By Merijntje Bronsgeest
The Schottky electron emitter is a primary electron-emitting resource in today’s electron beam gear. This ebook comprehensively covers the Schottky emitter, facing its theoretical in addition to useful features. the most questions which are addressed during this ebook are: what's the Schottky electron emitter? How does it paintings? and the way do its homes impact the functionality of electron beam equipment?
The concentration is at the direct hyperlink among the working stipulations of the resource and the homes of the beam on the goal point. This coupling is made transparent through discussing the impression of the working stipulations and the geometry of the resource and gun at the emission homes of the emitting floor, the impact of Coulomb interactions at the brightness and effort unfold within the first few millimeters of the beam direction, and the impression of the working stipulations and the form of the emitter at the outcomes of the beam on the aim. the ultimate bankruptcy combines a majority of these results to illustrate that there's a trade-off to be made among brightness, power unfold, and form stability.
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Additional resources for Physics of Schottky Electron Sources: Theory and Optimum Operation
The large spread is ascribed to both different measurement techniques and different experimental conditions. With respect to the latter it is noted that the work function of a given crystallographic orientation is in itself a function of the contamination level, temperature, and possibly field strength, as these can change the arrangements at the surface. A change in temperature, for example, may change the distribution of ion cores and electrons near the surface due to thermal expansion, atomic rearrangement (roughening, reconstruction), and/or a change of Work Function Variations across the Emitter Surface coverage.
Both the Schottky emitter and the conditions are not “standard,” and it is thus not expected to be an exact representation of what happens for a normal, emitting source. The tip of the emitter that was used had been arced in a prior experiment and was reshaped by etching (in NaOH) right before the experiment. And the emitter was heated inside an SEM chamber with a pressure of the order of 1 × 10–6 mbar, which is a factor 1,000 higher than in the standard operating conditions. 17 give the changes for two different areas on the surface.
We will demonstrate this below with experimental emission patterns. An emission pattern can be seen as a distorted and blurred “shadow image” of the emitting areas of a source and can measured with a setup, as that in Fig. 3. In the general setup the emission pattern is recorded behind the extractor, where a scintillator (yttrium-aluminum-garnet [YAG] or phosphor) converts electrons into photons. Photos of such setups are given in Fig. 4. 3 VACUUM Schematic experimental setup for recording emission patterns.