Ultrathick, low-stress nanostructured diamond films

Abstract

We describe a hot-filament chemical vapor deposition process for growing freestanding nanostructured diamond films, ∼80μm thick, with residual tensile stress levels ≲90MPa. We characterize the film microstructure, mechanical properties, chemical bond distribution, and elemental composition. Results show that our films are nanostructured with columnar grain diameters of ≲150nm and a highly variable grain length along the growth direction of ∼50–1500nm. These films have a rms surface roughness of ≲200nm for a 300×400μm2 scan, which is about one order of magnitude lower than the roughness of typical microcrystalline diamond films of comparable thickness. Soft x-ray absorption near-edge structure (XANES) spectroscopy indicates a large percentage of sp3 bonding in the films, consistent with a high hardness of 66GPa. Nanoindentation and XANES results are also consistent with a high phase and elemental purity of the films, directly measured by x-ray and electron diffraction, Rutherford backscattering spectrometry, and elastic recoil detection analysis. Cross-sectional transmission electron microscopy reveals a large density of planar defects within the grains, suggesting a high rate of secondary nucleation during film growth. These films represent a new class of smooth, ultrathick nanostructured diamond.