Yttria (Y2 O3 ) films have been grown on Si (100) and Si (111) substrates heated at 800 °C by vacuum evaporation. X-ray diffraction and reflection high-energy electron diffraction observations reveal the heteroepitaxial growth of Y2 O3 films on Si (100) and Si (111) substrates. The (111) oriented Y2 O3 films are grown directly on Si (111) substrates. The (100) oriented Y2 O3 films are grown on the thin (Y2 O3 )0.09 (ZrO2 )0.91 layer predeposited on Si (100) substrates instead of direct growth on Si (100) substrates.
We extend the treatment of Feynman for the polaron problem at OOK to the case at a finite temperature. A variational principle is applied to the free energy of polaron state. § 1. Introduction A slow electron in a polar crystal interacts strongly with the longitudinal optical modes of lattice vibrations, and behaves itself as a quasi-particle which is the so-called "polaron". The properties of a pola.ron have been investigated by various authors, but do not yet seem to be made perfectly clear. Of all problems concerning a polaron, its self-energy and mobility are fundamentally important.To compute the self-energy of polaron, Feynman'sl) method seems to be most excellent, as it was shown by Shultz 2 ) that Feynman's method gives lower selfenergy than any other methods which have been ever published. In the present paper we shall reform the F eynman' s treatment so as to be applicable to the case of finite temperatures, that is, Feynman's variational principle of the self-energy of polaron is replaced by the variation of the free energy. Numerical calculation is carried out for a certain value of coupling constant and its result is compared with that obtained by Fulton fi ) and by Yokota. 6) § 2. Static property of polaron state a1l; finite temperaturesIn this paper our units are chosen just as electron mass, Planck constant and optical phonon energy are unities. We shall consider the density matrix of the system which consists of one electron and longitudinal lattice vibrations, and average the part of the lattice vibrations by path-integral method. Such a calculation IS made by Abe S ) and the action of the polaron at finite temperatures is given by (1) where (d = 1/ k T and a is the coupling constant between an electron and lattice at
ZnS films were grown on Si (100) at high temperatures by pulsed laser deposition using a KrF excimer laser. The growth temperature was varied from 200 to 700 °C and all films were found to have a specific preferential orientation. With increasing Ts, growth rate decreased but the quality of the film improved. The highest quality ZnS film was obtained at 700 °C. The presence of ZnS+ ions among the ablation products of a ZnS target was verified by laser desorption time of flight mass spectroscopy measurements. ZnO was formed by thermal oxidation of ZnS and the films showed strong near band-edge emission at 3.26 eV.
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