TEM-Assisted Fabrication of Sub-10 nm Scanning Electrochemical Microscopy Tips.

High-resolution scanning electrochemical microscopy (SECM) is a powerful technique for mapping surface topography and reactivity on the nanoscale and investigating heterogeneous processes at the level of single nanoparticles. The ability to fabricate ultrasmall nanoelectrode tips is critical for the progress in nano-SECM. Despite long-term efforts to improve previously developed procedures, the preparation and characterization of disk-type polished tips with the radius <∼25 nm remains challenging and unpredictable. One of the problems is that the geometry of such tips is hard to characterize by either SEM or atomic force microscopy (AFM) that has been employed for examination of somewhat larger nanoelectrodes. Herein, we report a new approach to more predictable and reproducible two-step fabrication of ultrasmall (≤10 nm radius) polished Pt electrodes assisted by transmission electron microscopy (TEM) imaging. Both voltammetric and SECM responses of the prepared nanoelectrodes are consistent with the size and geometry extracted from TEM images. These tips can be used to attain sub-10 nm spatial resolution of SECM imaging and kinetic studies.