January lecture: Low-Dimensional Molecular Systems - Prof. Graham Leggett (University of Sheffield)
The annual series of Institute of Physics lectures resumes in November 2013 and continues until March 2014. All of the events are held in the Welcome Rooms of the Royal Society of Edinburgh and the talk begins at 19.30. All attendees are invited to arrive early for a sherry / soft drinks reception from 19.00. On-street parking is available free after 18.30 on site.
Low-Dimensional Molecular Systems - Prof. Graham Leggett (University of Sheffield)
Abstract: Many biological systems exhibit reduced dimensionality. The cellular membrane is a two-dimensional milieu in which isolated proteins, or small groups of interacting proteins, control complex processes. For example, a transmembrane proton gradient drives ATPsynthase to convert ADP to ATP. Our aim is the construction of biological nanostructures to test hypotheses about energy transfer in biological systems. This requires the development of sophisticated tools for organization of molecules on nanometre length scales. The integration of top-down (lithographic) and bottom-up (synthetic chemical) methodologies remains a major goal in nanoscience. At larger length scales, light-directed chemical synthesis, first reported two decades ago, provides a model for this integration, by combining the spatial selectivity of photolithography with the synthetic utility of photochemistry. We have sought to realise a similar integration at the nanoscale, by employing near-field optical probes to initiate selective chemical transformations in regions a few tens of nm in size. A combination of near-field exposure and an ultra-thin resist yields exceptional performance: in self-assembled monolayers, an ultimate resolution of 9 nm (ca. λ/30) has been achieved. A wide range of methodologies, based on monolayers of thiols, silanes and phosphonic acids, and thin films of nanoparticles and polymers, have been developed for use on metal and oxide surfaces, enabling the fabrication of metal nanowires, nanostructured polymers and nanopatterned oligonucleotides and proteins. Strategies based upon the use of nitrophenyl-based photocleavable protecting groups have enabled the introduction of synthetic chemical methodology into nanofabrication. Using near-field techniques, proteins may be immobilized site-specifically, with full retention of biological function, in nanoscopic regions. Nanoscale control of chemistry over macroscopic areas remains an important challenge. Recently parallel near-field lithography approaches have demonstrated the capacity to pattern macroscopic areas at high resolution, yielding feature sizes of ca. 100 nm over an area four orders of magnitude larger; they have also demonstrated the ability to function under fluid, yielding feature sizes of ca. 70 nm in photoresist under water and suggesting exciting possibilities for surface chemistry at the nanoscale. Finally, the monolayer patterning methods we have developed are by no means restricted to near-field lithography; all that is required is a suitable means of confining the optical excitation. For example, SAM photochemistry has been combined with interferometric exposure to facilitate the fabrication of periodic nanostructures (metal oxides and gold nanostructures with strong plasmon bands) over macroscopic areas in fast, simple, inexpensive processes, underlining the versatility of photochemistry as a nanofabrication tool.