Abstract
A study of enhanced field emission (EFE) from broad area polycrystalline niobium cathodes is presented. The experiment is centered around a purpose built UHV field emission scanning microscope that consists of a computer controlled sample micromanipulator and a rotatable high voltage anode holder for broad area and microtip anodes. We use a field emission (FE) scanning technique by moving the cathode in a raster pattern while the FE current is detected and recorded with a specially constructed high voltage regulator. Once a site is located it is examined in situ with a scanning electron microscope. In a preparation chamber the samples can be heat treated up to 2000°C without removal from UHV. We find that a heat treatment (HT) of the niobium samples at T = 1000°C results in a low number of FE sites which can be further decreased after firing at T = 1200°C. No emission between 30 and 90 MV /m at < nA occurs after a HT at T = 1400°C. Typical examples of localized FE sites and high resolution SEM images are presented.
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