Chemical vapour deposition of niobium diboride (NbB2)

Abstract

Niobium diboride was prepared by chemical vapour deposition from a gas mixture of NbCl5, BCl3, H2 and Ar on a quartz substrate heated to a temperature of 950–1200°C. Homogeneous films were formed from 950 to 1050°C, and pillar crystal from 1050 to 1200°C. Niobium diboride was found to react with the quartz substrate above 1200°C to form a silicide, Nb5Si3. The optimum molar compositions of the gas mixture used to grow crystals of NbB2 were 2.5–5.0 vol% of BCl3, and 2.5–5.5 vol% of NbCl5. In the presence of impurities of nickel regular hexagonal shaped pillar crystals of maximum 10 μm in a edge and 50 μm in length were obtained.