. General low-temperature reaction pathway from precursors to monomers before nucleation of compound semiconductor nanocrystals

    PubMed Central

    Yu, Kui; Liu, Xiangyang; Qi, Ting; Yang, Huaqing; Whitfield, Dennis M.; Y. Chen, Queena; Huisman, Erik J. C.; Hu, Changwei

    2016-01-01

    Little is known about the molecular pathway to monomers of semiconductor nanocrystals. Here we report a general reaction pathway, which is based on hydrogen-mediated ligand loss for the precursor conversion to ‘monomers' at low temperature before nucleation. We apply 31P nuclear magnetic resonance spectroscopy to monitor the key phosphorous-containing products that evolve from MXn+E=PPh2H+HY mixtures, where MXn, E=PPh2H, and HY are metal precursors, chalcogenide precursors, and additives, respectively. Surprisingly, the phosphorous-containing products detected can be categorized into two groups, Ph2P–Y and Ph2P(E)–Y. On the basis of our experimental and theoretical results, we propose two competing pathways to the formation of M2En monomers, each of which is accompanied by one of the two products. Our study unravels the pathway of precursor evolution into M2En monomers, the stoichiometry of which directly correlates with the atomic composition of the final compound nanocrystals. PMID:27531507

  12. Direct measurement of lattice dynamics and optical phonon excitation in semiconductor nanocrystals using femtosecond stimulated Raman spectroscopy.

    PubMed

    Hannah, Daniel C; Brown, Kristen E; Young, Ryan M; Wasielewski, Michael R; Schatz, George C; Co, Dick T; Schaller, Richard D

    2013-09-06

    We report femtosecond stimulated Raman spectroscopy measurements of lattice dynamics in semiconductor nanocrystals and characterize longitudinal optical (LO) phonon production during confinement-enhanced, ultrafast intraband relaxation. Stimulated Raman signals from unexcited CdSe nanocrystals produce a spectral shape similar to spontaneous Raman signals. Upon photoexcitation, stimulated Raman amplitude decreases owing to experimentally resolved ultrafast phonon generation rates within the lattice. We find a ∼600  fs, particle-size-independent depletion time attributed to hole cooling, evidence of LO-to-acoustic down-conversion, and LO phonon mode softening.

  13. Challenge to the Charging Model of Semiconductor-Nanocrystal Fluorescence Intermittency from Off-State Quantum Yields and Multiexciton Blinking

    NASA Astrophysics Data System (ADS)

    Zhao, Jing; Nair, Gautham; Fisher, Brent R.; Bawendi, Moungi G.

    2010-04-01

    Semiconductor nanocrystals emit light intermittently; i.e., they “blink,” under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core(shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10∶1. These results directly contradict the predictions of the charging model.

  14. Challenge to the Charging Model of Semiconductor-Nanocrystal Fluorescence Intermittency from Off-State Quantum Yields and Multiexciton Blinking

    PubMed Central

    Zhao, Jing; Nair, Gautham; Fisher, Brent R.; Bawendi, Moungi G.

    2012-01-01

    Semiconductor nanocrystals emit light intermittently; i.e., they “blink,” under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core (shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10:1. These results directly contradict the predictions of the charging model. PMID:20482016

  15. Challenge to the charging model of semiconductor-nanocrystal fluorescence intermittency from off-state quantum yields and multiexciton blinking.

    PubMed

    Zhao, Jing; Nair, Gautham; Fisher, Brent R; Bawendi, Moungi G

    2010-04-16

    Semiconductor nanocrystals emit light intermittently; i.e., they "blink," under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core(shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10:1. These results directly contradict the predictions of the charging model.

  16. Challenge to the Charging Model of Semiconductor-Nanocrystal Fluorescence Intermittency from Off-State Quantum Yields and Multiexciton Blinking

    SciTech Connect

    Zhao, Jing; Nair, Gautham; Fisher, Brent R.; Bawendi, Moungi G.

    2010-04-16

    Semiconductor nanocrystals emit light intermittently; i.e., they “blink,” under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core(shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10:1 . These results directly contradict the predictions of the charging model.

  17. Bioinspired solar water splitting, sensitized solar cells, and ultraviolet sensor based on semiconductor nanocrystal antenna/graphene nanoassemblies

    NASA Astrophysics Data System (ADS)

    Chang, Haixin; Lv, Xiaojun; Zheng, Zijian; Wu, Hongkai

    2011-11-01

    Graphene, two-dimensional carbon crystal with only one atom thickness, provides a general platform for nanoscale even atomic scale optoelectronics and photonics. Graphene has many advantages for optoelectronics such as high conductivity, high electronic mobility, flexibility and transparency. However, graphene also has disadvantages such as low light absorption which are unfavorable for optoelectronic devices. On the other hand, many natural photonic systems provide wonderful solution to enhance light absorption for solar energy harvesting and conversion, such as chlorophyll in green plants. Herein, learning from nature, we described bioinspired photocatalytic solar-driven water splitting, sensitized solar cells and ultraviolet optoelectronic sensors enabled by introducing photosensitive semiconductor nanocrystal antenna to graphene for constructing a series of graphene/nanocrystal nanoassemblies. We have demonstrated that high performance optoelectronic devices can come true with the introducing of photosensitive nanocrystal antenna elements.

  18. Bioinspired solar water splitting, sensitized solar cells, and ultraviolet sensor based on semiconductor nanocrystal antenna/graphene nanoassemblies

    NASA Astrophysics Data System (ADS)

    Chang, Haixin; Lv, Xiaojun; Zheng, Zijian; Wu, Hongkai

    2012-02-01

    Graphene, two-dimensional carbon crystal with only one atom thickness, provides a general platform for nanoscale even atomic scale optoelectronics and photonics. Graphene has many advantages for optoelectronics such as high conductivity, high electronic mobility, flexibility and transparency. However, graphene also has disadvantages such as low light absorption which are unfavorable for optoelectronic devices. On the other hand, many natural photonic systems provide wonderful solution to enhance light absorption for solar energy harvesting and conversion, such as chlorophyll in green plants. Herein, learning from nature, we described bioinspired photocatalytic solar-driven water splitting, sensitized solar cells and ultraviolet optoelectronic sensors enabled by introducing photosensitive semiconductor nanocrystal antenna to graphene for constructing a series of graphene/nanocrystal nanoassemblies. We have demonstrated that high performance optoelectronic devices can come true with the introducing of photosensitive nanocrystal antenna elements.

  19. Cyclotron Splittings in the Plasmon Resonances of Electronically Doped Semiconductor Nanocrystals Probed by Magnetic Circular Dichroism Spectroscopy.

    PubMed

    Hartstein, Kimberly H; Schimpf, Alina M; Salvador, Michael; Gamelin, Daniel R

    2017-04-10

    A fundamental understanding of the rich electronic structures of electronically doped semiconductor nanocrystals is vital for assessing the utility of these materials for future applications from solar cells to redox catalysis. Here, we examine the use of magnetic circular dichroism (MCD) spectroscopy to probe the infrared localized surface plasmon resonances of p-Cu2-xSe, n-ZnO, and tin-doped In2O3 (n-ITO) nanocrystals. We demonstrate that the MCD spectra of these nanocrystals can be analyzed by invoking classical cyclotron motions of their excess charge carriers, with experimental MCD signs conveying the carrier types (n or p) and experimental MCD intensities conveying the cyclotron splitting magnitudes. The experimental cyclotron splittings can then be used to quantify carrier effective masses (m*), with results that agree with bulk in most cases. MCD spectroscopy thus offers a unique measure of m* in free-standing colloidal semiconductor nanocrystals, raising new opportunities to investigate the influence of various other synthetic or environmental parameters on this fundamentally important electronic property.

  20. Hybrid semiconductor quantum dot-metal nanocrystal structures prepared by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Urbańczyk, A.; Hamhuis, G. J.; Nötzel, R.

    2011-05-01

    We report the formation of In nanocrystals and their alignment near dilute InAs quantum dots (QDs) on GaAs (0 0 1) by molecular beam epitaxy. The In nanocrystals exhibit surface plasmon resonances in the near-infrared range, which can be matched with the emission wavelength of In(Ga)As QDs. The alignment of the In nanocrystals near the InAs QDs is due to the strain-driven migration yielding single isolated QD-metal nanocrystal pairs and isolated QD-metal nanocrystal dimer structures, representing the basic hybrid QD-metal nanocrystal plasmonic nanostructures.

  1. Universal Near-Infrared and Mid-Infrared Optical Modulation for Ultrafast Pulse Generation Enabled by Colloidal Plasmonic Semiconductor Nanocrystals.

    PubMed

    Guo, Qiangbing; Yao, Yunhua; Luo, Zhi-Chao; Qin, Zhipeng; Xie, Guoqiang; Liu, Meng; Kang, Jia; Zhang, Shian; Bi, Gang; Liu, Xiaofeng; Qiu, Jianrong

    2016-09-21

    Field effect relies on the nonlinear current-voltage relation in semiconductors; analogously, materials that respond nonlinearly to an optical field can be utilized for optical modulation. For instance, nonlinear optical (NLO) materials bearing a saturable absorption (SA) feature an on-off switching behavior at the critical pumping power, thus enabling ultrafast laser pulse generation with high peak power. SA has been observed in diverse materials preferably in its nanoscale form, including both gaped semiconductor nanostructures and gapless materials like graphene; while the presence of optical bandgap and small carrier density have limited the active spectral range and intensity. We show here that solution-processed plasmonic semiconductor nanocrystals exhibit superbroadband (over 400 THz) SA, meanwhile with large modulation depth (∼7 dB) and ultrafast recovery (∼315 fs). Optical modulators fabricated using these plasmonic nanocrystals enable mode-locking and Q-switching operation across the near-infrared and mid-infrared spectral region, as exemplified here by the pulsed lasers realized at 1.0, 1.5, and 2.8 μm bands with minimal pulse duration down to a few hundreds of femtoseconds. The facile accessibility and superbroadband optical nonlinearity offered by these nonconventional plasmonic nanocrystals may stimulate a growing interest in the exploiting of relevant NLO and photonic applications.

  2. Synthesis, functionalization, and biological tagging applications of II-VI semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Wang, Jun

    Fluorescent labeling of biological molecules is a technique that is used widely for analytical purposes in biotechnology and bioengineering. It typically involves the use of an organic dye molecule linked to a moiety that selectively bonds a particular biological molecule, allowing the detection of the latter by the fluorescence of the dye molecule. Semiconductor nanocrystals or quantum dots have emerged as a new class of fluorescent markers with distinct advantages over the traditional organic dyes. Their attractive properties include narrow, symmetric, and bright emission, continuous excitation by any wavelength smaller than the emission wavelength, broad absorption spectrum, long lifetime, resistance to photobleaching, as well as excellent optical and chemical stability that allows their use in lengthy experiments. The focus of this thesis is the synthesis and surface functionalization of ZnSe quantum dots and (ZnSe)ZnS core-shell nanostructures, and their biological conjugation with DNA and protein. The ability to synthesize different populations of quantum dots with narrow emission spectra permits multiplexing, a property that is very important for simultaneous detection of several analytes, which would be very tedious and expensive if done sequentially. Highly luminescent ZnSe nanocrystals have been synthesized using a hot-injection colloidal method. The synthesis was performed in a stirred batch reactor containing liquid hexadecylamine at 310°C. The precursors were diethylzinc diluted in heptane and selenium powder mixed with trioctylphosphine. The mixture of reactants was injected into the batch reactor and the time of reaction was used to control the size and luminescence emission wavelength of the quantum dots. In order to optimize the process various parameters that can influence the photoluminescence property of quantum dots obtained were investigated, such as surfactant addition, temperature, precursor ratio, and mixing conditions. Capping of the Zn

  3. Study of surface and bulk electronic structure of II-VI semiconductor nanocrystals using Cu as a nanosensor.

    PubMed

    Grandhi, G Krishnamurthy; Tomar, Renu; Viswanatha, Ranjani

    2012-11-27

    Efficiency of the quantum dots based solar cells relies on charge transfer at the interface and hence on the relative alignment of the energy levels between materials. Despite a high demand to obtain size specific band offsets, very few studies exist where meticulous methods like photoelectron spectroscopy are used. However, semiconductor charging during measurements could result in indirect and possibly inaccurate measurements due to shift in valence and conduction band position. Here, in this report, we devise a novel method to study the band offsets by associating an atomic like state with the conduction band and hence obtaining an internal standard. This is achieved by doping copper in semiconductor nanocrystals, leading to the development of a characteristic intragap Cu-related emission feature assigned to the transition from the conduction band to the atomic-like Cu d state. Using this transition we determine the relative band alignment of II-VI semiconductor nanocrystals as a function of size in the below 10 nm size regime. The results are in excellent agreement with the available photoelectron spectroscopy data as well as the theoretical data. We further use this technique to study the excitonic band edge variation as a function of temperature in CdSe nanocrystals. Additionally, surface electronic structure of CdSe nanocrystals have been studied using quantitative measurements of absolute quantum yield and PL decay studies of the Cu related emission and the excitonic emission. The role of TOP and oleic acid as surface passivating ligand molecules has been studied for the first time.

  4. CdSe colloidal nanocrystals monolithically integrated in a pseudomorphic semiconductor epilayer

    SciTech Connect

    Larramendi, Erick M.; Schoeps, Oliver; Woggon, Ulrike; Artemyev, Mikhail V.; Schikora, Detlef; Lischka, Klaus

    2013-01-14

    As optically active emitters in a semiconductor matrix, core/shell and bare CdSe colloidal nanocrystals (CNCs) were monolithically incorporated in ZnSe pseudomorphic epilayers by molecular beam epitaxy (MBE). A suspension of wet chemically synthesized CNCs was sprayed ex-situ over a pseudomorphic ZnSe/GaAs(001) heterostructure using a nebulizer. Subsequently, the matrix material growth was resumed to form a capping layer by a slow MBE growth mode. Structural investigations show high crystalline quality and pseudomorphic epitaxial character of the whole hybrid CNC-matrix structure. The core/shell CNCs remain optically active following the embedding process. Their emission is blue shifted without a significant change on the spectral shape, and shows the same temperature dependence as that of the free exciton peak energy in zinc-blende CdSe at temperatures above 80 K. Our optical characterization of the samples showed that the embedded CNCs were stable and that the structure of the host was preserved. These results are encouraging for the fabrication of more complex optoelectronic devices based on CNCs.

  5. Doped Semiconductor-Nanocrystal Emitters with Optimal Photoluminescence Decay Dynamics in Microsecond to Millisecond Range: Synthesis and Applications

    PubMed Central

    2015-01-01

    Transition metal doped semiconductor nanocrystals (d-dots) possess fundamentally different emission properties upon photo- or electroexcitation, which render them as unique emitters for special applications. However, in comparison with intrinsic semiconductor nanocrystals, the potential of d-dots has been barely realized, because many of their unique emission properties mostly rely on precise control of their photoluminescence (PL) decay dynamics. Results in this work revealed that it would be possible to obtain bright d-dots with nearly single-exponential PL decay dynamics. By tuning the number of Mn2+ ions per dot from ∼500 to 20 in Mn2+ doped ZnSe nanocrystals (Mn:ZnSe d-dots), the single-exponential PL decay lifetime was continuously tuned from ∼50 to 1000 μs. A synthetic scheme was further developed for uniform and epitaxial growth of thick ZnS shell, ∼7 monolayers. The resulting Mn:ZnSe/ZnS core/shell d-dots were found to be essential for necessary environmental durability of the PL properties, both steady-state and transient ones, for the d-dot emitters. These characteristics combined with intense absorption and high PL quantum yields (70 ± 5%) enabled greatly simplified schemes for various applications of PL lifetime multiplexing using Mn:ZnSe/ZnS core/shell d-dots. PMID:27163024

  6. The interface effect on the band offset of semiconductor nanocrystals with type-I core-shell structure.

    PubMed

    Zhu, Ziming; Ouyang, Gang; Yang, Guowei

    2013-04-21

    In order to pursue the interface effect on the band offset of the semiconductor nanocrystals with the type-I core-shell structure, we have established a theoretical model to elucidate the underlying mechanism based on the atomic-bond-relaxation consideration and continuum mechanics. It was found that the size-dependent interface bond-nature-factor of the core-shell nanocrystals can be deduced on the basis of the proposed model. Taking the typical CdSe-ZnSe nanostructure as an example, we showed that the theoretical results were consistent with the experimental observations. These investigations provided a useful guide in opening up the possibility to engineer nanodevices with special optoelectronic properties.

  7. NMR studies of the surface structure and dynamics of semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Sachleben, Joseph R.; Wooten, E. Wrenn; Emsley, Lyndon; Pines, Alexander; Colvin, Vicki L.; Alivisatos, A. Paul

    1992-10-01

    1H NMR studies of thiophenol capping groups on cadmium sulfide nanocrystals demonstrate that the coverage of the capping molecule depends on the size of the nanocrystal. Data are presented which show that as the size of the nanocrystal increases, the coverage of thiophenol decreases. In addition, information about the overall tumbling of the nanocrystal and the motion of the capping groups relative to the surface can be obtained from linewidth studies, indicating that the rotation of the capping groups is hindered in the smaller nanocrystals ( r≈12 Å) and becomes less so in larger nanocrystals ( r≈20 Å). The coverage data are related to the electronic properties of this important class of compounds.

  8. Contact Radius and the Insulator-Metal Transition in Films Comprised of Touching Semiconductor Nanocrystals.

    PubMed

    Lanigan, Deanna; Thimsen, Elijah

    2016-07-26

    Nanocrystal assemblies are being explored for a number of optoelectronic applications such as transparent conductors, photovoltaic solar cells, and electrochromic windows. Majority carrier transport is important for these applications, yet it remains relatively poorly understood in films comprised of touching nanocrystals. Specifically, the underlying structural parameters expected to determine the transport mechanism have not been fully elucidated. In this report, we demonstrate experimentally that the contact radius, between touching heavily doped ZnO nanocrystals, controls the electron transport mechanism. Spherical nanocrystals are considered, which are connected by a circular area. The radius of this circular area is the contact radius. For nanocrystals that have local majority carrier concentration above the Mott transition, there is a critical contact radius. If the contact radius between nanocrystals is less than the critical value, then the transport mechanism is variable range hopping. If the contact radius is greater than the critical value, the films display behavior consistent with metallic electron transport.

  9. Nanocrystal synthesis

    SciTech Connect

    Tisdale, William; Prins, Ferry; Weidman, Mark; Beck, Megan

    2016-11-01

    A method of preparing monodisperse MX semiconductor nanocrystals can include contacting an M-containing precursor with an X donor to form a mixture, where the molar ratio between the M containing precursor and the X donor is large. Alternatively, if additional X donor is added during the reaction, a smaller ratio between the M containing precursor and the X donor can be used to prepare monodisperse MX semiconductor nanocrystals.

  10. Magnetic Fluorescent Delivery Vehicle using Uniform Mesoporous Silica Spheres Embedded with Monodisperse Magnetic and Semiconductor Nanocrystals

    SciTech Connect

    Kim, Jaeyun; Lee, Ji Eun; Lee, Jinwoo; Yu, Jung Ho; Kim, Byoung Chan; An, Kwangjin; Hwang, Yosun; Shin, Chae-Ho; Park, Je-Geun; Kim, Jungbae; Hyeon, Taeghwan

    2006-01-25

    Uniform sized colloidal nanocrystals have attracted much attention, because of their unique magnetic and optical properties, as compared with those of their bulk counterparts. Especially magnetic nanocrystals and quantum dots have been intensively pursued for biomedical applications such as contrast enhancement agents in magnetic resonance imaging, magnetic carriers for drug delivery system, biological labeling and diagnostics. Due to their large pore sizes and high surface areas, mesoporous materials and its composites with nanocrystals have attracted considerable attention. In order to use the nanocrystals as functional delivery carriers and catalytic supports, nanocrystals coated with porous silica shells are desirable. Herein, we report a synthetic procedure for the fabrication of monodisperse nanocrystals embedded in uniform pore-sized mesoporous silica spheres. As a representative example, we synthesized monodisperse magnetite (Fe3O4) nanocrystals embedded in mesoporous silica spheres and both magnetite nanocrystals and CdSe/ZnS quantum dots embedded in mesoporous silica spheres. Furthermore, these mesoporous silica spheres were applied to the uptake and controlled release of drugs.

  11. Fluorescence enhancement, blinking suppression, and gray states of individual semiconductor nanocrystals close to gold nanoparticles.

    PubMed

    Ma, Xuedan; Tan, Hua; Kipp, Tobias; Mews, Alf

    2010-10-13

    The optical properties of nanocrystals are drastically changed by the interaction with adjacent metal nanoparticles. By time-resolved photoluminescence spectroscopy, we investigate CdSe multishell nanocrystals coupled to self-assembled films of Au nanoparticles. The distance between emitter and metal is adjusted by coating the nanocrystals with silica shells. These NCs showed increased fluorescence intensity, a decreased fluorescence lifetime, strong blinking suppression, and fluorescence from gray states. These observations can be explained by the metal particle induced change of excitation and recombination rates.

  12. Electronic grade and flexible semiconductor film employing oriented attachment of colloidal ligand-free PbS and PbSe nanocrystals at room temperature

    NASA Astrophysics Data System (ADS)

    Shanker, G. Shiva; Swarnkar, Abhishek; Chatterjee, Arindom; Chakraborty, S.; Phukan, Manabjyoti; Parveen, Naziya; Biswas, Kanishka; Nag, Angshuman

    2015-05-01

    Electronic grade semiconductor films have been obtained via the sintering of solution processed PbS and PbSe nanocrystals at room temperature. Prior attempts to achieve similar films required the sintering of nanocrystals at higher temperatures (>350 °C), which inhibits the processing of such films on a flexible polymer substrate, and it is also expensive. We reduced the sintering temperature by employing two important strategies: (i) use of ligand-free nanocrystals and (ii) oriented attachment of nanocrystals. Colloidal ligand-free PbS and PbSe nanocrystals were synthesized at 70 °C with high yield (~70%). However, these nanocrystals start to agglomerate with time in formamide, and upon the removal of the solvation energy, nanocrystals undergo oriented attachment, forming larger elongated crystals. PbS and PbSe nanocrystal films made on both glass and flexible substrates at room temperature exhibit Ohmic behavior with optimum DC conductivities of 0.03 S m-1 and 0.08 S m-1, respectively. Mild annealing of the films at 150 °C increases the conductivity values to 1.1 S m-1 and 137 S m-1 for PbS and PbSe nanocrystal films, respectively. AC impedance was measured to distinguish the contributions from grain and grain boundaries to the charge transport mechanism. Charge transport properties remain similar after the repeated bending of the film on a flexible polymer substrate. Reasonably high thermoelectric Seebeck coefficients of 600 μV K-1 and 335 μV K-1 for PbS and PbSe nanocrystal pellets, respectively, were obtained at room temperature.Electronic grade semiconductor films have been obtained via the sintering of solution processed PbS and PbSe nanocrystals at room temperature. Prior attempts to achieve similar films required the sintering of nanocrystals at higher temperatures (>350 °C), which inhibits the processing of such films on a flexible polymer substrate, and it is also expensive. We reduced the sintering temperature by employing two important strategies

  13. Hierarchial Junction Solar Cells Based on Hyper-Branched Semiconductor Nanocrystals

    DTIC Science & Technology

    2009-06-30

    that copper (I) sulfide and iron disulfide pyrite generated a much broader impact for photovoltaic solar cell applications. First, a simple low...pure phase iron disulfide pyrite nanocrystals with high purity through a surfactant-assisted hydrothermal reaction. These nanocrystals represent new...and iron disulfide pyrite (FeS2) for photovoltaic solar cell application. First, we demonstrated a simple low temperature solution phase synthesis of

  14. Charging behavior of silicon nitride based non-volatile memory structures with embedded semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Horváth, Zs. J.; Basa, P.; Jászi, T.; Molnár, K. Z.; Pap, A. E.; Molnár, Gy.

    2013-03-01

    The charging behavior of MNS (metal-nitride-silicon) and MNOS (metal-nitride-oxide-silicon) structures containing Si or Ge nanocrystals were studied by capacitance-voltage (C-V) and memory window measurements and by simulation. Both the width of hysteresis of C-V characteristics and the injected charge exhibited exponential dependence on the charging voltage at moderate voltage values, while at high voltages the width of hysteresis of C-V characteristics and the injected charge exhibited saturation. The memory window for reference MNS structure without nanocrystals was wider than that for reference MNOS structures. The presence of nanocrystals enhanced the charging behavior of MNOS structures, but in MNS structures nanocrystals exhibited the opposite effect. The main conclusion is that the presence of nanocrystals or other deep levels close to the Si surface enhances the charge injection properties due to the increased tunneling probability, but nanocrystals or other deep levels located far from the Si surface in the nitride layer do not enhance, but even can degrade the charging behavior by the capture of charge carriers.

  15. Electronic grade and flexible semiconductor film employing oriented attachment of colloidal ligand-free PbS and PbSe nanocrystals at room temperature.

    PubMed

    Shanker, G Shiva; Swarnkar, Abhishek; Chatterjee, Arindom; Chakraborty, S; Phukan, Manabjyoti; Parveen, Naziya; Biswas, Kanishka; Nag, Angshuman

    2015-05-28

    Electronic grade semiconductor films have been obtained via the sintering of solution processed PbS and PbSe nanocrystals at room temperature. Prior attempts to achieve similar films required the sintering of nanocrystals at higher temperatures (>350 °C), which inhibits the processing of such films on a flexible polymer substrate, and it is also expensive. We reduced the sintering temperature by employing two important strategies: (i) use of ligand-free nanocrystals and (ii) oriented attachment of nanocrystals. Colloidal ligand-free PbS and PbSe nanocrystals were synthesized at 70 °C with high yield (∼70%). However, these nanocrystals start to agglomerate with time in formamide, and upon the removal of the solvation energy, nanocrystals undergo oriented attachment, forming larger elongated crystals. PbS and PbSe nanocrystal films made on both glass and flexible substrates at room temperature exhibit Ohmic behavior with optimum DC conductivities of 0.03 S m(-1) and 0.08 S m(-1), respectively. Mild annealing of the films at 150 °C increases the conductivity values to 1.1 S m(-1) and 137 S m(-1) for PbS and PbSe nanocrystal films, respectively. AC impedance was measured to distinguish the contributions from grain and grain boundaries to the charge transport mechanism. Charge transport properties remain similar after the repeated bending of the film on a flexible polymer substrate. Reasonably high thermoelectric Seebeck coefficients of 600 μV K(-1) and 335 μV K(-1) for PbS and PbSe nanocrystal pellets, respectively, were obtained at room temperature.

  16. Size- and Shape-dependent efficiency of PbSe nanocrystal and nanowire doped organic semiconductor photovoltaics

    NASA Astrophysics Data System (ADS)

    Li, Wenting; Murray, Christopher; Kagan, Cherie

    2009-03-01

    Hybrid solar cells based on nanocomposite organic semiconductors and IR sensitive PbSe nanocrystals (NCs) and nanowires (NWs) are fabricated and serve as a model system to test in PV devices. Wet chemical routes are used to synthesize PbSe NCs tunable in size, from 6 to 12nm in diameter, and in shape by tailoring the reaction temperature and selection of surfactants. PbSe NWs are also synthesized through oriented attachment in solution of NC building blocks to form straight, zigzag, helical, and branched NWs. We integrate PbSe NCs and NWs with the organic semiconductors P3HT and pentacene. We are able to fabricate organic-inorganic bulk heterojunctions with pentacene using a solution-processable precursor that is thermally converted to pentacene. We investigate the role of the organic semiconductor pentacene in the solar cell, both as a conductivity booster and as a more stable alternative to P3HT. We find that ligand exchange significantly increases photocurrent by replacing oleic acid ligands used in NC synthesis with shorter pyridine or octylamine ligands. We also report that tailoring the size and shape of the NCs and controlling the deposition and annealing conditions of the nanocomposites enhances the solar cell performance.

  17. Photovoltaic nanopillar radial junction diode architecture enhanced by integrating semiconductor quantum dot nanocrystals as light harvesters

    NASA Astrophysics Data System (ADS)

    Güzeltürk, Burak; Mutlugün, Evren; Wang, Xiaodong; Pey, Kin Leong; Demir, Hilmi Volkan

    2010-08-01

    We propose and demonstrate colloidal quantum dot hybridized, radial p-n junction based, nanopillar solar cells with photovoltaic performance enhanced by intimately integrating nanocrystals to serve as light harvesting agents around the light trapping pillars. By furnishing Si based nanopillar photovoltaic diodes with CdSe quantum dots, we experimentally showed up to sixfold enhancement in UV responsivity and ˜13% enhancement in overall solar conversion efficiency. The maximum responsivity enhancement achieved by incorporation of nanocrystals in the nanopillar architecture is found to be spectrally more than four times larger than the responsivity enhancement obtained using planar architecture of the same device.

  18. Seed-induced growth of flower-like Au-Ni-ZnO metal-semiconductor hybrid nanocrystals for photocatalytic applications.

    PubMed

    Chen, Yuanzhi; Zeng, Deqian; Cortie, Michael B; Dowd, Annette; Guo, Huizhang; Wang, Junbao; Peng, Dong-Liang

    2015-03-25

    The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications.

  19. Detection Techniques for Biomolecules using Semi-Conductor Nanocrystals and Magnetic Beads as Labels

    NASA Astrophysics Data System (ADS)

    Chatterjee, Esha

    Continued interest in the development of miniaturized and portable analytical platforms necessitates the exploration of sensitive methods for the detection of trace analytes. Nanomaterials, on account of their unique physical and chemical properties, are not only able to overcome many limitations of traditional detection reagents but also enable the exploration of many new signal transduction technologies. This dissertation presents a series of investigations of alternative detection techniques for biomolecules, involving the use of semi-conductor nanocrystals and magnetic beads as labels. Initial research focused on the development of quantum dot-encapsulating liposomes as a novel fluorescent label for immunoassays. This hybrid nanomaterial was anticipated to overcome the drawbacks presented by traditional fluorophores as well as provide significant signal amplification. Quantum dot-encapsulating liposomes were synthesized by the method of thin film hydration and characterized. The utility of these composite nanostructures for bioanalysis was demonstrated. However, the longterm instability of the liposomes hampered quantitative development. A second approach for assay development exploited the ability of gold nanoparticles to quench the optical signals obtained from quantum dots. The goal of this study was to demonstrate the feasibility of using aptamer-linked nanostructures in FRET-based quenching for the detection of proteins. Thrombin was used as the model analyte in this study. Experimental parameters for the assay were optimized. The assay simply required the mixing of the sample with the reagents and could be completed in less than an hour. The limit of detection for thrombin by this method was 5 nM. This homogeneous assay can be easily adapted for the detection of a wide variety of biochemicals. The novel technique of ferromagnetic resonance generated in magnetic bead labels was explored for signal transduction. This inductive detection technique lends

  20. Quantum dot sensitized solar cells. A tale of two semiconductor nanocrystals: CdSe and CdTe.

    PubMed

    Bang, Jin Ho; Kamat, Prashant V

    2009-06-23

    CdSe and CdTe nanocrystals are linked to nanostructured TiO2 films using 3-mercaptopropionic acid as a linker molecule for establishing the mechanistic aspects of interfacial charge transfer processes. Both these quantum dots are energetically capable of sensitizing TiO2 films and generating photocurrents in quantum dot solar cells. These two semiconductor nanocrystals exhibit markedly different external quantum efficiencies ( approximately 70% for CdSe and approximately 0.1% for CdTe at 555 nm). Although CdTe with a more favorable conduction band energy (E(CB) = -1.0 V vs NHE) is capable of injecting electrons into TiO2 faster than CdSe (E(CB) = -0.6 V vs NHE), hole scavenging by a sulfide redox couple remains a major bottleneck. The sulfide ions dissolved in aqueous solutions are capable of scavenging photogenerated holes in photoirradiated CdSe system but not in CdTe. The anodic corrosion and exchange of Te with S dominate the charge transfer at the CdTe interface. Factors that dictate the efficiency and photostability of CdSe and CdTe quantum dots are discussed.

  1. Wurtzite Cu2ZnSnS4 nanocrystals: a novel quaternary semiconductor.

    PubMed

    Lu, Xiaotang; Zhuang, Zhongbin; Peng, Qing; Li, Yadong

    2011-03-21

    A new wurtzite phase Cu(2)ZnSnS(4) was discovered and the corresponding nanocrystals have been successfully synthesized. They have been characterized in detail and showed the photoelectric response, which demonstrated their potential in the application of photovoltaic devices.

  2. Single-particle spectroscopy of I-III-VI semiconductor nanocrystals: spectral diffusion and suppression of blinking by two-color excitation

    NASA Astrophysics Data System (ADS)

    Sharma, Dharmendar Kumar; Hirata, Shuzo; Bujak, Lukasz; Biju, Vasudevanpillai; Kameyama, Tatsuya; Kishi, Marino; Torimoto, Tsukasa; Vacha, Martin

    2016-07-01

    Ternary I-III-VI semiconductor nanocrystals have been explored as non-toxic alternatives to II-VI semiconductors for optoelectronic and sensing applications, but large photoluminescence spectral width and moderate brightness restrict their practical use. Here, using single-particle photoluminescence spectroscopy on nanocrystals of (AgIn)xZn2(1-x)S2 we show that the photoluminescence band is inhomogeneously broadened and that size distribution is the dominant factor in the broadening. The residual homogeneous linewidth of individual nanocrystals reaches up to 75% of the ensemble spectral width. Single nanocrystals undergo spectral diffusion which also contributes to the inhomogeneous band. Excitation with two lasers with energies above and below the bandgap reveals coexistence of two emitting donor states within one particle. Spectral diffusion in such particles is due to temporal activation and deactivation of one such state. Filling of a trap state with a lower-energy laser enables optical modulation of photoluminescence intermittency (blinking) and leads to an almost two-fold increase in brightness.Ternary I-III-VI semiconductor nanocrystals have been explored as non-toxic alternatives to II-VI semiconductors for optoelectronic and sensing applications, but large photoluminescence spectral width and moderate brightness restrict their practical use. Here, using single-particle photoluminescence spectroscopy on nanocrystals of (AgIn)xZn2(1-x)S2 we show that the photoluminescence band is inhomogeneously broadened and that size distribution is the dominant factor in the broadening. The residual homogeneous linewidth of individual nanocrystals reaches up to 75% of the ensemble spectral width. Single nanocrystals undergo spectral diffusion which also contributes to the inhomogeneous band. Excitation with two lasers with energies above and below the bandgap reveals coexistence of two emitting donor states within one particle. Spectral diffusion in such particles is due

  3. Nanocrystal doped matrixes

    DOEpatents

    Parce, J. Wallace; Bernatis, Paul; Dubrow, Robert; Freeman, William P.; Gamoras, Joel; Kan, Shihai; Meisel, Andreas; Qian, Baixin; Whiteford, Jeffery A.; Ziebarth, Jonathan

    2010-01-12

    Matrixes doped with semiconductor nanocrystals are provided. In certain embodiments, the semiconductor nanocrystals have a size and composition such that they absorb or emit light at particular wavelengths. The nanocrystals can comprise ligands that allow for mixing with various matrix materials, including polymers, such that a minimal portion of light is scattered by the matrixes. The matrixes of the present invention can also be utilized in refractive index matching applications. In other embodiments, semiconductor nanocrystals are embedded within matrixes to form a nanocrystal density gradient, thereby creating an effective refractive index gradient. The matrixes of the present invention can also be used as filters and antireflective coatings on optical devices and as down-converting layers. Processes for producing matrixes comprising semiconductor nanocrystals are also provided. Nanostructures having high quantum efficiency, small size, and/or a narrow size distribution are also described, as are methods of producing indium phosphide nanostructures and core-shell nanostructures with Group II-VI shells.

  4. Crafting semiconductor organic-inorganic nanocomposites via placing conjugated polymers in intimate contact with nanocrystals for hybrid solar cells.

    PubMed

    Zhao, Lei; Lin, Zhiqun

    2012-08-22

    Semiconductor organic-inorganic hybrid solar cells incorporating conjugated polymers (CPs) and nanocrystals (NCs) offer the potential to deliver efficient energy conversion with low-cost fabrication. The CP-based photovoltaic devices are complimented by an extensive set of advantageous characteristics from CPs and NCs, such as lightweight, flexibility, and solution-processability of CPs, combined with high electron mobility and size-dependent optical properties of NCs. Recent research has witnessed rapid advances in an emerging field of directly tethering CPs on the NC surface to yield an intimately contacted CP-NC nanocomposite possessing a well-defined interface that markedly promotes the dispersion of NCs within the CP matrix, facilitates the photoinduced charge transfer between these two semiconductor components, and provides an effective platform for studying the interfacial charge separation and transport. In this Review, we aim to highlight the recent developments in CP-NC nanocomposite materials, critically examine the viable preparative strategies geared to craft intimate CP-NC nanocomposites and their photovoltaic performance in hybrid solar cells, and finally provide an outlook for future directions of this extraordinarily rich field.

  5. Carrier multiplication in semiconductor nanocrystals: theoretical screening of candidate materials based on band-structure effects.

    PubMed

    Luo, Jun-Wei; Franceschetti, Alberto; Zunger, Alex

    2008-10-01

    Direct carrier multiplication (DCM) occurs when a highly excited electron-hole pair decays by transferring its excess energy to the electrons rather than to the lattice, possibly exciting additional electron-hole pairs. Atomistic electronic structure calculations have shown that DCM can be induced by electron-hole Coulomb interactions, in an impact-ionization-like process whose rate is proportional to the density of biexciton states rho XX. Here we introduce a DCM "figure of merit" R2(E) which is proportional to the ratio between the biexciton density of states rhoXX and the single-exciton density of states rhoX, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R2(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E0 (the energy at which R2(E) becomes >or=1) is reduced, suggesting improved DCM. However, whether the normalized E0/epsilong increases or decreases as the dot size increases depends on dot material.

  6. Tuning optoelectronic properties of small semiconductor nanocrystals through surface ligand chemistry

    NASA Astrophysics Data System (ADS)

    Lawrence, Katie N.

    Semiconductor nanocrystals (SNCs) are a class of material with one dimension <100 nm, which display size, shape, and composition dependent photophysical (absorption and emission) properties. Ultrasmall SNCs are a special class of SNCs whose diameter is <3.0 nm and are strongly quantum confined leading to a high surface to volume ratio. Therefore, their electronic and photophysical properties are fundamentally dictated by their surface chemistry, and as such, even a minute variation of the surface ligation can have a colossal impact on these properties. Since the development of the hot injection-method by Bawendi et al., the synthetic methods of SNCs have evolved from high-temperature, highly toxic precursors to low-temperature, relatively benign precursors over the last 25 years. Unfortunately, optimization of their synthetic methods by appropriate surface ligation is still deficient. The deficiency lies in the incomplete or inappropriate surface passivation during the synthesis and/or post-synthetic modification procedure, which due to the high surface to volume ratio of ultrasmall SNCs, is a significant problem. Currently, direct synthetic methods produce SNCs that are either soluble in an aqueous media or soluble in organic solvents therefore limiting their applicability. In addition, use of insulating ligands hinder SNCs' transport properties and thus their potential application in solid state devices. Appropriate choice of surface ligation can provide 1) solubility, 2) stability, and 3) facilitate exciton delocalization. In this dissertation, the effects of appropriate surface ligation on strongly quantum confined ultrasmall SNCs was investigated. Due to their high surface to volume ratio, we are able to highly control their optical and electronic properties through surface ligand modification. Throughout this dissertation, we utilized a variety of ligands (e.g. oleylamine, cadmium benzoate, and PEGn-thiolate) in order to change the solubility of the SNC as

  7. Mechanochemical Solvent-Free Synthesis of Quaternary Semiconductor Cu-Fe-Sn-S Nanocrystals

    NASA Astrophysics Data System (ADS)

    Baláž, Peter; Baláž, Matej; Sayagués, María J.; Škorvánek, Ivan; Zorkovská, Anna; Dutková, Erika; Briančin, Jaroslav; Kováč, Jaroslav; Kováč, Jaroslav; Shpotyuk, Yaroslav

    2017-04-01

    In this study, we demonstrate a one-pot mechanochemical synthesis of the nanocomposite composed of stannite Cu2FeSnS4 and rhodostannite Cu2FeSn3S8 nanocrystals using a planetary ball mill and elemental precursors (Cu, Fe, Sn, S). By this approach, unique nanostructures with interesting properties can be obtained. Methods of XRD, Raman spectroscopy, UV-Vis, nitrogen adsorption, SEM, EDX, HRTEM, STEM, and SQUID magnetometry were applied. Quaternary tetragonal phases of stannite and rhodostannite with crystallite sizes 18-19 nm were obtained. The dominant Raman peaks corresponding to the tetragonal stannite structure corresponding to A-symmetry optical modes were identified in the spectra. The bandgap 1.25 eV calculated from UV-Vis absorption spectrum is very well-acceptable value for the application of the synthesized material. The SEM micrographs illustrate the clusters of particles in micron and submicron range. The formation of agglomerates is also illustrated on the TEM micrographs. Weak ferromagnetic properties of the synthesized nanocrystals were documented.

  8. Semiconductor nanocrystals functionalized with antimony telluride zintl ions for nanostructured thermoelectrics.

    PubMed

    Kovalenko, Maksym V; Spokoyny, Boris; Lee, Jong-Soo; Scheele, Marcus; Weber, Andrew; Perera, Susanthri; Landry, Daniel; Talapin, Dmitri V

    2010-05-19

    The energy efficiency of heat engines could be improved by the partial recovery of waste heat using thermoelectric (TE) generators. We show the possibility of designing nanostructured TE materials using colloidal inorganic nanocrystals functionalized with molecular antimony telluride complexes belonging to the family of Zintl ions. The unique advantage of using Zintl ions as the nanocrystal surface ligands is the possibility to convert them into crystalline metal chalcogenides, thus linking individual nanobuilding blocks into a macroscopic assembly of electronically coupled functional modules. This approach allows preserving the benefits of nanostructuring and quantum confinement while enabling facile charge transport through the interparticle boundaries. A developed methodology was applied for solution-based fabrication of nanostructured n- and p-type Bi(2-x)Sb(x)Te(3) alloys with tunable composition and PbTe-Sb(2)Te(3) nanocomposites with controlled grain size. Characterization of the TE properties of these materials showed that their Seebeck coefficients, electrical and thermal conductivities, and ZT values compared favorably with those of previously reported solution-processed TE materials.

  9. Luminescence properties of ZnS:Cu, Eu semiconductor nanocrystals synthesized by a hydrothermal process

    NASA Astrophysics Data System (ADS)

    Xin, Mei; Hu, Li-Zhong

    2013-08-01

    ZnS:Cu, Eu nanocrystals with an average diameter of ~ 80 nm are synthesized using a hydrothermal approach at 200 °C. The photoluminescence (PL) properties of the ZnS:Cu, Eu nanocrystals before and after annealing, as well as the doping form of Eu, are studied. The as-synthesized samples are characterized by X-ray diffraction, scanning electron microscopy, inductively coupled plasma-atomic emission spectrometry, and the excitation and emission spectra (PL). The results show that both Cu and Eu are indeed incorporated into the ZnS matrix. Compared with the PL spectrum of the Cu mono-doped sample, the PL emission intensity of the Cu and Eu-codoped sample increases and a peak appears at 516 nm, indicating that Eu3+ ions, which act as an impurity compensator and activator, are incorporated into the ZnS matrix, forming a donor level. Compared with the unannealed sample, the annealed one has an increased PL emission intensity and the peak position has a blue shift of 56 nm from 516 nm to 460 nm, which means that Eu3+ ions reduce to Eu2+ ions, thereby leading to the appearance of Eu2+ characteristic emission and generating effective host-to-Eu2+ energy transfer. The results indicate the potential applications of ZnS:Cu, Eu nanoparticles in optoelectronic devices.

  10. Robust photogeneration of H2 in water using semiconductor nanocrystals and a nickel catalyst.

    PubMed

    Han, Zhiji; Qiu, Fen; Eisenberg, Richard; Holland, Patrick L; Krauss, Todd D

    2012-12-07

    Homogeneous systems for light-driven reduction of protons to H(2) typically suffer from short lifetimes because of decomposition of the light-absorbing molecule. We report a robust and highly active system for solar hydrogen generation in water that uses CdSe nanocrystals capped with dihydrolipoic acid (DHLA) as the light absorber and a soluble Ni(2+)-DHLA catalyst for proton reduction with ascorbic acid as an electron donor at pH = 4.5, which gives >600,000 turnovers. Under appropriate conditions, the precious-metal-free system has undiminished activity for at least 360 hours under illumination at 520 nanometers and achieves quantum yields in water of over 36%.

  11. Near-Infrared Photoluminescence Enhancement in Ge/CdS and Ge/ZnS Core/Shell Nanocrystals: Utilizing IV/II-VI Semiconductor Epitaxy

    SciTech Connect

    Guo, Yijun; Rowland, Clare E; Schaller, Richard D; Vela, Javier

    2014-08-26

    Ge nanocrystals have a large Bohr radius and a small, size-tunable band gap that may engender direct character via strain or doping. Colloidal Ge nanocrystals are particularly interesting in the development of near-infrared materials for applications in bioimaging, telecommunications and energy conversion. Epitaxial growth of a passivating shell is a common strategy employed in the synthesis of highly luminescent II–VI, III–V and IV–VI semiconductor quantum dots. Here, we use relatively unexplored IV/II–VI epitaxy as a way to enhance the photoluminescence and improve the optical stability of colloidal Ge nanocrystals. Selected on the basis of their relatively small lattice mismatch compared with crystalline Ge, we explore the growth of epitaxial CdS and ZnS shells using the successive ion layer adsorption and reaction method. Powder X-ray diffraction and electron microscopy techniques, including energy dispersive X-ray spectroscopy and selected area electron diffraction, clearly show the controllable growth of as many as 20 epitaxial monolayers of CdS atop Ge cores. In contrast, Ge etching and/or replacement by ZnS result in relatively small Ge/ZnS nanocrystals. The presence of an epitaxial II–VI shell greatly enhances the near-infrared photoluminescence and improves the photoluminescence stability of Ge. Ge/II–VI nanocrystals are reproducibly 1–3 orders of magnitude brighter than the brightest Ge cores. Ge/4.9CdS core/shells show the highest photoluminescence quantum yield and longest radiative recombination lifetime. Thiol ligand exchange easily results in near-infrared active, water-soluble Ge/II–VI nanocrystals. We expect this synthetic IV/II–VI epitaxial approach will lead to further studies into the optoelectronic behavior and practical applications of Si and Ge-based nanomaterials.

