Investigation of localized electrochemical interfaces with advanced microscopic techniques : AFM-SECM and FIB/SEM tomography

Abstract

Combined scanning probe techniques (SPM) enable the investigation of localized surface properties. Amongst other hybrid methods, atomic force - scanning electrochemical microscopy (AFM-SECM) is highly attractive for studying processes at the solid/liquid interface, and also for investigations of liquid/liquid interfaces. In order to enhance the field of applications, AFM-SECM probes may be modified facilitating the requirements for biomedical applications and for usage with electroanalytical techniques. Whereas AFM-SECM provides predominantly information of surface processes, the combination of focused ion beam (FIB) and scanning electron microscopy (SEM) enables the detection and reconstruction of the inner structure of (nano)porous materials. Within the first part of this thesis, the focus of research is targeted towards modification of AFM-SECM probes facilitating biomedically relevant measurements, such as sensing hydrogen peroxide (H2O2) release or generation in close proximity to a sample surface (chapter 4), and localized pH sensing with associated surface changes (chapter 5). In chapter 6, detailed investigations of FIB-milled nanoporous arrays in silicon nitride (SiN) membranes are presented, which were used as solid-state support for electrochemistry at the interface between two immiscible electrolyte solutions (ITIES). The suitability of AFM-SECM in the investigation of micro- and nanoscale interfaces is shown by the performance of AFM-SECM with a conductive AFM tip, which was used to visualize the diffusion behavior at these nanoporous arrays. In addition, the localized electrochemical deposition of silica at the nanoITIES was used to visualize the location of the interface within the nanopores. FIB/SEM tomography was performed for the investigations of the location of this interface at such silica deposits.