Imaging subsurface reflection phase with quantized electrons

Lead quantum wells (QW) epitaxially grown on annealed Pb/Si(111) interface form a model system for the study of interactions between quantized electrons and adiabatically modulated boundaries. Tunnel spectra of this system reveal a previously unknown adiabatic shift of QW resonances due to lateral variations of the electronic reflection phase at the buried interface. With this effect, lateral distribution of the subsurface reflection phase can be probed, using scanning tunneling microscopy

Ballistic electron emission microscopy for nonepitaxial metal/semiconductor interfaces

We present a model of ballistic electron emission microscopy (BEEM) that includes elastic scattering at nonepitaxial metal/semiconductor interfaces. In the weak scattering limit, the model reduces to the traditional description of BEEM. In the strong scattering limit, the model quantitatively describes (1) the relative magnitudes of BEEM currents into the Γ, L, and X channels for Au/GaAs(100); (2) the relative magnitudes of the currents for Au/Si(100) and -(111); (3) the relative magnitudes of currents for Au/GaAs and Au/Si; and (4) the absolute magnitudes of the currents for these materials

Monte Carlo simulations of ballistic-electron-emission-microscopy imaging and spectroscopy of buried mesoscopic structures

Monte Carlo simulations of the transport of electrons injected into the Γ valley of GaAs are performed for ballistic-electron-emission-microscopy (BEEM) imaging and spatially resolved spectroscopy of model quantum dots and quantum wires buried beneath the Au-GaAs interface. To determine the spatial resolution and the energy resolution of BEEM for such buried mesoscopic structures, the current fluxes and the electron normal wave vector distributions are obtained as a function of the depth from the Au-GaAs interface. The BEEM current cross sections and the spatially resolved BEEM spectra on and off these structures are calculated in order to study their dependence on the depth and the scanning-tunneling microscope tip-to-sample bias

The thermal conductivity of Indian timbers. Part I. Variation of conductivity with density in the air-dry condition at ordinary temperature

Accurate data on the thermal conductivity of 56 species of Indian timbers, varying in density from 265 Kg./m.3 to 1310 Kg./m.3 in the air-dry condition at about 20°C., are reported. The data represent the first set of results covering this entire range of density reported from a single laboratory. The influence of convection and radiation on the conductivity of wood is discussed and the results compared with those of other investigators

Hall carrier density and magnetoresistance measurements in thin film vanadium dioxide across the metal-insulator transition

Temperature dependent magneto-transport measurements in magnetic fields of up to 12 Tesla were performed on thin film vanadium dioxide (VO2) across the metal-insulator transition (MIT). The Hall carrier density increases by 4 orders of magnitude at the MIT and accounts almost entirely for the resistance change. The Hall mobility varies little across the MIT and remains low, ~0.1cm2/V sec. Electrons are found to be the major carriers on both sides of the MIT. Small positive magnetoresistance in the semiconducting phase is measured

Diffusion of ions through some Indian timbers

A simple diffusion cell (which can be easily constructed from perspex sheeting) for studying the passage of molecules, ions, gases, vapours and liquids through wood and other membranes is described. The diffusion of ions through some species of Indian timbers under variety of conditions has been studied and the results reported. The results show that the diffusion of ions through wood obeys Fick's law as long as the ion does not react with any constituents of the wood. In other cases there is deviation from this law. The diffusion constant is largest in the axial direction and smallest in the tangential direction. As against other claims, for the species tested, ionic diffusion is higher through sapwood than through heartwood. Temperature increases the rate of diffusion of ions. Diffusion of copper sulphate through cellophane is in conformity with Fick's law and is of the same order as for some timbers

Anisotropic Metal-Insulator Transition in Epitaxial Thin Films

Quantum wells made of simple polyvalent metals represent a novel family of doped 2D Mott-Hubbard insulators. As scanning tunneling microscopy experiments show, these systems exhibit an anisotropic form of metal-insulator transition. Their elementary excitations possess coherent wave-like properties along the normal axis, and show an incoherent behavior in-plane. The development of such an anisotropic coherence is most likely related to Coulomb interaction between localized and delocalized thin film electronic states - 2D Kondo screening.Comment: 4 figures, submitted to PR

Squeezed Phonon States: Modulating Quantum Fluctuations of Atomic Displacements

We study squeezed quantum states of phonons, which allow the possibility of modulating the quantum fluctuations of atomic displacements below the zero-point quantum noise level of coherent phonon states. We calculate the corresponding expectation values and fluctuations of both the atomic displacement and the lattice amplitude operators, and also investigate the possibility of generating squeezed phonon states using a three-phonon parametric amplification process based on phonon-phonon interactions. Furthermore, we also propose a detection scheme based on reflectivity measurements.Comment: 4 pages, RevTeX. The previous entry had a wrong page number in the Journal-ref fiel

Thermoelectric effects in submicron heterostructure barriers

Nonisothermal electron transport in thin barrier heterostructures is investigated using Monte Carlo techniques. Particular attention is paid to the energy balance in thermionic emission, and the Joule heating in the barrier region. By introducing an energy relaxation length, an equation for the temperature distribution inside the device is derived. Conditions for creating a steady-state temperature gradient and for integrated cooling of electronic components are examined