  12. Carbon-shell-decorated p-semiconductor PbMoO4 nanocrystals for efficient and stable photocathode of photoelectrochemical water reduction

    NASA Astrophysics Data System (ADS)

    Wang, Ligang; Tang, Hanqin; Tian, Yang

    2016-07-01

    Photoelectrochemical (PEC) water splitting using semiconductors is a promising method for the future scalable production of renewable hydrogen fuels. The critical issues in PEC water splitting include the development of the photoelectrode materials with high efficiency and long-term stability, especially for p-type semiconductor photocathodes. Herein, we report the use of citric acid (CA) pyrolysis to prepare carbon-shell-decorated PbMoO4 (C@PbMoO4) nanocrystals via a simple solvothermal method. Different carbon shell thicknesses below 10 nm were generated by varying the amount of CA in the precursor solution. In contrast, without using CA, bare PbMoO4 nanocrystals were obtained. The PEC experiments showed that 2-nm carbon shell could preferably improve the water splitting performance of PbMoO4: the photocurrent density of 2-nm C@PbMoO4 is nearly 2-fold high as that of bare PbMoO4 at 0 V versus reversible hydrogen electrode (RHE). The surface charge transfer efficiency of 2-nm C@PbMoO4 in the PEC process was tested to increase from 83% to 90.4%, the charge separation efficiency enhanced 56%, and the PEC stability also greatly increased compared to those of the bare PbMoO4 nanocrystals. This strategy could be applied to other p-type semiconducting photocathodes for low-cost solar-fuel-generation devices.

  13. How Robust are Semiconductor Nanorods? Investigating the Stability and Chemical Decomposition Pathways of Photoactive Nanocrystals

    SciTech Connect

    Reichert, Malinda D; Lin, Chia-Cheng; Vela, Javier

    2014-07-08

    Anisotropic II–VI semiconductor nanostructures are important photoactive materials for various energy conversion and optical applications. However, aside from the many available surface chemistry studies and from their ubiquitous photodegradation under continuous illumination, the general chemical reactivity and thermal stability (phase and shape transformations) of these materials are poorly understood. Using CdSe and CdS nanorods as model systems, we have investigated the behavior of II–VI semiconductor nanorods against various conditions of extreme chemical and physical stress (acids, bases, oxidants, reductants, and heat). CdSe nanorods react rapidly with acids, becoming oxidized to Se or SeO2. In contrast, CdSe nanorods remain mostly unreactive when treated with bases or strong oxidants, although bases do partially etch the tips of the nanorods (along their axis). Roasting (heating in air) of CdSe nanorods results in rock-salt CdO, but neither CdSe nor CdO is easily reduced by hydrogen (H2). Another reductant, n-BuLi, reduces CdSe nanorods to metallic Cd. Variable temperature X-ray diffraction experiments show that axial annealing and selective axial melting of the nanorods precede particle coalescence. Furthermore, thermal analysis shows that the axial melting of II–VI nanorods is a ligand-dependent process. In agreement with chemical reactivity and thermal stability observations, silica-coating experiments show that the sharpest (most curved) II–VI surfaces are most active against heterogeneous nucleation of a silica shell. These results provide valuable insights into the fate and possible ways to enhance the stability and improve the use of II–VI semiconductor nanostructures in the fields of optics, magnetism, and energy conversion.

  14. Use of semiconductor nanocrystals to encode microbeads for multiplexed analysis of biological samples

    NASA Astrophysics Data System (ADS)

    Berestovoy, Mikhail A.; Bilan, Regina S.; Krivenkov, Victor; Nabiev, Igor; Sukhanova, Alyona

    2017-01-01

    Microbeads encoded with semiconductor quantum dots (QDs) are suitable tools for multiplexed analyses of various biological markers using flow cytometry. We have prepared a panel of microbeads encoded with QDs of different colors emitting with different luminescence intensities using the layer-by-layer deposition technique, which consists in layering of alternately charged polyelectrolytes and negatively charged QDs onto the surface of microbeads. This method allows QDs to be separated with one or several polymer layers in order to prevent Förster resonance energy transfer (FRET) and the resultant quenching of QD fluorescence in multicolor microbeads.

  15. Alloyed Mn-Cu-In-S nanocrystals: a new type of diluted magnetic semiconductor quantum dots.

    PubMed

    Liu, Qinghui; Deng, Ruiping; Ji, Xiangling; Pan, Daocheng

    2012-06-29

    A new type of Mn-Cu-In-S diluted magnetic semiconductor quantum dots was synthesized and reported for the first time. The quantum dots, with no highly toxic elements, not only show the same classic diluted magnetic behavior as Mn-doped CdSe, but also exhibit tunable luminescent properties in a relatively large window from 542 to 648 nm. An absolute photoluminescence quantum yield up to 20% was obtained after the shell growth of ZnS. This kind of magnetic/luminescent bi-functional Mn-Cu-In-S/ZnS core/shell quantum dot might serve as promising nanoprobes for use in dual-mode optical and magnetic resonance imaging techniques.

  16. Alloyed Mn-Cu-In-S nanocrystals: a new type of diluted magnetic semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Liu, Qinghui; Deng, Ruiping; Ji, Xiangling; Pan, Daocheng

    2012-06-01

    A new type of Mn-Cu-In-S diluted magnetic semiconductor quantum dots was synthesized and reported for the first time. The quantum dots, with no highly toxic elements, not only show the same classic diluted magnetic behavior as Mn-doped CdSe, but also exhibit tunable luminescent properties in a relatively large window from 542 to 648 nm. An absolute photoluminescence quantum yield up to 20% was obtained after the shell growth of ZnS. This kind of magnetic/luminescent bi-functional Mn-Cu-In-S/ZnS core/shell quantum dot might serve as promising nanoprobes for use in dual-mode optical and magnetic resonance imaging techniques.

  17. Biosynthesis of fluorescent CdS nanocrystals with semiconductor properties: Comparison of microbial and plant production systems.

    PubMed

    Al-Shalabi, Zahwa; Doran, Pauline M

    2016-04-10

    This study investigated fission yeast (Schizosaccharomyces pombe) and hairy roots of tomato (Solanum lycopersicum) as in vitro production vehicles for biological synthesis of CdS quantum dots. Cd added during the mid-growth phase of the cultures was detoxified within the biomass into inorganic sulphide-containing complexes with the quantum confinement properties of semiconductor nanocrystals. Significant differences were found between the two host systems in terms of nanoparticle production kinetics, yield and quality. The much slower growth rate of hairy roots compared with yeast is a disadvantage for commercial scaled-up production. Nanoparticle extraction from the biomass was less effective for the roots: 19% of the Cd present in the hairy roots was recovered after extraction compared with 34% for the yeast. The overall yield of CdS quantum dots was also lower for the roots: relative to the amount of Cd taken up into the biomass, 8.5% was recovered in yeast gel filtration fractions exhibiting quantum dot properties whereas the result for hairy roots was only 0.99%. Yeast-produced CdS crystallites were somewhat smaller with diameters of approximately 2-6 nm compared with those of 4-10nm obtained from the roots. The average ratio of inorganic sulphide to Cd for the purified and size-fractionated particles was 0.44 for the yeast and 1.6 for the hairy roots. Despite the limitations associated with hairy roots in terms of culture kinetics and product yield, this system produced CdS nanoparticles with enhanced photostability and 3.7-13-fold higher fluorescence quantum efficiency compared with those generated by yeast. This work demonstrates that the choice of cellular host can have a significant effect on nanoparticle functional properties as well as on the bioprocessing aspects of biological quantum dot synthesis. Copyright © 2016 Elsevier B.V. All rights reserved.

  18. Photoswitchable semiconductor nanocrystals with self-regulating photochromic Förster resonance energy transfer acceptors

    NASA Astrophysics Data System (ADS)

    Díaz, Sebastián A.; Gillanders, Florencia; Jares-Erijman, Elizabeth A.; Jovin, Thomas M.

    2015-01-01

    Photoswitchable molecules and nanoparticles constitute superior biosensors for a wide range of industrial, research and biomedical applications. Rendered reversible by spontaneous or deterministic means, such probes facilitate many of the techniques in fluorescence microscopy that surpass the optical resolution dictated by diffraction. Here we have devised a family of photoswitchable quantum dots (psQDs) in which the semiconductor core functions as a fluorescence donor in Förster resonance energy transfer (FRET), and multiple photochromic diheteroarylethene groups function as acceptors upon activation by ultraviolet light. The QDs were coated with a polymer bearing photochromic groups attached via linkers of different length. Despite the resulting nominal differences in donor-acceptor separation and anticipated FRET efficiencies, the maximum quenching of all psQD preparations was 38±2%. This result was attributable to the large ultraviolet absorption cross-section of the QDs, leading to preferential cycloreversion of photochromic groups situated closer to the nanoparticle surface and/or with a more favourable orientation.

  19. 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

  20. Selection of peptides with semiconductor binding specificity for directed nanocrystal assembly

    NASA Astrophysics Data System (ADS)

    Whaley, Sandra R.; English, D. S.; Hu, Evelyn L.; Barbara, Paul F.; Belcher, Angela M.

    2000-06-01

    In biological systems, organic molecules exert a remarkable level of control over the nucleation and mineral phase of inorganic materials such as calcium carbonate and silica, and over the assembly of crystallites and other nanoscale building blocks into complex structures required for biological function. This ability to direct the assembly of nanoscale components into controlled and sophisticated structures has motivated intense efforts to develop assembly methods that mimic or exploit the recognition capabilities and interactions found in biological systems. Of particular value would be methods that could be applied to materials with interesting electronic or optical properties, but natural evolution has not selected for interactions between biomolecules and such materials. However, peptides with limited selectivity for binding to metal surfaces and metal oxide surfaces have been successfully selected. Here we extend this approach and show that combinatorial phage-display libraries can be used to evolve peptides that bind to a range of semiconductor surfaces with high specificity, depending on the crystallographic orientation and composition of the structurally similar materials we have used. As electronic devices contain structurally related materials in close proximity, such peptides may find use for the controlled placement and assembly of a variety of practically important materials, thus broadening the scope for `bottom-up' fabrication approaches.

  1. Photoswitchable semiconductor nanocrystals with self-regulating photochromic Förster resonance energy transfer acceptors.

    PubMed

    Díaz, Sebastián A; Gillanders, Florencia; Jares-Erijman, Elizabeth A; Jovin, Thomas M

    2015-01-16

    Photoswitchable molecules and nanoparticles constitute superior biosensors for a wide range of industrial, research and biomedical applications. Rendered reversible by spontaneous or deterministic means, such probes facilitate many of the techniques in fluorescence microscopy that surpass the optical resolution dictated by diffraction. Here we have devised a family of photoswitchable quantum dots (psQDs) in which the semiconductor core functions as a fluorescence donor in Förster resonance energy transfer (FRET), and multiple photochromic diheteroarylethene groups function as acceptors upon activation by ultraviolet light. The QDs were coated with a polymer bearing photochromic groups attached via linkers of different length. Despite the resulting nominal differences in donor-acceptor separation and anticipated FRET efficiencies, the maximum quenching of all psQD preparations was 38±2%. This result was attributable to the large ultraviolet absorption cross-section of the QDs, leading to preferential cycloreversion of photochromic groups situated closer to the nanoparticle surface and/or with a more favourable orientation.

  2. Metal-semiconductor phase transition of order arrays of VO2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Lopez, Rene; Suh, Jae; Feldman, Leonard; Haglund, Richard

    2004-03-01

    The study of solid-state phase transitions at nanometer length scales provides new insights into the effects of material size on the mechanisms of structural transformations. Such research also opens the door to new applications, either because materials properties are modified as a function of particle size, or because the nanoparticles interact with a surrounding matrix material, or with each other. In this paper, we describe the formation of vanadium dioxide nanoparticles in silicon substrates by pulsed laser deposition of ion beam lithographically selected sites and thermal processing. We observe the collective behavior of 50 nm diameter VO2 oblate nanoparticles, 10 nm high, and ordered in square arrays with arbitrary lattice constant. The metal-semiconductor-transition of the VO2 precipitates shows different features in each lattice spacing substrate. The materials are characterized by electron microscopy, x-ray diffraction, Rutherford backscattering. The features of the phase transition are studied via infrared optical spectroscopy. Of particular interest are the enhanced scattering and the surface plasmon resonance when the particles reach the metallic state. This resonance amplifies the optical contrast in the range of near-infrared optical communication wavelengths and it is altered by the particle-particle coupling as in the case of noble metals. In addition the VO2 nanoparticles exhibit sharp transitions with up to 50 K of hysteresis, one of the largest values ever reported for this transition. The optical properties of the VO2 nanoarrays are correlated with the size of the precipitates and their inter-particle distance. Nonlinear and ultra fast optical measurements have shown that the transition is the fastest known solid-solid transformation. The VO2 nanoparticles show the same bulk property, transforming in times shorter than 150 fs. This makes them remarkable candidates for ultrafast optical and electronic switching applications.

  3. Mesoporous silica beads embedded with semiconductor quantum dots and iron oxide nanocrystals: dual-function microcarriers for optical encoding and magnetic separation.

    PubMed

    Sathe, Tushar R; Agrawal, Amit; Nie, Shuming

    2006-08-15

    Mesoporous beads are promising materials for embedding functional nanoparticles because of their nanometer-sized pores and large surface areas. Here we report the development of silica microbeads embedded with both semiconductor quantum dots (QD) and iron oxide (Fe3O4) nanocrystals as a new class of dual-function carriers for optical encoding and magnetic separation. The embedding (doping) process is carried out by either simultaneous or sequential addition of quantum dots and iron oxide (Fe3O4) nanocrystals in solution. The doping process is fast and quantitative, but the incorporated iron oxide strongly attenuates the signal intensity of QD fluorescence. We find that this attenuation is not due to conventional fluorescence quenching but is caused by the broad optical absorption spectrum of mixed-valence Fe3O4. For improved biocompatibility and reduced nonspecific binding, the encoded beads are further coated with amphiphilic polymers such as octylamine poly(acrylic acid). The results indicate that the polymer-coated beads are well suited for target capturing and enrichment, yielding magnetic separation efficiencies higher than 99%. By combining the multiplexing capability of QDs with the superparamagnetic properties of iron oxide nanocrystals, this class of encoded beads is expected to find broad applications in high-throughput and multiplexed biomolecular assays.

  4. Loosening quantum confinement: observation of real conductivity caused by hole polarons in semiconductor nanocrystals smaller than the Bohr radius.

    PubMed

    Ulbricht, Ronald; Pijpers, Joep J H; Groeneveld, Esther; Koole, Rolf; Donega, Celso de Mello; Vanmaekelbergh, Daniel; Delerue, Christophe; Allan, Guy; Bonn, Mischa

    2012-09-12

    We report on the gradual evolution of the conductivity of spherical CdTe nanocrystals of increasing size from the regime of strong quantum confinement with truly discrete energy levels to the regime of weak confinement with closely spaced hole states. We use the high-frequency (terahertz) real and imaginary conductivities of optically injected carriers in the nanocrystals to report on the degree of quantum confinement. For the smaller CdTe nanocrystals (3 nm < radius < 5 nm), the complex terahertz conductivity is purely imaginary. For nanocrystals with radii exceeding 5 nm, we observe the onset of real conductivity, which is attributed to the increasingly smaller separation between the hole states. Remarkably, this onset occurs for a nanocrystal radius significantly smaller than the bulk exciton Bohr radius a(B) ∼ 7 nm and cannot be explained by purely electronic transitions between hole states, as evidenced by tight-binding calculations. The real-valued conductivity observed in the larger nanocrystals can be explained by the emergence of mixed carrier-phonon, that is, polaron, states due to hole transitions that become resonant with, and couple strongly to, optical phonon modes for larger QDs. These polaron states possess larger oscillator strengths and broader absorption, and thereby give rise to enhanced real conductivity within the nanocrystals despite the confinement.

  5. Charge separation and transport in conjugated-polymer/semiconductor-nanocrystal composites studied by photoluminescence quenching and photoconductivity

    SciTech Connect

    Greenham, N.C.; Peng, X.; Alivisatos, A.P.

    1996-12-01

    We study the processes of charge separation and transport in composite materials formed by mixing cadmium selenide or cadmium sulfide nanocrystals with the conjugated polymer poly(2-methoxy,5-(2{prime}-ethyl)-hexyloxy-{ital p}-phenylenevinylene) (MEH-PPV). When the surface of the nanocrystals is treated so as to remove the surface ligand, we find that the polymer photoluminescence is quenched, consistent with rapid charge separation at the polymer/nanocrystal interface. Transmission electron microscopy of these quantum-dot/conjugated-polymer composites shows clear evidence for phase segregation with length scales in the range 10{endash}200 nm, providing a large area of interface for charge separation to occur. Thin-film photovoltaic devices using the composite materials show quantum efficiencies that are significantly improved over those for pure polymer devices, consistent with improved charge separation. At high concentrations of nanocrystals, where both the nanocrystal and polymer components provide continuous pathways to the electrodes, we find quantum efficiencies of up to 12{percent}. We describe a simple model to explain the recombination in these devices, and show how the absorption, charge separation, and transport properties of the composites can be controlled by changing the size, material, and surface ligands of the nanocrystals. {copyright} {ital 1996 The American Physical Society.}

  6. Silicon nanocrystal inks, films, and methods

    DOEpatents

    Wheeler, Lance Michael; Kortshagen, Uwe Richard

    2015-09-01

    Silicon nanocrystal inks and films, and methods of making and using silicon nanocrystal inks and films, are disclosed herein. In certain embodiments the nanocrystal inks and films include halide-terminated (e.g., chloride-terminated) and/or halide and hydrogen-terminated nanocrystals of silicon or alloys thereof. Silicon nanocrystal inks and films can be used, for example, to prepare semiconductor devices.

  7. Ion beam synthesis of CdS, ZnS, and PbS compound semiconductor nanocrystals

    SciTech Connect

    White, C.W.; Budai, J.D.; Meldrum, A.L.

    1997-12-01

    Sequential ion implantation followed by thermal annealing has been used to form encapsulated CdS, ZnS, and PbS nanocrystals in SiO{sub 2} and Al{sub 2}O{sub 3} matrices. In SiO{sub 2}, nanoparticles are nearly spherical and randomly oriented, and ZnS and PbS nanocrystals exhibit a bimodal size distribution. In Al{sub 2}O{sub 3}, nanoparticles are faceted and coherent with the matrix. Initial photoluminescence (PL) results are presented.

  8. Aqueous oxidation reaction enabled layer-by-layer corrosion of semiconductor nanoplates into single-crystalline 2D nanocrystals with single layer accuracy and ionic surface capping.

    PubMed

    Ji, Muwei; Xu, Meng; Zhang, Jun; Liu, Jiajia; Zhang, Jiatao

    2016-02-25

    A controllable aqueous oxidation reaction enabled layer-by-layer corrosion has been proposed to prepare high-quality two-dimensional (2D) semiconductor nanocrystals with single layer accuracy and well-retained hexagonal shapes. The appropriate oxidizing agent, such as H2O2, Fe(NO3)3, and HNO3, could not only corrode the layered-crystalline-structured Bi2Te3 nanoplates layer-by-layer to be a single quintuple layer, but also replace the organic barriers to be ionic ligands on the surface synergistically. AFM analysis was used to confirm the layer-by-layer exfoliation from the side to the center. Together with precise XRD, LRTEM and HRTEM characterizations, the controllable oxidation reaction enabled aqueous layer-by-layer corrosion mechanism has been studied.

  9. Quantum Chemical Calculations of the Influence of Anchor-Cum-Spacer Groups on Femtosecond Electron Transfer Times in Dye-Sensitized Semiconductor Nanocrystals.

    PubMed

    Persson, P; Lundqvist, M J; Ernstorfer, R; Goddard, W A; Willig, F

    2006-03-01

    Electronic properties of dye-sensitized semiconductor nanocrystals, consisting of perylene (Pe) chromophores attached to 2 nm TiO2 nanocrystals via different anchor-cum-spacer groups, have been studied theoretically using density functional theory (DFT) cluster calculations. Approximate effective electronic coupling strengths for the heterogeneous electron-transfer interaction have been extracted from the calculated electronic structures and are used to estimate femtosecond electron-transfer times theoretically. Results are presented for perylenes attached to the TiO2 via formic acid (Pe-COOH), propionic acid (Pe-CH2-CH2-COOH), and acrylic acid (Pe-CH [Formula: see text] CH-COOH). The calculated electron transfer times are between 5 and 10 fs with the formic acid and the conjugated acrylic acid bridges and about 35 fs with the saturated propionic acid bridge. The calculated electron injection times are of the same order of magnitude as the corresponding experimental values and qualitatively follow the experimental trend with respect to the influence of the different substitutions on the injection times.

  10. Collision-induced dissociation of II-VI semiconductor nanocrystal precursors, Cd2+ and Zn2+ complexes with trioctylphosphine oxide, sulfide, and selenide.

    PubMed

    Min, Won Ja; Jung, Sunghan; Lim, Sung Jun; Kim, Yongwook; Shin, Seung Koo

    2009-09-03

    The metal (M = Cd2+ and Zn2+) complexes with trioctylphosphine chalcogenide (TOPE, E = O, S, and Se) are prepared by electrospray ionization, and their relative stabilities and intramolecular reactions are studied by collision-induced dissociation (CID) with Xe under single collision conditions. These metal-TOPE complexes are considered as molecular precursors for the colloidal synthesis of II-VI compound semiconductor nanocrystals employing TOPO as a metal-coordinating solvent and TOPS or TOPSe as a chalcogen precursor. Of the various [M + nTOPE]2+ (n = 2-7) ions generated by ESI, the n = 2-4 complexes are characterized by CID as a function of collision energy. The collision energy at 50% dissociation (E50%) is determined from the cracking curve and the relative stabilities of the complexes are established. Between the two metal ions, the zinc-TOPE complexes are more stable than the cadmium-TOPE complexes when n = 2-3, whereas their stabilities are reversed when n = 4. Of the TOPE, TOPO binds most strongly to the metal ion, while TOPSe does most weakly. Upon CID, loss of TOPE occurs exclusively from the tetra-TOPE complexes, while extensive fragmentation of TOPE takes place from the di-TOPE complexes, showing the signature of the metal chacogenide formation. The nucleation of nanocrystals appears to begin with cracking of [M + 2TOPE]2+ (E = S and Se).

  11. Enhanced magneto-optical properties of semiconductor EuS nanocrystals assisted by surface plasmon resonance of gold nanoparticles.

    PubMed

    Kawashima, Akira; Nakanishi, Takayuki; Shibayama, Tamaki; Watanabe, Seiichi; Fujita, Koji; Tanaka, Katsuhisa; Koizumi, Hitoshi; Fushimi, Koji; Hasegawa, Yasuchika

    2013-10-18

    Remarkable magneto-optical properties of a new isolator material, that is, europium sulfide nanocrystals with gold (EuS-Au nanosystem), has been demonstrated for a future photo-information technology. Attachment of gold particles that exhibit surface plasmon resonance leads to amplification of the magneto-optical properties of the EuS nanocrystals. To construct the EuS-Au nanosystems, cubic EuS and spherical Au nanocrystals have been joined by a variety of organic linkers, that is, 1,2-ethanedithiol (EDT), 1,6-hexanedithiol (HDT), 1,10-decanedithiol (DDT), 1,4-bisethanethionaphthalene (NpEDT), or 1,4-bisdecanethionaphthalene (NpDDT) . Formation of these systems was observed by XRD, TEM, and absorption spectra measurements. The magneto-optical properties of the EuS-Au nanosystem have been characterized by using Faraday rotation spectroscopy. The Faraday rotation angle of the EuS-Au nanosystem is dependent on the Au particle size and interparticle distance between EuS and Au nanocrystals. Enhancement of the Faraday rotation of EuS-Au nanosystems was observed. The spin configuration in the excited state of the EuS-Au nanosystem was also investigated using photo-assisted electron paramagnetic resonance.

  12. Spectroscopic analysis on metal-oxide-semiconductor light-emitting diodes with buried Si nanocrystals and nano-pyramids in SiO(x) film.

    PubMed

    Lin, Gong-Ru

    2008-03-01

    The difference between the white and near-infrared electroluminescence of metal-oxide-semiconductor light-emitting diodes fabricated on 1,100 degrees C-annealed Si-rich SiO(x)/p-Si substrate with interfacial pyramidal Si dots (Si nano-pyramids) was characterized. By changing the substrate temperature and induced coupled plasma power during the plasma enhanced chemical vapor deposition of Si-rich SiO(x) films, the effects of the growth conditions on the defect- and Si nano-pyramid-related carrier transport and Si nanocrystal-related electroluminescence spectroscopy were also investigated. The annealed Si-rich SiO(x)/p-Si films grown at higher synthesized substrate temperate (350 degrees C) show the larger Si nano-pyramids precipitating near the Si/SiO2 interface. The indium tin oxide/Si-rich SiO(x)/p-Si/Al metal-oxide-semiconductor light-emitting diodes with Si-rich SiO(x) films exhibit different white-light electroluminescence spectra at wavelengths from 400 to 650 nm. The Si nanocrystal-related electroluminescence spectra at 650-850 nm are confirmed, whereas the electroluminescence spectra are shorter wavelengths is attributed to oxygen related defects. These defects become an electron-preferred transporting path within the Si-rich SiO(x) film, whose densities are decreased by increasing the substrate temperature or reducing the induced coupled plasma power. Defect-related white-light electroluminescence emits power for a relatively short lifetime. The lifetime can be lengthened and the electroluminescence power can be raised simultaneously by increasing deposition temperature to 350 degrees C and adjusting the induced coupled plasma power to a threshold of 30 W, which effectively increases the densities of Si nanocrystals and nano-pyramids in the Si-rich SiO(x) film with Si concentration of up to 40 at%. A nearly defect-free Si-rich SiO(x) sample can be grown under such conditions, which contributes to the most stable and largest near-infrared electroluminescence

  13. Nanocrystals for electronics.

    PubMed

    Panthani, Matthew G; Korgel, Brian A

    2012-01-01

    Semiconductor nanocrystals are promising materials for low-cost large-area electronic device fabrication. They can be synthesized with a wide variety of chemical compositions and size-tunable optical and electronic properties as well as dispersed in solvents for room-temperature deposition using various types of printing processes. This review addresses research progress in large-area electronic device applications using nanocrystal-based electrically active thin films, including thin-film transistors, light-emitting diodes, photovoltaics, and thermoelectrics.

  14. Design of a multi-coordinating polymer as a platform for functionalizing metal, metal oxide and semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Wang, Wentao; Ji, Xin; Kapur, Anshika; Mattoussi, Hedi

    2016-03-01

    We introduce a new set of amphiphilic polymers as multifunctional, metal-coordinating ligands adapted to surfacefunctionalize quantum dots (QDs), iron oxide nanoparticles (IONPs) and gold nanoparticles/nanorods (AuNPs/AuNRs). The ligand design relies on the introduction of several anchoring groups, hydrophilic moieties and reactive functionalities into a polymer chain, via one-step nucleophilic addition reaction. Such synthetic scheme also allows the insertion of target biomolecules during the ligand synthesis. This functionalization strategy yields nanocrystals that exhibit long-term colloidal stability over a broad range of biological conditions, such as pH changes and when mixed with growth media. When zwitterion groups are used as hydrophilic motifs, this provides compact nanocrystals that are compatible with conjugation to proteins via metal-polyhistidine self-assembly. In addition, we show that QDs ligated with these polymers can engage in energy or charge transfer interactions. Furthermore, nanocrystals coated with folic acid-modified polymers could promote the delivery of nanoparticle-conjugates into cancer cells via folate receptormediated endocytosis.

  15. LDRD-LW Final Report: 07-LW-041 "Magnetism in Semiconductor Nanocrystals: New Physics at the Nanoscale"

    SciTech Connect

    Meulenberg, R W; Lee, J I; McCall, S K

    2009-10-19

    The work conducted in this project was conducted with the aim of identifying and understanding the origin and mechanisms of magnetic behavior in undoped semiconductor nanocrystals (NCs), specifically those composed of CdSe. It was anticipated that the successful completion of this task would have the effect of addressing and resolving significant controversy over this topic in the literature. Meanwhile, application of the resultant knowledge was expected to permit manipulation of the magnetic properties, particularly the strength of any magnetic effects, which is of potential relevance in a range of advanced technologies. More specifically, the project was designed and research conducted with the goal of addressing the following series of questions: (1) How does the magnitude of the magnetism in CdSe NCs change with the organic molecules used to passivate their surface the NC size? i.e. Is the magnetism an intrinsic effect in the nanocrystalline CdSe (as observed for Au NCs) or a surface termination driven effect? (2) What is the chemical (elemental) nature of the magnetism? i.e. Are the magnetic effects associated with the Cd atoms or the Se atoms or both? (3) What is/are the underlying mechanism(s)? (4) How can the magnetism be controlled for further applications? To achieve this goal, several experimental/technical milestones were identified to be fulfilled during the course of the research: (A) The preparation of well characterized CdSe NCs with varying surface termination (B) Establishing the extent of the magnetism of these NCs using magnetometry (particularly using superconducting interference device [SQUID]) (C) Establishing the chemical nature of the magnetism using x-ray magnetic circular dichroism (XMCD) - the element specific nature of the technique allows identification of the element responsible for the magnetism (D) Identification of the effect of surface termination on the empty densities of states (DOS) using x-ray absorption spectroscopy (XAS

  16. Nanocrystal diffusion doping.

    PubMed

    Vlaskin, Vladimir A; Barrows, Charles J; Erickson, Christian S; Gamelin, Daniel R

    2013-09-25

    A diffusion-based synthesis of doped colloidal semiconductor nanocrystals is demonstrated. This approach involves thermodynamically controlled addition of both impurity cations and host anions to preformed seed nanocrystals under equilibrium conditions, rather than kinetically controlled doping during growth. This chemistry allows thermodynamic crystal compositions to be prepared without sacrificing other kinetically trapped properties such as shape, size, or crystallographic phase. This doping chemistry thus shares some similarities with cation-exchange reactions, but proceeds without the loss of host cations and excels at the introduction of relatively unreactive impurity ions that have not been previously accessible using cation exchange. Specifically, we demonstrate the preparation of Cd(1-x)Mn(x)Se (0 ≤ x ≤ ∼0.2) nanocrystals with narrow size distribution, unprecedentedly high Mn(2+) content, and very large magneto-optical effects by diffusion of Mn(2+) into seed CdSe nanocrystals grown by hot injection. Controlling the solution and lattice chemical potentials of Cd(2+) and Mn(2+) allows Mn(2+) diffusion into the internal volumes of the CdSe nanocrystals with negligible Ostwald ripening, while retaining the crystallographic phase (wurtzite or zinc blende), shape anisotropy, and ensemble size uniformity of the seed nanocrystals. Experimental results for diffusion doping of other nanocrystals with other cations are also presented that indicate this method may be generalized, providing access to a variety of new doped semiconductor nanostructures not previously attainable by kinetic routes or cation exchange.

  17. Enhanced photophysical properties of plasmonic magnetic metal-alloyed semiconductor heterostructure nanocrystals: a case study for the Ag@Ni/Zn1-xMgxO system.

    PubMed

    Paul, Sumana; Ghosh, Sirshendu; Saha, Manas; De, S K

    2016-05-14

    Understanding the effect of homovalent cation alloying in wide band gap ZnO and the formation of metal-semiconductor heterostructures is very important for maximisation of the photophysical properties of ZnO. Nearly monodisperse ZnO nanopyramid and Mg alloyed ZnO nanostructures have been successfully synthesized by one pot decomposition of metal stearate by using oleylamine both as activating and capping agent. The solid solubility of Mg(ii) ions in ZnO is limited to ∼30% without phase segregation. An interesting morphology change is found on increasing Mg alloying: from nanopyramids to self-assembled nanoflowers. The morphology change is explained by the oriented attachment process. The introduction of Mg into the ZnO matrix increases the band gap of the materials and also generates new zinc interstitial (Zni) and oxygen vacancy related defects. Plasmonic magnetic Ag@Ni core-shell (Ag as core and Ni as shell) nanocrystals are used as a seed material to synthesize Ag@Ni/Zn1-xMgxO complex heterostructures. Epitaxial growth is established between Ag(111) and ZnO(110) planes in the heterostructure. An epitaxial metal-semiconductor interface is very crucial for complete electron-hole (e-h) separation and enhancement of the exciton lifetime. The alloyed semiconductor-metal heterostructure is observed to be highly photocatalytically active for dye degradation as well as photodetection. Incorporation of magnetic Ni(0) makes the photocatalyst superparamagnetic at room temperature which is found to be helpful for catalyst regeneration.

  18. Enhanced photovoltaic performance of ultrathin Si solar cells via semiconductor nanocrystal sensitization: Energy transfer vs. optical coupling effects

    DOE PAGES

    Hoang, Son; Ashraf, Ahsan; Eisaman, Matthew D.; ...

    2015-12-07

    Excitonic energy transfer (ET) offers exciting opportunities for advances in optoelectronic devices such as solar cells. While recent experimental attempts have demonstrated its potential in both organic and inorganic photovoltaics (PVs), what remains to be addressed is quantitative understanding of how different ET modes contribute to PV performance and how ET contribution is differentiated from the classical optical coupling (OC) effects. In this study, we implement an ET scheme using a PV device platform, comprising CdSe/ZnS nanocrystal energy donor and 500 nm-thick ultrathin Si acceptor layers, and present the quantitative mechanistic description of how different ET modes, distinguished from themore » OC effects, increase the light absorption and PV efficiency. We find that nanocrystal sensitization enhances the short circuit current of ultrathin Si solar cells by up to 35%, of which the efficient ET, primarily driven by a long-range radiative mode, contributes to 38% of the total current enhancement. Lastly, these results not only confirm the positive impact of ET but also provide a guideline for rationally combining the ET and OC effects for improved light harvesting in PV and other optoelectronic devices.« less

  19. Enhanced photovoltaic performance of ultrathin Si solar cells via semiconductor nanocrystal sensitization: energy transfer vs. optical coupling effects.

    PubMed

    Hoang, Son; Ashraf, Ahsan; Eisaman, Matthew D; Nykypanchuk, Dmytro; Nam, Chang-Yong

    2016-03-21

    Excitonic energy transfer (ET) offers exciting opportunities for advances in optoelectronic devices such as solar cells. While recent experimental attempts have demonstrated its potential in both organic and inorganic photovoltaics (PVs), what remains to be addressed is quantitative understanding of how different ET modes contribute to PV performance and how ET contribution is differentiated from the classical optical coupling (OC) effects. In this study, we implement an ET scheme using a PV device platform, comprising CdSe/ZnS nanocrystal energy donor and 500 nm-thick ultrathin Si acceptor layers, and present the quantitative mechanistic description of how different ET modes, distinguished from the OC effects, increase the light absorption and PV efficiency. We find that nanocrystal sensitization enhances the short circuit current of ultrathin Si solar cells by up to 35%, of which the efficient ET, primarily driven by a long-range radiative mode, contributes to 38% of the total current enhancement. These results not only confirm the positive impact of ET but also provide a guideline for rationally combining the ET and OC effects for improved light harvesting in PV and other optoelectronic devices.

  20. Chemical design of nanocrystal solids.

    PubMed

    Kovalenko, Maksym V

    2013-01-01

    This account highlights our recent and present activities dedicated to chemical synthesis and applications of inorganic nanostructures. In particular, we discuss the potential of metal amides as precursors in the synthesis of metallic and semiconductor nanocrystals. We show the importance of surface chemical functionalization for the emergence of collective electronic properties in nanocrystal solids. We also demonstrate a new kind of long-range ordered, crystalline matter comprising colloidal nanocrystals and atomically defined inorganic clusters. Finally, we point the reader's attention to the high potential benefits of size- and shape-tunability of nanocrystals for achieving higher performance of rechargeable Li-ion battery electrodes.

  1. Absorption properties of one- and two-dimensional semiconductor nanocrystals in the presence of an electric field

    NASA Astrophysics Data System (ADS)

    Tepliakov, N. V.; Leonov, M. Yu.; Baranov, A. V.; Fedorov, A. V.; Rukhlenko, I. D.

    2017-01-01

    We have considered the broadening of optical absorption spectra of ensembles of randomly oriented nanorods and nanoplatelets that is caused by the action of a static electric field. It has been found that the linewidth in the spectra of the considered nanocrystals depends nonlinearly on the field strength and attains saturation in fields on the order of 100 kV/cm. We show that, due to a weak confinement, the electrooptical response of nanoplatelets is stronger than that of nanorods, which leads to a number of distinctive features in the field-induced broadening of the spectra of nanoplatelets and gives grounds to state that nanoplatelets are the most promising objects for use in electrooptical devices.

  2. Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO2 by capacitance voltage measurement on inverted metal oxide semiconductor structure

    NASA Astrophysics Data System (ADS)

    Zhang, Tian; Puthen-Veettil, Binesh; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-10-01

    We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO2. The ncSi thin films with high resistivity (200-400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO2/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 1018-1019 cm-3 despite their high resistivity. The saturation of doping at about 1.4 × 1019 cm-3 and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10-3 cm2/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

  3. Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO{sub 2} by capacitance voltage measurement on inverted metal oxide semiconductor structure

    SciTech Connect

    Zhang, Tian Puthen-Veettil, Binesh; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-10-21

    We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO{sub 2}. The ncSi thin films with high resistivity (200–400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO{sub 2}/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 10{sup 18}–10{sup 19 }cm{sup −3} despite their high resistivity. The saturation of doping at about 1.4 × 10{sup 19 }cm{sup −3} and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10{sup −3} cm{sup 2}/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

  4. Sorting fluorescent nanocrystals with DNA

    SciTech Connect

    Gerion, Daniele; Parak, Wolfgang J.; Williams, Shara C.; Zanchet, Daniela; Micheel, Christine M.; Alivisatos, A. Paul

    2001-12-10

    Semiconductor nanocrystals with narrow and tunable fluorescence are covalently linked to oligonucleotides. These biocompounds retain the properties of both nanocrystals and DNA. Therefore, different sequences of DNA can be coded with nanocrystals and still preserve their ability to hybridize to their complements. We report the case where four different sequences of DNA are linked to four nanocrystal samples having different colors of emission in the range of 530-640 nm. When the DNA-nanocrystal conjugates are mixed together, it is possible to sort each type of nanoparticle using hybridization on a defined micrometer -size surface containing the complementary oligonucleotide. Detection of sorting requires only a single excitation source and an epifluorescence microscope. The possibility of directing fluorescent nanocrystals towards specific biological targets and detecting them, combined with their superior photo-stability compared to organic dyes, opens the way to improved biolabeling experiments, such as gene mapping on a nanometer scale or multicolor microarray analysis.

  5. 3D assembly of semiconductor and metal nanocrystals: hybrid CdTe/Au structures with controlled content.

    PubMed

    Lesnyak, Vladimir; Wolf, André; Dubavik, Aliaksei; Borchardt, Lars; Voitekhovich, Sergei V; Gaponik, Nikolai; Kaskel, Stefan; Eychmüller, Alexander

    2011-08-31

    A 3D metal ion assisted assembly of nanoparticles has been developed. The approach relies on the efficient complexation of cadmium ions and 5-mercaptomethyltetrazole employed as the stabilizer of both colloidal CdTe and Au nanoparticles. It enables in a facile way the formation of hybrid metal-semiconductor 3D structures with controllable and tunable composition in aqueous media. By means of critical point drying, these assemblies form highly porous aerogels. The hybrid architectures obtained are characterized by electron microscopy, nitrogen adsorption, and optical spectroscopy methods.

  6. Substitutional doping in nanocrystal superlattices

    NASA Astrophysics Data System (ADS)

    Cargnello, Matteo; Johnston-Peck, Aaron C.; Diroll, Benjamin T.; Wong, Eric; Datta, Bianca; Damodhar, Divij; Doan-Nguyen, Vicky V. T.; Herzing, Andrew A.; Kagan, Cherie R.; Murray, Christopher B.

    2015-08-01

    Doping is a process in which atomic impurities are intentionally added to a host material to modify its properties. It has had a revolutionary impact in altering or introducing electronic, magnetic, luminescent, and catalytic properties for several applications, for example in semiconductors. Here we explore and demonstrate the extension of the concept of substitutional atomic doping to nanometre-scale crystal doping, in which one nanocrystal is used to replace another to form doped self-assembled superlattices. Towards this goal, we show that gold nanocrystals act as substitutional dopants in superlattices of cadmium selenide or lead selenide nanocrystals when the size of the gold nanocrystal is very close to that of the host. The gold nanocrystals occupy random positions in the superlattice and their density is readily and widely controllable, analogous to the case of atomic doping, but here through nanocrystal self-assembly. We also show that the electronic properties of the superlattices are highly tunable and strongly affected by the presence and density of the gold nanocrystal dopants. The conductivity of lead selenide films, for example, can be manipulated over at least six orders of magnitude by the addition of gold nanocrystals and is explained by a percolation model. As this process relies on the self-assembly of uniform nanocrystals, it can be generally applied to assemble a wide variety of nanocrystal-doped structures for electronic, optical, magnetic, and catalytic materials.

  7. Can high pressure I-II transitions in semiconductors be affected by plastic flow and nanocrystal precipitation in phase I?

    NASA Astrophysics Data System (ADS)

    Weinstein, B. A.; Lindberg, G. P.

    Pressure-Raman spectroscopy in ZnSe and ZnTe single crystals reveals that Se and Te nano-crystals (NCs) precipitate in these II-VI hosts for pressures far below their I-II phase transitions. The inclusions are evident from the appearance and negative pressure-shift of the A1 Raman peaks of Se and Te (trigonal phase). The Se and Te NCs nucleate at dislocations and grain boundaries that arise from pressure-induced plastic flow. This produces chemical and structural inhomogeneities in the zincblende phase of the host. At substantially higher pressures, the I-II transition proceeds in the presence of these inhomogenities. This can affect the transition's onset pressure Pt and width ΔPt, and the occurrence of metastable phases along the transition path. Precipitation models in metals show that nucleation of inclusions depends on the Peierls stress τp and a parameter α related to the net free energy gained on nucleation. For favorable values of τp and α, NC precipitation at pressures below the I-II transition could occur in other compounds. We propose criteria to judge whether this is likely based on the observed ranges of τp in the hosts, and estimates of α derived from the cohesive energy densities of the NC materials. One finds trends that can serve as a useful guide, both to test the proposed criteria, and to decide when closer scrutiny of phase transition experiments is warranted, e.g., in powders where high dislocation densities are initially created

  8. Composite material including nanocrystals and methods of making

    DOEpatents

    Bawendi, Moungi G.; Sundar, Vikram C.

    2010-04-06

    Temperature-sensing compositions can include an inorganic material, such as a semiconductor nanocrystal. The nanocrystal can be a dependable and accurate indicator of temperature. The intensity of emission of the nanocrystal varies with temperature and can be highly sensitive to surface temperature. The nanocrystals can be processed with a binder to form a matrix, which can be varied by altering the chemical nature of the surface of the nanocrystal. A nanocrystal with a compatibilizing outer layer can be incorporated into a coating formulation and retain its temperature sensitive emissive properties.

  9. Composite material including nanocrystals and methods of making

    DOEpatents

    Bawendi, Moungi G [Boston, MA; Sundar, Vikram C [New York, NY

    2008-02-05

    Temperature-sensing compositions can include an inorganic material, such as a semiconductor nanocrystal. The nanocrystal can be a dependable and accurate indicator of temperature. The intensity of emission of the nanocrystal varies with temperature and can be highly sensitive to surface temperature. The nanocrystals can be processed with a binder to form a matrix, which can be varied by altering the chemical nature of the surface of the nanocrystal. A nanocrystal with a compatibilizing outer layer can be incorporated into a coating formulation and retain its temperature sensitive emissive properties

  10. Recent developments of hybrid nanocrystal/polymer bulk heterojunction solar cells.

    PubMed

    Tang, Aiwei; Qu, Shengchun; Teng, Feng; Hou, Yanbing; Wang, Yongsheng; Wang, Zhanguo

    2011-11-01

    Hybrid nanocrystal/polymer bulk heterojunction (BHJ) solar cells consisting of colloidal inorganic semiconductor nanocrystals as electron acceptors and conjugated polymers as electron donors have been extensively investigated in the past few decades, which take advantage of the strongpoints of the inorganic semiconductor nanocrystals and the conjugated polymers. Currently, power conversion efficiency over 3% for the hybrid nanocrystal/polymer BHJ solar cells has been achieved. Although the development of hybrid nanocrystal/polymer BHJ solar cells lacks behind the international level, great progress in this research field has been made in China. In this article, we first review the general fabrication techniques and general working principles of hybrid nanocrystal/polymer BHJ solar cells. Secondly, we highlight the international and national developments of hybrid nanocrystal/polymer BHJ solar cells based on different types of semiconductor nanocrystals and conjugated polymers. Finally, we give a future outlook for the hybrid nanocrystal/polymer BHJ solar cells in the worldwide.

  11. Biomolecular Assembly of Gold Nanocrystals

    SciTech Connect

    Micheel, Christine Marya

    2005-05-20

    Over the past ten years, methods have been developed to construct discrete nanostructures using nanocrystals and biomolecules. While these frequently consist of gold nanocrystals and DNA, semiconductor nanocrystals as well as antibodies and enzymes have also been used. One example of discrete nanostructures is dimers of gold nanocrystals linked together with complementary DNA. This type of nanostructure is also known as a nanocrystal molecule. Discrete nanostructures of this kind have a number of potential applications, from highly parallel self-assembly of electronics components and rapid read-out of DNA computations to biological imaging and a variety of bioassays. My research focused in three main areas. The first area, the refinement of electrophoresis as a purification and characterization method, included application of agarose gel electrophoresis to the purification of discrete gold nanocrystal/DNA conjugates and nanocrystal molecules, as well as development of a more detailed understanding of the hydrodynamic behavior of these materials in gels. The second area, the development of methods for quantitative analysis of transmission electron microscope data, used computer programs written to find pair correlations as well as higher order correlations. With these programs, it is possible to reliably locate and measure nanocrystal molecules in TEM images. The final area of research explored the use of DNA ligase in the formation of nanocrystal molecules. Synthesis of dimers of gold particles linked with a single strand of DNA possible through the use of DNA ligase opens the possibility for amplification of nanostructures in a manner similar to polymerase chain reaction. These three areas are discussed in the context of the work in the Alivisatos group, as well as the field as a whole.

  12. Direct Binding of Fluorescent CdSe-ZnS Core shell Semiconductor Nanocrystals to Biological Macromolecules: Efficient Tool for Fluorescence Tagging of Biological Macromolecules

    NASA Astrophysics Data System (ADS)

    Mattoussi, Hedi; Anderson, George P.; Mauro, J. Matthew; Goldman, Ellen R.

