Ferroelectric nanostructures are attracting tremendous interest because they offer a promising route to novel integrated electronic devices such as non-volatile memories and probe-based mass data storage. Here, we demonstrate that high-density arrays of nanostructures of a ferroelectric polymer can be easily fabricated by a simple nano-embossing protocol, with integration densities larger than 33 Gbits inch(-2). The orientation of the polarization axis, about which the dipole moment rotates, is simultaneously aligned in plane over the whole patterned region. Internal structural defects are significantly eliminated in the nanostructures. The improved crystal orientation and quality enable well-defined uniform switching behaviour from cell to cell. Each nanocell shows a narrow and almost ideal square-shaped hysteresis curve, with low energy losses and a coercive field of approximately 10 MV m(-1), well below previously reported bulk values. These results pave the way to the fabrication of soft plastic memories compatible with all-organic electronics and low-power information technology.

No abstract

The role of external ionic strength in diatom biosilica formation was assessed by monitoring the nanostructural changes in the biosilica of the two marine diatom species Thalassiosira punctigera and Thalassiosira weissflogii that was obtained from cultures grown at two distinct salinities. Using physicochemical methods, we found that at lower salinity the specific surface area, the fractal dimensions, and the size of mesopores present in the biosilica decreased. Diatom biosilica appears to be denser at the lower salinity that was applied. This phenomenon can be explained by assuming aggregation of smaller coalescing silica particles inside the silica deposition vesicle, which would be in line with principles in silica chemistry. Apparently, external ionic strength has an important effect on diatom biosilica formation, making it tempting to propose that uptake of silicic acid and other external ions may take place simultaneously. Uptake and transport of reactants in the proximity of the expanding silica deposition vesicle, by (macro)pinocytosis, are more likely than intracellular stabilization and transport of silica precursors at the high concentrations that are necessary for the formation of the siliceous frustule components.biosilica ͉ silica nanostructure ͉ silicification ͉ silica chemistry D iatoms are known for the intriguing species-specific morphology of their siliceous exoskeletons, the frustules (1, 2), which consist of two silica valves (the epi-and hypovalve), siliceous girdle bands, and a protective organic casing that prevents dissolution of the siliceous parts in the aquatic environment. During cell division, a parental diatom cell undergoes cytokinesis, and each of the next two daughter cells produces a new hypovalve, a hypocingulum, and girdle band(s); the sequence of their formation differs among species (1, 2). After valve and girdle band completion, the daughter cells finally separate, and cell division continues. The silica of every new valve is formed in the silica deposition vesicle (SDV) that is located inside each daughter cell and is closely appressed to the plasma membrane along the cleavage furrow. The SDV rapidly expands two-dimensionally and subsequently thickens more slowly in the three-dimensional direction during formation of the new hypovalve (3, 4). In the course of this fast two-dimensional expansion process, the essential reactants for silica polymerization have to be transported efficiently to the SDV. Silicon transporters have been identified (5, 6), but there is no clear evidence that they transport sufficient amounts of silicic acid across the plasma membrane and/or SDV membrane to enable silica polymerization.In diatoms, both organic and inorganic compounds foster silica biomineralization and possibly control silica precipitation and direct the structures formed (7-9). Relevant organic compounds are silica-precipitating peptides such as silaffins and long-chain polyamines (8-10). They all have an intracellular origin and require specific targeting or intracellular transpo...

Partially fluorinated isocyanates were synthesized from hexamethylene diisocyanate (HDI) and an HDI trimer (Desmodur N3300). The perfluoroalkyl group (Rf) was C6F13 or C8F17, and the ratio between Rf and the isocyanate group (NCO) was 1/99 in the case of HDI or 1/49 in the case of N3300. Polymeric films with surface energies as low as 10 mN/m were obtained from mixtures of these partially fluorinated isocyanates and a previously reported hydroxyl-end-capped solventless liquid oligoester. Contact angles of water and hexadecane reached 120° and 80°, respectively, when less than 1 wt % of fluorine was present in the films. The surface enrichment of fluorine-containing species was confirmed by X-ray photoelectron spectroscopy (XPS) investigations. At a fluorine concentration of 0.5−1.0 wt %, the surface F/C atomic ratio (at a 15° takeoff angle) was greater than 1; the surface enrichment factor of fluorine was up to 600. The topological structures of the polymeric films were recorded by an atomic force microscope under tapping mode. While the height images indicated that the surface was smooth at the nanometer scale in a 1 μm × 1 μm area, the phase images revealed that fluorine-enriched domains were present at the surface. As the fluorine concentration increased, the fluorine-enriched domains grew from tiny spots (2−3 nm) to larger round domains (15−25 nm in diameter). The low surface energies of the films could be ascribed to the strong surface segregation of fluorinated species.