Production of carbon nanoclusters supported on a graphite foil by laser ablation under supercritical conditions

Microscopic model of charge density distribution for critical and supercritical states of carbon

“…Accounting for the exponential increase in the amplitude of the specific mode of fluctuations during spinodal decomposition of a labile liquid phase, 2 we considered this bimodal distribution of carbon nanoclusters as two superimposed distributions. One distribution with N = 5×10 5 atoms and T » T crit » 7×10 3 K was well fitted by the function I(N/Z) over the range of N/Z = = 8×10 4 -5×10 5 atoms, but over the range of N/Z = (2-4)×10 4 atoms, the experimental function I(N/Z) is inconsistent with the sharp distribution at N = 3×10 4 atoms and T » T crit . The temperature of the smaller carbon nanoclusters is much higher in accordance with the predictions of a current theory of the supercritical state 1 (R ~T -2/3 ) and can be estimated as T » » 2.8×10 4 K. This temperature of a local region in a lasergenerated plasma, where spinodal decomposition of the largest carbon nanoclusters takes place, is consistent with the temperatures (T < 3×10 4 K) in a near-surface 'opaqueness' region of the carbon plasma.…”

“…2 Under laser ablation of graphite, these carbon droplets were experimentally detected as charged carbon nanoclusters 3 in a gas phase by a real-time electrostatic probe technique (Figure 1), and they were also observed by scanning electron microscopy as neutral carbon nanoclusters deposited on a graphite foil surface by the laser quenching under supercritical conditions. 4 These experimental data 3,4 allow us to estimate the correlation radius R of critical density fluctuations (a characteristic size of spherical nanoclusters), which is about 10-30 nm (10 4 -10 6 atoms per cluster) for a mass density of the liquid carbon phase of near 2 g cm -3 . 5 The majority of physical and chemical properties of carbon nanoclusters are similar to those of a macroscopic condensed phase (e. g., thermionic emission, 6 delocalisation of an excessive charge, high stability and slow growth of the consequent ionisation potentials of multiply charged ions 7 ).…”

“…Two main terms of the expanded function I(N/Z) are related to two modes of nanoclusters centred at N/Z = 3×10 4 and N/Z = = 5×10 5 atoms. These bimodal distributions of [C N Z ] by N/Z and [C N 0 ] by N are shown in Figure 1 (curves 2 and 3).…”