Properties Of Hexagonal Boron Nitride Research Articles

Study on the tribological properties of hexagonal boron nitride flakes composite hydrophilic/hydrophobic ionic liquids films by self-assembly

Due to the weak out-of-plane van der Waals interaction between layers, hexagonal boron nitride (h-BN) with a stacking structure has been proven to be a promising lubrication material for its friction performance. However, obtaining h-BN composite films with excellent substrate bonding and low friction properties under high humidity remains challenging. Ionic liquids (ILs) composed of anions and cations that are liquid at or near room temperature have distinguished themselves in the field of lubrication (lubricating additives and lubricating films) due to their advantages of low saturated vapor pressure, good stability and high viscosity. Based on the relationship between lubrication performance and hygroscopicity of hydrophilic/hydrophobic ILs, a simple and flexible method for preparing h-BN composite hydrophilic/hydrophobic ILs films on metal substrates has been developed. h-BN has excellent antioxidant and moisture resistance as well as lubrication performance. Consequently, the influence of the hygroscopicity of ILs on the macroscopic tribological performance of h-BN composite hydrophilic/hydrophobic ILs films was investigated. The results showed that PVA/BNOH composite hydrophobic ILs films displayed a lower friction coefficient and outstanding wear resistance than those of PVA/BNOH composite hydrophilic ILs films in both atmosphere and high humidity. The synergies between the film layers, the intrinsic differences between the hydrophilic and hydrophobic ILs, and tribo-chemical reactions at friction interfaces greatly promoted the realization of excellent tribological performance of composite films. Additionally, the tribological properties of these films at high humidity were mainly related to the interaction between water molecules and the ILs.

The Roles of Impurities and Surface Area on Thermal Stability and Oxidation Resistance of BN Nanoplatelets.

This study considers the influence of purity and surface area on the thermal and oxidation properties of hexagonal boron nitride (h-BN) nanoplatelets, which represent crucial factors in high-temperature oxidizing environments. Three h-BN nanoplatelet-based materials, synthesized with different purity levels and surface areas (~3, ~56, and ~140 m2/g), were compared, including a commercial BN reference. All materials were systematically analyzed by various characterization techniques, including gas pycnometry, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared radiation, X-ray photoelectron spectroscopy, gas sorption analysis, and thermal gravimetric analysis coupled with differential scanning calorimetry. Results indicated that the thermal stability and oxidation resistance of the synthesized materials were improved by up to ~13.5% (or by 120 °C) with an increase in purity. Furthermore, the reference material with its high purity and low surface area (~4 m2/g) showed superior performance, which was attributed to the minimized reactive sites for oxygen diffusion due to lower surface area availability and fewer possible defects, highlighting the critical roles of both sample purity and accessible surface area in h-BN thermo-oxidative stability. These findings highlight the importance of focusing on purity and surface area control in developing BN-based nanomaterials, offering a path to enhance their performance in extreme thermal and oxidative conditions.

Exploring the structural, electronic, and hydrogen storage properties of hexagonal boron nitride and carbon nanotubes: insights from single-walled to doped double-walled configurations

This study investigates the structural intricacies and properties of single-walled nanotubes (SWNT) and double-walled nanotubes (DWNT) composed of hexagonal boron nitride (BN) and carbon (C). Doping with various atoms including light elements (B, N, O) and heavy metals (Fe, Co, Cu) is taken into account. The optimized configurations of SWNT and DWNT, along with dopant positions, are explored, with a focus on DWNT-BN-C. The stability analysis, employing binding energies, affirms the favorable formation of nanotube structures, with DWNT-C emerging as the most stable compound. Quantum stability assessments reveal significant intramolecular charge transfer in specific configurations. Electronic properties, including charge distribution, electronegativity, and electrical conductivity, are examined, showcasing the impact of doping. Energy gap values highlight the diverse electronic characteristics of the nanotubes. PDOS analysis provides insights into the contribution of atoms to molecular orbitals. UV–Vis absorption spectra unravel the optical transitions, showcasing the influence of nanotube size, dopant type, and location. Hydrogen storage capabilities are explored, with suitable adsorption energies indicating favorable hydrogen adsorption. The desorption temperatures for hydrogen release vary across configurations, with notable enhancements in specific doped DWNT-C variants, suggesting potential applications in high-temperature hydrogen release. Overall, this comprehensive investigation provides valuable insights into the structural, electronic, optical, and hydrogen storage properties of BN and C nanotubes, laying the foundation for tailored applications in electronics and energy storage.

