Multifunctional carbon nanoelectrodes fabricated by focused ion beam milling† Rahul Thakar, Anna E. Weber, Celeste A. Morris and Lane A. Baker * We report a strategy for fabrication of sub-micron, multifunctional carbon electrodes and application of these electrodes as probes for scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM). The fabrication process utilized chemical vapor deposition of parylene, followed by thermal pyrolysis to form conductive carbon and then further deposition of parylene to form an insulation layer. To achieve well-defined electrode geometries, two methods of electrode exposure were utilized. In the first method, carbon probes were masked in polydimethylsiloxane (PDMS) to obtain a cone-shaped electrode. In the second method, the electrode area was exposed via milling with a focused ion beam (FIB) to reveal a carbon ring electrode, carbon ring/platinum disk electrode, or carbon ring/nanopore electrode. Carbon electrodes were batch fabricated (35/batch) through the vapor deposition process and were characterized with scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and cyclic voltammetry (CV) measurements. Additionally, Raman spectroscopy was utilized to examine the effects of Ga + ion implantation, a result of FIB milling. Constant- height, feedback mode SECM was performed with conical carbon electrodes and carbon ring electrodes. We demonstrate the utility of carbon ring/nanopore electrodes with SECM-SICM to simultaneously collect topography, ion current and electrochemical current images. In addition, carbon ring/nanopore electrodes were utilized in substrate generation/tip collection (SG/TC) SECM. In SG/TC SECM, localized delivery of redox molecules affords a higher resolution, than when the redox molecules are present in the bath solution. Multifunctional geometries of carbon electrode probes will find utility in electroanalytical applications, in general, and more specifically with electrochemical microscopy as discussed herein. Introduction Scanning electrochemical microscopy (SECM) has developed into a powerful tool to investigate localized electrochemical reactions. Recent efforts have sought to enhance both spatial resolution and chemical information obtained with SECM. Progress in these areas is attributed to improvement in instru- mentation, 1–6 and measurement techniques. 6–10 For example, to enhance feedback and provide constant-distance regulation, SECM has been combined with force based measurements. 3,4,11–13 Other techniques to improve SECM include development of the scanning micropipet contact method 14 or scanning electro- chemical cell microscopy. 15,16 Girault and coworkers 17 have reported the use of so-stylus electrochemical probes that allow contact-mode SECM imaging. In addition, developments in hybrid techniques such as SECM-atomic force microscopy (SECM-AFM), 18–22 alternating current-SECM, 2,23–26 voltage- switching SECM 1 and SECM-SICM 27–30 provide alternative feedback mechanisms that have further helped to decouple the electrochemical and topographical signals obtained. Robust yet simple fabrication of nanoscale electrodes is central to any improvements since the quality of electrochemical signal is directly determined by the probe itself. 17,27,28,30–34 Moreover, successful integration of SECM with other techniques to enhance the chemical information obtained has relied on novel probe fabrication methods. 27–29,32,35 Here we describe a fabrication strategy to create multifunctional geometries of nanoscale carbon electrodes and demonstrate application of these electrodes in SECM and SECM–SICM. Advantages of carbon electrodes, for instance, a large potential scan window, resistance to bio-fouling, ease of surface modication, and a well-understood surface chemistry make carbon a compelling choice for electroanalytical detection. 36,37 Carbon ber 33,38,39 and glassy carbon electrodes are widely employed for electro- chemical applications in neuroelectrochemistry and SECM. These electrodes are straightforward to fabricate and robust in operation, but are typically large (e.g. diameters in the microm- eter range, 7 microns or higher) 40 and difficult to miniaturize. Pyrolyzed photoresist lms 41–43 have been successfully employed for electrode fabrication, but are better suited toward fabrication of planar carbon electrodes. Other approaches to fabricate Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, IN 47405, USA. E-mail: lanbaker@indiana.edu † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3an01216f Cite this: DOI: 10.1039/c3an01216f Received 20th June 2013 Accepted 23rd July 2013 DOI: 10.1039/c3an01216f www.rsc.org/analyst This journal is ª The Royal Society of Chemistry 2013 Analyst Analyst PAPER Published on 24 July 2013. Downloaded by Pennsylvania State University on 15/08/2013 20:08:42. View Article Online View Journal