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UBC Theses and Dissertations

Interaction of electron beams with carbon nanotubes Alam, Md. Kawsar


Carbon nanotubes have great potential for nanoscale devices. Previous studies have shown the prospects of carbon nanotubes as stable, low-voltage electron emitters for vacuum electronic applications. Yet, their electron emission mechanisms are far from being fully understood. For example, it is not completely clear how nanotubes interact with an external electron beam and generate secondary electrons. In addition to its fundamental scientific importance, understanding these mechanisms and properties will facilitate the engineering of nanotube-based devices for applications such as vacuum transistors, electron multipliers, X-ray devices for medical imaging, etc. This thesis presents an experimental and theoretical investigation into the interaction of electron beams with carbon nanotubes. First-principles simulations are carried out to qualitatively analyze the possible direct interaction mechanisms of electron beams with nanotubes. An experimental study of electron yield (total, backscattered and secondary electron yields) from individual nanotubes and collections of nanotubes is reported. The experiments reveal low secondary electron yield from individual nanotubes. A different backscattered electron emission behaviour compared to that in bulk materials is observed in nanotube forests due to unusually high electron penetration range in them. A semi-empirical Monte Carlo model for the interaction of electron beams with collections of nanotubes is presented. Physically-based empirical parameters are derived from the experimental data. The secondary electron yield from individual nanotubes is first investigated in the light of the commonly used energy loss model for solids. Finally, the problems of using the traditional models for individual nanotubes are identified and an approach to modeling secondary and backscattered electron emission from such nanostructures is presented. The experiments and analysis presented in this thesis provide a platform for investigating backscattered and secondary electron emission also from nanostructures other than nanotubes.

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