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Sample records for circular quantum dots

  1. The transfer matrix approach to circular graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Chau Nguyen, H.; Nguyen, Nhung T. T.; Nguyen, V. Lien

    2016-07-01

    We adapt the transfer matrix (T-matrix) method originally designed for one-dimensional quantum mechanical problems to solve the circularly symmetric two-dimensional problem of graphene quantum dots. Similar to one-dimensional problems, we show that the generalized T-matrix contains rich information about the physical properties of these quantum dots. In particular, it is shown that the spectral equations for bound states as well as quasi-bound states of a circular graphene quantum dot and related quantities such as the local density of states and the scattering coefficients are all expressed exactly in terms of the T-matrix for the radial confinement potential. As an example, we use the developed formalism to analyse physical aspects of a graphene quantum dot induced by a trapezoidal radial potential. Among the obtained results, it is in particular suggested that the thermal fluctuations and electrostatic disorders may appear as an obstacle to controlling the valley polarization of Dirac electrons.

  2. On the density of states of circular graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Chau Nguyen, H.; Nguyen, Nhung T. T.; Nguyen, V. Lien

    2017-10-01

    We suggest a simple approach to calculate the local density of states that effectively applies to any structure created by an axially symmetric potential on a continuous graphene sheet such as circular graphene quantum dots or rings. Calculations performed for the graphene quantum dot studied in a recent scanning tunneling microscopy measurement (Gutierrez et al 2016 Nat. Phys. 12 1069–75) show an excellent experimental-theoretical agreement.

  3. Negative circular polarization as a universal property of quantum dots

    SciTech Connect

    Taylor, Matthew W.; Spencer, Peter; Murray, Ray

    2015-03-23

    This paper shows that negative circular polarization, a spin flip of polarized carriers resulting in emission of opposite helicity, can be observed in undoped, n-doped, and p-doped InAs/GaAs quantum dots. These results contradict the usual interpretation of the effect. We show using power dependent and time resolved spectroscopy that the generation of negative circular polarization correlates with excited state emission. Furthermore, a longer spin lifetime of negatively polarized excitons is observed where emission is largely ground state in character.

  4. Excitation spectra of circular, few-electron quantum dots

    PubMed

    Kouwenhoven; Oosterkamp; Danoesastro; Eto; Austing; Honda; Tarucha

    1997-12-05

    Studies of the ground and excited states in semiconductor quantum dots containing 1 to 12 electrons showed that the quantum numbers of the states in the excitation spectra can be identified and compared with exact calculations. A magnetic field induces transitions between the ground and excited states. These transitions were analyzed in terms of crossings between single-particle states, singlet-triplet transitions, spin polarization, and Hund's rule. These impurity-free quantum dots allow "atomic physics" experiments to be performed in magnetic field regimes not accessible for atoms.

  5. One-qubit quantum gates in a circular graphene quantum dot: genetic algorithm approach.

    PubMed

    Amparán, Gibrán; Rojas, Fernando; Pérez-Garrido, Antonio

    2013-05-16

    The aim of this work was to design and control, using genetic algorithm (GA) for parameter optimization, one-charge-qubit quantum logic gates σx, σy, and σz, using two bound states as a qubit space, of circular graphene quantum dots in a homogeneous magnetic field. The method employed for the proposed gate implementation is through the quantum dynamic control of the qubit subspace with an oscillating electric field and an onsite (inside the quantum dot) gate voltage pulse with amplitude and time width modulation which introduce relative phases and transitions between states. Our results show that we can obtain values of fitness or gate fidelity close to 1, avoiding the leakage probability to higher states. The system evolution, for the gate operation, is presented with the dynamics of the probability density, as well as a visualization of the current of the pseudospin, characteristic of a graphene structure. Therefore, we conclude that is possible to use the states of the graphene quantum dot (selecting the dot size and magnetic field) to design and control the qubit subspace, with these two time-dependent interactions, to obtain the optimal parameters for a good gate fidelity using GA.

  6. Accuracy of circular polarization as a measure of spin polarization in quantum dot qubits.

    PubMed

    Pryor, C E; Flatté, M E

    2003-12-19

    A quantum dot spin light emitting diode provides a test of carrier spin injection into a qubit and a means for analyzing carrier spin injection and local spin polarization. Even with 100% spin-polarized carriers the emitted light may be only partially circularly polarized due to the geometry of the dot. We have calculated carrier polarization-dependent optical matrix elements for InAs/GaAs self-assembled quantum dots (SAQDs) for electron and hole spin injection into a range of quantum dot sizes and shapes, and for arbitrary emission directions. Calculations for typical SAQD geometries with emission along [110] show light that is only 5% circularly polarized for spin states that are 100% polarized along [110]. Measuring along the growth direction gives near unity conversion of spin to photon polarization and is the least sensitive to uncertainties in SAQD geometry.

  7. Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum Dots

    PubMed Central

    Tohgha, Urice; Deol, Kirandeep K.; Porter, Ashlin G.; Bartko, Samuel G.; Choi, Jung Kyu; Leonard, Brian M.; Varga, Krisztina; Kubelka, Jan; Muller, Gilles; Balaz, Milan

    2014-01-01

    Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by post-synthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Density functional theory (DFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The chirality was induced by the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand. PMID:24200288

  8. Concentric circular ring and nanodisk optical antenna enhanced multispectral quantum dot infrared photodetector with spectral localization

    NASA Astrophysics Data System (ADS)

    Zhang, Yingjie; Kemsri, Thitikorn; Li, Lin; Gu, Guiru; Lu, Xuejun

    2017-10-01

    In this paper, we report a concentric circular ring and nanodisk plasmonic optical antenna (POA) enhanced multispectral quantum dot infrared photodetector (QDIP). The circular ring and the nanodisk POA structures are designed to have plasmonic resonant wavelengths in the longwave infrared (LWIR) and the midwave infrared (MWIR) spectral regimes, respectively. The electric field (E-field) distributions are simulated and show spectral localization due to the distinct plasmonic resonant wavelengths of the POA structures. The circular ring is found to enhance the E-fields in the nanodisk regions due to the mutual coupling. A concentric circular ring and nanodisk POA enhanced multispectral QDIP was fabricated and tested. Multispectral enhancement was observed. The enhancement is compared to that of a QDIP with only the circular ring POA structure. The experiment data agree with the simulation. The concentric circular ring and nanodisk POA provides a compact planar structure for multispectral QDIP enhancement.

  9. Optically and electrically controlled circularly polarized emission from cholesteric liquid crystal materials doped with semiconductor quantum dots.

    PubMed

    Bobrovsky, Alexey; Mochalov, Konstantin; Oleinikov, Vladimir; Sukhanova, Alyona; Prudnikau, Anatol; Artemyev, Mikhail; Shibaev, Valery; Nabiev, Igor

    2012-12-04

    Novel types of electro- and photoactive quantum dot-doped cholesteric materials have been engineered. UV-irradiation or electric field application allows one to control the degree of circular polarization and intensity of fluorescence emission by prepared quantum dot-doped liquid crystal films. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Circular-polarization-sensitive metamaterial based on triple-quantum-dot molecules.

    PubMed

    Kotetes, Panagiotis; Jin, Pei-Qing; Marthaler, Michael; Schön, Gerd

    2014-12-05

    We propose a new type of chiral metamaterial based on an ensemble of artificial molecules formed by three identical quantum dots in a triangular arrangement. A static magnetic field oriented perpendicular to the plane breaks mirror symmetry, rendering the molecules sensitive to the circular polarization of light. By varying the orientation and magnitude of the magnetic field one can control the polarization and frequency of the emission spectrum. We identify a threshold frequency Ω, above which we find strong birefringence. In addition, Kerr rotation and circular-polarized lasing action can be implemented. We investigate the single-molecule lasing properties for different energy-level arrangements and demonstrate the possibility of circular-polarization conversion. Finally, we analyze the effect of weak stray electric fields or deviations from the equilateral triangular geometry.

  11. Giant Two-photon Absorption in Circular Graphene Quantum Dots in Infrared Region

    PubMed Central

    Feng, Xiaobo; Li, Zhisong; Li, Xin; Liu, Yingkai

    2016-01-01

    We investigate theoretically the two-photon absorption (TPA) for circular graphene quantum dots (GQDs) with the edge of armchair and zigzag on the basis of electronic energy states obtained by solving the Dirac-Weyl equation numerically under finite difference method. The expressions for TPA cross section are derived and the transition selection rules are obtained. Results reveal that the TPA is significantly greater in GQDs than conventional semiconductor QDs in infrared spectrum (2–6 um) with a resonant TPA cross section of up to 1011 GM. The TPA peaks are tuned by the GQDs’ size, edge and electron relaxation rate. PMID:27629800

  12. Beaming circularly polarized photons from quantum dots coupled with plasmonic spiral antenna.

    PubMed

    Rui, Guanghao; Chen, Weibin; Abeysinghe, Don C; Nelson, Robert L; Zhan, Qiwen

    2012-08-13

    Coupling nanoscale emitters via optical antennas enables comprehensive control of photon emission in terms of intensity, directivity and polarization. In this work we report highly directional emission of circularly polarized photons from quantum dots coupled to a spiral optical antenna. The structural chirality of the spiral antenna imprints spin state to the emitted photons. Experimental results reveal that a circular polarization extinction ratio of 10 is obtainable. Furthermore, increasing the number of turns of the spiral gives rise to higher antenna gain and directivity, leading to higher field intensity and narrower angular width of emission pattern in the far field. For a five-turn Archimedes' spiral antenna, field intensity increase up to 70-fold simultaneously with antenna directivity of 11.7 dB has been measured in the experiment. The highly directional circularly polarized photon emission from such optically coupled spiral antenna may find important applications in single molecule sensing, quantum optics information processing and integrated photonic circuits as a nanoscale spin photon source.

  13. Negative circular polarization dynamics in InP/InGaP quantum dots

    NASA Astrophysics Data System (ADS)

    Nekrasov, S. V.; Kusrayev, Yu G.; Akimov, I. A.; Korenev, V. L.; Langer, L.; Salewski, M.

    2016-08-01

    Photoluminescence (PL) negative circular polarization (NCP) dynamics of InP/InGaP quantum dots (QDs) was studied. Time resolved measurements of PL demonstrated that NCP vanishes, when transverse magnetic field is applied, while oscillations of polarization (that are typical for both low-dimensional and bulk materials) do not occur. Hole g-factor spread in the QD ensemble was supposed to be the most probable reason for such NCP magnetic field behavior. The dependence of NCP dynamics on the repetition period of excitation laser pulses was investigated. In case of fairly small repetition period (T = 13.3 ns) long living NCP (13.3 ns < t < 133 ns) was detected, what was ascribed to resident electron spin orientation, accumulated during many laser pulses. In that regime more than one luminescence polarization decay time exist.

  14. Quantum dot based immunosensor using 3D circular microchannels fabricated in PDMS.

    PubMed

    Morarka, Amit; Agrawal, Shailaja; Kale, Sonia; Kale, Anup; Ogale, Satish; Paknikar, Kishore; Bodas, Dhananjay

    2011-02-15

    Microchannel is basic functional component of microfluidic chip and every step-forward of its construction technique has been receiving concern all over the world. The present work describes a novel, rapid and simple fabrication technique for building 3D microchannels in poly(dimethyl siloxane) (PDMS) elastomer. These microchannels were used for rapid detection of antigens (E. coli) by quantum dot (QD) based approach. Luminescent QD (CdTe) were synthesized by aqueous method and characterized using high resolution transmission electron microscopy (HRTEM), fluorescence spectroscopy and X-ray diffraction (XRD). The QDs were functionalized with anti-E. coli antibodies for immuno-detection. The reported process allowed easier and faster method of fabrication of circular 3D micochannels and demonstrated their potential use in an immuno-biosensor device. Copyright © 2010 Elsevier B.V. All rights reserved.

  15. Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tartakovskii, Alexander

    2012-07-01

    Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by

  16. Self-Assembled Luminescent Quantum Dots To Generate Full-Color and White Circularly Polarized Light.

    PubMed

    Huo, Shengwei; Duan, Pengfei; Jiao, Tifeng; Peng, Qiuming; Liu, Minghua

    2017-09-25

    The design and fabrication of quantum dots (QDs) with circularly polarized luminescence (CPL) has been a great challenge in developing chiroptical materials. We herein propose an alternative to the use of chiral capping reagents on QDs for the fabrication of CPL-active QDs that is based on the supramolecular self-assembly of achiral QDs with chiral gelators. Full-color-tunable CPL-active QDs were obtained by simple mixing or gelation of a chiral gelator and achiral 3-mercaptopropionic acid capped QDs. In addition, the handedness of the CPL can be controlled by the supramolecular chirality of the gels. Moreover, QDs with circularly polarized white light emission were fabricated for the first time by tuning the blending ratio of colorful QDs in the gel. The chirality transfer in the co-assembly of the achiral QDs with the gelator and the spacer effect of the capping reagents on the QD surface are also discussed. This work provides new insight into the design of functional chiroptical materials. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Probing the Interaction of Quantum Dots with Chiral Capping Molecules Using Circular Dichroism Spectroscopy

    PubMed Central

    2016-01-01

    Circular dichroism (CD) induced at exciton transitions by chiral ligands attached to single component and core/shell colloidal quantum dots (QDs) was used to study the interactions between QDs and their capping ligands. Analysis of the CD line shapes of CdSe and CdS QDs capped with l-cysteine reveals that all of the features in the complex spectra can be assigned to the different excitonic transitions. It is shown that each transition is accompanied by a derivative line shape in the CD response, indicating that the chiral ligand can split the exciton level into two new sublevels, with opposite angular momentum, even in the absence of an external magnetic field. The role of electrons and holes in this effect could be separated by experiments on various types of core/shell QDs, and it was concluded that the induced CD is likely related to interactions of the highest occupied molecular orbitals of the ligands with the holes. Hence, CD was useful for the analysis of hole level–ligand interactions in quantum semiconductor heterostructures, with promising outlook toward better general understanding the properties of the surface of such systems. PMID:27960517

  18. Circular Dichroism of Electric-Field-Oriented CdSe/CdS Quantum Dots-in-Rods.

    PubMed

    Mukhina, Maria V; Baimuratov, Anvar S; Rukhlenko, Ivan D; Maslov, Vladimir G; Purcell Milton, Finn; Gun'ko, Yurii K; Baranov, Alexander V; Fedorov, Anatoly V

    2016-09-27

    Here we report anisotropy of intrinsic chiroptical response in CdSe/CdS quantum dot-in-rod systems. These nanostructures being oriented in an external electric field demonstrate dependence of circular dichroism signal on the orientation of the nanocrystals. The type of circular polarization in these nanostructures correlates with preferential direction of linear polarization, and the degree of circular polarization is the maximal for the first circular dichroism band corresponding to the absorption band edge. We also support our experimental data with a theoretical model. Using this model, we show a direct connection between theoretically derived morphological parameters of twisting in nanocrystals lattices and calculated from experimental data parameters of circular dichroism anisotropy.

  19. Full spectral and angular characterization of highly directional emission from nanocrystal quantum dots positioned on circular plasmonic lenses.

    PubMed

    Harats, Moshe G; Livneh, Nitzan; Zaiats, Gary; Yochelis, Shira; Paltiel, Yossi; Lifshitz, Efrat; Rapaport, Ronen

    2014-10-08

    We design a circular plasmonic lens for collimation of light emission from nanocrystal quantum dots at room temperature in the near IR spectral range. We implement a two-dimensional k-space imaging technique to obtain the full spectral-angular response of the surface plasmon resonance modes of the bare plasmonic lens. This method is also used to map the full spectral-angular emission from nanocrystal quantum dots positioned at the center of the circular plasmonic lens. A narrow directional emitting beam with a divergence angle of only ∼4.5° full width at half-maximum is achieved with a spectrally broad bandwidth of 30 nm. The spectrally resolved k-space imaging method allows us to get a direct comparison between the spectral-angular response of the resonant surface plasmon modes of the lens and the emission pattern of the quantum dots. This comparison gives a clear and detailed picture of the direct role of these resonant surface waves in directing the emission. The directional emission effect agrees well with calculations based on the coupled mode method. These results are a step toward fabricating an efficient room-temperature single photon source based on nanocrystal quantum dots.

  20. Charge transfer modeling in monolayer circular graphene quantum dots-ZnO nanowires system for application in photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Tamandani, Shahryar; Darvish, Ghafar

    2017-01-01

    We investigate electron transport between circular graphene quantum dots (CGQDs) and ZnO nanowires (ZnO NWs). This structure can be used as donor and acceptor in hybrid solar cells. We consider circular quantum dots (QDs) and use analytical calculation in order to estimate wavefunctions of GQD and ZnO NWs. After calculating the wavefunctions overlap, we use Marcus relation in order to calculate electron transfer rate. Also, we calculate this transfer rate for CdSe QDs-ZnO NWs system. Results from analytical calculation show that the transfer rate is limited to 1013 s-1. This result is in agreement with experimental results which are reported earlier. Such systems could be suitable for solar cells.

  1. Circular dichroism spectroscopy of chlorin e6 and its complexes with quantum dots in different media

    NASA Astrophysics Data System (ADS)

    Kundelev, E. V.; Orlova, A. O.; Maslov, V. G.; Baranov, A. V.; Fedorov, A. V.

    2017-01-01

    The circular dichroism (CD) spectra of chlorin e6 and its complexes with ZnS:Mn/ZnS and CdSe/ZnS quantum dots (QDs) in aqueous solutions with different pH, in methanol, and in dimethyl sulfoxide (DMSO) have been experimentally investigated. The changes in the CD spectra of free chlorin e6 caused by its complexing with semiconductor QDs are analyzed. The application of CD spectroscopy made it possible to record for the first time the CD spectrum of luminescent dimer of chlorin e6 and reveal a nonluminescent aggregate of chlorin e6 (interpreted preliminary as a "tetramer"), the anisotropy factor of which exceeds that of its monomer by a factor of 40. An analysis of the experimental data shows that chlorin e6 in a complex with QDs can be either in the monomeric form or in the form of a nonluminescent "tetramer." The interaction with a relatively low-stable luminescent dimer of chlorin e6 with QDs leads to its partial monomerization and formation of complexes where chlorin e6 is in the monomeric form.

  2. Exciton states in a circular graphene quantum dot: Magnetic field induced intravalley to intervalley transition

    NASA Astrophysics Data System (ADS)

    Li, L. L.; Zarenia, M.; Xu, W.; Dong, H. M.; Peeters, F. M.

    2017-01-01

    The magnetic-field dependence of the energy spectrum, wave function, binding energy, and oscillator strength of exciton states confined in a circular graphene quantum dot (CGQD) is obtained within the configuration interaction method. We predict that (i) excitonic effects are very significant in the CGQD as a consequence of a combination of geometric confinement, magnetic confinement, and reduced screening; (ii) two types of excitons (intravalley and intervalley) are present in the CGQD because of the valley degree of freedom in graphene; (iii) the intravalley and intervalley exciton states display different magnetic-field dependencies due to the different electron-hole symmetries of the single-particle energy spectra; (iv) with increasing magnetic field, the exciton ground state in the CGQD undergoes an intravalley to intervalley transition accompanied by a change of angular momentum; (v) the exciton binding energy does not increase monotonically with the magnetic field due to the competition between geometric and magnetic confinements; and (vi) the optical transitions of the intervalley and intravalley excitons can be tuned by the magnetic field, and valley-dependent excitonic transitions can be realized in a CGQD.

  3. Circular dichroism sensor based on cadmium sulfide quantum dots for chiral identification and detection of penicillamine.

    PubMed

    Ngamdee, Kessarin; Puangmali, Theerapong; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2015-10-22

    A new chemical sensor based on the measuring of circular dichroism signal (CD) was fabricated from cysteamine capped cadmium sulfide quantum dots (Cys-CdS QDs). The chiral-thiol molecules, d-penicillamine (DPA) and l-penicillamine (LPA), were used to evaluate potentials of this sensor. Basically, DPA and LPA provide very low CD signals. However, the CD signals of DPA and LPA can be enhanced in the presence of Cys-CdS QDs. The CD spectra of DPA and LPA exhibited a mirror image profile. Parameters affecting the determination of DPA and LPA were thoroughly investigated in details. Under the optimized condition, the CD signals of DPA and LPA displayed a linear relationship with the concentrations of both enantiomers, ranging from 1 to 35 μM. Detection limits of this sensor were 0.49 and 0.74 μM for DPA and LPA, respectively. To demonstrate a potential application of this sensor, the proposed sensor was used to determine DPA and LPA in real urine samples. It was confirmed that the proposed detection technique was reliable and could be utilized in a broad range of applications. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Circular dichroism spectroscopy of complexes based on semiconductor quantum dots and chlorin e6 molecules

    NASA Astrophysics Data System (ADS)

    Kundelev, Evgeny V.; Orlova, Anna O.; Maslov, Vladimir G.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2017-04-01

    Circular dichroism (CD) spectra of complexes based on ZnS:Mn/ZnS and CdSe/ZnS quantum dots (QDs) and chlorin e6 (Ce6) molecules in dimethyl sulfoxide (DMSO) and in aqueous solutions at different pH levels were investigated. The changes in CD spectra of Ce6 upon its bonding in complex with semiconductor QDs were analyzed. CD spectroscopy allowed us to obtain the CD spectrum of a luminescent Ce6 dimer and to identify a nonluminescent Ce6 aggregate, which is thought to be a tetramer. The dissymmetry factor of the tetramer is 40 times larger than that of the Ce6 monomer. The analysis of the obtained data showed that in complexes with QDs Ce6 can be either in the monomer form or in the form of a nonluminescent tetramer. The interaction of the relatively unstable luminescent Ce6 dimer with QDs leads to its partial monomerization and the formation of complexes with Ce6 in the monomer form. On the basis of time-dependent density functional theory calculations, we performed a geometry model of Ce6 dimer form with corresponding calculated absorption and CD spectra, which are in a qualitative agreement with the experimental data.

  5. Theory of confined states of positronium in spherical and circular quantum dots with Kane’s dispersion law

    PubMed Central

    2013-01-01

    Confined states of a positronium (Ps) in the spherical and circular quantum dots (QDs) are theoretically investigated in two size quantization regimes: strong and weak. Two-band approximation of Kane’s dispersion law and parabolic dispersion law of charge carriers are considered. It is shown that electron-positron pair instability is a consequence of dimensionality reduction, not of the size quantization. The binding energies for the Ps in circular and spherical QDs are calculated. The Ps formation dependence on the QD radius is studied. PMID:23826867

  6. A circular dichroism sensor for Ni(2+) and Co(2+) based on L-cysteine capped cadmium sulfide quantum dots.

    PubMed

    Tedsana, Wimonsiri; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2015-03-31

    A new circular dichroism sensor for detecting Ni(2+) and Co(2+) was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni(2+) or Co(2+). L-Cysteine capped cadmium sulfide quantum dots (L-Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of L-Cyst-CdS QDs was significantly changed in the presence of Ni(2+) and Co(2+). On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni(2+) or Co(2+), the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10-60 μM and 4-80 μM with low detection limits of 7.33 μМ and 1.13 μM for the detection of Ni(2+) and Co(2+), respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni(2+) and Co(2+) in real water samples, and the results agreed well with the analysis using the standard ICP-OES. Copyright © 2014 Elsevier B.V. All rights reserved.

  7. The circular current in a conducting mesoscopic ring with coupled quantum dot

    NASA Astrophysics Data System (ADS)

    Bo, Zhou

    2016-11-01

    In this paper, we investigate the circular current in the metallic ring coupled with two QDs connected with two ferromagnetic leads with the in-plane electric field ξ which is perpendicular to the wire applied to the ring by using the non-equilibrium Green's function technique. We find that in this systems the circular current in the ring can be tuned by the voltages between left and right electrodes, the temperature, the spin polarization, and the energy of the QDs and the electric field ɛ. With these parameters varied, the values and direction of the circular current can be controlled, so we can control the values and the directions of the magnetic field produced at the ring center. In addition, there also has the function of spin filter in the P and has the function of suppression of the circular current for large 𝒫 of the AP. So this structure has potential applications in designing spin-based quantum devices.

  8. Electronic and optical properties of a circular graphene quantum dot in a magnetic field: Influence of the boundary conditions

    NASA Astrophysics Data System (ADS)

    Grujić, M.; Zarenia, M.; Chaves, A.; Tadić, M.; Farias, G. A.; Peeters, F. M.

    2011-11-01

    An analytical approach, using the Dirac-Weyl equation, is implemented to obtain the energy spectrum and optical absorption of a circular graphene quantum dot in the presence of an external magnetic field. Results are obtained for the infinite-mass and zigzag boundary conditions. We found that the energy spectrum of a dot with the zigzag boundary condition exhibits a zero-energy band regardless of the value of the magnetic field, while for the infinite-mass boundary condition, the zero-energy states appear only for high magnetic fields. The analytical results are compared to those obtained from the tight-binding model: (i) we show the validity range of the continuum model and (ii) we find that the continuum model with the infinite-mass boundary condition describes rather well its tight-binding analog, which can be partially attributed to the blurring of the mixed edges by the staggered potential.

  9. Analytical modeling of photon absorption coefficient in mono and bilayer circular graphene quantum dots for light absorber applications

    NASA Astrophysics Data System (ADS)

    Tamandani, Shahryar; Darvish, Ghafar

    2017-02-01

    We present an analytical method to calculate photon absorption coefficient in mono and bilayer circular graphene quantum dots (CGQDs). We use kobo equation to extract new closed relation as the main goal. First, we calculate real and imaginary part of optical conductance separately. Then, joint density of states is obtained using a new relation that was extracted for the energy levels of mono and bilayer circular grapheme quantum dots. In this work we use closed equations to calculate energy levels in CGQDs. Next we obtain a new closed formula to calculate the photon absorption coefficient. The results show that the absorption coefficient is related to the size of CGQDs and number of layers. The photon absorption coefficient becomes lower with larger size of CGQDs. It is seen that the results of our method is compatible with the results of practical works. We also compare photon absorption in biased and unbiased bilayer CGQDs and investigate the effect of external magnetic field on photon absorption. rights reserved

  10. Extended linear regime of cavity-QED enhanced optical circular birefringence induced by a charged quantum dot

    NASA Astrophysics Data System (ADS)

    Hu, C. Y.; Rarity, J. G.

    2015-02-01

    Giant optical Faraday rotation (GFR) and giant optical circular birefringence (GCB) induced by a single quantum-dot spin in an optical microcavity can be regarded as linear effects in the weak-excitation approximation if the input field lies in the low-power limit [Hu et al., Phys. Rev. B 78, 085307 (2008), 10.1103/PhysRevB.78.085307; Hu et al., Phys. Rev. B 80, 205326 (2009), 10.1103/PhysRevB.80.205326]. In this work, we investigate the transition from the weak-excitation approximation moving into the saturation regime comparing a semiclassical approximation with the numerical results from a quantum optics toolbox [Tan, J. Opt. B 1, 424 (1999), 10.1088/1464-4266/1/4/312]. We find that the GFR and GCB around the cavity resonance in the strong-coupling regime are input field independent at intermediate powers and can be well described by the semiclassical approximation. Those associated with the dressed state resonances in the strong-coupling regime or merging with the cavity resonance in the Purcell regime are sensitive to input field at intermediate powers, and cannot be well described by the semiclassical approximation due to the quantum-dot saturation. As the GFR and GCB around the cavity resonance are relatively immune to the saturation effects, the rapid readout of single-electron spins can be carried out with coherent state and other statistically fluctuating light fields. This also shows that high-speed quantum entangling gates, robust against input power variations, can be built exploiting these linear effects.

  11. Beaming Circularly Polarized Photons from Quantum Dots Coupled with Plasmonic Spiral Antenna (Postprint)

    DTIC Science & Technology

    2014-01-01

    SYMBOLS Acronym Definition SPP Surface Plasmon Polaritons RHC Right-Hand Circular LHC Left-Hand Circular FIB Focused Ion Beam RHS Right-Handed Spiral CCD Charge-Coupled Detector FWHM Full Width at Half Maximum

  12. Absorption and Magnetic Circular Dichroism Analyses of Giant Zeeman Splittings in Diffusion-Doped Colloidal Cd(1-x)Mn(x)Se Quantum Dots.

    PubMed

    Barrows, Charles J; Vlaskin, Vladimir A; Gamelin, Daniel R

    2015-08-06

    Impurity ions can transform the electronic, magnetic, or optical properties of colloidal quantum dots. Magnetic impurities introduce strong dopant-carrier exchange coupling that generates giant Zeeman splittings (ΔEZ) of excitonic excited states. To date, ΔEZ in colloidal doped quantum dots has primarily been quantified by analysis of magnetic circular dichroism (MCD) intensities and absorption line widths (σ). Here, we report ΔEZ values detected directly by absorption spectroscopy for the first time in such materials, using colloidal Cd(1-x)Mn(x)Se quantum dots prepared by diffusion doping. A convenient method for decomposing MCD and absorption data into circularly polarized absorption spectra is presented. These data confirm the widely applied MCD analysis in the low-field, high-temperature regime, but also reveal a breakdown at low temperatures and high fields when ΔEZ/σ approaches unity, a situation not previously encountered in doped quantum dots. This breakdown is apparent for the first time here because of the extraordinarily large ΔEZ and small σ achieved by nanocrystal diffusion doping.

  13. Unraveling the Mesoscopic Character of Quantum Dots in Nanophotonics.

    PubMed

    Tighineanu, P; Sørensen, A S; Stobbe, S; Lodahl, P

    2015-06-19

    We provide a microscopic theory for semiconductor quantum dots that explains the pronounced deviations from the prevalent point-dipole description that were recently observed in spectroscopic experiments on quantum dots in photonic nanostructures. The deviations originate from structural inhomogeneities generating a large circular quantum current density that flows inside the quantum dot over mesoscopic length scales. The model is supported by the experimental data, where a strong variation of the multipolar moments across the emission spectrum of quantum dots is observed. Our work enriches the physical understanding of quantum dots and is of significance for the fields of nanophotonics, quantum photonics, and quantum-information science, where quantum dots are actively employed.

  14. New quantum dot sensors

    NASA Astrophysics Data System (ADS)

    Gun'ko, Y. K.; Moloney, M. M.; Gallagher, S.; Govan, J.; Hanley, C.

    2010-04-01

    Quantum dots (QDs) are fluorescent semiconductor (e.g. II-VI) nanocrystals, which have a strong characteristic spectral emission. This emission is tunable to a desired energy by selecting variable particle size, size distribution and composition of the nanocrystals. QDs have recently attracted enormous interest due to their unique photophysical properties and range of potential applications in photonics and biochemistry. The main aim of our work is develop new chiral quantum dots (QDs) and establish fundamental principles influencing their structure, properties and biosensing behaviour. Here we present the synthesis and characterisation of chiral CdSe semiconductor nanoparticles and their utilisation as new chiral biosensors. Penicillamine stabilised CdSe nanoparticles have shown both very strong and very broad luminescence spectra. Circular dichroism (CD) spectroscopy studies have revealed that the D- and Lpenicillamine stabilised CdSe QDs demonstrate circular dichroism and possess almost identical mirror images of CD signals. Studies of photoluminescence and CD spectra have shown that there is a clear relationship between defect emission and CD activity. We have also demonstrated that these new QDs can serve as fluorescent nanosensors for various chiral biomolecules including nucleic acids. These novel nanosensors can be potentially utilized for detection of various chiral biological and chemical species with the broad range of potential applications.

  15. Circular dichroism spectroscopy of complexes of semiconductor quantum dots with chlorin e6

    NASA Astrophysics Data System (ADS)

    Kundelev, Evgeny V.; Orlova, Anna O.; Maslov, Vladimir G.; Baranov, Alexsander V.; Fedorov, Anatoly V.

    2016-04-01

    Experimental investigation of circular dichroism (CD) spectra of complexes based on ZnS:Mn/ZnS and CdSe/ZnS QDs and chlorin e6 (Ce6) molecules in aqua solutions at different pH level, in methanol and in DMSO were carried out. The changes in CD spectra of Ce6 upon its bonding in complex with semiconductor QDs were analyzed. Application of CD spectroscopy allowed to obtain the CD spectrum of luminescent Ce6 dimer for the first time, and to discover a nonluminescent Ce6 aggregate, preliminary identified as a "tetramer", dissymmetry factor of which is 40 times larger than that for its monomer. The analysis of obtained data showed that in complexes with QDs Ce6 can be either in the monomeric form or in the form of non-luminescent tetramer. The interaction of relatively unstable luminescent Ce6 dimerwith QDs leads to its partial monomerization and formation complexes with chlorin e6 in monomeric form.

  16. Lasing action and extraordinary reduction in long radiative lifetime of type-II GaSb/GaAs quantum dots using circular photonic crystal nanocavity

    SciTech Connect

    Hsu, Kung-Shu; Chang, Shu-Wei; Hung, Wei-Chun; Chang, Chih-Chi; Lin, Wei-Hsun; Lin, Shih-Yen; Shih, Min-Hsiung; Lee, Po-Tsung; Chang, Yia-Chung

    2015-08-31

    We demonstrated the lasing action and remarkable reduction in long radiative lifetimes of type-II GaSb/GaAs quantum dots using a circular photonic-crystal nano-cavity with high Purcell factors. The associated enhancement in carrier recombination was surprisingly high and could even surpass type-I counterparts in similar conditions. These phenomena reveal that the type-II sample exhibited extremely low nonradiative recombination so that weak radiative transitions were more dominant than expected. The results indicate that type-II nanostructures may be advantageous for applications which require controllable radiative transitions but low nonradiative depletions.

  17. Quantum Dots: Theory

    SciTech Connect

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

    This review covers the description of the methodologies typically used for the calculation of the electronic structure of self-assembled and colloidal quantum dots. These are illustrated by the results of their application to a selected set of physical effects in quantum dots.

  18. Optically active quantum-dot molecules.

    PubMed

    Shlykov, Alexander I; Baimuratov, Anvar S; Baranov, Alexander V; Fedorov, Anatoly V; Rukhlenko, Ivan D

    2017-02-20

    Chiral molecules made of coupled achiral semiconductor nanocrystals, also known as quantum dots, show great promise for photonic applications owing to their prospective uses as configurable building blocks for optically active structures, materials, and devices. Here we present a simple model of optically active quantum-dot molecules, in which each of the quantum dots is assigned a dipole moment associated with the fundamental interband transition between the size-quantized states of its confined charge carriers. This model is used to analytically calculate the rotatory strengths of optical transitions occurring upon the excitation of chiral dimers, trimers, and tetramers of general configurations. The rotatory strengths of such quantum-dot molecules are found to exceed the typical rotatory strengths of chiral molecules by five to six orders of magnitude. We also study how the optical activity of quantum-dot molecules shows up in their circular dichroism spectra when the energy gap between the molecular states is much smaller than the states' lifetime, and maximize the strengths of the circular dichroism peaks by optimizing orientations of the quantum dots in the molecules. Our analytical results provide clear design guidelines for quantum-dot molecules and can prove useful in engineering optically active quantum-dot supercrystals and photonic devices.

  19. Quantum Dot Solar Cells

    NASA Technical Reports Server (NTRS)

    Raffaelle, Ryne P.; Castro, Stephanie L.; Hepp, Aloysius; Bailey, Sheila G.

    2002-01-01

    We have been investigating the synthesis of quantum dots of CdSe, CuInS2, and CuInSe2 for use in an intermediate bandgap solar cell. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Bawendi, et. al., in the early 1990's. However, unlike previous work in this area we have also utilized single-source precursor molecules in the synthesis process. We will present XRD, TEM, SEM and EDS characterization of our initial attempts at fabricating these quantum dots. Investigation of the size distributions of these nanoparticles via laser light scattering and scanning electron microscopy will be presented. Theoretical estimates on appropriate quantum dot composition, size, and inter-dot spacing along with potential scenarios for solar cell fabrication will be discussed.

  20. Quantum Dot Solar Cells

    NASA Technical Reports Server (NTRS)

    Raffaelle, Ryne P.; Castro, Stephanie L.; Hepp, Aloysius; Bailey, Sheila G.

    2002-01-01

    We have been investigating the synthesis of quantum dots of CdSe, CuInS2, and CuInSe2 for use in an intermediate bandgap solar cell. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Bawendi, et. al., in the early 1990's. However, unlike previous work in this area we have also utilized single-source precursor molecules in the synthesis process. We will present XRD, TEM, SEM and EDS characterization of our initial attempts at fabricating these quantum dots. Investigation of the size distributions of these nanoparticles via laser light scattering and scanning electron microscopy will be presented. Theoretical estimates on appropriate quantum dot composition, size, and inter-dot spacing along with potential scenarios for solar cell fabrication will be discussed.

  1. Optically active quantum dots

    NASA Astrophysics Data System (ADS)

    Gerard, Valerie; Govan, Joseph; Loudon, Alexander; Baranov, Alexander V.; Fedorov, Anatoly V.; Gun'ko, Yurii K.

    2015-10-01

    The main goal of our research is to develop new types of technologically important optically active quantum dot (QD) based materials, study their properties and explore their biological applications. For the first time chiral II-VI QDs have been prepared by us using microwave induced heating with the racemic (Rac), D- and L-enantiomeric forms of penicillamine as stabilisers. Circular dichroism (CD) studies of these QDs have shown that D- and L-penicillamine stabilised particles produced mirror image CD spectra, while the particles prepared with a Rac mixture showed only a weak signal. It was also demonstrated that these QDs show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. These QDs have demonstrated highly specific chiral recognition of various biological species including aminoacids. The utilisation of chiral stabilisers also allowed the preparation of new water soluble white emitting CdS nano-tetrapods, which demonstrated circular dichroism in the band-edge region of the spectrum. Biological testing of chiral CdS nanotetrapods displayed a chiral bias for an uptake of the D- penicillamine stabilised nano-tetrapods by cancer cells. It is expected that this research will open new horizons in the chemistry of chiral nanomaterials and their application in nanobiotechnology, medicine and optical chemo- and bio-sensing.

  2. Quantum dots for biophotonics.

    PubMed

    Yong, Ken-Tye

    2012-01-01

    This theme issue provides an excellent collection of reviews and original research articles on the study of various bioconjugated quantum dot formulations for diagnostics and therapy applications using biophotonic imaging and sensing approaches.

  3. A circular dichroism sensor for selective detection of Cd(2+) and S(2-) based on the in-situ generation of chiral CdS quantum dots.

    PubMed

    Sianglam, Pradthana; Kulchat, Sirinan; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2017-08-05

    We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd(2+) and S(2-) based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd(2+), S(2-), cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd(2+) or S(2-) concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd(2+) and S(2-), with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200μM and 7-125μM with detection limits of 59.7 and 1.6μM for Cd(2+) and S(2-), respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd(2+)) and HPLC (for S(2-)). Copyright © 2017 Elsevier B.V. All rights reserved.

  4. A circular dichroism sensor for selective detection of Cd2 + and S2 - based on the in-situ generation of chiral CdS quantum dots

    NASA Astrophysics Data System (ADS)

    Sianglam, Pradthana; Kulchat, Sirinan; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2017-08-01

    We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd2 + and S2 - based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd2 +, S2 -, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd2 + or S2 - concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd2 + and S2 -, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200 μM and 7-125 μM with detection limits of 59.7 and 1.6 μM for Cd2 + and S2 -, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd2 +) and HPLC (for S2 -).

  5. Quantum dot resonant tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Reed, Mark A.; Randall, John N.; Luscombe, James H.; Frensley, William R.; Aggarwal, Raj J.; Matyi, Richard J.; Moore, Tom M.; Wetsel, Anna E.

    The electronic transport through 3-dimensionally confined semiconductor quantum wells (quantum dots) is investigated and analyzed. The spectra corresponds to resonant tunneling from laterally-confined emitter contact subbands through the discrete 3-dimensionally confined quantum dot states. Momentum nonconservation is observed in these structures. Results on coupled quantum dot states (molccules) will be presented.

  6. Plasmonic fluorescent quantum dots.

    PubMed

    Jin, Yongdong; Gao, Xiaohu

    2009-09-01

    Combining multiple discrete components into a single multifunctional nanoparticle could be useful in a variety of applications. Retaining the unique optical and electrical properties of each component after nanoscale integration is, however, a long-standing problem. It is particularly difficult when trying to combine fluorophores such as semiconductor quantum dots with plasmonic materials such as gold, because gold and other metals can quench the fluorescence. So far, the combination of quantum dot fluorescence with plasmonically active gold has only been demonstrated on flat surfaces. Here, we combine fluorescent and plasmonic activities in a single nanoparticle by controlling the spacing between a quantum dot core and an ultrathin gold shell with nanometre precision through layer-by-layer assembly. Our wet-chemistry approach provides a general route for the deposition of ultrathin gold layers onto virtually any discrete nanostructure or continuous surface, and should prove useful for multimodal bioimaging, interfacing with biological systems, reducing nanotoxicity, modulating electromagnetic fields and contacting nanostructures.

  7. Chiral Graphene Quantum Dots.

    PubMed

    Suzuki, Nozomu; Wang, Yichun; Elvati, Paolo; Qu, Zhi-Bei; Kim, Kyoungwon; Jiang, Shuang; Baumeister, Elizabeth; Lee, Jaewook; Yeom, Bongjun; Bahng, Joong Hwan; Lee, Jaebeom; Violi, Angela; Kotov, Nicholas A

    2016-02-23

    Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the "crowded" edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functional theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to L/D-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.

  8. Chiral quantum dot based materials

    NASA Astrophysics Data System (ADS)

    Govan, Joseph; Loudon, Alexander; Baranov, Alexander V.; Fedorov, Anatoly V.; Gun'ko, Yurii

    2014-05-01

    Recently, the use of stereospecific chiral stabilising molecules has also opened another avenue of interest in the area of quantum dot (QD) research. The main goal of our research is to develop new types of technologically important quantum dot materials containing chiral defects, study their properties and explore their applications. The utilisation of chiral penicillamine stabilisers allowed the preparation of new water soluble white emitting CdS quantum nanostructures which demonstrated circular dichroism in the band-edge region of the spectrum. It was also demonstrated that all three types of QDs (D-, L-, and Rac penicillamine stabilised) show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. In this work the chiral CdS based quantum nanostructures have also been doped by copper metal ions and new chiral penicilamine stabilized CuS nanoparticles have been prepared and investigated. It was found that copper doping had a strong effect at low levels in the synthesis of chiral CdS nanostructures. We expect that this research will open new horizons in the chemistry of chiral nanomaterials and their application in biotechnology, sensing and asymmetric synthesis.

  9. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

    Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single

  10. Colloidal Double Quantum Dots.

    PubMed

    Teitelboim, Ayelet; Meir, Noga; Kazes, Miri; Oron, Dan

    2016-05-17

    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon

  11. Depth perception through circular movements of dots.

    PubMed

    Ito, Hiroyuki

    2010-01-01

    Elements that move with velocity gradients have been shown to give the impression of depth. In this study, it was found that dots in circular motion around a line of sight give a depth impression corresponding to the gradients of the angular velocities of circular motion on a screen. The results of two experiments show that depth perception through circular motion is as effective as that through expansion or spiral motion, but less effective than that through lateral motion parallax when the local speed distributions on the screen are matched. The present depth effect shows that expansion-contraction, spiral, and circular motions are a continuum in terms of producing depth effects; they differ from lateral motion parallax.

  12. PREFACE: Quantum Dot 2010

    NASA Astrophysics Data System (ADS)

    Taylor, Robert A.

    2010-09-01

    These conference proceedings contain the written papers of the contributions presented at Quantum Dot 2010 (QD2010). The conference was held in Nottingham, UK, on 26-30 April 2010. The conference addressed topics in research on: 1. Epitaxial quantum dots (including self-assembled and interface structures, dots defined by electrostatic gates etc): optical properties and electron transport quantum coherence effects spin phenomena optics of dots in cavities interaction with surface plasmons in metal/semiconductor structures opto-electronics applications 2. Novel QD structures: fabrication and physics of graphene dots, dots in nano-wires etc 3. Colloidal quantum dots: growth (shape control and hybrid nanocrystals such as metal/semiconductor, magnetic/semiconductor) assembly and surface functionalisation optical properties and spin dynamics electrical and magnetic properties applications (light emitting devices and solar cells, biological and medical applications, data storage, assemblers) The Editors Acknowledgements Conference Organising Committee: Maurice Skolnick (Chair) Alexander Tartakovskii (Programme Chair) Pavlos Lagoudakis (Programme Chair) Max Migliorato (Conference Secretary) Paola Borri (Publicity) Robert Taylor (Proceedings) Manus Hayne (Treasurer) Ray Murray (Sponsorship) Mohamed Henini (Local Organiser) International Advisory Committee: Yasuhiko Arakawa (Tokyo University, Japan) Manfred Bayer (Dortmund University, Germany) Sergey Gaponenko (Stepanov Institute of Physics, Minsk, Belarus) Pawel Hawrylak (NRC, Ottawa, Canada) Fritz Henneberger (Institute for Physics, Berlin, Germany) Atac Imamoglu (ETH, Zurich, Switzerland) Paul Koenraad (TU Eindhoven, Nethehrlands) Guglielmo Lanzani (Politecnico di Milano, Italy) Jungil Lee (Korea Institute of Science and Technology, Korea) Henri Mariette (CNRS-CEA, Grenoble, France) Lu Jeu Sham (San Diego, USA) Andrew Shields (Toshiba Research Europe, Cambridge, UK) Yoshihisa Yamamoto (Stanford University, USA) Artur

  13. Quantum Dot Sensitized Photoelectrodes

    PubMed Central

    Macdonald, Thomas J.; Nann, Thomas

    2011-01-01

    Quantum Dots (QDs) are promising alternatives to organic dyes as sensitisers for photocatalytic electrodes. This review article provides an overview of the current state of the art in this area. More specifically, different types of QDs with a special focus on heavy-metal free QDs and the methods for preparation and adsorption onto metal oxide electrodes (especially titania and zinc oxide) are discussed. Eventually, the key areas of necessary improvements are identified and assessed.

  14. Quantum DOT IR Photodetectors

    DTIC Science & Technology

    2012-07-01

    4.1.3  ROIC Control and Readout Electronics ................................................................ 16  4.2  Device measurements...the voltage of the detector modifies its spectral response. In this effort a DWELL Quantum Dot device was fabricated and tested. The results...agility. Because of delays in the fabrication of the ROIC device by MOSIS, those results will not available for the final report until approximately

  15. Plasmonic fluorescent quantum dots

    PubMed Central

    Jin, Yongdong

    2009-01-01

    Combining multiple discrete components into a single multifunctional nanoparticle could be useful in a variety of applications. Retaining the unique optical and electrical properties of each component after nanoscale integration is, however, a long-standing problem1,2. It is particularly difficult when trying to combine fluorophores such as semiconductor quantum dots with plasmonic materials such as gold, because gold and other metals can quench the fluorescence3,4. So far, the combination of quantum dot fluorescence with plasmonically active gold has only been demonstrated on flat surfaces5. Here, we combine fluorescent and plasmonic activities in a single nanoparticle by controlling the spacing between a quantum dot core and an ultrathin gold shell with nanometre precision through layer-by-layer assembly. Our wet-chemistry approach provides a general route for the deposition of ultrathin gold layers onto virtually any discrete nanostructure or continuous surface, and should prove useful for multimodal bioimaging6, interfacing with biological systems7, reducing nanotoxicity8, modulating electromagnetic fields5 and contacting nanostructures9,10. PMID:19734929

  16. Quantum transport in ballistic quantum dots

    NASA Astrophysics Data System (ADS)

    Ferry, D. K.; Akis, R. A.; Pivin, D. P., Jr.; Bird, J. P.; Holmberg, N.; Badrieh, F.; Vasileska, D.

    1998-10-01

    Carriers in small 3D quantum boxes take us from unintentional qquantum dots in MOSFETs (arising from the doping fluctuations) tto single-electron quantum dots in semiconductor hheterostructures. In between these two extremes are the realm of oopen, ballistic quantum dots, in which the transport can be quite regular. Several issues must be considered in treating the transport in these dots, among which are: (1) phase coherence within the dot; (2) the transition between semi-classical and fully quantum transport, (3) the role of the contacts, vis-à-vis the fabricated boundaries, and (4) the actual versus internal boundaries. In this paper, we discuss these issues, including the primary observables in experiment, the intrinsic nature of oscillatory behavior in magnetic field and dot size, and the connection to semi-classical transport emphasizing the importance of the filtering by the input (and output) quantum point contacts.

  17. Quantum Dot Spins and Photons

    NASA Astrophysics Data System (ADS)

    Atature, Mete

    2012-02-01

    Self-assembled semiconductor quantum dots are interesting and rich physical systems. Their inherently mesoscopic nature leads to a multitude of interesting interaction mechanisms of confined spins with the solid state environment of spins, charges and phonons. In parallel, the relatively clean spin-dependent optical transitions make quantum dots strong candidates for stationary and flying qubits within the context of spin-based quantum information science. The recently observed quantum dot resonance fluorescence has become a key enabler for further progress in this context. I will first discuss the real-time optical detection (or single-shot readout) of quantum dot spins, and then I will discuss how resonance fluorescence allows coherent generation of single photons suitable (and tailored) for linear-optics quantum computation and for establishing a high-efficiency spin-photon quantum interface within a distributed quantum network.

  18. Quantum dot cascade laser

    PubMed Central

    2014-01-01

    We demonstrated an unambiguous quantum dot cascade laser based on InGaAs/GaAs/InAs/InAlAs heterostructure by making use of self-assembled quantum dots in the Stranski-Krastanow growth mode and two-step strain compensation active region design. The prototype generates stimulated emission at λ ~ 6.15 μm and a broad electroluminescence band with full width at half maximum over 3 μm. The characteristic temperature for the threshold current density within the temperature range of 82 to 162 K is up to 400 K. Moreover, our materials show the strong perpendicular mid-infrared response at about 1,900 cm-1. These results are very promising for extending the present laser concept to terahertz quantum cascade laser, which would lead to room temperature operation. PACS 42.55.Px; 78.55.Cr; 78.67.Hc PMID:24666965

  19. Scanning Quantum Dot Microscopy

    NASA Astrophysics Data System (ADS)

    Wagner, Christian; Green, Matthew F. B.; Leinen, Philipp; Deilmann, Thorsten; Krüger, Peter; Rohlfing, Michael; Temirov, Ruslan; Tautz, F. Stefan

    2015-07-01

    We introduce a scanning probe technique that enables three-dimensional imaging of local electrostatic potential fields with subnanometer resolution. Registering single electron charging events of a molecular quantum dot attached to the tip of an atomic force microscope operated at 5 K, equipped with a qPlus tuning fork, we image the quadrupole field of a single molecule. To demonstrate quantitative measurements, we investigate the dipole field of a single metal adatom adsorbed on a metal surface. We show that because of its high sensitivity the technique can probe electrostatic potentials at large distances from their sources, which should allow for the imaging of samples with increased surface roughness.

  20. Efficient quantum dot-quantum dot and quantum dot-dye energy transfer in biotemplated assemblies.

    PubMed

    Achermann, Marc; Jeong, Sohee; Balet, Laurent; Montano, Gabriel A; Hollingsworth, Jennifer A

    2011-03-22

    CdSe semiconductor nanocrystal quantum dots are assembled into nanowire-like arrays employing microtubule fibers as nanoscale molecular "scaffolds." Spectrally and time-resolved energy-transfer analysis is used to assess the assembly of the nanoparticles into the hybrid inorganic biomolecular structure. Specifically, we demonstrate that a comprehensive study of energy transfer between quantum dot pairs on the biotemplate and, alternatively, between quantum dots and molecular dyes embedded in the microtubule scaffold comprises a powerful spectroscopic tool for evaluating the assembly process. In addition to revealing the extent to which assembly has occurred, the approach allows determination of particle-to-particle (and particle-to-dye) distances within the biomediated array. Significantly, the characterization is realized in situ, without need for further sample workup or risk of disturbing the solution-phase constructs. Furthermore, we find that the assemblies prepared in this way exhibit efficient quantum dot-quantum dot and quantum dot-dye energy transfer that affords faster energy-transfer rates compared to densely packed quantum dot arrays on planar substrates and to small-molecule-mediated quantum dot-dye couples, respectively.

  1. Quantum dots: Rethinking the electronics

    SciTech Connect

    Bishnoi, Dimple

    2016-05-06

    In this paper, we demonstrate theoretically that the Quantum dots are quite interesting for the electronics industry. Semiconductor quantum dots (QDs) are nanometer-scale crystals, which have unique photo physical, quantum electrical properties, size-dependent optical properties, There small size means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Cheaper than modern commercial solar cells while making use of a wider variety of photon energies, including “waste heat” from the sun’s energy. Quantum dots can be used in tandem cells, which are multi junction photovoltaic cells or in the intermediate band setup. PbSe (lead selenide) is commonly used in quantum dot solar cells.

  2. Quantum dots: Rethinking the electronics

    NASA Astrophysics Data System (ADS)

    Bishnoi, Dimple

    2016-05-01

    In this paper, we demonstrate theoretically that the Quantum dots are quite interesting for the electronics industry. Semiconductor quantum dots (QDs) are nanometer-scale crystals, which have unique photo physical, quantum electrical properties, size-dependent optical properties, There small size means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Cheaper than modern commercial solar cells while making use of a wider variety of photon energies, including "waste heat" from the sun's energy. Quantum dots can be used in tandem cells, which are multi junction photovoltaic cells or in the intermediate band setup. PbSe (lead selenide) is commonly used in quantum dot solar cells.

  3. Low Threshold Quantum Dot Lasers.

    PubMed

    Iyer, Veena Hariharan; Mahadevu, Rekha; Pandey, Anshu

    2016-04-07

    Semiconductor quantum dots have replaced conventional inorganic phosphors in numerous applications. Despite their overall successes as emitters, their impact as laser materials has been severely limited. Eliciting stimulated emission from quantum dots requires excitation by intense short pulses of light typically generated using other lasers. In this Letter, we develop a new class of quantum dots that exhibit gain under conditions of extremely low levels of continuous wave illumination. We observe thresholds as low as 74 mW/cm(2) in lasers made from these materials. Due to their strong optical absorption as well as low lasing threshold, these materials could possibly convert light from diffuse, polychromatic sources into a laser beam.

  4. Energy levels of hybrid monolayer-bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Mirzakhani, M.; Zarenia, M.; Ketabi, S. A.; da Costa, D. R.; Peeters, F. M.

