Heat conduction in semiconductors and dielectrics depends upon their phonon mean free paths that describe the average travelling distance between two consecutive phonon scattering events. Nondiffusive phonon transport is being exploited to extract phonon mean free path distributions. Here, we describe an implementation of a nanoscale thermal conductivity spectroscopy technique that allows for the study of mean free path distributions in optically absorbing materials with relatively simple fabrication and a straightforward analysis scheme. We pattern 1D metallic grating of various line widths but fixed gap size on sample surfaces. The metal lines serve as both heaters and thermometers in time-domain thermoreflectance measurements and simultaneously act as wiregrid polarizers that protect the underlying substrate from direct optical excitation and heating. We demonstrate the viability of this technique by studying length-dependent thermal conductivities of silicon at various temperatures. The thermal conductivities measured with different metal line widths are analyzed using suppression functions calculated from the Boltzmann transport equation to extract the phonon mean free path distributions with no calibration required. Furthermore, this table-top ultrafast thermal transport spectroscopy technique enables the study of mean free path spectra in a wide range of technologically important materials.

Transport Phenomena in Micro- and Nanoscale Functional Materials and Devices offers a pragmatic view on transport phenomena for micro- and nanoscale materials and devices, both as a research tool and as a means to implant new functions in materials. Chapters emphasize transport properties (TP) as a research tool at the micro/nano level and give an experimental view on underlying techniques. The relevance of TP is highlighted through the interplay between a micro/nanocarrier's characteristics and media characteristics: long/short-range order and disorder excitations, couplings, and in energy conversions. Later sections contain case studies on the role of transport properties in functional nanomaterials. This includes transport in thin films and nanostructures, from nanogranular films, to graphene and 2D semiconductors and spintronics, and from read heads, MRAMs and sensors, to nano-oscillators and energy conversion, from figures of merit, micro-coolers and micro-heaters, to spincaloritronics. - Presents a pragmatic description of electrical transport phenomena in micro- and nanoscale materials and devices from an experimental viewpoint - Provides an in-depth overview of the experimental techniques available to measure transport phenomena in micro- and nanoscale materials - Features case studies to illustrate how each technique works - Highlights emerging areas of interest in micro- and nanomaterial transport phenomena, including spintronics

Heat conduction in semiconductors and dielectrics involves cumulative contributions from phonons with different frequencies and mean free paths (MFPs). Knowing the phonon MFP distribution allows us to gain insight into the fundamental microscopic transport physics and has important implications for many energy applications. The key metric that quantifies the relative contributions of different phonon MFPs to thermal conductivity is termed thermal conductivity accumulation function. In this thesis, we advance a thermal conductivity spectroscopy technique based upon experimental observation of non-diffusive thermal transport using wire grid linear polarizer in conjunction with time-domain thermoreflectance (TDTR) pump-and-probe measurement setup. Consistent algorithm based on solution from the phonon Boltzmann transport equation (BTE) is also developed to approximately extract the thermal conductivity accumulation functions in materials studied. The heat flux suppression function appropriate for the experimental sample geometry relates the measured apparent thermal conductivities to the material's phonon MFP distributions. We develop a multi-dimensional thermal transport model based on the gray phonon BTE to find the suppression function relevant to our spectroscopy experiment. The simulation results reveal that the suppression function depends upon both the heater size and the heater array period. We also find that the suppression function depends significantly on the location of the temperature measurement. Residual suppression effect is observed for finite filling fractions (ratio of heater size to heater array period) due to the transport coupling in the underlying substrate induced by the neighboring heaters. Prior phonon MFP spectroscopy techniques suffer from one or several of the following limitations: (1) diffraction limited to micrometer lengthscales by focusing optics, (2) applying only to transparent materials, or (3) involving complex micro-fabrications. We explore an alternate approach here using wire grid linear polarizer in combination with TDTR measurement. The wire grid polarizer is designed with sub-wavelength gaps between neighboring heaters to prevent direct photo-excitation in the substrate while simultaneously functioning as heaters and thermometers during the measurement. The spectroscopy technique is demonstrated in crystalline silicon by studying length-dependent thermal transport across a range of lengthscales and temperatures. We utilize the calculated heat flux suppression functions and the measured size-dependent effective thermal conductivities to reconstruct the phonon MFPs in silicon and achieve reasonably good agreement with calculation results from first principle density function theory. Knowledge of phonon MFP distributions in thermoelectric materials will help design nanostructures to further reduce lattice thermal conductivity to achieve better thermoelectric performance in the next-generation thermoelectric devices. We apply the developed wire grid polarizer spectroscopy technique to study phonon MFP distributions in two thermoelectric materials: Nb0.95 Ti0.05FeSb and boron-doped nanocrystalline Si80Ge20B. We find that the dominant phonon MFPs that contribute to thermal conductivity in those two materials are in the a few tens to a few hundreds of nanometers. The measurement results also shed light on why nanostructuring is an effective approach to scattering phonons and improve the thermoelectric behavior.