    2000-03-01

    We present a study that describes a novel and direct approach of binding highly luminescent CdSe-ZnS core-shell nanocrystals to biological molecules for use as fluorescent probes in biosensing and diagnostics. We use dithiol-based groups as the surface capping agent, which provides nanocrystal dispersions with high quantum yield. The approach makes use of a recombinant protein, which binds directly to the dithiol cap, and provides addition stability of the quantum dots in water solutions. Hence stable and highly luminescent bound nanocrystal-biomolecules have been prepared. The present process provides aggregation-free solutions with a high luminescence yield. Combining the properties of the CdSe-ZnS (photochemical stability and wide range of emission wavelengths) and the simple binding approach, the resultant materials provide a sensitive and powerful tool for tagging of biological molecules. We will discuss the chemistry involved and present various characterization studies of these complex systems, such as photoluminescence spectroscopy, high-resolution microscopy. We will also discuss the use of these materials in immunoassays.

  13. Size-Dependent Raman Shifts for nanocrystals

    PubMed Central

    Gao, Yukun; Zhao, Xinmei; Yin, Penggang; Gao, Faming

    2016-01-01

    Raman spectroscopy is a very sensitive tool for probing semiconductor nanocrystals. The underlying mechanism behind the size-dependent Raman shifts is still quite controversial. Here we offer a new theoretical method for the quantum confinement effects on the Raman spectra of semiconductor nanocrystals. We propose that the shift of Raman spectra in nanocrystals can result from two overlapping effects: the quantum effect shift and surface effect shift. The quantum effect shift is extracted from an extended Kubo formula, the surface effect shift is determined via the first principles calculations. Fairly good prediction of Raman shifts can be obtained without the use of any adjustable parameter. Closer analysis shows that the size-dependent Raman shifts in Si nanocrystals mainly result from the quantum effect shifts. For nanodiamond, the proportion of surface effect shift in Raman shift is up to about 40%. Such model can also provide a good baseline for using Raman spectroscopy as a tool to measure size. PMID:27102066

  14. Artificial atoms on semiconductor surfaces

    PubMed Central

    Tisdale, W. A.; Zhu, X.-Y.

    2011-01-01

    Semiconductor nanocrystals are called artificial atoms because of their atom-like discrete electronic structure resulting from quantum confinement. Artificial atoms can also be assembled into artificial molecules or solids, thus, extending the toolbox for material design. We address the interaction of artificial atoms with bulk semiconductor surfaces. These interfaces are model systems for understanding the coupling between localized and delocalized electronic structures. In many perceived applications, such as nanoelectronics, optoelectronics, and solar energy conversion, interfacing semiconductor nanocrystals to bulk materials is a key ingredient. Here, we apply the well established theories of chemisorption and interfacial electron transfer as conceptual frameworks for understanding the adsorption of semiconductor nanocrystals on surfaces, paying particular attention to instances when the nonadiabatic Marcus picture breaks down. We illustrate these issues using recent examples from our laboratory. PMID:21097704

  15. Electric field dependent spectroscopy of single nanocrystal systems

    NASA Astrophysics Data System (ADS)

    LeBlanc, Sharonda L. Johnson

    A suite of single molecule spectroscopic techniques and data analysis methods were implemented to explore the complex role of electric fields in single semiconductor nanocrystal photophysics. This dissertation spans the synthesis, characterization, biological applications, and photophysics of semiconductor nanocrystals. The core single molecule techniques employed in the current work include time-resolved fluorescence, time-correlated single photon counting, single molecule spectroscopy, and photon correlation spectroscopy. Various electrode devices were patterned to investigate the optical properties of single nanocrystal systems under an applied electric field. Electric field dependent spectroscopy and data analysis have revealed distributed kinetics and multiple charging of nanocrystals. In addition, interactions of nanocrystal excited states with plasmonic gold films have revealed strong enhancement of multiple exciton emission from single nanocrystals, and control by an applied electric field. The broader implications of this work can be extended to bioimaging, light harvesting, electro-optics, and lasing technologies.

  16. Measuring the Valence of Nanocrystal Surfaces

    SciTech Connect

    Owen, Jonathan Scharle

    2016-11-30

    The goal of this project is to understand and control the interplay between nanocrystal stoichiometry, surface ligand binding and exchange, and the optoelectronic properties of semiconductor nanocrystals in solution and in thin solid films. We pursued three research directions with this goal in mind: 1) We characterized nanocrystal stoichiometry and its influence on the binding of L-type and X-type ligands, including the thermodynamics of binding and the kinetics of ligand exchange. 2) We developed a quantitative understanding of the relationship between surface ligand passivation and photoluminescence quantum yield. 3) We developed methods to replace the organic ligands on the nanocrystal with halide ligands and controllably deposit these nanocrystals into thin films, where electrical measurements were used to investigate the electrical transport and internanocrystal electronic coupling.

  17. Enhanced photovoltaic performance of ultrathin Si solar cells via semiconductor nanocrystal sensitization: Energy transfer vs. optical coupling effects

    SciTech Connect

    Hoang, Son; Ashraf, Ahsan; Eisaman, Matthew D.; Nykypanchuk, Dmytro; Nam, Chang -Yong

    2015-12-07

    Excitonic energy transfer (ET) offers exciting opportunities for advances in optoelectronic devices such as solar cells. While recent experimental attempts have demonstrated its potential in both organic and inorganic photovoltaics (PVs), what remains to be addressed is quantitative understanding of how different ET modes contribute to PV performance and how ET contribution is differentiated from the classical optical coupling (OC) effects. In this study, we implement an ET scheme using a PV device platform, comprising CdSe/ZnS nanocrystal energy donor and 500 nm-thick ultrathin Si acceptor layers, and present the quantitative mechanistic description of how different ET modes, distinguished from the OC effects, increase the light absorption and PV efficiency. We find that nanocrystal sensitization enhances the short circuit current of ultrathin Si solar cells by up to 35%, of which the efficient ET, primarily driven by a long-range radiative mode, contributes to 38% of the total current enhancement. Lastly, these results not only confirm the positive impact of ET but also provide a guideline for rationally combining the ET and OC effects for improved light harvesting in PV and other optoelectronic devices.

  18. Hybrid pn-junction solar cells based on layers of inorganic nanocrystals and organic semiconductors: optimization of layer thickness by considering the width of the depletion region.

    PubMed

    Saha, Sudip K; Guchhait, Asim; Pal, Amlan J

    2014-03-07

    We report the formation and characterization of hybrid pn-junction solar cells based on a layer of copper diffused silver indium disulfide (AgInS2@Cu) nanoparticles and another layer of copper phthalocyanine (CuPc) molecules. With copper diffusion in the nanocrystals, their optical absorption and hence the activity of the hybrid pn-junction solar cells was extended towards the near-IR region. To decrease the particle-to-particle separation for improved carrier transport through the inorganic layer, we replaced the long-chain ligands of copper-diffused nanocrystals in each monolayer with short-ones. Under illumination, the hybrid pn-junctions yielded a higher short-circuit current as compared to the combined contribution of the Schottky junctions based on the components. A wider depletion region at the interface between the two active layers in the pn-junction device as compared to that of the Schottky junctions has been considered to analyze the results. Capacitance-voltage characteristics under a dark condition supported such a hypothesis. We also determined the width of the depletion region in the two layers separately so that a pn-junction could be formed with a tailored thickness of the two materials. Such a "fully-depleted" device resulted in an improved photovoltaic performance, primarily due to lessening of the internal resistance of the hybrid pn-junction solar cells.

  19. Synthesis and Doping of Silicon Nanocrystals for Versatile Nanocrystal Inks

    NASA Astrophysics Data System (ADS)

    Kramer, Nicolaas Johannes

    The impact of nanotechnology on our society is getting larger every year. Electronics are becoming smaller and more powerful, the "Internet of Things" is all around us, and data generation is increasing exponentially. None of this would have been possible without the developments in nanotechnology. Crystalline semiconductor nanoparticles (nanocrystals) are one of the latest developments in the field of nanotechnology. This thesis addresses three important challenges for the transition of silicon nanocrystals from the lab bench to the marketplace: A better understanding of the nanocrystal synthesis was obtained, the electronic properties of the nanocrystals were characterized and tuned, and novel silicon nanocrystal inks were formed and applied using simple coating technologies. Plasma synthesis of nanocrystals has numerous advantages over traditional solution-based synthesis methods. While the formation of nanoparticles in low pressure nonthermal plasmas is well known, the heating mechanism leading to their crystallization is poorly understood. A combination of comprehensive plasma characterization with a nanoparticle heating model presented here reveals the underlying plasma physics leading to crystallization. The model predicts that the nanoparticles reach temperatures as high as 900 K in the plasma as a result of heating reactions on the nanoparticle surface. These temperatures are well above the gas temperature and sufficient for complete nanoparticle crystallization. Moving the field of plasma nanoparticle synthesis to atmospheric pressures is important for lowering its cost and making the process attractive for industrial applications. The heating and charging model for silicon nanoparticles was adapted in Chapter 3 to study plasmas maintained over a wide range of pressures (10 -- 105 Pa). The model considers three collisionality regimes and determines the dominant contribution of each regime under various plasma conditions. Strong nanoparticle cooling at

  20. The Surface Chemistry of Metal Chalcogenide Nanocrystals

    NASA Astrophysics Data System (ADS)

    Anderson, Nicholas Charles

    The surface chemistry of metal chalcogenide nanocrystals is explored through several interrelated analytical investigations. After a brief discussion of the nanocrystal history and applications, molecular orbital theory is used to describe the electronic properties of semiconductors, and how these materials behave on the nanoscale. Quantum confinement plays a major role in dictating the optical properties of metal chalcogenide nanocrystals, however surface states also have an equally significant contribution to the electronic properties of nanocrystals due to the high surface area to volume ratio of nanoscale semiconductors. Controlling surface chemistry is essential to functionalizing these materials for biological imaging and photovoltaic device applications. To better understand the surface chemistry of semiconducting nanocrystals, three competing surface chemistry models are presented: 1.) The TOPO model, 2.) the Non-stoichiometric model, and 3.) the Neutral Fragment model. Both the non-stoichiometric and neutral fragment models accurately describe the behavior of metal chalcogenide nanocrystals. These models rely on the covalent bond classification system, which divides ligands into three classes: 1.) X-type, 1-electron donating ligands that balance charge with excess metal at the nanocrystal surface, 2.) L-type, 2-electron donors that bind metal sites, and 3.) Z-type, 2-electron acceptors that bind chalcogenide sites. Each of these ligand classes is explored in detail to better understand the surface chemistry of metal chalcogenide nanocrystals. First, chloride-terminated, tri-n-butylphosphine (Bu 3P) bound CdSe nanocrystals were prepared by cleaving carboxylate ligands from CdSe nanocrystals with chlorotrimethylsilane in Bu3P solution. 1H and 31P{1H} nuclear magnetic resonance spectra of the isolated nanocrystals allowed assignment of distinct signals from several free and bound species, including surface-bound Bu3P and [Bu3P-H]+[Cl]- ligands as well as a Bu

  1. Infrared colloidal lead chalcogenide nanocrystals: synthesis, properties, and photovoltaic applications.

    PubMed

    Fu, Huiying; Tsang, Sai-Wing

    2012-04-07

    Simple solution phase, catalyst-free synthetic approaches that offer monodispersed, well passivated, and non-aggregated colloidal semiconductor nanocrystals have presented many research opportunities not only for fundamental science but also for technological applications. The ability to tune the electrical and optical properties of semiconductor nanocrystals by manipulating the size and shape of the crystals during the colloidal synthesis provides potential benefits to a variety of applications including photovoltaic devices, light-emitting diodes, field effect transistors, biological imaging/labeling, and more. Recent advances in the synthesis and characterization of colloidal lead chalcogenide nanocrystals and the achievements in colloidal PbS or PbSe nanocrystals solar cells have demonstrated the promising application of infrared-emitting colloidal lead chalcogenide nanocrystals in photovoltaic devices. Here, we review recent progress in the synthesis and optical properties of colloidal lead chalcogenide nanocrystals. We focus in particular upon the size- and shape-controlled synthesis of PbS, PbSe, and PbTe nanocrystals by using different precursors and various stabilizing surfactants for the growth of the colloidal nanocrystals. We also summarize recent advancements in the field of colloidal nanocrystals solar cells based on colloidal PbS and PbSe nanocrystals. This journal is © The Royal Society of Chemistry 2012

  2. Multifunctional nanocrystals

    DOEpatents

    Klimov, Victor I.; Hollingsworth, Jennifer A.; Crooker, Scott A.; Kim, Hyungrak

    2010-06-22

    Multifunctional nanocomposites are provided including a core of either a magnetic material or an inorganic semiconductor, and, a shell of either a magnetic material or an inorganic semiconductor, wherein the core and the shell are of differing materials, such multifunctional nanocomposites having multifunctional properties including magnetic properties from the magnetic material and optical properties from the inorganic semiconductor material. Various applications of such multifunctional nanocomposites are also provided.

  3. Multifunctional nanocrystals

    DOEpatents

    Klimov, Victor I.; Hollingsworth, Jennifer A.; Crooker, Scott A.; Kim, Hyungrak

    2007-08-28

    Multifunctional nanocomposites are provided including a core of either a magnetic material or an inorganic semiconductor, and, a shell of either a magnetic material or an inorganic semiconductor, wherein the core and the shell are of differing materials, such multifunctional nanocomposites having multifunctional properties including magnetic properties from the magnetic material and optical properties from the inorganic semiconductor material. Various applications of such multifunctional nanocomposites are also provided.

  4. Patterning nanocrystals using DNA

    SciTech Connect

    Williams, Shara Carol

    2003-01-01

    One of the goals of nanotechnology is to enable programmed self-assembly of patterns made of various materials with nanometer-sized control. This dissertation describes the results of experiments templating arrangements of gold and semiconductor nanocrystals using 2'-deoxyribonucleic acid (DNA). Previously, simple DNA-templated linear arrangements of two and three nanocrystals structures have been made.[1] Here, we have sought to assemble larger and more complex nanostructures. Gold-DNA conjugates with 50 to 100 bases self-assembled into planned arrangements using strands of DNA containing complementary base sequences. We used two methods to increase the complexity of the arrangements: using branched synthetic doublers within the DNA covalent backbone to create discrete nanocrystal groupings, and incorporating the nanocrystals into a previously developed DNA lattice structure [2][3] that self-assembles from tiles made of DNA double-crossover molecules to create ordered nanoparticle arrays. In the first project, the introduction of a covalently-branched synthetic doubler reagent into the backbone of DNA strands created a branched DNA ''trimer.'' This DNA trimer templated various structures that contained groupings of three and four gold nanoparticles, giving promising, but inconclusive transmission electron microscopy (TEM) results. Due to the presence of a variety of possible structures in the reaction mixtures, and due to the difficulty of isolating the desired structures, the TEM and gel electrophoresis results for larger structures having four particles, and for structures containing both 5 and 10 nm gold nanoparticles were inconclusive. Better results may come from using optical detection methods, or from improved sample preparation. In the second project, we worked toward making two-dimensional ordered arrays of nanocrystals. We replicated and improved upon previous results for making DNA lattices, increasing the size of the lattices to a length greater than

  5. Self-assembly of lead chalcogenide nanocrystals.

    PubMed

    Quan, Zewei; Valentin-Bromberg, Loriana; Loc, Welley Siu; Fang, Jiye

    2011-05-02

    This review focuses on recent developments in the self-assembly of lead chalcogenide nanocrystals into two- and three-dimensional superstructures. Self-assembly is categorized by the shapes of building blocks, including nanospheres, nanocubes, nano-octahedra, and nanostars. In the section on nanospheres, rapid assemblies of lead chalcogenide-based multicomponent nanocrystals with additional components, such as semiconductors, noble metals, and magnetic nanocrystals, are further highlighted. In situ self-assembly of lead chalcogenide nanocrystals into one-dimensional nanostructures at elevated temperatures is also covered. Each section of this paper highlights examples extracted from recent publications. Finally, relatively novel properties and applications arising from lead chalcogenide superlattices as typical examples are also discussed.

  6. Pyrite Nanocrystal Solar Cells: Promising, or Fool's Gold?

    PubMed

    Steinhagen, Chet; Harvey, Taylor B; Stolle, C Jackson; Harris, Justin; Korgel, Brian A

    2012-09-06

    Pyrite-phase iron sulfide (FeS2) nanocrystals were synthesized to form solvent-based dispersions, or "solar paint," to fabricate photovoltaic devices (PVs). Nanocrystals were sprayed onto substrates as absorber layers in devices with several different architectures, including Schottky barrier, heterojunction, and organic/inorganic hybrid architectures, to explore their viability as a PV material. None of the devices exhibited PV response. XRD and Raman spectroscopy confirmed the pyrite composition and phase purity of the nanocrystals. The electrical conductivity of the nanocrystal films was about 4 to 5 S/cm, more typical of metal nanocrystal films than semiconductor nanocrystal films, and the lack of PV response appears to derive from the highly conductive surface-related defects in pyrite that have been proposed.

  7. Colloidal inorganic nanocrystals: Nucleation, growth and biological applications

    NASA Astrophysics Data System (ADS)

    Lynch, Jared James

    Colloidal inorganic nanocrystals are a class of material whose size ranges from a few nanometers to a hundred nanometers in dimension. These nanocrystals have size dependent properties that differ significantly from the bulk material counterparts. Due to their unique physical properties colloidal inorganic nanocrystals have several promising applications in a diverse range of areas, such as biomedical diagnosis, catalysis, plasmonics, high-density data storage and solar energy conversion. This dissertation presents the study of the formation of iron oxide nanocrystals under the influence of solvent and Ar gas bubbles, the phase transfer of metal oxide nanocrystals into water using inorganic ions, and the doping of semiconductor CdS/ZnS core/shell nanocrystals with copper and silver ions. First, the formation of iron oxide nanocrystals is investigated in the presence of boiling solvent or Ar bubbles. Using a non-injection based synthesis method, the thermal decomposition of iron oleate was studied under various reaction conditions, and the role of the bubbles on the nucleation and growth of iron oxide nanocrystals was determined. Kinetics studies were used to elucidate how latent heat transfer from the bubbles allows for "active monomers" to form preferentially from exothermic reactions taking place during nucleation. General insights into colloidal inorganic nanocrystal formation are discussed. Second, a non-injection based synthesis for CdS/ZnS core/shell nanocrystals is used to make high quality semiconductor particles which are intentionally doped with Cu or Ag ions. The Ag ions effect on the optical properties of the CdS/ZnS nanocrystals is investigated. The absorption and fluorescence of the samples is measured as a function of time and temperature. Proposed mechanisms for the observations are given and thoroughly discussed. Comparisons between previous results for Cu doped CdS/ZnS nanocrystals are also made to further understand how doping of semiconductor

  8. Synthesis and investigation of optical properties of TOPO-capped CuInS{sub 2} semiconductor nanocrystal in the presence of different solvent

    SciTech Connect

    Asgary, Saeid; Mirabbaszadeh, Kavoos; Nayebi, Payman; Emadi, Hamid

    2014-03-01

    Graphical abstract: - Highlights: • TOPO-capped CuInS{sub 2} nanoparticles were synthesized by injection method. • Pure CuInS{sub 2} nanoparticle was obtained by injection in 200 °C. • The size, shape and optical properties of products were controlled. • Nanoparticles with size smaller than 10 nm and wurtzite phase was obtained. • The absorption and PL spectra of CuInS{sub 2} nanoparticles were tunable. - Abstract: In this work, synthesis of CuInS{sub 2} semiconductor nanoparticles by thermolysis of a mixed solution of CuAc, In(Ac){sub 3} and DDT in coordinating solvent and trioctylphosphine oxide (TOPO) as ligand was developed. CuInS{sub 2} nanoparticles with size of −10 nm and nanorods were obtained and optical properties controlled by adjusting the reaction parameters such as temperature and time. Also the shape of nanoparticles was controlled by various solvents elaborately. The as-prepared nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), UV–vis absorption, and photoluminescence (PL) spectroscopy. With the use of different solvent different morphology obtained. In the presence of oleylamine/octadecene rectangle-like nanorods obtained while with the use of oleic acid sphere-like nanoparticles achieved.

  9. Bi-photon imaging and diagnostics using ultra-small diagnostic probes engineered from semiconductor nanocrystals and single-domain antibodies

    NASA Astrophysics Data System (ADS)

    Hafian, Hilal; Sukhanova, Alyona; Chames, Patrick; Baty, Daniel; Pluot, Michel; Cohen, Jacques H. M.; Nabiev, Igor R.; Millot, Jean-Marc

    2012-10-01

    Semiconductor fluorescent quantum dots (QDs) have just demonstrated their numerous advantages over organic dyes in bioimaging and diagnostics. One of characteristics of QDs is a very large cross section of their twophoton absorption. A common approach to biodetection by means of QDs is to use monoclonal antibodies (mAbs) for targeting. Recently, we have engineered ultrasmall diagnostic nanoprobes (sdAb-QD) based on highly oriented conjugates of QDs with the single-domain antibodies (sdAbs) against cancer biomarkers. With a molecular weight of only 13 kDa (12-fold smaller than full-size mAbs) and extreme stability and capacity to refolding, sdAbs are the smallest functional Ab fragments capable of binding antigens with affinities comparable to those of conventional Abs. Ultrasmall diagnostic sdAb-QD nanoprobes were engineered through oriented conjugation of QDs with sdAbs. This study is the first to demonstrate the possibility of immunohistochemical imaging of colon carcinoma biomarkers with sdAb-QD conjugates by means of two-photon excitation. The optimal excitation conditions for imaging of the markers in clinical samples with sdAb-QD nanoprobes have been determined. The absence of sample autofluorescence significantly improves the sensitivity of biomarker detection with the use of the two-photon excitation diagnostic setup.

  10. Lead sulphide nanocrystal photodetector technologies

    NASA Astrophysics Data System (ADS)

    Saran, Rinku; Curry, Richard J.

    2016-02-01

    Light detection is the underlying principle of many optoelectronic systems. For decades, semiconductors including silicon carbide, silicon, indium gallium arsenide and germanium have dominated the photodetector industry. They can show excellent photosensitivity but are limited by one or more aspects, such as high production cost, high-temperature processing, flexible substrate incompatibility, limited spectral range or a requirement for cryogenic cooling for efficient operation. Recently lead sulphide (PbS) nanocrystals have emerged as one of the most promising new materials for photodetector fabrication. They offer several advantages including low-cost manufacturing, solution processability, size-tunable spectral sensitivity and flexible substrate compatibility, and they have achieved figures of merit outperforming conventional photodetectors. We review the underlying concepts, breakthroughs and remaining challenges in photodetector technologies based on PbS nanocrystals.

  11. Chemistry of sustainability-Part I: Carbon dioxide as an organic synthon and Part II: Study of thermodynamics of cation exchange reactions in semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Sathe, Ajay A.

    chapter introduces the role of nanomaterials in sustainable solar energy conversion and storage. The use of cation exchange reactions in nanocrystals to access novel materials is highlighted. Despite having shown tremendous promise in the synthetic applications, the fundamental measurements of the thermodynamic and kinetic parameters of a cation exchange reaction are largely non-existent. This impedes the future growth of this powerful methodology. The technique of isothermal titration calorimetry is introduced, and its importance to studying the thermochemical changes occurring during cation exchange is outlined. The final chapter presents results obtained from the isothermal titration calorimetry on the prototypical cation exchange reaction between cadmium selenide and silver ions. The role of nanoparticle size, identity of the silver salt, solvent, surface ligands and temperature is studied. Recommendations for future investigations using ITC as well as other characterization techniques for discerning the kinetics of cation exchange are presented. I believe that a more unified mechanistic understanding of the cation exchange process in nanomaterials will aid the development of more efficient and robust materials for applications in a wide variety of fields.

  12. Ultra-large-scale syntheses of monodisperse nanocrystals

    NASA Astrophysics Data System (ADS)

    Park, Jongnam; An, Kwangjin; Hwang, Yosun; Park, Je-Geun; Noh, Han-Jin; Kim, Jae-Young; Park, Jae-Hoon; Hwang, Nong-Moon; Hyeon, Taeghwan

    2004-12-01

    The development of nanocrystals has been intensively pursued, not only for their fundamental scientific interest, but also for many technological applications. The synthesis of monodisperse nanocrystals (size variation <5%) is of key importance, because the properties of these nanocrystals depend strongly on their dimensions. For example, the colour sharpness of semiconductor nanocrystal-based optical devices is strongly dependent on the uniformity of the nanocrystals, and monodisperse magnetic nanocrystals are critical for the next-generation multi-terabit magnetic storage media. For these monodisperse nanocrystals to be used, an economical mass-production method needs to be developed. Unfortunately, however, in most syntheses reported so far, only sub-gram quantities of monodisperse nanocrystals were produced. Uniform-sized nanocrystals of CdSe (refs 10,11) and Au (refs 12,13) have been produced using colloidal chemical synthetic procedures. In addition, monodisperse magnetic nanocrystals such as Fe (refs 14,15), Co (refs 16-18), γ-Fe2O3 (refs 19,20), and Fe3O4 (refs 21,22) have been synthesized by using various synthetic methods. Here, we report on the ultra-large-scale synthesis of monodisperse nanocrystals using inexpensive and non-toxic metal salts as reactants. We were able to synthesize as much as 40 g of monodisperse nanocrystals in a single reaction, without a size-sorting process. Moreover, the particle size could be controlled simply by varying the experimental conditions. The current synthetic procedure is very general and nanocrystals of many transition metal oxides were successfully synthesized using a very similar procedure.

  13. Plasmonic engineering of spontaneous emission from silicon nanocrystals

    PubMed Central

    Goffard, Julie; Gérard, Davy; Miska, Patrice; Baudrion, Anne-Laure; Deturche, Régis; Plain, Jérôme

    2013-01-01

    Silicon nanocrystals offer huge advantages compared to other semi-conductor quantum dots as they are made from an abundant, non-toxic material and are compatible with silicon devices. Besides, among a wealth of extraordinary properties ranging from catalysis to nanomedicine, metal nanoparticles are known to increase the radiative emission rate of semiconductor quantum dots. Here, we use gold nanoparticles to accelerate the emission of silicon nanocrystals. The resulting integrated hybrid emitter is 5-fold brighter than bare silicon nanocrystals. We also propose an in-depth analysis highlighting the role of the different physical parameters in the photoluminescence enhancement phenomenon. This result has important implications for the practical use of silicon nanocrystals in optoelectronic devices, for instance for the design of efficient down-shifting devices that could be integrated within future silicon solar cells. PMID:24037020

  14. Generalized and facile synthesis of semiconducting metal sulfide nanocrystals.

    PubMed

    Joo, Jin; Na, Hyon Bin; Yu, Taekyung; Yu, Jung Ho; Kim, Young Woon; Wu, Fanxin; Zhang, Jin Z; Hyeon, Taeghwan

    2003-09-10

    We report on the synthesis of semiconductor nanocrystals of PbS, ZnS, CdS, and MnS through a facile and inexpensive synthetic process. Metal-oleylamine complexes, which were obtained from the reaction of metal chloride and oleylamine, were mixed with sulfur. The reaction mixture was heated under appropriate experimental conditions to produce metal sulfide nanocrystals. Uniform cube-shaped PbS nanocrystals with particle sizes of 6, 8, 9, and 13 nm were synthesized. The particle size was controlled by changing the relative amount of PbCl(2) and sulfur. Uniform 11 nm sized spherical ZnS nanocrystals were synthesized from the reaction of zinc chloride and sulfur, followed by one cycle of size-selective precipitation. CdS nanocrystals that consist of rods, bipods, and tripods were synthesized from a reaction mixture containing a 1:6 molar ratio of cadmium to sulfur. Spherical CdS nanocrystals (5.1 nm sized) were obtained from a reaction mixture with a cadmium to sulfur molar ratio of 2:1. MnS nanocrystals with various sizes and shapes were synthesized from the reaction of MnCl(2) and sulfur in oleylamine. Rod-shaped MnS nanocrystals with an average size of 20 nm (thickness) x 37 nm (length) were synthesized from a 1:1 molar ratio of MnCl(2) and sulfur at 240 degrees C. Novel bullet-shaped MnS nanocrystals with an average size of 17 nm (thickness) x 44 nm (length) were synthesized from the reaction of 4 mmol of MnCl(2) and 2 mmol of sulfur at 280 degrees C for 2 h. Shorter bullet-shaped MnS nanocrystals were synthesized from a 3:1 molar ratio of MnCl(2) and sulfur. Hexagon-shaped MnS nanocrystals were also obtained. All of the synthesized nanocrystals were highly crystalline.

  15. Nickel nanocrystal formation on HfO2 dielectric for nonvolatile memory device applications

    NASA Astrophysics Data System (ADS)

    Lee, Jong Jin; Harada, Yoshinao; Pyun, Jung Woo; Kwong, Dim-Lee

    2005-03-01

    This letter presents the formation of nickel nanocrystal on HfO2 high-k dielectric and its application to the nonvolatile memory devices. The effects of the initial nickel layer thickness and annealing temperature on nickel nanocrystal formation are investigated. The n-metal-oxide-semiconductor field-effect transistor with nickel nanocrystals and HfO2 tunneling dielectrics is fabricated and its programming, data retention, and endurance properties are characterized to demonstrate its advantages for nonvolatile memory device applications.

  16. Stoichiometric control of lead chalcogenide nanocrystal solids to enhance their electronic and optoelectronic device performance.

    PubMed

    Oh, Soong Ju; Berry, Nathaniel E; Choi, Ji-Hyuk; Gaulding, E Ashley; Paik, Taejong; Hong, Sung-Hoon; Murray, Christopher B; Kagan, Cherie R

    2013-03-26

    We investigate the effects of stoichiometric imbalance on the electronic properties of lead chalcogenide nanocrystal films by introducing excess lead (Pb) or selenium (Se) through thermal evaporation. Hall-effect and capacitance-voltage measurements show that the carrier type, concentration, and Fermi level in nanocrystal solids may be precisely controlled through their stoichiometry. By manipulating only the stoichiometry of the nanocrystal solids, we engineer the characteristics of electronic and optoelectronic devices. Lead chalcogenide nanocrystal field-effect transistors (FETs) are fabricated at room temperature to form ambipolar, unipolar n-type, and unipolar p-type semiconducting channels as-prepared and with excess Pb and Se, respectively. Introducing excess Pb forms nanocrystal FETs with electron mobilities of 10 cm(2)/(V s), which is an order of magnitude higher than previously reported in lead chalcogenide nanocrystal devices. Adding excess Se to semiconductor nanocrystal solids in PbSe Schottky solar cells enhances the power conversion efficiency.

  17. Growth of platinum nanocrystals

    SciTech Connect

    2009-01-01

    Movie showing the growth of platinum nanocrystals in a liquid cell observed in situ using the JEOL 3010 TEM at the National Center for Electron Microscopy. This is the first ever-real time movie showing nucleation and growth by monomer attachment or by smaller nanocrystals coalescing to form larger nanocrystals. All the nanocrystals end up being roughly the same shape and size. http://newscenter.lbl.gov/feature-stories/2009/08/04/growth-spurts/

  18. Colloidal Nanocrystals Fluoresced by Surface Coordination Complexes

    PubMed Central

    Wang, Guan; Ji, Jianwei; Zhang, Xinwen; Zhang, Yan; Wang, Qiangbin; You, Xiaozeng; Xu, Xiangxing

    2014-01-01

    Colloidal Nanocrystals (NCs) with fluorescence originating from surface complexes are successfully prepared. The components of these NCs range from insulator, semiconductor to metal, with either pure phase, doped or core/shell structures. The photoluminescence of these NCs can be reversibly tuned across the visible to infrared spectrum, and even allow multi-color emission. A light emitting device is fabricated and a new in vivo cell imaging method is performed to demonstrate the power of this technology for emerging applications. PMID:24970242

  19. Field-effect electroluminescence in silicon nanocrystals.

    PubMed

    Walters, Robert J; Bourianoff, George I; Atwater, Harry A

    2005-02-01

    There is currently worldwide interest in developing silicon-based active optical components in order to leverage the infrastructure of silicon microelectronics technology for the fabrication of optoelectronic devices. Light emission in bulk silicon-based devices is constrained in wavelength to infrared emission, and in efficiency by the indirect bandgap of silicon. One promising strategy for overcoming these challenges is to make use of quantum-confined excitonic emission in silicon nanocrystals. A critical challenge for silicon nanocrystal devices based on nanocrystals embedded in silicon dioxide has been the development of a method for efficient electrical carrier injection. We report here a scheme for electrically pumping dense silicon nanocrystal arrays by a field-effect electroluminescence mechanism. In this excitation process, electrons and holes are both injected from the same semiconductor channel across a tunnelling barrier in a sequential programming process, in contrast to simultaneous carrier injection in conventional pn-junction light-emitting-diode structures. Light emission is strongly correlated with the injection of a second carrier into a nanocrystal that has been previously programmed with a charge of the opposite sign.

  20. Colloidal synthesis of biocompatible iron disulphide nanocrystals.

    PubMed

    Santos-Cruz, J; Nuñez-Anita, R E; Mayén-Hernández, S A; Martínez-Alvarez, O; Acosta-Torres, L S; de la Fuente-Hernández, J; Campos-González, E; Vega-González, M; Arenas-Arrocena, M C

    2017-08-06

    The aim of this research was to synthesis biocompatible iron disulphide nanocrystals at different reaction temperatures using the colloidal synthesis methodology. Synthesis was conducted at the 220-240 °C range of reaction temperatures at intervals of 5 °C in an inert argon atmosphere. The toxicity of iron disulphide nanocrystals was evaluated in vitro using mouse fibroblast cell line. Two complementary assays were conducted: the first to evaluate cell viability of the fibroblast via an MTT assay and the second to determine the preservation of fibroblast nuclei integrity through DAPI staining, which labels nuclear DNA in fluorescence microscopes. Through TEM and HRTEM, we observed a cubic morphology of pyrite iron disulphide nanocrystals ranging in sizes 25-50 nm (225 °C), 50-70 nm (230 °C) and >70 nm (235 °C). Through X-ray diffraction, we observed a mixture of pyrite and pyrrohotite in the samples synthesized at 225 °C and 240 °C, showing the best photocatalytic activity at 80% and 65%, respectively, for the degradation of methylene blue after 120 minutes. In all experimental groups, iron disulphide nanocrystals were biocompatible, i.e. no statistically significant differences were observed between experimental groups as shown in a one-way ANOVA and Tukey's test. Based on all of these results, we recommend non-cytotoxic semiconductor iron sulphide nanocrystals for biomedical applications.

  1. Fabrication and electronic transport studies of single nanocrystal systems

    SciTech Connect

    Klein, David Louis

    1997-05-01

    Semiconductor and metallic nanocrystals exhibit interesting electronic transport behavior as a result of electrostatic and quantum mechanical confinement effects. These effects can be studied to learn about the nature of electronic states in these systems. This thesis describes several techniques for the electronic study of nanocrystals. The primary focus is the development of novel methods to attach leads to prefabricated nanocrystals. This is because, while nanocrystals can be readily synthesized from a variety of materials with excellent size control, means to make electrical contact to these nanocrystals are limited. The first approach that will be described uses scanning probe microscopy to first image and then electrically probe surfaces. It is found that electronic investigations of nanocrystals by this technique are complicated by tip-sample interactions and environmental factors such as salvation and capillary forces. Next, an atomic force microscope technique for the catalytic patterning of the surface of a self assembled monolayer is described. In principle, this nano-fabrication technique can be used to create electronic devices which are based upon complex arrangements of nanocrystals. Finally, the fabrication and electrical characterization of a nanocrystal-based single electron transistor is presented. This device is fabricated using a hybrid scheme which combines electron beam lithography and wet chemistry to bind single nanocrystals in tunneling contact between closely spaced metallic leads. In these devices, both Au and CdSe nanocrystals show Coulomb blockade effects with characteristic energies of several tens of meV. Additional structure is seen the transport behavior of CdSe nanocrystals as a result of its electronic structure.

  2. Synthesis of new nanocrystal materials

    NASA Astrophysics Data System (ADS)

    Hassan, Yasser Hassan Abd El-Fattah

    Colloidal semiconductor nanocrystals (NCs) have sparked great excitement in the scientific community in last two decades. NCs are useful for both fundamental research and technical applications in various fields owing to their size and shape-dependent properties and their potentially inexpensive and excellent chemical processability. These NCs are versatile fluorescence probes with unique optical properties, including tunable luminescence, high extinction coefficient, broad absorption with narrow photoluminescence, and photobleaching resistance. In the past few years, a lot of attention has been given to nanotechnology based on using these materials as building blocks to design light harvesting assemblies. For instant, the pioneering applications of NCs are light-emitting diodes, lasers, and photovoltaic devices. Synthesis of the colloidal stable semiconductor NCs using the wet method of the pyrolysis of organometallic and chalcogenide precursors, known as hot-injection approach, is the chart-topping preparation method in term of high quality and monodisperse sized NCs. The advancement in the synthesis of these artificial materials is the core step toward their applications in a broad range of technologies. This dissertation focuses on exploring various innovative and novel synthetic methods of different types of colloidal nanocrystals, both inorganic semiconductors NCs, also known as quantum dots (QDs), and organic-inorganic metal halide-perovskite materials, known as perovskites. The work presented in this thesis focuses on pursuing fundamental understanding of the synthesis, material properties, photophysics, and spectroscopy of these nanostructured semiconductor materials. This thesis contains 6 chapters and conclusions. Chapters 1?3 focus on introducing theories and background of the materials being synthesized in the thesis. Chapter 4 demonstrates our synthesis of colloidal linker--free TiO2/CdSe NRs heterostructures with CdSe QDs grown in the presence of Ti

  3. Cadmium selenide semiconductor nanocrystals: a theoretical study

    NASA Astrophysics Data System (ADS)

    Eichkorn, Karin; Ahlrichs, Reinhart

    1998-05-01

    We consider a series of known ligand-stabilized clusters of CdSe and compute structure, electronic excitations and electron affinities with a density functional theory approach. The trend of computed properties on cluster size and especially the results for the largest cluster treated, [Cd 32Se 14(SeR) 36(PR 3) 4], R=H, display the effects encountered in the transition from molecular clusters to the solid state. We propose structural principles for ligand-stabilized CdSe clusters.

  4. Surface chemical modification of nanocrystals

    DOEpatents

    Helms, Brett Anthony; Milliron, Delia Jane; Rosen, Evelyn Louise; Buonsanti, Raffaella; Llordes, Anna

    2017-03-14

    Nanocrystals comprising organic ligands at surfaces of the plurality of nanocrystals are provided. The organic ligands are removed from the surfaces of the nanocrystals using a solution comprising a trialkyloxonium salt in a polar aprotic solvent. The removal of the organic ligands causes the nanocrystals to become naked nanocrystals with cationic surfaces.

  5. Low temperature thin films formed from nanocrystal precursors

    DOEpatents

    Alivisatos, A.P.; Goldstein, A.N.

    1993-11-16

    Nanocrystals of semiconductor compounds are produced. When they are applied as a contiguous layer onto a substrate and heated they fuse into a continuous layer at temperatures as much as 250, 500, 750 or even 1000 K below their bulk melting point. This allows continuous semiconductor films in the 0.25 to 25 nm thickness range to be formed with minimal thermal exposure. 9 figures.

  6. Low temperature thin films formed from nanocrystal precursors

    DOEpatents

    Alivisatos, A. Paul; Goldstein, Avery N.

    1993-01-01

    Nanocrystals of semiconductor compounds are produced. When they are applied as a contiguous layer onto a substrate and heated they fuse into a continuous layer at temperatures as much as 250, 500, 750 or even 1000.degree. K below their bulk melting point. This allows continuous semiconductor films in the 0.25 to 25 nm thickness range to be formed with minimal thermal exposure.

  7. Semiconductor heterostructure

    NASA Technical Reports Server (NTRS)

    Hovel, Harold John (Inventor); Woodall, Jerry MacPherson (Inventor)

    1978-01-01

    A technique for fabricating a semiconductor heterostructure by growth of a ternary semiconductor on a binary semiconductor substrate from a melt of the ternary semiconductor containing less than saturation of at least one common ingredient of both the binary and ternary semiconductors wherein in a single temperature step the binary semiconductor substrate is etched, a p-n junction with specific device characteristics is produced in the binary semiconductor substrate by diffusion of a dopant from the melt and a region of the ternary semiconductor of precise conductivity type and thickness is grown by virtue of a change in the melt characteristics when the etched binary semiconductor enters the melt.

  8. Semiconductor structure

    NASA Technical Reports Server (NTRS)

    Hovel, Harold J. (Inventor); Woodall, Jerry M. (Inventor)

    1979-01-01

    A technique for fabricating a semiconductor heterostructure by growth of a ternary semiconductor on a binary semiconductor substrate from a melt of the ternary semiconductor containing less than saturation of at least one common ingredient of both the binary and ternary semiconductors wherein in a single temperature step the binary semiconductor substrate is etched, a p-n junction with specific device characteristics is produced in the binary semiconductor substrate by diffusion of a dopant from the melt and a region of the ternary semiconductor of precise conductivity type and thickness is grown by virtue of a change in the melt characteristics when the etched binary semiconductor enters the melt.

  9. Highly Emissive Transition Metal Ion Doped Semiconducting Nanocrystals

    NASA Astrophysics Data System (ADS)

    Jana, Santanu; Srivastava, Bhupendra B.; Sarma, D. D.; Pradhan, Narayan

    2011-07-01

    Doped semiconductor nanocrystals (d-dots), specifically ones not containing heavy metal ions, have the potential to become a class of mainstream emissive materials. Mn- and Cu-doped ZnSe or ZnS d-dots can cover an emission window similar to that of the current workhorse of intrinsic quantum dot (q-dots) emitters, CdSe nanocrystals. We synthesized high quality stable Cu doped ZnSe in nonpolar as well as polar solvent. The emission intensity of these doped nanocrystals is found stable for months under UV irradiation, after different multifunctional ligand which is important for any biological detection. We have also synthesized the stable Mn doped ZnS in nonpolar solvent more than 50% QY.. The doped nanocrystals are characterized by TEM, XRD, EPR and ICP analysis.

  10. Mn-Doped Multinary CIZS and AIZS Nanocrystals.

    PubMed

    Manna, Goutam; Jana, Santanu; Bose, Riya; Pradhan, Narayan

    2012-09-20

    Multinary nanocrystals (CuInS2, CIS, and AgInS2, AIS) are widely known for their strong defect state emission. On alloying with Zn (CIZS and AIZS), stable and intense emission tunable in visible and NIR windows has already been achieved. In these nanocrystals, the photogenerated hole efficiently moves to the defect-induced state and recombines with the electron in the conduction band. As a result, the defect state emission is predominantly observed without any band edge excitonic emission. Herein, we report the doping of the transition-metal ion Mn in these nanocrystals, which in certain compositions of the host nanocrystals quenches this strong defect state emission and predominantly shows the spin-flip Mn emission. Though several Mn-doped semiconductor nanocrystals are reported in the literature, these nanocrystals are of its first kind that can be excited in the visible window, do not contain the toxic element Cd, and provide efficient emission. Hence, when Mn emission is required, these multinary nanocrystals can be the ideal versatile materials for widespread technological applications.

  11. Detection of toxic mercury ions using a ratiometric CdSe/ZnS nanocrystal sensor.

    PubMed

    Page, Leah E; Zhang, Xi; Jawaid, Ali M; Snee, Preston T

    2011-07-21

    We have developed a strategy for the ratiometric detection of toxic Hg(2+) ions using a semiconductor nanocrystal energy-transfer donor coupled to a mercury-sensitive "turn-on" dye acceptor. The results demonstrate a new paradigm of toxic metal sensing that resolves the difficulties with the use of semiconductor nanotechnology for this purpose.

  12. Chelating ligands for nanocrystals' surface functionalization.

    PubMed

    Querner, Claudia; Reiss, Peter; Bleuse, Joël; Pron, Adam

    2004-09-22

    A new family of ligands for the surface functionalization of CdSe nanocrystals is proposed, namely alkyl or aryl derivatives of carbodithioic acids (R-C(S)SH). The main advantages of these new ligands are as follows: they nearly quantitatively exchange the initial surface ligands (TOPO) in very mild conditions; they significantly improve the resistance of nanocrystals against photooxidation because of their ability of strong chelate-type binding to metal atoms; their relatively simple preparation via Grignard intermediates facilitates the development of new bifunctional ligands containing, in addition to the anchoring carbodithioate group, a second function, which enables the grafting of molecules or macromolecules of interest on the nanocrystal surface. To give an example of this approach, we report, for the first time, the grafting of an electroactive oligomer from the polyaniline family-aniline tetramer-on CdSe nanocrystals after their functionalization with 4-formyldithiobenzoic acid. The grafting proceeds via a condensation reaction between the aldehyde group of the ligand and the terminal primary amine group of the tetramer. The resulting organic/inorganic hybrid exhibits complete extinction of the fluorescence of its constituents, indicating efficient charge or energy transfer between the organic and the inorganic semiconductors.

  13. Conjugated polymer/nanocrystal nanocomposites for renewable energy applications in photovoltaics and photocatalysis.

    PubMed

    Su, Yu-Wei; Lin, Wei-Hao; Hsu, Yung-Jung; Wei, Kung-Hwa

    2014-11-01

    Conjugated polymer/nanocrystal composites have attracted much attention for use in renewable energy applications because of their versatile and synergistic optical and electronic properties. Upon absorbing photons, charge separation occurs in the nanocrystals, generating electrons and holes for photocurrent flow or reduction/oxidation (redox) reactions under proper conditions. Incorporating these nanocrystals into conjugated polymers can complement the visible light absorption range of the polymers for photovoltaics applications or allow the polymers to sensitize or immobilize the nanocrystals for photocatalysis. Here, the current developments of conjugated polymer/nanocrystal nanocomposites for bulk heterojunction-type photovoltaics incorporating Cd- and Pb-based nanocrystals or quantum dots are reviewed. The effects of manipulating the organic ligands and the concentration of the nanocrystal precursor, critical factors that affect the shape and aggregation of the nanocrystals, are also discussed. In the conclusion, the mechanisms through which conjugated polymers can sensitize semiconductor nanocrystals (TiO2 , ZnO) to ensure efficient charge separation, as well as how they can support immobilized nanocrystals for use in photocatalysis, are addressed.

