Vibrational Analysis of Single Molecules with Scanning Tunneling Microscopy

Abstract Molecular vibrational analysis investigates molecular vibrations and their interactions with their surrounding environment. It enables precise chemical identification, reveals intricate intra- and intermolecular coupling, and provides critical insights into the reaction mechanisms and dynamics. Since the first application for detecting single-molecule vibrations in 1998, scanning tunneling microscopy (STM) has advanced vibrational analysis to the ultimate spatial resolution. Single-molecule vibrational analysis using STM has uncovered otherwise inaccessible details of how molecular vibrations respond to nanoscale surface environments and has achieved chemical sensitivity down to the single bond level. Moreover, it offers the potential to probe, characterize, and manipulate vibrational dynamics with a combined spatial and temporal resolution. In this Review, we summarize recent advances and discuss future prospects for employing STM to investigate single-molecule vibrations from both spectroscopic and microscopic perspectives. We focus on three primary STM-based methodologies distinguished by their excitation mechanisms: inelastic electron-tunneling spectroscopy, tip-enhanced Raman spectroscopy, and infrared absorption spectroscopy. In addition, we discuss complementary readout and time-domain approaches, including STM action spectroscopy and time-resolved STM, which probe vibration-induced molecular actions and ultrafast vibrational dynamics, respectively.