Pulsed laser deposition of diamondlike carbon films on polycarbonate

Diamondlike carbon films have been deposited on polycarbonate by pulsed laser deposition technique by irradiating highly oriented pyrolytic graphite with high-energy excimer laser pulses (248 nm wavelength, 20 ns duration, and up to 37 J/cm(2) energy density). Irradiations were performed in different atmospheres: (1) moderate vacuum (10(-2) Pa), (2) nitrogen atmosphere (1 Pa), and (3) argon atmosphere (1 Pa). The structure of the deposited films was analyzed with Raman spectroscopy. In vacuum-deposited films, a transition from mainly disordered graphitic carbon to up to 80% ta-C occurs above a laser energy density threshold of 7 J/cm(2). No such transition was observed in films deposited in nitrogen up to energy densities as high as 33 J/cm(2). In argon atmosphere the transition is only observed at high-laser energy density, approximate to23 J/cm(2). The results are discussed in terms of combined ballistic and chemical effects affecting both plume dynamics and bonding configuration of the growing film. The Fourier transform infrared spectroscopy showed that films deposited in nitrogen atmosphere contain nitrogen and hydrogen, thus becoming unstable when exposed to air. The hardness of ta-C coated polycarbonate, as measured by nanoindentation technique, is about 8 GPa, while when disordered graphitic carbon was deposited on the substrates hardness does not exceed 5 GPa. Measurement of the internal stress in the deposited films suggests that atomic relaxation occurs for laser-pulse energies exceeding 10 J/cm(2), with residual stress values of the order of 1 GPa in films deposited in vacuum. In these conditions, given the strong interfacial chemical bonds, the adhesion strength is very high. In films deposited in nitrogen atmosphere the internal stress is almost constant for pulse laser energy up to 20 J/cm(2) while it slowly increases at higher energies. (C) 2003 American Institute of Physics.