Coating 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. 

Coating and thin films can be applied by a number of methods. In thermal or plasma spraying, a ceramic feedstock, either a powder or a rod, is fed to a gun from which it is sprayed onto a substrate. For the process of physical vapor deposition (PVD), which is conducted inside an enclosed chamber, a condensed phase is introduced into the gas phase by either evaporation or by sputtering. It then deposits by condensation or reaction onto a substrate. A plasma environment is sometimes used in conjunction with PVD to accelerate the deposition process or to improve the properties of the film. For coatings or films made by chemical vapor deposition (CVD), gas phase chemicals in an appropriate ratio inside a chamber are exposed to a solid surface at high temperature when the gaseous species strike the hot surface, they react to form the desired ceramic material. CVD-type reactions are also used to infiltrate porous substrates [chemical vapor infiltration (CVI)]. For some applications, the CVD reactions take place in a plasma environment to improve the deposition rate or the film properties. 

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. 

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. 

Zhang, S., Zhang, X., 2012. Toughness evaluation of hard coatings and thin films. Thin Solid Films 520, 2375-2389. 

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. 

Azofeifa, D. E., Clark, N., Amador, A. and Saenz, A. Determination of Hydrogen Absorption in Pd Coated A1 Thin Films, Thin Solid Films, Vol. 300,1997, pp. 295-8. 

---