Structure of Clean and Oxidized PdCu(100) Surfaces at the Atomic Scale
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In this thesis, clean and oxidized Pd(57)Cu(43)(100) single crystal surfaces were studied by LEED, STM and XPS in UHV conditions. The clean sample annealed to 300 degrees C has been found to either consist of ordered domains of Pd or Cu atoms forming a c(2 × 2) structure, or by a more disordered alloy c(2 × 2) structure of p4g symmetry. Small areas of (1 × 1) structure as well as screw dislocations and island- like formations are present on this surface. Annealing the clean sample to 600 degrees C causes Cu segregation to the surface as well as a shift towards higher binding energy of Pd 3d(5/2) core levels, and an almost defect- free surface with p(2 × 2) structure is seen. Oxidation at 300 degrees C of the surface annealed to 300 degrees C shows that a c(2 × 2) covers the whole surface for all oxygen dosages at 68L or above, and XPS spectra do not vary with oxygen dosage, hence the c(2 × 2) is inert in this case. For dosages of 1350L or above, oxide islands and a large number of defects could appear, depending on the preparation history of the sample. Oxidation at 300 degrees C and 600 degrees C of the Cu rich surface annealed to 600 degrees C reveals up to seven structures, which are p(2 × 2), c(2 × 2), (4 × 4)- like, hexagonal, maze- like, (2root(2) ×root(2))R45degrees missing row type and one more structure that could not be characterized. There is evidence that copper oxide phases are formed for the Cu rich surfaces annealed to 600 degrees C, but no bulk oxide was formed in any experiments. A detailed understanding of clean and oxidized Pd(57)Cu(43)(100) has been obtained at the atomic scale.