Characterization of Platinum Electrode Surfaces by Electrochemical Surface Forces Measurement

The surface forces between platinum, Pt, electrodes and those between the Pt electrode and mica in aqueous HClO₄ were measured at various potentials (<i>E</i>) applied to the electrodes using an electrochemical surface forces apparatus (EC-SFA). This apparatus uses the twin-path surface forces apparatus, recently developed for opaque samples. The influence of the proton adsorption on the surface interactions was studied. The Pt electrodes were prepared by the template-stripping procedure using glass templates. The electrode surfaces were smooth (RMS roughness: 0.26 nm for a 5 μm × 5 μm area) and polycrystalline based on the atomic force microscopy and cyclic voltammetry results, respectively. When the applied potential <i>E</i> was decreased from 0.5 to 0.2 V (vs Ag/AgCl), the electric double layer (EDL) repulsion between the Pt electrodes decreased. The absolute values of the surface potentials, |ψ₀|, calculated using the EDL theory were 58 and 43 mV at <i>E</i> = 0.5 and 0.2 V, respectively. The EDL force at <i>E</i> = 0.2 V was the local minimum, suggesting that the potential of the zero charge (PZC) of the Pt electrode was around 0.2 V in the 1 mM HClO₄ solution. With the further decreasing potential <i>E</i> from 0.2 to −0.2 V, the EDL repulsion remained similar in amplitude, took another minimum, |ψ₀| = 40 mV, at <i>E</i> = −0.1 V, and started to increase again at <i>E</i> = −0.1 V. These behaviors could be caused by proton adsorption on the Pt surface (Pt^δ−···H⁺), the electrochemical hydrogen adsorption (Pt–H), and the subsequent hydrogen evolution (H₂↑). The possibility for characterizing the hydrogen evolution processes on the Pt electrodes based on the surface forces measurement is discussed for the first time

Quasi-One-Step Six-Electron Electrochemical Reduction of an Octahedral Hexanuclear Molybdenum(II) Cluster

We report for the first time quasi-one-step six-electron electrochemical reduction of a new hexanuclear molybdenum­(II) bromide cluster having terminal 3,5-dinitrobenzoate ligands: [Mo₆Br₈(DNBA)₆]^2–. The electrochemical responses of the cluster were studied based on cyclic (CV), differential pulse, and normal pulse voltammetries, together with the analytical simulations of the CV and spectroelectrochemistry. CV simulations have revealed that the electrochemical reaction of the cluster proceeds in an EEEEEE scheme, and the potential differences between the two adjacent reduction steps are in the range of 15–30 mV. These potential differences indicate quite smooth and quasi-one-step six-electron reduction of the cluster

Emission Tuning of Heteroleptic Arylborane–Ruthenium(II) Complexes by Ancillary Ligands: Observation of Strickler–Berg-Type Relation

Novel heteroleptic arylborane–ruthenium­(II) complexes having a series of ancillary ligands L′ ([Ru­(B₂bpy)­L′₂]²⁺) in CH₃CN showed low-energy/intense metal-to-ligand charge transfer (MLCT)-type absorption and intense/long-lived emission compared to the reference complexes. The spectroscopic and photophysical properties of [Ru­(B₂bpy)­L′₂]²⁺ were shown to be manipulated synthetically by the electron-donating ability of the ancillary ligand(s). The intense and long-lived emission observed for [Ru­(B₂bpy)­L′₂]²⁺ in CH₃CN at 298 K is responsible for the accelerated radiative and decelerated nonradiative decay processes, which are controllable through the electronic structures of the ancillary ligand(s). On the basis of the present systematic study, furthermore, we succeeded in demonstrating the Strickler–Berg-type relation between the molar absorption coefficients of the MLCT bands and the radiative rate constants of the complexes

Simultaneous Formation and Spatial Patterning of ZnO on ITO Surfaces by Local Laser-Induced Generation of Microbubbles in Aqueous Solutions of [Zn(NH₃)₄]²⁺

We demonstrate the simultaneous formation and spatial patterning of ZnO nanocrystals on an indium–tin oxide (ITO) surface upon local heating using a laser (1064 nm) and subsequent formation of microbubbles. Laser irradiation of an ITO surface in aqueous [Zn­(NH₃)₄]²⁺ solution (1.0 × 10^–2 M at pH 12.0) under an optical microscope produced ZnO nanocrystals, the presence of which was confirmed by X-ray diffraction analysis and Raman microspectroscopy. Scanning the focused laser beam over the ITO surface generated a spatial ZnO pattern (height: ∼60 nm, width: ∼1 μm) in the absence of a template or mask. The Marangoni convection generated in the vicinity of the microbubbles resulted in a rapid concentration/accumulation of [Zn­(NH₃)₄]²⁺ around the microbubbles, which led to the formation of ZnO at the solid–bubble–solution three-phase contact line around the bubbles and thus afforded ZnO nanocrystals on the ITO surface upon local heating with a laser

Glycine Crystallization in Solution by CW Laser-Induced Microbubble on Gold Thin Film Surface

We have developed a novel laser-induced crystallization method utilizing local heat-induced bubble/water interface. Continuous laser beam of 1064 nm is focused on a gold nanoparticles thin film surface covered with glycine supersaturated aqueous solution. Light absorption of the film due to localized plasmon resonance caused local heating at the focal position and produced a single thermal vapor microbubble, which generated thermal gradient followed by convection flow around the bubble and eventually induced glycine crystallization and growth. The crystallization mechanism is discussed by considering gathering and accumulating molecules around the bubble/water interface assisted by convection flow and temperature jump