Joel I. Gersten

ELS studies of quantized accumulation layers on ZnO surfaces

Abstract Electron energy loss spectroscopy studies of clean ZnO surfaces under extreme accumulation layer conditions are presented. The experimental results are analyzed in terms of excitations due to coupled surface phonons and two-dimensional surface plasmons. The fair agreement between the experiment and theory strongly suggests that part of the losses are due to two-dimensional surface plasmons.

Theory of surface plasmarons: II. The effect of a finite thickness of the accumulation layer

Abstract In the presence of an accumulation layer of finite thickness the surface phonons, bulk phonons, and two-dimensional plasmons couple together to form a three-branched surface plasmaron spectrum. Dispersion curves and coupling constants for these plasmarons are evaluated. In the limit of thin accumulation layers one of the modes decouples and a two-mode spectrum emerges. These two modes are admixtures of surface phonons and two-dimensional plasmons.

Two-dimensional plasma oscillation on ZnO surfaces

Abstract Angle resolved, low energy electron spectroscopy is used to study collective excitations on accumulaton layers on ZnO. As the electron density in the accumulation layer is increased a prominent loss peak is observed which, at specular reflection angles, shifts from ~ 67 meV in the absence of surface electrons to ~320 meV in strong accumulation layers. This behavior is well accounted for theoretically in terms of scattering by two-dimensional plasmon-like collective surface excitations. A shift in energy of the loss peak position as a function of δθ, the deviation angle from specular reflection, was also measured.

PARAMAGNETIC PROPERTIES OF THE SR OVERDOPED (LA,SR)2CUO4 SYSTEM

Abstract The magnetic behavior of the non-superconducting Sr overdoped La 2− x Sr x CuO 4 x > 0.25 system was studied by Mossbauer spectroscopy (MS) and ESR studies on 0.3% 57 Fe doped materials. Both experimental techniques indicate clearly that in the metallic state, the CuO 2 planes are paramagnetic. The MS spectra are a superposition of two sub-spectra corresponding to inequivalent Fe sites. At 4.1 K, the complicated spectra are interpreted as due to local paramagnetic fluctuations of dilutte e, with slow relaxation rates. The ESR spectra are composed of two lines. The centroid of the most intense resonance line is independent of temperature and corresponds to well isolated paramagnetic Fe ions. Thus competition between SC and AFM exists only in the region of low x .

Magnetic properties of (Y,Er)Ba2Co3O8

The (Y,Er)Ba2Co3O8 compounds crystallize in a cubic perovskite-type (a=4.134A°) structure. DC magnetic susceptibility and Mossbauer-spectroscopy (MS) on57Fe doped materials, show that the Co sublattice does not order magnetically down to 1.5 K. MS reveal two inequivalent Co sites. Specific-heat and susceptibility studies show that Er in ErBa2Co3O8 orders magnetically at 3.2 K. The Cp(T) at H=0 T curves indicate a significant high electronic linear term of γ≈200 mJ/mol K2.

A solid‐state solar‐powered heat transfer device

A solar‐powered solid‐state heat transfer device capable of operating in either a refrigeration or a heat‐pump mode is proposed. The device’s operation is based on the combined utilization of the photovoltaic and Peltier effects.