LOCAL-STRUCTURE AND DYNAMICS OF A SEGREGATED C(2X2) SULFUR LAYER ON PD(001) STUDIED BY SCANNING TUNNELING MICROSCOPY

We report a scanning-tunneling-microscopy study of a S overlayer on Pd(001) obtained by diffusion of S atoms from the bulk to the surface. Atomically resolved images display the c (2 X 2) symmetry of the saturation coverage. A large variety of defects such as steps, vacancies, and antiphase domain boundaries were imaged. The high density of domain boundaries reduces the effective coverage to only 0.4 monolayer and stabilizes this nonideal overlayer. A model of the growth mechanism is proposed. Changes of the atomic structure on a time scale of a few minutes were observed and are discussed.