SURFACE-IONIZATION OF GADOLINIUM, TERBIUM AND DYSPROSIUM ON THE TUNGSTEN(110) SURFACE

A study of the surface ionization of gadolinium, terbium, and dysprosium (Gd, Tb, and Dy) is described and the results compared with the predictions of the Saha-Langmuir equation. A tentative measurement of holmium is also included. The experimental index parameter, E, which should be equal to the difference between the first ionization potential of the element and the apparent work function of the surface, was found to exceed the predicted value by the following amounts: Gd, 0.66 ± 0.14 eV; Tb, 0.27 ± 0.13 eV; and Dy, 0.24 ± 0.12 eV. The absolute ionization efficiencies were estimated by comparison of our gadolinium results with those reported by Dresser and Hudson. The preexponential coefficients are found to exceed the theoretically predicted values by an order of magnitude. Surface ionization efficiency of these rare earths is larger than predicted by the Saha-Langmuir equation by factors ranging from 5 to 25 at 2500 K. The (110) face of a tungsten single crystal was used as the ionizing surface, and its work function was determined to be 5.46 ± 0.11 eV in an auxiliary study of the emission of tungsten ions. © 1979.