Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Long viewed as a topic in classical physics, ferroelectricity can be described by a quantum mechanical ab initio theory. Thin-film nanoscale device structures integrated onto Si chips have made inroads into the semiconductor industry. Recent prototype applications include ultrafast switching, cheap room-temperature magnetic-field detectors, piezoelectric nanotubes for microfluidic systems, electrocaloric coolers for computers, phased-array radar, and three-dimensional trenched capacitors for dynamic random access memories. Terabit-per-square-inch ferroelectric arrays of lead zirconate titanate have been reported on Pt nanowire interconnects and nanorings with 5-nanometer diameters. Finally, electron emission from ferroelectrics yields cheap, high-power microwave devices and miniature x-ray and neutron sources.

http://science.sciencemag.org/content/sci/315/5814/954.full.pdf

Applications of Modern Ferroelectrics

This review covers important advances in recent years in the physics of thin-film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin-film form. The authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this the review covers the enormous progress that has been made in the first-principles computational approach to understanding ferroelectrics. The authors then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, this review ends with a look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in nonconventional nanoscale geometries.

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Physics of thin-film ferroelectric oxides

An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems' applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems' applications, and permittivity and loss in ferroelectric films-important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures. (c) 2006 American Institute of Physics.

/pdf/ferroelectric-thin-films-review-of-materials-properties-and-rc7umdkxk5.pdf

Ferroelectric thin films: Review of materials, properties, and applications

Understanding the suppression of ferroelectricity in perovskite thin films is a fundamental issue that has remained unresolved for decades. We report a synchrotron x-ray study of lead titanate as a function of temperature and film thickness for films as thin as a single unit cell. At room temperature, the ferroelectric phase is stable for thicknesses down to 3 unit cells (1.2 nanometers). Our results imply that no thickness limit is imposed on practical devices by an intrinsic ferroelectric size effect.

https://science.sciencemag.org/content/sci/304/5677/1650.full.pdf

Ferroelectricity in ultrathin perovskite films.

Defects exist in almost all materials and defect engineering at the atomic level is part of modern semiconductor technology Defects and their long-range strain fields can have a negative impact on the host materials In materials with confined dimensions, the influence of defects can be even more pronounced due to the enhanced relative volume of the 'defective' regions Here we report the dislocation-induced polarization instability of (001)-oriented Pb(Zr(052)Ti(048))O(3) (PZT) nanoislands, with an average height of approximately 9 nm, grown on compressive perovskite substrates Using quantitative high-resolution electron microscopy, we visualize the strain fields of edge-type misfit dislocations, extending predominantly into a PZT region with a height of approximately 4 nm and width of approximately 8 nm The lattice within this region deviates from the regular crystal structure Piezoresponse force microscopy indicates that such PZT nanoislands do not show ferroelectricity Our results suggest that misfit engineering is indispensable for obtaining nanostructured ferroelectrics with stable polarization

Impact of misfit dislocations on the polarization instability of epitaxial nanostructured ferroelectric perovskites.

Wafer-scale fabrication of ferroelectric oxide nanoshell tubes as well as ordered nanotube arrays have been accomplished using a simple and convenient fabrication method that allows full tailoring of tube dimensions as well as array pattern and size. Using different silicon and alumina templates, barium titanate and lead zirconate titanate tubes with diameters ranging from 50 nm up to several micrometers meter and lengths of more 100 μm have been fabricated. Ferroelectric switching of submicrometer tubes has been shown using piezoresponse scanning probe microscopy.

/pdf/nanoshell-tubes-of-ferroelectric-lead-zirconate-titanate-and-jgz4b678tj.pdf

Nanoshell tubes of ferroelectric lead zirconate titanate and barium titanate

Lead zirconate titanate nanoislands were obtained by a self-patterning method making use of the instability of ultrathin films during high-temperature treatments. After high-temperature annealing, the as-deposited film breaks into islands with a narrow size distribution. The single-crystal nanoislands were studied by scanning and high-resolution transmission electron microscopy, atomic force microscopy, and x-ray diffraction. They show an epitaxial relationship with the Nb-doped (001) SrTiO3 substrate. The ferroelectric switching of several individual islands was investigated by piezoresponse force microscopy.

/pdf/ferroelectric-epitaxial-nanocrystals-obtained-by-a-self-3hzppgcwqu.pdf

Ferroelectric epitaxial nanocrystals obtained by a self-patterning method

Bismuth ferrite nanopowders have been obtained by mechanochemical synthesis. The materials were characterized by high resolution electron microscopy, X-ray diffraction and NIR Raman scattering. The XRD pattern of the powder consists of reflections, characteristic of BiFeO 3 perovskite structure, superimposed on broad maxima that can be ascribed to an amorphous/disordered phase. The analysis of the two broad bands at low 2 θ angle yields mean distances of about 3 and 1.8 A which may be related to Bi O and Fe O bonds, respectively. The powder consists of loosely packed grains with a broad distribution of sizes between a few nm and 45 nm. The grains of sizes larger than about 30 nm exhibit well-developed crystalline structure.

Characterization of BiFeO3 nanopowder obtained by mechanochemical synthesis

Electroactive composites based on ferroelectric ceramic and polymer components are still of interest since their properties can be easily tailored to the requirements of smart structures, sensors and actuators. We studied the dielectric and pyroelectric response of poly(vinylidene fluoride) loaded with BaTiO3 nanograins obtained by mechanically activated synthesis from BaO and TiO2. The BaTiO3 nanopowder was characterized by X-ray diffraction, transmission electron microscopy and NIR Raman scattering. The relaxation processes in the polymer matrix were found to determine the dielectric response of the composites but with higher permittivity values due to the presence of BaTiO3. The activation energy of the segmental motion of the polymer matrix was found to increase with increasing contents of the filler. The dielectric response of the composites with volumetric fraction of BaTiO3 equal to and greater than 0.24 was found to be dominated by a broad maximum at ∼320 K, which we relate to the Curie point of the ferroelectric nanograins.

I. Szafraniak

Papers

Impact of misfit dislocations on the polarization instability of epitaxial nanostructured ferroelectric perovskites.

Nanoshell tubes of ferroelectric lead zirconate titanate and barium titanate

Ferroelectric epitaxial nanocrystals obtained by a self-patterning method

Characterization of BiFeO3 nanopowder obtained by mechanochemical synthesis

Dielectric and pyroelectric response of PVDF loaded with BaTiO3 obtained by mechanosynthesis