Multilayers by Self-Assembly
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MULTILAYERS BY SELF-ASSEMBLY M. Toprak, D.K. Kim, M. Mikhaylova, M. Muhammed Dept. of Material Science and Engineering, Royal Institute of Technology, Sweden. Nanoparticles, as building blocks, are important for the development of advanced, functional composite materials. Recent developments have shown that self-assembly of nanoparticles is a promising technique for the fabrication of complicate nanostructured materials. Self assembly of the nanoparticles into ordered structures on a substrate can be achieved through chemical treatment of the particle and/or substrate surface. The assembled nanoparticles can have a dramatic effect on the physical properties of the composite. A µCP technique has been employed to form a SAM of bifunctional silane (APTMS) in the region of contact. The stamps for the µCP are prepared by polymerization of polydimethysiloxane (PDMS) on a flat surface. Glass substrates have been used for optical absorption measurements. Oxide or metallic particles have been assembled on the patterned surface after a surface treatment. The self-assembled layer was subsequently treated with bifunctional molecules and multilayers of the same material or composites have been thus obtained. INTRODUCTION Chemical synthesis of nanostructures and hybrid organic-inorganic materials represent the fastest growing topics of today’s chemistry. Being at the interface of traditional disciplines, these areas of science present rich research grounds with potentially strong fundamental and technological impact. The self-assembly of nanoparticles into useful morphologies is a much anticipated development in the nanotechnology as it offers the promise of creating materials from well-characterized, nanometer-scale constituents with interesting properties [1]. Selfassembled mono- and multilayer films on solid substrates have generated considerable interests recently because of the potential for controlling the molecular architecture and chemical and physical properties of layered assemblies on surfaces. Self-assembly (SA) means spontaneous molecular assemblies on a substrate forming an ultrathin molecular film by the treatment of the substrate with a solution of an active organic molecules. The technique provides an ordered thin film fabricating in molecular level. Self-assembled monolayer (SAM)s are stabilized by various interactions in the monolayer. The first part is the head group that provides the most exothermic process, i.e., chemisorption on the substrate surface. As a result of the exothermic head groupsubstrate interactions, molecules try to occupy every available binding site on the surface, and in this process they push together molecules that have already adsorbed. The second part is the alkyl chain, and the energies associated with its interchain van der Waals interactions are order of few. The third molecular part is the terminal functionality, which governs surface properties and makes it possible to form multilayer films. Sarathy et al. prepared heterostructures consisting of alternate layers of semico
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