Do DLC-like features in Raman spectra of tribofilms really mean they are DLC formed by friction?

Abstract

Many previous studies of tribofilms have interpreted D- and G-bands in Raman spectra as evidence that diamond-like carbon (DLC) was formed during sliding. DLC and other amorphous-carbon films are produced by high-energy processes or high-temperature pyrolysis. Since neither of these conditions commonly occurs in a sliding interface, it seems unlikely that such materials could be produced during simple frictional sliding. To understand this apparent contradiction, we systematically analyzed tribofilms produced from vapor and liquid lubrication experiments using Raman spectroscopy with varied laser power and wavelength. The results provide evidence that DLC-like features in Raman spectra of tribofilms formed from organic molecules originate, not by tribochemical synthesis in situ during the tribo-testing as suggested previously, but rather from post-synthesis photochemical degradation of carbonaceous organic matter during the Raman analysis.

Molecular Structure and Environment Dependence of Shear-Driven Chemical Reactions: Tribopolymerization of Methylcyclopentane, Cyclohexane and Cyclohexene on Stainless Steel

“…Details of control experiments conducted to dispute the hypothesis claiming the tribochemical synthesis of a-C or H-DLC are provided in the subsequent paper [40].…”

“…However, it should be noted that a-C and DLC are usually produced by high-energy physical or chemical vapor deposition processes or pyrolysis at extremely high temperatures [38,39]. Thus, their formation must be tested and con rmed (or disputed) via independent analysis [40]. For a better understanding of tribochemical mechanism, having knowledge of the chemical nature of tribo lms is critical.…”

Investigation and Band Gap Analysis of Pulsed Dc Magnetron Sputtered Diamond‐Like Carbon to Enhance Contact‐Electrification and Durability of Triboelectric Nanogenerators

“…Figure 1d represents the Raman analysis carried out to identify the characteristic D and G bands in the DLC film, which correspond to sp 3 and sp 2 bonds, respectively. [ 55 ] Deconvolution of Raman peaks through Gaussian peaks fitting emerged with two peaks the G band at 1536.39 cm −1 and D band at 1333.9 cm −1 . These results are in good agreement with previous studies reported in the literature, showing the emergence of the G position in the spectrum range of 1528 – 1539 cm −1 .…”