IN-SITU SCANNING-TUNNELING-MICROSCOPY OBSERVATION OF A PORPHYRIN ADLAYER ON AN IODINE-MODIFIED PT(100) ELECTRODE

The adlayer structure of -tetrakis(N-methylpyridinium-4-yl)-21H,23H-po rhine tetrakis(p-toluenesulfonate) (TMPyP) at an iodine-modified Pt(10 0)(I-Pt(100)) surface was investigated in HClO4 solution by in situ sc anning tunneling microscopy (STM). The structure of the iodine adlayer was (root 2 x 5 root 2)R45 degrees. TMPyP molecules were adsorbed wit h flat-lying orientation at the I-Pt(100)) surface and aligned along t he [100] direction that was parallel to the row of iodine atoms. The v an der Waals type interaction between TMPyP and the iodine adlayer see ms to be relatively weak because of the characteristic structure of io dine, which allows TMPyP to diffuse on the iodine adlayer on Pt(100) i n specific directions to form a highly ordered array. The observed str ucture of TMPyP was very different from that found previously on I-Au( 111), I-Ag(111), and I-Pt(111). A square lattice was found to form on I-Pt(100) with a side-by-side configuration. It is concluded that the structure of the iodine adlayer plays an important role in the formati on of the ordered structure.