Borophene: New Sensation in Flatland

Abstract

Borophene, a 2D allotrope of boron and the lightest elemental Dirac material, is the latest very promising 2D material owing to its unique structural and electronic characteristics of the X3 and β12 phases. The high atomic density on ridgelines of the β12 phase of borophene provides a substantial orbital overlap, which leads to an excellent electron density in the conduction level and thus to a highly metallic behavior. These unique structural characteristics and electronic properties of borophene attract significant scientific interest. Herein, approaches for crystal growth/synthesis of these unique nanostructures and their potential technological applications are discussed. Various substrate‐supported ultrahigh‐vacuum growth techniques for borophene, such as molecular beam epitaxy, atomic layer deposition, and chemical vapor deposition, along with their challenges, are also summarized. The sonochemical exfoliation and modified Hummer's technique for the synthesis of free‐standing borophene are also discussed. Solution‐phase exfoliation seems to address the scalability issues and expands the applications of these unique materials to various fields, including renewable energy devices and ultrafast sensors. Furthermore, the electronic, optical, thermal, and elastic properties of borophene are thoroughly discussed and are compared with those of graphene and its “cousins.” Numerous frontline applications are envisaged and an outlook is presented.

Borophene via Micromechanical Exfoliation

“…[7] Borophene, being metallic in both β 12 and X 3 crystallographic phases, also has excellent elastic strength and electronic mobility, which altogether places it at a significant pedestal among 2D materials. The evolution of borophene is expected to bring in new dimensions to 2D-materialbased next-generation devices [8] (see the schematic plot in Figure 1a for the comparative presentation of ln (mobility) vs Young's modulus for various 2D materials). [9][10][11][12][13] Anisotropic atomic ordering results in enhanced electronic mobility ≈1.82 × 10 6 cm 2 V −1 s −1 , Young's modulus ≈398 N m −1 , and thermal conductivity along atomic ridgelines.…”

The Emergence and Evolution of Borophene

“…[ 6,10 ] 2D nanomaterials have become excellent candidates for biosensors due to their superior electrochemical performance, high surface‐to‐volume ratios, [ 219 ] more surface‐active sites, [ 220,221 ] and high electronic mobilities at monolayer thicknesses. [ 10,222 ]…”

Elemental 2D Materials: Solution‐Processed Synthesis and Applications in Electrochemical Ammonia Production

“…In general, borophene is 2D boron sheets with various unique characteristics. [215] Borophene displays structural anisotropy and polymorphism, which results in a wide range unique properties with enhanced tunabilities. [44] Interestingly, borophene for most structures is considered to be metallic and thus the lightest 2D metal, while also showing excellent properties and exhibiting optical transparency and mechanical compliance.…”