    2016-04-01

    Often real samples of graphene consist of islands of both monolayer and bilayer graphene. Bound states in such hybrid quantum dots are investigated for (i) a circular single-layer graphene quantum dot surrounded by an infinite bilayer graphene sheet and (ii) a circular bilayer graphene quantum dot surrounded by an infinite single-layer graphene. Using the continuum model and applying zigzag boundary conditions at the single-layer-bilayer graphene interface, we obtain analytical results for the energy levels and the corresponding wave spinors. Their dependence on perpendicular magnetic and electric fields are studied for both types of quantum dots. The energy levels exhibit characteristics of interface states, and we find anticrossings and closing of the energy gap in the presence of a bias potential.

  5. Electrostatically confined trilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Mirzakhani, M.; Zarenia, M.; Vasilopoulos, P.; Peeters, F. M.

    2017-04-01

    Electrically gating of trilayer graphene (TLG) opens a band gap offering the possibility to electrically engineer TLG quantum dots. We study the energy levels of such quantum dots and investigate their dependence on a perpendicular magnetic field B and different types of stacking of the graphene layers. The dots are modeled as circular and confined by a truncated parabolic potential which can be realized by nanostructured gates or position-dependent doping. The energy spectra exhibit the intervalley symmetry EKe(m ) =-EK'h(m ) for the electron (e ) and hole (h ) states, where m is the angular momentum quantum number and K and K ' label the two valleys. The electron and hole spectra for B =0 are twofold degenerate due to the intervalley symmetry EK(m ) =EK'[-(m +1 ) ] . For both ABC [α =1.5 (1.2) for large (small) R ] and ABA (α =1 ) stackings, the lowest-energy levels show approximately a R-α dependence on the dot radius R in contrast with the 1 /R3 one for ABC-stacked dots with infinite-mass boundary. As functions of the field B , the oscillator strengths for dipole-allowed transitions differ drastically for the two types of stackings.

  6. Hydrophobin-Encapsulated Quantum Dots.

    PubMed

    Taniguchi, Shohei; Sandiford, Lydia; Cooper, Maggie; Rosca, Elena V; Ahmad Khanbeigi, Raha; Fairclough, Simon M; Thanou, Maya; Dailey, Lea Ann; Wohlleben, Wendel; von Vacano, Bernhard; de Rosales, Rafael T M; Dobson, Peter J; Owen, Dylan M; Green, Mark

    2016-02-01

    The phase transfer of quantum dots to water is an important aspect of preparing nanomaterials that are suitable for biological applications, and although numerous reports describe ligand exchange, very few describe efficient ligand encapsulation techniques. In this report, we not only report a new method of phase transferring quantum dots (QDs) using an amphiphilic protein (hydrophobin) but also describe the advantages of using a biological molecule with available functional groups and their use in imaging cancer cells in vivo and other imaging applications.

  7. Quantum Entanglement of Quantum Dot Spin Using Flying Qubits

    DTIC Science & Technology

    2015-05-01

    QUANTUM ENTANGLEMENT OF QUANTUM DOT SPIN USING FLYING QUBITS UNIVERSITY OF MICHIGAN MAY 2015 FINAL TECHNICAL REPORT APPROVED FOR PUBLIC RELEASE...To) SEP 2012 – DEC 2014 4. TITLE AND SUBTITLE QUANTUM ENTANGLEMENT OF QUANTUM DOT SPIN USING FLYING QUBITS 5a. CONTRACT NUMBER FA8750-12-2-0333...semiconductor quantum dots doped with a single electron, made possible by the Coulomb blockade in this system. The quantum dots confine both electrons and

  8. Quantum dot quantum cascade infrared photodetector

    SciTech Connect

    Wang, Xue-Jiao; Zhai, Shen-Qiang; Zhuo, Ning; Liu, Jun-Qi E-mail: fqliu@semi.ac.cn; Liu, Feng-Qi E-mail: fqliu@semi.ac.cn; Liu, Shu-Man; Wang, Zhan-Guo

    2014-04-28

    We demonstrate an InAs quantum dot quantum cascade infrared photodetector operating at room temperature with a peak detection wavelength of 4.3 μm. The detector shows sensitive photoresponse for normal-incidence light, which is attributed to an intraband transition of the quantum dots and the following transfer of excited electrons on a cascade of quantum levels. The InAs quantum dots for the infrared absorption were formed by making use of self-assembled quantum dots in the Stranski–Krastanov growth mode and two-step strain-compensation design based on InAs/GaAs/InGaAs/InAlAs heterostructure, while the following extraction quantum stairs formed by LO-phonon energy are based on a strain-compensated InGaAs/InAlAs chirped superlattice. Johnson noise limited detectivities of 3.64 × 10{sup 11} and 4.83 × 10{sup 6} Jones at zero bias were obtained at 80 K and room temperature, respectively. Due to the low dark current and distinct photoresponse up to room temperature, this device can form high temperature imaging.

  9. Quantum-Dot Cellular Automata

    NASA Astrophysics Data System (ADS)

    Snider, Gregory

    2000-03-01

    Quantum-dot Cellular Automata (QCA) [1] is a promising architecture which employs quantum dots for digital computation. It is a revolutionary approach that holds the promise of high device density and low power dissipation. A basic QCA cell consists of four quantum dots coupled capacitively and by tunnel barriers. The cell is biased to contain two excess electrons within the four dots, which are forced to opposite "corners" of the four-dot cell by mutual Coulomb repulsion. These two possible polarization states of the cell will represent logic "0" and "1". Properly arranged, arrays of these basic cells can implement Boolean logic functions. Experimental results from functional QCA devices built of nanoscale metal dots defined by tunnel barriers will be presented. The experimental devices to be presented consist of Al islands, which we will call quantum dots, interconnected by tunnel junctions and lithographically defined capacitors. Aluminum/ aluminum-oxide/aluminum tunnel junctions were fabricated using a standard e-beam lithography and shadow evaporation technique. The experiments were performed in a dilution refrigerator at a temperature of 70 mK. The operation of a cell is evaluated by direct measurements of the charge state of dots within a cell as the input voltage is changed. The experimental demonstration of a functioning cell will be presented. A line of three cells demonstrates that there are no metastable switching states in a line of cells. A QCA majority gate will also be presented, which is a programmable AND/OR gate and represents the basic building block of QCA systems. The results of recent experiments will be presented. 1. C.S. Lent, P.D. Tougaw, W. Porod, and G.H. Bernstein, Nanotechnology, 4, 49 (1993).

  10. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

    Spectroscopy is carried out in almost every field of science, whenever light interacts with matter. Although sophisticated instruments with impressive performance characteristics are available, much effort continues to be invested in the development of miniaturized, cheap and easy-to-use systems. Current microspectrometer designs mostly use interference filters and interferometric optics that limit their photon efficiency, resolution and spectral range. Here we show that many of these limitations can be overcome by replacing interferometric optics with a two-dimensional absorptive filter array composed of colloidal quantum dots. Instead of measuring different bands of a spectrum individually after introducing temporal or spatial separations with gratings or interference-based narrowband filters, a colloidal quantum dot spectrometer measures a light spectrum based on the wavelength multiplexing principle: multiple spectral bands are encoded and detected simultaneously with one filter and one detector, respectively, with the array format allowing the process to be efficiently repeated many times using different filters with different encoding so that sufficient information is obtained to enable computational reconstruction of the target spectrum. We illustrate the performance of such a quantum dot microspectrometer, made from 195 different types of quantum dots with absorption features that cover a spectral range of 300 nanometres, by measuring shifts in spectral peak positions as small as one nanometre. Given this performance, demonstrable avenues for further improvement, the ease with which quantum dots can be processed and integrated, and their numerous finely tuneable bandgaps that cover a broad spectral range, we expect that quantum dot microspectrometers will be useful in applications where minimizing size, weight, cost and complexity of the spectrometer are critical.

  11. Nanoscale quantum-dot supercrystals

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    We develop a theory allowing one to calculate the energy spectra and wave functions of collective excitations in twoand three-dimensional quantum-dot supercrystals. We derive analytical expressions for the energy spectra of twodimensional supercrystals with different Bravias lattices, and use them to analyze the possibility of engineering the supercrystals' band structure. We demonstrate that the variation of the supercrystal's parameters (such as the symmetry of the periodic lattice and the properties of the quantum dots or their environment) enables an unprecedented control over its optical properties, thus paving a way towards the development of new nanophotonics materials.

  12. Quantum optics in coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Garrido, Mauricio

    Coupled quantum dots present an active field of study, both at the fundamental and applied level, due to their atomic and molecular-like energy structure and the ability to design and tune their parameters. Being single-photon emitters, they are systems that behave fully according to the laws of quantum mechanics. The work presented here involved the experimental study of the electro-optical properties of Indium Arsenide, coupled quantum dots. Initial experiments involved the use of spectroscopic methods such as photoluminescence and photoluminescence excitation (PLE). Through such techniques, the top dot's hole energy level structure was mapped and different types of resonant absorption were identified. The characterization of these excited states and the knowledge of how to resonantly excite into them is an integral part of the development of certain controlled spin gates in quantum computation. Additionally, a shift of the spectra in the electric field was observed with varying excitation wavelength through and above the wetting layer, which allowed for direct measurement of the optically-created electric field within the device. This extends the quantum dots' capabilities to using them as electric-field nano-probes and opens up the possibility of an all-optical, fast switching mechanism. In the course of these studies, a novel data visualization method for PLE in this type of system was developed. Finally, to study correlated photon effects, a Hanbury Brown - Twiss experiment was built which revealed bunching and antibunching signals typical of quantum statistics in biexciton cascade emissions. This is an important step towards the experimental investigation of entangled states in coupled quantum dots.

  13. Nanoscale and Single-Dot Patterning of Colloidal Quantum Dots.

    PubMed

    Xie, Weiqiang; Gomes, Raquel; Aubert, Tangi; Bisschop, Suzanne; Zhu, Yunpeng; Hens, Zeger; Brainis, Edouard; Van Thourhout, Dries

    2015-11-11

    Using an optimized lift-off process we develop a technique for both nanoscale and single-dot patterning of colloidal quantum dot films, demonstrating feature sizes down to ~30 nm for uniform films and a yield of 40% for single-dot positioning, which is in good agreement with a newly developed theoretical model. While first of all presenting a unique tool for studying physics of single quantum dots, the process also provides a pathway toward practical quantum dot-based optoelectronic devices.

  14. Optical Fiber Sensing Using Quantum Dots

    PubMed Central

    Jorge, Pedro; Martins, Manuel António; Trindade, Tito; Santos, José Luís; Farahi, Faramarz

    2007-01-01

    Recent advances in the application of semiconductor nanocrystals, or quantum dots, as biochemical sensors are reviewed. Quantum dots have unique optical properties that make them promising alternatives to traditional dyes in many luminescence based bioanalytical techniques. An overview of the more relevant progresses in the application of quantum dots as biochemical probes is addressed. Special focus will be given to configurations where the sensing dots are incorporated in solid membranes and immobilized in optical fibers or planar waveguide platforms.

  15. Quantum dot behavior in graphene nanoconstrictions.

    PubMed

    Todd, Kathryn; Chou, Hung-Tao; Amasha, Sami; Goldhaber-Gordon, David

    2009-01-01

    Graphene nanoribbons display an imperfectly understood transport gap. We measure transport through nanoribbon devices of several lengths. In long (>/=250 nm) nanoribbons we observe transport through multiple quantum dots in series, while shorter (quantum dots. New measurements indicate that dot size may scale with constriction width. We propose a model where transport occurs through quantum dots that are nucleated by background disorder potential in the presence of a confinement gap.

  16. Colloidal quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Sargent, Edward H.

    2012-03-01

    Solar cells based on solution-processed semiconductor nanoparticles -- colloidal quantum dots -- have seen rapid advances in recent years. By offering full-spectrum solar harvesting, these cells are poised to address the urgent need for low-cost, high-efficiency photovoltaics.

  17. Semiconductor double quantum dot micromaser.

    PubMed

    Liu, Y-Y; Stehlik, J; Eichler, C; Gullans, M J; Taylor, J M; Petta, J R

    2015-01-16

    The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from terahertz sources to quantum communication. Here we demonstrate a maser that is driven by single-electron tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain medium and are placed inside a high-quality factor microwave cavity. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold. Copyright © 2015, American Association for the Advancement of Science.

  18. Brightness-equalized quantum dots

    PubMed Central

    Lim, Sung Jun; Zahid, Mohammad U.; Le, Phuong; Ma, Liang; Entenberg, David; Harney, Allison S.; Condeelis, John; Smith, Andrew M.

    2015-01-01

    As molecular labels for cells and tissues, fluorescent probes have shaped our understanding of biological structures and processes. However, their capacity for quantitative analysis is limited because photon emission rates from multicolour fluorophores are dissimilar, unstable and often unpredictable, which obscures correlations between measured fluorescence and molecular concentration. Here we introduce a new class of light-emitting quantum dots with tunable and equalized fluorescence brightness across a broad range of colours. The key feature is independent tunability of emission wavelength, extinction coefficient and quantum yield through distinct structural domains in the nanocrystal. Precise tuning eliminates a 100-fold red-to-green brightness mismatch of size-tuned quantum dots at the ensemble and single-particle levels, which substantially improves quantitative imaging accuracy in biological tissue. We anticipate that these materials engineering principles will vastly expand the optical engineering landscape of fluorescent probes, facilitate quantitative multicolour imaging in living tissue and improve colour tuning in light-emitting devices. PMID:26437175

  19. Brightness-equalized quantum dots.

    PubMed

    Lim, Sung Jun; Zahid, Mohammad U; Le, Phuong; Ma, Liang; Entenberg, David; Harney, Allison S; Condeelis, John; Smith, Andrew M

    2015-10-05

    As molecular labels for cells and tissues, fluorescent probes have shaped our understanding of biological structures and processes. However, their capacity for quantitative analysis is limited because photon emission rates from multicolour fluorophores are dissimilar, unstable and often unpredictable, which obscures correlations between measured fluorescence and molecular concentration. Here we introduce a new class of light-emitting quantum dots with tunable and equalized fluorescence brightness across a broad range of colours. The key feature is independent tunability of emission wavelength, extinction coefficient and quantum yield through distinct structural domains in the nanocrystal. Precise tuning eliminates a 100-fold red-to-green brightness mismatch of size-tuned quantum dots at the ensemble and single-particle levels, which substantially improves quantitative imaging accuracy in biological tissue. We anticipate that these materials engineering principles will vastly expand the optical engineering landscape of fluorescent probes, facilitate quantitative multicolour imaging in living tissue and improve colour tuning in light-emitting devices.

  20. Designing quantum dots for solotronics

    PubMed Central

    Kobak, J.; Smoleński, T.; Goryca, M.; Papaj, M.; Gietka, K.; Bogucki, A.; Koperski, M.; Rousset, J.-G.; Suffczyński, J.; Janik, E.; Nawrocki, M.; Golnik, A.; Kossacki, P.; Pacuski, W.

    2014-01-01

    Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. It has already been shown that optical control of a magnetic ion spin is feasible using the carriers confined in a quantum dot. However, a serious obstacle was the quenching of the exciton luminescence by magnetic impurities. Here we show, by photoluminescence studies on thus-far-unexplored individual CdTe dots with a single cobalt ion and CdSe dots with a single manganese ion, that even if energetically allowed, nonradiative exciton recombination through single-magnetic-ion intra-ionic transitions is negligible in such zero-dimensional structures. This opens solotronics for a wide range of as yet unconsidered systems. On the basis of results of our single-spin relaxation experiments and on the material trends, we identify optimal magnetic-ion quantum dot systems for implementation of a single-ion-based spin memory. PMID:24463946

  1. Hyper-parallel photonic quantum computation with coupled quantum dots

    PubMed Central

    Ren, Bao-Cang; Deng, Fu-Guo

    2014-01-01

    It is well known that a parallel quantum computer is more powerful than a classical one. So far, there are some important works about the construction of universal quantum logic gates, the key elements in quantum computation. However, they are focused on operating on one degree of freedom (DOF) of quantum systems. Here, we investigate the possibility of achieving scalable hyper-parallel quantum computation based on two DOFs of photon systems. We construct a deterministic hyper-controlled-not (hyper-CNOT) gate operating on both the spatial-mode and the polarization DOFs of a two-photon system simultaneously, by exploiting the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics (QED). This hyper-CNOT gate is implemented by manipulating the four qubits in the two DOFs of a two-photon system without auxiliary spatial modes or polarization modes. It reduces the operation time and the resources consumed in quantum information processing, and it is more robust against the photonic dissipation noise, compared with the integration of several cascaded CNOT gates in one DOF. PMID:24721781

  2. Studies of electron spin in GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Craft, Daniel; Colton, John; Park, Tyler; White, Phil

    2013-03-01

    We have studied electron spins in GaAs quantum dots with a pump-probe technique that normally yields the T1 spin lifetime, the time required for initially polarized electrons to relax and randomize. Using a circularly polarized laser tuned to the wavelength response of the quantum dot we can ``pump'' the spins into alignment. After aligning the spins we can detect them using a second, linearly polarized ``probe'' laser. By changing the delay between the two lasers we can trace out the spin response over time. In contrast with other samples (bulk GaAs and a GaAs quantum well), where the spin response decayed exponentially with time, initial data on the quantum dots has shown an unexpected, oscillating behavior which dies out on the order of 700 ns, independent of both temperature and magnetic field.

  3. Optical control of the emission direction of a quantum dot

    SciTech Connect

    Luxmoore, I. J.; Wasley, N. A.; Fox, A. M.; Skolnick, M. S.; Ramsay, A. J.; Thijssen, A. C. T.; Oulton, R.; Hugues, M.

    2013-12-09

    Using the helicity of a non-resonant excitation laser, control over the emission direction of an InAs/GaAs quantum dot is demonstrated. The quantum dot is located off-center in a crossed-waveguide structure, such that photons of opposite circular polarization are emitted into opposite waveguide directions. By preferentially exciting spin-polarized excitons, the direction of emission can therefore be controlled. The directional control is quantified by using the ratio of the intensity of the light coupled into the two waveguides, which reaches a maximum of ±35%.

  4. Plasmonic quantum dot solar concentrator

    NASA Astrophysics Data System (ADS)

    Chandra, S.; Ahmed, H.; Doran, J.; McCormack, S. J.

    2017-02-01

    The quantum dot solar concentrator optical efficiency is undermined by the parameters of re-absorption, scattering, and escape cone losses. These losses can be address through enhancing quantum dot (QDs) absorption and emission. This have been achieved through plasmonic coupling between QDs and gold nanoparticles (Au NPs). The plasmonic composite of various concertation of QDs and Au NPs were studied. The spacing between QDs and Au NPs is controlled through concentration distribution of both QD and Au NPs in the plasmonic composite, and it showed a significant increase in absorption and which is more pronounced for higher spectral overlap of QDs and surface plasmon resonance (SPR) frequency. The optimum plasmonic coupling showed a 17 % increase in the fluorescence emission for QDs in plasmonic composite. The results have shown significant enhancement in absorption, fluorescence emission for the p-QDSC.

  5. Quantitative multiplexed quantum dot immunohistochemistry

    SciTech Connect

    Sweeney, E.; Ward, T.H.; Gray, N.; Womack, C.; Jayson, G.; Hughes, A.; Dive, C.; Byers, R.

    2008-09-19

    Quantum dots are photostable fluorescent semiconductor nanocrystals possessing wide excitation and bright narrow, symmetrical, emission spectra. These characteristics have engendered considerable interest in their application in multiplex immunohistochemistry for biomarker quantification and co-localisation in clinical samples. Robust quantitation allows biomarker validation, and there is growing need for multiplex staining due to limited quantity of clinical samples. Most reported multiplexed quantum dot staining used sequential methods that are laborious and impractical in a high-throughput setting. Problems associated with sequential multiplex staining have been investigated and a method developed using QDs conjugated to biotinylated primary antibodies, enabling simultaneous multiplex staining with three antibodies. CD34, Cytokeratin 18 and cleaved Caspase 3 were triplexed in tonsillar tissue using an 8 h protocol, each localised to separate cellular compartments. This demonstrates utility of the method for biomarker measurement enabling rapid measurement of multiple co-localised biomarkers on single paraffin tissue sections, of importance for clinical trial studies.

  6. Optophononics with Coupled Quantum Dots

    DTIC Science & Technology

    2014-02-18

    the molecular polaron can be used as an efficient and tunable coherent coupler for quantum states in spatially separated low-dimensional structures...cold finger of a closed cycle microscopy cryostat and kept at a temperature of 20K. A tunable diode laser with a tuning range from about 900 to 1,000...et al. Tunable exciton relaxation in vertically coupled semiconductor InAs quantum dots. Phys. Rev. B 84, 081404(R) (2011). 10 100 1,000 0 5 A m pl ifi

  7. Ultralow Noise Monolithic Quantum Dot Photonic Oscillators

    DTIC Science & Technology

    2013-10-28

    laser, the dual-mode quantum dot laser, and the optically- injected quantum dot distributed feedback laser. The key milestones achieved were: 1.) the...distributed feedback device using optical injection to generate microwave, mm- wave and THz signals, and 5.) the generation of relaxation oscillations over...a continuous 5 octaves (below 1 GHz to 40 GHz) in an optically- injected quantum dot laser. UU N/A N/A N/A 100-200 words 15 Shannon Denetchiley (505

  8. Modeling of the quantum dot filling and the dark current of quantum dot infrared photodetectors

    SciTech Connect

    Ameen, Tarek A.; El-Batawy, Yasser M.; Abouelsaood, A. A.

    2014-02-14

    A generalized drift-diffusion model for the calculation of both the quantum dot filling profile and the dark current of quantum dot infrared photodetectors is proposed. The confined electrons inside the quantum dots produce a space-charge potential barrier between the two contacts, which controls the quantum dot filling and limits the dark current in the device. The results of the model reasonably agree with a published experimental work. It is found that increasing either the doping level or the temperature results in an exponential increase of the dark current. The quantum dot filling turns out to be nonuniform, with a dot near the contacts containing more electrons than one in the middle of the device where the dot occupation approximately equals the number of doping atoms per dot, which means that quantum dots away from contacts will be nearly unoccupied if the active region is undoped.

  9. Bioconjugate recognition molecules to quantum dots as tumor probes.

    PubMed

    Liu, Tian-Cai; Wang, Jian-Hao; Wang, Hai-Qiao; Zhang, Hai-Li; Zhang, Zhi-Hong; Hua, Xiao-Feng; Cao, Yuan-Cheng; Zhao, Yuan-Di; Luo, Qing-Ming

    2007-12-15

    Transferrin and mouse anti-human CD71 monoclonal antibody were respectively conjugated covalently to the core/shell CdSe/ZnS quantum dots with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydrocylsulfo-succinimide (Sulfo-NHS). The conjugation worked well and the bioactivities of these macromolecules still remained, which was verified by column filtration, sodium dodecyl sulfate polyacrylamide gel electrophoresis, absorption spectra, fluorescence spectra, and circular dichroism spectrometry. Thus, these two kinds of quantum dot conjugates were used to recognize the tumor cells involved. In case of pseudo positivity, FITC-labeling secondary antibody IgG was used, and the results showed that as-prepared fluorescent quantum dot bioprobes were highly specific to tumor cells.

  10. Colloidal quantum dots as optoelectronic elements

    NASA Astrophysics Data System (ADS)

    Vasudev, Milana; Yamanaka, Takayuki; Sun, Ke; Li, Yang; Yang, Jianyong; Ramadurai, Dinakar; Stroscio, Michael A.; Dutta, Mitra

    2007-02-01

    Novel optoelectronic systems based on ensembles of semiconductor nanocrystals are addressed in this paper. Colloidal semiconductor quantum dots and related quantum-wire structures have been characterized optically; these optical measurements include those made on self-assembled monolayers of DNA molecules terminated on one end with a common substrate and on the other end with TiO II quantum dots. The electronic properties of these structures are modeled and compared with experiment. The characterization and application of ensembles of colloidal quantum dots with molecular interconnects are considered. The chemically-directed assembly of ensembles of colloidal quantum dots with biomolecular interconnects is demonstrated with quantum dot densities in excess of 10 +17 cm -3. A number of novel photodetectors have been designed based on the combined use of double-barrier quantum-well injectors, colloidal quantum dots, and conductive polymers. Optoelectronic devices including photodetectors and solar cells based on threedimensional ensembles of quantum dots are considered along with underlying phenomena such as miniband formation and the robustness of minibands to displacements of quantum dots in the ensemble.

  11. Few-electron quantum dots

    NASA Astrophysics Data System (ADS)

    Kouwenhoven, L. P.; Austing, D. G.; Tarucha, S.

    2001-06-01

    We review some electron transport experiments on few-electron, vertical quantum dot devices. The measurement of current versus source-drain voltage and gate voltage is used as a spectroscopic tool to investigate the energy characteristics of interacting electrons confined to a small region in a semiconducting material. Three energy scales are distinguished: the single-particle states, which are discrete due to the confinement involved; the direct Coulomb interaction between electron charges on the dot; and the exchange interaction between electrons with parallel spins. To disentangle these energies, a magnetic field is used to reorganize the occupation of electrons over the single-particle states and to induce changes in the spin states. We discuss the interactions between small numbers of electrons (between 1 and 20) using the simplest possible models. Nevertheless, these models consistently describe a large set of experiments. Some of the observations resemble similar phenomena in atomic physics, such as shell structure and periodic table characteristics, Hund's rule, and spin singlet and triplet states. The experimental control, however, is much larger than for atoms: with one device all the artificial elements can be studied by adding electrons to the quantum dot when changing the gate voltage.

  12. The statistical theory of quantum dots

    NASA Astrophysics Data System (ADS)

    Alhassid, Y.

    2000-10-01

    A quantum dot is a sub-micron-scale conducting device containing up to several thousand electrons. Transport through a quantum dot at low temperatures is a quantum-coherent process. This review focuses on dots in which the electron's dynamics are chaotic or diffusive, giving rise to statistical properties that reflect the interplay between one-body chaos, quantum interference, and electron-electron interactions. The conductance through such dots displays mesoscopic fluctuations as a function of gate voltage, magnetic field, and shape deformation. The techniques used to describe these fluctuations include semiclassical methods, random-matrix theory, and the supersymmetric nonlinear σ model. In open dots, the approximation of noninteracting quasiparticles is justified, and electron-electron interactions contribute indirectly through their effect on the dephasing time at finite temperature. In almost-closed dots, where conductance occurs by tunneling, the charge on the dot is quantized, and electron-electron interactions play an important role. Transport is dominated by Coulomb blockade, leading to peaks in the conductance that at low temperatures provide information on the dot's ground-state properties. Several statistical signatures of electron-electron interactions have been identified, most notably in the dot's addition spectrum. The dot's spin, determined partly by exchange interactions, can also influence the fluctuation properties of the conductance. Other mesoscopic phenomena in quantum dots that are affected by the charging energy include the fluctuations of the cotunneling conductance and mesoscopic Coulomb blockade.

  13. Imaging electrostatically confined Dirac fermions in graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Lee, Juwon; Wong, Dillon; Velasco, Jairo, Jr.; Rodriguez-Nieva, Joaquin F.; Kahn, Salman; Tsai, Hsin-Zon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Levitov, Leonid S.; Crommie, Michael F.

    2016-11-01

    Electrostatic confinement of charge carriers in graphene is governed by Klein tunnelling, a relativistic quantum process in which particle-hole transmutation leads to unusual anisotropic transmission at p-n junction boundaries. Reflection and transmission at these boundaries affect the quantum interference of electronic waves, enabling the formation of novel quasi-bound states. Here we report the use of scanning tunnelling microscopy to map the electronic structure of Dirac fermions confined in quantum dots defined by circular graphene p-n junctions. The quantum dots were fabricated using a technique involving local manipulation of defect charge within the insulating substrate beneath a graphene monolayer. Inside such graphene quantum dots we observe resonances due to quasi-bound states and directly visualize the quantum interference patterns arising from these states. Outside the quantum dots Dirac fermions exhibit Friedel oscillation-like behaviour. Bolstered by a theoretical model describing relativistic particles in a harmonic oscillator potential, our findings yield insights into the spatial behaviour of electrostatically confined Dirac fermions.

  14. Photovoltaic Current in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Switkes, M.; Marcus, C. M.; Campman, K.; Gossard, A. C.

    1998-03-01

    We investigate the DC photovoltaic current, I_pv, due to coherent ``pumping'' in open ( g >= e^2/h ) quantum dots with radio-frequency modulation of the confining potential(B. Spivak, F. Zhou, and M. T. Beal Monod, Phys. Rev. B 51), p. 13226 (1995). I_pv is on the order of 20 pA≈ 10ef for a modulation frequency f = 15 MHz. The photovoltaic current exhibits mesoscopic fluctuations with magnetic field and with the static shape of the confining potential which do not appear to be correlated with fluctuations in the conductance of the dot. The photovoltaic current induced by pumping with two independent shape distortion gates depends on their relative phase; the relationship of this phase to time reversal symmetry is investigated with a view toward defining a generalized Landauer-Büttiker relation.

  15. Charge state hysteresis in semiconductor quantum dots

    SciTech Connect

    Yang, C. H.; Rossi, A. Lai, N. S.; Leon, R.; Lim, W. H.; Dzurak, A. S.

    2014-11-03

    Semiconductor quantum dots provide a two-dimensional analogy for real atoms and show promise for the implementation of scalable quantum computers. Here, we investigate the charge configurations in a silicon metal-oxide-semiconductor double quantum dot tunnel coupled to a single reservoir of electrons. By operating the system in the few-electron regime, the stability diagram shows hysteretic tunnelling events that depend on the history of the dots charge occupancy. We present a model which accounts for the observed hysteretic behaviour by extending the established description for transport in double dots coupled to two reservoirs. We demonstrate that this type of device operates like a single-electron memory latch.

  16. A quantum dot in topological insulator nanofilm.

    PubMed

    Herath, Thakshila M; Hewageegana, Prabath; Apalkov, Vadym

    2014-03-19

    We introduce a quantum dot in topological insulator nanofilm as a bump at the surface of the nanofilm. Such a quantum dot can localize an electron if the size of the dot is large enough, ≳5 nm. The quantum dot in topological insulator nanofilm has states of two types, which belong to two ('conduction' and 'valence') bands of the topological insulator nanofilm. We study the energy spectra of such defined quantum dots. We also consider intraband and interband optical transitions within the dot. The optical transitions of the two types have the same selection rules. While the interband absorption spectra have multi-peak structure, each of the intraband spectra has one strong peak and a few weak high frequency satellites.

  17. STED nanoscopy with fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Hanne, Janina; Falk, Henning J.; Görlitz, Frederik; Hoyer, Patrick; Engelhardt, Johann; Sahl, Steffen J.; Hell, Stefan W.

    2015-05-01

    The widely popular class of quantum-dot molecular labels could so far not be utilized as standard fluorescent probes in STED (stimulated emission depletion) nanoscopy. This is because broad quantum-dot excitation spectra extend deeply into the spectral bands used for STED, thus compromising the transient fluorescence silencing required for attaining super-resolution. Here we report the discovery that STED nanoscopy of several red-emitting commercially available quantum dots is in fact successfully realized by the increasingly popular 775 nm STED laser light. A resolution of presently ~50 nm is demonstrated for single quantum dots, and sub-diffraction resolution is further shown for imaging of quantum-dot-labelled vimentin filaments in fibroblasts. The high quantum-dot photostability enables repeated STED recordings with >1,000 frames. In addition, we have evidence that the tendency of quantum-dot labels to blink is largely suppressed by combined action of excitation and STED beams. Quantum-dot STED significantly expands the realm of application of STED nanoscopy, and, given the high stability of these probes, holds promise for extended time-lapse imaging.

  18. Thick-shell nanocrystal quantum dots

    SciTech Connect

    Hollingsworth, Jennifer A; Chen, Yongfen; Klimov, Victor I; Htoon, Han; Vela, Javier

    2011-05-03

    Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1.5 nm and an outer shell, where said outer shell comprises multiple monolayers, wherein at least 30% of the quantum dots have an on-time fraction of 0.80 or greater under continuous excitation conditions for a period of time of at least 10 minutes.

  19. Research on Self-Assembling Quantum Dots.

    DTIC Science & Technology

    1995-10-30

    0K. in a second phase of this contract we turned our efforts to the fabrication and studies of self assembled quantum dots . We first demonstrated a...method for producing InAs-GasAs self assembled quantum dots (SAD) using MBE. (AN)

  20. STED nanoscopy with fluorescent quantum dots.

    PubMed

    Hanne, Janina; Falk, Henning J; Görlitz, Frederik; Hoyer, Patrick; Engelhardt, Johann; Sahl, Steffen J; Hell, Stefan W

    2015-05-18

    The widely popular class of quantum-dot molecular labels could so far not be utilized as standard fluorescent probes in STED (stimulated emission depletion) nanoscopy. This is because broad quantum-dot excitation spectra extend deeply into the spectral bands used for STED, thus compromising the transient fluorescence silencing required for attaining super-resolution. Here we report the discovery that STED nanoscopy of several red-emitting commercially available quantum dots is in fact successfully realized by the increasingly popular 775 nm STED laser light. A resolution of presently ∼ 50 nm is demonstrated for single quantum dots, and sub-diffraction resolution is further shown for imaging of quantum-dot-labelled vimentin filaments in fibroblasts. The high quantum-dot photostability enables repeated STED recordings with >1,000 frames. In addition, we have evidence that the tendency of quantum-dot labels to blink is largely suppressed by combined action of excitation and STED beams. Quantum-dot STED significantly expands the realm of application of STED nanoscopy, and, given the high stability of these probes, holds promise for extended time-lapse imaging.

  1. Excitonic quantum interference in a quantum dot chain with rings.

    PubMed

    Hong, Suc-Kyoung; Nam, Seog Woo; Yeon, Kyu-Hwang

    2008-04-16

    We demonstrate excitonic quantum interference in a closely spaced quantum dot chain with nanorings. In the resonant dipole-dipole interaction model with direct diagonalization method, we have found a peculiar feature that the excitation of specified quantum dots in the chain is completely inhibited, depending on the orientational configuration of the transition dipole moments and specified initial preparation of the excitation. In practice, these excited states facilitating quantum interference can provide a conceptual basis for quantum interference devices of excitonic hopping.

  2. Quantum-dot supercrystals for future nanophotonics

    PubMed Central

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

    2013-01-01

    The study of supercrystals made of periodically arranged semiconductor quantum dots is essential for the advancement of emerging nanophotonics technologies. By combining the strong spatial confinement of elementary excitations inside quantum dots and exceptional design flexibility, quantum-dot supercrystals provide broad opportunities for engineering desired optical responses and developing superior light manipulation techniques on the nanoscale. Here we suggest tailoring the energy spectrum and wave functions of the supercrystals' collective excitations through the variation of different structural and material parameters. In particular, by calculating the excitonic spectra of quantum dots assembled in two-dimensional Bravais lattices we demonstrate a wide variety of spectrum transformation scenarios upon alterations in the quantum dot arrangement. This feature offers unprecedented control over the supercrystal's electromagnetic properties and enables the development of new nanophotonics materials and devices.

  3. Biocompatible Quantum Dots for Biological Applications

    PubMed Central

    Rosenthal, Sandra J.; Chang, Jerry C.; Kovtun, Oleg; McBride, James R.; Tomlinson, Ian D.

    2011-01-01

    Semiconductor quantum dots are quickly becoming a critical diagnostic tool for discerning cellular function at the molecular level. Their high brightness, long-lasting, sizetunable, and narrow luminescence set them apart from conventional fluorescence dyes. Quantum dots are being developed for a variety of biologically oriented applications, including fluorescent assays for drug discovery, disease detection, single protein tracking, and intracellular reporting. This review introduces the science behind quantum dots and describes how they are made biologically compatible. Several applications are also included, illustrating strategies toward target specificity, and are followed by a discussion on the limitations of quantum dot approaches. The article is concluded with a look at the future direction of quantum dots. PMID:21276935

  4. Biocompatible Quantum Dots for Biological Applications

    SciTech Connect

    Rosenthal, Sandra; Chang, Jerry; Kovtun, Oleg; McBride, James; Tomlinson, Ian

    2011-01-01

    Semiconductor quantum dots are quickly becoming a critical diagnostic tool for discerning cellular function at the molecular level. Their high brightness, long-lasting, size-tunable, and narrow luminescence set them apart from conventional fluorescence dyes. Quantum dots are being developed for a variety of biologically oriented applications, including fluorescent assays for drug discovery, disease detection, single protein tracking, and intracellular reporting. This review introduces the science behind quantum dots and describes how they are made biologically compatible. Several applications are also included, illustrating strategies toward target specificity, and are followed by a discussion on the limitations of quantum dot approaches. The article is concluded with a look at the future direction of quantum dots.

  5. Optophononics with coupled quantum dots.

    PubMed

    Kerfoot, Mark L; Govorov, Alexander O; Czarnocki, Cyprian; Lu, Davis; Gad, Youstina N; Bracker, Allan S; Gammon, Daniel; Scheibner, Michael

    2014-01-01

    Modern technology is founded on the intimate understanding of how to utilize and control electrons. Next to electrons, nature uses phonons, quantized vibrations of an elastic structure, to carry energy, momentum and even information through solids. Phonons permeate the crystalline components of modern technology, yet in terms of technological utilization phonons are far from being on par with electrons. Here we demonstrate how phonons can be employed to render a single quantum dot pair optically transparent. This phonon-induced transparency is realized via the formation of a molecular polaron, the result of a Fano-type quantum interference, which proves that we have accomplished making typically incoherent and dissipative phonons behave in a coherent and non-dissipative manner. We find the transparency to be widely tunable by electronic and optical means. Thereby we show amplification of weakest coupling channels. We further outline the molecular polaron's potential as a control element in phononic circuitry architecture.

  6. Tailoring Magnetism in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Zutic, Igor; Abolfath, Ramin; Hawrylak, Pawel

    2007-03-01

    We study magnetism in magnetically doped quantum dots as a function of particle numbers, temperature, confining potential, and the strength of Coulomb interaction screening. We show that magnetism can be tailored by controlling the electron-electron Coulomb interaction, even without changing the number of particles. The interplay of strong Coulomb interactions and quantum confinement leads to enhanced inhomogeneous magnetization which persists at substantially higher temperatures than in the non-interacting case or in the bulk-like dilute magnetic semiconductors. We predict a series of electronic spin transitions which arise from the competition between the many-body gap and magnetic thermal fluctuations. Cond-mat/0612489. [1] R. Abolfath, P. Hawrylak, I. Zuti'c, preprint.

  7. Quantum dot spectroscopy using cavity quantum electrodynamics.

    PubMed

    Winger, Martin; Badolato, Antonio; Hennessy, Kevin J; Hu, Evelyn L; Imamoğlu, Ataç

    2008-11-28

    We show how cavity quantum electrodynamics using a tunable photonic crystal nanocavity in the strong-coupling regime can be used for single quantum dot spectroscopy. From the distinctive avoided crossings observed in the strongly coupled system we can identify the neutral and single positively charged exciton as well as the biexciton transitions. Moreover we are able to investigate the fine structure of those transitions and to identify a novel cavity mediated mixing of bright and dark exciton states, where the hyperfine interactions with lattice nuclei presumably play a key role. These results are enabled by a deterministic coupling scheme which allowed us to achieve unprecedented coupling strengths in excess of 150 microeV.

  8. Coherent optoelectronics with single quantum dots

    NASA Astrophysics Data System (ADS)

    Zrenner, A.; Ester, P.; Michaelis de Vasconcellos, S.; Hübner, M. C.; Lackmann, L.; Stufler, S.; Bichler, M.

    2008-11-01

    The optical properties of semiconductor quantum dots are in many respects similar to those of atoms. Since quantum dots can be defined by state-of-the-art semiconductor technologies, they exhibit long-term stability and allow for well-controlled and efficient interactions with both optical and electrical fields. Resonant ps excitation of single quantum dot photodiodes leads to new classes of coherent optoelectronic functions and devices, which exhibit precise state preparation, phase-sensitive optical manipulations and the control of quantum states by electrical fields.

  9. Quantum dots in aperiodic order

    NASA Astrophysics Data System (ADS)

    Hörnquist, Michael; Ouchterlony, Thomas

    1998-12-01

    We study numerically with a Green-function technique one-dimensional arrays of quantum dots with two different models. The arrays are ordered according to the Fibonacci, the Thue-Morse, and the Rudin-Shapiro sequences. As a comparison, results from a periodically ordered chain and also from a random chain are included. The focus is on how the conductance (calculated within the Landauer-Büttiker formalism) depends on the Fermi level. In the first model, we find that in some cases rather small systems (≈60 dots) behave in the same manner as very large systems (>16,000 dots) and this makes it possible in these cases to interpret our results for the small systems in terms of the spectral properties of the infinite systems. In particular, we find that it is possible to see some consequences of the singular continuous spectra that some of the systems possess, at least for temperatures up to 100 mK. In the second model, we study the phenomenon ohmic addition, i.e. when the resistances of the constrictions add up to the total resistance. It results that of the systems studied, it is only the Rudin-Shapiro system that has this behaviour for large structures, while the resistances of the Fibonacci and the Thue-Morse systems might reach a limiting value (as a periodic system does).

  10. Computational models for the berry phase in semiconductor quantum dots

    SciTech Connect

    Prabhakar, S. Melnik, R. V. N.; Sebetci, A.

    2014-10-06

    By developing a new model and its finite element implementation, we analyze the Berry phase low-dimensional semiconductor nanostructures, focusing on quantum dots (QDs). In particular, we solve the Schrödinger equation and investigate the evolution of the spin dynamics during the adiabatic transport of the QDs in the 2D plane along circular trajectory. Based on this study, we reveal that the Berry phase is highly sensitive to the Rashba and Dresselhaus spin-orbit lengths.

  11. Computational models for the berry phase in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Prabhakar, S.; Melnik, R. V. N.; Sebetci, A.

    2014-10-01

    By developing a new model and its finite element implementation, we analyze the Berry phase low-dimensional semiconductor nanostructures, focusing on quantum dots (QDs). In particular, we solve the Schrödinger equation and investigate the evolution of the spin dynamics during the adiabatic transport of the QDs in the 2D plane along circular trajectory. Based on this study, we reveal that the Berry phase is highly sensitive to the Rashba and Dresselhaus spin-orbit lengths.

  12. Polarization-correlated photons from a positively charged quantum dot

    NASA Astrophysics Data System (ADS)

    Cao, Y.; Bennett, A. J.; Farrer, I.; Ritchie, D. A.; Shields, A. J.

    2015-08-01

    Polarized cross-correlation spectroscopy on a quantum dot charged with a single hole shows the sequential emission of photons with common circular polarization. This effect is visible without magnetic field, but becomes more pronounced as the field along the quantization axis is increased. We interpret the data in terms of electron dephasing in the X+ state caused by the Overhauser field of nuclei in the dot. We predict the correlation time scale can be increased by accelerating the emission rate with cavity QED.

  13. Biodetection using fluorescent quantum dots

    NASA Astrophysics Data System (ADS)

    Speckman, Donna M.; Jennings, Travis L.; LaLumondiere, Steven D.; Klimcak, Charles M.; Moss, Steven C.; Loper, Gary L.; Beck, Steven M.

    2002-07-01

    Multi-pathogen biosensors that take advantage of sandwich immunoassay detection schemes and utilize conventional fluorescent dye reporter molecules are difficult to make into extremely compact and autonomous packages. The development of a multi-pathogen, immunoassay-based, fiber optic detector that utilizes varying sized fluorescent semiconductor quantum dots (QDs) as the reporter labels has the potential to overcome these problems. In order to develop such a quantum dot-based biosensor, it is essential to demonstrate that QDs can be attached to antibody proteins, such that the specificity of the antibody is maintained. We have been involved in efforts to develop a reproducible method for attaching QDs to antibodies for use in biodetection applications. We have synthesized CdSe/ZnS core-shell QDs of differing size, functionalized their surfaces with several types of organic groups for water solubility, and covalently attached these functionalized QDs to rabbit anti-ovalbumin antibody protein. We also demonstrated that these labeled antibodies exhibit selective binding to ovalbumin antigen. We characterized the QDs at each step in the overall synthesis by UV-VIS absorption spectroscopy and by picosecond (psec) transient photoluminescence (TPL) spectroscopy. TPL spectroscopy measurements indicate that QD lifetime depends on the size of the QD, the intensity of the optical excitation source, and whether or not they are functionalized and conjugated to antibodies. We describe details of these experiments and discuss the impact of our results on our biosensor development program.

  14. Magnetization reversal in circular vortex dots of small radius.

    PubMed

    Goiriena-Goikoetxea, M; Guslienko, K Y; Rouco, M; Orue, I; Berganza, E; Jaafar, M; Asenjo, A; Fernández-Gubieda, M L; Fernández Barquín, L; García-Arribas, A

    2017-08-10

    We present a detailed study of the magnetic behavior of Permalloy (Ni80Fe20 alloy) circular nanodots with small radii (30 nm and 70 nm) and different thicknesses (30 nm or 50 nm). Despite the small size of the dots, the measured hysteresis loops manifestly display the features of classical vortex behavior with zero remanence and lobes at high magnetic fields. This is remarkable because the size of the magnetic vortex core is comparable to the dot diameter, as revealed by magnetic force microscopy and micromagnetic simulations. The dot ground states are close to the border of the vortex stability and, depending on the dot size, the magnetization distribution combines attributes of the typical vortex, single domain states or even presents features resembling magnetic skyrmions. An analytical model of the dot magnetization reversal, accounting for the large vortex core size, is developed to explain the observed behavior, providing a rather good agreement with the experimental results. The study extends the understanding of magnetic nanodots beyond the classical vortex concept (where the vortex core spins have a negligible influence on the magnetic behavior) and can therefore be useful for improving emerging spintronic applications, such as spin-torque nano-oscillators. It also delimits the feasibility of producing a well-defined vortex configuration in sub-100 nm dots, enabling the intracellular magneto-mechanical actuation for biomedical applications.

  15. On-chip quantum optics with quantum dot microcavities.

    PubMed

    Stock, E; Albert, F; Hopfmann, C; Lermer, M; Schneider, C; Höfling, S; Forchel, A; Kamp, M; Reitzenstein, S

    2013-02-06

    A novel concept for on-chip quantum optics using an internal electrically pumped microlaser is presented. The microlaser resonantly excites a quantum dot microcavity system operating in the weak coupling regime of cavity quantum electrodynamics. This work presents the first on-chip application of quantum dot microlasers, and also opens up new avenues for the integration of individual microcavity structures into larger photonic networks.

  16. Towards hybrid circuit quantum electrodynamics with quantum dots

    NASA Astrophysics Data System (ADS)

    Viennot, Jérémie J.; Delbecq, Matthieu R.; Bruhat, Laure E.; Dartiailh, Matthieu C.; Desjardins, Matthieu M.; Baillergeau, Matthieu; Cottet, Audrey; Kontos, Takis

    2016-08-01

    Cavity quantum electrodynamics allows one to study the interaction between light and matter at the most elementary level. The methods developed in this field have taught us how to probe and manipulate individual quantum systems like atoms and superconducting quantum bits with an exquisite accuracy. There is now a strong effort to extend further these methods to other quantum systems, and in particular hybrid quantum dot circuits. This could turn out to be instrumental for a noninvasive study of quantum dot circuits and a realization of scalable spin quantum bit architectures. It could also provide an interesting platform for quantum simulation of simple fermion-boson condensed matter systems. In this short review, we discuss the experimental state of the art for hybrid circuit quantum electrodynamics with quantum dots, and we present a simple theoretical modeling of experiments.

  17. Quantum dots with single-atom precision.

    PubMed

    Fölsch, Stefan; Martínez-Blanco, Jesús; Yang, Jianshu; Kanisawa, Kiyoshi; Erwin, Steven C

    2014-07-01

    Quantum dots are often called artificial atoms because, like real atoms, they confine electrons to quantized states with discrete energies. However, although real atoms are identical, most quantum dots comprise hundreds or thousands of atoms, with inevitable variations in size and shape and, consequently, unavoidable variability in their wavefunctions and energies. Electrostatic gates can be used to mitigate these variations by adjusting the electron energy levels, but the more ambitious goal of creating quantum dots with intrinsically digital fidelity by eliminating statistical variations in their size, shape and arrangement remains elusive. We used a scanning tunnelling microscope to create quantum dots with identical, deterministic sizes. By using the lattice of a reconstructed semiconductor surface to fix the position of each atom, we controlled the shape and location of the dots with effectively zero error. This allowed us to construct quantum dot molecules whose coupling has no intrinsic variation but could nonetheless be tuned with arbitrary precision over a wide range. Digital fidelity opens the door to quantum dot architectures free of intrinsic broadening-an important goal for technologies from nanophotonics to quantum information processing as well as for fundamental studies of confined electrons.

  18. Parallel Photonic Quantum Computation Assisted by Quantum Dots in One-Side Optical Microcavities

    PubMed Central

    Luo, Ming-Xing; Wang, Xiaojun

    2014-01-01

    Universal quantum logic gates are important elements for a quantum computer. In contrast to previous constructions on one degree of freedom (DOF) of quantum systems, we investigate the possibility of parallel quantum computations dependent on two DOFs of photon systems. We construct deterministic hyper-controlled-not (hyper-CNOT) gates operating on the spatial-mode and the polarization DOFs of two-photon or one-photon systems by exploring the giant optical circular birefringence induced by quantum-dot spins in one-sided optical microcavities. These hyper-CNOT gates show that the quantum states of two DOFs can be viewed as independent qubits without requiring auxiliary DOFs in theory. This result can reduce the quantum resources by half for quantum applications with large qubit systems, such as the quantum Shor algorithm. PMID:25030424

  19. Fluorescent Quantum Dots for Biological Labeling

    NASA Technical Reports Server (NTRS)

    McDonald, Gene; Nadeau, Jay; Nealson, Kenneth; Storrie-Lomardi, Michael; Bhartia, Rohit

    2003-01-01

    Fluorescent semiconductor quantum dots that can serve as "on/off" labels for bacteria and other living cells are undergoing development. The "on/off" characterization of these quantum dots refers to the fact that, when properly designed and manufactured, they do not fluoresce until and unless they come into contact with viable cells of biological species that one seeks to detect. In comparison with prior fluorescence-based means of detecting biological species, fluorescent quantum dots show promise for greater speed, less complexity, greater sensitivity, and greater selectivity for species of interest. There are numerous potential applications in medicine, environmental monitoring, and detection of bioterrorism.

  20. Clocking an Array of Quantum Dots

    NASA Astrophysics Data System (ADS)

    Khatun, Mahfuza; Mandell, Eric

    2000-10-01

    Preferred Session: Condensed Matter Physics Clocking an Array of Quantum Dots* Eric Mandell and M. Khatun, Ball State University. We report a theoretical analysis of the time-dependent electric field due to a line of charged rods. The effects of both the real and image charge are taken into account. The rods are biased electrostatically to study the dynamical behavior of an array of quantum dots. The barrier heights between the quantum dots are controlled by the electric field. *Supported in part by the Indiana Academy of Science, Center for Energy Research/Education/Services(CERES) and the Office of Academic Research and Sponsored Programs, Ball State University.

  1. Electronic properties of aperiodic quantum dot chains

    NASA Astrophysics Data System (ADS)

    Korotaev, P. Yu.; Vekilov, Yu. Kh.; Kaputkina, N. E.

    2012-04-01

    The electronic spectral and transport properties of aperiodic quantum dot chains are investigated. The systems with singular continuous energy spectrum are considered: Thue-Morse chain, double-periodic chain, Rudin-Shapiro chain. The influence of electronic energy in quantum dot on the spectral properties, band structure, density of states and spectral resistivity, is discussed. Low resistivity regions correspond to delocalized states and these states could be current states. Also we discuss the magnetic field application as the way to tune electronic energy in quantum dot and to obtain metallic or insulating conducting states of the systems.

  2. Quantum dot-based theranostics

    NASA Astrophysics Data System (ADS)

    Ho, Yi-Ping; Leong, Kam W.

    2010-01-01

    Luminescent semiconductor nanocrystals, also known as quantum dots (QDs), have advanced the fields of molecular diagnostics and nanotherapeutics. Much of the initial progress for QDs in biology and medicine has focused on developing new biosensing formats to push the limit of detection sensitivity. Nevertheless, QDs can be more than passive bio-probes or labels for biological imaging and cellular studies. The high surface-to-volume ratio of QDs enables the construction of a ``smart'' multifunctional nanoplatform, where the QDs serve not only as an imaging agent but also a nanoscaffold catering for therapeutic and diagnostic (theranostic) modalities. This mini review highlights the emerging applications of functionalized QDs as fluorescence contrast agents for imaging or as nanoscale vehicles for delivery of therapeutics, with special attention paid to the promise and challenges towards QD-based theranostics.

  3. Entangled exciton states in quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Bayer, Manfred

    2002-03-01

    Currently there is strong interest in quantum information processing(See, for example, The Physics of Quantum Information, eds. D. Bouwmeester, A. Ekert and A. Zeilinger (Springer, Berlin, 2000).) in a solid state environment. Many approaches mimic atomic physics concepts in which semiconductor quantum dots are implemented as artificial atoms. An essential building block of a quantum processor is a gate which entangles the states of two quantum bits. Recently a pair of vertically aligned quantum dots has been suggested as optically driven quantum gate(P. Hawrylak, S. Fafard, and Z. R. Wasilewski, Cond. Matter News 7, 16 (1999).)(M. Bayer, P. Hawrylak, K. Hinzer, S. Fafard, M. Korkusinski, Z.R. Wasilewski, O. Stern, and A. Forchel, Science 291, 451 (2001).): The quantum bits are individual carriers either on dot zero or dot one. The different dot indices play the same role as a "spin", therefore we call them "isospin". Quantum mechanical tunneling between the dots rotates the isospin and leads to superposition of these states. The quantum gate is built when two different particles, an electron and a hole, are created optically. The two particles form entangled isospin states. Here we present spectrocsopic studies of single self-assembled InAs/GaAs quantum dot molecules that support the feasibility of this proposal. The evolution of the excitonic recombination spectrum with varying separation between the dots allows us to demonstrate coherent tunneling of carriers across the separating barrier and the formation of entangled exciton states: Due to the coupling between the dots the exciton states show a splitting that increases with decreasing barrier width. For barrier widths below 5 nm it exceeds the thermal energy at room temperature. For a given barrier width, we find only small variations of the tunneling induced splitting demonstrating a good homogeneity within a molecule ensemble. The entanglement may be controlled by application of electromagnetic field. For

  4. Single to quadruple quantum dots with tunable tunnel couplings

    SciTech Connect

    Takakura, T.; Noiri, A.; Obata, T.; Yoneda, J.; Yoshida, K.; Otsuka, T.; Tarucha, S.

