Assessments of the relation between the degree of order of the ultrafast laser deposited carbon film and the features of the Raman spectrum's D band

Highly oriented pyrolytic graphite (HOPG) is ablated by ultrashort laser pulses with different pulse durations (50 fs and 4 ps) and laser fluences (68 J/cm2 and 34 J/cm2) in vacuum (4 × 10− 4 Pa). Diamond like carbon (DLC) films are deposited by collecting the ejected material generated by laser pulses with intensities ranging from 0.85 × 1013 W/cm2 to 1.36 × 1015 W/cm2. The material compositions of the films are investigated using micro-Raman spectroscopy and the features of the obtained Raman spectra are analyzed by employing three different sets of peak fitting functions, including Breit-Wigner-Fano (BWF) and Lorentzian functions, two Gaussian functions, and two damped harmonic oscillator functions. It is found that when peak fitting functions with proper symmetry are employed, both D band's position and full width at half maximum (FWHM) can be used as the evaluation parameters for the degree of order of the deposited carbon films. Peak fitting results show that for DLC films, D band's position and FWHM increase as the increase of the degree of order of the films, which can be interpreted by the double-resonant Raman scattering model on account of the crystalline size confinement effect.