Cluster-assembled amorphous carbon nano-foam synthesised by high-pulse-rate laser ablation

We report on a new fractal amorphous carbon nano-foam with a large fraction of tetrahedrally-bonded atoms. The material was produced by high-repetition-rate laser ablation in an argon-atmosphere which resulted in a high collision frequency between carbon atoms and ions in the laser plume and argon atoms in the chamber. This creating the optimal vapor temperature and density for the efficient formation of 4-membered
bonds typical of diamond. The bulk density of various foam samples is in the range
whilst the specific surface area is 300–400 m2/g comparable to that of carbon aerogels. At low temperatures the as-deposited foam exhibits a strong positive electrostatic charge and non-linear current-voltage characteristics with strong hysteresis, indicative its insulating nature. After annealing, the resistivity of the foam measured at low-voltage (±30 V) is at room temperature and at 80 K, with virtually no hysteresis. The DC conductivity of this low-density carbon foam and its temperature dependence appears to be very close to that of RF-sputtered solid amorphous diamond-like carbon films.