Les différentes étapes de la formation d'un film adsorbé de gaz rare ou de méthane sur une surface uniforme de graphite

Abstract

Many examples show that the growth by adsorption of a crystal on a uniform surface takes place by successive monomolecular layers, as a consequence, the adsorption isothermes present a series of steps. The data obtained previously could be interpreted by supposing that each layer is formed either by building up of a single phase (steps of sigmoid shape) or by transition from a dilute to a condensed phase (steps with only one vertical part). The adsorption of rare gases or methane on the basal planes of graphite described in this paper, gives an example of a more complex growth of an adsorbed layer.This is the case for the first layer which passes through three successive two-dimensional states: presumably “gas”, “liquid” and “solid”; the two-dimensional solid may undergo rearrangements. The first step is then made up from several “sub-steps”.The comparison of our data with other data obtained by low energy electron diffraction shows that the first layer is different from the others not only by the diversity of the events accompanying its formation, but also by its higher density.