Atoms and molecules at a solid surface.

Some aspects of the interaction of gas-atoms and solid-surfaces are presented. By using simple mathematical models, an intuitive understanding of the interaction between atoms and surfaces has been achieved. By a logical extension of such techniques, it is shown how a general theory for the desorption of atoms from surfaces may be formulated. Potential parameters for the gas-surface interaction are deduced for a number of experimental systems using the published data for the surface residence times of adsorbed atoms. The growth of thin semiconducting films by Molecular Beam Epitaxy is described and the results of kinetic studies for the interaction of Ga and As4 beams with a GaAs (100) surface are discussed. By adopting some of the previously developed atomistic concepts, a microscopic model is proposed which explains some of the fundamental aspects of the growth mechanism employed by this method. As part of the kinetic study of Molecular Beam Epitaxy, the time-of-flight technique for measuring the velocity distribution of a beam was used. This method has been studied experimentally and detailed results are presented for As4 and Pb neutral beams. It is shown that when a quadrupole mass spectrometer with a cross beam ionizer is employed as a detector, serious errors arise from inherent time delays, which are observed to be strong functions of several operating parameters. The consequence of this instrument malfunction is discussed with particular reference to the measurement of energy accommodation coefficients.