Table of contents

It is suggested that electrons in the inversion layer at an Si-SiO₂ interface can behave like electrons in a two-dimensional disordered system. The conduction band will then have a tail of localized states and an associated mobility edge. It is shown that the wavefunctions of localized states near the edge (at energy E_c) will have a spatial extent which behaves as mod E-E_c mod ^-34/.

The structure of the 2p F^- valence band in LiF, as determined by high-resolution X-ray-induced photoelectron spectroscopy, is shown to be in good agreement with, though rather broader than, that calculated on the basis of the Hartree-Fock equation.

The one-band density of states for the Polk model for amorphous semiconductors is found by direct diagonalization for a 201-atom structure and some smaller structures. It is seen that the density of states has a definite two-peaked character. Implications for the lower half of the valence band and the middle portion of the vibrational density of states in amorphous silicon and germanium are discussed.

A functional form for the spontaneous order M₀ of the eight-vertex model is conjectured from an investigation of the structure of a low-temperature expansion of M₀. The precise expression then follows from the known result for the Ising case. The exponent beta is then obtained and three-exponent scaling used to predict the remaining exponents of the eight-vertex model from the known exponents.

The planar and spatial lattice versions of the Maier-Saupe model (1959, 1960) for a nematic liquid crystal are exactly solved for a one-dimensional lattice, without periodic boundary conditions. The two-molecule correlation functions are studied, and it is shown that these two models do not exhibit an order-disorder phase transition except at T=0, as is the case for the classical Heisenberg model in one dimension.

The dispersion relation for the normal modes of vibration in CsF at 295 K has been determined from neutron coherent inelastic scattering data obtained on the triple axis crystal spectrometer at the Saphir reactor, Wurenlingen. With an improved resolution of the spectrometer, the slopes of the acoustic branches near q=0 have been investigated at 85 K and 295 K to determine the velocities of sound and the elastic constants. The phonon frequencies are well fitted by a seven-parameter shell model involving nearest-neighbour interactions, a varying ionic charge, and the polarizabilities of both ions. The model was used to compute various physical properties of CsF to compare with other experiments.

The phonon dispersion relations of silicon and diamond have been calculated on the basis of the Clark-Gazis-Wallis type angular force model. A four parameter model has been found to give good agreement between the theoretical and experimental data.

A theoretical basis is given for the empirical relationship that has recently been found between the reduced thermal conductivity and reduced temperature in dielectric crystals. It is shown that knowledge of this relationship for a given material gives the temperature dependence of the net phonon relaxation time in the region of the conductivity maximum. It is suggested that deviations from the theoretical relationship can be largely explained in terms of the detailed phonon scattering mechanisms.

The valence and conduction electron energy bands of polyethylene are calculated. The deduced density of electron states is in good overall agreement with the recent photoelectron spectroscopy results of Wood et al. (1972). The method, based on the work of Chaney et al. (1972), avoids the introduction of physically ill-defined parameters characteristic of semi-empirical techniques, and the excessive computer time requirement of ab initio calculations.

The contribution to the Hall and drift mobility from the polar scattering by optical modes of p-type semiconductors for low electric fields is investigated including the essential effect of light to heavy hole band mobility and the Hall coefficient factor substantially whereas it hardly influences the heavy hole mobility. Polar scattering by optical modes is considered only. The importance of these effects in any real situation depends on the relative strength of the other scattering processes and this is discussed in several particular cases in a forthcoming paper.

For pt. I see ibid., vol. 6, 2967 (1973). The temperature dependence of the Hall and drift mobility of p-type ZnTe, CdTe, and ZnSe is investigated accounting for acoustic and optical deformation potential, piezoelectric, and polar optical scattering. In the case of p-ZnSe the mobility data published previously cannot be explained by these scattering mechanisms. For p-ZnTe and p-CdTe the calculated mobility is in good accord with experimental results below room temperature. Acoustic deformation potential and polar optical scattering are found to be the dominant scattering mechanisms in the temperature range considered here. The mobility of p-CdTe is calculated by treating the polaron heavy hole mass as adjustable. The value finally used is 0.8m₀.

An average nuclear effective charge, deduced from atomic experimental data, is introduced to describe the electronic properties of the tetrahedrally coordinated semiconductors. Ionization potentials, energy gaps, dielectric constants, cohesive energies and heats of formation can then be calculated, for all the A^IIIB^V and A^IIB^IVC₂^V compounds, with an overall accuracy of the order of 7%.

Point-ion calculations with ion-size corrections of the electronic structure of the F centre in MgF₂ predict a transition energy close to the experimental value of 4.8 eV. The hyperfine interactions with the first six shells of fluoride ions are well represented by the variational wavefunction orthogonalized to orthonormal core orbitals.

The magnetic excitations of cobalt fluoride have been studied both theoretically and experimentally. The theory of the magnetic excitations at low temperatures has been developed with the aid of the pseudo-boson technique in terms of the crystal field and spin-orbit parameters of the individual ions and of the exchange interactions between neighbouring ions. The model with surprisingly simple forms of exchange interaction gives a very good description of many of the experimental results. Measurements of the longitudinal spin correlations near the Neel temperature have been made with slow neutron inelastic scattering techniques. The results show that the longitudinal spin correlations have a small frequency width; the width at half maximum of the quasi-elastic peak is, at all temperatures and wavevectors, less than 0.12 THz.