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O: Oberflächenphysik

O 3: Adsorption I

O 3.4: Vortrag

Montag, 27. März 2006, 12:00–12:15, TRE Phys

Buckled iodine layers on Pt(100): evidence of a charge density wave? — •Björn Braunschweig and Winfried Daum — Institut für Physik und Physikalische Technologien, TU Clausthal, Leibnizstrasse 4, D-38678 Clausthal-Zellerfeld

The atomic structure of well-defined iodine-covered Pt(100) surfaces was examined by scanning tunnelling microscopy(STM) in air and electrolyte. At high iodine coverage the well-known (√2× 5√2)R45^∘-I adlattice on an unreconstructed Pt(100) substrate is observed. The adlayer consists of iodine rows which predominantly run along the [010] direction and form a characteristic double-row structure. Our STM images of the I-Pt(100) surface obtained in air show that the surface is covered with two distinctly different (√2× 5√2)R45^∘-I phases: one phase with weak buckling of the double-rows parallel to the steps along the [010] direction, and a second phase of strongly buckled iodine double-rows perpendicular to the steps. The buckling of both domains strongly depends on the tunneling resistance and is reversible. No buckling is observed in a 0.1M HClO₄ electrolyte for a wide range of tunneling conditions, in accordance with previous work. We suggest that the iodine adsorbate induces a periodic lattice distortion (Peierls distortion) of the substrate yielding a charge density wave. The distortion of the charge density may be lifted or enhanced by the strong electric field of the electric double layer of the Pt/electrolyte interface and by the tip-induced field at the Pt/air interface, respectively.