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Organopalladium species ({Pd}) immobilized on an Sterminated GaAs substrate (S/GaAs) effectively catalyzes C-C bond formation in the Mizoroki-Heck reaction with cycle durability. However, the immobilizing mechanism of {Pd} is unknown. In this study, we deposited Pd(OCOCH3)2 on S/GaAs in two different methods, namely dry-physical vapor-deposition and wetchemical deposition, and compared the catalytic activities in the Mizoroki-Heck reaction. Also, S-termination and {Pd}-immobilization on GaAs grains were performed by the wet-chemical method to monitor the change in the surface chemical structure during the preparation process with diffuse reflectance Fourier transform infrared spectroscopy (FT-IR). FT-IR measurements implied that the immobilization of catalytic active {Pd} was related to the OH groups on the S-terminated surface. {Pd}-S/GaAs prepared dryphysically showed poor catalytic activity, because {Pd} was not immobilized under absence of OH groups.

Ag/AgCl reaction at the Ag bilayer, which was underpotentially prepared on a Au(111) surface, was investigated using electrochemical quartz crystal microbalance (EQCM), scanning tunneling microscopy (STM), surface X-ray scattering (SXS), and electrochemical techniques. When the potential was scanned positively from -200 mV, the Cl^[-] ion was adsorbed on the Au(111) electrode surface around 0 mV, and then the phase transition of the adsorbed Cl^[-] ion layer from random orientation to (√3 x √3) structure took place at around +130 mV. The Ag bilayer and Cl^[-] ions were oxidatively reacted to form the AgCl monolayer with (√13 x √13)R13.9° structure around +200 mV, accompanied with the formation of AgCl monocrystalline clusters on the AgCl monolayer surface. The structure of the AgCl monolayer on the Au(111) surface was changed from (√13 x √13)R13.9° structure to (4 x 4) structure around +500 mV. When the potential was scanned back negatively, the AgCl monolayer was electrochemically reduced, and a Ag monolayer, not a bilayer, was formed on the Au(111) surface. In the subsequent potential cycles, the structural change between the Ag monolayer and the AgCl monolayer was reversibly observed. All oxidative structural changes were much slower than the reductive ones.

Ag/AgCl reaction at the Ag bilayer, which was underpotentially prepared on a Au(111) surface, was investigated using electrochemical quartz crystal microbalance (EQCM), scanning tunneling microscopy (STM), surface X-ray scattering (SXS), and electrochemical techniques. When the potential was scanned positively from -200 mV, the Cl^[-] ion was adsorbed on the Au(111) electrode surface around 0 mV, and then the phase transition of the adsorbed Cl^[-] ion layer from random orientation to (√3 x √3) structure took place at around +130 mV. The Ag bilayer and Cl^[-] ions were oxidatively reacted to form the AgCl monolayer with (√13 x √13)R13.9° structure around +200 mV, accompanied with the formation of AgCl monocrystalline clusters on the AgCl monolayer surface. The structure of the AgCl monolayer on the Au(111) surface was changed from (√13 x √13)R13.9° structure to (4 x 4) structure around +500 mV. When the potential was scanned back negatively, the AgCl monolayer was electrochemically reduced, and a Ag monolayer, not a bilayer, was formed on the Au(111) surface. In the subsequent potential cycles, the structural change between the Ag monolayer and the AgCl monolayer was reversibly observed. All oxidative structural changes were much slower than the reductive ones.

Organopalladium species ({Pd}) immobilized on an Sterminated GaAs substrate (S/GaAs) effectively catalyzes C-C bond formation in the Mizoroki-Heck reaction with cycle durability. However, the immobilizing mechanism of {Pd} is unknown. In this study, we deposited Pd(OCOCH3)2 on S/GaAs in two different methods, namely dry-physical vapor-deposition and wetchemical deposition, and compared the catalytic activities in the Mizoroki-Heck reaction. Also, S-termination and {Pd}-immobilization on GaAs grains were performed by the wet-chemical method to monitor the change in the surface chemical structure during the preparation process with diffuse reflectance Fourier transform infrared spectroscopy (FT-IR). FT-IR measurements implied that the immobilization of catalytic active {Pd} was related to the OH groups on the S-terminated surface. {Pd}-S/GaAs prepared dryphysically showed poor catalytic activity, because {Pd} was not immobilized under absence of OH groups., journal article

Potential-dependent surface structures of Au(111) and Au(100) single-crystal electrodes in a 50 mM H2SO4 solution were investigated at an atomic level using in situ surface X-ray scattering (SXS) techniques. It was confirmed that both the Au(111) and Au(100) surfaces were reconstructed with an attached submonolayer of an oxygen species, most probably water, at 0 V (vs Ag/AgCl). Results at +0.95 V supported a previously suggested model for both the Au(111) and the Au(100) electrodes that, based on infrared and scanning tunneling microscopy measurements, the surfaces were a (1 x 1) structure with the coadsorbed sulfate anion and hydronium cation (H3O+). At +1.05 V, where a small amount of an anodic current flowed, adsorption of a monolayer of oxygen species was observed on both surfaces. When the single-crystal gold electrodes were electrochemically oxidized at +1.40 V, the expansion of the gold surface by about one monolayer of Au atoms was observed, suggesting the penetration of oxygen into the surface gold layers (i.e., the formation of two layers of surface oxide). When the surface oxide was reduced at +0.65 V, the surface structure returned back to the structure observed at +0.95 V before the oxide formation (i.e., a (1 x 1) structure with coadsorbed sulfate anion and H3O+). When the potential was reduced to 0 V, the surfaces were reconstructed again but with slightly more random structures than those before the potential cycle.

The structure of a Te layer formed on a Au(111) substrate by underpotential deposition (UPD) in an electrolytic solution has been studied using in situ surface X-ray diffraction technique. The measurements were carried out for a series of samples which were kept at UPD potential for 4 to 59 h. The results revealed that the Te UPD layer is unstable. The top layer is analyzed to consist of the UPD Te atoms and Au atoms which diffuse from the Au(111) substrate. Also, the Te UPD layer does not have the structure with periodicity reported in previous works, such as (√3 x √3)R30° after ample time elapses. Stripping voltammetry for the Te UPD layer shows that the interaction between Te and Au increases with time, supporting the finding that the top layer is a mixture of Te and Au.