    2014-03-17

    We prepare a gate-defined quadruple quantum dot to study the gate-tunability of single to quadruple quantum dots with finite inter-dot tunnel couplings. The measured charging energies of various double dots suggest that the dot size is governed by the gate geometry. For the triple and quadruple dots, we study the gate-tunable inter-dot tunnel couplings. For the triple dot, we find that the effective tunnel coupling between side dots significantly depends on the alignment of the center dot potential. These results imply that the present quadruple dot has a gate performance relevant for implementing spin-based four-qubits with controllable exchange couplings.

  5. Quantum repeaters using orbitals in quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Ohshima, Toshio

    2016-09-01

    We propose quantum repeaters using quantum dot molecules, in which matter-photon entanglement is generated by Raman scatterings in lambda systems composed of various coherent exciton levels formed in the ensembles of asymmetric coupled quantum dots. In our scheme, the wavelength of Stokes and anti-Stokes photons can be chosen to fulfill the requirements of optical fiber communication. Further, the relative superposition phase in the entangled states can be stabilized by the active feedback to the gate voltage in quantum dot system. These characteristics are favorable for implementing our scheme in practice.

  6. Quantum Dots Investigated for Solar Cells

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Castro, Stephanie L.; Raffaelle, Ryne P.; Hepp, Aloysius F.

    2001-01-01

    The NASA Glenn Research Center has been investigating the synthesis of quantum dots of CdSe and CuInS2 for use in intermediate-bandgap solar cells. Using quantum dots in a solar cell to create an intermediate band will allow the harvesting of a much larger portion of the available solar spectrum. Theoretical studies predict a potential efficiency of 63.2 percent, which is approximately a factor of 2 better than any state-of-the-art devices available today. This technology is also applicable to thin-film devices--where it offers a potential four-fold increase in power-to-weight ratio over the state of the art. Intermediate-bandgap solar cells require that quantum dots be sandwiched in an intrinsic region between the photovoltaic solar cell's ordinary p- and n-type regions (see the preceding figure). The quantum dots form the intermediate band of discrete states that allow sub-bandgap energies to be absorbed. However, when the current is extracted, it is limited by the bandgap, not the individual photon energies. The energy states of the quantum dot can be controlled by controlling the size of the dot. Ironically, the ground-state energy levels are inversely proportional to the size of the quantum dots. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Ba Wendi et al., in the early 1990's. The most studied quantum dots prepared by this method have been of CdSe. To produce these dots, researchers inject a syringe of the desired organometallic precursors into heated triocytlphosphine oxide (TOPO) that has been vigorously stirred under an inert atmosphere (see the following figure). The solution immediately begins to change from colorless to yellow, then orange and red/brown, as the quantum dots increase in size. When the desired size is reached, the heat is removed from the flask. Quantum dots of different sizes can be identified by placing them under a "black light" and observing the various color differences in

  7. Synthetic Developments of Nontoxic Quantum Dots.

    PubMed

    Das, Adita; Snee, Preston T

    2016-03-03

    Semiconductor nanocrystals, or quantum dots (QDs), are candidates for biological sensing, photovoltaics, and catalysis due to their unique photophysical properties. The most studied QDs are composed of heavy metals like cadmium and lead. However, this engenders concerns over heavy metal toxicity. To address this issue, numerous studies have explored the development of nontoxic (or more accurately less toxic) quantum dots. In this Review, we select three major classes of nontoxic quantum dots composed of carbon, silicon and Group I-III-VI elements and discuss the myriad of synthetic strategies and surface modification methods to synthesize quantum dots composed of these material systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Spin Dynamics of Charged Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Stern, N. P.

    2005-03-01

    Colloidal semiconductor quantum dots are promising structures for controlling spin phenomena because of their highly size- tunable physical properties, ease of manufacture, and nanosecond-scale spin lifetimes at room temperature. Recent experiments have succeeded in controlling the charging of the lowest electronic state of colloidal quantum dots ootnotetextC. Wang, B. L. Wehrenberg, C. Y. Woo, and P. Guyot-Sionnest, J. Phys. Chem B 108, 9027 (2004).. Here we use time-resolved Faraday rotation measurements in the Voigt geometry to investigate the spin dynamics of colloidal CdSe quantum dot films in both a charged and uncharged state at room temperature. The charging of the film is controlled by applying a voltage in an electrochemical cell and is confirmed by absorbance measurements. Significant changes in the spin precession are observed upon charging, reflecting the voltage- controlled electron occupation of the quantum dot states and filling of surface states.

  9. Teleportation on a quantum dot array.

    PubMed

    de Pasquale, F; Giorgi, G; Paganelli, S

    2004-09-17

    We present a model of quantum teleportation protocol based on a double quantum dot array. The unknown qubit is encoded using a pair of quantum dots, with one excess electron, coupled by tunneling. It is shown how to create a maximally entangled state using an adiabatically increasing Coulomb repulsion between different dot pairs. This entangled state is exploited to perform teleportation again using an adiabatic coupling between itself and the incoming unknown state. Finally, a sudden separation of Bob's qubit allows a time evolution of Alice's, which amounts to a modified version of standard Bell measurement. A transmission over a long distance could be obtained by considering the entangled state of a chain of N coupled double quantum dots. The system is shown to be increasingly robust with N against decoherence due to phonons.

  10. Nanomaterials: Earthworms lit with quantum dots

    NASA Astrophysics Data System (ADS)

    Tilley, Richard D.; Cheong, Soshan

    2013-01-01

    Yeast, bacteria and fungi have been used to synthesize a variety of nanocrystals. Now, the metal detoxification process in the gut of an earthworm is exploited to produce biocompatible cadmium telluride quantum dots.

  11. Noninvasive detection of charge rearrangement in a quantum dot

    NASA Astrophysics Data System (ADS)

    Fricke, C.; Rogge, M. C.; Harke, B.; Reinwald, M.; Wegscheider, W.; Hohls, F.; Haug, R. J.

    2007-04-01

    We demonstrate new results on electron redistribution on a single quantum dot caused by magnetic field. A quantum point contact is used to detect changes in the quantum dot charge. We are able to measure both the change of the quantum dot charge and also changes of the electron configuration at constant number of electrons on the quantum dot. These features are used to exploit the quantum dot in a high magnetic field where transport through the quantum dot displays the effects of Landau shells and spin blockade.

  12. First principle thousand atom quantum dot calculations

    SciTech Connect

    Wang, Lin-Wang; Li, Jingbo

    2004-03-30

    A charge patching method and an idealized surface passivation are used to calculate the single electronic states of IV-IV, III-V, II-VI semiconductor quantum dots up to a thousand atoms. This approach scales linearly and has a 1000 fold speed-up compared to direct first principle methods with a cost of eigen energy error of about 20 meV. The calculated quantum dot band gaps are parametrized for future references.

  13. Renormalization in Periodically Driven Quantum Dots.

    PubMed

    Eissing, A K; Meden, V; Kennes, D M

    2016-01-15

    We report on strong renormalization encountered in periodically driven interacting quantum dots in the nonadiabatic regime. Correlations between lead and dot electrons enhance or suppress the amplitude of driving depending on the sign of the interaction. Employing a newly developed flexible renormalization-group-based approach for periodic driving to an interacting resonant level we show analytically that the magnitude of this effect follows a power law. Our setup can act as a non-Markovian, single-parameter quantum pump.

  14. Submonolayer Quantum Dot Infrared Photodetector

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  15. Quantum dots as biophotonics tools.

    PubMed

    Cesar, Carlos L

    2014-01-01

    This chapter provides a short review of quantum dots (QDs) physics, applications, and perspectives. The main advantage of QDs over bulk semiconductors is the fact that the size became a control parameter to tailor the optical properties of new materials. Size changes the confinement energy which alters the optical properties of the material, such as absorption, refractive index, and emission bands. Therefore, by using QDs one can make several kinds of optical devices. One of these devices transforms electrons into photons to apply them as active optical components in illumination and displays. Other devices enable the transformation of photons into electrons to produce QDs solar cells or photodetectors. At the biomedical interface, the application of QDs, which is the most important aspect in this book, is based on fluorescence, which essentially transforms photons into photons of different wavelengths. This chapter introduces important parameters for QDs' biophotonic applications such as photostability, excitation and emission profiles, and quantum efficiency. We also present the perspectives for the use of QDs in fluorescence lifetime imaging (FLIM) and Förster resonance energy transfer (FRET), so useful in modern microscopy, and how to take advantage of the usually unwanted blinking effect to perform super-resolution microscopy.

  16. Positioning of quantum dots on metallic nanostructures.

    PubMed

    Kramer, R K; Pholchai, N; Sorger, V J; Yim, T J; Oulton, R; Zhang, X

    2010-04-09

    The capability to position individual emitters, such as quantum dots, near metallic nanostructures is highly desirable for constructing active optical devices that can manipulate light at the single photon level. The emergence of the field of plasmonics as a means to confine light now introduces a need for high precision and reliability in positioning any source of emission, which has thus far been elusive. Placing an emission source within the influence of plasmonic structures now requires accuracy approaching molecular length scales. In this paper we report the ability to reliably position nanoscale functional objects, specifically quantum dots, with sub-100-nm accuracy, which is several times smaller than the diffraction limit of a quantum dot's emission light. Electron beam lithography-defined masks on metallic surfaces and a series of surface chemical functionalization processes allow the programmed assembly of DNA-linked colloidal quantum dots. The quantum dots are successfully functionalized to areas as small as (100 nm)(2) using the specific binding of thiolated DNA to Au/Ag, and exploiting the streptavidin-biotin interaction. An analysis of the reproducibility of the process for various pattern sizes shows that this technique is potentially scalable to the single quantum dot level with 50 nm accuracy accompanied by a moderate reduction in yield.

  17. Positioning of quantum dots on metallic nanostructures

    NASA Astrophysics Data System (ADS)

    Kramer, R. K.; Pholchai, N.; Sorger, V. J.; Yim, T. J.; Oulton, R.; Zhang, X.

    2010-04-01

    The capability to position individual emitters, such as quantum dots, near metallic nanostructures is highly desirable for constructing active optical devices that can manipulate light at the single photon level. The emergence of the field of plasmonics as a means to confine light now introduces a need for high precision and reliability in positioning any source of emission, which has thus far been elusive. Placing an emission source within the influence of plasmonic structures now requires accuracy approaching molecular length scales. In this paper we report the ability to reliably position nanoscale functional objects, specifically quantum dots, with sub-100-nm accuracy, which is several times smaller than the diffraction limit of a quantum dot's emission light. Electron beam lithography-defined masks on metallic surfaces and a series of surface chemical functionalization processes allow the programmed assembly of DNA-linked colloidal quantum dots. The quantum dots are successfully functionalized to areas as small as (100 nm)2 using the specific binding of thiolated DNA to Au/Ag, and exploiting the streptavidin-biotin interaction. An analysis of the reproducibility of the process for various pattern sizes shows that this technique is potentially scalable to the single quantum dot level with 50 nm accuracy accompanied by a moderate reduction in yield.

  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. Delivering quantum dots to cells: bioconjugated quantum dots for targeted and nonspecific extracellular and intracellular imaging.

    PubMed

    Biju, Vasudevanpillai; Itoh, Tamitake; Ishikawa, Mitsuru

    2010-08-01

    Bioconjugated nanomaterials offer endless opportunities to advance both nanobiotechnology and biomedical technology. In this regard, semiconductor nanoparticles, also called quantum dots, are of particular interest for multimodal, multifunctional and multiplexed imaging of biomolecules, cells, tissues and animals. The unique optical properties, such as size-dependent tunable absorption and emission in the visible and NIR regions, narrow emission and broad absorption bands, high photoluminescence quantum yields, large one- and multi-photon absorption cross-sections, and exceptional photostability are the advantages of quantum dots. Multimodal imaging probes are developed by interfacing the unique optical properties of quantum dots with magnetic or radioactive materials. Besides, crystalline structure of quantum dots adds scope for high-contrast X-ray and TEM imaging. Yet another unique feature of a quantum dot is its spacious and flexible surface which is promising to integrate multiple ligands and antibodies and construct multi-functional probes for bioimaging. In this critical review, we will summarize recent advancements in the preparation of biocompatible quantum dots, bioconjugation of quantum dots, and applications of quantum dots and their bioconjugates for targeted and nonspecific imaging of extracellular and intracellular proteins, organelles and functions (181 references).

  20. Zeeman transitions in spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Yakar, Y.; ćakır, B.; Yılmazer, F.; Özmen, A.

    2017-02-01

    In this study, the effects of external magnetic field on the energy states of a spherical quantum dot with infinite potential barrier have been investigated by using Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) method. Linear Zeeman states and Zeeman transition energies are calculated as a function of dot radius and magnetic field strength. We also carry out the effect of external magnetic field on the ground state binding energy. The results show that the impurity energy states, binding energy and Zeeman transition energies are strongly affected by magnetic field strength and dot radius.

  1. Computation of relative numerosity of circular dot textures.

    PubMed

    Raphael, Sabine; Dillenburger, Barbara; Morgan, Michael

    2013-02-12

    To find out whether there are separate visual mechanisms for size, density, and numerosity computation in textures, we investigated the ability of human observers both to discriminate differences in numerosity between approximately circular textures and to decide whether the differences were due to a change in circle size or dot density. The standard texture always contained 64 irregularly spaced fuzzy dots of random contrast polarity. Dots were added or subtracted from the test pattern either by changing the dot density with the pattern size constant or the pattern size with density constant. Observers had to decide whether size or density had changed and whether the change was an increase or a decrease (mixed task condition). In a separate condition, they reported differences in numerosity (numerosity condition). Numerosity changes were more accurately reported when they were correlated with changes in size than with changes in density, arguing against a single mechanism for numerosity. Observers showed a bias toward reporting larger patterns as denser and vice versa. The data were consistent with a mechanism in which observers compute numerosity from size and density signals and decide whether size or density had changed by the signal detection theory MAX rule after transforming signals into z-values. Because thresholds were not significantly lower in the numerosity condition than in the mixed task condition, we conclude that the direct numerosity mechanism, if it exists, must be noisier than the mechanisms that respond to changes in size and density.

  2. Metamorphic quantum dots: Quite different nanostructures

    SciTech Connect

    Seravalli, L.; Frigeri, P.; Nasi, L.; Trevisi, G.; Bocchi, C.

    2010-09-15

    In this work, we present a study of InAs quantum dots deposited on InGaAs metamorphic buffers by molecular beam epitaxy. By comparing morphological, structural, and optical properties of such nanostructures with those of InAs/GaAs quantum dot ones, we were able to evidence characteristics that are typical of metamorphic InAs/InGaAs structures. The more relevant are: the cross-hatched InGaAs surface overgrown by dots, the change in critical coverages for island nucleation and ripening, the nucleation of new defects in the capping layers, and the redshift in the emission energy. The discussion on experimental results allowed us to conclude that metamorphic InAs/InGaAs quantum dots are rather different nanostructures, where attention must be put to some issues not present in InAs/GaAs structures, namely, buffer-related defects, surface morphology, different dislocation mobility, and stacking fault energies. On the other hand, we show that metamorphic quantum dot nanostructures can provide new possibilities of tailoring various properties, such as dot positioning and emission energy, that could be very useful for innovative dot-based devices.

  3. Imaging Quantum Confinement in Multiple Graphene Quantum Dots

    NASA Astrophysics Data System (ADS)

    Wong, Dillon; Velasco, Jairo; Lee, Juwon; Rodriguez-Nieva, Joaquin; Kahn, Salman; Vo, Phong; Tsai, Hsinzon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Levitov, Leonid; Crommie, Michael

    Quantum dots provide a useful means for controlling the electronic and spin degrees of freedom of mesoscale and nanoscale materials. Here we demonstrate a new method for fabricating interacting graphene quantum dots that is compatible with electrostatic gating and visualization by way of scanning tunneling microscopy (STM). Using this new technique we have created and spatially characterized systems of two or more interacting quantum dots. Our results show that it is possible to engineer electronic wave functions in graphene with a high degree of spatial control.

  4. Advancements in the Field of Quantum Dots

    NASA Astrophysics Data System (ADS)

    Mishra, Sambeet; Tripathy, Pratyasha; Sinha, Swami Prasad.

    2012-08-01

    Quantum dots are defined as very small semiconductor crystals of size varying from nanometer scale to a few micron i.e. so small that they are considered dimensionless and are capable of showing many chemical properties by virtue of which they tend to be lead at one minute and gold at the second minute.Quantum dots house the electrons just the way the electrons would have been present in an atom, by applying a voltage. And therefore they are very judiciously given the name of being called as the artificial atoms. This application of voltage may also lead to the modification of the chemical nature of the material anytime it is desired, resulting in lead at one minute to gold at the other minute. But this method is quite beyond our reach. A quantum dot is basically a semiconductor of very tiny size and this special phenomenon of quantum dot, causes the band of energies to change into discrete energy levels. Band gaps and the related energy depend on the relationship between the size of the crystal and the exciton radius. The height and energy between different energy levels varies inversely with the size of the quantum dot. The smaller the quantum dot, the higher is the energy possessed by it.There are many applications of the quantum dots e.g. they are very wisely applied to:Light emitting diodes: LEDs eg. White LEDs, Photovoltaic devices: solar cells, Memory elements, Biology : =biosensors, imaging, Lasers, Quantum computation, Flat-panel displays, Photodetectors, Life sciences and so on and so forth.The nanometer sized particles are able to display any chosen colour in the entire ultraviolet visible spectrum through a small change in their size or composition.

  5. Quantum dots as active material for quantum cascade lasers: comparison to quantum wells

    NASA Astrophysics Data System (ADS)

    Michael, Stephan; Chow, Weng W.; Schneider, Hans Christian

    2016-03-01

    We review a microscopic laser theory for quantum dots as active material for quantum cascade lasers, in which carrier collisions are treated at the level of quantum kinetic equations. The computed characteristics of such a quantum-dot active material are compared to a state-of-the-art quantum-well quantum cascade laser. We find that the current requirement to achieve a comparable gain-length product is reduced compared to that of the quantum-well quantum cascade laser.

  6. Luminescent Quantum Dots as Ultrasensitive Biological Labels

    NASA Astrophysics Data System (ADS)

    Nie, Shuming

    2000-03-01

    Highly luminescent semiconductor quantum dots have been covalently coupled to biological molecules for use in ultrasensitive biological detection. This new class of luminescent labels is considerably brighter and more resistant againt photobleaching in comparison with organic dyes. Quantum dots labeled with the protein transferrin undergo receptor-mediated endocytosis (RME) in cultured HeLa cells, and those dots that were conjugated to immunomolecules recognize specific antibodies or antigens. In addition, we show that DNA functionalized quantum dots can be used to target specific genes by hybridization. We expect that quantum dot bioconjugates will have a broad range of biological applications, such as ligand-receptor interactions, real-time monitoring of molecular trafficking inside living cells, multicolor fluorescence in-situ hybridization (FISH), high-sensitivity detection in miniaturized devices (e.g., DNA chips), and fluorescent tagging of combinatorial chemical libraries. A potential clinical application is the use of quantum dots for ultrasensitive viral RNA detection, in which as low as 100 copies of hepatitis C and HIV viruses per ml blood should be detected.

  7. Quantum-dot-in-perovskite solids.

    PubMed

    Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Walters, Grant; Fan, Fengjia; Voznyy, Oleksandr; Yassitepe, Emre; Buin, Andrei; Hoogland, Sjoerd; Sargent, Edward H

    2015-07-16

    Heteroepitaxy-atomically aligned growth of a crystalline film atop a different crystalline substrate-is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned 'dots-in-a-matrix' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

  8. (In,Mn)As multilayer quantum dot structures

    SciTech Connect

    Bouravleuv, Alexei; Sapega, Victor; Nevedomskii, Vladimir; Khrebtov, Artem; Samsonenko, Yuriy; Cirlin, George

    2014-12-08

    (In,Mn)As multilayer quantum dots structures were grown by molecular beam epitaxy using a Mn selective doping of the central parts of quantum dots. The study of the structural and magneto-optical properties of the samples with three and five layers of (In,Mn)As quantum dots has shown that during the quantum dots assembly, the out-diffusion of Mn from the layers with (In,Mn)As quantum dots can occur resulting in the formation of the extended defects. To produce a high quality structures using the elaborated technique of selective doping, the number of (In,Mn)As quantum dot layers should not exceed three.

  9. Quantum analysis of plasmonic coupling between quantum dots and nanoparticles

    NASA Astrophysics Data System (ADS)

    Ahmad, SalmanOgli

    2016-10-01

    In this study, interaction between core-shells nanoparticles and quantum dots is discussed via the full-quantum-theory method. The electromagnetic field of the nanoparticles is derived by the quasistatic approximation method and the results for different regions of the nanoparticles are quantized from the time-harmonic to the wave equation. Utilizing the optical field quantization, the nanoparticles' and quantum dots' deriving amplitudes contributing to the excitation waves are determined. In the current model, two counterpropagating waves with two different frequencies are applied. We derived the Maxwell-Bloch equations from the Heisenberg-Langevin equations; thus the nanoparticles-quantum dots interaction is perused. Moreover, by full quantum analyzing of the analytical expression, the quantum-plasmonic coupling relation and the Purcell factor are achieved. We show that the spontaneous emission of quantum dots can be dramatically manipulated by engineering the plasmon-plasmon interaction in the core-shells nanoparticles. This issue is a very attractive point for designing a wide variety of quantum-plasmonic sensors. Through the investigation of the nanoparticle plasmonic interaction effects on absorbed power, the results show that the nanoparticles' and quantum dots' absorption saturation state can be switched to each other just by manipulation of their deriving amplitudes. In fact, we manage the interference between the two waves' deriving amplitudes just by the plasmonic interactions effect.

  10. Electromechanical transition in quantum dots

    NASA Astrophysics Data System (ADS)

    Micchi, G.; Avriller, R.; Pistolesi, F.

    2016-09-01

    The strong coupling between electronic transport in a single-level quantum dot and a capacitively coupled nanomechanical oscillator may lead to a transition towards a mechanically bistable and blocked-current state. Its observation is at reach in carbon-nanotube state-of-art experiments. In a recent publication [Phys. Rev. Lett. 115, 206802 (2015), 10.1103/PhysRevLett.115.206802] we have shown that this transition is characterized by pronounced signatures on the oscillator mechanical properties: the susceptibility, the displacement fluctuation spectrum, and the ring-down time. These properties are extracted from transport measurements, however the relation between the mechanical quantities and the electronic signal is not always straightforward. Moreover the dependence of the same quantities on temperature, bias or gate voltage, and external dissipation has not been studied. The purpose of this paper is to fill this gap and provide a detailed description of the transition. Specifically we find (i) the relation between the current-noise and the displacement spectrum; (ii) the peculiar behavior of the gate-voltage dependence of these spectra at the transition; (iii) the robustness of the transition towards the effect of external fluctuations and dissipation.

  11. Origins and optimization of entanglement in plasmonically coupled quantum dots

    SciTech Connect

    Otten, Matthew; Larson, Jeffrey; Min, Misun; Wild, Stefan M.; Pelton, Matthew; Gray, Stephen K.

    2016-08-11

    In this paper, a system of two or more quantum dots interacting with a dissipative plasmonic nanostructure is investigated in detail by using a cavity quantum electrodynamics approach with a model Hamiltonian. We focus on determining and understanding system configurations that generate multiple bipartite quantum entanglements between the occupation states of the quantum dots. These configurations include allowing for the quantum dots to be asymmetrically coupled to the plasmonic system. Analytical solution of a simplified limit for an arbitrary number of quantum dots and numerical simulations and optimization for the two- and three-dot cases are used to develop guidelines for maximizing the bipartite entanglements. For any number of quantum dots, we show that through simple starting states and parameter guidelines, one quantum dot can be made to share a strong amount of bipartite entanglement with all other quantum dots in the system, while entangling all other pairs to a lesser degree.

  12. Origins and optimization of entanglement in plasmonically coupled quantum dots

    DOE PAGES

    Otten, Matthew; Larson, Jeffrey; Min, Misun; ...

    2016-08-11

    In this paper, a system of two or more quantum dots interacting with a dissipative plasmonic nanostructure is investigated in detail by using a cavity quantum electrodynamics approach with a model Hamiltonian. We focus on determining and understanding system configurations that generate multiple bipartite quantum entanglements between the occupation states of the quantum dots. These configurations include allowing for the quantum dots to be asymmetrically coupled to the plasmonic system. Analytical solution of a simplified limit for an arbitrary number of quantum dots and numerical simulations and optimization for the two- and three-dot cases are used to develop guidelines formore » maximizing the bipartite entanglements. For any number of quantum dots, we show that through simple starting states and parameter guidelines, one quantum dot can be made to share a strong amount of bipartite entanglement with all other quantum dots in the system, while entangling all other pairs to a lesser degree.« less

  13. Origins and optimization of entanglement in plasmonically coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Otten, Matthew; Larson, Jeffrey; Min, Misun; Wild, Stefan M.; Pelton, Matthew; Gray, Stephen K.

    2016-08-01

    A system of two or more quantum dots interacting with a dissipative plasmonic nanostructure is investigated in detail by using a cavity quantum electrodynamics approach with a model Hamiltonian. We focus on determining and understanding system configurations that generate multiple bipartite quantum entanglements between the occupation states of the quantum dots. These configurations include allowing for the quantum dots to be asymmetrically coupled to the plasmonic system. Analytical solution of a simplified limit for an arbitrary number of quantum dots and numerical simulations and optimization for the two- and three-dot cases are used to develop guidelines for maximizing the bipartite entanglements. For any number of quantum dots, we show that through simple starting states and parameter guidelines, one quantum dot can be made to share a strong amount of bipartite entanglement with all other quantum dots in the system, while entangling all other pairs to a lesser degree.

  14. Quantum dots for light emitting diodes.

    PubMed

    Qasim, Khan; Lei, Wei; Li, Qing

    2013-05-01

    In this article we discuss the development and key advantages of quantum dot based light emitting diode (QD-LED) and other applications based on their color purity, stability, and solution processibility. Analysis of quantum dot based LEDs and the main challenges faced in this field, such as the QD luminescence quenching, QD charging in thin films, and external quantum efficiency are discussed in detail. The description about how different optical down-conversion and structures enabled researchers to overcome these challenges and to commercialize the products. The recent developments about how to overcome these difficulties have also been discussed in this article.

  15. Patterned semiconductor inverted quantum dot photonic devices

    NASA Astrophysics Data System (ADS)

    Coleman, J. J.

    2016-03-01

    A novel inverted quantum dot structure is presented, which consists of an InGaAs quantum well that has been periodically perforated and then filled with the higher bandgap GaAs barrier material. This structure exhibits a unique quantized energy structure something like a planar atomic bond structure and formation of allowed and forbidden energy bands instead of highly localized, fully discrete states. We describe the growth, processing and characteristics of inverted quantum dot structures and outline interesting and potentially important effects arising from the introduction of nanoscale features (<50 nm) in the active medium.

  16. Quantum Dots: Fundamentals, Applications, and Frontiers

    NASA Astrophysics Data System (ADS)

    Joyce, Bruce A.; Kelires, Pantelis C.; Naumovets, Anton G.; Vvedensky, Dimitri D.

    This volume contains papers delivered at a NATO Advanced Research Workshop and provides a broad introduction to all major aspects of quantum dot structures. Such structures have been produced for studies of basic physical phenomena, for device fabrication and, on a more speculative level, have been suggested as components of a solid-state realization of a quantum computer. The book is structured so that the reader is introduced to the methods used to produce and control quantum dots, followed by discussions of their structural, electronic, and optical properties.

  17. Dot-in-Well Quantum-Dot Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath; Bandara, Sumith; Ting, David; Hill, cory; Liu, John; Mumolo, Jason; Chang, Yia Chung

    2008-01-01

    Dot-in-well (DWELL) quantum-dot infrared photodetectors (QDIPs) [DWELL-QDIPs] are subjects of research as potentially superior alternatives to prior QDIPs. Heretofore, there has not existed a reliable method for fabricating quantum dots (QDs) having precise, repeatable dimensions. This lack has constituted an obstacle to the development of uniform, high-performance, wavelength-tailorable QDIPs and of focal-plane arrays (FPAs) of such QDIPs. However, techniques for fabricating quantum-well infrared photodetectors (QWIPs) having multiple-quantum- well (MQW) structures are now well established. In the present research on DWELL-QDIPs, the arts of fabrication of QDs and QWIPs are combined with a view toward overcoming the deficiencies of prior QDIPs. The longer-term goal is to develop focal-plane arrays of radiationhard, highly uniform arrays of QDIPs that would exhibit high performance at wavelengths from 8 to 15 m when operated at temperatures between 150 and 200 K. Increasing quantum efficiency is the key to the development of competitive QDIP-based FPAs. Quantum efficiency can be increased by increasing the density of QDs and by enhancing infrared absorption in QD-containing material. QDIPs demonstrated thus far have consisted, variously, of InAs islands on GaAs or InAs islands in InGaAs/GaAs wells. These QDIPs have exhibited low quantum efficiencies because the numbers of QD layers (and, hence, the areal densities of QDs) have been small typically five layers in each QDIP. The number of QD layers in such a device must be thus limited to prevent the aggregation of strain in the InAs/InGaAs/GaAs non-lattice- matched material system. The approach being followed in the DWELL-QDIP research is to embed In- GaAs QDs in GaAs/AlGaAs multi-quantum- well (MQW) structures (see figure). This material system can accommodate a large number of QD layers without excessive lattice-mismatch strain and the associated degradation of photodetection properties. Hence, this material

  18. Theoretical issues in silicon quantum dot qubits

    NASA Astrophysics Data System (ADS)

    Koh, Teck Seng

    Electrically-gated quantum dots in semiconductors is an excellent architecture on which to make qubits for quantum information processing. Silicon is attractive because of the potential for excellent manipulability, scalability, and for integration with classical electronics. This thesis describes several aspects of the theoretical issues related to quantum dot qubits in silicon. It may be broadly divided into three parts — (1) the hybrid qubit and quantum gates, (2) decoherence and (3) charge transport. In the first part, we present a novel architecture for a double quantum dot spin qubit, which we term the hybrid qubit, and demonstrate that implementing this qubit in silicon is feasible. Next, we consider both AC and DC quantum gating protocols and compare the optimal fidelities for these protocols that can be achieved for both the hybrid qubit and the more traditional singlet-triplet qubit. In the second part, we present evidence that silicon offers superior coherence properties by analyzing experimental data from which charge dephasing and spin relaxation times are extracted. We show that the internal degrees of freedom of the hybrid qubit enhance charge coherence, and demonstrate tunable spin loading of a quantum dot. In the last part, we explain three key features of spin-dependent transport — spin blockade, lifetime-enhanced transport and spin-flip cotunneling. We explain how these features arise in the conventional two-electron as well as the unconventional three-electron regimes, using a theoretical model that captures the key characteristics observed in the data.

  19. Quantum Hall ferrimagnetism in lateral quantum dot molecules.

    PubMed

    Abolfath, Ramin M; Hawrylak, Pawel

    2006-11-03

    We demonstrate the existence of ferrimagnetic and ferromagnetic phases in a spin phase diagram of coupled lateral quantum dot molecules in the quantum Hall regime. The spin phase diagram is determined from the Hartree-Fock configuration interaction method as a function of electron number N and magnetic field B. The quantum Hall ferrimagnetic phase corresponds to spatially imbalanced spin droplets resulting from strong interdot coupling of identical dots. The quantum Hall ferromagnetic phases correspond to ferromagnetic coupling of spin polarization at filling factors between nu=2 and nu=1.

  20. Quantum efficiency of a double quantum dot microwave photon detector

    NASA Astrophysics Data System (ADS)

    Wong, Clement; Vavilov, Maxim

    Motivated by recent interest in implementing circuit quantum electrodynamics with semiconducting quantum dots, we study charge transfer through a double quantum dot (DQD) capacitively coupled to a superconducting cavity subject to a microwave field. We analyze the DQD current response using input-output theory and determine the optimal parameter regime for complete absorption of radiation and efficient conversion of microwave photons to electric current. For experimentally available DQD systems, we show that the cavity-coupled DQD operates as a photon-to-charge converter with quantum efficiencies up to 80% C.W. acknowledges support by the Intelligence Community Postdoctoral Research Fellowship Program.

  1. Scalable quantum computer architecture with coupled donor-quantum dot qubits

    DOEpatents

    Schenkel, Thomas; Lo, Cheuk Chi; Weis, Christoph; Lyon, Stephen; Tyryshkin, Alexei; Bokor, Jeffrey

    2014-08-26

    A quantum bit computing architecture includes a plurality of single spin memory donor atoms embedded in a semiconductor layer, a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, wherein a first voltage applied across at least one pair of the aligned quantum dot and donor atom controls a donor-quantum dot coupling. A method of performing quantum computing in a scalable architecture quantum computing apparatus includes arranging a pattern of single spin memory donor atoms in a semiconductor layer, forming a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, applying a first voltage across at least one aligned pair of a quantum dot and donor atom to control a donor-quantum dot coupling, and applying a second voltage between one or more quantum dots to control a Heisenberg exchange J coupling between quantum dots and to cause transport of a single spin polarized electron between quantum dots.

  2. Robust effective Zeeman energy in monolayer MoS2 quantum dots

    NASA Astrophysics Data System (ADS)

    Dias, A. C.; Fu, Jiyong; Villegas-Lelovsky, L.; Qu, Fanyao

    2016-09-01

    We report a theoretical investigation on the energy spectrum and the effective Zeeman energy (EZE) in monolayer MoS2 circular quantum dots, subjected to an out-of-plane magnetic field. Interestingly, we observe the emergence of energy-locked modes, depending on the competition between the dot confinement and the applied magnetic field, for either the highest K-valley valence band or the lowest {{K}\\prime} -valley conduction band. Moreover, an unusual dot-size-independent EZE behavior of the highest valence and the lowest conduction bands is found. Although the EZEs are insensitive to the variation of quantum confinement, both of them grow linearly with the magnetic field, similar to that in the monolayer MoS2 material. The EZEs along with their ‘robustness’ against dot confinements open opportunities of a universal magnetic control over the valley degree of freedom, for quantum dots of all sizes.

  3. Surface treatment of nanocrystal quantum dots after film deposition

    DOEpatents

    Sykora, Milan; Koposov, Alexey; Fuke, Nobuhiro

    2015-02-03

    Provided are methods of surface treatment of nanocrystal quantum dots after film deposition so as to exchange the native ligands of the quantum dots for exchange ligands that result in improvement in charge extraction from the nanocrystals.

  4. Double quantum dots defined in bilayer graphene

    NASA Astrophysics Data System (ADS)

    Żebrowski, D. P.; Peeters, F. M.; Szafran, B.

    2017-07-01

    Artificial molecular states of double quantum dots defined in bilayer graphene are studied with the atomistic tight-binding method and its low-energy continuum approximation. We indicate that the extended electron wave functions have opposite parities on sublattices of the layers and that the ground-state wave-function components change from bonding to antibonding with the interdot distance. In the weak-coupling limit, the one most relevant for quantum dots defined electrostatically, the signatures of the interdot coupling include, for the two-electron ground state, formation of states with symmetric or antisymmetric spatial wave functions split by the exchange energy. In the high-energy part of the spectrum the states with both electrons in the same dot are found with the splitting of energy levels corresponding to simultaneous tunneling of the electron pair from one dot to the other.

  5. Innovative Ge Quantum Dot Functional Sensing/Metrology Devices

    DTIC Science & Technology

    2015-05-20

    Final 3. DATES COVERED (From - To) 20140507 - 20150506 4. TITLE AND SUBTITLE Innovative Ge Quantum Dot Functional Sensing/Metrology...15. SUBJECT TERMS Quantum Dots , Germanium (Ge) quantum dot 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER...07-05-2014 to 06-05-2015 4. TITLE AND SUBTITLE Innovative Ge Quantum Dot Functional Sensing/Metrology Devices 5a. CONTRACT NUMBER FA2386-14-1

  6. Carbon quantum dots and a method of making the same

    DOEpatents

    Zidan, Ragaiy; Teprovich, Joseph A.; Washington, Aaron L.

    2017-08-22

    The present invention is directed to a method of preparing a carbon quantum dot. The carbon quantum dot can be prepared from a carbon precursor, such as a fullerene, and a complex metal hydride. The present invention also discloses a carbon quantum dot made by reacting a carbon precursor with a complex metal hydride and a polymer containing a carbon quantum dot made by reacting a carbon precursor with a complex metal hydride.

  7. Isotopically enhanced triple-quantum-dot qubit.

    PubMed

    Eng, Kevin; Ladd, Thaddeus D; Smith, Aaron; Borselli, Matthew G; Kiselev, Andrey A; Fong, Bryan H; Holabird, Kevin S; Hazard, Thomas M; Huang, Biqin; Deelman, Peter W; Milosavljevic, Ivan; Schmitz, Adele E; Ross, Richard S; Gyure, Mark F; Hunter, Andrew T

    2015-05-01

    Like modern microprocessors today, future processors of quantum information may be implemented using all-electrical control of silicon-based devices. A semiconductor spin qubit may be controlled without the use of magnetic fields by using three electrons in three tunnel-coupled quantum dots. Triple dots have previously been implemented in GaAs, but this material suffers from intrinsic nuclear magnetic noise. Reduction of this noise is possible by fabricating devices using isotopically purified silicon. We demonstrate universal coherent control of a triple-quantum-dot qubit implemented in an isotopically enhanced Si/SiGe heterostructure. Composite pulses are used to implement spin-echo type sequences, and differential charge sensing enables single-shot state readout. These experiments demonstrate sufficient control with sufficiently low noise to enable the long pulse sequences required for exchange-only two-qubit logic and randomized benchmarking.

  8. Quantum-dot-based cell motility assay.

    PubMed

    Gu, Weiwei; Pellegrino, Teresa; Parak, Wolfgang J; Boudreau, Rosanne; Le Gros, Mark A; Gerion, Daniele; Alivisatos, A Paul; Larabell, Carolyn A

    2005-06-28

    Because of their favorable physical and photochemical properties, colloidal CdSe/ZnS-semiconductor nanocrystals (commonly known as quantum dots) have enormous potential for use in biological imaging. In this report, we present an assay that uses quantum dots as markers to quantify cell motility. Cells that are seeded onto a homogeneous layer of quantum dots engulf and absorb the nanocrystals and, as a consequence, leave behind a fluorescence-free trail. By subsequently determining the ratio of cell area to fluorescence-free track area, we show that it is possible to differentiate between invasive and noninvasive cancer cells. Because this assay uses simple fluorescence detection, requires no significant data processing, and can be used in live-cell studies, it has the potential to be a powerful new tool for discriminating between invasive and noninvasive cancer cell lines or for studying cell signaling events involved in migration.

  9. Angiogenic Profiling of Synthesized Carbon Quantum Dots.

    PubMed

    Shereema, R M; Sruthi, T V; Kumar, V B Sameer; Rao, T P; Shankar, S Sharath

    2015-10-20

    A simple method was employed for the synthesis of green luminescent carbon quantum dots (CQDs) from styrene soot. The CQDs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, and Raman spectroscopy. The prepared carbon quantum dots did not show cellular toxicity and could successfully be used for labeling cells. We also evaluated the effects of carbon quantum dots on the process of angiogenesis. Results of a chorioallantoic membrane (CAM) assay revealed the significant decrease in the density of branched vessels after their treatment with CQDs. Further application of CQDs significantly downregulated the expression levels of pro-angiogenic growth factors like VEGF and FGF. Expression of VEGFR2 and levels of hemoglobin were also significantly lower in CAMs treated with CQDs, indicating that the CQDs inhibit angiogenesis. Data presented here also show that CQDs can selectively target cancer cells and therefore hold potential in the field of cancer therapy.

  10. Exciton binding energy in semiconductor quantum dots

    SciTech Connect

    Pokutnii, S. I.

    2010-04-15

    In the adiabatic approximation in the context of the modified effective mass approach, in which the reduced exciton effective mass {mu} = {mu}(a) is a function of the radius a of the semiconductor quantum dot, an expression for the exciton binding energy E{sub ex}(a) in the quantum dot is derived. It is found that, in the CdSe and CdS quantum dots with the radii a comparable to the Bohr exciton radii a{sub ex}, the exciton binding energy E{sub ex}(a) is substantially (respectively, 7.4 and 4.5 times) higher than the exciton binding energy in the CdSe and CdS single crystals.

  11. Dynamics of plasmonic field polarization induced by quantum coherence in quantum dot-metallic nanoshell structures.

    PubMed

    Sadeghi, S M

    2014-09-01

    When a hybrid system consisting of a semiconductor quantum dot and a metallic nanoparticle interacts with a laser field, the plasmonic field of the metallic nanoparticle can be normalized by the quantum coherence generated in the quantum dot. In this Letter, we study the states of polarization of such a coherent-plasmonic field and demonstrate how these states can reveal unique aspects of the collective molecular properties of the hybrid system formed via coherent exciton-plasmon coupling. We show that transition between the molecular states of this system can lead to ultrafast polarization dynamics, including sudden reversal of the sense of variations of the plasmonic field and formation of circular and elliptical polarization.

  12. T1 spin lifetimes in n-doped quantum wells and dots

    NASA Astrophysics Data System (ADS)

    Colton, John; Clark, Ken; Craft, Daniel; Cutler, Jane; Meyer, David; Park, Tyler

    2012-02-01

    We have used a pump probe technique to measure T1 spin lifetimes in n-type GaAs quantum wells and InAs self-assembled quantum dots. The circularly polarized pump laser pulse aligns the spins; the linearly polarized probe laser pulse probes the spin states of the selected well (or dots) via the Kerr (or Faraday) effect at some later time. Results for the quantum well sample include a spin-filling effect that depends on the direction from which the probe laser wavelength approaches that of the well, and spin lifetimes ranging from 50 to 2000 ns (depending on temperature and field conditions). The InAs quantum dots, doped such that each dot has approximately one extra electron, display T1 lifetimes longer than 5 ms at 1 T and 1.5 K.

  13. Interaction of digestive enzymes with tunable light emitting quantum dots: a thorough Spectroscopic investigation.

    PubMed

    Ellappan, Vaishnavi; Kesavan, Manibalan; Ramalingam, Parameshwari; Kulandaivel, Jeganathan; Rajalingam, Renganathan

    2015-11-01

    In this article, we have examined the direct spectroscopic and microscopic evidence of efficient quantum dots-α-chymotrypsin (ChT) interaction. The intrinsic fluorescence of digestive enzyme is reduced in the presence of quantum dots through ground-state complex formation. Based on the fluorescence data, quenching rate constant, binding constant, and number of binding sites are calculated under optimized experimental conditions. Interestingly, fluorescence quenching method clearly illustrated the size dependent interaction of MPA-CdTe quantum dots. Conformational change of ChT was traced using synchronous fluorescence measurements, circular dichroism and FTIR spectroscopic methods. Furthermore, the AFM results revealed that the individual enzyme molecule dimensions were changed after interacting with quantum dot. Consequently, this result could be helpful for constructing safe and effective utilisation of QDs in biological applications. Copyright © 2015 John Wiley & Sons, Ltd.

  14. Nanopatterned Quantum Dot Lasers for High Speed, High Efficiency, Operation

    DTIC Science & Technology

    2015-04-27

    SECURITY CLASSIFICATION OF: Quantum dot (QD) active regions hold potential for realizing extremely high performance semiconductor diode lasers...2009 31-Dec-2014 Approved for Public Release; Distribution Unlimited Final Report: Nanopatterned Quantum Dot Lasers for High Speed, High Efficiency...Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 quantum dots , nanopatterning, MOCVD, laser REPORT DOCUMENTATION PAGE 11

  15. Fluorescence correlation spectroscopy using quantum dots: advances, challenges and opportunities.

    PubMed

    Heuff, Romey F; Swift, Jody L; Cramb, David T

    2007-04-28

    Semiconductor nanocrystals (quantum dots) have been increasingly employed in measuring the dynamic behavior of biomacromolecules using fluorescence correlation spectroscopy. This poses a challenge, because quantum dots display their own dynamic behavior in the form of intermittent photoluminescence, also known as blinking. In this review, the manifestation of blinking in correlation spectroscopy will be explored, preceded by an examination of quantum dot blinking in general.

  16. Quantum dot heterojunction solar cells: The mechanism of device operation and impacts of quantum dot oxidation

    NASA Astrophysics Data System (ADS)

    Ihly, Rachelle

    This thesis explores the understanding of the chemistry and physics of colloidal quantum dots for practical solar energy photoconversion. Solar cell devices that make use of PbS quantum dots generally rely on constant and unchanged optical properties such that band gap energies remain tuned within the device. The design and development of unique experiments to ascertain mechanisms of optical band gap shifts occurring in PbS quantum dot thin-films exposed to air are discussed. The systematic study of the absorption properties of PbS quantum dot films exposed to air, heat, and UV illumination as a function of quantum dot size has been described. A method to improve the air-stability of films with atomic layer deposition of alumina is demonstrated. Encapsulation of quantum dot films using a protective layer of alumina results in quantum dot solids that maintain tuned absorption for 1000 hours. This thesis focuses on the use of atomic force microscopy and electrical variants thereof to study the physical and electrical characteristics of quantum dot arrays. These types of studies have broad implications in understanding charge transport mechanisms and solar cell device operation, with a particular emphasis on quantum dot transistors and solar cells. Imaging the channel potential of a PbSe quantum dot thin-film in a transistor showed a uniform distribution of charge coinciding with the transistor current voltage characteristics. In a second study, solar cell device operation of ZnO/PbS heterojunction solar cells was investigated by scanning active cross-sections with Kelvin probe microscopy as a function of applied bias, illumination and device architecture. This technique directly provides operating potential and electric field profiles to characterize drift and diffusion currents occurring in the device. SKPM established a field-free region occurring in the quantum dot layer, indicative of diffusion-limited transport. These results provide the path to optimization of

  17. Bilayer graphene quantum dot defined by topgates

    SciTech Connect

    Müller, André; Kaestner, Bernd; Hohls, Frank; Weimann, Thomas; Pierz, Klaus; Schumacher, Hans W.

    2014-06-21

    We investigate the application of nanoscale topgates on exfoliated bilayer graphene to define quantum dot devices. At temperatures below 500 mK, the conductance underneath the grounded gates is suppressed, which we attribute to nearest neighbour hopping and strain-induced piezoelectric fields. The gate-layout can thus be used to define resistive regions by tuning into the corresponding temperature range. We use this method to define a quantum dot structure in bilayer graphene showing Coulomb blockade oscillations consistent with the gate layout.

  18. Potential clinical applications of quantum dots.

    PubMed

    Medintz, Igor L; Mattoussi, Hedi; Clapp, Aaron R

    2008-01-01

    The use of luminescent colloidal quantum dots in biological investigations has increased dramatically over the past several years due to their unique size-dependent optical properties and recent advances in biofunctionalization. In this review, we describe the methods for generating high-quality nanocrystals and report on current and potential uses of these versatile materials. Numerous examples are provided in several key areas including cell labeling, biosensing, in vivo imaging, bimodal magnetic-luminescent imaging, and diagnostics. We also explore toxicity issues surrounding these materials and speculate about the future uses of quantum dots in a clinical setting.

  19. Ambipolar quantum dots in intrinsic silicon

    SciTech Connect

    Betz, A. C. Gonzalez-Zalba, M. F.; Podd, G.; Ferguson, A. J.

    2014-10-13

    We electrically measure intrinsic silicon quantum dots with electrostatically defined tunnel barriers. The presence of both p- and n-type ohmic contacts enables the accumulation of either electrons or holes. Thus, we are able to study both transport regimes within the same device. We investigate the effect of the tunnel barriers and the electrostatically defined quantum dots. There is greater localisation of charge states under the tunnel barriers in the case of hole conduction, leading to higher charge noise in the p-type regime.

  20. Single quantum dots as local temperature markers.

    PubMed

    Li, Sha; Zhang, Kai; Yang, Jui-Ming; Lin, Liwei; Yang, Haw

    2007-10-01

    This work describes noncontact, local temperature measurements using wavelength shifts of CdSe quantum dots (QDs). Individual QDs are demonstrated to be capable of sensing temperature variations and reporting temperature changes remotely through optical readout. Temperature profiles of a microheater under different input voltages are evaluated based on the spectral shift of QDs on the heater, and results are consistent with a one-dimensional electrothermal model. The theoretical resolution of this technique could go down to the size of a single quantum dot using far-field optics for temperature characterizations of micro/nanostructures.

  1. Trapping of an electron in coupled quantum dots in graphene

    NASA Astrophysics Data System (ADS)

    Hewageegana, Prabath; Apalkov, Vadym

    2009-03-01

    Due to Klein’s tunneling the electronic states of a quantum dot in graphene have finite widths and an electron in quantum dot has a finite trapping time. This property introduces a special type of interdot coupling in a system of many quantum dots in graphene. The interdot coupling is realized not as a direct tunneling between quantum dots but as coupling through the continuum states of graphene. As a result the interdot coupling modifies both the positions and the widths of the energy levels of the quantum dot system. We study the system of quantum dots in graphene theoretically by analyzing the complex energy spectra of the quantum dot system. We show that in a double-dot system some energy levels become strongly localized with an infinite trapping time. Such strongly localized states are achieved only at one value of the interdot separation. We also study a periodic array of quantum dots in graphene within a tight-binding mode for a quantum dot system. The values of the hopping integrals in the tight-binding model are found from the expression for the energy spectra of the double quantum dot system. In the array of quantum dots the states with infinitely large trapping time are realized at all values of interdot separation smaller than some critical value. Such states have nonzero wave vectors.

  2. Quantum criticality in a double-quantum-dot system.

    PubMed

    Zaránd, Gergely; Chung, Chung-Hou; Simon, Pascal; Vojta, Matthias

    2006-10-20

    We discuss the realization of the quantum-critical non-Fermi-liquid state, originally discovered within the two-impurity Kondo model, in double-quantum-dot systems. Contrary to common belief, the corresponding fixed point is robust against particle-hole and various other asymmetries and is unstable only to charge transfer between the two dots. We propose an experimental setup where such charge transfer processes are suppressed, allowing a controlled approach to the quantum-critical state. We also discuss transport and scaling properties in the vicinity of the critical point.

  3. Probing silicon quantum dots by single-dot techniques

    NASA Astrophysics Data System (ADS)

    Sychugov, Ilya; Valenta, Jan; Linnros, Jan

    2017-02-01

    Silicon nanocrystals represent an important class of non-toxic, heavy-metal free quantum dots, where the high natural abundance of silicon is an additional advantage. Successful development in mass-fabrication, starting from porous silicon to recent advances in chemical and plasma synthesis, opens up new possibilities for applications in optoelectronics, bio-imaging, photovoltaics, and sensitizing areas. In this review basic physical properties of silicon nanocrystals revealed by photoluminescence spectroscopy, lifetime, intensity trace and electrical measurements on individual nanoparticles are summarized. The fabrication methods developed for accessing single Si nanocrystals are also reviewed. It is concluded that silicon nanocrystals share many of the properties of direct bandgap nanocrystals exhibiting sharp emission lines at low temperatures, on/off blinking, spectral diffusion etc. An analysis of reported results is provided in comparison with theory and with direct bandgap material quantum dots. In addition, the role of passivation and inherent interface/matrix defects is discussed.

  4. Quantum-confined Stark effects in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Wen, G. W.; Lin, J. Y.; Jiang, H. X.; Chen, Z.

    1995-08-01

    Quantum-confined Stark effects (QCSE) on excitons, i.e., the influence of a uniform electric field on the confined excitons in semiconductor quantum dots (QD's), have been studied by using a numerical matrix-diagonalization scheme. The energy levels and the wave functions of the ground and several excited states of excitons in CdS and CdS1-xSex quantum dots as functions of the size of the quantum dot and the applied electric field have been obtained. The electron and hole distributions and wave function overlap inside the QD's have also been calculated for different QD sizes and electric fields. It is found that the electron and hole wave function overlap decreases under an electric field, which implies an increased exciton recombination lifetime due to QCSE. The energy level redshift and the enhancement of the exciton recombination lifetime are due to the polarization of the electron-hole pair under the applied electric field.

  5. Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host.

    PubMed

    Lukishova, Svetlana G; Bissell, Luke J; Winkler, Justin; Stroud, C R

    2012-04-01

    Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.

  6. Full-colour quantum dot displays fabricated by transfer printing

    NASA Astrophysics Data System (ADS)

    Kim, Tae-Ho; Cho, Kyung-Sang; Lee, Eun Kyung; Lee, Sang Jin; Chae, Jungseok; Kim, Jung Woo; Kim, Do Hwan; Kwon, Jang-Yeon; Amaratunga, Gehan; Lee, Sang Yoon; Choi, Byoung Lyong; Kuk, Young; Kim, Jong Min; Kim, Kinam

    2011-03-01

    Light-emitting diodes with quantum dot luminophores show promise in the development of next-generation displays, because quantum dot luminophores demonstrate high quantum yields, extremely narrow emission, spectral tunability and high stability, among other beneficial characteristics. However, the inability to achieve size-selective quantum dot patterning by conventional methods hinders the realization of full-colour quantum dot displays. Here, we report the first demonstration of a large-area, full-colour quantum dot display, including in flexible form, using optimized quantum dot films, and with control of the nano-interfaces and carrier behaviour. Printed quantum dot films exhibit excellent morphology, well-ordered quantum dot structure and clearly defined interfaces. These characteristics are achieved through the solvent-free transfer of quantum dot films and the compact structure of the quantum dot networks. Significant enhancements in charge transport/balance in the quantum dot layer improve electroluminescent performance. A method using plasmonic coupling is also suggested to further enhance luminous efficiency. The results suggest routes towards creating large-scale optoelectronic devices in displays, solid-state lighting and photovoltaics.

  7. Imaging and Manipulating Energy Transfer Among Quantum Dots at Individual Dot Resolution.

    PubMed

    Nguyen, Duc; Nguyen, Huy A; Lyding, Joseph W; Gruebele, Martin

    2017-06-27

    Many processes of interest in quantum dots involve charge or energy transfer from one dot to another. Energy transfer in films of quantum dots as well as between linked quantum dots has been demonstrated by luminescence shift, and the ultrafast time-dependence of energy transfer processes has been resolved. Bandgap variation among dots (energy disorder) and dot separation are known to play an important role in how energy diffuses. Thus, it would be very useful if energy transfer could be visualized directly on a dot-by-dot basis among small clusters or within films of quantum dots. To that effect, we report single molecule optical absorption detected by scanning tunneling microscopy (SMA-STM) to image energy pooling from donor into acceptor dots on a dot-by-dot basis. We show that we can manipulate groups of quantum dots by pruning away the dominant acceptor dot, and switching the energy transfer path to a different acceptor dot. Our experimental data agrees well with a simple Monte Carlo lattice model of energy transfer, similar to models in the literature, in which excitation energy is transferred preferentially from dots with a larger bandgap to dots with a smaller bandgap.

