Formation of Pb Islands on Ge(100) and on Ge(110)

The differences in island formation for Pb on Ge(100) and Ge(110) at temperatures of 260-290K were measured using low energy electron microscopy (LEEM). Pb/Ge(100) exhibited explosive nucleation of Pb islands upon reaching a critical coverage, similar to our earlier measurements of Pb/Ge(111).[1] Pb/Ge(110) instead formed thin, 1-dimensional (1D) islands that grew along and did not exhibit height selection observed for the other Ge faces. The critical coverage for island growth was 1.06ML wrt Ge(110). The islands grew linearly with time, exhibiting collective diffusion behavior similar to Ag/Ge(110), which exhibited 1D island growth due to the rectangular symmetry of the substrate.[2] For both Pb/Ge(100) and Pb/Ge(110), 3D classical islands coexisted with non-classical islands in a narrow range of temperatures between 0ºC and room temperature. Classical Pb/Ge(110) islands formed in triangular and trapezoidal shapes that aligned with substrate crystallographic directions. We also examined the binding of Pb adatoms on Ge(100) and Ge(110) surfaces using first-principles calculations on slab models of the surfaces. We compared the binding energies and charge densities of Pb and Au-adatoms. The comparisons were done with both ad-atoms at the same sites on the surfaces, and then the ad-atoms and the substrates were relaxed to stable sites.

[1] A.R. Kim, Ph.D. dissertation, UC Davis (2022).

[2] C. H. Mullet, Ph.D. dissertation, UC Davis (2012).