Paper SS2-MoM5
The Growth and Evolution of Ag on Ge(111) Studied by LEEM

Monday, October 15, 2007, 9:20 am, Room 611

The clean Ge(111) surface has a c(2x8) reconstruction at room temperature. When Ag is dosed onto the surface two main structures are found, a low coverage (4x4) and a higher coverage (√3x√3)R30° phase. We have used the real-space imaging capabilities of a low energy electron microscope (LEEM) to investigate the growth, phase transitions, and dynamics of these phases. The (4x4) phase begins to form at temperatures above 200°C and coverages above 0.1ML. LEEM videos show the (4x4) phase grows with a high dependency on surface steps. This dependency on steps has been attributed to the high diffusivity of Ag adatoms along the step edges¹. The growth of the (4x4) phase also produces faceting of the surface which is shown in the LEEM images as the (4x4) phase grows from the steps. At higher coverages the (4x4) phase transitions into a (√3x√3)R30° phase. LEEM data of the growth of this phase shows little dependence on the steps with the phase propagating over the terraces. This growth pattern is attributed to the higher diffusivity of Ag adatoms across the (4x4) layer¹ reducing the advantage of diffusion along the steps. Near the desorption temperature, we have found an interesting phase transition as domains of (√3x√3)R30° abruptly transform to the lower coverage (4x4) and then to a disordered phase. The disordered phase produces no contrast in the LEEM images but if the condensed phases are allowed to completely disappear and the sample is then immediately cooled the (4x4) and (√3x√3)R30° phases recondense on the surface. This indicates that the Ag has not completely desorbed and is still present on the surface in a disordered phase.

¹ E. Suliga and M. Henzler, Journal of Physics C-Solid State Physics 16, 1543 (1983).