Penetration Parameter for an Adsorbed Layer of Polarizable Ions

• Published in: Journal of applied physics 1966-01, Vol.37 (9), p.3471-3482
• Main Authors: MacDonald, J. Ross, Barlow, C. A.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.1708884

We present several improvements in the calculation of the penetration parameter f, which is related to ionic and electronic work functions. A regular, hexagonal array of adions which are imaged in a conducting adsorbent plane is considered. The first improvement is the treatment of discrete adion charges and their images as non-ideal, finite-length dipoles instead of ideal dipoles as in almost all earlier treatments. Next, nonzero polarizability of adions is considered, discrete induced dipole moments are calculated in a self-consistent manner, and the effect of induced-dipole images is included. When the polarizability is nonzero, previous expressions for f are inadequate even when generalized in an obvious way, and an improved method of calculating f is presented. The inclusion of polarization effects leads to significant changes in the dependence of f on surface coverage of adions. Finally, f is calculated with and without polarization contributions for the situation where redistribution of the adsorbed array upon removal of an adion affects the desorption energy. Inclusion of redistribution also leads to appreciable changes in f. Under some circumstances, either with or without redistribution contributions, it is found to be easier to desorb an adion from an array than to desorb an isolated adion. In this case, the potential at the site of a removed adion may exceed that far away from the surface. To illustrate this phenomenon, which can lead to the establishment of a potential barrier against electron emission, or to a potential well enhancing emission, we give some curves of potential vs distance from the electrode along a line perpendicular to the electrode and through a removed adion site.