After our recent report on the formation of a $(3\mathrm{}\times 1)$ charge-density-wave phase in the quasi-one-dimensional system Br/Pt(110) we present a detailed investigation of the $c(2\mathrm{}\times 2)\Rightarrow (3\mathrm{}\times 1)$ transition in the Br/Pt(110) adsorption system. This includes the atomic structure of the $(3\mathrm{}\times 1)$ phase as determined by quantitative low-energy electron diffraction (LEED) and density functional theory calculations. While in the parent $c(2\mathrm{}\times 2)$ phase with coverage $\Theta =1/2\mathrm{}\mathrm{ML}$ the Br atoms occupy every second short-bridge site on the unreconstructed $(1\mathrm{}\times 1)$-Pt(110) surface, the adatoms in the $(3\mathrm{}\times 1)$ phase at coverage $\Theta =2/3\mathrm{}\mathrm{ML}$ 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 $1/2\mathrm{ML}<\Theta <~0.58\mathrm{ML}$ LEED intensity and scanning tunneling microscope (STM) measurements reveal the nucleation of $(3\mathrm{}\times 1)$ 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 $(3\mathrm{}\times 1)$ islands every third short-bridge site seems to be preferentially occupied.

• Received 3 September 2003

DOI:https://doi.org/10.1103/PhysRevB.69.195405