This work deals with a comparative study of plasma discharge generated by two geometrical configurations of cathodes through an investigation of their plasma parameters. A large hole diameter and depth (D = 40 mm, W = 50 mm) multi-hollow (MH) cathode compared with a plane (PL) cathode are presented for argon capacitively coupled radiofrequency discharge. The electrical characteristics of MH and PL cathodes have been measured in terms of the self-bias voltage (Vdc) while the Langmuir probe was used to measure electron density (ne) and electron temperature (Te) for a wide range of gas pressure (60–400 mTorr) and incident power (50–300 W). It is found that the hollow cathode effect (HCE) is optimum at 60 mTorr with 220 mTorr as a critical gas pressure for which a transition from HCE to insufficient HCE is seen. The electron temperature varies from 3 to 5 eV in the case of MH and PL cathodes with respect to incident power and gas pressure.

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Plasma enhanced chemical vapour deposition technique (PECVD) was used to grow diamond‐like carbon films using pure methane gas plasma. Structural, optical and mechanical properties of the obtained a‐C:H films were investigated as a function of bias voltage in the range 120–270 V, using different techniques. Elastic recoil detection analysis (ERDA) was employed to determine the hydrogen content and Fourier transform infrared spectroscopy (FTIR) was used to analyse the absorption of optically active hydrogen in the deposited films. The relative concentrations of sp2 and sp3 groups were determined from fitting of both X‐ray photoelectron spectroscopy (XPS) and FTIR spectra. Mechanical hardness and optical transmission were determined using nanoindentation and spectrophotometry, respectively. The results showed that the structure and properties of the films formed strongly depended on the applied bias voltage. In the range of energy considered the growth of the films was governed by a competition between both chemical and physical processes, with a dominance of physical process (subplantation) above 240 V, the energy at which more than 90% sp3 hybridization was obtained. Nanoindentation tests revealed hardness and Young's modulus of the films ranging from 12–15 and 116–155 GPa, respectively. The optical gap values deduced from the optical transmission spectra varied between 1.13 and 1.60 eV.

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