Hydrogen bonding at grain surfaces and boundaries of nanodiamond films detected by high resolution electron energy loss spectroscopy

Hydrogenated nanodiamond films consisting of 300 and $10–30nm$ grain sizes were examined by high resolution electron energy loss spectroscopy. C–H stretching modes were identified at 350, 360, and $375meV$⁠. The mode at $375meV$ was enhanced in the case of $10–30nm$ grain size and it is stable up to in situ annealing to $>800°C$⁠. Complete hydrogen desorption occurs upon annealing to $1000°C$⁠. Exposure of the nanodiamond film to atomic hydrogen results in a strong quenching of the $375meV$ C–H mode, most likely due to preferential etching of $(sp2)$-carbon-hydrogen at the surface and grain boundaries of the films.