Thickness of diamond-like carbon coatings quantified with Raman spectroscopy

A model is developed for quantifying the thickness of thin coatings and wear scars using Raman spectroscopy. The model, which assumes that both incident and Raman light obey Beer's law, was applied to Raman spectra from a diamond-like carbon (DLC) coating containing Si and O, known as DLN (diamond-like nanocomposite). The coatings ranged in thickness from 10 nm to 2 mum, according to stylus profilometry. Systematic variations in the Raman carbon (G band) and Si (1st order) peak intensities vs. thickness were found. Fits to the model gave an optical mean free path of lambda similar to 250 nm for DLN. This value is in good agreement with optical absorption coefficient values of other DLC films. Thickness profiles of wear tracks in the coatings determined by the model compared well with depths determined by profilometry. (C) 2003 Elsevier Science B.V. All rights reserved.