| Cubic nitride boron (c-BN) films have been prepared at room temperature (25℃) by radio frequency plasma enhanced pulsed laser deposition (RF-PEPLD), assisted with substrate negative bias. In this paper, we primarily studied the effect of laser energy density, radio frequency power, substrate bias and depositing time on the growth of c-BN films, and analyzed the formation process and mechanism of c-BN films deposited by RF-PEPLD method at room temperature.The second harmonic produced by a Q-switched Nd:YAG laser with wavelength e=532 nanometers (nm), pulse width 0 nanoseconds (ns) and repetition frequency i=1 Hz was used to bombard a highly pure solid hexagonal BN (h-BN) target (96%), with diameter of 2cm.In a vacuum chamber, boron nitride (BN) film was deposited on the single-crystal silicon substrate. Components, structure and surface morphology of the resulted films were identified by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and Scanning electronic microscopy (SEM). The analyses showed the content of cubic boron nitride in the resultant films on substrates was rather high and crystal particles of c-BN with uniform size, smooth crystal plane and regular shapes (quadrangle and hexagon) densely arrayed on the substrate. The experimental evidences indicated that three deposition parameters, i.e., energy density of laser, rf plasma power and substrate negative bias played key roles in the growth of the c-BN films at room temperature. On this basis, the explanation of formation process and mechanism of c-BN film was given. In the growth of c-BN films, the bombardment of particles with high energy plays a vital role. On the other hand, Explosive Boron Nitride (E-BN), another high-pressure phase of BN, was obtained in the resultant films. We also studied the thermodynamic parameters of the growth of E-BN films.Presently, the nucleation and growth mechanism of diamond hasn't been known completely. Thermodynamically, the nucleation and growth of diamond at low temperature and low pressure is still considered as a paralogism. We analyzed the nucleation act of diamond in Chemical Vapor Deposition (CVD) from the view of thermodynamics in the paper.A new nanothermodynamic approach was proposed, based on the established carbon thermodynamic equilibrium phase diagram. The study showed that the effect of surface tension induced by the nanosize curvature of critical nuclei could drive metastable phase region of diamond nucleation in carbon diagram into stable phase region, consequently, for both of homogenous and heterogeneous nucleation processes, diamond nucleation would be prior to graphite nucleation in competing growth of diamond and graphite upon chemical vapor deposition (CVD).Based on the above nanothermodynamic view, we also studied the effect of nanosize-induced additional pressure on Gibbs free energy of critical nuclei upon pulsed laser induced liquid-solid interfacial reaction (PLIIR). It was found that the smaller size of 2-5nm and lower forming energy of 1 X 10-15J of diamond nuclei were deduced in the pressure-temperature region of 10-15GPa and 4000-5000K created by PLIIR, from our analysis. Meanwhile, the probability of graphite to diamond transition was rather high, up to 10-3-10-2 in the same pressure-temperature region.In the end of the paper, we discussed the particular advantage of RF-PEPLD for deposition of c-BN thin films and the important meaning of the nanothermodynamic theory proposed by this paper.
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