Growth direction

Grain size in textured films. For films having a preferred growth direction—e.g., (111)—LEED can be used to determine the preferred direction and the grain size parallel to the surfrce. The preferred direction is obtained from the symmetry of the diffraction patterns, while the grain size is obtained from the shape in angle of diffracted beams. 

More recent extensions of the theory (see citations in [122]) gave indications that the orientation of the lamellae (under isotropic material parameters) is not necessarily parallel to the growth direction of the front but may be tilted so that the lamellae travel sideways at some specific angles [138]. Finally it was found that the standard model of eutectic solidification has an intrinsic scaling structure [141-147]... 

Table 1. Growth Rate and Growth Direction OF Some Rare-Earth Tetraborides...

Another way to obtain a seed is to dip a capillary tube into the melt. Surface tension causes the tube to fill and when it freezes inside, a smcdl seed results. The difficulty with this method is that it is difficult to obtain a tube of proper diameter, made of the proper material. Glass softens at too low a temperature and quartz melts around 1400-1500 °C. Usually, we are restricted to metals and even then, we must be able to cut the tube to obtain the seed, since it is confined within the tube. Once in a while, we can use the tube directly and obtain growth directly upon the seed, even though it has remained within the tube. 

The growth direction of MgCl2 is independent of the substrate symmetry [93]. Growth on a cubic crystal, namely Pd(lOO), leads to hexagonal LEED pattern. However, the structure of the films is much more complex due to the... 

FIG. 20-24 High -resolution TEM image of Si nanowires produced at 500 C and 24.1 MPa in supercritical hexane from gold seed crystals. Inset Electron diffraction pattern indexed for the <111> zone axis of Si indicates <110> growth direction. [Reprinted with permission from Lu et al. Nano Lett., 3(1), 93-99 (2003). Copyright 2003 American Chemical Society. ]... 

Growth direction along <100> on different types of Si identified14 I... 

SAXS is sensitive to variations in the electronic density in a material, and so provides information about the shape and size of clusters in micro PS. In contrast to the quantum wire structure proposed in early publications [Cal, Lei], the crystallites in micro PS are found to be almost spherical. There has been some evidence that the dimensions in the growth direction are somewhat smaller than those parallel to the surface [Fr2], The latter result, however, is still controversial because investigations by spectroscopic techniques indicate an opposite elongation [Mi4], A combination of grazing incidence diffraction (GID) and SAXS measurements on various freestanding micro PS films showed crystallite diameters from about 1.5 to 4 nm, depending on formation conditions. A good correlation between size reduction and blue shift of the PL peak position has been observed [Bi3],... 

A certain anisotropy of the refractive index along specific crystallographic axes indicates that the microstructures in the porous network are not spherical but somewhat elongated along the PS growth direction [Mi4], This birefringence is below 1% for micro PS, while it may reach values in the order of 10% for meso PS films formed on (110) oriented silicon wafers [Ko22]. 

Fig. 9.12 By an i ncrease in bias or doping density the round (a) or slightly faceted (b) cross-section of macropores becomes starshaped by branching (c, d) or spiking (e) along the (100) directions orthogonal to the growth direction, (f) The current density distribution at a pore tip. (g) SEM micrograph...

Fig. 9.14 While the preferred macropore growth direction on a (322) substrate is still (100), it becomes (113) for (111) substrates (4% HF, 5.6 mAcm"2, 4 12 cm n-type Si). After [Ro8].

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