Carbon-doped Hexagonal Boron Nitride Research Articles

Spectrum of Tunneling Transport through Phonon-Coupled Defect States in a Carbon-Doped Hexagonal Boron Nitride Barrier.

Defects in hexagonal boron nitride (h-BN) play important roles in tunneling transport through the h-BN barrier. Here, using carbon-doped h-BN (h-BN:C) as a tunnel barrier containing defects in a controlled manner, we investigated tunneling transport through defects in the h-BN:C/graphene heterostructures. Defect-assisted tunneling through a specific kind of carbon-related defect was observed in all measured devices, where the defect level was always located at ∼0.1 eV above the graphene's charge neutrality point. We revealed a phonon-assisted inelastic process in the defect-assisted tunneling, in which carriers tunnel through the defect with phonon emission. Furthermore, when the h-BN:C barrier was thick (12 layers, ∼4 nm), sequential tunneling through two defects became dominant, where the phonon-assisted inelastic process shows substantial effects between the two defects. This study reveals the contribution of phonons to defect-assisted tunneling transport, which is essential for the development of defect-related van der Waals (vdW) electronic techniques.

Ultrathin carbon doped hexagonal boron nitride films for electromagnetic interference shielding in the terahertz region

We have investigated the electromagnetic interference (EMI) shielding efficiency of carbon-doped hexagonal boron nitride (hBN) films in 0.3–1.8 THz regions using transmission-based terahertz time-domain spectroscopy (THz TDS). The hBN films were synthesized on Copper foils by atmospheric pressure chemical vapor deposition (APCVD) utilizing ammonia borane (AB) powder as a precursor. Carbon doping of BN films was achieved by using the intrinsic carbon dissolved in the Copper substrate. The EMI shielding efficiencies and the optical, dielectric, and electrical properties of the films were determined using THz TDS. The Absorbance is much greater than the Reflectance indicating that absorption is the dominant mechanism of shielding in these films. These carbon-doped hBN films show a high EMI shielding effectiveness, with 99.99 % EM radiation blocked. A maximum value of 30 dB and 55 dB at 1.72 THz were observed for films with 4.5 nm and 6.5 nm thicknesses. This is equivalent to shielding efficiency per unit thickness of 6667 dB/µm and 8460 dB/µm, which is among the highest reported for 2D materials.

Atomic and Electronic Structure of Defects in hBN: Enhancing Single-Defect Functionalities.

Defect centers in insulators play a critical role in creating important functionalities in materials: prototype qubits, single-photon sources, magnetic field probes, and pressure sensors. These functionalities are highly dependent on their midgap electronic structure and orbital/spin wave function contributions. However, in most cases, these fundamental properties remain unknown or speculative due to the defects being deeply embedded beneath the surface of highly resistive host crystals, thus impeding access through surface probes. Here, we directly inspected the atomic and electronic structures of defects in thin carbon-doped hexagonal boron nitride (hBN:C) by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Such investigation adds direct information about the electronic midgap states to the well-established photoluminescence response (including single-photon emission) of intentionally created carbon defects in the most commonly investigated van der Waals insulator. Our joint atomic-scale experimental and theoretical investigations reveal two main categories of defects: (1) single-site defects manifesting as donor-like states with atomically resolved structures observable via STM and (2) multisite defect complexes exhibiting a ladder of empty and occupied midgap states characterized by distinct spatial geometries. Combining direct probing of midgap states through tunneling spectroscopy with the inspection of the optical response of insulators hosting specific defect structures holds promise for creating and enhancing functionalities realized with individual defects in the quantum limit. These findings underscore not only the versatility of hBN:C as a platform for quantum defect engineering but also its potential to drive advancements in atomic-scale optoelectronics.

Annealing of blue quantum emitters in carbon-doped hexagonal boron nitride

Reliable methods to create quantum emitters in hexagonal boron nitride (hBN) are highly sought after for scalable applications in quantum photonic devices. Specifically, recent efforts have focused on defects in hBN with a zero phonon line at 2.8 eV (436 nm). Here, we employ carbon-doped hBN crystals that were irradiated by an electron beam to generate these emitters and perform annealing treatments to investigate the stability of the emitters. We find that the blue emitters are stable up to ∼800 °C. However, upon annealing to 1000 °C, the emitters disappear, and a family of other emitters appears in the region of hBN that had been irradiated by an electron beam. Our findings contribute to the understanding of emitter species and emitter formation in hBN.

