Monocrystalline orientation

Crystals growing on a substrate may be oriented every which way that is, the direction axes of individual crystallites can be randomly distributed. However, where one particular axis is oriented or fixed in nearly one direction, we speak about a single texture. When two axes are thus fixed or oriented, we speak about double texture. Monocrystalline orientation refers to a scenario in which there are three such nearly oriented axes, including epitaxial films. Orientation here is viewed with respect to any fixed (in space) frame of reference. Crystal planes and directions are illustrated in Figure 16.5. A brief discussion of the enumeration of these elements follows. 

Another recently discovered form of epitaxy is graphoepitaxy (Geis et al. 1979). Here a non-crystalline substrate (often the heat-resistant polymer polyi-mide, with or without a very thin metallic coating) is scored with grooves or pyramidal depressions the crystalline film deposited on such a substrate can have a sharp texture induced by the geometrical patterns. More recently, this has been tried out as an inexpensive way (because there is no need for a monocrystalline substrate) of preparing oriented ZnS films for electroluminescent devices (Kanata et al. 1988). 

The experimental studies of the surface properties of monocrystals of oxides of various metals recently conducted at well-controlled conditions [32, 210] enable one to proceed with detailed analysis of separate effects of various factors on characteristics of semiconductor gas sensors. In this direction numerous interesting results have been obtained regarding the fact of various electrophysical characteristics of monocrystalline adsorbents on the value of adsorption-related response. Among these characteristics there are crystallographic orientation of facets [211], availability of structural defects, the disorder in stoichiometry [32], application of metal additives, etc. These results are very useful while manufacturing sensors for specific gases with required characteristics. 

From measurement results, it is possible to identify polycrystalline materials from their structure, texture, porosity, monocrystalline materials on crystallographic orientation and glass, considering the heterogeneity of the vitreous phase. 

Wet chemical anisotropic etching of monocrystalline silicon has been widely applied in microtechnology (18,20). This method is based on the dependence of etching velocity on crystal orientation, so only a few basic geometries can be... 

The predominance of van der Waals interactions at solid metal/A1203 interfaces is also shown by the fact that whatever the orientation of monocrystalline AI2O3 surface, Cu particles are orientated with (111) faces parallel to the A1203 surface (Soper et al. 1996). This orientation maximises the number of metal atoms per unit area in nearest-neighbour interactions with A1203. A similar behaviour was found for non-reactive fee metals on carbon substrates i.e., for systems with predominant van der Waals interfacial interactions (Section 8.1). 

Rarely do all the grains comprising a polycrystal have the same size, orientation, or even shape. In fact, polycrystalline grains are morphologically dissimilar to their monocrystalline counterparts. 

It is noted that the polishing of the polysilicon film will employ the well-known technology of polishing monocrystalline silicon substrates. This gives an opportunity to examine the effect of polycrystallinity and thus of grain boundaries and grain orientation in CMP of Si. Doped vs. undoped polysilicon will also shed... 

Table 4.9 summarises our findings for the growth of metal particles on the two major type of ceria surfaces, (111) and (001). Results are identical for Rh and Pt catalysts. Moreover, the orientation relationships described in this table do hold for reduction temperatures in the range 473 K - 1173 K, whenever the supported particles remain metallic type and monocrystalline. As we will describe further, in the case of platinum catalysts, a transformation of the metallic particles into an intermetallic phase takes place at 1173 K. Though in this case specific orientation relationships have also been observed with respect to the support, their characteristics differ from those related in Table 4.9. 

Because of a preferential binding to a single face of clusters, some surfactants are known (CTAB, cetylmethyl ammonium bromide, for example) to drive the growth of metal nanocrystals unidirectionally.Single monocrystalline Pt nanorods, monodisperse in diameter (3-4 nm) and 20-40 nm long, were recently obtained by orientated coalescence of spherical seeds of 3-4 nm radiolytically produced in the presence of CTAB surfactant [10] (Fig. 3g). 

Let us consider a monocrystalline sample that contains chemically identical spin-1 nuclei. In our physical model it will be assumed that the quadrupole principal axes for each of the spins have the same orientation. The quadrupole Hamiltonian in the quadrupole principal axes frame is given as... 

Monocrystalline silicon samples (10x 10x0.28mm ) of (HI) and (100) crystallographic orientations were mounted at an axis of the system normally to compression flow at distances of 6-16 cm from the tip of MFC discharge device. The surface microrelief of the silicon samples was examined with high-resolution scamiing electron microscopy (SEM). 

A p-type, lO cm boron doped, (lOO)-oriented monocrystalline Si wafer was subjected to anosotropic chemical etching in 10% KOH at 80°C for 5-30 min to produce inverted 1.0-1.5 pm pyramids at the period of 1.5-2.0 pm. The pyramidal-film textured surface was transformed into a 1.5 pm thick PS layer by anodising in the aqueous 12% HF solution at the current density of 30 mA/cm. Phosphorus ions were implanted through the PS layer at 50 keV, 6-10 cm. A subsequent rapid thermal processing at 1000°C for 30 s formed shallow n -p jimction at the interface between the PS layer and the Si substrate. 

The trapping of polycyclic aromatic molecules in n-heptane monocrystalline matrices, prepared by slow cooling, leads to oriented molecules inside the paraffinic crystal lattice, and it appears that the trapping sites for coronene, perylene, and pyrene are similar to those observed earlier for quickly frozen solutions of coronene and designated pseudo-liquid sites and substitutional sites .28 From the former studies it seems that aggregation does not play a dominant role. A nitrogen-pumped laser has been used to excite perylene in n-octane at 4.2 in order to investigate non-linear dependence of fluorescence on excitation intensity in a Shpol skii system. The approximately square dependence of one of the vibronic emission lines on the excitation intensity is consistent with super-radiant emission.80... 

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