Vapour phase growth

Whiskers are normally obtained by vapour phase growth. They are monocrystalline, short fibres with extremely high strength because of their high aspect ratio (50 to 10 000). They have a diameter of a few microns, but they do not have uniform dimensions and properties. 

Vapour phase growth techniques have been reviewed by Faktor and Garrett (1974), Pamplin (1980), Hurle (1993) and Krabbes (1995). 

A single erystal of Ceo was grown on a CNT by vapour phase growth, as shown in Fig. 14.8. The CNTs and Ceo powders were placed separately at the opposite ends of an evacuated and sealed quartz tube and heated in a temperature gradient (873-723 K). 

The process of sintering by vapour phase transport is probably important to the growth of single crystals of solids from polycrystalline samples in a closed system, where the vapour species are the transporting gas, which may have the same or different chemical composition from die solid. An example where... 

This is the Wilson-Frenkel rate. With that rate an individual kink moves along a step by adsorbing more atoms from the vapour phase than desorbing. The growth rate of the step is then simply obtained as a multiple of Zd vF and the kink density. For small A/i the exponential function can be hnearized so that the step on a crystal surface follows a linear growth law... 

Although crystals can be grown from the liquid phase—either a solution or a melt—and also from the vapour phase, a degree of supersaturation, which depends on the characteristics of the system, is essential in all cases for crystal formation or growth to take place. Some solutes are readily deposited from a cooled solution whereas others crystallise only after removal of solvent. The addition of a substance to a system in order to alter equilibrium conditions is often used in precipitation processes where supersaturation is sometimes achieved by chemical reaction between two or more substances and one of the reaction products is precipitated. 

Condensation is generally a transient operation in which, as discussed by Ueda and Takashima(106), simultaneous heat and mass transfer are further complicated by the effects of spontaneous condensation in the bulk gaseous phase. After the creation of supersaturation in the vapour phase, nucleation normally occurs which may be homogeneous in special circumstances, but more usually heterogeneous. This process is followed by both crystal growth and agglomeration which lead to the formation of the final crystal product. As a rate process, the condensation of solids from vapours is less well understood than vaporisation(98). Strickland-Constable(107) has described a simple laboratory technique... 

The mechanism of growth of the films may be modelled by considering that the vapour phase transported to the substrate initially condenses in an amorphous state... 

Thin-film growth from 2D to 3D character vapour phase... 

The height and growth rate from the vapour phase are assumed to be identical for both amorphous and crystalline phases. Taking into account only the in-plane radial growth resulting from the lateral incorporation of amorphous material, the number dA of molecules incorporated into the crystalline spheruhte contained in a volume dV is Qr 2n Rh t) dR, where dR represents the increase of the radius and... 

The device may be formed by depositing alternating layers of cadmium telluride and mercury telluride by vapour phase deposition techniques and interdiffuse the layers, either during growth or subsequently, so as to form a mercury cadmium telluride layer. Reference is made to GB-A-2146663 (The Secretary of State for Defence, GB, 24.04.85) and GB-A-2203757 (Philips Electronic and Associated Industries Limited, GB, 26.10.88). 

Jones, A. C. (1993). Metalorganic precursors for vapour phase epitaxy, J. Crystal Growth 129, 728-773. 

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