Directly addressable sub-3 nm gold nanogaps fabricated by Nanoskiving using self-assembled monolayers as templates

This paper describes the fabrication of electrically addressable, high-aspect-ratio (>10000:1) nanowires of gold with square cross sections of 100 nm on each side that are separated by gaps of 1.7-2.2 nm which were defined using self-assembled monolayers (SAMs) as templates. We fabricated these nanowires and nanogaps without a clean room or any photo- or electron-beam lithographic processes by mechanically sectioning sandwich structures of gold separated by a SAM using an ultramicrotome. This process is a form of edge lithography known as Nanoskiving. These wires can be manually positioned by transporting them on drops of water and are directly electrically addressable; no further lithography is required to connect them to an electrometer. Once a block has been prepared for Nanoskiving (which takes less than one day), hundreds of thousands of nanogaps can be generated, on demand, at a rate of about one nanogap per second. After ashing the organic components with oxygen plasma, we measured the width of a free-standing gap formed from a SAM of 16-mercaptodohexanoic acid (2.4 nm in length) of 2.6 ± 0.5 nm by transmission electron microscopy. By fitting current-voltage plots of unashed gaps containing three alkanedithiolates of differing lengths to Simmons’ approximation, we derived a value of β = 0.75 Å(-1) (0.94 n(C)(-1)) at 500 mV. This value is in excellent agreement with literature values determined by a variety of methods, demonstrating that the gap-size can be controlled at resolutions as low as 2.5 Å (i.e., two carbon atoms).