  8. Magnetic control of dipolaritons in quantum dots.

    PubMed

    Rojas-Arias, J S; Rodríguez, B A; Vinck-Posada, H

    2016-12-21

    Dipolaritons are quasiparticles that arise in coupled quantum wells embedded in a microcavity, they are a superposition of a photon, a direct exciton and an indirect exciton. We propose the existence of dipolaritons in a system of two coupled quantum dots inside a microcavity in direct analogy with the quantum well case and find that, despite some similarities, dipolaritons in quantum dots have different properties and can lead to true dark polariton states. We use a finite system theory to study the effects of the magnetic field on the system, including the emission, and find that it can be used as a control parameter of the properties of excitons and dipolaritons, and the overall magnetic behaviour of the structure.

  9. Nuclear spin effects in semiconductor quantum dots.

    PubMed

    Chekhovich, E A; Makhonin, M N; Tartakovskii, A I; Yacoby, A; Bluhm, H; Nowack, K C; Vandersypen, L M K

    2013-06-01

    The interaction of an electronic spin with its nuclear environment, an issue known as the central spin problem, has been the subject of considerable attention due to its relevance for spin-based quantum computation using semiconductor quantum dots. Independent control of the nuclear spin bath using nuclear magnetic resonance techniques and dynamic nuclear polarization using the central spin itself offer unique possibilities for manipulating the nuclear bath with significant consequences for the coherence and controlled manipulation of the central spin. Here we review some of the recent optical and transport experiments that have explored this central spin problem using semiconductor quantum dots. We focus on the interaction between 10(4)-10(6) nuclear spins and a spin of a single electron or valence-band hole. We also review the experimental techniques as well as the key theoretical ideas and the implications for quantum information science.

  10. Theory of a double-quantum-dot spaser

    SciTech Connect

    Andrianov, E S; Pukhov, A A; Dorofeenko, A V; Vinogradov, A P; Lisyansky, A A

    2015-03-31

    We consider the influence of the number of quantum dots on spaser operation. It is shown that even in the presence of only two quantum dots, the spaser behaviour is qualitatively different from that of the previously studied spaser consisting of a nanoparticle and a single quantum dot. In particular, for nonzero detuning of resonant frequencies of a nanoparticle and quantum dots, an increase in the interaction constant between quantum dots first leads to a decrease in the spasing threshold and then to its growth and even the spasing breakdown. (nanostructures)

  11. Zinc sulfide quantum dots for photocatalytic and sensing applications

    NASA Astrophysics Data System (ADS)

    Sergeev, Alexander A.; Leonov, Andrei A.; Zhuikova, Elena I.; Postnova, Irina V.; Voznesenskiy, Sergey S.

    2017-09-01

    Herein, we report the photocatalytic and sensing applications of pure and Mn-doped ZnS quantum dots. The quantum dots were prepared by a chemical precipitation in an aqueous solution in the presence of glutathione as a stabilizing agent. The synthesized quantum dots were used as effective photocatalyst for the degradation of methylene blue dye. Interestingly, fully degradation of methylene blue dye was achieved in 5 min using pure ZnS quantum dots. Further, the synthesized quantum dots were used as efficient sensing element for methane fluorescent sensor. Interfering studies confirmed that the developed sensor possesses very good sensitivity and selectivity towards methane.

  12. Germanium quantum dots: Optical properties and synthesis

    NASA Astrophysics Data System (ADS)

    Heath, James R.; Shiang, J. J.; Alivisatos, A. P.

    1994-07-01

    Three different size distributions of Ge quantum dots (≳200, 110, and 60 Å) have been synthesized via the ultrasonic mediated reduction of mixtures of chlorogermanes and organochlorogermanes (or organochlorosilanes) by a colloidal sodium/potassium alloy in heptane, followed by annealing in a sealed pressure vessel at 270 °C. The quantum dots are characterized by transmission electron microscopy, x-ray powder diffraction, x-ray photoemission, infrared spectroscopy, and Raman spectroscopy. Colloidal suspensions of these quantum dots were prepared and their extinction spectra are measured with ultraviolet/visible (UV/Vis) and near infrared (IR) spectroscopy, in the regime from 0.6 to 5 eV. The optical spectra are correlated with a Mie theory extinction calculation utilizing bulk optical constants. This leads to an assignment of three optical features to the E(1), E(0'), and E(2) direct band gap transitions. The E(0') transitions exhibit a strong size dependence. The near IR spectra of the largest dots is dominated by E(0) direct gap absorptions. For the smallest dots the near IR spectrum is dominated by the Γ25→L indirect transitions.

  13. Synthesis of CdSe quantum dots for quantum dot sensitized solar cell

    SciTech Connect

    Singh, Neetu Kapoor, Avinashi; Kumar, Vinod; Mehra, R. M.

    2014-04-24

    CdSe Quantum Dots (QDs) of size 0.85 nm were synthesized using chemical route. ZnO based Quantum Dot Sensitized Solar Cell (QDSSC) was fabricated using CdSe QDs as sensitizer. The Pre-synthesized QDs were found to be successfully adsorbed on front ZnO electrode and had potential to replace organic dyes in Dye Sensitized Solar Cells (DSSCs). The efficiency of QDSSC was obtained to be 2.06 % at AM 1.5.

  14. Slow Electron Cooling in Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Pandey, Anshu; Guyot-Sionnest, Philippe

    2008-11-01

    Hot electrons in semiconductors lose their energy very quickly (within picoseconds) to lattice vibrations. Slowing this energy loss could prove useful for more efficient photovoltaic or infrared devices. With their well-separated electronic states, quantum dots should display slow relaxation, but other mechanisms have made it difficult to observe. We report slow intraband relaxation (>1 nanosecond) in colloidal quantum dots. The small cadmium selenide (CdSe) dots, with an intraband energy separation of ~0.25 electron volts, are capped by an epitaxial zinc selenide (ZnSe) shell. The shell is terminated by a CdSe passivating layer to remove electron traps and is covered by ligands of low infrared absorbance (alkane thiols) at the intraband energy. We found that relaxation is markedly slowed with increasing ZnSe shell thickness.

  15. Quantum dot at a Luttinger liquid edge

    NASA Astrophysics Data System (ADS)

    Rylands, Colin; Andrei, Natan

    2017-09-01

    We study a system consisting of a Luttinger liquid coupled to a quantum dot on the boundary. The Luttinger liquid is expressed in terms of fermions interacting via density-density coupling, and the dot is modeled as an interacting resonant level onto which the bulk fermions can tunnel. We solve the Hamiltonian exactly and construct all eigenstates. We study both the zero- and finite-temperature properties of the system, in particular, we compute the exact dot occupation as a function of the dot energy in all parameter regimes. The system is seen to flow from weak to strong coupling for all values of the bulk interaction, with the flow characterized by a nonperturbative Kondo scale. We identify the critical exponents at the weak- and strong-coupling regimes.

  16. New small quantum dots for neuroscience

    NASA Astrophysics Data System (ADS)

    Selvin, Paul

    2014-03-01

    In "New Small Quantum Dots for Neuroscience," Paul Selvin (University of Illinois, Urbana-Champaign) notes how the details of synapsis activity in the brain involves chemical receptors that facilitate the creation of the electrical connection between two nerves. In order to understand the details of this neuroscience phenomenon you need to be able to "see" what is happening at the scale of these receptors, which is around 10 nanometers. This is smaller than the diffraction limit of normal microscopy and it takes place on a 3 dimensional structure. Selvin describes the development of small quantum dots (on the order of 6-9 microns) that are surface-sensitized to interact with the receptors. This allows the application of photo-activated localized microscopy (PALM), a superresolution microscopy that can be scanned through focus to develop a 3D map on a scale that is the same size as the emitter, which in this case are the small quantum dots. The quantum dots are stable in time and provide access to the receptors which allows the imaging of the interactions taking place at the synoptic level.

  17. Producing Quantum Dots by Spray Pyrolysis

    NASA Technical Reports Server (NTRS)

    Banger, Kulbinder; Jin, Michael H.; Hepp, Aloysius

    2006-01-01

    An improved process for making nanocrystallites, commonly denoted quantum dots (QDs), is based on spray pyrolysis. Unlike the process used heretofore, the improved process is amenable to mass production of either passivated or non-passivated QDs, with computer control to ensure near uniformity of size.

  18. Nanocomposites of POC and quantum dots

    NASA Astrophysics Data System (ADS)

    Borriello, C.; Concilio, S.; Minarini, C.; Iannelli, P.; Di Luccio, T.

    2012-07-01

    New luminescent polymer nanocomposites were synthesized combining carbazole/oxadiazole copolymer (POC) and CdSe/ZnS quantum dots (QDs) surface passivated by ionic liquids. Ionic liquid ligands improve the photostability of QDs and their compatibility with polymer allowing the deposition of homogeneous nanocomposites films. The nanocomposites were characterized by UV and photoluminescence spectroscopy.

  19. Spin Wigner molecules in quantum dots

    NASA Astrophysics Data System (ADS)

    Zutic, Igor; Oszwaldowski, Rafal; Stano, Peter; Petukhov, A. G.

    2013-03-01

    The interplay of confinement and Coulomb interactions in quantum dots can lead to strongly correlated phases differing qualitatively from the Fermi liquid behavior. While in three dimensions the correlation-induced Wigner crystal is elusive and expected only in the limit of an extremely low carrier density, its nanoscale analog, the Wigner molecule, has been observed in quantum dots at much higher densities [1]. We explore how the presence of magnetic impurities in quantum dots can provide additional opportunities to study correlation effects and the resulting ordering in carrier and impurity spins[2]. By employing exact diagonalization we reveal that seemingly simple two-carrier quantum dots lead to a rich phase diagram [2,3]. We propose experiments to verify our predictions; in particular, we discuss interband optical transitions as a function of temperature and magnetic field. DOE-BES, meta-QUTE 259 ITMS NFP Grant No. 26240120022, CE SAS QUTE, EU 260 Project Q-essence, Grant No. APVV-0646-10, and SCIEX.

  20. Quantum-dot infrared photodetectors: a review

    NASA Astrophysics Data System (ADS)

    Stiff-Roberts, Adrienne D.

    2009-04-01

    Quantum-dot infrared photodetectors (QDIPs) are positioned to become an important technology in the field of infrared (IR) detection, particularly for high-temperature, low-cost, high-yield detector arrays required for military applications. High-operating temperature (>=150 K) photodetectors reduce the cost of IR imaging systems by enabling cryogenic dewars and Stirling cooling systems to be replaced by thermo-electric coolers. QDIPs are well-suited for detecting mid-IR light at elevated temperatures, an application that could prove to be the next commercial market for quantum dots. While quantum dot epitaxial growth and intraband absorption of IR radiation are well established, quantum dot non-uniformity remains as a significant challenge. Nonetheless, state-of-the-art mid-IR detection at 150 K has been demonstrated using 70-layer InAs/GaAs QDIPs, and QDIP focal plane arrays are approaching performance comparable to HgCdTe at 77 K. By addressing critical challenges inherent to epitaxial QD material systems (e.g., controlling dopant incorporation), exploring alternative QD systems (e.g., colloidal QDs), and using bandgap engineering to reduce dark current and enhance multi-spectral detection (e.g. resonant tunneling QDIPs), the performance and applicability of QDIPs will continue to improve.

  1. Optical properties of quantum-dot-doped liquid scintillators

    NASA Astrophysics Data System (ADS)

    Aberle, C.; Li, J. J.; Weiss, S.; Winslow, L.

    2013-10-01

    Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO.

  2. Optical properties of quantum-dot-doped liquid scintillators.

    PubMed

    Aberle, C; Li, J J; Weiss, S; Winslow, L

    2013-10-14

    Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO.

  3. Photonic crystal nanocavity laser with a single quantum dot gain.

    PubMed

    Nomura, Masahiro; Kumagai, Naoto; Iwamoto, Satoshi; Ota, Yasutomo; Arakawa, Yasuhiko

    2009-08-31

    We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain. The investigated nanocavities contain only 0.4 quantum dots on an average; an ultra-low density quantum dot sample (1.5 x 10(8) cm(-2)) is used so that a single quantum dot can be isolated from the surrounding quantum dots. Laser oscillation begins at a pump power of 42 nW under resonant condition, while the far-detuning conditions require ~145 nW for lasing. This spectral detuning dependence of laser threshold indicates substantial contribution of the single quantum dot to the total gain. Moreover, photon correlation measurements show a distinct transition from anti-bunching to Poissonian via bunching with the increase of the excitation power, which is also an evidence of laser oscillation using the single quantum dot gain.

  4. Optical properties of quantum-dot-doped liquid scintillators

    PubMed Central

    Aberle, C.; Li, J.J.; Weiss, S.; Winslow, L.

    2014-01-01

    Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO. PMID:25392711

  5. Quantum Dot Cellular Automata: Computing with Coupled Quantum-Dot Molecules

    NASA Astrophysics Data System (ADS)

    Porod, Wolfgang

    1998-05-01

    We have recently proposed a scheme of using coupled quantum dots to realize digital computing elements.(C. S. Lent, P. D. Tougaw, W. Porod, and G. H. Bernstein, Nanotechnology 4, 49 (1993); C. S. Lent, P. D. Tougaw, and W. Porod, Applied Physics Letters 62, 714 (1993).) Our scheme was inspired by recent work on nanometer-scale lithography in semiconductors which has permitted the construction of quantum dots which may be viewed as artificial atoms; furthermore, the principle of dot-dot coupling has also been demonstrated, thus realizing artificial semiconductor molecules. This talk will review the work of the Notre Dame group on the theory and modeling of cellular arrays of coupled quantum-dot molecules, which we refer to as quantum-dot cellular automata (QCA). We consider inhomogeneous arrays of quantum-dot molecules, where each molecule forms the basic unit in a cellular automaton-type array architecture. These cells (molecules) consists of four or five quantum dots in close enough proximity to enable electron tunneling between dots. Coulomb repulsion between electrons in the cell results in a bistable ground state whose configuration is determined by the configuration of neighboring cells. The electrons tend to occupy antipodal sites in one of two ground-state configurations which may be used to encode binary information. We have demonstrated that Boolean logic gates can be constructed, and simple design rules permit the fabrication of any logic function. The basic principle of QCA operation was demonstrated in recent experiments.(A. O. Orlov, I. Amlani, G. H. Bernstein, C. S. Lent, and G. L. Snider, Science 277, 928, (1997).)

  6. Single-dot optical emission from ultralow density well-isolated InP quantum dots

    SciTech Connect

    Ugur, A.; Hatami, F.; Masselink, W. T.; Vamivakas, A. N.; Lombez, L.; Atatuere, M.

    2008-10-06

    We demonstrate a straightforward way to obtain single well-isolated quantum dots emitting in the visible part of the spectrum and characterize the optical emission from single quantum dots using this method. Self-assembled InP quantum dots are grown using gas-source molecular-beam epitaxy over a wide range of InP deposition rates, using an ultralow growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/{mu}m{sup 2} is realized. The resulting isolated InP quantum dots embedded in an InGaP matrix are individually characterized without the need for lithographical patterning and masks on the substrate. Such low-density quantum dots show excitonic emission at around 670 nm with a linewidth limited by instrument resolution. This system is applicable as a single-photon source for applications such as quantum cryptography.

  7. Non-Markovian full counting statistics in quantum dot molecules.

    PubMed

    Xue, Hai-Bin; Jiao, Hu-Jun; Liang, Jiu-Qing; Liu, Wu-Ming

    2015-03-10

    Full counting statistics of electron transport is a powerful diagnostic tool for probing the nature of quantum transport beyond what is obtainable from the average current or conductance measurement alone. In particular, the non-Markovian dynamics of quantum dot molecule plays an important role in the nonequilibrium electron tunneling processes. It is thus necessary to understand the non-Markovian full counting statistics in a quantum dot molecule. Here we study the non-Markovian full counting statistics in two typical quantum dot molecules, namely, serially coupled and side-coupled double quantum dots with high quantum coherence in a certain parameter regime. We demonstrate that the non-Markovian effect manifests itself through the quantum coherence of the quantum dot molecule system, and has a significant impact on the full counting statistics in the high quantum-coherent quantum dot molecule system, which depends on the coupling of the quantum dot molecule system with the source and drain electrodes. The results indicated that the influence of the non-Markovian effect on the full counting statistics of electron transport, which should be considered in a high quantum-coherent quantum dot molecule system, can provide a better understanding of electron transport through quantum dot molecules.

  8. Non-Markovian full counting statistics in quantum dot molecules

    PubMed Central

    Xue, Hai-Bin; Jiao, Hu-Jun; Liang, Jiu-Qing; Liu, Wu-Ming

    2015-01-01

    Full counting statistics of electron transport is a powerful diagnostic tool for probing the nature of quantum transport beyond what is obtainable from the average current or conductance measurement alone. In particular, the non-Markovian dynamics of quantum dot molecule plays an important role in the nonequilibrium electron tunneling processes. It is thus necessary to understand the non-Markovian full counting statistics in a quantum dot molecule. Here we study the non-Markovian full counting statistics in two typical quantum dot molecules, namely, serially coupled and side-coupled double quantum dots with high quantum coherence in a certain parameter regime. We demonstrate that the non-Markovian effect manifests itself through the quantum coherence of the quantum dot molecule system, and has a significant impact on the full counting statistics in the high quantum-coherent quantum dot molecule system, which depends on the coupling of the quantum dot molecule system with the source and drain electrodes. The results indicated that the influence of the non-Markovian effect on the full counting statistics of electron transport, which should be considered in a high quantum-coherent quantum dot molecule system, can provide a better understanding of electron transport through quantum dot molecules. PMID:25752245

  9. Competition of static magnetic and dynamic photon forces in electronic transport through a quantum dot.

    PubMed

    Rauf Abdullah, Nzar; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar

    2016-09-21

    We investigate theoretically the balance of the static magnetic and the dynamical photon forces in the electron transport through a quantum dot in a photon cavity with a single photon mode. The quantum dot system is connected to external leads and the total system is exposed to a static perpendicular magnetic field. We explore the transport characteristics through the system by tuning the ratio, [Formula: see text], between the photon energy, [Formula: see text], and the cyclotron energy, [Formula: see text]. Enhancement in the electron transport with increasing electron-photon coupling is observed when [Formula: see text]. In this case the photon field dominates and stretches the electron charge distribution in the quantum dot, extending it towards the contact area for the leads. Suppression in the electron transport is found when [Formula: see text], as the external magnetic field causes circular confinement of the charge density around the dot.

  10. Quantum Dots and Their Multimodal Applications: A Review

    PubMed Central

    Bera, Debasis; Qian, Lei; Tseng, Teng-Kuan; Holloway, Paul H.

    2010-01-01

    Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

  11. Laterally-biased quantum dot infrared photodetector

    NASA Astrophysics Data System (ADS)

    Cardimona, D. A.; Morath, C. P.; Guidry, D. H.; Cowan, V. M.

    2013-07-01

    At the Air Force Research Laboratory, Space Vehicles Directorate, we are interested in improving the performance of or modifying the capabilities of infrared detectors in order to locate and identify dim and/or distant objects in space. One characteristic we are very interested in is multicolor detection. To this end, we have turned to a novel detector design that we have come to call a Lateral Quantum Dot Infrared Photodetector (LQDIP). In this design, InAs quantum dots are buried in a GaAs quantum well, which in turn is tunnel-coupled to another GaAs quantum well. Photoexcited electrons from the quantum dots tunnel over to the second well and are then swept out via a lateral (perpendicular to the growth direction) bias voltage. This architecture should exhibit the ability to tune to select infrared frequencies with reduced dark current and unity gain. The lateral photocurrent is directed by a vertical (parallel to the growth direction) gate voltage. We will discuss this detector architecture and the LQDIP operating principles and conditions, and we will present some preliminary results of current-voltage, photocurrent, differential conductance, and spectral measurements.

  12. Efficient Luminescence from Perovskite Quantum Dot Solids.

    PubMed

    Kim, Younghoon; Yassitepe, Emre; Voznyy, Oleksandr; Comin, Riccardo; Walters, Grant; Gong, Xiwen; Kanjanaboos, Pongsakorn; Nogueira, Ana F; Sargent, Edward H

    2015-11-18

    Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.

  13. Sensitivity of quantum-dot semiconductor lasers to optical feedback.

    PubMed

    O'Brien, D; Hegarty, S P; Huyet, G; Uskov, A V

    2004-05-15

    The sensitivity of quantum-dot semiconductor lasers to optical feedback is analyzed with a Lang-Kobayashi approach applied to a standard quantum-dot laser model. The carriers are injected into a quantum well and are captured by, or escape from, the quantum dots through either carrier-carrier or phonon-carrier interaction. Because of Pauli blocking, the capture rate into the dots depends on the carrier occupancy level in the dots. Here we show that different carrier capture dynamics lead to a strong modification of the damping of the relaxation oscillations. Regions of increased damping display reduced sensitivity to optical feedback even for a relatively large alpha factor.

  14. Scalable photonic quantum computing assisted by quantum-dot spin in double-sided optical microcavity.

    PubMed

    Wei, Hai-Rui; Deng, Fu-Guo

    2013-07-29

    We investigate the possibility of achieving scalable photonic quantum computing by the giant optical circular birefringence induced by a quantum-dot spin in a double-sided optical microcavity as a result of cavity quantum electrodynamics. We construct a deterministic controlled-not gate on two photonic qubits by two single-photon input-output processes and the readout on an electron-medium spin confined in an optical resonant microcavity. This idea could be applied to multi-qubit gates on photonic qubits and we give the quantum circuit for a three-photon Toffoli gate. High fidelities and high efficiencies could be achieved when the side leakage to the cavity loss rate is low. It is worth pointing out that our devices work in both the strong and the weak coupling regimes.

  15. Mitigation of Quantum Dot Cytotoxicity by Microencapsulation

    PubMed Central

    Romoser, Amelia; Ritter, Dustin; Majitha, Ravish; Meissner, Kenith E.; McShane, Michael; Sayes, Christie M.

    2011-01-01

    When CdSe/ZnS-polyethyleneimine (PEI) quantum dots (QDs) are microencapsulated in polymeric microcapsules, human fibroblasts are protected from acute cytotoxic effects. Differences in cellular morphology, uptake, and viability were assessed after treatment with either microencapsulated or unencapsulated dots. Specifically, QDs contained in microcapsules terminated with polyethylene glycol (PEG) mitigate contact with and uptake by cells, thus providing a tool to retain particle luminescence for applications such as extracellular sensing and imaging. The microcapsule serves as the “first line of defense” for containing the QDs. This enables the individual QD coating to be designed primarily to enhance the function of the biosensor. PMID:21814567

  16. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    NASA Technical Reports Server (NTRS)

    Pradhan, Prabhakar; Anantram, M. P.; Wang, K. L.; Roychowhury, V. P.; Saini, Subhash (Technical Monitor)

    1998-01-01

    A solid state model for quantum computation has potential advantages in terms of the ease of fabrication, characterization, and integration. The fundamental requirements for a quantum computer involve the realization of basic processing units (qubits), and a scheme for controlled switching and coupling among the qubits, which enables one to perform controlled operations on qubits. We propose a model for quantum computation based on optically coupled quantum dot arrays, which is computationally similar to the atomic model proposed by Cirac and Zoller. In this model, individual qubits are comprised of two coupled quantum dots, and an array of these basic units is placed in an optical cavity. Switching among the states of the individual units is done by controlled laser pulses via near field interaction using the NSOM technology. Controlled rotations involving two or more qubits are performed via common cavity mode photon. We have calculated critical times, including the spontaneous emission and switching times, and show that they are comparable to the best times projected for other proposed models of quantum computation. We have also shown the feasibility of accessing individual quantum dots using the NSOM technology by calculating the photon density at the tip, and estimating the power necessary to perform the basic controlled operations. We are currently in the process of estimating the decoherence times for this system; however, we have formulated initial arguments which seem to indicate that the decoherence times will be comparable, if not longer, than many other proposed models.

  17. Quantum Computation Using Optically Coupled Quantum Dot Arrays

    NASA Technical Reports Server (NTRS)

    Pradhan, Prabhakar; Anantram, M. P.; Wang, K. L.; Roychowhury, V. P.; Saini, Subhash (Technical Monitor)

    1998-01-01

    A solid state model for quantum computation has potential advantages in terms of the ease of fabrication, characterization, and integration. The fundamental requirements for a quantum computer involve the realization of basic processing units (qubits), and a scheme for controlled switching and coupling among the qubits, which enables one to perform controlled operations on qubits. We propose a model for quantum computation based on optically coupled quantum dot arrays, which is computationally similar to the atomic model proposed by Cirac and Zoller. In this model, individual qubits are comprised of two coupled quantum dots, and an array of these basic units is placed in an optical cavity. Switching among the states of the individual units is done by controlled laser pulses via near field interaction using the NSOM technology. Controlled rotations involving two or more qubits are performed via common cavity mode photon. We have calculated critical times, including the spontaneous emission and switching times, and show that they are comparable to the best times projected for other proposed models of quantum computation. We have also shown the feasibility of accessing individual quantum dots using the NSOM technology by calculating the photon density at the tip, and estimating the power necessary to perform the basic controlled operations. We are currently in the process of estimating the decoherence times for this system; however, we have formulated initial arguments which seem to indicate that the decoherence times will be comparable, if not longer, than many other proposed models.

  18. Entrapment in phospholipid vesicles quenches photoactivity of quantum dots.

    PubMed

    Generalov, Roman; Kavaliauskiene, Simona; Westrøm, Sara; Chen, Wei; Kristensen, Solveig; Juzenas, Petras

    2011-01-01

    Quantum dots have emerged with great promise for biological applications as fluorescent markers for immunostaining, labels for intracellular trafficking, and photosensitizers for photodynamic therapy. However, upon entry into a cell, quantum dots are trapped and their fluorescence is quenched in endocytic vesicles such as endosomes and lysosomes. In this study, the photophysical properties of quantum dots were investigated in liposomes as an in vitro vesicle model. Entrapment of quantum dots in liposomes decreases their fluorescence lifetime and intensity. Generation of free radicals by liposomal quantum dots is inhibited compared to that of free quantum dots. Nevertheless, quantum dot fluorescence lifetime and intensity increases due to photolysis of liposomes during irradiation. In addition, protein adsorption on the quantum dot surface and the acidic environment of vesicles also lead to quenching of quantum dot fluorescence, which reappears during irradiation. In conclusion, the in vitro model of phospholipid vesicles has demonstrated that those quantum dots that are fated to be entrapped in endocytic vesicles lose their fluorescence and ability to act as photosensitizers.

  19. Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

    PubMed Central

    Generalov, Roman; Kavaliauskiene, Simona; Westrøm, Sara; Chen, Wei; Kristensen, Solveig; Juzenas, Petras

    2011-01-01

    Quantum dots have emerged with great promise for biological applications as fluorescent markers for immunostaining, labels for intracellular trafficking, and photosensitizers for photodynamic therapy. However, upon entry into a cell, quantum dots are trapped and their fluorescence is quenched in endocytic vesicles such as endosomes and lysosomes. In this study, the photophysical properties of quantum dots were investigated in liposomes as an in vitro vesicle model. Entrapment of quantum dots in liposomes decreases their fluorescence lifetime and intensity. Generation of free radicals by liposomal quantum dots is inhibited compared to that of free quantum dots. Nevertheless, quantum dot fluorescence lifetime and intensity increases due to photolysis of liposomes during irradiation. In addition, protein adsorption on the quantum dot surface and the acidic environment of vesicles also lead to quenching of quantum dot fluorescence, which reappears during irradiation. In conclusion, the in vitro model of phospholipid vesicles has demonstrated that those quantum dots that are fated to be entrapped in endocytic vesicles lose their fluorescence and ability to act as photosensitizers. PMID:21931483

  20. Studies of silicon quantum dots prepared at different substrate temperatures

    NASA Astrophysics Data System (ADS)

    Al-Agel, Faisal A.; Suleiman, Jamal; Khan, Shamshad A.

    2017-03-01

    In this research work, we have synthesized silicon quantum dots at different substrate temperatures 193, 153 and 123 K at a fixed working pressure 5 Torr. of Argon gas. The structural studies of these silicon quantum dots have been undertaken using X-ray diffraction, Field Emission Scanning Electron Microscopy (FESEM) and High Resolution Transmission Electron Microscopy (HRTEM). The optical and electrical properties have been studied using UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Fluorescence spectroscopy and I-V measurement system. X-ray diffraction pattern of Si quantum dots prepared at different temperatures show the amorphous nature except for the quantum dots synthesized at 193 K which shows polycrystalline nature. FESEM images of samples suggest that the size of quantum dots varies from 2 to 8 nm. On the basis of UV-visible spectroscopy measurements, a direct band gap has been observed for Si quantum dots. FTIR spectra suggest that as-grown Si quantum dots are partially oxidized which is due exposure of as-prepared samples to air after taking out from the chamber. PL spectra of the synthesized silicon quantum dots show an intense peak at 444 nm, which may be attributed to the formation of Si quantum dots. Temperature dependence of dc conductivity suggests that the dc conductivity enhances exponentially by raising the temperature. On the basis above properties i.e. direct band gap, high absorption coefficient and high conductivity, these silicon quantum dots will be useful for the fabrication of solar cells.

  1. SU(4) Kondo entanglement in double quantum dot devices

    NASA Astrophysics Data System (ADS)

    Bonazzola, Rodrigo; Andrade, J. A.; Facio, Jorge I.; García, D. J.; Cornaglia, Pablo S.

    2017-08-01

    We analyze, from a quantum information theory perspective, the possibility of realizing an SU(4) entangled Kondo regime in semiconductor double quantum dot devices. We focus our analysis on the ground-state properties and consider the general experimental situation where the coupling parameters of the two quantum dots differ. We model each quantum dot with an Anderson-type Hamiltonian including an interdot Coulomb repulsion and tunnel couplings for each quantum dot to independent fermionic baths. We find that the spin and pseudospin entanglements can be made equal, and the SU(4) symmetry recovered, if the gate voltages are chosen in such a way that the average charge occupancies of the two quantum dots are equal, and the double occupancy on the double quantum dot is suppressed. We present density matrix renormalization group numerical results for the spin and pseudospin entanglement entropies, and analytical results for a simplified model that captures the main physics of the problem.

  2. Principles of conjugating quantum dots to proteins via carbodiimide chemistry

    NASA Astrophysics Data System (ADS)

    Song, Fayi; Chan, Warren C. W.

    2011-12-01

    The covalent coupling of nanomaterials to bio-recognition molecules is a critical intermediate step in using nanomaterials for biology and medicine. Here we investigate the carbodiimide-mediated conjugation of fluorescent quantum dots to different proteins (e.g., immunoglobulin G, bovine serum albumin, and horseradish peroxidase). To enable these studies, we developed a simple method to isolate quantum dot bioconjugates from unconjugated quantum dots. The results show that the reactant concentrations and protein type will impact the overall number of proteins conjugated onto the surfaces of the quantum dots, homogeneity of the protein-quantum dot conjugate population, quantum efficiency, binding avidity, and enzymatic kinetics. We propose general principles that should be followed for the successful coupling of proteins to quantum dots.

  3. Principles of conjugating quantum dots to proteins via carbodiimide chemistry.

    PubMed

    Song, Fayi; Chan, Warren C W

    2011-12-09

    The covalent coupling of nanomaterials to bio-recognition molecules is a critical intermediate step in using nanomaterials for biology and medicine. Here we investigate the carbodiimide-mediated conjugation of fluorescent quantum dots to different proteins (e.g., immunoglobulin G, bovine serum albumin, and horseradish peroxidase). To enable these studies, we developed a simple method to isolate quantum dot bioconjugates from unconjugated quantum dots. The results show that the reactant concentrations and protein type will impact the overall number of proteins conjugated onto the surfaces of the quantum dots, homogeneity of the protein-quantum dot conjugate population, quantum efficiency, binding avidity, and enzymatic kinetics. We propose general principles that should be followed for the successful coupling of proteins to quantum dots.

  4. Peptide-Decorated Tunable-Fluorescence Graphene Quantum Dots.

    PubMed

    Sapkota, Bedanga; Benabbas, Abdelkrim; Lin, Hao-Yu Greg; Liang, Wentao; Champion, Paul; Wanunu, Meni

    2017-03-22

    We report here the synthesis of graphene quantum dots with tunable size, surface chemistry, and fluorescence properties. In the size regime 15-35 nm, these quantum dots maintain strong visible light fluorescence (mean quantum yield of 0.64) and a high two-photon absorption (TPA) cross section (6500 Göppert-Mayer units). Furthermore, through noncovalent tailoring of the chemistry of these quantum dots, we obtain water-stable quantum dots. For example, quantum dots with lysine groups bind strongly to DNA in solution and inhibit polymerase-based DNA strand synthesis. Finally, by virtue of their mesoscopic size, the quantum dots exhibit good cell permeability into living epithelial cells, but they do not enter the cell nucleus.

  5. Silicon Quantum Dots for Quantum Information Processing

    DTIC Science & Technology

    2013-11-01

    levels of the dot up and down. This pulse train modulates the sensor current via a cross- capacitance at a frequency fpulse and the resulting current...excited-state energy levels were detected using a SET charge sensor , with the aid of pulsed-voltage spectroscopy. The energy of the first orbital...were studied in detail. The electron occupancy and excited-state energy levels were detected using a SET charge sensor , with the aid of pulsed-voltage

  6. Probing relaxation times in graphene quantum dots

    PubMed Central

    Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Müller, André; Stampfer, Christoph

    2013-01-01

    Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dots have been extensively investigated with respect to their excitation spectrum, spin-filling sequence and electron-hole crossover. However, their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular concerning the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here we report pulsed-gate transient current spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design that allows to individually tune the tunnelling barriers down to the low megahertz regime, while monitoring their asymmetry. Measuring transient currents through electronic excited states, we estimate a lower bound for charge relaxation times on the order of 60–100 ns. PMID:23612294

  7. Nanoscale optimization of quantum dot solar sells

    NASA Astrophysics Data System (ADS)

    Li, Yanshu; Sergeev, Andrei; Vagidov, Nizami; Mitin, Vladimir; Sablon, Kimberly; State Univ of NY-Buffalo Team; Army Research Laboratory Team

    2015-03-01

    Quantum dots (QDs) offer possibilities for nanoscale control of photoelectron processes via engineering the band structure and potential profile. Nanoscale potential profile (potential barriers) and nanoscale band engineering (AlGaAs atomically thin barriers) effectively suppress the photoelectron capture to QDs. QDs also increase conversion efficiency of the above-bandgap photons due to extraction of electrons from QDs via Coulomb interaction with hot electrons that excited by high-energy photons. To study the effects of the band structure engineering and nanoscale potential barriers on the photovoltaic performance we fabricated 3- μm base GaAs devices with various InAs quantum dot media and selective doping. All quantum dot devices show improvement in conversion efficiency compared with the reference cell. Quantum efficiency measurements allow us to associate the spectral characteristics of photoresponse enhancement with nanoscale structure of QD media. The dark current analysis provides valuable information about recombination in QD solar cells. The two-diode model well fit the scope of data and recovers the measured open circuit voltage.

  8. Theory of the Quantum Dot Hybrid Qubit

    NASA Astrophysics Data System (ADS)

    Friesen, Mark

    2015-03-01

    The quantum dot hybrid qubit, formed from three electrons in two quantum dots, combines the desirable features of charge qubits (fast manipulation) and spin qubits (long coherence times). The hybridized spin and charge states yield a unique energy spectrum with several useful properties, including two different operating regimes that are relatively immune to charge noise due to the presence of optimal working points or ``sweet spots.'' In this talk, I will describe dc and ac-driven gate operations of the quantum dot hybrid qubit. I will analyze improvements in the dephasing that are enabled by the sweet spots, and I will discuss the outlook for quantum hybrid qubits in terms of scalability. This work was supported in part by ARO (W911NF-12-0607), NSF (PHY-1104660), the USDOD, and the Intelligence Community Postdoctoral Research Fellowship Program. The views and conclusions contained in this presentation are those of the authors and should not be interpreted as representing the official policies or endorsements, either expressed or implied, of the US government.

  9. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

    SciTech Connect

    Betz, A. C. Broström, M.; Gonzalez-Zalba, M. F.; Tagliaferri, M. L. V.; Vinet, M.

    2016-05-16

    We present a reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consists of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired with improved silicon fabrication techniques, makes the corner state quantum dot approach a promising candidate for a scalable quantum information architecture.

  10. Controllable quantum scars in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Keski-Rahkonen, J.; Luukko, P. J. J.; Kaplan, L.; Heller, E. J.; Räsänen, E.

    2017-09-01

    Quantum scars are enhancements of quantum probability density along classical periodic orbits. We study the recently discovered phenomenon of strong perturbation-induced quantum scarring in the two-dimensional harmonic oscillator exposed to a homogeneous magnetic field. We demonstrate that both the geometry and the orientation of the scars are fully controllable with a magnetic field and a focused perturbative potential, respectively. These properties may open a path into an experimental scheme to manipulate electric currents in nanostructures fabricated in a two-dimensional electron gas.

  11. Quantum Optical Signature of Plasmonically Coupled Nanocrystal Quantum Dots.

    PubMed

    Wang, Feng; Karan, Niladri S; Nguyen, Hue Minh; Mangum, Benjamin D; Ghosh, Yagnaseni; Sheehan, Chris J; Hollingsworth, Jennifer A; Htoon, Han

    2015-10-01

    Small clusters of two to three silica-coated nanocrystals coupled to plasmonic gap-bar antennas can exhibit photon antibunching, a characteristic of single quantum emitters. Through a detailed analysis of their photoluminescence emissions characteristics, it is shown that the observed photon antibunching is the evidence of coupled quantum dot formation resulting from the plasmonic enhancement of dipole-dipole interaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Selection rules for probing biexcitons and electron spin transitions in isotropic quantum dot ensembles.

    PubMed

    Scholes, Gregory D

    2004-11-22

    Three-dimensional rotational averages are evaluated for third-order nonlinear spectroscopic measurements of quantum dots. Photon echo, transient grating, and transient absorption are explicitly considered. It is shown that (a) biexciton formation can be suppressed relative to other contributions to nonlinear spectroscopies for isotropic nanocrystal ensembles by choice of polarizations for the excitation pulses; (b) circularly polarized excitation light can differentiate between exciton spin states in nonlinear optical experiments; and (c) electron spin state flip kinetics can be probed directly in an isotropic quantum dot system by using certain sequences of linear cross-polarized pulses. Copyright 2004 American Institute of Physics.

  13. The impact of quantum dot filling on dual-band optical transitions via intermediate quantum states

    SciTech Connect

    Wu, Jiang; Passmore, Brandon; Manasreh, M. O.

    2015-08-28

    InAs/GaAs quantum dot infrared photodetectors with different doping levels were investigated to understand the effect of quantum dot filling on both intraband and interband optical transitions. The electron filling of self-assembled InAs quantum dots was varied by direct doping of quantum dots with different concentrations. Photoresponse in the near infrared and middle wavelength infrared spectral region was observed from samples with low quantum dot filling. Although undoped quantum dots were favored for interband transitions with the absence of a second optical excitation in the near infrared region, doped quantum dots were preferred to improve intraband transitions in the middle wavelength infrared region. As a result, partial filling of quantum dot was required, to the extent of maintaining a low dark current, to enhance the dual-band photoresponse through the confined electron states.

  14. Optical resonators and quantum dots: An excursion into quantum optics, quantum information and photonics

    NASA Astrophysics Data System (ADS)

    Bianucci, Pablo

    Modern communications technology has encouraged an intimate connection between Semiconductor Physics and Optics, and this connection shows best in the combination of electron-confining structures with light-confining structures. Semiconductor quantum dots are systems engineered to trap electrons in a mesoscopic scale (the are composed of ≈ 10000 atoms), resulting in a behavior resembling that of atoms, but much richer. Optical microresonators are engineered to confine light, increasing its intensity and enabling a much stronger interaction with matter. Their combination opens a myriad of new directions, both in fundamental Physics and in possible applications. This dissertation explores both semiconductor quantum dots and microresonators, through experimental work done with semiconductor quantum dots and microsphere resonators spanning the fields of Quantum Optics, Quantum Information and Photonics; from quantum algorithms to polarization converters. Quantum Optics leads the way, allowing us to understand how to manipulate and measure quantum dots with light and to elucidate the interactions between them and microresonators. In the Quantum Information area, we present a detailed study of the feasibility of excitons in quantum dots to perform quantum computations, including an experimental demonstration of the single-qubit Deutsch-Jozsa algorithm performedin a single semiconductor quantum dot. Our studies in Photonics involve applications of microsphere resonators, which we have learned to fabricate and characterize. We present an elaborate description of the experimental techniques needed to study microspheres, including studies and proof of concept experiments on both ultra-sensitive microsphere sensors and whispering gallery mode polarization converters.

  15. Spin thermopower in interacting quantum dots

    NASA Astrophysics Data System (ADS)

    Rejec, Tomaž; Žitko, Rok; Mravlje, Jernej; Ramšak, Anton

    2012-02-01

    Using analytical arguments and the numerical renormalization group method, we investigate the spin thermopower of a quantum dot in a magnetic field. In the particle-hole-symmetric situation, the temperature difference applied across the dot drives a pure spin current without accompanying charge current. For temperatures and fields at or above the Kondo temperature, but of the same order of magnitude, the spin-Seebeck coefficient is large, of the order of kB/|e|. Via a mapping, we relate the spin-Seebeck coefficient to the charge-Seebeck coefficient of a negative-U quantum dot where the corresponding result was recently reported by Andergassen [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.84.241107 84, 241107 (2011)]. For several regimes, we provide simplified analytical expressions. In the Kondo regime, the dependence of the spin-Seebeck coefficient on the temperature and the magnetic field is explained in terms of the shift of the Kondo resonance due to the field and its broadening with the temperature and the field. We also consider the influence of breaking the particle-hole symmetry and show that a pure spin current can still be realized, provided a suitable electric voltage is applied across the dot. Then, except for large asymmetries, the behavior of the spin-Seebeck coefficient remains similar to that found in the particle-hole-symmetric point.

  16. Planar Dirac electrons in magnetic quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, Ning; Zhu, Jia-Lin

    2012-05-01

    In this paper, we explore the size- and mass-dependent energy spectra and the electronic correlation of two- and three-electron graphene magnetic quantum dots. It is found that only the magnetic dots with large size can well confine the electrons. For large graphene magnetic dots with massless (ultra-relativity) electrons, the energy level structures of two Dirac electrons and even the ground state spin and angular momentum of three electrons are quite different from those of the usual semiconductor quantum dots. Also we reveal that such differences are not due to the magnetic confinement but originate from the character of the Coulomb interaction of two-component electronic wavefunctions in graphene. We reveal that the increase of the mass leads to both the crossover of the energy spectrum structures from the ultra-relativity to non-relativity ones and the increasing of the crystallization. The results are helpful for the understanding of the mass and size effects and may be useful in controlling the few-electron states in graphene-based nanodevices.

  17. Separability and dynamical symmetry of Quantum Dots

    SciTech Connect

    Zhang, P.-M.; Zou, L.-P.; Horvathy, P.A.; Gibbons, G.W.

    2014-02-15

    The separability and Runge–Lenz-type dynamical symmetry of the internal dynamics of certain two-electron Quantum Dots, found by Simonović et al. (2003), are traced back to that of the perturbed Kepler problem. A large class of axially symmetric perturbing potentials which allow for separation in parabolic coordinates can easily be found. Apart from the 2:1 anisotropic harmonic trapping potential considered in Simonović and Nazmitdinov (2013), they include a constant electric field parallel to the magnetic field (Stark effect), the ring-shaped Hartmann potential, etc. The harmonic case is studied in detail. -- Highlights: • The separability of Quantum Dots is derived from that of the perturbed Kepler problem. • Harmonic perturbation with 2:1 anisotropy is separable in parabolic coordinates. • The system has a conserved Runge–Lenz type quantity.

  18. Optically injected quantum-dot lasers.

    PubMed

    Erneux, T; Viktorov, E A; Kelleher, B; Goulding, D; Hegarty, S P; Huyet, G

    2010-04-01

    The response of an optically injected quantum-dot semiconductor laser (SL) is studied both experimentally and theoretically. In particular, the nature of the locking boundaries is investigated, revealing features more commonly associated with Class A lasers rather than conventional Class B SLs. Experimentally, two features stand out; the first is an absence of instabilities resulting from relaxation oscillations, and the second is the observation of a region of bistability between two locked solutions. Using rate equations appropriate for quantum-dot lasers, we analytically determine the stability diagram in terms of the injection rate and frequency detuning. Of particular interest are the Hopf and saddle-node locking boundaries that explain how the experimentally observed phenomena appear.

  19. Quantum Dot Detector Enhancement for Narrow Band Multispectral Applications

    DTIC Science & Technology

    2013-12-01

    Report contains color. 14. ABSTRACT The underlying principle of a photodetector is converting the optical signal into electrical signal. Under...enhancement of quantum dot photodetectors was also investigated. 15. SUBJECT TERMS quantum dot, quantum well, photodetectors , plasmonics 16...1.0 Introduction – Photodetectors .............................................................................................. 1 1.1 Types of

  20. Synthesis of Cesium Lead Halide Perovskite Quantum Dots

    ERIC Educational Resources Information Center

    Shekhirev, Mikhail; Goza, John; Teeter, Jacob D.; Lipatov, Alexey; Sinitskii, Alexander

    Synthesis of quantum dots is a valuable experiment for demonstration and discussion of quantum phenomena in undergraduate chemistry curricula. Recently, a new class of all-inorganic perovskite quantum dots (QDs) with a formula of CsPbX[subscript 3] (X = Cl, Br, I) was presented and attracted tremendous attention. Here we adapt the synthesis of…

  1. Deposition of Quantum Dots in a Capillary Tube.

    PubMed

    Kong, Yong Lin; Boulogne, François; Kim, Hyoungsoo; Nunes, Janine; Feng, Jie; Stone, Howard A

    2015-11-17

    The ability to assemble nanomaterials, such as quantum dots, enables the creation of functional devices that present unique optical and electronic properties. For instance, light-emitting diodes with exceptional color purity can be printed via the evaporative-driven assembly of quantum dots. Nevertheless, current studies of the colloidal deposition of quantum dots have been limited to the surfaces of a planar substrate. Here, we investigate the evaporation-driven assembly of quantum dots inside a confined cylindrical geometry. Specifically, we observe distinct deposition patterns, such as banding structures along the length of a capillary tube. Such coating behavior can be influenced by the evaporation speed as well as the concentration of quantum dots. Understanding the factors governing the coating process can provide a means to control the assembly of quantum dots inside a capillary tube, ultimately enabling the creation of novel photonic devices.

  2. Barrier Engineered Quantum Dot Infrared Photodetectors

    DTIC Science & Technology

    2015-06-01

    REPORT Kirtland AFB, NM 87117-5776 NUMBER(S) AFRL -RV-PS-TR-2015-0111 12. DISTRIBUTION / AVAILABILITY STATEMENT Approved for Public Release; Distribution... Kirtland AFB, NM 87117-5776 2 cys Official Record Copy AFRL /RVSS/David Cardimona 1 cy ... AFRL -RV-PS- AFRL -RV-PS- TR-2015-0111 TR-2015-0111 BARRIER ENGINEERED QUANTUM DOT INFRARED PHOTODETECTORS Sanjay Krishna Center for High Technology

  3. Multifunctional magnetic quantum dots for cancer theranostics.

    PubMed

    Singh, Surinder P

    2011-02-01

    The development of an innovative platform for cancer theranostics that will be capable of noninvasive imaging and treatment of cancerous tumors using biocompatible and multifunctional Fe3O4-ZnO core-shell magnetic quantum dots (M-QDs) is being explored. This multi-functional approach will facilitate deep tumor targeting using a combination of a specific cancer marker and an external magnetic field will simultaneously provide therapy that may evolve as a new paradigm in cancer theranostics.

  4. Intrinsic spin dynamics in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Valín-Rodríguez, Manuel

    2005-12-01

    We investigate the characteristic spin dynamics corresponding to semiconductor quantum dots within the multiband envelope function approximation (EFA). By numerically solving an 8 × 8 k·p Hamiltonian we treat systems based on different III-V semiconductor materials. It is shown that, even in the absence of an applied magnetic field, these systems show intrinsic spin dynamics governed by intraband and interband transitions leading to characteristic spin frequencies ranging from THz to optical frequencies.

  5. Carbon Nanotube Quantum Dots as THz Detectors

    DTIC Science & Technology

    2012-12-14

    devices that are viable for wafer -scale production. We recently started testing fabrication processes using epitaxial graphene on SiC in collaboration... laser sources at four different Fig. 4 Top: Drain current versus the gate voltage for different THz field intensities. Bottom: Temperature dependence...research. The first was the small coupling between the quantum dot and the powerful (10 mW) laser source. The second was the difficulty to reproduce the

  6. Relaxation dynamics in correlated quantum dots

    SciTech Connect

    Andergassen, S.; Schuricht, D.; Pletyukhov, M.; Schoeller, H.

    2014-12-04

    We study quantum many-body effects on the real-time evolution of the current through quantum dots. By using a non-equilibrium renormalization group approach, we provide analytic results for the relaxation dynamics into the stationary state and identify the microscopic cutoff scales that determine the transport rates. We find rich non-equilibrium physics induced by the interplay of the different energy scales. While the short-time limit is governed by universal dynamics, the long-time behavior features characteristic oscillations as well as an interplay of exponential and power-law decay.

  7. Single molecule study of silicon quantum dots

    NASA Astrophysics Data System (ADS)

    So, Woong Young; Li, Qi; Jin, Rongchao; Peteanu, Linda

    2016-09-01

    Recently, fluorescent Silicon (Si) Quantum Dots (QDs) have attracted much interest due to their high quantum yield, use of non-toxic and environmentally-benign chemicals, and water-solubility. However, more research is necessary to understand the energy level characteristics and single molecule behavior to enable their development for imaging applications. Therefore, single molecule time-resolved fluorescence spectroscopy of fluorescent Si QDs (cyan, green, and yellow) is needed. A rigorous analysis of time-resolved photon correlation spectroscopy and fluorescence lifetime data on single Si QDs at room temperature is presented.

  8. Si, Ge, and SiGe quantum wires and quantum dots

    NASA Astrophysics Data System (ADS)

    Pearsall, T. P.

    This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum structures based on group IV semiconductors. It discusses Si, Ge, and SiGe quantum wire and quantum dot structures, the synthesis of quantum wires and quantum dots, and applications of SiGe quantum-dot structures as photodetectors, light-emitting diodes, for optical amplification and as Si quantum-dot memories.

  9. Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study

    SciTech Connect

    Michael, Stephan; Chow, Weng; Schneider, Hans

    2016-05-01

    In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. We study the influence of two important quantum-dot material parameters, here, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density can compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. By minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.

  10. Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities

    NASA Astrophysics Data System (ADS)

    Wei, Hai-Rui; Deng, Fu-Guo

    2014-12-01

    Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low.

  11. Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities

    PubMed Central

    Wei, Hai-Rui; Deng, Fu-Guo

    2014-01-01

    Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low. PMID:25518899

  12. Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities.

    PubMed

    Wei, Hai-Rui; Deng, Fu-Guo

    2014-12-18

    Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low.

  13. Near-field magnetoabsorption of quantum dots

    NASA Astrophysics Data System (ADS)

    Simserides, Constantinos; Zora, Anna; Triberis, Georgios

    2006-04-01

    We investigate the effect of an external magnetic field of variable orientation and magnitude (up to 20T ) on the linear near-field optical absorption spectra of single and coupled III-V semiconductor quantum dots. We focus on the spatial as well as on the magnetic confinement, varying the dimensions of the quantum dots and the magnetic field. We show that the ground-state exciton binding energy can be manipulated utilizing the spatial and magnetic confinement. The effect of the magnetic field on the absorption spectra, increasing the near-field illumination spot, is also investigated. The zero-magnetic-field “structural” symmetry can be destroyed varying the magnetic field orientation and this affects the near-field spectra. The asymmetry induced (except for specific orientations along symmetry axes) by the magnetic field can be revealed in the near-field but not in the far-field spectra. We predict that near-field magnetoabsorption experiments, of realistic spatial resolution, will be in the position to bring to light the quantum dot symmetry. This exceptional symmetry-resolving power of the near-field magnetoabsorption is lost in the far field. The influence of the Coulomb interactions on the absorption spectra is also discussed. Finally, we show that certain modifications of the magnetoexcitonic structure can be uncovered using a realistically acute near-field probe of ≈20nm .

  14. Interfacing spins in an InGaAs quantum dot to a semiconductor waveguide circuit using emitted photons.

    PubMed

    Luxmoore, I J; Wasley, N A; Ramsay, A J; Thijssen, A C T; Oulton, R; Hugues, M; Kasture, S; Achanta, V G; Fox, A M; Skolnick, M S

    2013-01-18

    An in-plane spin-photon interface is essential for the integration of quantum dot spins with optical circuits. The optical dipole of a quantum dot lies in the plane and the spin is optically accessed via circularly polarized selection rules. Hence, a single waveguide, which can transport only one in-plane linear polarization component, cannot communicate the spin state between two points on a chip. To overcome this issue, we introduce a spin-photon interface based on two orthogonal waveguides, where the polarization emitted by a quantum dot is mapped to a path-encoded photon. We demonstrate operation by deducing the spin using the interference of in-plane photons. A second device directly maps right and left circular polarizations to antiparallel waveguides, surprising for a nonchiral structure but consistent with an off-center dot.

  15. Semiconductor quantum dot scintillation under gamma-ray irradiation.

    PubMed

    Létant, S E; Wang, T-F

    2006-12-01

    We recently demonstrated the ability of semiconductor quantum dots to convert alpha radiation into visible photons. In this letter, we report on the scintillation of quantum dots under gamma irradiation and compare the energy resolution of the 59 keV line of americium-241 obtained with our quantum dot-glass nanocomposite to that of a standard sodium iodide scintillator. A factor 2 improvement is demonstrated experimentally and interpreted theoretically using a combination of energy-loss and photon-transport models.

  16. Nanocarbons and quantum dots formation in new hybrid materials

    NASA Astrophysics Data System (ADS)

    Bogdanov, Kirill V.; Gromova, Yulia A.; Ermakov, Victor A.; Alaferdov, Andrei V.; Orlova, Anna O.; Moshkalev, Stanislav A.; Fedorov, Anatoly V.; Baranov, Alexander V.

    2014-05-01

    We present technique of obtaining complex hybrid structures combining the multi-walled carbon nanotubes or multi-layer graphene and luminescent hydrophobic semiconductor core/shell quantum dots CdSe/ZnS. As a result, a formation of quantum dot decorated carbon nanotubes and graphene films is evidenced by 2D microluminescence and micro-Raman mapping of quantum dots and nanocarbons, respectively, where a spatial correlation between the luminescence and Raman signals is found.