  14. Hot-injection synthesis of Ni-ZnO hybrid nanocrystals with tunable magnetic properties and enhanced photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Zeng, Deqian; Qiu, Yulong; Chen, Yuanzhi; Zhang, Qinfu; Liu, Xiang; Peng, Dong-Liang

    2017-04-01

    Magnetic metal-semiconductor hybrid nanocrystals containing ferromagnetic Ni and semiconductor ZnO have been prepared via a hot-injection route. The Ni-ZnO hybrid nanocrystals have a flower-like morphology that consists of Ni inner cores and ZnO petal shells. In spite of their large lattice mismatch, ZnO nanocrystals can still grow on faceted Ni nanocrystals to form stable interfaces. The composition of Ni-ZnO hybrid nanocrystals is readily controlled, and the average size of Ni core is tunable from 25 to 50 nm. Room temperature ferromagnetic properties are observed in these hybrid nanocrystals, and tunable magnetic properties also can be achieved by varying the size of Ni core. The as-prepared Ni-ZnO hybrid nanocrystals exhibit enhanced photocatalytic performance under ultraviolet light illumination as compared to pure ZnO nanocrystals. Furthermore, the superior reusability of hybrid nanocrystals for photocatalytic application is achieved by virtue of their magnetic properties. The facile and efficient seed-mediate strategy is particularly attractive to construct hybrid magnetic-semiconducting heterostructures. The as-obtained Ni-ZnO hybrid nanocrystals offer great potential for various applications due to their combined magnetic and semiconducting properties and low-cost earth-abundant availability.

  15. Biomineralization: Nanocrystals by design

    NASA Astrophysics Data System (ADS)

    Shang, Li; Nienhaus, Gerd Ulrich

    2015-10-01

    Nanocrystals with precisely defined structures offer promise as components of advanced materials yet they are challenging to create. Now, a nanocrystal made up of seven cadmium and twelve chloride ions has been synthesized via a biotemplating approach that uses a de novo designed protein.

  16. Silicon Nanocrystal Laser

    SciTech Connect

    Yu, J

    2005-03-09

    The purpose of this feasibility study project was to attempt to demonstrate the silicon-nanocrystal-based laser. Such a silicon laser (made using conventional silicon-manufacturing technologies) would provide the crucial missing link that would enable a completely-silicon-based photonic system. We prepared thin layers of silicon nanocrystal material by ion-implanting Si in fused silica substrates, followed by a high temperature anneal process. These Si nanocrystals produced intense photoluminescence when optically pumped with ultraviolet light. Laser structures based on Fabry-Perot cavity and distributed feedback (DFB) designs were fabricated using the Si nanocrystals as the ''lasing'' medium. We optically pumped the samples with CW lasers at 413nm wavelength to quickly assess the feasibility of making lasers out of the Nanocrystal Si material and to verify the gain coefficients reported by other research groups.

  17. Optical activity of chirally distorted nanocrystals

    NASA Astrophysics Data System (ADS)

    Tepliakov, Nikita V.; Baimuratov, Anvar S.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2016-05-01

    We develop a general theory of optical activity of semiconductor nanocrystals whose chirality is induced by a small perturbation of their otherwise achiral electronic subsystems. The optical activity is described using the quantum-mechanical expressions for the rotatory strengths and dissymmetry factors introduced by Rosenfeld. We show that the rotatory strengths of optically active transitions are decomposed on electric dipole and magnetic dipole contributions, which correspond to the electric dipole and magnetic dipole transitions between the unperturbed quantum states. Remarkably, while the two kinds of rotatory strengths are of the same order of magnitude, the corresponding dissymmetry factors can differ by a factor of 105. By maximizing the dissymmetry of magnetic dipole absorption one can significantly enhance the enantioselectivity in the interaction of semiconductor nanocrystals with circularly polarized light. This feature may advance chiral and analytical methods, which will benefit biophysics, chemistry, and pharmaceutical science. The developed theory is illustrated by an example of intraband transitions inside a semiconductor nanocuboid, whose rotatory strengths and dissymmetry factors are calculated analytically.

  18. Optical activity of chirally distorted nanocrystals

    SciTech Connect

    Tepliakov, Nikita V.; Baimuratov, Anvar S.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2016-05-21

    We develop a general theory of optical activity of semiconductor nanocrystals whose chirality is induced by a small perturbation of their otherwise achiral electronic subsystems. The optical activity is described using the quantum-mechanical expressions for the rotatory strengths and dissymmetry factors introduced by Rosenfeld. We show that the rotatory strengths of optically active transitions are decomposed on electric dipole and magnetic dipole contributions, which correspond to the electric dipole and magnetic dipole transitions between the unperturbed quantum states. Remarkably, while the two kinds of rotatory strengths are of the same order of magnitude, the corresponding dissymmetry factors can differ by a factor of 10{sup 5}. By maximizing the dissymmetry of magnetic dipole absorption one can significantly enhance the enantioselectivity in the interaction of semiconductor nanocrystals with circularly polarized light. This feature may advance chiral and analytical methods, which will benefit biophysics, chemistry, and pharmaceutical science. The developed theory is illustrated by an example of intraband transitions inside a semiconductor nanocuboid, whose rotatory strengths and dissymmetry factors are calculated analytically.

  19. Frequency upconverted lasing of nanocrystal quantum dots in microbeads

    NASA Astrophysics Data System (ADS)

    Zhang, Chunfeng; Zhang, Fan; Cheng, An; Kimball, Brian; Wang, Andrew Y.; Xu, Jian

    2009-11-01

    Stable, frequency upconverted lasing of semiconductor nanocrystal quantum dots was demonstrated in silica microbeads under two-photon pumping conditions. Upon infrared excitation, the stimulated emission of the nanocrystal-doped microbeads exhibits sharp peaks at λ ˜610 nm with narrow line widths of ≤1 nm. The lasing action has been attributed to the biexciton gain coupled to the whispering gallery modes in spherical cavities, as confirmed by time-resolved photoluminescence spectra. The lasing lifetime characterized in term of pulse numbers (˜106 pulses) was two orders of magnitude longer than that of the dye salt-based two-photon lasers.

  20. Statistical aging and nonergodicity in the fluorescence of single nanocrystals.

    PubMed

    Brokmann, X; Hermier, J-P; Messin, G; Desbiolles, P; Bouchaud, J-P; Dahan, M

    2003-03-28

    The relation between single particle and ensemble measurements is addressed for semiconductor CdSe nanocrystals. We record their fluorescence at the single molecule level and analyze their emission intermittency, which is governed by unusual random processes known as Lévy statistics. We report the observation of statistical aging and ergodicity breaking, both related to the occurrence of Lévy statistics. Our results show that the behavior of ensemble quantities, such as the total fluorescence of an ensemble of nanocrystals, can differ from the time-averaged individual quantities, and must be interpreted with care.

  1. Passivation effects in B doped self-assembled Si nanocrystals

    SciTech Connect

    Puthen Veettil, B. Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Zhang, Tian; Yang, Terry; Johnson, Craig; Conibeer, Gavin; Perez-Würfl, Ivan; McCamey, Dane

    2014-12-01

    Doping of semiconductor nanocrystals has enabled their widespread technological application in optoelectronics and micro/nano-electronics. In this work, boron-doped self-assembled silicon nanocrystal samples have been grown and characterised using Electron Spin Resonance and photoluminescence spectroscopy. The passivation effects of boron on the interface dangling bonds have been investigated. Addition of boron dopants is found to compensate the active dangling bonds at the interface, and this is confirmed by an increase in photoluminescence intensity. Further addition of dopants is found to reduce the photoluminescence intensity by decreasing the minority carrier lifetime as a result of the increased number of non-radiative processes.

  2. Prospects of nanoscience with nanocrystals

    DOE PAGES

    Kovalenko, Maksym V.; Manna, Liberato; Cabot, Andreu; ...

    2015-01-22

    Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very fewmore » semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. In addition, new phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.« less

  3. Prospects of nanoscience with nanocrystals

    SciTech Connect

    Kovalenko, Maksym V.; Manna, Liberato; Cabot, Andreu; Hens, Zeger; Talapin, Dmitri V.; Kagan, Cherie R.; Klimov, Victor I.; Rogach, Andrey L.; Reiss, Peter; Milliron, Delia J.; Guyot-Sionnnest, Philippe; Konstantatos, Gerasimos; Parak, Wolfgang J.; Hyeon, Taeghwan; Korgel, Brian A.; Murray, Christopher B.; Heiss, Wolfgang

    2015-01-22

    Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. In addition, new phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.

  4. Prospects of nanoscience with nanocrystals.

    PubMed

    Kovalenko, Maksym V; Manna, Liberato; Cabot, Andreu; Hens, Zeger; Talapin, Dmitri V; Kagan, Cherie R; Klimov, Victor I; Rogach, Andrey L; Reiss, Peter; Milliron, Delia J; Guyot-Sionnnest, Philippe; Konstantatos, Gerasimos; Parak, Wolfgang J; Hyeon, Taeghwan; Korgel, Brian A; Murray, Christopher B; Heiss, Wolfgang

    2015-02-24

    Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today's strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.

  5. Reversible solvent vapor-mediated phase changes in nanocrystal superlattices.

    PubMed

    Goodfellow, Brian W; Korgel, Brian A

    2011-04-26

    Colloidal nanocrystals are being explored for use in a variety of applications, from solar cells to transistors to medical diagnostics and therapy. Ordered assemblies of nanocrystals, or superlattices, are one particularly interesting class of these materials, in which the nanocrystals serve as modular building blocks to construct nanostructures by self-assembly with spatial and temporal complexity and unique properties. From a fundamental perspective, the nanocrystals are simple molecular models that can be manipulated and studied to test statistical mechanical and thermodynamic models of crystallization and disorder. An article by Bian et al. in this issue of ACS Nano reports surprising new phase behavior in semiconductor nanocrystal superlattices: reversible transitions between non-close-packed body-centered cubic (bcc) and body-centered tetragonal (bct) structures, and close-packed face-centered cubic (fcc) structures, observed by real-time in situ grazing incidence small-angle X-ray scattering (GISAXS) measurements, upon solvent vapor exposure and increased interparticle separation. These studies offer new insight and raise new questions about superlattice structure and the forces that control self-assembly. Accompanying computer simulations show that ligand-ligand interactions are important. Furthermore, it appears that ligand-coated nanocrystals have more in common with soft microphase-separated materials, like diblock copolymers and surfactant assemblies, than previously realized.

  6. Recent Progress in Photocatalysis Mediated by Colloidal II-VI Nanocrystals

    PubMed Central

    Wilker, Molly B; Schnitzenbaumer, Kyle J; Dukovic, Gordana

    2012-01-01

    The use of photoexcited electrons and holes in semiconductor nanocrystals as reduction and oxidation reagents is an intriguing way of harvesting photon energy to drive chemical reactions. This review focuses on recent research efforts to understand and control the photocatalytic processes mediated by colloidal II-VI nanocrystalline materials, such as cadmium and zinc chalcogenides. First, we highlight how nanocrystal properties govern the rates and efficiencies of charge-transfer processes relevant to photocatalysis. We then describe the use of nanocrystal catalyst heterostructures for fuel-forming reactions, most commonly H2 generation. Finally, we review the use of nanocrystal photocatalysis as a synthetic tool for metal–semiconductor nano-heterostructures. PMID:24115781

  7. Incorporating lanthanide cations with cadmium selenide nanocrystals: a strategy to sensitize and protect Tb(III).

    PubMed

    Chengelis, Demetra A; Yingling, Adrienne M; Badger, Paul D; Shade, Chad M; Petoud, Stéphane

    2005-12-07

    The electronic structure of CdSe semiconductor nanocrystals has been used to sensitize Tb3+ in solution by incorporation of Tb3+ cations into the nanocrystals during synthesis. Doping of luminescent Tb3+ metal ions in semiconductor nanocrystals utilizes the positive attributes of both species' photophysical properties, resulting in a final product with long luminescence lifetimes, sharp emission bands, high absorptivities, and strong resistance to decomposition. This strategy also helps protect the lanthanide cations from nonradiative deactivation from C-H, N-H, and O-H oscillators of solvent molecules or traditional organic lanthanide ligands, leading to long Tb3+ luminescence lifetimes. This new type of nanomaterial synergistically combines the photophysical properties of nanocrystals and Tb3+.

  8. Nonthermal plasma synthesis of metal sulfide nanocrystals from metalorganic vapor and elemental sulfur

    NASA Astrophysics Data System (ADS)

    Thimsen, Elijah; Kortshagen, Uwe R.; Aydil, Eray S.

    2015-08-01

    Nanocrystal synthesis in nonthermal plasmas has been focused on elemental group IV semiconductors such as Si and Ge. In contrast, very little is known about plasma synthesis of compound nanocrystals and the time is ripe to extend this synthesis approach to nanocrystals comprised of two or more elements such as metal sulfides, oxides and nitrides. Towards this end, we studied, in an argon-sulfur plasma, the synthesis of ZnS, Cu2S and SnS nanocrystals from metalorganic precursors diethyl Zn(II), hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane, and tetrakis(dimethylamido) Sn(IV), respectively. In situ optical emission spectroscopy was used to observe changes in relative concentrations of various plasma species during synthesis, while ex situ material characterization was used to examine the crystal structure, elemental composition and optical absorption of these nanocrystals. For a constant metalorganic vapor feed rate, the elemental composition of the nanocrystals was found to be independent of the sulfur flow rate into the plasma, above a small threshold value. At constant sulfur flow rate, the nanocrystal composition depended on the metalorganic vapor feed rate. Specifically, the ensemble metal atomic fraction in the nanocrystals was found to increase with increasing metalorganic vapor flow rates, resulting in more metal-rich crystal phases. The metalorganic feed rate can be used to control the composition and crystal phase of the metal-sulfide nanocrystals synthesized using this plasma process.

  9. Flexible and low-voltage integrated circuits constructed from high-performance nanocrystal transistors.

    PubMed

    Kim, David K; Lai, Yuming; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2012-01-01

    Colloidal semiconductor nanocrystals are emerging as a new class of solution-processable materials for low-cost, flexible, thin-film electronics. Although these colloidal inks have been shown to form single, thin-film field-effect transistors with impressive characteristics, the use of multiple high-performance nanocrystal field-effect transistors in large-area integrated circuits has not been shown. This is needed to understand and demonstrate the applicability of these discrete nanocrystal field-effect transistors for advanced electronic technologies. Here we report solution-deposited nanocrystal integrated circuits, showing nanocrystal integrated circuit inverters, amplifiers and ring oscillators, constructed from high-performance, low-voltage, low-hysteresis CdSe nanocrystal field-effect transistors with electron mobilities of up to 22 cm(2) V(-1) s(-1), current modulation >10(6) and subthreshold swing of 0.28 V dec(-1). We fabricated the nanocrystal field-effect transistors and nanocrystal integrated circuits from colloidal inks on flexible plastic substrates and scaled the devices to operate at low voltages. We demonstrate that colloidal nanocrystal field-effect transistors can be used as building blocks to construct complex integrated circuits, promising a viable material for low-cost, flexible, large-area electronics.

  10. Mapping the Atomistic Structure of Graded Core/Shell Colloidal Nanocrystals.

    PubMed

    Yarema, Maksym; Xing, Yunhua; Lechner, Rainer T; Ludescher, Lukas; Dordevic, Nikola; Lin, Weyde M M; Yarema, Olesya; Wood, Vanessa

    2017-09-15

    Engineering the compositional gradient for core/shell semiconductor nanocrystals improves their optical properties. To date, however, the structure of graded core/shell nanocrystal emitters has only been qualitatively described. In this paper, we demonstrate an approach to quantify nanocrystal structure, selecting graded Ag-In-Se/ZnSe core/shell nanocrystals as a proof-of-concept material. A combination of multi-energy small-angle X-ray scattering and electron microscopy techniques enables us to establish the radial distribution of ZnSe with sub-nanometer resolution. Using ab initio shape-retrieval analysis of X-ray scattering spectra, we further determine the average shape of nanocrystals. These results allow us to generate three-dimensional, atomistic reconstructions of graded core/shell nanocrystals. We use these reconstructions to calculate solid-state Zn diffusion in the Ag-In-Se nanocrystals and the lattice mismatch between nanocrystal monolayers. Finally, we apply these findings to propose design rules for optimal shell structure and record-luminescent core/shell nanocrystals.

  11. Probing the Fermi energy level and the density of states distribution in PbTe nanocrystal (quantum dot) solids by temperature-dependent thermopower measurements.

    PubMed

    Ko, Dong-Kyun; Murray, Christopher B

    2011-06-28

    The position of the Fermi energy level (E(F)) with respect to the energy level where the transport process occurs (transport energy level, E(T)) is an important parameter that determines the electrical properties of semiconductors. However, little attention has been devoted to investigating the position of E(F) in semiconductor nanocrystal solids, both theoretically and experimentally. In this study, we perform temperature-dependent thermopower measurements on PbTe nanocrystal solids to directly probe E(F) - E(T). We observe that as the size of the nanocrystals reduces, E(F) - E(T) increases primarily due to the widening of density of state (DOS) gap. Furthermore, by modifying the monodispersity of nanocrystals, we observe an increase in thermopower as the distribution of energy states sharpens. This work promotes a deeper understanding of thermal occupation of energy states as well as electronic transport processes in semiconductor nanocrystal solid systems.

  12. Chitin Liquid-Crystal-Templated Oxide Semiconductor Aerogels.

    PubMed

    Chau, Trang The Lieu; Le, Dung Quang Tien; Le, Hoa Thi; Nguyen, Cuong Duc; Nguyen, Long Viet; Nguyen, Thanh-Dinh

    2017-09-13

    Chitin nanocrystals have been used as a liquid crystalline template to fabricate layered oxide semiconductor aerogels. Anisotropic chitin liquid crystals are transformed to sponge-like aerogels by hydrothermally cross-linked gelation and lyophilization-induced solidification. The hydrothermal gelation of chitin aqueous suspensions then proceeds with peroxotitanate to form hydrogel composites that recover to form aerogels after freeze-drying. The homogeneous peroxotitanate/chitin composites are calcined to generate freestanding titania aerogels that exhibit the nanostructural integrity of layered chitin template. Our extended investigations show that coassembling chitin nanocrystals with other metal-based precursors also yielded semiconductor aerogels of perovskite BaTiO3 and CuOx nanocrystals. The potential of these materials is great to investigate these chitin sponges for biomedicine and these semiconductor aerogels for photocatalysis, gas sensing, and other applications. Our results present a new aerogel templating method of highly porous, ultralight materials with chitin liquid crystals.

  13. Ternary Silver Halide Nanocrystals.

    PubMed

    Abeyweera, Sasitha C; Rasamani, Kowsalya D; Sun, Yugang

    2017-07-18

    Nanocrystalline silver halides (AgX) such as AgCl, AgBr, and AgI, a class of semiconductor materials with characteristics of both direct and indirect band gaps, represent the most crucial components in traditional photographic processing. The nanocrystal surfaces provide sensitivity specks that can turn into metallic silver, forming an invisible latent image, upon exposure to light. The photographic processing implies that the AgX nanoparticles possess unique properties. First, pristine AgX nanoparticles absorb light only at low efficiency to convert surface AgX into tiny clusters of silver atoms. Second, AgX nanoparticles represent an excellent class of materials to capture electrons efficiently. Third, small metallic silver clusters can catalyze the reduction of AgX nanoparticles to Ag nanoparticles in the presence of mild reducing reagents, known as self-catalytic reduction. These properties indicate that AgX nanoparticles can be partially converted to metallic silver with high precision, leading to the formation of hybrid AgX/Ag nanoparticles. The nanosized metallic Ag usually exhibit intense absorption bands in the visible spectral region due to their strong surface plasmon resonances, which make the AgX/Ag nanoparticles a class of promising visible-light-driven photocatalysts for environmental remediation and CO2 reduction. Despite the less attention paid to their ability of capturing electrons, AgX nanoparticles might be a class of ideal electron shuttle materials to bridge light absorbers and catalysts on which electrons can drive chemical transformations. In this Account, we focus on ternary silver halide alloy (TSHA) nanoparticles, containing two types of halide ions, which increase the composition complexity of the silver halide nanoparticles. Interdiffusion of halide ions between two types of AgX at elevated temperatures has been developed for fabricating ternary silver halide alloy crystals, such as silver chlorobromide optical fibers for infrared

  14. On Ultrasmall Nanocrystals

    PubMed Central

    McBride, James R.; Dukes, Albert D.; Schreuder, Michael A.; Rosenthal, Sandra J.

    2010-01-01

    Ultrasmall nanocrystals are a growing sub-class of traditional nanocrystals that exhibit new properties at diameters typically below 2 nm. In this review, we define what constitutes an ultrasmall nanoparticle while distinguishing between ultrasmall and magic-size nanoparticles. After a brief overview of ultrasmall nanoparticles, including ultrasmall gold clusters, our recent work is presented covering the optical properties, structure, and application of ultrasmall CdSe nanocrystals. This unique material has potential application in solid state lighting due to its balanced white emission. This section is followed by a discussion on the blurring boundary between what can be considered a nanoparticle and a molecule. PMID:21132106

  15. Pyramidal and Chiral Groupings of Gold Nanocrystals Assembled Using DNA Scaffolds

    PubMed Central

    Mastroianni, Alexander; Claridge, Shelley; Alivisatos, A. Paul

    2009-01-01

    Nanostructures constructed from metal and semiconductor nanocrystals conjugated to, and organized by DNA are an emerging class of material with collective optical properties. We created discrete pyramids of DNA with gold nanocrystals at the tips. By taking small angle X-ray scattering (SAXS) measurments from solutions of these pyramids we confirmed that this pyramidal geometry creates structures which are more rigid in solution than linear DNA. We then took advantage of the tetrahedral symmetry to demonstrate construction of chiral nanostructures. PMID:19331419

  16. Photothermal theragnosis synergistic therapy based on bimetal sulphide nanocrystals rather than nanocomposites.

    PubMed

    Li, Bo; Ye, Kaichuang; Zhang, Yuxin; Qin, Jinbao; Zou, Rujia; Xu, Kaibing; Huang, Xiaojuan; Xiao, Zhiyin; Zhang, Wenjun; Lu, Xinwu; Hu, Junqing

    2015-02-25

    A new generation of photothermal theranostic agents is developed based on Cu3BiS3 nanocrystals. A computed tomography imaging response and photothermal effect, as well as near-infrared fluorescence emission, can be simultaneously achieved through Cu3BiS3 nanocrystals rather than frequently used nanocomposites. These results provide some insight into the synergistic effect from bimetal sulphide semiconductor compounds for photothermal theragnosis therapy.

  17. Pyramidal and Chiral Groupings of Gold Nanocrystals Assembled Using DNA Scaffolds

    SciTech Connect

    Mastroianni, Alexander; Claridge, Shelley; Alivisatos, A. Paul

    2009-03-30

    Nanostructures constructed from metal and semiconductor nanocrystals conjugated to, and organized by DNA are an emerging class of material with collective optical properties. We created discrete pyramids of DNA with gold nanocrystals at the tips. By taking small angle X-ray scattering (SAXS) measurments from solutions of these pyramids we confirmed that this pyramidal geometry creates structures which are more rigid in solution than linear DNA. We then took advantage of the tetrahedral symmetry to demonstrate construction of chiral nanostructures.

  18. Hypervalent surface interactions for colloidal stability and doping of silicon nanocrystals

    PubMed Central

    Wheeler, Lance M.; Neale, Nathan R.; Chen, Ting; Kortshagen, Uwe R.

    2013-01-01

    Colloidal semiconductor nanocrystals have attracted attention for cost-effective, solution-based deposition of quantum-confined thin films for optoelectronics. However, two significant challenges must be addressed before practical nanocrystal-based devices can be realized. The first is coping with the ligands that terminate the nanocrystal surfaces. Though ligands provide the colloidal stability needed to cast thin films from solution, these ligands dramatically hinder charge carrier transport in the resulting film. Second, after a conductive film is achieved, doping has proven difficult for further control of the optoelectronic properties of the film. Here we report the ability to confront both of these challenges by exploiting the ability of silicon to engage in hypervalent interactions with hard donor molecules. For the first time, we demonstrate the significant potential of applying the interaction to the nanocrystal surface. In this study, hypervalent interactions are shown to provide colloidal stability as well as doping of silicon nanocrystals. PMID:23893292

  19. Solution based synthesis of simple fcc Si nano-crystals under ambient conditions.

    PubMed

    Balcı, Mustafa H; Sæterli, Ragnhild; Maria, Jerome; Lindgren, Mikael; Holmestad, Randi; Grande, Tor; Einarsrud, Mari-Ann

    2013-02-28

    We demonstrate for the first time that simple face-centered cubic (fcc) silicon nano-crystals can be produced by a solution based bottom-up synthesis route under ambient conditions. Simple fcc Si nano-crystals (2-7 nm) were prepared at room temperature by using sodium cyclopentadienide as a reducing agent for silicon tetrachloride. Photoluminescence emission at 550 nm was observed for the fcc silicon nano-crystals upon excitation at 340 nm, indicating that fcc Si nano-crystals were exhibiting direct bandgap like semiconductor properties with very fast radiative recombination rates. The new synthesis route makes possible the production and study of simple fcc polymorphs of Si nano-crystals with an easy alteration of surface termination groups.

  20. Luminescence nanocrystals for solar cell enhancement.

    PubMed

    Liu, Shu-Man; Chen, Wei; Wang, Zhan-Guo

    2010-03-01

    Semiconductor nanocrystals (NCs) prepared by wet-chemical routes have been proposed as an attractive candidate for fabrication of the third-generation thin-film solar cells due to their quantum confinement effects and excellent dispersion ability in polymer films. However, to date, a solar cell incorporating semiconductor NCs in the photoactive layer still has rather low efficiency due to the low carrier mobility of the non-continued NC phase and the possible radiative recombination in NCs. To avoid these disadvantages, NCs have been proposed and applied as a luminescent species in a passive photon converting layer to modify the solar spectrum before the light enters the photovoltaic device. Photon conversion processes, including up-conversion, down-conversion, and down-shifting, have been observed in various colloidal NC samples and have great potential to enhance photovoltaic performance when applied to the existing single-junction solar cells or narrow-band molecular-based devices.

  1. Experimental and theoretical investigations of electronic and atomic structure of Si-nanocrystals formed in sapphire by ion implantation

    NASA Astrophysics Data System (ADS)

    Wainstein, D.; Kovalev, A.; Tetelbaum, D.; Mikhailov, A.; Bulutay, C.; Aydinli, A.

    2008-03-01

    The semiconductor nanocomposites based on Si nanocrystals in dielectric matrices attract a great amount of attention due to their ability for luminescence in visible and near-IR part of the electromagnetic spectrum. Si nanocrystals in sapphire matrix were formed by Si+ ion implantation with doses from 5×1016 to 3×1017 cm-2 at an accelerating voltage 100 kV and post-implantation annealing at 500 - 1100 °C for 2 hours. Depth distribution of lattice defects, impurities and Si nanocrystals, the peculiarities of interband electronic transitions were investigated by XPS and HREELS. The molecular orbitals and local electronic structure of the Al2O3 matrix with Si nanocrystals was calculated using an atomistic pseudopotential technique. The electronic structure of Si nanocrystals as determined from HREELS measurements is in good agreement with the theoretically calculated electronic structure for Si nanocrystals.

  2. Nanocrystal dispersed amorphous alloys

    NASA Technical Reports Server (NTRS)

    Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)

    2001-01-01

    Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.

  3. Nanocrystal-Powered Nanomotor

    SciTech Connect

    Regan, B.C.; Aloni, S.; Jensen, K.; Ritchie, R.O.; Zettl, A.

    2005-07-05

    We have constructed and operated a nanoscale linear motorpowered by a single metal nanocrystal ram sandwiched between mechanicallever arms. Low-level electrical voltages applied to the carbon nanotubelever arms cause the nanocrystal to grow or shrink in a controlledmanner. The length of the ram is adjustable from 0 to more than 150 nm,with extension speeds exceeding 1900 nm/s. The thermodynamic principlesgoverning motor operation resemble those driving frost heave, a naturalsolid-state linear motor.

  4. Defect Chemistry and Plasmon Physics of Colloidal Metal Oxide Nanocrystals.

    PubMed

    Lounis, Sebastien D; Runnerstrom, Evan L; Llordés, Anna; Milliron, Delia J

    2014-05-01

    Plasmonic nanocrystals of highly doped metal oxides have seen rapid development in the past decade and represent a class of materials with unique optoelectronic properties. In this Perspective, we discuss doping mechanisms in metal oxides and the accompanying physics of free carrier scattering, both of which have implications in determining the properties of localized surface plasmon resonances (LSPRs) in these nanocrystals. The balance between activation and compensation of dopants limits the free carrier concentration of the most common metal oxides, placing a ceiling on the LSPR frequency. Furthermore, because of ionized impurity scattering of the oscillating plasma by dopant ions, scattering must be treated in a fundamentally different way in semiconductor metal oxide materials when compared with conventional metals. Though these effects are well-understood in bulk metal oxides, further study is needed to understand their manifestation in nanocrystals and corresponding impact on plasmonic properties, and to develop materials that surpass current limitations in free carrier concentration.

  5. Quantum behavior of terahertz photoconductivity in silicon nanocrystals networks

    NASA Astrophysics Data System (ADS)

    Pushkarev, V.; Ostatnický, T.; Němec, H.; Chlouba, T.; Trojánek, F.; Malý, P.; Zacharias, M.; Gutsch, S.; Hiller, D.; Kužel, P.

    2017-03-01

    Quantum-size effects are essential for understanding the terahertz conductivity of semiconductor nanocrystals, particularly at low temperatures. We derived a quantum mechanical expression for the linear terahertz response of nanocrystals; its introduction into an appropriate effective medium model provides a comprehensive microscopic approach for the analysis of terahertz conductivity spectra as a function of frequency, temperature, and excitation fluence. We performed optical pump-terahertz probe experiments in multilayer Si quantum dot networks with various degrees of percolation at 300 and 20 K and with variable pump fluence (initial carrier density) over nearly three orders of magnitude. Our theoretical approach was successfully applied to quantitatively interpret all the measured data within a single model. A careful data analysis made it possible to assess the distribution of sizes of nanocrystals participating to the photoconduction. We show and justify that such conductivity-weighted distribution may differ from the size distribution obtained by standard analysis of transmission electron microscopy images.

  6. 2009 Clusters, Nanocrystals & Nanostructures GRC

    SciTech Connect

    Lai-Sheng Wang

    2009-07-19

    For over thirty years, this Gordon Conference has been the premiere meeting for the field of cluster science, which studies the phenomena that arise when matter becomes small. During its history, participants have witnessed the discovery and development of many novel materials, including C60, carbon nanotubes, semiconductor and metal nanocrystals, and nanowires. In addition to addressing fundamental scientific questions related to these materials, the meeting has always included a discussion of their potential applications. Consequently, this conference has played a critical role in the birth and growth of nanoscience and engineering. The goal of the 2009 Gordon Conference is to continue the forward-looking tradition of this meeting and discuss the most recent advances in the field of clusters, nanocrystals, and nanostructures. As in past meetings, this will include new topics that broaden the field. In particular, a special emphasis will be placed on nanomaterials related to the efficient use, generation, or conversion of energy. For example, we anticipate presentations related to batteries, catalysts, photovoltaics, and thermoelectrics. In addition, we expect to address the controversy surrounding carrier multiplication with a session in which recent results addressing this phenomenon will be discussed and debated. The atmosphere of the conference, which emphasizes the presentation of unpublished results and lengthy discussion periods, ensures that attendees will enjoy a valuable and stimulating experience. Because only a limited number of participants are allowed to attend this conference, and oversubscription is anticipated, we encourage all interested researchers from academia, industry, and government institutions to apply as early as possible. An invitation is not required. We also encourage all attendees to submit their latest results for presentation at the poster sessions. We anticipate that several posters will be selected for 'hot topic' oral

  7. Charge transport in metal oxide nanocrystal-based materials

    NASA Astrophysics Data System (ADS)

    Runnerstrom, Evan Lars

    matrix, and that the morphology and properties of the nanocomposites can be manipulated by changing the chemical composition of the deposition solution. Careful application of AC impedance spectroscopy techniques and DC measurements are used to show that the nanocomposites exhibit mixed ionic and electronic conductivity, where electronic charge is transported through the ITO nanocrystal phase, and ionic charge is transported through the polymer matrix phase. The synthetic methods developed here and understanding of charge transport ultimately lead to the fabrication of a solid state nanocomposite electrochromic device based on nanocrystals of ITO and cerium oxide. Part II of this dissertation considers electron transport within individual metal oxide nanocrystals themselves. It primarily examines relationships between synthetic chemistry, doping mechanisms in metal oxides, and the accompanying physics of free carrier scattering within the interior of highly doped metal oxide nanocrystals, with particular mind paid to ITO nanocrystals. Additionally, synthetic methods as well as metal oxide defect chemistry influences the balance between activation and compensation of dopants, which limits the nanocrystals' free carrier concentration. Furthermore, because of ionized impurity scattering of the oscillating electrons by dopant ions, scattering must be treated in a fundamentally different way in semiconductor metal oxide materials when compared with conventional metals. (Abstract shortened by ProQuest.).

  8. High-efficiency plasmon-enhanced and graphene-supported semiconductor/metal core-satellite hetero-nanocrystal photocatalysts for visible-light dye photodegradation and H2 production from water.

    PubMed

    Zhang, Jie; Wang, Ping; Sun, Jian; Jin, Yongdong

    2014-11-26

    Solar-driven photocatalytic process based on electron-hole pair production in semiconductors is a long sought-after solution to a green and renewable energy and has attracted a renaissance of interest recently. The relatively low photocatalytic efficiency, however, is a main obstacle to their practical applications. A promising attempt to solve this problem is by combined use of metal nanoparticles, by taking advantage of strong and localized plasmonic near-field to enhance solar absorption and to increase the electron-hole pair generation rate at the surface of semiconductor. Here, we report a semiconductor/metal visible-light photocatalyst based on CdSe/CdS-Au (QD-Au) core-satellite heteronanocrystals, and assemble them on graphene nanosheets for better photocatalytic reaction. The as-synthesized photocatalyst exhibits excellent plasmon-enhanced photocatalytic activities toward both photodegradation of organic dye and visible-light H2 generation from water. The H2 evolution rate achieves a maximum of 3113 μmol h(-1) g(-1) for the heteronanocrystal-graphene composites, which is about 155% enhancement compared to nonplasmonic QD-G sample and 340% enhancement compared to control QD-Au-G sample, and the apparent quantum efficiency (QE) reaches to 25.4% at wavelength of 450 nm.

  9. Binary superlattices from colloidal nanocrystals and giant polyoxometalate clusters.

    PubMed

    Bodnarchuk, Maryna I; Erni, Rolf; Krumeich, Frank; Kovalenko, Maksym V

    2013-04-10

    We report a new kind of long-range ordered binary superlattices comprising atomically defined inorganic clusters and colloidally synthesized nanocrystals. In a model system, we combined surfactant-encapsulated, nearly spherical giant polyoxometalate clusters containing 2.9 nm polyoxomolybdate or 2.5 nm polyoxovanadomolybdate cores with monodisperse colloidal semiconductor nanocrystals (PbS, CdSe, PbS/CdS; 4-11 nm). The results are rationalized on the basis of dense packing principles of sterically stabilized particles with predominantly hard-spherelike interparticle interactions. By varying the size-ratios and relative concentrations of constituents, we obtained known thermodynamically stable binary packings of hard-spheres such as NaCl, AlB2, and NaZn13 lattices and also CaCu5-type lattice and aperiodic quasicrystals with 12-fold symmetry. These results suggest that other kinds of cluster materials such as fullerenes and magic-sized metallic and semiconductor clusters can also be integrated into supramolecular assemblies with nanocrystals. Furthermore, synergistic effects are expected from the combination of redox and catalytic properties of polyoxometalates with excitonic and plasmonic properties of inorganic nanocrystals.

  10. Effect of location of Si or Ge nanocrystals on the memory behavior of MNOS structures

    NASA Astrophysics Data System (ADS)

    Horváth, Zs. J.; Basa, P.; Molnár, K. Z.; Molnár, Gy.; Jászi, T.; Pap, A. E.

    2013-06-01

    Charge injection and retention behaviors of metal-nitride-oxide-silicon (MNOS) memory structures with Si or Ge nanocrystals embedded at a depth of 3 nm in the nitride layer were studied. The effect of Si nanocrystals on these properties was opposite in comparison with that of Ge nanocrystals. To understand the origin of these opposite effects, the influence of the oxide thickness and of the depth, size and location of semiconductor nanocrystals has been studied on the charging behavior of MNOS non-volatile memory structures by the calculation of electron and hole tunneling probabilities, and by the simulation of memory window, memory hysteresis and retention behavior. For MNOS structures it is obtained that the presence of nanocrystals enhances the charge injection resulting in better performance, but only for structures with thin tunnel oxide layer (below 3 nm), and if the nanocrystals are located close to the oxide/nitride interface. In the case of very high tunneling probability, i.e., of high tunneling currents the system approaches equilibrium and the memory behavior collapses. There is a narrow range of oxide thickness or depth of nanocrystals, where the charging properties change very fast. Retention exhibits a very sharp dependence on the oxide thickness and on depth of nanocrystals as well. Most part of the experimental results can be explained on the basis of the results of simulations.

  11. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells

    PubMed Central

    Bozyigit, Deniz; Lin, Weyde M. M.; Yazdani, Nuri; Yarema, Olesya; Wood, Vanessa

    2015-01-01

    Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic–organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current–voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode–nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices. PMID:25625647

  12. A Chemical Approach to 3-D Lithographic Patterning of Si and GeNanocrystals

    SciTech Connect

    Sharp, I.D.; Xu, Q.; Yi, D.O.; Liao, C.Y.; Ager III, J.W.; Beeman, J.W.; Yu, K.M.; Robinson, J.T.; Dubon, O.D.; Chrzan, D.C.; Haller, E.E.

    2005-12-12

    Ion implantation into silica followed by thermal annealingis an established growth method for Si and Ge nanocrystals. Wedemonstrate that growth of Group IV semiconductor nanocrystals can besuppressed by co-implantation of oxygen prior to annealing. For Sinanocrystals, at low Si/O dose ratios, oxygen co-implantation leads to areduction of the average nanocrystal size and a blue-shift of thephotoluminescence emission energy. For both Si and Ge nanocrystals, atlarger Si/O or Ge/O dose ratios, the implanted specie is oxidized andnanocrystals do not form. This chemical deactivation was utilized toachieve patterned growth of Si and Ge nanocrystals. Si was implanted intoa thin SiO2 film on a Si substrate followed by oxygen implantationthrough an electron beam lithographically defined stencil mask. Thermalannealing of the co-implanted structure yields two-dimensionallypatterned growth of Si nanocrystals under the masked regions. We applieda previously developed process to obtain exposed nanocrystals byselective HF etching of the silica matrix to these patterned structures.Atomic force microscopy (AFM) of etched structures revealed that exposednanocrystals are not laterally displaced from their original positionsduring the etching process. Therefore, this process provides a means ofachieving patterned structures of exposed nanocrystals. The possibilitiesfor scaling this chemical-based lithography process to smaller featuresand for extending it to 3-D patterning is discussed.

  13. Nanocrystals encapsulated in SiO2 particles: silanization and homogenous coating for bio applications.

    PubMed

    Yang, Ping; Li, Xiaoyu; Zhang, Ruili; Liu, Ning; Zhang, Yulan

    2013-03-01

    Sol-gel procedures have been developed to encapsulate inorganic nanocrystals including metallic Au and II-VI semiconductor materials (CdSe/Cd(1-x)Zn(x)S) in SiO2 particles by using tetraethyl orthosilicate. The key strategy was the control of a sol-gel procedure. The anisotropic deposition of SiO2 monomers occurs because well-developed crystal facets having different affinity to SiO2 monomers. SiO2 monomers were not homogeneously deposited on nonspherical Au and CdSe/Cd(1-x)Zn(x)S nanocrystals. A surface silanization process, partly hydrolyzed tetraethyl orthosilicate were attached to the nanocrystals instead of initial ligands, plays an important role for the nanocrystals coated homogeneously with a SiO2 layer. Furthermore, CdSe/Cd(1-x)Zn(x)S nanocrystals were homogeneously coated with a thin SiO2 layer by the surface silanization process and a subsequent reverse micelle route. Colloidal Au nanocrystals were homogeneously coated with a SiO2 shell by the surface silanization process and subsequent Stöber synthesis without using a silane coupling agent or bulk polymer as the surface primer to render the Au surface vitreophilic. These results indicated partly hydrolyzed tetraethyl orthosilicate has an ability to replace the ligand on nanocrystals. After surface modification, the SiO2 particles with nanocrystals were conjugated with antibody for bioapplications.

  14. Synthesis and shape-tailoring of copper sulfide/indium sulfide-based nanocrystals.

    PubMed

    Han, Wei; Yi, Luoxin; Zhao, Nan; Tang, Aiwei; Gao, Mingyuan; Tang, Zhiyong

    2008-10-01

    Heterostructured Cu2S-In2S3 nanocrystals with various shapes and compositions were synthesized by a high-temperature precursor-injection method using the semiconductor nanocrystal Cu1.94S as a catalyst. The intrinsic cationic deficiencies formed at high temperature by Cu ions made the Cu1.94S nanocrystal a good candidate for catalyzing the nucleation and subsequent growth of In 2S3 nanocrystals, eventually leading to the formation of heterostructured Cu2S-In2S3 nanocrystals. Gelification of the reaction systems, which were composed of different types of nanocrystal precursors and solvent, was found to be a very effective measure for controlling the growth kinetics of the heterostructured particles. Consequently, matchsticklike Cu2S3-In2S3 heterostructured nanorods, teardroplike quasi-core/shell Cu2S@In2S3 nanocrystals, and pencil-like In2S3 nanorods were successfully obtained by manipulating the gelification of the reaction system; this formed a solid experimental basis for further discussion of the growth mechanisms for differently shaped and structured nanocrystals. By reaction with 1,10-phenanthroline, a reagent that strongly and selectively binds to Cu(+), a compositional transformation from binary matchsticklike Cu2S-In2S3 nanorods to pure In2S3 nanorods was successfully achieved.

  15. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells

    NASA Astrophysics Data System (ADS)

    Bozyigit, Deniz; Lin, Weyde M. M.; Yazdani, Nuri; Yarema, Olesya; Wood, Vanessa

    2015-01-01

    Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic-organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current-voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode-nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices.

  16. Photoluminescence Enhancement through Symmetry Breaking Induced by Defects in Nanocrystals.

    PubMed

    Sercel, Peter C; Shabaev, A; Efros, Al L

    2017-08-09

    We present a theoretical model for the effect of symmetry breaking introduced by the doping of semiconductor nanocrystals with Coulomb impurities. The presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through the mixing of the hole spin and parity sublevels, breaking the selection rules responsible for the exciton dark state in undoped nanocrystals. After reviewing the effects on the exciton fine structure and optical selection rules using symmetry theory, we present a perturbative model to quantify the effects. We find that the symmetry breaking proceeds by two mechanisms: First, mixing by even parity terms in the Coulomb multipole expansion results in an exciton fine structure consisting of three optically active doublets which are polarized along x, y, and z axes with a ground optically passive dark exciton state, and second, odd parity terms which break inversion symmetry significantly activate optical transitions which are optically forbidden in the unperturbed nanocrystal due to both spin and parity selection rules. In the case of small sized "quasi-spherical" nanocrystals, the introduction of a single positively charged Coulomb center is shown here to result in significant enhancement of the radiative decay rate at room temperatures by up to a factor of 10.

  17. A Silicon Nanocrystal Schottky Junction Solar Cell produced from Colloidal Silicon Nanocrystals

    PubMed Central

    2010-01-01

    Solution-processed semiconductors are seen as a promising route to reducing the cost of the photovoltaic device manufacture. We are reporting a single-layer Schottky photovoltaic device that was fabricated by spin-coating intrinsic silicon nanocrystals (Si NCs) from colloidal suspension. The thin-film formation process was based on Si NCs without any ligand attachment, exchange, or removal reactions. The Schottky junction device showed a photovoltaic response with a power conversion efficiency of 0.02%, a fill factor of 0.26, short circuit-current density of 0.148 mA/cm2, and open-circuit voltage of 0.51 V. PMID:20676200

  18. Nanocrystal Solar Cells

    SciTech Connect

    Gur, Ilan

    2006-01-01

    This dissertation presents the results of a research agenda aimed at improving integration and stability in nanocrystal-based solar cells through advances in active materials and device architectures. The introduction of 3-dimensional nanocrystals illustrates the potential for improving transport and percolation in hybrid solar cells and enables novel fabrication methods for optimizing integration in these systems. Fabricating cells by sequential deposition allows for solution-based assembly of hybrid composites with controlled and well-characterized dispersion and electrode contact. Hyperbranched nanocrystals emerge as a nearly ideal building block for hybrid cells, allowing the controlled morphologies targeted by templated approaches to be achieved in an easily fabricated solution-cast device. In addition to offering practical benefits to device processing, these approaches offer fundamental insight into the operation of hybrid solar cells, shedding light on key phenomena such as the roles of electrode-contact and percolation behavior in these cells. Finally, all-inorganic nanocrystal solar cells are presented as a wholly new cell concept, illustrating that donor-acceptor charge transfer and directed carrier diffusion can be utilized in a system with no organic components, and that nanocrystals may act as building blocks for efficient, stable, and low-cost thin-film solar cells.

  19. Designer Nanocrystal Materials for Photovoltaics

    NASA Astrophysics Data System (ADS)

    Kagan, Cherie

    Advances in synthetic methods allow a wide range of semiconductor nanocrystals (NCs) to be tailored in size and shape and to be used as building blocks in the design of NC solids. However, the long, insulating ligands commonly employed in the synthesis of colloidal NCs inhibit strong interparticle coupling and charge transport once NCs are assembled into the solids state as NC arrays. We will describe the range of short, compact ligand chemistries we employ to exchange the long, insulating ligands used in synthesis and to increase interparticle coupling. These ligand exchange processes can have a dramatic influence on NC surface chemistry as well as NC organization in the solids, showing examples of short-range order. Synergistically, we use 1) thermal evaporation and diffusion and 2) wet-chemical methods to introduce extrinsic impurities and non-stoichiometry to passivate surface traps and dope NC solids. NC coupling and doping provide control over the density of states and the carrier type, concentration, mobility, and lifetime, which we characterize by a range of electronic and spectroscopic techniques. We will describe the importance of engineering device interfaces to design NC materials for solar photovoltaics.

