Evidence for and role boron carbide icosahedra in the hardness of amorphous hydrogenated boron carbide

摘要

We report both infrared absorption and 11{sup left}B nuclear magnetic resonance measurements that provide evidence for the presence of boron carbide icosahedra in amorphous hydrogenated boron carbide (a-B:C:H) thin films. The infrared absorptionspectra are dominated by a broad line at 1280 cm{sup}-1 with a FWHM of 320 cm{sup}-1, and the 11{sup left}B nuclear magnetic resonance spectra are dominated by a line with a chemical shift of 4 ppm and FWHM of 35 ppm; similar features have been previously reported in polycrystalline boron carbide, where boron carbide icosahedra make up the unit cell. We also suggest that it is these icosahedra that increase the hardness of these films over those films without boron, by playing the role of nanoctystals in a nanocrystal/amorphous matrix composite system.