ROLE OF VIBRONIC INTERACTIONS IN QUASI-2D SYSTEM - PSEUDO-JAHN-TELLEREFFECT ON SURFACE AND ON INTERFACE

We propose a model taking vibronic interaction into account for the qu asi-2D system which consists of interacting electronic states of both the surface dangling bonds and the adsorbed atoms. The essential role in the interaction of this kind can be played by the vibronic part due to a pseudo-Jahn-Teller effect. Consideration of vibronic interaction leads to the appearance of new surface vibronic states and to unusual properties of the quasi-2D electronic subsystem in the close vicinity of the surface and interface. The cooperative pseudo-Jahn-Teller effe ct acts here in the framework of percolation scenario. From the point of view of the model, we explain the suppression of metal-like propert ies of the Si(111)7 x 7 surface caused by Ba adsorption.