Fluorine enables h-BN sheet to resist oxidizing failures in sulfur atmosphere

Corrosion is one of the most common ways in which metal components are damaged, especially under extreme conditions in the presence of sulfide ions. Due to the excellent properties of hexagonal boron nitride (h-BN) sheets, they can provide effective protection for facilities exposed to sulfur-containing atmospheres. In this paper, the thermodynamic and kinetic behavior of oxygen adsorbed on h-BN and defective D-h-BN sheets in a sulfur-containing atmosphere were performed by first-principles calculations. The adsorption energies, densities of state, band structures, differential charge densities and diffusion energy barriers were systematically investigated. The presence of sulfur reduces the diffusion energy barrier of oxygen, which accelerates the oxidative failure of h-BN sheets. Surprisingly, the F-modified h-BN sheet possesses a higher oxygen diffusion energy barrier, which explains its superior oxidation resistance. Therefore, h-BN sheets are a promising candidate as a protective material in sulfur-containing atmospheres.

Influence of neutron irradiation on the electronic properties of hexagonal boron nitride measured by terahertz time-domain spectroscopy

Due to the low atomic number of B, hexagonal boron nitride (hBN) has a large neutron scattering cross section and, therefore, is an ideal material for the realization of solid-state neutron detector. Here we apply the THz time-domain spectroscopy to study the effect of neutron irradiation on electronic properties of pyrolytic (PBN) and hot-pressed boron nitride (HBN). The key electronic parameters of these samples, such as the static dielectric constant ε b , the effective carrier density N*, the carrier relaxation time τ, and the electronic localization factor α, are determined optically, and their dependences upon the neutron irradiation fluence (NIF) are examined. We find that for hBN,N* and ε b decrease while τ and |α| increase with increasing NIF. These results can be used to further understand the neutron irradiation effects on the basic physical properties of hBN material. We believe that the results obtained from this work can benefit to the design and application of hBN material for neutron detectors.

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% 10 B, 80 at% 11 B) while using naturally abundant nitrogen (99.6 at% 14 N, 0.4 at% 15 N), that is, almost pure 14 N. In this study, the class of isotopically purified hBN crystals to 15 N is extended. Crystals in the four configurations, namely h10 B14 N, h11 B14 N, h10 B15 N, and h11 B15 N, are grown by the metal flux method using boron and nitrogen single isotope (> 99%) enriched sources, with nickel plus chromium as the solvent. In-depth Raman and photoluminescence spectroscopies demonstrate the high quality of the monoisotopic hBN crystals with vibrational and optical properties of the 15 N-purified crystals at the state-of-the-art of currently available 14 N-purified hBN. The growth of high-quality h10 B14 N, h11 B14 N, h10 B15 N, and h11 B15 N opens exciting perspectives for thermal conductivity control in heat management, as well as for advanced functionalities in quantum technologies.

Tunability of electronic and thermoelectric properties of hexagonal boron nitride with carbon impurities under magnetic field: Tight binding investigation

Utilizing the Kubo-Greenwood formula, Tight Binding calculations were employed to examine the electronic and thermoelectric properties of hexagonal boron nitride (h-BN) with carbon impurity instead of boron, nitrogen and pairs boron-nitrogen. The electronic properties of the pristine monolayer BN are markedly impacted by the introduction of carbon dopants and its band gap reduction is directly correlated with the concentration of carbon impurities. The electronic properties of doped h-BN are influenced by the presence of a magnetic field, leading to subband separation and band gap narrowing, independent of the impurity types. The thermal conductivity and magnetic susceptibility of the CBN-doped monolayer BN structure are higher than those of the BC and NC doped h-BN structures and for all structures, their properties have a strong dependence on the magnetic field. The Lorenz Number for all structures has peak at the TM temperature which shifts to a lower temperature as the impurity concentration decreases.

Amorphous BN-Based Synaptic Device with High Performance in Neuromorphic Computing.

The von Neumann architecture has faced challenges requiring high-fulfillment levels due to the performance gap between its processor and memory. Among the numerous resistive-switching random-access memories, the properties of hexagonal boron nitride (BN) have been extensively reported, but those of amorphous BN have been insufficiently explored for memory applications. Herein, we fabricated a Pt/BN/TiN device utilizing the resistive switching mechanism to achieve synaptic characteristics in a neuromorphic system. The switching mechanism is investigated based on the I-V curves. Utilizing these characteristics, we optimize the potentiation and depression to mimic the biological synapse. In artificial neural networks, high-recognition rates are achieved using linear conductance updates in a memristor device. The short-term memory characteristics are investigated in depression by controlling the conductance level and time interval.

