Voltammetric studies on the oxidation of ferrocene in acetone + 0.1 M Bu4NPF6 have been carried out at platinum and mercury microelectrodes over a wide temperature range which included the freezing point of mercury. The system is close to ideal at all electrode types. The dependence of the calculated diffusion coefficient on temperature obeys the Stokes-Einstein equation and enables a hydrodynamic radius of 3.2 Å to be calculated for ferrocene which may be compared with a crystallographic radius of 2.7 Å. This system, where the electrode is not intimately involved in the electrode process, provides reference data against which processes which do involve the mercury electrode may be assessed. It is known that the mercury electrode is involved in the electrochemical behavior of the of whether the mercury electrode is in the liquid or solid state. Thus, there is no abrupt change in the rate or nature of the electron transfer Hg(Et2dtp)2/[Et2dtp]−/[Hg(Et2dtp)3]− system (Et2dtp = S2P(OEt)2 O,O-diethyldithiophosphate). Under conditions where surface based effects are minimized, data are consistent with the reversible reaction scheme 2Hg° + 6[Et2dtp]− ⇌ 2[Hg(Et2dtp)3]− + 4e− (process 1) and 2[Hg(Et2dtp)3]− + Hg° ⇌ 3Hg(Et2dtp)2 + 2e− (process 2); overall Hg° + 2[Et2dtp]− ⇌ Hg(Et2dtp)2 + 2e− irrespective step at a mercury electrode at the freezing point of mercury in both non-interacting (ferrocene) and interacting systems. Data for the mercury dithiophosphate system were obtained at a conventional hanging mercury drop, a solid mercury drop, a dropping mercury electrode and at liquid and solid mercury coated platinum disk microelectrodes. Except for the dropping mercury electrode experiments, all data showed signs of a surface reaction, especially at low temperatures. Observation of the mercury microelectrodes by optical microscopy during voltammetric scans revealed that the non-ideality was caused by the formation of an insoluble product which passivated the electrode surface. Optical microscopy also confirmed that mercury microelectrodes formed on platinum disk substrates cover the entire surface and that a hemispherical model is appropriate for theoretical calculations. Digital simulations of the cyclic voltammograms obtained at a hanging mercury drop electrode are in moderate agreement with the proposed reaction scheme, with deviations from ideality being attributed to the presence of surface based reactions. Electrospray mass spectrometry of solutions containing equimolar concentrations of Hg(Et2dtp)2 and [Et2dtp]− confirmed the existence of [Hg(Et2dtp)3]− in solution at ambient temperature.

In-situ observation of spatially inhomogeneous glucose oxidase activity has been achieved using photoelectrochemical microscopy (PEM). The current variation caused by the temperature increase under the focused light spot was used to form the image. A biosensor electrode comprising glucose oxidase secured at a platinized carbon paper showed active regions 10–30 μm in diameter. The origin of these hot spots and factors influencing image contrast are considered.

We describe a novel technique fully compatible with silicon microelectronic technology for the synthesis of Ge nanocrystals. The approach followed involves UV-assisted low temperature dry oxidation of a strained Si0.8Ge0.2 layer. Initially, oxidation results in the selective formation of SiO2 under which accumulates a Ge-rich SiGe layer. Further irradiation and oxidation of this structure result in the incorporation of Ge nanocrystalline regions from 2 to 8 nm in diameter into the growing SiO2 layer. These Ge nanoparticles exhibit visible photoluminescence in the 550–800 nm range. The temperature of only 550 °C employed in our process is significantly less than the 800–850 °C levels necessary up till now for the reduction of SiGe oxides to form Ge nanocrystals. Regardless of size, the nanoparticles, being directly formed from the underlying substrate, always exhibit the diamond crystalline structure, as shown by high resolution transmission electron microscopy and Raman spectroscopy.

The photoelectrochemical behaviour of epitaxial samples of n-Ga1−x,AlxAs (0 ⩽ x ⩽ 0.31) has been investigated by several methods, including intensity-modulated photocurrent spectroscopy, under conditions where photoetching takes place. The surface potential distribution was found to be non-ideal; it depends on the level of illumination and on the pretreatment of the electrode. The potential dependence of the surface recombination rate has been used to derive the band bending in the semiconductor as a function of electrode potential. Extensive Fermi level pinning is observed close to flat band, and this has been related to the formation of adlayers by reduction of soluble arsenic(III) and gallium(III) species. High rates of surface recombination were observed after the electrochemical passivation of GaAlAs by a 5 nm oxide layer, indicating that the presence of an anodic oxide layer greatly increases the surface state density and reduces the band bending.

