Photo- and thermionic emission of MWPECVD nanocrystalline diamond films

•Photo- and thermionic emission of MWPECVD NCD films was compared.•The amount of incorporated hydrogen in the film was tuned by changing the grain size.•Higher emission was found in NCD film with BL grown at higher deposition temperature. Nanocrystalline diamond (NCD) films with and without a diamond buffer layer (BL) have been grown on p-type silicon substrates by microwave plasma enhanced chemical vapor deposition technique at different values of deposition temperature (652–884°C). The photo- and thermionic electron emission properties of NCD films have been investigated, illustrated and explained by analyzing the surface morphology and the grain shape determined by atomic force microscopy, the chemical-structural properties by Raman spectroscopy and nanocrystallites size by X-ray diffraction. The NCD films with BL grown at the highest deposition temperature have shown the highest photo- and thermionic emission currents.