Reinvestigation of the surface reconstruction of Cu(001)-(2x2)p4g-Pd

Three recent articles [T.D. Pope, M. Vos, H.T. Tang, K. Griffiths, I.V. Mitchell, P.R. Norton, W. Liu, Y.S. Li, I. Stensgaard, E. Laegsgaard, F. Besenbacher, Surf. Sci. 337 (1995) 79; J. Yao, Y.G. Shen, D.J. O'Connor, B.V. King, Surf. Sci. 359 (1996) 65; P.W. Murray, I. Stensgaard, E. Laegsgaard, F. Besenbacher, Surf. Sci. 365 (1996) 591] have attempted to determine the surface composition and structure of the (2 x 2)p4g phase induced by one monolayer (ML) Pd deposition at room temperature on a Cu(001) surface. In order to remove inconsistencies arising from previous studies, the 1 ML Pd/Cu(001) surface has been reinvestigated using low-energy ion scattering (LEIS), low-energy electron diffraction (LEED), three-dimensional (3D) classical scattering simulations and embedded-atom method (EAM) calculations. Using Li+ and He+ ion scattering with calibration measurements on reference samples of Cu(001) and Pd(001), the surface Pd composition of the 1 ML phase was independently determined to be 53+/-4% and 51+/-3%, respectively. The results obtained using K+ ion scattering, LEED and computer simulations are consistent with a surface structure which consists of 30% of a clock-rotated (001) Pd phase and 70% of an unreconstructed p(2 x 2) Cu-Pd phase. The stability of the (2 x 2)p4g phase has been confirmed by EAM calculations. (C) 1997 Elsevier Science B.V.