Showing papers by "Ludvik Martinu published in 1992"

Deposition and properties of diamondlike carbon films produced in microwave and radio-frequency plasma

Abstract: Hard a‐C:H films were grown in a dual frequency plasma sustained simultaneously by microwave and radio‐frequency power. ‘‘Optimum’’ growth conditions, namely those leading to the most pronounced sp3 structural features in the films, depend very strongly on the methane feed gas flow rate and on the argon concentration, in the case of CH4/Ar mixtures. These optimum conditions have been found to correspond to maximum values of ion flux at the growing film surface, and high concentrations of precursor species such as CH, C2, C3, and atomic hydrogen in the plasma, as revealed by optical emission spectroscopy. Films grown under optimum conditions have very high microhardness (∼50 GPa), high density (1.8 g/cm−3), and low internal stress (0.5 GPa). Addition of argon to the methane is shown to enhance the gas phase fragmentation and to raise the microhardness, but argon atoms trapped in the films’ structure increase the internal stress.

Structure-property relationships in dual-frequency plasma deposited hard a-C : H films

Abstract: Films of amorphous hydrogenated carbon (a-C:H) which are hard (30–50 GPa), dense (1.7-1.8 g cm-3), and low in stress (0.5 GPa), were deposited in a dual-frequency (microwave (MW)-r.f.) plasma system, where the substrates are placed on an r.f. powered electrode while simultaneously being exposed to a microwave discharge in CH4, or CH4-Ar mixtures. This MW-r.f. deposition mode, and/or the addition of argon to the hydrocarbon feed gas, result in highly efficient monomer fragmentation in the gas phase and in the creation of species which contribute to enhanced sp3 features in the deposits. Film properties such as microhardness, density, hydrogen content, and refractive index are related to microstructure and composition, which are determined by Fourier transform IR spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and elastic recoil detection. The MW-r.f. films exhibit a systematically lower stress, and a higher density than their r.f. counterparts. It is shown that the observed structure - property relationships can be interpreted if we distinguish three categories of a-C:H films with diamond-like properties, namely (a) hard carbon with bonded hydrogen, (b) hydrogen-doped (unbonded) carbon, and (c) hard, polymer-like material.

Diamond-like carbon films deposited in a dual microwave-radio-frequency plasma

Abstract: Diamond-like carbon (DLC) films were deposited from CH4 gas in microwave-radio-frequency (MW-RF) plasma consisting of a microwave discharge with RF power applied to the substrate. We report the effect of the negative d.c. substrate bias voltage on the deposition rate, ion flux and film structure. Substantially higher fluxes were measured in the MW-RF mode than in the “pure” RF mode owing to a higher rate of fragmentation and ionization of the CH4 molecules in the gas phase, as also indicated by optical emission spectroscopy. It has been found by Fourier transform IR spectroscopy that the DLC films deposited in the MW-RF discharge exhibit more sp3 character than the deposits from a “pure” RF plasma. It is shown that DLC films prepared at lower ion energy but higher ion flux in the dual-frequency mode exhibit superior characteristics.

Charge storage in plasma deposited thin films

Abstract: The authors describe the production of electrets prepared at ambient temperature in a dual-mode microwave/radiofrequency plasma reactor on single-crystal silicon substrates. They consist of 0.5-1.5- mu m-thick films of plasma silicon dioxide, plasma silicon nitride, plasma polymerized hexamethyldisilazane (pp-HMDSN), or a multilayer structure of these materials. The electret characteristics can be controlled by varying the plasma parameters and by a subsequent heat treatment, followed by a HMDSN-vapor surface modification. In order to characterize the charge storage capability, the samples were positively or negatively corona-charged and the charge decay was observed by measuring the surface potential at different temperatures. In addition, thermally stimulated current spectra were measured to obtain information about the activation processes. >

Fourier Transform Infrared Photoacoustic Spectroscopy of Amorphous Carbon Films

Abstract: Phase Fourier Transform Infrared Photoacoustic Spectroscopy (PHAS-FTIR/PAS) can distinguish between surface and bulk chemical structure. In the present work, PHASFTIR/PAS is applied to the study of hydrogenated amorphous carbon (a-C:H) films deposited in a dual microwave/radio-frequency plasma. It is shown that spectra correlate well with physico-chemical properties of a-C:H films.