Dedicated to Professor Dr. Erich Hückel on his 70th birthday
Version of Record online: 14 MAR 2006
Copyright © 1966 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Annalen der Physik
Volume 473, Issue 1-2, pages 53–70, 1966
How to Cite
Kaminsky, M. (1966), Mean Residence Times of Alkali Ions on Polycrystalline Wolfram Surfaces as Studied with a Pulsed-Molecular-Beam Mass Spectrometer. Ann. Phys., 473: 53–70. doi: 10.1002/andp.19664730107
Work performed under the auspices of the U. S. Atomic Energy Commission. Certain parts of the work summarized in this paper were presented earlier at the International Conference on Mas Spectrometry, Paris, September 14–18, 1964 and the 25th Annual Conference on Physical Electronics, MIT, March 1965.
- Issue online: 14 MAR 2006
- Version of Record online: 14 MAR 2006
- Manuscript Received: 12 NOV 1965
The mean residence time τi of alkali ions on both atomically clean and strongly gas-covered surfaces of polycrystalline wolfram has been studied with a recently developed technique of combining modulated atomic and/or molecular beams from vapors of alkali metals and alkali halides with phase-sensitive mass-spectrometic detection. The experimental arrangement allows the direct determination of the mean residence time τi of an ion on a metal surface under extremely clean surface conditions and at very small incident beam intensities (109− 1012 particles cm.−2 sec.−1) to avoid an influence of surface coverage by the beam material itself. In addition, it allows mass-spectrometric determination of the effect of the composition of the incident beam on τi. The dependence of τi on the surface temperature T is given by Frenkel's equation τi = τ exp (Ei/kT), where Ei is the ion desorption energy. With alkali chloride sources, the values tabulated below were determined over ranges within the temperature region 1100 °K < T < 1700 °K. The atomic and molecular composition of the beam significantly affected τi, e.g., for an incident beam of neutral sodium atoms, τ = (0.85 ± 0.05) × 10−13 sec. Ei = 2.69 ± 0.03 eV for Na+ on clean W.
The present experiments are being extended to determine the mean residence time τα of neutral alkali atoms on wolfram surfaces. Then with the aid of the more precisely determined values of Ei and Eα and with additional knowledge of the effective work function of the surface and of the ionization energy of the incident particle, it will be possible to decide such an important question as whether or not the surface states of adsorbed atoms differ from those for ions.