Capacitance structure

Capacitive biosensors [390] detect changes in the capacitance of an electrode upon the occurrence of a binding event. The capacitive structure comprises a series of components such as the electrochemical double layer including the diffuse layer from ions in solution, the grafting layer, and the biorecognition layer. Since the contribution of the biorecognition layer to the overall capacitance is typi-... 

Deposition and etching of surface films and removal of a sacrificial layer under the structural film can produce many different shapes. The most common shape is a capacitive structure that is attached to the single-crystal silicon substrate at an anchor and is free to move above the surface (Fig. 5.2.3). 

A constant phase element (CPE) was chosen to represent the capacitive structure consisting of the double layer on the calixarene membrane (Eq. 1),... 

Nasal vasculature may offer some insight into this question, though research to date has been equivocal. Nasal turbinate vessels can be classified as either capacitance vessels or resistive vessels. Capacitance vessels appear to vasodilate in response to infection while resistance vessels appear to respond to cold stimuli by vasoconstriction. Buccal vascular structures also respond to thermal stimuli but appear to respond principally to cutaneous stimuli. How pharyngeal and tracheobronchial submucosal vessels react to thermal stimuli is not known, though cold-induced asthma is believed to result from broncho-spasms caused by susceptible bronchial smooth muscle responding to exposure to cold dry air.- This asthmatic response suggests an inadequate vascular response to surface cooling. 

From the experimental results and theoretical approaches we learn that even the simplest interface investigated in electrochemistry is still a very complicated system. To describe the structure of this interface we have to tackle several difficulties. It is a many-component system. Between the components there are different kinds of interactions. Some of them have a long range while others are short ranged but very strong. In addition, if the solution side can be treated by using classical statistical mechanics the description of the metal side requires the use of quantum methods. The main feature of the experimental quantities, e.g., differential capacitance, is their nonlinear dependence on the polarization of the electrode. There are such sophisticated phenomena as ionic solvation and electrostriction invoked in the attempts of interpretation of this nonlinear behavior [2]. 

The power factor cos 6 is always a positive fraction between 0 and 1 (as long as 161 < 90°). The smaller the power factor, the greater the current that must be supplied to the circuit for a given active (useful) power output requirement. The increase in current associated with low power factors causes greater line losses or requires an increase in the capacity of the transmission equipment (wire size, transformers, etc.). As a result, for industrial applications there is often a power factor charge in the rate structure for supplying electricity. The usual situation is for loads to be inductive, and the industrial consumer may add capacitance to their circuits to correct the lagging power factor. 

In the second part of the 20th century, the tantalum capacitor industry became a major consumer of tantalum powder. Electrochemically produced tantalum powder, which is characterized by an inconsistent dendrite structure, does not meet the requirements of the tantalum capacitor industry and thus has never been used for this purpose. This is the reason that current production of tantalum powder is performed by sodium reduction of potassium fluorotantalate from molten systems that also contain alkali metal halides. The development of electronics that require smaller sizes and higher capacitances drove the tantalum powder industry to the production of purer and finer powder providing a higher specific charge — CV per gram. This trend initiated the vigorous and rapid development of a sodium reduction process. 

Schematic energy level diagrams of a metal/polymer/metal structure before and after the layers are in contact are shown in the top two drawings of Figure 11-6. Before contact, the metals and the polymer have relative energies determined by the metal work functions and the electron affinity and ionization potential of the polymer. After contact there is a built-in electric field in the structure due to the different Schottky energy barriers of the asymmetric metal contacts. Capacitance-voltage measurements demonstrate that the metal/polymer/metal structures are fully depleted and therefore the electric field is constant throughout the bulk of the structure [31, 35]. The built-in potential, Vhh i.e. the product of the constant built-in electric field and the layer thickness may be written...

Measurements of the double-layer capacitance provide valuable insights into adsorption and desorption processes, as well as into the structure of film-modified electrodes (6). 

The value a = 1 corresponds to ideal capacitive behavior. The fractal dimension D introduced by Mandelbrot275 is a formal quantity that attains a value between 2 and 3 for a fractal structure and reduces to 2 when the surface is flat. D is related to a by... 

The division of the interface into an inner layer and a diffuse layer has been a matter of discussion in view of the molecular dimensions of the inner layer.122-126,279-285 However, the contribution of a constant capacitance is an experimental fact. Furthermore, molecular theories for electrolytes near a charged hard wall282 as well as phenomenological nonlocal electrostatic theories283 predict such a component without artificial introduction of any inner layers. This turns out to be an effect of the short-range structure of the solvent.279-285... 

The local solvent structural information inherent in deviations from Parsons-Zobel plots suggests that this effect deserves further experimental investigation.126,283 284 The reported accuracy of recent capacitance data (5%) for dilute solutions,285 however, must be improved before unambiguous conclusions about deviations can be drawn. 

The electrical double-layer structure at Ga/DMF, In(Ga)/DMF, and Tl(Ga)/DMF interfaces upon the addition of various amounts of NaC104 as a surface-inactive electrolyte has been investigated by differential capacitance, as well as by the streaming electrode method.358 The capacitance of all the systems was found to be independent of the ac frequency, v. The potential of the diffuse layer minimum was independent of... 

Surface-enhanced Raman scattering (SERS) and differential capacitance methods have been used to study the interfacial solvent structure and... 

Zinc crystallizes in the hexagonal close-packed system its electronic structure is 4s2 and the melting point is 693 K. Since the zinc dissolution takes place at potentials very close to ffa0 the differential capacitance curves in the region of Ea=c in pure surface-inactive electrolyte solutions (KC1, pH = 3.7) can be determined directly for the Zn(llJO) face only... 

On the basis of experimental findings Heinze et al. propose the formation of a particularly stable, previously unknown tertiary structure between the charged chain segments and the solvated counterions in the polymer during galvanostatic or potentiostatic polymerization. During the discharging scan this structure is irreversibly altered. The absence of typical capacitive currents for the oxidized polymer film leads them to surmise that the postulated double layer effects are considerably smaller than previously assumed and that the broad current plateau is caused at least in part by faradaic redox processes. 

Fig. 3.1 Model of CdS deposition and recrystaUization. The changes in film structure are related to the features of the cyclic voltammogram and the capacitance plot broken line). The interpretation of the capacitance data in this way leads to a mean value of ffcds = 17 for the relative permittivity of the film. (Reprinted from [34], Copyright 2009, with permission from Elsevier)...

An alternative electrical method that has been used in the study of glass-ionomer cements has been the measurement of dielectric properties. Tay Braden (1981, 1984) measured the resistance and capacitance of setting cements at various times from mixing. From the results obtained, relative permittivity and resistivity were calculated. In general, as these cements set, their resistivity was found to fall rapidly, then to rise again. Both these results and the results of relative permittivity measurements were consistent with the cements comprising highly ionic and polar structures. 

Cortie, M.B., van der Lingen, E. and Pattrick, G. (2003) Catalysis and capacitance on nano-structured gold particles and sponges, in Proceedings of the Asia Pacific Nanotechnology Forum 2003, Cairns, Australia, World Scientific, Singapore, pp. 79-82. 

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