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Interface States in Bilayer Graphene Encapsulated by Hexagonal Boron Nitride
摘要： The threshold voltages at the onset of conduction for electron and hole branches can provide information on band gap values or the interface states in a gap. We measured conductivity of bilayer graphene encapsulated by hexagonal boron nitride as a function of back and top gates, where another bilayer graphene is used as a top gate. From the measured conductivity the transport gap values were extracted assuming zero interface trap states, and they are close to the theoretically expected gap values. From a little discrepancy an average density of interface states per energy within a band gap (Dit) is also estimated. The data clearly show that Dit decreases as a bilayer graphene band gap increases rather than being constant. Despite the decreasing trend of Dit, interestingly the total interface states within a gap increases linearly as a band gap increases. This is because of ~ 2 × 1010 cm-2 interface states localized at band edges even without a band gap, and other gap states are equally spread over the gap.
关键词： band gap,hexagonal boron nitride,bilayer graphene,transport gap,interface states
更新于2025-09-10 09:29:36
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Strength and toughness anisotropy in hexagonal boron nitride: An atomistic picture
摘要： Strength and toughness are two crucial mechanical properties of a solid that determine its ability to function reliably without undergoing failure in extreme conditions. While hexagonal boron nitride (hBN) is known to be elastically isotropic in the linear regime of mechanical deformation, its directional response to extreme mechanical loading remains less understood. Here, using a combination of density functional theory calculations and molecular dynamics simulations, we show that strength and crack nucleation toughness of pristine hBN are strongly anisotropic and chirality dependent. They vary nonlinearly with the chirality of the lattice under symmetry breaking deformation, and the anisotropic behavior is retained over a large temperature range with a decreasing trend at higher temperatures. An atomistic analysis reveals that bond deformation and associated distortion of electron density are nonuniform in the nonlinear regime of mechanical deformation, irrespective of the loading direction. This nonuniformity forms the physical basis for the observed anisotropy under static conditions, whereas reduction in nonuniformity and thermal softening reduce anisotropy at higher temperatures. The chirality-dependent anisotropic effects are well predicted by inverse cubic polynomials.
关键词： chirality,anisotropy,hexagonal boron nitride,molecular dynamics simulations,density functional theory,strength,toughness
更新于2025-09-10 09:29:36
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A universal method for large-yield and high-concentration exfoliation of two-dimensional hexagonal boron nitride nanosheets
摘要： Hexagonal boron nitride (hBN) is an ultra-wide bandgap insulating material, which possesses a graphite-like layered structure, and the two-dimensional (2D) hexagonal boron nitride nanosheets (hBNNS), exfoliated from the bulk hBN, have promising applications in electronic packaging and high-power devices, due to the high thermal conductivity, excellent thermal/chemical stability as well as the ultra-wide band gap. However, the exfoliation of hBNNS is still a challenge with respect to high cost, time consuming, and low yield. Herein, a facile hydrothermal exfoliation method was proposed for the first time to exfoliate the hBNNS in a large yield and high concentration. In the optimized hydrothermal conditions, the lithium ion (Li+) intercalation, isopropanol (IPA) solvent, and the strong stirring could give rise to a large exfoliation yield up to (cid:1)55% and a high concentration (cid:1)4.13 mg/mL. In addition, the exfoliated hBNNS could enhance the methyl orange (MO) photodegradation efficiency of TiO2 from 91% to 96.4 %. Most importantly, this hydrothermal exfoliation method could be a universal approach for the exfoliation of 2D materials.
