Impact of Thickness-Dependent Nanophotonic Effects on the Optical Response of Color Centers in Hexagonal Boron Nitride.

Among a broad diversity of color centers hosted in layered van der Waals materials, the negatively charged boron vacancy (V) center in hexagonal boron nitride (hBN) is garnering considerable attention for the development of quantum sensing units on a two-dimensional platform. In this work, we investigate how the optical response of an ensemble of V centers evolves with the hBN thickness in a range of a few to hundreds of nanometers. We show that the photoluminescence intensity features a nontrivial evolution with thickness, which is quantitatively reproduced by numerical calculations taking into account thickness-dependent variations of the absorption, radiative lifetime, and radiation pattern of V centers.

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.

Cathodoluminescence spectroscopy of monolayer hexagonal boron nitride.

Cathodoluminescence (CL) spectroscopy is a suitable technique for studying the luminescent properties of optoelectronic materials because CL has no limitation on the excitable bandgap energy and eliminates ambiguous signals due to simple light scattering and resonant Raman scattering potentially involved in the photoluminescence spectra. However, direct CL measurements of atomically thin two-dimensional materials have been difficult due to the small excitation volume that interacts with high-energy electron beams. Herein, distinct CL signals from a monolayer hexagonal BN (hBN), namely mBN, epitaxial film grown on a graphite substrate are shown by using a CL system capable of large-area and surface-sensitive excitation.

Boron and Nitrogen Isotope Effects on Hexagonal Boron Nitride Properties.

The unique physical, mechanical, chemical, optical, and electronic properties of hexagonal boron nitride (hBN) make it a promising 2D material for electronic, optoelectronic, nanophotonic, and quantum devices. Here, the changes in hBN's properties induced by isotopic purification in both boron and nitrogen are reported. Previous studies on isotopically pure hBN have focused on purifying the boron isotope concentration in hBN from its natural concentration (≈20 at% B, 80 at% B) while using naturally abundant nitrogen (99.

High p doped and robust band structure in Mg-doped hexagonal boron nitride.

In two dimensional materials, substitutional doping during growth can be used to alter the electronic properties. Here, we report on the stable growth of p-type hexagonal boron nitride (h-BN) using Mg-atoms as substitutional impurities in the h-BN honeycomb lattice. We use micro-Raman spectroscopy, angle-resolved photoemission measurements (nano-ARPES) and Kelvin probe force microscopy (KPFM) to study the electronic properties of Mg-doped h-BN grown by solidification from a ternary Mg-B-N system.

Preparation of Confined One-Dimensional Boron Nitride Chains in the 1-D Pores of Siliceous Zeolites under High-Pressure, High-Temperature Conditions.

Low-dimensional boron nitride (BN) chains were prepared in the one-dimensional pores of the siliceous zeolites theta-one (TON) and Mobil-twelve (MTW) by the infiltration, followed by the dehydrocoupling and pyrolysis of ammonia borane under high-pressure, high-temperature conditions. High-pressure X-ray diffraction in a diamond anvil cell and in a large-volume device was used to follow in situ these different steps in order to determine the optimal conditions for this process. Based on these results, millimeter-sized samples of BN/TON and BN/MTW were synthesized.

Bernal Boron Nitride Crystals Identified by Deep-Ultraviolet Cryomicroscopy.

The presence of metastable Bernal stacking boron nitride is verified by combining second harmonic generation (SHG) and photoluminescence (PL) spectroscopy. The scanning confocal cryomicroscope, operating in the deep-ultraviolet range, shows a one-to-one correlation between inversion symmetry breaking probed by SHG and the detection of an intense PL line at ∼6.035 eV, the specific signature of the noncentrosymmetric Bernal stacking.

Monolayer Boron Nitride: Hyperspectral Imaging in the Deep Ultraviolet.

The optical response of 2D materials and their heterostructures is the subject of intense research with advanced investigation of the luminescence properties in devices made of exfoliated flakes of few- down to one-monolayer thickness. Despite its prevalence in 2D materials research, hexagonal boron nitride (hBN) remains unexplored in this ultimate regime because of its ultrawide bandgap of about 6 eV and the technical difficulties related to performing microscopy in the deep-ultraviolet domain. Here, we report hyperspectral imaging at wavelengths around 200 nm in exfoliated hBN at low temperature.

Hexagonal Boron Nitride Crystal Growth from Iron, a Single Component Flux.

The highest quality hexagonal boron nitride (hBN) crystals are grown from molten solutions. For hBN crystal growth at atmospheric pressure, typically the solvent is a combination of two metals, one with a high boron solubility and the other to promote nitrogen solubility. In this study, we demonstrate that high-quality hBN crystals can be grown at atmospheric pressure using pure iron as a flux.

InAs quantum dot in a needlelike tapered InP nanowire: a telecom band single photon source monolithically grown on silicon.

Realizing single photon sources emitting in the telecom band on silicon substrates is essential to reach complementary-metal-oxide-semiconductor (CMOS) compatible devices that secure communications over long distances. In this work, we propose the monolithic growth of needlelike tapered InAs/InP quantum dot-nanowires (QD-NWs) on silicon substrates with a small taper angle and a nanowire diameter tailored to support a single mode waveguide. Such a NW geometry is obtained by a controlled balance over axial and radial growths during the gold-catalyzed growth of the NWs by molecular beam epitaxy.