Sample records for quantum dots experiment

  1. Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tartakovskii, Alexander

    2012-07-01

    Lithographic Techniques: III-V Semiconductors and Carbon: 15. Electrically controlling single spin coherence in semiconductor nanostructures Y. Dovzhenko, K. Wang, M. D. Schroer and J. R. Petta; 16. Theory of electron and nuclear spins in III-V semiconductor and carbon-based dots H. Ribeiro and G. Burkard; 17. Graphene quantum dots: transport experiments and local imaging S. Schnez, J. Guettinger, F. Molitor, C. Stampfer, M. Huefner, T. Ihn and K. Ensslin; Part VI. Single Dots for Future Telecommunications Applications: 18. Electrically operated entangled light sources based on quantum dots R. M. Stevenson, A. J. Bennett and A. J. Shields; 19. Deterministic single quantum dot cavities at telecommunication wavelengths D. Dalacu, K. Mnaymneh, J. Lapointe, G. C. Aers, P. J. Poole, R. L. Williams and S. Hughes; Index.

  2. 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.

  3. Quantum Dots in a Polymer Composite: A Convenient Particle-in-a-Box Laboratory Experiment

    ERIC Educational Resources Information Center

    Rice, Charles V.; Giffin, Guinevere A.

    2008-01-01

    Semiconductor quantum dots are at the forefront of materials science chemistry with applications in biological imaging and photovoltaic technologies. We have developed a simple laboratory experiment to measure the quantum-dot size from fluorescence spectra. A major roadblock of quantum-dot based exercises is the particle synthesis and handling;…

  4. Multi-Excitonic Quantum Dot Molecules

    NASA Astrophysics Data System (ADS)

    Scheibner, M.; Stinaff, E. A.; Doty, M. F.; Ware, M. E.; Bracker, A. S.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

    2006-03-01

    With the ability to create coupled pairs of quantum dots, the next step towards the realization of semiconductor based quantum information processing devices can be taken. However, so far little knowledge has been gained on these artificial molecules. Our photoluminescence experiments on single InAs/GaAs quantum dot molecules provide the systematics of coupled quantum dots by delineating the spectroscopic features of several key charge configurations in such quantum systems, including X, X^+,X^2+, XX, XX^+ (with X being the neutral exciton). We extract general rules which determine the formation of molecular states of coupled quantum dots. These include the fact that quantum dot molecules provide the possibility to realize various spin configurations and to switch the electron hole exchange interaction on and off by shifting charges inside the molecule. This knowledge will be valuable in developing implementations for quantum information processing.

  5. Double quantum dot memristor

    NASA Astrophysics Data System (ADS)

    Li, Ying; Holloway, Gregory W.; Benjamin, Simon C.; Briggs, G. Andrew D.; Baugh, Jonathan; Mol, Jan A.

    2017-08-01

    Memristive systems are generalizations of memristors, which are resistors with memory. In this paper, we present a quantum description of quantum dot memristive systems. Using this model we propose and experimentally demonstrate a simple and practical scheme for realizing memristive systems with quantum dots. The approach harnesses a phenomenon that is commonly seen as a bane of nanoelectronics, i.e., switching of a trapped charge in the vicinity of the device. We show that quantum dot memristive systems have hysteresis current-voltage characteristics and quantum jump-induced stochastic behavior. While our experiment requires low temperatures, the same setup could, in principle, be realized with a suitable single-molecule transistor and operated at or near room temperature.

  6. Charge reconfiguration in arrays of quantum dots

    NASA Astrophysics Data System (ADS)

    Bayer, Johannes C.; Wagner, Timo; Rugeramigabo, Eddy P.; Haug, Rolf J.

    2017-12-01

    Semiconductor quantum dots are potential building blocks for scalable qubit architectures. Efficient control over the exchange interaction and the possibility of coherently manipulating electron states are essential ingredients towards this goal. We studied experimentally the shuttling of electrons trapped in serial quantum dot arrays isolated from the reservoirs. The isolation hereby enables a high degree of control over the tunnel couplings between the quantum dots, while electrons can be transferred through the array by gate voltage variations. Model calculations are compared with our experimental results for double, triple, and quadruple quantum dot arrays. We are able to identify all transitions observed in our experiments, including cotunneling transitions between distant quantum dots. The shuttling of individual electrons between quantum dots along chosen paths is demonstrated.

  7. Spin-based quantum computation in multielectron quantum dots

    NASA Astrophysics Data System (ADS)

    Hu, Xuedong; Das Sarma, S.

    2001-10-01

    In a quantum computer the hardware and software are intrinsically connected because the quantum Hamiltonian (or more precisely its time development) is the code that runs the computer. We demonstrate this subtle and crucial relationship by considering the example of electron-spin-based solid-state quantum computer in semiconductor quantum dots. We show that multielectron quantum dots with one valence electron in the outermost shell do not behave simply as an effective single-spin system unless special conditions are satisfied. Our work compellingly demonstrates that a delicate synergy between theory and experiment (between software and hardware) is essential for constructing a quantum computer.

  8. 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).

  9. Quantum Dot Photonics

    NASA Astrophysics Data System (ADS)

    Kinnischtzke, Laura A.

    We report on several experiments using single excitons confined to single semiconductor quantum dots (QDs). Electric and magnetic fields have previously been used as experimental knobs to understand and control individual excitons in single quantum dots. We realize new ways of electric field control by changing materials and device geometry in the first two experiments with strain-based InAs QDs. A standard Schottky diode heterostructure is demonstrated with graphene as the Schottky gate material, and its performance is bench-marked against a diode with a standard gate material, semi-transparent nickel-chromium (NiCr). This change of materials increases the photon collection rate by eliminating absorption in the metallic NiCr layer. A second set of experiments investigates the electric field response of QDs as a possible metrology source. A linear voltage potential drop in a plane near the QDs is used to describe how the spatially varying voltage profile is also imparted on the QDs. We demonstrate a procedure to map this voltage profile as a preliminary route towards a full quantum sensor array. Lastly, InAs QDs are explored as potential spin-photon interfaces. We describe how a magnetic field is used to realize a reversible exchange of information between light and matter, including a discussion of the polarization-dependence of the photoluminesence, and how that can be linked to the spin of a resident electron or hole. We present evidence of this in two wavelength regimes for InAs quantum dots, and discuss how an external magnetic field informs the spin physics of these 2-level systems. This thesis concludes with the discovery of a new class of quantum dots. As-yet unidentified defect states in single layer tungsten diselenide (WSe 2 ) are shown to host quantum light emission. We explore the spatial extent of electron confinement and tentatively identify a radiative lifetime of 1 ns for these single photon emitters.

  10. 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.

  11. Quantum-dot cellular automata: Review and recent experiments (invited)

    NASA Astrophysics Data System (ADS)

    Snider, G. L.; Orlov, A. O.; Amlani, I.; Zuo, X.; Bernstein, G. H.; Lent, C. S.; Merz, J. L.; Porod, W.

    1999-04-01

    An introduction to the operation of quantum-dot cellular automata is presented, along with recent experimental results. Quantum-dot cellular automata (QCA) is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two electrometers. The dots are metal islands, which are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. The operation of this basic cell is confirmed by the externally controlled polarization change of the cell.

  12. Influence of the quantum dot geometry on p -shell transitions in differently charged quantum dots

    NASA Astrophysics Data System (ADS)

    Holtkemper, M.; Reiter, D. E.; Kuhn, T.

    2018-02-01

    Absorption spectra of neutral, negatively, and positively charged semiconductor quantum dots are studied theoretically. We provide an overview of the main energetic structure around the p -shell transitions, including the influence of nearby nominally dark states. Based on the envelope function approximation, we treat the four-band Luttinger theory as well as the direct and short-range exchange Coulomb interactions within a configuration interaction approach. The quantum dot confinement is approximated by an anisotropic harmonic potential. We present a detailed investigation of state mixing and correlations mediated by the individual interactions. Differences and similarities between the differently charged quantum dots are highlighted. Especially large differences between negatively and positively charged quantum dots become evident. We present a visualization of energetic shifts and state mixtures due to changes in size, in-plane asymmetry, and aspect ratio. Thereby we provide a better understanding of the experimentally hard to access question of quantum dot geometry effects. Our findings show a method to determine the in-plane asymmetry from photoluminescence excitation spectra. Furthermore, we supply basic knowledge for tailoring the strength of certain state mixtures or the energetic order of particular excited states via changes of the shape of the quantum dot. Such knowledge builds the basis to find the optimal QD geometry for possible applications and experiments using excited states.

  13. Synthesis of Cesium Lead Halide Perovskite Quantum Dots

    ERIC Educational Resources Information Center

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

    2017-01-01

    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…

  14. Detection of CdSe quantum dot photoluminescence for security label on paper

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

    Isnaeni,, E-mail: isnaeni@lipi.go.id; Sugiarto, Iyon Titok; Bilqis, Ratu

    CdSe quantum dot has great potential in various applications especially for emitting devices. One example potential application of CdSe quantum dot is security label for anti-counterfeiting. In this work, we present a practical approach of security label on paper using one and two colors of colloidal CdSe quantum dot, which is used as stamping ink on various types of paper. Under ambient condition, quantum dot is almost invisible. The quantum dot security label can be revealed by detecting emission of quantum dot using photoluminescence and cnc machine. The recorded quantum dot emission intensity is then analyzed using home-made program tomore » reveal quantum dot pattern stamp having the word ’RAHASIA’. We found that security label using quantum dot works well on several types of paper. The quantum dot patterns can survive several days and further treatment is required to protect the quantum dot. Oxidation of quantum dot that occurred during this experiment reduced the emission intensity of quantum dot patterns.« less

  15. 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.

  16. Spin interactions in InAs quantum dots

    NASA Astrophysics Data System (ADS)

    Doty, M. F.; Ware, M. E.; Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

    2006-03-01

    Fine structure splittings in optical spectra of self-assembled InAs quantum dots (QDs) generally arise from spin interactions between particles confined in the dots. We present experimental studies of the fine structure that arises from multiple charges confined in a single dot [1] or in molecular orbitals of coupled pairs of dots. To probe the underlying spin interactions we inject particles with a known spin orientation (by using polarized light to perform photoluminescence excitation spectroscopy experiments) or use a magnetic field to orient and/or mix the spin states. We develop a model of the spin interactions that aids in the development of quantum information processing applications based on controllable interactions between spins confined to QDs. [1] Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot, Phys. Rev. Lett. 95, 177403 (2005)

  17. Designing quantum dots for solotronics.

    PubMed

    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.

  18. 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

  19. Synthesis of quantum dots

    DOEpatents

    McDaniel, Hunter

    2017-10-17

    Common approaches to synthesizing alloyed quantum dots employ high-cost, air-sensitive phosphine complexes as the selenium precursor. Disclosed quantum dot synthesis embodiments avoid these hazardous and air-sensitive selenium precursors. Certain embodiments utilize a combination comprising a thiol and an amine that together reduce and complex the elemental selenium to form a highly reactive selenium precursor at room temperature. The same combination of thiol and amine acts as the reaction solvent, stabilizing ligand, and sulfur source in the synthesis of quantum dot cores. A non-injection approach may also be used. The optical properties of the quantum dots synthesized by this new approach can be finely tuned for a variety of applications by controlling size and/or composition of size and composition. Further, using the same approach, a shell can be grown around a quantum dot core that improves stability, luminescence efficiency, and may reduce toxicity.

  20. Quantum dot quantum cascade infrared photodetector

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

    Wang, Xue-Jiao; Zhai, Shen-Qiang; Zhuo, Ning

    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 chirpedmore » 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.« less

  1. Spectroscopy characterization and quantum yield determination of quantum dots

    NASA Astrophysics Data System (ADS)

    Contreras Ortiz, S. N.; Mejía Ospino, E.; Cabanzo, R.

    2016-02-01

    In this paper we show the characterization of two kinds of quantum dots: hydrophilic and hydrophobic, with core and core/shell respectively, using spectroscopy techniques such as UV-Vis, fluorescence and Raman. We determined the quantum yield in the quantum dots using the quinine sulphate as standard. This salt is commonly used because of its quantum yield (56%) and stability. For the CdTe excitation, we used a wavelength of 549nm and for the CdSe/ZnS excitation a wavelength of 527nm. The results show that CdSe/ZnS (49%) has better fluorescence, better quantum dots, and confirm the fluorescence result. The quantum dots have shown a good fluorescence performance, so this property will be used to replace dyes, with the advantage that quantum dots are less toxic than some dyes like the rhodamine. In addition, in this work we show different techniques to find the quantum dots emission: fluorescence spectrum, synchronous spectrum and Raman spectrum.

  2. Isotopically enhanced triple-quantum-dot qubit

    PubMed Central

    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.

    2015-01-01

    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. PMID:26601186

  3. Physics of lateral triple quantum-dot molecules with controlled electron numbers.

    PubMed

    Hsieh, Chang-Yu; Shim, Yun-Pil; Korkusinski, Marek; Hawrylak, Pawel

    2012-11-01

    We review the recent progress in theory and experiments with lateral triple quantum dots with controlled electron numbers down to one electron in each dot. The theory covers electronic and spin properties as a function of topology, number of electrons, gate voltage and external magnetic field. The orbital Hund's rules and Nagaoka ferromagnetism, magnetic frustration and chirality, interplay of quantum interference and electron-electron interactions and geometrical phases are described and related to charging and transport spectroscopy. Fabrication techniques and recent experiments are covered, as well as potential applications of triple quantum-dot molecule in coherent control, spin manipulation and quantum computation.

  4. Thermoelectric energy harvesting with quantum dots

    NASA Astrophysics Data System (ADS)

    Sothmann, Björn; Sánchez, Rafael; Jordan, Andrew N.

    2015-01-01

    We review recent theoretical work on thermoelectric energy harvesting in multi-terminal quantum-dot setups. We first discuss several examples of nanoscale heat engines based on Coulomb-coupled conductors. In particular, we focus on quantum dots in the Coulomb-blockade regime, chaotic cavities and resonant tunneling through quantum dots and wells. We then turn toward quantum-dot heat engines that are driven by bosonic degrees of freedom such as phonons, magnons and microwave photons. These systems provide interesting connections to spin caloritronics and circuit quantum electrodynamics.

  5. Phonon impact on optical control schemes of quantum dots: Role of quantum dot geometry and symmetry

    NASA Astrophysics Data System (ADS)

    Lüker, S.; Kuhn, T.; Reiter, D. E.

    2017-12-01

    Phonons strongly influence the optical control of semiconductor quantum dots. When modeling the electron-phonon interaction in several theoretical approaches, the quantum dot geometry is approximated by a spherical structure, though typical self-assembled quantum dots are strongly lens-shaped. By explicitly comparing simulations of a spherical and a lens-shaped dot using a well-established correlation expansion approach, we show that, indeed, lens-shaped dots can be exactly mapped to a spherical geometry when studying the phonon influence on the electronic system. We also give a recipe to reproduce spectral densities from more involved dots by rather simple spherical models. On the other hand, breaking the spherical symmetry has a pronounced impact on the spatiotemporal properties of the phonon dynamics. As an example we show that for a lens-shaped quantum dot, the phonon emission is strongly concentrated along the direction of the smallest axis of the dot, which is important for the use of phonons for the communication between different dots.

  6. Clinical Potential of Quantum Dots

    PubMed Central

    Iga, Arthur M.; Robertson, John H. P.; Winslet, Marc C.; Seifalian, Alexander M.

    2007-01-01

    Advances in nanotechnology have led to the development of novel fluorescent probes called quantum dots. Quantum dots have revolutionalized the processes of tagging molecules within research settings and are improving sentinel lymph node mapping and identification in vivo studies. As the unique physical and chemical properties of these fluorescent probes are being unraveled, new potential methods of early cancer detection, rapid spread and therapeutic management, that is, photodynamic therapy are being explored. Encouraging results of optical and real time identification of sentinel lymph nodes and lymph flow using quantum dots in vivo models are emerging. Quantum dots have also superseded many of the limitations of organic fluorophores and are a promising alternative as a research tool. In this review, we examine the promising clinical potential of quantum dots, their hindrances for clinical use and the current progress in abrogating their inherent toxicity. PMID:18317518

  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. 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.

  9. 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

  10. Quantum soldering of individual quantum dots.

    PubMed

    Roy, Xavier; Schenck, Christine L; Ahn, Seokhoon; Lalancette, Roger A; Venkataraman, Latha; Nuckolls, Colin; Steigerwald, Michael L

    2012-12-07

    Making contact to a quantum dot: Single quantum-dot electronic circuits are fabricated by wiring atomically precise metal chalcogenide clusters with conjugated molecular connectors. These wired clusters can couple electronically to nanoscale electrodes and be tuned to control the charge-transfer characteristics (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. 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

  12. 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

  13. Studies of quantum dots in the quantum Hall regime

    NASA Astrophysics Data System (ADS)

    Goldmann, Eyal

    We present two studies of quantum dots in the quantum Hall regime. In the first study, presented in Chapter 3, we investigate the edge reconstruction phenomenon believed to occur when the quantum dot filling fraction is n≲1 . Our approach involves the examination of large dots (≤40 electrons) using a partial diagonalization technique in which the occupancies of the deep interior orbitals are frozen. To interpret the results of this calculation, we evaluate the overlap between the diagonalized ground state and a set of trial wavefunctions which we call projected necklace (PN) states. A PN state is simply the angular momentum projection of a maximum density droplet surrounded by a ring of localized electrons. Our calculations reveal that PN states have up to 99% overlap with the diagonalized ground states, and are lower in energy than the states identified in Chamon and Wen's study of the edge reconstruction. In the second study, presented in Chapter 4, we investigate quantum dots in the fractional quantum Hall regime using a Hartree formulation of composite fermion theory. We find that under appropriate conditions, the chemical potential of the dots oscillates periodically with B due to the transfer of composite fermions between quasi-Landau bands. This effect is analogous the addition spectrum oscillations which occur in quantum dots in the integer quantum Hall regime. Period f0 oscillations are found in sharply confined dots with filling factors nu = 2/5 and nu = 2/3. Period 3 f0 oscillations are found in a parabolically confined nu = 2/5 dot. More generally, we argue that the oscillation period of dots with band pinning should vary continuously with B, whereas the period of dots without band pinning is f0 .

  14. Quantum Optics with Near-Lifetime-Limited Quantum-Dot Transitions in a Nanophotonic Waveguide.

    PubMed

    Thyrrestrup, Henri; Kiršanskė, Gabija; Le Jeannic, Hanna; Pregnolato, Tommaso; Zhai, Liang; Raahauge, Laust; Midolo, Leonardo; Rotenberg, Nir; Javadi, Alisa; Schott, Rüdiger; Wieck, Andreas D; Ludwig, Arne; Löbl, Matthias C; Söllner, Immo; Warburton, Richard J; Lodahl, Peter

    2018-03-14

    Establishing a highly efficient photon-emitter interface where the intrinsic linewidth broadening is limited solely by spontaneous emission is a key step in quantum optics. It opens a pathway to coherent light-matter interaction for, e.g., the generation of highly indistinguishable photons, few-photon optical nonlinearities, and photon-emitter quantum gates. However, residual broadening mechanisms are ubiquitous and need to be combated. For solid-state emitters charge and nuclear spin noise are of importance, and the influence of photonic nanostructures on the broadening has not been clarified. We present near-lifetime-limited linewidths for quantum dots embedded in nanophotonic waveguides through a resonant transmission experiment. It is found that the scattering of single photons from the quantum dot can be obtained with an extinction of 66 ± 4%, which is limited by the coupling of the quantum dot to the nanostructure rather than the linewidth broadening. This is obtained by embedding the quantum dot in an electrically contacted nanophotonic membrane. A clear pathway to obtaining even larger single-photon extinction is laid out; i.e., the approach enables a fully deterministic and coherent photon-emitter interface in the solid state that is operated at optical frequencies.

  15. Quantum dot in interacting environments

    NASA Astrophysics Data System (ADS)

    Rylands, Colin; Andrei, Natan

    2018-04-01

    A quantum impurity attached to an interacting quantum wire gives rise to an array of new phenomena. Using the Bethe Ansatz we solve exactly models describing two geometries of a quantum dot coupled to an interacting quantum wire: a quantum dot that is (i) side coupled and (ii) embedded in a Luttinger liquid. We find the eigenstates and determine the spectrum through the Bethe Ansatz equations. Using this we derive exact expressions for the ground-state dot occupation. The thermodynamics are then studied using the thermodynamics Bethe Ansatz equations. It is shown that at low energies the dot becomes fully hybridized and acts as a backscattering impurity or tunnel junction depending on the geometry and furthermore that the two geometries are related by changing the sign of the interactions. Although remaining strongly coupled for all values of the interaction in the wire, there exists competition between the tunneling and backscattering leading to a suppression or enhancement of the dot occupation depending on the sign of the bulk interactions.

  16. 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.

  17. Optical signatures of coupled quantum dots.

    PubMed

    Stinaff, E A; Scheibner, M; Bracker, A S; Ponomarev, I V; Korenev, V L; Ware, M E; Doty, M F; Reinecke, T L; Gammon, D

    2006-02-03

    An asymmetric pair of coupled InAs quantum dots is tuned into resonance by applying an electric field so that a single hole forms a coherent molecular wave function. The optical spectrum shows a rich pattern of level anticrossings and crossings that can be understood as a superposition of charge and spin configurations of the two dots. Coulomb interactions shift the molecular resonance of the optically excited state (charged exciton) with respect to the ground state (single charge), enabling light-induced coupling of the quantum dots. This result demonstrates the possibility of optically coupling quantum dots for application in quantum information processing.

  18. Optical Signatures of Coupled Quantum Dots

    NASA Astrophysics Data System (ADS)

    Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Ponomarev, I. V.; Korenev, V. L.; Ware, M. E.; Doty, M. F.; Reinecke, T. L.; Gammon, D.

    2006-02-01

    An asymmetric pair of coupled InAs quantum dots is tuned into resonance by applying an electric field so that a single hole forms a coherent molecular wave function. The optical spectrum shows a rich pattern of level anticrossings and crossings that can be understood as a superposition of charge and spin configurations of the two dots. Coulomb interactions shift the molecular resonance of the optically excited state (charged exciton) with respect to the ground state (single charge), enabling light-induced coupling of the quantum dots. This result demonstrates the possibility of optically coupling quantum dots for application in quantum information processing.

  19. Quantum dot-polymer conjugates for stable luminescent displays.

    PubMed

    Ghimire, Sushant; Sivadas, Anjaly; Yuyama, Ken-Ichi; Takano, Yuta; Francis, Raju; Biju, Vasudevanpillai

    2018-05-23

    The broad absorption of light in the UV-Vis-NIR region and the size-based tunable photoluminescence color of semiconductor quantum dots make these tiny crystals one of the most attractive antennae in solar cells and phosphors in electrooptical devices. One of the primary requirements for such real-world applications of quantum dots is their stable and uniform distribution in optically transparent matrices. In this work, we prepare transparent thin films of polymer-quantum dot conjugates, where CdSe/ZnS quantum dots are uniformly distributed at high densities in a chitosan-polystyrene copolymer (CS-g-PS) matrix. Here, quantum dots in an aqueous solution are conjugated to the copolymer by a phase transfer reaction. With the stable conjugation of quantum dots to the copolymer, we prevent undesired phase separation between the two and aggregation of quantum dots. Furthermore, the conjugate allows us to prepare transparent thin films in which quantum dots are uniformly distributed at high densities. The CS-g-PS copolymer helps us in not only preserving the photoluminescence properties of quantum dots in the film but also rendering excellent photostability to quantum dots at the ensemble and single particle levels, making the conjugate a promising material for photoluminescence-based devices.

  20. Entanglement in a quantum neural network based on quantum dots

    NASA Astrophysics Data System (ADS)

    Altaisky, M. V.; Zolnikova, N. N.; Kaputkina, N. E.; Krylov, V. A.; Lozovik, Yu E.; Dattani, N. S.

    2017-05-01

    We studied the quantum correlations between the nodes in a quantum neural network built of an array of quantum dots with dipole-dipole interaction. By means of the quasiadiabatic path integral simulation of the density matrix evolution in a presence of the common phonon bath we have shown the coherence in such system can survive up to the liquid nitrogen temperature of 77 K and above. The quantum correlations between quantum dots are studied by means of calculation of the entanglement of formation in a pair of quantum dots with the typical dot size of a few nanometers and interdot distance of the same order. We have shown that the proposed quantum neural network can keep the mixture of entangled states of QD pairs up to the above mentioned high temperatures.

  1. 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.

  2. 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. PMID:28903308

  3. Elimination of Bimodal Size in InAs/GaAs Quantum Dots for Preparation of 1.3-μm Quantum Dot Lasers

    NASA Astrophysics Data System (ADS)

    Su, Xiang-Bin; Ding, Ying; Ma, Ben; Zhang, Ke-Lu; Chen, Ze-Sheng; Li, Jing-Lun; Cui, Xiao-Ran; Xu, Ying-Qiang; Ni, Hai-Qiao; Niu, Zhi-Chuan

    2018-02-01

    The device characteristics of semiconductor quantum dot lasers have been improved with progress in active layer structures. Self-assembly formed InAs quantum dots grown on GaAs had been intensively promoted in order to achieve quantum dot lasers with superior device performances. In the process of growing high-density InAs/GaAs quantum dots, bimodal size occurs due to large mismatch and other factors. The bimodal size in the InAs/GaAs quantum dot system is eliminated by the method of high-temperature annealing and optimized the in situ annealing temperature. The annealing temperature is taken as the key optimization parameters, and the optimal annealing temperature of 680 °C was obtained. In this process, quantum dot growth temperature, InAs deposition, and arsenic (As) pressure are optimized to improve quantum dot quality and emission wavelength. A 1.3-μm high-performance F-P quantum dot laser with a threshold current density of 110 A/cm2 was demonstrated.

  4. Elimination of Bimodal Size in InAs/GaAs Quantum Dots for Preparation of 1.3-μm Quantum Dot Lasers.

    PubMed

    Su, Xiang-Bin; Ding, Ying; Ma, Ben; Zhang, Ke-Lu; Chen, Ze-Sheng; Li, Jing-Lun; Cui, Xiao-Ran; Xu, Ying-Qiang; Ni, Hai-Qiao; Niu, Zhi-Chuan

    2018-02-21

    The device characteristics of semiconductor quantum dot lasers have been improved with progress in active layer structures. Self-assembly formed InAs quantum dots grown on GaAs had been intensively promoted in order to achieve quantum dot lasers with superior device performances. In the process of growing high-density InAs/GaAs quantum dots, bimodal size occurs due to large mismatch and other factors. The bimodal size in the InAs/GaAs quantum dot system is eliminated by the method of high-temperature annealing and optimized the in situ annealing temperature. The annealing temperature is taken as the key optimization parameters, and the optimal annealing temperature of 680 °C was obtained. In this process, quantum dot growth temperature, InAs deposition, and arsenic (As) pressure are optimized to improve quantum dot quality and emission wavelength. A 1.3-μm high-performance F-P quantum dot laser with a threshold current density of 110 A/cm 2 was demonstrated.

  5. A tunable few electron triple quantum dot

    NASA Astrophysics Data System (ADS)

    Gaudreau, L.; Kam, A.; Granger, G.; Studenikin, S. A.; Zawadzki, P.; Sachrajda, A. S.

    2009-11-01

    In this paper, we report on a tunable few electron lateral triple quantum dot design. The quantum dot potentials are arranged in series. The device is aimed at studies of triple quantum dot properties where knowing the exact number of electrons is important as well as quantum information applications involving electron spin qubits. We demonstrate tuning strategies for achieving required resonant conditions such as quadruple points where all three quantum dots are on resonance. We find that in such a device resonant conditions at specific configurations are accompanied by complex charge transfer behavior.

  6. Hybrid quantum-classical modeling of quantum dot devices

    NASA Astrophysics Data System (ADS)

    Kantner, Markus; Mittnenzweig, Markus; Koprucki, Thomas

    2017-11-01

    The design of electrically driven quantum dot devices for quantum optical applications asks for modeling approaches combining classical device physics with quantum mechanics. We connect the well-established fields of semiclassical semiconductor transport theory and the theory of open quantum systems to meet this requirement. By coupling the van Roosbroeck system with a quantum master equation in Lindblad form, we introduce a new hybrid quantum-classical modeling approach, which provides a comprehensive description of quantum dot devices on multiple scales: it enables the calculation of quantum optical figures of merit and the spatially resolved simulation of the current flow in realistic semiconductor device geometries in a unified way. We construct the interface between both theories in such a way, that the resulting hybrid system obeys the fundamental axioms of (non)equilibrium thermodynamics. We show that our approach guarantees the conservation of charge, consistency with the thermodynamic equilibrium and the second law of thermodynamics. The feasibility of the approach is demonstrated by numerical simulations of an electrically driven single-photon source based on a single quantum dot in the stationary and transient operation regime.

  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...been to advance the frontier of quantum entangled semiconductor electrons using ultrafast optical techniques. The approach is based on

  8. 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.

  9. 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

  10. Complete Coherent Control of a Quantum Dot Strongly Coupled to a Nanocavity.

    PubMed

    Dory, Constantin; Fischer, Kevin A; Müller, Kai; Lagoudakis, Konstantinos G; Sarmiento, Tomas; Rundquist, Armand; Zhang, Jingyuan L; Kelaita, Yousif; Vučković, Jelena

    2016-04-26

    Strongly coupled quantum dot-cavity systems provide a non-linear configuration of hybridized light-matter states with promising quantum-optical applications. Here, we investigate the coherent interaction between strong laser pulses and quantum dot-cavity polaritons. Resonant excitation of polaritonic states and their interaction with phonons allow us to observe coherent Rabi oscillations and Ramsey fringes. Furthermore, we demonstrate complete coherent control of a quantum dot-photonic crystal cavity based quantum-bit. By controlling the excitation power and phase in a two-pulse excitation scheme we achieve access to the full Bloch sphere. Quantum-optical simulations are in good agreement with our experiments and provide insight into the decoherence mechanisms.

  11. Complete Coherent Control of a Quantum Dot Strongly Coupled to a Nanocavity

    NASA Astrophysics Data System (ADS)

    Dory, Constantin; Fischer, Kevin A.; Müller, Kai; Lagoudakis, Konstantinos G.; Sarmiento, Tomas; Rundquist, Armand; Zhang, Jingyuan L.; Kelaita, Yousif; Vučković, Jelena

    2016-04-01

    Strongly coupled quantum dot-cavity systems provide a non-linear configuration of hybridized light-matter states with promising quantum-optical applications. Here, we investigate the coherent interaction between strong laser pulses and quantum dot-cavity polaritons. Resonant excitation of polaritonic states and their interaction with phonons allow us to observe coherent Rabi oscillations and Ramsey fringes. Furthermore, we demonstrate complete coherent control of a quantum dot-photonic crystal cavity based quantum-bit. By controlling the excitation power and phase in a two-pulse excitation scheme we achieve access to the full Bloch sphere. Quantum-optical simulations are in good agreement with our experiments and provide insight into the decoherence mechanisms.

  12. QCAD simulation and optimization of semiconductor double quantum dots

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

    Nielsen, Erik; Gao, Xujiao; Kalashnikova, Irina

    2013-12-01

    We present the Quantum Computer Aided Design (QCAD) simulator that targets modeling quantum devices, particularly silicon double quantum dots (DQDs) developed for quantum qubits. The simulator has three di erentiating features: (i) its core contains nonlinear Poisson, e ective mass Schrodinger, and Con guration Interaction solvers that have massively parallel capability for high simulation throughput, and can be run individually or combined self-consistently for 1D/2D/3D quantum devices; (ii) the core solvers show superior convergence even at near-zero-Kelvin temperatures, which is critical for modeling quantum computing devices; (iii) it couples with an optimization engine Dakota that enables optimization of gate voltagesmore » in DQDs for multiple desired targets. The Poisson solver includes Maxwell- Boltzmann and Fermi-Dirac statistics, supports Dirichlet, Neumann, interface charge, and Robin boundary conditions, and includes the e ect of dopant incomplete ionization. The solver has shown robust nonlinear convergence even in the milli-Kelvin temperature range, and has been extensively used to quickly obtain the semiclassical electrostatic potential in DQD devices. The self-consistent Schrodinger-Poisson solver has achieved robust and monotonic convergence behavior for 1D/2D/3D quantum devices at very low temperatures by using a predictor-correct iteration scheme. The QCAD simulator enables the calculation of dot-to-gate capacitances, and comparison with experiment and between solvers. It is observed that computed capacitances are in the right ballpark when compared to experiment, and quantum con nement increases capacitance when the number of electrons is xed in a quantum dot. In addition, the coupling of QCAD with Dakota allows to rapidly identify which device layouts are more likely leading to few-electron quantum dots. Very efficient QCAD simulations on a large number of fabricated and proposed Si DQDs have made it possible to provide fast feedback for

  13. Three-terminal quantum-dot thermal management devices

    NASA Astrophysics Data System (ADS)

    Zhang, Yanchao; Zhang, Xin; Ye, Zhuolin; Lin, Guoxing; Chen, Jincan

    2017-04-01

    We theoretically demonstrate that the heat flows can be manipulated by designing a three-terminal quantum-dot system consisting of three Coulomb-coupled quantum dots connected to respective reservoirs. In this structure, the electron transport between the quantum dots is forbidden, but the heat transport is allowed by the Coulomb interaction to transmit heat between the reservoirs with a temperature difference. We show that such a system is capable of performing thermal management operations, such as heat flow swap, thermal switch, and heat path selector. An important thermal rectifier, i.e., a thermal diode, can be implemented separately in two different paths. The asymmetric configuration of a quantum-dot system is a necessary condition for thermal management operations in practical applications. These results should have important implications in providing the design principle for quantum-dot thermal management devices and may open up potential applications for the thermal management of quantum-dot systems at the nanoscale.

  14. 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.

  15. Quantum dot lasers: From promise to high-performance devices

    NASA Astrophysics Data System (ADS)

    Bhattacharya, P.; Mi, Z.; Yang, J.; Basu, D.; Saha, D.

    2009-03-01

    Ever since self-organized In(Ga)As/Ga(AI)As quantum dots were realized by molecular beam epitaxy, it became evident that these coherently strained nanostructures could be used as the active media in devices. While the expected advantages stemming from three-dimensional quantum confinement were clearly outlined, these were not borne out by the early experiments. It took a very detailed understanding of the unique carrier dynamics in the quantum dots to exploit their full potential. As a result, we now have lasers with emission wavelengths ranging from 0.7 to 1.54 μm, on GaAs, which demonstrate ultra-low threshold currents, near-zero chip and α-factor and large modulation bandwidth. State-of-the-art performance characteristics of these lasers are briefly reviewed. The growth, fabrication and characteristics of quantum dot lasers on silicon substrates are also described. With the incorporation of multiple quantum dot layers as a dislocation filter, we demonstrate lasers with Jth=900 A/cm 2. The monolithic integration of the lasers with guided wave modulators on silicon is also described. Finally, the properties of spin-polarized lasers with quantum dot active regions are described. Spin injection of electrons is done with a MnAs/GaAs tunnel barrier. Laser operation at 200 K is demonstrated, with the possibility of room temperature operation in the near future.

  16. 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.

  17. Ultrafast optical control of individual quantum dot spin qubits.

    PubMed

    De Greve, Kristiaan; Press, David; McMahon, Peter L; Yamamoto, Yoshihisa

    2013-09-01

    Single spins in semiconductor quantum dots form a promising platform for solid-state quantum information processing. The spin-up and spin-down states of a single electron or hole, trapped inside a quantum dot, can represent a single qubit with a reasonably long decoherence time. The spin qubit can be optically coupled to excited (charged exciton) states that are also trapped in the quantum dot, which provides a mechanism to quickly initialize, manipulate and measure the spin state with optical pulses, and to interface between a stationary matter qubit and a 'flying' photonic qubit for quantum communication and distributed quantum information processing. The interaction of the spin qubit with light may be enhanced by placing the quantum dot inside a monolithic microcavity. An entire system, consisting of a two-dimensional array of quantum dots and a planar microcavity, may plausibly be constructed by modern semiconductor nano-fabrication technology and could offer a path toward chip-sized scalable quantum repeaters and quantum computers. This article reviews the recent experimental developments in optical control of single quantum dot spins for quantum information processing. We highlight demonstrations of a complete set of all-optical single-qubit operations on a single quantum dot spin: initialization, an arbitrary SU(2) gate, and measurement. We review the decoherence and dephasing mechanisms due to hyperfine interaction with the nuclear-spin bath, and show how the single-qubit operations can be combined to perform spin echo sequences that extend the qubit decoherence from a few nanoseconds to several microseconds, more than 5 orders of magnitude longer than the single-qubit gate time. Two-qubit coupling is discussed, both within a single chip by means of exchange coupling of nearby spins and optically induced geometric phases, as well as over longer-distances. Long-distance spin-spin entanglement can be generated if each spin can emit a photon that is entangled

  18. 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

  19. Dicke states in multiple quantum dots

    NASA Astrophysics Data System (ADS)

    Sitek, Anna; Manolescu, Andrei

    2013-10-01

    We present a theoretical study of the collective optical effects which can occur in groups of three and four quantum dots. We define conditions for stable subradiant (dark) states, rapidly decaying super-radiant states, and spontaneous trapping of excitation. Each quantum dot is treated like a two-level system. The quantum dots are, however, realistic, meaning that they may have different transition energies and dipole moments. The dots interact via a short-range coupling which allows excitation transfer across the dots, but conserves the total population of the system. We calculate the time evolution of single-exciton and biexciton states using the Lindblad equation. In the steady state the individual populations of each dot may have permanent oscillations with frequencies given by the energy separation between the subradiant eigenstates.

  20. A 2 × 2 quantum dot array with controllable inter-dot tunnel couplings

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Uditendu; Dehollain, Juan Pablo; Reichl, Christian; Wegscheider, Werner; Vandersypen, Lieven M. K.

    2018-04-01

    The interaction between electrons in arrays of electrostatically defined quantum dots is naturally described by a Fermi-Hubbard Hamiltonian. Moreover, the high degree of tunability of these systems makes them a powerful platform to simulate different regimes of the Hubbard model. However, most quantum dot array implementations have been limited to one-dimensional linear arrays. In this letter, we present a square lattice unit cell of 2 × 2 quantum dots defined electrostatically in an AlGaAs/GaAs heterostructure using a double-layer gate technique. We probe the properties of the array using nearby quantum dots operated as charge sensors. We show that we can deterministically and dynamically control the charge occupation in each quantum dot in the single- to few-electron regime. Additionally, we achieve simultaneous individual control of the nearest-neighbor tunnel couplings over a range of 0-40 μeV. Finally, we demonstrate fast (˜1 μs) single-shot readout of the spin state of electrons in the dots through spin-to-charge conversion via Pauli spin blockade. These advances pave the way for analog quantum simulations in two dimensions, not previously accessible in quantum dot systems.

  1. Multi-million atom electronic structure calculations for quantum dots

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad

    stark shift, coherent coupling of electronic states in a quantum dot molecule etc.; (3) to assess the potential use of the quantum dots in real device implementation and to provide physical insight to the experimentalists. Full three dimensional strain and electronic structure simulations of quantum dot structures containing multi-million atoms are done using NEMO 3-D. Both single and vertically stacked quantum dot structures are analyzed in detail. The results show that the strain and the piezoelectricity significantly impact the electronic structure of these devices. This work shows that the InAs quantum dots when placed in the InGaAs quantum well red shifts the emission wavelength. Such InAs/GaAs-based optical devices can be used for optical-fiber based communication systems at longer wavelengths (1.3um -- 1.5um). Our atomistic simulations of InAs/InGaAs/GaAs quantum dots quantitatively match with the experiment and give the critical insight of the physics involved in these structures. A single quantum dot molecule is studied for coherent quantum coupling of electronic states under the influence of static electric field applied in the growth direction. Such nanostructures can be used in the implementation of quantum information technologies. A close quantitative match with the experimental optical measurements allowed us to get a physical insight into the complex physics of quantum tunnel couplings of electronic states as the device operation switches between atomic and molecular regimes. Another important aspect is to design the quantum dots for a desired isotropic polarization of the optical emissions. Both single and coupled quantum dots are studied for TE/TM ratio engineering. The atomistic study provides a detailed physical analysis of these computationally expensive large nanostructures and serves as a guide for the experimentalists for the design of the polarization independent devices for the optical communication systems.

  2. Valley splitting of single-electron Si MOS quantum dots

    DOE PAGES

    Gamble, John King; Harvey-Collard, Patrick; Jacobson, N. Tobias; ...

    2016-12-19

    Here, silicon-based metal-oxide-semiconductor quantum dots are prominent candidates for high-fidelity, manufacturable qubits. Due to silicon's band structure, additional low-energy states persist in these devices, presenting both challenges and opportunities. Although the physics governing these valley states has been the subject of intense study, quantitative agreement between experiment and theory remains elusive. Here, we present data from an experiment probing the valley states of quantum dot devices and develop a theory that is in quantitative agreement with both this and a recently reported experiment. Through sampling millions of realistic cases of interface roughness, our method provides evidence that the valley physicsmore » between the two samples is essentially the same.« less

  3. Using of Quantum Dots in Biology and Medicine.

    PubMed

    Pleskova, Svetlana; Mikheeva, Elza; Gornostaeva, Ekaterina

    2018-01-01

    Quantum dots are nanoparticles, which due to their unique physical and chemical (first of all optical) properties, are promising in biology and medicine. There are many ways for quantum dots synthesis, both in the form of nanoislands self-forming on the surfaces, which can be used as single-photon emitters in electronics for storing information, and in the form of colloidal quantum dots for diagnostic and therapeutic purposes in living systems. The paper describes the main methods of quantum dots synthesis and summarizes medical and biological ways of their use. The main emphasis is laid on the ways of quantum dots surface modification. Influence of the size and form of nanoparticles, charge on the surfaces of quantum dots, and cover type on the efficiency of internalization by cells and cell compartments is shown. The main mechanisms of penetration are considered.

  4. The thermoelectric efficiency of quantum dots in indium arsenide/indium phosphide nanowires

    NASA Astrophysics Data System (ADS)

    Hoffmann, Eric A.

    State of the art semiconductor materials engineering provides the possibility to fabricate devices on the lower end of the mesoscopic scale and confine only a handful of electrons to a region of space. When the thermal energy is reduced below the energetic quantum level spacing, the confined electrons assume energy levels akin to the core-shell structure of natural atoms. Such "artificial atoms", also known as quantum dots, can be loaded with electrons, one-by-one, and subsequently unloaded using source and drain electrical contacts. As such, quantum dots are uniquely tunable platforms for performing quantum transport and quantum control experiments. Voltage-biased electron transport through quantum dots has been studied extensively. Far less attention has been given to thermoelectric effects in quantum dots, that is, electron transport induced by a temperature gradient. This dissertation focuses on the efficiency of direct thermal-to-electric energy conversion in InAs/InP quantum dots embedded in nanowires. The efficiency of thermoelectric heat engines is bounded by the same maximum efficiency as cyclic heat engines; namely, by Carnot efficiency. The efficiency of bulk thermoelectric materials suffers from their inability to transport charge carriers selectively based on energy. Owing to their three-dimensional momentum quantization, quantum dots operate as electron energy filters---a property which can be harnessed to minimize entropy production and therefore maximize efficiency. This research was motivated by the possibility to realize experimentally a thermodynamic heat engine operating with near-Carnot efficiency using the unique behavior of quantum dots. To this end, a microscopic heating scheme for the application of a temperature difference across a quantum dot was developed in conjunction with a novel quantum-dot thermometry technique used for quantifying the magnitude of the applied temperature difference. While pursuing high-efficiency thermoelectric

  5. Toward the in vivo study of captopril-conjugated quantum dots

    NASA Astrophysics Data System (ADS)

    Manabe, Noriyoshi; Hoshino, Akiyoshi; Liang, Yi-qiang; Goto, Tomomasa; Kato, Norihiro; Yamamoto, Kenji

    2005-04-01

    Photo-luminescent semiconductor quantum dots are nanometer-size probes that have the potential to be applied to the fields of the bio-imaging and the study of the cell mobility inside the body. At the same time, on the other hand, quantum dots are expected to carry some kind of molecules to the local organ inside of the animal body, which leads to the expectation that they can be used as a medicine-carrier. For this purpose, we conjugate (2S)-1-[(2s)-2-Methyl-3-sulfanylpropionyl]pyrrolidine-2-carboxylic acid (cap) with the quantum dot. Cap has the effect as an anti-hypertension drug, which inhibits angiotensin 1 converting enzyme. We conjugated the quantum dot with cap by the exchange reaction avoiding the regions which holds medicinal effect. Quantum dot conjugated with cap (QD-cap) were 3-times brighter than thioglycerol-coated quantum dots (QD-OH). The particle size of cap was 1.1nm and that of QD-cap was 12nm. QD-cap was permeated into the HeLa cells, while QD-MUA were taken into the HeLa cells by endocytosis. In addition, no apoptosis was detected against the cells that permeated QD-cap, because there was no damage to DNA. These results indicated that QD-conjugated medicines (QD-medicine) could be safe in the experiment on the level of the cell. More over, when QD-cap was intravenously injected into Stroke-prone Spontaneously Hypertensive Rats (SHRSP), they reduced blood pressure at systole. Therefore, the anti-hypertension effect of cap remained after conjugated with the quantum dot. These results suggested that QD-medicine were effective on the animal level.

  6. Effect of self assembled quantum dots on carrier mobility, with application to modeling the dark current in quantum dot infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Youssef, Sarah; El-Batawy, Yasser M.; Abouelsaood, Ahmed A.

    2016-09-01

    A theoretical method for calculating the electron mobility in quantum dot infrared photodetectors is developed. The mobility calculation is based on a time-dependent, finite-difference solution of the Boltzmann transport equation in a bulk semiconductor material with randomly positioned conical quantum dots. The quantum dots act as scatterers of current carriers (conduction-band electrons in our case), resulting in limiting their mobility. In fact, carrier scattering by quantum dots is typically the dominant factor in determining the mobility in the active region of the quantum dot device. The calculated values of the mobility are used in a recently developed generalized drift-diffusion model for the dark current of the device [Ameen et al., J. Appl. Phys. 115, 063703 (2014)] in order to fix the overall current scale. The results of the model are verified by comparing the predicted dark current characteristics to those experimentally measured and reported for actual InAs/GaAs quantum dot infrared photodetectors. Finally, the effect of the several relevant device parameters, including the operating temperature and the quantum dot average density, is studied.

  7. Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

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

    Barettin, Daniele, E-mail: Daniele.Barettin@uniroma2.it; Auf der Maur, Matthias; De Angelis, Roberta

    2015-03-07

    We report on numerical simulations of InP surface lateral quantum-dot molecules on In{sub 0.48}Ga{sub 0.52 }P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateralmore » quantum-dot molecules. Continuum electromechanical, k{sup →}·p{sup →} bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.« less

  8. Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

    NASA Astrophysics Data System (ADS)

    Barettin, Daniele; Auf der Maur, Matthias; De Angelis, Roberta; Prosposito, Paolo; Casalboni, Mauro; Pecchia, Alessandro

    2015-03-01

    We report on numerical simulations of InP surface lateral quantum-dot molecules on In0.48Ga0.52P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateral quantum-dot molecules. Continuum electromechanical, k →.p → bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.

  9. Generation of heralded entanglement between distant quantum dot hole spins

    NASA Astrophysics Data System (ADS)

    Delteil, Aymeric

    Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, some of the major challenges are the efficient generation of entanglement between stationary (spin) and propagating (photon) qubits, the transfer of information from flying to stationary qubits, and the efficient generation of entanglement between distant stationary (spin) qubits. In this talk, I will present such experimental implementations achieved in our team with semiconductor self-assembled quantum dots.Not only are self-assembled quantum dots good single-photon emitters, but they can host an electron or a hole whose spin serves as a quantum memory, and then present spin-dependent optical selection rules leading to an efficient spin-photon quantum interface. Moreover InGaAs quantum dots grown on GaAs substrate can profit from the maturity of III-V semiconductor technology and can be embedded in semiconductor structures like photonic cavities and Schottky diodes.I will report on the realization of heralded quantum entanglement between two semiconductor quantum dot hole spins separated by more than five meters. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Moreover the efficient spin-photon interface provided by self-assembled quantum dots allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments carried out in other systems.Our results extend previous demonstrations in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of

  10. Polarization of the photoluminescence of quantum dots incorporated into quantum wires

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

    Platonov, A. V., E-mail: alexei.platonov@mail.ioffe.ru; Kochereshko, V. P.; Kats, V. N.

    The photoluminescence spectra of individual quantum dots incorporated into a quantum wire are studied. From the behavior of the spectra in a magnetic field, it is possible to estimate the exciton binding energy in a quantum dot incorporated into a quantum wire. It is found that the exciton photoluminescence signal emitted from a quantum dot along the direction of the nanowire axis is linearly polarized. At the same time, the photoluminescence signal propagating in the direction orthogonal to the nanowire axis is practically unpolarized. The experimentally observed effect is attributed to the nonaxial arrangement of the dot in the wiremore » under conditions of a huge increase in the exciton binding energy due to the effect of the image potential on the exciton.« less

  11. 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. Copyright © 2016 Elsevier B.V. All rights reserved.

  12. 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.

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

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

    Wu, Jiang, E-mail: jiang.wu@ucl.ac.uk; 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 wavelengthmore » 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.« less

  14. Spectroscopy of Single AlInAs Quantum Dots

    NASA Astrophysics Data System (ADS)

    Derebezov, I. A.; Gaisler, A. V.; Gaisler, V. A.; Dmitriev, D. V.; Toropov, A. I.; Kozhukhov, A. S.; Shcheglov, D. V.; Latyshev, A. V.; Aseev, A. L.

    2018-03-01

    A system of quantum dots based on Al x In1- x As/Al y Ga1- y As solid solutions is investigated. The use of Al x In1- x As wide-gap solid solutions as the basis of quantum dots substantially extends the spectral emission range to the short-wavelength region, including the wavelength region near 770 nm, which is of interest for the development of aerospace systems of quantum cryptography. The optical characteristics of Al x In1- x As single quantum dots grown by the Stranski-Krastanov mechanism were studied by cryogenic microphotoluminescence. The statistics of the emission of single quantum dot excitons was studied using a Hanbury Brown-Twiss interferometer. The pair photon correlation function indicates the sub-Poissonian nature of the emission statistics, which directly confirms the possibility of developing single-photon emitters based on Al x In1- x As quantum dots. The fine structure of quantum dot exciton states was investigated at wavelengths near 770 nm. The splitting of the exciton states is found to be similar to the natural width of exciton lines, which is of great interest for the development of entangled photon pair emitters based on Al x In1- x As quantum dots.

  15. Quantum strain sensor with a topological insulator HgTe quantum dot

    PubMed Central

    Korkusinski, Marek; Hawrylak, Pawel

    2014-01-01

    We present a theory of electronic properties of HgTe quantum dot and propose a strain sensor based on a strain-driven transition from a HgTe quantum dot with inverted bandstructure and robust topologically protected quantum edge states to a normal state without edge states in the energy gap. The presence or absence of edge states leads to large on/off ratio of conductivity across the quantum dot, tunable by adjusting the number of conduction channels in the source-drain voltage window. The electronic properties of a HgTe quantum dot as a function of size and applied strain are described using eight-band Luttinger and Bir-Pikus Hamiltonians, with surface states identified with chirality of Luttinger spinors and obtained through extensive numerical diagonalization of the Hamiltonian. PMID:24811674

  16. Interfacing a quantum dot with a spontaneous parametric down-conversion source

    NASA Astrophysics Data System (ADS)

    Huber, Tobias; Prilmüller, Maximilian; Sehner, Michael; Solomon, Glenn S.; Predojević, Ana; Weihs, Gregor

    2017-09-01

    Quantum networks require interfacing stationary and flying qubits. These flying qubits are usually nonclassical states of light. Here we consider two of the leading source technologies for nonclassical light, spontaneous parametric down-conversion and single semiconductor quantum dots. Down-conversion delivers high-grade entangled photon pairs, whereas quantum dots excel at producing single photons. We report on an experiment that joins these two technologies and investigates the conditions under which optimal interference between these dissimilar light sources may be achieved.

  17. Thick-shell nanocrystal quantum dots

    DOEpatents

    Hollingsworth, Jennifer A [Los Alamos, NM; Chen, Yongfen [Eugene, OR; Klimov, Victor I [Los Alamos, NM; Htoon, Han [Los Alamos, NM; Vela, Javier [Los Alamos, NM

    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.

  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. 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

  20. 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.

  1. 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.

  2. Investigation of Quantum Dot Lasers

    DTIC Science & Technology

    2004-08-09

    Accomplishments: • Introduction Since the first demonstration of room-temperature operation of self-assembled quantum-dot (QD) lasers about a...regions (JGaAs), wetting layer (JWL), and Auger recombination in the dots ( JAug ). for the present 1.3µm dots, the temperature invariant measured

  3. 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.

  4. Ultralow Noise Monolithic Quantum Dot Photonic Oscillators

    DTIC Science & Technology

    2013-10-28

    HBCU/MI) ULTRALOW NOISE MONOLITHIC QUANTUM DOT PHOTONIC OSCILLATORS LUKE LESTER UNIVERSITY OF NEW MEXICO 10/28/2013 Final Report DISTRIBUTION A...TELEPHONE NUMBER (Include area code) 24-10-2013 Final 01-06-2010 to 31-05-2013 Ultralow Noise Monolithic Quantum Dot Photonic Oscillators FA9550-10-1-0276...277-7647 Reset Grant Title: ULTRALOW NOISE MONOLITHIC QUANTUM DOT PHOTONIC OSCILLATORS Grant/Contract Number: FA9550-10-1-0276 Final Performance

  5. Measurement back-action: Listening with quantum dots

    NASA Astrophysics Data System (ADS)

    Ladd, Thaddeus D.

