Graphitic nanoclustering in pulsed laser deposited diamond-like-carbon and carbon nitride thin films

Abstract

In this work, Raman spectroscopy and electron paramagnetic resonance (EPR) are used to investigate sp2 carbon atoms nanoclustering in both diamond-like-carbon (DLC) and amorphous carbon nitride (CNx) films grown at room temperature by pulsed laser deposition. For DLC, ablation of a graphite target using a KrF laser was performed under vacuum, at different laser intensities. CNx growth was achieved using the same system to which a nitrogen atom source was added. For both types of films, increasing the laser intensity was found to reduce the size of the sp2 nanoclusters, as deduced from the variation of the D to the G Raman peaks intensity ratio. Moreover, the estimated size of the sp2 nanoclusters in CNx appears to be consistently larger than that in DLC films. The Lorentzian EPR signal, with a g-value of 2.0028 and room temperature linewidth ranging from approximately 2.3 to 3.9 G, gives further indication about clustering of sp2 paramagnetic centers (with measured spin densities >1020/cm3). For all films, the EPR linewidth was found to narrow down to approximately 2 G, when measured at 80 K. The EPR line broadening with increasing temperature is greater for the CNx films. Possible structural configurations of the nanoclusters, depending on laser intensity and nitrogen incorporation, are discussed.