Crystal plate stacks

Fig. 11.1 Examples of initial crystallization hits from a single on-chip screening experiment of a type II topoisomerase ATPase do-main/ADP, 12mgmL b (A) Irregular spherulite. (B) Phase separation and spherulites with nucleating microcrystals. (C) Thin plate clusters. (D) Thick plate stacks. (E) Well-formed microcrystals. (F) Large single crystals. All scale bars are 100 pm.

Another layered structure has been determined [343] on Ag3TlTe2 which, from its formula, might be a normal valence compound with monovalent cations. Its orthorhombic cell can be built up from layer packs Ag—Te—(Ag + Tl)—Te—Ag. These AgaTlTe2 units are stacked in such a way that the atoms of the two contacting Ag layers form zig-zag chains in [100] direction with a rather short Ag—Ag distance of 3.05 A which seems to indicate bonding between the layer units. For Ag ions (ionic radius 1.26 A) such an Ag—Ag distance would not be critical. However, if the outer Ag atoms of each layer unit really were ionized we would rather expect that adjacent units would shift by b/2 in order to increase the Ag—Ag distance. Anyway, on vapor-depositing the AgaTlTe2 films onto NaCl crystals, plate-like textures always formed. 

A crystal of kaolinite is made of a series of these double layers or sheets stacked parallel to each other and form small flat plates that are typically less than 1 pim in diameter and nearly hexagonal. Figure 12.15 is an electron micrograph of kaolinite crystals at a high magnification, showing the hexagonal crystal plates, some of which are piled one on top of the other. 

A beam from an actual sample will require a more elaborate slit S3rstem for collimation if the sample is broad. The Soller slit (Figure 4-7), a stack of thin parallel plates, is such a system. The reasoning that supports this construction is as follows. Were the sample a point or a line source, a slit between sample and crystal or a slit between crystal and detector would be enough for satisfactory collimation. With a two-dimensional sample, both slits would be needed to get this done. But this arrangement is wasteful of emitted intensity because the detector sees the sample as a line source. To use all the sample area effectively, a system of parallel slits is needed. To eliminate the divergent rays in such a system, the slits must be extended in the direction of the beam, and this leads to the parallel-plate construction in the Seller slit system. 

The CgQ surface coverage was determined to be 2.0 10 mol cm . The monolayer can be further modified with monomeric amine reagents, which demonstrates the potential of the self-assembly process for growing three-dimensional fullerene structures. Different surfaces such as quartz. Si-oxide [105] or ITO [102] were coated with multilayers of fullerene up to stacks of 9 layers. An imidirectional electron transfer is possible across the fullerene mulhlayers [102]. Not only can multiple layers of fullerenes be connected to a certain surface but amino-functionalized can also serve as a linker between two different surfaces. 3-Aminopropyl-tethered glass plates could be linked via a Cgg layer to 3-aminopropyl covered zeolite crystals [106]. 

This wax structure is the most common and consists primarily of linear n-paraffin molecules. The linearity of the wax molecules enables the wax to accumulate to form a uniform crystal lattice. The wax molecules actually stack together into a geometric form resembling a flat plate. 

These wax formations are not as symmetrical as plate crystals. Mal-shaped wax is composed of both linear and branched paraffin molecules. The branched paraffin molecules change the confirmation of the wax so that stacking and alignment typical in plate wax formation does not occur. The result is a wax crystal which is smaller than plate crystal wax. The temperature at which mal-shaped wax forms is also lower than plate crystal formation temperature. 

In crystals that are formed from small molecules, it is often found that large, flat molecules stack together like a pile of plates or saucers. This stacking imposes considerable order and can generate unusual optical or electrical properties. 

These minerals have different stacking of the silica and alumina layers, as well as, incorporating metal hydrates of Na, K, Mg, Al, or Fe between the silica and alumina layers. Clay minerals can also be characterized according to their morphological features including crystal habit (i.e., plates, rods, or rolled-up platelets) stacked in either a house of cards or blocklike aggregates giving a partide-size distribution. 

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