Effect of Repetition Rates of Laser Pulses on Microstructure and Optical Properties of Diamond-Like Carbon Films

Abstract

Hydrogen-free diamond-like carbon (DLC) thin films were prepared at different repetition rates of laser pulses by pulsed laser ablation of graphite target at room temperature. The microstructure of the thin films was characterized by Raman spectroscopy. Raman measurements showed that sp 3 bonded carbon fraction is reduced with increase of repetition rates of laser pulses from 5 to 20 Hz. Optical properties, namely photoluminescence (PL), optical absorption, extinction coefficient (k), and refractive index (n), were measured by fluorescence spectrophotometer, scanning spectrophotometer, and spectroscopic ellipsometer. By changing the repetition rates of laser pulses from 5 to 20 Hz, the PL and optical absorption were gradually increased, while the deposition rate and optical band gap of the films decreased strictly with the increase of repetition rate. The extinction coefficient (k) and refractive index (n) were found to be in the range of 0.468-0.938 and 1.92-2.27, respectively. These results indicate that repetition rate of laser pulses has a strong influence on the microstructure and optical properties of the films. Based on the experimental results, a possible causation about the effect of repetition rate on PL was proposed.

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“…These relationships agree with the results of Balon et al, Chhowalla et al, Ding et al and Marchon et al, which suggest that the films produced become more diamond-like with decreasing temperature. [17][18][19][20] To be biocompatible, a material must be stable within the human body. In vitro testing in SBF provides an inexpensive way to determine the stability of the DLC films.…”

“…The ratio of intensities of the two peaks I D /I G , the full width at half maximum of the G peak and the G peak position were normalised and are shown graphically in [17][18][19][20] To be biocompatible, a material must be stable within the human body. In vitro testing in SBF provides an inexpensive way to determine the stability of the DLC films.…”

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“…[17] Graphitization tends to increase the absorbance at shorter wavelengths more than at longer wavelengths. [18] Variations in 15 , 10. The inset images are photos of samples corresponding to data traces (a) (bottom) and (i) (top).…”