Defect structure in nanomaterials

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Ion tracks and other radiation-induced effects provide a means for controlled synthesis and modification of low-dimensional materials, such as nanoclusters and nanowires, allowing for efficient nano- and optoelectronic devices. Defect behavior in nanomaterials and nanostructures in its turn has often been found to differ substantially from that observed in bulk materials. Recent work has demonstrated spectacular optical and magnetic effects due to deliberately created defects or radiation-induced transformation of nanomaterials as well as radiation-induced displacements in low-dimensional insulators and semiconductors, with numerous potential applications.

We plan to discuss how such defects could be introduced controllably, categorized and controlled in nanostructures. Understanding and controlling defect properties in a wide class of advanced nanostructures novel 2D materials, multiferroics, quantum dots and wires, etc.


This is the main focus of the symposium. List of invited speakers : H. All abstracts must be submitted via E-MRS website. Symposium K organizers :. Size-dependent properties are observed such as quantum confinement in semiconductor particles, surface plasmon resonance in some metal particles and superparamagnetism in magnetic materials.

Mod-01 Lec-20 Defect Structure & Mechanical Behaviour of Nanomaterials

Nanoparticles exhibit a number of special properties relative to bulk material. For example, the bending of bulk copper wire, ribbon, etc. The change in properties is not always desirable. Suspensions of nanoparticles are possible because the interaction of the particle surface with the solvent is strong enough to overcome differences in density , which usually result in a material either sinking or floating in a liquid.

Nanoparticles often have unexpected visual properties because they are small enough to confine their electrons and produce quantum effects. For example, gold nanoparticles appear deep red to black in solution. The often very high surface area to volume ratio of nanoparticles provides a tremendous driving force for diffusion , especially at elevated temperatures. Sintering is possible at lower temperatures and over shorter durations than for larger particles. This theoretically does not affect the density of the final product, though flow difficulties and the tendency of nanoparticles to agglomerate do complicate matters.

Defect Structure in Nanomaterials (Electronic book text)

The surface effects of nanoparticles also reduces the incipient melting temperature. The smallest possible crystalline wires with cross-section as small as a single atom can be engineered in cylindrical confinement.

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Confinement provides mechanical stabilization and prevents linear atomic chains from disintegration; other structures of 1D nanowires are predicted to be mechanically stable even upon isolation from the templates. The most important representative graphene was discovered in Thin films with nanoscale thicknesses are considered nanostructures, but are sometimes not considered nanomaterials because they do not exist separately from the substrate. Some bulk materials contain features on the nanoscale, including nanocomposites , nanocrystalline materials , nanostructured films , and nanotextured surfaces.

Box-shaped graphene BSG nanostructure is an example of 3D nanomaterial. This nanostructure is a multilayer system of parallel hollow nanochannels located along the surface and having quadrangular cross-section. Nano materials are used in a variety of, manufacturing processes, products and healthcare including paints, filters, insulation and lubricant additives.

In healthcare Nanozymes are nanomaterials with enzyme-like characteristics. In paints nanomaterials are used to improve UV protection and improve ease of cleaning. In the air purification field, nano technology was used to combat the spread of MERS in Saudi Arabian hospitals in Worn and corroded parts can also be repaired with self-assembling anisotropic nanoparticles called TriboTEX. TWC converters have the advantage of controlling the emission of nitrogen oxides NOx , which are precursors to acid rain and smog.

Accordingly, the synthetic method should exhibit control of size in this range so that one property or another can be attained. Often the methods are divided into two main types, "bottom up" and "top down". Bottom up methods involve the assembly of atoms or molecules into nanostructured arrays. In these methods the raw material sources can be in the form of gases, liquids or solids. The latter require some sort of disassembly prior to their incorporation onto a nanostructure.

Bottom up methods generally fall into two categories: chaotic and controlled. Chaotic processes involve elevating the constituent atoms or molecules to a chaotic state and then suddenly changing the conditions so as to make that state unstable. Through the clever manipulation of any number of parameters, products form largely as a result of the insuring kinetics. The collapse from the chaotic state can be difficult or impossible to control and so ensemble statistics often govern the resulting size distribution and average size.

