Scanning electrochemical microscopy of one-dimensional nanostructure: Effects of nanostructure dimensions on the tip feedback current under unbiased conditions

Abstract

Scanning electrochemical microscopy (SECM) is developed as a powerful approach to electrochemical characterization of individual one-dimensional (1D) nanostructures under unbiased conditions. 1D nanostructures comprise high-aspect-ratio materials with both nanoscale and macroscale dimensions such as nanowires, nanotubes, nanobelts, and nanobands. Finite element simulations demonstrate that the feedback current at a disk-shaped ultramicroelectrode tip positioned above an unbiased nanoband, as prepared on an insulating substrate, is sensitive to finite dimensions of the band, i.e., micrometer length, nanometer width, and nanometer height from the insulating surface. The electron-transfer rate of a redox mediator at the nanoband surface depends not only on the intrinsic rate but also on the open-circuit potential of the nanoband, which is determined by the dimensions of the nanoband as well as the tip inner and outer radii, and tip-substrate distance. The theoretical predictions are confirmed experimentally by employing Au nanobands as fabricated on a SiO 2 surface by electron-beam lithography, thereby yielding well defined dimensions of 100 or 500 nm in width, 47 nm in height, and 50 μm in length. A 100 nm-wide nanoband can be detected by SECM imaging with ∼2 μm-diameter tips although the tip feedback current is compromised by finite electron-transfer kinetics for Ru(NH 3 ) 6 3+ at the nanoband surface.

Imaging of localized enzymatic peroxidase activity over unbiased individual gold nanowires by scanning electrochemical microscopy

“…However, the relatively extended length of the nanowire (2-3 mm) was still not sufficient for effective recycling of the electrons with the bulk mediator solution resulting in a negative feedback current response. Previously, Amemiya and co-workers 27,28 were able to record positive feedback images of lithographically cast gold nanobands (100 nm broad and 50 mm long) and single walled carbon nanotubes ($1.6 nm diameter and $2 mm long) on insulating surfaces with probes of diameters $2 mm and 10 mm, respectively. Although, the diameters of probes used to record these images were rather large compared to those of the ones used in our studies with AuNWs, the extremely extended lengths of these bands and nanowires were sufficient to exchange electrons with the bulk solution and to behave as bipolar substrates.…”

“…7A. Some of the recent research studies focused on the use of a single AuNW or AuNP to study catalytic properties and sensing, [25][26][27][28][29]37,38 which prompted us to image the distribution of HRP activity over individual AuNWs. Fig.…”

Scanning Electrochemical Microscopy of Individual Single-Walled Carbon Nanotubes

“…Moreover, quasi-steady-state feedback responses that are independent of probe scan rate were obtained from the unbiased SWNT, which is much longer than the tip diameter to effectively mediate FcTMA + oxidation at the exterior sidewall (Figure 1). 10 The feedback effect from the SWNT is not limited by electron transport through the nanotube. The tip feedback current above a SWNT varies linearly with the mediator concentration from 0.3 mM (Figure 4a) to 1 mM (data not shown) so that the tip current normalized with respect to i T,∞ (eq 1) is independent of the concentration.…”

Spatially Resolved Detection of a Nanometer-Scale Gap by Scanning Electrochemical Microscopy

“…A three-dimensional SECM diffusion problem with a nanoband under unbiased conditions was defined and solved by using COMSOL Multiphysics version 3.4 (COMSOL, Inc., Burlington, MA) as reported elsewhere 13, 16. A simulation report is attached as Supporting Information.…”

“…Gap-free Au nanobands were fabricated on the SiO 2 /Si substrate by electron-beam lithography and characterized in detail as reported elsewhere 13. A gap was formed by gradual degradation of a nanoband during storage.…”