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[en] A phenomenological investigation of the dc Josephson current in superconductor endash (S-) normal-metal endash (N) [semiconductor endash (Sm-)] superconductor junctions is carried out as a function of the carrier concentration in the barrier. The occurrence of a nonmonotonic dependence of the Josephson current on the carrier concentration is predicted within some limits. This study suggests that in S-N- (Sm-) S structures there is an optimum carrier concentration range which gives the maximum value of the Josephson current IC and the junction parameter ICRN. copyright 1997 The American Physical Society
[en] We study charge transport in a monolayer MoS2 nanoflake over a wide range of carrier density, temperature and electric bias. We find that the transport is best described by a percolating picture in which the disorder breaks translational invariance, breaking the system up into a series of puddles, rather than previous pictures in which the disorder is treated as homogeneous and uniform. Our work provides insight to a unified picture of charge transport in monolayer MoS2 nanoflakes and contributes to the development of next-generation MoS2-based devices. (paper)
[en] High precision electron probe microanalysis (EPMA) has been used to measure the correlation of oxygen deficiency with carrier concentration in thin films of amorphous indium oxide. This has shown that there are ten times as many oxygen vacancies as would be expected from the carrier concentration measurements, giving a doping efficiency of 0.1. It is therefore clear that the doping mechanism is more complex than the usual picture of every oxygen vacancy producing two free electrons
[en] Under the auspices of this funding, we have developed a program to synthesize and characterize highly monodispersed magnetic nanoparticles. We have been particularly interested in the origin of the exchange bias effect, which occurs in compound nanoparticles with a ferromagnetic core and an antiferromagnetic shell, and have mostly focused on Co/CoO core-shell nanoparticles. The exchange bias effect involves exchange coupling between the core moment and the antiferromagnetic shell which stabilizes the core moment, which would otherwise be quickly reorienting in ferromagnetic particles of this size.
[en] Two-photon absorption (TPA) testing is employed to analyze the laser-induced latchup sensitive-volume (SV) of a specially designed test structure. This method takes into account the existence of an onset region in which the probability of triggering latchup transitions from zero to one as the laser pulse energy increases. This variability is attributed to pulse-to-pulse variability, uncertainty in measurement of the pulse energy, and variation in local carrier density and temperature. For each spatial position, the latchup probability associated with a given energy is calculated from multiple pulses. The latchup probability data are well-described by a Weibull distribution. The results show that the area between p-n-p-n cell structures is more sensitive than the p+ and n+ source areas, and locations far from the well contacts are more sensitive than those near the contact region. The transition from low probability of latchup to high probability is more abrupt near the source contacts than it is for the surrounding areas.
[en] Optical gain spectra are computed for quantum dots under high excitation conditions, where there is a non-negligible two-dimensional carrier density surrounding the dots. Using a screened Hartree-Fock theory to describe the influence of the Coulomb interaction, we find different self-energy shifts for the dot and quantum-well transitions. Furthermore, in contrast to the result for quantum-well and bulk systems, the peak gain at the quantum-dot transition computed including Coulomb effects is reduced from its free carrier value
[en] We have synthesized K0.95(1)Ni1.86(2)Se2 single crystals. The single crystals contain K and Ni deficiencies not observed in KNi2Se2 polycrystals. Unlike KNi2Se2 polycrystals, the superconductivity is absent in single crystals. The detailed physical property study indicates that the K0.95Ni1.86Se2 single crystals exhibit heavy-fermion-like characteristics. The transition to a heavy fermion state below T ∼ 30 K results in an enhancement of the electron-like carrier density whereas the magnetic susceptibility shows little anisotropy and suggests the presence of both itinerant and localized Ni orbitals. (paper)
[en] We study two dimensional electron-hole system in quasi-equilibrium. By using the self-consistent screened T matrix approximation, we present density dependence of ionization ratio. We also discuss the photoluminescence spectra, which are compared with experiment over the wide carrier density range
[en] The measurement of relaxation time of carriers injected outside of the equilibrium in CdSe films, using excitation and test technique is presented. An increasing of the relaxation time (100 to 1500 femto seconds) with photo-excited carrier concentration was observed. (M.C.K.)