Phonons In Nanostructures

This book focuses on the theory of phonon interactions in nanoscale structures with particular emphasis on modern electronic and optoelectronic devices. The continuing progress in the fabrication of semiconductor nanostructures with lower dimensional features has led to devices with enhanced functionality and even novel devices with new operating principles. The critical role of phonon effects in such semiconductor devices is well known. There is therefore a great need for a greater awareness and understanding of confined phonon effects. A key goal of this book is to describe tractable models of confined phonons and how these are applied to calculations of basic properties and phenomena of semiconductor heterostructures. The level of presentation is appropriate for undergraduate and graduate students in physics and engineering with some background in quantum mechanics and solid state physics or devices. A basic understanding of electromagnetism and classical acoustics is assumed.

In the last ten years, the physics and technology of low dimensional structures has experienced a tremendous development. Quantum structures with vertical and lateral confinements are now routinely fabricated with feature sizes below 100 run. While quantization of the electron states in mesoscopic systems has been the subject of intense investigation, the effect of confinement on lattice vibrations and its influence on the electron-phonon interaction and energy dissipation in nanostructures received atten tion only recently. This NATO Advanced Research Workshop on Phonons in Sem iconductor Nanostructures was a forum for discussion on the latest developments in the physics of phonons and their impact on the electronic properties of low-dimensional structures. Our goal was to bring together specialists in lattice dynamics and nanos tructure physics to assess the increasing importance of phonon effects on the physical properties of one-(lD) and zero-dimensional (OD) structures. The Workshop addressed various issues related to phonon physics in III-V, II-VI and IV semiconductor nanostructures. The following topics were successively covered: Models for confined phonons in semiconductor nanostructures, latest experimental observations of confined phonons and electron-phonon interaction in two-dimensional systems, elementary excitations in nanostructures, phonons and optical processes in reduced dimensionality systems, phonon limited transport phenomena, hot electron effects in quasi - ID structures, carrier relaxation and phonon bottleneck in quantum dots.

The book provides a technical account of the basic physics of nanostructures, which are the foundation of the hardware found in all manner of computers. It will be of interest to semiconductor physicists and electronic engineers and advanced research students. Crystalline nanostructures have special properties associated with electrons and lattice vibrations and their interaction. The result of spatial confinement of electrons is indicated in the nomenclature of nanostructures: quantum wells, quantum wires, quantum dots. Confinement also has a profound effect on lattice vibrations. The documentation of the confinement of acoustic modes goes back to Lord Rayleigh's work in the late nineteenth century, but no such documentation exists for optical modes. It is only comparatively recently that any theory of the elastic properties of optical modes exists, and a comprehensive account is given in this book. A model of the lattice dynamics of the diamond lattice is given that reveals the quantitative distinction between acoustic and optical modes and the difference of connection rules that must apply at an interface. The presence of interfaces in nanostructures forces the hybridization of longitudinally and transversely polarized modes, along with, in polar material, electromagnetic modes. Hybrid acoustic and optical modes are described, with an emphasis on polar-optical phonons and their interaction with electrons. Scattering rates in single heterostructures, quantum wells and quantum wires are described and the anharmonic interaction in quantum dots discussed. A description is given of the effects of dynamic screening of hybrid polar modes and the production of hot phonons.

The book provides a technical account of the basic physics of nanostructures, which are the foundation of the hardware found in all manner of computers. It will be of interest to semiconductor physicists and electronic engineers and advanced research students. Crystalline nanostructures have special properties associated with electrons and lattice vibrations and their interaction. The result of spatial confinement of electrons is indicated in the nomenclature of nanostructures: quantum wells, quantum wires, quantum dots. Confinement also has a profound effect on lattice vibrations. The documentation of the confinement of acoustic modes goes back to Lord Rayleigh's work in the late nineteenth century, but no such documentation exists for optical modes. It is only comparatively recently that any theory of the elastic properties of optical modes exists, and a comprehensive account is given in this book. A model of the lattice dynamics of the diamond lattice is given that reveals the quantitative distinction between acoustic and optical modes and the difference of connection rules that must apply at an interface. The presence of interfaces in nanostructures forces the hybridization of longitudinally and transversely polarized modes, along with, in polar material, electromagnetic modes. Hybrid acoustic and optical modes are described, with an emphasis on polar-optical phonons and their interaction with electrons. Scattering rates in single heterostructures, quantum wells and quantum wires are described and the anharmonic interaction in quantum dots discussed. A description is given of the effects of dynamic screening of hybrid polar modes and the production of hot phonons.

The monograph is devoted to the investigation of physical processes that govern the phonon transport in bulk and nanoscale single-crystal samples of cubic symmetry. Special emphasis is given to the study of phonon focusing in cubic crystals and its influence on the boundary scattering and lattice thermal conductivity of bulk materials and nanostructures.

Application of nano-structures requires knowledge of their fundamental physical (mechanical, electro-magnetic, optical, etc.) characteristics. Thermodynamic properties associated with phonon displacements through the nano-samples are particularly interesting. Independent of the type of lattices, the thermodynamics of their subsystems (electrons, excitons, spin waves, etc.) is determined when the subsystem is in thermodynamic equilibrium with phonons. Besides, the acoustical characteristics as well as conductive and superconductive properties etc. could not be realistically explained without phonons. The fact which must be especially pointed out is that the role of phonons in nanostructures is much more impressive than in bulk structures. The main fact concerning phonon properties in nanostructures is the absence of the so-called acoustic phonons: for the exciting of phonons in nanostructures activation energy different from zero is necessary. These unexpected characteristics require revision of all conclusions obtained by bulk theories of phonons. Therefore, the contribution of phonon subsystems to thermodynamic is the first step in a research of nanostructure properties.

This fully updated second edition of The Physics of Phonons remains the most comprehensive theoretical discussion devoted to the study of phonons, a major area of condensed matter physics. It contains exciting new sections on phonon-related properties of solid surfaces, atomically thin materials (such as graphene and monolayer transition metal chalcogenides), in addition to nano- structures and nanocomposites, thermoelectric nanomaterials, and topological nanomaterials, with an entirely new chapter dedicated to topological nanophononics and chiralphononics. Although primarily theoretical in approach, the author refers to experimental results wherever possible, ensuring an ideal book for both experimental and theoretical researchers. The author begins with an introduction to crystal symmetry and continues with a discussion of lattice dynamics in the harmonic approximation, including the traditional phenomenological approach and the more recent ab initio approach, detailed for the first time in this book. A discussion of anharmonicity is followed by the theory of lattice thermal conductivity, presented at a level far beyond that available in any other book. The chapter on phonon interactions is likewise more comprehensive than any similar discussion elsewhere. The sections on phonons in superlattices, impure and mixed crystals, quasicrystals, phonon spectroscopy, Kapitza resistance, and quantum evaporation also contain material appearing in book form for the first time. The book is complemented by numerous diagrams that aid understanding and is comprehensively referenced for further study. With its unprecedented wide coverage of the field, The Physics of Phonons is an indispensable guide for advanced undergraduates, postgraduates, and researchers working in condensed matter physics and materials science. Features Fully updated throughout, with exciting new coverage on graphene, nanostructures and nanocomposites, thermoelectric nanomaterials, and topological nanomaterials. Authored by an authority on phonons. Interdisciplinary, with broad applications through condensed matter physics, nanoscience, and materials science. --