  20. Synthesis of nanocrystals and nanocrystal self-assembly

    NASA Astrophysics Data System (ADS)

    Chen, Zhuoying

    nanocrystals is presented. Different surfactants of amines, carboxylic acids, and alcohols were used to study the effect of size and morphological control over the nanocrystals. Techniques including X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and high-resolution electron microscopy are used to examine crystallinity and morphology. Chapter 3. By investigating the self-assembly of cadmium selenide-gold (CdSe-Au) nanoparticle mixtures by transmission electron microscopy after solvent evaporation, the effect of solvents in the formation process of CdSe-Au binary nanoparticle superlattices (BNSLs) was studied. 1-dodecanethiol was found to be critical in generating conditions necessary for superlattice formation, prior to the other factors that likely determine structure, highlighting the dual role of this organic polar molecule as both ligand and high boiling point/crystallization solvent. The influence of thiol was investigated under various concentrations (and also compared with other less polar solvents) in order to determine optimized conditions for self-assembly, for which relatively large (> 1 mum2) areas of superlattices could be routinely formed. Depending on appropriate selection of the radius ratio, AuCu or CaCu 5 binary superlattices of CdSe-Au nanoparticles were generated. Chapter 4. The preparation of binary nanoparticle superlattices obtained by self-assembly of two different semiconductor quantum dots is presented. Such a system is a means to include two discretized, quantum-confined, and complimentary semiconductor units in close proximity, which might exhibit interesting charge transport properties for applications such as solar cells. From a range of possible structures predicted, we observe an exclusive preference for the formation of Cuboctahedral AB13 (Cuboctahedral modification of NaZn13) and AB5 (isostructural with CaCu5) structures in the system of 8.1 nm CdTe and 4.4 nm CdSe nanoparticles. To understand further

  1. Germanium Nanocrystal Solar Cells

    NASA Astrophysics Data System (ADS)

    Holman, Zachary Charles

    Greenhouse gas concentrations in the atmosphere are approaching historically unprecedented levels from burning fossil fuels to meet the ever-increasing world energy demand. A rapid transition to clean energy sources is necessary to avoid the potentially catastrophic consequences of global warming. The sun provides more than enough energy to power the world, and solar cells that convert sunlight to electricity are commercially available. However, the high cost and low efficiency of current solar cells prevent their widespread implementation, and grid parity is not anticipated to be reached for at least 15 years without breakthrough technologies. Semiconductor nanocrystals (NCs) show promise for cheap multi-junction photovoltaic devices. To compete with photovoltaic materials that are currently commercially available, NCs need to be inexpensively cast into dense thin films with bulk-like electrical mobilities and absorption spectra that can be tuned by altering the NC size. The Group II-VI and IV-VI NC communities have had some success in achieving this goal by drying and then chemically treating colloidal particles, but the more abundant and less toxic Group IV NCs have proven more challenging. This thesis reports thin films of plasma-synthesized Ge NCs deposited using three different techniques, and preliminary solar cells based on these films. Germanium tetrachloride is dissociated in the presence of hydrogen in a nonthermal plasma to nucleate Ge NCs. Transmission electron microscopy and X-ray diffraction indicate that the particles are nearly monodisperse (standard deviations of 10-15% the mean particle diameter) and the mean diameter can be tuned from 4-15 nm by changing the residence time of the Ge NCs in the plasma. In the first deposition scheme, a Ge NC colloid is formed by reacting nanocrystalline powder with 1-dodecene and dispersing the functionalized NCs in a solvent. Films are then formed on substrates by drop-casting the colloid and allowing it to dry

  2. Germanium and Silicon Nanocrystal Thin-Film Field-Effect Transistors from Solution

    SciTech Connect

    Holman, Zachary C.; Liu, Chin-Yi; Kortshagen, Uwe R.

    2010-07-09

    Germanium and silicon have lagged behind more popular II-VI and IV-VI semiconductor materials in the emerging field of semiconductor nanocrystal thin film devices. We report germanium and silicon nanocrystal field-effect transistors fabricated by synthesizing nanocrystals in a plasma, transferring them into solution, and casting thin films. Germanium devices show n-type, ambipolar, or p-type behavior depending on annealing temperature with electron and hole mobilities as large as 0.02 and 0.006 cm2 V-1 s-1, respectively. Silicon devices exhibit n-type behavior without any postdeposition treatment, but are plagued by poor film morphology.

  3. Nanocrystal superlattices: No need to wait

    NASA Astrophysics Data System (ADS)

    Liu, Kun; Kumacheva, Eugenia

    2017-09-01

    In contrast with protocols reporting self-assembly of nanocrystals after synthesis, Pd nanocrystals rapidly form 3D micrometre-size superlattices during growth. The nanocrystals keep growing after assembly, tuning the size of the lattice.

  4. Oxide Nanocrystal Model Catalysts.

    PubMed

    Huang, Weixin

    2016-03-15

    Model catalysts with uniform and well-defined surface structures have been extensively employed to explore structure-property relationships of powder catalysts. Traditional oxide model catalysts are based on oxide single crystals and single crystal thin films, and the surface chemistry and catalysis are studied under ultrahigh-vacuum conditions. However, the acquired fundamental understandings often suffer from the "materials gap" and "pressure gap" when they are extended to the real world of powder catalysts working at atmospheric or higher pressures. Recent advances in colloidal synthesis have realized controlled synthesis of catalytic oxide nanocrystals with uniform and well-defined morphologies. These oxide nanocrystals consist of a novel type of oxide model catalyst whose surface chemistry and catalysis can be studied under the same conditions as working oxide catalysts. In this Account, the emerging concept of oxide nanocrystal model catalysts is demonstrated using our investigations of surface chemistry and catalysis of uniform and well-defined cuprous oxide nanocrystals and ceria nanocrystals. Cu2O cubes enclosed with the {100} crystal planes, Cu2O octahedra enclosed with the {111} crystal planes, and Cu2O rhombic dodecahedra enclosed with the {110} crystal planes exhibit distinct morphology-dependent surface reactivities and catalytic properties that can be well correlated with the surface compositions and structures of exposed crystal planes. Among these types of Cu2O nanocrystals, the octahedra are most reactive and catalytically active due to the presence of coordination-unsaturated (1-fold-coordinated) Cu on the exposed {111} crystal planes. The crystal-plane-controlled surface restructuring and catalytic activity of Cu2O nanocrystals were observed in CO oxidation with excess oxygen. In the propylene oxidation reaction with O2, 1-fold-coordinated Cu on Cu2O(111), 3-fold-coordinated O on Cu2O(110), and 2-fold-coordinated O on Cu2O(100) were identified

  5. Rigid Biopolymer Nanocrystal Systems for Controlling Multicomponent Nanoparticle Assembly and Orientation in Thin Film Solar Cells

    SciTech Connect

    Cha, Jennifer

    2016-10-31

    We have discovered techniques to synthesize well-defined DN conjugated nanostructures that are stable in a wide variety of conditions needed for DNA mediated assembly. Starting from this, we have shown that DNA can be used to control the assembly and integration of semiconductor nanocrystals into thin film devices that show photovoltaic effects.

  6. Preparation of ternary Cd1- x Zn x S nanocrystals with tunable ultraviolet absorption by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Zhang, Huihui; Liu, Limin; Li, Shaohua; Murowchick, James B.; Wisner, Clarissa; Leventis, Nickolas; Peng, Zhonghua; Tan, Guolong

    2015-03-01

    Composition-tunable ternary Cd1- x Zn x S nanocrystals are among the most extensively studied alloyed semiconductor nanocrystals. However, they are almost exclusively prepared by wet chemical routes, which lead to surface-capped nanoparticles. Herein, we present a simple mechanical alloying process to prepare uncapped Zn1- x Cd x S nanocrystals throughout the entire composition range. The resulting nanocrystals have average sizes smaller than 9 nm, are chemically homogenous, and exhibit linear lattice parameter-composition and close-to-linear band-gap-composition relationships. Continuous lattice contraction of the Cd1- x Zn x S nanocrystals with the atomic Zn concentration results in a successional enlargement of their band gap energies expanding from the visible region to the ultraviolet (UV) region, demonstrating the ability for precise control of band gap engineering through composition tuning and mechanical alloying. [Figure not available: see fulltext.

  7. Deep level transient spectroscopy (DLTS) on colloidal-synthesized nanocrystal solids.

    PubMed

    Bozyigit, Deniz; Jakob, Michael; Yarema, Olesya; Wood, Vanessa

    2013-04-24

    We demonstrate current-based, deep level transient spectroscopy (DLTS) on semiconductor nanocrystal solids to obtain quantitative information on deep-lying trap states, which play an important role in the electronic transport properties of these novel solids and impact optoelectronic device performance. Here, we apply this purely electrical measurement to an ethanedithiol-treated, PbS nanocrystal solid and find a deep trap with an activation energy of 0.40 eV and a density of NT = 1.7 × 10(17) cm(-3). We use these findings to draw and interpret band structure models to gain insight into charge transport in PbS nanocrystal solids and the operation of PbS nanocrystal-based solar cells.

  8. Dielectric properties of colloidal Gd2O3 nanocrystal films fabricated via electrophoretic deposition

    NASA Astrophysics Data System (ADS)

    Mahajan, S. V.; Dickerson, J. H.

    2010-03-01

    We investigated the dielectric characteristics of [Al/Gd2O3/Si] metal-oxide-semiconductor (MOS) capacitors, which were fabricated from films of gadolinium oxide (Gd2O3) nanocrystals used as the gate oxide layer. Electrophoretic deposition cast Gd2O3 nanocrystal films of different thicknesses by varying the concentration of the nanocrystal suspensions. Capacitance-voltage (C-V) measurements of the MOS capacitors exhibited hysteresis, which indicated potentially favorable charge-storage properties. The films' dielectric constant (κ =3.90), calculated from the C-V data, led to the packing density of nanocrystals within the film (66%), which is in the glassy regime approximated by randomly closed packed spheres.

  9. Exciton Energy Transfer from Halide Terminated Nanocrystals to Graphene in Solar Photovoltaics

    NASA Astrophysics Data System (ADS)

    Ajayi, Obafunso; Abramson, Justin; Anderson, Nicholas; Owen, Jonathan; Zhao, Yue; Kim, Phillip; Gesuele, Felice; Wong, Chee Wei

    2011-03-01

    Graphene, a zero-gap semiconductor, has been identified as an ideal electrode for nanocrystal solar cell photovoltaic applications due to its high carrier mobility. Further advances in efficient current extraction are required towards this end. We investigate the resonant energy transfer dynamics between photoexcited nanocrystals and graphene, where the energy transfer rate is characterized by the fluorescent quenching of the quantum dots in the presence of graphene. Energy transfer has been shown to have a d -4 dependence on the nanocrystal distance from the graphene surface, with a correction due to blinking statistics. We investigate this relationship with single and few layer graphene. We study halide-terminated CdSe quantum dots; where the absence of the insulating outershell improves the electronic coupling of the donor-acceptor system leads to improved electron transfer. We observe quenching of the halide terminated nanocrystals on graphene, with the quenching factor ρ defined as IQ /IG (the relative intensities on quartz and graphene).

  10. Direct printing of microstructures by femtosecond laser excitation of nanocrystals in solution

    SciTech Connect

    Shou, Wan; Pan, Heng

    2016-05-23

    We report direct printing of micro/sub-micron structures by femtosecond laser excitation of semiconductor nanocrystals (NCs) in solution. Laser excitation with moderate intensity (10{sup 11}–10{sup 12} W/cm{sup 2}) induces 2D and 3D deposition of CdTe nanocrystals in aqueous solution, which can be applied for direct printing of microstructures. It is believed that laser irradiation induces charge formation on nanocrystals leading to deposition. Furthermore, it is demonstrated that the charged nanocrystals can respond to external electrical bias, enabling a printing approach based on selective laser induced electrophoretic deposition. Finally, energy dispersive X-ray analysis of deposited structures shows oxidation occurs and deposited structure mainly consists of Cd{sub x}O.

  11. Real-time magnetic resonance imaging and quantification of lipoprotein metabolism in vivo using nanocrystals.

    PubMed

    Bruns, Oliver T; Ittrich, Harald; Peldschus, Kersten; Kaul, Michael G; Tromsdorf, Ulrich I; Lauterwasser, Joachim; Nikolic, Marija S; Mollwitz, Birgit; Merkel, Martin; Bigall, Nadja C; Sapra, Sameer; Reimer, Rudolph; Hohenberg, Heinz; Weller, Horst; Eychmüller, Alexander; Adam, Gerhard; Beisiegel, Ulrike; Heeren, Joerg

    2009-03-01

    Semiconductor quantum dots and superparamagnetic iron oxide nanocrystals have physical properties that are well suited for biomedical imaging. Previously, we have shown that iron oxide nanocrystals embedded within the lipid core of micelles show optimized characteristics for quantitative imaging. Here, we embed quantum dots and superparamagnetic iron oxide nanocrystals in the core of lipoproteins--micelles that transport lipids and other hydrophobic substances in the blood--and show that it is possible to image and quantify the kinetics of lipoprotein metabolism in vivo using fluorescence and dynamic magnetic resonance imaging. The lipoproteins were taken up by liver cells in wild-type mice and displayed defective clearance in knock-out mice lacking a lipoprotein receptor or its ligand, indicating that the nanocrystals did not influence the specificity of the metabolic process. Using this strategy it is possible to study the clearance of lipoproteins in metabolic disorders and to improve the contrast in clinical imaging.

  12. Real-time magnetic resonance imaging and quantification of lipoprotein metabolism in vivo using nanocrystals

    NASA Astrophysics Data System (ADS)

    Bruns, Oliver T.; Ittrich, Harald; Peldschus, Kersten; Kaul, Michael G.; Tromsdorf, Ulrich I.; Lauterwasser, Joachim; Nikolic, Marija S.; Mollwitz, Birgit; Merkel, Martin; Bigall, Nadja C.; Sapra, Sameer; Reimer, Rudolph; Hohenberg, Heinz; Weller, Horst; Eychmüller, Alexander; Adam, Gerhard; Beisiegel, Ulrike; Heeren, Joerg

    2009-03-01

    Semiconductor quantum dots and superparamagnetic iron oxide nanocrystals have physical properties that are well suited for biomedical imaging. Previously, we have shown that iron oxide nanocrystals embedded within the lipid core of micelles show optimized characteristics for quantitative imaging. Here, we embed quantum dots and superparamagnetic iron oxide nanocrystals in the core of lipoproteins-micelles that transport lipids and other hydrophobic substances in the blood-and show that it is possible to image and quantify the kinetics of lipoprotein metabolism in vivo using fluorescence and dynamic magnetic resonance imaging. The lipoproteins were taken up by liver cells in wild-type mice and displayed defective clearance in knock-out mice lacking a lipoprotein receptor or its ligand, indicating that the nanocrystals did not influence the specificity of the metabolic process. Using this strategy it is possible to study the clearance of lipoproteins in metabolic disorders and to improve the contrast in clinical imaging.

  13. Pseudo-direct bandgap transitions in silicon nanocrystals: effects on optoelectronics and thermoelectrics.

    PubMed

    Singh, Vivek; Yu, Yixuan; Sun, Qi-C; Korgel, Brian; Nagpal, Prashant

    2014-12-21

    While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in nanoscaled silicon semiconductors. Therefore, these results can have important implications for the design of optoelectronics and thermoelectric devices based on nanostructured silicon.

  14. Multiple exciton generation in colloidal silicon nanocrystals.

    PubMed

    Beard, Matthew C; Knutsen, Kelly P; Yu, Pingrong; Luther, Joseph M; Song, Qing; Metzger, Wyatt K; Ellingson, Randy J; Nozik, Arthur J

    2007-08-01

    Multiple exciton generation (MEG) is a process whereby multiple electron-hole pairs, or excitons, are produced upon absorption of a single photon in semiconductor nanocrystals (NCs) and represents a promising route to increased solar conversion efficiencies in single-junction photovoltaic cells. We report for the first time MEG yields in colloidal Si NCs using ultrafast transient absorption spectroscopy. We find the threshold photon energy for MEG in 9.5 nm diameter Si NCs (effective band gap identical with Eg = 1.20 eV) to be 2.4 +/- 0.1Eg and find an exciton-production quantum yield of 2.6 +/- 0.2 excitons per absorbed photon at 3.4Eg. While MEG has been previously reported in direct-gap semiconductor NCs of PbSe, PbS, PbTe, CdSe, and InAs, this represents the first report of MEG within indirect-gap semiconductor NCs. Furthermore, MEG is found in relatively large Si NCs (diameter equal to about twice the Bohr radius) such that the confinement energy is not large enough to produce a large blue-shift of the band gap (only 80 meV), but the Coulomb interaction is sufficiently enhanced to produce efficient MEG. Our findings are of particular importance because Si dominates the photovoltaic solar cell industry, presents no problems regarding abundance and accessibility within the Earth's crust, and poses no significant environmental problems regarding toxicity.

  15. Analytical modeling of localized surface plasmon resonance in heterostructure copper sulfide nanocrystals

    SciTech Connect

    Caldwell, Andrew H.; Ha, Don-Hyung; Robinson, Richard D.; Ding, Xiaoyue

    2014-10-28

    Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals is a relatively new field of investigation that promises greater tunability of plasmonic properties compared to metal nanoparticles. A novel process by which the LSPR in semiconductor nanocrystals can be altered is through heterostructure formation arising from solution-based cation exchange. Herein, we describe the development of an analytical model of LSPR in heterostructure copper sulfide-zinc sulfide nanocrystals synthesized via a cation exchange reaction between copper sulfide (Cu{sub 1.81}S) nanocrystals and Zn ions. The cation exchange reaction produces dual-interface, heterostructure nanocrystals in which the geometry of the copper sulfide phase can be tuned from a sphere to a thin disk separating symmetrically-grown sulfide (ZnS) grains. Drude model electronic conduction and Mie-Gans theory are applied to describe how the LSPR wavelength changes during cation exchange, taking into account the morphology evolution and changes to the local permittivity. The results of the modeling indicate that the presence of the ZnS grains has a significant effect on the out-of-plane LSPR mode. By comparing the results of the model to previous studies on solid-solid phase transformations of copper sulfide in these nanocrystals during cation exchange, we show that the carrier concentration is independent of the copper vacancy concentration dictated by its atomic phase. The evolution of the effective carrier concentration calculated from the model suggests that the out-of-plane resonance mode is dominant. The classical model was compared to a simplified quantum mechanical model which suggested that quantum mechanical effects become significant when the characteristic size is less than ∼8 nm. Overall, we find that the analytical models are not accurate for these heterostructured semiconductor nanocrystals, indicating the need for new model development for this emerging field.

  16. Semiconductor sensors

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C. (Inventor); Lagowski, Jacek (Inventor)

    1977-01-01

    A semiconductor sensor adapted to detect with a high degree of sensitivity small magnitudes of a mechanical force, presence of traces of a gas or light. The sensor includes a high energy gap (i.e., .about. 1.0 electron volts) semiconductor wafer. Mechanical force is measured by employing a non-centrosymmetric material for the semiconductor. Distortion of the semiconductor by the force creates a contact potential difference (cpd) at the semiconductor surface, and this cpd is determined to give a measure of the force. When such a semiconductor is subjected to illumination with an energy less than the energy gap of the semiconductors, such illumination also creates a cpd at the surface. Detection of this cpd is employed to sense the illumination itself or, in a variation of the system, to detect a gas. When either a gas or light is to be detected and a crystal of a non-centrosymmetric material is employed, the presence of gas or light, in appropriate circumstances, results in a strain within the crystal which distorts the same and the distortion provides a mechanism for qualitative and quantitative evaluation of the gas or the light, as the case may be.

  17. Semiconductor photoelectrochemistry

    NASA Technical Reports Server (NTRS)

    Buoncristiani, A. M.; Byvik, C. E.

    1983-01-01

    Semiconductor photoelectrochemical reactions are investigated. A model of the charge transport processes in the semiconductor, based on semiconductor device theory, is presented. It incorporates the nonlinear processes characterizing the diffusion and reaction of charge carriers in the semiconductor. The model is used to study conditions limiting useful energy conversion, specifically the saturation of current flow due to high light intensity. Numerical results describing charge distributions in the semiconductor and its effects on the electrolyte are obtained. Experimental results include: an estimate rate at which a semiconductor photoelectrode is capable of converting electromagnetic energy into chemical energy; the effect of cell temperature on the efficiency; a method for determining the point of zero zeta potential for macroscopic semiconductor samples; a technique using platinized titanium dioxide powders and ultraviolet radiation to produce chlorine, bromine, and iodine from solutions containing their respective ions; the photoelectrochemical properties of a class of layered compounds called transition metal thiophosphates; and a technique used to produce high conversion efficiency from laser radiation to chemical energy.

  18. Electronic structure study of wide band gap magnetic semiconductor (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals in paramagnetic and ferromagnetic phases

    NASA Astrophysics Data System (ADS)

    Dwivedi, G. D.; Joshi, Amish G.; Kumar, Shiv; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L.; Ghosh, A. K.; Chatterjee, Sandip

    2016-04-01

    X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La0.6Pr0.4)0.65Ca0.35MnO3 near Fermi-level. XMCD results indicate that Mn3+ and Mn4+ spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La0.6Pr0.4)0.65Ca0.35MnO3 system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below TC. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

  19. Switching between Plasmonic and Fluorescent Copper Sulfide Nanocrystals.

    PubMed

    van der Stam, Ward; Gudjonsdottir, Solrun; Evers, Wiel H; Houtepen, Arjan J

    2017-09-20

    Control over the doping density in copper sulfide nanocrystals is of great importance and determines its use in optoelectronic applications such as NIR optical switches and photovoltaic devices. Here, we demonstrate that we can reversibly control the hole carrier density (varying from >10(22) cm(-3) to intrinsic) in copper sulfide nanocrystals by electrochemical methods. We can control the type of charge injection, i.e., capacitive charging or ion intercalation, via the choice of the charge compensating cation (e.g., ammonium salts vs Li(+)). Further, the type of intercalating ion determines whether the charge injection is fully reversible (for Li(+)) or leads to permanent changes in doping density (for Cu(+)). Using fully reversible lithium intercalation allows us to switch between thin films of covellite CuS NCs (Eg = 2.0 eV, hole density 10(22) cm(-3), strong localized surface plasmon resonance) and low-chalcocite CuLiS NCs (Eg = 1.2 eV, intrinsic, no localized surface plasmon resonance), and back. Electrochemical Cu(+) ion intercalation leads to a permanent phase transition to intrinsic low-chalcocite Cu2S nanocrystals that display air stable fluorescence, centered around 1050 nm (fwhm ∼145 meV, PLQY ca. 1.8%), which is the first observation of narrow near-infrared fluorescence for copper sulfide nanocrystals. The dynamic control over the hole doping density and fluorescence of copper sulfide nanocrystals presented in this work and the ability to switch between plasmonic and fluorescent semiconductor nanocrystals might lead to their successful implementation into photovoltaic devices, NIR optical switches and smart windows.

  20. In Situ Preparation of Metal Halide Perovskite Nanocrystal Thin Films for Improved Light-Emitting Devices.

    PubMed

    Zhao, Lianfeng; Yeh, Yao-Wen; Tran, Nhu L; Wu, Fan; Xiao, Zhengguo; Kerner, Ross A; Lin, YunHui L; Scholes, Gregory D; Yao, Nan; Rand, Barry P

    2017-04-25

    Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CH3NH3PbI3 and CH3NH3PbBr3 perovskite nanocrystals with an average crystal size of 5.4 ± 0.8 nm and 6.4 ± 1.3 nm, respectively, as confirmed through transmission electron microscopy measurements. Additive-confined perovskite nanocrystals show significantly improved photoluminescence quantum yield and decay lifetime. Finally, we demonstrate highly efficient CH3NH3PbI3 red/near-infrared LEDs and CH3NH3PbBr3 green LEDs based on this strategy, achieving an external quantum efficiency of 7.9% and 7.0%, respectively, which represent a 40-fold and 23-fold improvement over control devices fabricated without the additives.

  1. Tuning the magnetic properties of metal oxide nanocrystal heterostructures by cation exchange.

    PubMed

    Sytnyk, Mykhailo; Kirchschlager, Raimund; Bodnarchuk, Maryna I; Primetzhofer, Daniel; Kriegner, Dominik; Enser, Herbert; Stangl, Julian; Bauer, Peter; Voith, Michael; Hassel, Achim Walter; Krumeich, Frank; Ludwig, Frank; Meingast, Arno; Kothleitner, Gerald; Kovalenko, Maksym V; Heiss, Wolfgang

    2013-02-13

    For three types of colloidal magnetic nanocrystals, we demonstrate that postsynthetic cation exchange enables tuning of the nanocrystal's magnetic properties and achieving characteristics not obtainable by conventional synthetic routes. While the cation exchange procedure, performed in solution phase approach, was restricted so far to chalcogenide based semiconductor nanocrystals, here ferrite-based nanocrystals were subjected to a Fe(2+) to Co(2+) cation exchange procedure. This allows tracing of the compositional modifications by systematic and detailed magnetic characterization. In homogeneous magnetite nanocrystals and in gold/magnetite core shell nanocrystals the cation exchange increases the coercivity field, the remanence magnetization, as well as the superparamagnetic blocking temperature. For core/shell nanoheterostructures a selective doping of either the shell or predominantly of the core with Co(2+) is demonstrated. By applying the cation exchange to FeO/CoFe(2)O(4) core/shell nanocrystals the Neél temperature of the core material is increased and exchange-bias effects are enhanced so that vertical shifts of the hysteresis loops are obtained which are superior to those in any other system.

  2. Research Update: Comparison of salt- and molecular-based iodine treatments of PbS nanocrystal solids for solar cells

    SciTech Connect

    Jähnig, Fabian; Bozyigit, Deniz; Yarema, Olesya; Wood, Vanessa

    2015-02-01

    Molecular- and salt-based chemical treatments are believed to passivate electronic trap states in nanocrystal-based semiconductors, which are considered promising for solar cells but suffer from high carrier recombination. Here, we compare the chemical, optical, and electronic properties of PbS nanocrystal-based solids treated with molecular iodine and tetrabutylammonium iodide. Surprisingly, both treatments increase—rather than decrease—the number density of trap states; however, the increase does not directly influence solar cell performance. We explain the origins of the observed impact on solar cell performance and the potential in using different chemical treatments to tune charge carrier dynamics in nanocrystal-solids.

  3. Quantum Confinement Regimes in CdTe Nanocrystals Probed by Single Dot Spectroscopy: From Strong Confinement to the Bulk Limit.

    PubMed

    Tilchin, Jenya; Rabouw, Freddy T; Isarov, Maya; Vaxenburg, Roman; Van Dijk-Moes, Relinde J A; Lifshitz, Efrat; Vanmaekelbergh, Daniel

    2015-08-25

    Sufficiently large semiconductor nanocrystals are a useful model system to characterize bulk-like excitons, with the electron and hole bound predominantly by Coulomb interaction. We present optical characterization of excitons in individual giant CdTe nanocrystals with diameters up to 25.5 nm at 4.2 K under varying excitation power and magnetic field strength. We determine values for the biexciton binding energy, diamagnetic shift constant, and Landé g-factor, which approach the bulk values with increasing nanocrystal size.

  4. Cu-doped CdS and ZnS nanocrystals grown onto thiolated silica-gel

    NASA Astrophysics Data System (ADS)

    Andrade, George Ricardo Santana; Nascimento, Cristiane da Cunha; Xavier, Paulo Adriano; Costa, Silvanio Silverio Lopes; Costa, Luiz Pereira; Gimenez, Iara F.

    2014-11-01

    CdS and ZnS nanocrystals were grown over specific binding sites onto a thiolated silica-gel aiming to favor defect emission processes. This strategy was found to be effective in yielding ZnS nanocrystals with simultaneous blue and blue-green emissions owing to different types of defects. The effects of doping with copper ions have been observed on the photoluminescence properties. The intensity of defect-related emissions from both semiconductor nanocrystals increased with increasing dopant concentration from 0.25% to 1.5% copper, consistent with the presence of sulfur vacancies. Higher dopant concentrations lead to concentration quenching.

  5. New self-assembled nanocrystal micelles for biolabels and biosensors.

    SciTech Connect

    Tallant, David Robert; Wilson, Michael C. (University of New Mexico, Albuquerque, NM); Leve, Erik W. (University of New Mexico, Albuquerque, NM); Fan, Hongyou; Brinker, C. Jeffrey; Gabaldon, John (University of New Mexico, Albuquerque, NM); Scullin, Chessa (University of New Mexico, Albuquerque, NM)

    2005-12-01

    The ability of semiconductor nanocrystals (NCs) to display multiple (size-specific) colors simultaneously during a single, long term excitation holds great promise for their use in fluorescent bio-imaging. The main challenges of using nanocrystals as biolabels are achieving biocompatibility, low non-specific adsorption, and no aggregation. In addition, functional groups that can be used to further couple and conjugate with biospecies (proteins, DNAs, antibodies, etc.) are required. In this project, we invented a new route to the synthesis of water-soluble and biocompatible NCs. Our approach is to encapsulate as-synthesized, monosized, hydrophobic NCs within the hydrophobic cores of micelles composed of a mixture of surfactants and phospholipids containing head groups functionalized with polyethylene glycol (-PEG), -COOH, and NH{sub 2} groups. PEG provided biocompatibility and the other groups were used for further biofunctionalization. The resulting water-soluble metal and semiconductor NC-micelles preserve the optical properties of the original hydrophobic NCs. Semiconductor NCs emit the same color; they exhibit equal photoluminescence (PL) intensity under long-time laser irradiation (one week) ; and they exhibit the same PL lifetime (30-ns). The results from transmission electron microscopy and confocal fluorescent imaging indicate that water-soluble semiconductor NC-micelles are biocompatible and exhibit no aggregation in cells. We have extended the surfactant/lipid encapsulation techniques to synthesize water-soluble magnetic NC-micelles. Transmission electron microscopy results suggest that water-soluble magnetic NC-micelles exhibit no aggregation. The resulting NC-micelles preserve the magnetic properties of the original hydrophobic magnetic NCs. Viability studies conducted using yeast cells suggest that the magnetic nanocrystal-micelles are biocompatible. We have demonstrated, for the first time, that using external oscillating magnetic fields to manipulate

  6. Macroporous Semiconductors

    PubMed Central

    Föll, Helmut; Leisner, Malte; Cojocaru, Ala; Carstensen, Jürgen

    2010-01-01

    Pores in single crystalline semiconductors come in many forms (e.g., pore sizes from 2 nm to > 10 µm; morphologies from perfect pore crystal to fractal) and exhibit many unique properties directly or as nanocompounds if the pores are filled. The various kinds of pores obtained in semiconductors like Ge, Si, III-V, and II-VI compound semiconductors are systematically reviewed, emphasizing macropores. Essentials of pore formation mechanisms will be discussed, focusing on differences and some open questions but in particular on common properties. Possible applications of porous semiconductors, including for example high explosives, high efficiency electrodes for Li ion batteries, drug delivery systems, solar cells, thermoelectric elements and many novel electronic, optical or sensor devices, will be introduced and discussed.

  7. Electrochemistry and electrogenerated chemiluminescence from silicon nanocrystal quantum dots.

    PubMed

    Ding, Zhifeng; Quinn, Bernadette M; Haram, Santosh K; Pell, Lindsay E; Korgel, Brian A; Bard, Allen J

    2002-05-17

    Reversible electrochemical injection of discrete numbers of electrons into sterically stabilized silicon nanocrystals (NCs) (approximately 2 to 4 nanometers in diameter) was observed by differential pulse voltammetry (DPV) in N,N'-dimethylformamide and acetonitrile. The electrochemical gap between the onset of electron injection and hole injection-related to the highest occupied and lowest unoccupied molecular orbitals-grew with decreasing nanocrystal size, and the DPV peak potentials above the onset for electron injection roughly correspond to expected Coulomb blockade or quantized double-layer charging energies. Electron transfer reactions between positively and negatively charged nanocrystals (or between charged nanocrystals and molecular redox-active coreactants) occurred that led to electron and hole annihilation, producing visible light. The electrogenerated chemiluminescence spectra exhibited a peak maximum at 640 nanometers, a significant red shift from the photoluminescence maximum (420 nanometers) of the same silicon NC solution. These results demonstrate that the chemical stability of silicon NCs could enable their use as redox-active macromolecular species with the combined optical and charging properties of semiconductor quantum dots.

  8. Precursor conversion kinetics and the nucleation of cadmium selenide nanocrystals.

    PubMed

    Owen, Jonathan S; Chan, Emory M; Liu, Haitao; Alivisatos, A Paul

    2010-12-29

    The kinetics of cadmium selenide (CdSe) nanocrystal formation was studied using UV-visible absorption spectroscopy integrated with an automated, high-throughput synthesis platform. Reaction of anhydrous cadmium octadecylphosphonate (Cd-ODPA) with alkylphosphine selenides (1, tri-n-octylphosphine selenide; 2, di-n-butylphenylphosphine selenide; 3, n-butyldiphenylphosphine selenide) in recrystallized tri-n-octylphosphine oxide was monitored by following the absorbance of CdSe at λ = 350 nm, where the extinction coefficient is independent of size, and the disappearance of the selenium precursor using {(1)H}(31)P NMR spectroscopy. Our results indicate that precursor conversion limits the rate of nanocrystal nucleation and growth. The initial precursor conversion rate (Q(o)) depends linearly on [1] (Q(o)(1) = 3.0-36 μM/s) and decreases as the number of aryl groups bound to phosphorus increases (1 > 2 > 3). Changes to Q(o) influence the final number of nanocrystals and thus control particle size. Using similar methods, we show that changing [ODPA] has a negligible influence on precursor reactivity while increasing the growth rate of nuclei, thereby decreasing the final number of nanocrystals. These results are interpreted in light of a mechanism where the precursors react in an irreversible step that supplies the reaction medium with a solute form of the semiconductor.

  9. Suppression of auger recombination in ""giant"" core/shell nanocrystals

    SciTech Connect

    Garcia Santamaria, Florencio; Vela, Javier; Schaller, Richard D; Hollingsworth, Jennifer A; Klimov, Victor I; Chen, Yongfen

    2009-01-01

    Many potential applications of semiconductor nanocrystals are hindered by nonradiative Auger recombination wherein the electron-hole (exciton) recombination energy is transferred to a third charge carrier. This process severely limits the lifetime and bandwidth of optical gain, leads to large nonradiative losses in light emitting diodes and photovoltaic cells, and is believed to be responsible for intermittency ('blinking') of emission from single nanocrystals. The development of nanostructures in which Auger recombination is suppressed has been a longstanding goal in colloidal nanocrystal research. Here, we demonstrate that such suppression is possible using so-called 'giant' nanocrystals that consist of a small CdSe core and a thick CdS shell. These nanostructures exhibit a very long biexciton lifetime ({approx}10 ns) that is likely dominated by radiative decay instead of non-radiative Auger recombination. As a result of suppressed Auger recombination, even high-order multiexcitons exhibit high emission efficiencies, which allows us to demonstrate optical amplification with an extraordinarily large bandwidth (>500 me V) and record low excitation thresholds.

  10. Non-blinking semiconductor colloidal quantum dots for biology, optoelectronics and quantum optics.

    PubMed

    Spinicelli, Piernicola; Mahler, Benoit; Buil, Stéphanie; Quélin, Xavier; Dubertret, Benoit; Hermier, Jean-Pierre

    2009-04-14

    Twinkle, twinkle: The blinking of semiconductor colloidal nanocrystals is the main inconvenience of these bright nanoemitters. There are various approaches for obtaining non-blinking nanocrystals, one of which is to grow a thick coat of CdS on the CdSe core (see picture). Applications of this method in the fields of optoelectronic devices, biologic labelling and quantum information processing are discussed.The blinking of semiconductor colloidal nanocrystals is the main inconvenience of these bright nanoemitters. For some years, research on this phenomenon has demonstrated the possibility to progress beyond this problem by suppressing this fluorescence intermittency in various ways. After a brief overview on the microscopic mechanism of blinking, we review the various approaches used to obtain non-blinking nanocrystals and discuss the commitment of this crucial improvement to applications in the fields of optoelectronic devices, biologic labelling and quantum information processing.

  11. Nanocrystal waveguide (NOW) laser

    DOEpatents

    Simpson, John T.; Simpson, Marcus L.; Withrow, Stephen P.; White, Clark W.; Jaiswal, Supriya L.

    2005-02-08

    A solid state laser includes an optical waveguide and a laser cavity including at least one subwavelength mirror disposed in or on the optical waveguide. A plurality of photoluminescent nanocrystals are disposed in the laser cavity. The reflective subwavelength mirror can be a pair of subwavelength resonant gratings (SWG), a pair of photonic crystal structures (PC), or a distributed feedback structure. In the case of a pair of mirrors, a PC which is substantially transmissive at an operating wavelength of the laser can be disposed in the laser cavity between the subwavelength mirrors to improve the mode structure, coherence and overall efficiency of the laser. A method for forming a solid state laser includes the steps of providing an optical waveguide, creating a laser cavity in the optical waveguide by disposing at least one subwavelength mirror on or in the waveguide, and positioning a plurality of photoluminescent nanocrystals in the laser cavity.

  12. Surface-enhanced Raman spectroscopy of semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Milekhin, A. G.; Sveshnikova, L. L.; Duda, T. A.; Yeryukov, N. A.; Rodyakina, E. E.; Gutakovskii, A. K.; Batsanov, S. A.; Latyshev, A. V.; Zahn, D. R. T.

    2016-01-01

    We review our recent results concerning surface-enhanced Raman scattering (SERS) by confined optical and surface optical phonons in semiconductor nanostructures including CdS, CuS, GaN, and ZnO nanocrystals, GaN and ZnO nanorods, and AlN nanowires. Enhancement of Raman scattering by confined optical phonons as well as appearance of new Raman modes with the frequencies different from those in ZnO bulk attributed to surface optical modes is observed in a series of nanostructures having different morphology located in the vicinity of metal nanoclusters (Ag, Au, and Pt). Assignment of surface optical modes is based on calculations performed in the frame of the dielectric continuum model. It is established that SERS by phonons has a resonant character. A maximal enhancement by optical phonons as high as 730 is achieved for CdS nanocrystals in double resonant conditions at the coincidence of laser energy with that of electronic transitions in semiconductor nanocrystals and localized surface plasmon resonance in metal nanoclusters. Even a higher enhancement is observed for SERS by surface optical modes in ZnO nanocrystals (above 104). Surface enhanced Raman scattering is used for studying phonon spectrum in nanocrystal ensembles with an ultra-low areal density on metal plasmonic nanostructures.

  13. Metal ions to control the morphology of semiconductor nanoparticles: copper selenide nanocubes.

    PubMed

    Li, Wenhua; Zamani, Reza; Ibáñez, Maria; Cadavid, Doris; Shavel, Alexey; Morante, Joan Ramon; Arbiol, Jordi; Cabot, Andreu

    2013-03-27

    Morphology is a key parameter in the design of novel nanocrystals and nanomaterials with controlled functional properties. Here, we demonstrate the potential of foreign metal ions to tune the morphology of colloidal semiconductor nanoparticles. We illustrate the underlying mechanism by preparing copper selenide nanocubes in the presence of Al ions. We further characterize the plasmonic properties of the obtained nanocrystals and demonstrate their potential as a platform to produce cubic nanoparticles with different composition by cation exchange.

  14. Tuning Equilibrium Compositions in Colloidal Cd1-xMnxSe Nanocrystals Using Diffusion Doping and Cation Exchange.

    PubMed

    Barrows, Charles J; Chakraborty, Pradip; Kornowske, Lindsey M; Gamelin, Daniel R

    2016-01-26

    The physical properties of semiconductor nanocrystals can be tuned dramatically via composition control. Here, we report a detailed investigation of the synthesis of high-quality colloidal Cd1-xMnxSe nanocrystals by diffusion doping of preformed CdSe nanocrystals. Until recently, Cd1-xMnxSe nanocrystals proved elusive because of kinetic incompatibilities between Mn(2+) and Cd(2+) chemistries. Diffusion doping allows Cd1-xMnxSe nanocrystals to be prepared under thermodynamic rather than kinetic control, allowing access to broader composition ranges. We now investigate this chemistry as a model system for understanding the characteristics of nanocrystal diffusion doping more deeply. From the present work, a Se(2-)-limited reaction regime is identified, in which Mn(2+) diffusion into CdSe nanocrystals is gated by added Se(2-), and equilibrium compositions are proportional to the amount of added Se(2-). At large added Se(2-) concentrations, a solubility-limited regime is also identified, in which x = xmax = ∼0.31, independent of the amount of added Se(2-). We further demonstrate that Mn(2+) in-diffusion can be reversed by cation exchange with Cd(2+) under exactly the same reaction conditions, purifying Cd1-xMnxSe nanocrystals back to CdSe nanocrystals with fine tunability. These chemistries offer exceptional composition control in Cd1-xMnxSe NCs, providing opportunities for fundamental studies of impurity diffusion in nanocrystals and for development of compositionally tuned nanocrystals with diverse applications ranging from solar energy conversion to spin-based photonics.

  15. Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties.

    PubMed

    Zeng, Deqian; Gong, Pingyun; Chen, Yuanzhi; Zhang, Qinfu; Xie, Qingshui; Peng, Dong-Liang

    2016-06-02

    Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.

  16. Ultrahigh resolution multicolor colocalization of single fluorescent nanocrystals

    SciTech Connect

    Michalet, X.; Lacoste, T.D.; Pinaud, F.; Chemla, D.S.; Alivisatos, A.P.; Weiss, S.

    2000-12-20

    A new method for in vitro and possibly in vivo ultrahigh-resolution colocalization and distance measurement between biomolecules is described, based on semiconductor nanocrystal probes. This ruler bridges the gap between FRET and far-field (or near-field scanning optical microscope) imaging and has a dynamic range from few nanometers to tens of micrometers. The ruler is based on a stage-scanning confocal microscope that allows the simultaneous excitation and localization of the excitation point-spread-function (PSF) of various colors nanocrystals while maintaining perfect registry between the channels. Fit of the observed diffraction and photophysics-limited images of the PSFs with a two-dimensional Gaussian allows one to determine their position with nanometer accuracy. This new high-resolution tool opens new windows in various molecular, cell biology and biotechnology applications.

  17. Giant five-photon absorption from multidimensional core-shell halide perovskite colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Chen, Weiqiang; Bhaumik, Saikat; Veldhuis, Sjoerd A.; Xing, Guichuan; Xu, Qiang; Grätzel, Michael; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

    2017-05-01

    Multiphoton absorption processes enable many technologically important applications, such as in vivo imaging, photodynamic therapy and optical limiting, and so on. Specifically, higher-order nonlinear absorption such as five-photon absorption offers significant advantages of greater spatial confinement, increased penetration depth, reduced autofluorescence, enhanced sensitivity and improved resolution over lower orders in bioimaging. Organic chromophores and conventional semiconductor nanocrystals are leaders in two-/three-photon absorption applications, but face considerable challenges from their small five-photon action cross-sections. Herein, we reveal that the family of halide perovskite colloidal nanocrystals transcend these constraints with highly efficient five-photon-excited upconversion fluorescence--unprecedented for semiconductor nanocrystals. Amazingly, their multidimensional type I (both conduction and valence band edges of core lie within bandgap of shell) core-shell (three-dimensional methylammonium lead bromide/two-dimensional octylammonium lead bromide) perovskite nanocrystals exhibit five-photon action cross-sections that are at least 9 orders larger than state-of-the-art specially designed organic molecules. Importantly, this family of halide perovskite nanocrystals may enable fresh approaches for next-generation multiphoton imaging applications.

  18. Nanocrystal/sol-gel nanocomposites

    DOEpatents

    Petruska, Melissa A [Los Alamos, NM; Klimov, Victor L [Los Alamos, NM

    2012-06-12

    The present invention is directed to solid composites including colloidal nanocrystals within a sol-gel host or matrix and to processes of forming such solid composites. The present invention is further directed to alcohol soluble colloidal nanocrystals useful in formation of sol-gel based solid composites

  19. Nanocrystal/sol-gel nanocomposites

    DOEpatents

    Petruska, Melissa A [Los Alamos, NM; Klimov, Victor L [Los Alamos, NM

    2007-06-05

    The present invention is directed to solid composites including colloidal nanocrystals within a sol-gel host or matrix and to processes of forming such solid composites. The present invention is further directed to alcohol soluble colloidal nanocrystals useful in formation of sol-gel based solid composites.

  20. Method of synthesizing pyrite nanocrystals

    DOEpatents

    Wadia, Cyrus; Wu, Yue

    2013-04-23

    A method of synthesizing pyrite nanocrystals is disclosed which in one embodiment includes forming a solution of iron (III) diethyl dithiophosphate and tetra-alkyl-ammonium halide in water. The solution is heated under pressure. Pyrite nanocrystal particles are then recovered from the solution.

  1. Mechanical Properties of Nanocrystal Supercrystals

    SciTech Connect

    Tam, Enrico; Podsiadlo, Paul; Shevchenko, Elena; Ogletree, D. Frank; Delplancke-Ogletree, Marie-Paule; Ashby, Paul D.

    2009-12-30

    Colloidal nanocrystals attract significant interest due to their potential applications in electronic, magnetic, and optical devices. Nanocrystal supercrystals (NCSCs) are particularly appealing for their well ordered structure and homogeneity. The interactions between organic ligands that passivate the inorganic nanocrystal cores critically influence their self-organization into supercrystals, By investigating the mechanical properties of supercrystals, we can directly characterize the particle-particle interactions in a well-defined geometry, and gain insight into both the self-assembly process and the potential applications of nanocrystal supercrystals. Here we report nanoindentation studies of well ordered lead-sulfide (Pbs) nanocrystal supercrystals. Their modulus and hardness were found to be similar to soft polymers at 1.7 GPa and 70 MPa respectively and the fractures toughness was 39 KPa/m1/2, revealing the extremely brittle nature of these materials.

  2. Nanocrystal/sol-gel nanocomposites

    DOEpatents

    Klimov, Victor L.; Petruska, Melissa A.

    2010-05-25

    The present invention is directed to a process for preparing a solid composite having colloidal nanocrystals dispersed within a sol-gel matrix, the process including admixing colloidal nanocrystals with an amphiphilic polymer including hydrophilic groups selected from the group consisting of --COOH, --OH, --SO.sub.3H, --NH.sub.2, and --PO.sub.3H.sub.2 within a solvent to form an alcohol-soluble colloidal nanocrystal-polymer complex, admixing the alcohol-soluble colloidal nanocrystal-polymer complex and a sol-gel precursor material, and, forming the solid composite from the admixture. The present invention is also directed to the resultant solid composites and to the alcohol-soluble colloidal nanocrystal-polymer complexes.