    2012-07-01

    Single electrons in quantum dots can be disturbed by the apparatus used to measure them. The disturbance can be mediated by incoherent phonons -- literally, noise. Engineering acoustic interference could negate these deleterious effects and bring quantum dots closer to becoming a robust quantum technology.

  6. Simultaneous deterministic control of distant qubits in two semiconductor quantum dots.

    PubMed

    Gamouras, A; Mathew, R; Freisem, S; Deppe, D G; Hall, K C

    2013-10-09

    In optimal quantum control (OQC), a target quantum state of matter is achieved by tailoring the phase and amplitude of the control Hamiltonian through femtosecond pulse-shaping techniques and powerful adaptive feedback algorithms. Motivated by recent applications of OQC in quantum information science as an approach to optimizing quantum gates in atomic and molecular systems, here we report the experimental implementation of OQC in a solid-state system consisting of distinguishable semiconductor quantum dots. We demonstrate simultaneous high-fidelity π and 2π single qubit gates in two different quantum dots using a single engineered infrared femtosecond pulse. These experiments enhance the scalability of semiconductor-based quantum hardware and lay the foundation for applications of pulse shaping to optimize quantum gates in other solid-state systems.

  7. 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.

  8. 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.

  9. 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.

  10. Graphene quantum dots, graphene oxide, carbon quantum dots and graphite nanocrystals in coals

    NASA Astrophysics Data System (ADS)

    Dong, Yongqiang; Lin, Jianpeng; Chen, Yingmei; Fu, Fengfu; Chi, Yuwu; Chen, Guonan

    2014-06-01

    Six coal samples of different ranks have been used to prepare single-layer graphene quantum dots (S-GQDs). After chemical oxidation and a series of centrifugation separation, every coal could be treated into two fractions, namely, CoalA and CoalB. According to the characterization results of TEM, AFM, XRD, Raman and FTIR, CoalA was revealed to be mainly composed of S-GQDs, which have an average height of about 0.5 nm and an average plane dimension of about 10 nm. The obtained S-GQDs showed excitation-dependent fluorescence and excellent electrochemiluminescence. CoalB was found to be some other carbon-based nanomaterials (CNMs), including agglomerated GQDs, graphene oxide, carbon quantum dots and agglomerated carbon nanocrystals. Generally, low-ranked coals might be more suitable for the preparation of S-GQDs. The production yield of S-GQDs from the six investigated coals decreased from 56.30% to 14.66% when the coal rank increased gradually. In contrast, high-ranked coals had high production yield of CoalB and might be more suitable for preparing other CNMs that were contained in CoalB, although those CNMs were difficult to separate from each other in our experiment.Six coal samples of different ranks have been used to prepare single-layer graphene quantum dots (S-GQDs). After chemical oxidation and a series of centrifugation separation, every coal could be treated into two fractions, namely, CoalA and CoalB. According to the characterization results of TEM, AFM, XRD, Raman and FTIR, CoalA was revealed to be mainly composed of S-GQDs, which have an average height of about 0.5 nm and an average plane dimension of about 10 nm. The obtained S-GQDs showed excitation-dependent fluorescence and excellent electrochemiluminescence. CoalB was found to be some other carbon-based nanomaterials (CNMs), including agglomerated GQDs, graphene oxide, carbon quantum dots and agglomerated carbon nanocrystals. Generally, low-ranked coals might be more suitable for the preparation of

  11. Aptamer-Modified Semiconductor Quantum Dots for Biosensing Applications

    PubMed Central

    Wen, Lin; Qiu, Liping; Wu, Yongxiang; Hu, Xiaoxiao; Zhang, Xiaobing

    2017-01-01

    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. PMID:28788080

  12. 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.

  13. Anomalous x-ray diffraction on InAs/GaAs quantum dot systems

    NASA Astrophysics Data System (ADS)

    Schulli, T. U.; Sztucki, M.; Chamard, V.; Metzger, T. H.; Schuh, D.

    2002-07-01

    Free-standing InAs quantum dots on a GaAs (001) substrate have been investigated using grazing incidence x-ray diffraction. To suppress the strong scattering contribution from the GaAs substrate, we performed anomalous diffraction experiments at the superstructure (200) reflection, showing that the relative intensities from the dots and the substrate undergo a significant change with the x-ray energy below and above the As K edge. Since the signal from the substrate material can essentially be suppressed, this method is ideally suited for the investigation of strain, shape, and interdiffusion of buried quantum dots and quantum dots embedded in heteroepitaxial multilayers. In addition, we show that it can be used as a tool for studying wetting layers.

  14. Metamorphic quantum dots: Quite different nanostructures

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

    Seravalli, L.; Frigeri, P.; Nasi, L.

    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 quantummore » 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.« less

  15. Photon-assisted tunneling in an asymmetrically coupled triple quantum dot

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

    Wang, Bao-Chuan; Cao, Gang, E-mail: gcao@ustc.edu.cn; Chen, Bao-Bao

    The gate-defined quantum dot is regarded as one of the basic structures required for scalable semiconductor quantum processors. Here, we demonstrate a structure that contains three quantum dots scaled in series. The electron number of each dot and the tunnel coupling between them can be tuned conveniently using splitting gates. We tune the quantum dot array asymmetrically such that the tunnel coupling between the right dot and the central dot is much larger than that between the left dot and the central dot. When driven by microwaves, the sidebands of the photon-assisted tunneling process appear not only in the left-to-centralmore » dot transition region but also in the left-to-right dot transition region. These sidebands are both attributed to the left-to-central transition for asymmetric coupling. Our result shows that there is a region of a triple quantum dot structure that remains indistinct when studied with a normal two-dimensional charge stability diagram; this will be helpful in future studies of the scalability of quantum dot systems.« less

  16. Silicon Quantum Dots with Counted Antimony Donor Implants

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

    Singh, Meenakshi; Pacheco, Jose L.; Perry, Daniel Lee

    2015-10-01

    Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. A focused ion beam is used to implant close to quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of ions implanted can be counted to a precision of a single ion. Regular coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization, are observed in devices with counted implants.

  17. Quantum-dots-encoded-microbeads based molecularly imprinted polymer.

    PubMed

    Liu, Yixi; Liu, Le; He, Yonghong; He, Qinghua; Ma, Hui

    2016-03-15

    Quantum dots encoded microbeads have various advantages such as large surface area, superb optical properties and the ability of multiplexing. Molecularly imprinted polymer that can mimic the natural recognition entities has high affinity and selectivity for the specific analyte. Here, the concept of utilizing the quantum dots encoded microbeads as the supporting material and the polydopamine as the functional monomer to form the core-shell molecular imprinted polymer was proposed for the first time. The resulted imprinted polymer can provide various merits: polymerization can complete in aqueous environment; fabrication procedure is facile and universal; the obvious economic advantage; the thickness of the imprinting layer is highly controllable; polydopamine coating can improve the biocompatibility of the quantum dot encoded microbeads. The rabbit IgG binding and flow cytometer experiment result showed the distinct advantages of this strategy: cost-saving, facile and fast preparation procedure. Most importantly, the ability for the multichannel detection, which makes the imprinted polydopamine modified encoded-beads very attractive in protein pre-concentration, recognition, separation and biosensing. Copyright © 2015 Elsevier B.V. All rights reserved.

  18. Record Charge Carrier Diffusion Length in Colloidal Quantum Dot Solids via Mutual Dot-To-Dot Surface Passivation.

    PubMed

    Carey, Graham H; Levina, Larissa; Comin, Riccardo; Voznyy, Oleksandr; Sargent, Edward H

    2015-06-03

    Through a combination of chemical and mutual dot-to-dot surface passivation, high-quality colloidal quantum dot solids are fabricated. The joint passivation techniques lead to a record diffusion length for colloidal quantum dots of 230 ± 20 nm. The technique is applied to create thick photovoltaic devices that exhibit high current density without losing fill factor. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

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

    Betz, A. C., E-mail: ab2106@cam.ac.uk; Broström, M.; Gonzalez-Zalba, M. F.

    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.

  20. 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.

  1. Universal quantum gates on electron-spin qubits with quantum dots inside single-side optical microcavities.

    PubMed

    Wei, Hai-Rui; Deng, Fu-Guo

    2014-01-13

    We present some compact quantum circuits for a deterministic quantum computing on electron-spin qubits assisted by quantum dots inside single-side optical microcavities, including the CNOT, Toffoli, and Fredkin gates. They are constructed by exploiting the giant optical Faraday rotation induced by a single-electron spin in a quantum dot inside a single-side optical microcavity as a result of cavity quantum electrodynamics. Our universal quantum gates have some advantages. First, all the gates are accomplished with a success probability of 100% in principle. Second, our schemes require no additional electron-spin qubits and they are achieved by some input-output processes of a single photon. Third, our circuits for these gates are simple and economic. Moreover, our devices for these gates work in both the weak coupling and the strong coupling regimes, and they are feasible in experiment.

  2. 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

  3. Spectroscopy of Charged Quantum Dot Molecules

    NASA Astrophysics Data System (ADS)

    Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Ponomarev, I. V.; Ware, M. E.; Doty, M. F.; Reinecke, T. L.; Gammon, D.; Korenev, V. L.

    2006-03-01

    Spins of single charges in quantum dots are attractive for many quantum information and spintronic proposals. Scalable quantum information applications require the ability to entangle and operate on multiple spins in coupled quantum dots (CQDs). To further the understanding of these systems, we present detailed spectroscopic studies of InAs CQDs with control of the discrete electron or hole charging of the system. The optical spectrum reveals a pattern of energy anticrossings and crossings in the photoluminescence as a function of applied electric field. These features can be understood as a superposition of charge and spin configurations of the two dots and represent clear signatures of quantum mechanical coupling. The molecular resonance leading to these anticrossings is achieved at different electric fields for the optically excited (trion) states and the ground (hole) states allowing for the possibility of using the excited states for optically induced coupling of the qubits.

  4. Negative exchange interactions in coupled few-electron quantum dots

    NASA Astrophysics Data System (ADS)

    Deng, Kuangyin; Calderon-Vargas, F. A.; Mayhall, Nicholas J.; Barnes, Edwin

    2018-06-01

    It has been experimentally shown that negative exchange interactions can arise in a linear three-dot system when a two-electron double quantum dot is exchange coupled to a larger quantum dot containing on the order of one hundred electrons. The origin of this negative exchange can be traced to the larger quantum dot exhibiting a spin tripletlike rather than singletlike ground state. Here we show using a microscopic model based on the configuration interaction (CI) method that both tripletlike and singletlike ground states are realized depending on the number of electrons. In the case of only four electrons, a full CI calculation reveals that tripletlike ground states occur for sufficiently large dots. These results hold for symmetric and asymmetric quantum dots in both Si and GaAs, showing that negative exchange interactions are robust in few-electron double quantum dots and do not require large numbers of electrons.

  5. A reconfigurable gate architecture for Si/SiGe quantum dots

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

    Zajac, D. M.; Hazard, T. M.; Mi, X.

    2015-06-01

    We demonstrate a reconfigurable quantum dot gate architecture that incorporates two interchangeable transport channels. One channel is used to form quantum dots, and the other is used for charge sensing. The quantum dot transport channel can support either a single or a double quantum dot. We demonstrate few-electron occupation in a single quantum dot and extract charging energies as large as 6.6 meV. Magnetospectroscopy is used to measure valley splittings in the range of 35–70 μeV. By energizing two additional gates, we form a few-electron double quantum dot and demonstrate tunable tunnel coupling at the (1,0) to (0,1) interdot charge transition.

  6. 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.

  7. Higher-order spin and charge dynamics in a quantum dot-lead hybrid system.

    PubMed

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

    2017-09-22

    Understanding the dynamics of open quantum systems is important and challenging in basic physics and applications for quantum devices and quantum computing. Semiconductor quantum dots offer a good platform to explore the physics of open quantum systems because we can tune parameters including the coupling to the environment or leads. Here, we apply the fast single-shot measurement techniques from spin qubit experiments to explore the spin and charge dynamics due to tunnel coupling to a lead in a quantum dot-lead hybrid system. We experimentally observe both spin and charge time evolution via first- and second-order tunneling processes, and reveal the dynamics of the spin-flip through the intermediate state. These results enable and stimulate the exploration of spin dynamics in dot-lead hybrid systems, and may offer useful resources for spin manipulation and simulation of open quantum systems.

  8. First principles study of edge carboxylated graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Abdelsalam, Hazem; Elhaes, Hanan; Ibrahim, Medhat A.

    2018-05-01

    The structure stability and electronic properties of edge carboxylated hexagonal and triangular graphene quantum dots are investigated using density functional theory. The calculated binding energies show that the hexagonal clusters with armchair edges have the highest stability among all the quantum dots. The binding energy of carboxylated graphene quantum dots increases by increasing the number of carboxyl groups. Our study shows that the total dipole moment significantly increases by adding COOH with the highest value observed in triangular clusters. The edge states in triangular graphene quantum dots with zigzag edges produce completely different energy spectrum from other dots: (a) the energy gap in triangular zigzag is very small as compared to other clusters and (b) the highest occupied molecular orbital is localized at the edges which is in contrast to other clusters where it is distributed over the cluster surface. The enhanced reactivity and the controllable energy gap by shape and edge termination make graphene quantum dots ideal for various nanodevice applications such as sensors. The infrared spectra are presented to confirm the stability of the quantum dots.

  9. Optical Signatures of Coupled Quantum Dots

    DTIC Science & Technology

    2006-02-03

    Optical Signatures of Coupled Quantum Dots E. A. Stinaff,1 M. Scheibner,1 A. S . Bracker,1 I. V. Ponomarev,1 V. L. Korenev ,2 M. E. Ware,1 M. F. Doty,1...possibility of optically coupling quantum dots for application in quantum information processing. S emiconductor approaches to quantum information can...REPORTS 3 FEBRUARY 2006 VOL 311 SCIENCE www.sciencemag.org636 o n A ug us t 1 4, 2 00 7 w w w . s ci en ce m ag .o rg D ow nl oa de d fr om Report

  10. Theory of Charged Quantum Dot Molecules

    NASA Astrophysics Data System (ADS)

    Ponomarev, I. V.; Scheibner, M.; Stinaff, E. A.; Bracker, A. S.; Doty, M. F.; Ware, M. E.; Gammon, D.; Reinecke, T. L.; Korenev, V. L.

    2006-03-01

    Recent optical spectroscopy of excitonic molecules in coupled quantum dots (CQDs) tuned by electric field reveal a richer diversity in spectral line patterns than in their single quantum dot counterparts. We developed a theoretical model that allows us to classify energies and intensities of various PL transitions. In this approach the electric field induced resonance tunneling of the electron and hole states occurs at different biases due to the inherent asymmetry of CQDs. The truncated many-body basis configurations for each molecule are constructed from antisymmetrized products of single-particle states, where the electron occupies only one ground state level in single QD and the hole can occupy two lowest levels of CQD system. The Coulomb interaction between particles is treated with perturbation theory. As a result the observed PL spectral lines can be described with a small number of parameters. The theoretical predictions account well for recent experiments.

  11. Synthesis and characterization of surface-modified colloidal CdTe Quantum Dots

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

    Rajh, T.; Micic, O.I.; Nozik, A.J.

    1993-11-18

    The controlled synthesis of quantized colloidal CdTe nanocrystals (in aqueous solutions) with narrow size distributions and stabilized against rapid oxidation was achieved by capping the quantum dot particles with 3-mercapto-1,2-propanediol. Nanocrystals (i.e., quantum dots) with mean diameters of 20, 25, 35, and 40 A were produced. Optical absorption spectra showed strong excitonic peaks at the smallest size; the absorption coefficient was shown to follow an inverse cube dependence on particle diameter, while the extinction coefficient per particle remained constant. The quantum yield for photoluminescence increased with decreasing particle size and reached 20% at 20 A. The valence band edges ofmore » the CdTe quantum dots were determined by pulse radiolysis experiments (hole injection from oxidizing radicals); the bandgaps were estimated from pulse radiolysis data (redox potentials of hole and electron injecting radicals) and from the optical spectra. The dependence of the CdTe bandgap on quantum dot size was found to be much weaker than predicted by the effective mass approximation; this result is consistent with recently published theoretical calculations by several groups. 36 refs., 5 figs., 1 tab.« less

  12. Coulomb-coupled quantum-dot thermal transistors

    NASA Astrophysics Data System (ADS)

    Zhang, Yanchao; Yang, Zhimin; Zhang, Xin; Lin, Bihong; Lin, Guoxing; Chen, Jincan

    2018-04-01

    A quantum-dot thermal transistor consisting of three Coulomb-coupled quantum dots coupled to the respective electronic reservoirs by tunnel contacts is established. The heat flows through the collector and emitter can be controlled by the temperature of the base. It is found that a small change in the base heat flow can induce a large heat flow change in the collector and emitter. The huge amplification factor can be obtained by optimizing the Coulomb interaction between the collector and the emitter or by decreasing the tunneling rate at the base. The proposed quantum-dot thermal transistor may open up potential applications in low-temperature solid-state thermal circuits at the nanoscale.

  13. InAs Colloidal Quantum Dots Synthesis via Aminopnictogen Precursor Chemistry.

    PubMed

    Grigel, Valeriia; Dupont, Dorian; De Nolf, Kim; Hens, Zeger; Tessier, Mickael D

    2016-10-05

    Despite their various potential applications, InAs colloidal quantum dots have attracted considerably less attention than more classical II-VI materials because of their complex syntheses that require hazardous precursors. Recently, amino-phosphine has been introduced as a cheap, easy-to-use and efficient phosphorus precursor to synthesize InP quantum dots. Here, we use aminopnictogen precursors to implement a similar approach for synthesizing InAs quantum dots. We develop a two-step method based on the combination of aminoarsine as the arsenic precursor and aminophosphine as the reducing agent. This results in state-of-the-art InAs quantum dots with respect to the size dispersion and band-gap range. Moreover, we present shell coating procedures that lead to the formation of InAs/ZnS(e) core/shell quantum dots that emit in the infrared region. This innovative synthesis approach can greatly facilitate the research on InAs quantum dots and may lead to synthesis protocols for a wide range of III-V quantum dots.

  14. Intracellular distribution of nontargeted quantum dots after natural uptake and microinjection

    PubMed Central

    Damalakiene, Leona; Karabanovas, Vitalijus; Bagdonas, Saulius; Valius, Mindaugas; Rotomskis, Ricardas

    2013-01-01

    Background: The purpose of this study was to elucidate the mechanism of natural uptake of nonfunctionalized quantum dots in comparison with microinjected quantum dots by focusing on their time-dependent accumulation and intracellular localization in different cell lines. Methods: The accumulation dynamics of nontargeted CdSe/ZnS carboxyl-coated quantum dots (emission peak 625 nm) was analyzed in NIH3T3, MCF-7, and HepG2 cells by applying the methods of confocal and steady-state fluorescence spectroscopy. Intracellular colocalization of the quantum dots was investigated by staining with Lysotracker®. Results: The uptake of quantum dots into cells was dramatically reduced at a low temperature (4°C), indicating that the process is energy-dependent. The uptake kinetics and imaging of intracellular localization of quantum dots revealed three accumulation stages of carboxyl-coated quantum dots at 37°C, ie, a plateau stage, growth stage, and a saturation stage, which comprised four morphological phases: adherence to the cell membrane; formation of granulated clusters spread throughout the cytoplasm; localization of granulated clusters in the perinuclear region; and formation of multivesicular body-like structures and their redistribution in the cytoplasm. Diverse quantum dots containing intracellular vesicles in the range of approximately 0.5–8 μm in diameter were observed in the cytoplasm, but none were found in the nucleus. Vesicles containing quantum dots formed multivesicular body-like structures in NIH3T3 cells after 24 hours of incubation, which were Lysotracker-negative in serum-free medium and Lysotracker-positive in complete medium. The microinjected quantum dots remained uniformly distributed in the cytosol for at least 24 hours. Conclusion: Natural uptake of quantum dots in cells occurs through three accumulation stages via a mechanism requiring energy. The sharp contrast of the intracellular distribution after microinjection of quantum dots in comparison

  15. Array of nanoparticles coupling with quantum-dot: Lattice plasmon quantum features

    NASA Astrophysics Data System (ADS)

    Salmanogli, Ahmad; Gecim, H. Selcuk

    2018-06-01

    In this study, we analyze the interaction of lattice plasmon with quantum-dot in order to mainly examine the quantum features of the lattice plasmon containing the photonic/plasmonic properties. Despite optical properties of the localized plasmon, the lattice plasmon severely depends on the array geometry, which may influence its quantum features such as uncertainty and the second-order correlation function. To investigate this interaction, we consider a closed system containing an array of the plasmonic nanoparticles and quantum-dot. We analyze this system with full quantum theory by which the array electric far field is quantized and the strength coupling of the quantum-dot array is analytically calculated. Moreover, the system's dynamics are evaluated and studied via the Heisenberg-Langevin equations to attain the system optical modes. We also analytically examine the Purcell factor, which shows the effect of the lattice plasmon on the quantum-dot spontaneous emission. Finally, the lattice plasmon uncertainty and its time evolution of the second-order correlation function at different spatial points are examined. These parameters are dramatically affected by the retarded field effect of the array nanoparticles. We found a severe quantum fluctuation at points where the lattice plasmon occurs, suggesting that the lattice plasmon photons are correlated.

  16. Temperature independent infrared responsivity of a quantum dot quantum cascade photodetector

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

    Wang, Feng-Jiao; Zhuo, Ning; Liu, Shu-Man, E-mail: liusm@semi.ac.cn

    2016-06-20

    We demonstrate a quantum dot quantum cascade photodetector with a hybrid active region of InAs quantum dots and an InGaAs quantum well, which exhibited a temperature independent response at 4.5 μm. The normal incident responsivity reached 10.3 mA/W at 120 K and maintained a value of 9 mA/W up to 260 K. It exhibited a specific detectivity above 10{sup 11} cm Hz{sup 1/2} W{sup −1} at 77 K, which remained at 10{sup 8} cm Hz{sup 1/2} W{sup −1} at 260 K. We ascribe the device's good thermal stability of infrared response to the three-dimensional quantum confinement of the InAs quantum dots incorporated in the active region.

  17. Tuning Single Quantum Dot Emission with a Micromirror.

    PubMed

    Yuan, Gangcheng; Gómez, Daniel; Kirkwood, Nicholas; Mulvaney, Paul

    2018-02-14

    The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved. Here, we use a movable gold micromirror to determine both the quantum yield of the bright state and the orientation of the excited state dipole of single quantum dots. We observe that the quantum yield of the bright state is close to unity for these single QDs. Furthermore, we also study the effect of a micromirror on blinking, and then evaluate excitation efficiency, biexciton quantum yield, and detection efficiency. The mirror does not modify the off-time statistics, but it does change the density of optical states available to the quantum dot and hence the on times. The duration of the on times can be lengthened due to an increase in the radiative recombination rate.

  18. Quantum control and process tomography of a semiconductor quantum dot hybrid qubit.

    PubMed

    Kim, Dohun; Shi, Zhan; Simmons, C B; Ward, D R; Prance, J R; Koh, Teck Seng; Gamble, John King; Savage, D E; Lagally, M G; Friesen, Mark; Coppersmith, S N; Eriksson, Mark A

    2014-07-03

    The similarities between gated quantum dots and the transistors in modern microelectronics--in fabrication methods, physical structure and voltage scales for manipulation--have led to great interest in the development of quantum bits (qubits) in semiconductor quantum dots. Although quantum dot spin qubits have demonstrated long coherence times, their manipulation is often slower than desired for important future applications, such as factoring. Furthermore, scalability and manufacturability are enhanced when qubits are as simple as possible. Previous work has increased the speed of spin qubit rotations by making use of integrated micromagnets, dynamic pumping of nuclear spins or the addition of a third quantum dot. Here we demonstrate a qubit that is a hybrid of spin and charge. It is simple, requiring neither nuclear-state preparation nor micromagnets. Unlike previous double-dot qubits, the hybrid qubit enables fast rotations about two axes of the Bloch sphere. We demonstrate full control on the Bloch sphere with π-rotation times of less than 100 picoseconds in two orthogonal directions, which is more than an order of magnitude faster than any other double-dot qubit. The speed arises from the qubit's charge-like characteristics, and its spin-like features result in resistance to decoherence over a wide range of gate voltages. We achieve full process tomography in our electrically controlled semiconductor quantum dot qubit, extracting high fidelities of 85 per cent for X rotations (transitions between qubit states) and 94 per cent for Z rotations (phase accumulation between qubit states).

  19. Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control.

    PubMed

    Sun, Liangfeng; Choi, Joshua J; Stachnik, David; Bartnik, Adam C; Hyun, Byung-Ryool; Malliaras, George G; Hanrath, Tobias; Wise, Frank W

    2012-05-06

    Infrared light-emitting diodes are currently fabricated from direct-gap semiconductors using epitaxy, which makes them expensive and difficult to integrate with other materials. Light-emitting diodes based on colloidal semiconductor quantum dots, on the other hand, can be solution-processed at low cost, and can be directly integrated with silicon. However, so far, exciton dissociation and recombination have not been well controlled in these devices, and this has limited their performance. Here, by tuning the distance between adjacent PbS quantum dots, we fabricate thin-film quantum-dot light-emitting diodes that operate at infrared wavelengths with radiances (6.4 W sr(-1) m(-2)) eight times higher and external quantum efficiencies (2.0%) two times higher than the highest values previously reported. The distance between adjacent dots is tuned over a range of 1.3 nm by varying the lengths of the linker molecules from three to eight CH(2) groups, which allows us to achieve the optimum balance between charge injection and radiative exciton recombination. The electroluminescent powers of the best devices are comparable to those produced by commercial InGaAsP light-emitting diodes. By varying the size of the quantum dots, we can tune the emission wavelengths between 800 and 1,850 nm.

  20. Quantum dots and nanocomposites.

    PubMed

    Mansur, Herman Sander

    2010-01-01

    Quantum dots (QDs), also known as semiconducting nanoparticles, are promising zero-dimensional advanced materials because of their nanoscale size and because they can be engineered to suit particular applications such as nonlinear optical devices (NLO), electro-optical devices, and computing applications. QDs can be joined to polymers in order to produce nanocomposites which can be considered a scientific revolution of the 21st century. One of the fastest moving and most exciting interfaces of nanotechnology is the use of QDs in medicine, cell and molecular biology. Recent advances in nanomaterials have produced a new class of markers and probes by conjugating semiconductor QDs with biomolecules that have affinities for binding with selected biological structures. The nanoscale of QDs ensures that they do not scatter light at visible or longer wavelengths, which is important in order to minimize optical losses in practical applications. Moreover, at this scale, quantum confinement and surface effects become very important and therefore manipulation of the dot diameter or modification of its surface allows the properties of the dot to be controlled. Quantum confinement affects the absorption and emission of photons from the dot. Thus, the absorption edge of a material can be tuned by control of the particle size. This paper reviews developments in the myriad of possibilities for the use of semiconductor QDs associated with molecules producing novel hybrid nanocomposite systems for nanomedicine and bioengineering applications.

  1. 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.

  2. 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

  3. 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

  4. Photoconductive gain and quantum efficiency of remotely doped Ge/Si quantum dot photodetectors

    NASA Astrophysics Data System (ADS)

    Yakimov, A. I.; Kirienko, V. V.; Armbrister, V. A.; Bloshkin, A. A.; Dvurechenskii, A. V.; Shklyaev, A. A.

    2016-10-01

    We study the effect of quantum dot charging on the mid-infrared photocurrent, optical gain, hole capture probability, and absorption quantum efficiency in remotely delta-doped Ge/Si quantum dot photodetectors. The dot occupation with holes is controlled by varying dot and doping densities. From our investigations of samples doped to contain from about one to nine holes per dot we observe an over 10 times gain enhancement and similar suppression of the hole capture probability with increased carrier population. The data are explained by quenching the capture process and increasing the photoexcited hole lifetime due to formation of the repulsive Coulomb potential of the extra holes inside the quantum dots. The normal incidence quantum efficiency is found to be strongly asymmetric with respect to applied bias polarity. Based on the polarization-dependent absorption measurements it is concluded that, at a positive voltage, when holes move toward the nearest δ-doping plane, photocurrent is originated from the bound-to-continuum transitions of holes between the ground state confined in Ge dots and the extended states of the Si matrix. At a negative bias polarity, the photoresponse is caused by optical excitation to a quasibound state confined near the valence band edge with subsequent tunneling to the Si valence band. In a latter case, the possibility of hole transfer into continuum states arises from the electric field generated by charge distributed between quantum dots and delta-doping planes.

  5. Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

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

    Xu, Xingsheng, E-mail: xsxu@semi.ac.cn

    For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreasedmore » with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.« less

  6. Optical Spectroscopy Of Charged Quantum Dot Molecules

    NASA Astrophysics Data System (ADS)

    Scheibner, M.; Bracker, A. S.; Stinaff, E. A.; Doty, M. F.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

    2007-04-01

    Coupling between two closely spaced quantum dots is observed by means of photoluminescence spectroscopy. Hole coupling is realized by rational crystal growth and heterostructure design. We identify molecular resonances of different excitonic charge states, including the important case of a doubly charged quantum dot molecule.

  7. Interaction of Water-Soluble CdTe Quantum Dots with Bovine Serum Albumin

    PubMed Central

    2011-01-01

    Semiconductor nanoparticles (quantum dots) are promising fluorescent markers, but it is very little known about interaction of quantum dots with biological molecules. In this study, interaction of CdTe quantum dots coated with thioglycolic acid (TGA) with bovine serum albumin was investigated. Steady state spectroscopy, atomic force microscopy, electron microscopy and dynamic light scattering methods were used. It was explored how bovine serum albumin affects stability and spectral properties of quantum dots in aqueous media. CdTe–TGA quantum dots in aqueous solution appeared to be not stable and precipitated. Interaction with bovine serum albumin significantly enhanced stability and photoluminescence quantum yield of quantum dots and prevented quantum dots from aggregating. PMID:27502633

  8. Four-Wave Mixing Spectroscopy of Quantum Dot Molecules

    NASA Astrophysics Data System (ADS)

    Sitek, A.; Machnikowski, P.

    2007-08-01

    We study theoretically the nonlinear four-wave mixing response of an ensemble of coupled pairs of quantum dots (quantum dot molecules). We discuss the shape of the echo signal depending on the parameters of the ensemble: the statistics of transition energies and the degree of size correlations between the dots forming the molecules.

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

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

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

    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.

  10. 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.

  11. Influence of quantum dot's quantum yield to chemiluminescent resonance energy transfer.

    PubMed

    Wang, Hai-Qiao; Li, Yong-Qiang; Wang, Jian-Hao; Xu, Qiao; Li, Xiu-Qing; Zhao, Yuan-Di

    2008-03-03

    The resonance energy transfer between chemiluminescence donor (luminol-H2O2 system) and quantum dots (QDs, emission at 593 nm) acceptors (CRET) was investigated. The resonance energy transfer efficiencies were compared while the oil soluble QDs, water soluble QDs (modified with thioglycolate) and QD-HRP conjugates were used as acceptor. The fluorescence of QD can be observed in the three cases, indicating that the CRET occurs while QD acceptor in different status was used. The highest CRET efficiency (10.7%) was obtained in the case of oil soluble QDs, and the lowest CRET efficiency (2.7%) was observed in the QD-HRP conjugates case. This result is coincident with the quantum yields of the acceptors (18.3% and 0.4%). The same result was observed in another similar set of experiment, in which the amphiphilic polymer modified QDs (emission at 675 nm) were used. It suggests that the quantum yield of the QD in different status is the crucial factor to the CRET efficiency. Furthermore, the multiplexed CRET between luminol donor and three different sizes QD acceptors was observed simultaneously. This work will offer useful support for improving the CRET studies based on quantum dots.

  12. Integrated photonics using colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Menon, Vinod M.; Husaini, Saima; Okoye, Nicky; Valappil, Nikesh V.

    2009-11-01

    Integrated photonic devices were realized using colloidal quantum dot composites such as flexible microcavity laser, microdisk emitters and integrated active-passive waveguides. The microcavity laser structure was realized using spin coating and consisted of an all-polymer distributed Bragg reflector with a poly-vinyl carbazole cavity layer embedded with InGaP/ZnS colloidal quantum dots. These microcavities can be peeled off the substrate yielding a flexible structure that can conform to any shape and whose emission spectra can be mechanically tuned. Planar photonic devices consisting of vertically coupled microring resonators, microdisk emitters, active-passive integrated waveguide structures and coupled active microdisk resonators were realized using soft lithography, photo-lithography, and electron beam lithography, respectively. The gain medium in all these devices was a composite consisting of quantum dots embedded in SU8 matrix. Finally, the effect of the host matrix on the optical properties of the quantum dots using results of steady-state and time-resolved luminescence measurements was determined. In addition to their specific functionalities, these novel device demonstrations and their development present a low-cost alternative to the traditional photonic device fabrication techniques.

  13. Photovoltaic Performance of a Nanowire/Quantum Dot Hybrid Nanostructure Array Solar Cell.

    PubMed

    Wu, Yao; Yan, Xin; Zhang, Xia; Ren, Xiaomin

    2018-02-23

    An innovative solar cell based on a nanowire/quantum dot hybrid nanostructure array is designed and analyzed. By growing multilayer InAs quantum dots on the sidewalls of GaAs nanowires, not only the absorption spectrum of GaAs nanowires is extended by quantum dots but also the light absorption of quantum dots is dramatically enhanced due to the light-trapping effect of the nanowire array. By incorporating five layers of InAs quantum dots into a 500-nm high-GaAs nanowire array, the power conversion efficiency enhancement induced by the quantum dots is six times higher than the power conversion efficiency enhancement in thin-film solar cells which contain the same amount of quantum dots, indicating that the nanowire array structure can benefit the photovoltaic performance of quantum dot solar cells.

  14. Photovoltaic Performance of a Nanowire/Quantum Dot Hybrid Nanostructure Array Solar Cell

    NASA Astrophysics Data System (ADS)

    Wu, Yao; Yan, Xin; Zhang, Xia; Ren, Xiaomin

    2018-02-01

    An innovative solar cell based on a nanowire/quantum dot hybrid nanostructure array is designed and analyzed. By growing multilayer InAs quantum dots on the sidewalls of GaAs nanowires, not only the absorption spectrum of GaAs nanowires is extended by quantum dots but also the light absorption of quantum dots is dramatically enhanced due to the light-trapping effect of the nanowire array. By incorporating five layers of InAs quantum dots into a 500-nm high-GaAs nanowire array, the power conversion efficiency enhancement induced by the quantum dots is six times higher than the power conversion efficiency enhancement in thin-film solar cells which contain the same amount of quantum dots, indicating that the nanowire array structure can benefit the photovoltaic performance of quantum dot solar cells.

  15. Orientation-dependent imaging of electronically excited quantum dots

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc; Goings, Joshua J.; Nguyen, Huy A.; Lyding, Joseph; Li, Xiaosong; Gruebele, Martin

    2018-02-01

    We previously demonstrated that we can image electronic excitations of quantum dots by single-molecule absorption scanning tunneling microscopy (SMA-STM). With this technique, a modulated laser beam periodically saturates an electronic transition of a single nanoparticle, and the resulting tunneling current modulation ΔI(x0, y0) maps out the SMA-STM image. In this paper, we first derive the basic theory to calculate ΔI(x0, y0) in the one-electron approximation. For near-resonant tunneling through an empty orbital "i" of the nanostructure, the SMA-STM signal is approximately proportional to the electron density |φi) (x0,y0)|quantum dots on the surface and roll them, thus imaging excited state electronic structure of a single quantum dot at different orientations. We use density functional theory to model ODMs at various orientations, for qualitative comparison with the SMA-STM experiment. The model demonstrates that our experimentally observed signal monitors excited states, localized by defects near the surface of an individual quantum dot. The sub-nanometer super-resolution imaging technique demonstrated here could become useful for mapping out the three-dimensional structure of excited states localized by defects within nanomaterials.

  16. Orientation-dependent imaging of electronically excited quantum dots.

    PubMed

    Nguyen, Duc; Goings, Joshua J; Nguyen, Huy A; Lyding, Joseph; Li, Xiaosong; Gruebele, Martin

    2018-02-14

    We previously demonstrated that we can image electronic excitations of quantum dots by single-molecule absorption scanning tunneling microscopy (SMA-STM). With this technique, a modulated laser beam periodically saturates an electronic transition of a single nanoparticle, and the resulting tunneling current modulation ΔI(x 0 , y 0 ) maps out the SMA-STM image. In this paper, we first derive the basic theory to calculate ΔI(x 0 , y 0 ) in the one-electron approximation. For near-resonant tunneling through an empty orbital "i" of the nanostructure, the SMA-STM signal is approximately proportional to the electron density φ i x 0 ,y 0 2 of the excited orbital in the tunneling region. Thus, the SMA-STM signal is approximated by an orbital density map (ODM) of the resonantly excited orbital at energy E i . The situation is more complex for correlated electron motion, but either way a slice through the excited electronic state structure in the tunneling region is imaged. We then show experimentally that we can nudge quantum dots on the surface and roll them, thus imaging excited state electronic structure of a single quantum dot at different orientations. We use density functional theory to model ODMs at various orientations, for qualitative comparison with the SMA-STM experiment. The model demonstrates that our experimentally observed signal monitors excited states, localized by defects near the surface of an individual quantum dot. The sub-nanometer super-resolution imaging technique demonstrated here could become useful for mapping out the three-dimensional structure of excited states localized by defects within nanomaterials.

  17. 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.

  18. Fermionic entanglement via quantum walks in quantum dots

    NASA Astrophysics Data System (ADS)

    Melnikov, Alexey A.; Fedichkin, Leonid E.

    2018-02-01

    Quantum walks are fundamentally different from random walks due to the quantum superposition property of quantum objects. Quantum walk process was found to be very useful for quantum information and quantum computation applications. In this paper we demonstrate how to use quantum walks as a tool to generate high-dimensional two-particle fermionic entanglement. The generated entanglement can survive longer in the presence of depolorazing noise due to the periodicity of quantum walk dynamics. The possibility to create two distinguishable qudits in a system of tunnel-coupled semiconductor quantum dots is discussed.

  19. Synthesis and Characterization of Mercaptoacetic Acid Capped Cadmium Sulphide Quantum Dots.

    PubMed

    Wageh, S; Maize, Mai; Donia, A M; Al-Ghamdi, Ahmed A; Umar, Ahmad

    2015-12-01

    This paper reports the facile synthesis and detailed characterization of mercaptoacetic acid capped cadmium sulphide (CdS) quantum dots using various cadmium precursors. The mercaptoacetic acid capped CdS quantum dots were prepared by facile and simple wet chemical method and characterized by several techniques such as energy dispersive spectroscopy (EDS), X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, UV-vis. spectroscopy, photoluminescence spectroscopy, high-resolution transmission microscopy (HRTEM) and thremogravimetric analysis. The EDS studies revealed that the prepared quantum dots possess higher atomic percentage of sulfur compared to cadmium due to the coordination of thiolate to the quantum dots surfaces. The X-ray and absorption analyses exhibited that the size of quantum dots prepared by cadmium acetate is larger than the quantum dots prepared by cadmium chloride and cadmium nitrate. The increase in size can be attributed to the low stability constant of cadmium acetate in comparison with cadmium chloride and cadmium nitrate. The FTIR and thermogravimetric analysis showed that the nature of capping molecule on the surface of quantum dots are different depending on the cadmium precursors which affect the emission from CdS quantum dots. Photoemission spectroscopy revealed that the emission of quantum dots prepared by cadmium acetate has high intensity band edge emission along with low intensity trapping state emission. However the CdS quantum dots prepared by cadmium chloride and cadmium nitrate produced only trapping state emissions.

  20. Highly sensitive humidity sensing properties of carbon quantum dots films

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

    Zhang, Xing; Ming, Hai; Liu, Ruihua

    2013-02-15

    Graphical abstract: Display Omitted Highlights: ► A humidity sensing device was fabricated based on carbon quantum dots (CQDs) films. ► The conductivity of the CQDs films shows a linear and rapid response to atmosphere humidity. ► The humidity sensing property was due to the hydrogen bonds between the functional groups on CQDs. -- Abstract: We reported the fabrication of a humidity sensing device based on carbon quantum dots (CQDs) film. The conductivity of the CQDs film has a linear and rapid response to relative humidity, providing the opportunity for the fabrication of humidity sensing devices. The mechanism of our humiditymore » sensor was proposed to be the formation of hydrogen bonds between carbon quantum dots and water molecules in the humidity environment, which significantly promote the electrons migration. In a control experiment, this hypothesis was confirmed by comparing the humidity sensitivity of candle soot (i.e. carbon nanoparticles) with and without oxygen containing groups on the surfaces.« less

  1. Recent Progress Towards Quantum Dot Solar Cells with Enhanced Optical Absorption.

    PubMed

    Zheng, Zerui; Ji, Haining; Yu, Peng; Wang, Zhiming

    2016-12-01

    Quantum dot solar cells, as a promising candidate for the next generation solar cell technology, have received tremendous attention in the last 10 years. Some recent developments in epitaxy growth and device structures have opened up new avenues for practical quantum dot solar cells. Unfortunately, the performance of quantum dot solar cells is often plagued by marginal photon absorption. In this review, we focus on the recent progress made in enhancing optical absorption in quantum dot solar cells, including optimization of quantum dot growth, improving the solar cells structure, and engineering light trapping techniques.

  2. Nanowire–quantum-dot lasers on flexible membranes

    NASA Astrophysics Data System (ADS)

    Tatebayashi, Jun; Ota, Yasutomo; Ishida, Satomi; Nishioka, Masao; Iwamoto, Satoshi; Arakawa, Yasuhiko

    2018-06-01

    We demonstrate lasing in a single nanowire with quantum dots as an active medium embedded on poly(dimethylsiloxane) membranes towards application in nanowire-based flexible nanophotonic devices. Nanowire laser structures with 50 quantum dots are grown on patterned GaAs(111)B substrates and then transferred from the as-grown substrates on poly(dimethylsiloxane) transparent flexible organosilicon membranes, by means of spin-casting and curing processes. We observe lasing oscillation in the transferred single nanowire cavity with quantum dots at 1.425 eV with a threshold pump pulse fluence of ∼876 µJ/cm2, which enables the realization of high-performance multifunctional NW-based flexible photonic devices.

  3. 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

  4. 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.

  5. Relaxation of ferroelectric states in 2D distributions of quantum dots: EELS simulation

    NASA Astrophysics Data System (ADS)

    Cortés, C. M.; Meza-Montes, L.; Moctezuma, R. E.; Carrillo, J. L.

    2016-06-01

    The relaxation time of collective electronic states in a 2D distribution of quantum dots is investigated theoretically by simulating EELS experiments. From the numerical calculation of the probability of energy loss of an electron beam, traveling parallel to the distribution, it is possible to estimate the damping time of ferroelectric-like states. We generate this collective response of the distribution by introducing a mean field interaction among the quantum dots, and then, the model is extended incorporating effects of long-range correlations through a Bragg-Williams approximation. The behavior of the dielectric function, the energy loss function, and the relaxation time of ferroelectric-like states is then investigated as a function of the temperature of the distribution and the damping constant of the electronic states in the single quantum dots. The robustness of the trends and tendencies of our results indicate that this scheme of analysis can guide experimentalists to develop tailored quantum dots distributions for specific applications.

  6. Computation of energy states of hydrogenic quantum dot with two-electrons

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

    Yakar, Y., E-mail: yuyakar@yahoo.com; Özmen, A., E-mail: aozmen@selcuk.edu.tr; Çakır, B., E-mail: bcakir@selcuk.edu.tr

    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.

  7. In situ electron-beam polymerization stabilized quantum dot micelles.

    PubMed

    Travert-Branger, Nathalie; Dubois, Fabien; Renault, Jean-Philippe; Pin, Serge; Mahler, Benoit; Gravel, Edmond; Dubertret, Benoit; Doris, Eric

    2011-04-19

    A polymerizable amphiphile polymer containing PEG was synthesized and used to encapsulate quantum dots in micelles. The quantum dot micelles were then polymerized using a "clean" electron beam process that did not require any post-irradiation purification. Fluorescence spectroscopy revealed that the polymerized micelles provided an organic coating that preserved the quantum dot fluorescence better than nonpolymerized micelles, even under harsh conditions. © 2011 American Chemical Society

  8. Wavelength-tunable entangled photons from silicon-integrated III-V quantum dots.

    PubMed

    Chen, Yan; Zhang, Jiaxiang; Zopf, Michael; Jung, Kyubong; Zhang, Yang; Keil, Robert; Ding, Fei; Schmidt, Oliver G

    2016-01-27

    Many of the quantum information applications rely on indistinguishable sources of polarization-entangled photons. Semiconductor quantum dots are among the leading candidates for a deterministic entangled photon source; however, due to their random growth nature, it is impossible to find different quantum dots emitting entangled photons with identical wavelengths. The wavelength tunability has therefore become a fundamental requirement for a number of envisioned applications, for example, nesting different dots via the entanglement swapping and interfacing dots with cavities/atoms. Here we report the generation of wavelength-tunable entangled photons from on-chip integrated InAs/GaAs quantum dots. With a novel anisotropic strain engineering technique based on PMN-PT/silicon micro-electromechanical system, we can recover the quantum dot electronic symmetry at different exciton emission wavelengths. Together with a footprint of several hundred microns, our device facilitates the scalable integration of indistinguishable entangled photon sources on-chip, and therefore removes a major stumbling block to the quantum-dot-based solid-state quantum information platforms.

  9. Field-emission from quantum-dot-in-perovskite solids

    PubMed Central

    García de Arquer, F. Pelayo; Gong, Xiwen; Sabatini, Randy P.; Liu, Min; Kim, Gi-Hwan; Sutherland, Brandon R.; Voznyy, Oleksandr; Xu, Jixian; Pang, Yuangjie; Hoogland, Sjoerd; Sinton, David; Sargent, Edward

    2017-01-01

    Quantum dot and well architectures are attractive for infrared optoelectronics, and have led to the realization of compelling light sensors. However, they require well-defined passivated interfaces and rapid charge transport, and this has restricted their efficient implementation to costly vacuum-epitaxially grown semiconductors. Here we report solution-processed, sensitive infrared field-emission photodetectors. Using quantum-dots-in-perovskite, we demonstrate the extraction of photocarriers via field emission, followed by the recirculation of photogenerated carriers. We use in operando ultrafast transient spectroscopy to sense bias-dependent photoemission and recapture in field-emission devices. The resultant photodiodes exploit the superior electronic transport properties of organometal halide perovskites, the quantum-size-tuned absorption of the colloidal quantum dots and their matched interface. These field-emission quantum-dot-in-perovskite photodiodes extend the perovskite response into the short-wavelength infrared and achieve measured specific detectivities that exceed 1012 Jones. The results pave the way towards novel functional photonic devices with applications in photovoltaics and light emission. PMID:28337981

  10. Design strategy for terahertz quantum dot cascade lasers.

    PubMed

    Burnett, Benjamin A; Williams, Benjamin S

    2016-10-31

    The development of quantum dot cascade lasers has been proposed as a path to obtain terahertz semiconductor lasers that operate at room temperature. The expected benefit is due to the suppression of nonradiative electron-phonon scattering and reduced dephasing that accompanies discretization of the electronic energy spectrum. We present numerical modeling which predicts that simple scaling of conventional quantum well based designs to the quantum dot regime will likely fail due to electrical instability associated with high-field domain formation. A design strategy adapted for terahertz quantum dot cascade lasers is presented which avoids these problems. Counterintuitively, this involves the resonant depopulation of the laser's upper state with the LO-phonon energy. The strategy is tested theoretically using a density matrix model of transport and gain, which predicts sufficient gain for lasing at stable operating points. Finally, the effect of quantum dot size inhomogeneity on the optical lineshape is explored, suggesting that the design concept is robust to a moderate amount of statistical variation.

  11. Cavity-Mediated Coherent Coupling between Distant Quantum Dots

    NASA Astrophysics Data System (ADS)

    Nicolí, Giorgio; Ferguson, Michael Sven; Rössler, Clemens; Wolfertz, Alexander; Blatter, Gianni; Ihn, Thomas; Ensslin, Klaus; Reichl, Christian; Wegscheider, Werner; Zilberberg, Oded

    2018-06-01

    Scalable architectures for quantum information technologies require one to selectively couple long-distance qubits while suppressing environmental noise and cross talk. In semiconductor materials, the coherent coupling of a single spin on a quantum dot to a cavity hosting fermionic modes offers a new solution to this technological challenge. Here, we demonstrate coherent coupling between two spatially separated quantum dots using an electronic cavity design that takes advantage of whispering-gallery modes in a two-dimensional electron gas. The cavity-mediated, long-distance coupling effectively minimizes undesirable direct cross talk between the dots and defines a scalable architecture for all-electronic semiconductor-based quantum information processing.

  12. [Effect of quantum dots CdSe/ZnS's concentration on its fluorescence].

    PubMed

    Jin, Min; Huang, Yu-hua; Luo, Ji-xiang

    2015-02-01

    The authors measured the absorption and the fluorescence spectra of the quantum dots CdSe/ZnS with 4 nm in size at different concentration with the use of the UV-Vis absorption spectroscopy and fluorescence spectrometer. The effect of quantum dots CdSe/ZnS's concentration on its fluorescence was especially studied and its physical mechanism was analyzed. It was observed that the optimal concentration of the quantum dots CdSe/ZnS for fluorescence is 2 micromole x L(-1). When the quantum dot's concentration is over 2 micromol x L(-1), the fluorescence is decreased with the increase in the concentration. While the quantum dot's concentration is less than 2 micromol x L(-1), the fluorescence is decreased with the decrease in the concentration. There are two main reasons: (1) fluorescence quenching and 2) the competition between absorption and fluorescence. When the quantum dot's concentration is over 2 micromol x L(-1), the distance between quantum dots is so close that the fluorescence quenching is induced. The closer the distance between quantum dots is, the more serious the fluorescence quenching is induced. Also, in this case, the absorption is so large that some of the quantum dots can not be excited because the incident light can not pass through the whole sample. As a result, the fluorescence is decreased with the increase in the quantum dot's concentration. As the quantum dot's concentration is below 2 micromol x L(-1), the distance between quantum dots is far enough that no more fluorescence quenching is induced. In this case, the fluorescence is determined by the particle number per unit volume. More particle number per unit volume produces more fluorescence. Therefore, the fluorescence is decreased with the decrease in the quantum dot's concentration.

  13. 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.

  14. Quantum dot-linked immunosorbent assay (QLISA) using orientation-directed antibodies.

    PubMed

    Suzuki, Miho; Udaka, Hikari; Fukuda, Takeshi

    2017-09-05

    An approach similar to the enzyme-linked immunosorbent assay (ELISA), with the advantage of saving time and effort but exhibiting high performance, was developed using orientation-directed half-part antibodies immobilized on CdSe/ZnS quantum dots. ELISA is a widely accepted assay used to detect the presence of a target substance. However, it takes time to quantify the target with specificity and sensitivity owing to signal amplification. In this study, CdSe/ZnS quantum dots are introduced as bright and photobleaching-tolerant fluorescent materials. Since hydrophilic surface coating of quantum dots rendered biocompatibility and functional groups for chemical reactions, the quantum dots were modified with half-sized antibodies after partial reduction. The half-sized antibody could be bound to a quantum dot through a unique thiol site to properly display the recognition domain for the core process of ELISA, which is an antigen-antibody interaction. The reducing conditions were investigated to generate efficient conjugates of quantum dots and half-sized antibodies. This was applied to IL-6 detection, as the quantification of IL-6 is significant owing to its close relationships with various biomedical phenomena that cause different diseases. An ELISA-like assay with CdSe/ZnS quantum dot institution (QLISA; Quantum dot-linked immunosorbent assay) was developed to detect 0.05ng/mL IL-6, which makes it sufficiently sensitive as an immunosorbent assay. Copyright © 2017 Elsevier B.V. All rights reserved.

  15. Growing High-Quality InAs Quantum Dots for Infrared Lasers

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Uhl, David

    2004-01-01

    An improved method of growing high-quality InAs quantum dots embedded in lattice-matched InGaAs quantum wells on InP substrates has been developed. InAs/InGaAs/InP quantum dot semiconductor lasers fabricated by this method are capable of operating at room temperature at wavelengths greater than or equal to 1.8 mm. Previously, InAs quantum dot lasers based on InP substrates have been reported only at low temperature of 77 K at a wavelength of 1.9 micrometers. In the present method, as in the prior method, one utilizes metalorganic vapor phase epitaxy to grow the aforementioned semiconductor structures. The development of the present method was prompted in part by the observation that when InAs quantum dots are deposited on an InGaAs layer, some of the InAs in the InGaAs layer becomes segregated from the layer and contributes to the formation of the InAs quantum dots. As a result, the quantum dots become highly nonuniform; some even exceed a critical thickness, beyond which they relax. In the present method, one covers the InGaAs layer with a thin layer of GaAs before depositing the InAs quantum dots. The purpose and effect of this thin GaAs layer is to suppress the segregation of InAs from the InGaAs layer, thereby enabling the InAs quantum dots to become nearly uniform (see figure). Devices fabricated by this method have shown near-room-temperature performance.

