Anodic regimes

The variety of electrolytes and the wide range of their concentrations, temperatures, and anodization regimes provide for a variety... 

It should be noted that anodization regimes have a major effect on oxide geometry. Palibroda233,234 has summarized the empirical dependences of the pore diameter, d, the density of pores, n, and the lifetime of initial barrier growth, r, on the ratio of the anodic voltage to the limiting voltage, Uamax, as follows ... 

Analysis of experimental data shows that the dependence of the geometrical parameters of oxides on the temperature and concentration of electrolyte is different for galvanostatic and potentio-static conditions (Fig. 35).221 It appears that potentiostatic anodization is limited mainly by processes in the bulk of the oxide and thus is not influenced by temperature (Fig. 35b), whereas the galvanostatic anodization regime involves oxide dissolution processes at the O/S interface depending both on Tel and Cel. 

There have been a number of investigations of the electret behavior of anodic oxides formed on various valve metals in different electrolytes and anodization regimes. The purpose of these... 

One way to achieve such improvements is by doping of aluminum oxide with properly selected impurities. These could be introduced by implantation into aluminum and subsequent transfer into the oxide during anodization.331 Alternatively, complex anions containing impurity atoms could be introduced into the anodizing bath [see Section IV(2)]. The incorporated anions influence the dielectric permittivity, E, of the oxide.176 Hence, one can manipulate the E value by changing the electrolyte concentration and anodization regime.91 According to the published data, rare-earth-doped... 

An n-type electrode is under reverse bias in this anodic regime, and so only a small dark current density in the order of a few pA cm-2 is observed, as shown in Fig. 4.11. The dark current increases by orders of magnitude if the breakdown field strength is reached at the electrode surface or at a pore tip present in the electrode, as discussed in Section 8.4. 

If the same experiment is performed with an n-type Si electrode under identical illumination intensity the anodic photocurrent is found to be larger than for the p-type electrode under cathodic conditions. This increase is small (about 10%) for current densities in excess of JPS. Figure 3.2 shows that in this anodic regime injected electrons are also detected at p-type electrodes. This allows us to interpret the 10% increase in photocurrent observed at n-type electrodes as electron injection during anodic oxide formation and dissolution. 

In contrast to p-type electrodes, an n-type electrode is under reverse conditions in the anodic regime. This has several consequences for pore formation. Significant currents in a reverse biased Schottky diode are expected under breakdown conditions or if injected or photogenerated minority carriers can be collected. Breakdown at the pore tip due to tunneling generates mainly mesopores, while avalanche breakdown forms larger etch pits. Both cases are discussed in Chapter 8. Macropore formation by collection of minority carriers is understood in detail and a quantitative description is possible [Le9], which is in contrast to the pore formation mechanisms discussed so far. 

If mapping of the defects is dispensable and only the average contamination level is of interest, measurements of the reverse dark current are sufficient to provide this information [Wi2]. This method is also applicable to n-type samples, which is in contrast to decoration of SCR defects by hydrogen bubbles, which is not possible in the anodic regime. 

Endres et al. [82] have demonstrated the suitability of an air- and water-stable ionic liquid for the electropolymerization of benzene. This synthesis is normally restricted to media such as concentrated sulfuric acid, liquid SO2 or liquid HF as the solution must be completely anhydrous. The ionic liquid used, l-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, can be dried to below 3 ppm water, and this ionic liquid is also exceptionally stable, particularly in the anodic regime. Using this ionic liquid, poly(para-phenylene) was successfully deposited onto platinum as a coherent, electroactive film. Electrochemical quartz crystal microbalance techniques were also used to study the deposition and redox behavior of the polymer from this ionic liquid (Section 7.4.1) [83]. 

Bias-dependent measurements were performed in order to check to what extent the mechanism depends on the electrical operation conditions. Fig. 43 shows double-logarithmic plots of the electrode polarization resistance (determined from the arc in the impedance spectrum) versus the microelectrode diameter observed at a cathodic bias of —300 mV and at an anodic bias of +300 mV respectively. In the cathodic case the electrode polarization resistance again scales with the inverse of the electrode area, whereas in the anodic case it scales with the inverse of the microelectrode diameter. These findings are supported by I-V measurements on LSM microelectrodes with diameters ranging from 30-80 pm the differential resistance is proportional to the inverse microelectrode area in the cathodic regime and comes close to an inverse linear relationship with the three-phase boundary (3PB) length in the anodic regime [161]. 

In the particular case considered here, it can therefore be deduced that in the anodic regime the surface path determines the overall current, since all steps of the... 

Due to their high electrical conductivity, metals constitute the most typical class of materials that can be studied by STM. In the context of porosity, silicon has been, by far, the most frequently studied metal using STM. Parkhutik et al. [36] made a rather pioneering application of STM to study the effect of silicon electrochemical anodization regime on the resulting porosity. Closely packed cylindrical mesopores were shown to form at low current densities, whereas branched, fibrous-like mesopores were obtained at high current densities. A simulation model was used to justify the formation of these two different types of pores. 

G. Hasse, 1. Carstensen, G. Popkirov, and H. Foil, Current transient analysis of the oxidizing process in the complete anodic regime of the Si-HF system. Mater. Sci. Eng. B69-70, 188, 2000. 

The electrochemical etching, with the intent of making the etched semiconductor porous, is performed in the anodic regime, so that positive charge is collected at the semiconductor-electrolyte interface. In order to increase the speed of the anodization process, electrical bias is applied to the sample through ohmic contacts. To protect the ohmic contacts on the... 

Porous anodic alumina attracts an attention of a scientific community due to an ordering nanostmcture resulting from self-regulated electrochemical anodic process. Aluminum is a unique material, which forms a regular porous oxide, composed of a packed array of columnar hexagonal cells, each having a cylindrical pore in the center [1], The cell size is known to be determined by the electrolyte and anodization regimes [1,2]. We have found that the cell size can be also tuned by Ti in Al-Ti alloys. The results obtained are presented in this paper. 

Initial film and anodization regimes, Uf,Jf Pore diameter, nm Pore wall thickness, mn Film porosity, % Volume expansion factor Refra- ctive index... 

Porous silicon (PS) is one of the nanoscale modifications of silicon. There are various approaches to PS producing that are now in use. The technique most generally employed today is known as wet anodization of a crystalline silicon. With this technique, yield parameters of porous material (porosity, pore size and shape, interpore distance) may be readily varied by anodization regimes. However, it is well known the problem of the PS stability influencing the physical properties of the PS layers. P S instability is c onditioned b y very large specific surface area of the porous material. 

The situation is different in the anodic regime. Gerischer [38] and HeUer [42] pointed out that the majority of semiconductors (in the dark for / -type or under illumination for n-type) are unstable against corrosion with valence band (photo)holes, as it is illustrated in Figs. 1 (c)... 

The anodic polymerization herein discussed must be con-duaed with a noble metal as anode, i.e., a metal that is not oxidatively dissolved in the anodic regime. Pt, Au, stainless steel, carbon, and conductive oxides (ITO, etc.) are examples of commonly used anodes. Interestingly enough, these substrates are common constituents of devices, such as actuators, sensors, solar cells, and electrochromic windows, in which thin films of conjugated polymers are desirable active layers. Last but not least, conjugated polymers can also be electrodeposited onto common metals (iron and copper) for sake of protection against corrosion, provided that the composition of the electrolytic medium is properly controlled. ... 

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