  3. Mn(2+)-Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content.

    PubMed

    Liu, Wenyong; Lin, Qianglu; Li, Hongbo; Wu, Kaifeng; Robel, István; Pietryga, Jeffrey M; Klimov, Victor I

    2016-11-16

    Impurity doping has been widely used to endow semiconductor nanocrystals with novel optical, electronic, and magnetic functionalities. Here, we introduce a new family of doped NCs offering unique insights into the chemical mechanism of doping, as well as into the fundamental interactions between the dopant and the semiconductor host. Specifically, by elucidating the role of relative bond strengths within the precursor and the host lattice, we develop an effective approach for incorporating manganese (Mn) ions into nanocrystals of lead-halide perovskites (CsPbX3, where X = Cl, Br, or I). In a key enabling step not possible in, for example, II-VI nanocrystals, we use gentle chemical means to finely and reversibly tune the nanocrystal band gap over a wide range of energies (1.8-3.1 eV) via postsynthetic anion exchange. We observe a dramatic effect of halide identity on relative intensities of intrinsic band-edge and Mn emission bands, which we ascribe to the influence of the energy difference between the corresponding transitions on the characteristics of energy transfer between the Mn ion and the semiconductor host.

  4. Cu2ZnSnS4 nanocrystals and graphene quantum dots for photovoltaics.

    PubMed

    Wang, Jun; Xin, Xukai; Lin, Zhiqun

    2011-08-01

    Semiconductor quantum dots exhibit great potential for applications in next generation high efficiency, low cost solar cells because of their unique optoelectronic properties. Cu(2)ZnSnS(4) (CZTS) nanocrystals and graphene quantum dots (GQDs) have recently received much attention as building blocks for use in solar energy conversion due to their outstanding properties and advantageous characteristics, including high optical absorptivity, tunable bandgap, and earth abundant chemical composition. In this Feature Article, recent advances in the synthesis and utilization of CZTS nanocrystals and colloidal GQDs for photovoltaics are highlighted, followed by an outlook on the future research efforts in these areas.

  5. Photovoltaic nanocrystal scintillators hybridized on Si solar cells for enhanced conversion efficiency in UV.

    PubMed

    Mutlugun, Evren; Soganci, Ibrahim Murat; Demir, Hilmi Volkan

    2008-03-17

    We propose and demonstrate semiconductor nanocrystal based photovoltaic scintillators integrated on solar cells to enhance photovoltaic device parameters including spectral responsivity, open circuit voltage, short circuit current, fill factor, and solar conversion efficiency in the ultraviolet. Hybridizing (CdSe)ZnS core-shell quantum dots of 2.4 nm in diameter on multi-crystalline Si solar cells for the first time, we show that the solar conversion efficiency is enhanced 2 folds under white light illumination similar to the solar spectrum. Such nanocrystal scintillators provide the ability to extend the photovoltaic activity towards UV.

  6. Tunable infrared absorption and visible transparency of colloidal aluminum-doped zinc oxide nanocrystals.

    PubMed

    Buonsanti, Raffaella; Llordes, Anna; Aloni, Shaul; Helms, Brett A; Milliron, Delia J

    2011-11-09

    Plasmonic nanocrystals have been attracting a lot of attention both for fundamental studies and different applications, from sensing to imaging and optoelectronic devices. Transparent conductive oxides represent an interesting class of plasmonic materials in addition to metals and vacancy-doped semiconductor quantum dots. Herein, we report a rational synthetic strategy of high-quality colloidal aluminum-doped zinc oxide nanocrystals. The presence of substitutional aluminum in the zinc oxide lattice accompanied by the generation of free electrons is proved for the first time by tunable surface plasmon absorption in the infrared region both in solution and in thin films.

  7. Quantification of the morphological transition in cadmium selenide nanocrystals as a function of reaction temperature

    NASA Astrophysics Data System (ADS)

    Cameron, Michael Tanner; Rogerson, Jordan A.; Blom, Douglas A.; Dukes, Albert D.

    2016-03-01

    Controlling the morphology of semiconductor nanocrystals has typically relied on controlling the concentration and species of surface ligands utilized in synthesis. Specific shapes, such as branched structures are of particular interest as the light harvesting and charge separating layer in a photovoltaic device. In this work we quantify how changes in the reaction temperature affect the resulting morphology of the nanocrystals. The narrowness of the temperature range over which the morphological transition occurred provides guidance to the tolerances necessary in the synthesis of CdSe utilized in commercial devices on a large scale.

  8. Luminescence in quantum-confined cadmium selenide nanocrystals and nanorods in external electric fields

    SciTech Connect

    Gurinovich, L. I. Lutich, A. A.; Stupak, A. P.; Prislopsky, S. Ya.; Rusakov, E. K.; Artemyev, M. V.; Gaponenko, S. V.; Demir, H. V.

    2009-08-15

    It is found that the absorption and luminescence spectra of CdSe nanocrystals and nanorods depend on the external electric field. It is shown that the external electric field quenches the P-polarized photoluminescence of CdSe nanorods to a degree higher than the degree of field-induced quenching of the S-polarized photoluminescence. It is established that the nanocrystals are more sensitive to the external electric field than the nanorods. The effect of the external electric field on the luminescence properties of the semiconductor nanorods is discussed.

  9. Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals

    PubMed Central

    Li, Mingjie; Bhaumik, Saikat; Goh, Teck Wee; Kumar, Muduli Subas; Yantara, Natalia; Grätzel, Michael; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

    2017-01-01

    Hot-carrier solar cells can overcome the Schottky–Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks. Here we show colloidal halide perovskite nanocrystals transcend these limitations and exhibit around two orders slower hot-carrier cooling times and around four times larger hot-carrier temperatures than their bulk-film counterparts. Under low pump excitation, hot-carrier cooling mediated by a phonon bottleneck is surprisingly slower in smaller nanocrystals (contrasting with conventional nanocrystals). At high pump fluence, Auger heating dominates hot-carrier cooling, which is slower in larger nanocrystals (hitherto unobserved in conventional nanocrystals). Importantly, we demonstrate efficient room temperature hot-electrons extraction (up to ∼83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films. These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells. PMID:28176882

  10. A general and robust strategy for the synthesis of nearly monodisperse colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Pang, Xinchang; Zhao, Lei; Han, Wei; Xin, Xukai; Lin, Zhiqun

    2013-06-01

    Colloidal nanocrystals exhibit a wide range of size- and shape-dependent properties and have found application in myriad fields, incuding optics, electronics, mechanics, drug delivery and catalysis, to name but a few. Synthetic protocols that enable the simple and convenient production of colloidal nanocrystals with controlled size, shape and composition are therefore of key general importance. Current strategies include organic solution-phase synthesis, thermolysis of organometallic precursors, sol-gel processes, hydrothermal reactions and biomimetic and dendrimer templating. Often, however, these procedures require stringent experimental conditions, are difficult to generalize, or necessitate tedious multistep reactions and purification. Recently, linear amphiphilic block co-polymer micelles have been used as templates to synthesize functional nanocrystals, but the thermodynamic instability of these micelles limits the scope of this approach. Here, we report a general strategy for crafting a large variety of functional nanocrystals with precisely controlled dimensions, compositions and architectures by using star-like block co-polymers as nanoreactors. This new class of co-polymers forms unimolecular micelles that are structurally stable, therefore overcoming the intrinsic instability of linear block co-polymer micelles. Our approach enables the facile synthesis of organic solvent- and water-soluble nearly monodisperse nanocrystals with desired composition and architecture, including core-shell and hollow nanostructures. We demonstrate the generality of our approach by describing, as examples, the synthesis of various sizes and architectures of metallic, ferroelectric, magnetic, semiconductor and luminescent colloidal nanocrystals.

  11. Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals.

    PubMed

    Li, Mingjie; Bhaumik, Saikat; Goh, Teck Wee; Kumar, Muduli Subas; Yantara, Natalia; Grätzel, Michael; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

    2017-02-08

    Hot-carrier solar cells can overcome the Schottky-Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks. Here we show colloidal halide perovskite nanocrystals transcend these limitations and exhibit around two orders slower hot-carrier cooling times and around four times larger hot-carrier temperatures than their bulk-film counterparts. Under low pump excitation, hot-carrier cooling mediated by a phonon bottleneck is surprisingly slower in smaller nanocrystals (contrasting with conventional nanocrystals). At high pump fluence, Auger heating dominates hot-carrier cooling, which is slower in larger nanocrystals (hitherto unobserved in conventional nanocrystals). Importantly, we demonstrate efficient room temperature hot-electrons extraction (up to ∼83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films. These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells.

  12. Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Mingjie; Bhaumik, Saikat; Goh, Teck Wee; Kumar, Muduli Subas; Yantara, Natalia; Grätzel, Michael; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

    2017-02-01

    Hot-carrier solar cells can overcome the Schottky-Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks. Here we show colloidal halide perovskite nanocrystals transcend these limitations and exhibit around two orders slower hot-carrier cooling times and around four times larger hot-carrier temperatures than their bulk-film counterparts. Under low pump excitation, hot-carrier cooling mediated by a phonon bottleneck is surprisingly slower in smaller nanocrystals (contrasting with conventional nanocrystals). At high pump fluence, Auger heating dominates hot-carrier cooling, which is slower in larger nanocrystals (hitherto unobserved in conventional nanocrystals). Importantly, we demonstrate efficient room temperature hot-electrons extraction (up to ~83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films. These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells.

  13. Tuning the Magnetic Properties of Metal Oxide Nanocrystal Heterostructures by Cation Exchange

    PubMed Central

    2013-01-01

    For three types of colloidal magnetic nanocrystals, we demonstrate that postsynthetic cation exchange enables tuning of the nanocrystal’s magnetic properties and achieving characteristics not obtainable by conventional synthetic routes. While the cation exchange procedure, performed in solution phase approach, was restricted so far to chalcogenide based semiconductor nanocrystals, here ferrite-based nanocrystals were subjected to a Fe2+ to Co2+ cation exchange procedure. This allows tracing of the compositional modifications by systematic and detailed magnetic characterization. In homogeneous magnetite nanocrystals and in gold/magnetite core shell nanocrystals the cation exchange increases the coercivity field, the remanence magnetization, as well as the superparamagnetic blocking temperature. For core/shell nanoheterostructures a selective doping of either the shell or predominantly of the core with Co2+ is demonstrated. By applying the cation exchange to FeO/CoFe2O4 core/shell nanocrystals the Neél temperature of the core material is increased and exchange-bias effects are enhanced so that vertical shifts of the hysteresis loops are obtained which are superior to those in any other system. PMID:23362940

  14. A general and robust strategy for the synthesis of nearly monodisperse colloidal nanocrystals.

    PubMed

    Pang, Xinchang; Zhao, Lei; Han, Wei; Xin, Xukai; Lin, Zhiqun

    2013-06-01

    Colloidal nanocrystals exhibit a wide range of size- and shape-dependent properties and have found application in myriad fields, incuding optics, electronics, mechanics, drug delivery and catalysis, to name but a few. Synthetic protocols that enable the simple and convenient production of colloidal nanocrystals with controlled size, shape and composition are therefore of key general importance. Current strategies include organic solution-phase synthesis, thermolysis of organometallic precursors, sol-gel processes, hydrothermal reactions and biomimetic and dendrimer templating. Often, however, these procedures require stringent experimental conditions, are difficult to generalize, or necessitate tedious multistep reactions and purification. Recently, linear amphiphilic block co-polymer micelles have been used as templates to synthesize functional nanocrystals, but the thermodynamic instability of these micelles limits the scope of this approach. Here, we report a general strategy for crafting a large variety of functional nanocrystals with precisely controlled dimensions, compositions and architectures by using star-like block co-polymers as nanoreactors. This new class of co-polymers forms unimolecular micelles that are structurally stable, therefore overcoming the intrinsic instability of linear block co-polymer micelles. Our approach enables the facile synthesis of organic solvent- and water-soluble nearly monodisperse nanocrystals with desired composition and architecture, including core-shell and hollow nanostructures. We demonstrate the generality of our approach by describing, as examples, the synthesis of various sizes and architectures of metallic, ferroelectric, magnetic, semiconductor and luminescent colloidal nanocrystals.

  15. Tuning light emission of PbS nanocrystals from infrared to visible range by cation exchange

    PubMed Central

    Binetti, Enrico; Striccoli, Marinella; Sibillano, Teresa; Giannini, Cinzia; Brescia, Rosaria; Falqui, Andrea; Comparelli, Roberto; Corricelli, Michela; Tommasi, Raffaele; Agostiano, Angela; Curri, M Lucia

    2015-01-01

    Colloidal semiconductor nanocrystals, with intense and sharp-line emission between red and near-infrared spectral regions, are of great interest for optoelectronic and bio-imaging applications. The growth of an inorganic passivation layer on nanocrystal surfaces is a common strategy to improve their chemical and optical stability and their photoluminescence quantum yield. In particular, cation exchange is a suitable approach for shell growth at the expense of the nanocrystal core size. Here, the cation exchange process is used to promote the formation of a CdS passivation layer on the surface of very small PbS nanocrystals (2.3 nm in diameter), blue shifting their optical spectra and yielding luminescent and stable nanostructures emitting in the range of 700–850 nm. Structural, morphological and compositional investigation confirms the nanocrystal size contraction after the cation-exchange process, while the PbS rock-salt crystalline phase is retained. Absorption and photoluminescence spectroscopy demonstrate the growth of a passivation layer with a decrease of the PbS core size, as inferred by the blue-shift of the excitonic peaks. The surface passivation strongly increases the photoluminescence intensity and the excited state lifetime. In addition, the nanocrystals reveal increased stability against oxidation over time. Thanks to their absorption and emission spectral range and the slow recombination dynamics, such highly luminescent nano-objects can find interesting applications in sensitized photovoltaic cells and light-emitting devices. PMID:27877842

  16. Charge transport properties of nanocrystals studied by electrostatic force microscopy

    NASA Astrophysics Data System (ADS)

    Hu, Zonghai

    2005-03-01

    Charge transport in semiconductor and metal nanocrystal multilayers between two electrodes is probed by electrostatic force microscopy. The in-plane charge diffusion coefficients are deduced from the charge distribution imaged in real time. Temperature dependence of the transport properties and effects of photoionization and oxidation are also investigated. Implications of these results on the transport mechanisms will be discussed. This work was supported by the ONR Young Investigator Award N000140410489, the American Chemical Society (ACS) PRF award # 41256-G10, and the startup funds at the University of Pennsylvania. MF acknowledges funding from the NSF IGERT program (Grant #DGE-0221664) and SENS.

  17. Microfluidic Technology: Uncovering the Mechanisms of Nanocrystal Nucleation and Growth.

    PubMed

    Lignos, Ioannis; Maceiczyk, Richard; deMello, Andrew J

    2017-05-16

    The controlled and reproducible formation of colloidal semiconductor nanocrystals (or quantum dots) is of central importance in nanoscale science and technology. The tunable size- and shape-dependent properties of such materials make them ideal candidates for the development of efficient and low-cost displays, solar cells, light-emitting devices, and catalysts. The formidable difficulties associated with the macroscale preparation of semiconductor nanocrystals (possessing bespoke optical and chemical properties) result from the fact that underlying reaction mechanisms are complex and that the reactive environment is difficult to control. Automated microfluidic reactors coupled with monitoring systems and optimization algorithms aim to elucidate complex reaction mechanisms that govern both nucleation and growth of nanocrystals. Such platforms are ideally suited for the efficient optimization of reaction parameters, assuring the reproducible synthesis of nanocrystals with user-defined properties. This Account aims to inform the nanomaterials community about how microfluidic technologies can supplement flask experimentation for the ensemble investigation of formation mechanisms and design of semiconductor nanocrystals. We present selected studies outlining the preparation of quantum dots using microfluidic systems with integrated analytics. Such microfluidic reaction systems leverage the ability to extract real-time information regarding optical, structural, and compositional characteristics of quantum dots during nucleation and growth stages. The Account further highlights our recent research activities focused on the development and application of droplet-based microfluidics with integrated optical detection systems for the efficient and rapid screening of reaction conditions and a better understanding of the mechanisms of quantum dot synthesis. We describe the features and operation of fully automated microfluidic reactors and their subsequent application to high

  18. Silicon nanocrystals as handy biomarkers

    NASA Astrophysics Data System (ADS)

    Fujioka, Kouki; Hoshino, Akiyoshi; Manabe, Noriyoshi; Futamura, Yasuhiro; Tilley, Richard; Yamamoto, Kenji

    2007-02-01

    Quantum dots (QDs) have brighter and longer fluorescence than organic dyes. Therefore, QDs can be applied to biotechnology, and have capability to be applied to medical technology. Currently, among the several types of QDs, CdSe with a ZnS shell is one of the most popular QDs to be used in biological experiments. However, when the CdSe QDs were applied to clinical technology, potential toxicological problems due to CdSe core should be considered. To eliminate the problem, silicon nanocrystals, which have the potential of biocompatibility, could be a candidate of alternate probes. Silicon nanocrystals have been synthesized using several techniques such as aerosol, electrochemical etching, laser pyrolysis, plasma deposition, and colloids. Recently, the silicon nanocrystals were reported to be synthesized in inverse micelles and also stabilized with 1-heptene or allylamine capping. Blue fluorescence of the nanocrystals was observed when excited with a UV light. The nanocrystals covered with 1-heptene are hydrophobic, whereas the ones covered with allylamine are hydrophilic. To test the stability in cytosol, the water-soluble nanocrystals covered with allylamine were examined with a Hela cell incorporation experiment. Bright blue fluorescence of the nanocrystals was detected in the cytosol when excited with a UV light, implying that the nanocrystals were able to be applied to biological imaging. In order to expand the application range, we synthesized and compared a series of silicon nanocrystals, which have variable surface modification, such as alkyl group, alcohol group, and odorant molecules. This study will provide a wider range of optoelectronic applications and bioimaging technology.

  19. Modifying growth of perylene diimide nanocrystals with poly(3-hexyl thiophene) as additives

    NASA Astrophysics Data System (ADS)

    Bu, Laju; Hayward, Ryan

    2014-03-01

    The shape, size, and crystallinity of organic semiconductors play vital roles in their applications in optoelectronics. Various methods to control crystallization of organic semiconductors, including thermal/solvent annealing, addition of poor solvents, and chemical structure modification, have been applied to improve the performance of organic photovoltaics. While soluble additives controlled crystallization are commonly found in biomineralization, pharmaceutics, and food science, they have rarely been applied to organic semiconductors. Here, we show that a p-type polymer, P3HT, serves as a soluble additive in crystallization of a n-type semiconductor, perylene diimide (PDI), by preferentially adsorbing on lateral crystal faces, which reduce lateral growth of PDI crystals relative to longitudinal growth, yielding extended 1-D nanofibers. Upon subsequent crystallization of P3HT, the PDI nanofibers serve as efficient nucleation sties, resulting in shish-kebab like p/n heterostuctures. Using ultrasound to enhance nucleation of PDI crystals, variations in P3HT molecular weight and concentration, and sonication temperature, allow PDI nanocrystal size and uniformity to be tuned. The uniform PDI nanocrystals can act as seeds to crystallize additional PDI to get segmented nanocrystals.

  20. Harvesting solar energy by means of charge-separating nanocrystals and their solids.

    PubMed

    Diederich, Geoffrey; O'Connor, Timothy; Moroz, Pavel; Kinder, Erich; Kohn, Elena; Perera, Dimuthu; Lorek, Ryan; Lambright, Scott; Imboden, Martene; Zamkov, Mikhail

    2012-08-23

    Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials offering a superior control over the spatial distribution of charge carriers across material interfaces. As this study demonstrates, a combination of donor-acceptor nanocrystal (NC) domains in a single nanoparticle can lead to the realization of efficient photocatalytic materials, while a layered assembly of donor- and acceptor-like nanocrystals films gives rise to photovoltaic materials. Initially the paper focuses on the synthesis of composite inorganic nanocrystals, comprising linearly stacked ZnSe, CdS, and Pt domains, which jointly promote photoinduced charge separation. These structures are used in aqueous solutions for the photocatalysis of water under solar radiation, resulting in the production of H2 gas. To enhance the photoinduced separation of charges, a nanorod morphology with a linear gradient originating from an intrinsic electric field is used. The inter-domain energetics are then optimized to drive photogenerated electrons toward the Pt catalytic site while expelling the holes to the surface of ZnSe domains for sacrificial regeneration (via methanol). Here we show that the only efficient way to produce hydrogen is to use electron-donating ligands to passivate the surface states by tuning the energy level alignment at the semiconductor-ligand interface. Stable and efficient reduction of water is allowed by these ligands due to the fact that they fill vacancies in the valence band of the semiconductor domain, preventing energetic holes from degrading it. Specifically, we show that the energy of the hole is transferred to the ligand moiety, leaving the semiconductor domain functional. This enables us to return the entire nanocrystal-ligand system to a functional state, when the ligands are degraded, by simply adding fresh ligands to the system. To promote a photovoltaic charge separation, we use a

  1. Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

    PubMed Central

    Diederich, Geoffrey; O'Connor, Timothy; Moroz, Pavel; Kinder, Erich; Kohn, Elena; Perera, Dimuthu; Lorek, Ryan; Lambright, Scott; Imboden, Martene; Zamkov, Mikhail

    2012-01-01

    Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials offering a superior control over the spatial distribution of charge carriers across material interfaces. As this study demonstrates, a combination of donor-acceptor nanocrystal (NC) domains in a single nanoparticle can lead to the realization of efficient photocatalytic1-5 materials, while a layered assembly of donor- and acceptor-like nanocrystals films gives rise to photovoltaic materials. Initially the paper focuses on the synthesis of composite inorganic nanocrystals, comprising linearly stacked ZnSe, CdS, and Pt domains, which jointly promote photoinduced charge separation. These structures are used in aqueous solutions for the photocatalysis of water under solar radiation, resulting in the production of H2 gas. To enhance the photoinduced separation of charges, a nanorod morphology with a linear gradient originating from an intrinsic electric field is used5. The inter-domain energetics are then optimized to drive photogenerated electrons toward the Pt catalytic site while expelling the holes to the surface of ZnSe domains for sacrificial regeneration (via methanol). Here we show that the only efficient way to produce hydrogen is to use electron-donating ligands to passivate the surface states by tuning the energy level alignment at the semiconductor-ligand interface. Stable and efficient reduction of water is allowed by these ligands due to the fact that they fill vacancies in the valence band of the semiconductor domain, preventing energetic holes from degrading it. Specifically, we show that the energy of the hole is transferred to the ligand moiety, leaving the semiconductor domain functional. This enables us to return the entire nanocrystal-ligand system to a functional state, when the ligands are degraded, by simply adding fresh ligands to the system4. To promote a photovoltaic charge separation, we use a

  2. Cellulose nanocrystal submonolayers by spin coating.

    PubMed

    Kontturi, Eero; Johansson, Leena-Sisko; Kontturi, Katri S; Ahonen, Päivi; Thüne, Peter C; Laine, Janne

    2007-09-11

    Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the nanocrystals is desired. Furthermore, the amount of nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose nanocrystals. The thicker films of charged nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose nanocrystals in the ultrathin regime (<100 nm).

  3. Microwave induced center-doping of silver ions in aqueous CdS nanocrystals with tunable, impurity and visible emission.

    PubMed

    Shen, Qihui; Liu, Yan; Xu, Jun; Meng, Changgong; Liu, Xiaoyang

    2010-08-21

    Under microwave radiation, Ag(+)-doped CdS semiconductor nanocrystals with high photoluminescence quantum yield (approximately 58%) and a surprisingly large optical window (480 to 630 nm) are formed controllably using a center-doping strategy and are optimized through a green approach in pure water solution.

  4. Facet engineered interface design of NaYF4:Yb,Tm upconversion nanocrystals on BiOCl nanoplates for enhanced near-infrared photocatalysis.

    PubMed

    Bai, Lijie; Jiang, Wenya; Gao, Chunxiao; Zhong, Shuxian; Zhao, Leihong; Li, Zhengquan; Bai, Song

    2016-12-07

    The combination of upconversion nanocrystals with a wide-bandgap semiconductor is an efficient strategy to develop near-infrared (NIR)-responsive photocatalysts. The photocatalytic activity of the hybrid structures is greatly determined by the efficiency of the energy transfer on the interface between upconversion nanocrystals and the semiconductor. In this work, we demonstrate the interface design of a NaYF4:Yb,Tm-BiOCl hybrid structure based on the choice of suitable BiOCl facets in depositing NaYF4:Yb,Tm upconversion nanocrystals. It was found that the selective deposition of NaYF4:Yb,Tm nanocrystals on the BiOCl(110) facet can greatly enhance the photocatalytic performance in dye degradation compared with the sample with NaYF4:Yb,Tm nanocrystals loaded on the BiOCl(001) facet. Two effects were believed to contribute to this enhancement: (1) a stronger UV emission absorption ability of the BiOCl(110) facet from NaYF4:Yb,Tm in generating more photo-induced charge carriers resulted from the narrower bandgap; (2) a shorter diffusion distance of photogenerated charge carriers to the BiOCl(110) reactive facet for surface catalytic reactions owing to the spatial charge separation between different facets. This work highlights the rational interfacial design of an upconversion nanocrystal-semiconductor hybrid structure for enhanced energy transfer in photocatalysis.

  5. Synthesis and photocatalytic properties of multi-morphological AuCu3-ZnO hybrid nanocrystals

    NASA Astrophysics Data System (ADS)

    Zeng, Deqian; Chen, Yuanzhi; Peng, Jian; Xie, Qingshui; Peng, Dong-Liang

    2015-10-01

    Noble metal-semiconductor hybrid nanocrystals represent an important class of materials for many potential applications, especially for photocatalysis. The utilization of transition metals to form alloys with noble metals can not only reduce the preparation costs, but may also offer tunable optical and catalytic properties for a broader range of applications. In this study, we report on the solution synthesis of AuCu3-ZnO hybrid nanocrystals with three interesting morphologies, including urchin-like, flower-like and multipod-like nanocrystals. In the synthetic strategy, Au-Cu bimetallic alloy seeds formed in situ are used to induce the heteroepitaxial growth of ZnO nanocrystals on the surface of bimetallic alloy cores; thus different types of morphologies can be achieved by controlling the reaction conditions. Through high-resolution transmission electron microscopy observations, well-defined interfaces between ZnO and AuCu3 are observed, which indicate that ZnO has a (0001) orientation and prefers to grow on AuCu3 {111} facets. The as-prepared hybrid nanocrystals demonstrate morphology- and composition-dependent surface plasmon resonance (SPR) absorption bands. In addition, much higher photocatalytic efficiency than pure ZnO nanocrystals is observed for the hybrid nanocrystals in the degradation of methylene blue. In particular, the multipod-like AuCu3-ZnO hybrid nanocrystals show the highest catalytic performance, as well as more than three times higher photocurrent density than the pure ZnO sample. The reported synthetic strategy provides a facile route to the effective combination of a plasmonic alloy with semiconductor components at the nanoscale in a controlled manner.

  6. Early stage of nanocrystal growth

    SciTech Connect

    2012-01-01

    Berkeley Lab researchers at the Molecular Foundry have elucidated important mechanisms behind oriented attachment, the phenomenon that drives biomineralization and the growth of nanocrystals. This electron microscopy movie shows the early stage of nanocrystal growth. Nanoparticles make transient contact at many points and orientations until their lattices are perfectly matched. The particles then make a sudden jump-to-contact to form attached aggregates. (Movie courtesy of Jim DeYoreo)

  7. Physical preparation and optical properties of CuSbS2 nanocrystals by mechanical alloying process

    NASA Astrophysics Data System (ADS)

    Zhang, Huihui; Xu, Qishu; Tan, Guolong

    2016-09-01

    CuSbS2 nanocrystals have been synthesized through mechanical alloying Cu, Sb and S elemental powders for 40 hs. The optical spectrum of as-milled CuSbS2 nano-powders demonstrates a direct gap of 1.35 eV and an indirect gap of 0.36 eV, which are similar to that of silicon and reveals the evidence for the indirect semiconductor characterization of CuSbS2. Afterwards, CuSbS2 nanocrystals were capped with trioctylphosphine oxide/trioctylphosphine/pyridine (TOPO/TOP). There appear four sharp absorption peaks within the region of 315 to 355 nm for the dispersion solution containing the capped nanocrystals. The multiple peaks are proposed to be originating from the energy level splitting of 1S electronic state into four discrete sub-levels, where electrons were excited into the conduction band and thus four exciton absorption peaks were produced.

  8. A novel organic-inorganic hybrid composition for controllably synthesizing AgI nanocrystals

    NASA Astrophysics Data System (ADS)

    Liu, Junxue; He, Sheng; An, Changhua; Zhang, Jun

    2017-05-01

    The ability to control the shape and morphology of semiconductor macro/nanocrystals is critical to applications such as photocatalysis, electrocatalysis, photonics and nanoelectronics. Despite significant advances in controlling the shapes by thermal decomposition and solvothermal methods, rigorous shape control by low temperature and aqueous phase controlling remains challenging. Herein, a facile synthetic method based on ethylenediamine assisted precursor transformation technique has been developed for the fabrication of AgI nanocrystals. The central features of our approach are the use of ethylenediamine (en) as complexant and the use of polyvinylpyrrolidone (PVP) as capping surfactants to form Ag(en)xI precursor, which is followed by removing en to form AgI crystals. This work provides new insights into the use of a novel organic-inorganic hybrid composition as precursors for nanocrystals synthesis and offers a potential route to achieve well-defined morphology of inorganic nanostructures with uniform shape and size.

  9. Size dependence of negative trion Auger recombination in photodoped CdSe nanocrystals.

    PubMed

    Cohn, Alicia W; Rinehart, Jeffrey D; Schimpf, Alina M; Weaver, Amanda L; Gamelin, Daniel R

    2014-01-08

    We report a systematic investigation of the size dependence of negative trion (T(-)) Auger recombination rates in free-standing colloidal CdSe nanocrystals. Colloidal n-type CdSe nanocrystals of various radii have been prepared photochemically, and their trion decay dynamics have been measured using time-resolved photoluminescence spectroscopy. Trion Auger time constants spanning 3 orders of magnitude are observed, ranging from 57 ps (radius R = 1.4 nm) to 2.2 ns (R = 3.2 nm). The data reveal a substantially stronger size dependence than found for bi- or multiexciton Auger recombination in CdSe or other semiconductor nanocrystals, scaling in proportion to R(4.3).

  10. Enhancing the Elasticity of Ultrathin Single-Wall Carbon Nanotube Films with Colloidal Nanocrystals.

    PubMed

    Alzaid, Meshal; Roth, Joseph; Wang, Yuezhou; Almutairi, Eid; Brown, Samuel L; Dumitrică, Traian; Hobbie, Erik K

    2017-08-15

    Thin bilayers of contrasting nanomaterials are ubiquitous in solution-processed electronic devices and have potential relevance to a number of applications in flexible electronics. Motivated by recent mesoscopic simulations demonstrating synergistic mechanical interactions between thin films of single-wall carbon nanotubes (SWCNTs) and spherical nanocrystal (NC) inclusions, we use a thin-film wrinkling approach to query the compressive mechanics of hybrid nanotube/nanocrystal coatings adhered to soft polymer substrates. Our results show an almost 2-fold enhancement in the Young modulus of a sufficiently thin SWCNT film associated with the presence of a thin interpenetrating overlayer of semiconductor NCs. Mesoscopic distinct-element method simulations further support the experimental findings by showing that the additional noncovalent interfaces introduced by nanocrystals enhance the modulus of the SWCNT network and hinder network wrinkling.

  11. Tunable and responsive plasmonic properties of metal oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Milliron, Delia

    2015-03-01

    Degenerately doped metal oxide semiconductors, like ITO, exhibit plasmonic resonance at near and mid-infrared wavelengths tunable by varying their composition. Nanocrystals of many such materials have now been synthesized and applications are emerging that leverage the responsiveness of their localized surface plasmon resonance (LSPR) to electronic charging and discharging. For example, electrochromic glass that can dynamically control heat loads in buildings is under development. In biological systems, plasmonic oxide nanocrystals can act as remote sensors, where changes in their optical absorption indicates biochemical redox has occurred. Nonetheless, significant fundamental questions remain open regarding the nature of the infrared optical response in these doped oxides. Dopant impurities influence the optoelectronic properties beyond simply donating free carriers. For example, the distribution of Sn in ITO was found to dramatically influence the line shape of the LSPR and the effective electron mobility. In addition, by post-synthetically modifying carrier concentrations (through photodoping or electrochemical doping), we have observed that aliovalent doping and electronic doping each modify LSPR spectra, providing access to a broad range of tunable optical properties. Heterogeneous broadening, uncovered by single nanocrystal spectroscopy, also contributes to ensemble line shapes, complicating direct interpretation of LSPR spectra. Finally, the possibility of electric field enhancement by metal oxide LSPRs is critically examined to suggest what future applications might be on the horizon.

  12. Fluorescence lifetime modification of single CdSe nanocrystals

    NASA Astrophysics Data System (ADS)

    Brokmann, Xavier; Coolen, Laurent; Desbiolles, Pierre; Dahan, Maxime; Hermier, Jean-Pierre

    2004-03-01

    Narrow spectral emission, high brightness, and photon antibunching make colloidal semiconductor CdSe quantum dots promising systems both as biological probes or as single photon sources for quantum information processing. However, their fluorescence properties exhibit surprisingly rich behaviour as non-ergodic on/off fluorescence intermittency [1] or lifetime fluctuation [2] that deserve further studies. Here, we study the fluorescence lifetime and the total emission intensity from a single CdSe nanocrystal successively placed close and far from a dielectric interface. Correlated to an independent measurement of the nanocrystal orientation, we demonstrate the ability of this procedure to measure both radiative and non-radiative lifetime on these single emitters. Our results are found to be intimately related to the 2D nature of the emitting dipole [3], and demonstrate that the emitting state quantum efficiency of CdSe nanocrystals is routinely higher than 95 %. [1] X.Brokmann et al., PRL 90, 120601 (2003) [2] G. Schlegel et al., PRL 88, 137401 (2002) [3] S.A. Empedocles et al., Nature 399, 126 (1999)

  13. Zero-reabsorption doped-nanocrystal luminescent solar concentrators.

    PubMed

    Erickson, Christian S; Bradshaw, Liam R; McDowall, Stephen; Gilbertson, John D; Gamelin, Daniel R; Patrick, David L

    2014-04-22

    Optical concentration can lower the cost of solar energy conversion by reducing photovoltaic cell area and increasing photovoltaic efficiency. Luminescent solar concentrators offer an attractive approach to combined spectral and spatial concentration of both specular and diffuse light without tracking, but they have been plagued by luminophore self-absorption losses when employed on practical size scales. Here, we introduce doped semiconductor nanocrystals as a new class of phosphors for use in luminescent solar concentrators. In proof-of-concept experiments, visibly transparent, ultraviolet-selective luminescent solar concentrators have been prepared using colloidal Mn(2+)-doped ZnSe nanocrystals that show no luminescence reabsorption. Optical quantum efficiencies of 37% are measured, yielding a maximum projected energy concentration of ∼6× and flux gain for a-Si photovoltaics of 15.6 in the large-area limit, for the first time bounded not by luminophore self-absorption but by the transparency of the waveguide itself. Future directions in the use of colloidal doped nanocrystals as robust, processable spectrum-shifting phosphors for luminescent solar concentration on the large scales required for practical application of this technology are discussed.

  14. Methods for synthesis of semiconductor nanocrystals and thermoelectric compositions

    NASA Technical Reports Server (NTRS)

    Ren, Zhifeng (Inventor); Chen, Gang (Inventor); Poudel, Bed (Inventor); Kumar, Shankar (Inventor); Wang, Wenzhong (Inventor); Dresselhaus, Mildred (Inventor)

    2007-01-01

    The present invention provides methods for synthesis of IV VI nanostructures, and thermoelectric compositions formed of such structures. In one aspect, the method includes forming a solution of a Group IV reagent, a Group VI reagent and a surfactant. A reducing agent can be added to the solution, and the resultant solution can be maintained at an elevated temperature, e.g., in a range of about 20.degree. C. to about 360.degree. C., for a duration sufficient for generating nanoparticles as binary alloys of the IV VI elements.

  15. Methods for synthesis of semiconductor nanocrystals and thermoelectric compositions

    DOEpatents

    Ren, Zhifeng; Chen, Gang; Poudel, Bed; Kumar, Shankar; Wang, Wenzhong; Dresselhaus, Mildred

    2007-08-14

    The present invention provides methods for synthesis of IV VI nanostructures, and thermoelectric compositions formed of such structures. In one aspect, the method includes forming a solution of a Group IV reagent, a Group VI reagent and a surfactant. A reducing agent can be added to the solution, and the resultant solution can be maintained at an elevated temperature, e.g., in a range of about 20.degree. C. to about 360.degree. C., for a duration sufficient for generating nanoparticles as binary alloys of the IV VI elements.

  16. Assemblies of Cellulose Nanocrystals

    NASA Astrophysics Data System (ADS)

    Kumacheva, Eugenia

    The entropically driven coassembly of nanorods (cellulose nanocrystals, CNCs) and different types of nanoparticles (NPs), including dye-labeled latex NPs, carbon dots and plasmonic NPs was experimentally studied in aqueous suspensions and in solid films. In mixed CNC-NP suspensions, phase separation into an isotropic NP-rich and a chiral nematic CNC-rich phase took place; the latter contained a significant amount of NPs. Drying the mixed suspension resulted in CNC-NP films with planar disordered layers of NPs, which alternated with chiral nematic CNC-rich regions. In addition, NPs were embedded in the chiral nematic domains. The stratified morphology of the films, together with a random distribution of NPs in the anisotropic phase, led to the films having close-to-uniform fluorescence, birefringence, and circular dichroism properties.

  17. Cu nanocrystal growth on peptide nanotubes by biomineralization: Size control of Cu nanocrystals by tuning peptide conformation

    NASA Astrophysics Data System (ADS)

    Banerjee, Ipsita A.; Yu, Lingtao; Matsui, Hiroshi

    2003-12-01

    With recent interest in seeking new biologically inspired device-fabrication methods in nanotechnology, a new biological approach was examined to fabricate Cu nanotubes by using sequenced histidine-rich peptide nanotubes as templates. The sequenced histidine-rich peptide molecules were assembled as nanotubes, and the biological recognition of the specific sequence toward Cu lead to efficient Cu coating on the nanotubes. Cu nanocrystals were uniformly coated on the histidine-incorporated nanotubes with high packing density. In addition, the diameter of Cu nanocrystal was controlled between 10 and 30 nm on the nanotube by controlling the conformation of histidine-rich peptide by means of pH changes. Those nanotubes showed significant change in electronic structure by varying the nanocrystal diameter; therefore, this system may be developed to a conductivity-tunable building block for microelectronics and biological sensors. This simple biomineralization method can be applied to fabricate various metallic and semiconductor nanotubes with peptides whose sequences are known to mineralize specific ions.

  18. Discrete energy bands in bulk semiconductors

    NASA Astrophysics Data System (ADS)

    Du, Maohua; Shi, Hongliang

    2015-03-01

    Bulk semiconductors typically have continuous valence and conduction bands. Discrete energy levels and bands have been sought after for various applications. For instance, discrete energy levels existing in semiconductor nanocrystals, or quantum does (QDs) have been proposed as a mechanism to suppress hot carrier thermalization and to enhance carrier multiplication in QD solar cells. Impurity bands in the band gap have been introduced for intermediate-band solar cells and for efficient visible light absorption and photocatalysis. In this talk, we show by first principles calculations that, in a multinary compound, a combination of large electronegativity difference between different cations (anions) and large nearest-neighbor distances in cation (anion) sublattices can lead to the splitting of the conduction (valence) band, resulting in several discrete and narrow energy bands separated by large energy gaps. We also discuss applications that may benefit from such electronic structure.

  19. Magnetic evolution of nickel ion doped In2O3 nanocrystals under high magnetic field

    NASA Astrophysics Data System (ADS)

    Sun, Yuanyuan; Hu, Changchun; Huang, Jie; Sun, Youbao; Xue, Xinkai; Sun, Qingbo

    2017-08-01

    High magnetic field (HMF) treatment is an important strategy to tune the physicochemical properties of traditional materials. Here, we take nickel ion doped In2O3 nanocrystals as an example and report that the magnetization behavior of diluted magnetic semiconductors can be easily tuned by HMF treatment. It is experimentally demonstrated that the room temperature ferromagnetism of lowly-doped nanocrystals can be greatly enhanced by HMF treatment while the paramagnetic properties of highly-doped samples is almost un-changed. These magnetic transition behaviors after HMF treatment are attributed to the rearrangement of magnetic ordering and the increment of grain-boundary defects. Our research not only points out an effective approach to induce the transition of spin states of diluted magnetic semiconductors but also provides a potentially efficient route to endow other traditional materials with novel physical properties.

  20. Silicon nanocrystal-noble metal hybrid nanoparticles

    NASA Astrophysics Data System (ADS)

    Sugimoto, H.; Fujii, M.; Imakita, K.

    2016-05-01

    We report a novel and facile self-limiting synthesis route of silicon nanocrystal (Si NC)-based colloidally stable semiconductor-metal (gold, silver and platinum) hybrid nanoparticles (NPs). For the formation of hybrid NPs, we employ ligand-free colloidal Si NCs with heavily boron (B) and phosphorus (P) doped shells. By simply mixing B and P codoped colloidal Si NCs with metal salts, hybrid NPs consisting of metal cores and Si NC shells are spontaneously formed. We demonstrate the synthesis of highly uniform and size controllable hybrid NPs. It is shown that codoped Si NCs act as a reducing agent for metal salts and also as a protecting layer to stop metal NP growth. The process is thus self-limiting. The development of a variety of Si NC-based hybrid NPs is a promising first step for the design of biocompatible multifunctional NPs with broad material choices for biosensing, bioimaging and solar energy conversion.We report a novel and facile self-limiting synthesis route of silicon nanocrystal (Si NC)-based colloidally stable semiconductor-metal (gold, silver and platinum) hybrid nanoparticles (NPs). For the formation of hybrid NPs, we employ ligand-free colloidal Si NCs with heavily boron (B) and phosphorus (P) doped shells. By simply mixing B and P codoped colloidal Si NCs with metal salts, hybrid NPs consisting of metal cores and Si NC shells are spontaneously formed. We demonstrate the synthesis of highly uniform and size controllable hybrid NPs. It is shown that codoped Si NCs act as a reducing agent for metal salts and also as a protecting layer to stop metal NP growth. The process is thus self-limiting. The development of a variety of Si NC-based hybrid NPs is a promising first step for the design of biocompatible multifunctional NPs with broad material choices for biosensing, bioimaging and solar energy conversion. Electronic supplementary information (ESI) available: Additional TEM images and extinction spectra of Si-metal hybrid NPs are shown in Fig. S1

  1. Off-Resonance Photosensitization of a Photorefractive Polymer Composite Using PbS Nanocrystals

    DOE PAGES

    Moon, Jong-Sik; Liang, Yichen; Stevens, Tyler E.; ...

    2015-05-26

    The photosensitization of photorefractive polymeric composites for operation at 633 nm is accomplished through the inclusion of narrow band gap semiconductor nanocrystals composed of PbS. Unlike previous studies involving photosensitization of photorefractive polymer composites with inorganic nanocrystals, we employ an off-resonance approach where the first excitonic transition associated with the PbS nanocrystals lies at ~1220 nm and not the wavelength of operation. Using this methodology, internal diffraction efficiencies exceeding 82%, two-beam-coupling gain coefficients of 211 cm–1, and response times of 34 ms have been observed, representing some of the best figures of merit reported for this class of materials. Furthermore,more » these data demonstrate the ability of semiconductor nanocrystals to compete effectively with traditional organic photosensitizers. In addition to superior performance, this approach also offers an inexpensive and easy means by which to photosensitize composite materials. Additionally, the photoconductive characteristics of the composites used for this study will also be considered.« less

  2. Off-Resonance Photosensitization of a Photorefractive Polymer Composite Using PbS Nanocrystals

    SciTech Connect

    Moon, Jong-Sik; Liang, Yichen; Stevens, Tyler E.; Monson, Todd C.; Huber, Dale L.; Mahala, Benjamin D.; Winiarz, Jeffrey G.

    2015-05-26

    The photosensitization of photorefractive polymeric composites for operation at 633 nm is accomplished through the inclusion of narrow band gap semiconductor nanocrystals composed of PbS. Unlike previous studies involving photosensitization of photorefractive polymer composites with inorganic nanocrystals, we employ an off-resonance approach where the first excitonic transition associated with the PbS nanocrystals lies at ~1220 nm and not the wavelength of operation. Using this methodology, internal diffraction efficiencies exceeding 82%, two-beam-coupling gain coefficients of 211 cm–1, and response times of 34 ms have been observed, representing some of the best figures of merit reported for this class of materials. Furthermore, these data demonstrate the ability of semiconductor nanocrystals to compete effectively with traditional organic photosensitizers. In addition to superior performance, this approach also offers an inexpensive and easy means by which to photosensitize composite materials. Additionally, the photoconductive characteristics of the composites used for this study will also be considered.

