Electrochemical deposition experimental materials

This chapter is divided into a number of sections that describe important details related to the conductive polymer/superconductor structures. First, information is provided concerning the preparation and characterization of various polymer/superconductor structures. Chemical and electrochemical deposition methods for localizing the polymers onto a number of cuprate phases are discussed. Section III is devoted to relevant background information related to the induction of superconductivity into metals and semiconductor systems via the proximity effect. More specifically, the four basic methods that have been used to study the occurrence of proximity effects in classical solid-state conductors are described (i.e., contact resistance, modulation of superconductivity in normal/superconductor bilayer structures, passage of supercurrent through superconductor/ normal/superconductor systems, and theoretical analyses). Sections IV and V are devoted to experimental studies of conductive polymer/superconductor interface resistances and modulation of superconductivity in the hybrid systems. Finally, there is a discussion of the initial experimental results that explores the possible induction of superconductivity into organic materials. 

The monotonic increase of immobilized material vith the number of deposition cycles in the LbL technique is vhat allo vs control over film thickness on the nanometric scale. Eilm growth in LbL has been very well characterized by several complementary experimental techniques such as UV-visible spectroscopy [66, 67], quartz crystal microbalance (QCM) [68-70], X-ray [63] and neutron reflectometry [3], Fourier transform infrared spectroscopy (ETIR) [71], ellipsometry [68-70], cyclic voltammetry (CV) [67, 72], electrochemical impedance spectroscopy (EIS) [73], -potential [74] and so on. The complement of these techniques can be appreciated, for example, in the integrated charge in cyclic voltammetry experiments or the redox capacitance in EIS for redox PEMs The charge or redox capacitance is not necessarily that expected for the complete oxidation/reduction of all the redox-active groups that can be estimated by other techniques because of the experimental timescale and charge-transport limitations. 

In an electrochemistry-NR experiment, the reflection of neutrons takes place at an interface consisting of five parallel phases as schematically shown in Figure 3.9. Table 3.1 lists the numerical values of the theoretical SLDs of the materials used in typical electrochemical studies. Each phase contributes to the overall measured NR, and to understand the shape of the experimental reflectivity curves it is instructive to examine the contribution of each individual lamina. To do this, a recursion scheme for stratified media described by Parratt [18] can be used to calculate the reflectivity of a simulated interface. These calculated reflectivities are then compared to the reflectivities predicted by the kinematic approximation. Consider a 20 A thick film of a hydrocarbon-based surfactant deposited on a gold/ cliromiurn-modified quartz sample. To simplify the analysis, a mixed D2O/H2O... 

There is, however, a specific advantage in the electrodeposition method, relating to the unique possibility of the determination of the amount of deposited material. For CdTe, the electrochemical reaction involves a charge turnover of six electrons for each deposited CdTe unit. This correlation is derived from basic chemistry, but it has also been experimentally confirmed by Ernst (2001), as shown in Fig. 6.11. This correlation holds for both planar and deeply structured substrates. Since the charge turnover can easily be measured by integrating the deposition current over time, the electrodeposition method affords a reliable and quantitative determination of the total amount of deposited material. 

The number of experimental variables available with chemical polymerization is greatly reduced because no electrochemical cell or electrodes are employed. The range of dopant counterions (A-) that may be incorporated into the PPy backbone during polymerization has also, until recently, been generally limited to ions associated with the oxidant. However, chemical polymerization remains of interest for processing purposes because it may be easier to scale up this batch process and it results in the formation of powders or colloidal dispersions. Furthermore, it is possible to use chemical deposition to coat other nonconducting materials. 

The experimental simplicity of these materials has led to intensive investigation. An early electrochemical example was the deposition of aluminum and several aluminum aUoys. The addition of AlClj leads to an acidic or basic character of the melt. This influences the potential window (Figure 1.7). 

Electrochemical methods have been widely used for the synthesis of conjugated polymers since they represent an easy, clean and versatile way of obtaining the targeted materials as coatings on conductive substrates. The subject was recently reviewed by Heinze et al. both from the theoretical and experimental points of view. Theoretical aspects focusing on the electrochemistry of PPy are also discussed in a recent book chapter. In the following sections will be briefly discussed the choice of experimental conditions suited for PPy deposition under various forms and for various applications. 

In realistic applications it is necessary as a third step to check the corrosion behavior experimentally under the various electrochemical conditions expected. Environmental changes might include adhesion of corrosive materials metallurgical changes might include selective dissolution or deposition of noble metals. It is essential to inspect the corrosion behavior of aluminum and its alloys in a field test. 

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