Raman and photoluminescence study of Hot Filament CVD diamond films grown onto WC-Co substrates

In this work, a Raman and photoluminescence (PL) study of synthetic diamond films grown by hot filament chemical vapor deposition (CVD) on WC-Co is presented. The changes in the Raman spectrum induced by the different pretreatments of the substrate and/or different growth parameters of the films are discussed. In particular, the spectra of the films grown at 740 °C substrate temperature, 36 mbar pressure and 1.7% methane content in the CH4-H2 gas mixture and after different substrate pretreatments show all the features commonly observed in nanocrystalline diamond films, overlapped with a large PL background. A significant level of compressive stress is qualitatively deduced by the shift of the diamond Raman peaks. The different pretreatments of the substrates seem to have no influence on the quality of the diamond films. On the contrary, in samples grown at 700 °C substrate temperature, 10 mbar pressure and 1% methane content in the CH4-H2 gas mixture, the contribution of the non-diamond carbon phases to the Raman spectrum substantially decreases, even though the diamond Raman peak remains shifted and broad. Impurities in the films have been identified by means of low-temperature PL measurements. W and Si-related optical centers have been clearly observed, together with a band at approximately 1.967 eV probably connected to a nitrogen-related defect center.