| The potential-dependent structure of the Bi underpotential deposition (UPD) adlayer on Au(100) in 0.1 M HClO4 was examined by in-situ surface x-ray scattering (SXS) measurements, revealing a complex sequence of different phases. Bi initially adsorbs to form a disordered adlayer. With decreasing potential three ordered adlayer phases are formed: a (3x3) structure consisting of square Bi tetramers, a c(✓2x3✓2)R45° structure, where the Bi adatoms are arranged in zigzag chains, and a quasi-hexagonal close-packed c(px2) adlayer, which is uniaxially incommensurate and compresses by ≈ 2% over a 30 mV stability range. According to detailed surface crystallographic studies the local structural arrangement in the first two phases resembles that of bulk Bi. Furthermore, x-ray scattering voltammetry indicates kinetically hindered phase transitions between the ordered phases and allows to confirm that only the c(✓2x3✓2)R45° structure is active towards electrocatalytic H2O2 reduction.;Magnesium Octakis(methylthio)tetraazaporphyrin (Mg(OMTTAP)), and Octakis(methylthio)porphyrazine (H2(OMTTAP)) were chosen as the model molecules to study the self-assembly of thin films on Au(111) substrate. In-situ scanning tunneling microscopy (STM) was used to study the submolecular structures of Mg(OMTTAP) and H2(OMTTAP) on the Au(111) surface in 0.1 M HC1O4. Both Mg(OMTTAP) and H2(OMTTAP) molecular films are made of donut shape features that can be assigned to single molecules adsorbed on Au(111). These features are arranged on the surface in a hexagonal close packed structure with a unit cell parameter equal to 14 A. The density functional theory (DFT) was used to investigate the electronic structures of these molecules.;Ag electrodeposited on the Mg(OMTTAP) modified Au(111) was also investigated by in-situ STM and Cyclic Voltammetry (CV). The new layer displays a clear (6x6) Ag adlayer on top of the Au and it appears as if the molecules have been removed from the surface. However, in part of the film the Mg(OMTTAP) adlayer is still visible. It is still unclear if the silver is on top or below the molecules.;The structure of Bi bulk deposited on Au(100) has been carried out in 0.1 M HClO4 using in-situ SXS. The orientations of very thin Bi(012) film on the Au(100) substrate is found to be similar to a Bi(012) thick film. Both films orient 0°, 0°+/-15°, 0°+/-28°, 90°, 90°+/-15°, 90°+/-28° to the Au[100] direction, respectively. However, there are two more peaks at 45°, 90°+45° for the thin film. This can be assigned to randomly oriented domains in the early stages of bulk deposition. |
