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15.1 Introduction
The main distinctive feature of nanomaterials is that they have structures on a nanometer scale. The class of nanostructured materials (nanomaterials) includes a variety of novel inorganic (ceramic nanoparticles, semiconductor quantum dots), organic (carbon nanotubes, fullerenes, polymers, molecular aggregates, moleculemetallic nanoparticle assemblies), and biological nanomaterials. To the nanomaterials belong artificially fabricated structures, photonic crystals, ordered solid surface patterns at nanometer scale, and organic-inorganic combinations of nanostructures (wires, rods, dots, etc.). Their optical properties are extremely fascinating and useful for a variety of applications.
Optics of nanostructured materials is a broad area covering different fields of both fundamental and applied science: optics of quantum confined systems, photonic crystals, nanoplasmonics, interaction of quantum particles with the optical incoherent and quantized field, etc. Nanostructured systems containing organic-inorganic interfaces open exciting possibilities for optical engineering. Artificially fabricated nanostructured materials (the so-called metamaterials), as well as those combined from inorganic and organic substances, present unique properties and open new areas for applications. Many features of nanomaterials optics can be understood within classic electrodynamics. For example, interactions with the optical local field generated due to plasma resonances in quantum confined systems can be well understood within classic Maxwell theory.
Optical properties of nanomaterials are size dependent; they do not naturally occur in larger bulk materials. The first principle theories of chemical, physical, and optical properties of simple atoms and molecules are fairly well understood, predictable, and no longer considered overly complex. This chapter demonstrates that this contrasts markedly with the current state of knowledge of the first principle optics of nanostructures. Through comparative analysis of the size-dependent optical response from nanomaterials, it is shown that although strides have been made in computational chemistry and physics, bridging across length scales from nano to macro remains a major challenge.
The first principles theory of the optics of nanostructured materials is considered here separately for at least two significant areas, depending on the nature of the optical field interacting with the nanostructures. One area governs the interaction of nanostructured materials with random (noncorrelated) optical fields. Quantum confinement and quantization of the charged quasi-particle motions are the main features that modify the optical response of nanostructures. The first principles theory of the optics of nanostructures has been actively studied within the last decade since the development of theoretical methods beyond the standard density functional theory (DFT). This part of optics is addressed in Secs. 15.2, 15.4, and in Appendix I. Nonlocalities of the electron potential energy modify quasiparticle excitations, resulting in specific features of the optical response that are unique for nanostructures.
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