Self-assembled gold silicide wires on bromine-passivated Si(110) surfaces

Thin Au films (∼45 nm) deposited by thermal evaporation under high vacuum on bromine-passivated Si(110) substrates, upon annealing showed the formation of long gold silicide wire-like islands on top of a thin uniform layer of gold silicide in a self-assembled Stranski–Krastanov growth process. Optical micrographs showed long, straight and narrow islands with aspect ratios as large as 200:1. Scanning electron microscopy images revealed the presence of facets. The islands are aligned along the [1̄10] direction on the Si(110) surface. Rutherford backscattering spectrometry measurements with an ion microbeam identified the islands to possess varying thickness across a single island as one would expect for islands having facets and also showed the uniform silicide layer over the Si substrate to be very thin (∼1.5 nm). The observed alignment of the gold silicide islands on the Si(110) surface has been explained in terms of the lattice mismatch between gold–silicide and silicon and invoking the theory of shape transition in heteroepitaxial growth. We have observed islands as long as 200 μm and as narrow as 100 nm in this nonultrahigh vacuum growth on chemically passivated Si(110) surfaces. The method, with properly optimized parameters, may provide a way to grow quantum wires.