The surface structure of BaO on Pt(111): (2×2)-reconstructed BaO(111)

NSR Catalysis studied using Scanning Tunnelling Microscopy

“…Figure 1a and 2 shows two images obtained after the adsorption of Ba, followed by oxidation under different conditions. In Figure 1a we believe we have formed the BaO(111) surface [9], whereas in figure 1b we propose that BaO 2 is formed [10]. The reason for these assignments is that the structure in 1a) is thermally stable, and the atomic spacing corresponds with that expected for the BaO(111) surface with a (2 · 2) reconstruction.…”

“…The reason for these assignments is that the structure in 1a) is thermally stable, and the atomic spacing corresponds with that expected for the BaO(111) surface with a (2 · 2) reconstruction. Note that the (111) BaO-(1 · 1) surface is polar and unstable and is therefore not expected to form, whereas theory predicts a (2 · 2) reconstruction for this surface, producing a near-neutral layer with low surface energy, figure 1b [9]. Other structures are identified under varying oxygen treatment conditions, which may be further reconstructions, all of them based on forming sub-structures which exhibit facets of the very low energy (100) surface [9].…”

“…Note that the (111) BaO-(1 · 1) surface is polar and unstable and is therefore not expected to form, whereas theory predicts a (2 · 2) reconstruction for this surface, producing a near-neutral layer with low surface energy, figure 1b [9]. Other structures are identified under varying oxygen treatment conditions, which may be further reconstructions, all of them based on forming sub-structures which exhibit facets of the very low energy (100) surface [9]. The structure in Figure 2 is believed to be peroxide due to the fact that it is only metastable at 600K, and because we have identified peroxide formation by parallel measurements using XPS (figure 3), where both states of oxygen can be identified.…”

“…b) Model of the (2 · 2) reconstruction of the BaO(111) surface; black ions are oxygen, whereas the dark grey are surface Ba, and light grey sub-surface Ba ions[9].…”

Work function reduction by BaO: Growth of crystalline barium oxide on Ag(001) and Ag(111) surfaces

“…Oxidation (or passivation) of the substrate surface and the difficulties associated with preserving a crystalline interface have hindered efforts to grow epitaxial BaO. A few groups have shown that crystalline BaO can be grown on various substrates at temperatures as low as room temperature using molecular beam epitaxy (MBE) [18][19][20][21], or laser-molecular beam epitaxy [22].…”