Successive ion layer adsorption and reaction

Li, J. J. Wang, Y. A. Guo, W. Keay, J. C. Mishima, T. D. Johnson, M. B. Peng, X. 2003. Large-scale synthesis of nearly monodisperse CdSe/CdS core/shell nanocrystals using air-stable reagents via successive ion layer adsorption and reaction. J.Am. Chem. Soc. 125 12567-12575. 

Jimenez-Gonzalez, A. Suarez-Parra, R. 1996. Effect of heat treatment on the properties of ZnO thin films prepared by successive ion layer adsorption and reaction (SILAR)./. Cryst. Growth 167 649-655. 

Successive Ion-Layer Adsorption and Reaction (SILAR) Process... 

NCs is indispensable. In the case of cadmium chalcogenide NCs, the concentration of a colloidal solution can be determined in good approximation by means of UV-vis absorption spectroscopy thanks to tabulated relationships between the excitonic peak, the NC size, and the molar absorption coefficient.96 An advanced approach for shell growth derived from chemical bath deposition techniques and aiming at the precise control of the shell thickness is the so-called SILAR (successive ion layer adsorption and reaction) method.97 It is based on the formation of one monolayer at a time by alternating the injections of cationic and anionic precursors and has been applied first for the synthesis of CdSe/CdS CS NCs. Monodispersity of the samples was maintained for CdS shell thicknesses of up to five monolayers on 3.5 nm core CdSe NCs, as reflected by the narrow PL linewidths obtained in the range of 23 to 26 nm FWHM. 

The two processes are known as SILAR (successive ion layer adsorption and reaction) and ILGAR (ion layer gas reaction). Both methods work best when a metal salt is chosen in which the metal ion has the same valence state as in the desired final compound. Depending on concentration, temperature and duration, the thickness of the deposited metal can be varied from approximately monolayer thickness to more continuous single- or multi-layer coverage. 

Most reliable and popular technique being followed for synthesizing highly stable core-shell semiconducting nanocrystals is Successive Ion Layer Adsorption and Reaction better known as SILAR [109]. The shell is formed by growing one monolayer at a time over the core nanocrystal s surface. In a typical synthesis, the cationic and anionic precursors are alternately added and made to adsorb on the cores surface followed by reaction. This way of adding cationic and anionic precursors in separate injections prevents the otherwise possible homogenous nucleation of shell material. 

Peng and coworkers [833] have adapted the successive ion layer adsorption and reaction (SILAR), an in-solution deposition method derived from the atomic layer epitaxy method used in growing thin films in vacuum, to prepare CdSe-CdS nanocrystals on gram scale batches using ordinary precursors such as CdO, S, and Se. Wei et al. [228] report a green synthetic route for CdSe/CdS core-shell nanoparticles in aqueous solution using Se powder as the selenium... 

Liquid-phase deposition is a method for the non-electrochemical production of polycrystalline ceramic films at low temperatures, along with other aqueous solution methods [chemical bath deposition (CBD), successive ion layer adsorption and reaction (SILAR), and electroless deposition (ED) with catalyst] has been developed as a potential substitute for vapor-phase and chemical-precursor systems. The method involves immersion of a substrate in an aqueous solution containing a precursor species (commonly a fluoro-anion) which hydrolyzes slowly to produce a supersaturated solution of the desired oxide, which then precipitates preferentially on the substrate surface, producing a conformal coating... 

Lindroos, S. Charreire, Y. Bonnin, D. Leskela, M. 1998. Growth and characterization of zinc sulfide thin films deposited by the successive ionic layer adsorption and reaction (SILAR) method using complexed zinc ions as the cation precursor. Mater. Res. Bull. 33 453—459. 

Sasagawa, M. Nosaka, Y. 2001. Studies on the effects of Cd ion sources and chelating reagents on atomic layer CdS deposition by successive ionic layer adsorption and reaction (SILAR) method. Phys. Chem. Chem. Phys. 3 3371-3376. 

Interestingly, ESA bears much formal similarities with the successive ionic layer adsorption and reaction (SILAR) method originally developed in 1985 by Nicolau et al. [82,83]. This technique allows to obtain thin inorganic films of controlled thickness based on successive adsorption from aqueous solutions of small ions on selected substrates. 

The above discussion of CO oxidation and N2O decomposition is, however, designed mainly to show the type of situation which can occur when either of two related properties may appear to determine catalyst activity. Probably in these reactions semiconductivity is of primary importance and electronic configuration of secondary importance, both because oxygen adsorption is likely to involve simple formation of negative ions and is therefore governed by boundary-layer considerations and also because a correlation of activity with electron configuration is not, in fact, so successful as one with semiconductivity. 

For the use of the diffusion layer model are ne ed parameters of active centre concentration and acidity constants Kp and Kd on the mineral s surface and also equilibrium constants of all specific complexation reactions. This model was successfully used at analysis of adsorption of such ions as Na+, SO or Cl poorly adsorbed on the surface of iron oxide type minerals. 

---