Effect of quench on crystallinity and alignment of boron nanowires

Fabrication of aligned single-crystalline boron nanowire (BNW) arrays has been a challenge so far. This motivated us to investigate the effect of quench on the crystallinity and alignment of BNW films made in a thermal vapor transfer process on Au-coated Si substrates. A remarkable improvement in both crystallinity and alignment has been observed in BNW films quenched from processing temperatures $\text{⩾1100\hspace{0.05em}°}\mathrm{C}.$ Without quench, the BNWs formed in the temperature range of $\text{900–1100\hspace{0.05em}°}\mathrm{C}$ are heavily tangled with either an amorphous or polycrystalline structure. If higher-temperature $\text{(⩾1100\hspace{0.05em}°}\mathrm{C})$ processing is followed by a quench, predominantly single-crystalline BNWs of a rhombohedral structure $\text{(a=10.94\hspace{0.5em}}\mathrm{\AA }$ and $\text{c=23.83\hspace{0.5em}}\mathrm{\AA })$ and (031) orientation aligned along the normal of the substrates can be obtained. We speculate that the strain induced along the BNW at large temperature gradient is responsible for the observed quench effect.