Van der Waals isotope heterostructures for engineering phonon polariton dispersions

Element isotopes are characterized by distinct atomic masses and nuclear spins, which can significantly influence material properties. Notably, however, isotopes in natural materials are homogenously distributed in space. Here, we propose a method to configure material properties by repositioning isotopes in engineered van der Waals (vdW) isotopic heterostructures. We showcase the properties of hexagonal boron nitride (hBN) isotopic heterostructures in engineering confined photon-lattice waves—hyperbolic phonon polaritons. By varying the composition, stacking order, and thicknesses of h10BN and h11BN building blocks, hyperbolic phonon polaritons can be engineered into a variety of energy-momentum dispersions. These confined and tailored polaritons are promising for various nanophotonic and thermal functionalities. Due to the universality and importance of isotopes, our vdW isotope heterostructuring method can be applied to engineer the properties of a broad range of materials.

First-principles study of graphene intercalation in h-BN based resistance random access memory

Graphene intercalation between metal electrode and resistance layers has attracted extensive experimental and theoretical research because of its capability to manipulate the electronic structure and properties of hexagonal boron nitride based resistance random access memory. Herein, the interface characteristic, adsorption and migration behavior of Ti on pristine and defective graphene intercalation have been systematically investigated by utilizing the density functional theory method, which could help accurately preset defects and regulate the permeation process. Analysis of the interfacial contact form showed that Ohmic-type contact occurs between intercalation and resistance layer interface due to the heavy doping effect caused by charge accumulation on the h-BN layer surface upon introduction of intercalation. Ti metal adsorption at hollow site on defective graphene containing grain boundary with double vacancies was more energetically favorable than that on pristine graphene without vacancy or with single vacancy, whereas the increase of adsorption energy caused by grain boundary defects that represented by pentagons and heptagons and double vacancies were very limited. Migration barrier calculations with defect distribution and vacancy indicated that the critical factor controlling ion penetration in the whole intercalation process is the presetting of single vacancy defect rather than the varying number of vacancies and the existence of grain boundary defect. This finding provides a new perspective aiding understanding and design of the defect-assisted graphene intercalation mechanism.

Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates.

The effect of point defects and interactions with the substrate are shown by density functional theory calculations to be of significant importance for the structure and functional properties of hexagonal boron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG) and Ni(111) substrates. The structure, surface chemistry, and electronic properties are calculated for h-BN systems with selected intrinsic, oxygen, and carbon defects and with graphene hybrid structures. The electronic structure of a pristine monolayer of h-BN is dependent on the type of substrate, as h-BN is decoupled electronically from the HOPG surface and acts as bulk-like h-BN, whereas on a Ni(111) substrate, metallic-like behavior is predicted. These different film/substrate systems therefore show different reactivities and defect chemistries. The formation energies for substitutional defects are significantly lower than for intrinsic defects regardless of the substrate, and vacancies formed during film deposition are expected to be filled by either ambient oxygen or carbon from impurities. Significantly lower formation energies for intrinsic and oxygen and carbon substitutional defects were predicted for h-BN on Ni(111). In-plane h-BCN hybrid structures were predicted to be terminated by N-C bonding. Substitutional carbon on the boron site imposes n-type semiconductivity in h-BN, and the n-type character increases significantly for h-BN on HOPG. The h-BN film surface becomes electronically decoupled from the substrate when exceeding monolayer thickness, showing that the surface electronic properties and point defect chemistry for multilayer h-BN films should be comparable to those of a freestanding h-BN layer.

Cross-plane thermal conductivity of h-BN thin films grown by pulsed laser deposition

The distinguished properties of hexagonal boron nitride (h-BN), specifically its atomically smooth surface, large critical electric field, and large electronic bandgap, make it ideal for thin film microelectronics and as an ultrawide bandgap semiconductor. Owing to weak van der Waals interactions between layers, h-BN exhibits a significant degree of anisotropic thermal conductivity. The in-plane thermal conductivity of h-BN has extensively been studied, yet the only measured data of cross-plane thermal conductivity (k⊥) are for exfoliated h-BN films. Exfoliation from bulk crystals is not a sustainable method for scalable production of h-BN due to its low repeatability, low yield, poor control of sample thickness, and limitation to small areas. Thus, it is necessary to investigate the thickness-dependence of k⊥ for thin films grown by a practical growth method, such as pulsed laser deposition (PLD), which enables the production of reliable and large-area h-BN films with a control of film thickness. We grew h-BN using PLD at 750 °C and observed a decreasing trend of k⊥ as thickness increases from 30 to 300 nm, varying from ∼1.5 to ∼0.2 W/(m K). We observed a relatively high k⊥ value for h-BN at a thickness of 30 nm, providing insight into the k⊥ of PLD-grown films suitable for electronics applications.

