Chemical Analysis of Ultra-Thin DLC Films and Lubricant/DLC Interface Using Plasmonic Sensors

The technical potential of a new plasmonic sensor, which can acquire surface-enhanced Raman spectra with high sensitivity by controlling surface plasmons is demonstrated for the chemical analysis of diamond-like carbon (DLC) films, lubricant films, and the DLC/lubricant interface on magnetic disks of sub-nanometer scale. The Raman spectra of thin DLC films and lubricated DLC carbon can be acquired with a high S/N ratio. Raman spectra of lubricated DLC carbon can also be acquired with the high S/N ratio. The wavenumber shift and intensity change of the Raman peaks of the phenyl and hydroxyl groups in the mixed lubricants (ADOH and Z-tetraol) show that the chemical interaction with the DLC surfaces of the phenyl group in the lubricant molecule decreases with increasing nitrogen content, whereas that of the hydroxyl group with the nitrogenated carbon increases. Raman spectra of nitrogenated DLC films are also acquired, the peaks show good agreement with density functional theory calculations. The calculated bonding energy indicates that the hydroxyl groups interact with the nitrogenated carbon.