Structural and mechanical properties of a-C:H thin films grown by RF-PECVD
ABSTRACT a-C:H thin films have been deposited by plasma enhanced chemical vapor deposition at 13.56 MHz in a large bias voltage range (200–600 V). Their mechanical properties have been studied through different techniques such as nanoindentation, profilometry and finally X-ray reflectometry in order to determine their hardness, elastic modulus, stress level, interfacial fracture energy and density. We show that the hardness, the Young modulus, the density and the stress level decrease with increasing bias voltage contrary to the interfacial fracture energy, hence the adhesion of the deposits. To understand this behavior, films microstructure has been characterized through the determination of hydrogen and sp3 hybridized carbon contents by ERDA, FTIR, Raman diffusion and ESR. We have demonstrated that a graphitization and a loss of hydrogen occur when the bias increases. Such evolutions are explained in terms of the subplantation model proposed by Lifshitz. Finally, hard and dense coatings can be grown at low bias as the sp3 carbon content is high, but their corresponding adhesion is low.
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ABSTRACT: Amorphous hydrogenated carbon (a-C:H) and amorphous deuterated carbon (a-C:D) films were prepared using plasma-enhanced chemical vapor deposition (PECVD) from CD4, H2, CD4 and D2 source gases. Fourteen different samples were prepared by changing the source gas ratios of CH4/H2, CH4/D2, CD4/H2, and CD4/D2. The concentrations of hydrogen (H) and deuterium (D) relative to carbon (C) in the films were determined by elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS). The sp2/(sp2 + sp3) ratios of the films were analyzed by near-edge X-ray absorption fine structure (NEXAFS) measurements. Hardness and mass density of the films were measured using a nanoindenter and X-ray reflectivity (XRR), respectively. For all combinations of source gas, the H and D concentrations varied by only 4.0 at.%. For the CH4/D2 source gas, the D concentration in the film increased from 0 at.% with the D2/(CH4 + D2) source gas combination to 11.2 at.% for the 80% D2/(CH4 + D2) source gas combination. The increase in D concentration exceeded the increase in total H and D concentration (3.4 at.%). For CH4/D2 source gas, the H concentration decreased as the D concentration increased. For the CD4/H2 source gas, we observed the opposite tendency. Additionally, an isotope effect between the a-C:H films and the a-C:D films was observed, with preferential incorporation of H over D. From the NEXAFS measurements, the sp2/(sp2 + sp3) ratios in all of the samples were between 38.8% and 40.8%. A correlation between the sp2/(sp2 + sp3) ratio and the H2 or D2 gas source ratio was not observed. The hardness and density of the films decreased when the H2 or D2 source gas ratio increased. Even though the H concentration in the a-C:H films was higher than the D concentration in the a-C:D films, the a-C:D films had lower hardness and mass density values. These findings suggest that information concerning the voids, nanostructures, sp2/sp3 ratios and H concentrations of hydrogenated amorphous carbon films is crucial for evaluation of their mechanical properties.Applied Surface Science 01/2013; · 2.54 Impact Factor
- Lithuanian Journal of Physics - LITH J PHYS. 01/2009; 49(1):97-103.
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ABSTRACT: Characteristics of radio-frequency plasma-enhanced chemical vapor deposition (PECVD) in the growth of carbon nanotubes (CNTs) in a CH<sub>4</sub>-N<sub>2</sub> mixed gas were investigated through characterization of the prepared CNTs and a numerical simulation. Preparation of the CNTs was performed by the single chamber plasma process where the catalyst sputter deposition using a capacitively coupled plasma and the PECVD using an inductively coupled plasma were carried out in the same discharge chamber. The characterization results indicated the usefulness of the single chamber process system. It was also found that CH<sub>4</sub>, HCN, and C<sub>2</sub>H<sub>6</sub> radicals mainly contributed to the growth of CNTs.IEEE Transactions on Plasma Science 09/2007; · 0.95 Impact Factor