Third order elastic constants of hexagonal boron nitride

Third order elastic constants of hexagonal Boron Nitride have been evaluated using the Lannard-Jones potential. The results obtained are presented and compared with the only available measurement ofC ₃₃₃ for this material.     

Fabrication of large area hexagonal boron nitride thin films for bendable capacitors

Highly reliable and bendable dielectrics are desired in flexible or bendable electronic devices for future applications. Hexagonal boron nitride （h-BN） can be used as bendable dielectric due to its wide band gap. Here, we fabricate high quality h-BN films with controllable thickness by a low pressure chemical vapor deposition method. We demonstrate a parallel-plate capacitor using h-BN film as the dielectric. The h-BN capacitors are reliable with a high breakdown field strength of -9.0 MV/cm. Tunneling current across the h-BN film is inversely exponential to the thickness of dielectric, which makes the capacitance drop significantly. The h-BN capacitor shows a best specific capacitance of 6.8 F/cm^2, which is one order of magnitude higher than the calculated value.     

High thermal conductivity of suspended few-layer hexagonal boron nitride sheets

The thermal conduction of suspended few-layer hexagonal boron nitride （h-BN） sheets was experimentally investigated using a noncontact micro-Raman spectroscopy method. The first-order temperature coefficients for monolayer （1L）, bilayer （2L） and nine-layer （9L） h-BN sheets were measured to be -（3.41 ± 0.12）× 10-2, -（3.15 ± 0.14） × 10-2 and -（3.78 ±0.16）× 10-2 cm-1.K-1, respectively. The room-temperature thermal conductivity of few-layer h-BN sheets was found to be in the range from 227 to 280 W.m-1-K-1, which is comparable to that of bulk h-BN, indicating their potential use as important components to solve heat dissipation problems in thermal management configurations.     

Wafer-Scale Single Crystal Hexagonal Boron Nitride Layers Grown by Submicron-Spacing Vapor Deposition

The direct growth of wafer-scale single crystal two-dimensional (2D) hexagonal boron nitride (h-BN) layer with a controllable thickness is highly desirable for 2D-material-based device applications. Here, for the first time, a facile submicron-spacing vapor deposition (SSVD) method is reported to achieve 2-inch single crystal h-BN layers with controllable thickness from monolayer to tens of nanometers on the dielectric sapphire substrates using a boron film as the solid source. In the SSVD growth, the boron film is fully covered by the same-sized sapphire substrate with a submicron spacing, leading to an efficient vapor diffusion transport. The epitaxial h-BN layer exhibits extremely high crystalline quality, as demonstrated by both a sharp Raman E_2g vibration mode (12 cm⁻¹) and a narrow X-ray rocking curve (0.10°). Furthermore, a deep ultraviolet photodetector and a ZrS₂/h-BN heterostructure fabricated from the h-BN layer demonstrate its fascinating properties and potential applications. This facile method to synthesize wafer-scale single crystal h-BN layers with controllable thickness paves the way to future 2D semiconductor-based electronics and optoelectronics.     

Oxygen-suppressed selective growth of monolayer hexagonal boron nitride on copper twin crystals

Controlled growth of hexagonal boron nitride (h-BN) with desired properties is essential for its wide range of applications.Here,we systematically carried out the chemical vapor deposition of monolayer h-BN on Cu twin crystals.It was found that h-BN nucleated and grew preferentially and simultaneously on the narrow twin crystal strips present in the Cu substrates.The density functional theory calculations revealed that the introduction of oxygen could efficiently tune the selectivity.This is because of the reduction in the dehydrogenation barrier of the precursor molecules by the introduction of oxygen.Our findings throw light on the direct growth of functional h-BN nanoribbons on nano-twinned crystal strips and switching of the growth behavior of h-BN films by oxygen.     

High-resolution characterization of hexagonal boron nitride coatings exposed to aqueous and air oxidative environments

Hexagonal boron nitride (h-BN) is believed to offer better passivation to metallic surfaces than graphene owing to its insulating nature,which facilitates blocking the flow of electrons,thereby preventing the occurrence of galvanic reactions.Nevertheless,this may not be the case when an h-BN-protected material is exposed to aqueous environments.In this work,we analyzed the stability of mono and multilayer h-BN stacks exposed to H2O2 and atmospheric conditions.Our experiments revealed that monolayer h-BN is as inefficient as graphene as a protective coating when exposed to H2O2.Multilayer h-BN offered a good degree of protection.Monolayer h-BN was found to be ineffective in an air atmosphere as well.Even a 10-15 layers-thick h-BN stack could not completely protect the surface of the metal under consideration.By combining Auger electron spectroscopy and secondary ion mass spectrometry techniques,we observed that oxygen could diffuse through the grain boundaries of the h-BN stack to reach the metallic substrate.Fortunately,because of the diffusive nature of the process,the oxidized area did not increase with time once a saturated state was reached.This makes multilayer (not monolayer) h-BN a suitable long-term oxidation barrier.Oxygen infiltration could not be observed by X-ray photoelectron spectroscopy.This technique cannot assess the chemical composition of the deeper layers of a material.Hence,the previous reports,which relied on XPS to analyze the passivating properties of h-BN and graphene,may have ignored some important subsurface phenomena.The results obtained in this study provide new insights into the passivating properties of mono and multilayer h-BN in aqueous media and the degradation kinetics of h-BN-coated metals exposed to an air environment.     