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

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

    Pozner, R.; Lifshitz, E.; Solid State Institute, Technion-Israel Institute of Technology, Haifa 32000

    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. Consideringmore » realistic microscopic parameters, our quantum-classical theoretical treatment of the TQD reveals the characteristics of the NVM.« less

  17. Vacuum-induced coherence in quantum dot systems

    NASA Astrophysics Data System (ADS)

    Sitek, Anna; Machnikowski, Paweł

    2012-11-01

    We present a theoretical study of vacuum-induced coherence in a pair of vertically stacked semiconductor quantum dots. The process consists in a coherent excitation transfer from a single-exciton state localized in one dot to a delocalized state in which the exciton occupation gets trapped. We study the influence of the factors characteristic of quantum dot systems (as opposed to natural atoms): energy mismatch, coupling between the single-exciton states localized in different dots, and different and nonparallel dipoles due to sub-band mixing, as well as coupling to phonons. We show that the destructive effect of the energy mismatch can be overcome by an appropriate interplay of the dipole moments and coupling between the dots which allows one to observe the trapping effect even in a structure with technologically realistic energy splitting of the order of milli-electron volts. We also analyze the impact of phonon dynamics on the occupation trapping and show that phonon effects are suppressed in a certain range of system parameters. This analysis shows that the vacuum-induced coherence effect and the associated long-living trapped excitonic population can be achieved in quantum dots.

  18. Patterned mist deposition of tri-colour CdSe/ZnS quantum dot films toward RGB LED devices

    NASA Astrophysics Data System (ADS)

    Pickering, S.; Kshirsagar, A.; Ruzyllo, J.; Xu, J.

    2012-06-01

    In this experiment a technique of mist deposition was explored as a way to form patterned ultra-thin-films of CdSe/ZnS core/shell nanocrystalline quantum dots using colloidal solutions. The objective of this study was to investigate the feasibility of mist deposition as a patterning method for creating multicolour quantum dot light emitting diodes. Mist deposition was used to create three rows of quantum dot light emitting diodes on a single device with each row having a separate colour. The colours chosen were red, green and yellow with corresponding peak wavelengths of 620 nm, 558 nm, and 587 nm. The results obtained from this experiment show that it is possible to create multicolour devices on a single substrate. The peak brightnesses obtained in this experiment for the red, green, and yellow were 508 cd/m, 507 cd/m, and 665 cd/m, respectively. The similar LED brightness is important in display technologies using colloidal quantum dots in a precursor solution to ensure one colour does not dominate the emitted spectrum. Results obtained in-terms of brightness were superior to those achieved with inkjet deposition. This study has shown that mist deposition is a viable method for patterned deposition applied to quantum dot light emitting diode display technologies.

  19. Optically Driven Spin Based Quantum Dots for Quantum Computing - Research Area 6 Physics 6.3.2

    DTIC Science & Technology

    2015-12-15

    quantum dots (SAQD) in Schottky diodes . Based on spins in these dots, a scalable architecture has been proposed [Adv. in Physics, 59, 703 (2010)] by us...housed in two coupled quantum dots with tunneling between them, as described above, may not be scalable but can serve as a node in a quantum network. The... tunneling -coupled two-electron spin ground states in the vertically coupled quantum dots for “universal computation” two spin qubits within the universe of

  20. Transport properties of a quantum dot and a quantum ring in series

    NASA Astrophysics Data System (ADS)

    Seo, Minky; Chung, Yunchul

    2018-01-01

    The decoherence mechanism of an electron interferometer is studied by using a serial quantum dot and ring device. By coupling a quantum dot to a quantum ring (closed-loop electron interferometer), we were able to observe both Coulomb oscillations and Aharonov-Bohm interference simultaneously. The coupled device behaves like an ordinary double quantum dot at zero magnetic field while the conductance of the Coulomb blockade peak is modulated by the electron interference at finite magnetic fields. By injecting one electron at a time (by exploiting the sequential tunneling of a quantum dot) into the interferometer, we were able to study the visibility of the electron interference at non-zero bias voltage. The visibility was found to decay rapidly as the electron energy was increased, which was consistent with the recently reported result for an electron interferometer. However, the lobe pattern and the sudden phase jump became less prominent. These results imply that the lobe pattern and the phase jump in an electron interferometer may be due to electron interactions inside the interferometer, as is predicted by the theory.

  1. Downconversion quantum interface for a single quantum dot spin and 1550-nm single-photon channel.

    PubMed

    Pelc, Jason S; Yu, Leo; De Greve, Kristiaan; McMahon, Peter L; Natarajan, Chandra M; Esfandyarpour, Vahid; Maier, Sebastian; Schneider, Christian; Kamp, Martin; Höfling, Sven; Hadfield, Robert H; Forchel, Alfred; Yamamoto, Yoshihisa; Fejer, M M

    2012-12-03

    Long-distance quantum communication networks require appropriate interfaces between matter qubit-based nodes and low-loss photonic quantum channels. We implement a downconversion quantum interface, where the single photons emitted from a semiconductor quantum dot at 910 nm are downconverted to 1560 nm using a fiber-coupled periodically poled lithium niobate waveguide and a 2.2-μm pulsed pump laser. The single-photon character of the quantum dot emission is preserved during the downconversion process: we measure a cross-correlation g(2)(τ = 0) = 0.17 using resonant excitation of the quantum dot. We show that the downconversion interface is fully compatible with coherent optical control of the quantum dot electron spin through the observation of Rabi oscillations in the downconverted photon counts. These results represent a critical step towards a long-distance hybrid quantum network in which subsystems operating at different wavelengths are connected through quantum frequency conversion devices and 1.5-μm quantum channels.

  2. Electron Spin Coherence Times in Si/SiGe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Jock, R. M.; He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.

    2014-03-01

    Single electron spin states in silicon have shown a great deal of promise as qubits due to their long spin relaxation (T1) and coherence (T2) times. Recent results exhibit a T2 of 250 us for electrons confined in Si/SiGe quantum dots at 350 mK. These experiments used conventional X-band (10 GHz) pulsed Electron Spin Resonance on a large area (3.5 mm x 20 mm), dual-gated, undoped Si/SiGe heterostructure quantum dots. These dots are induced in a natural Si quantum well by e-beam defined gates having a lithographic radius of 150 nm and pitch of 700 nm. The relatively large size of these dots led to closely spaced energy levels and long T2's could only be measured at sub-Kelvin temperatures. At 2K confined electrons displayed a 3 us T2, which is comparable to that of 2D electrons at that temperature. Decreasing the quantum dot size increases the electron confinement and reduces the effects of valley-splitting and spin-orbit coupling on the electron spin coherence times. We will report results on dots with 80 nm lithographic radii and a 375 nm pitch. This device displays an extended electron coherence time of 30 us at 2K, suggesting tighter confinement of electrons. Further measurements at lower temperatures are in progress. This work was supported in part by NSF through the Materials World Network program (DMR-1107606) and the Princeton MRSEC (DMR-0819860), and in part by the U.S. Army Research Office (W911NF-13-1-0179).

  3. Tunability and Stability of Lead Sulfide Quantum Dots in Ferritin

    NASA Astrophysics Data System (ADS)

    Peterson, J. Ryan; Hansen, Kameron

    Quantum dot solar cells have become one of the fastest growing solar cell technologies to date, and lead sulfide has proven to be an efficient absorber. However, one of the primary concerns in dye-sensitized quantum dot solar cell development is core degradation. We have synthesized lead sulfide quantum dots inside of the spherical protein ferritin in order to protect them from photocorrosion. We have studied the band gaps of these quantum dots and found them to be widely tunable inside ferritin just as they are outside the protein shell. In addition, we have examined their stability by measuring changes in photoluminescence as they are exposed to light over minutes and hours and found that the ferritin-enclosed PbS quantum dots have significantly better resistance to photocorrosion. Brigham Young University, National Science Foundation.

  4. Production of three-dimensional quantum dot lattice of Ge/Si core-shell quantum dots and Si/Ge layers in an alumina glass matrix.

    PubMed

    Buljan, M; Radić, N; Sancho-Paramon, J; Janicki, V; Grenzer, J; Bogdanović-Radović, I; Siketić, Z; Ivanda, M; Utrobičić, A; Hübner, R; Weidauer, R; Valeš, V; Endres, J; Car, T; Jerčinović, M; Roško, J; Bernstorff, S; Holy, V

    2015-02-13

    We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al2O3/Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells.

  5. Optically programmable electron spin memory using semiconductor quantum dots.

    PubMed

    Kroutvar, Miro; Ducommun, Yann; Heiss, Dominik; Bichler, Max; Schuh, Dieter; Abstreiter, Gerhard; Finley, Jonathan J

    2004-11-04

    The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled and embedded into active devices. It has been predicted that the atomic-like electronic structure of such quantum dots suppresses coupling of the spin to the solid-state quantum dot environment, thus protecting the 'spin' quantum information against decoherence. Here we demonstrate a single electron spin memory device in which the electron spin can be programmed by frequency selective optical excitation. We use the device to prepare single electron spins in semiconductor quantum dots with a well defined orientation, and directly measure the intrinsic spin flip time and its dependence on magnetic field. A very long spin lifetime is obtained, with a lower limit of about 20 milliseconds at a magnetic field of 4 tesla and at 1 kelvin.

  6. Facilitated preparation of bioconjugatable zwitterionic quantum dots using dual-lipid encapsulation.

    PubMed

    Shrake, Robert; Demillo, Violeta G; Ahmadiantehrani, Mojtaba; Zhu, Xiaoshan; Publicover, Nelson G; Hunter, Kenneth W

    2015-01-01

    Zwitterionic quantum dots prepared through incorporated zwitterionic ligands on quantum dot surfaces, are being paid significant attention in biomedical applications because of their excellent colloidal stability across a wide pH and ionic strength range, antifouling surface, good biocompatibility, etc. In this work, we report a dual-lipid encapsulation approach to prepare bioconjugatable zwitterionic quantum dots using amidosulfobetaine-16 lipids, dipalmitoyl-sn-glycero-3-phosphoethanolamine lipids with functional head groups, and CuInS2/ZnS quantum dots in a tetrahydrofuran/methanol/water solvent system with sonication. Amidosulfobetaine-16 is a zwitterionic lipid and dipalmitoyl-sn-glycero-3-phosphoethanolamine, with its functional head, provides bioconjugation capability. Under sonication, tetrahydrofuran/methanol containing amidosulfobetaine-16, dipalmitoyl-sn-glycero-3-phosphoethanolamine, and hydrophobic quantum dots are dispersed in water to form droplets. Highly water-soluble tetrahydrofuran/methanol in droplets is further displaced by water, which induces the lipid self-assembling on hydrophobic surface of quantum dots and thus forms water soluble zwitterionic quantum dots. The prepared zwitterionic quantum dots maintain colloidal stability in aqueous solutions with high salinity and over a wide pH range. They are also able to be conjugated with biomolecules for bioassay with minimal nonspecific binding. Copyright © 2014 Elsevier Inc. All rights reserved.

  7. In vivo cation exchange in quantum dots for tumor-specific imaging.

    PubMed

    Liu, Xiangyou; Braun, Gary B; Qin, Mingde; Ruoslahti, Erkki; Sugahara, Kazuki N

    2017-08-24

    In vivo tumor imaging with nanoprobes suffers from poor tumor specificity. Here, we introduce a nanosystem, which allows selective background quenching to gain exceptionally tumor-specific signals. The system uses near-infrared quantum dots and a membrane-impermeable etchant, which serves as a cation donor. The etchant rapidly quenches the quantum dots through cation exchange (ionic etching), and facilitates renal clearance of metal ions released from the quantum dots. The quantum dots are intravenously delivered into orthotopic breast and pancreas tumors in mice by using the tumor-penetrating iRGD peptide. Subsequent etching quenches excess quantum dots, leaving a highly tumor-specific signal provided by the intact quantum dots remaining in the extravascular tumor cells and fibroblasts. No toxicity is noted. The system also facilitates the detection of peritoneal tumors with high specificity upon intraperitoneal tumor targeting and selective etching of excess untargeted quantum dots. In vivo cation exchange may be a promising strategy to enhance specificity of tumor imaging.The imaging of tumors in vivo using nanoprobes has been challenging due to the lack of sufficient tumor specificity. Here, the authors develop a tumor-specific quantum dot system that permits in vivo cation exchange to achieve selective background quenching and high tumor-specific imaging.

  8. Size dependence in tunneling spectra of PbSe quantum-dot arrays.

    PubMed

    Ou, Y C; Cheng, S F; Jian, W B

    2009-07-15

    Interdot Coulomb interactions and collective Coulomb blockade were theoretically argued to be a newly important topic, and experimentally identified in semiconductor quantum dots, formed in the gate confined two-dimensional electron gas system. Developments of cluster science and colloidal synthesis accelerated the studies of electron transport in colloidal nanocrystal or quantum-dot solids. To study the interdot coupling, various sizes of two-dimensional arrays of colloidal PbSe quantum dots are self-assembled on flat gold surfaces for scanning tunneling microscopy and scanning tunneling spectroscopy measurements at both room and liquid-nitrogen temperatures. The tip-to-array, array-to-substrate, and interdot capacitances are evaluated and the tunneling spectra of quantum-dot arrays are analyzed by the theory of collective Coulomb blockade. The current-voltage of PbSe quantum-dot arrays conforms properly to a scaling power law function. In this study, the dependence of tunneling spectra on the sizes (numbers of quantum dots) of arrays is reported and the capacitive coupling between quantum dots in the arrays is explored.

  9. 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.

  10. Templated self-assembly of quantum dots from aqueous solution using protein scaffolds

    NASA Astrophysics Data System (ADS)

    Szuchmacher Blum, Amy; Soto, Carissa M.; Wilson, Charmaine D.; Whitley, Jessica L.; Moore, Martin H.; Sapsford, Kim E.; Lin, Tianwei; Chatterji, Anju; Johnson, John E.; Ratna, Banahalli R.

    2006-10-01

    Short, histidine-containing peptides can be conjugated to lysine-containing protein scaffolds to controllably attach quantum dots (QDs) to the scaffold, allowing for generic attachment of quantum dots to any protein without the use of specially engineered domains. This technique was used to bind quantum dots from aqueous solution to both chicken IgG and cowpea mosaic virus (CPMV), a 30 nm viral particle. These quantum dot protein assemblies were studied in detail. The IgG QD complexes were shown to retain binding specificity to their antigen after modification. The CPMV QD complexes have a local concentration of quantum dots greater than 3000 nmol ml-1, and show a 15% increase in fluorescence quantum yield over free quantum dots in solution.

  11. Quantum-dot spin-photon entanglement via frequency downconversion to telecom wavelength.

    PubMed

    De Greve, Kristiaan; Yu, Leo; McMahon, Peter L; Pelc, Jason S; Natarajan, Chandra M; Kim, Na Young; Abe, Eisuke; Maier, Sebastian; Schneider, Christian; Kamp, Martin; Höfling, Sven; Hadfield, Robert H; Forchel, Alfred; Fejer, M M; Yamamoto, Yoshihisa

    2012-11-15

    Long-distance quantum teleportation and quantum repeater technologies require entanglement between a single matter quantum bit (qubit) and a telecommunications (telecom)-wavelength photonic qubit. Electron spins in III-V semiconductor quantum dots are among the matter qubits that allow for the fastest spin manipulation and photon emission, but entanglement between a single quantum-dot spin qubit and a flying (propagating) photonic qubit has yet to be demonstrated. Moreover, many quantum dots emit single photons at visible to near-infrared wavelengths, where silica fibre losses are so high that long-distance quantum communication protocols become difficult to implement. Here we demonstrate entanglement between an InAs quantum-dot electron spin qubit and a photonic qubit, by frequency downconversion of a spontaneously emitted photon from a singly charged quantum dot to a wavelength of 1,560 nanometres. The use of sub-10-picosecond pulses at a wavelength of 2.2 micrometres in the frequency downconversion process provides the necessary quantum erasure to eliminate which-path information in the photon energy. Together with previously demonstrated indistinguishable single-photon emission at high repetition rates, the present technique advances the III-V semiconductor quantum-dot spin system as a promising platform for long-distance quantum communication.

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

    NASA Astrophysics Data System (ADS)

    Verma, Upendra Kumar; Kumar, Brijesh

    2017-10-01

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

  13. Bit-Serial Adder Based on Quantum Dots

    NASA Technical Reports Server (NTRS)

    Fijany, Amir; Toomarian, Nikzad; Modarress, Katayoon; Spotnitz, Mathew

    2003-01-01

    A proposed integrated circuit based on quantum-dot cellular automata (QCA) would function as a bit-serial adder. This circuit would serve as a prototype building block for demonstrating the feasibility of quantum-dots computing and for the further development of increasingly complex and increasingly capable quantum-dots computing circuits. QCA-based bit-serial adders would be especially useful in that they would enable the development of highly parallel and systolic processors for implementing fast Fourier, cosine, Hartley, and wavelet transforms. The proposed circuit would complement the QCA-based circuits described in "Implementing Permutation Matrices by Use of Quantum Dots" (NPO-20801), NASA Tech Briefs, Vol. 25, No. 10 (October 2001), page 42 and "Compact Interconnection Networks Based on Quantum Dots" (NPO-20855), which appears elsewhere in this issue. Those articles described the limitations of very-large-scale-integrated (VLSI) circuitry and the major potential advantage afforded by QCA. To recapitulate: In a VLSI circuit, signal paths that are required not to interact with each other must not cross in the same plane. In contrast, for reasons too complex to describe in the limited space available for this article, suitably designed and operated QCA-based signal paths that are required not to interact with each other can nevertheless 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. To enable a meaningful description of the proposed bit-serial adder, it is necessary to further recapitulate the description of a quantum-dot cellular automation from the first-mentioned prior article: A quantum-dot cellular automaton contains four quantum dots positioned at the corners of a square cell. The cell contains two extra mobile electrons that can tunnel (in the

  14. Quantum dot bioconjugates for ultrasensitive nonisotopic detection.

    PubMed

    Chan, W C; Nie, S

    1998-09-25

    Highly luminescent semiconductor quantum dots (zinc sulfide-capped cadmium selenide) have been covalently coupled to biomolecules for use in ultrasensitive biological detection. In comparison with organic dyes such as rhodamine, this class of luminescent labels is 20 times as bright, 100 times as stable against photobleaching, and one-third as wide in spectral linewidth. These nanometer-sized conjugates are water-soluble and biocompatible. Quantum dots that were labeled with the protein transferrin underwent receptor-mediated endocytosis in cultured HeLa cells, and those dots that were labeled with immunomolecules recognized specific antibodies or antigens.

  15. Two-electrons quantum dot in plasmas under the external fields

    NASA Astrophysics Data System (ADS)

    Bahar, M. K.; Soylu, A.

    2018-02-01

    In this study, for the first time, the combined effects of the external electric field, magnetic field, and confinement frequency on energies of two-electron parabolic quantum dots in Debye and quantum plasmas modeled by more general exponential cosine screened Coulomb (MGECSC) potential are investigated by numerically solving the Schrödinger equation using the asymptotic iteration method. The MGECSC potential includes four different potential forms when considering different sets of the parameters in potential. Since the plasma is an important experimental argument for quantum dots, the influence of plasmas modeled by the MGECSC potential on quantum dots is probed. The confinement frequency of quantum dots and the external fields created significant quantum restrictions on quantum dot. In this study, as well as discussion of the functionalities of the quantum restrictions for experimental applications, the parameters are also compared with each other in terms of influence and behaviour. In this manner, the motivation points of this study are summarized as follows: Which parameter can be alternative to which parameter, in terms of experimental applications? Which parameters exhibit similar behaviour? What is the role of plasmas on the corresponding behaviours? In the light of these research studies, it can be said that obtained results and performed discussions would be important in experimental and theoretical research related to plasma physics and/or quantum dots.

  16. Lateral excitonic switching in vertically stacked quantum dots

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

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

    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 alsomore » discussed.« less

  17. Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field

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

    Kushwaha, Manvir S.

    2014-12-15

    Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes) – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorptionmore » in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines’ random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level

  18. L-Cysteine Capped CdSe Quantum Dots Synthesized by Photochemical Route.

    PubMed

    Singh, Avinash; Kunwar, Amit; Rath, M C

    2018-05-01

    L-cysteine capped CdSe quantum dots were synthesized via photochemical route in aqueous solution under UV photo-irradiation. The as grown CdSe quantum dots exhibit broad fluorescence at room temperature. The CdSe quantum dots were found to be formed only through the reactions of the precursors, i.e., Cd(NH3)2+4 and SeSO2-3 with the photochemically generated 1-hydroxy-2-propyl radicals, (CH3)2COH radicals, which are formed through the process of H atom abstraction by the photoexcited acetone from 2-propanol. L-Cysteine was found to act as a suitable capping agent for the CdSe quantum dots and increases their biocompatability. Cytotoxicty effects of these quantum dots were evaluated in Chinese Hamster Ovary (CHO) epithelial cells, indicated a significant lower level for the L-cysteine capped CdSe quantum dots as compare to the bare ones.

  19. Autonomous quantum Maxwell's demon based on two exchange-coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Ptaszyński, Krzysztof

    2018-01-01

    I study an autonomous quantum Maxwell's demon based on two exchange-coupled quantum dots attached to the spin-polarized leads. The principle of operation of the demon is based on the coherent oscillations between the spin states of the system which act as a quantum iSWAP gate. Due to the operation of the iSWAP gate, one of the dots acts as a feedback controller which blocks the transport with the bias in the other dot, thus inducing the electron pumping against the bias; this leads to the locally negative entropy production. Operation of the demon is associated with the information transfer between the dots, which is studied quantitatively by mapping the analyzed setup onto the thermodynamically equivalent auxiliary system. The calculated entropy production in a single subsystem and information flow between the subsystems are shown to obey a local form of the second law of thermodynamics, similar to the one previously derived for classical bipartite systems.

  20. Magnon cotunneling through a quantum dot

    NASA Astrophysics Data System (ADS)

    Karwacki, Łukasz

    2017-11-01

    I consider a single-level quantum dot coupled to two reservoirs of spin waves (magnons). Such systems have been studied recently from the point of view of possible coupling between electronic and magnonic spin currents. However, usually weakly coupled systems were investigated. When coupling between the dot and reservoirs is not weak, then higher order processes play a role and have to be included. Here I consider cotunneling of magnons through a spin-occupied quantum dot, which can be understood as a magnon (spin) leakage current in analogy to leakage currents in charge-based electronics. Particular emphasis has been put on investigating the effect of magnetic field and temperature difference between the magnonic reservoirs.

  1. A Quantum Dot with Spin-Orbit Interaction--Analytical Solution

    ERIC Educational Resources Information Center

    Basu, B.; Roy, B.

    2009-01-01

    The practical applicability of a semiconductor quantum dot with spin-orbit interaction gives an impetus to study analytical solutions to one- and two-electron quantum dots with or without a magnetic field.

  2. Self-sustaining dynamical nuclear polarization oscillations in quantum dots.

    PubMed

    Rudner, M S; Levitov, L S

    2013-02-22

    Early experiments on spin-blockaded double quantum dots revealed robust, large-amplitude current oscillations in the presence of a static (dc) source-drain bias. Despite experimental evidence implicating dynamical nuclear polarization, the mechanism has remained a mystery. Here we introduce a minimal albeit realistic model of coupled electron and nuclear spin dynamics which supports self-sustained oscillations. Our mechanism relies on a nuclear spin analog of the tunneling magnetoresistance phenomenon (spin-dependent tunneling rates in the presence of an inhomogeneous Overhauser field) and nuclear spin diffusion, which governs dynamics of the spatial profile of nuclear polarization. The proposed framework naturally explains the differences in phenomenology between vertical and lateral quantum dot structures as well as the extremely long oscillation periods.

  3. Experimental observation of Fano effect in Ag nanoparticle-CdTe quantum dot hybrid system

    NASA Astrophysics Data System (ADS)

    Gurung, Sabina; Jayabalan, J.; Singh, Asha; Khan, Salahuddin; Chari, Rama

    2018-04-01

    We have experimentally measured the optical properties of Ag nanoparticle-CdTe quantum dot hybrid system and compared it with that of bare CdTe quantum dot colloid. It has been shown that the photoluminescence line shape of CdTe quantum dots becomes asymmetric in presence of Ag nanoparticles. The observed changes in the PL spectrum closely match the expected changes in the line shape due to Fano interaction between discrete level and continuum levels. Our experiment shows that a very small fraction of metal nanoparticles in the metal-semiconductor hybrid is sufficient to induce such changes in line shape which is in contrary to the earlier reported theoretical prediction on metal-semiconductor hybrid.

  4. Hot-electron transfer in quantum-dot heterojunction films.

    PubMed

    Grimaldi, Gianluca; Crisp, Ryan W; Ten Brinck, Stephanie; Zapata, Felipe; van Ouwendorp, Michiko; Renaud, Nicolas; Kirkwood, Nicholas; Evers, Wiel H; Kinge, Sachin; Infante, Ivan; Siebbeles, Laurens D A; Houtepen, Arjan J

    2018-06-13

    Thermalization losses limit the photon-to-power conversion of solar cells at the high-energy side of the solar spectrum, as electrons quickly lose their energy relaxing to the band edge. Hot-electron transfer could reduce these losses. Here, we demonstrate fast and efficient hot-electron transfer between lead selenide and cadmium selenide quantum dots assembled in a quantum-dot heterojunction solid. In this system, the energy structure of the absorber material and of the electron extracting material can be easily tuned via a variation of quantum-dot size, allowing us to tailor the energetics of the transfer process for device applications. The efficiency of the transfer process increases with excitation energy as a result of the more favorable competition between hot-electron transfer and electron cooling. The experimental picture is supported by time-domain density functional theory calculations, showing that electron density is transferred from lead selenide to cadmium selenide quantum dots on the sub-picosecond timescale.

  5. Controlling the Properties of Matter with Quantum Dots

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

    Klimov, Victor

    2017-03-22

    Solar cells and photodetectors could soon be made from new types of materials based on semiconductor quantum dots, thanks to new insights based on ultrafast measurements capturing real-time photoconversion processes. Photoconversion is a process wherein the energy of a photon, or quantum of light, is converted into other forms of energy, for example, chemical or electrical. Semiconductor quantum dots are chemically synthesized crystalline nanoparticles that have been studied for more than three decades in the context of various photoconversion schemes including photovoltaics (generation of photo-electricity) and photo-catalysis (generation of “solar fuels”). The appeal of quantum dots comes from the unmatchedmore » tunability of their physical properties, which can be adjusted by controlling the size, shape and composition of the dots. At Los Alamos, the research connects to the institutional mission of solving national security challenges through scientific excellence, in this case focusing on novel physical principles for highly efficient photoconversion, charge manipulation in exploratory device structures and novel nanomaterials.« less

  6. Entanglement of Electron Spins in Two Coupled Quantum Dots

    NASA Astrophysics Data System (ADS)

    Chen, Yuanzhen; Webb, Richard

    2004-03-01

    We study the entanglement of electron spins in a coupled quantum dots system at 70 mK. Two quantum dots are fabricated in a GaAs/AlGaAs heterostructure containing a high mobility 2-D electron gas. The two dots can be tuned independently and the electron spins in the dots are coupled through an exchange interaction between them. An exchange gate is used to vary the height and width of a potential barrier between the two dots, thus controlling the strength of the exchange interaction. Electrons are injected to the coupled dots by two independent DC currents and the output of the dots is incident on a beam splitter, which introduces quantum interferences. Cross-correlations of the shot noise of currents from the two output channels are measured and compared with theory (1). *Work supported by LPS and ARDA under MDA90401C0903 and NSF under DMR 0103223. (1) Burkard, Loss, & Sukhorukov, Phys. Rev. B61, R16303 (2000).

  7. Spin fine structure of optically excited quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Scheibner, M.; Doty, M. F.; Ponomarev, I. V.; Bracker, A. S.; Stinaff, E. A.; Korenev, V. L.; Reinecke, T. L.; Gammon, D.

    2007-06-01

    The interaction between spins in coupled quantum dots is revealed in distinct fine structure patterns in the measured optical spectra of InAs/GaAs double quantum dot molecules containing zero, one, or two excess holes. The fine structure is explained well in terms of a uniquely molecular interplay of spin-exchange interactions, Pauli exclusion, and orbital tunneling. This knowledge is critical for converting quantum dot molecule tunneling into a means of optically coupling not just orbitals but also spins.

  8. Functional Carbon Quantum Dots: A Versatile Platform for Chemosensing and Biosensing.

    PubMed

    Feng, Hui; Qian, Zhaosheng

    2018-05-01

    Carbon quantum dot has emerged as a new promising fluorescent nanomaterial due to its excellent optical properties, outstanding biocompatibility and accessible fabrication methods, and has shown huge application perspective in a variety of areas, especially in chemosensing and biosensing applications. In this personal account, we give a brief overview of carbon quantum dots from its origin and preparation methods, present some advance on fluorescence origin of carbon quantum dots, and focus on development of chemosensors and biosensors based on functional carbon quantum dots. Comprehensive advances on functional carbon quantum dots as a versatile platform for sensing from our group are included and summarized as well as some typical examples from the other groups. The biosensing applications of functional carbon quantum dots are highlighted from selective assays of enzyme activity to fluorescent identification of cancer cells and bacteria. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Silicon based quantum dot hybrid qubits

    NASA Astrophysics Data System (ADS)

    Kim, Dohun

    2015-03-01

    The charge and spin degrees of freedom of an electron constitute natural bases for constructing quantum two level systems, or qubits, in semiconductor quantum dots. The quantum dot charge qubit offers a simple architecture and high-speed operation, but generally suffers from fast dephasing due to strong coupling of the environment to the electron's charge. On the other hand, quantum dot spin qubits have demonstrated long coherence times, but their manipulation is often slower than desired for important future applications. This talk will present experimental progress of a `hybrid' qubit, formed by three electrons in a Si/SiGe double quantum dot, which combines desirable characteristics (speed and coherence) in the past found separately in qubits based on either charge or spin degrees of freedom. Using resonant microwaves, we first discuss qubit operations near the `sweet spot' for charge qubit operation. Along with fast (>GHz) manipulation rates for any rotation axis on the Bloch sphere, we implement two independent tomographic characterization schemes in the charge qubit regime: traditional quantum process tomography (QPT) and gate set tomography (GST). We also present resonant qubit operations of the hybrid qubit performed on the same device, DC pulsed gate operations of which were recently demonstrated. We demonstrate three-axis control and the implementation of dynamic decoupling pulse sequences. Performing QPT on the hybrid qubit, we show that AC gating yields π rotation process fidelities higher than 93% for X-axis and 96% for Z-axis rotations, which demonstrates efficient quantum control of semiconductor qubits using resonant microwaves. We discuss a path forward for achieving fidelities better than the threshold for quantum error correction using surface codes. This work was supported in part by ARO (W911NF-12-0607), NSF (PHY-1104660), DOE (DE-FG02-03ER46028), and by the Laboratory Directed Research and Development program at Sandia National Laboratories

  10. A fabrication guide for planar silicon quantum dot heterostructures

    NASA Astrophysics Data System (ADS)

    Spruijtenburg, Paul C.; Amitonov, Sergey V.; van der Wiel, Wilfred G.; Zwanenburg, Floris A.

    2018-04-01

    We describe important considerations to create top-down fabricated planar quantum dots in silicon, often not discussed in detail in literature. The subtle interplay between intrinsic material properties, interfaces and fabrication processes plays a crucial role in the formation of electrostatically defined quantum dots. Processes such as oxidation, physical vapor deposition and atomic-layer deposition must be tailored in order to prevent unwanted side effects such as defects, disorder and dewetting. In two directly related manuscripts written in parallel we use techniques described in this work to create depletion-mode quantum dots in intrinsic silicon, and low-disorder silicon quantum dots defined with palladium gates. While we discuss three different planar gate structures, the general principles also apply to 0D and 1D systems, such as self-assembled islands and nanowires.

  11. 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.

  12. 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.

  13. Quantum dot conjugates in a sub-micrometer fluidic channel

    DOEpatents

    Stavis, Samuel M [Ithaca, NY; Edel, Joshua B [Brookline, MA; Samiee, Kevan T [Ithaca, NY; Craighead, Harold G [Ithaca, NY

    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.

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

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

    See, Gloria G.; Xu, Lu; Nuzzo, Ralph G.

    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 themore » photonic crystal structure.« less

  15. Towards a feasible implementation of quantum neural networks using quantum dots

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

    Altaisky, Mikhail V., E-mail: altaisky@mx.iki.rssi.ru, E-mail: nzolnik@iki.rssi.ru; Zolnikova, Nadezhda N., E-mail: altaisky@mx.iki.rssi.ru, E-mail: nzolnik@iki.rssi.ru; Kaputkina, Natalia E., E-mail: nataly@misis.ru

    2016-03-07

    We propose an implementation of quantum neural networks using an array of quantum dots with dipole-dipole interactions. We demonstrate that this implementation is both feasible and versatile by studying it within the framework of GaAs based quantum dot qubits coupled to a reservoir of acoustic phonons. Using numerically exact Feynman integral calculations, we have found that the quantum coherence in our neural networks survive for over a hundred ps even at liquid nitrogen temperatures (77 K), which is three orders of magnitude higher than current implementations, which are based on SQUID-based systems operating at temperatures in the mK range.

  16. Intermediate-band photosensitive device with quantum dots having tunneling barrier embedded in organic matrix

    DOEpatents

    Forrest, Stephen R.

    2008-08-19

    A plurality of quantum dots each have a shell. The quantum dots are embedded in an organic matrix. At least the quantum dots and the organic matrix are photoconductive semiconductors. The shell of each quantum dot is arranged as a tunneling barrier to require a charge carrier (an electron or a hole) at a base of the tunneling barrier in the organic matrix to perform quantum mechanical tunneling to reach the respective quantum dot. A first quantum state in each quantum dot is between a lowest unoccupied molecular orbital (LUMO) and a highest occupied molecular orbital (HOMO) of the organic matrix. Wave functions of the first quantum state of the plurality of quantum dots may overlap to form an intermediate band.

  17. Charge Carrier Hopping Dynamics in Homogeneously Broadened PbS Quantum Dot Solids.

    PubMed

    Gilmore, Rachel H; Lee, Elizabeth M Y; Weidman, Mark C; Willard, Adam P; Tisdale, William A

    2017-02-08

    Energetic disorder in quantum dot solids adversely impacts charge carrier transport in quantum dot solar cells and electronic devices. Here, we use ultrafast transient absorption spectroscopy to show that homogeneously broadened PbS quantum dot arrays (σ hom 2 :σ inh 2 > 19:1, σ inh /k B T < 0.4) can be realized if quantum dot batches are sufficiently monodisperse (δ ≲ 3.3%). The homogeneous line width is found to be an inverse function of quantum dot size, monotonically increasing from ∼25 meV for the largest quantum dots (5.8 nm diameter/0.92 eV energy) to ∼55 meV for the smallest (4.1 nm/1.3 eV energy). Furthermore, we show that intrinsic charge carrier hopping rates are faster for smaller quantum dots. This finding is the opposite of the mobility trend commonly observed in device measurements but is consistent with theoretical predictions. Fitting our data to a kinetic Monte Carlo model, we extract charge carrier hopping times ranging from 80 ps for the smallest quantum dots to over 1 ns for the largest, with the same ethanethiol ligand treatment. Additionally, we make the surprising observation that, in slightly polydisperse (δ ≲ 4%) quantum dot solids, structural disorder has a greater impact than energetic disorder in inhibiting charge carrier transport. These findings emphasize how small improvements in batch size dispersity can have a dramatic impact on intrinsic charge carrier hopping behavior and will stimulate further improvements in quantum dot device performance.

  18. Combined atomic force microscopy and photoluminescence imaging to select single InAs/GaAs quantum dots for quantum photonic devices.

    PubMed

    Sapienza, Luca; Liu, Jin; Song, Jin Dong; Fält, Stefan; Wegscheider, Werner; Badolato, Antonio; Srinivasan, Kartik

    2017-07-24

    We report on a combined photoluminescence imaging and atomic force microscopy study of single, isolated self-assembled InAs quantum dots. The motivation of this work is to determine an approach that allows to assess single quantum dots as candidates for quantum nanophotonic devices. By combining optical and scanning probe characterization techniques, we find that single quantum dots often appear in the vicinity of comparatively large topographic features. Despite this, the quantum dots generally do not exhibit significant differences in their non-resonantly pumped emission spectra in comparison to quantum dots appearing in defect-free regions, and this behavior is observed across multiple wafers produced in different growth chambers. Such large surface features are nevertheless a detriment to applications in which single quantum dots are embedded within nanofabricated photonic devices: they are likely to cause large spectral shifts in the wavelength of cavity modes designed to resonantly enhance the quantum dot emission, thereby resulting in a nominally perfectly-fabricated single quantum dot device failing to behave in accordance with design. We anticipate that the approach of screening quantum dots not only based on their optical properties, but also their surrounding surface topographies, will be necessary to improve the yield of single quantum dot nanophotonic devices.

  19. 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.

  20. Strain-induced formation of fourfold symmetric SiGe quantum dot molecules.

    PubMed

    Zinovyev, V A; Dvurechenskii, A V; Kuchinskaya, P A; Armbrister, V A

    2013-12-27

    The strain field distribution at the surface of a multilayer structure with disklike SiGe nanomounds formed by heteroepitaxy is exploited to arrange the symmetric quantum dot molecules typically consisting of four elongated quantum dots ordered along the [010] and [100] directions. The morphological transition from fourfold quantum dot molecules to continuous fortresslike quantum rings with an increasing amount of deposited Ge is revealed. We examine key mechanisms underlying the formation of lateral quantum dot molecules by using scanning tunneling microscopy and numerical calculations of the strain energy distribution on the top of disklike SiGe nanomounds. Experimental data are well described by a simple thermodynamic model based on the accurate evaluation of the strain dependent part of the surface chemical potential. The spatial arrangement of quantum dots inside molecules is attributed to the effect of elastic property anisotropy.

  1. Periodic scarred States in open quantum dots as evidence of quantum Darwinism.

    PubMed

    Burke, A M; Akis, R; Day, T E; Speyer, Gil; Ferry, D K; Bennett, B R

    2010-04-30

    Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.

  2. Periodic Scarred States in Open Quantum Dots as Evidence of Quantum Darwinism

    NASA Astrophysics Data System (ADS)

    Burke, A. M.; Akis, R.; Day, T. E.; Speyer, Gil; Ferry, D. K.; Bennett, B. R.

    2010-04-01

    Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.

  3. 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. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots

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

    Robert, C., E-mail: cedric.robert@insa-rennes.fr, E-mail: cedric.robert@tyndall.ie; Pedesseau, L.; Cornet, C.

    The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.

  5. Gate tunable parallel double quantum dots in InAs double-nanowire devices

    NASA Astrophysics Data System (ADS)

    Baba, S.; Matsuo, S.; Kamata, H.; Deacon, R. S.; Oiwa, A.; Li, K.; Jeppesen, S.; Samuelson, L.; Xu, H. Q.; Tarucha, S.

    2017-12-01

    We report fabrication and characterization of InAs nanowire devices with two closely placed parallel nanowires. The fabrication process we develop includes selective deposition of the nanowires with micron scale alignment onto predefined finger bottom gates using a polymer transfer technique. By tuning the double nanowire with the finger bottom gates, we observed the formation of parallel double quantum dots with one quantum dot in each nanowire bound by the normal metal contact edges. We report the gate tunability of the charge states in individual dots as well as the inter-dot electrostatic coupling. In addition, we fabricate a device with separate normal metal contacts and a common superconducting contact to the two parallel wires and confirm the dot formation in each wire from comparison of the transport properties and a superconducting proximity gap feature for the respective wires. With the fabrication techniques established in this study, devices can be realized for more advanced experiments on Cooper-pair splitting, generation of Parafermions, and so on.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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. Long-wavelength infrared (LWIR) quantum-dot infrared photodetector (QDIP) focal plane array

    NASA Astrophysics Data System (ADS)

    Gunapala, S. D.; Bandara, S. V.; Hill, C. J.; Ting, D. Z.; Liu, J. K.; Rafol, S. B.; Blazejewski, E. R.; Mumolo, J. M.; Keo, S. A.; Krishna, S.; Chang, Y. C.; Shott, C. A.

    2006-05-01

    We have exploited the artificial atomlike properties of epitaxially self-assembled quantum dots for the development of high operating temperature long wavelength infrared (LWIR) focal plane arrays. Quantum dots are nanometer-scale islands that form spontaneously on a semiconductor substrate due to lattice mismatch. QDIPs are expected to outperform quantum well infrared detectors (QWIPs) and are expected to offer significant advantages over II-VI material based focal plane arrays. QDIPs are fabricated using robust wide bandgap III-V materials which are well suited to the production of highly uniform LWIR arrays. We have used molecular beam epitaxy (MBE) technology to grow multi-layer LWIR quantum dot structures based on the InAs/InGaAs/GaAs material system. JPL is building on its significant QWIP experience and is basically building a Dot-in-the-Well (DWELL) device design by embedding InAs quantum dots in a QWIP structure. This hybrid quantum dot/quantum well device offers additional control in wavelength tuning via control of dot-size and/or quantum well sizes. In addition the quantum wells can trap electrons and aide in ground state refilling. Recent measurements have shown a 10 times higher photoconductive gain than the typical QWIP device, which indirectly confirms the lower relaxation rate of excited electrons (photon bottleneck) in QDIPs. Subsequent material and device improvements have demonstrated an absorption quantum efficiency (QE) of ~ 3%. Dot-in-the-well (DWELL) QDIPs were also experimentally shown to absorb both 45o and normally incident light. Thus we have employed a reflection grating structure to further enhance the quantum efficiency. JPL has demonstrated wavelength control by progressively growing material and fabricating devices structures that have continuously increased in LWIR response. The most recent devices exhibit peak responsivity out to 8.1 microns. Peak detectivity of the 8.1μm devices has reached ~ 1 x 1010 Jones at 77 K. Furthermore

  10. Long-Wavelength Infrared (LWIR) Quantum Dot Infrared Photodetector (QDIP) Focal Plane Array

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath D.; Bandara, S. V.; Liu, J. K.; Hill, C. J.; Rafol, S. B.; Mumolo, J. M.; Shott, C. A.

    2006-01-01

    We have exploited the artificial atomlike properties of epitaxially self-assembled quantum dots for the development of high operating temperature long wavelength infrared (LWIR) focal plane arrays. Quantum dots are nanometer-scale islands that form spontaneously on a semiconductor substrate due to lattice mismatch. QDIPs are expected to outperform quantum well infrared detectors (QWIPs) and are expected to offer significant advantages over II-VI material based focal plane arrays. QDIPs are fabricated using robust wide bandgap III-V materials which are well suited to the production of highly uniform LWIR arrays. We have used molecular beam epitaxy (MBE) technology to grow multi-layer LWIR quantum dot structures based on the InAs/InGaAs/GaAs material system. JPL is building on its significant QWIP experience and is basically building a Dot-in-the-Well (DWELL) device design by embedding InAs quantum dots in a QWIP structure. This hybrid quantum dot/quantum well device offers additional control in wavelength tuning via control of dot-size and/or quantum well sizes. In addition the quantum wells can trap electrons and aide in ground state refilling. Recent measurements have shown a 10 times higher photoconductive gain than the typical QWIP device, which indirectly confirms the lower relaxation rate of excited electrons (photon bottleneck) in QDPs. Subsequent material and device improvements have demonstrated an absorption quantum efficiency (QE) of approx. 3%. Dot-in-the-well (DWELL) QDIPs were also experimentally shown to absorb both 45 deg. and normally incident light. Thus we have employed a reflection grating structure to further enhance the quantum efficiency. JPL has demonstrated wavelength control by progressively growing material and fabricating devices structures that have continuously increased in LWIR response. The most recent devices exhibit peak responsivity out to 8.1 microns. Peak detectivity of the 8.1 micrometer devices has reached approx. 1 x 10(exp 10

  11. Local Gate Control of a Carbon Nanotube Double Quantum Dot

    DTIC Science & Technology

    2016-04-04

    Nanotube Double Quantum Dot N. Mason,*† M. J. Biercuk,* C. M. Marcus† We have measured carbon nanotube quantum dots with multiple electro- static gates and...computation. Carbon nanotubes have been considered lead- ing candidates for nanoscale electronic applica- tions (1, 2). Previous measurements of nano- tube...electronics have shown electron confine- ment (quantum dot) effects such as single- electron charging and energy-level quantization (3–5). Nanotube

  12. Simultaneous multi-state stimulated emission in quantum dot lasers: experiment and analytical approach

    NASA Astrophysics Data System (ADS)

    Korenev, V. V.; Savelyev, A. V.; Zhukov, A. E.; Omelchenko, A. V.; Maximov, M. V.; Shernyakov, Yu. M.

    2012-06-01

    The theoretical investigation of the double-state lasing phenomena in InAs/InGaAs quantum dot lasers has been carried out. The new mechanism of the ground-state lasing quenching, which takes place in quantum dot (QD) laser operating in double-state lasing regime at high pump level, was proposed. The difference between electron and hole capture rates causes the depletion of the hole levels and consequently leads to the decrease of an output lasing power via QD ground state with the growth of injection. Moreover, it was shown that the hole-to-electron capture rates ratio strongly affects both the light-current curve and the key laser parameters. The model of the simultaneous lasing through the ground and excited QD states was developed which allows to describe the observed quenching quantitatively.

  13. Synthetic Control of Exciton Behavior in Colloidal Quantum Dots.

    PubMed

    Pu, Chaodan; Qin, Haiyan; Gao, Yuan; Zhou, Jianhai; Wang, Peng; Peng, Xiaogang

    2017-03-08

    Colloidal quantum dots are promising optical and optoelectronic materials for various applications, whose performance is dominated by their excited-state properties. This article illustrates synthetic control of their excited states. Description of the excited states of quantum-dot emitters can be centered around exciton. We shall discuss that, different from conventional molecular emitters, ground-state structures of quantum dots are not necessarily correlated with their excited states. Synthetic control of exciton behavior heavily relies on convenient and affordable monitoring tools. For synthetic development of ideal optical and optoelectronic emitters, the key process is decay of band-edge excitons, which renders transient photoluminescence as important monitoring tool. On the basis of extensive synthetic developments in the past 20-30 years, synthetic control of exciton behavior implies surface engineering of quantum dots, including surface cation/anion stoichiometry, organic ligands, inorganic epitaxial shells, etc. For phosphors based on quantum dots doped with transition metal ions, concentration and location of the dopant ions within a nanocrystal lattice are found to be as important as control of the surface states in order to obtain bright dopant emission with monoexponential yet tunable photoluminescence decay dynamics.

  14. Photoluminescence of patterned CdSe quantum dot for anti-counterfeiting label on paper

    NASA Astrophysics Data System (ADS)

    Isnaeni, Yulianto, Nursidik; Suliyanti, Maria Margaretha

    2016-03-01

    We successfully developed a method utilizing colloidal CdSe nanocrystalline quantum dot for anti-counterfeiting label on a piece of glossy paper. We deposited numbers and lines patterns of toluene soluble CdSe quantum dot using rubber stamper on a glossy paper. The width of line pattern was about 1-2 mm with 1-2 mm separation between lines. It required less than one minute for deposited CdSe quantum dot on glossy paper to dry and become invisible by naked eyes. However, patterned quantum dot become visible using long-pass filter glasses upon excitation of UV lamp or blue laser. We characterized photoluminescence of line patterns of quantum dot, and we found that emission boundaries of line patterns were clearly observed. The error of line size and shape were mainly due to defect of the original stamper. The emission peak wavelength of CdSe quantum dot was 629 nm. The emission spectrum of deposited quantum dot has full width at half maximum (FWHM) of 30-40 nm. The spectra similarity between deposited quantum dot and the original quantum dot in solution proved that our stamping method can be simply applied on glossy paper without changing basic optical property of the quantum dot. Further development of this technique is potential for anti-counterfeiting label on very important documents or objects.

  15. A real-time spectrum acquisition system design based on quantum dots-quantum well detector

    NASA Astrophysics Data System (ADS)

    Zhang, S. H.; Guo, F. M.

    2016-01-01

    In this paper, we studied the structure characteristics of quantum dots-quantum well photodetector with response wavelength range from 400 nm to 1000 nm. It has the characteristics of high sensitivity, low dark current and the high conductance gain. According to the properties of the quantum dots-quantum well photodetectors, we designed a new type of capacitive transimpedence amplifier (CTIA) readout circuit structure with the advantages of adjustable gain, wide bandwidth and high driving ability. We have implemented the chip packaging between CTIA-CDS structure readout circuit and quantum dots detector and tested the readout response characteristics. According to the timing signals requirements of our readout circuit, we designed a real-time spectral data acquisition system based on FPGA and ARM. Parallel processing mode of programmable devices makes the system has high sensitivity and high transmission rate. In addition, we realized blind pixel compensation and smoothing filter algorithm processing to the real time spectrum data by using C++. Through the fluorescence spectrum measurement of carbon quantum dots and the signal acquisition system and computer software system to realize the collection of the spectrum signal processing and analysis, we verified the excellent characteristics of detector. It meets the design requirements of quantum dot spectrum acquisition system with the characteristics of short integration time, real-time and portability.

  16. Internalization of targeted quantum dots by brain capillary endothelial cells in vivo.

    PubMed

    Paris-Robidas, Sarah; Brouard, Danny; Emond, Vincent; Parent, Martin; Calon, Frédéric

    2016-04-01

    Receptors located on brain capillary endothelial cells forming the blood-brain barrier are the target of most brain drug delivery approaches. Yet, direct subcellular evidence of vectorized transport of nanoformulations into the brain is lacking. To resolve this question, quantum dots were conjugated to monoclonal antibodies (Ri7) targeting the murine transferrin receptor. Specific transferrin receptor-mediated endocytosis of Ri7-quantum dots was first confirmed in N2A and bEnd5 cells. After intravenous injection in mice, Ri7-quantum dots exhibited a fourfold higher volume of distribution in brain tissues, compared to controls. Immunofluorescence analysis showed that Ri7-quantum dots were sequestered throughout the cerebral vasculature 30 min, 1 h, and 4 h post injection, with a decline of signal intensity after 24 h. Transmission electron microscopic studies confirmed that Ri7-quantum dots were massively internalized by brain capillary endothelial cells, averaging 37 ± 4 Ri7-quantum dots/cell 1 h after injection. Most quantum dots within brain capillary endothelial cells were observed in small vesicles (58%), with a smaller proportion detected in tubular structures or in multivesicular bodies. Parenchymal penetration of Ri7-quantum dots was extremely low and comparable to control IgG. Our results show that systemically administered Ri7-quantum dots complexes undergo extensive endocytosis by brain capillary endothelial cells and open the door for novel therapeutic approaches based on brain endothelial cell drug delivery. © The Author(s) 2015.

  17. 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.

  18. Suppression of low-frequency charge noise in gates-defined GaAs quantum dots

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

    You, Jie; Li, Hai-Ou, E-mail: haiouli@ustc.edu.cn, E-mail: gpguo@ustc.edu.cn; Wang, Ke

    To reduce the charge noise of a modulation-doped GaAs/AlGaAs quantum dot, we have fabricated shallow-etched GaAs/AlGaAs quantum dots using the wet-etching method to study the effects of two-dimensional electron gas (2DEG) underneath the metallic gates. The low-frequency 1/f noise in the Coulomb blockade region of the shallow-etched quantum dot is compared with a non-etched quantum dot on the same wafer. The average values of the gate noise are approximately 0.5 μeV in the shallow-etched quantum dot and 3 μeV in the regular quantum dot. Our results show the quantum dot low-frequency charge noise can be suppressed by the removal ofmore » the 2DEG underneath the metallic gates, which provides an architecture for noise reduction.« less

  19. Magneto-conductance fingerprints of purely quantum states in the open quantum dot limit

    NASA Astrophysics Data System (ADS)

    Mendoza, Michel; Ujevic, Sebastian

    2012-06-01

    We present quantum magneto-conductance simulations, at the quantum low energy condition, to study the open quantum dot limit. The longitudinal conductance G(E,B) of spinless and non-interacting electrons is mapped as a function of the magnetic field B and the energy E of the electrons. The quantum dot linked to the semi-infinite leads is tuned by quantum point contacts of variable width w. We analyze the transition from a quantum wire to an open quantum dot and then to an effective closed system. The transition, as a function of w, occurs in the following sequence: evolution of quasi-Landau levels to Fano resonances and quasi-bound states between the quasi-Landau levels, followed by the formation of crossings that evolve to anti-crossings inside the quasi-Landau level region. After that, Fano resonances are created between the quasi-Landau states with the final generation of resonant tunneling peaks. By comparing the G(E,B) maps, we identify the closed and open-like limits of the system as a function of the applied magnetic field. These results were used to build quantum openness diagrams G(w,B). Also, these maps allow us to determine the w-limit value from which we can qualitatively relate the closed system properties to the open one. The above analysis can be used to identify single spinless particle effects in experimental measurements of the open quantum dot limit.

  20. The photosensitivity of carbon quantum dots/CuAlO2 films composites.

    PubMed

    Pan, Jiaqi; Sheng, Yingzhuo; Zhang, Jingxiang; Wei, Jumeng; Huang, Peng; Zhang, Xin; Feng, Boxue

    2015-07-31

    Carbon quantum dots/CuAlO2 films were prepared by a simple route through which CuAlO2 films prepared by sol-gel on crystal quartz substrates were composited with carbon quantum dots on their surface. The characterization results indicated that CuAlO2 films were well combined with carbon quantum dots. The photoconductivity of carbon quantum dots/CuAlO2 films was investigated under illumination and darkness switching, and was demonstrated to be significantly enhanced compared with CuAlO2 films. Through analysis, this enhancement of photoconductivity was attributed to the carbon quantum dots with unique up-converted photoluminescence behavior.

