Processing of amorphous carbon films by ultrafast temperature treatment ina confined geometry

A pressure cell with an anvil made of sapphire and the other made of tungst en carbide, was constructed to process thin film samples using a high power Nd:YAG pulsed laser, in a regime of ultrafast quenching rate and confined geometry. The sapphire anvil worked as the optical window to the laser beam and also as a good thermal conductor substrate. Thin films of amorphous ca rbon deposited over copper substrate were processed under pressure by Nd:YA G laser pulses. This process induces the formation of a high temperature re gion at the sample surface during a very short time interval of the order o f the 8 ns laser pulse duration. To avoid the complete evaporation of the f ilm, an external pressure of about 0.5 to 1.0 GPa was applied, confining th e sample. With the aid of the nanosecond pulsed laser, absorbed on a very t hin film sample, this specially designed apparatus provides the means to pr oduce ultrafast quenching as the formation of a plume is suppressed and hea t dissipation is accelerated by the high thermal conductivity of the copper substrate and sapphire anvil. The processed samples were analyzed by micro Raman spectroscopy and the results indicated the formation of polyynic carb yne structures, as revealed by the presence of a characteristic Raman peak at about 2150 cm(-1). Another set of Raman peaks observed at 996, 1116, and 1498 cm(-1), also appeared when the amorphous carbon film was processed wi th a sequence of more than three consecutive laser pulses. These peaks, who se general aspect is very similar to that of polyacethylene (CnHn), could b e ascribed to the cumulenic carbyne structure, stabilized by some dispersed copper atoms. (C) 2001 American Institute of Physics.