Atomic layer deposition procedure

Many examples can be found in the literature on this point. The reducibility of vanadia catalysts has catalytic implications for selective oxidation reactions where they found real use. The support nature and the preparation method affect the reducibility of the vanadia phase. In Ref. [19] pure titania or bilayered titania/silica supports were chosen and concerning the vanadia deposition method, impregnation and atomic layer deposition procedures were performed. The reducibility of vanadia improved with increasing titania loading as shown by the calculated AOS. The lowest AOS were associated to vanadia on pure titania supports (Uox.av = 3.5) while vanadia on titania-silica supports achieved at maximum nox.av of 3.7-3.S. AOS of vanadium after reduction was independent of the preparation method. 

Nonaqueous sol-gel routes are not restricted to the deposition of preformed metal oxide nanoparticles. In feet, chemical principles such as ester elimination have been extended to atomic layer deposition, which enabled the coating of a wide range of materials (carbon nanotubes, wool, cellulose fibers, and single crystals) with a thin layer of amorphous titania or hafnia [115]. Detailed discussion of these procedures is out of the scope of this chapter, and the interested reader is referred to a more detailed review [195]. 

EC-ALE is the combination of UPD and ALE. Atomic layers of a compound s component elements are deposited at underpotentials in a cycle, to directly form a compound. It is generally a more complex procedure than most of the compound electrodeposition methods described in section 2.4.2, requiring a cycle to form each monolayer of the compound. However, it is layer-by-layer growth, avoiding 3-D nucleation, and offering increased degrees of freedom, atomic level control, and promoting of epitaxy. 

Also, thin films of semiconducting compounds were formed on a gold electrode. To obtain them, a methodology called electrochemical ALE (electrochemical atomic layer epitaxy) has been developed. This procedure is based on the formation of individual atomic layers of particular elements, which may further form a compound. Accordingly, in each cycle, a controlled formation of a monolayer of the particular compound occurs. The advantage of this methodology is that three-dimensional growth of one-elemental deposit is inhibited. 

The underpotential deposition of sulfur on Ag(l 11) is just the first step towards the realization of mono- and multilayers of semiconducting sulfides, such as CdS and PbS, by the alternated underpotential deposition of S and Cd (or Pb) atomic monolayers on the low-index faces of silver. This procedure, cdled electrochemical atomic layer... 

The second example involves the surface chemistry of the compound semiconductor CdSe synthesized epitaxially on Au(100) by underpotential deposition (UPD). By analogy with the gas-phase epitaxial deposition procedure, this UPD-based method has been dubbed electrochemical atomic layer epitaxy (ECALE) [6]. Unique information on the interfacial structure of the first adlayer of Se electrodeposited was revealed by STM experiments. 

In a similar procedure, the atomizer test, which depends on the behavior of an advancing rather than a receding contact angle, a fine mist of water is apphed to the metal surface and the spreading of water is observed. On a clean surface, water spreads to a uniform film. With oleic acid as the test soil, the atomizer test can detect the presence of 10 mg of soil per cm, less than a monomolecular layer (115). For steel that is to be electroplated, the copper dip test is often employed. Steel is dipped into a cupric salt solution and the eveimess of the resulting metallic copper deposit is noted. 

An alternative type of tip-induced nanostructuring has recently been proposed. In this method, a single-crystal surface covered by an underpotential-deposited mono-layer is scanned at a close tip-substrate distance in a certain surface area. This appears to lead to the incorporation of UPD atoms into the substrate lattice, yielding a localized alloy. This procedure works for Cu clusters on Pt(l 11), Pt(lOO), Au(l 11), and for some other systems, but a model for this type of nanostructuring has not been available until now. (Xiao et al., 2003). 

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