VARIABLE-TAKEOFF-ANGLE X-RAY-PHOTOELECTRON-SPECTROSCOPY EVIDENCE FOR AN ELECTRONICALLY MODIFIED SURFACE IN A-PU

Photoemission spectra of an alpha-Pu surface taken at 15-degrees and 85-degrees off normal show pronounced changes attributable to an expanded delta-like surface layer. Using estimates for the inelastic mean free path of the photoelectrons and the thickness of the surface layer, we obtain spectra of the bulk and surface. The significance of this phenomenon is discussed within the context of the more familiar surface reconstructions that occur in the heavy transition metals. In contrast to the latter, the behavior of Pu is determined by the energy gain associated with 5f spin and orbital polarization rather than the increased cohesion that accompanies surface contraction.