Abstract
Boron nitride (BN) is primarily a synthetically produced advanced ceramic material. It is isoelectronic to carbon and, like carbon, can exist as several polymorphic modifications. Microwave plasma chemical vapor deposition (MPCVD) of metastable wurtzite boron nitride is reported for the first time and found to be facilitated by the application of direct current (DC) bias to the substrate. The applied negative DC bias was found to yield a higher content of sp3 bonded BN in both cubic and metastable wurtzite structural forms. This is confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Nano-indentation measurements reveal an average coating hardness of 25 GPa with some measurements as high as 31 GPa, consistent with a substantial fraction of sp3 bonding mixed with the hexagonal sp2 bonded BN phase.
Highlights
Boron nitride (BN) is a covalently bonded ceramic material and a member of the GroupIII nitrides
We suggest that the ion bombardment created by the substrate bias introduces compressive stress to facilitate wurtzite BN (w-BN) formation
Boron nitride coatings were deposited in a microwave plasma chemical vapor deposition with and without direct current (DC) bias applied to the substrate
Summary
Boron nitride (BN) is a covalently bonded ceramic material and a member of the GroupIII nitrides. While r-BN is basically h-BN with a slight variation in the stacking of individual layers, w-BN is distorted c-BN Both r-BN and h-BN have sp hybridization, while c-BN and w-BN have sp hybridization in their covalent bond, giving rise to widely varying properties of the material. Among all the predominantly covalently bonded materials, c-BN and w-BN have the widest band gap (6.2 ± 0.2 eV) and can be doped for both p-type and n-type conductivity [5,6,7,8,9,10,11,12,13] Another interesting property of c-BN is its transparency to a broad range of electromagnetic radiation from the ultraviolet to the infrared [14]. It has recently been reported that c-BN can be biocompatible and non-cytotoxic, and can be used as a novel scaffold for biomedical applications [15]
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