Self-limiting of the thickness of diamond-like films deposited in the laser pyrolysis of liquid aromatic hydrocarbons

The process involving the self-regulation of the thickness of a diamond-like film, deposited on the interface between a transparent dielectric substrate (glass, sapphire, quartz) when a liquid aromatic hydrocarbon is heated by the radiation of a copper vapour laser, was observed and investigated. The film thickness reaches 100 nm and ceases to depend on the number of laser pulses, whereas the depth of the ablated region of the substrate, in which the film is deposited, increases monotonically. The self-regulation effect, observed over a wide range of pressures (from 0.08 to 10 bar), is caused both by the heating of the deposited film by the laser radiation to the graphitisation temperature and by its mechanical damage as a consequence of the difference between the coefficients of thermal expansion of the film and the substrate. The latter has been confirmed with the aid of x-ray Auger spectroscopy, the results of which indicate the formation in the liquid of a nanodisperse suspension of carbon particles with the diamond type of bonding.