On the nature of epitaxial crystal growth Déo, A. R.; Finch, George Ingle; Gharpurey, M. K.
Proceedings of the Royal Society of London. Series A, Mathematical and physical sciences,
07/1956, Volume:
236, Issue:
1204
Journal Article
Methylene blue and ammonium iodide crystals grow epitaxially on a mica cleavage surface, the orientation of the deposit crystals being determined by the substrate surface structure. Thus the ...orientation of a crystal growing from a nucleus formed on one side of a cleavage step may differ from that of a crystal seeded on the other side. Despite this, a growing crystal retains its original orientation on and after crossing such a step; growth is then no longer epitaxial. When sodium nitrate crystals growing epitaxially on a calcite cleavage surface are mechanically disordered, the crystals continue to grow in their deranged orientations uninfluenced by the substrate surface structure. It is concluded that in epitaxial crystal growth the substrate only determines the orientation of the first few atoms and that the further growth of this nucleus is no longer influenced by the substrate surface structure.
During an experimental study by Stimson and one of us of the electrical condition of a platinum sheet, it was found that the surface sometimes exhibited a charge at room temperature after a previous ...treatment consisting, in the main, of heating in oxygen and hydrogen alternately. It was found later that cathodically sputtered platinum films were not only frequently electrically charged at room temperature, but were also sometimes exceedingly active catalysts of the union of hydrogen and oxygen at room temperature. In the course of these experiments, it soon became evident that the conditions under which the sputtered films were prepared in some manner profoundly affected their catalytic properties, and the following investigation was therefore carried out with the object, inter alia, of determining in what manner and to what extent sputtering conditions influenced the catalytic and structural properties of the resulting films. The experiments of which an account is now given in the ensuing first part of this communication were begun by two of us (G. I. F. and N. S.) in September, 1929. Both catalytically active and inactive films were obtained, and the sputtering conditions determining their production sufficiently well defined to enable the different types of surface to be prepared at will. It soon became evident, however, that the activity or otherwise of the films was in some manner intimately associated with structural properties which, owing to their submicroscopic nature, defied direct examination by the means then at our disposal.
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