Self-assembled metal-semiconductor compound nanocrystals on Group IV semiconductor surfaces

Nanocrystals of material B may form on a substrate of material A in order to relieve the strain from the B/A crystalline mismatch. In the most simplistic approximation, if such an elastic relaxation outweighs the additional surface energy due to the island walls, it will create the thermodynamic tendency for the nanocrystal formation. Hence one can `engineer' ultra-small and crystallographically perfect nanocrystal self-assemblies by careful selection of a film/substrate system under appropriate growth conditions. In this work, intentional nanocrystal creation is demonstrated in semiconductor/semiconductor and metal/semiconductor systems, such as Ge/Si, Co/Si, and Co/Ge/Si. The growth of the nanocrystals was observed using in situ scanning tunnelling microscopy and reflection high energy electron diffraction. In spite of the marked differences in surface thermodynamics and kinetic pathways, the different material combinations lead to remarkably similar nanocrystal arrays on the surface.