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

Abstract

Nanowires with nanometer-scale gaps are an emerging class of nanomaterials with potential applications in electronics and optics. Here we demonstrate that the feedback mode of scanning electrochemical microscopy (SECM) allows for spatially resolved detection of a nanogap on the basis of its electrical conductivity. A gapped nanoband is employed as a model system to describe a mechanism of a unique feedback effect from a nanogap. Interestingly, both experiments and numerical simulations confirm that a peak current response is obtained when an SECM tip is laterally scanned above an insulating nanogap formed in an unbiased nanoband. On the other hand, no peak current response is expected for a highly conductive nanogap, which must be extremely narrow or filled with highly conductive molecules for efficient electron transport.Here we report on a novel application of scanning electrochemical microscopy (SECM) 1, 2 to spatially resolved detection of a nanometer-scale gap formed in a nanowire. A gapped nanowire is an emerging class of nanomaterial that has attracted tremendous attentions because of its potential applications in electronics and optics. 3, 4 An important progress during the past few years is that high-throughput and low-cost chemical methods have been developed to create a gapped nanowire without traditional lithography. 5-10 Electrical transport through a nanogap can be also tuned chemically by controlling the sizes of the gap 6 or by bridging the gap with conductive molecules 8 or polymers. 5, 10 Conventional methods of electrical characterization of a gapped nanowire, however, require good ohmic contact of both ends of a single nanowire with lithographically fabricated electrodes for an external bias and a current measurement. 5, 6, 8, 10 Moreover, these methods are not useful to resolve multiple nanogaps in a nanowire.SECM is a powerful technique for electrochemical characterization of nanomaterials and nanosystems at high spatial resolution. 2, 11 Recently, we employed the feedback mode of SECM to drive and probe electron transport at an individual nanoband, which is not attached to a contact electrode and is electrically isolated on an insulating substrate in an electrolyte solution (Figure 1). 12, 13 Specifically, a redox molecule (blue spheres) is electrolyzed at the tip of an ultramicroelectrode probe that is brought to the proximity of a nanoband. Electrolysis of the tip-generated species (orange spheres) at the nanoband surface regenerates the original redox species, which is detected amperometrically at the tip. Importantly, mediator regeneration at the surface of an unbiased nanoband drives electron transport through the nanoband and subsequent electrolysis of the original mediator at the exterior surface of the *To whom correspondence should be addressed. E-mail: E-mail: amemiya@pitt.edu. nanoband. Thus, a nanogap in a nanoband is expected to limit the lateral electron transport and affect the tip current response. NIH Public AccessThis work describes the proof-of-concept experimen...

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