metallic), is a new sensation in the flatland. [1][2][3] Incidentally, among various 2D materials, while boron nitride (BN) has large Young's modulus but compromised mobility, phosphorene and silicene have appreciable carrier mobility but compromised elastic behavior. [4] Graphene, considered the wonder material of this century fairs exceedingly well and its carrier mobility, as well as Young's modulus, are simultaneously high, which places it at a different pedestal. [5,6] However, e-h symmetry and spin symmetry in graphene result in insufficient signal/noise ratio in electronic as well as spintronic chips. [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. [14,15] In particular, for flexible electronic as well as spintronic chip applications, high electron mobility and Young's modulus are desirable simultaneously and borophene Borophene, the lightest among all Xenes, possesses extreme electronic mobility along with high carrier density and high Young's modulus. To accomplish device-quality borophene, novel approaches of realization of monolayers need to be urgently explored. In this work, micromechanical exfoliation is discovered to result in mono-and few-layered borophene of device quality. Borophene sheets are successfully fabricated down to monolayer thickness. Distinct crystallographic phases of borophene viz. XRD study reveals crystallographic phase transition from rhombohedral to several other eigen phases of borophene. The role of the destination substrates is held crucial in determining the final phase of the transferred sheet. The exfoliation energy is calculated by density functional theory. Molecular dynamics simulations are used to simulate the exfoliation process. Heterolayers of borophene, with black phosphorene (BP) or with molybdenum disulfide (MoS 2 ) atomic sheets, are found to result in photoexcited coupling quantum states. Gold-coated borophene bestows promising anchoring capability for surface-enhanced Raman spectroscopy (SERS). Successful demonstration of the electronic behavior of micromechanically exfoliated borophene and excitonic behavior of borophene-based heterolayers will guide future generation devices not only in electronics and excitonics, but also in thermal management, electronic packaging, hydrogen storage, hybrid energy storage, and clean energy solutions.
