Pinching and Probing of Polygonal Grain Boundaries

Abstract: In this study, sub-angstrom spatial resolution is achieved in mapping and spectroscopy of atoms and bonds within polygonal grain boundaries (GBs) of graphite using Scanning Tunneling Microscopy (STM). Robust van Hove singularities (VHS) are observed in addition to edge states under ambient conditions. The bias-dependent nature of these states reveals metallic traits of GB, through the charge accumulation and dissipation of localized electronic states. Utilizing a surface elastic deformation technique induced by STM tip allows pico-pinching of the GB, providing insights into its mechanical strength as well as in-situ strain-induced modification of their unique spectroscopy, revealing a tendency toward flattening of the electronic energy band dispersion. An initial atomic-level experimental technique of probing spin-polarized magnetic states is demonstrated, suggesting different densities for spin-up and spin-down states within a spin-degenerate band structure potentially applicable in spin transport or quantum spin sensing.