The researchers used a catalyst layout of evenly spaced (120 nm) gold-catalyst columns, arranged in rows that were 0.5, 1, 2, 4, 8 and 16 µm apart, to extract the growth precursor migration length on the oxidized surface. The value was found to be about 4 µm, which is about an order of magnitude larger than the migration length on a bare III-V surface.

This large precursor migration length affects growth conditions. Due to the large collection area, the precursor flow needed for growth is around 20 times smaller than the amount required for growth on oxide-free surfaces, which may affect the resulting nanowire properties.

In addition, pre-growth heating treatment at 450 °C (prior to growth at 400 °C) was found to increase nanowire nucleation yield. Untreated samples exhibited island growth and contained off-axis nanowires, grown from poorly nucleated catalysts. This finding is linked to catalyst-substrate interaction, and is the subject of subsequent work regarding this growth regime.

In future work, the group plans to fabricate vertical nanowire-based electronic devices; exploring their properties, and relating this information to the structural properties of the nanowires such as diameter, surface detail and crystalline structure and quality.

Full details can be found in the journal Nanotechnology.