SI-ALKALI METAL INTERFACE STUDY BY X-RAY STANDING WAVE TECHNIQUE IN ULTRAHIGH-VACUUM WITH SYNCHROTRON RADIATION

A structural study of a Si-alkali metal interface has been carried out by means of the X-ray standing wave (XSW) technique. The measurements have been performed in ultrahigh vacuum with synchrotron radiation. LEED and Auger spectroscopy have also been used as surface characterization tools. Cs atoms have been deposited on a Si(111)7 x 7 reconstructed surface held at room temperature. Coverages ranging from about 0.05 to about 0.4 ML have been studied. 7 x 7 LEED patterns slightly modified with respect to that of the Si reconstructed surface were obtained, the modifications being more evident for the highest coverage. The X-ray standing wave measurements were carried out using the (111) diffracting planes. Similar results have been obtained for all the coverages. They point out that Cs atoms must occupy more than one site and that they cannot be positioned on top of the adatoms.