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We discuss the use of the alloy catalyst AgAu to grow silicon nanowires and Si/Ge heterojunctions. Nanoscale particles of the catalyst with compositions Ag:Au varying from 2:1 to 1:2 can be fabricated and used to form Si nanowires with high crystal quality, and SiGe interfaces that are close to atomically abrupt. In situ experiments in the TEM are essential for investigating the mechanisms of growth with these alloy catalysts. We describe the relationship between growth kinetics and catalyst state, as well as the environmental stability of the alloy catalysts.

Fabrication of Si-Ge nanowire heterostructures offers great design flexibility in device applications, provided the interfaces are defect-free and compositionally abrupt. We use in-situ transmission electron microscopy to study nanowire growth, and find that abrupt Si-Ge interfaces can be fabricated in nanowires by a growth method that uses a solid AlAu2 catalyst. Growth of uniform segments of SiGe alloy in Si nanowires with sharp interfaces can also be realized using this method. We present in-situ measurements of nanowire growth kinetics and discuss the strain distribution and thermal stability in Si/Ge and Si/Ge/Si nanowire junction structures.