Field Dependence of Photoelectric Emission from Molybdenum

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Abstract
Photoelectric emission from a 5‐mil single‐crystal molybdenum wire was measured at 1000°K with accelerating fields from 0.8 to 142 kv/cm and monochromatic light in the range 238 to 297 mμ. Above 3.6 kv/cm, the data are in good agreement with Fowler‐Schottky theory. Apparent threshold energies increase from 4.44 to 4.52 ev with increasing illumination energy, as is expected from emitters of nonuniform work function. Two illumination directions, separated azimuthally by 90°, give identical results. Fowler plots yield identical thresholds of 4.41 ev at room temperature and 1000°K and a Richardson‐plot determination of the thermionic emission constants yields eφ**=4.33 ev and A**=38 amp/cm2‐deg2. The multiplicity of apparent work functions measured on a single specimen, as well as the marked dissimilarity in the emission constants of molybdenum in sheet and wire form, are explained in terms of patch effect. The theory for the periodic deviation from the photoelectric Schottky effect is extended to describe emitters at elevated temperatures. No evidence for the predicted deviation appears in the experimental photoelectric Schottky data.