Microstructure and phase composition evolution of nano-crystalline carbon films: Dependence on deposition temperature

Abstract

Nano-crystalline carbon films possessing a prevailing diamond or a graphite character, depending solely on substrate temperature and deposition time, can be deposited from a methane–hydrogen mixture by the direct current glow discharge plasma chemical vapor deposition method. In this study we investigate the evolution of nano-crystalline carbon films deposited in the 800–950 °C temperature range onto silicon substrates aiming to enlight the physicochemical processes leading to the formation of nano-diamond films. While at a deposition temperature of ∼880 °C the formation of a thin precursor graphitic film is followed by deposition of a film of diamond character, at higher and lower temperatures the films maintain their graphitic character. The morphology of the films and their growth rate vary with deposition temperature: slower growth rates and higher film roughness are obtained at lower temperatures suggesting the importance of kinetic effects during the growth process. For deposition times longer than ∼60 min, similar morphologies are obtained irrespectively of the deposition temperature. A preferred spatial alignment of the basal planes of the graphitic film at the interface with the silicon substrate was determined. The alignment was found to differ with deposition temperature: at 800 and 880 °C the alignment occurs along the graphitic â axis perpendicular to the silicon substrate, while at 950 °C the ĉ axis is aligned perpendicular to the silicon substrate. However, it was determined that for films a few hundred nm thick close to the evolving surface the films display a preferred alignment of the basal planes vertical to the surface, irrespectively of their orientation at the interface. The reason for this alignment is suggested to be associated with a stress relaxation mechanism in the graphitic films. It was determined that film growth is accompanied by the evolution of large local stresses which obtain a maximum value for the films deposited at 880 °C. The relaxation of these stresses is suggested to lead to the transformation of the graphitic material into the diamond phase. The narrow range of temperatures (880+/−10 °C) which enables the formation of the diamond phase indicates the importance of hydrogen adsorption/desorption processes in the nucleation and growth of the nano-crystalline diamond films. The morphological evolution of the films was analyzed by atomic force microscope. By electron diffraction and high-resolution transmission electron microscopy the phase composition of the films and their microstructure were examined. The alignment of the graphitic films within the near-surface region of the evolving films as a function of the deposition time and temperature was investigated by angle-resolved near edge x-ray absorption fine structure measurements. Raman spectroscopy was applied to determine the presence of stresses within the films and their phase composition.

Development of edge state on graphite surface induced by Ar+ irradiation studied using near-edge X-ray absorption fine structure spectroscopy

“…The broadening of the p * peak, in which the peak tail on the high energy side is extended to 286-287 eV, can originate from the functional groups. Actually, the r à CAH transition occurs in the approximate range of 286-288 eV [49][50][51], and the p à CAO and the r à CAO transitions are located over 287-291 eV [52][53][54]. Accordingly, we have concluded that the amount of oxygen-containing functional groups is below the detection limit in our experiments, and that the r-dangling bonds are mainly terminated by hydrogen atoms.…”

“…Thus, hydrogen and oxygen are considered to be plausible species that terminate dangling bonds. According to former studies, various transitions related to the states of functional groups [49][50][51][52][53][54] can occur in addition to the interlayer state [42,55,56] in the intermediate between the p * and the r * regions. In the present study, the PEY spectra of the pristine sample had a broad feature around 288 eV regardless of the angle of X-ray incidence, whereas the TEY spectra did not have such a feature, as shown in the insets of Fig.…”

Opto-electrical properties of amorphous carbon thin film deposited from natural precursor camphor

“…Raman spectra of camphor pyrolysed films are found very similar to a-C films containing 60% sp 2 -bonded carbon [3,28]. Another prominent broad peak that observed in the range of 1540-1560 cm À1 can be attributed to sp 2 -bonded carbon normally observed in the grain boundaries of diamond films at 1520 cm À1 [29]. The D-band intensity is found to increase markedly with the deposition temperature indicating increase of disorderliness in the film.…”

“…This clearly suggests the increase in graphitic contents along with disorderliness in the films prepared at higher deposition temperature. In the Raman spectra, it is also interesting to observe significant G-band shift with deposition temperature which is related to the stress in the film [29,33,34]. The shift of G-peak to higher wave number under applied stress obeys following equation [29].…”

“…In the Raman spectra, it is also interesting to observe significant G-band shift with deposition temperature which is related to the stress in the film [29,33,34]. The shift of G-peak to higher wave number under applied stress obeys following equation [29]. Table 1 summarizes the ratio of D-peak to G-peak, peak position and the stress in the film calculated from Eq.…”