The nucleation, growth, structure and epitaxy of thin surface films

Abstract A review is given of the evidence available on the mechanism of growth and the structure of thin deposited films. The main attention is devoted to the growth of metals onto single crystal substrates, particularly those formed by the evaporation technique. Some consideration of other types of deposit is also given, including chemically formed films and epitaxial silicon layers. A survey of the various experimental techniques which can be used for structural studies on thin films is given, but the main evidence presented is based upon electron diffraction and transmission electron microscopy. The mode of nucleation of the layers is described, and the evidence for the way in which the nuclei develop into a continuous deposit film is outlined. This includes the evidence obtained from growing films inside the electron microscope, which reveals two important processes. These are the ‘liquid-like’ coalescence of nuclei and islands, and recrystallization of islands. The various imperfection structures observed in thin films are described, and an attempt is made to explain the mechanisms by which these imperfections are formed during the growth of the film. Finally, the significance of the experimental evidence on growth and structure is discussed in relation to the occurrence of epitaxy, and an attempt is made to determine the most important directions for future studies of epitaxy.