New Phases of Boron Nitride Grown by Laser-Plasma Synchronous Chemical Vapor Deposition

Dense sp3-bonded phases of boron nitride (BN) are known to grow under extremely high-pressure and high-temperature conditions like diamond is. However, we found that they grew at low pressures around 10 Torr and temperatures below 800$^{\circ}$ by plasma-assisted chemical vapor deposition where a pulsed excimer-laser at 193nm irradiating on the growing film surface induced highly nonequillibirum conditions. New polytypic forms of sp3-bonded BN, i.e., 5H-, 6H-, and 30H-BN were found and their crystal structures were discussed in terms of metastability, ionicity, hexagonality, and close-packing index. Based on the detailed analyses of the polytypic strtuctures of BN in comparison with C, SiC and AlN, we propose the ``Bond Strength Initiative Rule'', which helps to explain the growth of nonequillibrium phases from the vapor.