Showing papers on "Quantum dot published in 2003"
TL;DR: This work characterized water-soluble cadmium selenide–zinc sulfide quantum dots for multiphoton imaging in live animals and found no evidence of blinking (fluorescence intermittency) in solution on nanosecond to millisecond time scales.
Abstract: The use of semiconductor nanocrystals (quantum dots) as fluorescent labels for multiphoton microscopy enables multicolor imaging in demanding biological environments such as living tissue. We characterized water-soluble cadmium selenide-zinc sulfide quantum dots for multiphoton imaging in live animals. These fluorescent probes have two-photon action cross sections as high as 47,000 Goeppert-Mayer units, by far the largest of any label used in multiphoton microscopy. We visualized quantum dots dynamically through the skin of living mice, in capillaries hundreds of micrometers deep. We found no evidence of blinking (fluorescence intermittency) in solution on nanosecond to millisecond time scales.
2,246 citations
Journal Article•
TL;DR: Optical microcavities confine light to small volumes by resonant recirculation as discussed by the authors, and are indispensable for a wide range of applications and studies, such as long-distance transmission of data over optical fibres; they also ensure narrow spot-size laser read/write beams in CD and DVD players.
Abstract: Optical microcavities confine light to small volumes by resonant recirculation. Devices trased on optical microcavities are already indispensable for a wide range of applications and studies, For example, microcavities made of active III-V semiconductor materials control laser emission spectra to enable long-distance transmission of data over optical fibres; they also ensure narrow spot-size laser read/write beams in CD and DVD players. In quantum optical devices, mocrocavities can coax atoms or quantum dots to emit spontaneous photons In a desired direction or can provide an environment where dissipative mechanhms such as spontaneous emission are overcome so that quantum entanglement of radiation and matter is possible. Applications of these remarkable devices are as diverse as their geometrical and resonant properties.
1,855 citations
1,640 citations
TL;DR: The design, formation and testing of QD–protein assemblies that function as chemical sensors that overcomes inherent QD donor–acceptor distance limitations are reported.
Abstract: The potential of luminescent semiconductor quantum dots (QDs) to enable development of hybrid inorganic-bioreceptor sensing materials has remained largely unrealized. We report the design, formation and testing of QD‐protein assemblies that function as chemical sensors. In these assemblies, multiple copies of Escherichia coli maltose-binding protein (MBP) coordinate to each QD by a C-terminal oligohistidine segment and function as sugar receptors. Sensors are selfassembled in solution in a controllable manner. In one configuration, a β-cyclodextrin-QSY9 dark quencher conjugate bound in the MBP saccharide binding site results in fluorescence resonance energy-transfer (FRET) quenching of QD photoluminescence. Added maltose displaces the β-cyclodextrin-QSY9, and QD photoluminescence increases in a systematic manner. A second maltose sensor assembly consists of QDs coupled with Cy3-labelled MBP bound to β-cyclodextrin-Cy3.5. In this case, the QD donor drives sensor function through a two-step FRET mechanism that overcomes inherent QD donor‐acceptor distance limitations. Quantum dot‐biomolecule assemblies constructed using these methods may facilitate development of new hybrid sensing materials.
1,600 citations
TL;DR: It is demonstrated that the spatial distribution of carriers can be controlled within the type-II quantum dots, which makes their properties strongly governed by the band offset of the comprising materials.
Abstract: Type-II band engineered quantum dots (CdTe/CdSe(core/shell) and CdSe/ZnTe(core/shell) heterostructures) are described. The optical properties of these type-II quantum dots are studied in parallel with their type-I counterparts. We demonstrate that the spatial distribution of carriers can be controlled within the type-II quantum dots, which makes their properties strongly governed by the band offset of the comprising materials. This allows access to optical transition energies that are not restricted to band gap energies. The type-II quantum dots reported here can emit at lower energies than the band gaps of comprising materials. The type-II emission can be tailored by the shell thickness as well as the core size. The enhanced control over carrier distribution afforded by these type-II materials may prove useful for many applications, such as photovoltaics and photoconduction devices.
1,259 citations
TL;DR: In this paper, the authors provide a critical summary of some recent developments of new concepts and new materials in thermoelectric materials research, including quantum wells, superlattices, quantum wires, and quantum dots.
