Accurate Simulations of Scanning Tunneling Microscope: Both Tip and Substrate States Matter

Abstract

Scanning tunneling microscope (STM) provides an atomic-scale characterization tool. To this end, high-resolution measurements and accurate simulations must closely cooperate. Emerging experimental techniques, e.g., substrate spacers and tip modifications, suppress metallic couplings and improve the resolution. On the other hand, development of STM simulation methods was inactive in the past decade. Conventional simulations focus on the electronic structure of the substrate, often overlooking detailed descriptions of the tip states. Meanwhile, the overwhelming usage of periodic boundary conditions ensures effective simulations of only neutral systems. In this Perspective, we highlight the recent progress that takes the effects of both tip and substrate into account under either Tersoff−Hamann or Bardeen's approximation, which provides an accurate analysis of measured high-resolution STM results, uncovers underlying concepts, and rationally designs experimental protocols for important chemical systems. We hope this Perspective will stimulate broad interest in advanced STM simulations, highlighting the way forward for STM investigations that involve complex geometrical and electronic structures.

Plasmon‐Molecule Interactions in Single‐Molecule Junctions

“…In 2023, S Duan and his colleagues conducted a simulation analysis that, for the first time, modeled the luminescence of the complete system of the tip, molecule and substrate. This study unveiled the significance of the tip and base states in STM‐induced molecular luminescence, offering theoretical support for a more profound understanding of the microscopic world [83] …”

“…This study unveiled the significance of the tip and base states in STM-induced molecular luminescence, offering theoretical support for a more profound understanding of the microscopic world. [83] The previously mentioned experimental research on plasmon-enhanced fluorescence in SMJs, along with the discourse and elucidation of photon emission mechanisms, not only show potential for the creation of innovative nanomolecular devices but also contribute significantly to other areas, like enhancing the efficiency of perovskite solar cells. [86] As depicted in Figure 8d, in 2020, Kim's research team was able to measure three vibrational modes with unique symmetries in a CuNc single molecule positioned within a nanocavity (Figure 7a).…”