Epitaxial Growth of RuO₂(100) on Ru(1010):  Surface Structure and Other Properties

We determined the surface structure of RuO 2 (100) formed on Ru(101̄0) by employing the techniques of low-energy electron diffraction (LEED) and density functional theory (DFT) calculations. The RuO 2 (100) film grows lattice-matched with its [010] direction along the [0001] direction of Ru(101̄0) (4.5% compressively strained), while it grows incommensurately with the [001] direction of RuO 2 (100) along the [1̄21̄0] direction of Ru(101̄0). The RuO 2 (100) surface is terminated by bridging O atoms, which are attached to the coordinatively unsaturated Ru (cus-Ru) atoms with a bond length of 2.01 Å. The other Ru−O bond lengths are in the range of 1.90−2.05 Å, typical for bulk RuO 2 . Due to the presence of cus-Ru atoms on RuO 2 (100), CO molecules adsorb quite strongly as evidenced by a desorption state at 300−400 K. The activity of the RuO 2 (100) surface for the CO oxidation reaction is similar to that of RuO 2 (110). The surface energies of RuO 2 (110) and RuO 2 (100) are 71 and 87 meV/Å 2, respectively.