Interface growth

During the vapor deposition process, the polymer chain ends remain truly aUve, ceasing to grow only when they are so far from the growth interface that fresh monomer can no longer reach them. No specific termination chemistry is needed, although subsequent to the deposition, reaction with atmospheric oxygen, as well as other chemical conversions that alter the nature of the free-radical chain ends, is clearly supported experimentally. 

Another analogous situation is present during the crystallization of the solute phase from liquid metal solutions. This leads to the production of protuberances upon the growth interface, which gradually... 

A third type of problem, that is often mistakenly confused with dendrite formation, is due to the presence of a reaction-product layer upon the growth interface if the electrode and electrolyte are not stable in the presence of each other. This leads to filamentary or hairy growth, and the deposit often appears to have a spongy character. During a subsequent discharge step the filaments often become disconnected from the underlying metal, so that they cannot participate in the electrochemical reaction, and the rechargeable capacity of the electrode is reduced. 

Decomposition of a single solid J- Nucleation - Growth Interface phenomena. Geometric control... 

A vertical CVD reactor (cf. Figure lb) consists of an axlsymmetrlc enclosure with the deposition surface perpendicular to the Incoming gas stream. The reactant gases are typically Introduced at the top and fiow down towards the heated susceptor. Thus, the least dense gas Is closest to the growth Interface which destabilizes the fiow. The result Is recirculation cells which Introduce not only film thickness and composition variations but also broaden Junctions between layers. This Is particularly of... 

Equation (6.11) is valid for the initial particle growth. Interface control of the growth kinetics would lead to a linear rate law. Details can be found, for example, in [H. Schmalzried (1981)]. 

In spite of these theoretical results, dendritic-type forms for solid-state precipitation processes are the exception rather than the rule. This may happen because the theory is for pure diffusion-limited growth. Interface-limited growth tends to be stabilizing because the composition gradient close to a growing precipitate is less steep when the reaction is partly interface-limited. Thus, G is smaller, and Eq. 20.73 shows that this is a stabilizing effect. This and several other possible explanations for the paucity of observations for unstable growth forms in solid-state... 

The monomer is consumed by two chemical reactions initiation, in which new polymer molecules are generated, and propagation, in which existing polymer molecules me extended to higher molecular weight. In steady state VDP, both reactions proceed continuously inside polymeric coating, in the reaction zone just behind the growth interface. 

Convection in Melt Growth. Convection in the melt is pervasive in all terrestrial melt growth systems. Sources for flows include buoyancy-driven convection caused by the solute and temperature dependence of the density surface tension gradients along melt-fluid menisci forced convection introduced by the motion of solid surfaces, such as crucible and crystal rotation in the CZ and FZ systems and the motion of the melt induced by the solidification of material. These flows are important causes of the convection of heat and species and can have a dominant influence on the temperature field in the system and on solute incorporation into the crystal. Moreover, flow transitions from steady laminar, to time-periodic, chaotic, and turbulent motions cause temporal nonuniformities at the growth interface. These fluctuations in temperature and concentration can cause the melt-crystal interface to melt and resolidify and can lead to solute striations (25) and to the formation of microdefects, which will be described later. 

If the reactor flow is dominated by forced convection and free of laminar eddies, the same expression (equation 25) can be used to estimate the maximum separation between the mixing point and the growth interface. For a given mass flow, the Peclet number, Pe, is independent of pressure, whereas the linear velocity increases with decreasing pressure therefore, the maximum allowable length increases with the square of the decreasing pressure, and operation at reduced reactor pressures is advantageous when sharp interfaces are desired. 

The main purpose of using the cone is to block the thermal radiation from the melt to crystal, so that the crystal can be cooler and pulled faster. Such an idea can be easily understood from the energy balance at the growth interface ... 

Fig. 5.4. Model of parallel-twin formation during crystal growth from Si melt. The growth interface is faceted as shown in (a), when a twin boundary is accidentally formed on a 111 facet face, another twin boundary is formed parallel to the first twin after lateral growth is promoted (from (b) to (d)). The direction of growth of the faceted dendrite should be parallel to the 111 facet plane in this model [16]...

Aqueous solutions containing anionic surfactants and alcohol cosurfactants were contacted with various oils. A microscope which utilized a vertical sample orientation and a video camera was used to observe and record the resulting diffusional processes. As a result, an improved and detailed viewing of intermediate phase growth, interface motion, and spontaneous emulsification was achieved. 

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