The oxidati of mer-W(CO)3(η1-dpm)(η2-dpm) (dpm=Ph2PCH2PPh2) under conventional voltammetric conditions is known to involve an overall two-electron oxidation process to give [W(CO)3(η2-dpm)2]2+ with no experimental evidence for postulated intermediates. Under steady-state or near steady-state conditions at platinum microelectrodes with radii greater than 25 μm the oxidation of mer-W(CO)3(η1-dpm)(η2-dpm) is observed to still proceed via a single two-electron process whereas at a 3 μm radius microelectrode two one-electron processes are observed. This dependence upon electrode size is consistent with a mechanism involving single electron transfer steps and internal chelating reactions. The first electron transfer step is mer-W(CO)3(η1-dpm)(η2-dpm)⇌mer-[W(CO)3(η1-dpm)(η2-dpm)]+ +e− (reaction a). Following this initial oxidation there are two competing pathways to further oxidation: mer-[W(CO)3(η1-dpm)(η2-dpm)]+→mer-[W(CO)3(η2-dpm)2]+ (b) followed by mer-[W(CO)3(η2-dpm)2]+→[W(CO)3(η2-dpm)2]2+ +e− (c) or mer-[W(CO)3(η1-dpm)(η2-dpm)]+⇌mer-[W(CO)3(η1-dpm)(η2-dpm)]2+ +e− (d) followed by mer-[W(CO)3(η1-dpm)(η2-dpm)]2+ → [W(CO)3(η2-dpm)2]2+ (e). Under conventional voltammetric conditions reaction sequence (a), (b), (c) gives rise to a single apparent two-electron process. Two one-electron processes are observed when the internal chelation step is outrun by the short time scale achieved under steady-state conditions or by very fast transient voltammetry at platinum microelectrodes. The fast scan rate technique provides direct evidence for the fleeting existence of the seventeen-electron mer-[W(CO)3(η1-dpm)(η2-dpm)]+ and the nineteen-electron [W(CO)3(η2-dpm)2]+ species. The complementary nature of the steady-state and transient regimes of voltammetry at microelectrodes is therefore demonstrated by the present study. The mechanism of the electrochemical oxidation of mer-W(CO)3(η1-dpm)(η2-dpm) at gold and carbon electrodes appears to be the same as at platinum. In contrast, at both conventional and microsized mercury electrodes weak interaction of the pendent phosphorus atom of mer-W(CO)3(η1-dpm)(η2-dpm) with mercury effectively slows down the rate of chelation following oxidation. Thus voltammetry at a mercury electrode allows the two one-electron oxidation steps for mer-W(CO)3(η1-dpm)(η2-dpm) to be observed under conventional voltammetric conditions. It is concluded therefore, that in the presence of a pendent phosphorus group, mercury electrode interaction provides another convenient method of studying unstable intermediates via what may be referred to as a surface trapping technique.

Interest in electrochemically synthesised conducting polymers has increased enormously in recent years, and polyaniline (PANI) has received particular attention because it appears to be more stable than many other systems. One of the main objectives of the current research effort in this area is to obtain information about the structural and electronic properties of PANI by using in-situ techniques such as ESR [l-3], IR [4-61 and UV/visible [3,7] spectroscopy to supplement conventional electrochemical measurements. A key element of this approach should be the correlation between the electrical and optical response of polymer films under a variety of experimental conditions, but the application of spectroscopic methods to the PAN1 system has been restricted largely to steady-state or potentiodynamic conditions, with the main emphasis being placed on the relationship between spectroscopic properties and the potential or the state of charge of the film. The purpose of the present communication is to show that the application of UV/visible spectroscopy can be extended to consider the periodic response. It will be shown that comparison of the potential modulated transmittance or absorbance with the corresponding periodic electrical response (i.e. the impedance 2 or admittance p) of the film leads to resolution of the controversy concerning the role of so-called “charging current” contribution [8,9] to the voltammetric response of PANI. Further details of this study are presented elsewhere [lo].