174 research outputs found
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
Quantum Phonon Optics: Coherent and Squeezed Atomic Displacements
In this paper we investigate coherent and squeezed quantum states of phonons.
The latter allow the possibility of modulating the quantum fluctuations of
atomic displacements below the zero-point quantum noise level of coherent
states. The expectation values and quantum fluctuations of both the atomic
displacement and the lattice amplitude operators are calculated in these
states---in some cases analytically. We also study the possibility of squeezing
quantum noise in the atomic displacement using a polariton-based approach.Comment: 6 pages, RevTe
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