Temperature measurement of microcrystals heated by electron bombardment: W tips from 2800K to 3650K

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Abstract
For controlled heating of metal microcrystals up to the melting point, the end of the field emitter tips are bombarded by an electron beam (8 keV, 400 mu A, 200 mu m beam diameter). To measure local temperatures on small areas down to 2 mu m diameter a special one-wavelength micropyrometer was built. Using an optical microscope, an image of the glowing tip was projected on to a screen outside the vacuum chamber. The screen has a movable hole behind which a one-wavelength filter and a photomultiplier are placed to measure local radiant intensities. The relative temperatures are obtained from Wien's law, and are absolutely calibrated by a thermocouple spot-welded on the emitter shank. Local relative temperatures and temperature gradients for a tungsten emitter are measured in the range between 2800K and 3650K, with an error and a stability better than 10K. For absolute temperatures the error is 50K when no evaporation occurs.