PROPERTIES OF UNHYDROGENATED DIAMOND-LIKE CARBON-FILMS DEPOSITED BY ARF EXCIMER-LASER

Unhydrogenated diamond-like carbon (DLC) films were prepared by 193 nm, 24 ns pulse duration, 2-10 Hz frequency, ArF excimer laser ablation of a high-purity graphite target. Alternatively, the laser plume was enhanced by means of an electrical discharge ignited synchronously with every laser pulse (the so-called laser-plasma technique). For this purpose a special graphite electrode at a bias of 3 kV was placed near the target. The effect of plasma ignition, along with the effects of substrate temperature and beam power density on the structure and mechanical and optical properties of the deposited films were studied. The laser plasma technique results in deposition rates five times as high in comparison with its laser ablation counterpart. DLC films deposited by laser ablation consist of a 'diamite' phase, with the Raman peak positioned at 1540 +/- 20 cm(-1), and amorphous sp(3) bonded carbon. Films deposited by the laser-plasma technique have a more complicated structure: their Raman spectra also show an interplane defect band and a crystalline graphitic phase. Adhesion of the DLC films to the substrates increases rapidly with increase in the substrate temperature and beam power density at the target. The typical hardness of the DLC films deposited under optimal conditions is 36 +/- 4 GPa. The DLC films are transparent in the infrared range 2-20 mu m, without any absorption band. The films showed a good stability in an HF-HNO3 mixture.