Solid thin-film coatings

Thin film coatings of nanocrystalline semiconductors, as collections of quantum dots (QD or Q-dot) attached to a solid surface, resemble in many ways semiconductor colloids dispersed in a liquid or solid phase and can be considered as a subsection of the latter category. The first 3D quantum size effect, on small Agl and CdS colloids, was observed and correctly explained, back in 1967 [109]. However, systematic studies in this field only began in the 1980s. 

Haaland, P. McKibben, J. Parodi, M. The Art and Science of Thin-Film Coating A Progress Report. Solid State Technol. 1995, 38, 83-89. 

The sol-gel process involves the transition of a system from a liquid "sol" (mostly colloidal) into a solid "gel" phase (11). By applying this methodology, it is possible to fabricate ceramic or glass materials in a wide variety of forms ultrafine or spherical-shaped powders, thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic ceramics and glasses, or extremely porous aerogel materials. 

Surfaces can be broadly described as the boundary between a condensed phase (solid, hquid) of matter and another material (solid, gas, or liquid). Surfaces are encountered in most aspects of life, from the contact of a car s wheel with the pavement (solid-solid interface) to the evaporation of a water droplet (liquid-gas interface). Equally as important, surfaces play a fundamental role in many chemical processes including catalysis, thin film coatings, and electrochemical oxidation and reduction. 

S. Uhlenbruck, N. Jordan, D. Sebold, H.P. Buchkremer, V.A.C. Haanappel and D. Stover, Thin Film Coating Technologies of (Ce,Gd)02.6 Interlayers for Application in Ceramic High-Temperature Fuel Cells, Thin Solid Films, 515,4053-4060(2007). 

Paolesse R., Natale C. D., Dall Orto V. C., et al.. Porphyrin thin films coated qnartz crystal microbalances prepared by electropolymerization techniqne. Thin Solid Films, 354, 245-250,1999. 

The investigation of the properties of metal clusters under different experimental conditions has provided useful information about the evolution of matter from the gas phase to the solid state. In particular, with respect to the kinetics of reaction, there is a large variation in reactivity as a function of the identity of the metal as well as cluster size. The explanation of these variations provide exciting new challenges. Understanding how the cluster geometry and electronic structure affect chemical reactivity can have an important influence in fields such as thin film coating and catalysis. 

The most important processes for thin-film formation are physical vapor deposition (PVD) processes. Basic PVD processes are evaporation and sputtering. The coating material is solid thin films are deposited by solid-liquid-vapor-solid phase transition in the case of evaporation and solid-vapor-solid transition in the case of sputtering. 

Chemical Vapor Deposition (CVD) is a chemical process to produce solid thin films on surfaces. Typically one or more precursor gases flow into a chamber containing heated objects that need to be coated. Chemical reactions take place on or near the hot surfaces. As a result, thin films are deposited on these surfaces. Volatile chemical by-products (which are frequently produced) can be removed by gas flowing through the reactirai chamber. 

Paolesse, R., C. Di Natale, V. Campo DaU Orto, A. Macagnano, A. Angelaccio, N. Motta, A. Sgarlata, J. Hurst, 1. Rezzano, M. Mascini, and A. D Amico (1999). Porphyrin thin films coated quartz crystal microbalances prepared by electropolymerisation technique. Thin Solid Films 354, 245-250. 

Yoshiki, H. Abe, K. Mitsui, T. (2006). SiCh thin film deposition on the inner surface of a poly(tetra-fluoroethylene) narrow tube by atmospheric pressure glow microplasma. Thin Solid Films, VoL 515, pp. 1394-1399 Yoshiki, H. Mitsui, T. (2008).TiO2 thin film coating on a capillary inner surface using atmospheric-pressure microplasma. Surf Coat Technol, Vol. 202, pp. 5266-5270... 

By contrast, CVD is a process in which gaseous precursors are reactively transformed into a thin film, coating or other solid-state material on the surface of a catalyst or substrate. It should be stressed that CVD is no longer limited to thin film growth this method is now the preferred route to generating fiber-optic preforms, " ... 

Plate 45 A researcher at the BOC Group Technical Centre, Murray Hill, New Jersey, USA, using an advanced Electron Spectroscopy For Chemical Analysis (ESCA) unit. ESCA provides qualitative and quantitative analysis of the chemistry of elements present in the outermost layers of solid materials. The unit is used in the development of thin-film coatings, medical sensors, molecular sieves and catalysts. See Photoelectron Spectrometers Photoelectron Spectroscopy. Reproduced with permission from Science Photo Library. 

Sol gel coating The coating of a surface with a fluid sol, which is a stable suspension of colloidal particles. The sol is then converted into a rigid porous mass called a gel, which is heated to melt and sinter the mass into a solid thin film. 

Four possible mechanisms for solid-state extraction (a) adsorption onto a solid substrate (b) absorption into a thin polymer or chemical film coated on a solid substrate (c) metal-ligand complexation in which the ligand is covalently bound to the solid substrate and (d) antibody-antigen binding in which the receptor is covalently bound to the solid substrate. 

Bonded Solid-Film Lubricants. Although a thin film of soHd lubricant that is burnished onto a wearing surface often is useful for break-in operations, over 95% are resin bonded for improved life and performance (62). Use of adhesive binders permits apphcations of coatings 5—20 p.m thick by spraying, dipping, or bmshing as dispersions in a volatile solvent. Some commonly used bonded lubricant films are Hsted in Table 12 (62) with a more extensive listing in Reference 61. 

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