Ballistic electron emission spectroscopy is used to investigate current attenuations in thin films of Pd/Si, from which the elastic and inelastic mean free paths are uniquely determined. The observed equality of transmission across Pd/Si(100) and Si(l 11) interfaces is attributed to interface scattering, on the basis of which a current transport model is developed that gives unprecedented agreement with experiment over a wide energy range.PACS numbers: 72.15.Lh, 73.50.Gr Hot electron scattering processes affect a variety of transport issues in metals and metal films, from current transfer ratios in metal-base transistors to escape depths in photoelectron and Auger electron spectroscopies. A common problem has been the determination of the elastic (X e ) and inelastic (A,,-) mean free paths (MFP) of the electrons in the metal from measured attenuation lengths. The most successful approach uses internal photoemission, with which the attenuation length X a is determined from the metal-thickness dependence of the quantum yield in a metal-semiconductor photodiode [1]. A, , -can be estimated by modeling the process [2,3], which is complicated due to the dependence on photon energy of the energy distribution of the photoexcited carriers, whose spatial distribution is also dependent on the optical absorption in the film. A further shortcoming is the narrow kinetic energy (£kin) range, limited by the band gap of the semiconductor, over which X a can be measured. These experimental as well as modeling complications are readily overcome by using ballistic electron emission microscopy (BEEM) on thin metal films deposited on semiconductors [4]. In BEEM, which is based on the scanning tunneling microscope (STM), nearly monochromatic electrons with energies determined by the basis Vj between the metal film and STM tip are injected and may traverse the layer to reach the metal-semiconductor (M-S) interface. If the electrons have sufficient energy to overcome the Schottky barrier eVo, they may cross the interface to be detected as a collector current I c in the semiconductor. X a can be obtained from the exponential decay of I c with film thickness, as previously reported for Au films on Si for £"kin~ 1 eV [5], Here we report I c attenuation studies of thin Pd films (8-90 A) on Si(lll) and Si (100) surfaces over an is kin range to 6 eV. For thicknesses ^ 40 A the attenuation curves become decidedly nonexponential with a shape that depends on E\^m. This behavior results from the interplay of two different scattering processes and affords a novel opportunity to extract their relevant MFP's. We present a simple model that treats the transport process from injection to collection as a random walk problem. From model fits to the attenuation data we uniquely determine the energy dependent X e (E) and Xt(E) in the 1-6 eV energy range.In addition, the nearly identical BEEM spectra for Pd on SiC111) and Si(100) for thickness w

Monolayer islands of pentacene deposited on silicon substrates with thermally grown oxides were studied by electric force microscopy (EFM) and scanning Kelvin probe microscopy (SKPM) in ultrahigh vacuum (UHV) after prior 10 min exposure to atmospheric ambient. On 25-nm-thick oxides, the pentacene islands are 0.5 V higher in electrostatic potential than the silicon dioxide background because of intrinsic contact potential differences. On 2-nm-thin oxides, tunneling across the oxides allows Fermi level equilibration with pentacene associated states. The surface potential difference depends on the doping of the underlying Si substrates. The Fermi level movement at the pentacene SiO2 interface was restricted and estimated to lie between 0.3 and 0.6 eV above the pentacene valence band maximum. It is proposed that hole traps in the pentacene or at the pentacene−oxide interface are responsible for the observations.

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Smooth films of n-In1−xGaxAs and p-GaSb1−yAsy were grown by molecular beam epitaxy. As a function of the compositions, x and y, the lattice constants vary linearly while the energy gaps show a downward bowing. Abrupt heterojunctions made of these alloys with close lattice matching exhibit a series of current-voltage characteristics which change from rectifying to Ohmic as x and y are reduced. The relative location of the band-edge energies of the two semiconductors at the interface is shown to account for the unusual characteristics observed experimentally.