  1. The photosensitivity of carbon quantum dots/CuAlO2 films composites

    NASA Astrophysics Data System (ADS)

    Pan, Jiaqi; Sheng, Yingzhuo; Zhang, Jingxiang; Wei, Jumeng; Huang, Peng; Zhang, Xin; Feng, Boxue

    2015-07-01

    Carbon quantum dots/CuAlO2 films were prepared by a simple route through which CuAlO2 films prepared by sol-gel on crystal quartz substrates were composited with carbon quantum dots on their surface. The characterization results indicated that CuAlO2 films were well combined with carbon quantum dots. The photoconductivity of carbon quantum dots/CuAlO2 films was investigated under illumination and darkness switching, and was demonstrated to be significantly enhanced compared with CuAlO2 films. Through analysis, this enhancement of photoconductivity was attributed to the carbon quantum dots with unique up-converted photoluminescence behavior.

  2. RKKY interaction in a chirally coupled double quantum dot system

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

    Heine, A. W.; Tutuc, D.; Haug, R. J.

    2013-12-04

    The competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction is investigated in a double quantum dots system, coupled via a central open conducting region. A perpendicular magnetic field induces the formation of Landau Levels which in turn give rise to the so-called Kondo chessboard pattern in the transport through the quantum dots. The two quantum dots become therefore chirally coupled via the edge channels formed in the open conducting area. In regions where both quantum dots exhibit Kondo transport the presence of the RKKY exchange interaction is probed by an analysis of the temperature dependence. The thus obtainedmore » Kondo temperature of one dot shows an abrupt increase at the onset of Kondo transport in the other, independent of the magnetic field polarity, i.e. edge state chirality in the central region.« less

  3. Electron Spin Optical Orientation in Charged Quantum Dots

    NASA Astrophysics Data System (ADS)

    Shabaev, A.; Gershoni, D.; Korenev, V. L.

    2005-03-01

    We present a theory of nonresonant optical orientation of electron spins localized in quantum dots. This theory explains the negative circularly polarized photoluminescence of singlet trions localized in quantum dots previously observed in experiments where trion polarization changed to negative with time and where the degree of the negative polarization increased with intensity of pumping light. We have shown that this effect can be explained by the accumulation of dark excitons that occurs due to the spin blocking of the singlet trion formation - the major mechanism of dark exciton recombination. The accumulation of dark excitons results from a lack of electrons with a spin matching the exciton polarization. The electron spin lifetime is shortened by a transverse magnetic field or a temperature increase. This takes the block off the dark exciton recombination and restores the positive degree of trion polarization. The presented theory gives good agreement with experimental data.

  4. A Transfer Hamiltonian Model for Devices Based on Quantum Dot Arrays

    PubMed Central

    Illera, S.; Prades, J. D.; Cirera, A.; Cornet, A.

    2015-01-01

    We present a model of electron transport through a random distribution of interacting quantum dots embedded in a dielectric matrix to simulate realistic devices. The method underlying the model depends only on fundamental parameters of the system and it is based on the Transfer Hamiltonian approach. A set of noncoherent rate equations can be written and the interaction between the quantum dots and between the quantum dots and the electrodes is introduced by transition rates and capacitive couplings. A realistic modelization of the capacitive couplings, the transmission coefficients, the electron/hole tunneling currents, and the density of states of each quantum dot have been taken into account. The effects of the local potential are computed within the self-consistent field regime. While the description of the theoretical framework is kept as general as possible, two specific prototypical devices, an arbitrary array of quantum dots embedded in a matrix insulator and a transistor device based on quantum dots, are used to illustrate the kind of unique insight that numerical simulations based on the theory are able to provide. PMID:25879055

  5. A transfer hamiltonian model for devices based on quantum dot arrays.

    PubMed

    Illera, S; Prades, J D; Cirera, A; Cornet, A

    2015-01-01

    We present a model of electron transport through a random distribution of interacting quantum dots embedded in a dielectric matrix to simulate realistic devices. The method underlying the model depends only on fundamental parameters of the system and it is based on the Transfer Hamiltonian approach. A set of noncoherent rate equations can be written and the interaction between the quantum dots and between the quantum dots and the electrodes is introduced by transition rates and capacitive couplings. A realistic modelization of the capacitive couplings, the transmission coefficients, the electron/hole tunneling currents, and the density of states of each quantum dot have been taken into account. The effects of the local potential are computed within the self-consistent field regime. While the description of the theoretical framework is kept as general as possible, two specific prototypical devices, an arbitrary array of quantum dots embedded in a matrix insulator and a transistor device based on quantum dots, are used to illustrate the kind of unique insight that numerical simulations based on the theory are able to provide.

  6. 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.

  7. Magneto-exciton transitions in laterally coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Barticevic, Zdenka; Pacheco, Monica; Duque, Carlos A.; Oliveira, Luiz E.

    2008-03-01

    We present a study of the electronic and optical properties of laterally coupled quantum dots. The excitonic spectra of this system under the effects of an external magnetic field applied perpendicular to the plane of the dots is obtained, with the potential of every individual dot taken as the superposition of a quantum well potential along the axial direction with a lateral parabolic confinement potential, and the coupled two- dot system then modeled by a superposition of the potentials of each dot, with their minima at different positions and truncated at the intersection plane. The wave functions and eigenvalues are obtained in the effective-mass approximation by using an extended variational approach in which the magneto- exciton states are simultaneously obtained [1]. The allowed magneto-exciton transitions are investigated by using circularly polarized radiation in the plane perpendicular to the magnetic field. We present results on the excitonic absorption coefficient as a function of the photon energy for different geometric quantum-dot confinement and magnetic-field values. Reference: [1] Z. Barticevic, M. Pacheco, C. A. Duque and L. E. Oliveira, Phys. Rev. B 68, 073312 (2003).

  8. Valley Phase and Voltage Control of Coherent Manipulation in Si Quantum Dots.

    PubMed

    Zimmerman, Neil M; Huang, Peihao; Culcer, Dimitrie

    2017-07-12

    With any roughness at the interface of an indirect-bandgap semiconducting dot, the phase of the valley-orbit coupling can take on a random value. This random value, in double quantum dots, causes a large change in the exchange splitting. We demonstrate a simple analytical method to calculate the phase, and thus the exchange splitting and singlet-triplet qubit frequency, for an arbitrary interface. We then show that, with lateral control of the position of a quantum dot using a gate voltage, the valley-orbit phase can be controlled over a wide range, so that variations in the exchange splitting can be controlled for individual devices. Finally, we suggest experiments to measure the valley phase and the concomitant gate voltage control.

  9. Spectral properties of finite two dimensional quantum dot arrays.

    NASA Astrophysics Data System (ADS)

    Cota, Ernesto; Ramírez, Felipe; Ulloa, Sergio E.

    1997-08-01

    Motivated by recent proposed geometries in cellular automata, we study arrays of four or five coupled quantum dots located at the corners and at the center of a square. We calculate the addition spectrum for dots with equal or different sizes at each site and compare with the case of linear arrays. We obtain the numerically exact solution for arrays with two electrons and study the properties of this system as a cell or building block of quantum dot cellular automata. We obtain the ``polarization" for each state and discuss its possible use as a two-state system or ``qubit," as proposed recently(C. S. Lent, P. D. Tougaw, and W. Porod, Appl. Phys. Lett. 62) 714, (1993). An extended Hubbard Hamiltonian is used which takes into account quantum confinement, intra- an inter-dot Coulomb interaction as well as tunneling between neighboring dots.

  10. Spectral properties of finite two dimensional quantum dot arrays.

    NASA Astrophysics Data System (ADS)

    Ramirez, Felipe; Cota, Ernesto; Ulloa, Sergio E.

    1997-03-01

    Motivated by recent proposed geometries in cellular automata, we study arrays of four or five coupled quantum dots located at the corners and at the center of a square. We calculate the addition spectrum for dots with equal or different sizes at each site and compare with the case of linear arrays. We obtain the numerically exact solution for arrays with two electrons and study the properties of this system as a cell or building block of quantum dot cellular automata. We obtain the ``polarization" for each state and discuss its possible use as a two-state system or ``qubit," as proposed recently(C. S. Lent, P. D. Tougaw, and W. Porod, Appl. Phys. Lett. 62) 714, (1993). An extended Hubbard Hamiltonian is used which takes into account quantum confinement, intra- an inter-dot Coulomb interaction as well as tunneling between neighboring dots.

  11. 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.

  12. Photoluminescence of patterned CdSe quantum dot for anti-counterfeiting label on paper

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

    Isnaeni,, E-mail: isnaeni@lipi.go.id; Yulianto, Nursidik; Suliyanti, Maria Margaretha

    We successfully developed a method utilizing colloidal CdSe nanocrystalline quantum dot for anti-counterfeiting label on a piece of glossy paper. We deposited numbers and lines patterns of toluene soluble CdSe quantum dot using rubber stamper on a glossy paper. The width of line pattern was about 1-2 mm with 1-2 mm separation between lines. It required less than one minute for deposited CdSe quantum dot on glossy paper to dry and become invisible by naked eyes. However, patterned quantum dot become visible using long-pass filter glasses upon excitation of UV lamp or blue laser. We characterized photoluminescence of line patterns of quantummore » dot, and we found that emission boundaries of line patterns were clearly observed. The error of line size and shape were mainly due to defect of the original stamper. The emission peak wavelength of CdSe quantum dot was 629 nm. The emission spectrum of deposited quantum dot has full width at half maximum (FWHM) of 30-40 nm. The spectra similarity between deposited quantum dot and the original quantum dot in solution proved that our stamping method can be simply applied on glossy paper without changing basic optical property of the quantum dot. Further development of this technique is potential for anti-counterfeiting label on very important documents or objects.« less

  13. Multi-bit dark state memory: Double quantum dot as an electronic quantum memory

    NASA Astrophysics Data System (ADS)

    Aharon, Eran; Pozner, Roni; Lifshitz, Efrat; Peskin, Uri

    2016-12-01

    Quantum dot clusters enable the creation of dark states which preserve electrons or holes in a coherent superposition of dot states for a long time. Various quantum logic devices can be envisioned to arise from the possibility of storing such trapped particles for future release on demand. In this work, we consider a double quantum dot memory device, which enables the preservation of a coherent state to be released as multiple classical bits. Our unique device architecture uses an external gating for storing (writing) the coherent state and for retrieving (reading) the classical bits, in addition to exploiting an internal gating effect for the preservation of the coherent state.

  14. Stability of quantum-dot excited-state laser emission under simultaneous ground-state perturbation

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

    Kaptan, Y., E-mail: yuecel.kaptan@physik.tu-berlin.de; Herzog, B.; Schöps, O.

    2014-11-10

    The impact of ground state amplification on the laser emission of In(Ga)As quantum dot excited state lasers is studied in time-resolved experiments. We find that a depopulation of the quantum dot ground state is followed by a drop in excited state lasing intensity. The magnitude of the drop is strongly dependent on the wavelength of the depletion pulse and the applied injection current. Numerical simulations based on laser rate equations reproduce the experimental results and explain the wavelength dependence by the different dynamics in lasing and non-lasing sub-ensembles within the inhomogeneously broadened quantum dots. At high injection levels, the observedmore » response even upon perturbation of the lasing sub-ensemble is small and followed by a fast recovery, thus supporting the capacity of fast modulation in dual-state devices.« less

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

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

    Singh, M., E-mail: msingh@sandia.gov; Luhman, D. R.; Lilly, M. P.

    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.

  16. Coal as an abundant source of graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Ye, Ruquan; Xiang, Changsheng; Lin, Jian; Peng, Zhiwei; Huang, Kewei; Yan, Zheng; Cook, Nathan P.; Samuel, Errol L. G.; Hwang, Chih-Chau; Ruan, Gedeng; Ceriotti, Gabriel; Raji, Abdul-Rahman O.; Martí, Angel A.; Tour, James M.

    2013-12-01

    Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.

  17. Coal as an abundant source of graphene quantum dots.

    PubMed

    Ye, Ruquan; Xiang, Changsheng; Lin, Jian; Peng, Zhiwei; Huang, Kewei; Yan, Zheng; Cook, Nathan P; Samuel, Errol L G; Hwang, Chih-Chau; Ruan, Gedeng; Ceriotti, Gabriel; Raji, Abdul-Rahman O; Martí, Angel A; Tour, James M

    2013-01-01

    Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.

  18. Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array.

    PubMed

    Hensgens, T; Fujita, T; Janssen, L; Li, Xiao; Van Diepen, C J; Reichl, C; Wegscheider, W; Das Sarma, S; Vandersypen, L M K

    2017-08-02

    Interacting fermions on a lattice can develop strong quantum correlations, which are the cause of the classical intractability of many exotic phases of matter. Current efforts are directed towards the control of artificial quantum systems that can be made to emulate the underlying Fermi-Hubbard models. Electrostatically confined conduction-band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical initialization of low-entropy states and readily adhere to the Fermi-Hubbard Hamiltonian. Until now, however, the substantial electrostatic disorder of the solid state has meant that only a few attempts at emulating Fermi-Hubbard physics on solid-state platforms have been made. Here we show that for gate-defined quantum dots this disorder can be suppressed in a controlled manner. Using a semi-automated and scalable set of experimental tools, we homogeneously and independently set up the electron filling and nearest-neighbour tunnel coupling in a semiconductor quantum dot array so as to simulate a Fermi-Hubbard system. With this set-up, we realize a detailed characterization of the collective Coulomb blockade transition, which is the finite-size analogue of the interaction-driven Mott metal-to-insulator transition. As automation and device fabrication of semiconductor quantum dots continue to improve, the ideas presented here will enable the investigation of the physics of ever more complex many-body states using quantum dots.

  19. Study of CdTe quantum dots grown using a two-step annealing method

    NASA Astrophysics Data System (ADS)

    Sharma, Kriti; Pandey, Praveen K.; Nagpal, Swati; Bhatnagar, P. K.; Mathur, P. C.

    2006-02-01

    High size dispersion, large average radius of quantum dot and low-volume ratio has been a major hurdle in the development of quantum dot based devices. In the present paper, we have grown CdTe quantum dots in a borosilicate glass matrix using a two-step annealing method. Results of optical characterization and the theoretical model of absorption spectra have shown that quantum dots grown using two-step annealing have lower average radius, lesser size dispersion, higher volume ratio and higher decrease in bulk free energy as compared to quantum dots grown conventionally.

  20. Resonance fluorescence revival in a voltage-controlled semiconductor quantum dot

    NASA Astrophysics Data System (ADS)

    Reigue, Antoine; Lemaître, Aristide; Gomez Carbonell, Carmen; Ulysse, Christian; Merghem, Kamel; Guilet, Stéphane; Hostein, Richard; Voliotis, Valia

    2018-02-01

    We demonstrate systematic resonance fluorescence recovery with near-unity emission efficiency in single quantum dots embedded in a charge-tunable device in a wave-guiding geometry. The quantum dot charge state is controlled by a gate voltage, through carrier tunneling from a close-lying Fermi sea, stabilizing the resonantly photocreated electron-hole pair. The electric field cancels out the charging/discharging mechanisms from nearby traps toward the quantum dots, responsible for the usually observed inhibition of the resonant fluorescence. Fourier transform spectroscopy as a function of the applied voltage shows a strong increase in the coherence time though not reaching the radiative limit. These charge controlled quantum dots can act as quasi-perfect deterministic single-photon emitters, with one laser pulse converted into one emitted single photon.

  1. Detection of viral infections using colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Bentzen, Elizabeth L.; House, Frances S.; Utley, Thomas J.; Crowe, James E., Jr.; Wright, David W.

    2006-02-01

    Fluorescence is a tool widely employed in biological assays. Fluorescent semiconducting nanocrystals, quantum dots (QDs), are beginning to find their way into the tool box of many biologist, chemist and biochemist. These quantum dots are an attractive alternative to the traditional organic dyes due to their broad excitation spectra, narrow emission spectra and photostability. Quantum dots were used to detect and monitor the progession of viral glycoproteins, F (fusion) and G (attachment), from Respiratory Syncytial Virus (RSV) in HEp-2 cells. Additionally, oligo-Qdot RNA probes have been developed for identification and detection of mRNA of the N(nucleocapsid) protein for RSV. The use of quantum dot-FISH probes provides another confirmatory route to diagnostics as well as a new class of probes for monitoring the flux and fate of viral RNA RSV is the most common cause of lower respiratory tract infection in children worldwide and the most common cause of hospitalization of infants in the US. Antiviral therapy is available for treatment of RSV but is only effective if given within the first 48 hours of infection. Existing test methods require a virus level of at least 1000-fold of the amount needed for infection of most children and require several days to weeks to obtain results. The use of quantum dots may provide an early, rapid method for detection and provide insight into the trafficking of viral proteins during the course of infection.

  2. Quantum Dot Nanobioelectronics and Selective Antimicrobial Redox Interventions

    NASA Astrophysics Data System (ADS)

    Goodman, Samuel Martin

    The unique properties of nanomaterials have engendered a great deal of interest in applying them for applications ranging from solid state physics to bio-imaging. One class of nanomaterials, known collectively as quantum dots, are defined as semiconducting crystals which have a characteristic dimension smaller than the excitonic radius of the bulk material which leads to quantum confinement effects. In this size regime, excited charge carriers behave like prototypical particles in a box, with their energy levels defined by the dimensions of the constituent particle. This is the source of the tunable optical properties which have drawn a great deal of attention with regards to finding appropriate applications for these materials. This dissertation is divided into multiple sections grouped by the type of application explored. The first sectoin investigates the energetic interactions of physically-coupled quantum dots and DNA, with the goal of gaining insight into how self-assembled molecular wires can bridge the energetic states of physically separated nanocrystals. Chapter 1 begins with an introduction to the properties of quantum dots, the conductive properties of DNA, and the common characterization methods used to characterize materials on the nanoscale. In Chapter 2 scanning tunneling measurements of QD-DNA constructs on the single particle level are presented which show the tunable coupling between the two materials and their resulting hybrid electronic structure. This is expanded upon in Chapter 3 where the conduction of photogenerated charges in QD-DNA hybrid thin films are characterized, which exhibit different charge transfer pathways through the constituent nucleobases depending on the energy of the incident light and resulting electrons. Complementary investigations of energy transfer mediated through DNA are presented in Chapter 4, with confirmation of Dexter-like transfer being facilitated through the oligonucleotides. The second section quantifies the

  3. Green, Rapid, and Universal Preparation Approach of Graphene Quantum Dots under Ultraviolet Irradiation.

    PubMed

    Zhu, Jinli; Tang, Yanfeng; Wang, Gang; Mao, Jiarong; Liu, Zhiduo; Sun, Tongming; Wang, Miao; Chen, Da; Yang, Yucheng; Li, Jipeng; Deng, Yuan; Yang, Siwei

    2017-04-26

    It is of great significance and importance to explore a mild, clean, and highly efficient universal approach for the synthesis of graphene quantum dots. Herein, we introduced a new green, rapid, and universal preparation approach for graphene quantum dots via the free-radical polymerization of oxygen-containing aromatic compounds under ultraviolet irradiation. This approach had a high yield (86%), and the byproducts are only H 2 O and CO 2 . The obtained graphene quantum dots were well-crystallized and showed remarkable optical and biological properties. The colorful, different-sized graphene quantum dots can be used in fluorescent bioimaging in vitro and in vivo. This approach is suitable not only for the preparation of graphene quantum dots but also for heteroatom-doped graphene quantum dots.

  4. Nuclear Spin Nanomagnet in an Optically Excited Quantum Dot

    NASA Astrophysics Data System (ADS)

    Korenev, V. L.

    2007-12-01

    Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins—the nuclear spin nanomagnet.

  5. Nuclear spin nanomagnet in an optically excited quantum dot.

    PubMed

    Korenev, V L

    2007-12-21

    Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins-the nuclear spin nanomagnet.

  6. Effects of Shape and Strain Distribution of Quantum Dots on Optical Transition in the Quantum Dot Infrared Photodetectors

    PubMed Central

    2008-01-01

    We present a systemic theoretical study of the electronic properties of the quantum dots inserted in quantum dot infrared photodetectors (QDIPs). The strain distribution of three different shaped quantum dots (QDs) with a same ratio of the base to the vertical aspect is calculated by using the short-range valence-force-field (VFF) approach. The calculated results show that the hydrostatic strain ɛHvaries little with change of the shape, while the biaxial strain ɛBchanges a lot for different shapes of QDs. The recursion method is used to calculate the energy levels of the bound states in QDs. Compared with the strain, the shape plays a key role in the difference of electronic bound energy levels. The numerical results show that the deference of bound energy levels of lenslike InAs QD matches well with the experimental results. Moreover, the pyramid-shaped QD has the greatest difference from the measured experimental data. PMID:20596318

  7. Lead Telluride Quantum Dot Solar Cells Displaying External Quantum Efficiencies Exceeding 120%

    PubMed Central

    2015-01-01

    Multiple exciton generation (MEG) in semiconducting quantum dots is a process that produces multiple charge-carrier pairs from a single excitation. MEG is a possible route to bypass the Shockley-Queisser limit in single-junction solar cells but it remains challenging to harvest charge-carrier pairs generated by MEG in working photovoltaic devices. Initial yields of additional carrier pairs may be reduced due to ultrafast intraband relaxation processes that compete with MEG at early times. Quantum dots of materials that display reduced carrier cooling rates (e.g., PbTe) are therefore promising candidates to increase the impact of MEG in photovoltaic devices. Here we demonstrate PbTe quantum dot-based solar cells, which produce extractable charge carrier pairs with an external quantum efficiency above 120%, and we estimate an internal quantum efficiency exceeding 150%. Resolving the charge carrier kinetics on the ultrafast time scale with pump–probe transient absorption and pump–push–photocurrent measurements, we identify a delayed cooling effect above the threshold energy for MEG. PMID:26488847

  8. Measurement of a heavy-hole hyperfine interaction in InGaAs quantum dots using resonance fluorescence.

    PubMed

    Fallahi, P; Yilmaz, S T; Imamoğlu, A

    2010-12-17

    We measure the strength and the sign of hyperfine interaction of a heavy hole with nuclear spins in single self-assembled quantum dots. Our experiments utilize the locking of a quantum dot resonance to an incident laser frequency to generate nuclear spin polarization. By monitoring the resulting Overhauser shift of optical transitions that are split either by electron or exciton Zeeman energy with respect to the locked transition using resonance fluorescence, we find that the ratio of the heavy-hole and electron hyperfine interactions is -0.09 ± 0.02 in three quantum dots. Since hyperfine interactions constitute the principal decoherence source for spin qubits, we expect our results to be important for efforts aimed at using heavy-hole spins in quantum information processing.

  9. Towards Violation of Classical Inequalities using Quantum Dot Resonance Fluorescence

    NASA Astrophysics Data System (ADS)

    Peiris, Manoj

    Self-assembled semiconductor quantum dots have attracted considerable interest recently, ranging from fundamental studies of quantum optics to advanced applications in the field of quantum information science. With their atom-like properties, quantum dot based nanophotonic devices may also substantially contribute to the development of quantum computers. This work presents experimental progress towards the understanding of light-matter interactions that occur beyond well-understood monochromatic resonant light scattering processes in semiconductor quantum dots. First, we report measurements of resonance fluorescence under bichromatic laser excitation. With the inclusion of a second laser, both first-order and second-order correlation functions are substantially altered. Under these conditions, the scattered light exhibits a rich spectrum containing many spectral features that lead to a range of nonlinear multiphoton dynamics. These observations are discussed and compared with a theoretical model. Second, we investigated the light scattered by a quantum dot in the presence of spectral filtering. By scanning the tunable filters placed in front of each detector of a Hanbury-Brown and Twiss setup and recording coincidence measurements, a \\two-photon spectrum" has been experimentally reconstructed for the first time. The two-photon spectrum contains a wealth of information about the cascaded emission involved in the scattering process, such as transitions occurring via virtual intermediate states. Our measurements also reveal that the scattered frequency-filtered light from a quantum dot violates the Cauchy-Schwarz inequality. Finally, Franson-interferometry has been performed using spectrally filtered light from quantum dot resonance fluorescence. Visibilities exceeding the classical limit were demonstrated by using a pair of folded Mach-Zehnder interferometers, paving the way for producing single time-energy entangled photon pairs that could violate Bell

  10. Chemically Triggered Formation of Two-Dimensional Epitaxial Quantum Dot Superlattices.

    PubMed

    Walravens, Willem; De Roo, Jonathan; Drijvers, Emile; Ten Brinck, Stephanie; Solano, Eduardo; Dendooven, Jolien; Detavernier, Christophe; Infante, Ivan; Hens, Zeger

    2016-07-26

    Two dimensional superlattices of epitaxially connected quantum dots enable size-quantization effects to be combined with high charge carrier mobilities, an essential prerequisite for highly performing QD devices based on charge transport. Here, we demonstrate that surface active additives known to restore nanocrystal stoichiometry can trigger the formation of epitaxial superlattices of PbSe and PbS quantum dots. More specifically, we show that both chalcogen-adding (sodium sulfide) and lead oleate displacing (amines) additives induce small area epitaxial superlattices of PbSe quantum dots. In the latter case, the amine basicity is a sensitive handle to tune the superlattice symmetry, with strong and weak bases yielding pseudohexagonal or quasi-square lattices, respectively. Through density functional theory calculations and in situ titrations monitored by nuclear magnetic resonance spectroscopy, we link this observation to the concomitantly different coordination enthalpy and ligand displacement potency of the amine. Next to that, an initial ∼10% reduction of the initial ligand density prior to monolayer formation and addition of a mild, lead oleate displacing chemical trigger such as aniline proved key to induce square superlattices with long-range, square micrometer order; an effect that is the more pronounced the larger the quantum dots. Because the approach applies to PbS quantum dots as well, we conclude that it offers a reproducible and rational method for the formation of highly ordered epitaxial quantum dot superlattices.

  11. Electrochemical Study and Applications of Selective Electrodeposition of Silver on Quantum Dots.

    PubMed

    Martín-Yerga, Daniel; Rama, Estefanía Costa; Costa-García, Agustín

    2016-04-05

    In this work, selective electrodeposition of silver on quantum dots is described. The particular characteristics of the nanostructured silver thus obtained are studied by electrochemical and microscopic techniques. On one hand, quantum dots were found to catalyze the silver electrodeposition, and on the other hand, a strong adsorption between electrodeposited silver and quantum dots was observed, indicated by two silver stripping processes. Nucleation of silver nanoparticles followed different mechanisms depending on the surface (carbon or quantum dots). Voltammetric and confocal microscopy studies showed the great influence of electrodeposition time on surface coating, and high-resolution transmission electron microscopy (HRTEM) imaging confirmed the initial formation of Janus-like Ag@QD nanoparticles in this process. By use of moderate electrodeposition conditions such as 50 μM silver, -0.1 V, and 60 s, the silver was deposited only on quantum dots, allowing the generation of localized nanostructured electrode surfaces. This methodology can also be employed for sensing applications, showing a promising ultrasensitive electrochemical method for quantum dot detection.

  12. Towards Scalable Entangled Photon Sources with Self-Assembled InAs /GaAs Quantum Dots

    NASA Astrophysics Data System (ADS)

    Wang, Jianping; Gong, Ming; Guo, G.-C.; He, Lixin

    2015-08-01

    The biexciton cascade process in self-assembled quantum dots (QDs) provides an ideal system for realizing deterministic entangled photon-pair sources, which are essential to quantum information science. The entangled photon pairs have recently been generated in experiments after eliminating the fine-structure splitting (FSS) of excitons using a number of different methods. Thus far, however, QD-based sources of entangled photons have not been scalable because the wavelengths of QDs differ from dot to dot. Here, we propose a wavelength-tunable entangled photon emitter mounted on a three-dimensional stressor, in which the FSS and exciton energy can be tuned independently, thereby enabling photon entanglement between dissimilar QDs. We confirm these results via atomistic pseudopotential calculations. This provides a first step towards future realization of scalable entangled photon generators for quantum information applications.

  13. Helical quantum states in HgTe quantum dots with inverted band structures.

    PubMed

    Chang, Kai; Lou, Wen-Kai

    2011-05-20

    We investigate theoretically the electron states in HgTe quantum dots (QDs) with inverted band structures. In sharp contrast to conventional semiconductor quantum dots, the quantum states in the gap of the HgTe QD are fully spin-polarized and show ringlike density distributions near the boundary of the QD and spin-angular momentum locking. The persistent charge currents and magnetic moments, i.e., the Aharonov-Bohm effect, can be observed in such a QD structure. This feature offers us a practical way to detect these exotic ringlike edge states by using the SQUID technique.

  14. Luminescent behavior of cadmium sulfide quantum dots for gallic acid estimation

    NASA Astrophysics Data System (ADS)

    Singh, Suman; Garg, Sourav; Chahal, Jitender; Raheja, Khushboo; Singh, Deepak; Singla, M. L.

    2013-03-01

    Thioglycolic acid capped cadmium sulfide (CdS/T) quantum dots have been synthesized using wet chemistry and their optical behavior has been investigated using UV-visible absorption and fluorescence spectroscopy. The role of the capping agent, sulfide source concentration, pH and temperature has been studied and discussed. Studies showed that alkaline pH leads to a decrease in the size of quantum dots and reflux temperature above 70 °C resulted in red-shift of emission spectra which is due to narrowing of the bandgap. Further, to reduce the toxicity and photochemical instability of quantum dots, the quantum dots have been functionalized with polyethylene glycol (PEG), which resulted in a 20% enhancement of the fluorescence intensity. The application potential of CdS/T-PEG quantum dots was further studied using gallic acid as a model compound. The sensing is based on fluorescence quenching of quantum dots in the presence of gallic acid, and this study showed linearity in the range from 1.3 × 10-8 to 46.5 × 10-8 mM, with a detection limit of 3.6 × 10-8 mM.

  15. Room-temperature lasing in a single nanowire with quantum dots

    NASA Astrophysics Data System (ADS)

    Tatebayashi, Jun; Kako, Satoshi; Ho, Jinfa; Ota, Yasutomo; Iwamoto, Satoshi; Arakawa, Yasuhiko

    2015-08-01

    Semiconductor nanowire lasers are promising as ultrasmall, highly efficient coherent light emitters in the fields of nanophotonics, nano-optics and nanobiotechnology. Although there have been several demonstrations of nanowire lasers using homogeneous bulk gain materials or multi-quantum-wells/disks, it is crucial to incorporate lower-dimensional quantum nanostructures into the nanowire to achieve superior device performance in relation to threshold current, differential gain, modulation bandwidth and temperature sensitivity. The quantum dot is a useful and essential nanostructure that can meet these requirements. However, difficulties in forming stacks of quantum dots in a single nanowire hamper the realization of lasing operation. Here, we demonstrate room-temperature lasing of a single nanowire containing 50 quantum dots by properly designing the nanowire cavity and tailoring the emission energy of each dot to enhance the optical gain. Our demonstration paves the way toward ultrasmall lasers with extremely low power consumption for integrated photonic systems.

  16. Semiconductor quantum dot super-emitters: spontaneous emission enhancement combined with suppression of defect environment using metal-oxide plasmonic metafilms

    NASA Astrophysics Data System (ADS)

    Sadeghi, Seyed M.; Wing, Waylin J.; Gutha, Rithvik R.; Sharp, Christina

    2018-01-01

    We demonstrate that a metal-oxide plasmonic metafilm consisting of a Si/Al oxide junction in the vicinity of a thin gold layer can quarantine excitons in colloidal semiconductor quantum dots against their defect environments. This process happens while the plasmon fields of the gold layer enhance spontaneous emission decay rates of the quantum dots. We study the emission dynamics of such quantum dots when the distance between the Si/Al oxide junction and the gold thin layer is varied. The results show that for distances less than a critical value the lifetime of the quantum dots can be elongated while they experience intense plasmon fields. This suggests that the metal-oxide metafilm can keep photo-excited electrons in the cores of the quantum dots, suppressing their migration to the surface defect sites. This leads to suppression of Auger recombination, offering quantum dot super-emitters with emission that is enhanced not only by the plasmon fields (Purcell effect), but also by strong suppression of the non-radiative decay caused by the defect sites.

  17. Quantum Dots: Proteomics characterization of the impact on biological systems

    NASA Astrophysics Data System (ADS)

    Pozzi-Mucelli, Stefano; Boschi, F.; Calderan, L.; Sbarbati, A.; Osculati, F.

    2009-05-01

    Over the past few years, Quantum Dots have been tested in most biotechnological applications that use fluorescence, including DNA array technology, immunofluorescence assays, cell and animal biology. Quantum Dots tend to be brighter than conventional dyes, because of the compounded effects of extinction coefficients that are an order of magnitude larger than those of most dyes. Their main advantage resides in their resistance to bleaching over long periods of time (minutes to hours), allowing the acquisition of images that are crisp and well contrasted. This increased photostability is especially useful for three-dimensional (3D) optical sectioning, where a major issue is bleaching of fluorophores during acquisition of successive z-sections, which compromises the correct reconstruction of 3D structures. The long-term stability and brightness of Quantum Dots make them ideal candidates also for live animal targeting and imaging. The vast majority of the papers published to date have shown no relevant effects on cells viability at the concentration used for imaging applications; higher concentrations, however, caused some issues on embryonic development. Adverse effects are due to be caused by the release of cadmium, as surface PEGylation of the Quantum Dots reduces these issues. A recently published paper shows evidences of an epigenetic effect of Quantum Dots treatment, with general histones hypoacetylation, and a translocation to the nucleus of p53. In this study, mice treated with Quantum Dots for imaging purposes were analyzed to investigate the impact on protein expression and networking. Differential mono-and bidimensional electrophoresis assays were performed, with the individuation of differentially expressed proteins after intravenous injection and imaging analysis; further, as several authors indicate an increase in reactive oxygen species as a possible mean of damage due to the Quantum Dots treatment, we investigated the signalling pathway of APE1/Ref1, a

  18. Resonant tunneling spectroscopy of valley eigenstates on a donor-quantum dot coupled system

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

    Kobayashi, T., E-mail: t.kobayashi@unsw.edu.au; Heijden, J. van der; House, M. G.

    We report on electronic transport measurements through a silicon double quantum dot consisting of a donor and a quantum dot. Transport spectra show resonant tunneling peaks involving different valley states, which illustrate the valley splitting in a quantum dot on a Si/SiO{sub 2} interface. The detailed gate bias dependence of double dot transport allows a first direct observation of the valley splitting in the quantum dot, which is controllable between 160 and 240 μeV with an electric field dependence 1.2 ± 0.2 meV/(MV/m). A large valley splitting is an essential requirement for implementing a physical electron spin qubit in a silicon quantum dot.

  19. Current Application of Quantum Dots (QD) in Cancer Therapy: A Review.

    PubMed

    Babu, Lavanya Thilak; Paira, Priyankar

    2017-01-01

    Semiconductor quantum dots proved themselves as efficient fluorescent probes in cancer detection and treatment. Their size, high stability, non-photobleaching and water solubility made them a unique fluorophore in place of conventional organic dyes. Newly emerged theranostic drug delivery system using quantum dots helped us in better understanding of the drug delivery mechanism inside the cells. Surface modified Quantum dots and their applications became wide in bioimaging, immunohistochemistry, tracking intracellular drug and intracellular molecules target. We have highlighted various applications of quantum dots in cancer treatment, drug delivery, flow cytometry, and theranostics. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

  20. Slow Auger Relaxation in HgTe Colloidal Quantum Dots.

    PubMed

    Melnychuk, Christopher; Guyot-Sionnest, Philippe

    2018-05-03

    The biexciton lifetimes in HgTe colloidal quantum dots are measured as a function of particle size. Samples produced by two synthetic methods, leading to partially aggregated or well-dispersed particles, exhibit markedly different dynamics. The relaxation characteristics of partially aggregated HgTe inhibit reliable determinations of the Auger lifetime. In well-dispersed HgTe quantum dots, the biexciton lifetime increases approximately linearly with particle volume, confirming trends observed in other systems. The extracted Auger coefficient is three orders of magnitude smaller than that for bulk HgCdTe materials with similar energy gaps. We discuss these findings in the context of understanding Auger relaxation in quantum-confined systems and their relevance to mid-infrared optoelectronic devices based on HgTe colloidal quantum dots.

  1. Evaporation-Induced Assembly of Quantum Dots into Nanorings

    PubMed Central

    Chen, Jixin; Liao, Wei-Ssu; Chen, Xin; Yang, Tinglu; Wark, Stacey E.; Son, Dong Hee; Batteas, James D.; Cremer, Paul S.

    2011-01-01

    Herein, we demonstrate the controlled formation of two-dimensional periodic arrays of ring-shaped nanostructures assembled from CdSe semiconductor quantum dots (QDs). The patterns were fabricated by using an evaporative templating method. This involves the introduction of an aqueous solution containing both quantum dots and polystyrene microspheres onto the surface of a planar hydrophilic glass substrate. The quantum dots became confined to the meniscus of the microspheres during evaporation, which drove ring assembly via capillary forces at the polystyrene sphere/glass substrate interface. The geometric parameters for nanoring formation could be controlled by tuning the size of the microspheres and the concentration of the QDs employed. This allowed hexagonal arrays of nanorings to be formed with thicknesses ranging from single dot necklaces to thick multilayer structures over surface areas of many square millimeters. Moreover, the diameter of the ring structures could be simultaneously controlled. A simple model was employed to explain the forces involved in the formation of nanoparticle nanorings. PMID:19206264

  2. Nanofabrication of Gate-defined GaAs/AlGaAs Lateral Quantum Dots

    PubMed Central

    Bureau-Oxton, Chloé; Camirand Lemyre, Julien; Pioro-Ladrière, Michel

    2013-01-01

    A quantum computer is a computer composed of quantum bits (qubits) that takes advantage of quantum effects, such as superposition of states and entanglement, to solve certain problems exponentially faster than with the best known algorithms on a classical computer. Gate-defined lateral quantum dots on GaAs/AlGaAs are one of many avenues explored for the implementation of a qubit. When properly fabricated, such a device is able to trap a small number of electrons in a certain region of space. The spin states of these electrons can then be used to implement the logical 0 and 1 of the quantum bit. Given the nanometer scale of these quantum dots, cleanroom facilities offering specialized equipment- such as scanning electron microscopes and e-beam evaporators- are required for their fabrication. Great care must be taken throughout the fabrication process to maintain cleanliness of the sample surface and to avoid damaging the fragile gates of the structure. This paper presents the detailed fabrication protocol of gate-defined lateral quantum dots from the wafer to a working device. Characterization methods and representative results are also briefly discussed. Although this paper concentrates on double quantum dots, the fabrication process remains the same for single or triple dots or even arrays of quantum dots. Moreover, the protocol can be adapted to fabricate lateral quantum dots on other substrates, such as Si/SiGe. PMID:24300661

  3. 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.

  4. Nanoscale patterning of colloidal quantum dots on transparent and metallic planar surfaces.

    PubMed

    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

    2012-09-07

    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 been recently developed. Herein, we present a simple method of patterning colloidal quantum dots for photonic nanostructures such as straight lines, rings and dot patterns either on transparent or metallic substrates. Sub-10 nm width of the patterned line could be achieved with a well-defined sidewall profile. Using this method, we demonstrate a surface plasmon launcher from a quantum dot cluster in the visible spectrum.

  5. Demonstration of quantum entanglement between a single electron spin confined to an InAs quantum dot and a photon.

    PubMed

    Schaibley, J R; Burgers, A P; McCracken, G A; Duan, L-M; Berman, P R; Steel, D G; Bracker, A S; Gammon, D; Sham, L J

    2013-04-19

    The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this Letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to a single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot's excited state. We obtain a lower bound on the fidelity of entanglement of 0.59±0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement-based spin-spin entanglement which does not require sub-nanosecond timing resolution, we estimate that this system would enable near ideal performance. The inferred (usable) entanglement generation rate is 3×10(3) s(-1). This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network.

  6. DNA nanosensor based on biocompatible graphene quantum dots and carbon nanotubes.

    PubMed

    Qian, Zhao Sheng; Shan, Xiao Yue; Chai, Lu Jing; Ma, Juan Juan; Chen, Jian Rong; Feng, Hui

    2014-10-15

    An ultrasensitive nanosensor based on fluorescence resonance energy transfer (FRET) between biocompatible graphene quantum dots and carbon nanotubes for DNA detection was reported. We take advantage of good biocompatibility and strong fluorescence of graphene quantum dots, base pairing specificity of DNA and unique fluorescence resonance energy transfer between graphene quantum dots and carbon nanotubes to achieve the analysis of low concentrations of DNA. Graphene quantum dots with high quantum yield up to 0.20 were prepared and served as the fluorophore of DNA probe. FRET process between graphene quantum dots-labeled probe and oxidized carbon nanotubes is easily achieved due to their efficient self-assembly through specific π-π interaction. This nanosensor can distinguish complementary and mismatched nucleic acid sequences with high sensitivity and good reproducibility. The detection method based on this nanosensor possesses a broad linear span of up to 133.0 nM and ultralow detection limit of 0.4 nM. The constructed nanosensor is expected to be highly biocompatible because of all its components with excellent biocompatibility. Copyright © 2014 Elsevier B.V. All rights reserved.

  7. Transcending binary logic by gating three coupled quantum dots.

    PubMed

    Klein, Michael; Rogge, S; Remacle, F; Levine, R D

    2007-09-01

    Physical considerations supported by numerical solution of the quantum dynamics including electron repulsion show that three weakly coupled quantum dots can robustly execute a complete set of logic gates for computing using three valued inputs and outputs. Input is coded as gating (up, unchanged, or down) of the terminal dots. A nanosecond time scale switching of the gate voltage requires careful numerical propagation of the dynamics. Readout is the charge (0, 1, or 2 electrons) on the central dot.

  8. Designing artificial 2D crystals with site and size controlled quantum dots.

    PubMed

    Xie, Xuejun; Kang, Jiahao; Cao, Wei; Chu, Jae Hwan; Gong, Yongji; Ajayan, Pulickel M; Banerjee, Kaustav

    2017-08-30

    Ordered arrays of quantum dots in two-dimensional (2D) materials would make promising optical materials, but their assembly could prove challenging. Here we demonstrate a scalable, site and size controlled fabrication of quantum dots in monolayer molybdenum disulfide (MoS 2 ), and quantum dot arrays with nanometer-scale spatial density by focused electron beam irradiation induced local 2H to 1T phase change in MoS 2 . By designing the quantum dots in a 2D superlattice, we show that new energy bands form where the new band gap can be controlled by the size and pitch of the quantum dots in the superlattice. The band gap can be tuned from 1.81 eV to 1.42 eV without loss of its photoluminescence performance, which provides new directions for fabricating lasers with designed wavelengths. Our work constitutes a photoresist-free, top-down method to create large-area quantum dot arrays with nanometer-scale spatial density that allow the quantum dots to interfere with each other and create artificial crystals. This technique opens up new pathways for fabricating light emitting devices with 2D materials at desired wavelengths. This demonstration can also enable the assembly of large scale quantum information systems and open up new avenues for the design of artificial 2D materials.

  9. Three-Dimensional Control of Self-Assembled Quantum Dot Configurations

    DTIC Science & Technology

    2010-06-17

    Lateral Quantum Dot Molecules Around Self-Assembled Nanoholes . Appl. Phys. Lett. 2003, 82, 2892–2894. 7. Alonso-Gonzalez, P.; Martin-Sanchez, J.; Gonzalez...Y.; Alen, B.; Fuster, D.; Gonzalez, L. Formation of Lateral Low Density In(Ga)As Quantum Dot Pairs in GaAs Nanoholes . Cryst. Growth Des. 2009, 9

  10. Energy structure and radiative lifetimes of InxGa1-xN /AlN quantum dots

    NASA Astrophysics Data System (ADS)

    Aleksandrov, Ivan A.; Zhuravlev, Konstantin S.

    2018-01-01

    We report calculations of the ground state transition energies and the radiative lifetimes in InxGa1-xN /AlN quantum dots with different size and indium content. The ground state transition energy and the radiative lifetime of the InxGa1-xN /AlN quantum dots can be varied over a wide range by changing the height of the quantum dot and the indium content. The sizes and compositions for quantum dots emitting in the wavelength range for fiber-optic telecommunications have been found. The radiative lifetime of the InxGa1-xN /AlN quantum dots increases with increase in quantum dot height at a constant indium content, and increases with increase in indium content at constant quantum dot height. For quantum dots with constant ground state transition energy the radiative lifetime decreases with increase in indium content.

  11. Ligand-Asymmetric Janus Quantum Dots for Efficient Blue-Quantum Dot Light-Emitting Diodes.

    PubMed

    Cho, Ikjun; Jung, Heeyoung; Jeong, Byeong Guk; Hahm, Donghyo; Chang, Jun Hyuk; Lee, Taesoo; Char, Kookheon; Lee, Doh C; Lim, Jaehoon; Lee, Changhee; Cho, Jinhan; Bae, Wan Ki

    2018-06-19

    We present ligand-asymmetric Janus quantum dots (QDs) to improve the device performance of quantum dot light-emitting diodes (QLEDs). Specifically, we devise blue QLEDs incorporating blue QDs with asymmetrically modified ligands, in which the bottom ligand of QDs in contact with ZnO electron-transport layer serves as a robust adhesive layer and an effective electron-blocking layer and the top ligand ensures uniform deposition of organic hole transport layers with enhanced hole injection properties. Suppressed electron overflow by the bottom ligand and stimulated hole injection enabled by the top ligand contribute synergistically to boost the balance of charge injection in blue QDs and therefore the device performance of blue QLEDs. As an ultimate achievement, the blue QLED adopting ligand-asymmetric QDs displays 2-fold enhancement in peak external quantum efficiency (EQE = 3.23%) compared to the case of QDs with native ligands (oleic acid) (peak EQE = 1.49%). The present study demonstrates an integrated strategy to control over the charge injection properties into QDs via ligand engineering that enables enhancement of the device performance of blue QLEDs and thus promises successful realization of white light-emitting devices using QDs.

  12. Quantum Phase Transitions in Cavity Coupled Dot systems

    NASA Astrophysics Data System (ADS)

    Kasisomayajula, Vijay; Russo, Onofrio

    2011-03-01

    We investigate a Quantum Dot System, in which the transconductance, in part, is due to spin coupling, with each dot subjected to a biasing voltage. When this system is housed in a QED cavity, the cavity dot coupling alters the spin coupling of the coupled dots significantly via the Purcell Effect. In this paper we show the extent to which one can control the various coupling parameters: the inter dot coupling, the individual dots coupling with the cavity and the coupled dots coupling with the cavity as a single entity. We show that the dots coupled to each other and to the cavity, the spin transport can be controlled selectively. We derive the conditions for such control explicitly. Further, we discuss the Quantum phase transition effects due to the charge and spin transport through the dots. The electron transport through the dots, electron-electron spin interaction and the electron-photon interaction are treated using the Non-equilibrium Green's Function Formalism. http://publish.aps.org/search/field/author/Trif_Mircea (Trif Mircea), http://publish.aps.org/search/field/author/Golovach_Vitaly_N (Vitaly N. Golovach), and http://publish.aps.org/search/field/author/Loss_Daniel (Daniel Loss), Phys. Rev. B 75, 085307 (2007)

  13. Subdecoherence time generation and detection of orbital entanglement in quantum dots.

    PubMed

    Brange, F; Malkoc, O; Samuelsson, P

    2015-05-01

    Recent experiments have demonstrated subdecoherence time control of individual single-electron orbital qubits. Here we propose a quantum-dot-based scheme for generation and detection of pairs of orbitally entangled electrons on a time scale much shorter than the decoherence time. The electrons are entangled, via two-particle interference, and transferred to the detectors during a single cotunneling event, making the scheme insensitive to charge noise. For sufficiently long detector dot lifetimes, cross-correlation detection of the dot charges can be performed with real-time counting techniques, providing for an unambiguous short-time Bell inequality test of orbital entanglement.

  14. Design and Synthesis of Antiblinking and Antibleaching Quantum Dots in Multiple Colors via Wave Function Confinement.

    PubMed

    Cao, Hujia; Ma, Junliang; Huang, Lin; Qin, Haiyan; Meng, Renyang; Li, Yang; Peng, Xiaogang

    2016-12-07

    Single-molecular spectroscopy reveals that photoluminescence (PL) of a single quantum dot blinks, randomly switching between bright and dim/dark states under constant photoexcitation, and quantum dots photobleach readily. These facts cast great doubts on potential applications of these promising emitters. After ∼20 years of efforts, synthesis of nonblinking quantum dots is still challenging, with nonblinking quantum dots only available in red-emitting window. Here we report synthesis of nonblinking quantum dots covering most part of the visible window using a new synthetic strategy, i.e., confining the excited-state wave functions of the core/shell quantum dots within the core quantum dot and its inner shells (≤ ∼5 monolayers). For the red-emitting ones, the new synthetic strategy yields nonblinking quantum dots with small sizes (∼8 nm in diameter) and improved nonblinking properties. These new nonblinking quantum dots are found to be antibleaching. Results further imply that the PL blinking and photobleaching of quantum dots are likely related to each other.

  15. A non-genetic approach to labelling acute myeloid leukemia and bone marrow cells with quantum dots.

    PubMed

    Zheng, Yanwen; Tan, Dongming; Chen, Zheng; Hu, Chenxi; Mao, Zhengwei J; Singleton, Timothy P; Zeng, Yan; Shao, Xuejun; Yin, Bin

    2014-06-01

    The difficulty in manipulation of leukemia cells has long hindered the dissection of leukemia pathogenesis. We have introduced a non-genetic approach of marking blood cells, using quantum dots. We compared quantum dots complexed with different vehicles, including a peptide Tat, cationic polymer Turbofect and liposome. Quantum dots-Tat showed the highest efficiency of marking hematopoietic cells among the three vehicles. Quantum dots-Tat could also label a panel of leukemia cell lines at varied efficiencies. More uniform intracellular distributions of quantum dots in mouse bone marrow and leukemia cells were obtained with quantum dots-Tat, compared with the granule-like formation obtained with quantum dots-liposome. Our results suggest that quantum dots have provided a photostable and non-genetic approach that labels normal and malignant hematopoietic cells, in a cell type-, vehicle-, and quantum dot concentration-dependent manner. We expect for potential applications of quantum dots as an easy and fast marking tool assisting investigations of various types of blood cells in the future.

  16. 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.

  17. Photosensitization of ZnO nanowires with CdSe quantum dots for photovoltaic devices.

    PubMed

    Leschkies, Kurtis S; Divakar, Ramachandran; Basu, Joysurya; Enache-Pommer, Emil; Boercker, Janice E; Carter, C Barry; Kortshagen, Uwe R; Norris, David J; Aydil, Eray S

    2007-06-01

    We combine CdSe semiconductor nanocrystals (or quantum dots) and single-crystal ZnO nanowires to demonstrate a new type of quantum-dot-sensitized solar cell. An array of ZnO nanowires was grown vertically from a fluorine-doped tin oxide conducting substrate. CdSe quantum dots, capped with mercaptopropionic acid, were attached to the surface of the nanowires. When illuminated with visible light, the excited CdSe quantum dots injected electrons across the quantum dot-nanowire interface. The morphology of the nanowires then provided the photoinjected electrons with a direct electrical pathway to the photoanode. With a liquid electrolyte as the hole transport medium, quantum-dot-sensitized nanowire solar cells exhibited short-circuit currents ranging from 1 to 2 mA/cm2 and open-circuit voltages of 0.5-0.6 V when illuminated with 100 mW/cm2 simulated AM1.5 spectrum. Internal quantum efficiencies as high as 50-60% were also obtained.

  18. Ultrafast universal quantum control of a quantum-dot charge qubit using Landau–Zener–Stückelberg interference

    PubMed Central

    Cao, Gang; Li, Hai-Ou; Tu, Tao; Wang, Li; Zhou, Cheng; Xiao, Ming; Guo, Guang-Can; Jiang, Hong-Wen; Guo, Guo-Ping

    2013-01-01

    A basic requirement for quantum information processing is the ability to universally control the state of a single qubit on timescales much shorter than the coherence time. Although ultrafast optical control of a single spin has been achieved in quantum dots, scaling up such methods remains a challenge. Here we demonstrate complete control of the quantum-dot charge qubit on the picosecond scale, orders of magnitude faster than the previously measured electrically controlled charge- or spin-based qubits. We observe tunable qubit dynamics in a charge-stability diagram, in a time domain, and in a pulse amplitude space of the driven pulse. The observations are well described by Landau–Zener–Stückelberg interference. These results establish the feasibility of a full set of all-electrical single-qubit operations. Although our experiment is carried out in a solid-state architecture, the technique is independent of the physical encoding of the quantum information and has the potential for wider applications. PMID:23360992

  19. 6.5% efficient perovskite quantum-dot-sensitized solar cell.

    PubMed

    Im, Jeong-Hyeok; Lee, Chang-Ryul; Lee, Jin-Wook; Park, Sang-Won; Park, Nam-Gyu

    2011-10-05

    Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2-3 nm sized perovskite (CH(3)NH(3))PbI(3) nanocrystal. Spin-coating of the equimolar mixture of CH(3)NH(3)I and PbI(2) in γ-butyrolactone solution (perovskite precursor solution) leads to (CH(3)NH(3))PbI(3) quantum dots (QDs) on nanocrystalline TiO(2) surface. By electrochemical junction with iodide/iodine based redox electrolyte, perovskite QD-sensitized 3.6 μm-thick TiO(2) film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm(-2)), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.