DFT screening exchange sX-LDA approach to study the origin of the indirect band gap of hexagonal boron nitride in its most stable phase

The present study is a theoretical work of the effect of the nonlocal screened exchange within the local density approximation (sX-LDA) functional on the structural and electronic properties of hexagonal Boron Nitride (h-BN). We obtained a visible renormalization of the band structure due to the inclusion of nonlocal correlation effects. Furthermore, we demonstrated that h-BN with AA’ stacking have an indirect band gap and the origin of the h-BN band gap width and its nature are strongly affected by Nitrogen electronic band structure. Here, we discuss also the exact nature of h-BN band gap and its value to give a sense to the wide variety of results obtained in the literature.

Investigation of tribological properties of hexagonal boron nitride reinforced AZ91 magnesium composites produced by powder metallurgy

Bu çalışmada, AZ91 magnezyum alaşımı ve AZ91 alaşımına ağırlıkça %10 hBN (hegzagonal bor nitrür) nanoparçacıkları takviye edilerek homojen kompozit malzeme karışımları yapıldı. Hazırlanan tozların soğuk presleme yöntemiyle 400 MPa basınç ile preslenmesi ve 590 C° sıcaklıkta argon atmosferinde sinterlemeleri gerçekleştirildi. Hazırlanan numunelerin mikroyapıları taramalı elektron mikroskobu (SEM) ve enerji dağılımlı X-ışınları (EDX) analizleri ile incelenmiştir. Numunelerin 20 saniye yükleme süresinde 5 farklı noktadan sertlik değerleri alındı ve bu sertlik değerlerinin ortalaması alınarak ortalama sertlik değerleri belirlendi. Aşınma testleri pin-on-disk deney cihazında farklı yük değerlerinde (5 N, 10 N ve 15 N) toplam 300 metre kayma mesafesinde, 50 mm/sn kayma hızında ve kuru şartlarda yapıldı. Sürtünme katsayısı değerleri ile aşınma sonucundaki ağırlık kayıpları incelendi. Yapılan deneyler sonucunda hBN katkısının AZ91 alaşımı üzerinde sertlik değerinde çok daha yüksek değerleri getirdiği görülmüştür. Yine aynı şekilde yapılan aşınma deneylerinde de hBN katkısı aşınmaya dirençli bir kompozit elde edilmesini sağlamıştır.

Shape influence on the tribological properties of hexagonal boron nitride nanoplates and nanospheres reinforced epoxy coating

Hexagonal boron nitride was known for its excellent lubricating capacity, however, the shape influence on the tribological properties of hexagonal boron nitride modified epoxy composite coatings was still a challenging requirement. Herein, the boron nitride nanoplates (BNNP) and nanospheres (BNNS) were modified by polydopamine to improve their dispersion in epoxy coatings and the shape influence of two nanoparticles on the tribological property was proved by the micro-morphologies of wear debris. When the mass content of polydopamine-modified BNNS was 0.25 wt%, the friction-reduction and anti-wear effects were the best, and the coefficient of friction and wear rate was reduced by 13.75% and 60.77%, respectively, compared with the pure epoxy coating. The ‘ball effect’ of BNNS provided rolling friction and the layer-structured debris exhibited good lubricating properties. The enhanced wear mechanism of BNNS provided wider potential application in the mechanical industry, automotive, aerospace, and infrastructure fields.

Graphene: Hexagonal Boron Nitride Composite Films with Low-Resistance for Flexible Electronics

The structure and electric properties of hexagonal boron nitride (h-BN):graphene composite with additives of the conductive polymer PEDOT:PSS and ethylene glycol were examined. The graphene and h-BN flakes synthesized in plasma with nanometer sizes were used for experiments. It was found that the addition of more than 10−3 mass% of PEDOT:PSS to the graphene suspension or h-BN:graphene composite in combination with ethylene glycol leads to a strong decrease (4–5 orders of magnitude, in our case) in the resistance of the films created from these suspensions. This is caused by an increase in the conductivity of PEDOT:PSS due to the interaction with ethylene glycol and synergetic effect on the composite properties of h-BN:graphene films. The addition of PEDOT:PSS to the h-BN:graphene composite leads to the correction of the bonds between nanoparticles and a weak change in the resistance under the tensile strain caused by the sample bending. A more pronounced flexibility of the composite films with tree components is demonstrated. The self-organization effects for graphene flakes and polar h-BN flakes lead to the formation of micrometer sized plates in drops and uniform-in-size nanoparticles in inks. The ratio of the components in the composite was found for the observed strong hysteresis and a negative differential resistance. Generally, PEDOT:PSS and ethylene glycol composite films are promising for their application as electrodes or active elements for logic and signal processing.