  17. UV Nano-Lights: Nonlinear Quantum Dot-Plasmon Coupling

    DTIC Science & Technology

    2014-08-01

    Final 3. DATES COVERED (From - To) 11-Mar-2013 to 10-Mar-2014 4. TITLE AND SUBTITLE UV Nano-Lights: Nonlinear Quantum Dot- Plasmon ...Nonlinear Quantum Dot- Plasmon Coupling 5a. CONTRACT NUMBER FA2386-13-1-4016 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) Eric...nonlinear emission from Quantum Dots through Plasmon Coupling PERIOD OF PERFORMANCE 11 March 2013 - 11 March 2014 RECIPIENT PRINCIPAL

  18. Molecular Profiling of Prostate Cancer Specimens Using Multicolor Quantum Dots

    DTIC Science & Technology

    2009-02-01

    0117 TITLE: Molecular profiling of prostate cancer specimens using Multicolor Quantum Dots PRINCIPAL INVESTIGATOR: Xiaohu Gao...profiling of prostate cancer specimens using Multicolor Quantum Dots 5a. CONTRACT NUMBER W81XWH-07-1-0117 5b. GRANT NUMBER PC061345 5c...based on the biology of their tumors. We proposed to develop oligonucleotide tagged quantum dots and antibodies for multiplexed imaging of prostate

  19. Quantum interface between light and nuclear spins in quantum dots

    NASA Astrophysics Data System (ADS)

    Schwager, Heike; Cirac, J. Ignacio; Giedke, Géza

    2010-01-01

    The coherent coupling of flying photonic qubits to stationary matter-based qubits is an essential building block for quantum-communication networks. We show how such a quantum interface can be realized between a traveling-wave optical field and the polarized nuclear spins in a singly charged quantum dot strongly coupled to a high-finesse optical cavity. By adiabatically eliminating the electron a direct effective coupling is achieved. Depending on the laser field applied, interactions that enable either write-in or read-out are obtained.

  20. Quantum transport through an array of quantum dots.

    PubMed

    Chen, Shuguang; Xie, Hang; Zhang, Yu; Cui, Xiaodong; Chen, Guanhua

    2013-01-07

    The transient current through an array of as many as 1000 quantum dots is simulated with two newly developed quantum mechanical methods. To our surprise, upon switching on the bias voltage, the current increases linearly with time before reaching its steady state value. And the time required for the current to reach its steady state value is proportional to the length of the array, and more interestingly, is exactly the time for a conducting electron to travel through the array at the Fermi velocity. These quantum phenomena can be understood by a simple analysis on the energetics of an equivalent classical circuit. An experimental design is proposed to confirm the numerical findings.

  1. Quantum transport through an array of quantum dots

    NASA Astrophysics Data System (ADS)

    Chen, Shuguang; Xie, Hang; Zhang, Yu; Cui, Xiaodong; Chen, Guanhua

    2012-12-01

    The transient current through an array of as many as 1000 quantum dots is simulated with two newly developed quantum mechanical methods. To our surprise, upon switching on the bias voltage, the current increases linearly with time before reaching its steady state value. And the time required for the current to reach its steady state value is proportional to the length of the array, and more interestingly, is exactly the time for a conducting electron to travel through the array at the Fermi velocity. These quantum phenomena can be understood by a simple analysis on the energetics of an equivalent classical circuit. An experimental design is proposed to confirm the numerical findings.

  2. Tuning the quantum critical crossover in quantum dots

    NASA Astrophysics Data System (ADS)

    Murthy, Ganpathy

    2005-03-01

    Quantum dots with large Thouless number g embody a regime where both disorder and interactions can be treated nonperturbatively using large-N techniques (with N=g) and quantum phase transitions can be studied. Here we focus on dots where the noninteracting Hamiltonian is drawn from a crossover ensemble between two symmetry classes, where the crossover parameter introduces a new, tunable energy scale independent of and much smaller than the Thouless energy. We show that the quantum critical regime, dominated by collective critical fluctuations, can be accessed at the new energy scale. The nonperturbative physics of this regime can only be described by the large-N approach, as we illustrate with two experimentally relevant examples. G. Murthy, PRB 70, 153304 (2004). G. Murthy, R. Shankar, D. Herman, and H. Mathur, PRB 69, 075321 (2004)

  3. Polarized quantum dot emission in electrohydrodynamic jet printed photonic crystals

    SciTech Connect

    See, Gloria G.; Xu, Lu; Nuzzo, Ralph G.; Sutanto, Erick; Alleyne, Andrew G.; Cunningham, Brian T.

    2015-08-03

    Tailored optical output, such as color purity and efficient optical intensity, are critical considerations for displays, particularly in mobile applications. To this end, we demonstrate a replica molded photonic crystal structure with embedded quantum dots. Electrohydrodynamic jet printing is used to control the position of the quantum dots within the device structure. This results in significantly less waste of the quantum dot material than application through drop-casting or spin coating. In addition, the targeted placement of the quantum dots minimizes any emission outside of the resonant enhancement field, which enables an 8× output enhancement and highly polarized emission from the photonic crystal structure.

  4. Terahertz transmission through rings of quantum dots-nanogap

    NASA Astrophysics Data System (ADS)

    Tripathi, Laxmi-Narayan; Bahk, Young-Mi; Choi, Geunchang; Han, Sanghoon; Park, Namkyoo; Kim, Dai-Sik

    2016-03-01

    We report resonant funneling of terahertz (THz) waves through (9 ± 1) nm wide quantum dots-nanogap of cadmium selenide quantum dots silver nanogap metamaterials. We observed a giant THz intensity enhancement (∼104) through the quantum dots-nanogap at the resonant frequency. We, further report the experimentally measured effective mode indices for these metamaterials. A finite difference time domain simulation of the nanogap enabled by the quantum dots supports the experimentally measured THz intensity enhancement across the nanogap. We propose that these low effective mode index terahertz resonators will be useful as bio/chemical sensors, gain-enhanced antennas, and wave guides.

  5. Polarized quantum dot emission in electrohydrodynamic jet printed photonic crystals

    NASA Astrophysics Data System (ADS)

    See, Gloria G.; Xu, Lu; Sutanto, Erick; Alleyne, Andrew G.; Nuzzo, Ralph G.; Cunningham, Brian T.

    2015-08-01

    Tailored optical output, such as color purity and efficient optical intensity, are critical considerations for displays, particularly in mobile applications. To this end, we demonstrate a replica molded photonic crystal structure with embedded quantum dots. Electrohydrodynamic jet printing is used to control the position of the quantum dots within the device structure. This results in significantly less waste of the quantum dot material than application through drop-casting or spin coating. In addition, the targeted placement of the quantum dots minimizes any emission outside of the resonant enhancement field, which enables an 8× output enhancement and highly polarized emission from the photonic crystal structure.

  6. Correlated electrons in coupled quantum dots and related phenomena

    NASA Astrophysics Data System (ADS)

    Ugajin, Ryuichi

    1998-01-01

    Three topics related to correlated electrons in coupled quantum dots are discussed. The first is quasi-resonance between multi-electron states, which causes hitherto unremarked types of resonant absorption in coupled quantum dots. The second is electron tunneling through a Hubbard gap, which is induced by an increase in the density of electrons in a quantum-dot chain under an overall confining potential. The third is Mott transition in a two-dimensional quantum-dot array induced by an external electric field. In this system, the metal-insulator transition goes through a heavy electron phase in which the density of correlated electrons fluctuates.

  7. Tolerance of Intrinsic Defects in PbS Quantum Dots.

    PubMed

    Zherebetskyy, Danylo; Zhang, Yingjie; Salmeron, Miquel; Wang, Lin-Wang

    2015-12-03

    Colloidal quantum dots exhibit various defects and deviations from ideal structures due to kinetic processes, although their band gap frequently remains open and clean. In this Letter, we computationally investigate intrinsic defects in a real-size PbS quantum dot passivated with realistic Cl-ligands. We show that the colloidal intrinsic defects are ionic in nature. Unlike previous computational results, we find that even nonideal, atomically nonstoichiometric quantum dots have a clean band gap without in-gap-states provided that quantum dots satisfy electronic stoichiometry.

  8. Realizing Rec. 2020 color gamut with quantum dot displays.

    PubMed

    Zhu, Ruidong; Luo, Zhenyue; Chen, Haiwei; Dong, Yajie; Wu, Shin-Tson

    2015-09-07

    We analyze how to realize Rec. 2020 wide color gamut with quantum dots. For photoluminescence, our simulation indicates that we are able to achieve over 97% of the Rec. 2020 standard with quantum dots by optimizing the emission spectra and redesigning the color filters. For electroluminescence, by optimizing the emission spectra of quantum dots is adequate to render over 97% of the Rec. 2020 standard. We also analyze the efficiency and angular performance of these devices, and then compare results with LCDs using green and red phosphors-based LED backlight. Our results indicate that quantum dot display is an outstanding candidate for achieving wide color gamut and high optical efficiency.

  9. Single-electron Spin Resonance in a Quadruple Quantum Dot.

    PubMed

    Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Ito, Takumi; Sugawara, Retsu; Noiri, Akito; Ludwig, Arne; Wieck, Andreas D; Tarucha, Seigo

    2016-08-23

    Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by conducting spin operations on a scaled up system. Here, we demonstrate single-electron spin resonance in a quadruple quantum dot. A few-electron quadruple quantum dot is formed within a magnetic field gradient created by a micro-magnet. We oscillate the wave functions of the electrons in the quantum dots by applying microwave voltages and this induces electron spin resonance. The resonance energies of the four quantum dots are slightly different because of the stray field created by the micro-magnet and therefore frequency-resolved addressable control of each electron spin resonance is possible.

  10. Silicon quantum dots: fine-tuning to maturity.

    PubMed

    Morello, Andrea

    2015-12-18

    Quantum dots in semiconductor heterostructures provide one of the most flexible platforms for the study of quantum phenomena at the nanoscale. The surging interest in using quantum dots for quantum computation is forcing researchers to rethink fabrication and operation methods, to obtain highly tunable dots in spin-free host materials, such as silicon. Borselli and colleagues report in Nanotechnology the fabrication of a novel Si/SiGe double quantum dot device, which combines an ultra-low disorder Si/SiGe accumulation-mode heterostructure with a stack of overlapping control gates, ensuring tight confining potentials and exquisite tunability. This work signals the technological maturity of silicon quantum dots, and their readiness to be applied to challenging projects in quantum information science.

  11. Single-electron Spin Resonance in a Quadruple Quantum Dot

    NASA Astrophysics Data System (ADS)

    Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R.; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Ito, Takumi; Sugawara, Retsu; Noiri, Akito; Ludwig, Arne; Wieck, Andreas D.; Tarucha, Seigo

    2016-08-01

    Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by conducting spin operations on a scaled up system. Here, we demonstrate single-electron spin resonance in a quadruple quantum dot. A few-electron quadruple quantum dot is formed within a magnetic field gradient created by a micro-magnet. We oscillate the wave functions of the electrons in the quantum dots by applying microwave voltages and this induces electron spin resonance. The resonance energies of the four quantum dots are slightly different because of the stray field created by the micro-magnet and therefore frequency-resolved addressable control of each electron spin resonance is possible.

  12. Single-electron Spin Resonance in a Quadruple Quantum Dot

    PubMed Central

    Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R.; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Ito, Takumi; Sugawara, Retsu; Noiri, Akito; Ludwig, Arne; Wieck, Andreas D.; Tarucha, Seigo

    2016-01-01

    Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by conducting spin operations on a scaled up system. Here, we demonstrate single-electron spin resonance in a quadruple quantum dot. A few-electron quadruple quantum dot is formed within a magnetic field gradient created by a micro-magnet. We oscillate the wave functions of the electrons in the quantum dots by applying microwave voltages and this induces electron spin resonance. The resonance energies of the four quantum dots are slightly different because of the stray field created by the micro-magnet and therefore frequency-resolved addressable control of each electron spin resonance is possible. PMID:27550534

  13. Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer.

    PubMed

    Zhao, Tianshuo; Goodwin, Earl D; Guo, Jiacen; Wang, Han; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2016-09-22

    Advanced architectures are required to further improve the performance of colloidal PbS heterojunction quantum dot solar cells. Here, we introduce a CdI2-treated CdSe quantum dot buffer layer at the junction between ZnO nanoparticles and PbS quantum dots in the solar cells. We exploit the surface- and size-tunable electronic properties of the CdSe quantum dots to optimize its carrier concentration and energy band alignment in the heterojunction. We combine optical, electrical, and analytical measurements to show that the CdSe quantum dot buffer layer suppresses interface recombination and contributes additional photogenerated carriers, increasing the open-circuit voltage and short-circuit current of PbS quantum dot solar cells, leading to a 25% increase in solar power conversion efficiency.

  14. Nanoscale patterning of colloidal quantum dots for surface plasmon generation

    NASA Astrophysics Data System (ADS)

    Park, Yeonsang; Roh, Young-Geun; Kim, Un Jeong; Chung, Dae-Young; Suh, Hwansoo; Kim, Jineun; Cheon, Sangmo; Lee, Jaesoong; Kim, Tae-Ho; Cho, Kyung-Sang; Lee, Chang-Won

    2013-03-01

    The patterning of colloidal quantum dots with nanometer resolution is essential for their application in photonics and plasmonics. Several patterning approaches, such as the use of polymer composites, molecular lock-and-key methods, inkjet printing, and microcontact printing of quantum dots, have limits in fabrication resolution, positioning and the variation of structural shapes. Herein, we present an adaptation of a conventional liftoff method for patterning colloidal quantum dots. This simple method is easy and requires no complicated processes. Using this method, we formed straight lines, rings, and dot patterns of colloidal quantum dots on metallic substrates. Notably, patterned lines approximately 10 nm wide were fabricated. The patterned structures display high resolution, accurate positioning, and well-defined sidewall profiles. To demonstrate the applicability of our method, we present a surface plasmon generator elaborated from quantum dots.

  15. Quantum-Dot-Based Telecommunication-Wavelength Quantum Relay

    NASA Astrophysics Data System (ADS)

    Huwer, J.; Stevenson, R. M.; Skiba-Szymanska, J.; Ward, M. B.; Shields, A. J.; Felle, M.; Farrer, I.; Ritchie, D. A.; Penty, R. V.

    2017-08-01

    The development of quantum relays for long-haul and attack-proof quantum communication networks operating with weak coherent laser pulses requires entangled photon sources at telecommunication wavelengths with intrinsic single-photon emission for most practical implementations. Using a semiconductor quantum dot emitting entangled photon pairs in the telecommunication O band, we demonstrate a quantum relay fulfilling both of these conditions. The system achieves a maximum fidelity of 94.5% for implementation of a standard four-state protocol with input states generated by a laser. We further investigate robustness against frequency detuning of the narrow-band input and perform process tomography of the teleporter, revealing operation for arbitrary pure input states, with an average gate fidelity of 83.6%. The results highlight the potential of semiconductor light sources for compact and robust quantum-relay technology that is compatible with existing communication infrastructures.

  16. Optical Properties of Zinc Oxide Quantum Dots

    NASA Astrophysics Data System (ADS)

    Hsieh, Wen-Feng; Hsu, Hsu-Cheng; Liao, Wan-Jiun; Cheng, Hsin-Ming; Lin, Kuo-Feng; Hsu, Wei-Tze; Pan, Chin-Jiu

    Size-dependence of efficient UV photoluminescence (PL) and absorption spectra of various sizes of zinc oxide (ZnO) quantum dots (QDs) give evidence for the quantum confinement effect. Bandgap enlargement is in agreement with the theoretical calculation based on the effective mass model for the size of ZnO QDs being comparable to the Bohr radius of bulk exciton. By using the modified spatial correlation model to fit the measured Raman spectra, we reveal that the Raman spectral shift and asymmetry for E2(high) mode are caused by localization of optical phonons. Furthermore, we present temperature-dependent PL of different sizes of ZnO particles. The unobvious LO-phonon replicas of free exciton (FX) were observed when the ZnO particle sizes were under 12 nm in diameter. The increasing exciton energy (Eb) with the decreasing quantum dot size can be obtained from temperature-dependent PL. From the temperature-dependent change of FX emission energy, we deduce that the exciton-LO phonon coupling strength reduces as the particle size decreases. The reduced exciton Bohr radius aB with particle size obtained from Eb and PL spectrum confirms that the exciton becomes less polar in turn reducing the Fröhlich interaction and the exciton-LO phonon interaction is reduced with decreasing size of the ZnO QDs. In addition, the nearly unchanged spectral shape in power dependent PL of ZnO quantum dots reveals stable exciton states without formation of biexcitons and exciton-exciton cattering.

  17. Hybrid passivated colloidal quantum dot solids

    NASA Astrophysics Data System (ADS)

    Ip, Alexander H.; Thon, Susanna M.; Hoogland, Sjoerd; Voznyy, Oleksandr; Zhitomirsky, David; Debnath, Ratan; Levina, Larissa; Rollny, Lisa R.; Carey, Graham H.; Fischer, Armin; Kemp, Kyle W.; Kramer, Illan J.; Ning, Zhijun; Labelle, André J.; Chou, Kang Wei; Amassian, Aram; Sargent, Edward H.

    2012-09-01

    Colloidal quantum dot (CQD) films allow large-area solution processing and bandgap tuning through the quantum size effect. However, the high ratio of surface area to volume makes CQD films prone to high trap state densities if surfaces are imperfectly passivated, promoting recombination of charge carriers that is detrimental to device performance. Recent advances have replaced the long insulating ligands that enable colloidal stability following synthesis with shorter organic linkers or halide anions, leading to improved passivation and higher packing densities. Although this substitution has been performed using solid-state ligand exchange, a solution-based approach is preferable because it enables increased control over the balance of charges on the surface of the quantum dot, which is essential for eliminating midgap trap states. Furthermore, the solution-based approach leverages recent progress in metal:chalcogen chemistry in the liquid phase. Here, we quantify the density of midgap trap states in CQD solids and show that the performance of CQD-based photovoltaics is now limited by electron-hole recombination due to these states. Next, using density functional theory and optoelectronic device modelling, we show that to improve this performance it is essential to bind a suitable ligand to each potential trap site on the surface of the quantum dot. We then develop a robust hybrid passivation scheme that involves introducing halide anions during the end stages of the synthesis process, which can passivate trap sites that are inaccessible to much larger organic ligands. An organic crosslinking strategy is then used to form the film. Finally, we use our hybrid passivated CQD solid to fabricate a solar cell with a certified efficiency of 7.0%, which is a record for a CQD photovoltaic device.

  18. Hybrid passivated colloidal quantum dot solids.

    PubMed

    Ip, Alexander H; Thon, Susanna M; Hoogland, Sjoerd; Voznyy, Oleksandr; Zhitomirsky, David; Debnath, Ratan; Levina, Larissa; Rollny, Lisa R; Carey, Graham H; Fischer, Armin; Kemp, Kyle W; Kramer, Illan J; Ning, Zhijun; Labelle, André J; Chou, Kang Wei; Amassian, Aram; Sargent, Edward H

    2012-09-01

    Colloidal quantum dot (CQD) films allow large-area solution processing and bandgap tuning through the quantum size effect. However, the high ratio of surface area to volume makes CQD films prone to high trap state densities if surfaces are imperfectly passivated, promoting recombination of charge carriers that is detrimental to device performance. Recent advances have replaced the long insulating ligands that enable colloidal stability following synthesis with shorter organic linkers or halide anions, leading to improved passivation and higher packing densities. Although this substitution has been performed using solid-state ligand exchange, a solution-based approach is preferable because it enables increased control over the balance of charges on the surface of the quantum dot, which is essential for eliminating midgap trap states. Furthermore, the solution-based approach leverages recent progress in metal:chalcogen chemistry in the liquid phase. Here, we quantify the density of midgap trap states in CQD solids and show that the performance of CQD-based photovoltaics is now limited by electron-hole recombination due to these states. Next, using density functional theory and optoelectronic device modelling, we show that to improve this performance it is essential to bind a suitable ligand to each potential trap site on the surface of the quantum dot. We then develop a robust hybrid passivation scheme that involves introducing halide anions during the end stages of the synthesis process, which can passivate trap sites that are inaccessible to much larger organic ligands. An organic crosslinking strategy is then used to form the film. Finally, we use our hybrid passivated CQD solid to fabricate a solar cell with a certified efficiency of 7.0%, which is a record for a CQD photovoltaic device.

  19. Thermoelectrics with Coulomb-coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Thierschmann, Holger; Sánchez, Rafael; Sothmann, Björn; Buhmann, Hartmut; Molenkamp, Laurens W.

    2016-12-01

    In this article we review the thermoelectric properties of three terminal devices with Coulomb-coupled quantum dots (QDs) as observed in recent experiments [1,2]. The system we consider consists of two Coulomb-blockade QDs, one of which can exchange electrons with only a single reservoir (heat reservoir), while the other dot is tunnel coupled with two reservoirs at a lower temperature (conductor). The heat reservoir and the conductor interact only via the Coulomb coupling of the quantum dots. It has been found that two regimes have to be considered. In the first one, the heat flow between the two systems is small. In this regime, thermally driven occupation fluctuations of the hot QD modify the transport properties of the conductor system. This leads to an effect called thermal gating. Experiments have shown how this can be used to control charge flow in the conductor by means of temperature in a remote reservoir. We further substantiate the observations with model calculations, and implications for the realisation of an all-thermal transistor are discussed. In the second regime, the heat flow between the two systems is relevant. Here the system works as a nanoscale heat engine, as proposed recently (Sánchez and Büttiker [3]). We review the conceptual idea, its experimental realisation and the novel features arising in this new kind of thermoelectric device such as decoupling of heat and charge flow.

  20. Adiabatic Spin Pumping with Quantum Dots

    NASA Astrophysics Data System (ADS)

    Mucciolo, Eduardo R.

    Electronic transport in mesoscopic systems has been intensively studied for more the last three decades. While there is a substantial understanding of the stationary regime, much less is know about phase-coherent nonequilibrium transport when pulses or ac perturbations are used to drive electrons at low temperatures and at small length scales. However, about 20 years ago Thouless proposed to drive nondissipative currents in quantum systems by applying simultaneously two phase-locked external perturbations. The so-called adiabatic pumping mechanism has been revived in the last few years, both theoretically and experimentally, in part because of the development of lateral semiconductor quantum dots. Here we will explain how open dots can be used to create spin-polarized currents with little or no net charge transfer. The pure spin pump we propose is the analog of a charge battery in conventional electronics and may provide a needed circuit element for spin-based electronics. We will also discuss other relevant issues such as rectification and decoherence and point out possible extensions of the mechanism to closed dots.

  1. Nonrenewal statistics in transport through quantum dots

    NASA Astrophysics Data System (ADS)

    Ptaszyński, Krzysztof

    2017-01-01

    The distribution of waiting times between successive tunneling events is an already established method to characterize current fluctuations in mesoscopic systems. Here, I investigate mechanisms generating correlations between subsequent waiting times in two model systems, a pair of capacitively coupled quantum dots and a single-level dot attached to spin-polarized leads. Waiting time correlations are shown to give insight into the internal dynamics of the system; for example they allow distinction between different mechanisms of the noise enhancement. Moreover, the presence of correlations breaks the validity of the renewal theory. This increases the number of independent cumulants of current fluctuation statistics, thus providing additional sources of information about the transport mechanism. I also propose a method for inferring the presence of waiting time correlations based on low-order current correlation functions. This method gives a way to extend the analysis of nonrenewal current fluctuations to the systems for which single-electron counting is not experimentally feasible. The experimental relevance of the findings is also discussed; for example reanalysis of previous results concerning transport in quantum dots is suggested.

  2. Amphoteric CdSe nanocrystalline quantum dots.

    PubMed

    Islam, Mohammad A

    2008-06-25

    The nanocrystal quantum dot (NQD) charge states strongly influence their electrical transport properties in photovoltaic and electroluminescent devices, optical gains in NQD lasers, and the stability of the dots in thin films. We report a unique electrostatic nature of CdSe NQDs, studied by electrophoretic methods. When we submerged a pair of metal electrodes, in a parallel plate capacitor configuration, into a dilute solution of CdSe NQDs in hexane, and applied a DC voltage across the pair, thin films of CdSe NQDs were deposited on both the positive and the negative electrodes. Extensive characterizations including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and Raman studies revealed that the films on both the positive and the negative electrodes were identical in every respect, clearly indicating that: (1) a fraction (<1%) of the CdSe NQDs in free form in hexane solution are charged and, more importantly, (2) there are equal numbers of positive and negative CdSe NQDs in the hexane solution. Experiments also show that the number of deposited dots is at least an order of magnitude higher than the number of initially charged dots, indicating regeneration. We used simple thermodynamics to explain such amphoteric nature and the charging/regeneration of the CdSe NQDs.

  3. Quantum Dots: An Experiment for Physical or Materials Chemistry

    ERIC Educational Resources Information Center

    Winkler, L. D.; Arceo, J. F.; Hughes, W. C.; DeGraff, B. A.; Augustine, B. H.

    2005-01-01

    An experiment is conducted for obtaining quantum dots for physical or materials chemistry. This experiment serves to both reinforce the basic concept of quantum confinement and providing a useful bridge between the molecular and solid-state world.

  4. Quantum Dots: An Experiment for Physical or Materials Chemistry

    ERIC Educational Resources Information Center

    Winkler, L. D.; Arceo, J. F.; Hughes, W. C.; DeGraff, B. A.; Augustine, B. H.

    2005-01-01

    An experiment is conducted for obtaining quantum dots for physical or materials chemistry. This experiment serves to both reinforce the basic concept of quantum confinement and providing a useful bridge between the molecular and solid-state world.

  5. Optical activity of helical quantum-dot supercrystals

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    The size of chiral nanoparticles is much smaller than the optical wavelength. As a result, the difference in interaction of enantiomers with circularly polarized light of different handedness is practically unobservable. Due to the large mismatch in scale, the problem of enhancement of enantioselectivity of optical properties of nanoparticles is particularly important for modern photonics. In this work, we show that ordering of achiral nanoparticles into a chiral supercrystal with dimensions comparable to the wavelength of light allows achieving nearly total dissymmetry of optical absorption and demonstrate this using a helical super-crystal made of semiconductor quantum dots as an example. The proposed approach may find numerous applications in various optical and analytical methods used in biomedicine, chemistry, and pharmacology.

  6. Non-Markovian coherent feedback control of quantum dot systems

    NASA Astrophysics Data System (ADS)

    Xue, Shibei; Wu, Rebing; Hush, Michael R.; Tarn, Tzyh-Jong

    2017-03-01

    In this paper we present a non-Markovian coherent feedback scheme for decoherence suppression in single quantum dot systems. The feedback loop is closed via a quantum tunnelling junction between the natural source and drain baths of the quantum dot. The exact feedback-controlled non-Markovian Langevin equation is derived for describing the dynamics of the quantum dot. To deal with the nonlinear memory function in the Langevin equation, we analyse the Green’s function-based root locus, from which we show that the decoherence of the quantum dot can be suppressed via increasing the feedback coupling strength. The effectiveness of decoherence suppression induced by non-Markovian coherent feedback is demonstrated by a single quantum dot example bathed with Lorentzian noises.

  7. Inversion of hysteresis in quantum dot controlled quantum-wire transistor

    NASA Astrophysics Data System (ADS)

    Müller, C. R.; Worschech, L.; Forchel, A.

    2009-05-01

    In a quantum-wire transistor, pronounced floating-gate function of quantum dots is demonstrated with large threshold hysteresis exceeding 1.5 V. The charge state of the quantum dots is electrically controlled and, by applying a critical bias voltage along the quantum wire, the charging mechanism of the quantum dots is deactivated or, for bias voltages above this critical bias point, even inverted. It is shown that the charging as well as discharging of the quantum dots can be selectively switched off; i.e., the floating-gate function of the quantum dots is suppressed. The inversion of the hysteresis is explained within the framework of a capacitor model and the control of the charging mechanism is attributed to a dynamic gate efficiency of the quantum wire, which can be either larger or smaller than the quantum dot gate efficiency.

  8. Electrostatically defined silicon quantum dots with counted antimony donor implants

    SciTech Connect

    Singh, M. Luhman, D. R.; Lilly, M. P.; Pacheco, J. L.; Perry, D.; Garratt, E.; Ten Eyck, G.; Bishop, N. C.; Wendt, J. R.; Manginell, R. P.; Dominguez, J.; Pluym, T.; Bielejec, E.; Carroll, M. S.

    2016-02-08

    Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors in 100 nm × 150 nm windows straddling quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular Coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants.

  9. Energy levels of bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    da Costa, D. R.; Zarenia, M.; Chaves, Andrey; Farias, G. A.; Peeters, F. M.

    2015-09-01

    Within a tight binding approach we investigate the energy levels of hexagonal and triangular bilayer graphene (BLG) quantum dots (QDs) with zigzag and armchair edges. We study AA- and AB- (Bernal) stacked BLG QDs and obtain the energy levels in both the absence and the presence of a perpendicular electric field (i.e., biased BLG QDs). Our results show that the size dependence of the energy levels is different from that of monolayer graphene QDs. The energy spectrum of AB-stacked BLG QDs with zigzag edges exhibits edge states which spread out into the opened energy gap in the presence of a perpendicular electric field. We found that the behavior of these edges states is different for the hexagonal and triangular geometries. In the case of AA-stacked BLG QDs, the electron and hole energy levels cross each other in both cases of armchair and zigzag edges as the dot size or the applied bias increases.

  10. Lateral excitonic switching in vertically stacked quantum dots

    SciTech Connect

    Jarzynka, Jarosław R.; McDonald, Peter G.; Galbraith, Ian; Shumway, John

    2016-06-14

    We show that the application of a vertical electric field to the Coulomb interacting system in stacked quantum dots leads to a 90° in-plane switching of charge probability distribution in contrast to a single dot, where no such switching exists. Results are obtained using path integral quantum Monte Carlo with realistic dot geometry, alloy composition, and piezo-electric potential profiles. The origin of the switching lies in the strain interactions between the stacked dots hence the need for more than one layer of dots. The lateral polarization and electric field dependence of the radiative lifetimes of the excitonic switch are also discussed.

  11. Nano-laser on silicon quantum dots

    NASA Astrophysics Data System (ADS)

    Huang, Wei-Qi; Liu, Shi-Rong; Qin, Chao-Jian; Lü, Quan; Xu, Li

    2011-04-01

    A new conception of nano-laser is proposed in which depending on the size of nano-clusters (silicon quantum dots (QD)), the pumping level of laser can be tuned by the quantum confinement (QC) effect, and the population inversion can be formed between the valence band and the localized states in gap produced from the surface bonds of nano-clusters. Here we report the experimental demonstration of nano-laser on silicon quantum dots fabricated by nanosecond pulse laser. The peaks of stimulated emission are observed at 605 nm and 693 nm. Through the micro-cavity of nano-laser, a full width at half maximum of the peak at 693 nm can reach to 0.5 nm. The theoretical model and the experimental results indicate that it is a necessary condition for setting up nano-laser that the smaller size of QD (d < 3 nm) can make the localized states into band gap. The emission energy of nano-laser will be limited in the range of 1.7-2.3 eV generally due to the position of the localized states in gap, which is in good agreement between the experiments and the theory.

  12. Performance analysis of quantum dots infrared photodetector

    NASA Astrophysics Data System (ADS)

    Liu, Hongmei; Zhang, Fangfang; Zhang, Jianqi; He, Guojing

    2011-08-01

    Performance analysis of the quantum dots infrared photodetector(QDIP), which can provide device designers with theoretical guidance and experimental verification, arouses a wide interest and becomes a hot research topic in the recent years. In the paper, in comparison with quantum well infrared photodetector(QWIP) characteristic, the performance of QDIP is mainly discussed and summarized by analyzing the special properties of quantum dots material. To be specific, the dark current density and the detectivity in the normalized incident phenomenon are obtained from Phillip performance model, the carrier lifetime and the dark current of QDIP are studied by combing with the "photon bottleneck" effect, and the detectivity of QDIP is theoretically derived from considering photoconduction gain under the influence of the capture probability. From the experimental results, a conclusion is made that QDIP can not only receive the normal incidence light, but also has the advantages of the long carrier life, the big photoconductive gain, the low dark current and so on, and it further illustrates a anticipated superiority of QDIP in performance and a wide use of QDIP in many engineering fields in the future.

  13. Increased normal incidence photocurrent in quantum dot infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Shao, Jiayi; Vandervelde, Thomas E.; Barve, Ajit; Stintz, Andreas; Krishna, Sanjay

    2012-12-01

    We have increased the ratio of s-polarization (normal incidence) to p-polarization photocurrent to 50% in a quantum dot-in-a-well based infrared photodetector form the typical s-p polarization ratio about 20%. This improvement was achieved by engineering the dot geometry and the quantum confinement via post growth capping materials of the Stranski Krastanov growth mode quantum dots (QDs). The TEM images show that the height to base ratio of shape engineered QDs was increased to 8 nm/12 nm from the control sample's ratio 4 nm/17 nm. The dot geometry correlates with the polarized photocurrent measurements of the detector.

  14. Controlling quantum dot energies using submonolayer bandstructure engineering

    SciTech Connect

    Yu, L.; Law, S.; Wasserman, D.; Jung, D.; Lee, M. L.; Shen, J.; Cha, J. J.

    2014-08-25

    We demonstrate control of energy states in epitaxially-grown quantum dot structures formed by stacked submonolayer InAs depositions via engineering of the internal bandstructure of the dots. Transmission electron microscopy of the stacked sub-monolayer regions shows compositional inhomogeneity, indicative of the presence of quantum dots. The quantum dot ground state is manipulated not only by the number of deposited InAs layers, but also by control of the thickness and material composition of the spacing layers between submonolayer InAs depositions. In this manner, we demonstrate the ability to shift the quantum dot ground state energy at 77 K from 1.38 eV to 1.88 eV. The results presented offer a potential avenue towards enhanced control of dot energies for a variety of optoelectronic applications.

  15. Implementing of Quantum Cloning with Spatially Separated Quantum Dot Spins

    NASA Astrophysics Data System (ADS)

    Wen, Jing-Ji; Yeon, Kyu-Hwang; Du, Xin; Lv, Jia; Wang, Ming; Wang, Hong-Fu; Zhang, Shou

    2016-07-01

    We propose some schemes for implementing optimal symmetric (asymmetric) 1 → 2 universal quantum cloning, optimal symmetric (asymmetric) 1 → 2 phase-covariant cloning, optimal symmetric 1 → 3 economical phase-covariant cloning and optimal symmetric 1 → 3 economical real state cloning with spatially separated quantum dot spins by choosing the single-qubit rotation angles appropriately. The decoherences of the spontaneous emission of QDs, cavity decay and fiber loss are suppressed since the effective long-distance off-resonant interaction between two distant QDs is mediated by the vacuum fields of the fiber and cavity, and during the whole process no system is excited.

  16. Quantum model for mode locking in pulsed semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Beugeling, W.; Uhrig, Götz S.; Anders, Frithjof B.

    2016-12-01

    Quantum dots in GaAs/InGaAs structures have been proposed as a candidate system for realizing quantum computing. The short coherence time of the electronic quantum state that arises from coupling to the nuclei of the substrate is dramatically increased if the system is subjected to a magnetic field and to repeated optical pulsing. This enhancement is due to mode locking: oscillation frequencies resonant with the pulsing frequencies are enhanced, while off-resonant oscillations eventually die out. Because the resonant frequencies are determined by the pulsing frequency only, the system becomes immune to frequency shifts caused by the nuclear coupling and by slight variations between individual quantum dots. The effects remain even after the optical pulsing is terminated. In this work, we explore the phenomenon of mode locking from a quantum mechanical perspective. We treat the dynamics using the central-spin model, which includes coupling to 10-20 nuclei and incoherent decay of the excited electronic state, in a perturbative framework. Using scaling arguments, we extrapolate our results to realistic system parameters. We estimate that the synchronization to the pulsing frequency needs time scales in the order of 1 s .

  17. A Nanowire-Based Plasmonic Quantum Dot Laser.

    PubMed

    Ho, Jinfa; Tatebayashi, Jun; Sergent, Sylvain; Fong, Chee Fai; Ota, Yasutomo; Iwamoto, Satoshi; Arakawa, Yasuhiko

    2016-04-13

    Quantum dots enable strong carrier confinement and exhibit a delta-function like density of states, offering significant improvements to laser performance and high-temperature stability when used as a gain medium. However, quantum dot lasers have been limited to photonic cavities that are diffraction-limited and further miniaturization to meet the demands of nanophotonic-electronic integration applications is challenging based on existing designs. Here we introduce the first quantum dot-based plasmonic laser to reduce the cross-sectional area of nanowire quantum dot lasers below the cutoff limit of photonic modes while maintaining the length in the order of the lasing wavelength. Metal organic chemical vapor deposition grown GaAs-AlGaAs core-shell nanowires containing InGaAs quantum dot stacks are placed directly on a silver film, and lasing was observed from single nanowires originating from the InGaAs quantum dot emission into the low-loss higher order plasmonic mode. Lasing threshold pump fluences as low as ∼120 μJ/cm(2) was observed at 7 K, and lasing was observed up to 125 K. Temperature stability from the quantum dot gain, leading to a high characteristic temperature was demonstrated. These results indicate that high-performance, miniaturized quantum dot lasers can be realized with plasmonics.

  18. Fast synthesize ZnO quantum dots via ultrasonic method.

    PubMed

    Yang, Weimin; Zhang, Bing; Ding, Nan; Ding, Wenhao; Wang, Lixi; Yu, Mingxun; Zhang, Qitu

    2016-05-01

    Green emission ZnO quantum dots were synthesized by an ultrasonic sol-gel method. The ZnO quantum dots were synthesized in various ultrasonic temperature and time. Photoluminescence properties of these ZnO quantum dots were measured. Time-resolved photoluminescence decay spectra were also taken to discover the change of defects amount during the reaction. Both ultrasonic temperature and time could affect the type and amount of defects in ZnO quantum dots. Total defects of ZnO quantum dots decreased with the increasing of ultrasonic temperature and time. The dangling bonds defects disappeared faster than the optical defects. Types of optical defects first changed from oxygen interstitial defects to oxygen vacancy and zinc interstitial defects. Then transformed back to oxygen interstitial defects again. The sizes of ZnO quantum dots would be controlled by both ultrasonic temperature and time as well. That is, with the increasing of ultrasonic temperature and time, the sizes of ZnO quantum dots first decreased then increased. Moreover, concentrated raw materials solution brought larger sizes and more optical defects of ZnO quantum dots. Copyright © 2015 Elsevier B.V. All rights reserved.

  19. Energy transfer in hybrid systems quantum dot-plasmonic nanostructures

    NASA Astrophysics Data System (ADS)

    Chaplik, A. V.

    2016-06-01

    Radiationless relaxation in hybrid systems quantum dot (QD)-plasmonic nanostructure is considered. For the system QD-2D plasma the relaxation rate extremely steeply depends on the radius of quantum dot while in the pair QD-cylindrical wire contacting each other this dependence is logarithmic weak.

  20. Quantum-dot cluster-state computing with encoded qubits

    SciTech Connect

    Weinstein, Yaakov S.; Hellberg, C. Stephen; Levy, Jeremy

    2005-08-15

    A class of architectures is advanced for cluster-state quantum computation using quantum dots. These architectures include using single and multiple dots as logical qubits. Special attention is given to supercoherent qubits introduced by Bacon et al. [Phys. Rev. Lett. 87, 247902 (2001)] for which we discuss the effects of various errors and present a means of error protection.

  1. Spin-dependent shot noise enhancement in a quantum dot

    NASA Astrophysics Data System (ADS)

    Ubbelohde, Niels; Fricke, Christian; Hohls, Frank; Haug, Rolf J.

    2013-07-01

    The spin-dependent dynamical blockade was investigated in a lateral quantum dot in a magnetic field. Spin-polarized edge channels in the two-dimensional leads and the spatial distribution of Landau orbitals in the dot modulate the tunnel coupling of the quantum dot level spectrum. In a measurement of the electron shot noise we observe a pattern of super-Poissonian noise which is correlated to the spin-dependent competition between different transport channels.

  2. Non-Equilibrium Quantum Dots: Transport

    DTIC Science & Technology

    1990-03-19

    William R Frensley, Rajni J Aggarwal, Richard J Matyi, Tom M Moore, and Anna E Wetsel for their contributions and R K Aldert, E D Pijan, D A Schultz, P...Peacock D C, Ritchie D A and Jones G A C 1988 J . Phys. C: Solid State Phys. L209 Moore T M and Wetsel A E 1988 Phys. Rev. Lett. 60 535 [lZ...Reed M A, Randall J N, Luscombe J H, Frensley W R, Aggarwal R J, Matyi R J, Moore T M and Wetsel A E 1989 Quantum Dot Resonant lbnnelling Spectroscopy

  3. Quantum dots confined in nanoporous alumina membranes

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Xia, Jianfeng; Wang, Jun; Shinar, Joseph; Lin, Zhiqun

    2006-09-01

    CdSe /ZnS core/shell quantum dots (QDs) were filled into porous alumina membranes (PAMs) by dip coating. The deposition of QDs induced changes in the refractive index of the PAMs. The amount of absorbed QDs was quantified by fitting the reflection and transmission spectra observed experimentally with one side open and freestanding (i.e., with two sides open) PAMs employed, respectively. The fluorescence of the QDs was found to be retained within the cylindrical nanopores of the PAMs.

  4. Luminescence studies of individual quantum dot photocatalysts.

    PubMed

    Amirav, Lilac; Alivisatos, A Paul

    2013-09-04

    Using far-field optical microscopy we report the first measurements of photoluminescence from single nanoparticle photocatalysts. Fluence-dependent luminescence is investigated from metal-semiconductor heterojunction quantum dot catalysts exposed to a variety of environments, ranging from gaseous argon to liquid water containing a selection of hole scavengers. The catalysts each exhibit characteristic nonlinear fluence dependence. From these structurally and environmentally sensitive trends, we disentangle the separate rate-determining steps in each particle across the very wide range of time scales, which follow the initial light absorption process. This information will significantly benefit the design of effective artificial photocatalytic systems for renewable direct solar-to-fuel energy conversion.

  5. Controlling quantum dot emission by plasmonic nanoarrays.

    PubMed

    Guo, R; Derom, S; Väkeväinen, A I; van Dijk-Moes, R J A; Liljeroth, P; Vanmaekelbergh, D; Törmä, P

    2015-11-02

    Metallic nanoparticle arrays support localized surface plasmon resonances (LSPRs) and propagating surface lattice resonances (SLRs). We study the control of quantum dot (QD) emission coupled to the optical modes of silver nanoparticle arrays, both experimentally and numerically. With a hybrid lithography-functionalization method, the QDs are deposited in the vicinity of the nanoparticles. Directionality and enhancement of the emission are observed in photoluminescence spectra and fluorescence lifetime measurements, respectively. Similar features are also demonstrated in the numerical simulations. The tunable emission of this type of hybrid structures could lead to potential applications in light sources.

  6. A hybrid silicon evanescent quantum dot laser

    NASA Astrophysics Data System (ADS)

    Jang, Bongyong; Tanabe, Katsuaki; Kako, Satoshi; Iwamoto, Satoshi; Tsuchizawa, Tai; Nishi, Hidetaka; Hatori, Nobuaki; Noguchi, Masataka; Nakamura, Takahiro; Takemasa, Keizo; Sugawara, Mitsuru; Arakawa, Yasuhiko

    2016-09-01

    We report the first demonstration of a hybrid silicon quantum dot (QD) laser, evanescently coupled to a silicon waveguide. InAs/GaAs QD laser structures with thin AlGaAs lower cladding layers were transferred by direct wafer bonding onto silicon waveguides defining cavities with adiabatic taper structures and distributed Bragg reflectors. The laser operates at temperatures up to 115 °C under pulsed current conditions, with a characteristic temperature T 0 of 303 K near room temperature. Furthermore, by reducing the width of the GaAs/AlGaAs mesa down to 8 µm, continuous-wave operation is realized at 25 °C.

  7. Quantum dot intermixing using excimer laser irradiation

    SciTech Connect

    Djie, H. S.; Ooi, B. S; Gunawan, O.

    2006-08-21

    The authors report a spatial control of the band gap in InGaAs/GaAs quantum dots (QDs) using the combined effects of pulsed excimer laser irradiation and impurity-free dielectric cap induced intermixing technique. A large band gap shift of up to 180 meV has been obtained under laser irradiation of 480 mJ/cm{sup 2} and 150 pulses to the SiO{sub 2} capped shallow QD structure, while the nonirradiated SiO{sub 2} and Si{sub x}N{sub y} capped QDs only exhibit band gap shifts of 18 and 91 meV, respectively.

  8. Quantum dot loaded immunomicelles for tumor imaging

    PubMed Central

    2010-01-01

    Background Optical imaging is a promising method for the detection of tumors in animals, with speed and minimal invasiveness. We have previously developed a lipid coated quantum dot system that doubles the fluorescence of PEG-grafted quantum dots at half the dose. Here, we describe a tumor-targeted near infrared imaging agent composed of cancer-specific monoclonal anti-nucleosome antibody 2C5, coupled to quantum dot (QD)-containing polymeric micelles, prepared from a polyethylene glycol/phosphatidylethanolamine (PEG-PE) conjugate. Its production is simple and involves no special equipment. Its imaging potential is great since the fluorescence intensity in the tumor is twofold that of non-targeted QD-loaded PEG-PE micelles at one hour after injection. Methods Para-nitrophenol-containing (5%) PEG-PE quantum dot micelles were produced by the thin layer method. Following hydration, 2C5 antibody was attached to the PEG-PE micelles and the QD-micelles were purified using dialysis. 4T1 breast tumors were inoculated subcutaneously in the flank of the animals. A lung pseudometastatic B16F10 melanoma model was developed using tail vein injection. The contrast agents were injected via the tail vein and mice were depilated, anesthetized and imaged on a Kodak Image Station. Images were taken at one, two, and four hours and analyzed using a methodology that produces normalized signal-to-noise data. This allowed for the comparison between different subjects and time points. For the pseudometastatic model, lungs were removed and imaged ex vivo at one and twenty four hours. Results The contrast agent signal intensity at the tumor was double that of the passively targeted QD-micelles with equally fast and sharply contrasted images. With the side views of the animals only tumor is visible, while in the dorsal view internal organs including liver and kidney are visible. Ex vivo results demonstrated that the agent detects melanoma nodes in a lung pseudometastatic model after a 24 hours

  9. Vacancy clusters in graphane as quantum dots.

    PubMed

    Singh, Abhishek K; Penev, Evgeni S; Yakobson, Boris I

    2010-06-22

    Complementary electronic properties and a tendency to form sharp graphene-graphane interfaces open tantalizing possibilities for two-dimensional nanoelectronics. First-principles density functional and tight-binding calculations show that graphane can serve as natural host for graphene quantum dots, clusters of vacancies in the hydrogen sublattice. Their size n, shape, and stability are governed by the aromaticity and interfaces, resulting in formation energies approximately 1/ radicaln eV/atom and preference to hexagonal clusters congruent with lattice hexagons (i.e., with armchair edge). Clusters exhibit large gaps approximately 15/ radicaln eV with size dependence typical for confined Dirac fermions.

  10. Protease sensing using nontoxic silicon quantum dots

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

  11. Quantum Dots for Molecular Diagnostics of Tumors

    PubMed Central

    Zdobnova, T.A.; Lebedenko, E.N.; Deyev, S.М.

    2011-01-01

    Semiconductor quantum dots (QDs) are a new class of fluorophores with unique physical and chemical properties, which allow to appreciably expand the possibilities for the current methods of fluorescent imaging and optical diagnostics. Here we discuss the prospects of QD application for molecular diagnostics of tumors ranging from cancer-specific marker detection on microplates to non-invasive tumor imagingin vivo. We also point out the essential problems that require resolution in order to clinically promote QD, and we indicate innovative approaches to oncology which are implementable using QD. PMID:22649672

  12. Trion decay in colloidal quantum dots.

    PubMed

    Jha, Praket P; Guyot-Sionnest, Philippe

    2009-04-28

    Using charged films of colloidal CdSe/CdS core/shell quantum dots of approximately 3.5 to 4.5 nm core diameters and 0.6 to 1.2 nm thick CdS shells, the radiative and nonradiative decay of the negatively charged exciton, the trion T-, are measured. The T- radiative rate is faster than the exciton by a factor of 2.2 +/- 0.4 and estimated at approximately 10 ns. The T- lifetime is approximately 0.7-1.5 ns for the samples measured and is longer than the biexciton lifetime by a factor or 7.5 +/- 1.7.

  13. Mesoscopic admittance of a double quantum dot

    SciTech Connect

    Cottet, Audrey; Mora, Christophe; Kontos, Takis

    2011-03-15

    We calculate the mesoscopic admittance G({omega}) of a double quantum dot (DQD), which can be measured directly using microwave techniques. This quantity reveals spectroscopic information on the DQD and is also directly sensitive to a Pauli spin blockade effect. We then discuss the problem of a DQD coupled to a high quality photonic resonator. When the photon correlation functions can be developed along a random-phase-approximation-like scheme, the response of the resonator gives an access to G({omega}).

  14. Interaction of porphyrins with CdTe quantum dots.

    PubMed

    Zhang, Xing; Liu, Zhongxin; Ma, Lun; Hossu, Marius; Chen, Wei

    2011-05-13

    Porphyrins may be used as photosensitizers for photodynamic therapy, photocatalysts for organic pollutant dissociation, agents for medical imaging and diagnostics, applications in luminescence and electronics. The detection of porphyrins is significantly important and here the interaction of protoporphyrin-IX (PPIX) with CdTe quantum dots was studied. It was observed that the luminescence of CdTe quantum dots was quenched dramatically in the presence of PPIX. When CdTe quantum dots were embedded into silica layers, almost no quenching by PPIX was observed. This indicates that PPIX may interact and alter CdTe quantum dots and thus quench their luminescence. The oxidation of the stabilizers such as thioglycolic acid (TGA) as well as the nanoparticles by the singlet oxygen generated from PPIX is most likely responsible for the luminescence quenching. The quenching of quantum dot luminescence by porphyrins may provide a new method for photosensitizer detection.

  15. Non-blinking quantum dot with a plasmonic nanoshell resonator.

    PubMed

    Ji, Botao; Giovanelli, Emerson; Habert, Benjamin; Spinicelli, Piernicola; Nasilowski, Michel; Xu, Xiangzhen; Lequeux, Nicolas; Hugonin, Jean-Paul; Marquier, Francois; Greffet, Jean-Jacques; Dubertret, Benoit

    2015-02-01

    Colloidal semiconductor quantum dots are fluorescent nanocrystals exhibiting exceptional optical properties, but their emission intensity strongly depends on their charging state and local environment. This leads to blinking at the single-particle level or even complete fluorescence quenching, and limits the applications of quantum dots as fluorescent particles. Here, we show that a single quantum dot encapsulated in a silica shell coated with a continuous gold nanoshell provides a system with a stable and Poissonian emission at room temperature that is preserved regardless of drastic changes in the local environment. This novel hybrid quantum dot/silica/gold structure behaves as a plasmonic resonator with a strong Purcell factor, in very good agreement with simulations. The gold nanoshell also acts as a shield that protects the quantum dot fluorescence and enhances its resistance to high-power photoexcitation or high-energy electron beams. This plasmonic fluorescent resonator opens the way to a new family of plasmonic nanoemitters with robust optical properties.

  16. Combinatorial Approach to Studying Metal Enhanced Fluorescence from Quantum Dots

    NASA Astrophysics Data System (ADS)

    Le, Nguyet; Corrigan, Timothy; Norton, Michael; Neff, David

    2013-03-01

    Fluorescence is extensively used in biochemistry for determining the concentration or purity of molecules in a biological environment. In metal-enhanced fluorescence (MEF), the fluorescence molecules separated from a metal surface by several nanometers can be enhanced. The fluorescent enhancement is dependent on the size and spacing of the nanoparticles, as has been shown previously for a number of fluorophore molecules. Fluorescence from quantum dots is of particular interest because the quantum dots do not lose fluorescence ability when exposed to light and they have higher intensity of fluorescence. The purpose of this study is to determine the effect of size and spacing on fluorescence intensity when coupling gold nano-particles with quantum dots. We employ a combinatorial approach, depositing gold particles ranging in diameter from 30 nm to 130 nm with varied spacings onto the substrate, followed by a protein spacer-layer and quantum dots. The fluorescence signal from the metal enhanced quantum dots were determined by confocal microscopy.

  17. Non-blinking quantum dot with a plasmonic nanoshell resonator

    NASA Astrophysics Data System (ADS)

    Ji, Botao; Giovanelli, Emerson; Habert, Benjamin; Spinicelli, Piernicola; Nasilowski, Michel; Xu, Xiangzhen; Lequeux, Nicolas; Hugonin, Jean-Paul; Marquier, Francois; Greffet, Jean-Jacques; Dubertret, Benoit

    2015-02-01

    Colloidal semiconductor quantum dots are fluorescent nanocrystals exhibiting exceptional optical properties, but their emission intensity strongly depends on their charging state and local environment. This leads to blinking at the single-particle level or even complete fluorescence quenching, and limits the applications of quantum dots as fluorescent particles. Here, we show that a single quantum dot encapsulated in a silica shell coated with a continuous gold nanoshell provides a system with a stable and Poissonian emission at room temperature that is preserved regardless of drastic changes in the local environment. This novel hybrid quantum dot/silica/gold structure behaves as a plasmonic resonator with a strong Purcell factor, in very good agreement with simulations. The gold nanoshell also acts as a shield that protects the quantum dot fluorescence and enhances its resistance to high-power photoexcitation or high-energy electron beams. This plasmonic fluorescent resonator opens the way to a new family of plasmonic nanoemitters with robust optical properties.

  18. Quantum dots find their stride in single molecule tracking

    PubMed Central

    Bruchez, Marcel P.

    2011-01-01

    Thirteen years after the demonstration of quantum dots as biological imaging agents, and nine years after the initial commercial introduction of bioconjugated quantum dots, the brightness and photostability of the quantum dots has enabled a range of investigations using single molecule tracking. These materials are being routinely utilized by a number of groups to track the dynamics of single molecules in reconstituted biophysical systems and on living cells, and are especially powerful for investigations of single molecules over long timescales with short exposure times and high pointing accuracy. New approaches are emerging where the quantum dots are used as “hard-sphere” probes for intracellular compartments. Innovations in quantum dot surface modification are poised to substantially expand the utility of these materials. PMID:22055494

  19. 3D super-resolution imaging with blinking quantum dots

    PubMed Central

    Wang, Yong; Fruhwirth, Gilbert; Cai, En; Ng, Tony; Selvin, Paul R.

