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

Nanocomposites, a high performance material exhibit unusual property combinations and unique design possibilities. With an estimated annual growth rate of about 25% and fastest demand to be in engineering plastics and elastomers, their potential is so striking that they are useful in several areas ranging from packaging to biomedical applications. In this unified overview the three types of matrix nanocomposites are presented underlining the need for these materials, their processing methods and some recent results on structure, properties and potential applications, perspectives including need for such materials in future space mission and other interesting applications together with market and safety aspects. Possible uses of natural materials such as clay based minerals, chrysotile and lignocellulosic fibers are highlighted. Being environmentally friendly, applications of nanocomposites offer new technology and business opportunities for several sectors of the aerospace, automotive, electronics and biotechnology industries.

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Nanocomposites: synthesis, structure, properties and new application opportunities

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

Bulk ferroelectrics undergo structural phase transformations at low temperatures, giving multi-stable (that is, multiple-minimum) degenerate states with spontaneous polarization. Accessing these states by applying, and varying the direction of, an external electric field is a key principle for the operation of devices such as non-volatile ferroelectric random access memories (NFERAMs). Compared with bulk ferroelectrics, low-dimensional finite ferroelectric structures promise to increase the storage density of NFERAMs 10,000-fold. But this anticipated benefit hinges on whether phase transitions and multi-stable states still exist in low-dimensional structures. Previous studies have suggested that phase transitions are impossible in one-dimensional systems, and become increasingly less likely as dimensionality further decreases. Here we perform ab initio studies of ferroelectric nanoscale disks and rods of technologically important Pb(Zr,Ti)O3 solid solutions, and demonstrate the existence of previously unknown phase transitions in zero-dimensional ferroelectric nanoparticles. The minimum diameter of the disks that display low-temperature structural bistability is determined to be 3.2 nm, enabling an ultimate NFERAM density of 60 x 10(12) bits per square inch-that is, five orders of magnitude larger than those currently available. Our results suggest an innovative use of ferroelectric nanostructures for data storage, and are of fundamental value for the theory of phase transition in systems of low dimensionality.

Unusual phase transitions in ferroelectric nanodisks and nanorods

The mechanical resonant response of a solid depends on its shape, density, elastic moduli and dissipation. We describe here instrumentation and computational methods for acquiring and analyzing the resonant ultrasound spectrum of very small (0.001 cm3) samples as a function of temperature, and provide examples to demonstrate the power of the technique. The information acquired is in some cases comparable to that obtained from other more conventional ultrasonic measurement techniques, but one unique feature of resonant ultrasound spectroscopy (RUS) is that all moduli are determined simultaneously to very high accuracy. Thus in circumstances where high relative or absolute accuracy is required for very small crystalline or other anisotropic samples RUS can provide unique information. RUS is also sensitive to the fundamental symmetry of the object under test so that certain symmetry breaking effects are uniquely observable, and because transducers require neither couplant nor a flat surface, broken fragments of a material can be quickly screened for phase transitions and other temperature-dependent responses.

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Resonant ultrasound spectroscopic techniques for measurement of the elastic moduli of solids

It is widely understood that many important properties of solids are conditioned or strongly influenced by lattice defects. This book covers the following subjects: elements of the theory of phase transitions in perfect crystals; phase transitions in imperfect crystals; space distribution of the order parameter induced by a point defect near the phase transition; phase transition anomalies in imperfect crystals: thermodynamic quantities and kinetic coefficients; scattering phenomena; polarized defects: bias field; model theories; and miscellaneous topics.

