Gold coverage and faceting of MBE grown silicon nanowires

In this paper, we investigate the faceting of molecular beam epitaxy (MBE) grown nanowires and the post-growth repartition of the gold used as catalyst. Electron microscopy analysis are performed using Scanning Transmission Electron Microscopy - High Angle Annular Dark Field (STEM-HAADF), electron tomography, and Energy-dispersive X-ray spectroscopy (EDS) to collect complementary information. The nanowires present very little to no faceting at the very top, very close to the catalyst, suggesting the nanowires grow with a quasi-circular section at the early stages of growth. The nanowires are then found to have an hexagonal and/or dodecagonal section and present a finer 'saw-tooth' faceting on the main faces. We find gold clusters spread on the surfaces of the nanowires, but we could not observe any gold inside the nanowires. Furthermore, the gold coverage is uneven on the different facets of the nanowire. The creation of these facets and the gold coverage are two linked phenomena balancing each other.