The Role of Ambient Gas and Pressure on the Structuring of Hard Diamond-Like Carbon Films Synthesized by Pulsed Laser Deposition

Abstract

Hard carbon thin films were synthesized on Si (100) and quartz substrates by the Pulsed Laser Deposition (PLD) technique in vacuum or methane ambient to study their suitability for applications requiring high mechanical resistance. The deposited films’ surface morphology was investigated by scanning electron microscopy, crystalline status by X-ray diffraction, packing and density by X-ray reflectivity, chemical bonding by Raman and X-ray photoelectron spectroscopy, adherence by “pull-out” measurements and mechanical properties by nanoindentation tests. Films synthesized in vacuum were a-C DLC type, while films synthesized in methane were categorized as a-C:H. The majority of PLD films consisted of two layers: one low density layer towards the surface and a higher density layer in contact with the substrate. The deposition gas pressure played a crucial role on films thickness, component layers thickness ratio, structure and mechanical properties. The films were smooth, amorphous and composed of a mixture of sp3-sp2 carbon, with sp3 content ranging between 50% and 90%. The thickness and density of the two constituent layers of a film directly determined its mechanical properties.

An Experimental Study on Nano-Carbon Films as an Anti-Wear Protection for Drilling Tools

“…In the ideal case of single bonds between carbon atoms (sp 3 hybridization), the structure will have similar mechanical properties to those of diamond [2]. In general, DLC contains a mix of single and double bonds, and the ratio of sp 3 /sp 2 hybridized carbon atoms dictates the mechanical behavior of this material [3,4].…”

“…According to the fit, there is a third band that is centered at 1230 cm −1 , typically ascribed to nanocrystalline or "amorphous" diamond [23,24]. The values for the sp 3 and sp 2 content were assessed from the sp 3 /sp 2 dependency on the I D /I G ratio and frequency of G band given in the works of Ferrari et al [25] and Irmer et al [26]. Based on the G band peak centered at 1560 cm −1 , and ratio I D /I G~1 .3, checking on the calibration curves in Figure 5 of [26] it seems that the films are a-C:H type of DLC, with a sp 3 /sp 2 ratio of 0.33, corresponding tõ 25% sp 3 coordinated carbon atoms and~75% sp 2 .…”

“…The results inferred from these measurements are presented in Table 2. The sample C1-F1, deposited at the lowest fluence, has the lowest density of 1.77 g/cm 3 . The samples C1-F2 are made of a single carbon layer, having the thickness of~60 nm and an estimated density of 1.8 g/cm 3 .…”

“…Similar values of thickness and density were observed when increasing the laser fluence at 4 J/cm 2 . The samples C1-F5 were the thickest (96 nm) and were formed of a single layer with density of 2 g/cm 3 .…”

“…The samples C1-F2 are made of a single carbon layer, having the thickness of ~60 nm and an estimated density of 1.8 g/cm 3 . By increasing the laser fluence to 3 J/cm 2 , a monolayer carbon film with a slightly increased density of 2 g/cm 3 and thickness of ~55 nm was synthesized. Similar values of thickness and density were observed when increasing the laser fluence at 4 J/cm 2 .…”