ELECTRIC DIPOLES ON CLEAN MICA SURFACES

A study of mica surfaces produced by cleavage in ultra-high-vacuum showed that the surface is clean (both synthetic as well as natural mica) and that the atomic structure below the cleaved layer remains essentially undisturbed. Half a monolayer of potassium ions resides on the surface and produces strong surface electric dipoles. The electric fields created during cleavage affect these dipoles to varying degrees depending on the pressure and kinds of gases present during cleavage. Below about 10 Torr, domains of parallel dipoles form and these cause the diffraction spots to shift or streak in the direction of the dipole axis. Cleavage at pressures below 10 Torr strains the surface and produces enough surface electron traps so that the incident electron beam can charge the surface to over 1000 V. This strain can be relaxed by electron bombardment at over 1000eV or heating to 100°C, leaving the surface permanently discharged. No indications of gas chemisorption have been found. Large amounts of occluded gases, notably hydrogen and nitrogen, evolve from natural mica during cleavage but the synthetic mica did not evolve any detectable gases. © 1969.