Formation of cluster-assembled carbon nano-foam by high-repetition-rate laser ablation

High-repetition-rate laser ablation and deposition of carbon vapours result s in the formation of quite different carbonaceous structures depending on the pressure of the ambient Ar gas in the chamber. Diamond-like carbon film s form at a pressure below approximate to 0.1 Torr whereas a diamondlike ca rbon nano-foam is created above 0.1 Torr. Although laser-deposited amorphou s carbon films have been extensively investigated in the past, here we pres ent what, to our knowledge, is the first report of the production of a gran ular low-density carbon nano-foam with rich fraction of sp(3) bonding. The bulk density of various foam samples was in the range (2-10) x 10(-3) g/cm( 3), and the specific surface area was 300-400 m(2)/g. The resistivity of th e foam measured at low-voltage (+/-30 V) is (1-3) x 10(9) Ohm cm at room te mperature and (1-10)x 10(13) Ohm cm at 80 K. The dc conductivity of this lo w-density carbon foam and its temperature dependence appears to be very clo se to that of RF-sputtered solid amorphous diamond-like carbon films. The presented kinetic analysis of the carbon vapour in the Ar ambient demon strates qualitative agreement between the predicted laser plume parameters and those measured in the experiments. Theoretical predictions of the param eters and the process of carbon vapour diffusion through the ambient gas, a llow us to propose a self-consisted periodic model leading to the formation of the carbon clusters in the experimental chamber.