(3x1)-Br/Pt(110) structure and the charge-density-wave-assisted c(2x2) to (3x1) phase transition -: art. no. 195405

After our recent report on the formation of a (3x1) charge-density-wave phase in the quasi-one-dimensional system Br/Pt(110) we present a detailed investigation of the c(2x2)-->(3x1) transition in the Br/Pt(110) adsorption system. This includes the atomic structure of the (3x1) phase as determined by quantitative low-energy electron diffraction (LEED) and density functional theory calculations. While in the parent c(2x2) phase with coverage Theta=1/2 ML the Br atoms occupy every second short-bridge site on the unreconstructed (1x1)-Pt(110) surface, the adatoms in the (3x1) phase at coverage Theta=2/3 ML reside in every third short-bridge and long-bridge sites. Charge densities and vertical relaxations of the Pt atoms forming the short- and long-bridge sites are different, thus yielding a modulation of both, the charge and the position of the outermost Pt atoms with a period of three nearest-neighbor spacings. For 1/2 ML<Thetaless than or equal to0.58 ML LEED intensity and scanning tunneling microscope (STM) measurements reveal the nucleation of (3x1) islands surrounded by areas with a local coverage of 1/2 ML. Within the latter areas the STM measurements indicate dynamical fluctuations of the Br positions at room temperature. In the time average every short-bridge site is sampled by the mobile Br atoms, but in the neighborhood of (3x1) islands every third short-bridge site seems to be preferentially occupied.