  3. Laser-induced growth of nanocrystals embedded in porous materials

    NASA Astrophysics Data System (ADS)

    Capoen, Bruno; Chahadih, Abdallah; El Hamzaoui, Hicham; Cristini, Odile; Bouazaoui, Mohamed

    2013-06-01

    Space localization of the linear and nonlinear optical properties in a transparent medium at the submicron scale is still a challenge to yield the future generation of photonic devices. Laser irradiation techniques have always been thought to structure the matter at the nanometer scale, but combining them with doping methods made it possible to generate local growth of several types of nanocrystals in different kinds of silicate matrices. This paper summarizes the most recent works developed in our group, where the investigated nanoparticles are either made of metal (gold) or chalcogenide semiconductors (CdS, PbS), grown in precursor-impregnated porous xerogels under different laser irradiations. This review is associated to new results on silver nanocrystals in the same kind of matrices. It is shown that, depending on the employed laser, the particles can be formed near the sample surface or deep inside the silica matrix. Photothermal and/or photochemical mechanisms may be invoked to explain the nanoparticle growth, depending on the laser, precursor, and matrix. One striking result is that metal salt reduction, necessary to the production of the corresponding nanoparticles, can efficiently occur due to the thermal wrenching of electrons from the matrix itself or due to multiphoton absorption of the laser light by a reducer additive in femtosecond regime. Very localized semiconductor quantum dots could also be generated using ultrashort pulses, but while PbS nanoparticles grow faster than CdS particles due to one-photon absorption, this better efficiency is counterbalanced by a sensitivity to oxidation. In most cases where the reaction efficiency is high, particles larger than the pores have been obtained, showing that a fast diffusion of the species through the interconnected porosity can modify the matrix itself. Based on our experience in these techniques, we compare several examples of laser-induced nanocrystal growth in porous silica xerogels, which allows

  4. Laser-induced growth of nanocrystals embedded in porous materials.

    PubMed

    Capoen, Bruno; Chahadih, Abdallah; El Hamzaoui, Hicham; Cristini, Odile; Bouazaoui, Mohamed

    2013-06-06

    Space localization of the linear and nonlinear optical properties in a transparent medium at the submicron scale is still a challenge to yield the future generation of photonic devices. Laser irradiation techniques have always been thought to structure the matter at the nanometer scale, but combining them with doping methods made it possible to generate local growth of several types of nanocrystals in different kinds of silicate matrices. This paper summarizes the most recent works developed in our group, where the investigated nanoparticles are either made of metal (gold) or chalcogenide semiconductors (CdS, PbS), grown in precursor-impregnated porous xerogels under different laser irradiations. This review is associated to new results on silver nanocrystals in the same kind of matrices. It is shown that, depending on the employed laser, the particles can be formed near the sample surface or deep inside the silica matrix. Photothermal and/or photochemical mechanisms may be invoked to explain the nanoparticle growth, depending on the laser, precursor, and matrix. One striking result is that metal salt reduction, necessary to the production of the corresponding nanoparticles, can efficiently occur due to the thermal wrenching of electrons from the matrix itself or due to multiphoton absorption of the laser light by a reducer additive in femtosecond regime. Very localized semiconductor quantum dots could also be generated using ultrashort pulses, but while PbS nanoparticles grow faster than CdS particles due to one-photon absorption, this better efficiency is counterbalanced by a sensitivity to oxidation. In most cases where the reaction efficiency is high, particles larger than the pores have been obtained, showing that a fast diffusion of the species through the interconnected porosity can modify the matrix itself. Based on our experience in these techniques, we compare several examples of laser-induced nanocrystal growth in porous silica xerogels, which allows

  5. Laser-induced growth of nanocrystals embedded in porous materials

    PubMed Central

    2013-01-01

    Space localization of the linear and nonlinear optical properties in a transparent medium at the submicron scale is still a challenge to yield the future generation of photonic devices. Laser irradiation techniques have always been thought to structure the matter at the nanometer scale, but combining them with doping methods made it possible to generate local growth of several types of nanocrystals in different kinds of silicate matrices. This paper summarizes the most recent works developed in our group, where the investigated nanoparticles are either made of metal (gold) or chalcogenide semiconductors (CdS, PbS), grown in precursor-impregnated porous xerogels under different laser irradiations. This review is associated to new results on silver nanocrystals in the same kind of matrices. It is shown that, depending on the employed laser, the particles can be formed near the sample surface or deep inside the silica matrix. Photothermal and/or photochemical mechanisms may be invoked to explain the nanoparticle growth, depending on the laser, precursor, and matrix. One striking result is that metal salt reduction, necessary to the production of the corresponding nanoparticles, can efficiently occur due to the thermal wrenching of electrons from the matrix itself or due to multiphoton absorption of the laser light by a reducer additive in femtosecond regime. Very localized semiconductor quantum dots could also be generated using ultrashort pulses, but while PbS nanoparticles grow faster than CdS particles due to one-photon absorption, this better efficiency is counterbalanced by a sensitivity to oxidation. In most cases where the reaction efficiency is high, particles larger than the pores have been obtained, showing that a fast diffusion of the species through the interconnected porosity can modify the matrix itself. Based on our experience in these techniques, we compare several examples of laser-induced nanocrystal growth in porous silica xerogels, which allows

  6. Optical properties and ensemble characteristics of size purified Silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Miller, Joseph Bradley

    Nanotechnology is at the forefront of current scientific research and nanocrystals are being hailed as the 'artificial' atoms of the 21st century. Semiconducting silicon nanocrystals (SiNCs) are prime candidates for potential commercial applications because of silicon's already ubiquitous presence in the semiconductor industry, nontoxicity and abundance in nature. For realization of these potential applications, the properties and behavior of SiNCs need to be understood and enhanced. In this report, some of the main SiNC synthesis schemes are discussed, including those we are currently experimenting with to create our own SiNCs and the one utilized to create the SiNCs used in this study. The underlying physics that governs the unique behavior of SiNCs is then presented. The properties of the as-produced SiNCs are determined to depend strongly on surface passivation and environment. Size purification, an important aspect of nanomaterial utilization, was successfully performed on our SiNCs though density gradient ultracentrifugation. We demonstrate that the size-purified fractions exhibit an enhanced ability for colloidal self-assembly, with better aligned nanocrystal energy levels which promotes greater photostability in close-packed films and produces a slight increase in photoluminescence (PL) quantum yield. The qualities displayed by the fractions are exploited to form SiNC clusters that exhibit photostable PL. An analysis of SiNC cluster (from individual nanocrystals to collections of more than one thousand) blinking and PL shows an improvement in their PL emitting 'on' times. Pure SiNC films and SiNC-polymer nanocomposites are created and the dependence of their PL on temperature is measured. For such nanocomposites, the coupling between the 'coffee-ring' effect and liquid-liquid phase separation is also examined for ternary mixtures of solvent, polymer and semiconducting nanocrystal. We discover that with the right SiNC-polymer concentration and polymer

  7. Diffusion of gold from the inner core to the surface of Ag(2)S nanocrystals.

    PubMed

    Yang, Jun; Ying, Jackie Y

    2010-02-24

    The diffusion of Au in Ag(2)S from the inner core to the surface of Ag(2)S was reported, and a new nanocomposite of core-shell Pt@Ag(2)S and Au nanoparticles has been derived through this diffusion phenomenon. Ostwald ripening was observed by transmission electron microscopy during the characterization of the nanocomposite. This elucidated the mechanism of formation of semiconductor-metal heterostructures as a consequence of Au diffusion in Ag(2)S nanocrystals.

  8. Continuous mesoporous titania nanocrystals: their growth in confined space and scope for application.

    PubMed

    Dutta, Saikat; Bhaumik, Asim

    2013-11-01

    Enjoying the single lifestyle: With an overwhelming efficiency compared to thermally sintered preformed nanocrystals, mesoporous single crystals (MSCs) of TiO2 constitute a new class of semiconductor materials for low-cost solar power, solar fuel, photocatalysis, and energy storage applications. This Highlight explores the benefits of template-directed seed-mediated growth in the confined space of a preseeded mesoporous template, and possible research avenues for further improvements.

  9. Synthesis of quantum dot nanocrystals and plasmonic nanoparticles using a segmented flow reactor

    NASA Astrophysics Data System (ADS)

    Mbwahnche, R. C.; Matyushkin, L. B.; Ryzhov, O. A.; Aleksandrova, O. A.; Moshnikov, V. A.

    2017-01-01

    The purpose of this research is to develop an automated method of synthesizing quantum dot nanocrystals and plasmonic nanoparticles using segmented flow rector synthesis as a new alternative to the batch method of synthesizing nanoparticles. A reactor was successfully applied to the synthesis of colloidal solutions of semiconductor (CdSe) and metal (Ag) nanoparticles. This instrument is applicable in both material science laboratories and industry.

  10. Cation coordination reactions on nanocrystals: surface/interface, doping control and advanced photocatalysis applications (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Zhang, Jiatao

    2016-10-01

    Abstract: Including the shape and size effect, the controllable doping, hetero-composite and surface/interface are the prerequisite of colloidal nanocrystals for exploring their optoelectronic properties, such as fluorescence, plasmon-exciton coupling, efficient electron/hole separation, and enhanced photocatalysis applications. By controlling soft acid-base coordination reactions between cation molecular complexes and colloidal nanocrystals, we showed that chemical thermodynamics could drive nanoscale monocrystalline growth of the semiconductor shell on metal nano-substrates and the substitutional heterovalent doping in semiconductor nanocrystals. We have demonstrated evolution of relative position of Au and II-VI semiconductor in Au-Semi from symmetric to asymmetric configuration, different phosphines initiated morphology engineering, oriented attachment of quantum dots into micrometer nanosheets with synergistic control of surface/interface and doing, which can further lead to fine tuning of plasmon-exciton coupling. Therefore, different hydrogen photocatalytic performance, Plasmon enhanced photocatalysis properties have been achieved further which lead to the fine tuning of plasmon-exciton coupling. Substitutional heterovalent doping here enables the tailoring of optical, electronic properties and photocatalysis applications of semiconductor nanocrystals because of electronic impurities (p-, n-type doping) control. References: (1) J. Gui, J. Zhang*, et al. Angew. Chem. Int. Ed. 2015, 54, 3683. (2) Q. Zhao, J. Zhang*, etc., Adv. Mater. 2014, 26, 1387. (3) J. Liu, Q. Zhao, S. G. Wang*, J. Zhang*, etc., Adv. Mater. 2015, 27-2753-2761. (4) H. Qian, J. Zhang*, etc., NPG Asia Mater. (2015) 7, e152. (5) M. Ji, M. Xu, etc., J. Zhang*, Adv. Mater. 2016, in proof. (6) S. Yu, J. T. Zhang, Y. Tang, M. Ouyang*, Nano Lett. 2015, 15, 6282-6288. (7) J. Zhang, Y. Tang, K. Lee and M. Ouyang*, Science 2010, 327, 1634. (8) J. Zhang, Y. Tang, K. Lee, M. Ouyang*, Nature 2010, 466

  11. A dual-colored bio-marker made of doped ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Wu, Y. L.; Fu, S.; Tok, A. I. Y.; Zeng, X. T.; Lim, C. S.; Kwek, L. C.; Boey, F. C. Y.

    2008-08-01

    Bio-compatible ZnO nanocrystals doped with Co, Cu and Ni cations, surface capped with two types of aminosilanes and titania are synthesized by a soft chemical process. Due to the small particle size (2-5 nm), surface functional groups and the high photoluminescence emissions at the UV and blue-violet wavelength ranges, bio-imaging on human osteosarcoma (Mg-63) cells and histiocytic lymphoma U-937 monocyte cells showed blue emission at the nucleus and bright turquoise emission at the cytoplasm simultaneously. This is the first report on dual-color bio-images labeled by one semiconductor nanocrystal colloidal solution. Bright green emission was detected on mung bean seedlings labeled by all the synthesized ZnO nanocrystals. Cytotoxicity tests showed that the aminosilanes capped nanoparticles are non-toxic. Quantum yields of the nanocrystals varied from 79% to 95%. The results showed the potential of the pure ZnO and Co-doped ZnO nanocrystals for live imaging of both human cells and plant systems.

  12. Electrogenerated chemiluminescence from a CdSe nanocrystal film and its sensing application in aqueous solution.

    PubMed

    Zou, Guizheng; Ju, Huangxian

    2004-12-01

    Electrogenerated chemiluminescence (ECL) of semiconductor quantum dots in aqueous solutions and its first sensing application were studied by depositing CdSe nanocrystals (NCs) on a paraffin-impregnated graphite electrode (PIGE). The CdSe nanocrystal thin film exhibited two ECL peaks at -1.20 (ECL-1) and -1.50 V (ECL-2) in pH 9.3, 0.1 M PBS during the cyclic sweep between 0 and -1.8 V at 20 mV s(-1). The electron-transfer reaction between individual electrochemically reduced nanocrystal species and oxidant coreactants such as H(2)O(2) and reduced dissolved oxygen led to ECL-1. When mass NCs packed densely in the film were reduced electrochemically, assembly of reduced nanocrystal species could react with coreactants to produce another ECL signal, ECL-2. ECL-1 showed higher sensitivity to the concentration of oxidant coreactants than ECL-2 and thus was used for ECL detection of coreactant, H(2)O(2). A linear response of ECL-1 to H(2)O(2) was observed in the concentration range of 2.5 x 10(-7)-6 x 10(-5) M with a detection limit of 1.0 x10(-7) M. The fabrication of 10 CdSe nanocrystal thin-film modified PIGEs displayed an acceptable reproducibility with a RSD of 1.18% obtained at H(2)O(2) level of 10 microM.

  13. Lead Halide Perovskites and Other Metal Halide Complexes As Inorganic Capping Ligands for Colloidal Nanocrystals

    PubMed Central

    2014-01-01

    Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MXn, where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV–VI, II–VI, and III–V semiconductor nanocrystals. In particular, we show that the Lewis acid–base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20–30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50–65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface. PMID:24746226

  14. Influence of Dopant Distribution on the Plasmonic Properties of Indium Tin Oxide Nanocrystals

    SciTech Connect

    Lounis, SD; Runnerstrom, EL; Bergerud, A; Nordlund, D; Milliron, DJ

    2014-05-14

    Doped metal oxide nanocrystals represent an exciting frontier for colloidal synthesis of plasmonic materials, displaying unique optoelectronic properties and showing promise for a variety of applications. However, fundamental questions about the nature of doping in these materials remain. In this article, the strong influence of radial dopant distribution on the optoelectronic properties of colloidal indium tin oxide nanocrystals is reported. Comparing elemental depth-profiling by X-ray photoelectron spectroscopy (XPS) with detailed modeling and simulation of the optical extinction of these nanocrystals using the Drude model for free electrons, a correlation between surface segregation of tin ions and the average activation of dopants is observed. A strong influence of surface segregation of tin on the line shape of the localized surface plasmon resonance (LSPR) is also reported. Samples with tin segregated near the surface show a symmetric line shape that suggests weak or no damping of the plasmon by ionized impurities. It is suggested that segregation of tin near the surface facilitates compensation of the dopant ions by electronic defects and oxygen interstitials, thus reducing activation. A core shell model is proposed to explain the observed differences in line shape. These results demonstrate the nuanced role of dopant distribution in determining the optoelectronic properties of semiconductor nanocrystals and suggest that more detailed study of the distribution and structure of defects in plasmonic colloidal nanocrystals is warranted.

  15. Colloidal CIGS and CZTS nanocrystals: A precursor route to printed photovoltaics

    SciTech Connect

    Akhavan, Vahid A.; Goodfellow, Brian W.; Panthani, Matthew G.; Steinhagen, Chet; Harvey, Taylor B.; Stolle, C. Jackson; Korgel, Brian A.

    2012-05-15

    This review article summarizes our research focused on Cu(In{sub 1-x}Ga{sub x})Se{sub 2} (CIGS) nanocrystals, including their synthesis and implementation as the active light absorbing material in photovoltaic devices (PVs). CIGS PV layers are typically made using a high temperature (>450 Degree-Sign C) process in which Cu, In and Ga are sequentially or co-evaporated and selenized. We have sought to use CIGS nanocrystals synthesized with the desired stoichiometry to deposit PV device layers without high temperature processing. This approach, using spray deposition of the CIGS light absorber layers, without high temperature selenization, has enabled up to 3.1% power conversion efficiency under AM 1.5 solar illumination. Although the device efficiency is too low for commercialization, these devices provide a proof-of-concept that solution-deposited CIGS nanocrystal films can function in PV devices, enabling unconventional device architectures and materials combinations, including the use of flexible, inexpensive and light-weight plastic substrates. - Graphical abstract: The semiconductor light-absorbing layers in photovoltaic devices can be deposited under ambient conditions using nanocrystal inks. Devices can be fabricated on glass or on mechanically flexible plastic substrates. Highlights: Black-Right-Pointing-Pointer CIGS and CZTS nanocrystals are synthesized and formulated into inks. Black-Right-Pointing-Pointer Nanocrystal films are spray deposited and used as light absorbing layers in photovoltaic devices. Black-Right-Pointing-Pointer Photovoltaic devices were constructed from nanowire mats. Black-Right-Pointing-Pointer Photovoltaic device efficiency is limited by electrical transport in the nanocrystal layers.

  16. Tuning of electrical charging effects for ferromagnetic Mn-doped ZnO nanocrystals embedded into a SiO{sub 2} layer fabricated by KrF excimer laser irradiation

    SciTech Connect

    Lee, Sejoon; Kim, Deuk Young; Won Kang, Tae; Cho, Hyung Koun

    2009-07-15

    The ZnMnO nanocrystals were formed by the laser irradiation of the sputter-deposited ZnMnO ultrathin layer using a 248 nm KrF excimer laser, and the size and density of the nanocrystals were observed to be controllable by modulations of either the energy density or the frequency of the irradiated pulsed-laser beam. Metal-oxide-semiconductor capacitors fabricated using ZnMnO nanocrystals clearly showed the electrical charging effect, and it was observed that the memory window depends on the size and density of nanocrystals. For measurements of the spontaneous magnetization, ZnMnO nanocrystals showed to have room-temperature ferromagnetism with M{sub r} of approx1.5 emu/cm{sup 3} and H{sub c} 167 Oe. By using ferromagnetism in ZnMnO nanocrystals, tuning of the memory window was demonstrated. Namely, it was clearly observed that the flat-band voltage shift of approx1.25 V can be modulated to be approx0.8 V by applying the magnetic field. This is attributed to the modulation of probabilities for tunneling events due to the increased magnetoelectrical repulsion between spin-polarized carriers in ZnMnO dilute magnetic semiconductor nanocrystals and unpolarized carriers in p-Si under the magnetic field. These results suggest that ZnMnO nanocrystals can be used for spin-functional memory devices.

  17. Linearly arranged polytypic CZTSSe nanocrystals

    PubMed Central

    Fan, Feng-Jia; Wu, Liang; Gong, Ming; Chen, Shi You; Liu, Guang Yao; Yao, Hong-Bin; Liang, Hai-Wei; Wang, Yi-Xiu; Yu, Shu-Hong

    2012-01-01

    Even colloidal polytypic nanostructures show promising future in band-gap tuning and alignment, researches on them have been much less reported than the standard nano-heterostructures because of the difficulties involved in synthesis. Up to now, controlled synthesis of colloidal polytypic nanocrsytals has been only realized in II-VI tetrapod and octopod nanocrystals with branched configurations. Herein, we report a colloidal approach for synthesizing non-branched but linearly arranged polytypic I2-II-IV-VI4 nanocrystals, with a focus on polytypic non-stoichiometric Cu2ZnSnSxSe4−x nanocrystals. Each synthesized polytypic non-stoichiometric Cu2ZnSnSxSe4−x nanocrystal is consisted of two zinc blende-derived ends and one wurtzite-derived center part. The formation mechanism has been studied and the phase composition can be tuned through adjusting the reaction temperature, which brings a new band-gap tuning approach to Cu2ZnSnSxSe4-x nanocrystals. PMID:23233871

  18. Semiconductor Quantum Dots with Photoresponsive Ligands.

    PubMed

    Sansalone, Lorenzo; Tang, Sicheng; Zhang, Yang; Thapaliya, Ek Raj; Raymo, Françisco M; Garcia-Amorós, Jaume

    2016-10-01

    Photochromic or photocaged ligands can be anchored to the outer shell of semiconductor quantum dots in order to control the photophysical properties of these inorganic nanocrystals with optical stimulations. One of the two interconvertible states of the photoresponsive ligands can be designed to accept either an electron or energy from the excited quantum dots and quench their luminescence. Under these conditions, the reversible transformations of photochromic ligands or the irreversible cleavage of photocaged counterparts translates into the possibility to switch luminescence with external control. As an alternative to regulating the photophysics of a quantum dot via the photochemistry of its ligands, the photochemistry of the latter can be controlled by relying on the photophysics of the former. The transfer of excitation energy from a quantum dot to a photocaged ligand populates the excited state of the species adsorbed on the nanocrystal to induce a photochemical reaction. This mechanism, in conjunction with the large two-photon absorption cross section of quantum dots, can be exploited to release nitric oxide or to generate singlet oxygen under near-infrared irradiation. Thus, the combination of semiconductor quantum dots and photoresponsive ligands offers the opportunity to assemble nanostructured constructs with specific functions on the basis of electron or energy transfer processes. The photoswitchable luminescence and ability to photoinduce the release of reactive chemicals, associated with the resulting systems, can be particularly valuable in biomedical research and can, ultimately, lead to the realization of imaging probes for diagnostic applications as well as to therapeutic agents for the treatment of cancer.

  19. Preparation of nanocrystals and nanocomposites of nanocrystal-conjugated polymer, and their photophysical properties in confined geometries

    NASA Astrophysics Data System (ADS)

    Xu, Jun

    Semiconductors nanocrystals (NCs), also called quantum dots (QDs), have attracted tremendous interest over the past decade in the fields of physics, chemistry, and engineering. Due to the quantum-confined nature of QDs, the variation of particle size provides continuous and predictable changes in fluorescence emission. On the other hand, conjugated polymers (CPs) have been extensively studied for two decades due to their semiconductor-like optical and electronic properties. The electron and energy transfer between NCs and CPs occur in solar cells and light emitting diodes (LEDs), respectively. Placing CPs in direct contact with a NC (i.e., preparing NC-CP nanocomposites) carries advantage over cases where NC aggregation dominates. Such NC-CP nanocomposites possess a well-defined interface that significantly promotes the charge or energy transfer between these two components. However, very few studies have centered on such direct integration. We prepared NCs and NC-CP nanocomposites based on heck coupling and investigated the energy and charge transfer between semiconductor NCs (i.e., CdSe QDs), CPs (i.e., poly(3-hexyl thiophene) (P3HT)) in the nanocomposites in confined geometries. Two novel strategies were used to confine NC and/or NC-CP nanocomposites: (a) directly immobilizing nanohybrids, QDs and nanorods in nanoscopic porous alumina membrane (PAM), and (b) confining the QDs and CPs in sphere-on-flat geometry to induce self-assembly. While investigating the confinement effect, gradient concentric ring patterns of high regularity form spontaneously simply by allowing a droplet of solution containing either conjugated polymer or semiconductor nanocrystal in a consecutive stick-slip motion in a confined geometry. Such constrained evaporation can be utilized as a simple, cheap, and robust strategy for self-assembling various materials with easily tailored optical and electronic properties into spatially ordered, two-dimensional patterns. These self

  20. Preparation of nanocrystals and nanocomposites of nanocrystal-conjugated polymer, and their photophysical properties in confined geometries

    SciTech Connect

    Xu, Jun

    2007-01-01

    Semiconductors nanocrystals (NCs), also called quantum dots (QDs), have attracted tremendous interest over the past decade in the fields of physics, chemistry, and engineering. Due to the quantum-confined nature of QDs, the variation of particle size provides continuous and predictable changes in fluorescence emission. On the other hand, conjugated polymers (CPs) have been extensively studied for two decades due to their semiconductor-like optical and electronic properties. The electron and energy transfer between NCs and CPs occur in solar cells and light emitting diodes (LEDs), respectively. Placing CPs in direct contact with a NC (i.e., preparing NC-CP nanocomposites) carries advantage over cases where NC aggregation dominates. Such NC-CP nanocomposites possess a well-defined interface that significantly promotes the charge or energy transfer between these two components. However, very few studies have centered on such direct integration. We prepared NCs and NC-CP nanocomposites based on heck coupling and investigated the energy and charge transfer between semiconductor NCs (i.e., CdSe QDs), CPs (i.e., poly(3-hexyl thiophene) (P3HT)) in the nanocomposites in confined geometries. Two novel strategies were used to confine NC and/or NC-CP nanocomposites: (a) directly immobilizing nanohybrids, QDs and nanorods in nanoscopic porous alumina membrane (PAM) , and (b) confining the QDs and CPs in sphere-on-flat geometry to induce self-assembly. While investigating the confinement effect, gradient concentric ring patterns of high regularity form spontaneously simply by allowing a droplet of solution containing either conjugated polymer or semiconductor nanocrystal in a consecutive stick-slip mothion in a confined geometry. Such constrained evaporation can be utilized as a simple, cheap, and robust strategy for self-assembling various materials with easily tailored optical and electronic properties into spatially ordered, two-dimensional patterns. These self

  1. Nanocrystal powered nanomotor

    DOEpatents

    Regan, Brian C [Los Angeles, CA; Zettl, Alexander K [Kensington, CA; Aloni, Shaul [Albany, CA

    2011-01-04

    A nanoscale nanocrystal which may be used as a reciprocating motor is provided, comprising a substrate having an energy differential across it, e.g. an electrical connection to a voltage source at a proximal end; an atom reservoir on the substrate distal to the electrical connection; a nanoparticle ram on the substrate distal to the atom reservoir; a nanolever contacting the nanoparticle ram and having an electrical connection to a voltage source, whereby a voltage applied between the electrical connections on the substrate and the nanolever causes movement of atoms between the reservoir and the ram. Movement of the ram causes movement of the nanolever relative to the substrate. The substrate and nanolever preferably comprise multiwalled carbon nanotubes (MWNTs) and the atom reservoir and nanoparticle ram are preferably metal (e.g. indium) deposited as small particles on the MWNTs. The substrate may comprise a silicon chip that has been fabricated to provide the necessary electrodes and other electromechanical structures, and further supports an atomic track, which may comprise an MWNT.

  2. Nanocrystals for luminescent solar concentrators.

    PubMed

    Bradshaw, Liam R; Knowles, Kathryn E; McDowall, Stephen; Gamelin, Daniel R

    2015-02-11

    Luminescent solar concentrators (LSCs) harvest sunlight over large areas and concentrate this energy onto photovoltaics or for other uses by transporting photons through macroscopic waveguides. Although attractive for lowering solar energy costs, LSCs remain severely limited by luminophore reabsorption losses. Here, we report a quantitative comparison of four types of nanocrystal (NC) phosphors recently proposed to minimize reabsorption in large-scale LSCs: two nanocrystal heterostructures and two doped nanocrystals. Experimental and numerical analyses both show that even the small core absorption of the leading NC heterostructures causes major reabsorption losses at relatively short transport lengths. Doped NCs outperform the heterostructures substantially in this critical property. A new LSC phosphor is introduced, nanocrystalline Cd(1-x)Cu(x)Se, that outperforms all other leading NCs by a significant margin in both small- and large-scale LSCs under full-spectrum conditions.

  3. Nanocrystal assembly for tandem catalysis

    DOEpatents

    Yang, Peidong; Somorjai, Gabor; Yamada, Yusuke; Tsung, Chia-Kuang; Huang, Wenyu

    2014-10-14

    The present invention provides a nanocrystal tandem catalyst comprising at least two metal-metal oxide interfaces for the catalysis of sequential reactions. One embodiment utilizes a nanocrystal bilayer structure formed by assembling sub-10 nm platinum and cerium oxide nanocube monolayers on a silica substrate. The two distinct metal-metal oxide interfaces, CeO.sub.2--Pt and Pt--SiO.sub.2, can be used to catalyze two distinct sequential reactions. The CeO.sub.2--Pt interface catalyzed methanol decomposition to produce CO and H.sub.2, which were then subsequently used for ethylene hydroformylation catalyzed by the nearby Pt--SiO.sub.2 interface. Consequently, propanal was selectively produced on this nanocrystal bilayer tandem catalyst.

  4. Doping silicon nanocrystals and quantum dots

    NASA Astrophysics Data System (ADS)

    Oliva-Chatelain, Brittany L.; Ticich, Thomas M.; Barron, Andrew R.

    2016-01-01

    The ability to incorporate a dopant element into silicon nanocrystals (NC) and quantum dots (QD) is one of the key technical challenges for the use of these materials in a number of optoelectronic applications. Unlike doping of traditional bulk semiconductor materials, the location of the doping element can be either within the crystal lattice (c-doping), on the surface (s-doping) or within the surrounding matrix (m-doping). A review of the various synthetic strategies for doping silicon NCs and QDs is presented, concentrating on the efficacy of the synthetic routes, both in situ and post synthesis, with regard to the structural location of the dopant and the doping level. Methods that have been applied to the characterization of doped NCs and QDs are summarized with regard to the information that is obtained, in particular to provide researchers with a guide to the suitable techniques for determining dopant concentration and location, as well as electronic and photonic effectiveness of the dopant.

  5. Memory and coupling in nanocrystal optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Fairfield, Jessamyn A.

    Optoelectronic devices incorporating semiconducting nanocrystals are promising for many potential applications. Nanocrystals whose size is below the exciton Bohr radius have optical absorption and emission that is tunable with size, due to the quantum confinement of the charge carriers. However, the same confinement that yields these optical properties also makes electrical conduction in a film of nanocrystals occur via tunneling, due to the high energy barrier between nanocrystals. Hence, the extraction of photo-generated charge carriers presents a significant challenge. Several approaches to optimizing the reliability and efficiency of optoelectronic devices using semiconducting nanocrystals are explored herein. Force microscopy is used to investigate charge behavior in nanocrystal films. Plasmonic structures are lithographically defined to enhance electric field and thus charge collection efficiency in two-electrode nanocrystal devices illuminated at plasmonically resonant wavelengths. Graphene substrates are shown to couple electronically with nanocrystal films, improving device conduction while maintaining carrier quantum confinement within the nanocrystal. And finally, the occupancy of charge carrier traps is shown to both directly impact the temperature-dependent photocurrent behavior, and be tunable using a combination of illumination and electric field treatments. Trap population manipulation is robustly demonstrated and verified using a variety of wavelength, intensity, and time-dependent measurements of photocurrent in nanogap nanocrystal devices, emphasizing the importance of measurement history and the possibility of advanced device behavior tuning based on desired operating conditions. Each of these experiments reveals a path toward understanding and optimizing semiconducting nanocrystal optoelectronic devices.

  6. Generalized syntheses of nanocrystal-graphene hybrids in high-boiling-point organic solvents

    NASA Astrophysics Data System (ADS)

    Pang, Danny Wei-Ping; Yuan, Fang-Wei; Chang, Yan-Cheng; Li, Guo-An; Tuan, Hsing-Yu

    2012-07-01

    Nanocrystal-graphene have been proposed as a new kind of promising hybrid for a wide range of application areas including catalysts, electronics, sensors, biomedicine, and energy storage, etc. Although a variety of methods have been developed for the preparation of hybrids, a facile and general synthetic approach is still highly required. In this study, nanocrystal-graphene hybrids were successfully synthesized in high-boiling-point organic solvents. Graphene oxide (GO) nanosheets were modified by oleylamine (OLA) to form a OLA-GO complex in order to be readily incorporated into hydrophobic synthesis. A rich library of highly crystalline nanocrystals, with types including noble metal, metal oxide, magnetic material and semiconductor were successfully grown on chemically converted graphene (CCG), which is simultaneously reduced from GO during the synthesis. High boiling-point solvents afford sufficient thermal energy to assure the high-quality crystalline nature of NCs, therefore the post-annealing process is obviated. Controlled experiments revealed that OLA-GO triggers heterogeneous nucleation and serves as excellent nuclei anchorage media. The protocol developed here brings one step closer to achieve ``unity in diversity'' on the preparation of nanocrystal-graphene hybrids.Nanocrystal-graphene have been proposed as a new kind of promising hybrid for a wide range of application areas including catalysts, electronics, sensors, biomedicine, and energy storage, etc. Although a variety of methods have been developed for the preparation of hybrids, a facile and general synthetic approach is still highly required. In this study, nanocrystal-graphene hybrids were successfully synthesized in high-boiling-point organic solvents. Graphene oxide (GO) nanosheets were modified by oleylamine (OLA) to form a OLA-GO complex in order to be readily incorporated into hydrophobic synthesis. A rich library of highly crystalline nanocrystals, with types including noble metal, metal

  7. Competition effects among size, dimensionality and pressure on modulating bandgap of CdSe and ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Jiang, Xiao Bao; Sheng, Hong Chao; Gu, Xiao Yan; Shi, Ming Xiao

    2015-12-01

    Size, dimensionality and pressure play important roles on modulating band gap (Eg) of semiconductor nanocrystals, and have attracted extensive attention in recent years. In this letter, a simple thermodynamic model is developed and the competition relation among size, dimensionality and pressure effects on Eg is discussed. The accuracy of our prediction is confirmed by the experimental data and simulation results of CdSe and ZnO nanocrystals. This model provides a new insight into the size, dimensionality and pressure effects on Eg and guides the optimal selection as design quantum devices.

  8. Injected nanocrystals for targeted drug delivery

    PubMed Central

    Lu, Yi; Li, Ye; Wu, Wei

    2016-01-01

    Nanocrystals are pure drug crystals with sizes in the nanometer range. Due to the advantages of high drug loading, platform stability, and ease of scaling-up, nanocrystals have been widely used to deliver poorly water-soluble drugs. Nanocrystals in the blood stream can be recognized and sequestered as exogenous materials by mononuclear phagocytic system (MPS) cells, leading to passive accumulation in MPS-rich organs, such as liver, spleen and lung. Particle size, morphology and surface modification affect the biodistribution of nanocrystals. Ligand conjugation and stimuli-responsive polymers can also be used to target nanocrystals to specific pathogenic sites. In this review, the progress on injected nanocrystals for targeted drug delivery is discussed following a brief introduction to nanocrystal preparation methods, i.e., top-down and bottom-up technologies. PMID:27006893

  9. Solvent-like ligand-coated ultrasmall cadmium selenide nanocrystals: strong electronic coupling in a self-organized assembly.

    PubMed

    Lawrence, Katie N; Johnson, Merrell A; Dolai, Sukanta; Kumbhar, Amar; Sardar, Rajesh

    2015-07-21

    Strong inter-nanocrystal electronic coupling is a prerequisite for delocalization of exciton wave functions and high conductivity. We report 170 meV electronic coupling energy of short chain poly(ethylene glycol) thiolate-coated ultrasmall (<2.5 nm in diameter) CdSe semiconductor nanocrystals (SNCs) in solution. Cryo-transmission electron microscopy analysis showed the formation of a pearl-necklace assembly of nanocrystals in solution with regular inter-nanocrystal spacing. The electronic coupling was studied as a function of CdSe nanocrystal size where the smallest nanocrystals exhibited the largest coupling energy. The electronic coupling in spin-cast thin-film (<200 nm in thickness) of poly(ethylene glycol) thiolate-coated CdSe SNCs was studied as a function of annealing temperature, where an unprecedentedly large, ∼400 meV coupling energy was observed for 1.6 nm diameter SNCs, which were coated with a thin layer of poly(ethylene glycol) thiolates. Small-angle X-ray scattering measurements showed that CdSe SNCs maintained an order array inside the films. The strong electronic coupling of SNCs in a self-organized film could facilitate the large-scale production of highly efficient electronic materials for advanced optoelectronic device application.

  10. Non-native Co-, Mn-, and Ti-oxyhydroxide nanocrystals in ferritin for high efficiency solar energy conversion.

    PubMed

    Erickson, S D; Smith, T J; Moses, L M; Watt, R K; Colton, J S

    2015-01-09

    Quantum dot solar cells seek to surpass the solar energy conversion efficiencies achieved by bulk semiconductors. This new field requires a broad selection of materials to achieve its full potential. The 12 nm spherical protein ferritin can be used as a template for uniform and controlled nanocrystal growth, and to then house the nanocrystals for use in solar energy conversion. In this study, precise band gaps of titanium, cobalt, and manganese oxyhydroxide nanocrystals within ferritin were measured, and a change in band gap due to quantum confinement effects was observed. The range of band gaps obtainable from these three types of nanocrystals is 2.19-2.29 eV, 1.93-2.15 eV, and 1.60-1.65 eV respectively. From these measured band gaps, theoretical efficiency limits for a multi-junction solar cell using these ferritin-enclosed nanocrystals are calculated and found to be 38.0% for unconcentrated sunlight and 44.9% for maximally concentrated sunlight. If a ferritin-based nanocrystal with a band gap similar to silicon can be found (i.e. 1.12 eV), the theoretical efficiency limits are raised to 51.3% and 63.1%, respectively. For a current matched cell, these latter efficiencies become 41.6% (with an operating voltage of 5.49 V), and 50.0% (with an operating voltage of 6.59 V), for unconcentrated and maximally concentrated sunlight respectively.

  11. Examining the Roles of Emulsion Droplet Size and Surfactant in the Interfacial Instability-Based Fabrication Process of Micellar Nanocrystals

    NASA Astrophysics Data System (ADS)

    Sun, Yuxiang; Mei, Ling; Han, Ning; Ding, Xinyi; Yu, Caihao; Yang, Wenjuan; Ruan, Gang

    2017-06-01

    The interfacial instability process is an emerging general method to fabricate nanocrystal-encapsulated micelles (also called micellar nanocrystals) for biological detection, imaging, and therapy. The present work utilized fluorescent semiconductor nanocrystals (quantum dots or QDs) as the model nanocrystals to investigate the interfacial instability-based fabrication process of nanocrystal-encapsulated micelles. Our experimental results suggest intricate and intertwined roles of the emulsion droplet size and the surfactant poly (vinyl alcohol) (PVA) used in the fabrication process of QD-encapsulated poly (styrene-b-ethylene glycol) (PS-PEG) micelles. When no PVA is used, no emulsion droplet and thus no micelle is successfully formed; Emulsion droplets with large sizes ( 25 μm) result in two types of QD-encapsulated micelles, one of which is colloidally stable QD-encapsulated PS-PEG micelles while the other of which is colloidally unstable QD-encapsulated PVA micelles; In contrast, emulsion droplets with small sizes ( 3 μm or smaller) result in only colloidally stable QD-encapsulated PS-PEG micelles. The results obtained in this work not only help to optimize the quality of nanocrystal-encapsulated micelles prepared by the interfacial instability method for biological applications but also offer helpful new knowledge on the interfacial instability process in particular and self-assembly in general.

  12. Magneto-optical Faraday rotation of semiconductor nanoparticles embedded in dielectric matrices.

    PubMed

    Savchuk, Andriy I; Stolyarchuk, Ihor D; Makoviy, Vitaliy V; Savchuk, Oleksandr A

    2014-04-01

    Faraday rotation has been studied for CdS, CdTe, and CdS:Mn semiconductor nanoparticles synthesized by colloidal chemistry methods. Additionally these materials were prepared in a form of semiconductor nanoparticles embedded in polyvinyl alcohol films. Transmission electron microscopy and atomic force microscopy analyses served as confirmation of nanocrystallinity and estimation of the average size of the nanoparticles. Spectral dependence of the Faraday rotation for the studied nanocrystals and nanocomposites is correlated with a blueshift of the absorption edge due to the confinement effect in zero-dimensional structures. Faraday rotation spectra and their temperature behavior in Mn-doped nanocrystals demonstrates peculiarities, which are associated with s, p-d exchange interaction between Mn²⁺ ions and band carriers in diluted magnetic semiconductor nanostructures.

  13. Interactions and Assemblies of Polymeric Materials and Colloidal Nanocrystals

    NASA Astrophysics Data System (ADS)

    Williams, Teresa Elaine

    Our need to reduce global energy use is well known and without question, not just from an economic standpoint but also to decrease human impact on climate change. Emerging advances in this area result from the ability to tailor-make materials and energy-saving devices using solution-phase chemistry and deposition techniques. Colloidally synthesized nanocrystals, with their tunable size, shape, and composition, and unusual optical and electronic properties, are leading candidates in these efforts. Because of recent advances in colloidal chemistries, the inventory of monodisperse nanocrystals has expanded to now include metals, semiconductors, magnetic materials, and dielectric materials. For a variety of applications, an active layer composed of a thin film of randomly close-packed nanocrystals is not ideal for optimized device performance; here, the ability to arrange these nano building units into mesoporous (2 nm < d < 50 nm) architectures is highly desirable. Given this, the goal of the work in this dissertation is to determine and understand the design rules that govern the interactions between ligand-stripped nanocrystals and polymeric materials, leading to their hierarchical assembly into colloidal nanocrystal frameworks. I also include the development of quantitative, and novel, characterization techniques, and the application of such frameworks in energy efficiency devices such as electrochromic windows. Understanding the local environment of nanocrystal surfaces and their interaction with surrounding media is vital to their controlled assembly into higher-order structures. Though work has continued in this field for over a decade, researchers have yet to provide a simple and straightforward procedure to scale across nanoscale material systems and applications allowing for synthetic and structural tunability and quantitative characterization. In this dissertation, I have synthesized a new class of amphiphilic block copolymer architecture-directing agents

  14. "Nanocrystal bilayer for tandem catalysis"

    SciTech Connect

    Yamada, Yusuke; Tsung, Chia Kuang; Huang, Wenyu; Huo, Ziyang; E.Habas, Susan E; Soejima, Tetsuro; Aliaga, Cesar E; Samorjai, Gabor A; Yang, Peidong

    2011-01-24

    Supported catalysts are widely used in industry and can be optimized by tuning the composition and interface of the metal nanoparticles and oxide supports. Rational design of metal-metal oxide interfaces in nanostructured catalysts is critical to achieve better reaction activities and selectivities. We introduce here a new class of nanocrystal tandem catalysts that have multiple metal-metal oxide interfaces for the catalysis of sequential reactions. We utilized a nanocrystal bilayer structure formed by assembling platinum and cerium oxide nanocube monolayers of less than 10 nm on a silica substrate. The two distinct metal-metal oxide interfaces, CeO2-Pt and Pt-SiO2, can be used to catalyse two distinct sequential reactions. The CeO2-Pt interface catalysed methanol decomposition to produce CO and H2, which were subsequently used for ethylene hydroformylation catalysed by the nearby Pt-SiO2 interface. Consequently, propanal was produced selectively from methanol and ethylene on the nanocrystal bilayer tandem catalyst. This new concept of nanocrystal tandem catalysis represents a powerful approach towards designing high-performance, multifunctional nanostructured catalysts

  15. A new family of wurtzite-phase Cu2ZnAS4-x and CuZn2AS4 (A = Al, Ga, In) nanocrystals for solar energy conversion applications.

    PubMed

    Ghosh, Anima; Palchoudhury, Soubantika; Thangavel, Rajalingam; Zhou, Ziyou; Naghibolashrafi, Nariman; Ramasamy, Karthik; Gupta, Arunava

    2016-01-07

    A new family of quaternary semiconductors Cu2ZnAS4-x and CuZn2AS4 (A = Al, Ga, In) has been synthesized in the form of wurtzite phase nanocrystals for the first time. The nanocrystals can be converted to the stannite phase via thermal annealing under a N2 atmosphere. A direct band gap in the visible wavelength region combined with a high absorption cross-section makes these materials promising for solar energy conversion applications.

  16. Nanocrystals Research for Energy Efficient and Clean Energy Technologies:

    SciTech Connect

    Rosenthal, Sandra J

    2013-12-17

    Efforts centered on: nanocrystal photovoltaic fabrication, ultrafast dynamics and aberration-corrected STEM characterization of II-VI core, core/shell and alloyed nanocrystals, and fundamental investigation and applications of ultrasmall white light-emitting CdSe nanocrystal.

  17. Highly crosslinked poly(dimethylsiloxane) microbeads with uniformly dispersed quantum dot nanocrystals.

    PubMed

    Shojaei-Zadeh, Shahab; Morris, Jeffrey F; Couzis, Alex; Maldarelli, Charles

    2011-11-01

    This study demonstrates how luminescent semiconductor nanocrystals (quantum dots or QDs) can be dispersed uniformly in a poly(dimethylsiloxane) (PDMS) matrix by polymerizing a mixture of the prepolymer oligomers and the nanocrystals with a relatively large concentration of crosslinking molecules. A microfluidic device is used to fabricate PDMS microbeads embedded with the QDs by using flow focusing to first form monodisperse droplets of the prepolymer/crosslinker/nanocrystal mixture in a continuous aqueous phase. The droplets are subsequently collected, and heated to polymerize them into solid microbead composites. The degree of aggregation of the nanocrystals in the matrix is studied by measuring the nonradiative resonance energy transfer (RET) between the nanocrystals. For this purpose, two quantum dots are used with maxima in their luminescence emission spectrum at 560 nm and 620 nm. When the nanocrystals are within the Förster radius (approximately 10 nm) of each other, exciton energy cascades from the QDs which emit at the shorter wavelength to the QDs which emit at the longer wavelength. This energy transfer is quantified, for two concentration ratios of the prepolmer to the crosslinker, by measuring the deviation of the microbead luminescence spectrum from a reference spectrum obtained by dispersing the QD mixture in a solvent (toluene) in which the nanocrystals do not aggregate. For a low concentration of crosslinking molecules relative to the prepolymer (5:1 by weight prepolymer to crosslinker), strong RET is observed as the emission of the 620 nm QDs is increased and the 560 nm QDs is decreased relative to the reference. In the emission spectrum for a higher concentration of crosslinkers (2:1 by weight prepolymer to crosslinker), the resonance energy transfer is less relative to the case of the low concentration of crosslinkers, and the spectrum more closely resembles the reference. This result indicates that the increase in the crosslinker concentration

  18. Penternary chalcogenides nanocrystals as catalytic materials for efficient counter electrodes in dye-synthesized solar cells

    PubMed Central

    Özel, Faruk; Sarılmaz, Adem; İstanbullu, Bilal; Aljabour, Abdalaziz; Kuş, Mahmut; Sönmezoğlu, Savaş

    2016-01-01

    The penternary chalcogenides Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 were successfully synthesized by hot-injection method, and employed as a catalytic materials for efficient counter electrodes in dye-synthesized solar cells (DSSCs). The structural, compositional, morphological and optical properties of these pentenary semiconductors were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS) and ultraviolet-visible (UV–Vis) spectroscopy. The Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 nanocrystals had a single crystalline, kesterite phase, adequate stoichiometric ratio, 18–25 nm particle sizes which are forming nanospheres, and band gap energy of 1.18 and 1.45 eV, respectively. Furthermore, the electrochemical impedance spectroscopy and cyclic voltammograms indicated that Cu2CoSn(SeS)4 nanocrystals as counter electrodes exhibited better electrocatalytic activity for the reduction of iodine/iodide electrolyte than that of Cu2ZnSn(SeS)4 nanocrystals and conventional platinum (Pt). The photovoltaic results demonstrated that DSSC with a Cu2CoSn(SeS)4 nanocrystals-based counter electrode achieved the best efficiency of 6.47%, which is higher than the same photoanode employing a Cu2ZnSn(SeS)4 nanocrystals (3.18%) and Pt (5.41%) counter electrodes. These promising results highlight the potential application of penternary chalcogen Cu2CoSn(SeS)4 nanocrystals in low-cost, high-efficiency, Pt-free DSSCs. PMID:27380957

  19. Penternary chalcogenides nanocrystals as catalytic materials for efficient counter electrodes in dye-synthesized solar cells.

    PubMed

    Özel, Faruk; Sarılmaz, Adem; İstanbullu, Bilal; Aljabour, Abdalaziz; Kuş, Mahmut; Sönmezoğlu, Savaş

    2016-07-06

    The penternary chalcogenides Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 were successfully synthesized by hot-injection method, and employed as a catalytic materials for efficient counter electrodes in dye-synthesized solar cells (DSSCs). The structural, compositional, morphological and optical properties of these pentenary semiconductors were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS) and ultraviolet-visible (UV-Vis) spectroscopy. The Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 nanocrystals had a single crystalline, kesterite phase, adequate stoichiometric ratio, 18-25 nm particle sizes which are forming nanospheres, and band gap energy of 1.18 and 1.45 eV, respectively. Furthermore, the electrochemical impedance spectroscopy and cyclic voltammograms indicated that Cu2CoSn(SeS)4 nanocrystals as counter electrodes exhibited better electrocatalytic activity for the reduction of iodine/iodide electrolyte than that of Cu2ZnSn(SeS)4 nanocrystals and conventional platinum (Pt). The photovoltaic results demonstrated that DSSC with a Cu2CoSn(SeS)4 nanocrystals-based counter electrode achieved the best efficiency of 6.47%, which is higher than the same photoanode employing a Cu2ZnSn(SeS)4 nanocrystals (3.18%) and Pt (5.41%) counter electrodes. These promising results highlight the potential application of penternary chalcogen Cu2CoSn(SeS)4 nanocrystals in low-cost, high-efficiency, Pt-free DSSCs.