关键词： Hydrothermal exfoliation,Nanosheets,2D materials,Hexagonal boron nitride,Solubility parameters theory,Universal approach
更新于2025-09-10 09:29:36
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Impacts of in-plane strain on commensurate graphene/hexagonal boron nitride superlattices
摘要： Due to atomically thin structure, graphene/hexagonal boron nitride (G/hBN) heterostructures are intensively sensitive to the external mechanical forces and deformations being applied to their lattice structure. In particular, strain can lead to the modification of the electronic properties of G/hBN. Furthermore, moiré structures driven by misalignment of graphene and hBN layers introduce new features to the electronic behavior of G/hBN. Utilizing ab initio calculation, we study the strain-induced modification of the electronic properties of diverse stacking faults of G/hBN when applying in-plane strain on both layers, simultaneously. We observe that the interplay of few percent magnitude in-plane strain and moiré pattern in the experimentally applicable systems leads to considerable valley drifts, band gap modulation and enhancement of the substrate-induced Fermi velocity renormalization. Furthermore, we find that regardless of the strain alignment, the zigzag direction becomes more efficient for electronic transport, when applying in-plane non-equibiaxial strains.
关键词： strain,graphene/hexagonal boron nitride,moiré pattern,electronic properties
更新于2025-09-10 09:29:36
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[IEEE 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Shanghai (2018.8.8-2018.8.11)] 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Effect of Catalysts on Hydrothermal Preparation of boron nitride nanostructures
摘要： Boron nitride (BN) has attracted intense interests due to its excellent thermal conductivity and electrical insulation, which make it a promising thermal interface material for electronic packaging. Conventionally, the BN nanostructures were made from high cost method, e.g. chemical vapor deposition (CVD), which was restricted by the extremely high reaction temperature as well as the expensive instruments. Herein, a facile hydrothermal method was presented, where the catalysts were used to tune the phase and morphologies of the BN products starting from the boron and nitrogen sources. With different catalysts, the phase of the products could be changed from the orthorhombic to cubic BN, and the morphology underwent an evolution from nanorods to nanoflowers. The results are of great significance for the large-scale fabrication of BN nanostructures in a low cost.
关键词： Nanoflowers,Hydrothermal synthesis,Morphology evolution,Nanorods,Boron nitride,Catalyst
更新于2025-09-10 09:29:36
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Probing the nanoscale origin of strain and doping in graphene-hBN heterostructures
摘要： We use confocal Raman microscopy and a recently proposed vector analysis scheme to investigate the nanoscale origin of strain and carrier concentration in exfoliated graphene-hexagonal boron nitride (hBN) heterostructures on silicon dioxide (SiO2). Two types of heterostructures are studied: graphene on SiO2 partially covered by hBN, and graphene fully encapsulated between two hBN flakes. We extend the vector analysis method to produce separated spatial maps of the strain and doping variation across the heterostructures. This allows us to visualise and directly quantify the much-speculated effect of the environment on carrier concentration in graphene. Moreover, we demonstrate that variations in strain and carrier concentration in graphene arise from nanoscale features of the heterostructures such as fractures, folds and bubbles trapped between layers. For bubbles in hBN-encapsulated graphene, hydrostatic strain is shown to be greatest at bubble centres, whereas the maximum carrier concentration is localised at bubble edges. Raman spectroscopy is shown to be a non-invasive tool for probing strain and doping in graphene, which could prove useful for engineering of two-dimensional devices.
关键词： hexagonal boron nitride,Raman,strain,van der Waals heterostructures,graphene,hBN,doping
更新于2025-09-09 09:28:46
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Recent progress in synthesis, properties and applications of hexagonal boron nitride based heterostructures
摘要： Featuring an absence of dangling bonds, large band gap, low dielectric constant, excellent chemical inertness, atomically thin hexagonal boron nitride (h-BN) is considered as an ideal candidate for the integration with graphene and other 2D materials. During the past years, great efforts have been devoted to the research area of h-BN based heterostructures from fundamental study to practical applications. In this review, we summarize the recent progress in the synthesis, novel properties and potential applications of h-BN based heterostructures, especially the synthesis technique. Firstly, various approaches for the preparation of both in-plane and vertical stacked h-BN based heterostructures are introduced in detail, including top-down strategies associated with exfoliation-transfer processes and bottom-up strategies such as chemical vapor deposition (CVD)-based growth. Secondly, we discuss some novel properties arise in these heterostructures. Then, several promising applications in electronic and optoelectronic devices based on these heterostructures are also reviewed. Finally, we discuss the main challenges and possible research directions in this field.
