High-Temperature Molecular Beam Epitaxy of Hexagonal Boron Nitride with High Active Nitrogen Fluxes

Homoepitaxy of Boron Nitride on Exfoliated Hexagonal Boron Nitride Flakes

Although large efforts have been made to improve the growth of hexagonal boron nitride (hBN) by heteroepitaxy, the non-native substrates remain a fundamental factor that limits the quality. This problem can be solved by homoepitaxy, which is the growth of hBN on hBN substrates. In this report, we demonstrate the homoepitaxial growth of triangular BN grains on exfoliated hBN flakes by Metal-Organic Vapor Phase Epitaxy and show by atomic force microscopy and photoluminescence that the stacking of these triangular islands can deviate from the AA' stacking of hBN. We show that the stacking order is enforced by the crystallographic direction of the edge of the exfoliated hBN flakes, with armchair edges allowing for centrosymmetric stacking, whereas zigzag edges lead to the growth of noncentrosymmetric BN polytypes. Our results indicate pathways to grow homoepitaxial BN with tunable layer stacking, which is required to induce piezoelectricity or ferroelectricity.

The Growth of Hexagonal Boron Nitride Quantum Dots on Polycrystalline Nickel Films by Plasma-Assisted Molecular Beam Epitaxy

In this report, quantum dots of hexagonal boron nitride (h-BN) were fabricated on the surface of polycrystalline Ni film at low growth temperatures (700, 750, and 800 °C) by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction could trace the surface condition during the growth and perform the formation of BN. The observation of surface morphology by scanning electron microscopy and atomic force microscopy showed the nanodots of BN on Ni films. The existence of crystal h-BN quantum dots was determined by the analysis of Raman spectra and Kevin probe force microscopy. The cathodoluminescence of h-BN quantum dots performed at the wavelength of 546 and 610 nm, attributed to the trapping centers involving impurities and vacancies. Moreover, the influence of temperatures for the substrate and boron source cell was also investigated in the report. When the k-cell temperature of boron and growth temperature of substrate increased, the emission intensity of cathodoluminescence spectra increased, indicating the better growth parameters for h-BN quantum dots.

The Effect of SiC Content on Microstructure and Microwave Heating Rate of h-BN/SiC Ceramics Fabricated by Spark Plasma Sintering

Hexagonal boron nitride/silicon carbide (h-BN/SiC) ceramics were fabricated by a spark plasma sintering (SPS) method. Phase and microstructure of ceramics were characterized and observed, respectively, using the X-ray diffraction, scanning electron microscope and electron probe microanalysis. The effect of molar ratios of SiC to h-BN on the microstructure, relative density, hardness, thermal conductivity, and the heating rate by microwaves on the ceramics were investigated. The results showed that the orientation of flake-like h-BN was significantly influenced by SiC content in h-BN/SiC ceramics. With the increasing of SiC content, the h-BN flakes gradually became an isotropic distribution from the preferred orientation aligning in a SPS pressure direction. The relative density of h-BN/SiC ceramics was 97.6 ± 0.9% at a molar ratio of SiC to h-BN of 40/60 mol%. The preferential orientation of h-BN flakes contributed to a relatively high thermal conductivity along the SPS pressure direction, which was beneficial to increasing the heating rate of h-BN/SiC ceramics in microwave fields.