    2013-01-01

    Quantum dots are promising candidates for single molecule imaging due to their exceptional photophysical properties, including their intense brightness and resistance to photobleaching. They are also notorious for their blinking. Here we report a novel way to take advantage of quantum dot blinking to develop an imaging technique in three-dimensions with nanometric resolution. We first applied this method to simulated images of quantum dots, and then to quantum dots immobilized on microspheres. We achieved imaging resolutions (FWHM) of 8–17 nm in the x-y plane and 58 nm (on coverslip) or 81 nm (deep in solution) in the z-direction, approximately 3–7 times better than what has been achieved previously with quantum dots. This approach was applied to resolve the 3D distribution of epidermal growth factor receptor (EGFR) molecules at, and inside of, the plasma membrane of resting basal breast cancer cells. PMID:24093439

  20. Quantum Dots in Diagnostics and Detection: Principles and Paradigms

    PubMed Central

    Pisanic, T. R.; Zhang, Y.; Wang, T. H.

    2014-01-01

    Quantum dots are semiconductor nanocrystals that exhibit exceptional optical and electrical behaviors not found in their bulk counterparts. Following seminal work in the development of water-soluble quantum dots in the late 1990's, researchers have sought to develop interesting and novel ways of exploiting the extraordinary properties of quantum dots for biomedical applications. Since that time, over 10,000 articles have been published related to the use of quantum dots in biomedicine, many of which regard their use in detection and diagnostic bioassays. This review presents a didactic overview of fundamental physical phenomena associated with quantum dots and paradigm examples of how these phenomena can and have been readily exploited for manifold uses in nanobiotechnology with a specific focus on their implementation in in vitro diagnostic assays and biodetection. PMID:24770716

  1. Quantum dots in diagnostics and detection: principles and paradigms.

    PubMed

    Pisanic, T R; Zhang, Y; Wang, T H

    2014-06-21

    Quantum dots are semiconductor nanocrystals that exhibit exceptional optical and electrical behaviors not found in their bulk counterparts. Following seminal work in the development of water-soluble quantum dots in the late 1990's, researchers have sought to develop interesting and novel ways of exploiting the extraordinary properties of quantum dots for biomedical applications. Since that time, over 10,000 articles have been published related to the use of quantum dots in biomedicine, many of which regard their use in detection and diagnostic bioassays. This review presents a didactic overview of fundamental physical phenomena associated with quantum dots and paradigm examples of how these phenomena can and have been readily exploited for manifold uses in nanobiotechnology with a specific focus on their implementation in in vitro diagnostic assays and biodetection.

  2. Numerical simulation of optical feedback on a quantum dot lasers

    SciTech Connect

    Al-Khursan, Amin H.; Ghalib, Basim Abdullattif; Al-Obaidi, Sabri J.

    2012-02-15

    We use multi-population rate equations model to study feedback oscillations in the quantum dot laser. This model takes into account all peculiar characteristics in the quantum dots such as inhomogeneous broadening of the gain spectrum, the presence of the excited states on the quantum dot and the non-confined states due to the presence of wetting layer and the barrier. The contribution of quantum dot groups, which cannot follow by other models, is simulated. The results obtained from this model show the feedback oscillations, the periodic oscillations which evolves to chaos at higher injection current of higher feedback levels. The frequency fluctuation is attributed mainly to wetting layer with a considerable contribution from excited states. The simulation shows that is must be not using simple rate equation models to express quantum dots working at excited state transition.

  3. Band like Electronic Structures in Square Hollow Quantum Dots by 3D-MHFKS Calculation

    NASA Astrophysics Data System (ADS)

    Takizawa, Tokihiro; Okada, Hoshihito; Matsuse, Takehiro

    To find novel aspects of the electronic structures in quantum dots (QD) from a view point of spatial broken symmetry, 3-dimensional-mesh Hartree-Fock-Kohn-Sham (3D-MHFKS) calculations1 are applied to the interacting electron system of electron number N in a symmetry broken hollow QD. For the case of a square hollow quantum dot confined in square hard wall (HW) potential (SSHQD), the magnetic (B) field dependence of the obtained single particle energy levels and chemical potentials in B-N diagram are shown to have a band like electronic structures over the wide B-field range up to 20T. To clarify the origin of the band like electronic structures in SSHQD, 3D-MHFKS calculations are also applied for the mixed symmetry QD's with a circular hollow in square HW potential (SCHQD) and with a square hollow in circular HW potential (CSHQD).

  4. 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.

  5. Electron states in semiconductor quantum dots

    SciTech Connect

    Dhayal, Suman S.; Ramaniah, Lavanya M.; Ruda, Harry E.; Nair, Selvakumar V.

    2014-11-28

    In this work, the electronic structures of quantum dots (QDs) of nine direct band gap semiconductor materials belonging to the group II-VI and III-V families are investigated, within the empirical tight-binding framework, in the effective bond orbital model. This methodology is shown to accurately describe these systems, yielding, at the same time, qualitative insights into their electronic properties. Various features of the bulk band structure such as band-gaps, band curvature, and band widths around symmetry points affect the quantum confinement of electrons and holes. These effects are identified and quantified. A comparison with experimental data yields good agreement with the calculations. These theoretical results would help quantify the optical response of QDs of these materials and provide useful input for applications.

  6. Semiconductor Quantum Dots for Biomedicial Applications

    PubMed Central

    Shao, Lijia; Gao, Yanfang; Yan, Feng

    2011-01-01

    Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed analysis of immunocomplexes or DNA hybridization processes, cell sorting and tracing, in vivo imaging and diagnostics in biomedicine. Meanwhile, QDs can be used as labels for the electrochemical detection of DNA or proteins. This article reviews the synthesis and toxicity of QDs and their optical and electrochemical bioanalytical applications. Especially the application of QDs in biomedicine such as delivering, cell targeting and imaging for cancer research, and in vivo photodynamic therapy (PDT) of cancer are briefly discussed. PMID:22247690

  7. Semiconductor quantum dot-sensitized solar cells

    PubMed Central

    Tian, Jianjun; Cao, Guozhong

    2013-01-01

    Semiconductor quantum dots (QDs) have been drawing great attention recently as a material for solar energy conversion due to their versatile optical and electrical properties. The QD-sensitized solar cell (QDSC) is one of the burgeoning semiconductor QD solar cells that shows promising developments for the next generation of solar cells. This article focuses on recent developments in QDSCs, including 1) the effect of quantum confinement on QDSCs, 2) the multiple exciton generation (MEG) of QDs, 3) fabrication methods of QDs, and 4) nanocrystalline photoelectrodes for solar cells. We also make suggestions for future research on QDSCs. Although the efficiency of QDSCs is still low, we think there will be major breakthroughs in developing QDSCs in the future. PMID:24191178

  8. Semiconductor quantum dot-sensitized solar cells.

    PubMed

    Tian, Jianjun; Cao, Guozhong

    2013-10-31

    Semiconductor quantum dots (QDs) have been drawing great attention recently as a material for solar energy conversion due to their versatile optical and electrical properties. The QD-sensitized solar cell (QDSC) is one of the burgeoning semiconductor QD solar cells that shows promising developments for the next generation of solar cells. This article focuses on recent developments in QDSCs, including 1) the effect of quantum confinement on QDSCs, 2) the multiple exciton generation (MEG) of QDs, 3) fabrication methods of QDs, and 4) nanocrystalline photoelectrodes for solar cells. We also make suggestions for future research on QDSCs. Although the efficiency of QDSCs is still low, we think there will be major breakthroughs in developing QDSCs in the future.

  9. Silicon quantum dots for biological applications.

    PubMed

    Chinnathambi, Shanmugavel; Chen, Song; Ganesan, Singaravelu; Hanagata, Nobutaka

    2014-01-01

    Semiconductor nanoparticles (or quantum dots, QDs) exhibit unique optical and electronic properties such as size-controlled fluorescence, high quantum yields, and stability against photobleaching. These properties allow QDs to be used as optical labels for multiplexed imaging and in drug delivery detection systems. Luminescent silicon QDs and surface-modified silicon QDs have also been developed as potential minimally toxic fluorescent probes for bioapplications. Silicon, a well-known power electronic semiconductor material, is considered an extremely biocompatible material, in particular with respect to blood. This review article summarizes existing knowledge related to and recent research progress made in the methods for synthesizing silicon QDs, as well as their optical properties and surface-modification processes. In addition, drug delivery systems and in vitro and in vivo imaging applications that use silicon QDs are also discussed.

  10. Facile synthetic method for pristine graphene quantum dots and graphene oxide quantum dots: origin of blue and green luminescence.

    PubMed

    Liu, Fei; Jang, Min-Ho; Ha, Hyun Dong; Kim, Je-Hyung; Cho, Yong-Hoon; Seo, Tae Seok

    2013-07-19

    Pristine graphene quantum dots and graphene oxide quantum dots are synthesized by chemical exfoliation from the graphite nanoparticles with high uniformity in terms of shape (circle), size (less than 4 nm), and thickness (monolayer). The origin of the blue and green photoluminescence of GQDs and GOQDs is attributed to intrinsic and extrinsic energy states, respectively.

  11. Andreev molecules in semiconductor nanowire double quantum dots.

    PubMed

    Su, Zhaoen; Tacla, Alexandre B; Hocevar, Moïra; Car, Diana; Plissard, Sébastien R; Bakkers, Erik P A M; Daley, Andrew J; Pekker, David; Frolov, Sergey M

    2017-09-19

    Chains of quantum dots coupled to superconductors are promising for the realization of the Kitaev model of a topological superconductor. While individual superconducting quantum dots have been explored, control of longer chains requires understanding of interdot coupling. Here, double quantum dots are defined by gate voltages in indium antimonide nanowires. High transparency superconducting niobium titanium nitride contacts are made to each of the dots in order to induce superconductivity, as well as probe electron transport. Andreev bound states induced on each of dots hybridize to define Andreev molecular states. The evolution of these states is studied as a function of charge parity on the dots, and in magnetic field. The experiments are found in agreement with a numerical model.Quantum dots in a nanowire are one possible approach to creating a solid-state quantum simulator. Here, the authors demonstrate the coupling of electronic states in a double quantum dot to form Andreev molecule states; a potential building block for longer chains suitable for quantum simulation.

  12. Spin polarization of neutral excitons in quantum dots: the role of the carrier collection area.

    PubMed

    Moskalenko, Evgenii; Larsson, Arvid; Holtz, Per Olof

    2010-08-27

    A high degree (approximately 55%) of circular polarization has been observed for the neutral exciton in InAs/GaAs quantum dots (QDs). The possibility to record non-zero polarization of the neutral exciton is explained in terms of different capture times of the light electron compared with the heavier holes into the QDs from the wetting layer. This interpretation is supported by the progressive reduction of the polarization degree with increasing QD density, and also with increasing temperature.

  13. Electron Spin Qubits in Si/SiGe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Eriksson, Mark

    2010-10-01

    It is intriguing that silicon, the central material of modern classical electronics, also has properties well suited to quantum electronics. Recent advances in Si/SiGe quantum devices have enabled the creation of high-quality silicon quantum dots, also known as artificial atoms. Motivated in part by the potential for very long spin coherence times in this material, we are pursuing the development of individual electron spin qubits in silicon quantum dots. I will discuss recent demonstrations of single-shot spin measurement in a Si/SiGe quantum dot spin qubit, and the demonstration of spin-relaxation times longer than one second in such a system. These and similar measurements depend on a knowledge of tunnel rates between quantum dots and nearby reservoirs or between pairs of quantum dots. Measurements of such rates provide an opportunity to revisit classic experiments in quantum mechanics. At the same time, the unique features of the silicon conduction band lead to novel and unexpected effects, demonstrating that Si/SiGe quantum dots provide a highly controlled experimental system in which to study ideas at the heart of quantum physics.

  14. Quantum Dot Enabled Molecular Sensing and Diagnostics

    PubMed Central

    Zhang, Yi; Wang, Tza-Huei

    2012-01-01

    Since its emergence, semiconductor nanoparticles known as quantum dots (QDs) have drawn considerable attention and have quickly extended their applicability to numerous fields within the life sciences. This is largely due to their unique optical properties such as high brightness and narrow emission band as well as other advantages over traditional organic fluorophores. New molecular sensing strategies based on QDs have been developed in pursuit of high sensitivity, high throughput, and multiplexing capabilities. For traditional biological applications, QDs have already begun to replace traditional organic fluorophores to serve as simple fluorescent reporters in immunoassays, microarrays, fluorescent imaging applications, and other assay platforms. In addition, smarter, more advanced QD probes such as quantum dot fluorescence resonance energy transfer (QD-FRET) sensors, quenching sensors, and barcoding systems are paving the way for highly-sensitive genetic and epigenetic detection of diseases, multiplexed identification of infectious pathogens, and tracking of intracellular drug and gene delivery. When combined with microfluidics and confocal fluorescence spectroscopy, the detection limit is further enhanced to single molecule level. Recently, investigations have revealed that QDs participate in series of new phenomena and exhibit interesting non-photoluminescent properties. Some of these new findings are now being incorporated into novel assays for gene copy number variation (CNV) studies and DNA methylation analysis with improved quantification resolution. Herein, we provide a comprehensive review on the latest developments of QD based molecular diagnostic platforms in which QD plays a versatile and essential role. PMID:22916072

  15. Excitation transfer in stacked quantum dot chains

    NASA Astrophysics Data System (ADS)

    Kanjanachuchai, Songphol; Xu, Ming; Jaffré, Alexandre; Jittrong, Apichart; Chokamnuai, Thitipong; Panyakeow, Somsak; Boutchich, Mohamed

    2015-05-01

    Stacked InAs quantum dot chains (QDCs) on InGaAs/GaAs cross-hatch pattern (CHP) templates yield a rich emission spectrum with an unusual carrier transfer characteristic compared to conventional quantum dot (QD) stacks. The photoluminescent spectra of the controlled, single QDC layer comprise multiple peaks from the orthogonal QDCs, the free-standing QDs, the CHP, the wetting layers and the GaAs substrate. When the QDC layers are stacked, employing a 10 nm GaAs spacer between adjacent QDC layers, the PL spectra are dominated by the top-most stack, indicating that the QDC layers are nominally uncoupled. Under high excitation power densities when the high-energy peaks of the top stack are saturated, however, low-energy PL peaks from the bottom stacks emerge as a result of carrier transfers across the GaAs spacers. These unique PL signatures contrast with the state-filling effects in conventional, coupled QD stacks and serve as a means to quickly assess the presence of electronic coupling in stacks of dissimilar-sized nanostructures.

  16. Using quantum dot photoluminescence for load detection

    SciTech Connect

    Moebius, M. Hartwig, M.; Martin, J.; Baumann, R. R.; Otto, T.; Gessner, T.

    2016-08-15

    We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL) of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N′,N′-Tetrakis(3-methylphenyl)-3,3′-dimethylbenzidine (HMTPD) and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

  17. Colloidal quantum dot light-emitting devices.

    PubMed

    Wood, Vanessa; Bulović, Vladimir

    2010-01-01

    Colloidal quantum dot light-emitting devices (QD-LEDs) have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI). We review the key advantages of using quantum dots (QDs) in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs - optical excitation, Förster energy transfer, and direct charge injection - that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desirable color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (>65 lumens per Watt). We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs.

  18. Fourier transform spectra of quantum dots

    NASA Astrophysics Data System (ADS)

    Damian, V.; Ardelean, I.; Armăşelu, Anca; Apostol, D.

    2009-09-01

    Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed cultures of phototrophic and heterotrophic microorganisms.

  19. Fourier transform spectra of quantum dots

    NASA Astrophysics Data System (ADS)

    Damian, V.; Ardelean, I.; Armăşelu, Anca; Apostol, D.

    2010-05-01

    Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed cultures of phototrophic and heterotrophic microorganisms.

  20. Competing interactions in semiconductor quantum dots

    DOE PAGES

    van den Berg, R.; Brandino, G. P.; El Araby, O.; ...

    2014-10-14

    In this study, we introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions atmore » longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.« less

  1. Using quantum dot photoluminescence for load detection

    NASA Astrophysics Data System (ADS)

    Moebius, M.; Martin, J.; Hartwig, M.; Baumann, R. R.; Otto, T.; Gessner, T.

    2016-08-01

    We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL) of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N',N'-Tetrakis(3-methylphenyl)-3,3'-dimethylbenzidine (HMTPD) and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

  2. Competing interactions in semiconductor quantum dots

    SciTech Connect

    van den Berg, R.; Brandino, G. P.; El Araby, O.; Konik, R. M.; Gritsev, V.; Caux, J. -S.

    2014-10-14

    In this study, we introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions at longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.

  3. Open quantum dots in graphene: Scaling relativistic pointer states

    NASA Astrophysics Data System (ADS)

    Ferry, D. K.; Huang, L.; Yang, R.; Lai, Y.-C.; Akis, R.

    2010-04-01

    Open quantum dots provide a window into the connection between quantum and classical physics, particularly through the decoherence theory, in which an important set of quantum states are not "washed out" through interaction with the environment-the pointer states provide connection to trapped classical orbits which remain stable in the dots. Graphene is a recently discovered material with highly unusual properties. This single layer, one atom thick, sheet of carbon has a unique bandstructure, governed by the Dirac equation, in which charge carriers imitate relativistic particles with zero rest mass. Here, an atomic orbital-based recursive Green's function method is used for studying the quantum transport. We study quantum fluctuations in graphene and bilayer graphene quantum dots with this recursive Green's function method. Finally, we examine the scaling of the domiant fluctuation frequency with dot size.

  4. Charge-extraction strategies for colloidal quantum dot photovoltaics

    NASA Astrophysics Data System (ADS)

    Lan, Xinzheng; Masala, Silvia; Sargent, Edward H.

    2014-03-01

    The solar-power conversion efficiencies of colloidal quantum dot solar cells have advanced from sub-1% reported in 2005 to a record value of 8.5% in 2013. Much focus has deservedly been placed on densifying, passivating and crosslinking the colloidal quantum dot solid. Here we review progress in improving charge extraction, achieved by engineering the composition and structure of the electrode materials that contact the colloidal quantum dot film. New classes of structured electrodes have been developed and integrated to form bulk heterojunction devices that enhance photocharge extraction. Control over band offsets, doping and interfacial trap state densities have been essential for achieving improved electrical communication with colloidal quantum dot solids. Quantum junction devices that not only tune the optical absorption spectrum, but also provide inherently matched bands across the interface between p- and n-materials, have proven that charge separation can occur efficiently across an all-quantum-tuned rectifying junction.

  5. Experimental circular quantum secret sharing over telecom fiber network.

    PubMed

    Wei, Ke-Jin; Ma, Hai-Qiang; Yang, Jian-Hui

    2013-07-15

    We present a robust single photon circular quantum secret sharing (QSS) scheme with phase encoding over 50 km single mode fiber network using a circular QSS protocol. Our scheme can automatically provide a perfect compensation of birefringence and remain stable for a long time. A high visibility of 99.3% is obtained. Furthermore, our scheme realizes a polarization insensitive phase modulators. The visibility of this system can be maintained perpetually without any adjustment to the system every time we test the system.

  6. Leveraging Crystal Anisotropy for Deterministic Growth of InAs Quantum Dots with Narrow Optical Linewidths

    DTIC Science & Technology

    2013-08-29

    spin qubit for quantum information. KEYWORDS: Quantum dot , InAs, molecular beam epitaxy, site...removes a major obstacle toward sophisticated quantum dot complexes such as a quantum network of spin qubits . Methods. Substrate Patterning. Lines and...controlled, quantum information, single photon source Epitaxial quantum dots (QDs) have atom-like electronicproperties, including long coherence

  7. Multiple Exciton Generation in Semiconductor Quantum Dots.

    PubMed

    Beard, Matthew C

    2011-06-02

    Multiple exciton generation in quantum dots (QDs) has been intensively studied as a way to enhance solar energy conversion by utilizing the excess energy in the absorbed photons. Among other useful properties, quantum confinement can both increase Coulomb interactions that drive the MEG process and decrease the electron-phonon coupling that cools hot excitons in bulk semiconductors. However, variations in the reported enhanced quantum yields (QYs) have led to disagreements over the role that quantum confinement plays. The enhanced yield of excitons per absorbed photon is deduced from a dynamical signature in the transient absorption or transient photoluminescence and is ascribed to the creation of biexcitons. Extraneous effects such as photocharging are partially responsible for the observed variations. When these extraneous effects are reduced, the MEG efficiency, defined in terms of the number of additional electron-hole pairs produced per additional band gap of photon excitation, is about two times better in PbSe QDs than that in bulk PbSe. Thin films of electronically coupled QDs have shown promise in simple photon-to-electron conversion architectures. If the MEG efficiency can be further enhanced and charge separation and transport can be optimized within QD films, then QD solar cells can lead to third-generation solar energy conversion technologies.

  8. Ferritin-Templated Quantum-Dots for Quantum Logic Gates

    NASA Technical Reports Server (NTRS)

    Choi, Sang H.; Kim, Jae-Woo; Chu, Sang-Hyon; Park, Yeonjoon; King, Glen C.; Lillehei, Peter T.; Kim, Seon-Jeong; Elliott, James R.

    2005-01-01

    Quantum logic gates (QLGs) or other logic systems are based on quantum-dots (QD) with a stringent requirement of size uniformity. The QD are widely known building units for QLGs. The size control of QD is a critical issue in quantum-dot fabrication. The work presented here offers a new method to develop quantum-dots using a bio-template, called ferritin, that ensures QD production in uniform size of nano-scale proportion. The bio-template for uniform yield of QD is based on a ferritin protein that allows reconstitution of core material through the reduction and chelation processes. One of the biggest challenges for developing QLG is the requirement of ordered and uniform size of QD for arrays on a substrate with nanometer precision. The QD development by bio-template includes the electrochemical/chemical reconsitution of ferritins with different core materials, such as iron, cobalt, manganese, platinum, and nickel. The other bio-template method used in our laboratory is dendrimers, precisely defined chemical structures. With ferritin-templated QD, we fabricated the heptagonshaped patterned array via direct nano manipulation of the ferritin molecules with a tip of atomic force microscope (AFM). We also designed various nanofabrication methods of QD arrays using a wide range manipulation techniques. The precise control of the ferritin-templated QD for a patterned arrangement are offered by various methods, such as a site-specific immobilization of thiolated ferritins through local oxidation using the AFM tip, ferritin arrays induced by gold nanoparticle manipulation, thiolated ferritin positioning by shaving method, etc. In the signal measurements, the current-voltage curve is obtained by measuring the current through the ferritin, between the tip and the substrate for potential sweeping or at constant potential. The measured resistance near zero bias was 1.8 teraohm for single holoferritin and 5.7 teraohm for single apoferritin, respectively.

  9. Luminescent properties of cadmium selenide quantum dots in fluorophosphate glasses

    NASA Astrophysics Data System (ADS)

    Lipatova, Zh. O.; Kolobkova, E. V.; Babkina, A. N.

    2016-11-01

    The optical properties of fluorophosphate glasses with CdSe quantum dots are studied. Secondary heat treatment at a temperature exceeding the glass transition temperature resulted in the formation of quantum dots with sizes of 3.7-6.2 nm. The influence of the semiconductor component concentration on the spectral-luminescent characteristics of glasses is shown. It is experimentally demonstrated that glasses with a lower CdSe concentration have a higher absolute luminescence quantum yield.

  10. Quantum fluctuations in semiconductor quantum dots and their contributions to the self-energy functions of exciton states

    NASA Astrophysics Data System (ADS)

    Mutygullina, A. A.; Khamadeev, M. A.; Blum, D. O.; Shirdelhavar, A. H.

    2017-06-01

    Influence of quantum fluctuations in a system consisting of a quantum dot and the reservoir of acoustic phonons on processes in which the quantum dot takes part is investigated. Under some conditions this influence is shown to be very strong. We find a contribution from the quantum fluctuations to the self-energy function of the exciton coupled to the quantum dot.

  11. Spins of Andreev states in double quantum dots

    NASA Astrophysics Data System (ADS)

    Su, Zhaoen; Chen, Jun; Yu, Peng; Hocervar, Moira; Plissard, Sebastien; Car, Diana; Tacla, Alexandre; Daley, Andrew; Pekker, David; Bakkers, Erik; Frolov, Sergey

    Andreev (or Shiba) states in coupled double quantum dots is an open field. Here we demonstrate the realization of Andreev states in double quantum dots in an InSb nanowire coupled to two NbTiN superconductors. The magnetic field dependence of the Andreev states has been explored to resolve the spins in different double dot configurations. The experiment helps to understand the interplay between pair correlation, exchange energy and charging energy with a well-controlled system. It also opens the possibility to implement Majorana modes in Kitaev chains made of such dots.

  12. On-chip quantum optics with quantum dots and superconducting resonators

    NASA Astrophysics Data System (ADS)

    Deng, Guang-Wei; Guo, Guo-Ping; Guo, Guang-Can

    2016-11-01

    Benefit from the recent nanotechnology process, people can integrate different nanostructures on a single chip. Particularly, quantum dots (QD), which behave as artificial atoms, have been shown to couple with a superconducting resonator, indicating that quantum-dot based quantum chip has a highly scalable possibility. Here we show a quantum chip architecture by combining graphene quantum dots and superconducting resonators together. A double quantum dot (DQD) and a microwave hybrid system can be described by the Jaynes-Cummings model, while a multi-quantum-dots system is conformed to the Tavis-Cummings model. These simple quantum optics models are experimentally realized in our device, providing a compelling platform for both graphene study and potential applications.

  13. Single spins in self-assembled quantum dots.

    PubMed

    Warburton, Richard J

    2013-06-01

    Self-assembled quantum dots have excellent photonic properties. For instance, a single quantum dot is a high-brightness, narrow-linewidth source of single photons. Furthermore, the environment of a single quantum dot can be tailored relatively easily using semiconductor heterostructure and post-growth processing techniques, enabling electrical control of the quantum dot charge and control over the photonic modes with which the quantum dot interacts. A single electron or hole trapped inside a quantum dot has spintronics applications. Although the spin dephasing is rather rapid, a single spin can be manipulated using optical techniques on subnanosecond timescales. Optical experiments are also providing new insights into old issues, such as the central spin problem. This Review provides a snapshot of this active field, with some indications for the future. It covers the basic materials and optical properties of single quantum dots, techniques for initializing, manipulating and reading out single spin qubits, and the mechanisms that limit the electron-spin and hole-spin coherence.

  14. Solution-processed colloidal lead sulfide quantum dots for near-infrared quantum information processing applications

    NASA Astrophysics Data System (ADS)

    Bose, Ranojoy

    In this thesis, we study solution-processed lead sulfide quantum dots for near-infrared quantum information and communication applications. Quantum dots processed through synthetic routes and colloidally suspended in solution offer far-reaching device application possibilities that are unparalelled in traditional self-assembled quantum dots. Lead sulfide quantum dots are especially promising for near-infrared quantum optics due to their optical emission at the wavelengths of fiber-optic communications (1.3--1.5 microm). The broad absorption spectrum of these quantum dots can be used for solar light-harvesting applications, to which end the results of Chapter 2---where we study Forster resonance energy transfer in quantum dot solids---provide remarkable insights into photon emission from quantum-dot based solar cells. In subsequent chapters, we explore quantum-dot photonic crystal applications, where exciton-photon interactions in the cavity environment remarkably allow for the emission of indistinguishable single photons that are important for distribution of high-security quantum keys---being highly sensitive to 'eavesdropping'. Particularly, the suggestion of the solution-processed QED system is novel compared to traditional self-assembled systems, and as we will discuss, offer integration and processing capabilities that are unprecedented, and perform well at wavelength ranges where standard QED systems scale poorly. The results of chapters 3--6 are therefore significant in the general field of cavity quantum electrodynamics.

  15. Quantum Monte Carlo finite temperature electronic structure of quantum dots

    NASA Astrophysics Data System (ADS)

    Leino, Markku; Rantala, Tapio T.

    2002-08-01

    Quantum Monte Carlo methods allow a straightforward procedure for evaluation of electronic structures with a proper treatment of electronic correlations. This can be done even at finite temperatures [1]. We test the Path Integral Monte Carlo (PIMC) simulation method [2] for one and two electrons in one and three dimensional harmonic oscillator potentials and apply it in evaluation of finite temperature effects of single and coupled quantum dots. Our simulations show the correct finite temperature excited state populations including degeneracy in cases of one and three dimensional harmonic oscillators. The simulated one and two electron distributions of a single and coupled quantum dots are compared to those from experiments and other theoretical (0 K) methods [3]. Distributions are shown to agree and the finite temperature effects are discussed. Computational capacity is found to become the limiting factor in simulations with increasing accuracy. Other essential aspects of PIMC and its capability in this type of calculations are also discussed. [1] R.P. Feynman: Statistical Mechanics, Addison Wesley, 1972. [2] D.M. Ceperley, Rev.Mod.Phys. 67, 279 (1995). [3] M. Pi, A. Emperador and M. Barranco, Phys.Rev.B 63, 115316 (2001).

  16. Steady state quantum discord for circularly accelerated atoms

    SciTech Connect

    Hu, Jiawei; Yu, Hongwei

    2015-12-15

    We study, in the framework of open quantum systems, the dynamics of quantum entanglement and quantum discord of two mutually independent circularly accelerated two-level atoms in interaction with a bath of fluctuating massless scalar fields in the Minkowski vacuum. We assume that the two atoms rotate synchronically with their separation perpendicular to the rotating plane. The time evolution of the quantum entanglement and quantum discord of the two-atom system is investigated. For a maximally entangled initial state, the entanglement measured by concurrence diminishes to zero within a finite time, while the quantum discord can either decrease monotonically to an asymptotic value or diminish to zero at first and then followed by a revival depending on whether the initial state is antisymmetric or symmetric. When both of the two atoms are initially excited, the generation of quantum entanglement shows a delayed feature, while quantum discord is created immediately. Remarkably, the quantum discord for such a circularly accelerated two-atom system takes a nonvanishing value in the steady state, and this is distinct from what happens in both the linear acceleration case and the case of static atoms immersed in a thermal bath.

  17. Laser synthesis and size tailor of carbon quantum dots

    NASA Astrophysics Data System (ADS)

    Hu, Shengliang; Liu, Jun; Yang, Jinlong; Wang, Yanzhong; Cao, Shirui

    2011-12-01

    Carbon quantum dots (C-dots) with average sizes of about 3, 8, and 13 nm were synthesized by laser irradiation of graphite flakes in polymer solution. The obtained C-dots display size and excitation wavelength dependent photoluminescence behavior. The size control of C-dots can be realized by tuning laser pulse width. The original reason could be the effects of laser pulse width on the conditions of nucleation and growth of C-dots. Compared with short-pulse-width laser, the long-pulse-width laser would be better fitted to the size and morphology control of nanostructures in the different material systems.

  18. Quantum dot nanoparticle conjugation, characterization, and applications in neuroscience

    NASA Astrophysics Data System (ADS)

    Pathak, Smita

    Quantum dot are semiconducting nanoparticles that have been used for decades in a variety of applications such as solar cells, LEDs and medical imaging. Their use in the last area, however, has been extremely limited despite their potential as revolutionary new biological labeling tools. Quantum dots are much brighter and more stable than conventional fluorophores, making them optimal for high resolution imaging and long term studies. Prior work in this area involves synthesizing and chemically conjugating quantum dots to molecules of interest in-house. However this method is both time consuming and prone to human error. Additionally, non-specific binding and nanoparticle aggregation currently prevent researchers from utilizing this system to its fullest capacity. Another critical issue that has not been addressed is determining the number of ligands bound to nanoparticles, which is crucial for proper interpretation of results. In this work, methods to label fixed cells using two types of chemically modified quantum dots are studied. Reproducible non-specific artifact labeling is consistently demonstrated if antibody-quantum dot conditions are less than optimal. In order to explain this, antibodies bound to quantum dots were characterized and quantified. While other groups have qualitatively characterized antibody functionalized quantum dots using TEM, AFM, UV spectroscopy and gel electrophoresis, and in some cases have reported calculated estimates of the putative number of total antibodies bound to quantum dots, no quantitative experimental results had been reported prior to this work. The chemical functionalization and characterization of quantum dot nanocrystals achieved in this work elucidates binding mechanisms of ligands to nanoparticles and allows researchers to not only translate our tools to studies in their own areas of interest but also derive quantitative results from these studies. This research brings ease of use and increased reliability to

  19. A triple quantum dot based nano-electromechanical memory device

    SciTech Connect

    Pozner, R.; Lifshitz, E.; Peskin, U.

    2015-09-14

    Colloidal quantum dots (CQDs) are free-standing nano-structures with chemically tunable electronic properties. This tunability offers intriguing possibilities for nano-electromechanical devices. In this work, we consider a nano-electromechanical nonvolatile memory (NVM) device incorporating a triple quantum dot (TQD) cluster. The device operation is based on a bias induced motion of a floating quantum dot (FQD) located between two bound quantum dots (BQDs). The mechanical motion is used for switching between two stable states, “ON” and “OFF” states, where ligand-mediated effective interdot forces between the BQDs and the FQD serve to hold the FQD in each stable position under zero bias. Considering realistic microscopic parameters, our quantum-classical theoretical treatment of the TQD reveals the characteristics of the NVM.

  20. Gate-controlled electromechanical backaction induced by a quantum dot.

    PubMed

    Okazaki, Yuma; Mahboob, Imran; Onomitsu, Koji; Sasaki, Satoshi; Yamaguchi, Hiroshi

    2016-04-11

    Semiconductor-based quantum structures integrated into mechanical resonators have emerged as a unique platform for generating entanglement between macroscopic phononic and mesocopic electronic degrees of freedom. A key challenge to realizing this is the ability to create and control the coupling between two vastly dissimilar systems. Here, such coupling is demonstrated in a hybrid device composed of a gate-defined quantum dot integrated into a piezoelectricity-based mechanical resonator enabling milli-Kelvin phonon states to be detected via charge fluctuations in the quantum dot. Conversely, the single electron transport in the quantum dot can induce a backaction onto the mechanics where appropriate bias of the quantum dot can enable damping and even current-driven amplification of the mechanical motion. Such electron transport induced control of the mechanical resonator dynamics paves the way towards a new class of hybrid semiconductor devices including a current injected phonon laser and an on-demand single phonon emitter.

  1. Gate-controlled electromechanical backaction induced by a quantum dot

    PubMed Central

    Okazaki, Yuma; Mahboob, Imran; Onomitsu, Koji; Sasaki, Satoshi; Yamaguchi, Hiroshi

    2016-01-01

    Semiconductor-based quantum structures integrated into mechanical resonators have emerged as a unique platform for generating entanglement between macroscopic phononic and mesocopic electronic degrees of freedom. A key challenge to realizing this is the ability to create and control the coupling between two vastly dissimilar systems. Here, such coupling is demonstrated in a hybrid device composed of a gate-defined quantum dot integrated into a piezoelectricity-based mechanical resonator enabling milli-Kelvin phonon states to be detected via charge fluctuations in the quantum dot. Conversely, the single electron transport in the quantum dot can induce a backaction onto the mechanics where appropriate bias of the quantum dot can enable damping and even current-driven amplification of the mechanical motion. Such electron transport induced control of the mechanical resonator dynamics paves the way towards a new class of hybrid semiconductor devices including a current injected phonon laser and an on-demand single phonon emitter. PMID:27063939

  2. Full counting statistics of quantum dot resonance fluorescence

    PubMed Central

    Matthiesen, Clemens; Stanley, Megan J.; Hugues, Maxime; Clarke, Edmund; Atatüre, Mete

    2014-01-01

    The electronic energy levels and optical transitions of a semiconductor quantum dot are subject to dynamics within the solid-state environment. In particular, fluctuating electric fields due to nearby charge traps or other quantum dots shift the transition frequencies via the Stark effect. The environment dynamics are mapped directly onto the fluorescence under resonant excitation and diminish the prospects of quantum dots as sources of indistinguishable photons in optical quantum computing. Here, we present an analysis of resonance fluorescence fluctuations based on photon counting statistics which captures the underlying time-averaged electric field fluctuations of the local environment. The measurement protocol avoids dynamic feedback on the electric environment and the dynamics of the quantum dot's nuclear spin bath by virtue of its resonant nature and by keeping experimental control parameters such as excitation frequency and external fields constant throughout. The method introduced here is experimentally undemanding. PMID:24810097

  3. Recombination in quantum dot sensitized solar cells.

    PubMed

    Mora-Seró, Iván; Giménez, Sixto; Fabregat-Santiago, Francisco; Gómez, Roberto; Shen, Qing; Toyoda, Taro; Bisquert, Juan

    2009-11-17

    Quantum dot sensitized solar cells (QDSCs) have attracted significant attention as promising third-generation photovoltaic devices. In the form of quantum dots (QDs), the semiconductor sensitizers have very useful and often tunable properties; moreover, their theoretical thermodynamic efficiency might be as high as 44%, better than the original 31% calculated ceiling. Unfortunately, the practical performance of these devices still lags behind that of dye-sensitized solar cells. In this Account, we summarize the strategies for depositing CdSe quantum dots on nanostructured mesoporous TiO(2) electrodes and discuss the methods that facilitate improvement in the performance and stability of QDSCs. One particularly significant factor for solar cells that use polysulfide electrolyte as the redox couple, which provides the best performance among QDSCs, is the passivation of the photoanode surface with a ZnS coating, which leads to a dramatic increase of photocurrents and efficiencies. However, these solar cells usually show a poor current-potential characteristic, so a general investigation of the recombination mechanisms is required for improvements. A physical model based on recombination through a monoenergetic TiO(2) surface state that takes into account the effect of the surface coverage has been developed to better understand the recombination mechanisms of QDSCs. The three main methods of QD adsorption on TiO(2) are (i) in situ growth of QDs by chemical bath deposition (CBD), (ii) deposition of presynthesized colloidal QDs by direct adsorption (DA), and (iii) deposition of presynthesized colloidal QDs by linker-assisted adsorption (LA). A systematic investigation by impedance spectroscopy of QDSCs prepared by these methods showed a decrease in the charge-transfer resistance and increased electron lifetimes for CBD samples; the same result was found after ZnS coating because of the covering of the TiO(2) surface. The increase of the lifetime with the ZnS treatment

  4. Hybrid Circuit QED with Double Quantum Dots

    NASA Astrophysics Data System (ADS)

    Petta, Jason

    2014-03-01

    Cavity quantum electrodynamics explores quantum optics at the most basic level of a single photon interacting with a single atom. We have been able to explore cavity QED in a condensed matter system by placing a double quantum dot (DQD) inside of a high quality factor microwave cavity. Our results show that measurements of the cavity field are sensitive to charge and spin dynamics in the DQD.[2,3] We can explore non-equilibrium physics by applying a finite source-drain bias across the DQD, which results in sequential tunneling. Remarkably, we observe a gain as large as 15 in the cavity transmission when the DQD energy level detuning is matched to the cavity frequency. These results will be discussed in the context of single atom lasing.[4] I will also describe recent progress towards reaching the strong-coupling limit in cavity-coupled Si DQDs. In collaboration with Manas Kulkarni, Yinyu Liu, Karl Petersson, George Stehlik, Jacob Taylor, and Hakan Tureci. We acknowledge support from the Sloan and Packard Foundations, ARO, DARPA, and NSF.

  5. Quantum Dots Microstructured Optical Fiber for X-Ray Detection

    NASA Technical Reports Server (NTRS)

    DeHaven, Stan; Williams, Phillip; Burke, Eric

    2015-01-01

    Microstructured optical fibers containing quantum dots scintillation material comprised of zinc sulfide nanocrystals doped with magnesium sulfide are presented. These quantum dots are applied inside the microstructured optical fibers using capillary action. The x-ray photon counts of these fibers are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The results of the fiber light output and associated effects of an acrylate coating and the quantum dot application technique are discussed.

  6. Quantum Dots Microstructured Optical Fiber for X-Ray Detection

    NASA Technical Reports Server (NTRS)

    DeHaven, S. L.; Williams, P. A.; Burke, E. R.

    2015-01-01

    A novel concept for the detection of x-rays with microstructured optical fibers containing quantum dots scintillation material comprised of zinc sulfide nanocrystals doped with magnesium sulfide is presented. These quantum dots are applied inside the microstructured optical fibers using capillary action. The x-ray photon counts of these fibers are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The results of the fiber light output and associated effects of an acrylate coating and the quantum dots application technique are discussed.

  7. Graphene mediated Stark shifting of quantum dot energy levels

    SciTech Connect

    Kinnischtzke, Laura; Badolato, Antonio; Goodfellow, Kenneth M.; Vamivakas, A. Nick; Chakraborty, Chitraleema; Lai, Yi-Ming; Fält, Stefan; Wegscheider, Werner

    2016-05-23

    We demonstrate an optoelectronic device comprised of single InAs quantum dots in an n-i-Schottky diode where graphene has been used as the Schottky contact. Deterministic electric field tuning is shown using Stark-shifted micro-photoluminescence from single quantum dots. The extracted dipole moments from the Stark shifts are comparable to conventional devices where the Schottky contact is a semi-transparent metal. Neutral and singly charged excitons are also observed in the well-known Coulomb-blockade plateaus. Our results indicate that graphene is a suitable replacement for metal contacts in quantum dot devices which require electric field control.

  8. Quantum dots microstructured optical fiber for x-ray detection

    NASA Astrophysics Data System (ADS)

    DeHaven, S. L.; Williams, P. A.; Burke, E. R.

    2016-02-01

    A novel concept for the detection of x-rays with microstructured optical fibers containing quantum dots scintillation material comprised of zinc sulfide nanocrystals doped with magnesium sulfide is presented. These quantum dots are applied inside the microstructured optical fibers using capillary action. The x-ray photon counts of these fibers are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The results of the fiber light output and associated effects of an acrylate coating and the quantum dots application technique are discussed.

  9. Semiconductor Quantum Dots in Chemical Sensors and Biosensors

    PubMed Central

    Frasco, Manuela F.; Chaniotakis, Nikos

    2009-01-01

    Quantum dots are nanometre-scale semiconductor crystals with unique optical properties that are advantageous for the development of novel chemical sensors and biosensors. The surface chemistry of luminescent quantum dots has encouraged the development of multiple probes based on linked recognition molecules such as peptides, nucleic acids or small-molecule ligands. This review overviews the design of sensitive and selective nanoprobes, ranging from the type of target molecules to the optical transduction scheme. Representative examples of quantum dot-based optical sensors from this fast-moving field have been selected and are discussed towards the most promising directions for future research. PMID:22423206

  10. Energy levels in self-assembled quantum arbitrarily shaped dots.

    PubMed

    Tablero, C

    2005-02-08

    A model to determine the electronic structure of self-assembled quantum arbitrarily shaped dots is applied. This model is based principally on constant effective mass and constant potentials of the barrier and quantum dot material. An analysis of the different parameters of this model is done and compared with those which take into account the variation of confining potentials, bands, and effective masses due to strain. The results are compared with several spectra reported in literature. By considering the symmetry, the computational cost is reduced with respect to other methods in literature. In addition, this model is not limited by the geometry of the quantum dot.

  11. Graphene mediated Stark shifting of quantum dot energy levels

    NASA Astrophysics Data System (ADS)

    Kinnischtzke, Laura; Goodfellow, Kenneth M.; Chakraborty, Chitraleema; Lai, Yi-Ming; Fält, Stefan; Wegscheider, Werner; Badolato, Antonio; Vamivakas, A. Nick

    2016-05-01

    We demonstrate an optoelectronic device comprised of single InAs quantum dots in an n-i-Schottky diode where graphene has been used as the Schottky contact. Deterministic electric field tuning is shown using Stark-shifted micro-photoluminescence from single quantum dots. The extracted dipole moments from the Stark shifts are comparable to conventional devices where the Schottky contact is a semi-transparent metal. Neutral and singly charged excitons are also observed in the well-known Coulomb-blockade plateaus. Our results indicate that graphene is a suitable replacement for metal contacts in quantum dot devices which require electric field control.

  12. Plasmonic quantum dot solar cells for enhanced infrared response

    NASA Astrophysics Data System (ADS)

    Feng Lu, Hao; Mokkapati, Sudha; Fu, Lan; Jolley, Greg; Hoe Tan, Hark; Jagadish, Chennupati

    2012-03-01

    Enhanced near infrared photoresponse in plasmonic InGaAs/GaAs quantum dot solar cells (QDSC) is demonstrated. Long wavelength light absorption in the wetting-layer and quantum-dot region of the quantum dot solar cell is enhanced through scattering of light by silver nanoparticles deposited on the solar cell surface. Plasmonic light trapping results in simultaneous increase in short-circuit current density by 5.3% and open circuit voltage by 0.9% in the QDSC, leading to an overall efficiency enhancement of 7.6%.

  13. Nonequilibrium spin noise in a quantum dot ensemble

    NASA Astrophysics Data System (ADS)

    Smirnov, D. S.; Glasenapp, Ph.; Bergen, M.; Glazov, M. M.; Reuter, D.; Wieck, A. D.; Bayer, M.; Greilich, A.

    2017-06-01

    The spin noise in singly charged self-assembled quantum dots is studied theoretically and experimentally under the influence of a perturbation, provided by additional photoexcited charge carriers. The theoretical description takes into account generation and relaxation of charge carriers in the quantum dot system. The spin noise is measured under application of above barrier excitation for which the data are well reproduced by the developed model. Our analysis demonstrates a strong difference of the recharging dynamics for holes and electrons in quantum dots.

  14. What Quantum Dots Can Do for You

    NASA Astrophysics Data System (ADS)

    Salamo, Gregory

    2008-03-01

    Recent clever techniques for fabricating nanosize materials, one-atomic-layer-at-a-time, have simultaneously opened a door to a fantastic adventure at the frontier of physics, chemistry, biology, and engineering. Nanosize materials simply do not behave as the bulk. Indeed, the rules that govern the growth and behavior of these tiny structures are unexplored. In this talk we will discuss our recent efforts to be the architect of their shape, size, density, and position of nanostructures and along the way, the interactions between them that lead to their optical and electrical behavior. While self-assembly is providing exciting quantum dot (QD) structures to explore, like the QD molecules shown here, it is equally exciting to try to use the rules we uncover to encourage QD formation to take a desired path. Can we understand the formation of faceted nanostructures? Can we encourage or seed dot structures to form specific arrays? Is it possible to engineer greater homogeneity of dot shape and size? Can we design both the optical and electrical behavior of either individual or arrays of nanostructures to mimic those we find in nature? In this talk we will review our progress to answer these questions and discuss the possibilities and challenges ahead. For example, we will discuss the formation of individual faceted nanostructures as well as the fabrication of a vertically and laterally ordered QD stacks forming three-dimensional QD arrays. As another example, we will discuss the importance of surfaces with high Miller indices, as a template to the formation of nanostructures as well as their potential role in determining the shape and increased size uniformity of the confined structures. Importantly, these observations lead to an even more basic question of when and why high index surfaces are stable. Indeed, we have found that in order to understand the origin of high index surfaces that bound nanostructures we have to study them directly.

  15. PREFACE: Quantum dots as probes in biology

    NASA Astrophysics Data System (ADS)

    Cieplak, Marek

    2013-05-01

    The recent availability of nanostructured materials has resulted in an explosion of research focused on their unique optical, thermal, mechanical and magnetic properties. Optical imagining, magnetic enhancement of contrast and drug delivery capabilities make the nanoparticles of special interest in biomedical applications. These materials have been involved in the development of theranostics—a new field of medicine that is focused on personalized tests and treatment. It is likely that multimodal nanomaterials will be responsible for future diagnostic advances in medicine. Quantum dots (QD) are nanoparticles which exhibit luminescence either through the formation of three-dimensional excitons or excitations of the impurities. The excitonic luminescence can be tuned by changing the size (the smaller the size, the higher the frequency). QDs are usually made of semiconducting materials. Unlike fluorescent proteins and organic dyes, QDs resist photobleaching, allow for multi-wavelength excitations and have narrow emission spectra. The techniques to make QDs are cheap and surface modifications and functionalizations can be implemented. Importantly, QDs could be synthesized to exhibit useful optomagnetic properties and, upon functionalization with an appropriate biomolecule, directed towards a pre-selected target for diagnostic imaging and photodynamic therapy. This special issue on Quantum dots in Biology is focused on recent research in this area. It starts with a topical review by Sreenivasan et al on various physical mechanisms that lead to the QD luminescence and on using wavelength shifts for an improvement in imaging. The next paper by Szczepaniak et al discusses nanohybrids involving QDs made of CdSe coated by ZnS and combined covalently with a photosynthetic enzyme. These nanohybrids are shown to maintain the enzymatic activity, however the enzyme properties depend on the size of a QD. They are proposed as tools to study photosynthesis in isolated

  16. Optoelectronic Applications of Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Wang, Zhiping; Zhang, Nanzhu; Brenneman, Kimber; Wu, Tsai Chin; Jung, Hyeson; Biswas, Sushmita; Sen, Banani; Reinhardt, Kitt; Liao, Sicheng; Stroscio, Michael A.; Dutta, Mitra

    This chapter highlights recent optoelectronic applications of colloidal quantum dots (QDs). In recent years, many colloidal QD-based optoelectronic devices, and device concepts have been proposed and studied. Many of these device concepts build on traditional optoelectronic device concepts. Increasingly, many new optoelectronic device concepts have been based on the use of biomolecule QD complexes. In this chapter, both types of structures are discussed. Special emphasis is placed on new optoelectronic device concepts that incorporate DNA-based aptamers in biomolecule QD complexes. Not only are the extensions of traditional devices and concepts realizable, such as QD-based photo detectors, displays, photoluminescent and photovoltaic devices, light-emitting diodes (LEDs), photovoltaic devices, and solar cells, but new devices concepts such a biomolecule-based molecular sensors possible. This chapter highlights a number of such novel QD-based devices and device concepts.

  17. Quantum dots as a possible oxygen sensor

    NASA Astrophysics Data System (ADS)

    Ziółczyk, Paulina; Kur-Kowalska, Katarzyna; Przybyt, Małgorzata; Miller, Ewa

    Results of studies on optical properties of low toxicity quantum dots (QDs) obtained from copper doped zinc sulfate are discussed in the paper. The effect of copper admixture concentration and solution pH on the fluorescence emission intensity of QDs was investigated. Quenching of QDs fluorescence by oxygen was reported and removal of the oxygen from the environment by two methods was described. In the chemical method oxygen was eliminated by adding sodium sulfite, in the other method oxygen was removed from the solution using nitrogen gas. For elimination of oxygen by purging the solution with nitrogen the increase of fluorescence intensity with decreasing oxygen concentration obeyed Stern-Volmer equation indicating quenching. For the chemical method Stern-Volmer equation was not fulfilled. The fluorescence decays lifetimes were determined and the increase of mean lifetimes at the absence of oxygen support hypothesis that QDs fluorescence is quenched by oxygen.

  18. Correlation energy of anisotropic quantum dots

    SciTech Connect

    Zhao Yan; Loos, Pierre-Francois; Gill, Peter M. W.

    2011-09-15

    We study the D-dimensional high-density correlation energy E{sub c} of the singlet ground state of two electrons confined by a harmonic potential with Coulombic repulsion. We allow the harmonic potential to be anisotropic and examine the behavior of E{sub c} as a function of the anisotropy {alpha}{sup -1}. In particular, we are interested in the limit where the anisotropy goes to infinity ({alpha}{yields}0) and the electrons are restricted to a lower-dimensional space. We show that tuning the value of {alpha} from 0 to 1 allows a smooth dimensional interpolation and we demonstrate that the usual model, in which a quantum dot is treated as a two-dimensional system, is inappropriate. Finally, we provide a simple function which reproduces the behavior of E{sub c} over the entire range of {alpha}.

  19. Quantum Dots Confined in Nanoporous Alumina Membranes

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Xia, Jianfeng; Wang, Jun; Shinar, Joseph; Lin, Zhiqun

    2007-03-01

    Precise control over the dispersion and lateral distribution of quantum dots (QDs) within nanoscopic porous media provides a unique route to manipulate the optical and/or electronic properties of QDs in a very simple and controllable manner for applications related to light emitting, optoelectronic, and sensor devices. Here we filled nanoporous alumina membranes (PAMs) with CdSe/ZnS core/shell QDs by dip coating. The deposition of QDs induced changes in the refractive index of PAMs. The amount of absorbed QDs was quantified by fitting the reflection and transmission spectra observed experimentally with one side open and freestanding (i.e., with two sides open) PAMs employed, respectively. The fluorescence of the QDs was found to be retained within the cylindrical nanopores of PAMs.

  20. Quantum dot based 3D photonic devices

    NASA Astrophysics Data System (ADS)

    Sakellari, Ioanna; Kabouraki, Elmina; Gray, David; Vamvakaki, Maria; Farsari, Maria

    2017-02-01

    In this work, we present our most recent results on the fabrication of 3D high-resolution woodpile photonic crystals containing an organic-inorganic silicon-zirconium (Si-Zr) composite and cadmium sulfide (CdS) quantum dots (QDs). The structures are fabricated by combining 3D Direct Laser Writing by two-photon absorption and in-situ synthesis of CdS nanoparticles inside the 3D photonic matrix. The CdS-Zr-Si composite material exhibits a high nonlinear refractive index value measured by means of Z-scan method. 3D woodpile photonic structures with varying inlayer periodicity from 600nm to 500nm show clear photonic stop bands in the wavelength region between 1000nm to 450nm.

  1. Andreev Conductance of a Chaotic Quantum Dot

    NASA Astrophysics Data System (ADS)

    Clerk, A. A.; Brouwer, P. W.; Ambegaokar, V.

    2000-03-01

    Using random matrix theory, we study the full magnetic field (B) and voltage (V) dependence of the Andreev conductance of a chaotic quantum dot coupled via point contacts to both a normal metal and a superconductor. We recover previous results in the zero and large B,V limits, but also observe interesting non-monotonic behaviour in the crossover regime. Our results demonstrate that the induced superconductivity effect previously seen in calculations of the density of states (J.A. Melsen, P.W. Brouwer, K.M. Frahm and C.W.J. Beenakker, Europhys. Lett., 35), 7 (1996). can also have a pronounced signature in the conductance; this may explain certain anomalous features observed in recent experiments on metallic normal-superconducting point contacts (P. Chalsani, S.K. Uphadyay, R.A. Buhrman, unpublished.).

  2. Highly Fluorescent Noble Metal Quantum Dots

    PubMed Central

    Zheng, Jie; Nicovich, Philip R.; Dickson, Robert M.

