A General Route to Nanoparticle Thin Films and Coatings
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A General Route to Nanoparticle Thin Films and Coatings B. Mukherjee and N. Ravishankar Materials Research Center, Indian Institute of Science, Bangalore, India. Abstract Nanoparticles thin films have wide range of applications such as nanoelectronics, magnetic storage devices, SERS substrate fabrication, optical grating and antireflective coating. Present work describes a method to prepare large area nanoparticles thin film of the order of few square centimeters. Thin film deposition has been done successfully on a wide range of conducting as well as non conducting substrates such as carbon-coated copper grid, silicon, m-plane of alumina, glass and (100) plane of NaCl single crystal. SEM, TEM and AFM studies have been done for microstructural characterization of the thin films. A basic mechanism has been proposed towards the understanding of the deposition process. Introduction Considerable attention has recently been directed towards preparation of large area nanoparticle thin films and nanoparticle coatings. This is essential as usefulness of nanocrystals critically depends on the ability to build nano architectures in controlled manner. The most important applications[1-5] of these nanocrystal assemblies are in the preparation of Surface-Enhanced Raman Spectroscopy (SERS) substrate, anti-reflective coatings, magnetic storage media and nanoelectronics components all of which rely on nanoparticle thin films over large areas. Other moderate day-to-day applications (industrial, automotive, architectural and antimicrobial coating etc.) that exploit desired properties of nanoparticles (optical transparency, scratch abrasion resistance, hardness/toughness, conductivity, and UV/IR attenuation) also depend on coating of nanoparticles on desired substrates. Self assembly or its combination with LB technique[6, 7] has prove to be the most successful method to fabricate large 2D, 3D superlattices with hexagonal close packing. However the area of the fabricated superlattice is limited from tens of microns to a few hundreds of micron at best. Another approach [6-10] is to physisorb or chemisorb surface-functionalized nanoparticles on a pretreated substrate with suitable surface termination. However, the coverage of the thin film created in this technique very low (30%-60%). Another possibility to create large area nanoparticle assembly is by employing physical thin-film deposition methods but the control of size, shape in these methods is not good and aggregation is unavoidable. More recently, a novel nanoparticle thin film deposition method based on supercritical CO2 as anti-solvent has been developed to deposit nanoparticles on a solid substrate. The thin film formed in this case is uniform, dense, and free of defects that are generally associated with evaporation of the solvent and attendant surface tension problems. Recently, a lot of focus has been drawn towards biological application[11, 12] which largely relies on nanoparticle coating and/or attachment on different microscopic and sub-microscopi
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