The formation and characterisation of micro- and nanostructured surfaces through combinations of top-down and bottom-up fabrication methodologies

Abstract

The research presented in this thesis explores work on micro and nanoscale patterning and structuring, towards 3D patterning of surfaces. The undertaking of such work is key to the advancement in areas such as microelectronics, nanotechnology and device and sensor fabrication. Chapter 1 (Nanotechnology: Introduction to Small Technology) presents an introduction to the background of the thesis research and information on the concepts and techniques used throughout the thesis. The first experimental chapter, Chapter 2 (Laying the Molecular Foundations) explores the patterning of monomolecular self-assembled-monolayers (instead of conventional polymeric resists) with electron beam lithography to form chemical patterns on gold surfaces. The chemical patterns on the surface then direct the self-assembly of gold nanoparticles with complementary chemistry. Chapter 3 (From the Foundations Upwards) utilises the self-assembling ability of the nanoparticles from the previous chapter and explores how they can be incorporated into a multilayer structure on a surface. This multilayer assembly is achieved by the layer-by-layer deposition methodology in conjunction with a charged polyelectrolyte. The layer-by-layer deposition process is followed with three different characterization techniques and the results compared. The chapter also examines other routes to directly patterning the layer-by-layer assembled structures such as photolithography and microfluidics. Chapter 4 (Printing and Scratching) explores the versatility of the nanoparticles and polyelectrolytes (from Chapter 3) towards alternative deposition techniques; in this case, a standard consumer-grade inkjet printer is used to deposit the materials to surfaces. Futhermore, an Atomic Force Microscope is then used to define patterns and structures in the printed structures. Chapter 5 (Corrugations and Collagen) introduces the recovery and transfer of micro/nanostructured gold surfaces from gold-coated CD-R disks to silicon substrates as a route for producing cheap, structured gold substrates. The previous chapters examine methods to control the location of materials on surfaces, the corrugated gold substrates fabricated for this chapter are used to demonstrate that the actual orientation of materials themselves can also be controlled. In this case, the naturally occurring, fibrous and bio-technologically interesting material collagen is oriented on a surface by simply rotating the surface in a suspension of collagen in a novel device fabricated for these experiments. The final experimental chapter, Chapter 6 (DNA based Foundations and Walls) uses surface chemical modification to immobilise synthetic hairpin oligonucleotides carrying a photolabile group, on a silicon surface. Once immobilised on a surface, the oligonucleotides are patterned using photolithography to leave exposed single strands, which, through the specific assembly properties of DNA, are used to direct the spatially specific assembly of complementary strands carrying molecular dye or nanoparticle labels. This hybrid system shows that self-assembly processes found in nature can be combined with chemical modification of surfaces and oligonucleotide strands to also form 3D dimensional structured surfaces