关键词： heterostructures,application,hexagonal boron nitride,property,synthesis
更新于2025-09-09 09:28:46
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[IEEE 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Shanghai (2018.8.8-2018.8.11)] 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Facile Preparation of Silver Nanoparticles Decorated Boron Nitride Nanotube Hybrids
摘要： Blending polymer with thermally conductivity Metal nanoparticles-fillers, which can reducing ITR at a high fillers contents, have recently attracted intense attention. The interfacial thermal resistance (ITR) between fillers at a high filler doping contents causes a limited improvement of thermal conductivity. Fortunately, silver nanoparticles decorated fillers have potential to improve thermally conductivity by reducing ITR between fillers at a high filler content. However, how to fabricate pony-size silver nanoparticles decorated fillers hybrids simply is still a challenge. Herein, we report a facile synthesis of decorating boron nitride nanotube (BNNT) hybrids with AgNP (10-20 nm) by replacing between the Ag+ and -OH on the defect sites of BNNT. This strategy is a viable way to prepare metal nanoparticles-fillers which can be used in highly thermal conductivity.
关键词： boron nitride nanotube,thermal conductivity,hybrids,silver nanoparticles,interfacial thermal resistance
更新于2025-09-09 09:28:46
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Influence of Defects in Boron Nitride Nanotubes in the Adsorption of Molecules. Insights from B3LYP-D2* Periodic Simulations
摘要： The adsorption of H2O, NH3 and HCOOH as polar molecules and C6H6 and CH4 as non-polar ones on a series of zig-zag (6,0) single-walled boron nitride nanotubes (BNNTs) both being defect-free (P_BNNT) and containing defects at the nanotube walls has been studied by means of B3LYP-D2* periodic calculations. We focused on defects derived from monovacancies of B (N-rich_BNNT) and N (B-rich_BNNT) atoms and also on Stone-Wales defects (SW_BNNT). The adsorption of polar molecules with defective BNNTs is generally based on dative interactions and H-bonding, and their adsorption energies strongly depend on the type of BNNT. N-rich_BNNT is the most reactive nanotube towards adsorption of polar molecules, as in all cases deprotonation of the polar molecules is spontaneously given upon adsorption. The strength in the adsorption energies is followed by B-rich_BNNT, SW_BNNT and P_BNNT. Adsorption of non-polar molecules is mainly dictated by dispersion interactions, and, accordingly, the adsorption energies are almost constant for a given molecule irrespective of the type of nanotube.
关键词： adsorption,vacancies,periodic simulations,boron nitride nanotubes,DFT,Stone-Wales defect
更新于2025-09-09 09:28:46
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Green and Efficient Production of Boron Nitride Nanosheets via Oxygen Doping-Facilitated Liquid Exfoliation
摘要： As the structural analogue of graphene, boron nitride nanosheets (BNNSs) are anticipated to have a wide range of potential applications. BNNSs exhibit good mechanical properties, outstanding thermal conductivity, oxidation and chemical stability and are excellent electrical insulators. While BNNSs have gained recognition as one of the most versatile 2D materials in recent years, their application in research and industry is still hampered by the lack of methods to produce BNNSs in large quantity and a cost-effective way. In this study, we report highly efficient h-BN exfoliation via the oxygen doping-facilitated liquid exfoliation. Oxygen atoms are introduced into the hexagonal boron nitride (h-BN) structure via a facile thermal treatment. The relationship of thermal treatment, structural changes and h-BN exfoliation are studied to elucidate the key factor for advancing the BNNS production. The optimum concentration of hydroxyl groups and weakening of interlayer interactions have synergistically facilitated the delamination of h-BN in water under mild exfoliation conditions, resulting in up to 1255% yield increment and without noticeable new defects in the BNNS structure as compared with the untreated control. An efficient and environmentally friendly exfoliation process of h-BN is a crucial starting point towards the cost-effective and mass production of BNNSs which is needed for the currently identified and myriad future applications of BNNSs.
关键词： oxygen-doping,nanoplatelets,boron nitride nanosheets,2D nanomaterials
更新于2025-09-09 09:28:46