Abstract:
Thin carbon films were deposited in nitrogen environment using C60 as target by pulsed laser deposition and the Raman spectra (RS), transmittance and reflectance spectra data have been collected and analyzed in this thesis work. Every RS curve is fitted with the characteristics peak. The evolution of D (disorder peak), G (characteristic peak of graphite) and F (due to fullerene) peak and reason behind their variations is studied. The structural modification due to N2 doping of C60 is investigated through individual peak position, full width half maximum (FWHM), integrated area of D peak/integrated area of G peak (Id/Ig), integrated area of D peak/integrated area of F peak (Id/If) and integrated area of F peak/integrated area of G peak (If/Ig) ratios. From the analysis it is found that the curves can be splitted in to 3 peaks.The emergence of D (~1350 cm-1) and G (~1590 cm-1) peaks indicates the occurring of high disintegration in C60 due to high fluence. But the peak around 1520 cm-1 is the shifted C60¬ Raman peak indicating the presence of C60. With the increase of nitrogen partial pressure (NPP), the G peak initially up shifted and then decreases gradually and remains almost constant at higher NPP. The downshifting of D peak (from its actual value) indicates the presence of sp3 C. The F (fullerene) peak decreases continuously with the increase of N2 content due to the presence of C60 like structure. Id/ Ig ratio increases initially and then decreases. Id/ If is decreasing and If/ Ig is increasing with N2 incorporation. The D- FWHM decreases, F- FWHM increases. When N2 content is low, more damaged C60 is found and curved graphene like structure is attained. But with high N2 incorporation instead of graphene more nitrogen incorporated polymerized C60 is formed. N2 incorporation decreases bond angle disorder and increases crystallites. The characteristics peak is modeled with the combination of Gaussian and Lorentzian line shape as a function of NPP and correlated with other Raman spectra fitting parameters. The optical absorption co-efficient of the films is calculated from the transmittance and reflectance of the films. From the optical absorption behavior near the absorption edge the band gap and Tauc parameter of the films is calculated. Tauc Parameter which is measure of the steepness of the band tail (Urbach region) density of state shows increase with increases of N2 pressure which indicates less disorder. At high N2 Tauc parameter decreases which may be due to drastic change in the structure. Structural properties like disorder, crystallinity found from Raman spectra data is correlated with those of optical absorption analysis. The results obtained for these films are compared with the previously reported carbon films produced from camphor and graphite. The conclusion is made based on investigation of the analyses whether the thin films deposited are applicable to electronic devices.
