Near- and far-field Raman spectroscopic studies of nanodiamond composite films deposited by coaxial arc plasma

Abstract

Raman spectroscopic studies on nanodiamond composite (NDC) films, comprising nano-sized diamond grains and an amorphous carbon (a-C) matrix, deposited by coaxial arc plasma deposition are challenging because the scattering of the nano-sized diamond grains competes with the strong signal of the a-C matrix. To unravel the nanocomposite structure of NDC films, both far- and near-field Raman spectroscopy were employed. Based on the comparison of visible and ultraviolet far-field Raman data, component spectra based on either nanodiamond or a-C were estimated by a peak-decomposition procedure based on band fitting. Near-field optical resolution achieved via tip-enhanced Raman spectroscopy reveals sharper peaks of both the nanodiamond and the amorphous carbon than the far-field spectra. Consequently, the peak-decomposition procedure is not required, which evidently indicates the effective detection of nanodiamond grains embedded in a-C matrices and is a direct result of the high spatial resolution that limits the number of probed grains. The size of the nanocrystals could additionally be estimated from the profile and position of a diamond peak. This work demonstrates that tip-enhanced Raman spectroscopy is a powerful nondestructive method for nanodiamond composite films, which allows direct access to parameters hitherto only available via average data.