AREAL FRACTION EFFECTS DURING LATE-STAGE CLUSTERING ON SURFACES

Late stage cluster growth on surfaces is studied as a function of the areal coverage of the cluster phase for the system Sn on Si(111). Variations in the cluster size distributions were measured with increased precision based on relative measurements on the same sample using ultra-high vacuum deposition with the partial retraction of a mask. In addition, a variation of cluster growth rate on areal coverage was measured. The results show that the cluster growth rate increases by a factor of two with an increase in the areal coverage between 0.1% and 2%. This effect is larger than the increase predicted for three-dimensional systems (precipitate growth in a surrounding solution). Similarly, relative cluster distribution widths increase by 20% at 0.1% areal coverage and 30%-40% at 2% areal coverage. These effects are again larger than the predicted values for two- and three-dimensional systems.