Abstract
The field emission microscope has been used to investigate the surface of an alloy of a few percent zirconium in molybdenum. The field emission patterns indicate that a high-temperature flash (2000°K) reduces the surface concentration of zirconium to zero. Subsequent heat treatment at 1000°K brings Zr to the emitting surface where it adsorbs preferentially in small clusters on the lattice steps of the {100} planes. These clusters are easily observed because of their high electron emission. Their emission characteristics reveal them to be smooth layers of low work function (2.94±0.01 ev) rather than protruding crystallites. When the bulk concentration of zirconium in the alloy is increased from 1% to 5% the emission patterns change markedly but there is little effect on the adsorption characteristics of the surface. Surface migration, desorption, and bulk diffusion of zirconium were found to proceed rapidly at temperatures above 1200°K, 1500°K, and 2000°K, respectively. Measurements of activation energies for surface migration and desorption gave 2.7±0.3 ev and 4.15±0.15 ev, respectively.
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