Metal oxide charges interface properties

These studies indicate that the charge transfer at the metal-oxide interface alters the electronic structure of the metal thin film, which in turn affects the adsorption of molecules to these surfaces. Understanding the effect that an oxide support has on molecular adsorption can give insight into how local environmental factors control the reactivity at the metal surface, presenting new avenues for tuning the properties of metal thin films and nanoparticles. Coupled with the knowledge of how particle size and shape modify the metal s electronic properties, these results can be used to predict how local structure and environment influence the reactivity at the metal surface. 

Sodium contamination and drift effects have traditionally been measured using static bias-temperature stress on metal-oxide-silicon (MOS) capacitors (7). This technique depends upon the perfection of the oxidized silicon interface to permit its use as a sensitive detector of charges induced in the silicon surface as a result of the density and distribution of mobile ions in the oxide above it. To measure the sodium ion barrier properties of another insulator by an analogous procedure, oxidized silicon samples would be coated with the film in question, a measured amount of sodium contamination would be placed on the surface, and a top electrode would be affixed to attempt to drift the sodium through the film with an applied dc bias voltage. Resulting inward motion of the sodium would be sensed by shifts in the MOS capacitance-voltage characteristic. 

The phenomena presented in this book were discussed in many reviews. For example, Schwarz [13] discussed methods used to characterize the acid base properties of catalysts. The review on sorption on solid - aqueous solution interface by Parks [14] includes also principles of surface science. The book Environmental Chemistry of Aluminum edited by Sposito reviews the solution and surface chemistry of aluminum compounds. Chapter 3 [15] provides thermochemical data for aluminum compounds. Chapter 5 [16] lists the points of zero charge of aluminum oxides, oxohydroxides and hydroxides with many references on adsorption of metal cations and various anions on these materials. Unlike the present book, which is confined to sorption from solution at room temperature, publications on coprecipitation and adsorption from gas phase or at elevated temperatures are also cited there. Brown et al. [17] reviewed on dry and wet surface chemistry of metal oxides. Stumm [18] reviewed sorption of ions on iron and aluminum oxides. The review by Schindler and Stumm [19] is devoted to surface charging and specific adsorption on oxides. Schindler [19] published a review on similar topic in German. Many other reviews related to specific topics are cited in respective chapters. 

Adsorption of an electropositive probe such as a Na atom provides another test of how the metal/oxide interface affects the properties of a deposited metal cluster. On metal surfaces the deposition of alkali metals at low coverage results in a net electron charge transfer to the metal surface [216]. For coverages below... 

Pseudocapacitors store charge based on reversible (faradaic) charge transfer reactions with ions in the electrolyte. For example, in a metal oxide (such as RUO2 or I1O2) electrode, charge storage results from a sequence of redox reactions. Electrochemical capacitors (ECs) based on such pseudocapacitive materials will have both faradaic and nonfaradaic contributions. The optimization of both EDLCs and pseudocapacitors depends on understanding how features at the nanoscale (e.g. pore size distribution, crystaUite or particle size) affect ion and electron transport and the fundamental properties of electrochemical interfaces. 

J.T.G. Overbeek, Electrokinetic phenomena, in Colloid Science, Vol. I (H. R. Kruyt, ed.). Elsevier, Amsterdam, 1952. R. O. James and T. W. Healy, Adsorption of hydrolyzable metal ions at the oxide-water interface. II Charge reversal of SiOa and Ti02 colloids by adsorbed Co(II), La(III), and Th(IV) as model systems, J. Colloid Interface Science 40 53 (1972). C.-P. Huang and W, Stumm, Specific adsorption of cations on hydrous a-Al203, /. Colloid Interface Science 43 409 (1973). S. L. Swartzen-Allen and . Matijevid, Colloid and surface properties of clay suspensions. II Electrophoresis and cation adsorption of montmorillonite, /. Colloid Interface Sci. 50 143(1975). G. R. Wiese, R. O. James, D. E. Yates, and T. W. Healy, Electrochemistry of the colloid-water interface, in Electrochemistry (J. O M. Bockris, ed.). Butterworths, London, 1976. D, W. Fuerstenau, D. Man-mohan, and S. Raghavan, The adsorption of alkaline-earth metal ions at the rutile/aqueous solution interface, in P. H. Tewari, op. cit. ... 

Organic semiconductors are used in many active devices. Many can be processed in solution and can therefore be printed. The charge transport properties largely depend on the deposition conditions, which are influenced by the nse of solvents, the deposition technique, concentration, interfaces and so on. Most of the organic semiconductors used today are p-type (e.g., pentacene and polythiophene), but the first n-type materials have also become available and these mean that complementary metal-oxide-semiconductor (CMOS) circuits can now be fabricated. 

The nature of the barrier to charge transfer at the metal-oxide interface is open to speculation. Assuming semiconducting properties for the Pt-oxide layer, this additional barrier may simply represent the nonlinear resistance of a metal-semiconductor junction, i.e., resistance of a diode biased in the conduction direction. For high bias voltages, the current-voltage relation for such a junction may be expressed by an equation of the form of Eq. (31). 

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