Nanoparticles Featuring Electromagnetic Properties: From Science to Engineering

Recent improvements in nanomaterials are opening interesting perspectives in materials science, physics and technology as a consequence of the variety of novel physical and chemical effects emerging at the nanometer scale, and because of the wide range of their existing and prospective applications. In fact, nanomaterials play a crucial role in our modern society which increasingly relies on widespread employ of advanced technology and innovative products. Nanoparticles and nanoparticulate media or metamaterials constitute a considerable fraction of nanostructured materials presently under study. Nanoparticles can be synthesized starting from metallic elements or alloys, compounds, dielectrics; they can be characterized by inner chemical homogeneity or inner chemical differentiation. Although chemical differentiation (as in core-shell systems) may often naturally arise as a by-product of the production technique, it provides additional features and customized properties which can be looked for and exploited for specific applications. Although nanoparticles always display interesting properties as functional materials, they are seldom used by themselves: in many instances, nanoparticles are either dispersed or inserted in host materials or combined with them, resulting in fluid or solid nanocomposites characterized by functional and structural properties which often derive from the combination of those of the nanogranular material proper and those of the hosting medium. Novel nanoparticle-based composites have a variety of applications in different areas, particularly in Information and Communication Technologies (ICTs), in Greentech and environmental sciences as well as in advanced biomedicine. From this viewpoint, the process of dispersion of a nanoparticle population in a host is a crucial point in nanoparticle technology, as the performance of final products is profoundly affected by the state of dispersion or aggregation of embedded nanoparticles. Functionalization of the nanoparticles is also fundamental, since a real nanocomposite is such that a strong chemical bond between matrix and dispersoid is preferred to a weak physical one, allowing better continuity and easier transmission of either thermal or mechanical loads, as well as electrical conduction. Although the scientific and technological interest for fine particles has stemmed in mid-XXth century, it has dramatically increased in the last two decades. In nanogranular materials the nanometric structure—as resulting from nanoparticle synthesis, post-treatment, functionalization and/or inclusion in specific host materials— largely affects the macroscopic properties, giving rise to a wide variety of new phenomena and specific applications. Current research in the area of nanomaterials is aimed to tailor their structure, morphology and physical (e.g., magnetic, electrical, optical) response at the nanometer scale, and to correlate it to the macroscopic properties on the basis of specific applicative demands. Nanoparticulate materials provide a crosslink between bulk materials and atomic/molecular-level structures. While the physical properties of bulk materials are typically independent of their size, size-dependent properties and responses are a distinctive feature of materials science at the nanoscale. Such properties include, e.g., melting temperature; Young modulus and maximum elongation at breaking; dielectric constant; refractive index and optical absorption. A major challenge for the practical use of nanoparticulate media in micro- and nanoelectronics as well as in biomedicine is the robust control of nanoparticle geometric features, surface functionalization, dispersion degree. In fact, practical use of all types of nanoparticles depends in general on some common, basic requirements: their size and shape should be as uniform as possible (the ideal case would correspond to a very narrow - ideally, delta-like - distribution of particle radii); the fabrication of regular linear, planar or spatial arrays should be possible; nanoparticle functionalization by means of inert materials should be achieved in order to reduce the spontaneous aggregation and to keep the nanoparticles themselves from direct contact with the environment (this is a fundamental requirement in sensor devices applied to biomedicine and in nanoparticle-based solutions for drug delivery: most of the biomedical applications require that metallic or oxide nanoparticles be coated by a chemically inert material). Nevertheless we do not exclude that controlled though non-monodisperse nanoparticle populations should result in extremely interesting properties: for example the packing factor of nanoparticles coated on a certain substrate increases when the diameter distribution is broad and the conversion through sinterization to a fully dense layer is greatly enhanced. Similarly, a mass production of nanocomposite materials may still be based on non-regular assemblies of nanoparticles, when their alignment and electrical percolation is granted by diffusion limited aggregation phenomena, such as dendrite growth. During the past two decades, many chemical synthesis routes have been proposed and implemented to obtain large quantities of nanosized "building blocks", well identified and disentangled, in a single reaction. Other self-assembly methods are based upon physical effects, and make use of atomic force microscopy as a suitable tool to create atomic clusters or nanoparticles. All bottom-up techniques allow one to obtain nanoparticles with an average size much lower than that attained using top-down techniques such as optical lithography. However, self-assembly of magnetic building blocks on a macroscopic length scale with nanometer precision is still a technically challenging task, even at the level of laboratory demonstrators. Such mesostructured materials, ranging from nanometer order to micrometer one up to macroscopic level will represent the technological break-through milestone for current century research. In this book, a state-of-the-art overview of the most recent trends in nanoparticle science and of current base and applied research activity on different families of nanoparticulate metamaterials is given. In the Editors' view, a most exciting feature of the nanoparticle world is the intimate interconnection and cross-fertilization of different spheres such as: complex preparation routes, sophisticated measurements, theoretical advances, modern functional property characterization, innovative applications and ensuing technology. Therefore, a monographic Volume such as this one should contain an appropriate blend of all these issues, allowing the reader to easily grasp some of the most intellectually stimulating recent outcomes in this fascinating subject area. This volume is divided in chapters addressing different issues of present-day nanoparticle science and technology. Modern, affordable preparation methods are reviewed. Up-to-date topics such as functionalized nanoparticles, mesostructured materials, nanocomposite dielectrics and conductors and magnetic materials, magnetic nanofluids, ordered nanoparticle arrays, nanoparticle-infiltrated nanopores, nanofillers, nanogranular metallic films, are covered in some detail. Theoretical and experimental investigations regarding nanoparticle interaction and effects of nanogranularity on the conduction properties of low-dimensional electron systems are presented. Application-oriented research in the areas of ICT (Information and Communication Technology) and environment protection is discussed