Oxide structure in evaporated aluminum films

Abstract

Transmission electron microscopy, small-angle and selected-area diffraction, and surface-plasmon dispersion studies are used to characterize the microstructure of evaporated aluminum films. The grain size of the films is obtained from the width of the Bragg reflections. Energy-loss studies show that the surface-plasmon dispersion is a function of the average grain size for films grown at low condensation rates, i.e., ``dirty'' films, while the average surface-plasmon energy for all films, ``clean'' and ``dirty'', is close to 6.7 eV, the value characteristic of an aluminum-aluminum oxide interface. In clean films the dispersion depends on thickness in the normal fashion and no dependence on grain size is detected. We conclude that in dirty films a thin layer of oxide surrounds each grain. Small-angle electron scattering and out-of-focus transmission electron microscopy identify a cluster effect in which somewhat larger oxide boundaries surround clusters of approximately 36 grains (in most films). A similar structure is shown to develop at a stage in the growth of gold films.