Interfacial energy cell-solid

Figure 1, Interfacial energy diagram for the SnO anode in contact with the components of the irorir-thionine photogalvanic cell at pH = 2. Solid lines aqueous sulfuric acid. Dashed lines sulfuric acid in 50 v/v % aqueous CH CN. Taken from Ref. 17.

The first intermediate phase formed at pH 7.4 is octacalcium phosphate (OCP) The transformation of OCP to HAP is thermodynamically favoured and occurs partly as an in situ solid state process, possibly due to the close structural arrangements and low interfacial energies between the two phases. The process appears to take place by hydrolysis of the OCP phase one unit cell thickness of OCP (dioo = 18.68 A) hydrolysing to form a two unit cell thickness of HAP (2 dioo = 16.32 A) and resulting in a contraction of 2.36 A along the [100] axis ... 

Interfacial energy between two solids can thus be extremely low, if they have different composition but similar crystal lattices in their symmetries and their cell parameters. We can note that this is the origin of the phenomena of heterogenous primary nucleation starting from the liquid phases, whose ultimate demonstration is the epitaxy. This interfacial energy can on the contrary be very high if the networks are very different in molar volumes and from the crystallographic point of view. 

Because of the presence of a well-defined energy gap between the conduction and the valence band, semiconductors are ideally suited for investigation of the interfacial interactions between immobilized molecular components and solid substrates. In this chapter, interfacial assemblies based on nanocrystalline TiOz modified with metal polypyridyl complexes will be specifically considered. It will be shown that efficient interaction can be obtained between a molecular component and the semiconductor substrate by a matching of their electronic and electrochemical properties. The nature of the interfacial interaction between the two components will be discussed in detail. The application of such assemblies as solar cells will also be considered. The photophysical processes observed for interfacial triads, consisting of nanocrystalline TiO 2 surfaces modified with molecular dyads, will be discussed. Of particular interest in this discussion is how the interaction between the semiconductor surface and the immobilized molecular components modifies the photophysical pathways normally observed for these compounds in solution. 

Deep-level states play an important role in solid-state devices through their behavior as recombination centers. For example, deep-level states are tmdesirable when they facilitate electronic transitions that reduce the efficiency of photovoltaic cells. In other cases, the added reaction pathways for electrons result in desired effects. Electroluminescent panels, for example, rely on electronic transitions that result in emission of photons. The energy level of the states caused by introduction of dopants determines the color of the emitted light. Interfacial states are believed to play a key role in electroluminescence, and commercieil development of this technology will hinge on understanding the relationship between fabrication techniques and tile formation of deep-level states. Deep-level states also influence the performance of solid-state varistors. 

In 1976, the first regenerative PECs with substantial and sustained solar to electrical conversion efficiency were demonstrated. These PECs are based on n-type cadmium chalcogenide (S, Se or Te) electrodes immersed in aqueous polychalcogenide electrolytes. The cells were introduced by Hodes, Cahen, and Manassen (31), Wrighton and coworkers [32], and Heller and Miller [33] and were capable of converting up to 7% of insolation to electrical energy. Most investigations of these systems focused on solid-state and interfacial aspects of these PECs and photodriven oxidation of polysulfide at the photoelectrode was represented ... 

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