In situ TEM investigations of dendritic growth of Au particles on HOPG

Gold was vapor deposited onto thin substrates of highly oriented pyrolytic graphite at room temperature inside a transmission electron microscope, which was modified for in situ experimentation. The kinetics of nucleation and dendritic growth of particles was recorded in real time. Two growth modes of particles were observed on different parts of the substrate. Small particles with high nucleation density populated defective substrate areas, where condensation was complete, as was verified by quantitative analysis of x-ray fluorescence, while on virtually undisturbed areas, the nucleation density was much lower, condensation initially incomplete, and particles grew dendritic. The lateral growth speeds of the latter were found to be strongly correlated to the sizes of the respective capture areas. This is attributed to similar heights of the particles, starting at about 1 nm soon after nucleation. The growth kinetics of individual aggregates were compared with a diffusion model, which allowed us to estimate the adatom mean diffusion length before desorption to about 400 nm. Relying on a value for the surface lifetime of a gold adatom of less than IO ms at room temperature, as reported in the literature, this results in an upper limit for the diffusion barrier of 0.24 eV on graphite. [S0163-1829(98)04643-8].