Due to their extraordinary properties, boron nitride nanosheets (BNNSs) have great promise for many applications. However, the difficulty of their efficient preparation and their poor dispersibility in liquids are the current factors that limit this. A simple yet efficient sugar‐assisted mechanochemical exfoliation (SAMCE) method is developed here to simultaneously achieve their exfoliation and functionalization. This method has a high actual exfoliation yield of 87.3%, and the resultant BNNSs are covalently grafted with sugar (sucrose) molecules, and are well dispersed in both water and organic liquids. A new mechanical force–induced exfoliation and chemical grafting mechanism is proposed based on experimental and density functional theory investigations. Thanks to the good dispersibility of the nanosheets, flexible and transparent BNNS/poly(vinyl alcohol) (PVA) composite films with multifunctionality is fabricated. Compared to pure PVA films, the composite films have a remarkably improved tensile strength and thermal dissipation capability. Noteworthy, they are flame retardant and can effectively block light from the deep blue to the UV region. This SAMCE production method has proven to be highly efficient, green, low cost, and scalable, and is extended to the exfoliation and functionalization of other two‐dimensional (2D) materials including MoS2, WS2, and graphite.
With the advances of the electronics industry, the continuing trend of miniaturization and integration imposes challenges of efficient heat removal in nanoelectronic devices. Two-dimensional (2D) materials, especially graphene and hexagonal boron nitride (h-BN), are widely accepted as ideal candidates for thermal management materials due to their high intrinsic thermal conductivity and good mechanical flexibility. In this review, we introduce phonon dynamics of solid materials and thermal measurement methods at nanoscale, and highlight the unique thermal properties of 2D materials in relation to sample thickness, domain size, and interfaces. In addition, we discuss recent achievements of thermal management applications in which 2D materials act as heat spreader and thermal interface materials based on their controlled growth and selfassembly. Finally, critical consideration on the challenges and opportunities in thermal management applications of 2D materials is presented.
Atomically thin 2D materials have received intense interest both scientifically and technologically. Bismuth oxyselenide (Bi 2 O 2 Se) is a semiconducting 2D material with high electron mobility and good stability, making it promising for high-performance electronics and optoelectronics. Here, an ambient-pressure vapor-solid (VS) deposition approach for the growth of millimeter-size 2D Bi 2 O 2 Se single crystal domains with thicknesses down to one monolayer is reported. The VS-grown 2D Bi 2 O 2 Se has good crystalline quality, chemical uniformity, and stoichiometry. Field-effect transistors (FETs) are fabricated using this material and they show a small contact resistivity of 55.2 Ω cm measured by a transfer line method. Upon light irradiation, a phototransistor based on the Bi 2 O 2 Se FETs exhibits a maximum responsivity of 22 100 AW −1 , which is a record among currently reported 2D semiconductors and approximately two orders of magnitude higher than monolayer MoS 2 . The Bi 2 O 2 Se phototransistor shows a gate tunable photodetectivity up to 3.4 × 10 15 Jones and an on/off ratio up to ≈10 9 , both of which are much higher than phototransistors based on other 2D materials reported so far. The results of this study indicate a method to grow large 2D Bi 2 O 2 Se single crystals that have great potential for use in optoelectronic applications.
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