Sheet-like layers

Crystalline silicon is the most widely used semiconductor material today, with a maiket share of above 90%. Because of its indirect electronic band structure, however, the material is not able to emit light effectively and therefore carmot be used for key applications like light-emitting diodes or lasers. Selected one- or two-dimensional silicon compounds like linear or branched polysilylenes [1] or layered structures like siloxene [2], however, possess a direct band gap and therefore exhibit intense visible photoluminescence. Siloxene, a solid-state polymer with a sheet-like layered structure and an empirical formula Si H (OH) , in particular, is considered as an alternative material for Si-based liuninescent devices. Detailed studies of stmctural and photophysical properties of the material, however, are strraigly impeded by its insolubility in organic solvents. 

Cell Adhesion and Detachment, Figure 6 Cell detachment using the thermally responsive polymer PNIPAM. A surface coated with the polymer is seeded with human keratinocytes cells which form a sheet-like layer at 37° C (a). When the temperature is lowered to 20°C, the cells are released from fhe surface (b) as a sheet Taken from [9]... 

Nanoclays have sheet-like (layered silicate) structure with high-aspect ratios (between 100 1 and 1500 1) and with at least one dimension of the particle in the nanometer range. Nanoclays are generally hydrophilic and therefore incompatible with a wide range of polymers. The prerequisite for successful formation of polymer/clay nanocomposites is therefore alteration of the clay polarity to make the clay organophilic. Once the nanoclays are purified and chemically surface-treated so that the clay... 

These considerations lead us to the conclusion that the structure of the boundary layer is neither of the parallel unimolecular sheet type suggested by Helmholtz nor diffuse as postulated by Gouy. Since the ions close to the surface do not actually fall into the surface it is clear that part of the boundary layer must be regarded as sheet-like in character whilst the following simple calculation shows that part must also be diffuse. At a negatively charged. M... 

Figure 8 Atomic displacements in the M-O (M = La, Bi, Tl, Pb) rock salt-like layers of the copper-based superconductors. The view is perpendicular to the MO sheet. (A) Ladder-like arrangement of M and O atoms observed in orthorhombic La2Cu04, Bi2Sr2Can.1Cun 02n+4, and Tl2Ba2Cu06. (B) and (C) Atomic arrangement of Bi and O atoms as islands and chains that form when the atoms are displaced from the mirror positions shown in (A) (see text).

Eggleston and Bailey (1967) published a study on dioctahedral chlorite and gave five examples of chlorites having a pyrophyllite-like layer and a brucite-like sheet (designated di/trioctahedral by the authors with the trioctahedral sheet including all species of chlorite with 5 to 6 octahedral cations per formula unit and dioctahedral 4 to 5 octahedral cations per formula unit). Identification of di/trioctahedral chlorites is indirectly accomplished. Eggleston and Bailey stated that identification depends on the intermediate value of c (060), on chemical analysis of impure material, and on the ideal compositions of the recrystallization products of static heating . The composition of one such chlorite for which they refined the structure is ... 

Another group of materials that has displayed high oxide ion conductivity is based upon a layered bismuth perovskite-based structure, first reported by Aurivillius in 1949 [90-92], The so-called Aurivillius phases are chemically expressed normally as Bi2A B 03 +3 [82], where A is a large 12-coordinated cation and B a small 6-coordinated cation. The structure is formed by n perovskite-like layers, (A 1B 03n+1)2, sandwiched between bismuth-oxygen fluorite-type sheets, (Bi/) 2 [93,94],... 

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