Abstract
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 10nm. 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 (< 1V∕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.
Highlights
Using a bright source is essential in microscopy applications
We will see in this article that a projection microscope is perfectly suited to characterizing sources and in particular their size, whatever the emitted particles [4, 5]
The projection microscope is a derivative of the field ion or field electron microscope, where only the emission profile and the structure of the emitter itself are observed
Summary
The wave-like nature of particles is best observed using a bright source. It is only after the invention of the laser that the holography described and demonstrated by D. Brightness corresponds to the emitted intensity at a given energy I(E) under an angle of cone ⌦ coming from a zone s on the source itself: B. A thermo-electronic electron source such as a heated filament, very intense, cannot match the brightness of field emission sources such as an ultra-thin tungsten tip: the emission area is much too large. We will see in this article that a projection microscope is perfectly suited to characterizing sources and in particular their size, whatever the emitted particles [4, 5]. An electron source consisting of an insulating crystal deposited on a carbon fiber, as described in several articles [6, 7, 8, 9, 10], was characterized with these methods and will be described here
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