    2009-01-01

    Highly fluorescent, water-soluble, few-atom noble metal quantum dots have been created that behave as multi-electron artificial atoms with discrete, size-tunable electronic transitions throughout the visible and near IR. These “molecular metals” exhibit highly polarizable transitions and scale in size according to the simple relation, Efermi/N1/3, predicted by the free electron model of metallic behavior. This simple scaling indicates that fluorescence arises from intraband transitions of free electrons and that these conduction electron transitions are the low number limit of the plasmon – the collective dipole oscillations occurring when a continuous density of states is reached. Providing the “missing link” between atomic and nanoparticle behavior in noble metals, these emissive, water-soluble Au nanoclusters open new opportunities for biological labels, energy transfer pairs, and light emitting sources in nanoscale optoelectronics. PMID:17105412

  3. Quantum dots: synthesis, bioapplications, and toxicity

    PubMed Central

    2012-01-01

    This review introduces quantum dots (QDs) and explores their properties, synthesis, applications, delivery systems in biology, and their toxicity. QDs are one of the first nanotechnologies to be integrated with the biological sciences and are widely anticipated to eventually find application in a number of commercial consumer and clinical products. They exhibit unique luminescence characteristics and electronic properties such as wide and continuous absorption spectra, narrow emission spectra, and high light stability. The application of QDs, as a new technology for biosystems, has been typically studied on mammalian cells. Due to the small structures of QDs, some physical properties such as optical and electron transport characteristics are quite different from those of the bulk materials. PMID:22929008

  4. Semiconductor quantum dot-inorganic nanotube hybrids.

    PubMed

    Kreizman, Ronen; Schwartz, Osip; Deutsch, Zvicka; Itzhakov, Stella; Zak, Alla; Cohen, Sidney R; Tenne, Reshef; Oron, Dan

    2012-03-28

    A synthetic route for preparation of inorganic WS(2) nanotube (INT)-colloidal semiconductor quantum dot (QD) hybrid structures is developed, and transient carrier dynamics on these hybrids are studied via transient photoluminescence spectroscopy utilizing several different types of QDs. Measurements reveal efficient resonant energy transfer from the QDs to the INT upon photoexcitation, provided that the QD emission is at a higher energy than the INT direct gap. Charge transfer in the hybrid system, characterized using QDs with band gaps below the INT direct gap, is found to be absent. This is attributed to the presence of an organic barrier layer due to the relatively long-chain organic ligands of the QDs under study. This system, analogous to carbon nanotube-QD hybrids, holds potential for a variety of applications, including photovoltaics, luminescence tagging and optoelectronics.

  5. Phonon Overlaps in Molecular Quantum Dot Systems

    NASA Astrophysics Data System (ADS)

    Chang, Connie; Sethna, James

    2004-03-01

    We model the amplitudes and frequencies of the vibrational sidebands for the new molecular quantum dot systems. We calculate the Franck-Condon phonon overlaps in the 3N-dimensional configuration sapce. We solve the general case where the vibrational frequencies and eigenmodes change during the transition. We perform PM3 and DFT calculations for the case of the dumb bell-shaped C140 molecule. We find that the strongest amplitudes are associated with the 11 meV stretch mode, in agreement with experiment. The experimental amplitudes vary from molecule to molecule; indicating that the molecular overlaps are environment dependent. We explore overlaps in the presence of external electric fields from image charges and counter ions.

  6. Monolithic mode-locked quantum dot lasers

    NASA Astrophysics Data System (ADS)

    Penty, R. V.; Thompson, M. G.; White, I. H.

    2008-02-01

    Monolithic mode-locked laser diodes based on QD active regions are regarded as potentially suitable for a large range of photonic applications due to their compactness, mechanical stability and robustness, high potential repetition rates and low potential jitter. Their inherent properties, such as high differential gain, low chirp and fast saturable absorption have led to demonstration of improved performance over their QW equivalents. Low background loss and the relatively long lengths of quantum dot laser devices also have encouraged studies of mode-locking at repetition rates previously not explored in monolithic devices. Applications include biomedicine, high-speed data transmission, clock signal generation and electro-optic sampling. This paper reviews some of the work at Cambridge on the realization of such devices.

  7. Selenium quantum dots: Preparation, structure, and properties

    NASA Astrophysics Data System (ADS)

    Qian, Fuli; Li, Xueming; Tang, Libin; Lai, Sin Ki; Lu, Chaoyu; Lau, Shu Ping

    2017-01-01

    An interesting class of low-dimensional nanomaterials, namely, selenium quantum dots (SeQDs), which are composed of nano-sized selenium particles, is reported in this study. The SeQDs possess a hexagonal crystal structure. They can be synthesized in large quantity by ultrasound liquid-phase exfoliation using NbSe2 powders as the source material and N-Methyl-2-pyrrolidone (NMP) as the dispersant. During sonication, the Nb-Se bonds dissociate; the SeQDs are formed, while niobium is separated by centrifugation. The SeQDs have a narrow diameter distribution from 1.9 to 4.6 nm and can be dispersed with high stability in NMP without the need for passivating agents. They exhibit photoluminescence properties that are expected to find useful applications in bioimaging, optoelectronics, as well as nanocomposites.

  8. Nanosecond colloidal quantum dot lasers for sensing.

    PubMed

    Guilhabert, B; Foucher, C; Haughey, A-M; Mutlugun, E; Gao, Y; Herrnsdorf, J; Sun, H D; Demir, H V; Dawson, M D; Laurand, N

    2014-03-24

    Low-threshold, gain switched colloidal quantum dot (CQD) distributed-feedback lasers operating in the nanosecond regime are reported and proposed for sensing applications for the first time to the authors' knowledge. The lasers are based on a mechanically-flexible polymeric, second order grating structure overcoated with a thin-film of CQD/PMMA composite. The threshold fluence of the resulting lasers is as low as 0.5 mJ/cm² for a 610 nm emission and the typical linewidth is below 0.3 nm. The emission wavelength of the lasers can be set at the design stage and laser operation between 605 nm and 616 nm, while using the exact same CQD gain material, is shown. In addition, the potential of such CQD lasers for refractive index sensing in solution is demonstrated by immersion in water.

  9. Tellurium quantum dots: Preparation and optical properties

    NASA Astrophysics Data System (ADS)

    Lu, Chaoyu; Li, Xueming; Tang, Libin; Lai, Sin Ki; Rogée, Lukas; Teng, Kar Seng; Qian, Fuli; Zhou, Liangliang; Lau, Shu Ping

    2017-08-01

    Herein, we report an effective and simple method for producing Tellurium Quantum dots (TeQDs), zero-dimensional nanomaterials with great prospects for biomedical applications. Their preparation is based on the ultrasonic exfoliation of Te powder dispersed in 1-methyl-2-pyrrolidone. Sonication causes the van der Waals forces between the structural hexagons of Te to break so that the relatively coarse powder breaks down into nanoscale particles. The TeQDs have an average size of about 4 nm. UV-Vis absorption spectra of the TeQDs showed an absorption peak at 288 nm. Photoluminescence excitation (PLE) and photoluminescence (PL) are used to study the optical properties of TeQDs. Both the PLE and PL peaks revealed a linear relationship against the emission and excitation energies, respectively. TeQDs have important potential applications in biological imaging and catalysis as well as optoelectronics.

  10. Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids.

    PubMed

    Talgorn, Elise; Gao, Yunan; Aerts, Michiel; Kunneman, Lucas T; Schins, Juleon M; Savenije, T J; van Huis, Marijn A; van der Zant, Herre S J; Houtepen, Arjan J; Siebbeles, Laurens D A

    2011-09-25

    Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron-hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots.

  11. Collective Rabi dynamics of electromagnetically coupled quantum-dot ensembles

    NASA Astrophysics Data System (ADS)

    Glosser, Connor; Shanker, B.; Piermarocchi, Carlo

    2017-09-01

    Rabi oscillations typify the inherent nonlinearity of optical excitations in quantum dots. Using an integral kernel formulation to solve the three-dimensional Maxwell-Bloch equations in ensembles of up to 104 quantum dots, we observe features in Rabi oscillations due to the interplay of nonlinearity, nonequilibrium excitation, and electromagnetic coupling between the dots. This approach allows us to observe the dynamics of each dot in the ensemble without resorting to spatial averages. Our simulations predict synchronized multiplets of dots that exchange energy, dots that dynamically couple to screen the effect of incident external radiation, localization of the polarization due to randomness and interactions, as well as wavelength-scale regions of enhanced and suppressed polarization.

  12. Structural changes in R-phycoerythrin upon CdS quantum dot synthesis in tunnel cavities of protein molecules.

    PubMed

    Bekasova, O D; Shubin, V V; Safenkova, I V; Kovalyov, L I; Kurganov, B I

    2013-11-01

    Structural changes in R-phycoerythrin used as a matrix for the synthesis of CdS quantum dots have been analyzed by circular dichroism spectrometry. In deionized water, quantum dot synthesis in the tunnel cavity of the R-phycoerythrin molecule proved to be accompanied by uncoiling of α-helices and changes in the conformation of its chromophore groups, with consequent decay of protein fluorescence. Since R-phycoerythrin fluorescence is important for practical applications, conditions for quantum dot synthesis have been optimized by replacing deionized water with 0.01 M MES buffer, pH 5.7. Under such conditions, the size of the CdS quantum dots (determined from atomic force microscopy images) remains the same as in deionized water, but quantum dots cause only minor structural changes in protein molecules, as follows from circular dichroism and absorption spectra. The thermostability of R-phycoerythrin is enhanced, as indicated by an increase in the experimental activation energy for denaturation (from 140.8 to 149.9 kJ/mol) and the intensity of R-phycoerythrin fluorescence is also enhanced approximately twofold. Copyright © 2013 Elsevier B.V. All rights reserved.

  13. Tunable Few-Electron Quantum Dots as Spin Qubits

    NASA Astrophysics Data System (ADS)

    Elzerman, Jeroen; Hanson, Ronald; Greidanus, Jacob; Willems van Beveren, Laurens; de Franceschi, Silvano; Vandersypen, Lieven; Tarucha, Seigo; Kouwenhoven, Leo

    2003-03-01

    Recently it was proposed to make a quantum bit using the spin of an electron in a quantum dot. We present the first experimental steps towards realizing a system of two coupled qubits. The Zeeman splitting between the two spin states defining the qubit is measured for a one-electron dot in a parallel magnetic field. For a two-electron dot, we control the spin singlet-triplet energy difference with a perpendicular magnetic field, and we induce a transition from singlet to triplet ground state. We find relaxation from triplet to singlet to be extremely slow (> 1 mus), which is promising for quantum computing. We couple two few-electron dots, creating the first fully tunable few-electron double dot. Its charge configuration can be read out with a nearby QPC acting as an integrated charge detector.

  14. Spin effects in InAs self-assembled quantum dots

    PubMed Central

    2011-01-01

    We have studied the polarized resolved photoluminescence in an n-type resonant tunneling diode (RTD) of GaAs/AlGaAs which incorporates a layer of InAs self-assembled quantum dots (QDs) in the center of a GaAs quantum well (QW). We have observed that the QD circular polarization degree depends on applied voltage and light intensity. Our results are explained in terms of the tunneling of minority carriers into the QW, carrier capture by InAs QDs and bias-controlled density of holes in the QW. PMID:21711647

  15. Spin effects in InAs self-assembled quantum dots.

    PubMed

    Dos Santos, Ednilson C; Gobato, Yara Galvão; Brasil, Maria Jsp; Taylor, David A; Henini, Mohamed

    2011-02-03

    We have studied the polarized resolved photoluminescence in an n-type resonant tunneling diode (RTD) of GaAs/AlGaAs which incorporates a layer of InAs self-assembled quantum dots (QDs) in the center of a GaAs quantum well (QW). We have observed that the QD circular polarization degree depends on applied voltage and light intensity. Our results are explained in terms of the tunneling of minority carriers into the QW, carrier capture by InAs QDs and bias-controlled density of holes in the QW.

  16. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications.

    PubMed

    Wen, Lin; Qiu, Liping; Wu, Yongxiang; Hu, Xiaoxiao; Zhang, Xiaobing

    2017-07-28

    Semiconductor quantum dots have attracted extensive interest in the biosensing area because of their properties, such as narrow and symmetric emission with tunable colors, high quantum yield, high stability and controllable morphology. The introduction of various reactive functional groups on the surface of semiconductor quantum dots allows one to conjugate a spectrum of ligands, antibodies, peptides, or nucleic acids for broader and smarter applications. Among these ligands, aptamers exhibit many advantages including small size, high chemical stability, simple synthesis with high batch-to-batch consistency and convenient modification. More importantly, it is easy to introduce nucleic acid amplification strategies and/or nanomaterials to improve the sensitivity of aptamer-based sensing systems. Therefore, the combination of semiconductor quantum dots and aptamers brings more opportunities in bioanalysis. Here we summarize recent advances on aptamer-functionalized semiconductor quantum dots in biosensing applications. Firstly, we discuss the properties and structure of semiconductor quantum dots and aptamers. Then, the applications of biosensors based on aptamer-modified semiconductor quantum dots by different signal transducing mechanisms, including optical, electrochemical and electrogenerated chemiluminescence approaches, is discussed. Finally, our perspectives on the challenges and opportunities in this promising field are provided.

  17. Multi-million atom electronic structure calculations for quantum dots

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad

    Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined

  18. Ultrafast optical spin echo in a single quantum dot

    NASA Astrophysics Data System (ADS)

    Press, David; de Greve, Kristiaan; McMahon, Peter L.; Ladd, Thaddeus D.; Friess, Benedikt; Schneider, Christian; Kamp, Martin; Höfling, Sven; Forchel, Alfred; Yamamoto, Yoshihisa

    2010-06-01

    Many proposed photonic quantum networks rely on matter qubits to serve as memory elements. The spin of a single electron confined in a semiconductor quantum dot forms a promising matter qubit that may be interfaced with a photonic network. Ultrafast optical spin control allows gate operations to be performed on the spin within a picosecond timescale, orders of magnitude faster than microwave or electrical control. One obstacle to storing quantum information in a single quantum dot spin is the apparent nanosecond-timescale dephasing due to slow variations in the background nuclear magnetic field. Here we use an ultrafast, all-optical spin echo technique to increase the decoherence time of a single quantum dot electron spin from nanoseconds to several microseconds. The ratio of decoherence time to gate time exceeds 105, suggesting strong promise for future photonic quantum information processors and repeater networks.

  19. Barrier engineering in quantum dots in a well detector

    NASA Astrophysics Data System (ADS)

    Krishna, Sanjay

    2012-01-01

    Quantum dot infrared photodetectors have generated a lot of interest in the recent past due to their potential for low dark current and high operating temperature. We demonstrate the use of thin AlGaAs barrier layers in the quantum dots in a well (DWELL) heterostructure to enhance the quantum confinement of carriers in the excited energy level. By controlling the excited state energy of the DWELL structure between the confinement enhancing (CE) barriers and near the continuum level of the barrier between the stacks, high quantum confinement as well as high escape probability for the photoexcited carriers has been obtained. High responsivity and detectivity of 6.5x1010 cm.Hz1/2W-1 (77K, 0.6V, 7.5mm, f/2), a factor of 10 improvement over a control sample without the CE barriers has been measured. The effect of changing the quantum well thickness and quantum dot size is also reported.

  20. Long-distance coherent coupling in a quantum dot array.

    PubMed

    Braakman, F R; Barthelemy, P; Reichl, C; Wegscheider, W; Vandersypen, L M K

    2013-06-01

    Controlling long-distance quantum correlations is central to quantum computation and simulation. In quantum dot arrays, experiments so far rely on nearest-neighbour couplings only, and inducing long-distance correlations requires sequential local operations. Here, we show that two distant sites can be tunnel-coupled directly. The coupling is mediated by virtual occupation of an intermediate site, with a strength that is controlled via the energy detuning of this site. It permits a single charge to oscillate coherently between the outer sites of a triple dot array without passing through the middle, as demonstrated through the observation of Landau-Zener-Stückelberg interference. The long-distance coupling significantly improves the prospects of fault-tolerant quantum computation using quantum dot arrays, and opens up new avenues for performing quantum simulations in nanoscale devices.

  1. Unravelling quantum dot array simulators via singlet-triplet measurements

    NASA Astrophysics Data System (ADS)

    Gray, Johnnie; Bayat, Abolfazl; Puddy, Reuben K.; Smith, Charles G.; Bose, Sougato

    2016-11-01

    Recently, singlet-triplet measurements in double dots have emerged as a powerful tool in quantum information processing. In parallel, quantum dot arrays are being envisaged as analog quantum simulators of many-body models. Thus motivated, we explore the potential of the above singlet-triplet measurements for probing and exploiting the ground state of a Heisenberg spin chain in such a quantum simulator. We formulate an efficient protocol to discriminate the achieved many-body ground state with other likely states. Moreover, the transition between quantum phases, arising from the addition of frustrations in a J1-J2 model, can be systematically explored using the same set of measurements. We show that the proposed measurements have an application in producing long distance heralded entanglement between well separated quantum dots. Relevant noise sources, such as nonzero temperatures and nuclear spin interactions, are considered.

  2. Heterovalent cation substitutional doping for quantum dot homojunction solar cells.

    PubMed

    Stavrinadis, Alexandros; Rath, Arup K; de Arquer, F Pelayo García; Diedenhofen, Silke L; Magén, César; Martinez, Luis; So, David; Konstantatos, Gerasimos

    2013-01-01

    Colloidal quantum dots have emerged as a material platform for low-cost high-performance optoelectronics. At the heart of optoelectronic devices lies the formation of a junction, which requires the intimate contact of n-type and p-type semiconductors. Doping in bulk semiconductors has been largely deployed for many decades, yet electronically active doping in quantum dots has remained a challenge and the demonstration of robust functional optoelectronic devices had thus far been elusive. Here we report an optoelectronic device, a quantum dot homojunction solar cell, based on heterovalent cation substitution. We used PbS quantum dots as a reference material, which is a p-type semiconductor, and we employed Bi-doping to transform it into an n-type semiconductor. We then combined the two layers into a homojunction device operating as a solar cell robustly under ambient air conditions with power conversion efficiency of 2.7%.

  3. Heterovalent cation substitutional doping for quantum dot homojunction solar cells

    NASA Astrophysics Data System (ADS)

    Stavrinadis, Alexandros; Rath, Arup K.; de Arquer, F. Pelayo García; Diedenhofen, Silke L.; Magén, César; Martinez, Luis; So, David; Konstantatos, Gerasimos

    2013-12-01

    Colloidal quantum dots have emerged as a material platform for low-cost high-performance optoelectronics. At the heart of optoelectronic devices lies the formation of a junction, which requires the intimate contact of n-type and p-type semiconductors. Doping in bulk semiconductors has been largely deployed for many decades, yet electronically active doping in quantum dots has remained a challenge and the demonstration of robust functional optoelectronic devices had thus far been elusive. Here we report an optoelectronic device, a quantum dot homojunction solar cell, based on heterovalent cation substitution. We used PbS quantum dots as a reference material, which is a p-type semiconductor, and we employed Bi-doping to transform it into an n-type semiconductor. We then combined the two layers into a homojunction device operating as a solar cell robustly under ambient air conditions with power conversion efficiency of 2.7%.

  4. Majorana dc Josephson current mediated by a quantum dot.

    PubMed

    Xu, Luting; Li, Xin-Qi; Sun, Qing-Feng

    2017-05-17

    The Josephson supercurrent through a hybrid Majorana-quantum dot-Majorana junction is investigated. We particularly analyze the effect of spin-selective coupling between the Majorana and quantum dot states, which only emerges in the topological phase and will influence the current through bent junctions and/or in the presence of magnetic fields in the quantum dot. We find that the characteristic behavior of the supercurrent through this system is quite counterintuitive, differing remarkably from the resonant tunneling, e.g. through the similar (normal phase) superconductor-quantum dot-superconductor junction. Our analysis is carried out under the influence of the full set-up parameters and for both the [Formula: see text] and [Formula: see text] periodic currents. The present study is expected to be relevant to the future exploration of applications of Majorana-nanowire circuits.

  5. Berry phase jumps and giant nonreciprocity in Dirac quantum dots

    NASA Astrophysics Data System (ADS)

    Rodriguez-Nieva, Joaquin F.; Levitov, Leonid S.

    2016-12-01

    We predict that a strong nonreciprocity in the resonance spectra of Dirac quantum dots can be induced by the Berry phase. The nonreciprocity arises in relatively weak magnetic fields and is manifest in anomalously large field-induced splittings of quantum dot resonances which are degenerate at B =0 due to time-reversal symmetry. This exotic behavior, which is governed by field-induced jumps in the Berry phase of confined electronic states, is unique to quantum dots in Dirac materials and is absent in conventional quantum dots. The effect is strong for gapless Dirac particles and can overwhelm the B -induced orbital and Zeeman splittings. A finite Dirac mass suppresses the effect. The nonreciprocity, predicted for generic two-dimensional Dirac materials, is accessible through Faraday and Kerr optical rotation measurements and scanning tunneling spectroscopy.

  6. Probing of Unembedded Metallic Quantum Dots with Positrons

    SciTech Connect

    Fischer, C G; Denison, A B; Weber, M H; Wilcoxon, J P; Woessner, S; Lynn, K G

    2003-08-01

    We employed the two detector coincident Doppler Broadening Technique (coPAS) to investigate Ag, Au and Ag/Au alloy quantum dots of varying sizes which were deposited in thin layers on glass slides. The Ag quantum dots range from 2 to 3 nm in diameter, while the Ag/Au alloy quantum dots exhibit Ag cores of 2 nm and 3 nm and Au shells of varying thickness. We investigate the possibility of positron confinement in the Ag core due to positron affinity differences between Ag and Au. We describe the results and their significance to resolving the issue of whether positrons annihilate within the quantum dot itself or whether surface and positron escape effects play an important role.

  7. Engineering multifunctional magnetic-quantum dot barcodes by flow focusing.

    PubMed

    Giri, Supratim; Li, Dawei; Chan, Warren C W

    2011-04-14

    A simple one-step flow focusing method was used to embed both magnetic nanoparticles and quantum dots in microbeads in controlled ratios to generate a large library of molecular barcodes for biological applications.

  8. Electro-absorption of silicene and bilayer graphene quantum dots

    SciTech Connect

    Abdelsalam, Hazem; Talaat, Mohamed H.; Lukyanchuk, Igor; Portnoi, M. E.; Saroka, V. A.

    2016-07-07

    We study numerically the optical properties of low-buckled silicene and AB-stacked bilayer graphene quantum dots subjected to an external electric field, which is normal to their surface. Within the tight-binding model, the optical absorption is calculated for quantum dots, of triangular and hexagonal shapes, with zigzag and armchair edge terminations. We show that in triangular silicene clusters with zigzag edges a rich and widely tunable infrared absorption peak structure originates from transitions involving zero energy states. The edge of absorption in silicene quantum dots undergoes red shift in the external electric field for triangular clusters, whereas blue shift takes place for hexagonal ones. In small clusters of bilayer graphene with zigzag edges the edge of absorption undergoes blue/red shift for triangular/hexagonal geometry. In armchair clusters of silicene blue shift of the absorption edge takes place for both cluster shapes, while red shift is inherent for both shapes of the bilayer graphene quantum dots.

  9. Quantum Dots in the Therapy: Current Trends and Perspectives.

    PubMed

    Pohanka, Miroslav

    2017-01-01

    Quantum dots are an emerging nanomaterial with broad use in technical disciplines; however, their application in the field of biomedicine becomes also relevant and significant possibilities have appeared since the discovery in 1980s. The current review is focused on the therapeutic applications of quantum dots which become an emerging use of the particles. They are introduced as potent carriers of drugs and as a material well suited for the diagnosis of disparate pathologies like visualization of cancer cells or pathogenic microorganisms. Quantum dots toxicity and modifications for the toxicity reduction are discussed here as well. Survey of actual papers and patents in the field of quantum dots use in the biomedicine is provided. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  10. Heterovalent cation substitutional doping for quantum dot homojunction solar cells

    PubMed Central

    Stavrinadis, Alexandros; Rath, Arup K.; de Arquer, F. Pelayo García; Diedenhofen, Silke L.; Magén, César; Martinez, Luis; So, David; Konstantatos, Gerasimos

    2013-01-01

    Colloidal quantum dots have emerged as a material platform for low-cost high-performance optoelectronics. At the heart of optoelectronic devices lies the formation of a junction, which requires the intimate contact of n-type and p-type semiconductors. Doping in bulk semiconductors has been largely deployed for many decades, yet electronically active doping in quantum dots has remained a challenge and the demonstration of robust functional optoelectronic devices had thus far been elusive. Here we report an optoelectronic device, a quantum dot homojunction solar cell, based on heterovalent cation substitution. We used PbS quantum dots as a reference material, which is a p-type semiconductor, and we employed Bi-doping to transform it into an n-type semiconductor. We then combined the two layers into a homojunction device operating as a solar cell robustly under ambient air conditions with power conversion efficiency of 2.7%. PMID:24346430

  11. Fundamental and applied aspects of luminescence of colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Razumov, V. F.

    2017-03-01

    The spectral luminescent characteristics of colloidal quantum dots as a new class of luminophores are discussed and state-of-the-art investigations, problems, and prospects for their applications are considered.

  12. Quantum dot conjugates in a sub-micrometer fluidic channel

    DOEpatents

    Stavis, Samuel M.; Edel, Joshua B.; Samiee, Kevan T.; Craighead, Harold G.

    2008-07-29

    A nanofluidic channel fabricated in fused silica with an approximately 500 nm square cross section was used to isolate, detect and identify individual quantum dot conjugates. The channel enables the rapid detection of every fluorescent entity in solution. A laser of selected wavelength was used to excite multiple species of quantum dots and organic molecules, and the emission spectra were resolved without significant signal rejection. Quantum dots were then conjugated with organic molecules and detected to demonstrate efficient multicolor detection. PCH was used to analyze coincident detection and to characterize the degree of binding. The use of a small fluidic channel to detect quantum dots as fluorescent labels was shown to be an efficient technique for multiplexed single molecule studies. Detection of single molecule binding events has a variety of applications including high throughput immunoassays.

  13. Quantum dot conjugates in a sub-micrometer fluidic channel

    DOEpatents

    Stavis, Samuel M.; Edel, Joshua B.; Samiee, Kevan T.; Craighead, Harold G.

    2010-04-13

    A nanofluidic channel fabricated in fused silica with an approximately 500 nm square cross section was used to isolate, detect and identify individual quantum dot conjugates. The channel enables the rapid detection of every fluorescent entity in solution. A laser of selected wavelength was used to excite multiple species of quantum dots and organic molecules, and the emission spectra were resolved without significant signal rejection. Quantum dots were then conjugated with organic molecules and detected to demonstrate efficient multicolor detection. PCH was used to analyze coincident detection and to characterize the degree of binding. The use of a small fluidic channel to detect quantum dots as fluorescent labels was shown to be an efficient technique for multiplexed single molecule studies. Detection of single molecule binding events has a variety of applications including high throughput immunoassays.

  14. Optical properties of few layered graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Pratap Choudhary, Raghvendra; Shukla, Shobha; Vaibhav, Kumar; Bhagwan Pawar, Pranav; Saxena, Sumit

    2015-09-01

    Quantum dots provide a unique opportunity to study the confinement effects of electronic wave function on the properties of materials. We have investigated the optical properties of graphene quantum dots synthesized using ultra-fast light-matter interactions followed by one step reduction process. Atomic-scale morphological information suggests the presence of both zigzag and armchair edges in these quantum dots. Optical characterizations were performed using absorption, photoluminescence, and infrared spectroscopy. A shift in the emission spectrum and disappearance of n → π* transition in the absorption spectrum on reduction of the ablated samples confirmed the formation of graphene quantum dots. First principles calculations are in good agreement with the experimentally reported infrared data.

  15. Improved dot size uniformity and luminescense of InAs quantum dots on InP substrate

    NASA Technical Reports Server (NTRS)

    Qiu, Y.; Uhl, D.

    2002-01-01

    InAs self-organized quantum dots have been grown in InGaAs quantum well on InP substrates by metalorganic vapor phase epitaxy. Atomic Force Microscopy confirmed of quantum dot formation with dot density of 3X10(sup 10) cm(sup -2). Improved dot size uniformity and strong room temperature photoluminescence up to 2 micron were observed after modifying the InGaAs well.

  16. Improved dot size uniformity and luminescense of InAs quantum dots on InP substrate

    NASA Technical Reports Server (NTRS)

    Qiu, Y.; Uhl, D.

    2002-01-01

    InAs self-organized quantum dots have been grown in InGaAs quantum well on InP substrates by metalorganic vapor phase epitaxy. Atomic Force Microscopy confirmed of quantum dot formation with dot density of 3X10(sup 10) cm(sup -2). Improved dot size uniformity and strong room temperature photoluminescence up to 2 micron were observed after modifying the InGaAs well.

  17. Coherent radiation by quantum dots and magnetic nanoclusters

    NASA Astrophysics Data System (ADS)

    Yukalov, V. I.; Yukalova, E. P.

    2014-03-01

    The assemblies of either quantum dots or magnetic nanoclusters are studied. It is shown that such assemblies can produce coherent radiation. A method is developed for solving the systems of nonlinear equations describing the dynamics of such assemblies. The method is shown to be general and applicable to systems of different physical nature. Despite mathematical similarities of dynamical equations, the physics of the processes for quantum dots and magnetic nanoclusters is rather different. In a quantum dot assembly, coherence develops due to the Dicke effect of dot interactions through the common radiation field. For a system of magnetic clusters, coherence in the spin motion appears due to the Purcell effect caused by the feedback action of a resonator. Self-organized coherent spin radiation cannot arise without a resonator. This principal difference is connected with the different physical nature of dipole forces between the objects. Effective dipole interactions between the radiating quantum dots, appearing due to photon exchange, collectivize the dot radiation. While the dipolar spin interactions exist from the beginning, yet before radiation, and on the contrary, they dephase spin motion, thus destroying the coherence of moving spins. In addition, quantum dot radiation exhibits turbulent photon filamentation that is absent for radiating spins.

  18. Coherent radiation by quantum dots and magnetic nanoclusters

    SciTech Connect

    Yukalov, V. I.; Yukalova, E. P.

    2014-03-31

    The assemblies of either quantum dots or magnetic nanoclusters are studied. It is shown that such assemblies can produce coherent radiation. A method is developed for solving the systems of nonlinear equations describing the dynamics of such assemblies. The method is shown to be general and applicable to systems of different physical nature. Despite mathematical similarities of dynamical equations, the physics of the processes for quantum dots and magnetic nanoclusters is rather different. In a quantum dot assembly, coherence develops due to the Dicke effect of dot interactions through the common radiation field. For a system of magnetic clusters, coherence in the spin motion appears due to the Purcell effect caused by the feedback action of a resonator. Self-organized coherent spin radiation cannot arise without a resonator. This principal difference is connected with the different physical nature of dipole forces between the objects. Effective dipole interactions between the radiating quantum dots, appearing due to photon exchange, collectivize the dot radiation. While the dipolar spin interactions exist from the beginning, yet before radiation, and on the contrary, they dephase spin motion, thus destroying the coherence of moving spins. In addition, quantum dot radiation exhibits turbulent photon filamentation that is absent for radiating spins.

  19. A triangular triple quantum dot with tunable tunnel couplings

    NASA Astrophysics Data System (ADS)

    Noiri, A.; Kawasaki, K.; Otsuka, T.; Nakajima, T.; Yoneda, J.; Amaha, S.; Delbecq, M. R.; Takeda, K.; Allison, G.; Ludwig, A.; Wieck, A. D.; Tarucha, S.

    2017-08-01

    A two-dimensional arrangement of quantum dots (QDs) with finite inter-dot tunnel coupling provides a promising platform for studying complicated spin correlations as well as for constructing large-scale quantum computers. Here, we fabricate a tunnel-coupled triangular triple QD with a novel gate geometry in which three dots are defined by positively biasing the surface gates. At the same time, the small area in the center of the triangle is depleted by negatively biasing the top gate placed above the surface gates. The size of the small center depleted area is estimated from the Aharonov-Bohm oscillation measured for the triangular channel but incorporating no gate-defined dots, with a value consistent with the design. With this approach, we can bring the neighboring gate-defined dots close enough to one another to maintain a finite inter-dot tunnel coupling. We finally confirm the presence of the inter-dot tunnel couplings in the triple QD from the measurement of tunneling current through the dots in the stability diagram. We also show that the charge occupancy of each dot and that the inter-dot tunnel couplings are tunable with gate voltages.

  20. Dynamical symmetries in Kondo tunneling through complex quantum dots.

    PubMed

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2002-10-07

    Kondo tunneling reveals hidden SO(n) dynamical symmetries of evenly occupied quantum dots. As is exemplified for an experimentally realizable triple quantum dot in parallel geometry, the possible values n=3,4,5,7 can be easily tuned by gate voltages. Following construction of the corresponding o(n) algebras, scaling equations are derived and Kondo temperatures are calculated. The symmetry group for a magnetic field induced anisotropic Kondo tunneling is SU(2) or SO(4).

  1. Deformation potentials of CdSe quantum dots

    SciTech Connect

    Li, Jingbo; Wang, Lin-Wang

    2004-06-02

    The size dependent deformation potentials of CdSe quantum dots are studied by first principle and semi-empirical pseudopotentials calculations. They find that the amplitude of the quantum dot deformation potential is only slightly larger than the bulk value, and this increase is mostly caused by the off {Lambda} point deformation potentials in the bulk, which are larger in amplitude than the {Lambda} point deformation potential.

  2. Los Alamos Quantum Dots for Solar, Display Technology

    ScienceCinema

    Klimov, Victor

    2016-07-12

    Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry. Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100 percent. These properties have recently become the basis of a new technology – quantum dot displays – employed, for example, in the newest generation of e-readers and video monitors.

  3. Los Alamos Quantum Dots for Solar, Display Technology

    SciTech Connect

    Klimov, Victor

    2015-04-13

    Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry. Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100 percent. These properties have recently become the basis of a new technology – quantum dot displays – employed, for example, in the newest generation of e-readers and video monitors.

  4. Ultrafast optical properties of lithographically defined quantum dot amplifiers

    SciTech Connect

    Miaja-Avila, L.; Verma, V. B.; Mirin, R. P.; Silverman, K. L.; Coleman, J. J.

    2014-02-10

    We measure the ultrafast optical response of lithographically defined quantum dot amplifiers at 40 K. Recovery of the gain mostly occurs in less than 1 picosecond, with some longer-term transients attributable to carrier heating. Recovery of the absorption proceeds on a much longer timescale, representative of relaxation between quantum dot levels and carrier recombination. We also measure transparency current-density in these devices.

  5. UV Nano Lights - Nonlinear Quantum Dot-Plasmon Coupling

    DTIC Science & Technology

    2016-06-20

    AFRL-AFOSR-JP-TR-2016-0072 UV Nano- Lights - Nonlinear Quantum Dot-Plasmon Coupling Eric Waclawik QUEENSLAND UNIVERSITY OF TECHNOLOGY Final Report 06...Final 3.  DATES COVERED (From - To)  03 Feb 2014 to 02 Feb 2016 4.  TITLE AND SUBTITLE UV Nano- Lights - Nonlinear Quantum Dot-Plasmon Coupling 5a...coupled to gold (Au) nanoparticles, were examined both theoretically and experimentally. This work was performed to establish if confined light fields

  6. Resonant Scattering of Surface Plasmon Polaritons by Dressed Quantum Dots

    DTIC Science & Technology

    2014-06-23

    Resonant scattering of surface plasmon polaritons by dressed quantum dots Danhong Huang,1 Michelle Easter,2 Godfrey Gumbs,3 A. A. Maradudin,4 Shawn... polariton waves (SPP) by embedded semiconductor quantum dots above the dielectric/metal interface is explored in the strong-coupling regime. In con- trast to...induced polarization field, treated as a source term9 arising from photo-excited electrons, allows for a resonant scattering of surface plasmon- polariton

  7. Programmable Periodicity of Quantum Dot Arrays with DNA Origami Nanotubes

    PubMed Central

    2010-01-01

    To fabricate quantum dot arrays with programmable periodicity, functionalized DNA origami nanotubes were developed. Selected DNA staple strands were biotin-labeled to form periodic binding sites for streptavidin-conjugated quantum dots. Successful formation of arrays with periods of 43 and 71 nm demonstrates precise, programmable, large-scale nanoparticle patterning; however, limitations in array periodicity were also observed. Statistical analysis of AFM images revealed evidence for steric hindrance or site bridging that limited the minimum array periodicity. PMID:20681601

  8. Quantized charge pumping through a carbon nanotube double quantum dot

    NASA Astrophysics Data System (ADS)

    Chorley, S. J.; Frake, J.; Smith, C. G.; Jones, G. A. C.; Buitelaar, M. R.

    2012-04-01

    We demonstrate single-electron pumping in a gate-defined carbon nanotube double quantum dot. By periodic modulation of the potentials of the two quantum dots, we move the system around charge triple points and transport exactly one electron or hole per cycle. We investigate the pumping as a function of the modulation frequency and amplitude and observe good current quantization up to frequencies of 18 MHz where rectification effects cause the mechanism to break down.

  9. Whispering-gallery mode microcavity quantum-dot lasers

    SciTech Connect

    Kryzhanovskaya, N V; Maximov, M V; Zhukov, A E

    2014-03-28

    This review examines axisymmetric-cavity quantum-dot microlasers whose emission spectrum is determined by whisperinggallery modes. We describe the possible designs, fabrication processes and basic characteristics of the microlasers and demonstrate the possibility of lasing at temperatures above 100 °C. The feasibility of creating multichannel optical sources based on a combination of a broadband quantum-dot laser and silicon microring modulators is discussed. (review)

  10. Optimal excitation conditions for indistinguishable photons from quantum dots

    NASA Astrophysics Data System (ADS)

    Huber, Tobias; Predojević, Ana; Föger, Daniel; Solomon, Glenn; Weihs, Gregor

    2015-12-01

    In this paper, we present a detailed, all optical study of the influence of different excitation schemes on the indistinguishability of single photons from a single InAs quantum dot. For this study, we measure the Hong-Ou-Mandel interference of consecutive photons from the spontaneous emission of an InAs quantum dot state under various excitation schemes and different excitation conditions and give a comparison.

  11. Colloidal quantum dot materials for infrared optoelectronics

    NASA Astrophysics Data System (ADS)

    Arinze, Ebuka S.; Nyirjesy, Gabrielle; Cheng, Yan; Palmquist, Nathan; Thon, Susanna M.

    2015-09-01

    Colloidal quantum dots (CQDs) are an attractive material for optoelectronic applications because they combine flexible, low-cost solution-phase synthesis and processing with the potential for novel functionality arising from their nanostructure. Specifically, the bandgap of films composed of arrays of CQDs can be tuned via the quantum confinement effect for tailored spectral utilization. PbS-based CQDs can be tuned throughout the near and mid-infrared wavelengths and are a promising materials system for photovoltaic devices that harvest non-visible solar radiation. The performance of CQD solar cells is currently limited by an absorption-extraction compromise, whereby photon absorption lengths in the near infrared spectral regime exceed minority carrier diffusion lengths in the bulk films. Several light trapping strategies for overcoming this compromise and increasing the efficiency of infrared energy harvesting will be reviewed. A thin-film interference technique for creating multi-colored and transparent solar cells will be presented, and a discussion of designing plasmonic nanomaterials based on earth-abundant materials for integration into CQD solar cells is developed. The results indicate that it should be possible to achieve high absorption and color-tunability in a scalable nanomaterials system.

  12. Bandgap engineering in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Chia, C. K.; Dong, J. R.; Chua, S. J.; Tripathy, S.

    2006-02-01

    Intermixing in InAs quantum dots (QDs) grown by molecular-beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) techniques on GaAs and InP substrates have been investigated by rapid thermal annealing (RTA) and laser-irradiation techniques. In all cases, substantial energy shifts have been observed after RTA and laser annealing. A comparison between the intermixed QD and quantum well (QW) structures shows distinguished differences in photoluminescence (PL) intensity and full-width at half-maximum (FWHM). For QD structures, an increase in PL intensity and a reduction in FWHM were observed after intermixing, whereas for QW structures the FWHM increased and the PL intensity reduced after intermixing, suggesting degradation of the material quality in the QWs after intermixing. Examination of the role of the surrounding matrix in intermixing process shows that InAs QDs placed in a InGaAs QW can retain its good optical quality after high temperature annealing, as the InGaAs QW provides a foundation for the QDs to be fully desorbed in the well.

  13. Optical Studies of Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Yükselici, H.; Allahverdi, Ç.; Aşıkoğlu, A.; Ünlü, H.; Baysal, A.; Çulha, M.; İnce, R.; İnce, A.; Feeney, M.; Athalin, H.

    Optical absorption (ABS), steady-state photoluminescence (PL), resonant Raman, and photoabsorption (PA) spectroscopies are employed to study quantum-size effects in II-VI semiconductor quantum dots (QDs) grown in glass samples. We observe a size-dependent shift in the energetic position of the first exciton peak and have examined the photoinduced evolution of the differential absorption spectra. The Raman shifts of the phonon modes are employed to monitor stoichiometric changes in the composition of the QDs during growth. Two sets of glass samples were prepared from color filters doped with CdS x Se1 - x and Zn x Cd1 - x Te. We analyze the optical properties of QDs through the ABS, PL, resonant Raman, and PA spectroscopies. The glass samples were prepared from commercially available semiconductor doped filters by a two-step thermal treatment. The average size of QDs is estimated from the energetic position of the first exciton peak in the ABS spectrum. A calculation based on a quantized-state effective mass model in the strong confinement regime predicts that the average radius of QDs in the glass samples ranges from 2.9 to 4.9 nm for CdTe and from 2.2 to 9.3 nm for CdS0. 08Se0. 92. We have also studied the nonlinear optical properties of QDs by reviewing the results of size-dependent photoinduced modulations in the first exciton band of CdTe QDs studied by PA spectroscopy.

  14. Bismides: 2D structures and quantum dots

    NASA Astrophysics Data System (ADS)

    Pačebutas, Vaidas; Butkutė, Renata; Čechavičius, Bronislovas; Stanionytė, Sandra; Pozingytė, Evelina; Skapas, Martynas; Selskis, Algirdas; Geižutis, Andrejus; Krotkus, Arūnas

    2017-09-01

    The growth and characterization of ternary GaAsBi and quaternary GaInAsBi compound quantum wells (QWs) on GaAs substrates is presented in this study. The influence of technological parameters, such as different growth modes, substrate temperatures, beam equivalent pressure ratios and thermal treating on structural and luminescent properties of QWs is discussed. The complex structural investigations using x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy revealed high crystal structure, smooth surfaces and abrupt interfaces of both GaAsBi and GaInAsBi QWs. The temperature dependent photoluminescence measurements demonstrated emission wavelengths up to 1.43 µm in room temperature PL spectra measured for GaAsBi/GaAs QWs containing 12% Bi, whereas GaInAsBi QWs with 4.2% of bismuth inserted between GaAs barriers has reached 1.25 µm. Moreover, the annealing at high temperatures of GaAsBi/AlAs QWs stimulated agglomeration of bismuth to quantum dots in the well layers, emitting at 1.5 µm. The achieved wavelengths are the longest ones declared for the GaAsBi and GaInAsBi QW structures grown on the GaAs substrate, therefore bismide-based QWs are the promising structures for applications in infrared devices.

  15. Optical nuclear spin polarization in quantum dots

    NASA Astrophysics Data System (ADS)

    Li, Ai-Xian; Duan, Su-Qing; Zhang, Wei

    2016-10-01

    Hyperfine interaction between electron spin and randomly oriented nuclear spins is a key issue of electron coherence for quantum information/computation. We propose an efficient way to establish high polarization of nuclear spins and reduce the intrinsic nuclear spin fluctuations. Here, we polarize the nuclear spins in semiconductor quantum dot (QD) by the coherent population trapping (CPT) and the electric dipole spin resonance (EDSR) induced by optical fields and ac electric fields. By tuning the optical fields, we can obtain a powerful cooling background based on CPT for nuclear spin polarization. The EDSR can enhance the spin flip-flop rate which may increase the cooling efficiency. With the help of CPT and EDSR, an enhancement of 1300 times of the electron coherence time can be obtained after a 10-ns preparation time. Project partially supported by the National Natural Science Foundations of China (Grant Nos. 11374039 and 11174042) and the National Basic Research Program of China (Grant Nos. 2011CB922204 and 2013CB632805).

  16. Controlled Photon Switch Assisted by Coupled Quantum Dots

    PubMed Central

    Luo, Ming-Xing; Ma, Song-Ya; Chen, Xiu-Bo; Wang, Xiaojun

    2015-01-01

    Quantum switch is a primitive element in quantum network communication. In contrast to previous switch schemes on one degree of freedom (DOF) of quantum systems, we consider controlled switches of photon system with two DOFs. These controlled photon switches are constructed by exploring the optical selection rules derived from the quantum-dot spins in one-sided optical microcavities. Several double controlled-NOT gate on different joint systems are greatly simplified with an auxiliary DOF of the controlling photon. The photon switches show that two DOFs of photons can be independently transmitted in quantum networks. This result reduces the quantum resources for quantum network communication. PMID:26095049

  17. Coupling capacitance between double quantum dots tunable by the number of electrons in Si quantum dots

    SciTech Connect

    Uchida, Takafumi Arita, Masashi; Takahashi, Yasuo; Fujiwara, Akira

    2015-02-28

    Tunability of capacitive coupling in the Si double-quantum-dot system is discussed by changing the number of electrons in quantum dots (QDs), in which the QDs are fabricated using pattern-dependent oxidation (PADOX) of a Si nanowire and multi-fine-gate structure. A single QD formed by PADOX is divided into multiple QDs by additional oxidation through the gap between the fine gates. When the number of electrons occupying the QDs is large, the coupling capacitance increases gradually and almost monotonically with the number of electrons. This phenomenon is attributed to the gradual growth in the effective QD size due to the increase in the number of electrons in the QDs. On the other hand, when the number of electrons changes in the few-electron regime, the coupling capacitance irregularly changes. This irregularity can be observed even up to 40 electrons. This behavior is attributable the rough structure of Si nano-dots made by PADOX. This roughness is thought to induce complicated change in the electron wave function when an electron is added to or subtracted from a QD.

  18. Intrinsic Chirality of CdSe/ZnS Quantum Dots and Quantum Rods.

    PubMed

    Mukhina, Maria V; Maslov, Vladimir G; Baranov, Alexander V; Fedorov, Anatoly V; Orlova, Anna O; Purcell-Milton, Finn; Govan, Joseph; Gun'ko, Yurii K

    2015-05-13

    A new class of chiral nanoparticles is of great interest not only for nanotechnology, but also for many other fields of scientific endeavor. Normally the chirality in semiconductor nanocrystals is induced by the initial presence of chiral ligands/stabilizer molecules. Here we report intrinsic chirality of ZnS coated CdSe quantum dots (QDs) and quantum rods (QRs) stabilized by achiral ligands. As-prepared ensembles of these nanocrystals have been found to be a racemic mixture of d- and l-nanocrystals which also includes a portion of nonchiral nanocrystals and so in total the solution does not show a circular dichroism (CD) signal. We have developed a new enantioselective phase transfer technique to separate chiral nanocrystals using an appropriate chiral ligand and obtain optically active ensembles of CdSe/ZnS QDs and QRs. After enantioselective phase transfer, the nanocrystals isolated in organic phase, still capped with achiral ligands, now display circular dichroism (CD). We propose that the intrinsic chirality of CdSe/ZnS nanocrystals is caused by the presence of naturally occurring chiral defects.

  19. Direct Imaging of Electron States in Open Quantum Dots

    NASA Astrophysics Data System (ADS)

    Aoki, N.; Brunner, R.; Burke, A. M.; Akis, R.; Meisels, R.; Ferry, D. K.; Ochiai, Y.

    2012-03-01

    We use scanning gate microscopy to probe the ballistic motion of electrons within an open GaAs/AlGaAs quantum dot. Conductance maps are recorded by scanning a biased tip over the open quantum dot while a magnetic field is applied. We show that, for specific magnetic fields, the measured conductance images resemble the classical transmitted and backscattered trajectories and their quantum mechanical analogue. In addition, we prove experimentally, with this direct measurement technique, the existence of pointer states. The demonstrated direct imaging technique is essential for the fundamental understanding of wave function scarring and quantum decoherence theory.

  20. Interaction of solitons with a string of coupled quantum dots

    SciTech Connect

    Kumar, Vijendra Swami, O. P. Nagar, A. K.; Taneja, S.

    2016-05-06

    In this paper, we develop a theory for discrete solitons interaction with a string of coupled quantum dots in view of the local field effects. Discrete nonlinear Schrodinger (DNLS) equations are used to describe the dynamics of the string. Numerical calculations are carried out and results are analyzed with the help of matlab software. With the help of numerical solutions we demonstrate that in the quantum dots string, Rabi oscillations (RO) are self trapped into stable bright Rabi solitons. The Rabi oscillations in different types of nanostructures have potential applications to the elements of quantum logic and quantum memory.

  1. On-chip generation and guiding of quantum light from a site-controlled quantum dot

    SciTech Connect

    Jamil, Ayesha; Farrer, Ian; Griffiths, Jonathan P.; Jones, Geb A. C.; Ritchie, David A.; Skiba-Szymanska, Joanna; Kalliakos, Sokratis; Ward, Martin B.; Ellis, David J. P.; Shields, Andrew J.; Schwagmann, Andre; Brody, Yarden

    2014-03-10

    We demonstrate the emission and routing of single photons along a semiconductor chip originating from carrier recombination in an actively positioned InAs quantum dot. Device–scale arrays of quantum dots are formed by a two–step regrowth process. We precisely locate the propagating region of a unidirectional photonic crystal waveguide with respect to the quantum dot nucleation site. Under pulsed optical excitation, the multiphoton emission probability from the waveguide's exit is 12% ± 5% before any background correction. Our results are a major step towards the deterministic integration of a quantum emitter with the waveguiding components of photonic quantum circuits.

  2. Quantum computation: algorithms and implementation in quantum dot devices

    NASA Astrophysics Data System (ADS)

    Gamble, John King

    In this thesis, we explore several aspects of both the software and hardware of quantum computation. First, we examine the computational power of multi-particle quantum random walks in terms of distinguishing mathematical graphs. We study both interacting and non-interacting multi-particle walks on strongly regular graphs, proving some limitations on distinguishing powers and presenting extensive numerical evidence indicative of interactions providing more distinguishing power. We then study the recently proposed adiabatic quantum algorithm for Google PageRank, and show that it exhibits power-law scaling for realistic WWW-like graphs. Turning to hardware, we next analyze the thermal physics of two nearby 2D electron gas (2DEG), and show that an analogue of the Coulomb drag effect exists for heat transfer. In some distance and temperature, this heat transfer is more significant than phonon dissipation channels. After that, we study the dephasing of two-electron states in a single silicon quantum dot. Specifically, we consider dephasing due to the electron-phonon coupling and charge noise, separately treating orbital and valley excitations. In an ideal system, dephasing due to charge noise is strongly suppressed due to a vanishing dipole moment. However, introduction of disorder or anharmonicity leads to large effective dipole moments, and hence possibly strong dephasing. Building on this work, we next consider more realistic systems, including structural disorder systems. We present experiment and theory, which demonstrate energy levels that vary with quantum dot translation, implying a structurally disordered system. Finally, we turn to the issues of valley mixing and valley-orbit hybridization, which occurs due to atomic-scale disorder at quantum well interfaces. We develop a new theoretical approach to study these effects, which we name the disorder-expansion technique. We demonstrate that this method successfully reproduces atomistic tight-binding techniques

  3. Fluorescence from a quantum dot and metallic nanosphere hybrid system

    SciTech Connect

    Schindel, Daniel G.; Singh, Mahi R.

    2014-03-31

    We present energy absorption and interference in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. A control field is applied to induce dipole moments in the nanosphere and the quantum dot, and a probe field is applied to monitor absorption. Dipole moments in the quantum dot or the metal nanosphere are induced, both by the external fields and by each other's dipole fields. Thus, in addition to direct polarization, the metal nanosphere and the quantum dot will sense one another via the dipole-dipole interaction. The density matrix method was used to show that the absorption spectrum can be split from one peak to two peaks by the control field, and this can also be done by placing the metal sphere close to the quantum dot. When the two are extremely close together, a self-interaction in the quantum dot produces an asymmetry in the absorption peaks. In addition, the fluorescence efficiency can be quenched by the addition of a metal nanosphere. This hybrid system could be used to create ultra-fast switching and sensing nanodevices.

  4. Fluorescence from a quantum dot and metallic nanosphere hybrid system

    NASA Astrophysics Data System (ADS)

    Schindel, Daniel G.; Singh, Mahi R.

    2014-03-01

    We present energy absorption and interference in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. A control field is applied to induce dipole moments in the nanosphere and the quantum dot, and a probe field is applied to monitor absorption. Dipole moments in the quantum dot or the metal nanosphere are induced, both by the external fields and by each other's dipole fields. Thus, in addition to direct polarization, the metal nanosphere and the quantum dot will sense one another via the dipole-dipole interaction. The density matrix method was used to show that the absorption spectrum can be split from one peak to two peaks by the control field, and this can also be done by placing the metal sphere close to the quantum dot. When the two are extremely close together, a self-interaction in the quantum dot produces an asymmetry in the absorption peaks. In addition, the fluorescence efficiency can be quenched by the addition of a metal nanosphere. This hybrid system could be used to create ultra-fast switching and sensing nanodevices.

  5. Quantum dot enhancement of bacteriorhodopsin-based electrodes.

    PubMed

    Griep, Mark H; Walczak, Karl A; Winder, Eric M; Lueking, Donald R; Friedrich, Craig R

    2010-02-15

    Nanoscale sensing arrays utilizing the unique properties of the optical protein bacteriorhodopsin and colloidal semiconductor quantum dots are being developed for toxin detection applications. This paper describes an innovative method to activate bacteriorhodopsin-based electrodes with the optical output of quantum dots, producing an enhanced electrical response from the protein. Results show that the photonic emission of CdSe/ZnS quantum dots is absorbed by the bacteriorhodopsin retinal and initiates the proton pumping sequence, resulting in an electrical output from a bacteriorhodopsin-based electrode. It is also shown that activated quantum dots in sub-10nm proximity to bacteriorhodopsin further amplify the photovoltaic response of the protein by approximately 23%, compared to without attached quantum dots, suggesting direct energy transfer mechanisms beyond photonic emission alone. The ability of quantum dots to activate nanoscale regions on bacteriorhodopsin-based electrodes could allow sub-micron sensing arrays to be created due to the ability to activate site-specific regions on the array. Copyright 2009 Elsevier B.V. All rights reserved.