Abstract: Efficient solid state energy conversion based on the Peltier effect for cooling and the Seebeck effect for power generation calls for materials with high electrical conductivity σ, high Seebeck coefficient S, and low thermal conductivity k. Identifying materials with a high thermoelectric figure of merit Z(= S2σ/k) has proven to be an extremely challenging task. After 30 years of slow progress, thermoelectric materials research experienced a resurgence, inspired by the developments of new concepts and theories to engineer electron and phonon transport in both nanostructures and bulk materials. This review provides a critical summary of some recent developments of new concepts and new materials. In nanostructures, quantum and classical size effects provide opportunities to tailor the electron and phonon transport through structural engineering. Quantum wells, superlattices, quantum wires, and quantum dots have been employed to change the band structure, energy levels, and density of states of elect...
932 citations
TL;DR: This work demonstrates that composition and internal structure are two important parameters that can be used to tune the optical and electronic properties of multicomponent, alloyed quantum dots.
Abstract: Alloyed semiconductor quantum dots (cadmium selenium telluride) with both homogeneous and gradient internal structures have been prepared to achieve continuous tuning of the optical properties without changing the particle size. Our results demonstrate that composition and internal structure are two important parameters that can be used to tune the optical and electronic properties of multicomponent, alloyed quantum dots. A surprising finding is a nonlinear relationship between the composition and the absorption/emission energies, leading to new properties not obtainable from the parent binary systems. With red-shifted light emission up to 850 nm and quantum yields up to 60%, this new class of alloyed quantum dots opens new possibilities in band gap engineering and in developing near-infrared fluorescent probes for in vivo molecular imaging and biomarker detection.
890 citations
TL;DR: It is shown that coherent time evolution of charge states (pseudospin qubit) in a semiconductor double quantum dot is investigated with a high-speed voltage pulse that controls the energy and decoherence of the system.
Abstract: We investigate coherent time evolution of charge states (pseudospin qubit) in a semiconductor double quantum dot. This fully tunable qubit is manipulated with a high-speed voltage pulse that controls the energy and decoherence of the system. Coherent oscillations of the qubit are observed for several combinations of many-body ground and excited states of the quantum dots. Possible decoherence mechanisms in the present device are also discussed.
696 citations
TL;DR: Ferromagnetism with T(C) > 350 K is observed in aggregated nanocrystals of Co(2+):ZnO that unambiguously demonstrates the existence of intrinsic high-T(C), ferromagnetsism in this class of DMSs.
Abstract: We report a method for the preparation of colloidal ZnO-diluted magnetic semiconductor quantum dots (DMS-QDs) by alkaline-activated hydrolysis and condensation of zinc acetate solutions in dimethyl sulfoxide (DMSO). Mechanistic studies reveal that Co2+ and Ni2+ dopants inhibit nucleation and growth of ZnO nanocrystals. In particular, dopants are quantitatively excluded from the critical nuclei but are incorporated nearly isotropically during subsequent growth of the nanocrystals. The smaller nanocrystal diameters that result upon doping are explained by the Gibbs−Thompson relationship between lattice strain and crystal solubility. We describe methods for cleaning the nanocrystal surfaces of exposed dopants and for redispersion of the final DMS-QDs. Homogeneous substitutional doping is verified by high-resolution low-temperature electronic absorption and magnetic circular dichroism (MCD) spectroscopies. A “giant Zeeman effect” is observed in the band gap transition of Co2+:ZnO DMS-QDs. MCD and Zeeman spect...
621 citations
TL;DR: Fluorescent semiconductor nanocrystals (quantum dots [QDs] are hypothesized to be excellent contrast agents for biomedical assays and imaging.
Abstract: Fluorescent semiconductor nanocrystals (quantum dots [QDs]) are hypothesized to be excellent contrast agents for biomedical assays and imaging. A unique property of QDs is that their absorbance increases with increasing separation between excitation and emission wavelengths. Much of the enthusiasm for using QDs in vivo stems from this property, since photon yield should be proportional to the integral of the broadband absorption. In this study, we demonstrate that tissue scatter and absorbance can sometimes offset increasing QD absorption at bluer wavelengths, and counteract this potential advantage. By using a previously validated mathematical model, we explored the effects of tissue absorbance, tissue scatter, wavelength dependence of the scatter, water-to-hemoglobin ratio, and tissue thickness on QD performance. We conclude that when embedded in biological fluids and tissues, QD excitation wavelengths will often be quite constrained, and that excitation and emission wavelengths should be selected carefully based on the particular application. Based on our results, we produced near-infrared QDs optimized for imaging surface vasculature with white light excitation and a silicon CCD camera, and used them to image the coronary vasculature in vivo. Taken together, our data should prove useful in designing fluorescent QD contrast agents optimized for specific biomedical applications.
