Nanostructure formation solutions

Dimitrios Maroudas, Modeling of Radical-Surface Interactions in the Plasma-Enhanced Chemical Vapor Deposition of Silicon Thin Films Sanat Kumar, M. Antonio Floriano, and Athanassiors Z. Panagiotopoulos, Nanostructured Formation and Phase Separation in Surfactant Solutions Stanley I. Sandler, Amadeu K. Sum, and Shiang-Tai Lin, Some Chemical Engineering Applications of Quantum Chemical Calculations... 

Sanat Kumar, M. Antonio Floriano, and Athanassiors Z. Panagiotopoulos, Nanostructured Formation and Phase Separation in Surfactant Solutions... 

Water Solutions of Amphiphilic Polymers Nanostructure Formation and Possibilities for Catalysis... 

The sol-gel method is a low temperature synthesis route for complex oxides [42]. It can be used to make complex functional oxide nanowires inside the pores of templates. In addition to the sol-gel method precursor-based solution deposition routes can also be used for nanostructure formation [43]. In both cases a postdeposition high temperature anneal (>500-600 °C) is needed to form the required stoichiometric phase. Due to the requirement of a high temperature anneal, alumina templates are used as the polycarbonate membranes decompose at a much lower temperature. For chemical solution deposition the membrane is dipped directly into the precursor solution. For sol-gel growth generally the required sol is prepared and the template is put into the sol for a required period (e.g. 0.5-1 h). After removing the membrane from the sol it is dried and then annealed at higher temperature before the required phase is formed. A schematic of the sol-gel route is shown in Figure 21.10. 

In the acidic route (with pH < 2), both kinetic and thermodynamic controlling factors need to be considered. First, the acid catalysis speeds up the hydrolysis of silicon alkoxides. Second, the silica species in solution are positively charged as =SiOH2 (denoted as I+). Finally, the siloxane bond condensation rate is kinetically promoted near the micelle surface. The surfactant (S+)-silica interaction in S+X 11 is mediated by the counterion X-. The micelle-counterion interaction is in thermodynamic equilibrium. Thus the factors involved in determining the total rate of nanostructure formation are the counterion adsorption equilibrium of X on the micellar surface, surface-enhanced concentration of I+, and proton-catalysed silica condensation near the micellar surface. From consideration of the surfactant, the surfactants first form micelles as a combination of the S+X assemblies, which then form a liquid crystal with molecular silicate species, and finally the mesoporous material is formed through inorganic polymerization and condensation of the silicate species. In the S+X I+ model, the surfactant-to-counteranion... 

NANOSTRUCTURE FORMATION AND PHASE SEPARATION IN SURFACTANT SOLUTIONS... 

Porous anodic alumina (PAA) films attracts an interest because of possibility of low-cost and short time production of highly ordered nanostructures. Possibility of magnetic [1], semiconducting [2] and photonic [3] nanostructure formation on the basis of PAA was demonstrated last decade. It is known that highly ordered PAA films may be formed on pretextured aluminum surface [4]. There are the two commonly used techniques of ordered nanorelief formation by electropolishing in perchloric acid ethanolic solution [5] or by two-step anodization [6]. 

Koker L, Kolasinski KW (2001) Laser-assisted formation of porous silicon in diverse fluoride solutions reactions kinetics and mechanistic implications. J Phys Chem B 105 3864-3871 Kolasinski KW (2010) Charge transfer and nanostructure formation during electroless etching of silicon. J Phys Chem C 114 22098-22105... 

Such structure direction was successful because sol-gel processes could produce oxide nanoparticles in solution of sizes typically below 5 nm. Larger particles are usually immiscible with moderately sized polymer blocks and segregate from BCPs [11, 41]. The size compatibility between BCPs and oxide particles is crucial for controlled nanostructure formation. 

Ceramics are nonmetaUic solids, insulators or semiconductors, and include oxides, non-oxides, and composites. Nanostructure formation of ceramics has been studied in the Wiesner group mainly by using BCPs as structure-directing agents for ceramic sol nanoparticles. To that end, ceramic sol nanoparticles prepared by the sol-gel process are mixed with a BCP solution for self-assembly of BCP/ceramic nanoparticles. In this way, a variety of nanostractures are accessible by varying the volumetric ratio of BCP and inorganic sol. The group has extensively studied aluminosilicates and transitimi metal oxides. 

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