Analysis of the influence of impurity gas on the hydrogen storage performance of Ti/2C-BN

Ti-modified carbon-doped hexagonal boron nitride (Ti/2C-BN) at a concentration of 25 at% exhibits excellent hydrogen storage performance at room temperature. However, the presence of impurities in large-scale hydrogen production processes such as fossil fuel reforming and biomass gasification may contaminate the surface of hydrogen storage materials. Therefore, it is necessary to study the influence of common impurity gases in hydrogen sources, including O2, CO2, H2S, N2, CO, H2O, CH4, Ar, and He, on the adsorption capacity of H2 after pre-adsorption on the Ti/2C-BN surface, as well as their mechanism of influence. The VASP program package based on density functional theory (DFT) is employed to perform relevant simulation calculations. The results show that the hydrogen storage performance on Ti/2C-BN is not affected by CH4, Ar and He. Although O2, CO2 and CO will occupy the active site of the material, the adsorption energy of H2 is between physical adsorption and chemical adsorption, and its influence can be neglected. The adsorption energy of H2 is increased by H2O. The material is poisoned by H2S and N2, causing its adsorption energy to fall below −0.1 eV.

First-principles Study in the Electronic Structure of Carbon-doped Hexagonal Boron Nitride

First-principles Study in the Electronic Structure of Carbon-doped Hexagonal Boron Nitride

An Effective Electrochemical Platform for Chloramphenicol Detection Based on Carbon-Doped Boron Nitride Nanosheets.

Currently, accurate quantification of antibiotics is a prerequisite for health care and environmental governance. The present work demonstrated a novel and effective electrochemical strategy for chloramphenicol (CAP) detection using carbon-doped hexagonal boron nitride (C-BN) as the sensing medium. The C-BN nanosheets were synthesized by a molten-salt method and fully characterized using various techniques. The electrochemical performances of C-BN nanosheets were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that the electrocatalytic activity of h-BN was significantly enhanced by carbon doping. Carbon doping can provide abundant active sites and improve electrical conductivity. Therefore, a C-BN-modified glassy carbon electrode (C-BN/GCE) was employed to determine CAP by differential pulse voltammetry (DPV). The sensor showed convincing analytical performance, such as a wide concentration range (0.1 µM-200 µM, 200 µM-700 µM) and low limit of detection (LOD, 0.035 µM). In addition, the proposed method had high selectivity and desired stability, and can be applied for CAP detection in actual samples. It is believed that defect-engineered h-BN nanomaterials possess a wide range of applications in electrochemical sensors.

Thermodynamic stability and optical properties of C-doping-induced defects in hexagonal boron nitride as potential single-photon emitters

Quantum information technologies have triggered enormous interest in single-photon emitters (SPEs), such as local defects in wide-band-gap semiconductors. Recently, visible single-photon emission was observed in carbon-doped hexagonal boron nitride (h-BN), yet the structure giving rise to the emission has not been unambiguously identified. Further progress in the rational design of SPEs requires a deep insight into all the ground-state properties, the electronic structure of the defects in question, and their relationship with the optical properties. To this end, we apply state-of-the-art computational methods to evaluate the stability and optical properties of defects that can be responsible for the above-mentioned experimental findings. For our analysis, we select seven possible C-based defects: (i) C substitutes B $({\mathrm{C}}_{\mathrm{B}})$, (ii) C substitutes N $({\mathrm{C}}_{\mathrm{N}})$, (iii) C substitutes N and nearest B and N are interchanged $({\mathrm{C}}_{\mathrm{N}}{\mathrm{N}}_{\mathrm{B}})$, (iv) C substitutes N and there is a nearby B vacancy $({V}_{\mathrm{B}}{\mathrm{C}}_{\mathrm{N}})$, and (v) three different configurations of ${V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}}$ (C substitutes B and a nearby N vacancy). We perform calculations of the electronic structure using the linear response approach ($GW$ method), followed by finding the solution to the Bethe-Salpeter equation to obtain the excitation spectra of dynamically stable defects. Our density-functional-theory-based calculations of the optimized geometries and their \ensuremath{\Gamma}-point phonon frequencies reveal that ${V}_{\mathrm{B}}{\mathrm{C}}_{\mathrm{N}}$ is dynamically unstable and undergoes a transformation to one corrugated ${V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}}$ structure. Likewise, the flat ${V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}}$ (with ${C}_{2\mathrm{v}}$ symmetry) lies on a very shallow and anharmonic minimum that would also relax toward the corrugated ${V}_{\mathrm{N}}{\mathrm{C}}_{\mathrm{B}}$ structure. Clearly, our results demonstrate how important is to attest to the dynamical stability of any proposed structure. Upon comparing our results of the considered defects with the reported experimental SPE spectra, we show that only the ${\mathrm{C}}_{\mathrm{N}}$ defect has an excitation spectrum fitting the conditions for the observed single-photon emission. Importantly, this defect is found to be the most thermodynamically stable among those under consideration.