515 citations
TL;DR: This review covers the emerging field of nanobiotechnology, in which nanoparticles are applied to the analysis of biomolecules, and discusses the next generation of nanoparticles that will be utilized in the life sciences, such as nanodots and carbon nanotubes.
TL;DR: Heterostructured nucleation was achieved with a dual-peptide virus engineered to express two distinct peptides within the same viral capsid, representing a genetically controlled biological synthesis route to a semiconductor nanoscale heterostructure.
Abstract: The highly organized structure of M13 bacteriophage was used as an evolved biological template for the nucleation and orientation of semiconductor nanowires. To create this organized template, peptides were selected by using a pIII phage display library for their ability to nucleate ZnS or CdS nanocrystals. The successful peptides were expressed as pVIII fusion proteins into the crystalline capsid of the virus. The engineered viruses were exposed to semiconductor precursor solutions, and the resultant nanocrystals that were templated along the viruses to form nanowires were extensively characterized by using high-resolution analytical electron microscopy and photoluminescence. ZnS nanocrystals were well crystallized on the viral capsid in a hexagonal wurtzite or a cubic zinc blende structure, depending on the peptide expressed on the viral capsid. Electron diffraction patterns showed single-crystal type behavior from a polynanocrystalline area of the nanowire formed, suggesting that the nanocrystals on the virus were preferentially oriented with their [001] perpendicular to the viral surface. Peptides that specifically directed CdS nanocrystal growth were also engineered into the viral capsid to create wurtzite CdS virus-based nanowires. Lastly, heterostructured nucleation was achieved with a dual-peptide virus engineered to express two distinct peptides within the same viral capsid. This work represents a genetically controlled biological synthesis route to a semiconductor nanoscale heterostructure.
TL;DR: A multi– high-frequency electron paramagnetic resonance method is used to probe the magnetic excitations of a dimer of single-molecule magnets, and the measured spectra display well-resolved quantum transitions involving coherent superposition states of both molecules.
Abstract: A multi- high-frequency electron paramagnetic resonance method is used to probe the magnetic excitations of a dimer of single-molecule magnets. The measured spectra display well-resolved quantum transitions involving coherent superposition states of both molecules. The behavior may be understood in terms of an isotropic superexchange coupling between pairs of single-molecule magnets, in analogy with several recently proposed quantum devices based on artificially fabricated quantum dots or clusters. These findings highlight the potential utility of supramolecular chemistry in the design of future quantum devices based on molecular nanomagnets.
TL;DR: In this article, surface-related emission in highly luminescent CdSe quantum dots with controlled quantum yield and photooxidation by time-resolved photoluminescence measurements was investigated.
Abstract: We report our experimental studies of surface-related emission in highly luminescent CdSe quantum dots (QDs) with controlled quantum yield and photooxidation by time-resolved photoluminescence measurements. This kind of surface-related emission, with a radiative lifetime of tens of nanoseconds, implies the involvement of surface states in the carrier recombination process of such highly luminescent CdSe QDs.
TL;DR: In this article, water-soluble semiconductor nanocrystals presenting simultaneously high band-edge photoluminescence quantum efficiencies (as high as 60% at room temperature), monoexponential exciton decays, and no observable defect-related emission are obtained.
Abstract: Colloidal CdTe quantum dots prepared in TOP/DDA (trioctylphosphine/dodecylamine) are transferred into water by the use of amino−ethanethiol•HCl (AET) or mercaptopropionic acid (MPA). This results in an increase in the photoluminescence quantum efficiency and a longer exciton lifetime. For the first time, water-soluble semiconductor nanocrystals presenting simultaneously high band-edge photoluminescence quantum efficiencies (as high as 60% at room temperature), monoexponential exciton decays, and no observable defect-related emission are obtained.
TL;DR: The unusual temperature dependence of the magnetization coercivity is discussed in terms of a temperature-dependent exchange interaction involving paramagnetic Ni2+ ions.
Abstract: Ferromagnetism with T c > 350 K is observed in the diluted magnetic semiconductor Ni 2 + :ZnO synthesized from solution. Whereas colloidal Ni 2 + :ZnO nanocrystals are paramagnetic, their aggregation gives rise to robust ferromagnetism. The appearance of ferromagnetism is attributed to the increase in domain volumes and the generation of lattice defects upon aggregation. The unusual temperature dependence of the magnetization coercivity is discussed in terms of a temperature-dependent exchange interaction involving paramagnetic Ni 2 + ions.
