Moiré superlattice and two-dimensional free-electron-like states of indium triple-layer structure on Si(111)

We studied the growth of an indium triple-atomic-layer film and the two-dimensional free-electron-like electronic states on Si(111) by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES). By depositing In on the In/Si(111)- √ 7 × √ 3-rect surface below 100 K, followed by brief postannealing up to 140 K, we successfully obtained well-crystalline films exhibiting sharp superstructure LEED spots. We revealed an (11 × 11) superlattice of the triple-layer structure, while both LEED and STM showed a (5.5 × 5.5) pseudoperiodicity. This pseudoperiodicity was attributed to the moiré interference between the Si(111)-(11 × 11) lattice (a = 3.84 Å) and the In (13 × 13) hexagonal lattice, which has a lattice constant of 3.25 Å, with the ratio very close to 13/11. ARPES measurements unveiled two free-electron-like states with Fermi wave vectors of 1.32 and 1.46 Å⁻¹. We also observed replica Fermi surfaces, which are associated with the reciprocal lattice vectors of both the (1 × 1) Si(111) and the In hexagonal layers. This further confirms the hexagonal atomic arrangement of the In triple-layer structure

A flat-lying dimer as a key intermediate in NO reduction on Cu(100)

The reaction of nitric oxide (NO) on Cu(100) is studied by scanning tunneling microscopy, electron energy loss spectroscopy and density functional theory calculations. The NO molecules adsorb mainly as monomers at 64 K, and react and dissociate to yield oxygen atoms on the surface at ∼70 K. The temperature required for the dissociation is significantly low for Cu(100), compared to those for Cu(111) and Cu(110). The minimum energy pathway of the reaction is via (NO)₂ formation, which converts into a flat-lying ONNO and then dissociates into N₂O and O with a considerably low activation energy. We propose that the formation of (NO)₂ and flat-lying ONNO is the key to the exceptionally high reactivity of NO on Cu(100)