High Density of Quantum-Sized Silicon Nanowires with Different Polytypes Grown with Bimetallic Catalysts

When Si nanowires (NWs) have diameters below about 10 nm, their band gap increases as their diameter decreases; moreover, it can be direct if the material adopts the metastable diamond hexagonal structure. To prepare such wires, we have developed an original variant of the vapor-liquid-solid process based on the use of a bimetallic Cu-Sn catalyst in a plasma-enhanced chemical vapor deposition reactor, which allows us to prevent droplets from coalescing and favors the growth of a high density of NWs with a narrow diameter distribution. Controlling the deposited thickness of the catalyst materials at the subnanometer level allows us to get dense arrays (up to 6 x 10(10) cm(-2)) of very-small-diameter NWs of 6 nm on average (standard deviation of 1.6 nm) with crystalline cores of about 4 nm. The transmission electron microscopy analysis shows that both 3C and 2H polytypes are present, with the 2H hexagonal diamond structure appearing in 5-13% of the analyzed NWs per sample.

Automated summary

A novel variant of the vapor-liquid-solid process using bimetallic Cu-Sn catalyst has been developed to grow high-density nanowires with narrow diameter distribution and stable diameter. By controlling the deposited thickness of the catalyst materials, nanowire arrays with an average diameter of 6 nm were achieved, with different polytypes identified through transmission electron microscopy analysis.