Effect of Deposition Time on Structure and Properties of DLC Films Prepared by RF Magnetron Sputtering

To address the compatible application requirements for infrared anti-reflection and corrosion resistance of infrared windows in vehicle-mounted thermal imaging systems. DLC films with different deposition times (1, 2, 3, and 4 h) are deposited on silicon substrates via radio frequency (RF) magnetron sputtering. The morphological features and chemical bonding states of the films are characterized by SEM, Raman and XPS. Combined with transmittance measurements in the 3–5 μm waveband and 24 h neutral salt spray tests, the influence of deposition times on the infrared transmittance performance and salt spray corrosion resistance of DLC films is investigated. The results show that the film thickness increases gradually with the increase in deposition times. The sp²/sp³ ratio increases from 1.31 to 1.62, indicating a strengthened graphitization tendency. Meanwhile, film-substrate interface defects emerge and aggravate progressively from absence to presence. The average transmittance enhancement rate in the 3–5 μm waveband shows a trend of first increasing and then decreasing. It rises from 26.36% at 1 h to 29.86% at 2 h, which is due to the interference anti-reflection effect induced by thickness matching, and then decreases to 7.86% at 4 h. The deterioration of transmittance performance is mainly caused by the synergistic effect of enhanced scattering induced by film-substrate interface defects and increased absorption resulting from aggravated graphitization. The 24 h neutral salt spray tests demonstrate that only the sample with 1 h deposition time exhibits no peeling or delamination. The occurrence of such phenomena in the other samples is attributed to the synergistic effect of reduced structural stability caused by the decrease in sp³ content and the presence of film-substrate interface defects. This study provides experimental data support for the process optimization of DLC films on infrared windows of vehicle-mounted thermal imaging systems.