Bright sources under the projection microscope: using an insulating crystal on a conductor as electron source

• Published in: European physical journal. Applied physics Vol. 97; p. 13
• Main Authors: Lapena, Laurent, Bedrane, Djouher, Degiovanni, Alain, Salançon, Evelyne
• Format: Journal Article
• Language: English
• Published: EDP Sciences 2022
• Subjects: Condensed Matter; Materials Science; Physics
• ISSN: 1286-0042; 1286-0050
• DOI: 10.1051/epjap/2022210260

The development of bright sources is allowing technological breakthroughs, especially in the field of microscopy. This requires a very advanced control and understanding of the emission mechanisms. For bright electron sources, a projection microscope with a field emission tip provides an interference image that corresponds to a holographic recording. Image reconstruction can be performed digitally to form a “real” image of the object. However, interference images can only be obtained with a bright source that is small: often, an ultra-thin tip of tungsten whose radius of curvature is of the order of 10 nm . The contrast and ultimate resolution of this image-projecting microscope depend only on the size of the apparent source. Thus, a projection microscope can be used to characterize source brightness: for example, analyzing the interference contrast enables the size of the source to be estimated. Ultra-thin W tips are not the only way to obtain bright sources: field emission can also be achieved by applying voltages leading to a weak macroscopic electric field (< 1 V ∕μm) to insulating micron crystals deposited on conductors with a large radius of curvature (> 10 μm). Moreover, analyzing the holograms reveals the source size, and the brightness of these new emitters equals that of traditional field emission sources.