Test of the Ardell distribution function for two-dimensional adsorbate islands using thermal desorption spectroscopy

The thermal desorption of atoms from two-dimensional deposit islands on a s ubstrate may be limited by the rate of desorption from island edges. In ear lier work, Slavin and Young developed a theory for the form of the desorpti on curves for such systems, as a function of the average island size, that agreed well with experimental data until just beyond the peak maximum. The fitting procedure provided values for the desorption energy, the average is land radius, the standard deviation of the island-size distribution functio n, and the frequency of vibration of an atom at an island edge. The current study extends this work by incorporating a theoretical expression for the initial distribution of island sizes, due to Ardell, into the previous theo ry. The Ardell function provides a value for the average initial island rad ius and the standard deviation of the distribution without any curve fittin g, if the surface coverage and the number of islands are known. It also ena bles the experimental thermal desorption data to be fitted over the entire desorption curve, which provides an independent check on the experimental v alue for surface coverage. The results using the Ardell distribution are in good agreement with all the parameters obtainable from the experimental da ta.