Boron nitride for enhanced oxidative dehydrogenation of ethylbenzene

It is demonstrated experimentally and confirmed theoretically that highly defective boron nitride showed outstanding performance for oxidative dehydrogenation of ethylbenzene. The catalyst is derived from carbon-doped hexagonal boron nitride nanosheets synthesized via a two-step reaction when participating the oxidative dehydrogenation reaction. The first step yields a polymeric precursor with the atomic positions of B, C, N relatively constrained, which is conducive for the formation of carbon atomic clusters uniformly dispersed throughout the BN framework. During the oxidative dehydrogenation of ethylbenzene to styrene, the nanoscale carbon clusters are removed and highly defective boron nitride (D-BN) is obtained, exposing boron-rich zigzag edges of BN that act as the catalytic sites. The catalytic performance of D-BN is therefore remarkably better than un-doped h-BN. Our results indicate that dispersed C-doping in h-BN is highly effective in terms of defect formation and resultant enhanced activity in oxidative dehydrogenation reactions. Carbon-doped boron nitride with uniformly dispersed dopants at nanoscale was obtained. Atomic carbon clusters are removed during oxidative dehydrogenation reaction, leading to the formation of highly active sites for catalytic conversion of ethylbenzene to styrene.

Electronic structure and scanning tunneling microscopy images of heterostructures consisting of graphene and carbon-doped hexagonal boron nitride layers

Electronic structure and scanning tunneling microscopy images of heterostructures consisting of graphene and carbon-doped hexagonal boron nitride layers

Shallow and deep levels in carbon-doped hexagonal boron nitride crystals

We study shallow and deep levels in carbon-doped hexagonal boron nitride crystals precipitated from a molten metal solution in a high-temperature furnace. Reflectance and photoluminescence under deep ultraviolet excitation are complemented by spatially resolved experiments by means of a scanning confocal micro-photoluminescence setup operating in the ultraviolet. Isotopically controlled carbon doping does not induce any energy shift of the well-known deep-level emission at 4.1 eV. Our detailed characterization in a series of carbon-doped crystals reveals that the incorporation of carbon during the growth process results in a distinct class of shallow and deep levels in hexagonal boron nitride, calling into question the exact role of carbon in the growth of hexagonal boron nitride and its direct or indirect influence on the formation of the crystal defects.

Synergistic View of Magnetism, Chemical Activation, and Oxygen Reduction Reaction as Well as Oxygen Evolution Reaction Catalysis of Carbon-Doped Hexagonal Boron Nitride from First Principles

Although substitution of carbon (C) in hexagonal boron nitride (hBN) has been reported to form islands of graphene; C-doped hBN has also been experimentally reported in recent years to be a possible catalytic host to the oxygen reduction reaction (ORR), as well as a possible ferromagnet at room temperature. In this work, we explore from first principles the connection between these different aspects of C-doped hBN. We find the formation of graphene islands covering unequal number of B and N sites in hBN to be energetically plausible. They possess a net non-zero magnetic moment and are also found to be substantially more chemically active than their nonmagnetic counterparts covering equal number of B and N sites. On-site Coulomb repulsion between electrons, known to be responsible for magnetism in bipartite lattices such as graphene and hBN, is also found to play a central role in chemical activation of not only the C atoms at the zigzag interface of magnetic graphene islands and hBN but also boron (B) sit...

Delocalization Error in DFT-Predicted Extreme Long-Range Functionalization of Carbon-Doped Hexagonal Boron Nitride

Delocalization error is a serious failure of approximate density functional theory (DFT). This work shows how delocalization error affects the predicted catalytic activity of carbon-doped hexagonal boron nitride. While the charge and spin of an isolated carbon dopant are themselves predicted to be localized, nonhybrid DFT approximations predict spurious long-range transfer of charge and spin from such dopants to distant hydrogen adatom and molecular oxygen adsorbates. This effect mirrors nonhybrid DFT approximations’ predicted spurious long-range charge transfer in other systems, for example, dissociated heteronuclear diatomics Liᵟ⁺–Fᵟ⁻. The effect is robust to simulation details, occurring in finite-cluster, one-dimensionally periodic, and plane-wave periodic supercell simulations. In extreme cases, a single carbon dopant is predicted to activate molecular oxygen adsorbed 50 nm away and activate an isolated O₂ molecule suspended 1 μm away. The effect is traced to nonhybrid approximations’ delocalization error, which produces incorrect convex curves of energy as a function of fractional charge transfer from the carbon dopant to molecular oxygen. Long-range-corrected hybrid DFT approximations mitigate these delocalization errors and predict that carbon dopants will only activate adjacent molecular oxygen. This motivates adoption of long-range-corrected hybrids in future DFT simulations of doped boron-nitride nanostructures.

