Field-Induced Resonance States at a Surface

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Abstract
Observations of the field ionization of gases near a metal surface have shown the presence of a well-defined oscillating structure in the parent-ion energy distributions. The energy separations of the peaks in the structure are of the order of several volts. The separations increase with field. Peak positions are to first order independent of temperature and surface crystal orientation. The structure is interpreted in terms of resonant states formed by the combination of the externally applied field and the surface potential. Electrons from the ionizing gas atoms are partially reflected from the surface and interfere constructively to enhance the transmission into the metal for surface-to-atom separations corresponding to maxima in the observed distributions. The energy separations of the peaks are approximately given by the eigenvalues of a one-dimensional triangular well outlined by the electric field and surface. Numerical lifetime calculations, using one-dimensional macroscopic potentials appropriate to the case of field ionization, agree semiquantitatively with experiment.