Series of CCT-STM images showing the time evolution of the formation of oxygen adsorption-induced nanostructures as a function of exposure on Cu(100) (upper row) and (bottom row) at oxygen pressure of and sample temperature of 373 K. Exposure increases to the right: 0, , , , and ( and ).
Surface concentration of oxygen as a function of exposure on Cu(100) (solid line) and (dashed line) at 373 K and of obtained by XPS. Oxygen coverages below 0.6 ML are analyzed using the intensity ratio of and XPS peaks. Inelastic electron background analysis was applied to the points that have error bars. Four distinct oxidation stages, marked as I–IV, are observed.
Morphologies of oxide and silver surface structures for selected exposures obtained by inelastic electron background analysis of the XAES and XPS signals. (a) transition on Cu(100), (b) transition on , and (c) transition on . The bottom row shows the corresponding background-subtracted signals after the exposures of and .
(a) Relative surface concentration of silver on and Cu(Ag) alloys as a function of exposure (XPS emission angle of ). The inset shows signals after the exposures of (I) and (II) . (b) ARXPS on before and after the exposure of . The two data points (solid squares) from the reference surface are also shown for comparison.
CCT-STM images of Ag islands surrounded by phase after exposure of at 373 K on . (a) , . One ordered oval-shaped Ag island decorated by disordered Ag aggregates. The Ag island is elongated in the direction rotated with respect to the  direction. The image is drift corrected. (b) , . Three disordered Ag aggregates. Both images are Fourier filtered to emphasize the atomic resolution on reconstructed area. Line profiles (bottom row) are taken along the white lines.
CCT-STM images of surface oxidation-induced nanostructures on after exposure of at 373 K. (a) , . The missing rows of the reconstructions are imaged as dark depressed stripes that are more pronounced in the  direction as a consequence of asymmetric tip apex. The bright oval- and rectangle-shaped structures correspond to the Ag and islands, respectively. (b) , . reconstruction on terrace. (c) point spectra on Ag ( 1) and ( 2) islands [points marked in (a) and (d)] with a fixed tip-sample separation (, , ). [(d) and (e)] Line scans from (a) and (b), respectively.
(a) Surface concentration of oxygen up to saturation coverage as a function of exposure on Cu(100) (solid line) and (dashed line) at and . CCT-STM images of surface after exposure of (b) 100 L and (c) 550 L .
A schematic of the various stages in the surface oxidation on . (a) Initial stage prior to the oxidations. Low pressure regime, : (b) small oval-shaped Ag islands nucleate. The Ag islands are alloyed in the Cu substrate and elongated in the direction (rotated from the direction). (c) The missing-row reconstruction (O/Cu) nucleates. Ag island mean size increases and density decreases. (d) The oxygen uptake saturates when the areas between the Ag islands are fully reconstructed by adsorbed oxygen. High pressure regime, : (e) rapid nucleation and growth of the phase on terraces in addition to low surface density of the islands. Ag is displaced forming disordered aggregates and ordered oval-shaped Ag islands. The Ag islands are elongated in directions that are rotated or from the direction. The Ag structures are protruded above the Cu substrate surface, indicating that the Ag is mainly unalloyed to the Cu. (f) The areas grow and Ag aggregates gradually disappear. (g) The islands continue to grow. Finally, the top layer of the surface is covered only by structure (on terraces or islands), and subsurface oxide is formed. The triangles at the sides of the figures point to the original interface between the Cu(100) substrate and Ag overlayer.
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