Laser-induced synthesis of cubic BN nanoneedles: a new approach to fabricating nanomaterials for advanced applications

This study demonstrates a novel laser processing technique for the direct conversion of amorphous boron nitride (a-BN) into phase-pure cubic boron nitride (c-BN) nanoneedles. c-BN is a promising material for power electronics due to its unique properties, including hardness, chemical durability, and thermal resistance. However, the production of phase-pure c-BN nanodots and thin films under ambient conditions has been hindered by significant challenges. This study shows that nanosecond laser irradiation induces the melting of BN, resulting in the formation of an undercooled molten BN phase. At a threshold energy density of 0.3 J/cm2, a first-order phase change from a-BN to phase-pure single-crystalline c-BN is observed. Detailed analysis employing high-resolution scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), high-resolution Raman spectroscopy, and photoluminescence investigations confirms the formation of c-BN nanoneedles. Ab initio molecular dynamics simulations of pulsed laser melting and quenching further elucidate the direct conversion of molten BN into c-BN. Laser-irradiated c-BN crystallites exhibit sharp emission lines at approximately 1.97 eV and 2.15 eV, corresponding to the radiation-cubic (RC) centers and consistent with photoluminescence from inherent vibrionic defects connected to nitrogen-vacancy defects. This innovative laser processing technique offers a scalable and cost-effective method for producing nano- and microcrystalline c-BN thin films, thereby opening avenues for applications in nanophotonics, quantum computing, and high-power and radio frequency (RF) electronics.