TL;DR: A new family of oligomeric alkyl phosphine ligands for nanocrystal quantum dots show effective binding affinity to quantum dot surfaces and present a chemically flexible structure that can be used for further chemistry, such as cross-linking, copolymerization, and conjugation to biomolecules.
Abstract: We report a new family of oligomeric alkyl phosphine ligands for nanocrystal quantum dots. These oligomeric phosphines show effective binding affinity to quantum dot surfaces. They form thin and secure organic shells that stabilize quantum dots in diverse environments including serum and polymer matrices. They maintain the initial as-grown photoluminescence quantum yield of the quantum dots and enable homogeneous incorporation into various matrices. They present a chemically flexible structure that can be used for further chemistry, such as cross-linking, copolymerization, and conjugation to biomolecules.
TL;DR: The steady-state photoluminescence (PL) properties of cadmium selenide quantum dots (QDs) with a zinc sulfide overlayer [(CdSe)ZnS] can be strongly dependent on temperature in the range from 100 to 315 K as discussed by the authors.
Abstract: The steady-state photoluminescence (PL) properties of cadmium selenide quantum dots (QDs) with a zinc sulfide overlayer [(CdSe)ZnS] can be strongly dependent on temperature in the range from 100 to 315 K. The PL intensity from 50 to 55 A (CdSe)ZnS QDs in poly(lauryl methacrylate) matrices increases by a factor of ∼5 when the temperature is decreased from 315 to 100 K, and the peak of the emission band is blueshifted by 20 nm over the same range. The change in PL intensity is appreciable, linear, and reversible (−1.3% per °C) for temperatures close to ambient conditions. These properties of (CdSe)ZnS dots are retained in a variety of matrices including polymer and sol–gel films, and they are independent of excitation wavelength above the band gap. The significant temperature dependence of the luminescence combined with its insensitivity to oxygen quenching establishes (CdSe)ZnS dots as optical temperature indicators for temperature-sensitive coatings.
TL;DR: In this paper, photo-and electroluminescence of PbS nanocrystals in a conjugated polymer matrix was reported, with an internal quantum efficiency up to 1.2%.
Abstract: Nanocomposites consisting of PbS nanocrystals in a conjugated polymer matrix were fabricated. We report results of photo- and electroluminescence across the range of 1000 to 1600 nm with tunability obtained via the quantum-size effect. The intensity of electroluminescence reached values corresponding to an internal quantum efficiency up to 1.2%. We discuss the impact of using different-length capping ligands on the transfer of excitations from polymer matrix to nanocrystals.
TL;DR: Growth of indium phosphide (InP) quantum wires having diameters in the strong-confinement regime are reported and a comparison of their bandgaps with those previously reported for InP quantum dots are compared.
Abstract: The size dependence of the bandgap is the most identifiable aspect of quantum confinement in semiconductors; the bandgap increases as the nanostructure size decreases. The bandgaps in one-dimensional (1D)-confined wells, 2D-confined wires, and 3D-confined dots should evolve differently with size as a result of the differing dimensionality of confinement. However, no systematic experimental comparisons of analogous 1D, 2D or 3D confinement systems have been made. Here we report growth of indium phosphide (InP) quantum wires having diameters in the strong-confinement regime, and a comparison of their bandgaps with those previously reported for InP quantum dots. We provide theoretical evidence to establish that the quantum confinement observed in the InP wires is weakened to the expected extent, relative to that in InP dots, by the loss of one confinement dimension. Quantum wires sometimes behave as strings of quantum dots, and we propose an analysis to generally distinguish quantum-wire from quantum-dot behaviour.
TL;DR: This work uses electron counting to measure directly the quantum dot's tunnelling rate and the occupational probabilities of its charge state and provides evidence in favour of long (10 µs or more) inelastic scattering times in nearly isolated dots.
Abstract: Nanostructures in which strong (Coulomb) interactions exist between electrons are predicted to exhibit temporal electronic correlations1. Although there is ample experimental evidence that such correlations exist2, electron dynamics in engineered nanostructures have been observed directly only on long timescales3. The faster dynamics associated with electrical currents or charge fluctuations4 are usually inferred from direct (or quasi-direct) current measurements. Recently, interest in electron dynamics has risen, in part owing to the realization that additional information about electronic interactions can be found in the shot noise5 or higher statistical moments6,7 of a direct current. Furthermore, interest in quantum computation has stimulated investigation of quantum bit (qubit) readout techniques8,9, which for many condensed-matter systems ultimately reduces to single-shot measurements of individual electronic charges. Here we report real-time observation of individual electron tunnelling events in a quantum dot using an integrated radio-frequency single-electron transistor10,11. We use electron counting to measure directly the quantum dot's tunnelling rate and the occupational probabilities of its charge state. Our results provide evidence in favour of long (10 µs or more) inelastic scattering times in nearly isolated dots.
