Controlled Growth of Architectured Boron Nitride Films by Chemical Vapor Deposition in Model Microchannels

Architectured sp2 boron nitride films were synthesized by controlled growth in silicon microchannels of BN nanowalls (NWs) by chemical vapor deposition from a BCl3–NH3–N2 gas mixture at 700 °C. Advanced characterizations by scanning electron microscopy, transmission electron microscopy (TEM), Raman spectroscopy, and atomic force microscopy demonstrated the gradual evolution of the BN film microstructure inside the microchannel, from disordered turbostratic (t-BN) at the entrance to a textured BN NW film toward the bottom. Such a change in the microstructure was attributed to local gas-phase changes (e.g., precursor depletion, HCl formation) along the microchannel. The microstructure transition can be tailored by adjusting the channel opening height. Complementary structural and chemical analyses with high spatial resolution (TEM, electron energy loss spectroscopy, X-ray photoelectron spectroscopy) revealed the remarkably well-organized structure of the NWs, given their low deposition temperature, providing insights into their growth mechanism. The curvature and reorientation of the originally flat t-BN layers allow the lateral growth of NWs, preferentially perpendicular to the substrate. Meanwhile, t-BN is codeposited between the NWs. The final microtexture of the film, combining nanowalls and disordered t-BN, demonstrates the structural versatility of sp2-BN, including organized and disordered forms, as well as various structural defects.