Showing papers by "Nathan S. Lewis published in 1988"

Preparation of STM tips for in‐situ characterization of electrode surfaces

Abstract: SUMMARY The total current between the tip and the sample in a scanning tunnelling microscopy study of a solid/liquid interface can be dominated by Faradaic charge transfer currents. In such a situation, feedback control of the tunnelling gap, and imaging, is precluded. In this contribution we describe the preparation of glass and polymer coated STM tips that possess < 100 A2 of exposed metal. These tips effectively discriminate against Faradaic current and enable STM imaging in the presence of reversible electroactive solution species at appreciable tip/sample biases.

Cyclic voltammetry at semiconductor photoelectrodes. 1. Ideal surface-attached redox couples with ideal semiconductor behavior

Abstract: Working curves for the cyclic voltammetric behavior of semiconductor electrodes have been generated by consideration of a model electrode circuit. The circuit consists of an ideal photodiode in series with a metal electrode. The electroactive material is considered to be an ideally behaving, surface-attached redox couple. The solution for the diode/electrode current-voltage characteristic has been solved numerically. Simulations have been performed under varying levels of illumination and for different values of the diode barrier height, the voltage scan rate, and the amount of electroactive material. Chopped scans have also been simulated, where the forward scan is in the light and the reverse scan is in the dark. Emphasis has been placed on modeling cyclic voltammetric data under common experimental conditions, in order to provide a basis for comparison with experiments in the literature.

Design of a scanning tunneling microscope for electrochemical applications

Abstract: A design for a scanning tunneling microscope that is well suited for electrochemical investigations is presented. The construction of the microscope ensures that only the tunneling tip and the sample participate in electrochemical reactions. The design also allows rapid replacement of the tip or sample, and enables facile introduction of auxiliary electrodes for use in electrochemical experiments. The microscope utilizes stepper motor driven approach mechanics in order to achieve fully remote operation and to allow reproducible coarse control of tip/sample spacings for electrochemical experiments. Highly ordered pyrolytic graphite images at atomic resolution in air and aqueous solutions can be obtained with this microscope.

Studies of polycrystalline n-GaAs junctions: effects of metal ion chemisorption on the photoelectrochemical properties of n-GaAs/KOH-Se-/2-, n-GaAs/CH3CN-ferrocene+/0, and n-GaAs/Au interfaces

Abstract: Current-voltage and spectral response properties were determined for polycrystalline n-GaAs photoanodes in contact with aqueous KOH-Se/sup -2/-/ and nonaqueous CH/sub 3/CN-ferrocene/sup +/0/-LiClO/sub 4/ electrolytes. The n-GaAs/KOH-Se/sup -/2-/ system initially exhibited poor junction behavior, but chemisorption of Ru/sup III/, Rh/sup III/, Ir/sup III/, Co/sup III/, or Os/sup III/ ions onto the GaAs photoanode was found to yield improved I-V properties. The trend in I-V improvement correlated with improved electrocatalysis of Se/sup 2/minus// oxidation at p-GaAs, N/sup +/-GaAs, and In/sub 2/O/sub 3/ electrode surfaces. The n-GaAs/CH/sub 3/CH system displayed excellent junction behavior and did not respond to metal chemisorption treatments. These results are consistent with the metal-ion-induced improvements being predominantly due to electrocatalytic effects.