N-type semiconductivity

Ceria is another type of mixed conducting oxide which has been shown already to induce electrochemical promotion.71 Ceria is a catalyst support of increasing technological importance.73 Due to its nonstoichiometry and significant oxygen storage capacity it is also often used as a promoting additive on other supports (e.g. y-A Cb) in automobile exhaust catalysts.79 It is a fluorite type oxide with predominant n-type semiconductivity. The contribution of its ionic conductivity has been estimated to be 1-3% at 350°C.71... 

Anodization generally results in the formation of films with limited thickness, uncertain composition, defects, and small crystallite size. Thus, the barrier nature of the n-type semiconducting CdS film obtained in the previous manner makes it too thin to form the basis of Cu2S/CdS or CdTe/CdS solar cells by the normal dipping process. Heterojunction cells of low efficiency have, however, been made by anodization followed by vacuum deposition of the added layer (CU2S). 

Bolts JM, Wrighton MS (1978) Chemically derivatized n-type semiconducting germanium photoelectrodes. Persistent attachment and photoelectrochemical activity of ferrocene derivatives. J Am Chem Soc 100 5257-5262... 

Elhs AB, Kaiser SW, Bolts JM, Wrighton MS (1977) Study of n-type semiconducting cadmium chalcogenide-based photoelectrochemical cells employing polychalcogenide electrolytes. J Am Chem Soc 99 2839-2848... 

Kubiak CP, Schneemeyer LF, Wrighton MS (1980) Visible fight driven generation of chlorine and bromine. Photooxidation of chloride and bromide in aqueous solution at illuminated n-type semiconducting molybdenum diselenide and molybdenum disulfide electrodes. J Am Chem Soc 102 6898-6900... 

Schneemeyer LF, Wrighton MS (1979) Flat-band potential of n-type semiconducting molybdenum disulfide by cyclic voltammetry of two-electron reductants Interface energetics and the sustained photooxidation of chloride. J Am Chem Soc 101 6496-6500... 

Aliovalent additives are often called donor dopants, when they tend to provide electrons and enhance intrinsic n-type semiconducting behavior, or acceptor dopants, when they tend to give a population of mobile holes and enhance /j-typc semiconducting behavior. The process of creating electronic defects in a crystal in this way is called valence induction. 

Tin oxide is a semiconductor with a wide band gap of Eg 3.7 eV, which can easily be doped with oxygen vacancies and chlorine acting as donor states. It is stable in aqueous solutions and hence a suitable material for n-type semiconducting electrodes. 

An example is shown in Fig. 8.9, where the photocurrent generated in n-type semiconducting WO3 is plotted for three different wavelengths... 

With ionic crystals, there are some rather interesting possibilities. A large part of the perturbation which a free surface introduces is associated with the change in the electrostatic environment of an ion in going from the interior to the surface. If the normally filled valence band is associated with the anions (as is the case with the alkali halides and with certain n-type semiconducting oxides), the surface perturbation acts in the direction of producing a band of surface states with its center lying above the center of the normal anion band. This anion surface band will normally be completely filled. Conversely, for the normally empty cation band (the... 

Ellis AB, Bolts JM, Wrighton MS (1977) Characterization of n-type semiconducting indium phosphide photoelectrodes stabilization to photoanodic dissolution in aqueous solutions of telluride and ditelluride ions. J Electrochem Soc 124 1603-1607... 

Steyrleuthner R, Schubert M, falser E, Blakesley JC, Chen Z, Facchetti A, Neher D (2010) Bulk electron transport and charge injection in a high mobility n-type semiconducting polymer. Adv Mater 22 2799... 

Figure 5.5 Band model of the mechanisms of p-type (left) and n-type semiconduction. Arrows represent thermal excitation of electrons.

Figure 4. Relative positions of hole decomposition potentials for the semiconductor and desired redox potentials for a photoelectrocheniical cell using n-type semiconducting electrodes. All examples are thermodynamically unstable, but (b) is kinetically more stable than (a).

In practice both natural and synthetic crystals are oxygen deficient, leading to donor levels approximately 0.1 eY below the bottom of the conduction band and consequently to n-type semiconductivity. Doping the crystal with group V elements also induces n-type semiconductivity the usual dopant is antimony. The ground state electronic configuration of the Sb atom is 5s2p3, and when it... 

The sensing action by metal oxides depends on several factors such as grain size (available surface area) and surface states as well as the efficiency with which the test gas molecules adsorb on the surface [25-27]. The sensing mechanism of n-type semiconducting metal oxides involves... 

In general, for an anion-deficient (n-type) semiconducting oxide ... 

Electronic Conductivity. Pluorides usually are good insulators owing to the wide band gap of more than 6eV in most compounds. In some cases it is possible, however, to obtain n-type semiconducting properties by doping, for example, in Cdp2(Y). Exceptional metallic conductivity is observed in the metal-rich compound Ag2p, even superconductivity in Hg3 jAsp6 - despite the presence of fluoride. Mixed-valence silver fluorides have been recently discussed as possible candidates for superconductivity. ... 

The carbene derivative La Cs2(Ad) can form nanorods during single-crystal growth, which shows an unusual FET (field effect transistor) property. Because thin films or whiskers of empty fullerenes and solids of EMFs are well known to show n-type semiconductivity, the nanorods arep-type [186], which will surely find applications in such fields as nanoelectronics. 

The photocurrent doubling has been verified for the photo-oxidation at the ZnO photoelectrode of a large variety of organic and also some inorganic spedes . Subsequently, similar observations have been made for other n-type semiconducting photoanodes cadmium sulfide cadmium selenide strontium titanate and titanium dioxide Rather in contrast with the behaviour of other above mentioned photoelectrodes (i.e., ZnO, CdS and CdSe), in the case of the Ti02 photoanode the multiplication of the photocurrent appears to be more effective in acidic than in alkaline solu-tions ... 

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