Control of nanogap dimensions in selectively etched nanowire heterostructures.

摘要

Progress in translating nanoscience into useful nanotechnologies has been limited by an inability to drive down fabrication costs, improve throughputs, and achieve a high level of reproducibility over nanoscale structures and the properties that are controlled by size. One important nanomaterial that has incited substantial interest over the past decade is Porous Anodic Alumina (PAA). [1] The widespread use of PAA as a sacrificial template in the electrochemical synthesis of high-aspect-ratio nanomaterials has been inhibited in large part by complications related to its brittle behavior and the lack of uniformity in pore structure over large areas. The control over the shape of the growth front of electrodeposited materials in a PAA template remains as a significant challenge. This requirement is particularly relevant to "on-wire lithography" (OWL), where the inner segment of a tri-layered electrodeposited nanowire is selectively etched to achieve a nanogap of equivalent dimensionality. [2] Such a nanogap with dimensions controlled at nanometer-scale precision would have the potential to enable practical applications of molecular electronics [3] and nanoplasmonics [4].;In this work, polyethyleneimine (PEI) is used for the planarization of electrodeposited nanowire growth fronts in PAA templates. The addition of highly branched, low molecular weight PEI to an electrolytic bath provides improved uniformity in the relative distribution of nanowire growth rates from pore to pore, and allows for a more precise control over the electrochemical growth process. [5] This utility of PEI is demonstrated for the synthesis of Au-Ag-Au nanowire arrays. Upon the completion of electrodeposition, chemical etching of the Ag segment is performed, leaving behind a nanogap of a width that is determined by the thickness of the Ag segment. The achievement of electrodeposited multicomponent nanowires that yield sub-10 nm gaps in nanowires having a diameter below 100 nm is the only such demonstration to date. Finally, an electro-less process will be described for the deposition of Ag segments that allows for the creation of gaps on the order of a few atomic monolayers of Ag.