Growth from vapor

The basic criteria to consider in crystal growth from vapor, solution, and melt phases are therefore whether the phase is condensed or dilute, and whether the phase involves a solute-solvent interaction or not. 

Melt draw Pyrolysis Vapor deposition Growth from melt Growth from vapor... 

Large entropy change produces smooth surfaces and faceted interfaces. Examples are growth of silicates from the melt and the growth from vapor or dilute solutions. 

Recent developments in the application of molecular dynamics promise a resolution of many questions in nucleation theory. A review of simulation methods in nucleation theory and of their results is given in [2.39]. Consequently, a survey will not be undertaken here. However, some of the results of SCHIEVE and co-workers [2.40-42] will be discussed here as they throw light on several questions of importance in terms of modelling aerosol growth from vapor condensation. 

For crystal growth from the vapor phase, one better chooses the transition probability appropriate to the physical situation. The adsorption occurs ballistically with its rate dependent only on the chemical potential difference Aj.1, while the desorption rate contains all the information of local conformation on the surface [35,48]. As long as the system is close to equilibrium, the specific choice of the transition probability is not of crucial importance. 

V. Chirita, E. P. Munger, J.-E. Sundgren, J. E. Greene. Enhanced cluster mobilities on Pt(lll) during film growth from the vapor phase. Appl Phys Lett 72 127, 1998. 

Fig. 2.2 Bottom-up synthesis methods, (a) Catalytic vapor deposition (b) epitaxial growth from SiC.

In contrast to solid state crystallization, crystallization from vapor, solution, and melt phases, which correspond to ambient phases having random structures, may be further classified into condensed and dilute phases. Vapor and solution phases are dilute phases, in which the condensation process of mass transfer plays an essential role in crystal growth. In the condensed melt phase, however, heat transfer plays the essential role. In addition to heat and mass transfer, an additional factor, solute-solvent interaction, should be taken into account. 

In Fig. 12.4 the velocity of crystal growth from the vapor is plotted as a function of the excess vapor pressure (P — Peq). When the surface acts as an ideal sink for incoming vapor atoms, the plot indicates that the velocity of growth should vary linearly with (P - Peq). When the sink efficiency is lower, the curve of v vs. (P - Peq) falls below the ideal curve. Use the results of Exercise 12.1 to demonstrate that the velocity of growth for the model employed there can be expressed in the form... 

One aspect of crystal growth from the vapor is the diffusive transport of adatoms to ledges (see Exercise 12.1). A suggestion is that the motion of ledges can be ignored in the analysis of crystal growth if... 

Crystal growth from the vapor phase has been treated in Chapter 12. An expression for the net atom flux, Jv, gained at a macroscopically flat crystal surface during growth from the vapor has been obtained in Exercise 12.2 in the form of Eq. 12.27. To treat surfaces possessing nonuniform curvature, this relationship can be generalized in the form... 

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