- Brandon Holybee, The University of Illinois, Urbana-Champaign
This seminar describes research to characterize the topographical and compositional evolution of the GaSb surface from the as-is surface to the early stages of ion-induced nanopattern formation utilizing operando techniques. For the topographical study, operando grazing-incidence small-angle x-ray scattering experiments conducted at Brookhaven National Laboratory revealed a nonlinear topographical evolution of GaSb under all ion conditions and showed that a threshold fluence must be reached before ion-induced nanopatterning begins. For the compositional study, operando low-energy ion scattering spectroscopy (LEISS) and operando x-ray photoelectron spectroscopy (XPS) were developed in the IGNIS facility at the University of Illinois. The LEISS results showed that the very surface becomes enriched with Sb for all ion cases; the operando XPS results showed Ga enrichment. This suggests a nonuniform compositional depth profile with an Sb-enriched surface and a Ga-enriched subsurface region. Collaborative work utilizing the experimental results with a massive-scale molecular dynamics (MD) simulation of GaSb under 500e V Kr+ irradiation showed that under the MD simulation, the experimentally determined composition of GaSb just before ion-induced nanopatterning leads to the formation of Ga and Sb metallic clusters. The results suggest that ion-induced phase separation, combined with sputter shielding, could be the driving mechanisms leading to ion-induced nanopatterning in GaSb.