TL;DR: In this paper, a few-electron double quantum dot defined in a two-dimensional electron gas was realized by means of surface gates on top of a GaAs/AlGaAs heterostructure.
Abstract: We report on the realization of a few-electron double quantum dot defined in a two-dimensional electron gas by means of surface gates on top of a GaAs/AlGaAs heterostructure. Two quantum point contacts are placed in the vicinity of the double quantum dot and serve as charge detectors. These enable determination of the number of conduction electrons on each dot. This number can be reduced to zero, while still allowing transport measurements through the double dot. Microwave radiation is used to pump an electron from one dot to the other by absorption of a single photon. The experiments demonstrate that this quantum dot circuit can serve as a good starting point for a scalable spin-qubit system.
TL;DR: In this article, the authors investigated the radiative lifetime of electron-hole excitations in colloidal CdSe nanocrystal quantum dots over nearly three orders of magnitude in temperature (300 K to 380 mK).
Abstract: We investigate the strongly temperature-dependent radiative lifetime of electron–hole excitations in colloidal CdSe nanocrystal quantum dots over nearly three orders of magnitude in temperature (300 K to 380 mK). These studies reveal an intrinsic, radiative upper limit of ∼1 μs for the storage of excitons below 2 K. At higher temperatures, exciton lifetimes are consistent with thermal activation from the dark-exciton ground state, but with two different activation thresholds.
TL;DR: In this article, the photoluminescence of colloidal CdSe and (core)shell (CdSe)ZnS quantum dots has been observed when the dots are illuminated above the band-gap energy.
Abstract: Enhancement of the photoluminescence (PL) of colloidal CdSe and (core)shell (CdSe)ZnS quantum dots has been observed when the dots are illuminated above the band-gap energy. The effect occurs in dots suspended in a variety of organic or aqueous environments. During periods of constant illumination, the exciton PL quantum yield was found to reach a value of up to 60 times that of the solution of as-prepared quantum dots and, if illumination continued, subsequently declined slowly because of photooxidation. When returned to the dark, the PL reverted to near its original value. The rate and magnitude of photoenhancement are found to depend on the illumination wavelength, the presence of a ZnS shell, the solvent environment, and the concentration of surfactant molecules. Time-resolved measurements of the fluorescence decay reveal multiexponential kinetics and an average lifetime that lengthens during the illumination period and shortens when quantum dots are returned to darkness. It is postulated that the stabilization of surface trap states, lengthening their average lifetime, could occur by a light-activated rearrangement of surfactant molecules, thus increasing the probability of thermalization back to the lowest emitting exciton state and enhancing the quantum dot PL.
TL;DR: In this paper, the authors present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm.
Abstract: We present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm. In addition, our calculations show that the surface of nanodiamond particles larger than approximately 1 nm reconstructs in a fullerenelike manner, giving rise to a new family of carbon clusters: bucky diamonds. Signatures of these surface reconstructions are compatible with pre-edge features observed in measured absorption spectra.
TL;DR: Gly-His-Leu- leu- Leu-Cys coated CdS quantum dots detected Cu2+ and Ag+ selectively with high sensitivity, below 0.5 microM.
TL;DR: CdSe-ZnS core-shell quantum dots (QDs) act as photochemical centers for lighting up the dynamics of telomerization or DNA replication.
Abstract: CdSe−ZnS core−shell quantum dots (QDs) act as photochemical centers for lighting-up the dynamics of telomerization or DNA replication.
TL;DR: In this paper, a controlled synthesis of multiwalled carbon nanotube−quantum dot (CNT-QD) heterojunctions using the ethylene carbodiimide coupling procedure (EDC) was reported.
Abstract: We report the controlled synthesis of multiwalled carbon nanotube−quantum dot (CNT-QD) heterojunctions using the ethylene carbodiimide coupling procedure (EDC). Thiol-stabilized ZnS-capped CdSe quantum dots containing amine terminal groups (QD−NH2) were conjugated with acid-treated multiwalled carbon nanotubes (MWCNT) ranging from 400 nm to 4 μm in length. Scanning and transmission electron microscopy were used to characterize the conjugation process.