Situ Surface Conductivity Measurements

Another in situ nonelectrochemical method is the measurement of the electric conductivity of thin Pt films deposited on isolated substrate, usually glass.The conductivity of such films changes in a characteristic way with potential as a result of changes in the electronic properties of the metal electrode surface induced by the electric field across the metal-electrolyte 

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Although the electronic conductivity of an interphase that is present on an electrode can be related to various optoelectronic properties that are also measurable with spectroscopic techniques, the direct measurement of surface conductivities is not a spectroelectrochemical method. It is nevertheless a surface sensitive method that provides results closely related to those of other methods discussed in this book. Data on the electrosorption of alcohols on gold electrodes [45] or the electrode potential dependent conductivity of intrinsically conducting polymers [46] have been obtained with in situ surface conductivity measurements. Figure 4.4 shows the electrical resistance of a poly(2-propylaniline) film measured in situ under experimental conditions suppressing any influence of solution phase conduction. The influence of... 

The existence of various hydrogen species on platinum, palladium, and iridium surfaces has also been verified by in situ modulated specular and internal reflection spectroscopy and surface conductance measurements... 

On and D represent lattice oxygen ions and surface anion vacancies, respectively, and ( ) designates a free adsorption site. The CO2 produced can remain adsorbed at the surface or be readsorbed later as a stable carbonate at the active surface, thus effecting the self-poisoning that is invariably observed. The direct participation of lattice oxygen in the oxidation reaction has been substantiated in this study by in-situ electrical conductivity measurements. 

Another polypyrrole/polyamide composite film was obtained by the electrode coating method [84]. In this work the polyamide film was obtained in situ by coating a stainless steel electrode with a polyamic acid film followed by imidization with pyridine and acetic anhydride. The coated electrode was submitted to a constant current in a pyrrole/LiC104 solution in acetonitrile. The surface conductivity measured after detaching the composite film from the electrode showed a strong dependence on the charge density used in the synthesis, i.e. on the amount of pyrrole polymerized in the composite. The maximum value obtained was 2 S cm . Combination of polypyrrole with this polyamide was shown to increase markedly its thermal and environmental stability. 

The structure/property relationships in materials subjected to shock-wave deformation is physically very difficult to conduct and complex to interpret due to the dynamic nature of the shock process and the very short time of the test. Due to these imposed constraints, most real-time shock-process measurements are limited to studying the interactions of the transmitted waves arrival at the free surface. To augment these in situ wave-profile measurements, shock-recovery techniques were developed in the late 1950s to assess experimentally the residual effects of shock-wave compression on materials. The object of soft-recovery experiments is to examine the terminal structure/property relationships of a material that has been subjected to a known uniaxial shock history, then returned to an ambient pressure... 

Lyden et al. [92] used in situ electrical impedance measurements to investigate the role of disorder in polysulfide PEC with electrodeposited, polycrystalline CdSe photoanodes. Their results were consistent with disorder-dominated percolation conduction and independent of any CdS formed on the anode surface (as verified by measurements in sulfide-free electrolyte). The source of the observed frequency dispersion was located at the polycrystalline electrode/electrolyte interface. 

Monolayers prepared from TMTTF octadecyl TCNQ and TTF-octadecyl TCNQ on glycerin subphase Surface-pressure/surface-area measurements and in situ conductivity Lateral d.c. conductivity was of the order of 1 Scm"1 741... 

This article has addressed a number of issues relating to the electrical properties of paper or fibrous structures. It was shown that reliable measurement methods are now available for estimating both the bulk and surface conductivities of paper. In the case of the bulk conductivity, a new in situ pressure conductivity cell was described which significantlyreduces contact resistance. The surface conductivity can be determined by the application of a modified four-point probe method first used on paper by Cronch<15). It was shown that the degree of refining has a small effect on the bulk conductivity of paper. 

In situ conductivity measurements [52, 53, 164, 189, 195-202], luminescence techniques [203], different spectroscopies in combination with electrochemical methods [35-39, 82, 114, 115, 153-156, 204-208], and surface plasmon resonance [209] have also supplied valuable information about the ionic and electronic charge-transfer and charge transport processes. Microscopies have given new insights into the structure and morphology of surface polymer films, as well as their changes with the experimental conditions [151-159, 210-218]. The successful... 

In liquid ECAFM applications, the AFM tip and sample surface comprise the working and counter electrodes of an electrochemical cell. Additionally, a reference electrode can be incorporated into the liquid cell allowing the instrument to effectively perform as a three-electrode electrochemical cell. The technique has expanded into several applications where electrosynthesis and electrodeposition reactions can take place simultaneously with imaging [54]. Electrical connections can be made between the tip and enzymes on a surface to measure electron transfer and conductivity [44,52,55]. In addition, the tip can be functionalized with electroactive biomolecules to perform redox reactions and measure the amperometric and voltammetric response in situ [56]. 

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