Laser Annealing Of Amorphous Carbon Films

摘要

Amorphous (α-C) Carbon thin films were deposited, using pulsed laser deposition (PLD) with a Nd:YAG laser (1064 nm, 7 ns), from a pyrolytic graphite target, on (100) silicon and refractory metal (Mo) substrates to a film thickness of 55,400 and 500 nm. Samples were grown at RT and then annealed by a laser annealing technique, to reduce residual stress and induce a locally confined "graphitization" process. The films were exposed to irradiation, in vacuum, by a Nd:YAG pulsed laser, operating at different wavelengths (VIS, N-UV) and increasing values of energy from 6-100 mJ/pulse. The thinner films were completely destroyed by N-UV laser treatment also at lower energies, owing to the almost direct propagation of heat to the Si substrate with melting and ruinous blistering effects. For thicker films the Raman micro-analysis evidenced the influence of laser treatments on the sp~3/sp~2 content evolution, and established the formation of aromatic nano-structures of average dimension 4.1÷4.7 nm (derived from the I_D/I_G peak ratio), at fluence values round 50 mJ/cm～2 for N-UV and 165 mJ/ cm～2 for VIS laser irradiation. Higher fluences were not suitable for α-Carbon "graphitization", since a strong ablation process was the prominent effect of irradiation. Grazing incidence XRD (GI-XRD) used to evaluate the dimension and texturing of nano-particles confirmed the findings of Raman analysis. The effects of irradiation on surface morphology were studied by SEM analysis.