Characterization of Batch-Microfabricated Scanning Electrochemical-Atomic Force Microscopy Probes

Abstract

A procedure for the batch microfabrication of scanning electrochemical-atomic force microscopy (SECM-AFM) probes is described. The process yields sharp AFM tips, incorporating a triangular-shaped electrode (base width 1 microm, height 0.65 microm) at the apex. Microfabrication was typically carried out on (1)/(4) 3-in. wafers, yielding 60 probes in each run. The measured spring constant of the probes was in the range 1-1.5 N m(-1). To date, processing has been carried out twice successfully, with an estimated success rate for the fabrication process in excess of 80%, based on field emission-scanning electron microscopy imaging of all probes and current-voltage measurements on a random selection of approximately 30 probes. Steady-state voltammetric measurements for the reduction of Ru(NH(3))(6)(3+) in aqueous solution indicate that the electrode response is well-defined, reproducible, and quantitative, based on a comparison of the experimental diffusion-limited current with finite element simulations of the corresponding mass transport (diffusion) problem. Topographical imaging of a sputtered Au film with the SECM-AFM probes demonstrates lateral resolution comparable to that of conventional Si(3)N(4) AFM probes. Combined electrochemical-topographical imaging studies have been carried out on two model substrates: a 10-microm-diameter disk ultramicroelectrode (UME) and an array of 1-microm-diameter UMEs, spaced 12.5 microm apart (center to center). In both cases, an SECM-AFM probe was first employed to image the topography of the substrates. The tip was then moved back a defined distance from the surface and use to detect Ru(NH(3))(6)(2+) produced at the substrate, biased at a potential to reduce Ru(NH(3))(6)(3+), present in bulk solution, at a diffusion-controlled rate (substrate generation-tip collection mode). These studies establish the success of the batch process for the mass microfabrication of SECM-AFM tips.

Simultaneous imaging of the topography and electrochemical activity of a 2D carbon nanotube network using a dual functional L-shaped nanoprobe

“…8 However, in the electrochemical current signal, mixed information regarding the local activity and the tip-to-sample distance remains an issue. Diverse approaches, including shear force, 9 intermittent contact (IC)-SECM, 10 combined SECM-scanning ion conductance microscopy (SICM), 11 and SECM-AFM, [12][13][14][15] have been applied to enable fine distance control of electrochemical scanning probes. Recently, double-barrel carbon nanoprobes (DBCNPs) were developed for combined SECM-SICM and were used for simultaneous topographical and electrochemical imaging of a variety of substrates such as microelectrodes, nanoporous membranes, and PC12 cells.…”

“…SECM-AFM has been used to study the local electrochemical activity of various substrates, enzyme activity, [20][21][22] and membrane ion transport. 8,23,24 Furthermore, SECM-AFM probes with nanoelectrodes have been developed to improve the electrochemical resolution; 12,13,15,[25][26][27][28][29][30] however, the application of high-resolution SECM-AFMs with disk-type nanoelectrodes is limited to the characterization of probes using the "lift-up" mode to avoid short circuiting. 27,30 In the lift-up mode, the probe tip is lifted from the substrate by a predefined distance to collect electrochemical data while tracing the surface topography recorded in the previous surface scan during which the probe was in contact with the surface.…”

Nanoscale intermittent contact-scanning electrochemical microscopy

“…Another approach has been to integrate an UME into a tip for atomic force microscopy (AFM), in combined SECM-AFM [16][17][18][19][20], with high resolution tips having been made using nanowires grown on single-walled carbon nanotubes [21]. Nanoscale SECM is also possible by performing the scan in a thin liquid layer, which means the tip does not require insulation, in a technique comparable to scanning tunneling microscopy (STM) [22].…”

Electrochemical current-sensing atomic force microscopy in conductive solutions

“…The latter was partially etched to expose the conductive tip. Macpherson and Unwin used EBL to create triangular-shaped gold electrodes at the apex of a Si 3 N 4 cantilever as well as contact lines [29]. The whole probes were subsequently insulated with Si 3 N 4 and the tips were then exposed by RIE.…”