Semiconductor anodes, electrochemical

Semiconductor fabrication techniques permit the feature size of Si-based devices to reach into the deep submicron regime [i]. Additionally, Si can be anodized electrochemically or chemically (e.g., in an HF-containing electrolyte) to produce a sponge-like porous layer of silicon, with pore dimensions that range from several microns in width to only a few nanometers [ii]. These properties of Si make it a useful substrate for fabricating sensor platforms, photonic devices and fuel cell electrodes [iii]. 

Fornarini, L., Stirpe, F., Scrosati, 8. and Razzini, G., Electrochemical Solar Cells with Layer-Type Semiconductor Anodes. Performance of n-MoSs Cells, Solar Energy Materials, 5, 107, (1981). 

L. Fomarini, F. Stirpe, and B. Scrosati, Electrochemical solar cells with layer-type semiconductor anodes. Nonaqueous electrolyte cells, J. Electrochem. Soc. 129, 1155, 1982. 

Electrochemical and photoelectrochemical control of semiconductor anodic decomposition reactions allow for controlled fabrication of fine structures on semiconductor surfaces, for example, diffraction gratings, lenses, and MEMs structures [13-22]. These processes are usually carried out under conditions where the oxidation products are soluble in the electrolyte. Patterns are... 

Carbon monoxide detectors are in widespread use in the workplace and home. Metal oxide (e.g. Sn02) semiconductor and electrochemical sensors are commonly used, (a) Explain how an Sn02 sensor for CO works, (b) An electrochemical sensor employs platinum electrodes with aqueous sulfuric acid as the electrolyte. CO is oxidized at the anode. Write half equations for the anode and cathode reactions. Outline how the cell works as a quantitative sensor for CO. 

The (photo)electrochemical behavior of p-InSe single-crystal vdW surface was studied in 0.5 M H2SO4 and 1.0 M NaOH solutions, in relation to the effect of surface steps on the crystal [183]. The pH-potential diagram was constructed, in order to examine the thermodynamic stability of the InSe crystals (Fig. 5.12). The mechanism of photoelectrochemical hydrogen evolution in 0.5 M H2SO4 and the effect of Pt modification were discussed. A several hundred mV anodic shift of the photocurrent onset potential was observed by depositing Pt on the semiconductor electrode. 

Bard AJ, Wrighton MS (1977) Thermodynamic potential forthe anodic dissolution of n-type semiconductors - A crucial factor controlling durability and efficiency in photoelectrochem-ical cells and an important criterion in the selection of new electrode/electrolyte systems. J Electrochem Soc 124 1706-1710... 

Because of the excess holes with an energy lower than the Fermi level that are present at the n-type semiconductor surface in contact with the solution, electron ttansitions from the solution to the semiconductor electrode are facilitated ( egress of holes from the electrode to the reacting species ), and anodic photocurrents arise. Such currents do not arise merely from an acceleration of reactions which, at the particular potential, will also occur in the dark. According to Eq. (29.6), the electrochemical potential, corresponds to a more positive value of electrode potential (E ) than that which actually exists (E). Hence, anodic reactions can occur at the electrode even with redox systems having an equilibrium potential more positive than E (between E and E ) (i.e., reactions that are prohibited in the dark). 

It was learned that pitting-type metal and semiconductor corrosion is attended by the generation of noise seen in the form of dynamic irregularities in the changes of the anodic potential and current density. Thus, electrochemical noise studies were applied to the corrosion and passivation of metals and to their activation by external chemical (activating additives in the electrolyte) or electrochemical (anodic or cathodic polarization) agents. 

In addition to the stoichiometry of the anodic oxide the knowledge about electronic and band structure properties is of importance for the understanding of electrochemical reactions and in situ optical data. As has been described above, valence band spectroscopy, preferably performed using UPS, provides information about the distribution of the density of electronic states close to the Fermi level and about the position of the valence band with respect to the Fermi level in the case of semiconductors. The UPS data for an anodic oxide film on a gold electrode in Fig. 17 clearly proves the semiconducting properties of the oxide with a band gap of roughly 1.6 eV (assuming n-type behaviour). 

Formation of porous silicon is an anodic dissolution process, which consists of carrier transport in the semiconductor, electrochemical reactions at the interface, and mass transport of the reactants and reaction products in the electrolyte. There are a... 

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