  20. Penternary chalcogenides nanocrystals as catalytic materials for efficient counter electrodes in dye-synthesized solar cells

    NASA Astrophysics Data System (ADS)

    Özel, Faruk; Sarılmaz, Adem; Istanbullu, Bilal; Aljabour, Abdalaziz; Kuş, Mahmut; Sönmezoğlu, Savaş

    2016-07-01

    The penternary chalcogenides Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 were successfully synthesized by hot-injection method, and employed as a catalytic materials for efficient counter electrodes in dye-synthesized solar cells (DSSCs). The structural, compositional, morphological and optical properties of these pentenary semiconductors were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS) and ultraviolet-visible (UV-Vis) spectroscopy. The Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 nanocrystals had a single crystalline, kesterite phase, adequate stoichiometric ratio, 18-25 nm particle sizes which are forming nanospheres, and band gap energy of 1.18 and 1.45 eV, respectively. Furthermore, the electrochemical impedance spectroscopy and cyclic voltammograms indicated that Cu2CoSn(SeS)4 nanocrystals as counter electrodes exhibited better electrocatalytic activity for the reduction of iodine/iodide electrolyte than that of Cu2ZnSn(SeS)4 nanocrystals and conventional platinum (Pt). The photovoltaic results demonstrated that DSSC with a Cu2CoSn(SeS)4 nanocrystals-based counter electrode achieved the best efficiency of 6.47%, which is higher than the same photoanode employing a Cu2ZnSn(SeS)4 nanocrystals (3.18%) and Pt (5.41%) counter electrodes. These promising results highlight the potential application of penternary chalcogen Cu2CoSn(SeS)4 nanocrystals in low-cost, high-efficiency, Pt-free DSSCs.

  1. (Plasmonic Metal Core)/(Semiconductor Shell) Nanostructures

    NASA Astrophysics Data System (ADS)

    Fang, Caihong

    Over the past several years, integration of metal nanocrystals that can support localized surface plasmon has been demonstrated as one of the most promising methods to the improvement of the light-harvesting efficiency of semiconductors. Ag and Au nanocrystals have been extensively hybridized with semiconductors by either deposition or anchoring. However, metal nanocrystals tend to aggregate, reshape, detach, or grow into large nanocrystals, leading to a loss of the unique properties seen in the original nanocrystals. Fortunately, core/shell nanostructures, circumventing the aforementioned problems, have been demonstrated to exhibit superior photoactivities. To further improve the light-harvesting applications of (plasmonic metal core)/(semiconductor shell) nanostructures, it is vital to understand the plasmonic and structural evolutions during the preparation processes, design novel hybrid nanostructures, and improve their light-harvesting performances. In this thesis, I therefore studied the plasmonic and structural evolutions during the formation of (Ag core)/(Ag2S shell) nanostructures. Moreover, I also prepared (noble metal core)/(TiO2 shell) nanostructures and investigated their plasmonic properties and photon-harvesting applications. Clear understanding of the sulfidation process can enable fine control of the plasmonic properties as well as the structural composition of Ag/Ag 2S nanomaterials. Therefore, I investigated the plasmonic and structural variations during the sulfidation process of Ag nanocubes both experimentally and numerically. The sulfidation reactions were carried out at both the ensemble and single-particle levels. Electrodynamic simulations were also employed to study the variations of the plasmonic properties and plasmon modes. Both experiment and simulation results revealed that sulfidation initiates at the vertices of Ag nanocubes. Ag nanocubes are then gradually truncated and each nanocube becomes a nanosphere eventually. The cubic

  2. Comparison of Carrier Multiplication Yields in PbS and PbSe Nanocrystals: The Role of Competing Energy-Loss Processes

    SciTech Connect

    Stewart, J. T.; Padiha, L. A.; Qazilbash, M. M.; Petryga, J. M.; Midgett, A. G.; Luther, J. M.; Beard, M. C.; Nozik, A. J.; Klimov, V. I.

    2012-02-08

    Infrared band gap semiconductor nanocrystals are promising materials for exploring generation III photovoltaic concepts that rely on carrier multiplication or multiple exciton generation, the process in which a single high-energy photon generates more than one electron-hole pair. In this work, we present measurements of carrier multiplication yields and biexciton lifetimes for a large selection of PbS nanocrystals and compare these results to the well-studied PbSe nanocrystals. The similar bulk properties of PbS and PbSe make this an important comparison for discerning the pertinent properties that determine efficient carrier multiplication. We observe that PbS and PbSe have very similar biexciton lifetimes as a function of confinement energy. Together with the similar bulk properties, this suggests that the rates of multiexciton generation, which is the inverse of Auger recombination, are also similar. The carrier multiplication yields in PbS nanocrystals, however, are strikingly lower than those observed for PbSe nanocrystals. We suggest that this implies the rate of competing processes, such as phonon emission, is higher in PbS nanocrystals than in PbSe nanocrystals. Indeed, our estimations for phonon emission mediated by the polar Froehlich-type interaction indicate that the corresponding energy-loss rate is approximately twice as large in PbS than in PbSe.

  3. Energy transfer processes in semiconductor quantum dots: bacteriorhodopsin hybrid system

    NASA Astrophysics Data System (ADS)

    Rakovich, Aliaksandra; Sukhanova, Alyona; Bouchonville, Nicolas; Molinari, Michael; Troyon, Michel; Cohen, Jacques H. M.; Rakovich, Yury; Donegan, John F.; Nabiev, Igor

    2009-05-01

    The potential impact of nanoscience on energy transfer processes in biomolecules was investigated on the example of a complex between fluorescent semiconductor nanocrystals and photochromic membrane protein. The interactions between colloidal CdTe quantum dots (QDs) and bacteriorhodopsin (bR) protein were studied by a variety of spectroscopic techniques, including integrated and time-resolved fluorescence spectroscopies, zeta potential and size measurement, and fluorescence correlation spectroscopy. QDs' luminescence was found to be strongly modulated by bacteriorhodopsin, but in a controllable way. Decreasing emission lifetimes and blue shifts in QDs' emission at increasing protein concentrations suggest that quenching occurs via Förster resonance energy transfer. On the other hand, concave Stern-Volmer plots and sigmoidal photoluminescence quenching curves imply that the self-assembling of NCs and bR exists, and the number of nanocrystals (NCs) per bacteriorhodopsin contributing to energy transfer can be determined from the inflection points of sigmoidal curves. This number was found to be highly dependent not only on the spectral overlap between NC emission and bR absorption bands, but also on nanocrystal surface charge. These results demonstrate the potential of how inorganic nanoscale materials can be employed to improve the generic molecular functions of biomolecules. The observed interactions between CdTe nanocrystals and bacteriorhodopsin can provide the basis for the development of novel functional materials with unique photonic properties and applications in areas such as all-optical switching, photovoltaics and data storage.

  4. Cellulose nanocrystals: synthesis, functional properties, and applications

    PubMed Central

    George, Johnsy; Sabapathi, SN

    2015-01-01

    Cellulose nanocrystals are unique nanomaterials derived from the most abundant and almost inexhaustible natural polymer, cellulose. These nanomaterials have received significant interest due to their mechanical, optical, chemical, and rheological properties. Cellulose nanocrystals primarily obtained from naturally occurring cellulose fibers are biodegradable and renewable in nature and hence they serve as a sustainable and environmentally friendly material for most applications. These nanocrystals are basically hydrophilic in nature; however, they can be surface functionalized to meet various challenging requirements, such as the development of high-performance nanocomposites, using hydrophobic polymer matrices. Considering the ever-increasing interdisciplinary research being carried out on cellulose nanocrystals, this review aims to collate the knowledge available about the sources, chemical structure, and physical and chemical isolation procedures, as well as describes the mechanical, optical, and rheological properties, of cellulose nanocrystals. Innovative applications in diverse fields such as biomedical engineering, material sciences, electronics, catalysis, etc, wherein these cellulose nanocrystals can be used, are highlighted. PMID:26604715

  5. Intermetallic Nanocrystals: Syntheses and Catalytic Applications.

    PubMed

    Yan, Yucong; Du, Jingshan S; Gilroy, Kyle D; Yang, Deren; Xia, Younan; Zhang, Hui

    2017-02-24

    At the forefront of nanochemistry, there exists a research endeavor centered around intermetallic nanocrystals, which are unique in terms of long-range atomic ordering, well-defined stoichiometry, and controlled crystal structure. In contrast to alloy nanocrystals with no elemental ordering, it is challenging to synthesize intermetallic nanocrystals with a tight control over their size and shape. Here, recent progress in the synthesis of intermetallic nanocrystals with controllable sizes and well-defined shapes is highlighted. A simple analysis and some insights key to the selection of experimental conditions for generating intermetallic nanocrystals are presented, followed by examples to highlight the viable use of intermetallic nanocrystals as electrocatalysts or catalysts for various reactions, with a focus on the enhanced performance relative to their alloy counterparts that lack elemental ordering. Within the conclusion, perspectives on future developments in the context of synthetic control, structure-property relationships, and applications are discussed.

  6. Modeling and simulation of floating gate nanocrystal FET devices and circuits

    NASA Astrophysics Data System (ADS)

    Hasaneen, El-Sayed A. M.

    The nonvolatile memory market has been growing very fast during the last decade, especially for mobile communication systems. The Semiconductor Industry Association International Technology Roadmap for Semiconductors states that the difficult challenge for nonvolatile semiconductor memories is to achieve reliable, low power, low voltage performance and high-speed write/erase. This can be achieved by aggressive scaling of the nonvolatile memory cells. Unfortunately, scaling down of conventional nonvolatile memory will further degrade the retention time due to the charge loss between the floating gate and drain/source contacts and substrate which makes conventional nonvolatile memory unattractive. Using nanocrystals as charge storage sites reduces dramatically the charge leakage through oxide defects and drain/source contacts. Floating gate nanocrystal nonvolatile memory, FG-NCNVM, is a candidate for future memory because it is advantageous in terms of high-speed write/erase, small size, good scalability, low-voltage, low-power applications, and the capability to store multiple bits per cell. Many studies regarding FG-NCNVMs have been published. Most of them have dealt with fabrication improvements of the devices and device characterizations. Due to the promising FG-NCNVM applications in integrated circuits, there is a need for circuit a simulation model to simulate the electrical characteristics of the floating gate devices. In this thesis, a FG-NCNVM circuit simulation model has been proposed. It is based on the SPICE BSIM simulation model. This model simulates the cell behavior during normal operation. Model validation results have been presented. The SPICE model shows good agreement with experimental results. Current-voltage characteristics, transconductance and unity gain frequency (fT) have been studied showing the effect of the threshold voltage shift (DeltaVth) due to nanocrystal charge on the device characteristics. The threshold voltage shift due to

  7. Electronic Structure of Germanium Nanocrystal Films Probed with Synchrotron Radiation

    SciTech Connect

    Bostedt, C

    2002-05-01

    The fundamental structure--property relationship of semiconductor quantum dots has been investigated. For deposited germanium nanocrystals strong quantum confinement effects have been determined with synchrotron radiation based x-ray absorption and photoemission techniques. The nanocrystals are condensed out of the gas phase with a narrow size distribution and subsequently deposited in situ onto various substrates. The particles are crystalline in the cubic phase with a structurally disordered surface shell and the resulting film morphology depends strongly on the substrate material and condition. The disordered surface region has an impact on the overall electronic structure of the particles. In a size-dependent study, the conduction and valence band edge of germanium nanocrystals have been measured for the first time and compared to the bulk crystal. The band edges move to higher energies as the particle size is decreased, consistent with quantum confinement theory. To obtain a more accurate analysis of confinement effects in the empty states, a novel analysis method utilizing an effective particle size for the x-ray absorption experiment, which allows a deconvolution of absorption edge broadening effects, has been introduced. Comparison of the present study to earlier studies on silicon reveals that germanium exhibits stronger quantum confinement effects than silicon. Below a critical particle size of 2.3 {+-} 0.7 nm, the band gap of germanium becomes larger than that of silicon--even if it is the opposite for bulk materials. This result agrees phenomenologically with effective mass and tight binding theories but contradicts the findings of recent pseudopotential calculations. The discrepancy between theory and experiments is attributed to the differences in the theoretical models and experimental systems. The experimentally observed structural disorder of the particle surface has to be included in the theoretical models.

  8. Exciton-plasmon and spin-plasmon interactions in hybrid semiconductor-metal nanostructures

    NASA Astrophysics Data System (ADS)

    Govorov, Alexander

    2011-03-01

    Coulomb and electromagnetic interactions between excitons and plasmons in nanocrystals cause several effects: energy transfer between nanoparticles, plasmon enhancement, Lamb shifts of exciton lines, Fano interference. In a complex composed of semiconductor quantum dot and metal nanoparticle, plasmons interact with spin-polarized excitons. This interaction leads to the formation of coupled spin-plasmon excitations and to spin-dependent Fano resonances. If an exciton-plasmon system includes chiral elements (chiral molecules or nanocrystals), the exciton-plasmon interaction is able to create new plasmonic lines in circular dichroism spectra.

  9. Silicon Nanocrystal Nonvolatile Memories

    NASA Astrophysics Data System (ADS)

    Muralidhar, R.; Sadd, M. A.; White, B. E.

    In 1959, physicist Richard Feynman delivered his "There's Plenty of Room Left at the Bottom" lecture [1] to the American Physical Society that spawned the field of nanotechnology. In that lecture, Feynman discussed two themes that are critical to the work presented here. The first was the recognition of the tremendous opportunities associated with the ability to miniaturize computers. At the time of his lecture, the most powerful computers consumed entire rooms, and Feynman realized the tremendous gains that could be realized in performance if the technology could be reduced to the size of one's thumbnail. The second important area Feynman touched on was the unique opportunities that surround the manipulation of matter at the atomic level to create materials with unique and, hopefully, useful properties. Both of these ideas have now been realized as evidenced by the exponential growth of the semiconductor industry over the last 40 years and the tremendous explosion in nanotechnology research, development, and product introduction over the last decade

  10. Exciton Relaxation Dynamics and Ultra-Efficient Exciton Multiplication in Nanocrystals: A New Model and Relevance to Solar Photon Conversion

    NASA Astrophysics Data System (ADS)

    Nozik, Arthur

    2005-03-01

    In bulk semiconductors photoinitiated electron-hole pair multiplication can occur via impact ionization (I.I.). However, this process requires photon energies of 4-5 times the bandgap because of the need to conserve crystal momentum and the competing rate of phonon emission. This limits the application of I.I. to increase the solar conversion efficiency in photovoltaic devices. For nanocrystal QDs, these constraints are relaxed, and exciton multiplication is thus expected to be greatly enhanced (1). Greatly enhanced exciton multiplication in PbSe nanocrystals was first confirmed by Schaller and Klimov (2). We report ultra-efficient multiple exciton generation (MEG) in PbSe and PbS nanocrystals, and explain our results by a new theoretical model based on the coherent superposition of excitonic states whereby multiple excitons are created instantaneously upon photon absorption (3); such a coherent process has never been reported before in semiconductors. Astonishingly high quantum yields of 300 %, indicating creation of three excitons/photon for every nanocrystal, have been observed in PbSe at photon energies four times the energy gap. The new model predicts the occurrence of quantum beats between the coupled coherent states, and we observe such quantum beats in PbSe and PbS nanocrystals. Another prediction of the new model, supported by our data, is that the threshold photon energy for MEG in PbSe nanocrystals is twice its energy gap. These results have important implications for greatly improved optoelectronic devices. Refs: (1) A.J. Nozik, Physica E14, 115 (2002); (2) R. Schaller and V. Klimov, Phys. Rev. Letts. 92, 186601(2004); (3) R.J. Ellingson, M.C. Beard, P.Yu, O.I. Micic, A.J. Nozik, A. Shabaev, Al. L. Efros, submitted to Science (2004)

  11. Polar optical phonons in semiconducting CdS nanocrystals

    SciTech Connect

    Belogorokhov, A. I. Belogorokhov, I. A.; Miranda, R. P.; Vasilevskii, M. I.; Gavrilov, S. A.

    2007-02-15

    We have experimentally and theoretically studied IR-active optical phonons, which are spatially confined in the volume of semiconducting CdS nanocrystals of various shapes synthesized in a dielectric matrix (porous aluminum oxide). Within an approach admitting the mixing of all expected types of vibrations, the complete sets of phonon modes are determined for a spherical quantum dot (QD) and a cylindrical quantum wire (QW) in this matrix. Based on these results, the polarizability spectra of QDs and QWs, as well as the effective dielectric function of a composite material containing such nanoparticles, are calculated for the far-IR wavelength range. It is established that the spectrum of the dielectric function exhibits specific features in the region between the transverse and longitudinal optical phonon frequencies of the massive semiconductor material. These features explain the rather unusual structure of the IR spectra of the composite samples studied.

  12. Superior Optical Properties of Perovskite Nanocrystals as Single Photon Emitters.

    PubMed

    Hu, Fengrui; Zhang, Huichao; Sun, Chun; Yin, Chunyang; Lv, Bihu; Zhang, Chunfeng; Yu, William W; Wang, Xiaoyong; Zhang, Yu; Xiao, Min

    2015-12-22

    The power conversion efficiency of photovoltaic devices based on semiconductor perovskites has reached ∼20% after just several years of research efforts. With concomitant discoveries of other promising applications in lasers, light-emitting diodes, and photodetectors, it is natural to anticipate what further excitement these exotic perovskites could bring about. Here we report on the observation of single photon emission from single CsPbBr3 perovskite nanocrystals (NCs) synthesized from a facile colloidal approach. Compared with traditional metal-chalcogenide NCs, these CsPbBr3 NCs exhibit nearly 2 orders of magnitude increase in their absorption cross sections at similar emission colors. Moreover, the radiative lifetime of CsPbBr3 NCs is greatly shortened at both room and cryogenic temperatures to favor an extremely fast output of single photons. The above superior optical properties have paved the way toward quantum-light applications of perovskite NCs in various quantum information processing schemes.

  13. High-performance thermoelectric nanocomposites from nanocrystal building blocks

    NASA Astrophysics Data System (ADS)

    Ibáñez, Maria; Luo, Zhishan; Genç, Aziz; Piveteau, Laura; Ortega, Silvia; Cadavid, Doris; Dobrozhan, Oleksandr; Liu, Yu; Nachtegaal, Maarten; Zebarjadi, Mona; Arbiol, Jordi; Kovalenko, Maksym V.; Cabot, Andreu

    2016-03-01

    The efficient conversion between thermal and electrical energy by means of durable, silent and scalable solid-state thermoelectric devices has been a long standing goal. While nanocrystalline materials have already led to substantially higher thermoelectric efficiencies, further improvements are expected to arise from precise chemical engineering of nanoscale building blocks and interfaces. Here we present a simple and versatile bottom-up strategy based on the assembly of colloidal nanocrystals to produce consolidated yet nanostructured thermoelectric materials. In the case study on the PbS-Ag system, Ag nanodomains not only contribute to block phonon propagation, but also provide electrons to the PbS host semiconductor and reduce the PbS intergrain energy barriers for charge transport. Thus, PbS-Ag nanocomposites exhibit reduced thermal conductivities and higher charge carrier concentrations and mobilities than PbS nanomaterial. Such improvements of the material transport properties provide thermoelectric figures of merit up to 1.7 at 850 K.

  14. Emerging applications of fluorescent nanocrystals quantum dots for micrometastases detection.

    PubMed

    Mahmoud, Wael; Sukhanova, Alyona; Oleinikov, Vladimir; Rakovich, Yury P; Donegan, John F; Pluot, Michel; Cohen, Jacques H M; Volkov, Yuri; Nabiev, Igor

    2010-02-01

    The occurrence of metastases is one of the main causes of death in many cancers and the main cause of death for breast cancer patients. Micrometastases of disseminated tumour cells and circulating tumour cells are present in more than 30% of breast cancer patients without any clinical or even histopathological signs of metastasis. Low abundance of these cell types in clinical diagnostic material dictates the necessity of their enrichment prior to reliable detection. Current micrometastases detection techniques are based on immunocytochemical and molecular methods suffering from low efficiency of tumour cells enrichment and observer-dependent interpretation. The use of highly fluorescent semiconductor nanocrystals, also known as "quantum dots" and nanocrystal-encoded microbeads tagged with a wide panel of antibodies against specific tumour markers offers unique possibilities for ultra-sensitive micrometastases detection in patients' serum and tissues. The nanoparticle-based diagnostics provides an opportunity for highly sensitive parallel quantification of specific proteins in a rapid and low-cost method, thereby providing a link between the primary tumour and the micrometastases for early diagnosis.

  15. CdSe nanocrystals ingrained dielectric nanocomposites: synthesis and photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Dey, Chirantan; Goswami, Madhumita; Karmakar, Basudeb

    2015-01-01

    Cadmium selenide (CdSe) nanocrystals ingrained dielectric nanocomposites in a B2O3-SiO2-Al2O3-Na2O-K2O borosilicate glass system were synthesized by a single step in situ melt quenching technique. The sizes of the nanocrystals as well as the band gap of the nanocomposites were controlled by both concentration of CdSe and post thermal treatment duration. The nanocomposites were characterized by different instrumental techniques including detailed photoluminescence studies. The sizes of the CdSe nanocrystals were found to alter in the range 4-16 nm as estimated from the effective mass approximation model and optical absorption spectroscopy. However, the TEM analysis revealed the generation of two different size ranges, 3-4 and 23-45 nm, of the particles within the dielectric matrix. Selected area diffraction (SAED) and x-ray diffraction (XRD) patterns authenticate the formation of hexagonal nanostructures of CdSe. These nanocomposites were found to be capable of exhibiting strong visible red luminescence around 715 nm on excitation at 446 nm. This has originated from the electron-hole recombination of CdSe nanocrystal and defects or traps related transitions. The properties of these nanocomposites advocate their significant applications as semiconductor based luminescent materials.

  16. Colloidal nanocrystals for quality lighting and displays: milestones and recent developments

    NASA Astrophysics Data System (ADS)

    Erdem, Talha; Demir, Hilmi Volkan

    2016-06-01

    Recent advances in colloidal synthesis of nanocrystals have enabled high-quality high-efficiency light-emitting diodes, displays with significantly broader color gamut, and optically-pumped lasers spanning the whole visible regime. Here we review these colloidal platforms covering the milestone studies together with recent developments. In the review, we focus on the devices made of colloidal quantum dots (nanocrystals), colloidal quantum rods (nanorods), and colloidal quantum wells (nanoplatelets) as well as those of solution processed perovskites and phosphor nanocrystals. The review starts with an introduction to colloidal nanocrystal photonics emphasizing the importance of colloidal materials for light-emitting devices. Subsequently,we continue with the summary of important reports on light-emitting diodes, in which colloids are used as the color converters and then as the emissive layers in electroluminescent devices. Also,we review the developments in color enrichment and electroluminescent displays. Next, we present a summary of important reports on the lasing of colloidal semiconductors. Finally, we summarize and conclude the review presenting a future outlook.

  17. Atomistic understanding of cation exchange in PbS nanocrystals using simulations with pseudoligands

    PubMed Central

    Fan, Zhaochuan; Lin, Li-Chiang; Buijs, Wim; Vlugt, Thijs J. H.; van Huis, Marijn A.

    2016-01-01

    Cation exchange is a powerful tool for the synthesis of nanostructures such as core–shell nanocrystals, however, the underlying mechanism is poorly understood. Interactions of cations with ligands and solvent molecules are systematically ignored in simulations. Here, we introduce the concept of pseudoligands to incorporate cation-ligand-solvent interactions in molecular dynamics. This leads to excellent agreement with experimental data on cation exchange of PbS nanocrystals, whereby Pb ions are partially replaced by Cd ions from solution. The temperature and the ligand-type control the exchange rate and equilibrium composition of cations in the nanocrystal. Our simulations reveal that Pb ions are kicked out by exchanged Cd interstitials and migrate through interstitial sites, aided by local relaxations at core–shell interfaces and point defects. We also predict that high-pressure conditions facilitate strongly enhanced cation exchange reactions at elevated temperatures. Our approach is easily extendable to other semiconductor compounds and to other families of nanocrystals. PMID:27160371

  18. Thermal activation of non-radiative Auger recombination in charged colloidal nanocrystals.

    PubMed

    Javaux, C; Mahler, B; Dubertret, B; Shabaev, A; Rodina, A V; Efros, Al L; Yakovlev, D R; Liu, F; Bayer, M; Camps, G; Biadala, L; Buil, S; Quelin, X; Hermier, J-P

    2013-03-01

    Applications of semiconductor nanocrystals such as biomarkers and light-emitting optoelectronic devices require that their fluorescence quantum yield be close to 100%. However, such quantum yields have not been obtained yet, in part, because non-radiative Auger recombination in charged nanocrystals could not be suppressed completely. Here, we synthesize colloidal core/thick-shell CdSe/CdS nanocrystals with 100% quantum yield and completely quenched Auger processes at low temperatures, although the nanocrystals are negatively photocharged. Single particle and ensemble spectroscopy in the temperature range 30-300 K shows that the non-radiative Auger recombination is thermally activated around 200 K. Experimental results are well described by a model suggesting a temperature-dependent delocalization of one of the trion electrons from the CdSe core and enhanced Auger recombination at the abrupt CdS outer surface. These results point to a route for the design of core/shell structures with 100% quantum yield at room temperature.

  19. Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites

    PubMed Central

    Yakunin, Sergii; Protesescu, Loredana; Krieg, Franziska; Bodnarchuk, Maryna I.; Nedelcu, Georgian; Humer, Markus; De Luca, Gabriele; Fiebig, Manfred; Heiss, Wolfgang; Kovalenko, Maksym V.

    2015-01-01

    Metal halide semiconductors with perovskite crystal structures have recently emerged as highly promising optoelectronic materials. Despite the recent surge of reports on microcrystalline, thin-film and bulk single-crystalline metal halides, very little is known about the photophysics of metal halides in the form of uniform, size-tunable nanocrystals. Here we report low-threshold amplified spontaneous emission and lasing from ∼10 nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 (X=Cl, Br or I, or mixed Cl/Br and Br/I systems). We find that room-temperature optical amplification can be obtained in the entire visible spectral range (440–700 nm) with low pump thresholds down to 5±1 μJ cm−2 and high values of modal net gain of at least 450±30 cm−1. Two kinds of lasing modes are successfully observed: whispering-gallery-mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 nanocrystals and random lasing in films of CsPbX3 nanocrystals. PMID:26290056

  20. Generalized syntheses of nanocrystal-graphene hybrids in high-boiling-point organic solvents.

    PubMed

    Pang, Danny Wei-Ping; Yuan, Fang-Wei; Chang, Yan-Cheng; Li, Guo-An; Tuan, Hsing-Yu

    2012-08-07

    Nanocrystal-graphene have been proposed as a new kind of promising hybrid for a wide range of application areas including catalysts, electronics, sensors, biomedicine, and energy storage, etc. Although a variety of methods have been developed for the preparation of hybrids, a facile and general synthetic approach is still highly required. In this study, nanocrystal-graphene hybrids were successfully synthesized in high-boiling-point organic solvents. Graphene oxide (GO) nanosheets were modified by oleylamine (OLA) to form a OLA-GO complex in order to be readily incorporated into hydrophobic synthesis. A rich library of highly crystalline nanocrystals, with types including noble metal, metal oxide, magnetic material and semiconductor were successfully grown on chemically converted graphene (CCG), which is simultaneously reduced from GO during the synthesis. High boiling-point solvents afford sufficient thermal energy to assure the high-quality crystalline nature of NCs, therefore the post-annealing process is obviated. Controlled experiments revealed that OLA-GO triggers heterogeneous nucleation and serves as excellent nuclei anchorage media. The protocol developed here brings one step closer to achieve "unity in diversity" on the preparation of nanocrystal-graphene hybrids.

  1. Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites

    NASA Astrophysics Data System (ADS)

    Yakunin, Sergii; Protesescu, Loredana; Krieg, Franziska; Bodnarchuk, Maryna I.; Nedelcu, Georgian; Humer, Markus; de Luca, Gabriele; Fiebig, Manfred; Heiss, Wolfgang; Kovalenko, Maksym V.

    2015-08-01

    Metal halide semiconductors with perovskite crystal structures have recently emerged as highly promising optoelectronic materials. Despite the recent surge of reports on microcrystalline, thin-film and bulk single-crystalline metal halides, very little is known about the photophysics of metal halides in the form of uniform, size-tunable nanocrystals. Here we report low-threshold amplified spontaneous emission and lasing from ~10 nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 (X=Cl, Br or I, or mixed Cl/Br and Br/I systems). We find that room-temperature optical amplification can be obtained in the entire visible spectral range (440-700 nm) with low pump thresholds down to 5+/-1 μJ cm-2 and high values of modal net gain of at least 450+/-30 cm-1. Two kinds of lasing modes are successfully observed: whispering-gallery-mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 nanocrystals and random lasing in films of CsPbX3 nanocrystals.

  2. Concentration dependent carriers dynamics in CsPbBr3 perovskite nanocrystals film with transient grating

    NASA Astrophysics Data System (ADS)

    Wang, Yinghui; Wang, Yanting; Dev Verma, Sachin; Tan, Mingrui; Liu, Qinghui; Yuan, Qilin; Sui, Ning; Kang, Zhihui; Zhou, Qiang; Zhang, Han-Zhuang

    2017-05-01

    The concentration dependence of the carrier dynamics is a key parameter to describe the photo-physical properties of semiconductor films. Here, we investigate the carrier dynamics in the CsPbBr3 perovskite nanocrystal film by employing the transient grating (TG) technique with continuous bias light. The concentration of initial carriers is determined by the average number of photons per nanocrystals induced by pump light (⟨N⟩). The multi-body interaction would appear and accelerate the TG dynamics with ⟨N⟩. When ⟨N⟩ is more than 3.0, the TG dynamics slightly changes, which implies that the Auger recombination would be the highest order multi-body interaction in carrier recombination dynamics. The concentration of non-equilibrium carriers in the film is controlled by the average number of photons per nanocrystals excited by continuous bias light (⟨nne⟩). Increasing ⟨nne⟩ would improve the trapping-detrapping process by filling the trapping state, which would accelerate the carrier diffusion and add the complexity of the mono-molecular recombination mechanism. The results should be useful to further understand the mechanism of carrier dynamics in the CsPbBr3 perovskite nanocrystal film and of great importance for the operation of the corresponding optoelectronic devices.

  3. Direct Measurements of Magnetic Polarons in Cd1–xMnx Se Nanocrystals from Resonant Photoluminescence

    DOE PAGES

    Rice, W. D.; Liu, W.; Pinchetti, V.; ...

    2017-04-07

    In semiconductors, quantum confinement can greatly enhance the interaction between band carriers (electrons and holes) and dopant atoms. One manifestation of this enhancement is the increased stability of exciton magnetic polarons in magnetically doped nanostructures. In the limit of very strong 0D confinement that is realized in colloidal semiconductor nanocrystals, a single exciton can exert an effective exchange field Bex on the embedded magnetic dopants that exceeds several tesla. Here we use the very sensitive method of resonant photoluminescence (PL) to directly measure the presence and properties of exciton magnetic polarons in colloidal Cd1–xMnxSe nanocrystals. Despite small Mn2+ concentrations (xmore » = 0.4–1.6%), large polaron binding energies up to ~26 meV are observed at low temperatures via the substantial Stokes shift between the pump laser and the resonant PL maximum, indicating nearly complete alignment of all Mn2+ spins by Bexex ≈ 10 T in these nanocrystals, in good agreement with theoretical estimates. Further, the emission line widths provide direct insight into the statistical fluctuations of the Mn2+ spins. In conclusion, these resonant PL studies provide detailed insight into collective magnetic phenomena, especially in lightly doped nanocrystals where conventional techniques such as nonresonant PL or time-resolved PL provide ambiguous results.« less

  4. Quantitative tunneling spectroscopy of nanocrystals

    SciTech Connect

    First, Phillip N; Whetten, Robert L; Schaaff, T Gregory

    2007-05-25

    The proposed goals of this collaborative work were to systematically characterize the electronic structure and dynamics of 3-dimensional metal and semiconducting nanocrystals using scanning tunneling microscopy/spectroscopy (STM/STS) and ballistic electron emission spectroscopy (BEES). This report describes progress in the spectroscopic work and in the development of methods for creating and characterizing gold nanocrystals. During the grant period, substantial effort also was devoted to the development of epitaxial graphene (EG), a very promising materials system with outstanding potential for nanometer-scale ballistic and coherent devices ("graphene" refers to one atomic layer of graphitic, sp2 -bonded carbon atoms [or more loosely, few layers]). Funding from this DOE grant was critical for the initial development of epitaxial graphene for nanoelectronics

  5. Subtle Chemistry of Colloidal, Quantum-Confined Semiconductor Nanostructures

    SciTech Connect

    Hughes, B. K.; Luther, J. M.; Beard, M. C.

    2012-06-26

    Nanoscale colloidal semiconductor structures with at least one dimension small enough to experience quantum confinement effects have captured the imagination and attention of scientists interested in controlling various chemical and photophysical processes. Aside from having desirable quantum confinement properties, colloidal nanocrystals are attractive because they are often synthesized in low-temperature, low-cost, and potentially scalable manners using simple benchtop reaction baths. Considerable progress in producing a variety of shapes, compositions, and complex structures has been achieved. However, there are challenges to overcome in order for these novel materials to reach their full potential and become new drivers for commercial applications. The final shape, composition, nanocrystal-ligand structure, and size can depend on a delicate interplay of precursors, surface ligands, and other compounds that may or may not participate in the reaction. In this Perspective, we discuss current efforts toward better understanding how the reactivity of the reagents can be used to produce unique and complex nanostructures.

  6. Photoelectrosynthesis at semiconductor electrodes

    SciTech Connect

    Nozik, A. J.

    1980-12-01

    The general principles of photoelectrochemistry and photoelectrosynthesis are reviewed and some new developments in photoelectrosynthesis are discussed. Topics include energetics of semiconductor-electrolyte interfaces(band-edge unpinning); hot carrier injection at illuminated semiconductor-electrolyte junctions; derivatized semiconductor electrodes; particulate photoelectrochemical systems; layered compounds and other new materials; and dye sensitization. (WHK)

  7. Semiconductor ohmic contact

    NASA Technical Reports Server (NTRS)

    Hawrylo, F. Z.; Kressel, H.

    1977-01-01

    Contact formed on p-type surface of semiconductor laser has several advantages: highly conductive degenerate region and narrow band gap provides surface for good metal-to-semiconductor contact; lattice parameter of GaAs is 5.6533 A; improved lattice match eases interface strain which reduces interface cracking of semiconductor material.

  8. Synthesis of optimized indium phosphide/zinc sulfide core/shell nanocrystals and titanium dioxide nanotubes for quantum dot sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Lee, Seungyong

    Synthesis of InP/ZnS core/shell nanocrystals and TiO 2 nanotubes and the optimization study to couple them together were explored for quantum dot sensitized solar cells. Its intrinsic nontoxicity makes the direct band gap InP/ZnS core/shell be one of the most promising semiconductor nanocrystals for optoelectric applications, with the advantage of tuning the optical absorption range in the desired solar spectrum region. Highly luminescent and monodisperse InP/ZnS nanocrystals were synthesized in a non-coordinating solvent. By varying the synthesis scheme, different size InP/ZnS nanocrystals with emission peaks ranging from 520 nm to 620 nm were grown. For the purpose of ensuring air stability, a ZnS shell was grown. The ZnS shell improves the chemical stability in terms of oxidation prevention. Transmission electron microscopy (TEM) image shows that the nanocrystals are highly crystalline and monodisperse. Free-standing TiO2 nanotubes were produced by an anodization method using ammonium fluoride. The free-standing nanotubes were formed under the condition that the chemical dissolution speed associated with fluoride concentration was faster than the speed of Ti oxidation. Highly ordered free-standing anatase form TiO2 nanotubes, which are transformed by annealing at the optimized temperature, are expected to be ideal for coupling with the prepared InP/ZnS nanocrystals. Electrophoretic deposition was carried out to couple the InP/ZnS nanocrystals with the TiO2 nanotubes. Under the adjusted applied voltage condition, the current during the electrophoretic deposition decreased continuously with time. The amount of the deposited nanocrystals was estimated by calculation and the evenly deposited nanocrystals on the TiO2 nanotubes were observed by TEM.

  9. Formation of In x Ga1-x As nanocrystals in thin Si layers by ion implantation and flash lamp annealing

    NASA Astrophysics Data System (ADS)

    Wutzler, Rene; Rebohle, Lars; Prucnal, Slawomir; Grenzer, Jörg; Hübner, René; Böttger, Roman; Skorupa, Wolfgang; Helm, Manfred

    2017-06-01

    The integration of high-mobility III-V compound semiconductors emerges as a promising route for Si device technologies to overcome the limits of further down-scaling. In this paper, a non-conventional approach of the combination of ion beam implantation with short-time flash lamp annealing is employed to fabricate In x Ga1-x As nanocrystals and to study their crystallization process in thin Si layers. The implantation fluence ratio of Ga and In ions has been varied to tailor the final nanocrystal composition. Raman spectroscopy and x-ray diffraction analyses verify the formation of ternary III-V nanocrystals within the Si layer. Transmission electron microscopy reveals single-crystalline precipitates with a low number of defects. A liquid epitaxy mechanism is used to describe the formation process of III-V nanocrystals after melting of the implanted thin Si layer by flash lamp annealing. The fabricated In x Ga1-x As nanocrystals are mainly Ga-rich with respect to the implanted Ga/In ratio.

  10. Formation of Copper Zinc Tin Sulfide Thin Films from Colloidal Nanocrystal Dispersions via Aerosol-Jet Printing and Compaction.

    PubMed

    Williams, Bryce A; Mahajan, Ankit; Smeaton, Michelle A; Holgate, Collin S; Aydil, Eray S; Francis, Lorraine F

    2015-06-03

    A three-step method to create dense polycrystalline semiconductor thin films from nanocrystal liquid dispersions is described. First, suitable substrates are coated with nanocrystals using aerosol-jet printing. Second, the porous nanocrystal coatings are compacted using a weighted roller or a hydraulic press to increase the coating density. Finally, the resulting coating is annealed for grain growth. The approach is demonstrated for making polycrystalline films of copper zinc tin sulfide (CZTS), a new solar absorber composed of earth-abundant elements. The range of coating morphologies accessible through aerosol-jet printing is examined and their formation mechanisms are revealed. Crack-free albeit porous films are obtained if most of the solvent in the aerosolized dispersion droplets containing the nanocrystals evaporates before they impinge on the substrate. In this case, nanocrystals agglomerate in flight and arrive at the substrate as solid spherical agglomerates. These porous coatings are mechanically compacted, and the density of the coating increases with compaction pressure. Dense coatings annealed in sulfur produce large-grain (>1 μm) polycrystalline CZTS films with microstructure suitable for thin-film solar cells.

  11. Biosensing with Luminescent Semiconductor Quantum Dots

    PubMed Central

    Sapsford, Kim E.; Pons, Thomas; Medintz, Igor L.; Mattoussi, Hedi

    2006-01-01

    Luminescent semiconductor nanocrystals or quantum dots (QDs) are a recently developed class of nanomaterial whose unique photophysical properties are helping to create a new generation of robust fluorescent biosensors. QD properties of interest for biosensing include high quantum yields, broad absorption spectra coupled to narrow size-tunable photoluminescent emissions and exceptional resistance to both photobleaching and chemical degradation. In this review, we examine the progress in adapting QDs for several predominantly in vitro biosensing applications including use in immunoassays, as generalized probes, in nucleic acid detection and fluorescence resonance energy transfer (FRET) - based sensing. We also describe several important considerations when working with QDs mainly centered on the choice of material(s) and appropriate strategies for attaching biomolecules to the QDs.

  12. Bright-Exciton Fine-Structure Splittings in Single Perovskite Nanocrystals

    NASA Astrophysics Data System (ADS)

    Yin, Chunyang; Chen, Liyang; Song, Nan; Lv, Yan; Hu, Fengrui; Sun, Chun; Yu, William W.; Zhang, Chunfeng; Wang, Xiaoyong; Zhang, Yu; Xiao, Min

    2017-07-01

    Here we show that, in single perovskite CsPbI3 nanocrystals synthesized from a colloidal approach, a bright-exciton fine-structure splitting as large as hundreds of μ eV can be resolved with two orthogonally and linearly polarized photoluminescence peaks. This doublet could switch to a single peak when a single CsPbI3 nanocrystal is photocharged to eliminate the electron-hole exchange interaction. The above findings have prepared an efficient platform suitable for probing exciton and spin dynamics of semiconductor nanostructures at the visible-wavelength range, from which a variety of practical applications such as in entangled photon-pair source and quantum information processing can be envisioned.

  13. Enhancing the Photoluminescence of Peptide-Coated Nanocrystals with Shell Composition and UV Irradiation

    PubMed Central

    Tsay, James M.; Doose, Sören; Pinaud, Fabien; Weiss, Shimon

    2005-01-01

    The composition and structure of inorganic shells grown over CdSe semiconductor nanocrystal dots and rods were optimized to yield enhanced photoluminescence properties after ligand exchange followed by coating with phytochelatin-related peptides. We show that, in addition to the peptides imparting superior colloidal properties and providing biofunctionality in a single-step reaction, the improved shells and pretreatment with UV irradiation resulted in high quantum yields for the nanocrystals in water. Moreover, peptide coating caused a noticeable red-shift in the absorption and emission spectra for one of the tested shells, suggesting that exciton–molecular orbital (X–MO) coupling might take place in these hybrid inorganic–organic composite materials. PMID:16429593

  14. Unitary lens semiconductor device

    DOEpatents

    Lear, K.L.

    1997-05-27

    A unitary lens semiconductor device and method are disclosed. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors. 9 figs.

  15. Unitary lens semiconductor device

    DOEpatents

    Lear, Kevin L.

    1997-01-01

    A unitary lens semiconductor device and method. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors.

  16. Hollow nanocrystals and method of making

    DOEpatents

    Alivisatos, A Paul [Oakland, CA; Yin, Yadong [Moreno Valley, CA; Erdonmez, Can Kerem [Berkeley, CA

    2011-07-05

    Described herein are hollow nanocrystals having various shapes that can be produced by a simple chemical process. The hollow nanocrystals described herein may have a shell as thin as 0.5 nm and outside diameters that can be controlled by the process of making.

  17. Pinned emission from ultrasmall cadmium selenide nanocrystals.

    PubMed

    Dukes, Albert D; Schreuder, Michael A; Sammons, Jessica A; McBride, James R; Smith, Nathanael J; Rosenthal, Sandra J

    2008-09-28

    We report pinning of the emission spectrum in ultrasmall CdSe nanocrystals with a diameter of 1.7 nm and smaller. It was observed that the first emission feature ceased to blueshift once the band edge absorption reached 420 nm, though the band edge absorption continued to blueshift with decreasing nanocrystal diameter.

  18. Structure Map for Embedded Binary Alloy Nanocrystals

    SciTech Connect

    Yuan, C.W.; Shin, S.J.; Liao, C.Y.; Guzman, J.; Stone, P.R.; Watanabe, M.; Ager III, J.W.; Haller, E.E.; Chrzan, D.C.

    2008-09-20

    The equilibrium structure of embedded nanocrystals formed from strongly segregating binary-alloys is considered within a simple thermodynamic model. The model identifies two dimensionlessinterface energies that dictate the structure, and allows prediction of the stable structure for anychoice of these parameters. The resulting structure map includes three distinct nanocrystal mor-phologies: core/shell, lobe/lobe, and completely separated spheres.

  19. Synthesis and characterization of embedded germanium nanocrystals

    NASA Astrophysics Data System (ADS)

    Xu, Qing

    Isotopically pure Ge nanocrystals have been synthesized by ion implantation followed by thermal annealing in amorphous silica and crystalline sapphire matrix. The structure, and the mechanical and thermal properties of the two systems are studied and compared. Ge cluster nucleation during implantation is observed in as-implanted silica samples. It results in the wide size distribution observed after thermal annealing. Theoretical calculations predict that if the nucleation during implantation can be suppressed, a much narrower size distribution is achievable. As-grown Ge nanocrystals are under large compressive stress, 1.2GPa for nanocrystals embedded in silica, and 4GPa for those embedded in sapphire. The stress can be gradually relieved by vapor etching, liberating the nanocrystals from the matrix as well as post-growth thermal treatments. One of the main sources of the stress observed in the sapphire system is the volume expansion of Ge clusters in the liquid/solid phase transformation which occurs during the cooling process from annealing temperature to room temperature, as the density of liquid Ge is larger by 4.6% than that of solid Ge. The large stress and damage in the sapphire matrix lead to a unique double-peak size distribution of the Ge nanocrystals. However, the in situ transmission electron microscopy (TEM) experiments indicate that the Ge nanocrystals embedded in silica are already in their solid phase at the annealing temperature. Therefore, the stress originates from other sources. Vapor etching with HF solutions enables a gradual exposure of embedded Ge nanocrystals in SiO2, while the liquid etching in HF solution leaves fully liberated Ge nanocrystals loosely packed on the Si substrate. Transfer of liberated Ge nanocrystals to other surfaces is achieved by solution dispersion and subsequent evaporation. The patterning of nanocrystals has been achieved by a combination of lithography, coimplantation and electron irradiation. The latter one will

  20. Nanocrystal technology, drug delivery and clinical applications

    PubMed Central

    Junghanns, Jens-Uwe A H; Müller, Rainer H

    2008-01-01

    Nanotechnology will affect our lives tremendously over the next decade in very different fields, including medicine and pharmacy. Transfer of materials into the nanodimension changes their physical properties which were used in pharmaceutics to develop a new innovative formulation principle for poorly soluble drugs: the drug nanocrystals. The drug nanocrystals do not belong to the future; the first products are already on the market. The industrially relevant production technologies, pearl milling and high pressure homogenization, are reviewed. The physics behind the drug nanocrystals and changes of their physical properties are discussed. The marketed products are presented and the special physical effects of nanocrystals explained which are utilized in each market product. Examples of products in the development pipelines (clinical phases) are presented and the benefits for in vivo administration of drug nanocrystals are summarized in an overview. PMID:18990939