Vibrational Property of alpha-Borophene Determined by Tip-Enhanced Raman Spectroscopy

We report a Raman characterization of the alpha borophene polymorph by scanning tunneling microscopy combined with tip-enhanced Raman spectroscopy. A series of Raman peaks were discovered, which can be well related with the phonon modes calculated based on an asymmetric buckled alpha structure. The unusual enhancement of high-frequency Raman peaks in TERS spectra of alpha borophene is found and associated with its unique buckling when landed on the Ag(111) surface. Our paper demonstrates the advantages of TERS, namely high spatial resolution and selective enhancement rule, in studying the local vibrational properties of materials in nanoscale.