Building Materials Molecule-by-Molecule
More about the Snomipede
Miniaturisation has been a characteristic and critical feature of technological advance over the past few decades. The spectacular advances in computing power that we have seen have been the result of the ingenious development of manufacturing processes to enable the construction of ever smaller components in semiconductor chips. However, we are beginning to approach length scales where there may be fundamental limitations on the properties of silicon that will restrict the performance improvements that can be achieved. This is prompting many scientists to explore the use of carbon-based molecules to construct electronic circuits. Miniaturised organic molecular electronic devices would have light weight and flexibility, and they may offer many other advantages. Organic display technologies (LCD displays) have provided much lower rates of energy consumption, for example, and higher portability. However, there are currently no convenient ways to manufacture highly miniaturised organic circuits. Miniaturised assemblies of carbon-based molecules are not only useful in electronics. The most important carbon-based molecules are those that form the basis of life and of biological processes. Recently there has been a great deal of interest in building artificial structures that can interact with biological molecules on very small length scales. From the point of view of developing a better understanding of the world, it is possible that by studying the behaviour of molecules that regulate processes such as photosynthesis, which is the basis for life on earth, we may be able to better harness the complex mechanisms that Nature has developed. In medicine, the ability to build assemblies of molecules one-by-one would lead to enormous power to use artificial assemblies to guide the behaviour and growth of body structures. For example, synthetic templates could be used to engineer the reconnection of nerves severed in injury, or to repair skin destroyed by third degree burns. Miniaturised devices based on biological molecules might also be used to carry out very high sensitivity investigation of genetic material, helping doctors to rapidly build a picture of a patient's genetic profile and best target therapies to their needs. The key feature in all of these technologies is that progress is critically dependent upon the ability to arrange and organise molecules on very small length scales - close to the dimensions of a single protein molecule, just ten billionths of a metre. There are no established tools for doing this over any significant area. This proposal seeks to transform this situation by developing a new tool that can be used to organise molecules one-by-one over a huge range of scale, from one protein up to macroscopic distances. It will do this by adapting a new writing tool, scanning near-field photolithography (SNP). Photolithography uses light to form patterns, by passing the light through a mask which contains holes. As the holes become very small, the light begins to diffract, and ceases to form a well-defined pattern. SNP uses the near-field effect to overcome this problem. This involves using a very small hole, through which light is passed, brought very close to a solid surface. The hole can be in the end of an optical fibre. SNP can create structures 10 - 20 times smaller than is usually possible using photolithography even under the best conditions. However, the criticism might be made that despite its astonishing resolution, this approach is slow. The important feature of this project will be that an array of a large number of these near-field probes will be made, and operated simultaneously, so that many "pens" write together. This will mean that a large number of very tiny structures can be fabricated in parallel. New types of probes will be designed in which the hole is placed in the end of a tiny hollow pyramid situated at the end of a lever. The lever controls the motion of the tip, into which light is directed (or within which light is generated). This will give much greater flexibility. Large arrays of levers will be built and operated together. The result will be a tool for making molecular structures with both enormous precision and great speed. This may make it possible for the first time to think about manufacturing large objects, and large numbers of objects, that consist of molecular nanostructures (ie built molecule-by-molecule) to address all of the applications described above and many more besides.
S. Sun and G. J. Leggett, "Matching the resolution of Electron Beam Lithography using Scanning Near-field Photolithography", Nano Lett.4 (2004) 1381-1384
S. Sun and G. J. Leggett, "Generation of Nanostructures by Scanning Near-field Photolithogrophy of Self-Assembled Monolayers and Wet Chemical Etching", Nano Letters 2 (2002) 1223-1227.
S. Sun, K.S. L. Chong and G. J. Leggett, "Scanning Near-field Optical Lithography of Self-assembled Monolayers", J. Am. Chem. Soc. 124 (2002) 2414-2415.
G. J. Leggett, "Biological Nanostructures: Platforms for Analytical Chemistry at the sub-Zeptomolar Level", invited article, The Analyst, 130 (2005) 159-264.
Material Copyright © 2008 Graham Leggett