  20. Transient Evolutional Dynamics of Quantum-Dot Molecular Phase Coherence for Sensitive Optical Switching

    NASA Astrophysics Data System (ADS)

    Shen, Jian Qi; Gu, Jing

    2018-04-01

    Atomic phase coherence (quantum interference) in a multilevel atomic gas exhibits a number of interesting phenomena. Such an atomic quantum coherence effect can be generalized to a quantum-dot molecular dielectric. Two quantum dots form a quantum-dot molecule, which can be described by a three-level Λ-configuration model { |0> ,|1> ,|2> } , i.e., the ground state of the molecule is the lower level |0> and the highly degenerate electronic states in the two quantum dots are the two upper levels |1> ,|2> . The electromagnetic characteristics due to the |0>-|1> transition can be controllably manipulated by a tunable gate voltage (control field) that drives the |2>-|1> transition. When the gate voltage is switched on, the quantum-dot molecular state can evolve from one steady state (i.e., |0>-|1> two-level dressed state) to another steady state (i.e., three-level coherent-population-trapping state). In this process, the electromagnetic characteristics of a quantum-dot molecular dielectric, which is modified by the gate voltage, will also evolve. In this study, the transient evolutional behavior of the susceptibility of a quantum-dot molecular thin film and its reflection spectrum are treated by using the density matrix formulation of the multilevel systems. The present field-tunable and frequency-sensitive electromagnetic characteristics of a quantum-dot molecular thin film, which are sensitive to the applied gate voltage, can be utilized to design optical switching devices.

  1. Cadmium-containing nanoparticles: Perspectives on pharmacology and toxicology of quantum dots

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

    Rzigalinski, Beverly A.; Strobl, Jeannine S.

    2009-08-01

    The field of nanotechnology is rapidly expanding with the development of novel nanopharmaceuticals that have potential for revolutionizing medical treatment. The rapid pace of expansion in this field has exceeded the pace of pharmacological and toxicological research on the effects of nanoparticles in the biological environment. The development of cadmium-containing nanoparticles, known as quantum dots, show great promise for treatment and diagnosis of cancer and targeted drug delivery, due to their size-tunable fluorescence and ease of functionalization for tissue targeting. However, information on pharmacology and toxicology of quantum dots needs much further development, making it difficult to assess the risksmore » associated with this new nanotechnology. Further, nanotechnology poses yet another risk for toxic cadmium, which will now enter the biological realm in nano-form. In this review, we discuss cadmium-containing quantum dots and their physicochemical properties at the nano-scale. We summarize the existing work on pharmacology and toxicology of cadmium-containing quantum dots and discuss perspectives in their utility in disease treatment. Finally, we identify critical gaps in our knowledge of cadmium quantum dot toxicity, and how these gaps need to be assessed to enable quantum dot nanotechnology to transit safely from bench to bedside.« less

  2. Measurements of undoped accumulation-mode SiGe quantum dot devices

    NASA Astrophysics Data System (ADS)

    Eng, Kevin; Borselli, Mathew; Holabird, Kevin; Milosavljevic, Ivan; Schmitz, Adele; Deelman, Peter; Huang, Biqin; Sokolich, Marko; Warren, Leslie; Hazard, Thomas; Kiselev, Andrey; Ross, Richard; Gyure, Mark; Hunter, Andrew

    2012-02-01

    We report transport measurements of undoped single-well accumulation-mode SiGe quantum dot devices with an integrated dot charge sensor. The device is designed so that individual forward-biased circular gates have dominant control of dot charge occupancy, and separate intervening gates have dominant control of tunnel rates and exchange coupling. We have demonstrated controlled loading of the first electron in single and double quantum dots. We used magneto-spectroscopy to measure singlet-triplet splittings in our quantum dots: values are typically ˜0.1 meV. Tunnel rates of single electrons to the baths can be controlled from less than 1 Hz to greater than 10 MHz. We are able to control the (0,2) to (1,1) coupling in a double quantum dot from under-coupled (tc < kT˜ 5μeV) to over-coupled (tc ˜ 0.1 meV) with a bias control of one exchange gate. Sponsored by the United States Department of Defense. Approved for Public Release, Distribution Unlimited. The views expressed are those of the author and do not reflect the official policy or position of the Department of Defense or the U.S. Government.

  3. Growth of group II-VI semiconductor quantum dots with strong quantum confinement and low size dispersion

    NASA Astrophysics Data System (ADS)

    Pandey, Praveen K.; Sharma, Kriti; Nagpal, Swati; Bhatnagar, P. K.; Mathur, P. C.

    2003-11-01

    CdTe quantum dots embedded in glass matrix are grown using two-step annealing method. The results for the optical transmission characterization are analysed and compared with the results obtained from CdTe quantum dots grown using conventional single-step annealing method. A theoretical model for the absorption spectra is used to quantitatively estimate the size dispersion in the two cases. In the present work, it is established that the quantum dots grown using two-step annealing method have stronger quantum confinement, reduced size dispersion and higher volume ratio as compared to the single-step annealed samples. (

  4. Quantum-dot temperature profiles during laser irradiation for semiconductor-doped glasses

    NASA Astrophysics Data System (ADS)

    Nagpal, Swati

    2002-12-01

    Temperature profiles around laser irradiated CdX (X=S, Se, and Te) quantum dots in borosilicate glasses were theoretically modeled. Initially the quantum dots heat up rapidly, followed by a gradual increase of temperature. Also it is found that larger dots reach higher temperatures for the same pulse characteristics. After the pulse is turned off, the dots initially cool rapidly, followed by a gradual decrease in temperature.

  5. Semiconductor quantum dots as an ideal source of polarization-entangled photon pairs on-demand: a review

    NASA Astrophysics Data System (ADS)

    Huber, Daniel; Reindl, Marcus; Aberl, Johannes; Rastelli, Armando; Trotta, Rinaldo

    2018-07-01

    More than 80 years have passed since the first publication on entangled quantum states. Over this period, the concept of spookily interacting quantum states became an emerging field of science. After various experiments proving the existence of such non-classical states, visionary ideas were put forward to exploit entanglement in quantum information science and technology. These novel concepts have not yet come out of the experimental stage, mostly because of the lack of suitable, deterministic sources of entangled quantum states. Among many systems under investigation, semiconductor quantum dots are particularly appealing emitters of on-demand, single polarization-entangled photon pairs. While it was originally believed that quantum dots must exhibit a limited degree of entanglement related to decoherence effects typical of the solid-state, recent studies have invalidated this preconception. We review the relevant experiments which have led to these important discoveries and discuss the remaining challenges for the anticipated quantum technologies.

  6. Mode locking of electron spin coherences in singly charged quantum dots.

    PubMed

    Greilich, A; Yakovlev, D R; Shabaev, A; Efros, Al L; Yugova, I A; Oulton, R; Stavarache, V; Reuter, D; Wieck, A; Bayer, M

    2006-07-21

    The fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum information processing. We show here that dephasing can be overcome by using a periodic train of light pulses to synchronize the phases of the precessing spins, and we demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. This mode locking leads to constructive interference of contributions to Faraday rotation and presents potential applications based on robust quantum coherence within an ensemble of dots.

  7. Covalent functionalized black phosphorus quantum dots

    NASA Astrophysics Data System (ADS)

    Scotognella, Francesco; Kriegel, Ilka; Sassolini, Simone

    2018-01-01

    Black phosphorus (BP) nanostructures enable a new strategy to tune the electronic and optical properties of this atomically thin material. In this paper we show, via density functional theory calculations, the possibility to modify the optical properties of BP quantum dots via covalent functionalization. The quantum dot selected in this study has chemical formula P24H12 and has been covalent functionalized with one or more benzene rings or anthracene. The effect of functionalization is highlighted in the absorption spectra, where a red shift of the absorption is noticeable. The shift can be ascribed to an electron delocalization in the black phosphorus/organic molecule nanostructure.

  8. Reducing inhomogeneity in the dynamic properties of quantum dots via self-aligned plasmonic cavities

    NASA Astrophysics Data System (ADS)

    Demory, Brandon; Hill, Tyler A.; Teng, Chu-Hsiang; Deng, Hui; Ku, P. C.

    2018-01-01

    A plasmonic cavity is shown to greatly reduce the inhomogeneity of dynamic optical properties such as quantum efficiency and radiative lifetime of InGaN quantum dots. By using an open-top plasmonic cavity structure, which exhibits a large Purcell factor and antenna quantum efficiency, the resulting quantum efficiency distribution for the quantum dots narrows and is no longer limited by the quantum dot inhomogeneity. The standard deviation of the quantum efficiency can be reduced to 2% while maintaining the overall quantum efficiency at 70%, making InGaN quantum dots a viable candidate for high-speed quantum cryptography and random number generation applications.

  9. Reducing inhomogeneity in the dynamic properties of quantum dots via self-aligned plasmonic cavities.

    PubMed

    Demory, Brandon; Hill, Tyler A; Teng, Chu-Hsiang; Deng, Hui; Ku, P C

    2018-01-05

    A plasmonic cavity is shown to greatly reduce the inhomogeneity of dynamic optical properties such as quantum efficiency and radiative lifetime of InGaN quantum dots. By using an open-top plasmonic cavity structure, which exhibits a large Purcell factor and antenna quantum efficiency, the resulting quantum efficiency distribution for the quantum dots narrows and is no longer limited by the quantum dot inhomogeneity. The standard deviation of the quantum efficiency can be reduced to 2% while maintaining the overall quantum efficiency at 70%, making InGaN quantum dots a viable candidate for high-speed quantum cryptography and random number generation applications.

  10. Absorption spectra and optical transitions in InAs/GaAs self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Cusack, M. A.; Briddon, P. R.; Jaros, M.

    1997-08-01

    We have applied the multiband effective mass/valence force field method to the calculation of optical transitions and absorption spectra in InAs/GaAs self-organized dots of different sizes. We have found that the apparently conflicting assignments of luminescence features to optical transitions in different experiments are in fact entirely compatible with each other. Whether the optical signature of a dot is constructed from transitions between states of the same quantum numbers, or via additional processes between the ground conduction state and a low-lying valence state depends on the aspect ratio of the quantum dot radius and height. The states involved can be predicted from a simple particle in a rigid rectangular box model.

  11. Quantum Dots for Live Cell and In Vivo Imaging

    PubMed Central

    Walling, Maureen A; Novak, Jennifer A; Shepard, Jason R. E

    2009-01-01

    In the past few decades, technology has made immeasurable strides to enable visualization, identification, and quantitation in biological systems. Many of these technological advancements are occurring on the nanometer scale, where multiple scientific disciplines are combining to create new materials with enhanced properties. The integration of inorganic synthetic methods with a size reduction to the nano-scale has lead to the creation of a new class of optical reporters, called quantum dots. These semiconductor quantum dot nanocrystals have emerged as an alternative to organic dyes and fluorescent proteins, and are brighter and more stable against photobleaching than standard fluorescent indicators. Quantum dots have tunable optical properties that have proved useful in a wide range of applications from multiplexed analysis such as DNA detection and cell sorting and tracking, to most recently demonstrating promise for in vivo imaging and diagnostics. This review provides an in-depth discussion of past, present, and future trends in quantum dot use with an emphasis on in vivo imaging and its related applications. PMID:19333416

  12. Self-assembled InN quantum dots on side facets of GaN nanowires

    NASA Astrophysics Data System (ADS)

    Bi, Zhaoxia; Ek, Martin; Stankevic, Tomas; Colvin, Jovana; Hjort, Martin; Lindgren, David; Lenrick, Filip; Johansson, Jonas; Wallenberg, L. Reine; Timm, Rainer; Feidenhans'l, Robert; Mikkelsen, Anders; Borgström, Magnus T.; Gustafsson, Anders; Ohlsson, B. Jonas; Monemar, Bo; Samuelson, Lars

    2018-04-01

    Self-assembled, atomic diffusion controlled growth of InN quantum dots was realized on the side facets of dislocation-free and c-oriented GaN nanowires having a hexagonal cross-section. The nanowires were synthesized by selective area metal organic vapor phase epitaxy. A 3 Å thick InN wetting layer was observed after growth, on top of which the InN quantum dots formed, indicating self-assembly in the Stranski-Krastanow growth mode. We found that the InN quantum dots can be tuned to nucleate either preferentially at the edges between GaN nanowire side facets, or directly on the side facets by tuning the adatom migration by controlling the precursor supersaturation and growth temperature. Structural characterization by transmission electron microscopy and reciprocal space mapping show that the InN quantum dots are close to be fully relaxed (residual strain below 1%) and that the c-planes of the InN quantum dots are tilted with respect to the GaN core. The strain relaxes mainly by the formation of misfit dislocations, observed with a periodicity of 3.2 nm at the InN and GaN hetero-interface. The misfit dislocations introduce I1 type stacking faults (…ABABCBC…) in the InN quantum dots. Photoluminescence investigations of the InN quantum dots show that the emissions shift to higher energy with reduced quantum dot size, which we attribute to increased quantum confinement.

  13. Nanosecond-timescale spin transfer using individual electrons in a quadruple-quantum-dot device

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

    Baart, T. A.; Jovanovic, N.; Vandersypen, L. M. K.

    2016-07-25

    The ability to coherently transport electron-spin states between different sites of gate-defined semiconductor quantum dots is an essential ingredient for a quantum-dot-based quantum computer. Previous shuttles using electrostatic gating were too slow to move an electron within the spin dephasing time across an array. Here, we report a nanosecond-timescale spin transfer of individual electrons across a quadruple-quantum-dot device. Utilizing enhanced relaxation rates at a so-called hot spot, we can upper bound the shuttle time to at most 150 ns. While actual shuttle times are likely shorter, 150 ns is already fast enough to preserve spin coherence in, e.g., silicon based quantum dots.more » This work therefore realizes an important prerequisite for coherent spin transfer in quantum dot arrays.« less

  14. Atomistic theory of excitonic fine structure in InAs/InP nanowire quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Świderski, M.; Zieliński, M.

    2017-03-01

    Nanowire quantum dots have peculiar electronic and optical properties. In this work we use atomistic tight binding to study excitonic spectra of artificial molecules formed by a double nanowire quantum dot. We demonstrate a key role of atomistic symmetry and nanowire substrate orientation rather than cylindrical shape symmetry of a nanowire and a molecule. In particular for [001 ] nanowire orientation we observe a nonvanishing bright exciton splitting for a quasimolecule formed by two cylindrical quantum dots of different heights. This effect is due to interdot coupling that effectively reduces the overall symmetry, whereas single uncoupled [001 ] quantum dots have zero fine structure splitting. We found that the same double quantum dot system grown on [111 ] nanowire reveals no excitonic fine structure for all considered quantum dot distances and individual quantum dot heights. Further we demonstrate a pronounced, by several orders of magnitude, increase of the dark exciton optical activity in a quantum dot molecule as compared to a single quantum dot. For [111 ] systems we also show spontaneous localization of single particle states in one of nominally identical quantum dots forming a molecule, which is mediated by strain and origins from the lack of the vertical inversion symmetry in [111 ] nanostructures of overall C3 v symmetry. Finally, we study lowering of symmetry due to alloy randomness that triggers nonzero excitonic fine structure and the dark exciton optical activity in realistic nanowire quantum dot molecules of intermixed composition.

  15. Attachment of Quantum Dots on Zinc Oxide Nanorods

    NASA Astrophysics Data System (ADS)

    Seay, Jared; Liang, Huan; Harikumar, Parameswar

    2011-03-01

    ZnO nanorods grown by hydrothermal technique are of great interest for potential applications in photovoltaic and optoelectronic devices. In this study we investigate the optimization of the optical absorption properties by a low temperature, chemical bath deposition technique. Our group fabricated nanorods on indium tin oxide (ITO) substrate with precursor solution of zinc nitrate hexahydrate and hexamethylenetramine (1:1 molar ratio) at 95C for 9 hours. In order to optimize the light absorption characteristics of ZnO nanorods, CdSe/ZnS core-shell quantum dots (QDs) of various diameters were attached to the surface of ZnO nanostructures grown on ITO and gold-coated silicon substrates. Density of quantum dots was varied by controlling the number drops on the surface of the ZnO nanorods. For a 0.1 M concentration of QDs of 10 nm diameter, the PL intensity at 385 nm increased as the density of the quantum dots on ZnO nanostructures was increased. For quantum dots at 1 M concentration, the PL intensity at 385 nm increased at the beginning and then decreased at higher density. We will discuss the observed changes in PL intensity with QD concentration with ZnO-QD band structure and recombination-diffusion processes taking place at the interface.

  16. Polarization control of quantum dot emission by chiral photonic crystal slabs

    NASA Astrophysics Data System (ADS)

    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 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 quantum dots 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 quantum dots, and can be close to 100% for some single quantum dots.

  17. Time-resolved photoluminescence measurements of InP/ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Thi Thuy, Pham; Thi Dieu Thuy, Ung; Chi, Tran Thi Kim; Phuong, Le Quang; Liem, Nguyen Quang; Li, Liang; Reiss, Peter

    2009-09-01

    This paper reports the results on the time-resolved photoluminescence study of InP/ZnS core/shell quantum dots. The ZnS shell played a decisive role to passivate imperfections on the surface of InP quantum dots, consequently giving rise to a strong enhancement of the photoluminescence from the InP core. Under appropriate excitation conditions, not only the emission from the InP core but also that from the ZnS shell was observed. The emission peak in InP core quantum dots varied as a function of quantum dots size, ranging in the 600 - 700 nm region; while the ZnS shell showed emission in the blue region around 470 nm, which is interpreted as resulting from defects in ZnS.

  18. Room-temperature lasing operation of a quantum-dot vertical-cavity surface-emitting laser

    NASA Astrophysics Data System (ADS)

    Saito, Hideaki; Nishi, Kenichi; Ogura, Ichiro; Sugou, Shigeo; Sugimoto, Yoshimasa

    1996-11-01

    Self-assembled growth of quantum dots by molecular-beam epitaxy is used to form the active region of a vertical-cavity surface-emitting laser (VCSEL). Ten layers of InGaAs quantum dots are stacked in order to increase the gain. This quantum-dot VCSEL has a continuous-wave operating current of 32 mA at room temperature. Emission spectra at various current injections demonstrate that the lasing action is associated with a higher-order transition in the quantum dots.

  19. Electron tunneling characteristics of a cubic quantum dot, (PbS){sub 32}

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

    Gupta, Sanjeev K., E-mail: sanjeevg@mtu.edu, E-mail: haiying.he@valpo.edu; Banyai, Douglas; Pandey, Ravindra

    The electron transport properties of the cubic quantum dot, (PbS){sub 32}, are investigated. The stability of the quantum dot has been established by recent scanning tunneling microscope experiments [B. Kiran, A. K. Kandalam, R. Rallabandi, P. Koirala, X. Li, X. Tang, Y. Wang, H. Fairbrother, G. Gantefoer, and K. Bowen, J. Chem. Phys. 136(2), 024317 (2012)]. In spite of the noticeable energy band gap (∼2 eV), a relatively high tunneling current for (PbS){sub 32} is predicted affirming the observed bright images for (PbS){sub 32}. The calculated I-V characteristics of (PbS){sub 32} are predicted to be substrate-dependent; (PbS){sub 32} on themore » Au (001) exhibits the molecular diode-like behavior and the unusual negative differential resistance effect, though this is not the case with (PbS){sub 32} on the Au (110). Appearance of the conduction channels associated with the hybridized states of quantum dot and substrate together with their asymmetric distribution at the Fermi level seem to determine the tunneling characteristics of the system.« less

  20. Self-organized formation of quantum dots of a material on a substrate

    DOEpatents

    Zhang, Zhenyu; Wendelken, John F.; Chang, Ming-Che; Pai, Woei Wu

    2001-01-01

    Systems and methods are described for fabricating arrays of quantum dots. A method for making a quantum dot device, includes: forming clusters of atoms on a substrate; and charging the clusters of atoms such that the clusters of atoms repel one another. The systems and methods provide advantages because the quantum dots can be ordered with regard to spacing and/or size.

  1. Arginine-glycine-aspartic acid-conjugated dendrimer-modified quantum dots for targeting and imaging melanoma.

    PubMed

    Li, Zhiming; Huang, Peng; Lin, Jing; He, Rong; Liu, Bing; Zhang, Xiaomin; Yang, Sen; Xi, Peng; Zhang, Xuejun; Ren, Qiushi; Cui, Daxiang

    2010-08-01

    Angiogenesis is essential for the development of malignant tumors and provides important targets for tumor diagnosis and therapy. Quantum dots have been broadly investigated for their potential application in cancer molecular imaging. In present work, CdSe quantum dots were synthesized, polyamidoamine dendrimers were used to modify surface of quantum dots and improve their solubility in water solution. Then, dendrimer-modified CdSe quantum dots were conjugated with arginine-glycine-aspartic acid (RGD) peptides. These prepared nanoprobes were injected into nude mice loaded with melanoma (A375) tumor xenografts via tail vessels, IVIS imaging system was used to image the targeting and bio-distribution of as-prepared nanoprobes. The dendrimer-modified quantum dots exhibit water-soluble, high quantum yield, and good biocompatibility. RGD-conjugated quantum dots can specifically target human umbilical vein endothelial cells (HUVEC) and A375 melanoma cells, as well as nude mice loaded with A735 melanoma cells. High-performance RGD-conjugated dendrimers modified quantum dot-based nanoprobes have great potential in application such as tumor diagnosis and therapy.

  2. Dynamical thermalization in isolated quantum dots and black holes

    NASA Astrophysics Data System (ADS)

    Kolovsky, Andrey R.; Shepelyansky, Dima L.

    2017-01-01

    We study numerically a model of quantum dot with interacting fermions. At strong interactions with small conductance the model is reduced to the Sachdev-Ye-Kitaev black-hole model while at weak interactions and large conductance it describes a Landau-Fermi liquid in a regime of quantum chaos. We show that above the Åberg threshold for interactions there is an onset of dynamical themalization with the Fermi-Dirac distribution describing the eigenstates of an isolated dot. At strong interactions in the isolated black-hole regime there is also the onset of dynamical thermalization with the entropy described by the quantum Gibbs distribution. This dynamical thermalization takes place in an isolated system without any contact with a thermostat. We discuss the possible realization of these regimes with quantum dots of 2D electrons and cold ions in optical lattices.

  3. Effect of the Semiconductor Quantum Dot Shell Structure on Fluorescence Quenching by Acridine Ligand

    NASA Astrophysics Data System (ADS)

    Linkov, P. A.; Vokhmintcev, K. V.; Samokhvalov, P. S.; Laronze-Cochard, M.; Sapi, J.; Nabiev, I. R.

    2018-02-01

    The main line of research in cancer treatment is the development of methods for early diagnosis and targeted drug delivery to cancer cells. Fluorescent semiconductor core/shell nanocrystals of quantum dots (e.g., CdSe/ZnS) conjugated with an anticancer drug, e.g., an acridine derivative, allow real-time tracking and control of the process of the drug delivery to tumors. However, linking of acridine derivatives to a quantum dot can be accompanied by quantum dot fluorescence quenching caused by electron transfer from the quantum dot to the organic molecule. In this work, it has been shown that the structure of the shell of the quantum dot plays the decisive role in the process of photoinduced charge transfer from the quantum dot to the acridine ligand, which is responsible for fluorescence quenching. It has been shown that multicomponent ZnS/CdS/ZnS shells of CdSe cores of quantum dots, which have a relatively small thickness, make it possible to significantly suppress a decrease in the quantum yield of fluorescence of quantum dots as compared to both the classical ZnS thin shell and superthick shells of the same composition. Thus, core/multicomponent shell CdSe/ZnS/CdS/ZnS quantum dots can be used as optimal fluorescent probes for the development of systems for diagnosis and treatment of cancer with the use of anticancer compounds based on acridine derivatives.

  4. A linear triple quantum dot system in isolated configuration

    NASA Astrophysics Data System (ADS)

    Flentje, Hanno; Bertrand, Benoit; Mortemousque, Pierre-André; Thiney, Vivien; Ludwig, Arne; Wieck, Andreas D.; Bäuerle, Christopher; Meunier, Tristan

    2017-06-01

    The scaling up of electron spin qubit based nanocircuits has remained challenging up till date and involves the development of efficient charge control strategies. Here, we report on the experimental realization of a linear triple quantum dot in a regime isolated from the reservoir. We show how this regime can be reached with a fixed number of electrons. Charge stability diagrams of the one, two, and three electron configurations where only electron exchange between the dots is allowed are observed. They are modeled with the established theory based on a capacitive model of the dot systems. The advantages of the isolated regime with respect to experimental realizations of quantum simulators and qubits are discussed. We envision that the results presented here will make more manipulation schemes for existing qubit implementations possible and will ultimately allow to increase the number of tunnel coupled quantum dots which can be simultaneously controlled.

  5. Theory of Spin States of Quantum Dot Molecules

    NASA Astrophysics Data System (ADS)

    Ponomarev, I. V.; Reinecke, T. L.; Scheibner, M.; Stinaff, E. A.; Bracker, A. S.; Doty, M. F.; Gammon, D.; Korenev, V. L.

    2007-04-01

    The photoluminescence spectrum of an asymmetric pair of coupled InAs quantum dots in an applied electric field shows a rich pattern of level anticrossings, crossings and fine structure that can be understood as a superposition of charge and spin configurations. We present a theoretical model that provides a description of the energy positions and intensities of the optical transitions in exciton, biexciton and charged exciton states of coupled quantum dots molecules.

  6. 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...in the form of the localised surface plasmon resonance of the gold component of nanoparticle hybrids could enhance nonlinear emission by several

  7. 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...in the form of the localised surface plasmon resonance of the gold component of nanoparticle hybrids could enhance nonlinear emission by several

  8. Suppression of Overhauser Effect in the Exciton-Nuclear Spin System of GaAs Quantum Dot

    DTIC Science & Technology

    2001-06-01

    the exciton-nuclear spin system of GaAs quantum dot V L. Korenevt, I. A. Merkulovt, D. Gammonj, Al. L. Efrosj, T. A. Kennedyl, M. Rosenj, D. S ...Katzerj and S . W. Brown§ t loffe Physico-Technical Institute, St Petersburg, Russia I Naval Research Laboratory, Washington DC 20375, USA § NIST...2.5 s -1 for N - 105 nuclei in the quantum dot [51 and rb - 0.1 ns [9]. The estimation is in agreement with experiment (Texp ; 3 s ). Coupling of

  9. Synthesis and characterization of graphene quantum dots/cobalt ferrite nanocomposite

    NASA Astrophysics Data System (ADS)

    Ramachandran, Shilpa; Sathishkumar, M.; Kothurkar, Nikhil K.; Senthilkumar, R.

    2018-02-01

    A facile method has been developed for the synthesis of a graphene quantum dots/cobalt ferrite nanocomposite. Graphene quantum dots (GQDs) were synthesized by a simple bottom-up method using citric acid, followed by the co-precipitation of cobalt ferrite nanoparticles on the graphene quantum dots. The morphology, structural analysis, optical properties, magnetic properties were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-vis absorption spectroscopy, fluorescence spectroscopy, vibrating sample magnetometry (VSM) measurements. The synthesized nanocomposite showed good fluorescence and superparamagnetic properties, which are important for biomedical applications.

  10. Fabrication of (In,Ga)As quantum-dot chains on GaAs(100)

    NASA Astrophysics Data System (ADS)

    Wang, Z. M.; Holmes, K.; Mazur, Yu. I.; Salamo, G. J.

    2004-03-01

    Nanostructure evolution during the growth of multilayers of In0.5Ga0.5As/GaAs (100) by molecular-beam epitaxy is investigated to control the formation of lines of quantum dots called quantum-dot chains. It is found that the dot chains can be substantially increased in length by the introduction of growth interruptions during the initial stages of growth of the GaAs spacer layer. Quantum-dot chains that are longer than 5 μm are obtained by adjusting the In0.5Ga0.5As coverage and growth interruptions. The growth procedure is also used to create a template to form InAs dots into chains with a predictable dot density. The resulting dot chains offer the possibility to engineer carrier interaction among dots for novel physical phenomena and potential devices.

  11. Laser-driven two-electron quantum dot in plasmas

    NASA Astrophysics Data System (ADS)

    Bahar, M. K.; Soylu, A.

    2018-06-01

    We have investigated the energies of two-electron parabolic quantum dots (TEPQdots) embedded in plasmas characterized by more general exponential cosine screened Coulomb (MGECSC) potential under the action of a monochromatic, linearly polarized laser field by solving the corresponding Schrödinger equation numerically via the asymptotic iteration method. The four different cases of the MGECSC potential constituted by various sets of the potential parameters are reckoned in modeling of the interactions in the plasma environments which are Debye and quantum plasmas. The plasma environment is a remarkable experimental argument for the quantum dots and the interactions in plasma environments are different compared to the interactions in an environment without plasma and the screening specifications of the plasmas can be controlled through the plasma parameters. These findings constitute our major motivation in consideration of the plasma environments. An appreciable confinement effect is made up by implementing the laser field on the TEPQdot. The influences of the laser field on the system are included by using the Ehlotzky approximation, and then Kramers-Henneberger transformation is carried out for the corresponding Schrödinger equation. The influences of the ponderomotive force on two-electron quantum dots embedded in plasmas are investigated. The behaviours, the similarities and the functionalities of the laser field, the plasma environment, and the quantum dot confinement are also scrutinized. In addition, the role of the plasma environments in the mentioned analysis is also discussed in detail.

  12. Demonstration of Quantum Entanglement between a Single Electron Spin Confined to an InAs Quantum Dot and a Photon

    NASA Astrophysics Data System (ADS)

    Schaibley, J. R.; Burgers, A. P.; McCracken, G. A.; Duan, L.-M.; Berman, P. R.; Steel, D. G.; Bracker, A. S.; Gammon, D.; Sham, L. J.

    2013-04-01

    The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this Letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to a single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot’s excited state. We obtain a lower bound on the fidelity of entanglement of 0.59±0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement-based spin-spin entanglement which does not require sub-nanosecond timing resolution, we estimate that this system would enable near ideal performance. The inferred (usable) entanglement generation rate is 3×103s-1. This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network.

  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. Effect of organic materials used in the synthesis on the emission from CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Won; Yang, Ho-Soon; Hong, K. S.; Kim, S. M.

    2013-12-01

    Quantum-dot nanocrystals have particular optical properties due to the quantum confinement effect and the surface effect. This study focuses on the effect of surface conditions on the emission from quantum dots. The quantum dots prepared with 1-hexadecylamine (HDA) in the synthesis show strong emission while the quantum dots prepared without HDA show weak emission, as well as emission from surface energy traps. The comparison of the X-ray patterns of these two sets of quantum dots reveals that HDA forms a layer on the surface of quantum dot during the synthesis. This surface passivation with a layer of HDA reduces surface energy traps, therefore the emission from surface trap levels is suppressed in the quantum dots synthesized with HDA.

  15. Understanding/Modelling of Thermal and Radiation Benefits of Quantum Dot Solar Cells

    DTIC Science & Technology

    2008-07-11

    GaAs solar cells have been investigated. Strain compensation is a key step in realizing high- efficiency quantum dots solar cells (QDSC). InAs...factor. A strong correlation between the temperature dependent quantum dot electroluminescence peak emission wavelength and the sub-GaAs bandgap...increased efficiency and radiation resistance devices. The incorporation of quantum dots (QDs) into traditional single or multi-junction crystalline solar

  16. Rashba effect in an asymmetric quantum dot in a magnetic field

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, S.; Cahay, M.

    2002-12-01

    We derive an expression for the total spin-splitting energy in an asymmetric quantum dot with ferromagnetic contacts, subjected to a transverse electric field. Such a structure has been shown by one of us to act as a spintronic quantum gate with in-built qubit readers and writers (Phys. Rev. B61, 13813 (2000)). The ferromagnetic contacts result in a magnetic field that causes a Zeeman splitting of the electronic states in the quantum dot. We show that this Zeeman splitting can be finely tuned with a transverse electric field as a result of nonvanishing Rashba spin-orbit coupling in an asymmetric quantum dot. This feature is critical for implementing a quantum gate.

  17. Infrared Focal Plane Arrays Based on Semiconductor Quantum Dots

    DTIC Science & Technology

    2002-01-01

    an ensemble of self -assembled InAs/GaAs or InAs/InP quantum dots (QDs) are typically in the range of 10-30 monolayers [1]. Here, we report on InAs...photoconductive properties of QDIPs based on self organized InAs quantum dots grown on In.52Al.48As/InP(100), using the MBE technique. Dr. Gendry grew the...composed of 10 layers of self assembled InAs dots, separated by 500 Å thick InAlAs (lattice matched to the semi-insulating InP substrate) barrier

  18. 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.

  19. Transport properties of strongly correlated electrons in quantum dots studied with a simple circuit model.

    PubMed

    Martins, G B; Büsser, C A; Al-Hassanieh, K A; Anda, E V; Moreo, A; Dagotto, E

    2006-02-17

    Numerical calculations are shown to reproduce the main results of recent experiments involving nonlocal spin control in quantum dots [Craig, Science 304, 565 (2004).]. In particular, the experimentally reported zero-bias-peak splitting is clearly observed in our studies. To understand these results, a simple "circuit model" is introduced and shown to qualitatively describe the experiments. The main idea is that the splitting originates in a Fano antiresonance, which is caused by having one quantum dot side connected in relation to the current's path. This scenario provides an explanation of the results of Craig et al. that is an alternative to the RKKY proposal, also addressed here.

  20. Density-functional theory simulation of large quantum dots

    NASA Astrophysics Data System (ADS)

    Jiang, Hong; Baranger, Harold U.; Yang, Weitao

    2003-10-01

    Kohn-Sham spin-density functional theory provides an efficient and accurate model to study electron-electron interaction effects in quantum dots, but its application to large systems is a challenge. Here an efficient method for the simulation of quantum dots using density-function theory is developed; it includes the particle-in-the-box representation of the Kohn-Sham orbitals, an efficient conjugate-gradient method to directly minimize the total energy, a Fourier convolution approach for the calculation of the Hartree potential, and a simplified multigrid technique to accelerate the convergence. We test the methodology in a two-dimensional model system and show that numerical studies of large quantum dots with several hundred electrons become computationally affordable. In the noninteracting limit, the classical dynamics of the system we study can be continuously varied from integrable to fully chaotic. The qualitative difference in the noninteracting classical dynamics has an effect on the quantum properties of the interacting system: integrable classical dynamics leads to higher-spin states and a broader distribution of spacing between Coulomb blockade peaks.

  1. Laser location and manipulation of a single quantum tunneling channel in an InAs quantum dot.

    PubMed

    Makarovsky, O; Vdovin, E E; Patané, A; Eaves, L; Makhonin, M N; Tartakovskii, A I; Hopkinson, M

    2012-03-16

    We use a femtowatt focused laser beam to locate and manipulate a single quantum tunneling channel associated with an individual InAs quantum dot within an ensemble of dots. The intensity of the directed laser beam tunes the tunneling current through the targeted dot with an effective optical gain of 10(7) and modifies the curvature of the dot's confining potential and the spatial extent of its ground state electron eigenfunction. These observations are explained by the effect of photocreated hole charges which become bound close to the targeted dot, thus acting as an optically induced gate electrode.

  2. Compact and highly stable quantum dots through optimized aqueous phase transfer

    NASA Astrophysics Data System (ADS)

    Tamang, Sudarsan; Beaune, Grégory; Poillot, Cathy; De Waard, Michel; Texier-Nogues, Isabelle; Reiss, Peter

    2011-03-01

    A large number of different approaches for the aqueous phase transfer of quantum dots have been proposed. Surface ligand exchange with small hydrophilic thiols, such as L-cysteine, yields the lowest particle hydrodynamic diameter. However, cysteine is prone to dimer formation, which limits colloidal stability. We demonstrate that precise pH control during aqueous phase transfer dramatically increases the colloidal stability of InP/ZnS quantum dots. Various bifunctional thiols have been applied. The formation of disulfides, strongly diminishing the fluorescence QY has been prevented through addition of appropriate reducing agents. Bright InP/ZnS quantum dots with a hydrodynamic diameter <10 nm and long-term stability have been obtained. Finally we present in vitro studies of the quantum dots functionalized with the cell-penetrating peptide maurocalcine.

  3. Staircase Quantum Dots Configuration in Nanowires for Optimized Thermoelectric Power

    PubMed Central

    Li, Lijie; Jiang, Jian-Hua

    2016-01-01

    The performance of thermoelectric energy harvesters can be improved by nanostructures that exploit inelastic transport processes. One prototype is the three-terminal hopping thermoelectric device where electron hopping between quantum-dots are driven by hot phonons. Such three-terminal hopping thermoelectric devices have potential in achieving high efficiency or power via inelastic transport and without relying on heavy-elements or toxic compounds. We show in this work how output power of the device can be optimized via tuning the number and energy configuration of the quantum-dots embedded in parallel nanowires. We find that the staircase energy configuration with constant energy-step can improve the power factor over a serial connection of a single pair of quantum-dots. Moreover, for a fixed energy-step, there is an optimal length for the nanowire. Similarly for a fixed number of quantum-dots there is an optimal energy-step for the output power. Our results are important for future developments of high-performance nanostructured thermoelectric devices. PMID:27550093

  4. Quantum Dot Platform for Single-Cell Molecular Profiling

    NASA Astrophysics Data System (ADS)

    Zrazhevskiy, Pavel S.

    In-depth understanding of the nature of cell physiology and ability to diagnose and control the progression of pathological processes heavily rely on untangling the complexity of intracellular molecular mechanisms and pathways. Therefore, comprehensive molecular profiling of individual cells within the context of their natural tissue or cell culture microenvironment is essential. In principle, this goal can be achieved by tagging each molecular target with a unique reporter probe and detecting its localization with high sensitivity at sub-cellular resolution, primarily via microscopy-based imaging. Yet, neither widely used conventional methods nor more advanced nanoparticle-based techniques have been able to address this task up to date. High multiplexing potential of fluorescent probes is heavily restrained by the inability to uniquely match probes with corresponding molecular targets. This issue is especially relevant for quantum dot probes---while simultaneous spectral imaging of up to 10 different probes is possible, only few can be used concurrently for staining with existing methods. To fully utilize multiplexing potential of quantum dots, it is necessary to design a new staining platform featuring unique assignment of each target to a corresponding quantum dot probe. This dissertation presents two complementary versatile approaches towards achieving comprehensive single-cell molecular profiling and describes engineering of quantum dot probes specifically tailored for each staining method. Analysis of expanded molecular profiles is achieved through augmenting parallel multiplexing capacity with performing several staining cycles on the same specimen in sequential manner. In contrast to other methods utilizing quantum dots or other nanoparticles, which often involve sophisticated probe synthesis, the platform technology presented here takes advantage of simple covalent bioconjugation and non-covalent self-assembly mechanisms for straightforward probe

  5. Quantum-dot-sensitized solar cells.

    PubMed

    Rühle, Sven; Shalom, Menny; Zaban, Arie

    2010-08-02

    Quantum-dot-sensitized solar cells (QDSCs) are a promising low-cost alternative to existing photovoltaic technologies such as crystalline silicon and thin inorganic films. The absorption spectrum of quantum dots (QDs) can be tailored by controlling their size, and QDs can be produced by low-cost methods. Nanostructures such as mesoporous films, nanorods, nanowires, nanotubes and nanosheets with high microscopic surface area, redox electrolytes and solid-state hole conductors are borrowed from standard dye-sensitized solar cells (DSCs) to fabricate electron conductor/QD monolayer/hole conductor junctions with high optical absorbance. Herein we focus on recent developments in the field of mono- and polydisperse QDSCs. Stability issues are adressed, coating methods are presented, performance is reviewed and special emphasis is given to the importance of energy-level alignment to increase the light to electric power conversion efficiency.

  6. Polarized electrons, trions, and nuclei in charged quantum dots

    NASA Astrophysics Data System (ADS)

    Bracker, A. S.; Tischler, J. G.; Korenev, V. L.; Gammon, D.

    2003-07-01

    We have investigated spin polarization in GaAs quantum dots. Excitons and trions are polarized directly by optical excitation and studied through polarization of photoluminescence. Electrons and nuclei are polarized indirectly through subsequent relaxation processes. Polarized electrons are identified by the Hanle effect for exciton and trion photoluminescence, while polarized nuclei are identified through the Overhauser effect in individual charged quantum dots.

  7. Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications.

    PubMed

    Ellis, Matthew A; Grandinetti, Giovanna; Fichter, Katye M; Fichter, Kathryn M

    2016-02-06

    Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, quantum dots should be highly fluorescent and small/monodisperse in size. While commonly used cadmium-based quantum dots possess these qualities, they are potentially toxic due to the possible release of Cd(2+) ions through nanoparticle degradation. Indium-based quantum dots, specifically InP/ZnS, have recently been explored as a viable alternative to cadmium-based quantum dots due to their relatively similar fluorescence characteristics and size. The synthesis presented here uses standard hot-injection techniques for effective nanoparticle growth; however, nanoparticle properties such as size, emission wavelength, and emission intensity can drastically change due to small changes in the reaction conditions. Therefore, reaction conditions such temperature, reaction duration, and precursor concentration should be maintained precisely to yield reproducible products. Because quantum dots are not inherently soluble in aqueous solutions, they must also undergo surface modification to impart solubility in water. In this protocol, an amphiphilic polymer is used to interact with both hydrophobic ligands on the quantum dot surface and bulk solvent water molecules. Here, a detailed protocol is provided for the synthesis of highly fluorescent InP/ZnS quantum dots that are suitable for use in biomedical applications.

  8. Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

    PubMed Central

    Ellis, Matthew A.; Grandinetti, Giovanna; Fichter, Katye M.

    2016-01-01

    Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, quantum dots should be highly fluorescent and small/monodisperse in size. While commonly used cadmium-based quantum dots possess these qualities, they are potentially toxic due to the possible release of Cd2+ ions through nanoparticle degradation. Indium-based quantum dots, specifically InP/ZnS, have recently been explored as a viable alternative to cadmium-based quantum dots due to their relatively similar fluorescence characteristics and size. The synthesis presented here uses standard hot-injection techniques for effective nanoparticle growth; however, nanoparticle properties such as size, emission wavelength, and emission intensity can drastically change due to small changes in the reaction conditions. Therefore, reaction conditions such temperature, reaction duration, and precursor concentration should be maintained precisely to yield reproducible products. Because quantum dots are not inherently soluble in aqueous solutions, they must also undergo surface modification to impart solubility in water. In this protocol, an amphiphilic polymer is used to interact with both hydrophobic ligands on the quantum dot surface and bulk solvent water molecules. Here, a detailed protocol is provided for the synthesis of highly fluorescent InP/ZnS quantum dots that are suitable for use in biomedical applications. PMID:26891282

  9. Single photon emission from charged excitons in CdTe/ZnTe quantum dots

    NASA Astrophysics Data System (ADS)

    Belyaev, K. G.; Rakhlin, M. V.; Sorokin, S. V.; Klimko, G. V.; Gronin, S. V.; Sedova, I. V.; Mukhin, I. S.; Ivanov, S. V.; Toropov, A. A.

    2017-11-01

    We report on micro-photoluminescence studies of individual self-organized CdTe/ZnTe quantum dots intended for single-photon-source applications in a visible spectral range. The quantum dots surface density below 1010 per cm2 was achieved by using a thermally activated regime of molecular beam epitaxy that allowed fabrication of etched mesa-structures containing only a few emitting quantum dots. The single photon emission with the autocorrelation function g(2)(0)<0.2 was detected and identified as recombination of charged excitons in the individual quantum dot.

  10. High-performance semiconductor quantum-dot single-photon sources

    NASA Astrophysics Data System (ADS)

    Senellart, Pascale; Solomon, Glenn; White, Andrew

    2017-11-01

    Single photons are a fundamental element of most quantum optical technologies. The ideal single-photon source is an on-demand, deterministic, single-photon source delivering light pulses in a well-defined polarization and spatiotemporal mode, and containing exactly one photon. In addition, for many applications, there is a quantum advantage if the single photons are indistinguishable in all their degrees of freedom. Single-photon sources based on parametric down-conversion are currently used, and while excellent in many ways, scaling to large quantum optical systems remains challenging. In 2000, semiconductor quantum dots were shown to emit single photons, opening a path towards integrated single-photon sources. Here, we review the progress achieved in the past few years, and discuss remaining challenges. The latest quantum dot-based single-photon sources are edging closer to the ideal single-photon source, and have opened new possibilities for quantum technologies.

  11. Los Alamos Quantum Dots for Solar, Display Technology

    ScienceCinema

    Klimov, Victor

    2018-05-01

    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.

  12. Studying nanotoxic effects of CdTe quantum dots in Trypanosoma cruzi

    NASA Astrophysics Data System (ADS)

    Stahl, C. V.; Almeida, D. B.; de Thomaz, A. A.; Fontes, A.; Menna-Barreto, R. F. S.; Santos-Mallet, J. R.; Cesar, C. L.; Gomes, S. A. O.; Feder, D.

    2010-02-01

    Many studies have been done in order to verify the possible nanotoxicity of quantum dots in some cellular types. Protozoan pathogens as Trypanosoma cruzi, etiologic agent of Chagas1 disease is transmitted to humans either by blood-sucking triatomine vectors, blood transfusion, organs transplantation or congenital transmission. The study of the life cycle, biochemical, genetics, morphology and others aspects of the T. cruzi is very important to better understand the interactions with its hosts and the disease evolution on humans. Quantum dot, nanocrystals, highly luminescent has been used as tool for experiments in in vitro and in vivo T. cruzi life cycle development in real time. We are now investigating the quantum dots toxicity on T. cruzi parasite cells using analytical methods. In vitro experiments were been done in order to test the interference of this nanoparticle on parasite development, morphology and viability (live-death). Ours previous results demonstrated that 72 hours after parasite incubation with 200 μM of CdTe altered the development of T. cruzi and induced cell death by necrosis in a rate of 34%. QDs labeling did not effect: (i) on parasite integrity, at least until 7 days; (ii) parasite cell dividing and (iii) parasite motility at a concentration of 2 μM CdTe. This fact confirms the low level of cytotoxicity of these QDs on this parasite cell. In summary our results is showing T. cruzi QDs labeling could be used for in vivo cellular studies in Chagas disease.

  13. Effective theory of monolayer TMDC double quantum dots

    NASA Astrophysics Data System (ADS)

    David, Alessandro; Burkard, Guido; Kormányos, Andor

    2018-07-01

    Monolayer transition metal dichalcogenides (TMDCs) are promising candidates for quantum technologies, such as spin qubits in quantum dots, because they are truly two-dimensional semiconductors with a direct band gap. In this work, we analyse theoretically the behaviour of a double quantum dot (DQD) system created in the conduction band of these materials, with two electrons in the (1,1) charge configuration. Motivated by recent experimental progress, we consider several scenarios, including different spin–orbit splittings in the two dots and including the case when the valley degeneracy is lifted due to an insulating ferromagnetic substrate. Finally, we discuss in which cases it is possible to reduce the low energy subspace to the lowest Kramers pairs. We find that in this case the low energy model is formally identical to the Heisenberg exchange Hamiltonian, indicating that such Kramers pairs may serve as qubit implementations.

  14. Atomistic analysis of valley-orbit hybrid states and inter-dot tunnel rates in a Si double quantum dot

    NASA Astrophysics Data System (ADS)

    Ferdous, Rifat; Rahman, Rajib; Klimeck, Gerhard

    2014-03-01

    Silicon quantum dots are promising candidates for solid-state quantum computing due to the long spin coherence times in silicon, arising from small spin-orbit interaction and a nearly spin free host lattice. However, the conduction band valley degeneracy adds an additional degree of freedom to the electronic structure, complicating the encoding and operation of qubits. Although the valley and the orbital indices can be uniquely identified in an ideal silicon quantum dot, atomic-scale disorder mixes valley and orbital states in realistic dots. Such valley-orbit hybridization, strongly influences the inter-dot tunnel rates.Using a full-band atomistic tight-binding method, we analyze the effect of atomic-scale interface disorder in a silicon double quantum dot. Fourier transform of the tight-binding wavefunctions helps to analyze the effect of disorder on valley-orbit hybridization. We also calculate and compare inter-dot inter-valley and intra-valley tunneling, in the presence of realistic disorder, such as interface tilt, surface roughness, alloy disorder, and interface charges. The method provides a useful way to compute electronic states in realistically disordered systems without any posteriori fitting parameters.

  15. Scanning gate imaging of two coupled quantum dots in single-walled carbon nanotubes.

    PubMed

    Zhou, Xin; Hedberg, James; Miyahara, Yoichi; Grutter, Peter; Ishibashi, Koji

    2014-12-12

    Two coupled single wall carbon nanotube quantum dots in a multiple quantum dot system were characterized by using a low temperature scanning gate microscopy (SGM) technique, at a temperature of 170 mK. The locations of single wall carbon nanotube quantum dots were identified by taking the conductance images of a single wall carbon nanotube contacted by two metallic electrodes. The single electron transport through single wall carbon nanotube multiple quantum dots has been observed by varying either the position or voltage bias of a conductive atomic force microscopy tip. Clear hexagonal patterns were observed in the region of the conductance images where only two sets of overlapping conductance rings are visible. The values of coupling capacitance over the total capacitance of the two dots, C(m)/C(1(2)) have been extracted to be 0.21 ∼ 0.27 and 0.23 ∼ 0.28, respectively. In addition, the interdot coupling (conductance peak splitting) has also been confirmed in both conductance image measurement and current-voltage curves. The results show that a SGM technique enables spectroscopic investigation of coupled quantum dots even in the presence of unexpected multiple quantum dots.

  16. Optical manipulation of electron spin in quantum dot systems

    NASA Astrophysics Data System (ADS)

    Villas-Boas, Jose; Ulloa, Sergio; Govorov, Alexander

    2006-03-01

    Self-assembled quantum dots (QDs) are of particular interest for fundamental physics because of their similarity with atoms. Coupling two of such dots and addressing them with polarized laser light pulses is perhaps even more interesting. In this paper we use a multi-exciton density matrix formalism to model the spin dynamics of a system with single or double layers of QDs. Our model includes the anisotropic electron-hole exchange in the dots, the presence of wetting layer states, and interdot tunneling [1]. Our results show that it is possible to switch the spin polarization of a single self-assembled quantum dot under elliptically polarized light by increasing the laser intensity. In the nonlinear mechanism described here, intense elliptically polarized light creates an effective exchange channel between the exciton spin states through biexciton states, as we demonstrate by numerical and analytical methods. We further show that the effect persists in realistic ensembles of dots, and we propose alternative ways to detect it. We also extend our study to a double layer of quantum dots, where we find a competition between Rabi frequency and tunneling oscillations. [1] J. M. Villas-Boas, S. E. Ulloa, and A. O. Govorov, Phys. Rev. Lett. 94, 057404 (2005); Phys. Rev. B 69, 125342 (2004).

  17. Quantum Monte Carlo Studies of Interaction-Induced Localization in Quantum Dots and Wires

    NASA Astrophysics Data System (ADS)

    Devrim Güçlü, A.

    2009-03-01

    We investigate interaction-induced localization of electrons in both quantum dots and inhomogeneous quantum wires using variational and diffusion quantum Monte Carlo methods. Quantum dots and wires are highly tunable systems that enable the study of the physics of strongly correlated electrons. With decreasing electronic density, interactions become stronger and electrons are expected to localize at their classical positions, as in Wigner crystallization in an infinite 2D system. (1) Dots: We show that the addition energy shows a clear progression from features associated with shell structure to those caused by commensurability of a Wigner crystal. This cross-over is, then, a signature of localization; it occurs near rs˜20. For higher values of rs, the configuration symmetry of the quantum dot becomes fully consistent with the classical ground state. (2) Wires: We study an inhomogeneous quasi-one-dimensional system -- a wire with two regions, one at low density and the other high. We find that strong localization occurs in the low density quantum point contact region as the gate potential is increased. The nature of the transition from high to low density depends on the density gradient -- if it is steep, a barrier develops between the two regions, causing Coulomb blockade effects. We find no evidence for ferromagnetic spin polarization for the range of parameters studied. The picture emerging here is in good agreement with the experimental measurements of tunneling between two wires. Collaborators: C. J. Umrigar (Cornell), Hong Jiang (Fritz Haber Institut), Amit Ghosal (IISER Calcutta), and H. U. Baranger (Duke).

  18. Intermediate-band photosensitive device with quantum dots embedded in energy fence barrier

    DOEpatents

    Forrest, Stephen R.; Wei, Guodan

    2010-07-06

    A plurality of layers of a first semiconductor material and a plurality of dots-in-a-fence barriers disposed in a stack between a first electrode and a second electrode. Each dots-in-a-fence barrier consists essentially of a plurality of quantum dots of a second semiconductor material embedded between and in direct contact with two layers of a third semiconductor material. Wave functions of the quantum dots overlap as at least one intermediate band. The layers of the third semiconductor material are arranged as tunneling barriers to require a first electron and/or a first hole in a layer of the first material to perform quantum mechanical tunneling to reach the second material within a respective quantum dot, and to require a second electron and/or a second hole in a layer of the first semiconductor material to perform quantum mechanical tunneling to reach another layer of the first semiconductor material.

  19. Synthesis, characterization and cells and tissues imaging of carbon quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Li, Qilong; Zhou, JingE.; Wang, Yiting; Yu, Lei; Peng, Hui; Zhu, Jianzhong

    2017-10-01

    Compare to other quantum dots, carbon quantum dots have its own incomparable advantages, such as low cell toxicity, favorable biocompatibility, cheap production cost, mild reaction conditions, easy to large-scale synthesis and functionalization. In this thesis, we took citric acid monohydrate and diethylene glycol bis (3-aMinopropyl) ether as materials, used decomposition method to acquire carbon quantum dots (CQDs) which can emission blue fluorescence under ultraviolet excitation. In the aspect of application, we achieved the biological imaging of CQDs in vivo and in vitro.

  20. Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots.

