Evaluation of ultrananocrystalline diamond size by UV Raman spectroscopy and a phonon confinement model

This study applied ultraviolet (UV) Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) to investigate phonon modes and chemical bonding in ultrananocrystalline diamond films. XPS analysis revealed distinct carbon hybridization states, with the ultrananocrystalline diamond film exhibiting dominant sp³ bonding and the diamond nanowire film showing reduced sp³ content alongside sp² hybridization. The sp³-bonded T_2g phonon mode, selectively probed by UV Raman spectroscopy via near-resonance enhancement, demonstrated crystallite sizes of 5.6 nm for ultrananocrystalline diamond and 2.1 nm for nanowires through characteristic phonon confinement effects. The measured dimensions showed quantitative agreement with theoretical confinement models, confirming phonon localization within nanodiamond domains. The combined results demonstrated that nanoscale carbon hybridization governs the material properties, with the XPS-derived sp³/sp² ratios directly correlating with the Raman-measured phonon confinement effects.