Recent advances in preparation,properties and device applications of two-dimensional h-BN and its vertical heterostructures

Two-dimensional (2D) layered materials, such as graphene, hexagonal boron nitride (h-BN), molybdenum disulfide (MoS₂), have attracted tremendous interest due to their atom-thickness structures and excellent physical properties. h-BN has predominant advantages as the dielectric substrate in FET devices due to its outstanding properties such as chemically inert surface, being free of dangling bonds and surface charge traps, especially the large-band-gap insulativity. h-BN involved vertical heterostructures have been widely exploited during the past few years. Such heterostructures adopting h-BN as dielectric layers exhibit enhanced electronic performance, and provide further possibilities for device engineering. Besides, a series of intriguing physical phenomena are observed in certain vertical heterostructures, such as superlattice potential induced replication of Dirac points, band gap tuning, Hofstadter butterfly states, gate-dependent pseudospin mixing. Herein we focus on the rapid developments of h-BN synthesis and fabrication of vertical heterostructures devices based on h-BN, and review the novel properties as well as the potential applications of the heterostructures composed of h-BN.     

导热氮化硼复合绝缘纸的制备与性能研究

为解决纸基绝缘材料散热不足的问题,本研究利用3-氨丙基三乙氧基硅烷（APTES）对六方氮化硼（h-BN）填料进行表面改性处理后,添加到纸浆纤维中制备具有良好热传导性能和绝缘性能的导热氮化硼复合绝缘纸。研究结果表明,APTES对h-BN改性成功且改性h-BN导热填料热稳定性略有下降;当混合尺寸改性h-BN导热填料添加量为40 wt%时,绝缘纸的导热系数和体积电阻率分别为0.682 W/（m·K）和4.72×1014 Ω·cm,比原纸分别提高了387%和84.4%。     

Simultaneously enhanced thermal conductivity and dielectric properties of borosilicate glass-based LTCC with AlN and h-BN additions

Microwave devices with reduced dielectric loss and electronic components with increased integration density necessitate the higher performance of electronic packaging materials. The h-BN/AlN/CaCO₃-MgO-B₂O₃-SiO₂-Li₂CO₃ glass composites were prepared via tape-casting and then sintered by pressureless and hot-pressing, respectively. The thermal conductivity of pressureless sintered composite was increased to 6.55 W/(m·K) by incorporating 3 wt% h-BN, and the thermal expansion of 4.47 ppm/K was achieved along with low dielectric constant of 5.76 and dielectric loss of 7.02 × 10⁻⁴ at 24 GHz. In contrast, the hot-pressing sintered composite containing 4 wt% h-BN exhibited higher thermal conductivity of 10.3 W/(m·K) and lower dielectric loss of 4.77 × 10⁻⁴. The microstructure characterization indicated the construction of heat conduction networks, and XRD analysis illustrated the formation of crystallization in the glass. Such low-temperature co-fired ceramic (LTCC) with high thermal conductivity and low dielectric loss would be a promising candidate for electronic packaging and 5G communication applications.     

NiCrFeAl/h-BN.SiO2可磨耗封严涂层抗冲刷性能研究

利用METCO 6P-Ⅱ火焰喷涂制备NiCrFeAl/h-BN.SiO₂可磨耗封严涂层,采用SiO₂对NiCrFeAl/h-BN进行改性,改善涂层的可磨耗性。采用不同氧气/乙炔流量比(氧燃比)制备可磨耗封严涂层,并对涂层抗冲刷性能进行评价。结果显示：NiCrFeAl在喷涂过程中熔化并包覆h-BN和SiO₂粒子;随氧燃比的升高,金属相熔化更加充分,h-BN和SiO₂粒子在涂层中分布的均匀性提高,涂层表面洛氏硬度由50.8 HR15Y提高到70.3 HR15Y,结合强度升高;涂层冲刷后形貌表现出粘着磨损和磨粒磨损特征,冲刷表面粗糙度随氧燃比升高而降低,金属相对非金属相的充分包裹提高了涂层的内聚力,涂层质量损失降低,抗冲刷性能提高。     

钛合金表面激光熔覆 h-BN 固体润滑涂层

目的优化钛合金激光熔覆固体润滑涂层的熔覆工艺参数,提高钛合金表面耐磨性能。方法采用Nd∶YAG激光器,分别在高功率和低功率条件下,在TC4钛合金表面制备h-BN固体自润滑涂层。观察分析熔覆陶瓷层的宏观形貌、物相组成、显微组织和硬度,采用摩擦磨损试验仪对熔覆层的摩擦学性能进行研究。结果低激光功率下,熔覆材料上浮流失严重,熔覆层的相成分主要是Ti N,Ti B,Ti B2等硬质相,硬度较高,存在裂纹。高激光功率下,基材的熔化稀释较好地抑制了润滑相h-BN的上浮,减少了溅射损失,发生了包晶反应,生成了单质金属Ti,熔覆层硬度低,但摩擦磨损试验表明,涂层中润滑相h-BN含量的增加使得形成了更好的润滑膜,降低了摩擦系数。结论在输出电流400 A,脉宽5 ms,频率12Hz,扫描速度120 mm/min,搭接率50%~60%的条件下进行激光熔覆,所得熔覆层的表面状态平整,耐摩擦性能最好。     

