Nano scale investigation of particulate contribution to diamond like carbon film by pulsed laser deposition

Abstract

Diamond like carbon (DLC) films were synthesized by a Pulsed Laser Deposition technique at room temperature, with the laser pulse energy varying from 100 to 400 mJ. The films synthesized at different pulse energies are labeled as DLC-100, DLC-200, DLC-300 and DLC-400. Due to laser ablation, the DLC films contained a continuous phase and particulates embedded in it. These films were characterized using X-ray Photoelectron Emission Spectroscopy (XPS), Raman spectroscopy based intensity mapping and Atomic Force Acoustic Microscopy (AFAM). Carbon co-ordination inhomogeneity in DLC films was monitored by intensity mapping of the Raman peaks. The average sp² cluster size in the particulates was calculated from the intensity ratio of the D and G peaks of the Raman spectra (I_D/I_G ratio) obtained from the particulate region and was found to vary from 0.85 to 1.41 nm with various laser pulse energies. Nanometric surface spatial elasticity distribution was mapped using AFAM, which revealed the presence of nanoscale surface irregularities in all the DLC films. The number density of particulates in the present DLC films is maximum in DLC-400 and minimum in DLC-100. Relative stiffness value of all the DLC films with its particulate regions were determined and compared with respect to the relative stiffness of Si. Raman spectroscopic intensity mapping and AFAM studies revealed that carbon co-ordination and local elasticity distribution across the film and particulate of DLC films are observed to depend upon sp² bonded carbons possessing different aromatic orders and sp³ content. The sp³ bonding content present in DLC films synthesized at different laser pulse energies was obtained from X-ray photoelectron spectra. DLC-300 was found to be the stiffest film (∼4.5 times of Si) with highest sp³ content (53%).