Polar faces

Various investigations into the epitaxial deposition of CdS onto different singlecrystal substrates have been carried out by Lincot et al. On InP, which is closely lattice matched to CdS (<0.1% difference), epitaxial deposition (c-axis of hexagonal CdS perpendicular to the substrate) occurs on the (111) P polar face of the InP but polycrystalline deposition on the (111) In face [49,56]. This difference was clearly due to differing chemical or electrostatic interaction between the InP faces... 

CoO(lll) O-terminated polar face of NaCl structure top layer contraction -5% [-15%] DLEED 96)... 

In the smectic phases of the amphiphilic series, although the hydrocarbon chains themselves have a liquid arrangement, a degree of ordering of the polar ends of the molecules (-CH2X) on the polar face of the micelles is possible. This ordering would be expected to vary with tern-... 

The ability of the series to induce beta-galactosidase transgene expression in COS-7 cells was measured and compared with Lipofectin (quaternary ammonium salt lipid). The transfection activity of the bile acid conjugates ranged from low (38%) in product 2c to 1000% in product 4c, as compared to Lipofectin , which was ranked as 100%. The in vitro success of these unusual cationic facial amphiphiles is inspiring for the development of more efficient chemical methods based on tissue/cell targeting enabled by the polar face of the amphiphile. 

In nature, polypeptides with amphiphilic structures are known to form transmembrane channels formed by an assembly of several helices, so as to present their polar faces inward and their apolar faces outward. In view of such behavior, the photochromic amphiphilic polypeptide was incorporated into a cationic bilayer membrane composed of dipalmitoyl phosphatidyl choline.11201 Fluorescence and microscopic measurements provided evidence that the polypeptide was able to form bundles of helical molecules analogous to their natural counterparts, which acted as transmembrane channels for K+ ions. Irradiation, and the consequent transacts isomerization of the azobenzene link, caused a bending of the molecular structure and a destabilization of the transmembrane bundles. Therefore, formation of ion permeable channels would be favored or inhibited depending on whether the azo moiety... 

A switching electrode having nanometer dimensions leads to profound difference in poling of fe thin films and fe bulk crystals. In the case of fe thin films with a thickness of about 100 nm, a voltage application between the bottom electrode and an afm tip of 50-100 nm radius forms a quasi-homogeneous electric field. Such a distribution implies a conventional polarization reversal setup as in the case of uniform switching electrodes applied to polar faces of a fe sample. 

New promising technologies for future electron-beam lithography applications based on pyroelectrically induced electron emission from LiNbOs ferroelectrics [22] were recently proposed [23], The developed system possessing micrometer scale resolution used 1 1 electron beam projection. The needed electron pattern was obtained by means of deposited micrometer-size Ti-spots on the polar face of LiNbOs. Another solution for the high resolution electron lithography may be found in nanodomain patterning of a ferroelectric template. 

The classical experimental setup developed for fe polarization reversal implies a singledomain fe sample sandwiched between two electrodes [28], While conventional domain inversion techniques use equal sized electrodes covering the polar faces of fe templates, nanodomain inversion occurs under totally different conditions when the bottom electrode is a uniform plate and the upper one is a point contact. Two different kinds of the upper switching mobile nanoelectrodes may be considered afm tip (and/or array of tips) and electron drop formed using electron beam exposure. When a voltage stress is applied to the nanoelectrode, both the electric field intensity and its spatial distribution strongly differ in fe thin films (thin fe crystals) and bulk fe crystals. 

A variety of studies have suggested that in the presence of lipid, the apoprotein components of lipoproteins assume regions of high helical content which exhibit two faces of opposite polarity. When these proteins are on the surface of a lipoprotein particle, the nonpolar face can interact with the nonpolar lipid components of the particle, whereas the polar face interacts with the polar head groups of cholesterol and phospholipid, and the aqueous environment of the bloodstream (Fig. 2). 

If an ionic crystal has two opposite polar faces, then, in order for the total crystal to be charge neutral, the two opposing faces must be of opposite types. This effect can readily be observed macroscopically a well known case is ZnO. ZnO has a tetrahedrally coordinated wurtzite crystal structure in the [0001] direction, it consists of alternating planes of Zn and O ions [1]. When a sample... 

ZnO adopts the wurtzite structure in which Zn and O are both tetrahedrally coordinated to their counter ions. The 0-terminated (000 1) and Zn-terminated (0001) basal faces, as well as the non-polar (1010) prism face have all been the subject of adsorbate structure determinations. As regards their clean structures, LEED-IV was utilised as a probe over twenty years ago [117,118], and very recently they have been reexamined with SXRD [119-121]. From these measurements it was found that neither polar face relaxes greatly, a feature ascribed to surface enhanced covalency [121], For the (1010) face, SXRD [120] indicates only small displacements of the surface Zn and O away from their bulk terminated positions. 

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