Crystal structure change in multilayer GeH flakes by hydrogen desorption under ultrahigh vacuum environments

To confirm the feasibility of the theoretically proposed method of forming free-standing germanene [Araidai et al., J. Appl. Phys. 128, 125301 (2020).], we have experimentally investigated hydrogen desorption properties from the hydrogen-terminated germanane (GeH) flakes. Thermal desorption spectroscopy analysis revealed that hydrogen desorption occurred during the heating under an ultrahigh vacuum environment, corresponding to mass loss of 1.0 wt%. Moreover, we have found that using an ultrahigh vacuum ambient and short-time annealing for hydrogen desorption is a key to sustain the crystal structures.

Layer-by-Layer Pyramid Formation from Low-Energy Ar+ Bombardment and Annealing of Ge (110)

Isolated pyramids, 30–80 nm wide and 3–20 nm tall, form during sputter-annealing cycles on the Ge (110) surface. Pyramids have four walls with {19 13 1} faceting and a steep mound at the apex. We used scanning tunneling microscopy (STM) under ultrahigh vacuum conditions to periodically image the surface at ion energies between 100 eV and 500 eV and incremental total flux. Pyramids are seen using Ar+ between 200 eV and 400 eV, and require Ag to be present on the sample or sample holder. We suspect that the pyramids are initiated by Ag co-sputtered onto the surface. Growth of pyramids is due to the gathering of step edges with (16 × 2) reconstruction around the pyramid base during layer-by-layer removal of the substrate, and conversion to {19 13 1} faceting. The absence of pyramids using Ar+ energies above 400 eV is likely due to surface damage that is insufficiently annealed.