Scanning electrochemical microscopy ͑SECM͒ has been used to study electron transfer at Al and Al alloy surfaces, employing the mediators hydroquinone, hydroquinone sulfonate, anthraquinone-2,6-disulfonate, and anthraquinone-2-sulfonate. Both oxidation and reduction processes are examined. SECM, in combination with scanning electron microscopy/energy-dispersive X-ray analysis, reveals that Cu-containing secondary phase particles exhibit the highest electron transfer activity for both oxidation and reduction reactions on the AA 2024-T3 surface. Although electron transfer is fastest at the intermetallic particles, it also occurs on the alloy matrix under acidic conditions. The charge carried by the mediator appears to have little influence on the electron transfer process despite the fact that the matrix oxide surface is positively charged below pH 7.

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The electrochemical activity of Au electrodes held at constant potential for anodic detection of carbohydrates in alkaline media eventually decays to zero. This loss of response is a consequence of the accumulation of adsorbed oxidation products on the electrode surface. Although it is well-known that these "poisons" can be removed by oxidative desorption simultaneously with formation of surface oxide, we have discovered that electrodes fouled during the detection of glucose yield a cathodic peak at -0.77 V vs SCE resulting from reductive desorption of these species. Incorporation of the reductive desorption process into wave forms for pulsed electrochemical detection (PED) permits a significant decrease in the time periods traditionally allowed for the oxidative and reductive reactivation of the electrode with a resulting increase in wave form frequency. A 6.7-Hz wave form using E(red) = -1.00 V (t(red) = 10 ms), E(oxd) = +0.60 V (t(oxd) = 10 ms), and E(det) = +0.10 V (t(del) = 50 ms, t(int) = 50 ms) is applied for detection of glucose in a LC-PED system and is demonstrated to yield a sub-picomole detection limit with a linear dynamic range extending over three decades.

A variety of surface-sensitive techniques are used to elucidate the reaction pathways, as well as adsorbate structures, associated with thermal activation of CF3J following adsorption on Ru(001) at 100 K. XPS shows that the C-I bond of CF3I dissociates below 200 K to form CF3(ad) and I(ad); the subsequent reactions of CF2 are best viewed as being regulated by the availability of surface sites. CF3(ad) dissociates to CF2(ad) below 200 K. Further CF3 dissociation, some of which is activated by H(ad), occurs between 200 and 400 K until all available sites are filled. Desorption of the remaining CF3, peaking at 705 K, once again opens surface sites for decomposition. This is followed by recombination of the products to form CF3(g). No evidence for CF(ad) is ever observed. Hydrogen coadsorption studies explain interesting features associated with fluorine evolution. HREELS and ESDIAD results indicate that CF3 adopts a tilted configuration on Ru(001).

We have investigated the thermally-induced and electron-impact-induced chemistry of CF 3 I on Ni(100) following adsorption at 100 K. The data support a model for the thermally-induced chemistry, in which CF 3 I dissociates to CF 3 and I, either upon adsorption or at slightly-elevated temperatures. Most CF 3 decomposes to adsorbed C and F. Above 75% saturation of the first layer, the availability of surface sites for decomposition decreases to a level where some adsorbed CF 3 remains intact and desorbs as such. Bombardment of multilayer CF 3 I by lowenergy electrons introduces new chemistry. Electron-induced decomposition (EID) of the parent molecule occurs through both C-I and C-F bond scission, with a measured cross section of 1.5 X 10 -16 cm 2 (upper limit). Thermally-induced desorption from the electron-bombarded surface indicates a number of EID fragment reactions, most notably carbon -carbon bond formation, as evidenced by C 2 F 3 I+, C 2 F 4 +, C 2 F 5 +, C 3 F 5 +, and C 4 F 7 +. To our knowledge, this is the first report of C-C bond formation in small fluorocarbons adsorbed on metal surfaces. Abstract: We have investigated the thermally-induced and electron-impact-induced chemistry of CF31 on Ni( 100) following adsorption at 100 K. The data support a model for the thermally-induced chemistry, in which CF31 dissociates to CF3 and I, either upon adsorption or at slightly-elevated temperatures. Most CF3 decomposes to adsorbed C and F. Above 75% saturation of the first layer, the availability of surface sites for decomposition decreases to a level where some adsorbed CF3 remains intact and desorbs as such. Bombardment of multilayer CF31 by lowenergy electrons introduces new chemistry. Electron-induced decomposition (ED) of the parent molecule occurs through both C-I and C-F bond scission, with a measured cross section of 1.5 x cm2 (upper limit). Thermallyinduced desorption from the electron-bombarded surface indicates a number of EID fragment reactions, most notably carbon-carbon bond formation, as evidenced by C2F31+, C2F4+, C2F5+, C3F5+, and C&+. To our knowledge, this is the first report of C-C bond formation in small fluorocarbons adsorbed on metal surfaces.