Promotores: T.H. Oosterkamp, N. de Jonge
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This thesis is about the research performed on novel field emission sources. Having a better electron source can reduce the time needed to obtain an electron microscope image and enable studying processes at a higher resolution. We chose to fabricate electron sources by means of mounting individual nanometer-sized structures, such as nanotubes and nanowires, onto sharp conductive needles. These nanostructures have interesting electrical and/or mechanical properties, which make them attractive candidates for novel field emission sources. By using a home-built nanomanipulator inside an electron microscope, we could select and mount an individual nanostructure onto a sharp needle. Because we fabricated samples with only a single emitting structure, it is possible to study its morphology before and/or after field emission experiments inside a high resolution TEM and relate it to the electron emission characteristics. We found that the emission pattern from a naturally closed carbon nanotube showed a symmetry that can be related to the symmetric positions of the carbon atoms of the hemi-spherically shaped cap. We discovered that we could “repair” damaged carbon nanotubes and succeeded in re-obtaining closed caps during field emission experiments on carbon nanotubes that were cut to length with an electron beam.