Operando Observation of Molecular-Scale Manipulation Using Electrochemical Tip-Enhanced Raman Spectroscopy

Tip functionalization in scanning tunneling microscopy (STM) has become a routine strategy to improve the imaging resolution. Under ultrahigh vacuum and low-temperature conditions, individual molecule(s) can be transferred between the substrate and the tip when proper bias potential is applied, allowing for molecular-scale manipulation and controlled single-bond formation. However, little work related to tip functionalization in electrochemical (EC) environments has been carried out. To bridge that gap, this paper generalizes tip functionalization strategies from UHV conditions to the solid-liquid interfaces. Specifically, we demonstrate the bias-induced functionalization of an Ag tip with cobalt phthalocyanine molecules in EC-STM. Tip-enhanced Raman spectroscopy is employed for the operando detection of the molecule(s) on the tip. We also show that the tip functionalization process may be reversed in some cases, regaining a pristine tip. The control over molecular transfer between the substrate and the tip not only provides guidance to avoid undesired tip modification in EC-STM experiments, but also offers the capability of molecular manipulation at the solid-liquid interface.