Pulsed-laser deposition and boron-blending of diamond-like carbon (DLC) thin films

Diamond-like carbon (DLC) films, both pure and doped with boron, were prepared by pulsed laser deposition (PLD) with a XeCl excimer laser employing polycrystalline graphite and boron carbide targets. As substrates served silicon(111) wafers. The deposition parameters such as the laser intensity, vacuum, supporting gas conditions, substrate temperature, target-substrate distance, substrate combination and composition could be controlled independently, and thus, were used to modify the film properties and composition. Optical emission diagnostics of the laser plasma was performed at various locations between the target and the substrate. In the high power regime (> 108 W cm−2), pulsed laser evaporation resulted in the emission of excited C2 molecule radicals. High incident energies were necessary for surmounting potential barriers to the formation of sp3 bonds. Films with the highest sp3 content were formed with small distance between target and substrate, high laser intensities (I ≈ 109 W cm−2), and low base pressures (<10−5 mbar). The room temperature laser-deposited films showed a single broad laser Raman band peaked around 1530 cm−1 typical for unhydrogenated diamond-like a-C films. Coevaporation of a B4C target led to a-C:B films exhibiting laser Raman spectra practically similar to the a-C films.