Defects and Structural Phase Transitions

Diphenylalanine (FF) peptide nanotubes (PNTs) represent a unique class of self-assembled functional biomaterials owing to a wide range of useful properties including nanostructural variability, mechanical rigidity and chemical stability. In addition, strong piezoelectric activity has recently been observed paving the way to their use as nanoscale sensors and actuators. In this work, we fabricated both horizontal and vertical FF PNTs and examined their optical second harmonic generation and local piezoresponse as a function of temperature. The measurements show a gradual decrease in polarization with increasing temperature accompanied by an irreversible phase transition into another crystalline phase at about 140‐150 ◦ C. The results are corroborated by the molecular dynamic simulations predicting an order‐disorder phase transition into a centrosymmetric (possibly, orthorhombic) phase with antiparallel polarization orientation in neighbouring FF rings. Partial piezoresponse hysteresis indicates incomplete polarization switching due to the high coercive field in FF PNTs. S Online supplementary data available from stacks.iop.org/JPhysD/43/462001/mmedia (Some figures in this article are in colour only in the electronic version)

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Temperature-driven phase transformation in self-assembled diphenylalanine peptide nanotubes

Self-assembled peptide nanotubes (PNT) are unique nanoscale objects having a great potential for a multitude of applications. Strong piezoactivity and polar properties in aromatic dipeptides were recently observed in stand-alone nanotubes using piezoresponse force microscopy and 2nd harmonic generation. In this work, we report macroscopic dielectric and polarization vs. field measurements on pressed PNTs before and after annealing at 150 °C. The results corroborate nanoscale study and present a clear evidence of ferroelectric-like behaviour and phase transition in this technologically important material. The dielectric constant of PNT pellets obeys apparent Curie-Weiss (CW) law with the CW constant C ≈ 230 °C and transition temperature at T ≈ 142 °C.

Evidence of ferroelectricity and phase transition in pressed diphenylalanine peptide nanotubes

Piezoelectricity is one of the common ferroelectric material properties, along with pyroelectricity, optical birefringence phenomena, etc There has been widespread observation of piezoelectric and ferroelectric phenomena in many biological systems and molecules, and these are referred to as biopiezoelectricity and bioferroelectricity Investigations have been made of these properties in biological and organic macromolecular systems on the nanoscale, by techniques such as atomic force microscopy (AFM) and piezoresponse force microscopy (PFM) This chapter presents a short overview of the main issues of piezoelectricity and ferroelectricity, and their manifestation in organic and biological objects, materials and molecular systems As a showcase of novel biopiezomaterials, the investigation of diphenylalanine (FF) peptide nanotubes (PNTs) is described in more detail FF PNTs present a unique class of self-assembled functional biomaterials, owing to a wide range of useful properties, including nanostructural variability, mechanical rigidity and chemical stability The discovery of strong piezoactivity and polarization in aromatic dipeptides [ACS Nano 4, 610, 2010] opened up a new perspective for their use as nanoactuators, nanomotors and molecular machines as well for possible biomedical applications

Piezoelectricity and Ferroelectricity in Biomaterials: From Proteins to Self-assembled Peptide Nanotubes

The paper presents short review of the works performed during the last few years in the field of the alkoxy-derived ferroelectric films. PZT films were prepared using titanium and zirconium alkoxides and Pb(CH3COO)2· 2H2O as precursors. Different way of lead acetate dehydration and the impact of lead excess in the precursor solutions on the properties of the PZT films are discussed. Trimetallic alkoxide systems Bi(OR)3-Ta(OR)5-ROH (R = Me, Et or i Pr) were studied as precursors for preparation of SrBi2Ta2O9 films. Films prepared from these solutions and annealed at the temperature between 700 and 750°C demonstrated the remanent polarization Pr* − P^r = 7–9 μC/cm2. Ba1-xSrxTiO3 films we applied from modified alkoxide solutions. Decomposition of the organic phase in the course of thermal treatment of the films is studied by IR-spectroscopy. The dependence of the dielectric permittivity of the films via the annealing temperature is reported. Preparation of LiNbO3, SrZr0.2Ti0.8O3, Zr0.8Sn0.2TiO4 is briefly discussed.

Alexander Sigov

Papers

Defects and Structural Phase Transitions

Temperature-driven phase transformation in self-assembled diphenylalanine peptide nanotubes

Evidence of ferroelectricity and phase transition in pressed diphenylalanine peptide nanotubes

Piezoelectricity and Ferroelectricity in Biomaterials: From Proteins to Self-assembled Peptide Nanotubes

Sol-Gel Derived Ferroelectric Thin Films: Avenues for Control of Microstructural and Electric Properties