Study on the effect of substrate temperature on the infrared transmittance of DLC films fabricated by magnetron sputtering

Diamond-like carbon (DLC) films offer a promising solution to enhance the surface hardness of conventional anti-reflection materials used for infrared optical windows. This work investigates the influence of substrate temperature on the microstructure and the infrared transmittance of DLC films within the 3-5 µm wavelength range. The DLC films are deposited on single-crystal silicon substrates via radio-frequency magnetron sputtering at calibrated substrate temperatures ranging from 25°C to 185 °C. Experimental results show that the presence of DLC films significantly improves the average transmittance compared with the uncoated substrate. A non-linear dependence of the substrate temperature on the infrared transmittance of DLC films is observed. The maximum sp 3 bond content of 0.484 occurs at 95 °C, yet corresponds to the minimum average transmittance enhancement of 20.87% across the 3-5 µm spectral region. Further theoretical analysis reveals that the increase of sp 3 bonding in the DLC film can increase its refractive index, thereby reducing its transmission efficiency. These findings provide essential experimental insights for optimizing the preparation of high-performance DLC films in the 3-5 µm spectral region.