    PubMed

    Huber, Daniel; Reindl, Marcus; Huo, Yongheng; Huang, Huiying; Wildmann, Johannes S; Schmidt, Oliver G; Rastelli, Armando; Trotta, Rinaldo

    2017-05-26

    The development of scalable sources of non-classical light is fundamental to unlocking the technological potential of quantum photonics. Semiconductor quantum dots are emerging as near-optimal sources of indistinguishable single photons. However, their performance as sources of entangled-photon pairs are still modest compared to parametric down converters. Photons emitted from conventional Stranski-Krastanov InGaAs quantum dots have shown non-optimal levels of entanglement and indistinguishability. For quantum networks, both criteria must be met simultaneously. Here, we show that this is possible with a system that has received limited attention so far: GaAs quantum dots. They can emit triggered polarization-entangled photons with high purity (g (2) (0) = 0.002±0.002), high indistinguishability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity (0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dot entanglement sources in future quantum technologies.

  1. Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots

    PubMed Central

    Huber, Daniel; Reindl, Marcus; Huo, Yongheng; Huang, Huiying; Wildmann, Johannes S.; Schmidt, Oliver G.; Rastelli, Armando; Trotta, Rinaldo

    2017-01-01

    The development of scalable sources of non-classical light is fundamental to unlocking the technological potential of quantum photonics. Semiconductor quantum dots are emerging as near-optimal sources of indistinguishable single photons. However, their performance as sources of entangled-photon pairs are still modest compared to parametric down converters. Photons emitted from conventional Stranski–Krastanov InGaAs quantum dots have shown non-optimal levels of entanglement and indistinguishability. For quantum networks, both criteria must be met simultaneously. Here, we show that this is possible with a system that has received limited attention so far: GaAs quantum dots. They can emit triggered polarization-entangled photons with high purity (g(2)(0) = 0.002±0.002), high indistinguishability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity (0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dot entanglement sources in future quantum technologies. PMID:28548081

  2. Cubic GaN quantum dots embedded in zinc-blende AlN microdisks

    NASA Astrophysics Data System (ADS)

    Bürger, M.; Kemper, R. M.; Bader, C. A.; Ruth, M.; Declair, S.; Meier, C.; Förstner, J.; As, D. J.

    2013-09-01

    Microresonators containing quantum dots find application in devices like single photon emitters for quantum information technology as well as low threshold laser devices. We demonstrate the fabrication of 60 nm thin zinc-blende AlN microdisks including cubic GaN quantum dots using dry chemical etching techniques. Scanning electron microscopy analysis reveals the morphology with smooth surfaces of the microdisks. Micro-photoluminescence measurements exhibit optically active quantum dots. Furthermore this is the first report of resonator modes in the emission spectrum of a cubic AlN microdisk.

  3. Resonant tunneling in graphene pseudomagnetic quantum dots.

    PubMed

    Qi, Zenan; Bahamon, D A; Pereira, Vitor M; Park, Harold S; Campbell, D K; Neto, A H Castro

    2013-06-12

    Realistic relaxed configurations of triaxially strained graphene quantum dots are obtained from unbiased atomistic mechanical simulations. The local electronic structure and quantum transport characteristics of y-junctions based on such dots are studied, revealing that the quasi-uniform pseudomagnetic field induced by strain restricts transport to Landau level- and edge state-assisted resonant tunneling. Valley degeneracy is broken in the presence of an external field, allowing the selective filtering of the valley and chirality of the states assisting in the resonant tunneling. Asymmetric strain conditions can be explored to select the exit channel of the y-junction.

  4. Fabrication and characterization of silicon quantum dots in Si-rich silicon carbide films.

    PubMed

    Chang, Geng-Rong; Ma, Fei; Ma, Dayan; Xu, Kewei

    2011-12-01

    Amorphous Si-rich silicon carbide films were prepared by magnetron co-sputtering and subsequently annealed at 900-1100 degrees C. After annealing at 1100 degrees C, this configuration of silicon quantum dots embedded in amorphous silicon carbide formed. X-ray photoelectron spectroscopy was used to study the chemical modulation of the films. The formation and orientation of silicon quantum dots were characterized by glancing angle X-ray diffraction, which shows that the ratio of silicon and carbon significantly influences the species of quantum dots. High-resolution transmission electron microscopy investigations directly demonstrated that the formation of silicon quantum dots is heavily dependent on the annealing temperatures and the ratio of silicon and carbide. Only the temperature of about 1100 degrees C is enough for the formation of high-density and small-size silicon quantum dots due to phase separation and thermal crystallization. Deconvolution of the first order Raman spectra shows the existence of a lower frequency peak in the range 500-505 cm(-1) corresponding to silicon quantum dots with different atom ratio of silicon and carbon.

  5. Harnessing Sun's Energy with Quantum Dots Based Next Generation Solar Cell.

    PubMed

    Halim, Mohammad A

    2012-12-27

    Our energy consumption relies heavily on the three components of fossil fuels (oil, natural gas and coal) and nearly 83% of our current energy is consumed from those sources. The use of fossil fuels, however, has been viewed as a major environmental threat because of their substantial contribution to greenhouse gases which are responsible for increasing the global average temperature. Last four decades, scientists have been searching for alternative sources of energy which need to be environmentally clean, efficient, cost-effective, renewable, and sustainable. One of the promising sustainable sources of energy can be achieved by harnessing sun energy through silicon wafer, organic polymer, inorganic dye, and quantum dots based solar cells. Among them, quantum dots have an exceptional property in that they can excite multiple electrons using only one photon. These dots can easily be synthesized, processed in solution, and incorporated into solar cell application. Interestingly, the quantum dots solar cells can exceed the Shockley - Queisser limit; however, it is a great challenge for other solar cell materials to exceed the limit. Theoretically, the quantum dots solar cell can boost the power conversion efficiency up to 66% and even higher to 80%. Moreover, in changing the size of the quantum dots one can utilize the Sun's broad spectrum of visible and infrared ranges. This review briefly overviews the present performance of different materials-based solar cells including silicon wafer, dye-sensitized, and organic solar cells. In addition, recent advances of the quantum dots based solar cells which utilize cadmium sulfide/selenide, lead sulfide/selenide, and new carbon dots as light harvesting materials has been reviewed. A future outlook is sketched as to how one could improve the efficiency up to 10% from the current highest efficiency of 6.6%.

  6. Quantum Well and Quantum Dot Modeling for Advanced Infrared Detectors and Focal Plane Arrays

    NASA Technical Reports Server (NTRS)

    Ting, David; Gunapala, S. D.; Bandara, S. V.; Hill, C. J.

    2006-01-01

    This viewgraph presentation reviews the modeling of Quantum Well Infrared Detectors (QWIP) and Quantum Dot Infrared Detectors (QDIP) in the development of Focal Plane Arrays (FPA). The QWIP Detector being developed is a dual band detector. It is capable of running on two bands Long-Wave Infrared (LWIR) and Medium Wavelength Infrared (MWIR). The same large-format dual-band FPA technology can be applied to Quantum Dot Infrared Photodetector (QDIP) with no modification, once QDIP exceeds QWIP in single device performance. Details of the devices are reviewed.

  7. Fluorescence properties of 3-amino phenylboronic acid and its interaction with glucose and ZnS:Cu quantum dots.

    PubMed

    Kur-Kowalska, Karolina; Przybyt, Małgorzata; Ziółczyk, Paulina; Sowiński, Przemysław; Miller, Ewa

    2014-08-14

    Preliminary results of a study of the interaction between 3-amino phenylboronic acid and glucose or ZnS:Cu quantum dots are presented in this paper. ZnS:Cu quantum dots with mercaptopropionic acid as a capping agent were obtained and characterized. Quenching of 3-amino phenylboronic acid fluorescence was studied by steady-state and timeresolved measurements. For fluorescence quenching with glucose the results of steady-state measurements fulfill Stern-Volmer equation. The quenching constants are increasing with growing pH. The decay of fluorescence is monoexponential with lifetime about 8.4 ns, which does not depend on pH and glucose concentration indicating static quenching. The quenching constant can be interpreted as apparent equilibrium constant of estrification of boronic group with diol. Quantum dots are also quenching 3-amino phenylboronic acid fluorescence. Fluorescence lifetime, in this case, is slightly decreasing with increasing concentration of quantum dots. The quenching constants are increasing slightly with pH's growth. Quenching mechanism of 3-amino phenylboronic acid fluorescence by quantum dots needs further experiments to be fully explained. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. Graphene quantum dots as enhanced plant growth regulators: effects on coriander and garlic plants.

    PubMed

    Chakravarty, Disha; Erande, Manisha B; Late, Dattatray J

    2015-10-01

    We report investigations on the use of graphene quantum dots for growth enhancement in coriander (Coriandrum sativam L.) and garlic (Allium sativum) plants. The as-received seeds of coriander and garlic were treated with 0.2 mg mL(-1) of graphene quantum dots for 3 h before planting. Graphene quantum dots enhanced the growth rate in coriander and garlic plants, including leaves, roots, shoots, flowers and fruits, when the seeds were treated with graphene quantum dots. Our investigations open up the opportunity to use graphene quantum dots as plant growth regulators that can be used in a variety of other food plants for high yield. © 2015 Society of Chemical Industry.

  9. Si/SiGe quadruple quantum dots with direct barrier gates

    NASA Astrophysics Data System (ADS)

    Ward, Daniel; Gamble, John; Foote, Ryan; Savage, Donald; Lagally, Max; Coppersmith, Susan; Eriksson, Mark

    2014-03-01

    We have fabricated a quadruple quantum dot in a Si/SiGe heterostructure with the aim of demonstrating a two-qubit quantum gate. This device makes use of direct barrier gates, in which individual gates are placed directly over the quantum dots and tunnel barriers. This design enables rational control of both energies and tunnel rates in coupled quantum dots. In this talk we discuss the design, fabrication, and initial characterization of the device. This work was supported in part by ARO (W911NF-12-0607), NSF (DMR-1206915), and the United States Department of Defense. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressly or implied, of the US Government.

  10. Spectrum Tunable Quantum Dot-In-A-Well Infrared Detector Arrays for Thermal Imaging

    DTIC Science & Technology

    2008-09-01

    Spectrum tunable quantum dot-in-a- well infrared detector arrays for thermal imaging Jonathan R. Andrews1, Sergio R. Restaino1, Scott W. Teare2...Materials at the University of New Mexico has been investigating quantum dot and quantum well detectors for thermal infrared imaging applications...SEP 2008 2. REPORT TYPE 3. DATES COVERED 00-00-2008 to 00-00-2008 4. TITLE AND SUBTITLE Spectrum tunable quantum dot-in-a- well infrared

  11. Mesoscopic Elastic Distortions in GaAs Quantum Dot Heterostructures.

    PubMed

    Pateras, Anastasios; Park, Joonkyu; Ahn, Youngjun; Tilka, Jack A; Holt, Martin V; Reichl, Christian; Wegscheider, Werner; Baart, Timothy A; Dehollain, Juan Pablo; Mukhopadhyay, Uditendu; Vandersypen, Lieven M K; Evans, Paul G

    2018-05-09

    Quantum devices formed in high-electron-mobility semiconductor heterostructures provide a route through which quantum mechanical effects can be exploited on length scales accessible to lithography and integrated electronics. The electrostatic definition of quantum dots in semiconductor heterostructure devices intrinsically involves the lithographic fabrication of intricate patterns of metallic electrodes. The formation of metal/semiconductor interfaces, growth processes associated with polycrystalline metallic layers, and differential thermal expansion produce elastic distortion in the active areas of quantum devices. Understanding and controlling these distortions present a significant challenge in quantum device development. We report synchrotron X-ray nanodiffraction measurements combined with dynamical X-ray diffraction modeling that reveal lattice tilts with a depth-averaged value up to 0.04° and strain on the order of 10 -4 in the two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. Elastic distortions in GaAs/AlGaAs heterostructures modify the potential energy landscape in the 2DEG due to the generation of a deformation potential and an electric field through the piezoelectric effect. The stress induced by metal electrodes directly impacts the ability to control the positions of the potential minima where quantum dots form and the coupling between neighboring quantum dots.

  12. Tandem luminescent solar concentrators based on engineered quantum dots

    NASA Astrophysics Data System (ADS)

    Wu, Kaifeng; Li, Hongbo; Klimov, Victor I.

    2018-02-01

    Luminescent solar concentrators (LSCs) can serve as large-area sunlight collectors for terrestrial and space-based photovoltaics. Due to their high emission efficiencies and readily tunable emission and absorption spectra, colloidal quantum dots have emerged as a new and promising type of LSC fluorophore. Spectral tunability of the quantum dots also facilitates the realization of stacked multilayered LSCs, where enhanced performance is obtained through spectral splitting of incident sunlight, as in multijunction photovoltaics. Here, we demonstrate a large-area (>230 cm2) tandem LSC based on two types of nearly reabsorption-free quantum dots spectrally tuned for optimal solar-spectrum splitting. This prototype device exhibits a high optical quantum efficiency of 6.4% for sunlight illumination and solar-to-electrical power conversion efficiency of 3.1%. The efficiency gains due to the tandem architecture over single-layer devices quickly increase with increasing LSC size and can reach more than 100% in structures with window sizes of more than 2,500 cm2.

  13. Coulomb Mediated Hybridization of Excitons in Coupled Quantum Dots.

    PubMed

    Ardelt, P-L; Gawarecki, K; Müller, K; Waeber, A M; Bechtold, A; Oberhofer, K; Daniels, J M; Klotz, F; Bichler, M; Kuhn, T; Krenner, H J; Machnikowski, P; Finley, J J

    2016-02-19

    We report Coulomb mediated hybridization of excitonic states in optically active InGaAs quantum dot molecules. By probing the optical response of an individual quantum dot molecule as a function of the static electric field applied along the molecular axis, we observe unexpected avoided level crossings that do not arise from the dominant single-particle tunnel coupling. We identify a new few-particle coupling mechanism stemming from Coulomb interactions between different neutral exciton states. Such Coulomb resonances hybridize the exciton wave function over four different electron and hole single-particle orbitals. Comparisons of experimental observations with microscopic eight-band k·p calculations taking into account a realistic quantum dot geometry show good agreement and reveal that the Coulomb resonances arise from broken symmetry in the artificial semiconductor molecule.

  14. Perspective: The future of quantum dot photonic integrated circuits

    NASA Astrophysics Data System (ADS)

    Norman, Justin C.; Jung, Daehwan; Wan, Yating; Bowers, John E.

    2018-03-01

    Direct epitaxial integration of III-V materials on Si offers substantial manufacturing cost and scalability advantages over heterogeneous integration. The challenge is that epitaxial growth introduces high densities of crystalline defects that limit device performance and lifetime. Quantum dot lasers, amplifiers, modulators, and photodetectors epitaxially grown on Si are showing promise for achieving low-cost, scalable integration with silicon photonics. The unique electrical confinement properties of quantum dots provide reduced sensitivity to the crystalline defects that result from III-V/Si growth, while their unique gain dynamics show promise for improved performance and new functionalities relative to their quantum well counterparts in many devices. Clear advantages for using quantum dot active layers for lasers and amplifiers on and off Si have already been demonstrated, and results for quantum dot based photodetectors and modulators look promising. Laser performance on Si is improving rapidly with continuous-wave threshold currents below 1 mA, injection efficiencies of 87%, and output powers of 175 mW at 20 °C. 1500-h reliability tests at 35 °C showed an extrapolated mean-time-to-failure of more than ten million hours. This represents a significant stride toward efficient, scalable, and reliable III-V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with complementary metal-oxide-semiconductor (CMOS) foundries.

  15. Plastic scintillator enhancement through Quantum Dot

    NASA Astrophysics Data System (ADS)

    Tam, Alan; Boyraz, Ozdal; Nilsson, Mikael

    2017-08-01

    Plastic scintillators such as Polyvinyl Toluene (PVT) are used for radiation detection but due to their poor performance they are not widely implemented. In order to circumnavigate this, dopants are added to enhance scintillation by energy transfer otherwise lost through non-radiative processes. In this work, we exploit the effects of energy transfer through the use of short wavelength emission Cadmium Sulfide Quantum Dots (QD) as the transfer stimulant. Scintillation enhancement was observed as Cadmium Sulfide QD with scintillating dyes are embedded in PVT polymer matrix for beta and gamma radiation. Energy transfer was observed between Quantum Dots, scintillating dye, and the host polymer. Different concentrations of QD and 2,5-diphenyloxazole (PPO) dye are investigated to characterize the energy transfer.

  16. Combination of short-length TiO2 nanorod arrays and compact PbS quantum-dot thin films for efficient solid-state quantum-dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Zhang, Zhengguo; Shi, Chengwu; Chen, Junjun; Xiao, Guannan; Li, Long

    2017-07-01

    Considering the balance of the hole diffusion length and the loading quantity of quantum-dots, the rutile TiO2 nanorod array with the length of 600 nm, the diameter of 20 nm, and the areal density of 500 μm-2 is successfully prepared by the hydrothermal method using the aqueous grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170 °C for 105 min. The compact PbS quantum-dot thin film on the TiO2 nanorod array is firstly obtained by the spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol (EDT). The result reveals that the strong interaction between lead and EDT is very important to control the crystallite size of PbS quantum-dots and obtain the compact PbS quantum-dot thin film on the TiO2 nanorod array. The all solid-state sensitized solar cell with the combination of the short-length, high-density TiO2 nanorod array and the compact PbS quantum-dot thin film achieves the photoelectric conversion efficiency of 4.10%, along with an open-circuit voltage of 0.52 V, a short-circuit photocurrent density of 13.56 mA cm-2 and a fill factor of 0.58.

  17. Photoluminescence Enhancement of Silole-Capped Silicon Quantum Dots Based on Förster Resonance Energy Transfer.

    PubMed

    Kim, Seongwoong; Kim, Sungsoo; Ko, Young Chun; Sohn, Honglae

    2015-07-01

    Photoluminescent porous silicon were prepared by an electrochemical etch of n-type silicon under the illumination with a 300 W tungsten filament bulb for the duration of etch. The red photoluminescence emitting at 650 nm with an excitation wavelength of 450 nm is due to the quantum confinement of silicon quantum dots in porous silicon. HO-terminated red luminescent PS was obtained by an electrochemical treatment of fresh PS with the current of 150 mA for 60 seconds in water and sodium chloride. As-prepared PS was sonicated, fractured, and centrifuged in toluene solution to obtain photoluminescence silicon quantum dots. Dichlorotetraphenylsilole exhibiting an emission band at 520 nm was reacted with HO-terminated silicon quantum dots to give a silole-capped silicon quantum dots. The optical characterization of silole-derivatized silicon quantum dots was investigated by UV-vis and fluorescence spectrometer. The fluorescence emission efficiency of silole-capped silicon quantum dots was increased by about 2.5 times due to F6rster resonance energy transfer from silole moiety to silicon quantum dots.

  18. Color-selective photodetection from intermediate colloidal quantum dots buried in amorphous-oxide semiconductors.

    PubMed

    Cho, Kyung-Sang; Heo, Keun; Baik, Chan-Wook; Choi, Jun Young; Jeong, Heejeong; Hwang, Sungwoo; Lee, Sang Yeol

    2017-10-10

    We report color-selective photodetection from intermediate, monolayered, quantum dots buried in between amorphous-oxide semiconductors. The proposed active channel in phototransistors is a hybrid configuration of oxide-quantum dot-oxide layers, where the gate-tunable electrical property of silicon-doped, indium-zinc-oxide layers is incorporated with the color-selective properties of quantum dots. A remarkably high detectivity (8.1 × 10 13 Jones) is obtained, along with three major findings: fast charge separation in monolayered quantum dots; efficient charge transport through high-mobility oxide layers (20 cm 2  V -1  s -1 ); and gate-tunable drain-current modulation. Particularly, the fast charge separation rate of 3.3 ns -1 measured with time-resolved photoluminescence is attributed to the intermediate quantum dots buried in oxide layers. These results facilitate the realization of efficient color-selective detection exhibiting a photoconductive gain of 10 7 , obtained using a room-temperature deposition of oxide layers and a solution process of quantum dots. This work offers promising opportunities in emerging applications for color detection with sensitivity, transparency, and flexibility.The development of highly sensitive photodetectors is important for image sensing and optical communication applications. Cho et al., report ultra-sensitive photodetectors based on monolayered quantum dots buried in between amorphous-oxide semiconductors and demonstrate color-detecting logic gates.

  19. Increased InAs quantum dot size and density using bismuth as a surfactant

    NASA Astrophysics Data System (ADS)

    Dasika, Vaishno D.; Krivoy, E. M.; Nair, H. P.; Maddox, S. J.; Park, K. W.; Jung, D.; Lee, M. L.; Yu, E. T.; Bank, S. R.

    2014-12-01

    We have investigated the growth of self-assembled InAs quantum dots using bismuth as a surfactant to control the dot size and density. We find that the bismuth surfactant increases the quantum dot density, size, and uniformity, enabling the extension of the emission wavelength with increasing InAs deposition without a concomitant reduction in dot density. We show that these effects are due to bismuth acting as a reactive surfactant to kinetically suppress the surface adatom mobility. This mechanism for controlling quantum dot density and size has the potential to extend the operating wavelength and enhance the performance of various optoelectronic devices.

  20. Visualization of Current and Mapping of Elements in Quantum Dot Solar Cells

    DOE PAGES

    Niezgoda, J. Scott; Ng, Amy; Poplawsky, Jonathan D.; ...

    2015-12-17

    The delicate influence of properties such as high surface state density and organic-inorganic boundaries on the individual quantum dot electronic structure complicates pursuits toward forming quantitative models of quantum dot thin films ab initio. Our report describes the application of electron beam-induced current (EBIC) microscopy to depleted-heterojunction colloidal quantum dot photovoltaics (DH-CQD PVs), a technique which affords one a map of current production within the active layer of a PV device. The effects of QD sample size polydispersity as well as layer thickness in CQD active layers as they pertain to current production within these PVs are imaged and explained.more » The results from these experiments compare well with previous estimations, and confirm the ability of EBIC to function as a valuable empirical tool for the design and betterment of DH-CQD PVs. Lastly, extensive and unexpected PbS QD penetration into the mesoporous TiO 2 layer is observed through imaging of device cross sections by energy-dispersive X-ray spectroscopy combined with scanning transmission electron microscopy. Finally, the effects of this finding are discussed and corroborated with the EBIC studies on similar devices.« less

  1. Photon antibunching from a single quantum-dot-microcavity system in the strong coupling regime.

    PubMed

    Press, David; Götzinger, Stephan; Reitzenstein, Stephan; Hofmann, Carolin; Löffler, Andreas; Kamp, Martin; Forchel, Alfred; Yamamoto, Yoshihisa

    2007-03-16

    We observe antibunching in the photons emitted from a strongly coupled single quantum dot and pillar microcavity in resonance. When the quantum dot was spectrally detuned from the cavity mode, the cavity emission remained antibunched, and also anticorrelated from the quantum dot emission. Resonant pumping of the selected quantum dot via an excited state enabled these observations by eliminating the background emitters that are usually coupled to the cavity. This device demonstrates an on-demand single-photon source operating in the strong coupling regime, with a Purcell factor of 61+/-7 and quantum efficiency of 97%.

  2. Interactions between N-acetyl-L-cysteine protected CdTe quantum dots and doxorubicin through spectroscopic method

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

    Yang, Xiupei, E-mail: xiupeiyang@163.com; College of Chemistry and Chemical Engineering, China West Normal University, Nanchong 637000; Lin, Jia

    2015-06-15

    Highlights: • CdTe quantum dots with the diameter of 3–5 nm were synthesized in aqueous solution. • The modified CdTe quantum dots showed well fluorescence properties. • The interaction between the CdTe quantum dots and doxorubicin (DR) was investigated. - Abstract: N-acetyl-L-cysteine protected cadmium telluride quantum dots with a diameter of 3–5 nm were synthesized in aqueous solution. The interaction between N-acetyl-L-cysteine/cadmium telluride quantum dots and doxorubicin was investigated by ultraviolet–visible absorption and fluorescence spectroscopy at physiological conditions (pH 7.2, 37 °C). The results indicate that electron transfer has occurred between N-acetyl-L-cysteine/cadmium telluride quantum dots and doxorubicin under light illumination.more » The quantum dots react readily with doxorubicin to form a N-acetyl-L-cysteine/cadmium telluride-quantum dots/doxorubicin complex via electrostatic attraction between the −NH{sub 3}{sup +} moiety of doxorubicin and the −COO{sup −} moiety of N-acetyl-L-cysteine/cadmium telluride quantum dots. The interaction of N-acetyl-L-cysteine/cadmium telluride-quantum dots/doxorubicin complex with bovine serum albumin was studied as well, showing that the complex might induce the conformation change of bovine serum due to changes in microenvironment of bovine serum.« less

  3. Electron-Nuclear Dynamics in a Quantum Dot under Nonunitary Electron Control

    DTIC Science & Technology

    2011-07-20

    relevant because inco - herent interactions are needed to initialize and read out the system. These experiments in quantum dots (QDs) ob- served dynamic...relaxation process is several orders of magnitude faster than what is used in Refs. [3,5]. The system we consider is a single electron trapped in a QD

  4. Quantum interference of electrically generated single photons from a quantum dot.

    PubMed

    Patel, Raj B; Bennett, Anthony J; Cooper, Ken; Atkinson, Paola; Nicoll, Christine A; Ritchie, David A; Shields, Andrew J

    2010-07-09

    Quantum interference lies at the foundation of many protocols for scalable quantum computing and communication with linear optics. To observe these effects the light source must emit photons that are indistinguishable. From a technological standpoint, it would be beneficial to have electrical control over the emission. Here we report of an electrically driven single-photon source emitting indistinguishable photons. The device consists of a layer of InAs quantum dots embedded in the intrinsic region of a p-i-n diode. Indistinguishability of consecutive photons is tested in a two-photon interference experiment under two modes of operation, continuous and pulsed current injection. We also present a complete theory based on the interference of photons with a Lorentzian spectrum which we compare to both our continuous wave and pulsed experiments. In the former case, a visibility was measured limited only by the timing resolution of our detection system. In the case of pulsed injection, we employ a two-pulse voltage sequence which suppresses multi-photon emission and allows us to carry out temporal filtering of photons which have undergone dephasing. The characteristic Hong-Ou-Mandel 'dip' is measured, resulting in a visibility of 64 +/- 4%.

  5. The emission wavelength dependent photoluminescence lifetime of the N-doped graphene quantum dots

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

    Deng, Xingxia; School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210; University of Chinese Academy of Sciences, Beijing 100049

    2015-12-14

    Aromatic nitrogen doped graphene quantum dots were investigated by steady-state and time-resolved photoluminescence (PL) techniques. The PL lifetime was found to be dependent on the emission wavelength and coincident with the PL spectrum, which is different from most semiconductor quantum dots and fluorescent dyes. This result shows the synergy and competition between the quantum confinement effect and edge functional groups, which may have the potential to guide the synthesis and expand the applications of graphene quantum dots.

  6. Fast current blinking in individual PbS and CdSe quantum dots.

    PubMed

    Maturova, Klara; Nanayakkara, Sanjini U; Luther, Joseph M; van de Lagemaat, Jao

    2013-06-12

    Fast current intermittency of the tunneling current through single semiconductor quantum dots was observed through time-resolved intermittent contact conductive atomic force microscopy in the dark and under illumination at room temperature. The current through a single dot switches on and off at time scales ranging from microseconds to seconds with power-law distributions for both the on and off times. On states are attributed to the resonant tunneling of charges from the electrically conductive AFM tip to the quantum dot, followed by transfer to the substrate, whereas off states are attributed to a Coulomb blockade effect in the quantum dots that shifts the energy levels out of resonance conditions due to the presence of the trapped charge, while at the same bias. The observation of current intermittency due to Coulomb blockade effects has important implications for the understanding of carrier transport through arrays of quantum dots.

  7. Fast Single-Shot Hold Spin Readout in Double Quantum Dots

    NASA Astrophysics Data System (ADS)

    Bogan, Alexander; Studenikin, Sergei; Korkusinski, Marek; Aers, Geof; Gaudreau, Louis; Zawadzki, Piotr; Sachrajda, Andy; Tracy, Lisa; Reno, John; Hargett, Terry

    Solid state spin qubits in quantum dots hold promise as scalable, high-density qubits in quantum information processing architectures. While much of the experimental investigation of these devices and their physics has focused on confined electron spins, hole spins in III-V semiconductors are attractive alternatives to electrons due to the reduced hyperfine coupling between the spin and the incoherent nuclear environment. In this talk, we will discuss a measurement protocol of the hole spin relaxation time T1 in a gated lateral GaAs double quantum dot tuned to the one and two-hole regimes, as well as a new technique for single-shot projective measurement of a single spin in tens of nanoseconds or less. The technique makes use of fast non-spin-conserving inter-dot transitions permitted by strong spin-orbit interactions for holes, as well as the latching of the charge state of the second quantum dot for enhanced sensitivity. This technique allows a direct measurement of the single spin relaxation time on time-scales set by physical device rather than by limitations of the measurement circuit.

  8. Photonic emitters and circuits based on colloidal quantum dot composites

    NASA Astrophysics Data System (ADS)

    Menon, Vinod M.; Husaini, Saima; Valappil, Nikesh; Luberto, Matthew

    2009-02-01

    We discuss our work on light emitters and photonic circuits realized using colloidal quantum dot composites. Specifically we will report our recent work on flexible microcavity laser, microdisk emitters and integrated active - passive waveguides. The entire microcavity laser structure was realized using spin coating and consisted of an all-polymer distributed Bragg reflector with a poly-vinyl carbazole cavity layer embedded with InGaP/ZnS colloidal quantum dots. These microcavities can be peeled off the substrate yielding a flexible structure that can conform to any shape and whose emission spectra can be mechanically tuned. The microdisk emitters and the integrated waveguide structures were realized using soft lithography and photo-lithography, respectively and were fabricated using a composite consisting of quantum dots embedded in SU8 matrix. Finally, we will discuss the effect of the host matrix on the optical properties of the quantum dots using results of steady-state and time-resolved luminescence measurements. In addition to their specific functionalities, these novel device demonstrations and their development present a low cost alternative to the traditional photonic device fabrication techniques.

  9. Input-output theory for spin-photon coupling in Si double quantum dots

    NASA Astrophysics Data System (ADS)

    Benito, M.; Mi, X.; Taylor, J. M.; Petta, J. R.; Burkard, Guido

    2017-12-01

    The interaction of qubits via microwave frequency photons enables long-distance qubit-qubit coupling and facilitates the realization of a large-scale quantum processor. However, qubits based on electron spins in semiconductor quantum dots have proven challenging to couple to microwave photons. In this theoretical work we show that a sizable coupling for a single electron spin is possible via spin-charge hybridization using a magnetic field gradient in a silicon double quantum dot. Based on parameters already shown in recent experiments, we predict optimal working points to achieve a coherent spin-photon coupling, an essential ingredient for the generation of long-range entanglement. Furthermore, we employ input-output theory to identify observable signatures of spin-photon coupling in the cavity output field, which may provide guidance to the experimental search for strong coupling in such spin-photon systems and opens the way to cavity-based readout of the spin qubit.

  10. CdSe quantum dot internalization by Bacillus subtilis and Escherichia coli

    NASA Astrophysics Data System (ADS)

    Kloepfer, Jeremiah A.; Mielke, Randall E.; Nadeau, Jay L.

    2004-06-01

    Biological labeling has been demonstrated with CdSe quantum dots in a variety of animal cells, but bacteria are harder to label because of their cell walls. We discuss the challenges of using minimally coated, bare CdSe quantum dots as luminescent internal labels for bacteria. These quantum dots were solubilized with mercaptoacetic acid and conjugated to adenine. Significant evidence for the internal staining of Bacillus subtilis (Gram positive) and Escherichia coli (Gram negative) using these structures is presented via steady-state emission, epifluorescence microscopy, transmission electron microscopy, and energy dispersive spectroscopy. In particular, the E. coli adenine auxotroph, and not the wild type, took up adenine coated quantum dots, and this only occurred in adenine deficient growth media. Labeling strength was enhanced by performing the incubation under room light. This process was examined with steady-state emission spectra and time-resolved luminescence profiles obtained from time-correlated-single-photon counting.

  11. The influence of bio-conjugation on photoluminescence of CdSe/ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Torchynska, Tetyana V.; Vorobiev, Yuri V.; Makhniy, Victor P.; Horley, Paul P.

    2014-11-01

    We report a considerable blue shift in the luminescence spectra of CdSe/ZnS quantum dots conjugated to anti-interleukin-10 antibodies. This phenomenon can be explained theoretically by accounting for bio-conjugation as a process causing electrostatic interaction between a quantum dot and an antibody, which reduces effective volume of the dot core. To solve the Schrödinger equation for an exciton confined in the quantum dot, we use mirror boundary conditions that were successfully tested for different geometries of quantum wells.

  12. Synthesis and Properties of Water-Soluble Blue-Emitting Mn-Alloyed CdTe Quantum Dots.

    PubMed

    Tynkevych, Olena; Karavan, Volodymyr; Vorona, Igor; Filonenko, Svitlana; Khalavka, Yuriy

    2018-05-02

    In this work, we prepared CdTe quantum dots, and series of Cd 1-x Mn x Te-alloyed quantum dots with narrow size distribution by an ion-exchange reaction in water solution. We found that the photoluminescence peaks are shifted to higher energies with the increasing Mn 2+ content. So far, this is the first report of blue-emitting CdTe-based quantum dots. By means of cyclic voltammetry, we detected features of electrochemical activity of manganese energy levels formed inside the Cd 1-x Mn x Te-alloyed quantum dot band gap. This allowed us to estimate their energy position. We also demonstrate paramagnetic behavior for Cd 1-x Mn x Te-alloyed quantum dots which confirmed the successful ion-exchange reaction.

  13. Synthesis and Properties of Water-Soluble Blue-Emitting Mn-Alloyed CdTe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tynkevych, Olena; Karavan, Volodymyr; Vorona, Igor; Filonenko, Svitlana; Khalavka, Yuriy

    2018-05-01

    In this work, we prepared CdTe quantum dots, and series of Cd1-xMnxTe-alloyed quantum dots with narrow size distribution by an ion-exchange reaction in water solution. We found that the photoluminescence peaks are shifted to higher energies with the increasing Mn2+ content. So far, this is the first report of blue-emitting CdTe-based quantum dots. By means of cyclic voltammetry, we detected features of electrochemical activity of manganese energy levels formed inside the Cd1-xMnxTe-alloyed quantum dot band gap. This allowed us to estimate their energy position. We also demonstrate paramagnetic behavior for Cd1-xMnxTe-alloyed quantum dots which confirmed the successful ion-exchange reaction.

  14. An orientation analysis method for protein immobilized on quantum dot particles

    NASA Astrophysics Data System (ADS)

    Aoyagi, Satoka; Inoue, Masae

    2009-11-01

    The evaluation of orientation of biomolecules immobilized on nanodevices is crucial for the development of high performance devices. Such analysis requires ultra high sensitivity so as to be able to detect less than one molecular layer on a device. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has sufficient sensitivity to evaluate the uppermost surface structure of a single molecular layer. The objective of this study is to develop an orientation analysis method for proteins immobilized on nanomaterials such as quantum dot particles, and to evaluate the orientation of streptavidin immobilized on quantum dot particles by means of TOF-SIMS. In order to detect fragment ions specific to the protein surface, a monoatomic primary ion source (Ga +) and a cluster ion source (Au 3+) were employed. Streptavidin-immobilized quantum dot particles were immobilized on aminosilanized ITO glass plates at amino groups by covalent bonding. The reference samples streptavidin directly immobilized on ITO plates were also prepared. All samples were dried with a freeze dryer before TOF-SIMS measurement. The positive secondary ion spectra of each sample were obtained using TOF-SIMS with Ga + and Au 3+, respectively, and then they were compared so as to characterize each sample and detect the surface structure of the streptavidin immobilized with the biotin-immobilized quantum dots. The chemical structures of the upper surface of the streptavidin molecules immobilized on the quantum dot particles were evaluated with TOF-SIMS spectra analysis. The indicated surface side of the streptavidin molecules immobilized on the quantum dots includes the biotin binding site.

  15. Magic angle for barrier-controlled double quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, Xu-Chen; Wang, Xin

    2018-01-01

    We show that the exchange interaction of a singlet-triplet spin qubit confined in double quantum dots, when being controlled by the barrier method, is insensitive to a charged impurity lying along certain directions away from the center of the double-dot system. These directions differ from the polar axis of the double dots by the magic angle, equaling arccos(1 /√{3 })≈54 .7∘ , a value previously found in atomic physics and nuclear magnetic resonance. This phenomenon can be understood from an expansion of the additional Coulomb interaction created by the impurity, but also relies on the fact that the exchange interaction solely depends on the tunnel coupling in the barrier-control scheme. Our results suggest that for a scaled-up qubit array, when all pairs of double dots rotate their respective polar axes from the same reference line by the magic angle, crosstalk between qubits can be eliminated, allowing clean single-qubit operations. While our model is a rather simplified version of actual experiments, our results suggest that it is possible to minimize unwanted couplings by judiciously designing the layout of the qubits.

  16. The Effect of Temperature on Photoluminescence Enhancement of Quantum Dots in Brain Slices.

    PubMed

    Zhao, Fei; Kim, Jongsung

    2017-04-01

    In this paper, we investigated the effect of temperature on photoluminescence of quantum dots immobilized on the surface of an optical fiber in a rat brain slice. The optical fiber was silanized with 3-aminopropyl trimethoxysilane (APTMS), following which quantum dots with carboxyl functional group were immobilized on the optical fiber via amide bond formation. The effect of temperature on the fluorescence intensity of the quantum dots in rat brain slices was studied. This report shows that the fluorescence intensity of quantum dots increases with the increase of temperature of the brain slice. The fluorescence enhancement phenomenon appears to take place via electron transfer related to pH increase. With the gradual increase of temperature, the fluorescence intensity of quantum dots in solution decreased, while that in the brain slice increased. This enhanced thermal performance of QDs in brain slice makes suggestion for the study of QDs-based brain temperature sensors.

  17. Direct photonic coupling of a semiconductor quantum dot and a trapped ion.

    PubMed

    Meyer, H M; Stockill, R; Steiner, M; Le Gall, C; Matthiesen, C; Clarke, E; Ludwig, A; Reichel, J; Atatüre, M; Köhl, M

    2015-03-27

    Coupling individual quantum systems lies at the heart of building scalable quantum networks. Here, we report the first direct photonic coupling between a semiconductor quantum dot and a trapped ion and we demonstrate that single photons generated by a quantum dot controllably change the internal state of a Yb^{+} ion. We ameliorate the effect of the 60-fold mismatch of the radiative linewidths with coherent photon generation and a high-finesse fiber-based optical cavity enhancing the coupling between the single photon and the ion. The transfer of information presented here via the classical correlations between the σ_{z} projection of the quantum-dot spin and the internal state of the ion provides a promising step towards quantum-state transfer in a hybrid photonic network.

  18. NREL, University of Washington Scientists Elevate Quantum Dot Solar Cell

    Science.gov Websites

    World Record to 13.4 Percent | NREL | News | NREL NREL, University of Washington Scientists Elevate Quantum Dot Solar Cell World Record to 13.4 Percent News Release: NREL, University of Washington Scientists Elevate Quantum Dot Solar Cell World Record to 13.4 Percent October 27, 2017 Researchers at the

  19. Colloidal-Quantum-Dot Ring Lasers with Active Color Control.

    PubMed

    le Feber, Boris; Prins, Ferry; De Leo, Eva; Rabouw, Freddy T; Norris, David J

    2018-02-14

    To improve the photophysical performance of colloidal quantum dots for laser applications, sophisticated core/shell geometries have been developed. Typically, a wider bandgap semiconductor is added as a shell to enhance the gain from the quantum-dot core. This shell is designed to electronically isolate the core, funnel excitons to it, and reduce nonradiative Auger recombination. However, the shell could also potentially provide a secondary source of gain, leading to further versatility in these materials. Here we develop high-quality quantum-dot ring lasers that not only exhibit lasing from both the core and the shell but also the ability to switch between them. We fabricate ring resonators (with quality factors up to ∼2500) consisting only of CdSe/CdS/ZnS core/shell/shell quantum dots using a simple template-stripping process. We then examine lasing as a function of the optical excitation power and ring radius. In resonators with quality factors >1000, excitons in the CdSe cores lead to red lasing with thresholds at ∼25 μJ/cm 2 . With increasing power, green lasing from the CdS shell emerges (>100 μJ/cm 2 ) and then the red lasing begins to disappear (>250 μJ/cm 2 ). We present a rate-equation model that can explain this color switching as a competition between exciton localization into the core and stimulated emission from excitons in the shell. Moreover, by lowering the quality factor of the cavity we can engineer the device to exhibit only green lasing. The mechanism demonstrated here provides a potential route toward color-switchable quantum-dot lasers.

  20. 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.

  1. High-fidelity gates in quantum dot spin qubits

    PubMed Central

    Koh, Teck Seng; Coppersmith, S. N.; Friesen, Mark

    2013-01-01

    Several logical qubits and quantum gates have been proposed for semiconductor quantum dots controlled by voltages applied to top gates. The different schemes can be difficult to compare meaningfully. Here we develop a theoretical framework to evaluate disparate qubit-gating schemes on an equal footing. We apply the procedure to two types of double-dot qubits: the singlet–triplet and the semiconducting quantum dot hybrid qubit. We investigate three quantum gates that flip the qubit state: a DC pulsed gate, an AC gate based on logical qubit resonance, and a gate-like process known as stimulated Raman adiabatic passage. These gates are all mediated by an exchange interaction that is controlled experimentally using the interdot tunnel coupling g and the detuning ϵ, which sets the energy difference between the dots. Our procedure has two steps. First, we optimize the gate fidelity (f) for fixed g as a function of the other control parameters; this yields an that is universal for different types of gates. Next, we identify physical constraints on the control parameters; this yields an upper bound that is specific to the qubit-gate combination. We show that similar gate fidelities should be attainable for singlet-triplet qubits in isotopically purified Si, and for hybrid qubits in natural Si. Considerably lower fidelities are obtained for GaAs devices, due to the fluctuating magnetic fields ΔB produced by nuclear spins. PMID:24255105

  2. High-fidelity gates in quantum dot spin qubits.

    PubMed

    Koh, Teck Seng; Coppersmith, S N; Friesen, Mark

    2013-12-03

    Several logical qubits and quantum gates have been proposed for semiconductor quantum dots controlled by voltages applied to top gates. The different schemes can be difficult to compare meaningfully. Here we develop a theoretical framework to evaluate disparate qubit-gating schemes on an equal footing. We apply the procedure to two types of double-dot qubits: the singlet-triplet and the semiconducting quantum dot hybrid qubit. We investigate three quantum gates that flip the qubit state: a DC pulsed gate, an AC gate based on logical qubit resonance, and a gate-like process known as stimulated Raman adiabatic passage. These gates are all mediated by an exchange interaction that is controlled experimentally using the interdot tunnel coupling g and the detuning [Symbol: see text], which sets the energy difference between the dots. Our procedure has two steps. First, we optimize the gate fidelity (f) for fixed g as a function of the other control parameters; this yields an f(opt)(g) that is universal for different types of gates. Next, we identify physical constraints on the control parameters; this yields an upper bound f(max) that is specific to the qubit-gate combination. We show that similar gate fidelities (~99:5%) should be attainable for singlet-triplet qubits in isotopically purified Si, and for hybrid qubits in natural Si. Considerably lower fidelities are obtained for GaAs devices, due to the fluctuating magnetic fields ΔB produced by nuclear spins.

  3. Calculation of exchange interaction for modified Gaussian coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Khordad, R.

    2017-08-01

    A system of two laterally coupled quantum dots with modified Gaussian potential has been considered. Each quantum dot has an electron under electric and magnetic field. The quantum dots have been considered as hydrogen-like atoms. The physical picture has translated into the Heisenberg spin Hamiltonian. The Schrödinger equation using finite element method has been numerically solved. The exchange energy factor has been calculated as a functions of electric field, magnetic field, and the separation distance between the centers of the dots ( d). According to the results, it is found that there is the transition from anti-ferromagnetic to ferromagnetic for constant electric field. Also, the transition occurs from ferromagnetic to anti-ferromagnetic for constant magnetic field (B>1 T). With decreasing the distance between the centers of the dots and increasing magnetic field, the transition occurs from anti-ferromagnetic to ferromagnetic. It is found that a switching of exchange energy factor is presented without canceling the interactions of the electric and magnetic fields on the system.

  4. Substrate driven photochemistry of CdSe quantum dot films: charge injection and irreversible transformations on oxide surfaces.

    PubMed

    Tvrdy, Kevin; Kamat, Prashant V

    2009-04-23

    The photochemical behavior of CdSe quantum dots anchored to different surfaces was probed through their deposition on glass, SiO2, and TiO2 films. Following visible light irradiation under ambient conditions, CdSe quantum dots deposited on semiconducting TiO2 surface degraded, where no such degradation was observed when deposited on inert SiO2 surface or glass. Fluorescence decay and transient absorption experiments confirmed that charge injection from excited CdSe into TiO2 occurs with an apparent rate constant of 5.62 x 10(8) s(-1) and is the primary event responsible for photodegradation. In the presence of air, injected electrons are scavenged by surface adsorbed oxygen leaving behind reactive holes which induce anodic corrosion of CdSe quantum dots. In a vacuum environment, minimal CdSe degradation was observed as electron scavenging by oxygen is replaced with charge recombination between injected electrons and holes in CdSe nanocrystals. Spectroscopic measurements presented in this study highlight the role of both substrate and medium in dictating the photochemistry of CdSe quantum dots.

  5. Quantum dots and nanoparticles for photodynamic and radiation therapies of cancer

    PubMed Central

    Juzenas, Petras; Chen, Wei; Sun, Ya-Ping; Coelho, Manuel Alvaro Neto; Generalov, Roman; Generalova, Natalia; Christensen, Ingeborg Lie

    2009-01-01

    Semiconductor quantum dots and nanoparticles composed of metals, lipids or polymers have emerged with promising applications for early detection and therapy of cancer. Quantum dots with unique optical properties are commonly composed of cadmium contained semiconductors. Cadmium is potentially hazardous, and toxicity of such quantum dots to living cells, and humans, is not yet systematically investigated. Therefore, search for less toxic materials with similar targeting and optical properties is of further interest. Whereas, the investigation of luminescence nanoparticles as light sources for cancer therapy is very interesting. Despite advances in neurosurgery and radiotherapy the prognosis for patients with malignant gliomas has changed little for the last decades. Cancer treatment requires high accuracy in delivering ionizing radiation to reduce toxicity to surrounding tissues. Recently some research has been focused in developing photosensitizing quantum dots for production of radicals upon absorption of visible light. In spite of the fact that visible light is safe, this approach is suitable to treat only superficial tumours. Ionizing radiation (X-rays and gamma rays) penetrate much deeper thus offering a big advantage in treating patients with tumours in internal organs. Such concept of using quantum dots and nanoparticles to yield electrons and radicals in photodynamic and radiation therapies as well their combination is reviewed in this article. PMID:18840487

  6. Blinking correlation in nanocrystal quantum dots probed with novel laser scanning confocal microscopy methods

    NASA Astrophysics Data System (ADS)

    Hefti, Ryan Alf

    Semiconductor quantum dots have a vast array of applications: as fluorescent labels in biological systems, as physical or chemical sensors, as components in photovoltaic technology, and in display devices. An attribute of nearly every quantum dot is its blinking, or fluorescence intermittency, which tends to be a disadvantage in most applications. Despite the fact that blinking has been a nearly universal phenomenon among all types of fluorescent constructs, it is more prevalent in quantum dots than in traditional fluorophores. Furthermore, no unanimously accepted model of quantum dot blinking yet exists. The work encompassed by this dissertation began with an in-depth study of molecular motor protein dynamics in a variety of environments using two specially developed techniques, both of which feature applicability to live cell systems. Parked-beam confocal microscopy was utilized to increase temporal resolution of molecular motor motion dynamics by an order of magnitude over other popular methods. The second technique, fast-scanning confocal microscopy (FSCM), was used for long range observation of motor proteins. While using FSCM on motor protein assays, we discovered an unusual phenomenon. Single quantum dots seemingly communicated with neighboring quantum dots, indicated by a distinct correlation in their blinking patterns. In order to explain this novel correlation phenomenon, the majority of blinking models developed thus far would suggest a dipole-dipole interaction or a Coulomb interaction between singly charged quantum dots. However, our results indicate that the interaction energy is higher than supported by current models, thereby prompting a renewed examination. We propose that the blinking correlation we observed is due to a Coulomb interaction on the order of 3-4 elementary charges per quantum dot and that multiple charging of individual quantum dots may be required to plunge them into a non-emissive state. As a result of charging, charge carriers are

  7. Platinum assisted by carbon quantum dots for methanol electro-oxidation

    NASA Astrophysics Data System (ADS)

    Pan, Dan; Li, Xingwei; Zhang, Aofeng

    2018-01-01

    Various types of fuel cells as clean and portable power sources show a great attraction, especially direct methanol fuel cell (DMFC) having high energy density, low operating temperature and convenient fuel storage. However, the preparation of low-cost Pt-based catalysts with satisfactory catalytic performance still faces many challenges for its commercialization on large scale. Here, Pt catalysts assisted by carbon quantum dots (CQDs) are reported. The synergistic effect of carbon quantum dots and Pt metals is similar to a bi-component catalyst, such as PtRu. First, carbon quantum dots derived from Vulcan XC-72 carbon black are synthesized by mixed acid etching. Then, carbon black (Vulcan XC-72) is soaked in carbon quantum dots solution for several days to obtain carbon black modified by carbon quantum dots (XC-72-CQDs). Finally, Pt catalysts are supported on XC-72-CQDs (Pt/XC-72-CQDs) through a simple chemical reduction method. For methanol electro-oxidation reaction, the catalytic performance of Pt/XC-72-CQDs is compared with commercial PtRu/C (30% Pt + 15% Ru). Results show that a typical product (Pt/XC-72-CQDs5) exhibits a better catalytic activity than PtRu/C. In cyclic voltammetry test, the specific activity of Pt/XC-72-CQDs5 is 1.06 mA cm-2 Pt and 477.6 mA mg-1 Pt, while that of PtRu/C is 0.77 mA cm-2 Pt and 280.6 mA mg-1 Pt.

  8. Purcell effect in triangular plasmonic nanopatch antennas with three-layer colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Eliseev, S. P.; Kurochkin, N. S.; Vergeles, S. S.; Sychev, V. V.; Chubich, D. A.; Argyrakis, P.; Kolymagin, D. A.; Vitukhnovskii, A. G.

    2017-05-01

    A model describing a plasmonic nanopatch antenna based on triangular silver nanoprisms and multilayer cadmium chalcogenide quantum dots is introduced. Electromagnetic-field distributions in nanopatch antennas with different orientations of the quantum-dot dipoles are calculated for the first time with the finite element method for numerical electrodynamics simulations. The energy flux through the surface of an emitting quantum dot is calculated for the configurations with the dot in free space, on an aluminum substrate, and in a nanopatch antenna. It is shown that the radiative part of the Purcell factor is as large as 1.7 × 102 The calculated photoluminescence lifetimes of a CdSe/CdS/ZnS colloidal quantum dot in a nanopatch antenna based on a silver nanoprism agree well with the experimental results.

  9. Correlated Coulomb Drag in Capacitively Coupled Quantum-Dot Structures.

    PubMed

    Kaasbjerg, Kristen; Jauho, Antti-Pekka

    2016-05-13

    We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs)-a bias-driven dot coupled to an unbiased dot where transport is due to Coulomb mediated energy transfer drag. To this end, we introduce a master-equation approach that accounts for higher-order tunneling (cotunneling) processes as well as energy-dependent lead couplings, and identify a mesoscopic Coulomb drag mechanism driven by nonlocal multielectron cotunneling processes. Our theory establishes the conditions for a nonzero drag as well as the direction of the drag current in terms of microscopic system parameters. Interestingly, the direction of the drag current is not determined by the drive current, but by an interplay between the energy-dependent lead couplings. Studying the drag mechanism in a graphene-based CQD heterostructure, we show that the predictions of our theory are consistent with recent experiments on Coulomb drag in CQD systems.

  10. [Imaging of surface cell antigens on the tumor sections of lymph nodes using fluorescence quantum dots].

    PubMed

    Rafalovskaia-Orlovskaia, E P; Gorgidze, L A; Gladkikh, A A; Tauger, S M; Vorob'ev, I A

    2012-01-01

    The usefulness of quantum dots for the immunofluorescent detection of surface antigens on the lymphoid cells has been studied. To optimize quantum dots detection we have upgraded fluorescent microscope that allows obtaining multiple images from different quantum dots from one section. Specimens stained with quantum dots remained stable over two weeks and practically did not bleach under mercury lamp illumination during tens of minutes. Direct conjugates of primary mouse monoclonal antibodies with quantum dots demonstrated high specificity and sufficient sensitivity in the case of double staining on the frozen sections. Because of the high stability of quantum dots' fluorescence, this method allows to analyze antigen coexpression on the lymphoid tissue sections for diagnostic purposes. The spillover of fluorescent signals from quantum dots into adjacent fluorescent channels, with maxima differing by 40 nm, did not exceed 8%, which makes the spectral compensation is practically unnecessary.

  11. Electrically protected resonant exchange qubits in triple quantum dots.

    PubMed

    Taylor, J M; Srinivasa, V; Medford, J

    2013-08-02

    We present a modulated microwave approach for quantum computing with qubits comprising three spins in a triple quantum dot. This approach includes single- and two-qubit gates that are protected against low-frequency electrical noise, due to an operating point with a narrowband response to high frequency electric fields. Furthermore, existing double quantum dot advances, including robust preparation and measurement via spin-to-charge conversion, are immediately applicable to the new qubit. Finally, the electric dipole terms implicit in the high frequency coupling enable strong coupling with superconducting microwave resonators, leading to more robust two-qubit gates.

