CVD synthesis of multi-layered polycrystalline diamond films with reduced roughness using time-limited injections of N2 gas

Multi-layered polycrystalline diamond (PCD) films were synthesized using microwave plasma-assisted chemical vapor deposition (CVD) with periodical addition (injections) of N-2 gas to the standard CH4-H-2 gas mixture. The aim of such an approach was to reduce the roughness of the films while preserving the overall high quality and phase purity of the PCD material. The thicknesses of the films were in the range of 5 to 51 mu m, while the number of layers was from 1 to 15. The introduction of even the smallest amount of nitrogen leads to a significant (more than 2-fold) increase in the growth rate of PCD films. Optimized injection regimes allowed the reduction of the relative roughness (S-q/thickness) of the PCD films by more than 3 times in comparison with standard microcrystalline diamond film grown under similar conditions without N-2 addition. The proposed method of periodic injection of N-2 during growth restricted the formation of continuous NCD layers, which improved the overall sp3/sp2 ratio in comparison with standard multi-layered MCD/NCD materials. The obtained multi-layered PCD materials with reduced roughness may be used for the formation of protective and hard covers, optical coatings, electrochemical and thermal management applications. Prime novelty statement: The multi-layered PCD films were synthesized in a microwave plasma CVD in regimes with short-term periodic N-2 injections in CH4-H-2 process gas; the average growth rate is doubled owing to the pulsed nitrogen injection, while the surface roughness is reduced by more than 3 times in comparison with a standard (no N-2 injection) microcrystalline film.