Electrical behavior of GaAs–AlAs heterostructures

We report an experimental study of the electrical behavior of GaAs–AlAs–GaAs heterostructures grown by metal–organic chemical vapor deposition. The structures consisted of a layer of AlAs several thousand angstroms thick sandwiched between layers of GaAs which were a few microns thick. The top layer of GaAs was doped degenerately n-type with Se, while the bottom layer was nondegenerately doped. Capacitance–voltage (C–V) and curent–voltage (I–V) curves were obtained as a function of temperature, illumination, and rate of data acquisition. Deep-level transient spectroscopy (DLTS) measurements were also made. The C–V showed hysteresis near zero bias with the capacitance being larger when the voltage was swept from reverse to forward bias in the dark. The C–V displayed a light sensitive peak near zero bias. With illumination, the capacitance was greater, and no hysteresis was observed. We explain these phenomena as being due to deep levels near the AlAs–GaAs interface; DLTS has confirmed this. I–V curves taken in darkness also showed hysteresis. We take this as further evidence of deep levels. Additionally, capacitance failed to level off in reverse bias, indicating a lack of inversion in the samples

The NASA Ames Research Center one- and two-dimensional stratospheric models. Part 2: The two-dimensional model

The two-dimensional model of stratospheric constituents is presented in detail. The derivation of pertinent transport parameters and the numerical solution of the species continuity equations, including a technique for treating the stiff differential equations that represent the chemical kinetic terms, and appropriate methods for simulating the diurnal variations of the solar zenith angle and species concentrations are discussed. Predicted distributions of tracer constituents (ozone, carbon 14, nitric acid) are compared with observed distributions

Non equilibrium thermodynamics and cosmological pancakes formation

We investigate the influence of non equilibrium thermodynamics on cosmological structure formation. In this paper, we consider the collapse of planar perturbations usually called "Zel'dovich pancakes". We have developed for that purpose a new two fluids (gas and dark matter) hydrodynamical code, with three different thermodynamical species: electrons, ions and neutral particles (T_e\ne T_i \ne T_n). We describe in details the complex structure of accretion shock waves. We include several relevant processes for a low density, high temperature, collisional plasma such as non-equilibrium chemical reactions, cooling, shock heating, thermal energy equipartition between electrons, ions and neutral particles and electronic conduction. We find two different regions in the pancake structure: a thermal precursor ahead of the compression front and an equipartition wave after the compression front where electrons and ions temperatures differ significantly. This complex structure may have two interesting consequences: pre-heating of unshocked regions in the vicinity of massive X-ray clusters and ions and electrons temperatures differences in the outer regions of X-rays clusters.Comment: 30 pages, including 8 figures, accepted for publication in The Astrophysical Journa

Surfactant-aided exfoliation of molydenum disulphide for ultrafast pulse generation through edge-state saturable absorption

We use liquid phase exfoliation to produce dispersions of molybdenum disulphide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical structures of the bile salt surfactants play a crucial role in the exfoliation and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched in single and few (<6) layer flakes with large edge to surface area ratio. We use the dispersions to fabricate free-standing polymer composite wide-band saturable absorbers to develop mode-locked and Q- switched fibre lasers, tunable from 1535-1565 and 1030-1070 nm, respectively. We attribute this sub-bandgap optical absorption and its nonlinear saturation behaviour to edge-mediated states introduced within the material band-gap of the exfoliated MoS2 nanoflakes.Comment: 6 pages, 5 figure

The ConStratO model of handover: a tool to support technology design and evaluation

Handovers are a specific kind of multidisciplinary team meeting. Shift handovers and transfers are both regular features of hospital work but there is currently great variation in how such handovers are conducted, presenting a challenging for those seeking to develop technology to support handover. This paper presents the ConStratO model of handover, which captures aspects of the context that influence how the handover is conducted, a range of different handover strategies relating to different aspects of the handover, and possible outcomes of handover. The model is based on detailed data collection in a range of clinical settings. We present the model as a tool for developing and evaluating technology support for handover