Spectroscopic analysis of a-C and a-CN_x films prepared by ultrafast high repetition rate pulsed laser deposition

摘要

The effect of nitrogen partial pressure on amorphous carbon nitride (a-CN_x (0.0≤ x ≤ 0.17) and laser fluence on amorphous carbon (a-C) films prepared by ultrafast high repetition rate pulsed laser deposition has been studied. The chemical bonding structure of the films was investigated by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared (FTIR) analysis. XPS studies of films revealed an increase in the CN sites at the expense of CC bonded carbon sites as nitrogen content in the films increased. Films (a-C) prepared as a function of laser fluence showed an increase in sp~3-bonded carbon as laser fluence was increased from 0.36 to 1.7 J/cm~2. The I_D/I_G ratio and G peak position increased as a function of nitrogen whereas the full width at half maximum (FWHM) of the G peak decreased. This is indicative of either an increase in the size or number of the sp~2 sites. Films prepared as a function of laser fluence revealed a decrease of the I_D/I_G ratio and an increase in the FWHM of the G peak. The use of two visible excitation wavelengths when analyzing the samples indicated a resonant process. FTIR analysis revealed an increase in the peaks attributed to C=N bonds as well as indicated a tiny amount of C≡N bonds within the nitrogen-doped films. Additionally, surface morphology analysis showed a greater particle density on films prepared at the highest laser energy in comparison to those prepared at lower fluences. Film hardness characterized by nanoindentation revealed that films became softer as a function of nitrogen content.