Paper SS+NS-ThA6
Growth of Ag/Ge(111) Phases Studied with LEEM and LEED

Thursday, November 1, 2012, 3:40 pm, Room 21

Low energy electron microscopy (LEEM) and low energy electron diffraction (LEED) were used to study the growth of structural phases of Ag deposited on Ge(111) above and below the Ag desorption temperature. Ag deposited on Ge(111) formed three main surface phases above 100°C: (4x4), (√3x√3)R30°, and (3x1). At a given coverage, (4x4) island size increased with deposition temperature and decreased with deposition rate. The (4x4) structure nucleated at steps edges and grew only at steps for samples with very high step density. While the √3 structure did not show a preference for nucleating at steps, its growth was bounded by substrate step bunches. The (3x1) was the only Ag phase on the surface for deposition at 370°C and coverage Θ <0.1 ML, forming domains large enough to be resolved in LEEM images. The (3x1) and (4x4) phases coexisted for T < 350°C and 0.1<Θ <0.38 ML, while the (3x1) and √3 phases coexisted for T>400°C and Θ>0.4 ML. LEEM images of Ag desorption from Ge(1 1 1) at T>575°C showed that Ag (4x4) and √3 phases reversibly transform to a disordered (1x1) phase, with desorption proceeding from the edges of disordered (1x1) domains and the (1x1) phase being slightly less dense than the (4x4) phase. For sufficiently high deposition rates, Ag was observed to accumulate on Ge(111) above the 575°C desorption temperature. For deposition between 580 and 640°C, a silver layer formed with a (3x1) LEED pattern; upon completion of that layer, a √ 3 layer formed. For deposition at 660°C, only the (3x1) layer formed. Desorption proceeded by the reverse sequence of phases.

Funded by NSF CHE-0719504 and NSF PHY-1004848