Atomic-Scale Inelastic Electron Tunneling Spectroscopic Mapping of Bilayer Borophene

The synthesis of bilayer borophene was recently reported [1], but many questions remain about the atomic-scale physical and electronic properties of this new 2D phase of boron. Predicted to be a phonon-mediated superconductor [2], the low-energy electronic and vibrational properties of 2D boron are of particular interest. Here, we use atomically resolved inelastic electron tunneling spectroscopy (IETS) mapping to study bilayer borophene with a CO-functionalized scanning tunneling microscope tip. The resulting IETS spectra possess low-energy features that are distinct from single-layer borophene, providing experimental evidence for theoretically predicted interlayer vibrational modes. Moreover, IETS mapping reveals spatially resolved differences between the hollow hexagon sites and interlayer bonding sites for bilayer borophene, thus providing unprecedented atomic-scale insight into 2D boron beyond the single-atomic-layer limit.

[1] X. Liu, et al. “Borophene synthesis beyond the single-atomic-layer limit,” Nature Materials, 21, 35-40 (2022).

[2] M. Gao, et al. “Prediction of phonon-mediated superconductivity in borophene,” Physical Review B, 95, 024505 (2017).