Potential well

About: Potential well is a research topic. Over the lifetime, 1430 publications have been published within this topic receiving 30812 citations.

Photoluminescence properties of highly dispersed ZnO quantum dots in polyvinylpyrrolidone nanotubes prepared by a single capillary electrospinning

Abstract: Highly dispersed ZnO quantum dots (QDs) in polyvinylpyrrolidone (PVP) nanotubes have been prepared by a single capillary electrospinning. The structure and optical properties characterizations were performed by x-ray diffraction, scanning and transmission electron microscopy, absorption, photoluminescence, and resonant Raman spectra. In the composites, PVP molecules passivate the surface defects of ZnO QDs and prevent the aggregations of ZnO QDs. As a result, the composites exhibit narrower band edge emissions and less laser thermal effects. Blueshifted band gap, enlarged exciton energy, and less exciton-longitudinal optical (LO) phonon interaction due to the quantum confinement effect have also been observed.

Semiclassical description of a two-dimensional electron in a strong magnetic field and an external potential.

Abstract: We study the effects of tunneling between the classical trajectories of a two-dimensional electron in a strong magnetic field and a slowly varying external potential on the quantum energy levels of the electron and on the phonon-induced hopping rate of localized states. The tunneling is important when the classical orbits pass within a few magnetic lengths of a saddle point of the potential. We discuss first the case of a double-well potential with a single saddle point. For energies well below the potential energy at the saddle point, the spectrum is of the form one expects for two wells very distant from one another. For energies well above the energy at the saddle point, the spectrum is similar to that of a single-well potential. The spectrum evolves smoothly from the former to the latter in the energy interval between these two limits. In addition, we study the spectrum for orbits coupled at two saddle points, and show that our technique can be applied to any number of orbits coupled at any number of saddle points. The method may be used to find the energy spectrum of an electron in a slowly varying random potential. We also calculate the tunnel splitting of states of a symmetric double well, and the phonon-induced hopping rate between localized states of an asymmetric double well. In both cases, we find that these quantities fall off as Gaussians in the distance of closest approach of the classical trajectories to the saddle point.

Nanophotonic devices based on quantum systems embedded in frequency bandgap media

Abstract: The present invention describes nanophotonic materials and devices for both classical and quantum optical signal processing, transmission, amplification, and generation of light, which are based on a set of quantum systems having a discrete energy levels, such as atoms, molecules, or quantum dots, embedded in a frequency bandgap medium, such as artificial photonic crystals (photonic bandgap materials) or natural frequency dispersive media, such as ionic crystals, molecular crystals, or semiconductors, exhibiting a frequency (photonic) bandgap for propagating electromagnetic modes coupled to optical transitions in the quantum systems. If the frequency of one of optical transitions, called the working transition, lies inside the frequency bandgap of the medium, then spontaneous decay of the working transition into propagating photon modes is completely suppressed. Moreover, the excitation of the working transition and a photon form a photon-quantum system bound state lying inside the photonic bandgap of the medium, in which radiation is localized in the vicinity of the quantum system. In a quantum system “wire” or a quantum system “waveguide”, made of spatially disordered quantum systems, or in a chain quantum system waveguide made of a periodically ordered identical quantum systems, wave functions of the photon-quantum system bound states localized on different quantum systems overlap each other and develop a photonic passband lying inside bandgap of the photonic bandgap medium. Photons with frequencies lying inside the photonic passband propagate along the quantum system waveguide. Since the working transition cannot be excited twice, the passband photons interact with each other extremely strongly both in one waveguide and in different waveguides that are located sufficiently close to each other. These unique nonlinear properties of the quantum system waveguides are proposed to use for engineering key nanophotonic devices, such as all-optical and electro-optical switches, modulators, transistors, control-NOT logic gates, nonlinear directional couplers, electro-optical modulators and converters, generators of entangled photon states, passband optical amplifiers and lasers, as well as all-optical integrated circuits for both classical and quantum optical signal processing, including quantum computing.

Disorder and suppression of quantum confinement effects in Pd nanoparticles.

Abstract: Size-selectable ligand-passivated crystalline and amorphous Pd nanoparticles ( < 4 nm) are synthesized by a novel two-phase process and verified by high-resolution transmission electron microscopy. Scanning tunneling spectroscopy preformed at 5 K on these two types of nanoparticles exhibits clear Coulomb blockade and Coulomb staircases. Size dependent multipeak spectral features in the differential conductance curve are observed for the crystalline Pd particles but not for the amorphous particles. Theoretical analysis shows that these spectral features are related to the quantized electronic states in the crystalline Pd particle. The suppression of the quantum confinement effect in the amorphous particle arises from the reduction of the degeneracy of the eigenstates and the level broadening due to the reduced lifetime of the electronic states.

Facile microwave approach to controllable boron nitride quantum dots

Abstract: Boron nitride quantum dots (BNQDs), as promising metal-free quantum dots with unique photoelectric properties, have been controllably fabricated by a facile and high-efficiency microwave irradiation technique in this work. Though a number of attempts have been reported so far, it remains challenging to explore an effective approach to synthesize high-quality BNQDs with uniform size, well dispersion and high quantum yield (QY). Microwave irradiation strategy is identified as an advanced and beneficial method not only for high-efficiency energy inputting but also time-saving in comparison with the reported solvothermal process. Encouragingly, the particle size and QY of BNQDs can be well controlled by adjusting microwave reaction temperature as well as duration time. The average diameter of the as-prepared blue luminescent BNQDs ranges from 1.98 to 7.05 nm with QY up to 23.44%. Furthermore, attributed to the unique nanostructure, quantum confinement effect, and high dielectric loss, the as-prepared BNQDs exhibits an optimal reflection loss of −19.6 dB at 8.9 GHz with a broad effective absorption bandwidth of 5.02 GHz in the frequency range of 2–18 GHz, demonstrating as potential microwave absorption material in electromagnetic interference field.