Monitoring Scanning Electrochemical Microscopy Approach Curves with Mid-Infrared Spectroscopy: Toward a Novel Current-Independent Positioning Mode

摘要

Single-bounce attenuated total reflection infrared spec-ntroscopy in the 3 20 µm range (mid-infrared, MIR) hasnbeen combined with scanning electrochemical microscopyn(SECM) for in situ spectroscopic detection of electro-nchemically induced localized surface modifications usingnan ultramicroelectrode (UME). In this study, a novelncurrent-independent approach for positioning the UMEnin aqueous electrolyte solution is presented using eithernchanges of infrared (IR) absorption intensity associatednwith borosilicate glass (BSG), which is used as shieldingnmaterial of the UME wire, or by monitoring IR changesnof the water spectrum within the penetration depth of thenevanescent field due to displacement of water moleculesnin the volume between the sample surface and the UMEnwithin the evanescent field. The experimental results shownthat the UME penetrates into the exponentially decayingnevanescent field in close vicinity (a few micrometer) to thenattenuated total reflection (ATR) crystal surface. Hence,nthe resulting intensity changes of the IR absorptionnspectra for borosilicate glass (increase) and for watern(decrease) can be used to determine the position of thenUME relative to the ATR crystal surface independent ofnthe current measured at the UME.