Influence of substrate temperature on formation of ultrananocrystalline diamond films deposited by HFCVD argon-rich gas mixture

The influence of the substrate temperature on the formation of ultrananocrystalline diamond (UNCD) thin films, prepared by an argon-based hot filament chemical vapor deposition (HFCVD), is discussed in this work. The gas mixture used for diamond growth was 1 vol.% methane, 9 vol.% hydrogen and 90 vol.% argon at a total flow rate of 200 sccm and at a total pressure of 30 Torr. The substrate temperature range was from 550 to 850 °C at deposition time of 8 h. Mass growth rate was determined at different deposition temperatures. The activation energy for UNCD growth, determined from the Arrhenius plot, was lower (5.7 kcal/mol) than the values found for standard diamond deposition (around 11 kcal/mol). In this work, we suggest that the activation energy was lower because the growth of these films occurs at conditions that there is a high growth competition between diamond phase and sp² phases. To support this hypothesis, systematic characterization studies based on Raman scattering spectroscopy, high-resolution X-ray diffractometry and high-resolution scanning electron microscopy were performed.