Two-subband electron transport in nonideal quantum wells

Electron transport in nonideal quantum wells (QW) with large-scale variations of energy levels is studied when two subbands are occupied. Although the mean fluctuations of these two levels are screened by the in-plane redistribution of electrons, the energies of both levels remain nonuniform over the plane. The effect of random inhomogeneities on the classical transport is studied within the framework of a local response approach for weak disorder. Both short-range and small-angle scattering mechanisms are considered. Magnetotransport characteristics and the modulation of the effective conductivity by transverse voltage are evaluated for different kinds of confinement potentials (hard wall QW, parabolic QW, and stepped QW).Comment: 10 pages, 6 figure

Magnetophonons in short-period superlattices

We report the observation of magnetophonon resonances on the background of the longitudinal magneto-conductance in short-period GaAs/AlAs semiconductor superlattices. Both the GaAs and the AlAs longitudinal optical phonons are observed. We show how the enhancement of the magnetophonon effect with electric field is connected to the shift of the electron distribution towards the high-velocity and low-density-of-states region at the midpoint of the reduced Brillouin zone. The observed temperature dependence can be explained by considering the competition between the phonon population and the electron lifetime. The two superposed series of the GaAs and the AlAs optical phonons are shifted when hydrostatic pressure is applied and the relative strength of each series changes as the Gamma miniband comes closer to the X states.status: publishe

Analysis of biodiesel and frying vegetable oils by means of FTIR photoacoustic spectroscopy

Fourier Transform Infrared Photoacoustic Spectroscopy was used to determine the mid-infrared vibrational modes of biodiesel and vegetable oils. Our results indicate that this method can contribute significantly to the biodiesel wash process during the sample preparation. Besides, by analyzing the spectra of vegetable oils used to fry snacks we could to monitor the degradation in function of the fried time