An approach to sol-gel film formation is described, involving electrochem. control of pH near a conductive surface, in which methyltrimethoxysilane (MeTMOS) is deposited onto indium tin oxide (ITO) and Au surfaces. The method is based on a 2-step sol-gel prepn. procedure in which MeTMOS is first pre-hydrolyzed and then polycondensed. A const. neg. potential is applied to the electrode surface, increasing the concn. of hydroxyl ions, which act as a catalyst in the condensation process. This results in greater control over the deposition process and thus over film properties. [on SciFinder(R)]

The feedback mode of the scanning electrochem. microscope (SECM) was used for studying a surface-catalyzed electron-transfer reaction. As a model system the authors examd. the redn. of protons by reduced N,N'-dimethyl-4,4'-bipyridinium, methylviologen radical cation, MV+•, catalyzed by a platinum surface. The exptl. configuration comprises a biased amalgamated Au ultramicroelectrode (UME) that approaches an unbiased Pt UME substrate of the same radius. MV+• that is electrochem. generated at the amalgamated UME is oxidized at the Pt surface as a result of reducing protons. This novel configuration permits the simultaneous measurement of the catalytic current and the mixed potential (open-circuit potential) attained at the Pt surface. The results are interpreted by an electrochem. model which was previously suggested; however, the authors' approach makes it possible to measure, for the 1st time, the current-potential relation predicted by the theory. The authors' results indicate that methylviologen behaves reversibly under all the exptl. conditions, and that the rate const. of hydrogen evolution, that is calcd., is in perfect agreement with previous reports. The significant advantages of the authors' approach are discussed as well as its applicability for studying other electrochem. systems. [on SciFinder(R)]

The alternating direction implicit finite difference method (ADIFDM) was used to simulate the steady-state as well as the transient (chronoamperometric) behavior of sphere-cap microelectrodes (SCMs). The necessary steps to implement the ADIFDM for solving the rather complex geometry involved are described. The results for the steady-state behavior are in excellent agreement with a previously suggested anal. soln. making the ADIFDM an excellent tool to develop a comprehensive theory for SCMs. [on SciFinder(R)]

Electrochem. polymn. of 2',5'-bis(1-methylpyrrol-2-yl)thiophene (NSN) was carried out by scanning electrochem. microscopy, using Ru(bpy)33+ as oxidant for the polymn. process and for the ultramicroelectrode surface-distance probe. While this led to deposition of flat layers of polymer on a PMMA substrate, use of the weak oxidant IrCl62- gave sets of thin needles. Micrographs of the various patterns are shown (with resolns. of ≈ 15 μm) and the mechanism of polymn. is discussed. [on SciFinder(R)]

The formation of self-assembled monolayers (SAMs) of ω-mercaptoalkanoic acids on a mercury surface under potential control was studied. Cyclic voltammetry and a.c. voltammetry were used for studying the different phases and transitions that the homologous series of these thiols form and undergo. The thiols are either physisorbed or chemisorbed depending on the applied potential and the transition between these two states occurs through a faradaic process. Also, the chemisorption of the thiols results in multilayer deposition when the thiol monolayer does not block electron transfer. Finally, the implications of this study to the formation and manipulation of SAMs of ω-functionalized alkanethiols on Hg are discussed. [on SciFinder(R)]