Photoemission study of the U/Si (111) interface

The electronic and geometric structures of thin uranium overlayers deposite d on a clean Si(111)-(7 x 7) surface have been studied by X-ray photoelectr on spectroscopy (XPS) and low-energy electron diffraction (LEED). Three dif ferent stages of interaction between the deposited uranium and the silicon substrate are found, depending on the uranium coverage. A transition from l ocalized to delocalized U 5f states is observed as the uranium thickness in creases in the room-temperature depositions. Annealing of the substrate at 700 degrees C results in clear spots in the LEED observations, suggesting t he possible formation of ordered uranium silicide phases at the interface. (C) 2000 Elsevier Science B.V. All rights reserved.