Abstract
Brightness of an electron source is key for the high spatial resolution of electron microscopy and analysis. A small source size is essential for high brightness, and it has been achieved by using small crystal facets; however, the emission current is reduced when the facet area is decreased. To achieve a small source size while maintaining a large emission current, we conceived of the novel idea of a facetless electron source with a curved emission surface. Computational simulations of electron trajectories revealed that the virtual source, which is the spot at which back-projected trajectories are focused, of a facetless source was smaller than that of the conventional source with a facet and that the brightness of the facetless source was approximately four times larger. To achieve electron emission from a curved surface, we fabricated a facetless source by coating amorphous carbon on a metallic electron source. Electron emission from the coated surface showed a homogeneous pattern, which is clear evidence for emission from the curved surface of the facetless source.
Highlights
Electron microscopes are widely used to visualize nano-meter structures of conductive metals and semiconductors and organic polymers and bio-related materials
It shows the relationship between the apex radii and the simulated virtual source diameters, and the blue and red data represent the results for the facetless source and Field emission (FE) source with a facet, respectively
We describe the results of electron emission experiments to demonstrate the fabrication of the curved emission surface of the facetless source
Summary
Electron microscopes are widely used to visualize nano-meter structures of conductive metals and semiconductors and organic polymers and bio-related materials. For decreasing the source size further than with tungsten FE sources, recently, nano-crystals of conductive materials have been developed, and carbon nanotube, LaB6 nanowire, and graphene-coated sources have been reported in the past few years. These sources can produce a bright electron beam; the small emission area causes a small emission current, and this is unfavorable for constructing large current electron optics. We calculated virtual sources from simulated electron trajectories from the conventional FE source with a facet and a facetless source, whose shape was curved and whose work function was homogeneous. By comparing the emission pattern before and after the coating, we evaluated whether the curved emission surface and homogeneous work function were achieved with the treatment
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