Surface conductivity measurement

Instrumentation. Thin films of the material to be studied (mostly metals) are deposited onto insulating substrates (glass, mica) for a typical setup, see Fig. 7.27. Films of intrinsically conducting polymers are deposited by casting from their solution or by electropolymerization [262, 263]. 

The electronic resistance of poly aniline changes reversibly from the poorly conducting reduced (undoped) through the medium oxidized (doped) state to the strongly oxidized state and back without any significant difference between the initial and 

The terms surface conductivity and surface resistance are used equally. 

A lower resistance in the oxidized state and a broader electrode potential range wherein no irreversible change occurs are observed. 

Adsorbates of molecules or ions from solution onto the electrode as a function of electrode potential or concentration in solution can be investigated. The electrode to be investigated is prepared as a thin film by vapor deposition onto a suitable insulating (monocrystalline, if desired) substrate. For simultaneous measurements of film resistance and electrode potential an electrode design as depicted in Fig. 7.30 provides an optimum compromise between current distribution and a minimum of interference between both measurements [258], 

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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... 

Reproducible and accurate measurements of electrical conductivity of paper are of great importance in a number of technologies. Two commonly measured electrical parameters of paper are its surface and bulk conductivity. A method for measuring surface conductivity has been reported by Greismer 13, and his recommendations were incorporated in D.C. surface conductivity measurements reported by Howlett and Landheer 14. ... 

Yamiguchi H, Itoh S, Igarashi S, Naitoh K, Hasegawa R (1998) TXRF analysis of solution samples using polyester film as a disposable sample-carrier cover. Anal Sci 14 909-912 Yan B-D, Meilink SL, Warren GW, Wynblatt P (1987) Water absorption and surface conductivity measurements on alpha-alumina. IEEE Trans Components Hybrids Manufact Tech CHMT-10 247-251 Yashiro W, Ito Y, Takahasi M, Takahashi T (2001) Darwin s theory for the grazing incidence geometry. Surf Sci 490 394-408... 

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... 

For surface conductivity measurement, two ends of a thin film of semiconductor are connected with platinum wires. The entire surface except the top surface of the film is covered with an insulating paint. This film is then immersed in a solution of known pH whose temperature is controlled very accurately. Surface resistance is measured versus temperature (normally in the range of —10°C to 4-25 °C). This experiment is repeated at different pH values. Log of the surface conductivity is plotted versus reciprocal of the absolute temperature to get the activation energy. This calculation is carried out for each pH. Finally, a plot of activation energy versus pH is plotted, which shows either a minimum with n-type semiconductor or a maximum with p-type semiconductor. These pH values correspond to point of zero charge (pzc) of the material. 

Fig. 10 Surface conductivity measurements of thin films ofa-Fe203 and p-SnSe. Log of surface conductivity versus pH at different temperatures for (a) n-a-FeiO-i (b) p-SnSe. Activation energy of surface conductivity versus pH for (c) n-0 -Fe2O3 and (d) p-SnSe.

Surface Conductivity Measurement, Fig. 1 The linear relationship of s oAP/rjXiPs versus 1/h for a slit capillary (or 1/R for a cylindrical capillary) by using Eq. 14 (or Eq. 13) to determine the zeta potential and the surface conductivity by the streaming potential method experimental... 

Surface Conductivity Measurement, Fig. 7 Specific surface conductivity, versus the applied voltage and the capillary diameter, for a 10 cm long capillary tube, for (a) C = 10" M KCl, (b) C = 10" M KQ... 

Harrick [100] proposed to use internal reflection spectroscopy to investigate the surface electron states in the dielectric-semiconductor systems. In contrast to the indirect methods of the field-effect and surface conductivity measurements, measurement of the optical absorption allows one to determine the spectral distribution of the surface states directly. However, assuming that the surface state... 

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. 

In the described techniques, the contact resistance-related issues usually are more typical in the through-plane measurements than in the in-plane measurements. However, surface conductivity measurements are also affected by the contact resistance. These types of experiments are sensitive to undesired electric noise (Tong 2011). Also, the qualities of all electric connections are of great importance. Preconditions for reliable results are careful construction of the measuring unit and sample preparation and quality management of testing procedures with reference probes. The environment has effects on the conductivity values and temperature, but humidity in particular may cause inaccurate results (Boudenne et al. 2011). 

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