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Correlation of acetylene plasma discharge environment and the optical and electronic properties of the hydrogenated amorphous carbon films
摘要： Thin films from polymeric and graphitic hydrogenated amorphous carbon (a-C:H) were deposited over a glass substrate from acetylene (C2H2) plasma by using a conventional plasma enhanced chemical vapor deposition (PECVD). Radio frequency capacitively coupled plasma (RF CCP) source operating at a frequency of 13.56 MHz was used for generation of the discharge. Optical emission spectroscopy (OES) results showed strong optical emissions from diacetylene ion C4H2+ at a wavelength of 506 nm. The energy dispersive X-Ray (EDS) measurements illustrated that the carbon content in the deposited films increased with increasing of power. The Raman and IR results demonstrated that the films deposited at low bias voltages 340 V are so called polymeric a-C:H with high sp3 fraction and high hydrogen content, while the films deposited at high bias voltages 877 V are so called graphitic a-C:H with low sp3 fraction and low hydrogen content. Quantitative information were obtained from fitting the high asymmetrical vibrational modes of Raman and IR spectra by using Fano model expression together with Lorentzian function. The results presented here point out that there is a relation between the intensity of C4H2+ ion emissions and the deposited films properties.
关键词： Optical Emission,diacetylene ion,RF CCP,Hydrogenated amorphous carbon,FTIR,Raman spectroscopy
更新于2025-11-14 15:30:11
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European Microscopy Congress 2016: Proceedings || Revisiting the EELS analyses and its coupling with multi-wavelength Raman spectroscopy: the case of hydrogenated amorphous carbon thin films
摘要： Thanks to the long-term stability of their properties, hydrogenated amorphous carbon (a:C-H) thin films are very promising materials for numerous applications including coatings for spatial applications.1 In order to improve their performances, a full understanding of their local chemistry is highly required. Fifteen years ago, according to the seminal work of Ferrari et al.,2 EELS was the most used technique to get such kind of quantitative information on these materials. Nowadays the complexity of the physics phenomena behind EELS is well known3 and this technique is regarded as time-consuming and difficult to interpret properly. Other optical techniques such as Raman spectroscopy are now clearly favored by the scientific community. However they still lack of the spatial resolution that EELS in a STEM offers for getting direct chemical information. a-C:H thin films, with a thickness around 300 nm, were deposited on a Si wafer and submitted to isothermal annealing at 500°C with different annealing times up to 2500 minutes. The hydrogen content was monitored by multi-wavelength (MW) Raman using a set of reference materials. To determine the sp2 fraction (sp2 %) from core-loss EELS, the R ratio (R = Iπ*(ΔE)/I(π*(ΔE)+σ*(ΔE)) was determined first by taking into account the asymmetry of the π* character (Fig. 1a).4,5 This value was then normalized by the maximum R value (RREF) that could be obtained from a HOPG sample in the same experimental condition using relativistic calculations (Fig. 1b).6 When needed, this method was also slightly modified to take into account the contribution of heterospecies. In addition, the mass density and the oxygen content was derived from low-loss and core-loss spectra, respectively. The EELS C-K edge spectra (Fig. 2a) present all a typical signature of amorphous carbons. However, the intensity of the massif above 292 eV differs from sample to sample and clearly highlights a slight variation of the sp2 %. The samples annealed 2500 min also presents a supplementary peak (red arrow in Fig. 2a), which is related to the oxidation of the thin film. As expected, the sp2 % increases with the annealing time (Fig. 2b). This effect is related to the H desorption of the thin films as monitored by Raman spectroscopy. Two samples do not follow this trend: the as-deposited sample and the sample annealed 2500 minutes. This latter presents a strong oxidation, leading to a decrease of the sp2 %. On the other hand, the as-deposited sample shows variation of the C-K edge fine structures (Fig. 3a) highlighting chemical inhomogneities in the thin film. This sample presents a strong gradient of the sp2 % induced by the deposition process (Fig. 3b) which is cured with the annealing time. All these results will be detailed together with the influence of the oxidation on the chemical and physical properties. In addition, the coupling of MW Raman, infrared and EELS spectroscopies to extract a wealth of chemical information will be discussed. Our results provide a complete combination of C-hybridization, spatial elemental analyses and structural defects studies for shedding light on these complex materials.7,8
关键词： Raman,Hydrogenated Amorphous Carbon,EELS,sp2 fraction
更新于2025-09-19 17:15:36
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Hydrogenated amorphous carbon films with different nanostructure: a comparative study
摘要： The introduction of curved graphite fragments into hydrogenated amorphous carbon films has been studied, and their contents are always estimated by TEM and Raman. Here, we detailedly discussed the advantage and disadvantage of TEM and Raman fit method. Combined with FTIR results, we claified the chemical structures of the structural films and the bonded sites of doped H. The curved graphite structures included hexahydric carbon rings, and amorphous carbon (a-C) structures had rich olefinic groups and H. Finally, the differences among TEM, Raman, FTIR and H analysis in terms of the contents of curved graphite fragments were discussed.
关键词： FTIR,nanostructure,Raman,a-C:H,hydrogenated amorphous carbon film
更新于2025-09-10 09:29:36