S.G. Davison

Green function theory of chemisorption on sp-hybrid crystals

Abstract A self-consistent Green function calculation of the adatom charge transfer (Δ q ) and the chemisorption energy (Δ E ) is performed for hydrogen and the halogens on Si and Ge substrates, which are modeled by sp-hybrid orbital chains. The effect of Shockley surface states on the hydrogen chemisorption process is studied in some detail. From the chemisorption point of view, the behaviour of Si resembles that of Ge, the (111) surfaces having a smaller value of |Δ E | than the (100) ones for all the adsorbates considered. In the case of the halogens, the strong reactivity of fluorine is confirmed by the large values obtained for Δ q and |Δ F |.

Surface field effects on Tamm states

Abstract A detailed investigation has been made of the influence of applied linear surface fields on the surface states of δ-barrier and δ-well crystals. It is found that the applied fields can shift the surface state energy levels and enhance or hinder their existence. The paper concludes by correcting some earlier results of Phariseaus.

Methodology for ion neutralization at solid/electrolyte interfaces

Abstract When ion scattering from a solid/electrolyte is studied, the complexity of the system mandates the use of simple models. To this end, the two-level approach is adopted to investigate the surface ion neutralization process in a binary-collision model of ion scattering from a solid surface. A refined version of this model is obtained, by introducing the surface density of states, which enables substrate effects to be incorporated in a straightforward manner. The difficulties encountered at solid/electrolyte interfaces, as they pertain to the theoretical treatment of surface ion neutralization, are discussed in detail.

Chemisorption on supported-metal catalysts

A Gree-function formalism is developed to describe the electronic and chemisorption properties of a supported-metal composite substrate. Within the framework of the tight-binding approximation, the metal catalyst is represented by a finite chain of d-orbitals, while the semi-infinite semiconductor support is characterized by a linear chain of alternating s- and p-orbitals. The Anderson-Newns model is used to calculate the chemisorption energy and adatom charge transfer for hydrogen chemisorption on the Ni/ZnO composite system.

Electron-optical-phonon interaction in a trilayer system of polar crystals

Abstract The long-wavelength optical vibration in a trilayer system of polar crystals is studied by using a continuum model. The optical polarization modes of the lattice vibration and the Hamiltonian of the interaction between an electron and the optical phonons are derived. It is found that there are six branches of interface optical modes in a trilayer system. The numerical results for several practical systems are given. The dispersion relations, eigenvectors of the polarization modes and the electron-phonon coupling functions are discussed. The results indicate that some surprising experimental phenomena are expected.

Two-channel surface ion neutralization

Abstract A previously described many-electron treatment of charge transfer in surface-ion scattering is extended to the case where there are two neutralization channels. Experiments have shown that in some cases an ion can be neutralized either as a ground-state or as an excited-state atom; a specific example is Li+ ions scattered from cesiated tungsten. This system is investigated and the relative proportions of the various products are calculated as functions of ion kinetic energy and surface work function. Additionally, the effect of ion neutralization on the excitation spectrum of the solid is examined.

Rosen-Zener approximation in surface-ion scattering theory

Abstract The Rosen-Zener formula, for transition probabilities in the atomic two-level problem, is used to develop a many-level treatment of the surface-ion-neutralization probability.

Applied-field effects on molecular switches

Electron transmission through an electrified composite metal-doped polymer-metal system is investigated by means of the Lippmann-Schwinger equation. The electric field, applied via the metal leads, acts across the polymer chain containing the single-impurity atom, which behaves as a molecular switch. The Stark-ladder effect in the doped polymer is described by utilizing the recursive-Green-function (RGF) approach, where repeated use of the Dyson equation gives rise to a continued-fraction form of the RGF, which can be expressed analytically as a ratio of Bessel functions. Molecular switch control of the transmission is achieved by adjusting the parameters characterizing the impurity. The influence of the applied field on the transmission process is discussed.

Recursive Green-function study of Wannier - Stark effect in tight-binding systems

The Wannier - Stark effect in electrified tight-binding systems is investigated, via the recursive Green-function technique, which involves repeated use of the Dyson equation. Green functions for finite, semi-infinite and infinite systems are generated in the site representation in the form of continued fractions, which are then expressed analytically as ratios of Bessel functions. The local densities of states at the surface and in the bulk are presented and their dependence on the applied field discussed.

Role of surface states in ion scattering

Abstract The effect of localized surface states on the process of charge transfer between ions and solid surfaces has been examined theoretically. Calculated results reproduce in a qualitative manner the experimentally-observed oscillation in the ion occupancy as a function of ion kinetic energy, and show that surface states play a potentially dominant role in surface-ion scattering.