Synthesis and characterization of large-area single-crystal sheets of borophene on Cu(111) surface

Borophene, a theoretically proposed two-dimensional boron allotrope, has attracted attention as a candidate material platform for high-speed and flexible electronics. However, the single-crystal domains produced so far are too small for device fabrication. We report on synthesis of borophene on Cu(111) monitored in situ by low-energy electron microscopy (LEEM), diffraction and scanning tunneling microscopy, and ex-situ by X-ray photoelectron spectroscopy and atomic force microscopy. By growing borophene on Cu(111) surfaces, we obtain large single-crystal domains, up to 100 μm². We show that the crystal structure is a novel triangular network with h = 1/5 concentration of hexagonal vacancies. LEEM imaging capabilities provide detailed information about borophene growth, island faceting, evaporation and sub-surface dissolution. Data and calculations indicate charge-transfer coupling to substrate without significant covalent bonding. Our work sets the stage for fabricating borophene-based devices and substantiates the idea of borophene as a model for artificial 2D materials development.

R. Wu et al., “Large-area single-crystal sheets of borophene on Cu(111) surfaces”, Nature Nanotechnology 14, 44-49 (2019)