| dc.description.abstract | Existing nanofabrication methods typically rely on techniques such as optical lithography, electron-beam lithography or focused ion beam milling that enable high fidelity patterning but suffer from various limitations in terms of high-cost, feature size, low throughput, poor scalability to large areas or restrictive choices of substrate and electrode materials. Achieving both nanometre precision of patterning and parallel fabrication over large length-scales is difficult to achieve using conventional nanofabrication methodologies. The main achievement of this thesis is the development of novel patterning techniques that allow both nanoscale patterning precision and wafer-scale parallel fabrication, while at the same time being compatible with conventional nanofabrication equipment and processes.
Adhesion lithography (a-lith) is a simple method for forming nanoscale gaps between dissimilar metals. In its usual form, a metal is patterned on a substrate, and conformally coated with an alkyl-functionalized self-assembled monolayer (SAM), rendering it non-adhesive to other metals; a second metal is then deposited uniformly over the full area of the substrate; finally, the parts of the second metal that are in contact with the self-assembled monolayer are stripped away using an adhesive tape or film, leaving the first and second metals side-by-side on the substrate, with a nanoscale spacing between them. In this thesis we first show an adaptation of adhesion lithography, which I call self-peeling adhesion lithography (SPAL). It is shown that, by depositing onto the second metal an adhesive film with high internal strain, it is possible to induce spontaneous delamination of the peeling layer without the need for any applied force. The modified procedure simplifies implementation and eliminates external stresses that can cause unwanted widening of the gap. At the time the work was published the resulting gap-widths of ~10 nm were the smallest that had been reported using a-lith.
To further improve the resolution and versatility of the a-lith procedure, I then developed a new form of a-lith that used multilayer adhesion modifiers formed from metal-ligated chains of self-assembled monolayers (“molecular rulers”). The new procedure – which I call size-tuneable adhesion lithography (STAL) – allows the gap-width to be tuned over the range 3 – 30 nm by adjusting the number of SAM molecules in the chain (with a resolution of a few nm, corresponding to the length of the molecules).
By combining STAL with another nanoscale patterning technique known as nanosphere lithography (NSL), it is possible to fabricate massively parallel nanogap arrays containing hundreds of millions of ring-shaped nanogaps (RSNs) of controllable diameter, width and pitch. Importantly STAL retains all the advantages of conventional a-lith – namely it involves only a few simple processing steps that can be carried out at room temperature, it uses inexpensive equipment, it can be used to fabricate nanogaps of arbitrary shape formed from dissimilar metals, and it can be applied over large areas (> 1 cm2) – while at the same-time providing control over the gap-width down to the 3 nm level. The technique has potential applications in many areas of nanoscale science and technology, and has been used here to fabricate molecular rectifiers and high performance substrates for surface-enhanced Raman spectroscopy (SERS). | en_US |