  6. Long-Term Retention of Fluorescent Quantum Dots In Vivo

    NASA Astrophysics Data System (ADS)

    Ballou, Byron; Ernst, Lauren A.; Andreko, Susan; Eructiez, Marcel P.; Lagerholm, B. Christoffer; Waggoner, Alan S.

    Quantum dots that emit in the near-infrared can be used in vivo to follow circulation, to target the reticuloendothelial system, and to map lymphatic drainage from normal tissues and tumors. We have explored the role of surface charge and passivation by polyethylene glycol in determining circulating lifetimes and sites of deposition. Use of long polyethylene glycol polymers increases circulating lifetime. Changing surface charge can partially direct quantum dots to the liver and spleen, or the lymph nodes. Quantum dots are cleared in the order liver > spleen > bone marrow > lymph nodes. Quantum dots retained by lymph nodes maintained fluorescence for two years, suggesting either that the coating is extremely stable or that some endosomes preserve quantum dot function. We also explored migration from tumors to sentinel lymph nodes using tumor models in mice; surface charge and size make little difference to transport from tumors. Antibody and Fab-conjugates of polymer-coated quantum dots failed to target tumors in vivo, probably because of size.

  7. Heparin conjugated quantum dots for in vitro imaging applications.

    PubMed

    Maguire, Ciaran Manus; Mahfoud, Omar Kazem; Rakovich, Tatsiana; Gerard, Valerie Anne; Prina-Mello, Adriele; Gun'ko, Yurii; Volkov, Yuri

    2014-11-01

    In this work heparin-gelatine multi-layered cadmium telluride quantum dots (QDgel/hep) were synthesised using a novel 'one-pot' method. The QDs produced were characterised using various spectroscopic and physiochemical techniques. Suitable QDs were then selected and compared to thioglycolic acid stabilised quantum dots (QDTGA) and gelatine coated quantum dots (QDgel) for utilisation in in vitro imaging experiments on live and fixed permeabilised THP-1, A549 and Caco-2 cell lines. Exposure of live THP-1 cells to QDgel/hep resulted in localisation of the QDs to the nucleus of the cells. QDgel/hep show affinity for the nuclear compartment of fixed permeabilised THP-1 and A549 cells but remain confined to cytoplasm of fixed permeabilised Caco-2 cells. It is postulated that heparin binding to the CD11b receptor facilitates the internalisation of the QDs into the nucleus of THP-1 cells. In addition, the heparin layer may reduce the unfavourable thrombogenic nature of quantum dots observed in vivo. In this study, heparin conjugated quantum dots were found to have superior imaging properties compared to its native counterparts. The authors postulate that heparin binding to the CD11b receptor facilitates QD internalization to the nucleus, and the heparin layer may reduce the in vivo thrombogenic properties of quantum dots. Copyright © 2014 Elsevier Inc. All rights reserved.

  8. Rhizopus stolonifer mediated biosynthesis of biocompatible cadmium chalcogenide quantum dots.

    PubMed

    Mareeswari, P; Brijitta, J; Harikrishna Etti, S; Meganathan, C; Kaliaraj, Gobi Saravanan

    2016-12-01

    We report an efficient method to biosynthesize biocompatible cadmium telluride and cadmium sulphide quantum dots from the fungus Rhizopus stolonifer. The suspension of the quantum dots exhibited purple and greenish-blue luminescence respectively upon UV light illumination. Photoluminescence spectroscopy, X-ray diffraction, and transmission electron microscopy confirms the formation of the quantum dots. From the photoluminescence spectrum the emission maxima is found to be 424 and 476nm respectively. The X-ray diffraction of the quantum dots matches with results reported in literature. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability evaluation carried out on 3-days transfer, inoculum 3×10(5) cells, embryonic fibroblast cells lines shows that more than 80% of the cells are viable even after 48h, indicating the biocompatible nature of the quantum dots. A good contrast in imaging has been obtained upon incorporating the quantum dots in human breast adenocarcinoma Michigan Cancer Foundation-7 cell lines. Copyright © 2016 Elsevier Inc. All rights reserved.

  9. Synergistic Tunability of Fluorescence Using Coupled Quantum Dots

    NASA Astrophysics Data System (ADS)

    Sengupta, Sucheta; Acharya, Somobrata

    2011-07-01

    Size and shape controlled semiconductor quantum dots have been widely adopted in tailoring nanomaterials properties, which basically utilize band edge engineering extending the band gap to larger values than the bulk. However, the long range electronic transition tunability is difficult to achieve using size or shape controlled quantum dots. Alternatively, chemically coupled quantum dots offer a novel route for tuning long range electronic transitions of semiconductors via band offset engineering at the material interface. We report on a simple route of tailoring visible emissions over long range by chemically designing coupled dots comprising of ZnSe and CdS quantum dots. Long range tunability of visible emissions originated from strong interdot dispersion, which can not be realized from individual quantum dots. A variation of component size or extend of coupling led to the tuning of visible emission wavelengths, the intensity of which can be controlled by temperature. The first principles electronic structure calculations based on density functional theory reveals the type-II nature of chemical bonding at CdS/ZnSe interface which plays a crucial role in tailoring the long range emissions. Such novel class of asymmetric coupled structures may offer a basis for diverse set of building blocks for optoelectronic devices, ultrahigh density memories and quantum information processing.

  10. Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots

    SciTech Connect

    Cundiff, Steven T.

    2016-05-03

    This final report describes the activities undertaken under grant "Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots". The goal of this program was to implement optical 2-dimensional Fourier transform spectroscopy and apply it to electronic excitations, including excitons, in semiconductors. Specifically of interest are quantum wells that exhibit disorder due to well width fluctuations and quantum dots. In both cases, 2-D spectroscopy will provide information regarding coupling among excitonic localization sites.

  11. Growth and Characterization of III-V Nitride Quantum Dots and Quantum Wires

    DTIC Science & Technology

    2010-03-26

    REPORT Growth and Characterization of III - V Nitride Quantum Dots and Quantum Wires 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: Our research program...ANSI Std. Z39.18 - 14-Sep-2009 Final report Growth and Characterization of III - V Nitride Quantum Dots and Quantum Wires Statement of the...has two interrelated components: the growth of GaN nanowires and the fabrication of electronic devices, including gas sensors, on these nanowires . A

  12. Computation of energy states of hydrogenic quantum dot with two-electrons

    SciTech Connect

    Yakar, Y.; Özmen, A. Çakır, B.

    2016-03-25

    In this study we have investigated the electronic structure of the hydrogenic quantum dot with two electrons inside an impenetrable potential surface. The energy eigenvalues and wavefunctions of the ground and excited states of spherical quantum dot have been calculated by using the Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) method, and the energies are investigated as a function of dot radius. The results show that as dot radius increases, the energy of quantum dot decreases.

  13. Si quantum dot structures and their applications

    NASA Astrophysics Data System (ADS)

    Shcherbyna, L.; Torchynska, T.

    2013-06-01

    This paper presents briefly the history of emission study in Si quantum dots (QDs) in the last two decades. Stable light emission of Si QDs and NCs was observed in the spectral ranges: blue, green, orange, red and infrared. These PL bands were attributed to the exciton recombination in Si QDs, to the carrier recombination through defects inside of Si NCs or via oxide related defects at the Si/SiOx interface. The analysis of recombination transitions and the different ways of the emission stimulation in Si QD structures, related to the element variation for the passivation of surface dangling bonds, as well as the plasmon induced emission and rare earth impurity activation, have been presented. The different applications of Si QD structures in quantum electronics, such as: Si QD light emitting diodes, Si QD single union and tandem solar cells, Si QD memory structures, Si QD based one electron devices and double QD structures for spintronics, have been discussed as well. Note the significant worldwide interest directed toward the silicon-based light emission for integrated optoelectronics is related to the complementary metal-oxide semiconductor compatibility and the possibility to be monolithically integrated with very large scale integrated (VLSI) circuits. The different features of poly-, micro- and nanocrystalline silicon for solar cells, that is a mixture of both amorphous and crystalline phases, such as the silicon NCs or QDs embedded in a α-Si:H matrix, as well as the thin film 2-cell or 3-cell tandem solar cells based on Si QD structures have been discussed as well. Silicon NC based structures for non-volatile memory purposes, the recent studies of Si QD base single electron devices and the single electron occupation of QDs as an important component to the measurement and manipulation of spins in quantum information processing have been analyzed as well.

  14. Influence of surface states of CuInS2 quantum dots in quantum dots sensitized photo-electrodes

    NASA Astrophysics Data System (ADS)

    Peng, Zhuoyin; Liu, Yueli; Wu, Lei; Zhao, Yinghan; Chen, Keqiang; Chen, Wen

    2016-12-01

    Surface states are significant factor for the enhancement of electrochemical performance in CuInS2 quantum dot sensitized photo-electrodes. DDT, OLA, MPA, and S2- ligand capped CuInS2 quantum dot sensitized photo-electrodes are prepared by thermolysis, solvethermal and ligand-exchange processes, respectively, and their optical properties and photoelectrochemical properties are investigated. The S2- ligand enhances the UV-vis absorption and electron-hole separation property as well as the excellent charge transfer performance of the photo-electrodes, which is attributed to the fact that the atomic S2- ligand for the interfacial region of quantum dots may improve the electron transfer rate. These S2--capped CuInS2 quantum dot sensitized photo-electrodes exhibit the excellent photoelectrochemical efficiency and IPCE peak value, which is higher than that of the samples with DDT, OLA and MPA ligands.

  15. Single-Photon Superradiance from a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Tighineanu, Petru; Daveau, Raphaël S.; Lehmann, Tau B.; Beere, Harvey E.; Ritchie, David A.; Lodahl, Peter; Stobbe, Søren

    2016-04-01

    We report on the observation of single-photon superradiance from an exciton in a semiconductor quantum dot. The confinement by the quantum dot is strong enough for it to mimic a two-level atom, yet sufficiently weak to ensure superradiance. The electrostatic interaction between the electron and the hole comprising the exciton gives rise to an anharmonic spectrum, which we exploit to prepare the superradiant quantum state deterministically with a laser pulse. We observe a fivefold enhancement of the oscillator strength compared to conventional quantum dots. The enhancement is limited by the base temperature of our cryostat and may lead to oscillator strengths above 1000 from a single quantum emitter at optical frequencies.

  16. High quantum yield ZnO quantum dots synthesizing via an ultrasonication microreactor method.

    PubMed

    Yang, Weimin; Yang, Huafang; Ding, Wenhao; Zhang, Bing; Zhang, Le; Wang, Lixi; Yu, Mingxun; Zhang, Qitu

    2016-11-01

    Green emission ZnO quantum dots were synthesized by an ultrasonic microreactor. Ultrasonic radiation brought bubbles through ultrasonic cavitation. These bubbles built microreactor inside the microreactor. The photoluminescence properties of ZnO quantum dots synthesized with different flow rate, ultrasonic power and temperature were discussed. Flow rate, ultrasonic power and temperature would influence the type and quantity of defects in ZnO quantum dots. The sizes of ZnO quantum dots would be controlled by those conditions as well. Flow rate affected the reaction time. With the increasing of flow rate, the sizes of ZnO quantum dots decreased and the quantum yields first increased then decreased. Ultrasonic power changed the ultrasonic cavitation intensity, which affected the reaction energy and the separation of the solution. With the increasing of ultrasonic power, sizes of ZnO quantum dots first decreased then increased, while the quantum yields kept increasing. The effect of ultrasonic temperature on the photoluminescence properties of ZnO quantum dots was influenced by the flow rate. Different flow rate related to opposite changing trend. Moreover, the quantum yields of ZnO QDs synthesized by ultrasonic microreactor could reach 64.7%, which is higher than those synthesized only under ultrasonic radiation or only by microreactor.

  17. Hole-Nuclear Spin Interaction in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Eble, B.; Testelin, C.; Desfonds, P.; Bernardot, F.; Balocchi, A.; Amand, T.; Miard, A.; Lemaître, A.; Marie, X.; Chamarro, M.

    2009-04-01

    We have measured the carrier spin dynamics in p-doped InAs/GaAs quantum dots by pump-probe and time-resolved photoluminescence experiments. We obtained experimental evidence of the hyperfine interaction between hole and nuclear spins. In the absence of an external magnetic field, our calculations based on dipole-dipole coupling between the hole and the quantum dot nuclei lead to a hole-spin dephasing time for an ensemble of dots of 14 ns, in close agreement with experiments.

  18. State hybridization shapes the photocurrent in triple quantum dot nanojunctions

    SciTech Connect

    Beltako, Katawoura; Cavassilas, Nicolas; Michelini, Fabienne

    2016-08-15

    We investigated a prototype of a quantum dot based photodetector made of a dot absorber interconnected with two lateral dot filters in contact with semiconducting leads. Using the nonequilibrium Green's function technique, we found that there are two opposite evolutions of the photocurrent in the vicinity of the tunnel resonance for such a kind of nanodevice. This evolution depends on where the strongest hybridization of states happens, and hence still reveals a quantum effect. If the filter states hybridize more with the absorber states than the ones of the leads, the photocurrent shows a maximum at the tunnel resonance, while it is minimized in the opposite case.

  19. Coupled Landau-Zener-Stückelberg quantum dot interferometers

    NASA Astrophysics Data System (ADS)

    Gallego-Marcos, Fernando; Sánchez, Rafael; Platero, Gloria

    2016-02-01

    We investigate the interplay between long-range and direct photon-assisted transport in a triple quantum dot chain where local ac voltages are applied to the outer dots. We propose the phase difference between the two ac voltages as an external parameter, which can be easily tuned to manipulate the current characteristics. For gate voltages in phase opposition we find quantum destructive interferences analogous to the interferences in closed-loop undriven triple dots. As the voltages oscillate in phase, interferences between multiple paths give rise to dark states. Those totally cancel the current, and could be experimentally resolved.

  20. Annealing-induced change in quantum dot chain formation mechanism

    SciTech Connect

    Park, Tyler D.; Colton, John S.; Farrer, Jeffrey K.; Yang, Haeyeon; Kim, Dong Jun

    2014-12-15

    Self-assembled InGaAs quantum dot chains were grown using a modified Stranski-Krastanov method in which the InGaAs layer is deposited under a low growth temperature and high arsenic overpressure, which suppresses the formation of dots until a later annealing process. The dots are capped with a 100 nm GaAs layer. Three samples, having three different annealing temperatures of 460°C, 480°C, and 500°C, were studied by transmission electron microscopy. Results indicate two distinct types of dot formation processes: dots in the 460°C and 480°C samples form from platelet precursors in a one-to-one ratio whereas the dots in the sample annealed at 500°C form through the strain-driven self-assembly process, and then grow larger via an additional Ostwald ripening process whereby dots grow into larger dots at the expense of smaller seed islands. There are consequently significant morphological differences between the two types of dots, which explain many of the previously-reported differences in optical properties. Moreover, we also report evidence of indium segregation within the dots, with little or no indium intermixing between the dots and the surrounding GaAs barrier.

  1. Annealing-induced change in quantum dot chain formation mechanism

    NASA Astrophysics Data System (ADS)

    Park, Tyler D.; Colton, John S.; Farrer, Jeffrey K.; Yang, Haeyeon; Kim, Dong Jun

    2014-12-01

    Self-assembled InGaAs quantum dot chains were grown using a modified Stranski-Krastanov method in which the InGaAs layer is deposited under a low growth temperature and high arsenic overpressure, which suppresses the formation of dots until a later annealing process. The dots are capped with a 100 nm GaAs layer. Three samples, having three different annealing temperatures of 460°C, 480°C, and 500°C, were studied by transmission electron microscopy. Results indicate two distinct types of dot formation processes: dots in the 460°C and 480°C samples form from platelet precursors in a one-to-one ratio whereas the dots in the sample annealed at 500°C form through the strain-driven self-assembly process, and then grow larger via an additional Ostwald ripening process whereby dots grow into larger dots at the expense of smaller seed islands. There are consequently significant morphological differences between the two types of dots, which explain many of the previously-reported differences in optical properties. Moreover, we also report evidence of indium segregation within the dots, with little or no indium intermixing between the dots and the surrounding GaAs barrier.

  2. Theory of spin blockade in a triple quantum dots

    NASA Astrophysics Data System (ADS)

    Hsieh, Chang-Yu; Shim, Yun-Pil; Hawrylak, Pawel

    2011-03-01

    We present a theory of electronic properties and spin blockade in a linear triple quantum dots. We use micoroscopic LCHO-CI and double-band Hubbard model to analyze the electronic and spin properties of a triple quantum dots near a symmetrical quadruple point involving the (1,1,1) configuration which is essential for implementing quantum information processing with electron spin. We calculate spectral functions and relate them via the rate equation, including coupling with a phonon bath, to current as a function of applied bias. We show that the spin blockade in a triple quantum dots can serve as a spectroscopic tool to distinguish spin polarized states from spin depolarized states. We also show that a spin blockade is developed only at high bias when an onsite triplet state on the edge quantum dot connected to the source lead becomes accessible in the transport window. In contradiction to the case of double quantum dot molecule, the onsite triplet is not only essential for lifting spin blockade but also important for building up spin polarisation and spin blockade in the system. The authors would like to acknowledge financial support from NSERC, OGS, and QuantumWorks.

  3. Optically active quantum dots in monolayer WSe2

    NASA Astrophysics Data System (ADS)

    Srivastava, Ajit; Sidler, Meinrad; Allain, Adrien V.; Lembke, Dominik S.; Kis, Andras; Imamoğlu, A.

    2015-06-01

    Semiconductor quantum dots have emerged as promising candidates for the implementation of quantum information processing, because they allow for a quantum interface between stationary spin qubits and propagating single photons. In the meantime, transition-metal dichalcogenide monolayers have moved to the forefront of solid-state research due to their unique band structure featuring a large bandgap with degenerate valleys and non-zero Berry curvature. Here, we report the observation of zero-dimensional anharmonic quantum emitters, which we refer to as quantum dots, in monolayer tungsten diselenide, with an energy that is 20-100 meV lower than that of two-dimensional excitons. Photon antibunching in second-order photon correlations unequivocally demonstrates the zero-dimensional anharmonic nature of these quantum emitters. The strong anisotropic magnetic response of the spatially localized emission peaks strongly indicates that radiative recombination stems from localized excitons that inherit their electronic properties from the host transition-metal dichalcogenide. The large ˜1 meV zero-field splitting shows that the quantum dots have singlet ground states and an anisotropic confinement that is most probably induced by impurities or defects. The possibility of achieving electrical control in van der Waals heterostructures and to exploit the spin-valley degree of freedom renders transition-metal-dichalcogenide quantum dots interesting for quantum information processing.

  4. Toward quantitatively fluorescent carbon-based "quantum" dots.

    PubMed

    Anilkumar, Parambath; Wang, Xin; Cao, Li; Sahu, Sushant; Liu, Jia-Hui; Wang, Ping; Korch, Katerina; Tackett, Kenneth N; Parenzan, Alexander; Sun, Ya-Ping

    2011-05-01

    Carbon-based "quantum" dots (or "carbon dots") are generally defined as surface-passivated small carbon nanoparticles that are brightly fluorescent. Apparently, the carbon particle surface passivation in carbon dots is critical to their fluorescence performance. An effective way to improve the surface passivation is to dope the surface of the precursor carbon nanoparticles with an inorganic salt, followed by the typical functionalization with organic molecules. In this work we passivated small carbon nanoparticles by a combination of the surface-doping with nanoscale semiconductors and the organic functionalization, coupled with gel column fractionation to harvest the most fluorescent carbon dots, which exhibited fluorescence emission quantum yields of up to 78%. Experimental and mechanistic issues relevant to potentially further improve the performance of carbon dots toward their being quantitatively fluorescent are discussed.

  5. Thermoelectric study of dissipative quantum-dot heat engines

    NASA Astrophysics Data System (ADS)

    De, Bitan; Muralidharan, Bhaskaran

    2016-10-01

    This paper examines the thermoelectric response of a dissipative quantum-dot heat engine based on the Anderson-Holstein model in two relevant operating limits, (i) when the dot phonon modes are out of equilibrium, and (ii) when the dot phonon modes are strongly coupled to a heat bath. In the first case, a detailed analysis of the physics related to the interplay between the quantum-dot level quantization, the on-site Coulomb interaction, and the electron-phonon coupling on the thermoelectric performance reveals that an n -type heat engine performs better than a p -type heat engine. In the second case, with the aid of the dot temperature estimated by incorporating a thermometer bath, it is shown that the dot temperature deviates from the bath temperature as electron-phonon interaction in the dot becomes stronger. Consequently, it is demonstrated that the dot temperature controls the direction of phonon heat currents, thereby influencing the thermoelectric performance. Finally, the conditions on the maximum efficiency with varying phonon couplings between the dot and all the other macroscopic bodies are analyzed in order to reveal the nature of the optimum junction.

  6. Compact Interconnection Networks Based on Quantum Dots

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Toomarian, Nikzad; Modarress, Katayoon; Spotnitz, Matthew

    2003-01-01

    Architectures that would exploit the distinct characteristics of quantum-dot cellular automata (QCA) have been proposed for digital communication networks that connect advanced digital computing circuits. In comparison with networks of wires in conventional very-large-scale integrated (VLSI) circuitry, the networks according to the proposed architectures would be more compact. The proposed architectures would make it possible to implement complex interconnection schemes that are required for some advanced parallel-computing algorithms and that are difficult (and in many cases impractical) to implement in VLSI circuitry. The difficulty of implementation in VLSI and the major potential advantage afforded by QCA were described previously in Implementing Permutation Matrices by Use of Quantum Dots (NPO-20801), NASA Tech Briefs, Vol. 25, No. 10 (October 2001), page 42. To recapitulate: Wherever two wires in a conventional VLSI circuit cross each other and are required not to be in electrical contact with each other, there must be a layer of electrical insulation between them. This, in turn, makes it necessary to resort to a noncoplanar and possibly a multilayer design, which can be complex, expensive, and even impractical. As a result, much of the cost of designing VLSI circuits is associated with minimization of data routing and assignment of layers to minimize crossing of wires. Heretofore, these considerations have impeded the development of VLSI circuitry to implement complex, advanced interconnection schemes. On the other hand, with suitable design and under suitable operating conditions, QCA-based signal paths can be allowed to cross each other in the same plane without adverse effect. In principle, this characteristic could be exploited to design compact, coplanar, simple (relative to VLSI) QCA-based networks to implement complex, advanced interconnection schemes. The proposed architectures require two advances in QCA-based circuitry beyond basic QCA-based binary

  7. Cooper pair splitting in parallel quantum dot Josephson junctions

    PubMed Central

    Deacon, R. S.; Oiwa, A.; Sailer, J.; Baba, S.; Kanai, Y.; Shibata, K.; Hirakawa, K.; Tarucha, S.

    2015-01-01

    Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair. PMID:26130172

  8. Carbon nanotube quantum dots as highly sensitive THz spectrometers

    NASA Astrophysics Data System (ADS)

    Rinzan, Mohamed; Jenkins, Greg; Drew, Dennis; Shafranjuk, Serhii; Barbara, Paola

    2012-02-01

    We show that carbon nanotube quantum dots (CNT-Dots) coupled to antennas are extremely sensitive, broad-band, terahertz quantum detectors. Their response is due to photon-assisted single-electron tunneling (PASET)[1], but cannot be fully understood with orthodox PASET models[2]. We consider intra-dot excitations and non-equilibrium cooling to explain the anomalous response. REFERENCES: [1] Y. Kawano, S. Toyokawa, T. Uchida and K. Ishibashi, THz photon assisted tunneling in carbon-nanotube quantum dots, Journal of Applied Physics 103, 034307 (2008). [2] P. K. Tien and J. P. Gordon, Multiphoton Process Observed in the Interaction of Microwave Fields with the Tunneling between Superconductor Films, Phys. Rev. 129, 647 (1963).

  9. Electronic structure of rectangular HgTe quantum dots

    NASA Astrophysics Data System (ADS)

    Li, Jian; Zhang, Dong; Zhu, Jia-Ji

    2017-09-01

    We theoretically investigate the single- and few-electron ground-states properties of HgTe topological insulator quantum dots with rectangular hard-wall confining potential using configuration interaction method. For the case of single electron, the edge states is robust against the deformation from a square quantum dot to a rectangular ones, in contrast to the bulk states, the energy gap of the QDs increased due to the coupling of the opposite edge states; for the case of few electrons, the electrons first fill the edge states in the bulk band gap and the addition energy exhibit universal even-odd oscillation due to the shape-independent two-fold degeneracy of the edge states. The size of this edge shell can be controlled by tuning the dot size, shape or the bulk band gap via lateral or vertical electric gating respectively of the HgTe quantum dot.

  10. Cooper pair splitting in parallel quantum dot Josephson junctions.

    PubMed

    Deacon, R S; Oiwa, A; Sailer, J; Baba, S; Kanai, Y; Shibata, K; Hirakawa, K; Tarucha, S

    2015-07-01

    Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair.

  11. Fast electron spin resonance controlled manipulation of spin injection into quantum dots

    SciTech Connect

    Merz, Andreas Siller, Jan; Schittny, Robert; Krämmer, Christoph; Kalt, Heinz; Hetterich, Michael

    2014-06-23

    In our spin-injection light-emitting diodes, electrons are spin-polarized in a semimagnetic ZnMnSe spin aligner and then injected into InGaAs quantum dots. The resulting electron spin state can be read out by measuring the circular polarization state of the emitted light. Here, we resonantly excite the Mn 3d electron spin system with microwave pulses and perform time-resolved measurements of the spin dynamics. We find that we are able to control the spin polarization of the injected electrons on a microsecond timescale. This electron spin resonance induced spin control could be one of the ingredients required to utilize the quantum dot electrons or the Mn spins as qubits.

  12. Emission redistribution from a quantum dot-bowtie nanoantenna

    NASA Astrophysics Data System (ADS)

    Regler, Armin; Schraml, Konrad; Lyamkina, Anna A.; Spiegl, Matthias; Müller, Kai; Vuckovic, Jelena; Finley, Jonathan J.; Kaniber, Michael

    2016-07-01

    We present a combined experimental and simulation study of a single self-assembled InGaAs quantum dot coupled to a nearby (˜25 nm) plasmonic antenna. Microphotoluminescence spectroscopy shows a ˜2.4× increase of intensity, which is attributed to spatial far-field redistribution of the emission from the quantum dot-antenna system. Power-dependent studies show similar saturation powers of 2.5 μW for both coupled and uncoupled quantum dot emission in polarization-resolved measurements. Moreover, time-resolved spectroscopy reveals the absence of Purcell enhancement of the quantum dot coupled to the antenna as compared with an uncoupled dot, yielding comparable exciton lifetimes of τ˜0.5 ns. This observation is supported by numerical simulations, suggesting only minor Purcell-effects of <2× for emitter-antenna separations >25 nm. The observed increased emission from a coupled quantum dot-plasmonic antenna system is found to be in good qualitative agreement with numerical simulations and will lead to a better understanding of light-matter coupling in such semiconductor-plasmonic hybrid systems.

  13. Analysis of the efficiency of intermediate band solar cells based on quantum dot supercrystals

    SciTech Connect

    Heshmati, S; Golmohammadi, S; Abedi, K; Taleb, H

    2014-03-28

    We have studied the influence of the quantum-dot (QD) width and the quantum-dot conduction band (QD-CB) offset on the efficiency of quantum-dot intermediate band solar cells (QD-IBSCs). Simulation results demonstrate that with increasing QD-CB offset and decreasing QD width, the maximum efficiency is achieved. (laser applications and other topics in quantum electronics)

  14. Computer-automated tuning of semiconductor double quantum dots into the single-electron regime

    SciTech Connect

    Baart, T. A.; Vandersypen, L. M. K.; Eendebak, P. T.; Reichl, C.; Wegscheider, W.

    2016-05-23

    We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the double quantum dots into the single-electron regime. The algorithm only requires (1) prior knowledge of the gate design and (2) the pinch-off value of the single gate T that is shared by all the quantum dots. This work significantly alleviates the user effort required to tune multiple quantum dot devices.

  15. Effect of carrier dynamics and temperature on two-state lasing in semiconductor quantum dot lasers

    SciTech Connect

    Korenev, V. V. Savelyev, A. V.; Zhukov, A. E.; Omelchenko, A. V.; Maximov, M. V.

    2013-10-15

    It is analytically shown that the both the charge carrier dynamics in quantum dots and their capture into the quantum dots from the matrix material have a significant effect on two-state lasing phenomenon in quantum dot lasers. In particular, the consideration of desynchronization in electron and hole capture into quantum dots allows one to describe the quenching of ground-state lasing observed at high injection currents both qualitatevely and quantitatively. At the same time, an analysis of the charge carrier dynamics in a single quantum dot allowed us to describe the temperature dependences of the emission power via the ground- and excited-state optical transitions of quantum dots.

  16. Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study

    DOE PAGES

    Michael, Stephan; Chow, Weng; Schneider, Hans

    2016-05-01

    In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. We study the influence of two important quantum-dot material parameters, here, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density canmore » compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. By minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.« less

  17. Quantum Hall effect in semiconductor systems with quantum dots and antidots

    SciTech Connect

    Beltukov, Ya. M.; Greshnov, A. A.

    2015-04-15

    The integer quantum Hall effect in systems of semiconductor quantum dots and antidots is studied theoretically as a factor of temperature. It is established that the conditions for carrier localization in quantum-dot systems favor the observation of the quantum Hall effect at higher temperatures than in quantum-well systems. The obtained numerical results show that the fundamental plateau corresponding to the transition between the ground and first excited Landau levels can be retained up to a temperature of T ∼ 50 K, which is an order of magnitude higher than in the case of quantum wells. Implementation of the quantum Hall effect at such temperatures requires quantum-dot systems with controllable characteristics, including the optimal size and concentration and moderate geometrical and composition fluctuations. In addition, ordered arrangement is desirable, hence quantum antidots are preferable.

  18. Polarization control of quantum dot emission by chiral photonic crystal slabs.

    PubMed

    Lobanov, Sergey V; Weiss, Thomas; Gippius, Nikolay A; Tikhodeev, Sergei G; Kulakovskii, Vladimir D; Konishi, Kuniaki; Kuwata-Gonokami, Makoto

    2015-04-01

    We investigate theoretically the polarization properties of the quantum dot's (QDs) optical emission from chiral photonic crystal structures made of achiral materials in the absence of external magnetic field at room temperature. The mirror symmetry of the local electromagnetic field is broken in this system due to the decreased symmetry of the chiral modulated layer. As a result, the radiation of randomly polarized QDs normal to the structure becomes partially circularly polarized. The sign and degree of circular polarization are determined by the geometry of the chiral modulated structure and depend on the radiation frequency. A degree of circular polarization up to 99% can be achieved for randomly distributed QDs, and can be close to 100% for some single QDs.

  19. Inducing vortex formation in multilayered circular dots using remanent curves

    NASA Astrophysics Data System (ADS)

    Kim, Dong-Ok; Ryeol Lee, Dong; Choi, Yongseong; Metlushko, Vitali; Park, Jihwey; Kim, Jae-Young; Bong Lee, Ki

    2012-11-01

    We report field manipulation of magnetic vortex states in Co(30 nm)/Cu(3 nm)/Ni80Fe20 (20 nm)-multilayer dot arrays via remanent curve. The element-resolved resonant x-ray magnetic measurements, combined with micromagnetic simulations, show vortex formation in the Co layer but not in the NiFe layer along the major hysteresis loop. Although the two magnetic layers are not directly coupled due to the presence of the Cu interlayer, the NiFe layer is strongly influenced by the dipolar field from uncompensated magnetic poles in the Co layer. Using remanent curves, we demonstrate that the single vortex state can be induced simultaneously in both layers.

  20. Large Scale Quantum Coherence of Nearly Circular Wavepackets

    SciTech Connect

    Reinhold, Carlos O; Yoshida, S.; Burgdorfer, J.; Wyker, B.; Mestayer, J. J.; Dunning, F. B.

    2009-01-01

    We demonstrate that the quantum coherence of mesoscopic very-high-n, n {approx} 305, Rydberg wave packets travelling along nearly circular orbits can be maintained on microsecond time scales corresponding to hundreds of classical orbital periods. The coherence is probed through collapses and revivals of periodic oscillations in the average electron position. The temporal interferences of spatially separated Schroedinger cat-like wave packets are also observed. A novel hybrid quantum-classical trajectory method is employed to simulate the wave packet dynamics.

  1. Ultrasensitive solution-cast quantum dot photodetectors.

    PubMed

    Konstantatos, Gerasimos; Howard, Ian; Fischer, Armin; Hoogland, Sjoerd; Clifford, Jason; Klem, Ethan; Levina, Larissa; Sargent, Edward H

    2006-07-13

    Solution-processed electronic and optoelectronic devices offer low cost, large device area, physical flexibility and convenient materials integration compared to conventional epitaxially grown, lattice-matched, crystalline semiconductor devices. Although the electronic or optoelectronic performance of these solution-processed devices is typically inferior to that of those fabricated by conventional routes, this can be tolerated for some applications in view of the other benefits. Here we report the fabrication of solution-processed infrared photodetectors that are superior in their normalized detectivity (D*, the figure of merit for detector sensitivity) to the best epitaxially grown devices operating at room temperature. We produced the devices in a single solution-processing step, overcoating a prefabricated planar electrode array with an unpatterned layer of PbS colloidal quantum dot nanocrystals. The devices showed large photoconductive gains with responsivities greater than 10(3) A W(-1). The best devices exhibited a normalized detectivity D* of 1.8 x 10(13) jones (1 jones = 1 cm Hz(1/2) W(-1)) at 1.3 microm at room temperature: today's highest performance infrared photodetectors are photovoltaic devices made from epitaxially grown InGaAs that exhibit peak D* in the 10(12) jones range at room temperature, whereas the previous record for D* from a photoconductive detector lies at 10(11) jones. The tailored selection of absorption onset energy through the quantum size effect, combined with deliberate engineering of the sequence of nanoparticle fusing and surface trap functionalization, underlie the superior performance achieved in this readily fabricated family of devices.

  2. Surface Induced Magnetism in Quantum Dots

    SciTech Connect

    Meulenberg, R W; Lee, J I

    2009-08-20

    The study of nanometer sized semiconductor crystallites, also known as quantum dots (QDs), has seen rapid advancements in recent years in scientific disciplines ranging from chemistry, physics, biology, materials science, and engineering. QD materials of CdSe, ZnSe, InP, as well as many others, can be prepared in the size range of 1-10 nm producing uniform, nearly monodisperse materials that are typically coated with organic molecules [1-3]. The strength of charge carrier confinement, which dictates the size-dependent properties, in these QDs depends on the nature of the material and can be correlated to the Bohr radius for the system of interest. For instance, the Bohr radius for CdSe is {approx} 5 nm, while in the more covalent structure of InP, the Bohr radius approaches {approx} 10 nm. The study of CdSe QDs has been particularly extensive during the last decade because they exhibit unique and tunable optical properties and are readily synthesized with high-crystallinity and narrow size dispersions. Although the core electronic properties of CdSe are explained in terms of the quantum confinement model, experimental efforts to elucidate the surface structure of these materials have been limited. Typically, colloidal CdSe QDs are coated with an organic surfactant, which typically consists of an organo-phosphine, -thiol, or -amine, that has the function of energetically relaxing defect states via coordination to partially coordinated surface atoms. The organic surfactant also acts to enhance carrier confinement and prevent agglomeration of the particles. Chemically, it has been shown that the bonding of the surfactant to the CdSe QD occurs through Cd atoms resulting cleavage of the Se atoms and formation of a Cd-rich (i.e. non-stoichiometric) particle [5].

  3. 2 Micrometers InAsSb Quantum-dot Lasers

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Uhl, David; Keo, Sam

    2004-01-01

    InAsSb quantum-dot lasers near 2 micrometers were demonstrated in cw operation at room temperature with a threshold current density of 733 A,/cm(sup 2), output power of 3 mW/facet and a differential quantum efficiency of 13%.

  4. Quantum dots: Time to get the nukes out

    NASA Astrophysics Data System (ADS)

    Schroer, Michael D.; Petta, Jason R.

    2008-07-01

    The ability to electrically control spin dynamics in quantum dots makes them one of the most promising platforms for solid-state quantum-information processing. Minimizing the influence of the nuclear spin environment is an important step towards realizing such promise.

  5. Electrical control of single hole spins in nanowire quantum dots.

    PubMed

    Pribiag, V S; Nadj-Perge, S; Frolov, S M; van den Berg, J W G; van Weperen, I; Plissard, S R; Bakkers, E P A M; Kouwenhoven, L P

    2013-03-01

    The development of viable quantum computation devices will require the ability to preserve the coherence of quantum bits (qubits). Single electron spins in semiconductor quantum dots are a versatile platform for quantum information processing, but controlling decoherence remains a considerable challenge. Hole spins in III-V semiconductors have unique properties, such as a strong spin-orbit interaction and weak coupling to nuclear spins, and therefore, have the potential for enhanced spin control and longer coherence times. A weaker hyperfine interaction has previously been reported in self-assembled quantum dots using quantum optics techniques, but the development of hole-spin-based electronic devices in conventional III-V heterostructures has been limited by fabrication challenges. Here, we show that gate-tunable hole quantum dots can be formed in InSb nanowires and used to demonstrate Pauli spin blockade and electrical control of single hole spins. The devices are fully tunable between hole and electron quantum dots, which allows the hyperfine interaction strengths, g-factors and spin blockade anisotropies to be compared directly in the two regimes.

  6. 2 Micrometers InAsSb Quantum-dot Lasers

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Uhl, David; Keo, Sam

    2004-01-01

    InAsSb quantum-dot lasers near 2 micrometers were demonstrated in cw operation at room temperature with a threshold current density of 733 A,/cm(sup 2), output power of 3 mW/facet and a differential quantum efficiency of 13%.

  7. Quantum-cascade laser-based vibrational circular dichroism.

    PubMed

    Lüdeke, Steffen; Pfeifer, Marcel; Fischer, Peer

    2011-04-20

    Vibrational circular dichroism (VCD) spectra were recorded with a tunable external-cavity quantum-cascade laser (QCL). In comparison with standard thermal light sources in the IR, QCLs provide orders of magnitude more power and are therefore promising for VCD studies in strongly absorbing solvents. The brightness of this novel light source is demonstrated with VCD and IR absorption measurements of a number of compounds, including proline in water.

  8. Sunlight assisted photodegradation by tin oxide quantum dots

    NASA Astrophysics Data System (ADS)

    Shajira, P. S.; Prabhu, V. Ganeshchandra; Bushiri, M. Junaid

    2015-12-01

    Rutile phase of SnO2 quantum dots of average size of 2.5 nm were synthesized at a growth temperature of 70 °C and characterized with XRD, TEM, FTIR and Raman analysis. The effective strain within the lattice of SnO2 quantum dots was calculated by Williamson-Hall method. The broad peaks in XRD as well as Raman spectra and the presence of Raman bands at 569 and 432 cm-1 are due to lower crystallinity of nanoparticles. The optical band gap of SnO2 quantum dots was increased to 3.75 eV attributed to the quantum size effect. SnO2 quantum dots were annealed in air atmosphere and the crystallite size of the particles increased with annealing temperature. Sunlight assisted photodegration property of SnO2 quantum dots was investigated with vanillin as a model system and it shows the photodegradation efficiency of 87%. The photoluminescence and photodegradation efficiency of nanocrystallite SnO2 decreases with increase of crystallite size contributed to the reduction in population of defects and surface area.

  9. Size-Minimized Quantum Dots for Molecular and Cellular Imaging

    NASA Astrophysics Data System (ADS)

    Smith, Andrew M.; Wen, Mary M.; Wang, May D.; Nie, Shuming

    Semiconductor quantum dots, tiny light-emitting particles on thenanometer scale, are emerging as a new class of fluorescent labels for a broad range of molecular and cellular applications. In comparison with organic dyes and fluorescent proteins, they have unique optical and electronic properties such as size-tunable light emission, intense signal brightness, resistance to photobleaching, and broadband absorption for simultaneous excitation of multiple fluorescence colors. Here we report new advances in minimizing the hydrodynamic sizes of quantum dots using multidentate and multifunctional polymer coatings. A key finding is that a linear polymer containing grafted amine and thiol coordinating groups can coat nanocrystals and lead to a highly compact size, exceptional colloidal stability, strong resistance to photobleaching, and high fluorescence quantum yields. This has allowed a new generation of bright and stable quantum dots with small hydrodynamic diameters between 5.6 and 9.7 nm with tunable fluorescence emission from the visible (515 nm) to the near infrared (720 nm). These quantum dots are well suited for molecular and cellular imaging applications in which the nanoparticle hydrodynamic size needs to be minimized. Together with the novel properties of new strain-tunable quantum dots, these findings will be especially useful for multicolor and super-resolution imaging at the single-molecule level.

  10. Magnetic field dependence of energy levels in biased bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    da Costa, D. R.; Zarenia, M.; Chaves, Andrey; Farias, G. A.; Peeters, F. M.

    2016-02-01

    Using the tight-binding approach, we study the influence of a perpendicular magnetic field on the energy levels of hexagonal, triangular, and circular bilayer graphene (BLG) quantum dots (QDs) with zigzag and armchair edges. We obtain the energy levels for AB (Bernal)-stacked BLG QDs in both the absence and the presence of a perpendicular electric field (i.e., biased BLG QDs). We find different regions in the spectrum of biased QDs with respect to the crossing point between the lowest-electron and -hole Landau levels of a biased BLG sheet. Those different regions correspond to electron states that are localized at the center, edge, or corner of the BLG QD. Quantum Hall corner states are found to be absent in circular BLG QDs. The spatial symmetry of the carrier density distribution is related to the symmetry of the confinement potential, the position of zigzag edges, and the presence or absence of interlayer inversion symmetry.

  11. Development of quantum well, quantum dot, and type II superlattice infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Ting, David Z.; Soibel, Alexander; Keo, Sam A.; Rafol, B., , Sir; Mumolo, Jason M.; Liu, John K.; Hill, Cory J.; Khoshakhlagh, Arezou; Höglund, Linda; Luong, Edward M.; Gunapala, Sarath D.

    2014-01-01

    We present an overview of III-V semiconductor-based infrared detector and focal plane array development at the NASA Jet Propulsion Laboratory in recent years. Topics discussed include: (1) the development of long-wavelength quantum well infrared photodetector for imaging spectrometer applications, (2) the concept and realization of the submonolayer quantum dot infrared photodetector (SML-QDIP) as an alternative to the standard QDIP-based on Stranski-Krastanov (SK) quantum dots, (3) the mid-wavelength infrared quantum dot barrier infrared detector with extended cutoff wavelength, and (4) high-performance type-II superlattice long-wavelength infrared detectors based on the complementary barrier infrared detector architecture.

  12. Enhancement of pumped current in quantum dots

    NASA Astrophysics Data System (ADS)

    Ramos, Juan Pablo; Foa, Luis; Apel, Victor Marcelo; Orellana, Pedro

    A direct current usually requires the application of a non-zero potential difference between source and drain, but on nanoscale systems (NSS) it is possible to obtain a non-zero current while the potential difference is zero. The effect is known as quantum charge pumping (QCP) and it is due to the interference provided by the existence of a time-dependent potential (TDP). QCP can be generated by a TDP in non-adiabatic limit. An example of this is a system composed by a ring with a dot embedded on it, under the application of an oscillating TDP. By the action of a magnetic field across the system, a pumped current is generated, since time reversal symmetry is broken. Decoherence is crucial, both from a scientific and technological point of view. In NSS it is expected that decoherence, among others things, decreases the QCP amplitude. In this context, we study what is the effect of a bath on the pumped current in our system. We find that for certain values of magnetic flux, the bath-system produce amplification of the pumped current.

  13. Immune cells tracing using quantum dots

    NASA Astrophysics Data System (ADS)

    Hoshino, Akiyoshi; Fujioka, Kouki; Kawamura, Yuki I.; Toyama-Sorimachi, Noriko; Yasuhara, Masato; Dohi, Taeko; Yamamoto, Kenji

    2006-02-01

    Fluorescent nanoparticles, such as nanocrystal quantum dots (QDs), have potential to be applied to molecular biology and bioimaging, since some nanocrystals emit higher and longer lasting fluorescence than conventional organic probes do. Here we report an example of labeling immune cells by QDs. We collected splenic CD4 + T-lymphocyte and peritoneal macrophages from mice. Then cells were labeled with QDs. QDs are incorporated into the T-lymphocyte and macrophages immediately after addition and located in the cytoplasm via endocytosis pathway. The fluorescence of QDs held in the endosomes was easily detected for more than a week. In addition, T-lymphocytes labeled with QDs were stable and cell proliferation or cytokine production including IL-2 and IFN-γ was not affected. When QD-labeled T-lymphocytes were adoptively transferred intravenously to mice, they remained in the peripheral blood and spleen up to a week. Using QD-labeled peritoneal macrophages, we studied cell traffic during inflammation on viscera in peritoneum cavity. QD-labeled macrophages were transplanted into the peritoneum of the mouse, and colitis was induced by intracolonic injection of a hapten, trinitrobenzensulfonic acid. With the aid of stong signals of QDs, we found that macrophage accumuled on the inflammation site of the colon. These results suggested that fluorescent probes of QDs might be useful as bioimaging tools for tracing target cells in vivo.

  14. Asymmetric shape transitions of epitaxial quantum dots

    NASA Astrophysics Data System (ADS)

    Wei, Chaozhen; Spencer, Brian J.

    2016-06-01

    We construct a two-dimensional continuum model to describe the energetics of shape transitions in fully faceted epitaxial quantum dots (strained islands) via minimization of elastic energy and surface energy at fixed volume. The elastic energy of the island is based on a third-order approximation, enabling us to consider shape transitions between pyramids, domes, multifaceted domes and asymmetric intermediate states. The energetics of the shape transitions are determined by numerically calculating the facet lengths that minimize the energy of a given island type of prescribed island volume. By comparing the energy of different island types with the same volume and analysing the energy surface as a function of the island shape parameters, we determine the bifurcation diagram of equilibrium solutions and their stability, as well as the lowest barrier transition pathway for the island shape as a function of increasing volume. The main result is that the shape transition from pyramid to dome to multifaceted dome occurs through sequential nucleation of facets and involves asymmetric metastable transition shapes. We also explicitly determine the effect of corner energy (facet edge energy) on shape transitions and interpret the results in terms of the relative stability of asymmetric island shapes as observed in experiment.

  15. Carbon Quantum Dots for Zebrafish Fluorescence Imaging

    PubMed Central

    Kang, Yan-Fei; Li, Yu-Hao; Fang, Yang-Wu; Xu, Yang; Wei, Xiao-Mi; Yin, Xue-Bo

    2015-01-01

    Carbon quantum dots (C-QDs) are becoming a desirable alternative to metal-based QDs and dye probes owing to their high biocompatibility, low toxicity, ease of preparation, and unique photophysical properties. Herein, we describe fluorescence bioimaging of zebrafish using C-QDs as probe in terms of the preparation of C-QDs, zebrafish husbandry, embryo harvesting, and introduction of C-QDs into embryos and larvae by soaking and microinjection. The multicolor of C-QDs was validated with their imaging for zebrafish embryo. The distribution of C-QDs in zebrafish embryos and larvae were successfully observed from their fluorescence emission. the bio-toxicity of C-QDs was tested with zebrafish as model and C-QDs do not interfere to the development of zebrafish embryo. All of the results confirmed the high biocompatibility and low toxicity of C-QDs as imaging probe. The absorption, distribution, metabolism and excretion route (ADME) of C-QDs in zebrafish was revealed by their distribution. Our work provides the useful information for the researchers interested in studying with zebrafish as a model and the applications of C-QDs. The operations related zebrafish are suitable for the study of the toxicity, adverse effects, transport, and biocompatibility of nanomaterials as well as for drug screening with zebrafish as model. PMID:26135470

  16. Multiplexed modular genetic targeting of quantum dots.

    PubMed

    Saurabh, Saumya; Beck, Lauren E; Maji, Suvrajit; Baty, Catherine J; Wang, Yi; Yan, Qi; Watkins, Simon C; Bruchez, Marcel P

    2014-11-25

    While DNA-directed nanotechnology is now a well-established platform for bioinspired nanoscale assembly in vitro, the direct targeting of various nanomaterials in living biological systems remains a significant challenge. Hybrid biological systems with integrated and targeted nanomaterials may have interesting and exploitable properties, so methods for targeting various nanomaterials to precise biological locations are required. Fluorescence imaging has benefited from the use of nanoparticles with superior optical properties compared to fluorescent organic dyes or fluorescent proteins. While single-particle tracking (SPT) in living cells with genetically encoded proteins is limited to very short trajectories, the high photon output of genetically targeted and multiplexed quantum dots (QDs) would enable long-trajectory analysis of multiple proteins. However, challenges with genetic targeting of QDs limit their application in these experiments. In this report, we establish a modular method for targeting QD nanoparticles selectively to multiple genetically encoded tags by precomplexing QD-streptavidin conjugates with cognate biotinylated hapten molecules. This approach enables labeling and SPT of multiple genetically encoded proteins on living cells at high speed and can label expressed proteins in the cytosol upon microinjection into living cells. While we demonstrate labeling with three distinct QD conjugates, the approach can be extended to other specific hapten-affinity molecule interactions and alternative nanoparticles, enabling precise directed targeting of nanoparticles in living biological systems.

  17. Hole transfer from single quantum dots.

    PubMed

    Song, Nianhui; Zhu, Haiming; Jin, Shengye; Lian, Tianquan

    2011-11-22

    Photoinduced hole transfer dynamics from single CdSe/CdS(3ML)/CdZnS(2ML)/ZnS(2ML) core/multishell quantum dots (QDs) to phenothiazine (PTZ) molecules were studied by single QD fluorescence spectroscopy to investigate the static and dynamic heterogeneities of the hole transfer process as well as its effect on the blinking dynamics of QDs. Ensemble-averaged transient absorption and fluorescence decay measurements show that excitons in QDs dissociate by transferring the valence band hole to PTZ with a time constant of 50 ns for the 1:1 PTZ-QD complex, and the subsequent charge recombination process (i.e., electron transfer from the conduction band of the reduced QD to oxidized PTZ to regenerate the complex in the ground state) occurs mainly on the 100 to 1000 ns time scale. Single QD-PTZ complexes show pronounced correlated fluctuations of fluorescence intensity and lifetime with time. In addition to the dynamic fluctuation, there are considerable heterogeneities of average hole transfer rate among different QD-PTZ complexes. The hole transfer process has little effect on the statistics of the off-states, which is often believed to be positively charged QDs with a valence band hole. Instead, it increases the probability of weakly emissive or "gray" states.

  18. Quantum dot mediated imaging of atherosclerosis

    NASA Astrophysics Data System (ADS)

    Jayagopal, Ashwath; Su, Yan Ru; Blakemore, John L.; Linton, MacRae F.; Fazio, Sergio; Haselton, Frederick R.

    2009-04-01

    The progression of atherosclerosis is associated with leukocyte infiltration within lesions. We describe a technique for the ex vivo imaging of cellular recruitment in atherogenesis which utilizes quantum dots (QD) to color-code different cell types within lesion areas. Spectrally distinct QD were coated with the cell-penetrating peptide maurocalcine to fluorescently-label immunomagnetically isolated monocyte/macrophages and T lymphocytes. QD-maurocalcine bioconjugates labeled both cell types with a high efficiency, preserved cell viability, and did not perturb native leukocyte function in cytokine release and endothelial adhesion assays. QD-labeled monocyte/macrophages and T lymphocytes were reinfused in an ApoE-/- mouse model of atherosclerosis and age-matched controls and tracked for up to four weeks to investigate the incorporation of cells within aortic lesion areas, as determined by oil red O (ORO) and immunofluorescence ex vivo staining. QD-labeled cells were visible in atherosclerotic plaques within two days of injection, and the two cell types colocalized within areas of subsequent ORO staining. Our method for tracking leukocytes in lesions enables high signal-to-noise ratio imaging of multiple cell types and biomarkers simultaneously within the same specimen. It also has great utility in studies aimed at investigating the role of distinct circulating leukocyte subsets in plaque development and progression.

  19. Toxicity of carbon group quantum dots

    NASA Astrophysics Data System (ADS)

    Hanada, Sanshiro; Fujioka, Kouki; Hoshino, Akiyoshi; Manabe, Noriyoshi; Hirakuri, Kenji; Yamamoto, Kenji

    2009-02-01

    Carbon group quantum dots (QDs) such as carbon, silicon and germanium, have potential for biomedical applications such as bio-imaging markers and drug delivery systems and are expected to demonstrate several advantages over conventional fluorescent QDs such as CdSe, especially in biocompatibility. We assessed biocompatibility of newly manufactured silicon QDs (Si-QDs), by means of both MTT assay and LDH assay for HeLa cells in culture and thereby detected the cellular toxicity by administration of high concentration of Si-QD (>1000 μg/mL), while we detected the high toxicity by administration of over 100 μg/mL of CdSe-QDs. As a hypothesis for the cause of the cellular toxicity, we measured oxy-radical generation from the QDs by means of luminol reaction method. We detected generation of oxy-radicals from the Si-QDs and those were decreased by radical scavenger such as superoxide dismutase (SOD) and N-acetyl cysteine (NAC). We concluded that the Si-QD application to cultured cells in high concentration led cell membrane damage by oxy-radicals and combination usage with radical scavenger is one of the answers.

  20. Advancing colloidal quantum dot photovoltaic technology

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Arinze, Ebuka S.; Palmquist, Nathan; Thon, Susanna M.

    2016-06-01

    Colloidal quantum dots (CQDs) are attractive materials for solar cells due to their low cost, ease of fabrication and spectral tunability. Progress in CQD photovoltaic technology over the past decade has resulted in power conversion efficiencies approaching 10%. In this review, we give an overview of this progress, and discuss limiting mechanisms and paths for future improvement in CQD solar cell technology.We briefly summarize nanoparticle synthesis and film processing methods and evaluate the optoelectronic properties of CQD films, including the crucial role that surface ligands play in materials performance. We give an overview of device architecture engineering in CQD solar cells. The compromise between carrier extraction and photon absorption in CQD photovoltaics is analyzed along with different strategies for overcoming this trade-off. We then focus on recent advances in absorption enhancement through innovative device design and the use of nanophotonics. Several light-trapping schemes, which have resulted in large increases in cell photocurrent, are described in detail. In particular, integrating plasmonic elements into CQD devices has emerged as a promising approach to enhance photon absorption through both near-field coupling and far-field scattering effects. We also discuss strategies for overcoming the single junction efficiency limits in CQD solar cells, including tandem architectures, multiple exciton generation and hybrid materials schemes. Finally, we offer a perspective on future directions for the field and the most promising paths for achieving higher device efficiencies.