THEORY OF DIELECTRIC SCREENING OF AN IMPURITY AT SURFACE OF AN ELECTRON GAS

A dielectric formalism is developed which is applicable to an electron gas with a surface. This formalism is then used to obtain a theory of static surface impurity screening. Expressions for the screening charge around the surface impurity are obtained and then numerically evaluated. It is found that there is considerably more structure to the surface impurity Friedel oscillations than to those of a volume impurity. Furthermore, the screened surface impurity seems to be of longer range than a volume impurity. It is shown that this impurity theory is a reasonable model for ionic adsorption on metal surfaces. For ion-metal separations of the order of a Fermi wavelength, the classical image force arising from supposed surface polarization charge has no validity. One must consider volume polarization processes in which the unscreened impurity field penetrates into the imperfect conductor. Then it is shown why the image-force models have given reasonable numerical results in spite of the irrelevance of the model. © 1969.