Vapor Phase Nanoparticle Synthesis

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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The approaches used for preparation of inorganic nanomaterials can be divided into two broad categories solution-phase colloidal synthesis and gas-phase synthesis. Metal and semiconductor nanoparticles are usually synthesized via solution-phase colloidal techniques,4,913 whereas high-temperature gas-phase processes like chemical vapor deposition (CVD), pulsed laser deposition (PLD), and vapor transfer are widely used for synthesis of high-quality semiconductor nanowires and carbon nanotubes.6,7 Such division reflects only the current research bias, as promising routes to metallic nanoparticles are also available based on vapor condensation14 and colloidal syntheses of high-quality semiconductor nanowires.15... 

Flagan RC, Lunden MM (2004) Particle structure control in nanoparticle synthesis from the vapor phase. 204 113-124... 

There are various nanoparticle production methods reported. Most common approaches include solid-state methods (grinding and milling), vapor methods (physical vapor deposition and chemical vapor deposition), chemical synthesis/ solution methods (sol-gel approach and colloidal chemistry), and gas-phase synthesis methods [1]. Chemical approaches are the most popular methods for the production of nanoparticles. Other novel production methods include microwave techniques, a supercritical fluid precipitation process, and biological techniques. 

Production of preformed nanoparticles in the gas phase Several methods have been found to produce gas-phase nanoparticles. However, they all involve the production of a supersaturated metal vapor that condenses into particles. This method is the most flexible technique for the synthesis of metal nanoparticles and it is the way to produce tightly mass-selected nanoparticles of virtually any material or alloy in environments ranging from free particles... 

Swihart, M. T. Vapor-phase synthesis of nanoparticles. Cuirent Opinion in Colloid... 

Nanoparticle synthesis takes place in the following phases Liquid-phase synthesis and vapor-phase synthesis. 

Ghiaci M, Aghaei H, Abbaspur A. Size-controlled synthesis of Zr02-Ti02 nanoparticles prepared via reverse micelle method investigation of particle size effect on the catalytic performance in vapor phase Beckmann learrangemenL Mater Res Bull 2008 43(5) 1255-62. 

Yang Y, Saoud KM, Abdelsayed V, Glaspell G, Deevi S, El-ShaU MS (2006) Vapor phase synthesis of supported Pd, Au, and unsupported bimetaUic nanoparticle catalysts for CO oxidation. Catal Commun 7 281-284... 

Nanocomposites of conducting polymers exhibit improved physicochemical and biological properties as compared to their individual counterparts. The integration of secondary component within conducting polymer leads to dramatic increase in different properties that are useful from an application point of view. Size, shape and controlled distribution of the dispersed phase are the critical factors to control the desired properties of a nanocomposite. Different approaches such as in situ synthesis, one-pot synthesis, electrochemical polymerization and vapor-phase polymerization have been employed to synthesize the nanocomposites of conducting polymers with metal or metal oxide nanoparticles, carbon-based materials, ternary nanocomposites, etc. All of these methods have certain advantages and drawbacks. Functional nanocomposites synthesized by these methods display many... 

The formation of semiconductor nanoparticles and related stmctures exhibiting quantum confinement within LB films has been pmsued vigorously. In 1986, the use of the metal ions in LB films as reactants for the synthesis of nanoscale phases of materials was described [167]. Silver particles, 1-2 mn in size, were produced by the treatment of silver be-henate LB films with hydrazine vapor. The reaction of LB films of metal salts (Cd, Ag, Cu, Zn, Ni, and Pb ) of behenic acid with H2S was mentioned. The use of HCl, HBr, or HI was noted as a route to metal halide particles. In 1988, nanoparticles of CdS in the Q-state size range (below 5 mn) were prepared inside LB films of cadmium arachi-... 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

The physical process alters the physical properties of particles such as size, shape, and the phases of matter. Mechanical grinding and vapor condensation of matter in the form of nanoparticles are examples of physical methods of synthesis. 

In this process, the precursor is vaporized and deposited in a vacuum chamber. The synthesis was carried out at pressure of 1 mtorr retaining the vacuum level at 10-0. IMPa with temperature ranging from room temperature to 500°C. Vapour phase nucleation takes place in dense cloud vapour by collision. The atoms are passed through a gas to provide necessary collision and cooling for the nucleation. It is economical and the deposition rate is high. In this process, the decomposition of the precursor is sometimes difficult. The nanoparticles obtained from a supersaturated vapour are usually longer than the cluster. 

Techniques for the preparation of metal cluster/nanoparticles can be classified into three primary categories condensed phase, gas phase, and vacuum methods. In condensed phase synthesis, metal and semiconductor nanoparticles are prepared by means of chemical synthesis, which is also known as wet chemical preparation. In gas phase synthesis, metal is vaporized, and the vaporized atoms are condensed in the presence or absence of an inert gas. In vacuum methods, the metal of interest is vaporized with high-energy Ar, Kr ions, or laser beams in a vacuum, and thus generated metal vapor is deposited on a support. 

Moseley PT, Norris JOW, Williams DE (1991) Techniques and mechanisms in gas sensing. Adam Hilger, Bristol Nakaso K, Han B, Ahn KH, Choi M, Okuyama K (2003) Synthesis of non-agglomerated nanoparticles by an electrospray assisted chemical vapor deposition (ES-CVD) method. J Aerosol Sci 34 869-881 Narendar Y, Messing GL (1997) Mechanisms of phase separation in gel-based synthesis of multicomponent metal oxides. Catal Today 35 247-268... 

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