Terence O'brien

Application of diamond-like carbon films as hermetic coatings on optical fibres

Abstract The application of diamond-like carbon (DLC) films as hermetic coatings on optical fibres was investigated. Films with refractive indices in the range 1.7-2.0 (at λ = 675 nm) were deposited at pressures up to 5 Torr. The hermeticity of the coatings was determined using water penetration studies monitored using a combination of spectroscopic ellipsometry and atomic force microscopy. The resistance to moisture penetration was found to be better for higher refractive index films. The coatings were applied to optical fibres in a continuous in-line system as the fibre was drawn. Coatings of thicknesses in the range of 10–30 nm were achieved on quartz fibres with outer diameters of 200–1000 μm at fibre drawing speeds of up to 3 m min−1.

Comparison of diamond-like carbon films deposited from 40 kHz and 13.56 MHz r.f. plasmas

Abstract R.f. plasma discharges are a standard method for depositing diamond-like carbon (DLC) films. This work looks at the effect of the r.f. driving frequency by studying films deposited at both 40kHz and 13.56 MHz. Films were grown on a 10 cm diameter driven electrode from CH4 H2 and C2H2 H2 gas mixtures onto 75 × 25 mm2 soda glass substrates at process pressures in the range 6–80 Pa (0.05–0.6 Torr). Film growth was monitored by in situ ellipsometry (at 675 nm) which allows measurement of the refractive index, extinction coefficient and thickness. The refractive index has been shown previously to be a reliable measure of film quality as determined by the hardness, scratch resistance and wear resistance. Films are assessed as a function of deposition pressure and r.f. frequency. The film quality is seen to improve as the pressure decreases and as the r.f. power increases for both driving frequencies. It is necessary to deposit 13.56 MHz films at low pressure, typically less than 12 Pa (0.1 Torr). Similar quality films may be deposited at 40 kHz at pressures up to 80 Pa (0.6 Torr).

QUANTITATIVE MEASUREMENTS OF ATOMIC-HYDROGEN DURING THE DEPOSITION OF DIAMOND-LIKE CARBON-FILMS

Abstract Measurements of the level of atomic hydrogen in a 13.56 MHz r.f. plasma were obtained during the deposition of diamond-like carbon (DLC) films. Two techniques were used, firstly multiphoton laser induced fluorescence (MPLIF), and secondly a novel combination of Langmuir probe and emission spectroscopy. In the latter technique the data obtained from electron energy distribution functions (EEDFs) and hydrogen emission line intensities were combined using a computer modelling technique to give the atomic hydrogen concentration. This system can potentially be used as a portable atomic hydrogen probe. The results were compared with those obtained using the MPLIF technique which was calibrated using a hydrogen transfer standard. The transfer standard was calibrated by titration. The two techniques were used to measure atomic hydrogen, initially in a hydrogen plasma and subsequently in acetylene-hydrogen containing plasmas during the deposition of DLC films. In conjunction with these measurements, in situ ellipsometry was used to obtain the film thickness, refractive indices and extinction coefficients. A correlation was obtained relating the concentration of atomic hydrogen with the in situ ellipsometry data for films with refractive index between 1.6 and 2.1 (at 675 nm).

The effect of atomic hydrogen on diamond-like carbon film production

Abstract A method of making quantitative measurements of atomic hydrogen levels in diamond-like carbon (DLC) deposition plasmas is discussed. Multiphoton laser induced fluorescence (MPLIF) is used to detect ground state hydrogen atoms. The choice of excitation scheme to maximize the ratio of fluorescence signal to ionization is explained. The MPLIF measurements are calibrated using a combination of a flow reactor and titration absolute standard, and a transferable hot filament atomic hydrogen source specifically designed for installation in the DLC deposition system. The characteristics of the complete system are described, and initial measurements in hot filament reactors are presented.