Experimental and theoretical study of Co adsorbed at the surface of Cu: Reconstructions, charge-density waves, surface magnetism, and oxygen adsorption

Abstract

We have deposited in ultrahigh vacuum Co on top of clean, well-ordered Cu surfaces. The deposition of Co is followed by Auger spectroscopy and by low-energy-electron diffraction. At room temperatures, Co does not diffuse into the substrate: Co grows in two-dimensional islands to form the first layer and from then on the growth is layer by layer. The system Co-Cu(100) shows a $c(2\mathrm{}\times 2)$ reconstruction when the Cu surface is clean and a $p(2\mathrm{}\times 2)$ reconstruction when certain impurities are present at the interface. The system Co-Cu(111) shows no reconstruction and the Co grows forming an hcp lattice. The reconstructions of the Co-Cu(100) system are interpreted as being due to ferromagnetic-induced charge-density waves as a detailed electronic-structure calculation reveals. The magnetization and exchange splitting of one layer of Co on top of the Cu(100) surface are very similar to the Co bulk values. We have also studied the adsorption of oxygen in the Co-Cu(100) system for different Co coverages. Our results indicate that as far as oxygen is concerned, the reactivity of Co is not affected by its state of aggregation.