Fabrication and characterization of boron-related nanowires

Abstract

A thermal vapor transport process has been employed for fabrication of boron-related (boron, boron–silicon alloys, and MgB 2) nanowire films on Au-coated Si and MgO substrates. Tangled polycrystalline as well as aligned single-crystalline boron nanowires (BNWs) have been obtained and their growth mechanism investigated at different growth temperatures, cooling rates, and vapor sources. The growth temperature was found critical to the nucleation of the BNWs and different growth modes were observed in different temperature ranges. The temperature ramping rate in the cooling process after the high-temperature growth of the BNWs was found crucial for the formation of crystalline structures and for controlling the alignment of BNWs. We have observed that slow cooling at 1–5 °C/min resulted in non-textured BNWs, while fast cooling at ∼90 °C/min induced crystallization of the non-textured BNWs. We have also found that the alignment of the BNWs depended on the cooling rate. At a slow cooling rate the BNWs were heavily tangled while at a higher cooling rate they aligned well with the normal of the substrate. By manipulating the growth parameters, we have obtained two types of nanowire junctions. One was via fusing two nanowires together and the other, via joining them with another material.