Abstract
Electrodes exhibiting controlled nanoscale separations are required in devices for light detection, semiconductor electronics and medical diagnostics. Here we use low-cost lithography to define micron-separated electrodes, which we downscale to create three-dimensional electrodes separated by nanoscale gaps. Only by devising a new strategy, which we term electrochemical self-inhibited reagent depletion, were we able to produce a robust self-limiting nanogap manufacturing technology. We investigate the method using experiment and simulation and find that, when electrodeposition is carried out using micron-spaced electrodes simultaneously poised at the same potential, these exhibit self-inhibited reagent depletion, leading to defined and robust nanogaps. Particularly remarkable is the formation of fractal electrodes that exhibit interpenetrating jagged elements that consistently avoid electrical contact. We showcase the new technology by fabricating photodetectors with responsivities (A/W) that are one hundred times higher than previously reported photodetectors operating at the same low (1–3 V) voltages. The new strategy adds to the nanofabrication toolkit method that unites top–down template definition with bottom–up three-dimensional nanoscale features.
Highlights
Electrodes exhibiting controlled nanoscale separations are required in devices for light detection, semiconductor electronics and medical diagnostics
We began by forming a scaled-up version of the intended chip architecture, a template that would be realized using standard photolithographic techniques
Using scanning electron microscopy (SEM) analysis, we observe the spacing between electrodes at the nearest point to be B50 nm (Fig. 1d,e)
Summary
Electrodes exhibiting controlled nanoscale separations are required in devices for light detection, semiconductor electronics and medical diagnostics. Various methods have been developed to fabricate nanoscale features with nanometre separations, including block copolymer lithography[16,17,18], galvanic displacement[19,20], interference lithography[21,22] and nanosphere-patterned etching[23,24] These methods are generally inexpensive and scalable; they typically lack top–down control required to fabricate addressable nanoscale-separated electrodes. The definition of addressable isolated electrodes at the nanoscale[25] can be performed with serial direct-write methods including dip-pen[26,27] and electron beam lithography[28,29] These offer impressive critical dimensions with precise top–down control that, can be difficult to scale. We termed this prospective mechanism, which would require verification via both experiment and modelling, self-inhibited reagent depletion (SIRD)
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