Ultrafast ablation with high-pulse-rate Nd:YAG lasers.: Part II:: Experiments on deposition of diamond-like carbon films

The novel technique of ultrafast pulsed laser deposition has been experimentally demonstrated by depositing high quality diamond-like carbon films using high repetition rate Nd:YAG lasers. A very effective evaporation regime was achieved by keeping the laser intensity on the target surface close to the optimum values determined in Part 1 [1] of this paper. Evaporation of the target by low energy laser pulses at an intensity of 10(9) W/cm(2) allows the elimination of particles from the vapour and results in films with very high surface quality, whilst the very high repetition rate increases the overall deposition rate. Results are presented on the evaporation of carbon using either a 10 kHz, 120 ns Q-switched Nd:YAG laser, or a 76 MHz 60 ps mode-locked Nd:YAG laser. The number of particles visible in optical microscope on the DLC film deposited using the mode-locked laser was less than one particle per mm(2). SEM images demonstrated that the deposited film had a very fine surface texture of with nanoscale irregularities on the surface. AFM surface microroughness measurements revealed a saturation-like behaviour of the RMS roughness at the level 12 nm over the whole deposited surface area for 10 kHz Q-switched laser evaporation and almost an atomic level (< 1 nm) roughness for the 76 MHz mode-locked laser evaporation. Raman spectroscopy of the deposited films indicated that they were a mixture of sp(3) and sp(2) bonded amorphous carbon. The thickness of the diamond-like carbon film deposited simultaneously on two 4 inch silicon wafers varied by only +/-5% over an area of similar to 250 cm(2) and the deposition rate was similar to 2 - 6 Angstrom/s at a distance of similar to 150 mm from the target.