Potential barrier of mica-metal contact

To study the relationship between the composition of the dielectric surface and the potential barrier, photocurrent spectra were measured for cleared mica (muscovite) which could be expected theoretically not to have any free chemical bonds at its surface. Barrier heights and densities of surface states were examined for specimens whose surfaces were irradiated by a neutral Ar beam to remove contamination and adsorbed gas or to modify their composition. It was found that the barrier height of a mica-metal contact was not altered by a short period of irradiation with the Ar beam or by exposure to the air after irradiation. A long period of irradiation (40 min) resulted in damage to the mica surface, and the density of surface states increased up to about 3 times (1.2×10¹⁴ states cm^-2 eV ^-1) that of the untreated specimen. It was found by ESCA (electron spectroscopy for chemical analysis) that potassium and sodium atoms were sputtered by the long period of irradiation, causing imperfections or disordering in the surface structure of the mica. The surface states created by the irradiation are believed to be dependent on the free bonds that formed as a result of the above imperfections