Vapor processing methods seem to be the only ones that can provide highly pure materials with structural control at the atomic level or nanometer scale . Moreover, vapor processing routs can produce ultra-fine powders, multilayers, and functionally graded materials, as well as composite materials with well-controlled dimensions and unique structures at a lower processing temperature. Vapor processing techniques used for fabrication of nanophase materials can be classified into physical vapor deposition (PVD), chemical vapor deposition (CVD), and aerosol-based processes and flame-assisted deposition methods [36, 37]. The first two have been widely applied for preparation of nanostructured films. PVD can be subdivided into evaporation, sputtering, and ion-plating processes based on the different ways of generating the gaseous species (Fig. 1). The classification of CVD processes based on the different heating methods can be as follows: (1) thermally activated, (2) photo-assisted, (3) plasma-assisted, (4) metalorganic, and (5) atomic layer epitaxy (Fig. 1).
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