Accordingly, nanoparticle formation is controlled through manipulation of the end state of the products. Examples of chaotic processes are laser ablation, exploding wire, arc, flame pyrolysis, combustion, and precipitation synthesis techniques. Controlled processes involve the controlled delivery of the constituent atoms or molecules to the site s of nanoparticle formation such that the nanoparticle can grow to a prescribed sizes in a controlled manner.

Generally the state of the constituent atoms or molecules are never far from that needed for nanoparticle formation. Accordingly, nanoparticle formation is controlled through the control of the state of the reactants.

Defect Structure in Nanomaterials - 1st Edition

Examples of controlled processes are self-limiting growth solution, self-limited chemical vapor deposition , shaped pulse femtosecond laser techniques, and molecular beam epitaxy. Novel effects can occur in materials when structures are formed with sizes comparable to any one of many possible length scales , such as the de Broglie wavelength of electrons, or the optical wavelengths of high energy photons. In these cases quantum mechanical effects can dominate material properties.

One example is quantum confinement where the electronic properties of solids are altered with great reductions in particle size.

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The optical properties of nanoparticles, e. This effect does not come into play by going from macrosocopic to micrometer dimensions, but becomes pronounced when the nanometer scale is reached. In addition to optical and electronic properties, the novel mechanical properties of many nanomaterials is the subject of nanomechanics research. When added to a bulk material, nanoparticles can strongly influence the mechanical properties of the material, such as the stiffness or elasticity.

For example, traditional polymers can be reinforced by nanoparticles such as carbon nanotubes resulting in novel materials which can be used as lightweight replacements for metals. Such composite materials may enable a weight reduction accompanied by an increase in stability and improved functionality.

Finally, nanostructured materials with small particle size such as zeolites , and asbestos , are used as catalysts in a wide range of critical industrial chemical reactions. The further development of such catalysts can form the basis of more efficient, environmentally friendly chemical processes. The first observations and size measurements of nano-particles were made during the first decade of the 20th century.

He published a book in There are traditional techniques developed during the 20th century in interface and colloid science for characterizing nanomaterials. These are widely used for first generation passive nanomaterials specified in the next section. These methods include several different techniques for characterizing particle size distribution. This characterization is imperative because many materials that are expected to be nano-sized are actually aggregated in solutions. Some of methods are based on light scattering.

Others apply ultrasound , such as ultrasound attenuation spectroscopy for testing concentrated nano-dispersions and microemulsions. There is also a group of traditional techniques for characterizing surface charge or zeta potential of nano-particles in solutions. This information is required for proper system stabilzation, preventing its aggregation or flocculation.

These methods include microelectrophoresis , electrophoretic light scattering and electroacoustics. The last one, for instance colloid vibration current method is suitable for characterizing concentrated systems. The chemical processing and synthesis of high performance technological components for the private, industrial and military sectors requires the use of high purity ceramics , polymers , glass-ceramics and material composites.

Defect-induced effects in nanomaterials

In condensed bodies formed from fine powders, the irregular sizes and shapes of nanoparticles in a typical powder often lead to non-uniform packing morphologies that result in packing density variations in the powder compact. Uncontrolled agglomeration of powders due to attractive van der Waals forces can also give rise to in microstructural inhomogeneities. Differential stresses that develop as a result of non-uniform drying shrinkage are directly related to the rate at which the solvent can be removed, and thus highly dependent upon the distribution of porosity. Such stresses have been associated with a plastic-to-brittle transition in consolidated bodies, and can yield to crack propagation in the unfired body if not relieved.

In addition, any fluctuations in packing density in the compact as it is prepared for the kiln are often amplified during the sintering process, yielding inhomogeneous densification. Some pores and other structural defects associated with density variations have been shown to play a detrimental role in the sintering process by growing and thus limiting end-point densities.

Differential stresses arising from inhomogeneous densification have also been shown to result in the propagation of internal cracks, thus becoming the strength-controlling flaws. It would therefore appear desirable to process a material in such a way that it is physically uniform with regard to the distribution of components and porosity, rather than using particle size distributions which will maximize the green density. The containment of a uniformly dispersed assembly of strongly interacting particles in suspension requires total control over particle-particle interactions.

A number of dispersants such as ammonium citrate aqueous and imidazoline or oleyl alcohol nonaqueous are promising solutions as possible additives for enhanced dispersion and deagglomeration.

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