C. Deisl

Halogen-induced corrosion of platinum.

The interaction of Cl with Pt(110) was studied in UHV by scanning tunneling microscopy, low-energy electron diffraction, temperature-programmed desorption, and DFT calculations. Up to half a monolayer (ML) of Cl forms an adsorbate structure. Compression to higher local coverages leads to erosion of Pt atoms from the top layer and formation of PtCl(4) pentamers. Annealing results in healing of the Pt defects and formation of a long-range-ordered PtCl(4)/Cl/Pt(110) adlayer that is remarkably similar to the adlayer structure found after deposition of [PtCl(4)](2-) from an electrolyte onto Au(100). Coadsorption of 0.5 ML of Cl with CO initiates PtCl(4) formation, but no volatile compounds are formed under these conditions. In similar experiments with Br, the original Pt surface is left intact, even if Br is compressed to local coverages of 0.75 ML, in agreement with the expected lower corrosion activity of Br.

Structure tuning by Fermi-surface shifts in low-dimensional systems

In low-dimensional systems, electron-electron correlation as well as electron-phonon coupling is enhanced. This tends to link the geometry to the Fermi-surface position, for instance via formation of charge-density waves. The quasi-one-dimensional c(2×2)-Br/Pt(110) surface system is used here to explore this effect. NO adsorption gives rise to a considerable Fermi-surface shift and causes the system to go through a succession of complex phases comprising commensurate, long-range-ordered structures, as well as periodic and chaotic soliton lattices. The structural evolution is in qualitative agreement with the predictions of the discrete Frenkel-Kontorova model.

Molecular adsorption on the quasi-one-dimensional c(2 × 2)-Br/Pt(110) surface

NO and CO adsorption on a self-assembled layer of quasi-one-dimensional (1D) halogen-bridged Pt chains is investigated. An anomalous, long-range adsorbate–adsorbate interaction is indicated by temperature programmed desorption and scanning tunneling microscopy. The adsorbates trigger a transition into a charge density wave (CDW) groundstate. The coverage dependent concentration of solitons partly accounts for the observed variation of the desorption energy.