Gas-liquid coexistence curves terminate at their critical points, where second-order phase transitions occur. The specific heat and compressibility increase greatly as the fluid systems approach their critical points. As a result, thermal diffusion is suppressed and the perturbations of the temperature, pressure and density propagate as acoustic waves. In this paper, we irradiate near-critical benzene with a laser beam of 266 nm in wavelength, the energy flux of which is 1.3 and 3.9 mW mm~(-2), and show that benzene is dissociated and various carbon nano/microstructures such as carbon onions and coils are created. Carbon onions are produced in both subcritical (200 deg C) and supercritical (290 deg C) benzene, whereas carbon coils are produced on an alloy catalyst composed of (Fe:Cr:Ni = 74:18:8) in supercritical benzene irradiated with a laser beam of 3.9 mW mm~(-2). The operational temperature of the present method is much lower than that used in conventional carbon structure synthesizing methods and a large number of carbon structures, such as carbon onions and coils, are produced in supercritical benzene.
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