Crystallization orientation effects

M.F. Florstemeyer et al A large deformation atomistic study examining crystal orientation effects on the stress-strain relationship. Int. J. Plasticity 18, 203-209 (2002)... 

Crystal Orientation Effects. A study of the complete oxidation of ethylene has been carried out on the (100), (110), and (111) faces of a silver single crystal at 523—634 The rate of production of carbon dioxide was not dependent... 

Since the major limitation on depth resolution arises from the sputtering process itself and from the sputter-induced microtopography, many attempts have been made to minimize such effects. The main aim is to suppress both the crystal orientation effects and the increase in roughness by rotating the sample during sputtering, as suggested by Zalar. If that is done in the correct way, then the sputter crater can be produced with a flat bottom, in the center of which is the analyzed area (79, 80]. 

Face-centered cubic crystals of rare gases are a useful model system due to the simplicity of their interactions. Lattice sites are occupied by atoms interacting via a simple van der Waals potential with no orientation effects. The principal problem is to calculate the net energy of interaction across a plane, such as the one indicated by the dotted line in Fig. VII-4. In other words, as was the case with diamond, the surface energy at 0 K is essentially the excess potential energy of the molecules near the surface. 

Crystallization. Acidified aluminum sulfate solutions can be supercooled 10 °C or more below the saturation point. However, once nucleation begins, the crystallization rate is rapid and the supersaturated solution sets up. The onset of nucleation in a gentiy stirred supersaturated solution is marked by the appearance of silky, curling streamers of microscopic nuclei resulting from orientation effects of hydraulic currents on the thin, platelike crystals. Without agitation, nucleation in an acidified solution, in glass tubes, can yield extended crystalline membranes of such thinness to exhibit colors resulting from optical interference. 

Gupta [28] presents results on the effect of crystal orientation on shock propagation in LiF crystals. This work supports earlier studies and shows... 

SIMS, and SNMS in rare cases, such as for HgCdJTei samples or some polymers, the sample structure can be modified by the incident ion beam. These effects can often be eliminated or minimized by limitii the total number of particles incident on the sample, increasing the analytical area, or by cooling the sample. Also, if channeling of the ion beam occurs in a crystal sample, this must be included in the data analysis or serious inaccuracies can result. To avoid unwanted channelii, samples are often manipulated during the analysis to present an average or random crystal orientation. 

In Chapter 3 it was pointed out that certain rod-like polymers showed many of the attributes of liquid crystals in the melt. In particular, these molecules were oriented in shear to such an extent that interchain entanglement was small and the melts had a low viscosity. On cooling of the melt these rod-like molecules remained oriented, effectively self-reinforcing the polymer in the direction of flow. The essential differences in the properties of liquid crystal polymers... 

Yield Stress The effect of hydrogen on the yield stress of iron and steels is unpredictable. For very pure iron single crystals and polycrystals the yield stress is frequently found to be decreased by hydrogen, but it may increase or stay the same, depending on the dislocation structure, crystal orientation and purity of the iron . Little information is available for steels. 

The experimental data bearing on the question of the effect of different metals and different crystal orientations on the properties of the metal-electrolyte interface have been discussed by Hamelin et al.27 The results of capacitance measurements for seven sp metals (Ag, Au, Cu, Zn, Pb, Sn, and Bi) in aqueous electrolytes are reviewed. The potential of zero charge is derived from the maximum of the capacitance. Subtracting the diffuse-layer capacitance, one derives the inner-layer capacitance, which, when plotted against surface charge, shows a maximum close to qM = 0. This maximum, which is almost independent of crystal orientation, is explained in terms of the reorientation of water molecules adjacent to the metal surface. Interaction of different faces of metal with water, ions, and organic molecules inside the outer Helmholtz plane are discussed, as well as adsorption. 

The rate of an electrode reaction is a function of three principle types of species charge carriers on the surface, active surface atoms and reactant species in the solution as illustrated in Figure 23. That is, r cc [h] [Siactive] [A]. Carrier concentration and reactant concentration do not, in general, depend on surface orientation while active surface atoms may be a function of surface orientation. Anisotropic effect occurs when the rate determining step depends on the active surface atoms that vary with crystal orientation of the surface. On the other hand, reactions are isotropic when the concentration of active surface atoms is not a function of surface orientation or when the rate determining step does not involve active surface atoms. 

This effect might be interpreted by the Bethe dynamic potential approximation, which does not take into account the crystal orientation (as in the Blackman correction case) nor crystal thickness parameters. In terms of this approach, the effect of weak beams can be included in two-beam theory by replacing the potential coefficients, Vh, by ... 

We now assume that we have properly recorded rocking curves available, and that a substrate with a single epitaxial layer >0.5 //m thick (and less than, say, 5 m) is measured. This will result in two peaks, one each from the substrate and layer. The same analysis will apply to multiple peaks (other than those from superlattices) provided that they are well separated so that interference effects are minimised. The basic parameters are derived as follows, with the symmetric reflection used unless otherwise specified. The examples are given for (001) substrates and layers, but are quite general (with the caution that if the Poisson ratio is required, the value appropriate to the crystal orientation should strictly be used). 

The zeolite provides the environment for shape selective chemistry and is also a high surface area support on which to disperse platinum in a relatively confined environment. The small platinum crystals within the zeolite channels and the orientation effect of the channel window are responsible for the high efficiency of the Pt-KL catalyst to convert linear paraffin to aromatics. Zeolite KL also provides an electron rich environment to enhance stronger platinum-substrate interaction via stronger platinum-support interaction. A review on the subject can be found in the article written by Meriasdeau and Naccache [85]. 

Single crystals are of critical importance to the study of complex solids such as the new high temperature superconductors. Single crystals are free of grain boundary effects and allow measurements of physical properties as a function of crystal orientation. 

In bulk material, the resistivity is independent of crystal orientation because silicon is cubic. However, if the carriers are constrained to travel in a very thin sheet, eg, in an inversion layer, the mobility, and thus the resistivity, become anisotropic (18). Mobility is also sensitive to both hydrostatic pressure and uniaxial tension and compression, which gives rise to a substantial piezoresistive effect. Because of crystal symmetry, however, there is no piezoelectric effect. The resistivity gradually decreases as hydrostatic pressure is increased, and then abrupdy drops several orders of magnitude at ca 11 GPa (160,000 psi), where a phase transformation occurs and silicon becomes a metal (35). The longitudinal piezoresistive coefficient varies with the direction of stress, the impurity concentration, and the temperature. At about 25°C, given stress in a (100) direction and resistivities of a few hundredths of an O-cm, the coefficient values are 500—600 m2/N (50—60 cm2/dyn). 

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