Raman spectroscopic studies of stress-induced structure alteration in diamond-like carbon films

In this paper, Raman spectral mappings were carried out on Vickers indentation prints introduced on DLC films prepared with different substrate bias voltages (SBV). The mapping results showed clear differences in the intensity ratio, I-D/I-G, and band shifts for D and G peaks in samples fabricated with and without applying SBV. These spectral characteristics arose from the cumulative effect of a compressive (residual) stress field and structural alterations including sp(2) and sp(3) carbon disorder upon generation of the indentation print. Additional quantitative stress analyses, which employed spectral line scans on the film cross sections, revealed clear differences in magnitude for the compressive stresses stored in the films, as well as in-depth structural variations resulting from different SBV being applied during fabrication. An increasing level of residual compressive stress in the DLC films with increasing SBV may directly contribute to the observed decreased adhesion to the substrates and to the increased Vickers hardness.