Electrochemical Fabrication of High-Quality STM-TERS Tips for Nanoscale Imaging

Tip-enhanced Raman spectroscopy (TERS) is a powerful technique capable of simultaneously obtaining the morphological and chemical fingerprint information of target samples with nanoscale spatial resolution. The core of TERS is the plasmonic tip, dictating the sensitivity and spatial resolution of TERS measurements. However, traditional electrochemical fabrication of the widely used Au tips involves the use of highly volatile concentrated HCl, which may lead to severe corrosion to the experimental setup. Herein, realizing the indispensable role of proton and Cl− in Au etching, we rationally designed a recipe of less volatile and corrosive LiCl/HCl etchant by maintaining a high Cl− concentration (6 M) with a moderate concentration of H+ to rapidly etch Au. Furthermore, in situ optical monitoring revealed that a microscale bamboo-like topography and an enlarged macroscopic cone angle are related to the “pinning and sudden-drop” mechanism. The obtained tips exhibit a high spatial resolution and provide more than a two-fold increase in average lower-bound TERS enhancement compared with that obtained with concentrated HCl recipe. This recipe provides a practical route toward reliable batch fabrication of high-performance STM-TERS tips for nanoscale imaging while substantially mitigating equipment corrosion.