Theoretical Studies of Nucleation and Growth

To study the nucleation and growth of Au nanoclusters in silica within the above theoretical frame, we implanted fused silica slides with 190keV-energy Au ions, at room temperature and current densities lower than 2 pA/cm, to reduce sample heating [49,50]. The implantation conditions were chosen to have, after annealing, a subsurface buried layer of Au nanoparticle precipitation of about... 

Three reactions occur when a Ti02-opacified porcelain enamel frit is fired crystallization of anatase, crystalllization of rutile, and inversion of anatase to rutile. The concepts of nucleation and growth theory have been applied to these three reactions to develop an overall kinetic law of transformation which predicts the concentrations of anatase and of rutile as function of the firing conditions. This theoretical development has been found to agree with the results of quantitative X-ray studies. 

The resistance to nucleation is associated with the surface energy of forming small clusters. Once beyond a critical size, the growth proceeds with the considerable driving force due to the supersaturation or subcooling. It is the definition of this critical nucleus size that has consumed much theoretical and experimental research. We present a brief description of the classic nucleation theory along with some examples of crystal nucleation and growth studies. 

Interest in the crucial processes of nucleation and the growth of solids from fluid phases has a long and multidisciplinary history [50-53]. This research topic involves chemistry, chemical physics, material science, chemical engineering and physics, and, as a consequence, both theoretical and experimental studies were carried out by specialists in these fields. Thus, the following discussion does not pretend to be an exhaustive literature coverage of what is known about nucleation and growth, but rather, through recent articles, tries to review contributions especially relevant to controlled chemical vapour deposition of nanoparticles, always from a multidisciplinary point of view. 

Most nucleation studies of CD have treated either the hydroxide or hydroxide-complex mechanisms (see later) or have not clearly defined which mechanism was, indeed, operative under the conditions of the experiments. Due to the paucity of dependable experimental data, therefore, we consider nucleation and growth by the ion-by-ion mechanism, to a large extent, from a theoretical viewpoint. 

The kinetics and mechanisms of 3D Me deposition have been intensively studied by electrochemical impedance spectroscopy (EIS) as well as classical electrochemical techniques during the last two decades. Different simplified models of 2D nucleation and growth were theoretically treated in terms of their impedance behavior by Armstrong and Metcalfe [6.72] and Eppelboin et al. [6.73]. Later, a more realistic model of a partially blocked electrode surface was developed and analyzed by Schmidt, Lorenz et al. [6.75-6.78]. 

Recently, nucleation and growth processes taking place in the initial stages of electrodeposition of alloys were studied theoretically and experimentally by Milchev and Lacmann [6.141-6.143]. 

In theoretical studies on diamond nucleation, thermodynamic theory, homogeneous and heterogeneous chemical kinetics, classical nucleation theory, adsorption-desorption kinetics and equilibrium have been considered to predict preferential conditions for diamond nucleation and growth. A narrow range of conditions, such as pressure (supersaturation), temperature,... 

Theoretical calculations and experimental studies [28] suggested that smaller, colloidal diamond particles of about lOnm may be stable at lower pressures and higher temperatures than macroscopic diamond. A so called crystallite size effect [29] might account for metastable diamond nucleation and growth under hydro-thermal conditions. Thus, the HPHT graphite-diamond equilibriiun should only be applied to crystallites >100nm in diameter [28]. 

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