Multifunctional nanocrystalline chromium boride thin films

Abstract

The present study highlights the growth and properties of chromium diboride films (100–300 nm thickness) deposited on to various substrates (Cu, borosilicate glass and fused silica) by thermal evaporation process. X-ray diffraction patterns showed that films were slightly boron deficient. This was confirmed using EDX measurements which indicated a nominal composition of CrB_1.5. However, electron diffraction patterns showed the presence of CrB₂ leading to the inference that the films were composites of CrB₂ and CrB_1.5. The films were nanocrystalline with crystallite sizes of the order of 15–20 nm. Scanning electron micrographs revealed that the film morphology is substrate dependent. The films on borosilicate glass and fused silica were optically transparent and insulating at thickness of ~100 nm. The thicker films were opaque and conducting. There was enhancement in reflectance of Cu substrates from 25 to 50% in the near IR wavelength region due to the chromium boride coatings. The hardness of the films was 10 GPa on Cu while it was 8 GPa on glass substrates.