  12. State-conditional coherent charge qubit oscillations in a Si/SiGe quadruple quantum dot

    NASA Astrophysics Data System (ADS)

    Ward, Daniel R.; Kim, Dohun; Savage, Donald E.; Lagally, Max G.; Foote, Ryan H.; Friesen, Mark; Coppersmith, Susan N.; Eriksson, Mark A.

    2016-10-01

    Universal quantum computation requires high-fidelity single-qubit rotations and controlled two-qubit gates. Along with high-fidelity single-qubit gates, strong efforts have been made in developing robust two-qubit logic gates in electrically gated quantum dot systems to realise a compact and nanofabrication-compatible architecture. Here we perform measurements of state-conditional coherent oscillations of a charge qubit. Using a quadruple quantum dot formed in a Si/SiGe heterostructure, we show the first demonstration of coherent two-axis control of a double quantum dot charge qubit in undoped Si/SiGe, performing Larmor and Ramsey oscillation measurements. We extract the strength of the capacitive coupling between a pair of double quantum dots by measuring the detuning energy shift (≈75 μeV) of one double dot depending on the excess charge configuration of the other double dot. We further demonstrate that the strong capacitive coupling allows fast, state-conditional Landau-Zener-Stückelberg oscillations with a conditional π phase flip time of about 80 ps, showing a promising pathway towards multi-qubit entanglement and control in semiconductor quantum dots.

  13. State-conditional coherent charge qubit oscillations in a Si/SiGe quadruple quantum dot

    DOE PAGES

    Ward, Daniel R.; Kim, Dohun; Savage, Donald E.; ...

    2016-10-18

    Universal quantum computation requires high-fidelity single-qubit rotations and controlled two-qubit gates. Along with high-fidelity single-qubit gates, strong efforts have been made in developing robust two-qubit logic gates in electrically gated quantum dot systems to realise a compact and nanofabrication-compatible architecture. Here we perform measurements of state-conditional coherent oscillations of a charge qubit. Using a quadruple quantum dot formed in a Si/SiGe heterostructure, we show the first demonstration of coherent two-axis control of a double quantum dot charge qubit in undoped Si/SiGe, performing Larmor and Ramsey oscillation measurements. We extract the strength of the capacitive coupling between a pair of doublemore » quantum dots by measuring the detuning energy shift (≈75 μeV) of one double dot depending on the excess charge configuration of the other double dot. Finally, we further demonstrate that the strong capacitive coupling allows fast, state-conditional Landau–Zener–Stückelberg oscillations with a conditional π phase flip time of about 80 ps, showing a promising pathway towards multi-qubit entanglement and control in semiconductor quantum dots.« less

  14. State-conditional coherent charge qubit oscillations in a Si/SiGe quadruple quantum dot

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

    Ward, Daniel R.; Kim, Dohun; Savage, Donald E.

    Universal quantum computation requires high-fidelity single-qubit rotations and controlled two-qubit gates. Along with high-fidelity single-qubit gates, strong efforts have been made in developing robust two-qubit logic gates in electrically gated quantum dot systems to realise a compact and nanofabrication-compatible architecture. Here we perform measurements of state-conditional coherent oscillations of a charge qubit. Using a quadruple quantum dot formed in a Si/SiGe heterostructure, we show the first demonstration of coherent two-axis control of a double quantum dot charge qubit in undoped Si/SiGe, performing Larmor and Ramsey oscillation measurements. We extract the strength of the capacitive coupling between a pair of doublemore » quantum dots by measuring the detuning energy shift (≈75 μeV) of one double dot depending on the excess charge configuration of the other double dot. Finally, we further demonstrate that the strong capacitive coupling allows fast, state-conditional Landau–Zener–Stückelberg oscillations with a conditional π phase flip time of about 80 ps, showing a promising pathway towards multi-qubit entanglement and control in semiconductor quantum dots.« less

  15. CdSe quantum dot internalization by Bacillus subtilis and Escherichia coli

    NASA Technical Reports Server (NTRS)

    Kloepfer, Jeremiah A.; Mielke, Randall E.; Nadeau, Jay L.

    2004-01-01

    Biological labeling has been demonstrated with CdSe quantum dots in a variety of animal cells, but bacteria are harder to label because of their cell walls. We discuss the challenges of using minimally coated, bare CdSe quantum dots as luminescent internal labels for bacteria.

  16. Exciton shelves for charge and energy transport in third-generation quantum-dot devices

    NASA Astrophysics Data System (ADS)

    Goodman, Samuel; Singh, Vivek; Noh, Hyunwoo; Casamada, Josep; Chatterjee, Anushree; Cha, Jennifer; Nagpal, Prashant

    2014-03-01

    Quantum dots are semiconductor nanocrystallites with size-dependent quantum-confined energy levels. While they have been intensively investigated to utilize hot-carriers for photovoltaic applications, to bridge the mismatch between incident solar photons and finite bandgap of semiconductor photocells, efficient charge or exciton transport in quantum-dot films has proven challenging. Here we show development of new coupled conjugated molecular wires with ``exciton shelves'', or different energy levels, matched with the multiple energy levels of quantum dots. Using single nanoparticle and ensemble device measurements we show successful extraction and transport of both bandedge and high-energy charge carriers, and energy transport of excitons. We demonstrate using measurements of electronic density of states, that careful matching of energy states of quantum-dot with molecular wires is important, and any mismatch can generate midgap states leading to charge recombination and reduced efficiency. Therefore, these exciton-shelves and quantum dots can lead to development of next-generation photovoltaic and photodetection devices using simultaneous transport of bandedge and hot-carriers or energy transport of excitons in these nanostructured solution-processed films.

  17. Interaction of solitons with a string of coupled quantum dots

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

    Kumar, Vijendra, E-mail: vsmedphysics@gmail.com; Swami, O. P., E-mail: omg1789@gmail.com; Nagar, A. K., E-mail: ajaya.nagar@gmail.com

    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.

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

    PubMed

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

    2015-10-14

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

  19. Coulomb Oscillations in a Gate-Controlled Few-Layer Graphene Quantum Dot.

    PubMed

    Song, Yipu; Xiong, Haonan; Jiang, Wentao; Zhang, Hongyi; Xue, Xiao; Ma, Cheng; Ma, Yulin; Sun, Luyan; Wang, Haiyan; Duan, Luming

    2016-10-12

    Graphene quantum dots could be an ideal host for spin qubits and thus have been extensively investigated based on graphene nanoribbons and etched nanostructures; however, edge and substrate-induced disorders severely limit device functionality. Here, we report the confinement of quantum dots in few-layer graphene with tunable barriers, defined by local strain and electrostatic gating. Transport measurements unambiguously reveal that confinement barriers are formed by inducing a band gap via the electrostatic gating together with local strain induced constriction. Numerical simulations according to the local top-gate geometry confirm the band gap opening by a perpendicular electric field. We investigate the magnetic field dependence of the energy-level spectra in these graphene quantum dots. Experimental results reveal a complex evolution of Coulomb oscillations with the magnetic field, featuring kinks at level crossings. The simulation of energy spectrum shows that the kink features and the magnetic field dependence are consistent with experimental observations, implying the hybridized nature of energy-level spectrum of these graphene quantum dots.

  20. Coherent coupling between a quantum dot and a donor in silicon

    DOE PAGES

    Harvey-Collard, Patrick; Jacobson, N. Tobias; Rudolph, Martin; ...

    2017-10-18

    Individual donors in silicon chips are used as quantum bits with extremely low error rates. However, physical realizations have been limited to one donor because their atomic size causes fabrication challenges. Quantum dot qubits, in contrast, are highly adjustable using electrical gate voltages. This adjustability could be leveraged to deterministically couple donors to quantum dots in arrays of qubits. In this work, we demonstrate the coherent interaction of a 31P donor electron with the electron of a metal-oxide-semiconductor quantum dot. We form a logical qubit encoded in the spin singlet and triplet states of the two-electron system. We show thatmore » the donor nuclear spin drives coherent rotations between the electronic qubit states through the contact hyperfine interaction. This provides every key element for compact two-electron spin qubits requiring only a single dot and no additional magnetic field gradients, as well as a means to interact with the nuclear spin qubit.« less

  1. Curcumin Quantum Dots Mediated Degradation of Bacterial Biofilms.

    PubMed

    Singh, Ashish K; Prakash, Pradyot; Singh, Ranjana; Nandy, Nabarun; Firdaus, Zeba; Bansal, Monika; Singh, Ranjan K; Srivastava, Anchal; Roy, Jagat K; Mishra, Brahmeshwar; Singh, Rakesh K

    2017-01-01

    Bacterial biofilm has been reported to be associated with more than 80% of bacterial infections. Curcumin, a hydrophobic polyphenol compound, has anti-quorum sensing activity apart from having antimicrobial action. However, its use is limited by its poor aqueous solubility and rapid degradation. In this study, we attempted to prepare quantum dots of the drug curcumin in order to achieve enhanced solubility and stability and investigated for its antimicrobial and antibiofilm activity. We utilized a newer two-step bottom up wet milling approach to prepare Curcumin Quantum Dots (CurQDs) using acetone as a primary solvent. Minimum inhibitory concentration against select Gram-positive and Gram-negative bacteria was performed. The antibiofilm assay was performed at first using 96-well tissue culture plate and subsequently validated by Confocal Laser Scanning Microscopy. Further, biofilm matrix protein was isolated using formaldehyde sludge and TCA/Acetone precipitation method. Protein extracted was incubated with varying concentration of CurQDs for 4 h and was subjected to SDS-PAGE. Molecular docking study was performed to observe interaction between curcumin and phenol soluble modulins as well as curli proteins. The biophysical evidences obtained from TEM, SEM, UV-VIS, fluorescence, Raman spectroscopy, and zeta potential analysis confirmed the formation of curcumin quantum dots with increased stability and solubility. The MICs of curcumin quantum dots, as observed against both select gram positive and negative bacterial isolates, was observed to be significantly lower than native curcumin particles. On TCP assay, Curcumin observed to be having antibiofilm as well as biofilm degrading activity. Results of SDS-PAGE and molecular docking have shown interaction between biofilm matrix proteins and curcumin. The results indicate that aqueous solubility and stability of Curcumin can be achieved by preparing its quantum dots. The study also demonstrates that by sizing down the

  2. Electrically tunable g factors in quantum dot molecular spin states.

    PubMed

    Doty, M F; Scheibner, M; Ponomarev, I V; Stinaff, E A; Bracker, A S; Korenev, V L; Reinecke, T L; Gammon, D

    2006-11-10

    We present a magnetophotoluminescence study of individual vertically stacked InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied electric field tunes the relative energies of the two dots, we observe a strong resonant increase or decrease in the g factors of different spin states that have molecular wave functions distributed over both quantum dots. We propose a phenomenological model for the change in g factor based on resonant changes in the amplitude of the wave function in the barrier due to the formation of bonding and antibonding orbitals.

  3. Electrically Tunable g Factors in Quantum Dot Molecular Spin States

    NASA Astrophysics Data System (ADS)

    Doty, M. F.; Scheibner, M.; Ponomarev, I. V.; Stinaff, E. A.; Bracker, A. S.; Korenev, V. L.; Reinecke, T. L.; Gammon, D.

    2006-11-01

    We present a magnetophotoluminescence study of individual vertically stacked InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied electric field tunes the relative energies of the two dots, we observe a strong resonant increase or decrease in the g factors of different spin states that have molecular wave functions distributed over both quantum dots. We propose a phenomenological model for the change in g factor based on resonant changes in the amplitude of the wave function in the barrier due to the formation of bonding and antibonding orbitals.

  4. Quantum Dot-Based Luminescent Oxygen Channeling Assay for Potential Application in Homogeneous Bioassays.

    PubMed

    Zhuang, Si-Hui; Guo, Xin-Xin; Wu, Ying-Song; Chen, Zhen-Hua; Chen, Yao; Ren, Zhi-Qi; Liu, Tian-Cai

    2016-01-01

    The unique photoproperties of quantum dots are promising for potential application in bioassays. In the present study, quantum dots were applied to a luminescent oxygen channeling assay. The reaction system developed in this study was based on interaction of biotin with streptavidin. Carboxyl-modified polystyrene microspheres doped with quantum dots were biotinylated and used as acceptors. Photosensitizer-doped carboxyl-modified polystyrene microspheres were conjugated with streptavidin and used as donors. The results indicated that the singlet oxygen that was released from the donor beads diffused into the acceptor beads. The acceptor beads were then exited via thioxene, and were subsequently fluoresced. To avoid generating false positives, a high concentration (0.01 mg/mL) of quantum dots is required for application in homogeneous immunoassays. Compared to a conventional luminescent oxygen channeling assay, this quantum dots-based technique requires less time, and would be easier to automate and miniaturize because it requires no washing to remove excess labels.

  5. Modeling and simulation of InGaN/GaN quantum dots solar cell

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

    Aissat, A., E-mail: sakre23@yahoo.fr; LASICOMLaboratory, Faculty of Sciences, University of Blida 1; Benyettou, F.

    2016-07-25

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In{sub 0.25}Ga{sub 0.75}N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In{sub 0.25}Ga{sub 0.75}N/GaN quantum dots with pin solar cell. The conversion efficiencymore » begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.« less

  6. A modified gradient approach for the growth of low-density InAs quantum dot molecules by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sharma, Nandlal; Reuter, Dirk

    2017-11-01

    Two vertically stacked quantum dots that are electronically coupled, so called quantum dot molecules, are of great interest for the realization of solid state building blocks for quantum communication networks. We present a modified gradient approach to realize InAs quantum dot molecules with a low areal density so that single quantum dot molecules can be optically addressed. The individual quantum dot layers were prepared by solid source molecular beam epitaxy depositing InAs on GaAs(100). The bottom quantum dot layer has been grown without substrate rotation resulting in an In-gradient across the surface, which translated into a density gradient with low quantum dot density in a certain region of the wafer. For the top quantum dot layer, separated from the bottom quantum dot layer by a 6 nm thick GaAs barrier, various InAs amounts were deposited without an In-gradient. In spite of the absence of an In-gradient, a pronounced density gradient is observed for the top quantum dots. Even for an In-amount slightly below the critical thickness for a single dot layer, a density gradient in the top quantum dot layer, which seems to reproduce the density gradient in the bottom layer, is observed. For more or less In, respectively, deviations from this behavior occur. We suggest that the obvious influence of the bottom quantum dot layer on the growth of the top quantum dots is due to the strain field induced by the buried dots.

  7. Semiconductor quantum dot scintillation under gamma-ray irradiation

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

    Letant, S E; Wang, T

    2006-08-23

    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-ray irradiation, and compare the energy resolution of the 59 keV line of Americium 241 obtained with our quantum dot-glass nanocomposite material 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. These results demonstrate the potential of quantum dots for room-temperature gamma-ray detection, which has applications in medical imaging, environmental monitoring, as well asmore » security and defense. Present technology in gamma radiation detection suffers from flexibility and scalability issues. For example, bulk Germanium provides fine energy resolution (0.2% energy resolution at 1.33 MeV) but requires operation at liquid nitrogen temperature. On the other hand, Cadmium-Zinc-Telluride is a good room temperature detector ( 1% at 662 keV) but the size of the crystals that can be grown is limited to a few centimeters in each direction. Finally, the most commonly used scintillator, Sodium Iodide (NaI), can be grown as large crystals but suffers from a lack of energy resolution (7% energy resolution at 662 keV). Recent advancements in nanotechnology6-10 have provided the possibility of controlling materials synthesis at the molecular level. Both morphology and chemical composition can now be manipulated, leading to radically new material properties due to a combination of quantum confinement and surface to volume ratio effects. One of the main consequences of reducing the size of semiconductors down to nanometer dimensions is to increase the energy band gap, leading to visible luminescence, which suggests that these materials could be used as scintillators. The visible band gap of quantum dots would also ensure both efficient photon

  8. Near-infrared quantum dots for HER2 localization and imaging of cancer cells.

    PubMed

    Rizvi, Sarwat B; Rouhi, Sepideh; Taniguchi, Shohei; Yang, Shi Yu; Green, Mark; Keshtgar, Mo; Seifalian, Alexander M

    2014-01-01

    Quantum dots are fluorescent nanoparticles with unique photophysical properties that allow them to be used as diagnostic, therapeutic, and theranostic agents, particularly in medical and surgical oncology. Near-infrared-emitting quantum dots can be visualized in deep tissues because the biological window is transparent to these wavelengths. Their small sizes and free surface reactive groups that can be conjugated to biomolecules make them ideal probes for in vivo cancer localization, targeted chemotherapy, and image-guided cancer surgery. The human epidermal growth factor receptor 2 gene (HER2/neu) is overexpressed in 25%-30% of breast cancers. The current methods of detection for HER2 status, including immunohistochemistry and fluorescence in situ hybridization, are used ex vivo and cannot be used in vivo. In this paper, we demonstrate the application of near-infrared-emitting quantum dots for HER2 localization in fixed and live cancer cells as a first step prior to their in vivo application. Near-infrared-emitting quantum dots were characterized and their in vitro toxicity was established using three cancer cell lines, ie, HepG2, SK-BR-3 (HER2-overexpressing), and MCF7 (HER2-underexpressing). Mouse antihuman anti-HER2 monoclonal antibody was conjugated to the near-infrared-emitting quantum dots. In vitro toxicity studies showed biocompatibility of SK-BR-3 and MCF7 cell lines with near-infrared-emitting quantum dots at a concentration of 60 μg/mL after one hour and 24 hours of exposure. Near-infrared-emitting quantum dot antiHER2-antibody bioconjugates successfully localized HER2 receptors on SK-BR-3 cells. Near-infrared-emitting quantum dot bioconjugates can be used for rapid localization of HER2 receptors and can potentially be used for targeted therapy as well as image-guided surgery.

  9. Focal-Plane Arrays of Quantum-Dot Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath; Wilson, Daniel; Hill, Cory; Liu, John; Bandara, Sumith; Ting, David

    2007-01-01

    Focal-plane arrays of semiconductor quantum-dot infrared photodetectors (QDIPs) are being developed as superior alternatives to prior infrared imagers, including imagers based on HgCdTe devices and, especially, those based on quantum-well infrared photodetectors (QWIPs). HgCdTe devices and arrays thereof are difficult to fabricate and operate, and they exhibit large nonunformities and high 1/f (where f signifies frequency) noise. QWIPs are easier to fabricate and operate, can be made nearly uniform, and exhibit lower 1/f noise, but they exhibit larger dark currents, and their quantization only along the growth direction prevents them from absorbing photons at normal incidence, thereby limiting their quantum efficiencies. Like QWIPs, QDIPs offer the advantages of greater ease of operation, greater uniformity, and lower 1/f noise, but without the disadvantages: QDIPs exhibit lower dark currents, and quantum efficiencies of QDIPs are greater because the three-dimensional quantization of QDIPs is favorable to the absorption of photons at normal or oblique incidence. Moreover, QDIPs can be operated at higher temperatures (around 200 K) than are required for operation of QWIPs. The main problem in the development of QDIP imagers is to fabricate quantum dots with the requisite uniformity of size and spacing. A promising approach to be tested soon involves the use of electron-beam lithography to define the locations and sizes of quantum dots. A photoresist-covered GaAs substrate would be exposed to the beam generated by an advanced, high-precision electron beam apparatus. The exposure pattern would consist of spots typically having a diameter of 4 nm and typically spaced 20 nm apart. The exposed photoresist would be developed by either a high-contrast or a low-contrast method. In the high-contrast method, the spots would be etched in such a way as to form steep-wall holes all the way down to the substrate. The holes would be wider than the electron beam spots perhaps as

  10. Transport through an impurity tunnel coupled to a Si/SiGe quantum dot

    DOE PAGES

    Foote, Ryan H.; Ward, Daniel R.; Prance, J. R.; ...

    2015-09-11

    Achieving controllable coupling of dopants in silicon is crucial for operating donor-based qubit devices, but it is difficult because of the small size of donor-bound electron wavefunctions. Here in this paper, we report the characterization of a quantum dot coupled to a localized electronic state and present evidence of controllable coupling between the quantum dot and the localized state. A set of measurements of transport through the device enable the determination that the most likely location of the localized state is consistent with a location in the quantum well near the edge of the quantum dot. Finally, our results aremore » consistent with a gate-voltage controllable tunnel coupling, which is an important building block for hybrid donor and gate-defined quantum dot devices.« less

  11. Quantum Dots for Molecular Pathology

    PubMed Central

    True, Lawrence D.; Gao, Xiaohu

    2007-01-01

    Assessing malignant tumors for expression of multiple biomarkers provides data that are critical for patient management. Quantum dot-conjugated probes to specific biomarkers are powerful tools that can be applied in a multiplex manner to single tissue sections of biopsies to measure expression levels of multiple biomarkers. PMID:17251330

  12. Charge noise in quantum dot qubits: beyond the Markovian approximation.

    NASA Astrophysics Data System (ADS)

    Yang, Yuan-Chi; Friesen, Mark; Coppersmith, S. N.

    Charge noise is a limiting factor in the performance of semiconductor quantum dot qubits, including both spin and charge qubits. In this work, we develop an analytical formalism for treating semiclassical noise beyond the Markovian approximation, which allows us to investigate noise models relevant for quantum dots, such as 1 / f noise. We apply our methods to both charge qubits and quantum dot hybrid qubits, and study the effects of charge noise on single-qubit rotations in these systems. The formalism is also directly applicable to the case of strong microwave driving, for which the rotating wave approximation breaks down. This work was supported in part by ARO (W911NF-12-0607) and ONR (N00014-15-1-0029), and the University of Wisconsin-Madison.

  13. Quantum dot properties in the multiband envelope-function approximation using boundary conditions based upon first-principles quantum calculations

    NASA Astrophysics Data System (ADS)

    Flory, Curt A.; Musgrave, Charles B.; Zhang, Zhiyong

    2008-05-01

    A number of physical processes involving quantum dots depend critically upon the “evanescent” electron eigenstate wave function that extends outside of the material surface into the surrounding region. These processes include electron tunneling through quantum dots, as well as interactions between multiple quantum dot structures. In order to unambiguously determine these evanescent fields, appropriate boundary conditions have been developed to connect the electronic solutions interior to the semiconductor quantum dot to exterior vacuum solutions. In standard envelope function theory, the interior wave function consists of products of band edge and envelope functions, and both must be considered when matching to the external solution. While the envelope functions satisfy tractable equations, the band edge functions are generally not known. In this work, symmetry arguments in the spherically symmetric approximation are used in conjunction with the known qualitative behavior of bonding and antibonding orbitals to catalog the behavior of the band edge functions at the unit cell boundary. This physical approximation allows consolidation of the influence of the band edge functions to two simple surface parameters that are incorporated into the boundary conditions and are straightforwardly computed by using numerical first-principles quantum techniques. These new boundary conditions are employed to analyze an isolated spherically symmetric semiconductor quantum dot in vacuum within the analytical model of Sercel and Vahala [Phys. Rev. Lett. 65, 239 (1990); Phys. Rev. B 42, 3690 (1990)]. Results are obtained for quantum dots made of GaAs and InP, which are compared with ab initio calculations that have appeared in the literature.

  14. Investigation of trypsin-CdSe quantum dot interactions via spectroscopic methods and effects on enzymatic activity.

    PubMed

    Kaur, Gurvir; Tripathi, S K

    2015-01-05

    The paper presents the interactions between trypsin and water soluble cadmium selenide (CdSe) quantum dots investigated by spectrophotometric methods. CdSe quantum dots have strong ability to quench the intrinsic fluorescence of trypsin by a static quenching mechanism. The quenching has been studied at three different temperatures where the results revealed that electrostatic interactions exist between CdSe quantum dots and trypsin and are responsible to stabilize the complex. The Scatchard plot from quenching revealed 1 binding site for quantum dots by trypsin, the same has been confirmed by making isothermal titrations of quantum dots against trypsin. The distance between donor and acceptor for trypsin-CdSe quantum dot complexes is calculated to be 2.8 nm by energy transfer mechanisms. The intrinsic fluorescence of CdSe quantum dots has also been enhanced by the trypsin, and is linear for concentration of trypsin ranging 1-80 μl. All the observations evidence the formation of trypsin-CdSe quantum dot conjugates, where trypsin retains the enzymatic activity which in turn is temperature and pH dependent. Copyright © 2014 Elsevier B.V. All rights reserved.

  15. Green biosynthesis of biocompatible CdSe quantum dots in living Escherichia coli cells

    NASA Astrophysics Data System (ADS)

    Yan, Zhengyu; Qian, Jing; Gu, Yueqing; Su, Yilong; Ai, Xiaoxia; Wu, Shengmei

    2014-03-01

    A green and efficient biosynthesis method to prepare fluorescence-tunable biocompatible cadmium selenide quantum dots using Escherichia coli cells as biological matrix was proposed. Decisive factors in biosynthesis of cadmium selenide quantum dots in a designed route in Escherichia coli cells were elaborately investigated, including the influence of the biological matrix growth stage, the working concentration of inorganic reactants, and the co-incubation duration of inorganic metals to biomatrix. Ultraviolet-visible, photoluminescence, and inverted fluorescence microscope analysis confirmed the unique optical properties of the biosynthesized cadmium selenide quantum dots. The size distribution of the nanocrystals extracted from cells and the location of nanocrystals foci in vivo were also detected seriously by transmission electron microscopy. A surface protein capping layer outside the nanocrystals was confirmed by Fourier transform infrared spectroscopy measurements, which were supposed to contribute to reducing cytotoxicity and maintain a high viability of cells when incubating with quantum dots at concentrations as high as 2 μM. Cell morphology observation indicated an effective labeling of living cells by the biosynthesized quantum dots after a 48 h co-incubation. The present work demonstrated an economical and environmentally friendly approach to fabricating highly fluorescent quantum dots which were expected to be an excellent fluorescent dye for broad bio-imaging and labeling.

  16. Characterizing and engineering tunable spin functionality inside indium arsenide/gallium arsenide quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Liu, Weiwen

    The continual downsizing of the basic functional units used in the electronics industry has motivated the study of the quantum computation and related topics. To overcome the limitations of classical physics and engineering, some unique quantum mechanical features, especially entanglement and superpositions have begun to be considered as important properties for future bits. Including these quantum mechanical features is attractive because the ability to utilize quantum mechanics can dramatically enhance computational power. Among the various ways of constructing the basic building blocks for quantum computation, we are particularly interested in using spins inside epitaxially grown InAs/GaAs quantum dot molecules as quantum bits (qubits). The ability to design and engineer nanostructures with tailored quantum properties is critical to engineering quantum computers and other novel electro-optical devices and is one of the key challenges for scaling up new ideas for device application. In this thesis, we will focus on how the structure and composition of quantum dot molecules can be used to control spin properties and charge interactions. Tunable spin and charge properties can enable new, more scalable, methods of initializing and manipulating quantum information. In this thesis, we demonstrate one method to enable electric-field tunability of Zeeman splitting for a single electron spin inside a quantum dot molecules by using heterostructure engineering techniques to modify the barrier that separates quantum dots. We describe how these structural changes to the quantum dot molecules also change charge interactions and propose ways to use this effect to enable accurate measurement of coulomb interactions and possibly charge occupancy inside these complicated quantum dot molecules.

  17. Harnessing Sun’s Energy with Quantum Dots Based Next Generation Solar Cell

    PubMed Central

    Halim, Mohammad A.

    2012-01-01

    Our energy consumption relies heavily on the three components of fossil fuels (oil, natural gas and coal) and nearly 83% of our current energy is consumed from those sources. The use of fossil fuels, however, has been viewed as a major environmental threat because of their substantial contribution to greenhouse gases which are responsible for increasing the global average temperature. Last four decades, scientists have been searching for alternative sources of energy which need to be environmentally clean, efficient, cost-effective, renewable, and sustainable. One of the promising sustainable sources of energy can be achieved by harnessing sun energy through silicon wafer, organic polymer, inorganic dye, and quantum dots based solar cells. Among them, quantum dots have an exceptional property in that they can excite multiple electrons using only one photon. These dots can easily be synthesized, processed in solution, and incorporated into solar cell application. Interestingly, the quantum dots solar cells can exceed the Shockley-Queisser limit; however, it is a great challenge for other solar cell materials to exceed the limit. Theoretically, the quantum dots solar cell can boost the power conversion efficiency up to 66% and even higher to 80%. Moreover, in changing the size of the quantum dots one can utilize the Sun’s broad spectrum of visible and infrared ranges. This review briefly overviews the present performance of different materials-based solar cells including silicon wafer, dye-sensitized, and organic solar cells. In addition, recent advances of the quantum dots based solar cells which utilize cadmium sulfide/selenide, lead sulfide/selenide, and new carbon dots as light harvesting materials has been reviewed. A future outlook is sketched as to how one could improve the efficiency up to 10% from the current highest efficiency of 6.6%. PMID:28348320

  18. Transparent Ultra-High-Loading Quantum Dot/Polymer Nanocomposite Monolith for Gamma Scintillation.

    PubMed

    Liu, Chao; Li, Zhou; Hajagos, Tibor Jacob; Kishpaugh, David; Chen, Dustin Yuan; Pei, Qibing

    2017-06-27

    Spectroscopic gamma-photon detection has widespread applications for research, defense, and medical purposes. However, current commercial detectors are either prohibitively expensive for wide deployment or incapable of producing the characteristic gamma photopeak. Here we report the synthesis of transparent, ultra-high-loading (up to 60 wt %) Cd x Zn 1-x S/ZnS core/shell quantum dot/polymer nanocomposite monoliths for gamma scintillation by in situ copolymerization of the partially methacrylate-functionalized quantum dots in a monomer solution. The efficient Förster resonance energy transfer of the high-atomic-number quantum dots to lower-band-gap organic dyes enables the extraction of quantum-dot-borne excitons for photon production, resolving the problem of severe light yield deterioration found in previous nanoparticle-loaded scintillators. As a result, the nanocomposite scintillator exhibited simultaneous improvements in both light yield (visible photons produced per MeV of gamma-photon energy) and gamma attenuation. With these enhancements, a 662 keV Cs-137 gamma photopeak with 9.8% resolution has been detected using a 60 wt % quantum-dot nanocomposite scintillator, demonstrating the potential of such a nanocomposite system in the development of high-performance low-cost spectroscopic gamma detectors.

  19. Hot electron dynamics at semiconductor surfaces: Implications for quantum dot photovoltaics

    NASA Astrophysics Data System (ADS)

    Tisdale, William A., III

    Finding a viable supply of clean, renewable energy is one of the most daunting challenges facing the world today. Solar cells have had limited impact in meeting this challenge because of their high cost and low power conversion efficiencies. Semiconductor nanocrystals, or quantum dots, are promising materials for use in novel solar cells because they can be processed with potentially inexpensive solution-based techniques and because they are predicted to have novel optoelectronic properties that could enable the realization of ultra-efficient solar power converters. However, there is a lack of fundamental understanding regarding the behavior of highly-excited, or "hot," charge carriers near quantum-dot and semiconductor interfaces, which is of paramount importance to the rational design of high-efficiency devices. The elucidation of these ultrafast hot electron dynamics is the central aim of this Dissertation. I present a theoretical framework for treating the electronic interactions between quantum dots and bulk semiconductor surfaces and propose a novel experimental technique, time-resolved surface second harmonic generation (TR-SHG), for probing these interactions. I then describe a series of experimental investigations into hot electron dynamics in specific quantum-dot/semiconductor systems. A two-photon photoelectron spectroscopy (2PPE) study of the technologically-relevant ZnO(1010) surface reveals ultrafast (sub-30fs) cooling of hot electrons in the bulk conduction band, which is due to strong electron-phonon coupling in this highly polar material. The presence of a continuum of defect states near the conduction band edge results in Fermi-level pinning and upward (n-type) band-bending at the (1010) surface and provides an alternate route for electronic relaxation. In monolayer films of colloidal PbSe quantum dots, chemical treatment with either hydrazine or 1,2-ethanedithiol results in strong and tunable electronic coupling between neighboring quantum dots

  20. Biosynthesis of luminescent CdS quantum dots using plant hairy root culture

    NASA Astrophysics Data System (ADS)

    Borovaya, Mariya N.; Naumenko, Antonina P.; Matvieieva, Nadia A.; Blume, Yaroslav B.; Yemets, Alla I.

    2014-12-01

    CdS nanoparticles have a great potential for application in chemical research, bioscience and medicine. The aim of this study was to develop an efficient and environmentally-friendly method of plant-based biosynthesis of CdS quantum dots using hairy root culture of Linaria maroccana L. By incubating Linaria root extract with inorganic cadmium sulfate and sodium sulfide we synthesized stable luminescent CdS nanocrystals with absorption peaks for UV-visible spectrometry at 362 nm, 398 nm and 464 nm, and luminescent peaks at 425, 462, 500 nm. Transmission electron microscopy of produced quantum dots revealed their spherical shape with a size predominantly from 5 to 7 nm. Electron diffraction pattern confirmed the wurtzite crystalline structure of synthesized cadmium sulfide quantum dots. These results describe the first successful attempt of quantum dots synthesis using plant extract.

  1. Single colloidal quantum dots as sources of single photons for quantum cryptography

    NASA Astrophysics Data System (ADS)

    Pisanello, Ferruccio; Qualtieri, Antonio; Leménager, Godefroy; Martiradonna, Luigi; Stomeo, Tiziana; Cingolani, Roberto; Bramati, Alberto; De Vittorio, Massimo

    2011-02-01

    Colloidal nanocrystals, i.e. quantum dots synthesized trough wet-chemistry approaches, are promising nanoparticles for photonic applications and, remarkably, their quantum nature makes them very promising for single photon emission at room temperature. In this work we describe two approaches to engineer the emission properties of these nanoemitters in terms of radiative lifetime and photon polarization, drawing a viable strategy for their exploitation as room-temperature single photon sources for quantum information and quantum telecommunications.

  2. Sharp peaks in the conductance of a double quantum dot and a quantum-dot spin valve at high temperatures: A hierarchical quantum master equation approach

    NASA Astrophysics Data System (ADS)

    Wenderoth, S.; Bätge, J.; Härtle, R.

    2016-09-01

    We study sharp peaks in the conductance-voltage characteristics of a double quantum dot and a quantum dot spin valve that are located around zero bias. The peaks share similarities with a Kondo peak but can be clearly distinguished, in particular as they occur at high temperatures. The underlying physical mechanism is a strong current suppression that is quenched in bias-voltage dependent ways by exchange interactions. Our theoretical results are based on the quantum master equation methodology, including the Born-Markov approximation and a numerically exact, hierarchical scheme, which we extend here to the spin-valve case. The comparison of exact and approximate results allows us to reveal the underlying physical mechanisms, the role of first-, second- and beyond-second-order processes and the robustness of the effect.

  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. Simulation of a broadband nano-biosensor based on an onion-like quantum dot-quantum well structure

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

    Absalan, H; SalmanOgli, A; Rostami, R

    The fluorescence resonance energy transfer is studied between modified quantum-dots and quantum-wells used as a donor and an acceptor. Because of the unique properties of quantum dots, including diverse surface modification flexibility, bio-compatibility, high quantum yields and wide absorption, their use as nano-biosensors and bio-markers used in diagnosis of cancer is suggested. The fluorescence resonance energy transfer is simulated in a quantum dot-quantum well system, where the energy can flow from donor to acceptor. If the energy transfer can be either turned on or off by a specific interaction, such as interaction with any dyes, a molecular binding event ormore » a cleavage reaction, a sensor can be designed (under assumption that the healthy cells have a known effect or unyielding effect on output parameters while cancerous cells, due to their pandemic optical properties, can impact the fluorescence resonance energy transfer parameters). The developed nano-biosensor can operate in a wide range of wavelengths (310 - 760 nm). (laser applications in biology and medicine)« less

  5. Quantum Dots for Solar Cell Application

    NASA Astrophysics Data System (ADS)

    Poudyal, Uma

    Solar energy has been anticipated as the most important and reliable source of renewable energy to address the ever-increasing energy demand. To harvest solar energy efficiently, diverse kinds of solar cells have been studied. Among these, quantum dot sensitized solar cells have been an interesting group of solar cells mainly due to tunable, size-dependent electronic and optical properties of quantum dots. Moreover, doping these quantum dots with transition metal elements such as Mn opens avenue for improved performance of solar cells as well as for spin based technologies. In this dissertation, Mn-doped CdSe QDs (Mn-CdSe) have been synthesized by Successive Ionic Layer Adsorption and Reaction (SILAR) method. They are used in solar cells to study the effect of Mn doping in the performance of solar cells. Incident photon to current-conversion efficiency (IPCE) is used to record the effect of Mn-doping. Intensity modulated photovoltage and photocurrent spectroscopy (IMVS/PS) has been used to study the carrier dynamics in these solar cells. Additionally, the magnetic properties of Mn-CdSe QDs is studied and its possible origin is discussed. Moreover, CdS/CdSe QDs have been used to study the effect of liquid, gel and solid electrolyte in the performance and stability of the solar cells. Using IPCE spectra, the time decay measurements are presented and the possible reactions between the QD and the electrolytes are explained.

  6. Electronic Structure of Helium Atom in a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Saha, Jayanta K.; Bhattacharyya, S.; Mukherjee, T. K.

    2016-03-01

    Bound and resonance states of helium atom have been investigated inside a quantum dot by using explicitly correlated Hylleraas type basis set within the framework of stabilization method. To be specific, precise energy eigenvalues of bound 1sns (1Se) (n = 1-6) states and the resonance parameters i.e. positions and widths of 1Se states due to 2sns (n = 2-5) and 2pnp (n = 2-5) configurations of confined helium below N = 2 ionization threshold of He+ have been estimated. The two-parameter (Depth and Width) finite oscillator potential is used to represent the confining potential due to the quantum dot. It has been explicitly demonstrated that the electronic structural properties become sensitive functions of the dot size. It is observed from the calculations of ionization potential that the stability of an impurity ion within a quantum dot may be manipulated by varying the confinement parameters. A possibility of controlling the autoionization lifetime of doubly excited states of two-electron ions by tuning the width of the quantum cavity is also discussed here. TKM Gratefully Acknowledges Financial Support under Grant No. 37(3)/14/27/2014-BRNS from the Department of Atomic Energy, BRNS, Government of India. SB Acknowledges Financial Support under Grant No. PSW-160/14-15(ERO) from University Grants Commission, Government of India

  7. Double Tunneling Injection Quantum Dot Lasers for High Speed Operation

    DTIC Science & Technology

    2017-10-23

    Double Tunneling-Injection Quantum Dot Lasers for High -Speed Operation The views, opinions and/or findings contained in this report are those of...SECURITY CLASSIFICATION OF: 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 13. SUPPLEMENTARY NOTES 12. DISTRIBUTION AVAILIBILITY STATEMENT 6...State University Title: Double Tunneling-Injection Quantum Dot Lasers for High -Speed Operation Report Term: 0-Other Email: asryan@vt.edu Distribution

  8. Quantum Dot Solar Cell Fabrication Protocols

    DOE PAGES

    Chernomordik, Boris D.; Marshall, Ashley R.; Pach, Gregory F.; ...

    2016-09-26

    Colloidally synthesized quantum-confined semiconducting spherical nanocrystals, often referred to as quantum dots (QDs), offer a high degree of chemical, optical, and electronic tunability. As a result, there is an increasing interest in employing colloidal QDs for electronic and optical applications that is reflected in a growing number of publications. In this protocol we provide detailed procedures for the fabrication of QD solar cells specifically employing PbSe and PbS QDs. Here we include details that are learned through experience, beyond those in typical methodology sections, and include example pictures and videos to aid in fabricating QD solar cells. Although successful solarmore » cell fabrication is ultimately learned through experience, this protocol is intended to accelerate that process. The protocol developed here is intended to be a general starting point for developing PbS and PbSe QD test bed solar cells. We include steps for forming conductive QD films via dip coating as well as spin coating. Finally, we provide protocols that detail the synthesis of PbS and PbSe QDs through a unique cation exchange reaction and discuss how different QD synthetic routes could impact the resulting solar cell performance.« less

  9. Quantum Dot Solar Cell Fabrication Protocols

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

    Chernomordik, Boris D.; Marshall, Ashley R.; Pach, Gregory F.

    Colloidally synthesized quantum-confined semiconducting spherical nanocrystals, often referred to as quantum dots (QDs), offer a high degree of chemical, optical, and electronic tunability. As a result, there is an increasing interest in employing colloidal QDs for electronic and optical applications that is reflected in a growing number of publications. In this protocol we provide detailed procedures for the fabrication of QD solar cells specifically employing PbSe and PbS QDs. Here we include details that are learned through experience, beyond those in typical methodology sections, and include example pictures and videos to aid in fabricating QD solar cells. Although successful solarmore » cell fabrication is ultimately learned through experience, this protocol is intended to accelerate that process. The protocol developed here is intended to be a general starting point for developing PbS and PbSe QD test bed solar cells. We include steps for forming conductive QD films via dip coating as well as spin coating. Finally, we provide protocols that detail the synthesis of PbS and PbSe QDs through a unique cation exchange reaction and discuss how different QD synthetic routes could impact the resulting solar cell performance.« less

  10. A strongly interacting polaritonic quantum dot

    NASA Astrophysics Data System (ADS)

    Jia, Ningyuan; Schine, Nathan; Georgakopoulos, Alexandros; Ryou, Albert; Clark, Logan W.; Sommer, Ariel; Simon, Jonathan

    2018-06-01

    Polaritons are promising constituents of both synthetic quantum matter1 and quantum information processors2, whose properties emerge from their components: from light, polaritons draw fast dynamics and ease of transport; from matter, they inherit the ability to collide with one another. Cavity polaritons are particularly promising as they may be confined and subjected to synthetic magnetic fields controlled by cavity geometry3, and furthermore they benefit from increased robustness due to the cavity enhancement in light-matter coupling. Nonetheless, until now, cavity polaritons have operated only in a weakly interacting mean-field regime4,5. Here we demonstrate strong interactions between individual cavity polaritons enabled by employing highly excited Rydberg atoms as the matter component of the polaritons. We assemble a quantum dot composed of approximately 150 strongly interacting Rydberg-dressed 87Rb atoms in a cavity, and observe blockaded transport of photons through it. We further observe coherent photon tunnelling oscillations, demonstrating that the dot is zero-dimensional. This work establishes the cavity Rydberg polariton as a candidate qubit in a photonic information processor and, by employing multiple resonator modes as the spatial degrees of freedom of a photonic particle, the primary ingredient to form photonic quantum matter6.

  11. Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering.

    PubMed

    Pan, Jun; Quan, Li Na; Zhao, Yongbiao; Peng, Wei; Murali, Banavoth; Sarmah, Smritakshi P; Yuan, Mingjian; Sinatra, Lutfan; Alyami, Noktan M; Liu, Jiakai; Yassitepe, Emre; Yang, Zhenyu; Voznyy, Oleksandr; Comin, Riccardo; Hedhili, Mohamed N; Mohammed, Omar F; Lu, Zheng Hong; Kim, Dong Ha; Sargent, Edward H; Bakr, Osman M

    2016-10-01

    A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite (CsPbX 3 , X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-pair-capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Spin–cavity interactions between a quantum dot molecule and a photonic crystal cavity

    PubMed Central

    Vora, Patrick M.; Bracker, Allan S.; Carter, Samuel G.; Sweeney, Timothy M.; Kim, Mijin; Kim, Chul Soo; Yang, Lily; Brereton, Peter G.; Economou, Sophia E.; Gammon, Daniel

    2015-01-01

    The integration of InAs/GaAs quantum dots into nanophotonic cavities has led to impressive demonstrations of cavity quantum electrodynamics. However, these demonstrations are primarily based on two-level excitonic systems. Efforts to couple long-lived quantum dot electron spin states with a cavity are only now succeeding. Here we report a two-spin–cavity system, achieved by embedding an InAs quantum dot molecule within a photonic crystal cavity. With this system we obtain a spin singlet–triplet Λ-system where the ground-state spin splitting exceeds the cavity linewidth by an order of magnitude. This allows us to observe cavity-stimulated Raman emission that is highly spin-selective. Moreover, we demonstrate the first cases of cavity-enhanced optical nonlinearities in a solid-state Λ-system. This provides an all-optical, local method to control the spin exchange splitting. Incorporation of a highly engineerable quantum dot molecule into the photonic crystal architecture advances prospects for a quantum network. PMID:26184654

  13. Resonant electronic excitation energy transfer by Dexter mechanism in the quantum dot system

    NASA Astrophysics Data System (ADS)

    Samosvat, D. M.; Chikalova-Luzina, O. P.; Vyatkin, V. M.; Zegrya, G. G.

    2016-11-01

    In present work the energy transfer between quantum dots by the exchange (Dexter) mechanism is analysed. The interdot Coulomb interaction is taken into consideration. It is assumed that the quantum dot-donor and the quantum dot-acceptor are made from the same compound A3B5 and embedded in the matrix of other material creating potential barriers for electron and holes. The dependences of the energy transfer rate on the quantum-dot system parameters are found using the Kane model that provides the most adequate description spectra of semiconductors A3B5. Numerical calculations show that the rate of the energy transfer by Dexter mechanism is comparable to the rate of the energy transfer by electrostatic mechanism at the distances approaching to the contact ones.

  14. Effect of growth interruption in 1.55 μm InAs/InAlGaAs quantum dots on InP grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Jung, Daehwan; Ironside, Daniel J.; Bank, Seth R.; Gossard, Arthur C.; Bowers, John E.

    2018-05-01

    We report the effect of growth interruptions on the structural and optical properties of InAs/InAlGaAs/InP quantum dots using molecular beam epitaxy. We find that the surface quantum dots experience an unintended ripening process during the sample cooling stage, which reshapes the uncapped InAs nanostructures. To prevent this, we performed a partial capping experiment to effectively inhibit structural reconfiguration of surface InAs nanostructures during the cooling stage, revealing that InAs nanostructures first form quantum dashes and then transform into quantum dots via a ripening process. Our result suggests that the appearance of buried InAs/InAlGaAs nanostructures can be easily misunderstood by surface analysis.

  15. A high-temperature single-photon source from nanowire quantum dots.

    PubMed

    Tribu, Adrien; Sallen, Gregory; Aichele, Thomas; André, Régis; Poizat, Jean-Philippe; Bougerol, Catherine; Tatarenko, Serge; Kheng, Kuntheak

    2008-12-01

    We present a high-temperature single-photon source based on a quantum dot inside a nanowire. The nanowires were grown by molecular beam epitaxy in the vapor-liquid-solid growth mode. We utilize a two-step process that allows a thin, defect-free ZnSe nanowire to grow on top of a broader, cone-shaped nanowire. Quantum dots are formed by incorporating a narrow zone of CdSe into the nanowire. We observe intense and highly polarized photoluminescence even from a single emitter. Efficient photon antibunching is observed up to 220 K, while conserving a normalized antibunching dip of at most 36%. This is the highest reported temperature for single-photon emission from a nonblinking quantum-dot source and principally allows compact and cheap operation by using Peltier cooling.

  16. Spatially selective assembly of quantum dot light emitters in an LED using engineered peptides.

    PubMed

    Demir, Hilmi Volkan; Seker, Urartu Ozgur Safak; Zengin, Gulis; Mutlugun, Evren; Sari, Emre; Tamerler, Candan; Sarikaya, Mehmet

    2011-04-26

    Semiconductor nanocrystal quantum dots are utilized in numerous applications in nano- and biotechnology. In device applications, where several different material components are involved, quantum dots typically need to be assembled at explicit locations for enhanced functionality. Conventional approaches cannot meet these requirements where assembly of nanocrystals is usually material-nonspecific, thereby limiting the control of their spatial distribution. Here we demonstrate directed self-assembly of quantum dot emitters at material-specific locations in a color-conversion LED containing several material components including a metal, a dielectric, and a semiconductor. We achieve a spatially selective immobilization of quantum dot emitters by using the unique material selectivity characteristics provided by the engineered solid-binding peptides as smart linkers. Peptide-decorated quantum dots exhibited several orders of magnitude higher photoluminescence compared to the control groups, thus, potentially opening up novel ways to advance these photonic platforms in applications ranging from chemical to biodetection.

  17. Chemical nature and structure of organic coating of quantum dots is crucial for their application in imaging diagnostics

    PubMed Central

    Bakalova, Rumiana; Zhelev, Zhivko; Kokuryo, Daisuke; Spasov, Lubomir; Aoki, Ichio; Saga, Tsuneo

    2011-01-01

    Background: One of the most attractive properties of quantum dots is their potential to extend the opportunities for fluorescent and multimodal imaging in vivo. The aim of the present study was to clarify whether the composition and structure of organic coating of nanoparticles are crucial for their application in vivo. Methods: We compared quantum dots coated with non-crosslinked amino-functionalized polyamidoamine (PAMAM) dendrimers, quantum dots encapsulated in crosslinked carboxyl-functionalized PAMAM dendrimers, and silica-shelled amino-functionalized quantum dots. A multimodal fluorescent and paramagnetic quantum dot probe was also developed and analyzed. The probes were applied intravenously in anesthetized animals for visualization of brain vasculature using two-photon excited fluorescent microscopy and visualization of tumors using fluorescent IVIS® imaging (Caliper Life Sciences, Hopkinton, MA) and magnetic resonance imaging. Results: Quantum dots coated with non-crosslinked dendrimers were cytotoxic. They induced side effects in vivo, including vasodilatation with a decrease in mean arterial blood pressure and heart rate. The quantum dots penetrated the vessels, which caused the quality of fluorescent imaging to deteriorate. Quantum dots encapsulated in crosslinked dendrimers had low cytotoxicity and were biocompatible. In concentrations <0.3 nmol quantum dots/kg bodyweight, these nanoparticles did not affect blood pressure and heart rate, and did not induce vasodilatation or vasoconstriction. PEGylation (PEG [polyethylene glycol]) was an indispensable step in development of a quantum dot probe for in vivo imaging, based on silica-shelled quantum dots. The non-PEGylated silica-shelled quantum dots possessed low colloidal stability in high-salt physiological fluids, accompanied by rapid aggregation in vivo. The conjugation of silica-shelled quantum dots with PEG1100 increased their stability and half-life in the circulation without significant

  18. Hole Transfer from Low Band Gap Quantum Dots to Conjugated Polymers in Organic/Inorganic Hybrid Photovoltaics.

    PubMed

    Colbert, Adam E; Janke, Eric M; Hsieh, Stephen T; Subramaniyan, Selvam; Schlenker, Cody W; Jenekhe, Samson A; Ginger, David S

    2013-01-17

    We use photoinduced absorption (PIA) spectroscopy to investigate pathways for photocurrent generation in hybrid organic/inorganic quantum dot bulk heterojunction solar cells. We study blends of the conjugated polymer poly(2,3-bis(2-(hexyldecyl)quinoxaline-5,8-diyl-alt-N-(2-hexyldecyl)dithieno[3,2-b:2',3'-d]pyrrole) (PDTPQx-HD) with PbS quantum dots and find that positively charged polarons are formed on the conjugated polymer following selective photoexcitation of the PbS quantum dots. This result provides a direct spectroscopic fingerprint demonstrating that photoinduced hole transfer occurs from the photoexcited quantum dots to the host polymer. We compute the relative yields of long-lived holes following photoexcitation of both the polymer and quantum dot phases and estimate that more long-lived polarons are produced per photon absorbed by the polymer phase than by the quantum dot phase.

  19. Comparative photoluminescence study of close-packed and colloidal InP/ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Thuy, Ung Thi Dieu; Thuy, Pham Thi; Liem, Nguyen Quang; Li, Liang; Reiss, Peter

    2010-02-01

    This letter reports on the comparative photoluminescence study of InP/ZnS quantum dots in the close-packed solid state and in colloidal solution. The steady-state photoluminescence spectrum of the close-packed InP/ZnS quantum dots peaks at a longer wavelength than that of the colloidal ones. Time-resolved photoluminescence shows that the close-packed quantum dots possess a shorter luminescence decay time and strongly increased spectral shift with the time delayed from the excitation moment in comparison with the colloidal ones. The observed behavior is discussed on the basis of energy transfer enabled by the short interparticle distance between the close-packed quantum dots.

  20. Deterministic optical polarisation in nitride quantum dots at thermoelectrically cooled temperatures.

    PubMed

    Wang, Tong; Puchtler, Tim J; Patra, Saroj K; Zhu, Tongtong; Jarman, John C; Oliver, Rachel A; Schulz, Stefan; Taylor, Robert A

    2017-09-21

    We report the successful realisation of intrinsic optical polarisation control by growth, in solid-state quantum dots in the thermoelectrically cooled temperature regime (≥200 K), using a non-polar InGaN system. With statistically significant experimental data from cryogenic to high temperatures, we show that the average polarisation degree of such a system remains constant at around 0.90, below 100 K, and decreases very slowly at higher temperatures until reaching 0.77 at 200 K, with an unchanged polarisation axis determined by the material crystallography. A combination of Fermi-Dirac statistics and k·p theory with consideration of quantum dot anisotropy allows us to elucidate the origin of the robust, almost temperature-insensitive polarisation properties of this system from a fundamental perspective, producing results in very good agreement with the experimental findings. This work demonstrates that optical polarisation control can be achieved in solid-state quantum dots at thermoelectrically cooled temperatures, thereby opening the possibility of polarisation-based quantum dot applications in on-chip conditions.