导热绝缘h-BN/MVQ/EVA复合材料的双逾渗效应

将h-BN加入到MVQ和EVA混合物中制备导热绝缘h-BN/MVQ/EVA复合材料,SEM结果表明h-BN选择性分布在EVA,与杨氏方程理论一致.h-BN/MVQ/EVA复合材料中的双逾渗效应,有助于力学性能和导热性能的提升.h-BN/MVQ/EVA复合材料的热导率与h-BN含量和MVQ/EVA比值有关.当EVA质量分数为30%时,h-BN/MVQ/EVA复合材料热导率的相对值最大.h-BN/MVQ/EVA复合材料的拉伸强度和断裂伸长率与EVA含量有关,随着EVA和h-BN含量的增加,复合材料的介电常数降低.     

介质衬底上生长h-BN二维原子晶体的研究进展

六方氮化硼(h-BN)二维原子晶体以其独特的结构、优异的性质以及广泛的应用前景引起了人们的普遍关注。高质量h-BN材料的制备是其性质研究与实际应用的前提。机械剥离的h-BN尺寸有限, 普遍采用的化学气相沉积(CVD)技术通常以过渡金属为衬底, 器件应用时需要将h-BN转移到其它衬底上。因此, 在介质衬底上直接生长h-BN成为二维材料研究领域的一个重要发展方向。本文总结了近年来介质衬底(包括: Si基衬底、蓝宝石衬底和石英衬底等)上直接生长h-BN二维原子晶体的主要进展。人们采用CVD、金属有机气相外延法(MOVPE)、物理气相沉积法(PVD)等方法, 通过提高生长温度、衬底表面处理、两步生长等工艺实现了介质衬底上直接生长h-BN。此外, 还介绍了介质衬底上h-BN二维原子晶体的主要应用。     

Effect of reactant Ti/B4C ratio on the stoichiometry and mechanical properties of h-BN-Ti(C,N) prepared by combustion synthesis

h-BN-Ti(C,N) ceramic composites were prepared by combustion synthesis from B₄C-Ti powder compacts ignited under high gaseous nitrogen pressure. The influences of Ti/B₄C ratio in reactant on the combustion temperature and velocity, phase composition and N content in Ti(C,N) phase were analyzed through theoretical and experimental studies. Experimental results show that combustion temperature and velocity increased with the increase of Ti/B₄C ratio in reactant. TiN is the preferential formation phase under high nitrogen pressure, which resulted in higher N content in Ti(C,N) phase. Mechanical properties of the composites increased with the increase of Ti/B₄C ratio because of higher Ti(C,N) content in products.     

Densification behavior and microstructure development in TiB2 ceramics doped with h-BN

This paper aims to study the impacts of h-BN additive on the microstructural features and sintering behavior of TiB₂. For this objective, two different samples of monolithic TiB₂ and TiB₂-5 wt% h-BN were fabricated using spark plasma sintering (SPS) technique at 1900 °C. An external pressure of 40 MPa was exerted to the specimens during the sintering, and they were maintained at the maximum sintering temperature for 7 min. The characterization of as-fabricated ceramics was carried out using thermodynamical investigations, field emission SEM, and X-ray diffractometer. The thermodynamical and XRD studies revealed that the sintering process was non-reactive for both samples. However, introducing h-BN noticeably promoted the sinterability of TiB₂ through activating the liquid phase sintering mechanism, and a near-fully dense composite was attained. The fractographical assessment manifested that the intergranular fracture was the dominant type in both monolithic and h-BN doped specimens. Finally, the quantitative image analysis indicated the role of h-BN in refining the microstructure of the doped TiB₂ ceramic.     

石墨烯/h-BN面内异质结构热输运的分子动力学研究

采用非平衡分子动力学方法探究石墨烯/h-BN面内异质结构界面热导的影响因素,讨论了单空位缺陷和Stone-Wales (SW)缺陷在近界面不同位置时的声子热输运活动。模拟结果证明,当h-BN一侧单空位缺陷远离界面,界面热导随之降低; SW缺陷则由共价键类型和位置决定其对界面热导的影响,由此揭示缺陷的类型和位置对界面热导带来的调节作用。此外,讨论了界面处存在单空位缺陷时,温度变化影响界面热导背后的潜在机理。本研究对微观尺度下的二维异质结构材料的热导性能提供理论参考和实验指导。