Mechanical and Antibacterial Properties of h-BN-TiO2 Nanocomposite-Modified Glass Ionomer Cement

This study investigated the mechanical properties and antibacterial properties of hexagonal boron nitride and titanium dioxide (h-BN-TiO2) nanocomposite modified traditional glass ionomer cement. The mechanism of formation of the h-BN-TiO2 nanocomposite was elucidated by conducting molecular dynamics (MD) simulations using the Material Studio (MS) software. Furthermore, synthesis of h-BN-TiO2 nanocomposite by the original growth method using hexagonal boron nitride nanosheets (h-BNNs) and titanium dioxide nanoparticles (TiO2 Nps) and characterization using TEM and AFM to determine their particle sizes, morphologies, and structures. The mechanical properties and antibacterial efficacies of the glass ionomer cement composites were analyzed based on the different mass fractions (0, 0.3, 0.7, 1.1, and 1.5 wt%) of the h-BN-TiO2 nanocomposite. The results showed when the concentration of the h-BN-TiO2 nanocomposite was 1.1 wt%, the Compressive strength (CS) and Vicker hardness (VHN) were 80.2% and 149.65% higher, respectively, compared to the glass ionomer cement without any h-BN-TiO2 nanocomposite. Also, the increase in the concentration of the h-BN-TiO2 nanocomposite led to a decrease in both the coefficient of friction (COF) and solubility, but a 93.4% increase in the antibacterial properties of the glass ionomer cement composites. The cell survival rate of each group was more than 70% after 48 h, but the difference was not statistically significant (p > 0.05). Therefore, the h-BN-TiO2 nanocomposite served as a reinforcing material for glass ionomer cement, which can be useful in clinical dentistry and provide a new strategy for improving the clinical utility of glass ionomer cement.

Hexagonal boron nitride: optical properties in the deep ultraviolet

We review the recent advance in the understanding of the optoelectronic properties of hexagonal boron nitride (hBN) in the deep ultraviolet. The comparison between bulk hBN and monolayer hBN highlights some of their major differences such the bandgap nature, the excitonic binding energy and the phonon-assisted broadening of the excitonic lines. Perspectives point out the relevance of addressing the regime of hBN samples made of a very few number of monolayers, including twisted hBN monolayers in the context of twistronics.

Investigation of the Surface Properties of Hexagonal Boron Nitride and Boron Phosphate by Inverse Gas Chromatography at Infinite Dilution.

The boron-based ceramics namely hexagonal boron nitride (h-BN) and boron phosphate (BPO4) were synthesized and characterized by Fourier transform infrared spectroscopy and X-ray diffraction analysis. The surface properties of h-BN and BPO4 were examined by inverse gas chromatography method. The dispersive surface energy and the acidic-basic character of h-BN, and BPO4 surfaces were estimated by the retention time with probes such as n-hexane, n-heptane, n-octane, n-nonane, n-decane, acetone, ethyl acetate, dichloromethane, chloroform and tetrahydrofuran at infinite dilution region. The dispersive surface free energies calculated using both Schultz and Dorris-Gray methods, decreased linearly with increasing temperature. The specific adsorption free energy and the specific adsorption enthalpy corresponding to acid-base surface interactions were determined. By correlating with the donor and acceptor numbers of the probes, the acidic and the basic parameters of the h-BN and BPO4 were calculated. The values obtained for and parameters indicated that h-BN has a basic character, whereas BPO4 has an acidic character.

Ion-beam Modification of the Local Luminescent Properties of Hexagonal Boron Nitride

Hexagonal boron nitride is a promising material of modern optoelectronics. Point defects in this material can serve as single-photon sources. In this paper we investigate the modification of the luminescent properties of hexagonal boron nitride by means of local irradiation with focused gallium and helium ion beams. It is demonstrated that the intensity of band-to-band cathodoluminescence monotonically decreases with increasing ion fluence for both gallium and helium. The luminescence band of about 2 eV may become more intense after exposure to He ions with certain ion fluence. The effect of complete quenching of luminescence after gallium irradiation is used to estimate the diffusion length of excess charge carriers. Keywords: point defects, cathodoluminescence, scanning helium ion microscope, excess charge carriers.