Microstructural evolution of Ag/GaAs (110)

We have monitored the microstructural evolution of Ag films grown on in situ cleaved GaAs(110) surfaces using nm spatial resolution secondary electron microscopy. Ag coverages between 1/2 ML and 256 ML were investigated for films deposited from an Ag Knudsen cell onto both room temperature (RT) and 250°C substrates. The initial stages of growth are markedly different for these two deposition temperatures. The room temperature grown films consist of approximately hemispherical islands while the 250°C films result in needle-like islands elongated along the 〈110〉 direction. This elongation may be due to a number of factors including anisotropic surface diffusion or bonding along the 〈100〉 and 〈110〉 directions, corrugations in the GaAs(110) surface or better lattice matching of Ag(100) to the GaAs(110) direction. At higher coverages, the films appear similar when lengths are scaled to account for increased diffusion at higher temperatures. The islands in the RT film impinge at lower coverages than the 250°C film and the RT film becomes quasi-continuous near 256 ML. The 250°C film forms larger, more widely spaced islands which impinge but do not form a quasi-continuous film for even the highest coverage. Island size distributions will be used to discuss the growth mechanisms for these films.