This 21st Century Nanoscience Handbook will be the most comprehensive, up-to-date large reference work for the field of nanoscience. Handbook of Nanophysics, by the same editor, published in the fall of 2010, was embraced as the first comprehensive reference to consider both fundamental and applied aspects of nanophysics. This follow-up project has been conceived as a necessary expansion and full update that considers the significant advances made in the field since 2010. It goes well beyond the physics as warranted by recent developments in the field. Key Features: Provides the most comprehensive, up-to-date large reference work for the field. Chapters written by international experts in the field. Emphasises presentation and real results and applications. This handbook distinguishes itself from other works by its breadth of coverage, readability and timely topics. The intended readership is very broad, from students and instructors to engineers, physicists, chemists, biologists, biomedical researchers, industry professionals, governmental scientists, and others whose work is impacted by nanotechnology. It will be an indispensable resource in academic, government, and industry libraries worldwide. The fields impacted by nanoscience extend from materials science and engineering to biotechnology, biomedical engineering, medicine, electrical engineering, pharmaceutical science, computer technology, aerospace engineering, mechanical engineering, food science, and beyond.

Starting from a broad overview of heat transport based on the Boltzmann Transport Equation, this book presents a comprehensive analysis of heat transport in bulk and nanomaterials based on a kinetic-collective model (KCM). This has become key to understanding the field of thermal transport in semiconductors, and represents an important stride. The book describes how heat transport becomes hydrodynamic at the nanoscale, propagating very much like a viscous fluid and manifesting vorticity and friction-like behavior. It introduces a generalization of Fourier’s law including a hydrodynamic term based on collective behavior in the phonon ensemble. This approach makes it possible to describe in a unifying way recent experiments that had to resort to unphysical assumptions in order to uphold the validity of Fourier’s law, demonstrating that hydrodynamic heat transport is a pervasive type of behavior in semiconductors at reduced scales.

This book consolidates information about multifunctional epoxy as a frontier material, its composites, engineering and applications in a very detailed manner that encompasses the entire spectrum of up-to-date literature citations, current market trends and patents. It highlights latest experimental and theoretical studies on the atypical properties of epoxy resins such as self-healing, thermally and electrically conductivity; and its applications in devices where there is reliance on unsustainable sourced inorganic materials with comparable properties. It caters to polymer chemists, physicists and engineers who are interested in the field of next generation epoxy polymers.

Polymer-Based Multifunctional Nanocomposites and Their Applications provides an up-to-date review of the latest advances and developments in the field of polymer nanocomposites. It will serve as a one-stop reference resource on important research accomplishments in the area of multifunctional nanocomposites, with a particular emphasis placed on the use of nanofillers and different functionality combinations. Edited and written by an expert team of researchers in the field, the book provides a practical analysis of functional polymers, nanoscience, and nanotechnology in important and developing areas, such as transportation engineering, mechanical systems, aerospace manufacturing, construction materials, and more. The book covers both theory and experimental results regarding the relationships between the effective properties of polymer composites and those of polymer matrices and reinforcements. - Presents a thorough and up-to-date review of the latest advances and developments in the field of multifunctional polymer nanocomposites - Integrates coverage of fundamentals, research and development, and the range of applications for multifunctional polymers and their composites, such as in the automotive, aerospace, biomedical and electrical industries - Supports further technological developments by discussing both theory and real world experimental data from academia and industry

Knowledge of phonon mean free path (MFP) distribution is critically important to engineering size effects. Phenomenological models of phonon relaxation times can give us some sense about the mean free path distribution, but they are not accurate. Further improvement of thermoelectric performance requires the phonon MFP to be known. In this thesis, we improve recently developed thermal conductivity spectroscopy technique to experimentally measure MFPs using ultrafast transient thermoreflectance method. By optically heating lithographically patterned metallic nanodot arrays, we are able to probe heat transfer at length scales down to 100 nm, far below the diffraction limit for visible light. We demonstrate the new implementation by measuring MFPs in sapphire at room temperature. A multidimensional transport model based on the grey phonon Boltzmann equation is developed and solved to study the quasi-ballistic transport occurring in the spectroscopy experiments. To account for the nonlinear dispersion relation, we present a variance reduced Monte Carlo scheme to solve the full Boltzmann transport equation and compare the simulation results with experimental data on silicon.

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.