Synthesis metal-organic chemical vapor deposition

For their rich potential in various applications described in the previous section, the synthesis and assembly of various ZnO micro and nanostructures have been extensively explored using both gas-phase and solution-based approaches. The most commonly used gas-phase growth approaches for synthesizing ZnO structures at the nanometer and micrometer scale include physical vapor deposition (40, 41), pulsed laser deposition (42), chemical vapor deposition (43), metal-organic chemical vapor deposition (44), vapor-liquid-solid epitaxial mechanisms (24, 28, 29, 45), and epitaxial electrodeposition (46). In solution-based synthesis approaches, growth methods such as hydrothermal decomposition processes (47, 48) and homogeneous precipitation of ZnO in aqueous solutions (49-51) were pursued. 

R. Tu, T. Kimura and T. Goto, Rapid Synthesis of Yttria-Partially-Stabilized Zirconia Films by Metal-Organic Chemical Vapor Deposition, Mater. Trans., 43, 2354-2356 (2002). 

Different fabrication methods such as the thermal evaporation [4], MOCVD (metal organic chemical vapor deposition) [5], laser ablation and wet chemical synthesis [6,7] have been reported for the preparation of ZnO nanoparticles and films. 

With the advent of sophisticated techniques such as molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MCXTVD), synthesis of heterostructure such as multiple quantum wells or superlattices with precise interface layer down to one monolayer have been routinely possible. This not only allows modulation of electronic properties such as carrier confinement and concentration profile, but also optical confinement and wave guiding properties with appropriate choice of refractive indices of the materials. Such precise controls over the growth and material properties have opened the field of band gap engineering . 

Similar to metal organics, organometallic compounds have a sufficient vapor pressure and stability at their evaporation temperatures to be useful as reactants in gas-phase synthesis such a chemical vapor deposition. Given the central metal atom, there are some design considerations for increasing the vapor pressure in complexes, which is helped by choosing the appropriate structure and ligands ... 

Similar to chemical vapor deposition, reactants or precursors for chemical vapor synthesis are volatile metal-organics, carbonyls, hydrides, chlorides, etc. delivered to the hot-wall reactor as a vapor. A typical laboratory reactor consists of a precursor delivery system, a reaction zone, a particle collector, and a pumping system. Modification of the precursor delivery system and the reaction zone allows synthesis of pure oxide, doped oxide, or multi-component nanoparticles. For example, copper nanoparticles can be prepared from copper acetylacetone complexes [70], while europium doped yttiria can be obtained from their organometallic precursors [71]. 

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