Structural Characterization of Boron Sheets beyond the Monolayer and Implication for Experimental Synthesis and Identification.

Abstract

The successful synthesis of quasi-freestanding bilayer borophene has aroused much attention for its superior physical properties and holds great promise for future electronic devices. Herein, we comprehensively explore six boron sheets beyond the monolayer and structurally characterize them via various methods using first-principles calculations for experimental references. On the basis of atomic models of borophenes, simulated scanning tunneling microscope (STM) images show different morphologies at different bias voltages and are explained by the partial densities of states and the height differences in the vertical direction. Simulated transmission electron microscope images further probe the internal atomic arrangement of boron sheets and compensate for the shortcomings of STM images to better distinguish different phases of boron sheets. The interlayer coupling strength is stronger in bilayer borophenes than in the three-layer system via the electron localization function and Mulliken bond population. In addition, simulated X-ray diffraction and infrared spectra show different characteristic peaks and corresponding vibrational modes to further characterize these boron sheets. These theoretical results can decrease the prime cost and provide vital guidance for the experimental synthesis and identification of boron sheets beyond the monolayer.