An Experimental Test of Nucleation Theory: Formation of Rare Gas Crystals

In situ electron microscopic observations have been made upon the rare gas solids during nucleation on cooled graphite substrates. In particular, the saturation density of nuclei has been measured as a function of temperature and arrival rate with a view to testing current nucleation theory, as expounded by Walton. An important feature of this experiment is that the relevant parameters for these systems, such as surface diffusion and cluster energies, are known. Consequently it has been possible to make an absolute check on the theory, which is found to fit well, particularly when describing critical nuclei of small size.