Thermionic Emission from Barium-coated Ultra-pure Nickel in the Emission Microscope†

After a comprehensive theory of thermionic electron emission from barium-coated alloyed nickel was established in some other place, the present investigations, using the large-screen emission microscope, served to confirm it by covering also the phenomena on polycrystalline ultra-pure nickel. Barium droplet formation was found in abundance, but of short life only. Inadequate ion densities in the contact layer are responsible for woak retaining forces, so that early evaporation leads to barium monolayer conditions without the existence of emission reversal in any instant. Hence the conclusion is drawn that the work function of ultra-pure nickel planes generally must be smaller than in the presence of abundant impurities. Poor contrast between crystal faces prevails, although very large crystal shapes emerge after rocrystallization Contrast anomaly is present but to a lesser degree than with alloyed nickel. Brief exposure to oxygen in the hot state results in a uniform and sharp increase of emissivity overruling anisotropic crystal properties Magnetic domain patterns reproduced by thermionic electrons high above the Curie point of nickel are caused by the remanent ability in the surface layer to polarize because of initial work-hardening and the directionality of the inducing magnetic lens field, particularly at the nickel surface where thermally disoriented internal lattice spins cannot cancel them fully..Removal of work hardening by excessive heating permanently cancels these fringe patterns Barium migration and evaporation mechanisms were visualized on the 21 in. screen as a dynamic streaming of barium droplets breaking loose from pools, progressively shrinking and sweeping toward hotter regions of the nickel surface.