Elucidation of the thermophysical mechanism of hexagonal boron nitride as nanofluids additives

This study systematically investigated the physicochemical characteristics of hexagonal boron nitride (h-BN) nanoparticles dispersed in polyalphaolefin 6 (PAO6) from a molecular level to explore the thermal stability of nano-lubricants. The nanoparticles were characterized via transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive spectrometry (EDS) to analyze the chemical bonds, element distribution, and impurity. We not only theoretically reveal the rheological behavior of nano-lubricants but also propose precise models to predict the viscosity. Moreover, this study comprehensively analyzed the thermal stability of nano-lubricants under different gas environments through thermogravimetric analysis and revealed that the nanofluid thermal stability was improved owing to the small-size effect. The results show that the thermal conductivity of the nano-lubricants was significantly higher than that of PAO6. Finally, the mechanism of thermal property enhancement by the h-BN nanoparticles is revealed.     

叶酸靶向含硼脂质体的制备及其包封率的测定

制备具有良好靶向性及包封率高的硼脂质体,为硼中子俘获治疗方法的研究与应用建立了一个有效的靶向给药途径.采用复乳法及薄膜—超声分散法制备叶酸靶向硼脂质体,利用高效液相色谱法检测4—羟基苯硼酸4—Hydroxyphenylboronicacid (HBA)脂质体、2—噻吩硼酸2—thiophenylboric acid(TBA)脂质体、4—叔丁基苯硼酸4—tert-Butylphenylboronic Acid(BBA)脂质体的含量及包封率,以包封率为评价指标,采用单因素法优化脂质体的制备处方和工艺条件.筛选出HBA、TBA、BBA最优的色谱条件,分别绘制出标准曲线,结果表明在1 ～ 100 μg/mL范围内线性关系良好.HBA、TBA、BBA脂质体在最优制备处方和工艺条件下包封率分别为25.7％、38.9％、94.8％.BBA脂质体优化后的制备处方和工艺条件如下:胆固醇与磷脂质量比为1∶1,药脂比为1∶50,pH值为7.4,按该处方工艺制备的BBA脂质体包封率在94.8％.制备叶酸靶向脂质体的优选处方和制备工艺稳定可行,质量控制方法简单、准确,包封率高.     

Aligned Growth of Millimeter‐Size Hexagonal Boron Nitride Single‐Crystal Domains on Epitaxial Nickel Thin Film

Atomically thin hexagonal boron nitride (h‐BN) is gaining significant attention for many applications such as a dielectric layer or substrate for graphene‐based devices. For these applications, synthesis of high‐quality and large‐area h‐BN layers with few defects is strongly desirable. In this work, the aligned growth of millimeter‐size single‐crystal h‐BN domains on epitaxial Ni (111)/sapphire substrates by ion beam sputtering deposition is demonstrated. Under the optimized growth conditions, single‐crystal h‐BN domains up to 0.6 mm in edge length are obtained, the largest reported to date. The formation of large‐size h‐BN domains results mainly from the reduced Ni‐grain boundaries and the improved crystallinity of Ni film. Furthermore, the h‐BN domains show well‐aligned orientation and excellent dielectric properties. In addition, the sapphire substrates can be repeatedly used with almost no limit. This work provides an effective approach for synthesizing large‐scale high‐quality h‐BN layers for electronic applications.     

Elaboration of thermophysical performance enhancement mechanism of functionalized boron nitride/graphite hybrid nanofluids

This study mainly investigated the physicochemical characteristics of ethylene glycol/ water (EG/W) based hydroxyl-functionalized boron nitride (BN-OH) and graphite (G) hybrid nanofluids. A novel simple and efficient annealing method was proposed to have hexagonal boron nitride (h-BN) nanoparticles functionalized to improve the synergistic role between hybrid G/BN-OH nanoparticles. Meanwhile, the dispersion stability, thermal stability, and rheological behavior of diverse nanofluids (h-BN, BN-OH, G, G/BN and G/BH-OH) were comprehensively evaluated. The results showed that the G/BN-OH hybrid nanofluids demonstrate both better dispersion stability and thermal stability, as well as a lower increase in viscosity. In addition, the thermal conductivity of G/BN-OH hybrid nanofluids was increased by up to 18.05% with a concentration of 0.2 wt% when compared to the base fluid. Ultimately, the complicated theoretical mechanism of thermophysical performance augment for G/BH-OH hybrid nanofluids was reliably presented. The enhanced thermal conductivity of nanofluids may be attributed to the formation of adsorption layers and the synergistic effect of the thermal conductivity network.