Growth of Nitrogen Incorporated Ultrananocrystalline Diamond Coating on Graphite by Hot Filament Chemical Vapor Deposition

Abstract

This article shows the results of experiments to grow Nitrogen incorporated ultrananocrystalline diamond (N-UNCD) films on commercial natural graphite (NG)/Cu anodes by hot chemical vapor deposition (HFCVD) using a gas mixture of Ar/CH4/N2/H2. The experiments focused on studying the effect of the pressure in the HFCVD chamber, filament-substrate distance, and temperature of the substrate. It was found that a substrate distance of 3.0 cm and a substrate temperature of 575 C were optimal to grow N-UNCD film on the graphite surface as determined by Raman spectroscopy, SEM, and TEM imaging. XPS analysis shows N incorporation through the film. Subsequently, the substrate surface temperature was increased using a heater, while keeping the substrate-filament distance constant at 3.0 cm. In this case, Raman spectra and SEM images of the substrate surface showed a major composition of graphite in the film as the substrate-surface temperature increased. Finally, the process pressure was increased to 10 Torr where it was seen that the growth of N-UNCD film occurred at 2.0 cm at a substrate temperature of 675 C. These results suggest that as the process pressure increases a smaller substrate-filament distance and consequently a higher substrate surface temperature can still enable the N-UNCD film growth by HFCVD. This effect is explained by a mean free path analysis of the main precursors H2 and CH3 molecules traveling from the filament to the surface of the substrate The potential impact of the process developed to grow electrically conductive N-UNCD films using the relatively low-cost HFCVD process is that this process can be used to grow N-UNCD films on commercial NG/Cu anodes for Li-ion batteries (LIBs), to enable longer stable capacity energy vs. charge/discharge cycles.

Comparative X-ray photoelectron spectroscopy analysis of nitrogen atoms implanted in graphite and diamond

“…In this sense, a material's related effect, which may turn out to be critical for the development of diamond electronics, was observed in the experiments involving the implantation of low-energy N + ions in EGSCD. The observed effect was that low-energy N-atom implantation in EGSCD induced a diamond surface/subsurface insulator-electrical conductivity transformation, similar to prior research by Auciello et al, which resulted in the development of N-UNCD films with N-atom inserted in grain boundaries, providing electrons for electrical conductivity (Gruen et al, 2004;Villarreal et al, 2022). The hypothesis considered for the explanation of the electrical conductivity of N-UNCD films confirmed by systematic experiments (Gruen et al, 2004;Villarreal et al, 2022) is that the N atoms inserted in grain boundaries react chemically with C atom open bonds, releasing electrons for conduction through the boundaries.…”

“…The observed effect was that low-energy N-atom implantation in EGSCD induced a diamond surface/subsurface insulator-electrical conductivity transformation, similar to prior research by Auciello et al, which resulted in the development of N-UNCD films with N-atom inserted in grain boundaries, providing electrons for electrical conductivity (Gruen et al, 2004;Villarreal et al, 2022). The hypothesis considered for the explanation of the electrical conductivity of N-UNCD films confirmed by systematic experiments (Gruen et al, 2004;Villarreal et al, 2022) is that the N atoms inserted in grain boundaries react chemically with C atom open bonds, releasing electrons for conduction through the boundaries. The hypothesis to explain the transition of the SCD from insulator to electrically conductive material, due to N atoms implanted in the surface/subsurface region of SCD, is that N atoms link with C atom open bonds around the vacancies, releasing electrons for electrical conduction and is not due to graphitization of the N-implanted surface/subsurface region.…”