Low energy electron induced processes of relevance to focused electron beam induced processing, astrobiology and related fields

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When a molecule in a solid adsorbs energy from ultra-violet light, x-rays or another type of high energy radiation, it will likely be ionised and eject an electron. Occasionally this electron will have considerable energy and can travel far in the solid, ionizing other molecules along the way. Mostly however, the electron will be of low energy and unable to travel very far or to ionise further molecules. In most models of radiation damage, such low energy electrons (LEEs) and their effects are usually ignored, but their effect can be surprisingly important. This research program concerns LEEs and the chemistry they can induce in different types of materials. When firing beams of LEEs on thin solid samples, we have often observed that an electron can be temporarily captured by a condensed molecule to form a transient negative ion (TNI) and this greatly enhances energy transfer to the molecule. Formation of a TNI can also cause the fragmentation of the molecule, when the incident electron's energy is too small for ionization and sometimes for electronic excitation. Molecular fragments created in this way may then react with neighbouring molecules producing further chemical change. For example, our work has shown that molecules as large as DNA can be broken by LEEs, a result with significant implications for how radiation is used to treat cancer. Here we propose research in two LEE application areas. In Focused Electron Beam Induced Deposition, beams of high energy electrons can be used to build nanometer scale structures by breaking volatile "precursor molecules" onto smaller, but stickier fragments. Many LEEs are generated by the high energy beams and are thought to contribute to the deposition process possibly by the formation of TNI. We intend to measure how LEEs interact with precursor molecules to help improve our understanding and control of the deposition process. In interstellar dust clouds , LEEs are also liberated by the passage radiation through the condensed gases that accumulate on grains and may thus play a role in the synthesis of the simple organic molecules, building blocks for life that have already been detected on meteorites. In our experiments, we simulate such processes in the laboratory.