A combination of LEED, RHEED and AES has been used to observe lead and thallium growing in a layer-by-layer manner on (111) silver, and in the Stranski-Krastanov mode on (111) copper. Ordered sub-monolayer structures were observed for growth on the silver substrate but not for the copper substrate. However, for growth on the copper substrate a substantial contraction in the lead and thallium nearest-neighbour spacing ( approximately 3%) was observed at an approximately one monolayer coverage. It is suggested that the resulting strain in the overlayer may be responsible for the Stranski-Krastanov growth mode. Non-parallel epitaxial layers were formed by lead on silver, and by thallium on both copper and silver. The occurrence of such deposits may be linked with directional bonding forces at the interface, and/or stabilised via the existence of low-angle tilt boundaries in the overgrowth.

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We obtain valuable information about medium-range order in amorphous semiconductors from variable coherence microscopy, a new quantitative approach to TEM. The technique reveals three-body and higher-order atomic correlation functions, which are sensitive to medium-range order. Preliminary experimental evidence for structural changes on annealing has been found for amorphous semiconductor films, with pronounced medium-range order seen only in unannealed films.