Oxidation of SO2 over C-doped boron nitride nanosheets: The role of C-doping, and solvent effects

In this work, density functional theory calculations are performed to examine the catalytic oxidation of SO2 in the presence of O2 molecule over carbon-doped hexagonal boron nitride nanosheets (h-BNNSs). The SO2 oxidation over these surfaces is characterized as a two-step mechanism; (a) SO2 + O2 → SO3 + O* and (b) SO2 + O* → SO3. According to the obtained results, the activation energies and reaction mechanism depend greatly on the substitution site of the C-doped h-BNNS. That is, the catalytic activity of C atom located on top of the B-vacancy site of h-BNNS is larger than that of on top of the N-vacancy. Moreover, it is found that the energy barriers for the oxidation of SO2 are considerably decreased in an aqueous solution. For a given substrate, the activation energy for the oxidation of H2SO3 is much larger than that of SO2, suggesting that the direct conversion of SO2 to SO3 should be the main reaction pathway for the oxidation of SO2. The results of present study could contribute to design highly active BN-based catalysts to oxidize SO2 molecule.

Nanorice-like Structure of Carbon-Doped Hexagonal Boron Nitride as an Efficient Metal-Free Catalyst for Oxygen Electroreduction

A rational design of electrocatalyst for oxygen reduction reaction (ORR) with activity 2–3 times higher than platinum has been of great demand for low temperature fuel cell applications. Particularly, metal-free ORR electrocatalysis has recently been explored rigorously because of limitations such as high price and scarcity of the state-of-the-art platinum catalyst. Here, we present a simple one-step method for the synthesis of carbon-doped hexagonal boron nitride (BNC) by a chemical vapor deposition method. An inert and insulating h-BN has been made active by carbon doping. From the structural analysis using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), we confirmed the formation of novel BNC nanostructures. BNC nanostructures exhibit rice grain-like shape having length ∼ 50 nm with interlayer distance of 0.34 nm, indicating hexagonal stacking of BN layers. As-synthesized BNC nanostructures obtained after annealing at 850 °C (BNC2-850) show interesting catalytic activity toward ORR ...

Rich interfacial chemistry and properties of carbon-doped hexagonal boron nitride nanosheets revealed by electronic structure calculations

The effect of C doping to hexagonal boron nitride (h-BN) to its electronic structure is examined by first principles calculations using the association from π-electron systems of organic molecules embedded in a two-dimensional insulator. In a monolayered carbon-doped structure, odd-number doping with carbon atoms confers metallic properties with different work functions. Various electronic interactions occur between two layers with odd-number carbon substitution. A direct sp3 covalent chemical bond is formed when C replaces adjacent B and N in different layers. A charge transfer complex between layers is found when C replaces B and N in the next-neighboring region, which results in narrower band gaps (e.g., 0.37 eV). Direct bonding between C and B atoms is found when two C atoms in different layers are at a certain distance.

Introduction of carbon-boron atomic groups as an efficient strategy to boost formic acid production toward CO2 electrochemical reduction.

Introducing C-B diatomic groups in carbon-doped hexagonal boron nitride (h-BN) flakes resulted in high activity and selectivity for HCOOH in CO2 electroreduction. The activation of CO2 was prone to occur on B atoms while the activation of the proton occurred on C atoms. The volcano-type relation of Faradaic efficiency for HCOOH production over carbon content originates from the balance of H* and COOH* intermediates in carbon-doped h-BN catalysts.

Carbon-Doped Hexagonal Boron Nitride: Analysis as π-Conjugate Molecules Embedded in Two Dimensional Insulator

We analyzed the electronic structures of carbon-doped hexagonal boron nitride, focusing on the comparison with the corresponding π-conjugate hydrocarbon molecules and odd-number substitution by first principle calculation. The band gaps are about the half that of the HOMO-LUMO gaps of corresponding hydrocarbons, except for the cis-butadiene structure in which aromatic hexagonal ring formation is important. Odd number doping makes metallic materials with very different work functions, depending upon the difference in B and N numbers, and has an expected application as electrodes for flexible devices.

Magnetic states and optical properties of single-layer carbon-doped hexagonal boron nitride

We show that carbon-doped hexagonal boron nitride (h-BN) has extraordinary properties with many possible applications. We demonstrate that the substitution-induced impurity states, associated with carbon atoms, and their interactions dictate the electronic structure and properties of C-doped h-BN. Furthermore, we show that stacking of localized impurity states in small C clusters embedded in h-BN forms a set of discrete energy levels in the wide gap of h-BN. The electronic structures of these C clusters have a plethora of applications in optics, magneto-optics, and opto-electronics.