  1. Size and shape dependent optical properties of InAs quantum dots

    NASA Astrophysics Data System (ADS)

    Imran, Ali; Jiang, Jianliang; Eric, Deborah; Yousaf, Muhammad

    2018-01-01

    In this study Electronic states and optical properties of self assembled InAs quantum dots embedded in GaAs matrix have been investigated. Their carrier confinement energies for single quantum dot are calculated by time-independent Schrödinger equation in which hamiltonianian of the system is based on effective mass approximation and position dependent electron momentum. Transition energy, absorption coefficient, refractive index and high frequency dielectric constant for spherical, cylindrical and conical quantum dots with different sizes in different dimensions are calculated. Comparative studies have revealed that size and shape greatly affect the electronic transition energies and absorption coefficient. Peaks of absorption coefficients have been found to be highly shape dependent.

  2. 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

  3. Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin

    NASA Astrophysics Data System (ADS)

    He, Yu; He, Yu-Ming; Wei, Yu-Jia; Jiang, Xiao; Chen, Kai; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Höfling, Sven

    2017-08-01

    Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of 0.796 ±0.020 . Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path, and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 m. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axes on the Bloch sphere, with an average fidelity of 78.5%.

  4. Bright colloidal quantum dot light-emitting diodes enabled by efficient chlorination

    NASA Astrophysics Data System (ADS)

    Li, Xiyan; Zhao, Yong-Biao; Fan, Fengjia; Levina, Larissa; Liu, Min; Quintero-Bermudez, Rafael; Gong, Xiwen; Quan, Li Na; Fan, James; Yang, Zhenyu; Hoogland, Sjoerd; Voznyy, Oleksandr; Lu, Zheng-Hong; Sargent, Edward H.

    2018-03-01

    The external quantum efficiencies of state-of-the-art colloidal quantum dot light-emitting diodes (QLEDs) are now approaching the limit set by the out-coupling efficiency. However, the brightness of these devices is constrained by the use of poorly conducting emitting layers, a consequence of the present-day reliance on long-chain organic capping ligands. Here, we report how conductive and passivating halides can be implemented in Zn chalcogenide-shelled colloidal quantum dots to enable high-brightness green QLEDs. We use a surface management reagent, thionyl chloride (SOCl2), to chlorinate the carboxylic group of oleic acid and graft the surfaces of the colloidal quantum dots with passivating chloride anions. This results in devices with an improved mobility that retain high external quantum efficiencies in the high-injection-current region and also feature a reduced turn-on voltage of 2.5 V. The treated QLEDs operate with a brightness of 460,000 cd m-2, significantly exceeding that of all previously reported solution-processed LEDs.

  5. Single-electron-occupation metal-oxide-semiconductor quantum dots formed from efficient poly-silicon gate layout

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

    Carroll, Malcolm S.; rochette, sophie; Rudolph, Martin

    We introduce a silicon metal-oxide-semiconductor quantum dot structure that achieves dot-reservoir tunnel coupling control without a dedicated barrier gate. The elementary structure consists of two accumulation gates separated spatially by a gap, one gate accumulating a reservoir and the other a quantum dot. Control of the tunnel rate between the dot and the reservoir across the gap is demonstrated in the single electron regime by varying the reservoir accumulation gate voltage while compensating with the dot accumulation gate voltage. The method is then applied to a quantum dot connected in series to source and drain reservoirs, enabling transport down tomore » the single electron regime. Finally, tuning of the valley splitting with the dot accumulation gate voltage is observed. This split accumulation gate structure creates silicon quantum dots of similar characteristics to other realizations but with less electrodes, in a single gate stack subtractive fabrication process that is fully compatible with silicon foundry manufacturing.« less

  6. Stark-shift of impurity fundamental state in a lens shaped quantum dot

    NASA Astrophysics Data System (ADS)

    Aderras, L.; Bah, A.; Feddi, E.; Dujardin, F.; Duque, C. A.

    2017-05-01

    We calculate the Stark effect and the polarisability of shallow-donor impurity located in the centre of lens shaped quantum dot by a variational method and in the effective-mass approximation. Our theoretical model assumes an infinite confinement to describe the barriers at the dot boundaries and the electric field is considered to be applied in the z-direction. The systematic theoretical investigation contains results with the quantum dot size and the strength of the external field. Our calculations reveal that the interval wherein the polarisability varies depends strongly on the dot size.

  7. Mn-doped Ge self-assembled quantum dots via dewetting of thin films

    NASA Astrophysics Data System (ADS)

    Aouassa, Mansour; Jadli, Imen; Bandyopadhyay, Anup; Kim, Sung Kyu; Karaman, Ibrahim; Lee, Jeong Yong

    2017-03-01

    In this study, we demonstrate an original elaboration route for producing a Mn-doped Ge self-assembled quantum dots on SiO2 thin layer for MOS structure. These magnetic quantum dots are elaborated using dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing at high temperature of an amorphous Ge:Mn (Mn: 40%) nanolayer deposed at very low temperature by high-precision Solid Source Molecular Beam Epitaxy on SiO2 thin film. The size of quantum dots is controlled with nanometer scale precision by varying the nominal thickness of amorphous film initially deposed. The magnetic properties of the quantum-dots layer have been investigated by superconducting quantum interference device (SQUID) magnetometry. Atomic force microscopy (AFM), x-ray energy dispersive spectroscopy (XEDS) and transmission electron microscopy (TEM) were used to examine the nanostructure of these materials. Obtained results indicate that GeMn QDs are crystalline, monodisperse and exhibit a ferromagnetic behavior with a Curie temperature (TC) above room temperature. They could be integrated into spintronic technology.

  8. Universal Adiabatic Quantum Computing using Double Quantum Dot Charge Qubits

    NASA Astrophysics Data System (ADS)

    Ryan-Anderson, Ciaran; Jacobson, N. Tobias; Landahl, Andrew

    Adiabatic quantum computation (AQC) provides one path to achieving universal quantum computing in experiment. Computation in the AQC model occurs by starting with an easy to prepare groundstate of some simple Hamiltonian and then adiabatically evolving the Hamiltonian to obtain the groundstate of a final, more complex Hamiltonian. It has been shown that the circuit model can be mapped to AQC Hamiltonians and, thus, AQC can be made universal. Further, these Hamiltonians can be made planar and two-local. We propose using double quantum dot charge qubits (DQDs) to implement such universal AQC Hamiltonians. However, the geometry and restricted set of interactions of DQDs make the application of even these 2-local planar Hamiltonians non-trivial. We present a construction tailored to DQDs to overcome the geometric and interaction contraints and allow for universal AQC. These constraints are dealt with in this construction by making use of perturbation gadgets, which introduce ancillary qubits to mediate interactions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  9. Fine structure and optical pumping of spins in individual semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Bracker, Allan S.; Gammon, Daniel; Korenev, Vladimir L.

    2008-11-01

    We review spin properties of semiconductor quantum dots and their effect on optical spectra. Photoluminescence and other types of spectroscopy are used to probe neutral and charged excitons in individual quantum dots with high spectral and spatial resolution. Spectral fine structure and polarization reveal how quantum dot spins interact with each other and with their environment. By taking advantage of the selectivity of optical selection rules and spin relaxation, optical spin pumping of the ground state electron and nuclear spins is achieved. Through such mechanisms, light can be used to process spins for use as a carrier of information.

  10. Can the oscillator strength of the quantum dot bandgap transition exceed unity?

    NASA Astrophysics Data System (ADS)

    Hens, Z.

    2008-10-01

    We discuss the apparent contradiction between the Thomas-Reiche-Kuhn sum rule for oscillator strengths and recent experimental data on the oscillator strength of the band gap transition of quantum dots. Starting from two simple single electron model systems, we show that the sum rule does not limit this oscillator strength to values below unity, or below the number of electrons in the highest occupied single electron state. The only upper limit the sum rule imposes on the oscillator strength of the quantum dot band gap transition is the total number of electrons in the quantum dot.

  11. Magnetic properties of graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Espinosa-Ortega, T.; Luk'yanchuk, I. A.; Rubo, Y. G.

    2013-05-01

    Using the tight-binding approximation we calculated the diamagnetic susceptibility of graphene quantum dots (GQDs) of different geometrical shapes and characteristic sizes of 2-10 nm, when the magnetic properties are governed by the electron edge states. Two types of edge states can be discerned: the zero-energy states (ZESs), located exactly at the zero-energy Dirac point, and the dispersed edge states (DESs), with the energy close but not exactly equal to zero. DESs are responsible for a temperature-independent diamagnetic response, while ZESs provide a temperature-dependent spin paramagnetism. Hexagonal, circular, and randomly shaped GQDs contain mainly DESs, and, as a result, they are diamagnetic. The edge states of the triangular GQDs are of ZES type. These dots reveal the crossover between spin paramagnetism, dominating for small dots and at low temperatures, and orbital diamagnetism, dominating for large dots and at high temperatures.

  12. Nonlinear heat transport in ferromagnetic-quantum dot-superconducting systems

    NASA Astrophysics Data System (ADS)

    Hwang, Sun-Yong; Sánchez, David

    2018-03-01

    We analyze the heat current traversing a quantum dot sandwiched between a ferromagnetic and a superconducting electrode. The heat flow generated in response to a voltage bias presents rectification as a function of the gate potential applied to the quantum dot. Remarkably, in the thermally driven case the heat shows a strong diode effect with large asymmetry ratios that can be externally tuned with magnetic fields or spin-polarized tunneling. Our results thus demonstrate the importance of hybrid systems as promising candidates for thermal applications.

  13. Classical and quantum optical correlation effects between single quantum dots: The role of the hopping photon

    NASA Astrophysics Data System (ADS)

    Hughes, S.; Gotoh, H.; Kamada, H.

    2006-09-01

    We present a theoretical study of photon-coupled single quantum dots in a semiconductor. A series of optical effects are demonstrated, including a subradiant dark resonance, superradiance, reversible spontaneous emission decay, and pronounced exciton entanglement. Both classical and quantum optical approaches are presented using a self-consistent formalism that treats real and virtual photon exchange on an equal footing and can account for different quantum dot properties, surface effects, and retardation in the dipole-dipole coupling, all of which are shown to play a non-negligible role.

  14. Theoretical study of polarization dependence of carrier-induced refractive index change of quantum dot.

    PubMed

    Miao, Qingyuan; Yang, Ziyi; Dong, Jianji; He, Ping-An; Huang, Dexiu

    2018-02-05

    The influences of dot material component, barrier material component, aspect ratio and carrier density on the refractive index changes of TE mode and TM mode of columnar quantum dot are analyzed, and a multiparameter adjustment method is proposed to realize low polarization dependence of refractive index change. Then the quantum dots with low polarization dependence of refractive index change (<1.5%) within C-band (1530 nm - 1565 nm) are designed, and it shows that quantum dots with different material parameters are anticipated to have similar characteristics of low polarization dependence.

  15. Phosphine-free synthesis and characterization of type-II ZnSe/CdS core-shell quantum dots

    NASA Astrophysics Data System (ADS)

    Ghasemzadeh, Roghayyeh; Armanmehr, Mohammad Hasan; Abedi, Mohammad; Fateh, Davood Sadeghi; Bahreini, Zaker

    2018-01-01

    A phosphine-free route for synthesis of type-II ZnSe/CdS core-shell quantum dots, using green, low cost and environmentally friendly reagents and phosphine-free solvents such as 1-octadecene (ODE) and liquid paraffin has been reported. Hot-injection technique has been used for the synthesis of ZnSe core quantum dots. The CdS shell quantum dots prepared by reaction of CdO precursor and S powder in 1-octadecene (ODE). The ZnSe/CdS core-shell quantum dots were synthesized via successive ion layer adsorption and reaction (SILAR) technique. The characterization of produced quantum dots were performed by absorption and fluorescence spectroscopy, X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The results showed the formation of type-II ZnSe/CdS core-shell quantum dots with FWHM 32 nm and uniform size distribution.

  16. Enhanced Photon Extraction from a Nanowire Quantum Dot Using a Bottom-Up Photonic Shell

    NASA Astrophysics Data System (ADS)

    Jeannin, Mathieu; Cremel, Thibault; Häyrynen, Teppo; Gregersen, Niels; Bellet-Amalric, Edith; Nogues, Gilles; Kheng, Kuntheak

    2017-11-01

    Semiconductor nanowires offer the possibility to grow high-quality quantum-dot heterostructures, and, in particular, CdSe quantum dots inserted in ZnSe nanowires have demonstrated the ability to emit single photons up to room temperature. In this paper, we demonstrate a bottom-up approach to fabricate a photonic fiberlike structure around such nanowire quantum dots by depositing an oxide shell using atomic-layer deposition. Simulations suggest that the intensity collected in our NA =0.6 microscope objective can be increased by a factor 7 with respect to the bare nanowire case. Combining microphotoluminescence, decay time measurements, and numerical simulations, we obtain a fourfold increase in the collected photoluminescence from the quantum dot. We show that this improvement is due to an increase of the quantum-dot emission rate and a redirection of the emitted light. Our ex situ fabrication technique allows a precise and reproducible fabrication on a large scale. Its improved extraction efficiency is compared to state-of-the-art top-down devices.

  17. Towards zero-threshold optical gain using charged semiconductor quantum dots

    DOE PAGES

    Wu, Kaifeng; Park, Young -Shin; Lim, Jaehoon; ...

    2017-10-16

    Colloidal semiconductor quantum dots are attractive materials for the realization of solution-processable lasers. However, their applications as optical-gain media are complicated by a non-unity degeneracy of band-edge states, because of which multiexcitons are required to achieve the lasing regime. This increases the lasing thresholds and leads to very short optical gain lifetimes limited by nonradiative Auger recombination. Here, we show that these problems can be at least partially resolved by employing not neutral but negatively charged quantum dots. By applying photodoping to specially engineered quantum dots with impeded Auger decay, we demonstrate a considerable reduction of the optical gain thresholdmore » due to suppression of ground-state absorption by pre-existing carriers. Moreover, by injecting approximately one electron per dot on average, we achieve a more than twofold reduction in the amplified spontaneous emission threshold, bringing it to the sub-single-exciton level. Furthermore, these measurements indicate the feasibility of ‘zero-threshold’ gain achievable by completely blocking the band-edge state with two electrons.« less

  18. Towards zero-threshold optical gain using charged semiconductor quantum dots

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

    Wu, Kaifeng; Park, Young -Shin; Lim, Jaehoon

    Colloidal semiconductor quantum dots are attractive materials for the realization of solution-processable lasers. However, their applications as optical-gain media are complicated by a non-unity degeneracy of band-edge states, because of which multiexcitons are required to achieve the lasing regime. This increases the lasing thresholds and leads to very short optical gain lifetimes limited by nonradiative Auger recombination. Here, we show that these problems can be at least partially resolved by employing not neutral but negatively charged quantum dots. By applying photodoping to specially engineered quantum dots with impeded Auger decay, we demonstrate a considerable reduction of the optical gain thresholdmore » due to suppression of ground-state absorption by pre-existing carriers. Moreover, by injecting approximately one electron per dot on average, we achieve a more than twofold reduction in the amplified spontaneous emission threshold, bringing it to the sub-single-exciton level. Furthermore, these measurements indicate the feasibility of ‘zero-threshold’ gain achievable by completely blocking the band-edge state with two electrons.« less

  19. Quantum Dot-Photonic Crystal Cavity QED Based Quantum Information Processing

    DTIC Science & Technology

    2012-08-14

    Majumdar, A. Faraon, M . Toishi, N. Stolz, P. Petroff, J. Vuckovic. Resonant Excitation of a Quantum Dot Strongly Coupled to a Photonic Crystal...11 J. O’Brien, A. Furusawa , J. Vuckovic. Photonic Quantum Technologies, Nature Photonics, (12 2009): . doi: 2010/08/30 15:11:17 10 D. Englund, A...devices via micron-scale electrical heaters, Applied Physics Letters, ( 2009): . doi: 2009/08/19 13:18:36 7 M . Toishi, D. Englund, A. Faraon, J

  20. Two-state semiconductor laser self-mixing velocimetry exploiting coupled quantum-dot emission-states: experiment, simulation and theory

    PubMed Central

    Gioannini, Mariangela; Dommermuth, Marius; Drzewietzki, Lukas; Krestnikov, Igor; Livshits, Daniil; Krakowski, Michel; Breuer, Stefan

    2014-01-01

    We exploit the coupled emission-states of a single-chip semiconductor InAs/GaAs quantum-dot laser emitting simultaneously on ground-state (λGS = 1245 nm) and excited-state (λES = 1175 nm) to demonstrate coupled-two-state self-mixing velocimetry for a moving diffuse reflector. A 13 Hz-narrow Doppler beat frequency signal at 317 Hz is obtained for a reflector velocity of 3 mm/s, which exemplifies a 66-fold improvement in width as compared to single-wavelength self-mixing velocimetry. Simulation results reveal the physical origin of this signal, the coupling of excited-state and ground-state photons via the carriers, which is unique for quantum-dot lasers and reproduce the experimental results with excellent agreement. PMID:25321809

  1. Enhanced hot-carrier cooling and ultrafast spectral diffusion in strongly coupled PbSe quantum-dot solids.

    PubMed

    Gao, Yunan; Talgorn, Elise; Aerts, Michiel; Trinh, M Tuan; Schins, Juleon M; Houtepen, Arjan J; Siebbeles, Laurens D A

    2011-12-14

    PbSe quantum-dot solids are of great interest for low cost and efficient photodetectors and solar cells. We have prepared PbSe quantum-dot solids with high charge carrier mobilities using layer-by-layer dip-coating with 1,2-ethanediamine as substitute capping ligands. Here we present a time and energy resolved transient absorption spectroscopy study on the kinetics of photogenerated charge carriers, focusing on 0-5 ps after photoexcitation. We compare the observed carrier kinetics to those for quantum dots in dispersion and show that the intraband carrier cooling is significantly faster in quantum-dot solids. In addition we find that carriers diffuse from higher to lower energy sites in the quantum-dot solid within several picoseconds.

  2. Application of CdSe quantum dots for the direct detection of TNT.

    PubMed

    Yi, Kui-Yu

    2016-02-01

    CdSe quantum dots were synthesized through a simple, green organic-phase method. Paraffin was used as the reaction solvent and a reducing agent, oleic acid was the reaction ligand, and oleyl amine was the stabilizer. Based on the phenomenon of TNT quenched oil-soluble CdSe quantum dot fluorescence, a simple, fast, and direct method of TNT detection was established. Under optimum conditions, the degree of fluorescence quenching of oil-soluble CdSe quantum dots had a good linear correlation with TNT concentration in the 1.0×10(-7)-5.0×10(-5) mol/L range, and the correlation coefficient was 0.9990. TNT detection limit was 2.1×10(-8)mol/L. The method was successfully used to determine TNT-explosion dust samples, results were satisfactory. The fluorescence quenching mechanism of oil-soluble CdSe quantum dots by TNT was also discussed. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  3. Study of alloy disorder in quantum dots through multi-million atom simulations

    NASA Technical Reports Server (NTRS)

    Kilmeck, Gerhard; Oyafuso, Fabiano; Boykin, T. B.; Bowen, R. C.; von Allmen, Paul A.

    2003-01-01

    A tight binding model which includes s, p, d, s orbitals is used to examine the electronic structures of an ensemble of dome-shaped In0.6 Ga0.4 As quantum dots. Given ensembles of identically sized quantum dots, variations in composition and configuration yield a linewidth broadening of less than 0.35 meV, much smaller than the total broadening determined from photoluminescence experiments. It is also found that the computed disorder-induced broadening is very sensitive to the applied boundary conditions, so that care must be taken to ensure proper convergence of the numerical results. Examination of local eigenenergies as functions of position shows similar convergence problems and indicates that an inaccurate resolution of the equilibrium atomic positions due to truncation of the simulation domain may be the source of the slow ground state convergence.

  4. A comparison between semi-spheroid- and dome-shaped quantum dots coupled to wetting layer

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

    Shahzadeh, Mohammadreza; Sabaeian, Mohammad, E-mail: Sabaeian@scu.ac.ir

    2014-06-15

    During the epitaxial growth method, self-assembled semi-spheroid-shaped quantum dots (QDs) are formed on the wetting layer (WL). However for sake of simplicity, researchers sometimes assume semi-spheroid-shaped QDs to be dome-shaped (hemisphere). In this work, a detailed and comprehensive study on the difference between electronic and transition properties of dome- and semi-spheroid-shaped quantum dots is presented. We will explain why the P-to-S intersubband transition behaves the way it does. The calculated results for intersubband P-to-S transition properties of quantum dots show two different trends for dome-shaped and semi-spheroid-shaped quantum dots. The results are interpreted using the probability of finding electron insidemore » the dome/spheroid region, with emphasis on the effects of wetting layer. It is shown that dome-shaped and semi-spheroid-shaped quantum dots feature different electronic and transition properties, arising from the difference in lateral dimensions between dome- and semi-spheroid-shaped QDs. Moreover, an analogy is presented between the bound S-states in the quantum dots and a simple 3D quantum mechanical particle in a box, and effective sizes are calculated. The results of this work will benefit researchers to present more realistic models of coupled QD/WL systems and explain their properties more precisely.« less

  5. Charge transport in strongly coupled quantum dot solids

    NASA Astrophysics Data System (ADS)

    Kagan, Cherie R.; Murray, Christopher B.

    2015-12-01

    The emergence of high-mobility, colloidal semiconductor quantum dot (QD) solids has triggered fundamental studies that map the evolution from carrier hopping through localized quantum-confined states to band-like charge transport in delocalized and hybridized states of strongly coupled QD solids, in analogy with the construction of solids from atoms. Increased coupling in QD solids has led to record-breaking performance in QD devices, such as electronic transistors and circuitry, optoelectronic light-emitting diodes, photovoltaic devices and photodetectors, and thermoelectric devices. Here, we review the advances in synthesis, assembly, ligand treatments and doping that have enabled high-mobility QD solids, as well as the experiments and theory that depict band-like transport in the QD solid state. We also present recent QD devices and discuss future prospects for QD materials and device design.

  6. Charge transport in strongly coupled quantum dot solids.

    PubMed

    Kagan, Cherie R; Murray, Christopher B

    2015-12-01

    The emergence of high-mobility, colloidal semiconductor quantum dot (QD) solids has triggered fundamental studies that map the evolution from carrier hopping through localized quantum-confined states to band-like charge transport in delocalized and hybridized states of strongly coupled QD solids, in analogy with the construction of solids from atoms. Increased coupling in QD solids has led to record-breaking performance in QD devices, such as electronic transistors and circuitry, optoelectronic light-emitting diodes, photovoltaic devices and photodetectors, and thermoelectric devices. Here, we review the advances in synthesis, assembly, ligand treatments and doping that have enabled high-mobility QD solids, as well as the experiments and theory that depict band-like transport in the QD solid state. We also present recent QD devices and discuss future prospects for QD materials and device design.

  7. Spin relaxation in quantum dots due to electron exchange with leads.

    PubMed

    Vorontsov, A B; Vavilov, M G

    2008-11-28

    We calculate spin relaxation rates in lateral quantum dot systems due to electron exchange between dots and leads. Using rate equations, we develop a theoretical description of the experimentally observed electric current in the spin blockade regime of double quantum dots. A single expression fits the entire current profile and describes the structure of both the conduction peaks and the suppressed ("valley") region. Extrinsic rates calculated here have to be taken into account for accurate extraction of intrinsic relaxation rates due to the spin-orbit and hyperfine spin scattering mechanisms from spin blockade measurements.

  8. Folic acid-CdTe quantum dot conjugates and their applications for cancer cell targeting

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

    Suriamoorthy, Preethi; Zhang, Xing; Hao, Guiyang

    2010-12-01

    In this study, we report the preparation,luminescence, and targeting properties of folic acid- CdTe quantum dot conjugates. Water-soluble CdTe quantum dots were synthesized and conjugated with folic acid using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-N-hydroxysuccinimide chemistry. The in-fluence of folic acid on the luminescence properties of CdTe quantum dots was investigated, and no energy transfer between them was observed. To investigate the efficiency of folic acid-CdTe nanoconjugates for tumor targeting, pure CdTe quantum dots and folic acid-coated CdTe quantum dots were incubated with human naso- pharyngeal epidermal carcinoma cell line with positive expressing folic acid receptors (KB cells) and lung cancer cells without expressionmore » of folic acid receptors (A549 cells). For the cancer cells with positive folate receptors (KB cells), the uptake for CdTe quantum dots is very low, but for folic acid-CdTe nanoconjugates, the uptake is very high. For the lung cancer cells without folate receptors (A549 cells), the uptake for folic acid- CdTe nanoconjugates is also very low. The results indicate that folic acid is an effective targeting molecule for tumor cells with overexpressed folate receptors.« less

  9. Undoped Si/SiGe Depletion-Mode Few-Electron Double Quantum Dots

    NASA Astrophysics Data System (ADS)

    Borselli, Matthew; Huang, Biqin; Ross, Richard; Croke, Edward; Holabird, Kevin; Hazard, Thomas; Watson, Christopher; Kiselev, Andrey; Deelman, Peter; Alvarado-Rodriguez, Ivan; Schmitz, Adele; Sokolich, Marko; Gyure, Mark; Hunter, Andrew

    2011-03-01

    We have successfully formed a double quantum dot in the sSi/SiGe material system without need for intentional dopants. In our design, a two-dimensional electron gas is formed in a strained silicon well by forward biasing a global gate. Lateral definition of quantum dots is established with reverse-biased gates with ~ 40 nm critical dimensions. Low-temperature capacitance and Hall measurements confirm electrons are confined in the Si-well with mobilities > 10 4 cm 2 / V - s . Further characterization identifies practical gate bias limits for this design and will be compared to simulation. Several double dot devices have been brought into the few-electron Coulomb blockade regime as measured by through-dot transport. Honeycomb diagrams and nonlinear through-dot transport measurements are used to quantify dot capacitances and addition energies of several meV. Sponsored by United States Department of Defense. Approved for Public Release, Distribution Unlimited.

  10. Excited-state relaxation in PbSe quantum dots

    NASA Astrophysics Data System (ADS)

    An, Joonhee M.; Califano, Marco; Franceschetti, Alberto; Zunger, Alex

    2008-04-01

    In solids the phonon-assisted, nonradiative decay from high-energy electronic excited states to low-energy electronic excited states is picosecond fast. It was hoped that electron and hole relaxation could be slowed down in quantum dots, due to the unavailability of phonons energy matched to the large energy-level spacings ("phonon-bottleneck"). However, excited-state relaxation was observed to be rather fast (⩽1ps) in InP, CdSe, and ZnO dots, and explained by an efficient Auger mechanism, whereby the excess energy of electrons is nonradiatively transferred to holes, which can then rapidly decay by phonon emission, by virtue of the densely spaced valence-band levels. The recent emergence of PbSe as a novel quantum-dot material has rekindled the hope for a slow down of excited-state relaxation because hole relaxation was deemed to be ineffective on account of the widely spaced hole levels. The assumption of sparse hole energy levels in PbSe was based on an effective-mass argument based on the light effective mass of the hole. Surprisingly, fast intraband relaxation times of 1-7ps were observed in PbSe quantum dots and have been considered contradictory with the Auger cooling mechanism because of the assumed sparsity of the hole energy levels. Our pseudopotential calculations, however, do not support the scenario of sparse hole levels in PbSe: Because of the existence of three valence-band maxima in the bulk PbSe band structure, hole energy levels are densely spaced, in contradiction with simple effective-mass models. The remaining question is whether the Auger decay channel is sufficiently fast to account for the fast intraband relaxation. Using the atomistic pseudopotential wave functions of Pb2046Se2117 and Pb260Se249 quantum dots, we explicitly calculated the electron-hole Coulomb integrals and the P →S electron Auger relaxation rate. We find that the Auger mechanism can explain the experimentally observed P →S intraband decay time scale without the need to

  11. Quantum-dot based nanothermometry in optical plasmonic recording media

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

    Maestro, Laura Martinez; Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122; Zhang, Qiming

    2014-11-03

    We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media.

  12. Overview of Stabilizing Ligands for Biocompatible Quantum Dot Nanocrystals

    PubMed Central

    Zhang, Yanjie; Clapp, Aaron

    2011-01-01

    Luminescent colloidal quantum dots (QDs) possess numerous advantages as fluorophores in biological applications. However, a principal challenge is how to retain the desirable optical properties of quantum dots in aqueous media while maintaining biocompatibility. Because QD photophysical properties are directly related to surface states, it is critical to control the surface chemistry that renders QDs biocompatible while maintaining electronic passivation. For more than a decade, investigators have used diverse strategies for altering the QD surface. This review summarizes the most successful approaches for preparing biocompatible QDs using various chemical ligands. PMID:22247651

  13. In-situ laser nano-patterning for ordered InAs/GaAs(001) quantum dot growth

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Shi, Zhenwu; Huo, Dayun; Guo, Xiaoxiang; Zhang, Feng; Chen, Linsen; Wang, Qinhua; Zhang, Baoshun; Peng, Changsi

    2018-04-01

    A study of in-situ laser interference nano-patterning on InGaAs wetting layers was carried out during InAs/GaAs (001) quantum dot molecular beam epitaxy growth. Periodic nano-islands with heights of a few atomic layers were obtained via four-beam laser interference irradiation on the InGaAs wetting layer at an InAs coverage of 0.9 monolayer. The quantum dots nucleated preferentially at edges of nano-islands upon subsequent deposition of InAs on the patterned surface. When the nano-islands are sufficiently small, the patterned substrate could be spontaneously re-flattened and an ordered quantum dot array could be produced on the smooth surface. This letter discusses the mechanisms of nano-patterning and ordered quantum dot nucleation in detail. This study provides a potential technique leading to site-controlled, high-quality quantum dot fabrication.

  14. 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.

  15. Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Chacon, Rebecca; Uhl, David; Yang, Rui

    2005-01-01

    In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 microns or more near room temperature. InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strainenergy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 microns, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots. In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.

  16. Size-Dependent Optoelectronic Properties and Controlled Doping of Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Engel, Jesse Hart

    Given a rapidly developing world, the need exists for inexpensive renewable energy alternatives to help avoid drastic climate change. Photovoltaics have the potential to fill the energy needs of the future, but significant cost decreases are necessary for widespread adoption. Semiconductor nanocrystals, also known as quantum dots, are a nascent technology with long term potential to enable inexpensive and high efficiency photovoltaics. When deposited as a film, quantum dots form unique nanocomposites whose electronic and optical properties can be broadly tuned through manipulation of their individual constituents. The contents of this thesis explore methods to understand and optimize the optoelectronic properties of PbSe quantum dot films for use in photovoltaic applications. Systematic optimization of photovoltaic performance is demonstrated as a function of nanocrystal size, establishing the potential for utilizing extreme quantum confinement to improve device energetics and alignment. Detailed investigations of the mechanisms of electrical transport are performed, revealing that electronic coupling in quantum dot films is significantly less than often assumed based on optical shifts. A method is proposed to employ extended regions of built-in electrical field, through controlled doping, to sidestep issues of poor transport. To this end, treatments with chemical redox agents are found to effect profound and reversible doping within nanocrystal films, sufficient to enable their use as chemical sensors, but lacking the precision required for optoelectronic applications. Finally, a novel doping method employing "redox buffers" is presented to enact precise, stable, and reversible charge-transfer doping in porous semiconductor films. An example of oxidatively doping PbSe quantum dot thin films is presented, and the future potential for redox buffers in photovoltaic applications is examined.

  17. Precise Control of Quantum Confinement in Cesium Lead Halide Perovskite Quantum Dots via Thermodynamic Equilibrium.

    PubMed

    Dong, Yitong; Qiao, Tian; Kim, Doyun; Parobek, David; Rossi, Daniel; Son, Dong Hee

    2018-05-09

    Cesium lead halide (CsPbX 3 ) nanocrystals have emerged as a new family of materials that can outperform the existing semiconductor nanocrystals due to their superb optical and charge-transport properties. However, the lack of a robust method for producing quantum dots with controlled size and high ensemble uniformity has been one of the major obstacles in exploring the useful properties of excitons in zero-dimensional nanostructures of CsPbX 3 . Here, we report a new synthesis approach that enables the precise control of the size based on the equilibrium rather than kinetics, producing CsPbX 3 quantum dots nearly free of heterogeneous broadening in their exciton luminescence. The high level of size control and ensemble uniformity achieved here will open the door to harnessing the benefits of excitons in CsPbX 3 quantum dots for photonic and energy-harvesting applications.

  18. Electric-Field Sensing with a Scanning Fiber-Coupled Quantum Dot

    NASA Astrophysics Data System (ADS)

    Cadeddu, D.; Munsch, M.; Rossi, N.; Gérard, J.-M.; Claudon, J.; Warburton, R. J.; Poggio, M.

    2017-09-01

    We demonstrate the application of a fiber-coupled quantum dot (QD) in a tip as a scanning probe for electric-field imaging. We map the out-of-plane component of the electric field induced by a pair of electrodes by the measurement of the quantum-confined Stark effect induced on a QD spectral line. Our results are in agreement with finite-element simulations of the experiment. Furthermore, we present results from analytic calculations and simulations which are relevant to any electric-field sensor embedded in a dielectric tip. In particular, we highlight the impact of the tip geometry on both the resolution and sensitivity.

  19. On-Demand Single Photons with High Extraction Efficiency and Near-Unity Indistinguishability from a Resonantly Driven Quantum Dot in a Micropillar.

    PubMed

    Ding, Xing; He, Yu; Duan, Z-C; Gregersen, Niels; Chen, M-C; Unsleber, S; Maier, S; Schneider, Christian; Kamp, Martin; Höfling, Sven; Lu, Chao-Yang; Pan, Jian-Wei

    2016-01-15

    Scalable photonic quantum technologies require on-demand single-photon sources with simultaneously high levels of purity, indistinguishability, and efficiency. These key features, however, have only been demonstrated separately in previous experiments. Here, by s-shell pulsed resonant excitation of a Purcell-enhanced quantum dot-micropillar system, we deterministically generate resonance fluorescence single photons which, at π pulse excitation, have an extraction efficiency of 66%, single-photon purity of 99.1%, and photon indistinguishability of 98.5%. Such a single-photon source for the first time combines the features of high efficiency and near-perfect levels of purity and indistinguishabilty, and thus opens the way to multiphoton experiments with semiconductor quantum dots.

  20. Ultrafast electronic dynamics in unipolar n-doped indium gallium arsenide/gallium arsenide self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Wu, Zong-Kwei J.

    2006-12-01

    Photodetectors based on intraband infrared absorption in the quantum dots have demonstrated improved performance over its quantum well counterpart by lower dark current, relative temperature insensitivity, and its ability for normal incidence operation. Various scattering processes, including phonon emission/absorption and carrier-carrier scattering, are critical in understanding device operation on the fundamental level. In previous studies, our group has investigated carrier dynamics in both low- and high-density regime. Ultrafast electron-hole scattering and the predicted phonon bottleneck effect in intrinsic quantum dots have been observed. Further examination on electron dynamics in unipolar structures is presented in this thesis. We used n-doped quantum dot in mid-infrared photodetector device structure to study the electron dynamics in unipolar structure. Differential transmission spectroscopy with mid-infrared intraband pump and optical interband probe was implemented to measure the electron dynamics directly without creating extra electron-hole pair, Electron relaxation after excitation was measured under various density and temperature conditions. Rapid capture into quantum dot within ˜ 10 ps was observed due to Auger-type electron-electron scattering. Intradot relaxation from the quantum dot excited state to the ground state was also observed on the time scale of 100 ps. With highly doped electron density in the structure, the inter-sublevel relaxation is dominated by Auger-type electron-electron scattering and the phonon bottleneck effect is circumvented. Nanosecond-scale recovery in larger-sized quantum dots was observed, not intrinsic to electron dynamics but due to band-bending and built-in voltage drift. An ensemble Monte Carlo simulation was also established to model the dynamics in quantum dots and in goad agreement with the experimental results. We presented a comprehensive picture of electron dynamics in the unipolar quantum dot structure

  1. Magnetic field induced optical gain in a dilute nitride quaternary semiconductor quantum dot

    NASA Astrophysics Data System (ADS)

    Mageshwari, P. Uma; Peter, A. John; Lee, Chang Woo

    2016-10-01

    Effects of magnetic field strength on the electronic and optical properties are brought out in a Ga0.661In0.339N0.0554As0.9446/GaAs quantum dot for the applications of desired wavelength in opto-electronic devices. The band alignment is obtained using band anticrossing model and the model solid theory. The magnetic field dependent electron-heavy hole transition energies with the dot radius in a GaInNAs/GaAs quantum dot are investigated. The magnetic field induced oscillator strength as a function of dot radius is studied. The resonant peak values of optical absorption coefficients and the changes of refractive index with the application of magnetic field strength in a GaInNAs/GaAs quantum dot are obtained. The magnetic field induced threshold current density and the maximum optical gain are found in a GaInNAs/GaAs quantum dot. The results show that the optimum wavelength for fibre optical communication networks can be obtained with the variation of applied magnetic field strength and the outcomes may be useful for the design of efficient lasers based on the group III-N-V semiconductors.

  2. Emission polarization control in semiconductor quantum dots coupled to a photonic crystal microcavity.

    PubMed

    Gallardo, E; Martínez, L J; Nowak, A K; van der Meulen, H P; Calleja, J M; Tejedor, C; Prieto, I; Granados, D; Taboada, A G; García, J M; Postigo, P A

    2010-06-07

    We study the optical emission of single semiconductor quantum dots weakly coupled to a photonic-crystal micro-cavity. The linearly polarized emission of a selected quantum dot changes continuously its polarization angle, from nearly perpendicular to the cavity mode polarization at large detuning, to parallel at zero detuning, and reversing sign for negative detuning. The linear polarization rotation is qualitatively interpreted in terms of the detuning dependent mixing of the quantum dot and cavity states. The present result is relevant to achieve continuous control of the linear polarization in single photon emitters.

  3. Fabrication of nanoscale heterostructures comprised of graphene-encapsulated gold nanoparticles and semiconducting quantum dots for photocatalysis.

    PubMed

    Li, Yuan; Chopra, Nitin

    2015-05-21

    Patterned growth of multilayer graphene shell encapsulated gold nanoparticles (GNPs) and their covalent linking with inorganic quantum dots are demonstrated. GNPs were grown using a xylene chemical vapor deposition process, where the surface oxidized gold nanoparticles catalyze the multilayer graphene shell growth in a single step process. The graphene shell encapsulating gold nanoparticles could be further functionalized with carboxylic groups, which were covalently linked to amine-terminated quantum dots resulting in GNP-quantum dot heterostructures. The compositions, morphologies, crystallinity, and surface functionalization of GNPs and their heterostructures with quantum dots were evaluated using microscopic, spectroscopic, and analytical methods. Furthermore, optical properties of the derived architectures were studied using both experimental methods and simulations. Finally, GNP-quantum dot heterostructures were studied for photocatalytic degradation of phenol.

  4. Graphene based quantum dots.

    PubMed

    Zhang, H G; Hu, H; Pan, Y; Mao, J H; Gao, M; Guo, H M; Du, S X; Greber, T; Gao, H-J

    2010-08-04

    Laterally localized electronic states are identified on a single layer of graphene on ruthenium by low temperature scanning tunneling spectroscopy (STS). The individual states are separated by 3 nm and comprise regions of about 90 carbon atoms. This constitutes a highly regular quantum dot-array with molecular precision. It is evidenced by quantum well resonances (QWRs) with energies that relate to the corrugation of the graphene layer. The dI/dV conductance spectra are modeled by a layer height dependent potential-well with a delta-function potential that describes the barrier for electron penetration into graphene. The resulting QWRs are strongest and lowest in energy on the isolated 'hill' regions with a diameter of 2 nm, where the graphene is decoupled from the surface.

  5. Coherently-enabled environmental control of optics and energy transfer pathways of hybrid quantum dot-metallic nanoparticle systems.

    PubMed

    Hatef, Ali; Sadeghi, Seyed M; Fortin-Deschênes, Simon; Boulais, Etienne; Meunier, Michel

    2013-03-11

    It is well-known that optical properties of semiconductor quantum dots can be controlled using optical cavities or near fields of localized surface plasmon resonances (LSPRs) of metallic nanoparticles. In this paper we study the optics, energy transfer pathways, and exciton states of quantum dots when they are influenced by the near fields associated with plasmonic meta-resonances. Such resonances are formed via coherent coupling of excitons and LSPRs when the quantum dots are close to metallic nanorods and driven by a laser beam. Our results suggest an unprecedented sensitivity to the refractive index of the environment, causing significant spectral changes in the Förster resonance energy transfer from the quantum dots to the nanorods and in exciton transition energies. We demonstrate that when a quantum dot-metallic nanorod system is close to its plasmonic meta-resonance, we can adjust the refractive index to: (i) control the frequency range where the energy transfer from the quantum dot to the metallic nanorod is inhibited, (ii) manipulate the exciton transition energy shift of the quantum dot, and (iii) disengage the quantum dot from the metallic nanoparticle and laser field. Our results show that near meta-resonances the spectral forms of energy transfer and exciton energy shifts are strongly correlated to each other.

  6. Exchange interaction and tunneling-induced transparency in coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Borges, H. S.; Alcalde, A. M.; Ulloa, Sergio E.

    2014-11-01

    We investigate the optical response of quantum dot molecules coherently driven by polarized laser light. Our description includes the splitting in excitonic levels caused by isotropic and anisotropic exchange interactions. We consider interdot transitions mediated by hole tunneling between states with the same total angular momentum and between bright and dark exciton states as allowed by spin-flip hopping between the dots in the molecule. Using realistic experimental parameters we demonstrate that the excitonic states coupled by tunneling exhibit a rich and controllable optical response. We show that through the appropriate control of an external electric field and light polarization, the tunneling coupling establishes an efficient destructive quantum interference path that creates a transparency window in the absorption spectra whenever states of appropriate symmetry are mixed by the carrier tunneling. We explore the relevant parameter space that allows probing this phenomenon in experiments. Controlled variation in applied field and laser detuning would allow the optical characterization of spin-preserving and spin-flip hopping amplitudes in such systems by measuring the width of the tunneling-induced transparency windows.

  7. Many-body exciton states in self-assembled quantum dots coupled to a Fermi sea

    NASA Astrophysics Data System (ADS)

    Kleemans, N. A. J. M.; van Bree, J.; Govorov, A. O.; Keizer, J. G.; Hamhuis, G. J.; Nötzel, R.; Silov, A. Yu.; Koenraad, P. M.

    2010-07-01

    Many-body interactions give rise to fascinating physics such as the X-ray Fermi-edge singularity in metals, the Kondo effect in the resistance of metals with magnetic impurities and the fractional quantum Hall effect. Here we report the observation of striking many-body effects in the optical spectra of a semiconductor quantum dot interacting with a degenerate electron gas. A semiconductor quantum dot is an artificial atom, the properties of which can be controlled by means of a tunnel coupling between a metallic contact and the quantum dot. Previous studies concern mostly the regime of weak tunnel coupling, whereas here we investigate the regime of strong coupling, which markedly modifies the optical spectra. In particular we observe two many-body exciton states: Mahan and hybrid excitons. These experimental results open the route towards the observation of a tunable Kondo effect in excited states of semiconductors and are of importance for the technological implementation of quantum dots in devices for quantum information processing.

  8. Coherent electron-spin-resonance manipulation of three individual spins in a triple quantum dot

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

    Noiri, A.; Yoneda, J.; Nakajima, T.

    2016-04-11

    Quantum dot arrays provide a promising platform for quantum information processing. For universal quantum simulation and computation, one central issue is to demonstrate the exhaustive controllability of quantum states. Here, we report the addressable manipulation of three single electron spins in a triple quantum dot using a technique combining electron-spin-resonance and a micro-magnet. The micro-magnet makes the local Zeeman field difference between neighboring spins much larger than the nuclear field fluctuation, which ensures the addressable driving of electron-spin-resonance by shifting the resonance condition for each spin. We observe distinct coherent Rabi oscillations for three spins in a semiconductor triple quantummore » dot with up to 25 MHz spin rotation frequencies. This individual manipulation over three spins enables us to arbitrarily change the magnetic spin quantum number of the three spin system, and thus to operate a triple-dot device as a three-qubit system in combination with the existing technique of exchange operations among three spins.« less

  9. Quantum dots grown in the InSb/GaSb system by liquid-phase epitaxy

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

    Parkhomenko, Ya. A.; Dement’ev, P. A.; Moiseev, K. D., E-mail: mkd@iropt2.ioffe.rssi.ru

    2016-07-15

    The first results of the liquid-phase epitaxial growth of quantum dots in the InSb/GaSb system and atomic-force microscopy data on the structural characteristics of the quantum dots are reported. It is shown that the surface density, shape, and size of nanoislands depend on the deposition temperature and the chemical properties of the matrix surface. Arrays of InSb quantum dots on GaSb (001) substrates are produced in the temperature range T = 450–465°C. The average dimensions of the quantum dots correspond to a height of h = 3 nm and a base dimension of D = 30 nm; the surface densitymore » is 3 × 10{sup 9} cm{sup –2}.« less

  10. Enhanced spin figure of merit in an Aharonov-Bohm ring with a double quantum dot

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

    Zhou, Xingfei; Qi, Fenghua; Jin, Guojun, E-mail: gjin@nju.edu.cn

    2014-04-21

    We theoretically investigate the thermoelectric effects in an Aharonov-Bohm ring with a serially coupled double quantum dot embedded in one arm. An external magnetic field is perpendicularly applied to the two dots. Using the nonequilibrium Green's function method in the linear-response regime, we calculate the charge and spin figures of merit. When the energy levels of the two quantum dots are equal and the system is connected to two normal leads, a large spin figure of merit (Z{sub s}T ≈ 4.5) accompanying with a small charge figure of merit (Z{sub c}T ≈ 0) can be generated due to the remarkable bipolar effect. Further, whenmore » the system is connected to two ferromagnetic leads, the spin figure of merit can reach even a higher value about 9. Afterwards, we find that Z{sub s}T is enhanced while Z{sub c}T is reduced in the coaction of the Aharonov-Bohm flux and Rashba spin-orbit coupling. It is argued that the bipolar effect is positive (negative) to spin (charge) figure of merit in the presence of level detuning of the two quantum dots and intradot Coulomb interactions, respectively. Also, we propose a possible experiment to verify our results.« less

  11. Cadmium sulfide quantum dots induce oxidative stress and behavioral impairments in the marine clam Scrobicularia plana.

    PubMed

    Buffet, Pierre-Emmanuel; Zalouk-Vergnoux, Aurore; Poirier, Laurence; Lopes, Christelle; Risso-de-Faverney, Christine; Guibbolini, Marielle; Gilliland, Douglas; Perrein-Ettajani, Hanane; Valsami-Jones, Eugenia; Mouneyrac, Catherine

    2015-07-01

    Cadmium sulfide (CdS) quantum dots have a number of current applications in electronics and solar cells and significant future potential in medicine. The aim of the present study was to examine the toxic effects of CdS quantum dots on the marine clam Scrobicularia plana exposed for 14 d to these nanomaterials (10 µg Cd L(-1) ) in natural seawater and to compare them with soluble Cd. Measurement of labile Cd released from CdS quantum dots showed that 52% of CdS quantum dots remained in the nanoparticulate form. Clams accumulated the same levels of Cd regardless of the form in which it was delivered (soluble Cd vs CdS quantum dots). However, significant changes in biochemical responses were observed in clams exposed to CdS quantum dots compared with soluble Cd. Increased activities of catalase and glutathione-S-transferase were significantly higher in clams exposed in seawater to Cd as the nanoparticulate versus the soluble form, suggesting a specific nano effect. The behavior of S. plana in sediment showed impairments of foot movements only in the case of exposure to CdS quantum dots. The results show that oxidative stress and behavior biomarkers are sensitive predictors of CdS quantum dots toxicity in S. plana. Such responses, appearing well before changes might occur at the population level, demonstrate the usefulness of this model species and type of biomarker in the assessment of nanoparticle contamination in estuarine ecosystems. © 2015 SETAC.

  12. Comparison of the Optical Properties of Graphene and Alkyl-terminated Si and Ge Quantum Dots.

    PubMed

    de Weerd, Chris; Shin, Yonghun; Marino, Emanuele; Kim, Joosung; Lee, Hyoyoung; Saeed, Saba; Gregorkiewicz, Tom

    2017-10-31

    Semiconductor quantum dots are widely investigated due to their size dependent energy structure. In particular, colloidal quantum dots represent a promising nanomaterial for optoelectronic devices, such as photodetectors and solar cells, but also luminescent markers for biotechnology, among other applications. Ideal materials for these applications should feature efficient radiative recombination and absorption transitions, altogether with spectral tunability over a wide range. Group IV semiconductor quantum dots can fulfill these requirements and serve as an alternative to the commonly used direct bandgap materials containing toxic and/or rare elements. Here, we present optical properties of butyl-terminated Si and Ge quantum dots and compare them to those of graphene quantum dots, finding them remarkably similar. We investigate their time-resolved photoluminescence emission as well as the photoluminescence excitation and linear absorption spectra. We contemplate that their emission characteristics indicate a (semi-) resonant activation of the emitting channel; the photoluminescence excitation shows characteristics similar to those of a molecule. The optical density is consistent with band-to-band absorption processes originating from core-related states. Hence, these observations strongly indicate a different microscopic origin for absorption and radiative recombination in the three investigated quantum dot systems.

  13. 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.

  14. 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.

  15. Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates.

    PubMed

    Patty, Kira; Sadeghi, Seyed M; Campbell, Quinn; Hamilton, Nathan; West, Robert G; Mao, Chuanbin

    2014-09-21

    We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.

  16. Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates

    PubMed Central

    Patty, Kira; Sadeghi, Seyed M.; Campbell, Quinn; Hamilton, Nathan; West, Robert G.; Mao, Chuanbin

    2014-01-01

    We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide. PMID:25316953

  17. Confinement control mechanism for two-electron Hulthen quantum dots in plasmas

    NASA Astrophysics Data System (ADS)

    Bahar, M. K.; Soylu, A.

    2018-05-01

    In this study, for the first time, the energies of two-electron Hulthen quantum dots (TEHQdots) embedded in Debye and quantum plasmas modeled by the more general exponential cosine screened Coulomb (MGECSC) potential under the combined influence of electric and magnetic fields are investigated by numerically solving the Schrödinger equation using the asymptotic iteration method. To do this, the four different forms of the MGECSC potential, which set through the different cases of the potential parameters, are taken into consideration. We propose that plasma environments form considerable quantum mechanical effects for quantum dots and other atomic systems and that plasmas are important experimental arguments. In this study, by considering the quantum dot parameters, the external field parameters, and the plasma screening parameters, a control mechanism of the confinement on energies of TEHQdots and the frequency of the radiation emitted by TEHQdots as a result of any excitation is discussed. In this mechanism, the behaviors, similarities, the functionalities of the control parameters, and the influences of plasmas on these quantities are explored.

  18. 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

  19. Ligand removal and photo-activation of CsPbBr3 quantum dots for enhanced optoelectronic devices.

    PubMed

    Moyen, Eric; Kanwat, Anil; Cho, Sinyoung; Jun, Haeyeon; Aad, Roy; Jang, Jin

    2018-05-10

    Perovskite quantum dots have recently emerged as a promising light source for optoelectronic applications. However, integrating them into devices while preserving their outstanding optical properties remains challenging. Due to their ionic nature, perovskite quantum dots are extremely sensitive and degrade on applying the simplest processes. To maintain their colloidal stability, they are surrounded by organic ligands; these prevent efficient charge carrier injection in devices and have to be removed. Here we report on a simple method, where a moderate thermal process followed by exposure to UV in air can efficiently remove ligands and increase the photo-luminescence of the room temperature synthesized perovskite quantum dot thin films. Annealing is accompanied by a red shift of the emission wavelength, usually attributed to the coalescence and irreversible degradation of the quantum dots. We show that it is actually related to the relaxation of the quantum dots upon the ligand removal, without the creation of non-radiative recombining defects. The quantum dot surface, as devoid of ligands, is subsequently photo-oxidized and smoothened upon exposure to UV in air, which drastically enhances their photo-luminescence. This adequate combination of treatments improves by more than an order of magnitude the performances of perovskite quantum dot light emitting diodes.

  20. Complete quantum control of a single quantum dot spin using ultrafast optical pulses.

    PubMed

    Press, David; Ladd, Thaddeus D; Zhang, Bingyang; Yamamoto, Yoshihisa

    2008-11-13

    A basic requirement for quantum information processing systems is the ability to completely control the state of a single qubit. For qubits based on electron spin, a universal single-qubit gate is realized by a rotation of the spin by any angle about an arbitrary axis. Driven, coherent Rabi oscillations between two spin states can be used to demonstrate control of the rotation angle. Ramsey interference, produced by two coherent spin rotations separated by a variable time delay, demonstrates control over the axis of rotation. Full quantum control of an electron spin in a quantum dot has previously been demonstrated using resonant radio-frequency pulses that require many spin precession periods. However, optical manipulation of the spin allows quantum control on a picosecond or femtosecond timescale, permitting an arbitrary rotation to be completed within one spin precession period. Recent work in optical single-spin control has demonstrated the initialization of a spin state in a quantum dot, as well as the ultrafast manipulation of coherence in a largely unpolarized single-spin state. Here we demonstrate complete coherent control over an initialized electron spin state in a quantum dot using picosecond optical pulses. First we vary the intensity of a single optical pulse to observe over six Rabi oscillations between the two spin states; then we apply two sequential pulses to observe high-contrast Ramsey interference. Such a two-pulse sequence realizes an arbitrary single-qubit gate completed on a picosecond timescale. Along with the spin initialization and final projective measurement of the spin state, these results demonstrate a complete set of all-optical single-qubit operations.