Download or read book Phonon governed Heat Conduction in Nanostructures written by Karunarathna Kuruppu Mudiyanselage Nalaka Priyadarsana Samaraweera and published by . This book was released on 2018 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this study is to investigate phonon-governed thermal conductivity (TC) in nanostructures which include nanowires, hetero-structures and combinations of them. The selection of these nanostructures is based on their attractive performance as efficient thermoelectric materials giving ultra-low TC. Firstly, an investigation of unique thermal transport features of nanowires using a combined analysis based on multi-step normal mode decomposition (NMD) and Green-Kubo(GK) method is undertaken. The Lennard-Jones materials are chosen because of less computational demand. The convergence issue of the TC of nanowires is addressed providing details pertinent to two case studies. The non-monotonic trend of the TC of nanowires is also investigated showing that the principal cause for the observed trend is due to the competing effects of the long wavelength phonons and phonon-surface scatterings as the cross-sectional width is changed. A computational framework is developed to decompose the different modal contribution to the TC of shell alloy nanowires (SANWs) and, thereby, several important conclusions are drawn on the reduced TC of SANWs.The TC of Si/Ge random layer nanowires (RLNWs) is systematically investigated and compared against superlattice nanowires (SLNWs). It is demonstrated that for all physical and geometrical conditions investigated here, RLNWs show reduced TC over corresponding SLNWs via NEMD simulations. An anomalous trend in the TC of RLNWs (larger than the bulk counterpart) is observed at higher cross-sectional widths and it is explained as a competing effect of phonon localisation and wall scattering. Moreover, it is illustrated that the effectiveness of thermal insulating performance of RLNW depends on the fraction of coherent phonons that exists and how effectively those phonons are subject to localisation. Finally, we demonstrate the reduced TC of Si nanotwinned random layer (NTRL) structures over corresponding superlattice and twin-free counterparts. Via NEMD simulations, it is shown that ~55 and 53% over twin-free counterparts can be attained for the structures of total length 90 and 170nm respectively. Furthermore, the random nanotwinned effect is applied for Si/Ge random layer structures seeking further reduction of TC. A significant reduction in TC of Si/Ge structures exceeding the TC of the corresponding amorphous Si structure is achieved.

Download or read book Phonon Focusing and Phonon Transport written by Igor Gaynitdinovich Kuleyev and published by Walter de Gruyter GmbH & Co KG. This book was released on 2020-06-08 with total page 221 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Phonon Thermal Transport in Silicon Based Nanomaterials written by Hai-Peng Li and published by Springer. This book was released on 2018-09-08 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this Brief, authors introduce the advance in theoretical and experimental techniques for determining the thermal conductivity in nanomaterials, and focus on review of their recent theoretical studies on the thermal properties of silicon–based nanomaterials, such as zero–dimensional silicon nanoclusters, one–dimensional silicon nanowires, and graphenelike two–dimensional silicene. The specific subject matters covered include: size effect of thermal stability and phonon thermal transport in spherical silicon nanoclusters, surface effects of phonon thermal transport in silicon nanowires, and defects effects of phonon thermal transport in silicene. The results obtained are supplemented by numerical calculations, presented as tables and figures. The potential applications of these findings in nanoelectrics and thermoelectric energy conversion are also discussed. In this regard, this Brief represents an authoritative, systematic, and detailed description of the current status of phonon thermal transport in silicon–based nanomaterials. This Brief should be a highly valuable reference for young scientists and postgraduate students active in the fields of nanoscale thermal transport and silicon-based nanomaterials.

Download or read book Observation and Manipulation of the Wave Nature of Phonon Thermal Transport Through Superlattices written by Maria Nickolayevna Luckyanova and published by . This book was released on 2015 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the scale of electronic, photonic, and energy harvesting devices has shrunk, the importance of understanding nanoscale thermal transport has grown. In this thesis, we investigate thermal transport through superlattices (SLs), periodic layers of thin films, to better understand thermal conduction at these small scales. The classical picture of nanoscale thermal transport invokes a picture of diffusive scattering of phonons, or lattice vibrations, at the interfaces and boundaries in structures. This picture has been used to explain experimental thermal transport results for a wide variety of nanostructures. Despite the omnipresence of this particle-transport picture of phonon heat conduction, the community has continuously sought an experimental demonstration of the wave regime of thermal transport in nanostructures. In this thesis, we report the first experimental observations of the regimes of coherent phonon transport and phonon localization in thermal conduction through nanostructures. First, in order to better understand thermal transport through SLs, we present measurements of anisotropic thermal conductivity in the same GaAs/AlAs SLs using two different optical techniques, time-domain thermoreflectance (TDTR) for cross-plane measurements, and transient thermal grating (TTG) for in-plane measurements. The results of this study lend insight into the role of interface scattering, previously understood to be the dominant scattering mechanism in these structures, in SLs. The experimentally measured thermal conductivities are compared to results from first principles simulations, and the agreement between the two helps to validate atomistic simulation techniques of transport through SLs. The role of coherent phonon transport is explored by using the TDTR technique to measure the thermal conductivities of SLs with the same period thicknesses but varying numbers of periods. This experimental approach is a departure from traditional studies of SLs where period thicknesses are varied while the SL is grown to be thermally thick. This shift in the experimental paradigm allows us to explore previously elusive phenomena in nanoscale thermal transport. Combined with first principles and Green's functions simulations, the results of these experiments are the first experimental observation of coherent phonon transport through SLs. Finally, experiments on GaAs/AlAs SLs with varying concentrations of ErAs nanodots at the interfaces show the ability to destroy this phonon coherence. The thermal conductivities of such SLs with constant period thicknesses and varying numbers of periods show an overall reduction in thermal conductivity with increasing ErAs concentration. In addition, at low temperatures samples with ErAs at the interfaces show a maximum in thermal conductivity with shorter sample length and then a drop-off for longer samples. These results are signatures of phonon localization, a previously unobserved thermal transport phenomenon.

Download or read book First Principles Modeling of Phonon Heat Conduction in Nanoscale Crystalline Structures written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The inability to remove heat efficiently is currently one of the stumbling blocks toward further miniaturization and advancement of electronic, optoelectronic, and micro-electro-mechanical devices. In order to formulate better heat removal strategies and designs, it is first necessary to understand the fundamental mechanisms of heat transport in semiconductor thin films. Modeling techniques, based on first principles, can play the crucial role of filling gaps in our understanding by revealing information that experiments are incapable of. Heat conduction in crystalline semiconductor films occurs by lattice vibrations that result in the propagation of quanta of energy called phonons. If the mean free path of the traveling phonons is larger than the film thickness, thermodynamic equilibrium ceases to exist, and thus, the Fourier law of heat conduction is invalid. In this scenario, bulk thermal conductivity values, which are experimentally determined by inversion of the Fourier law itself, cannot be used for analysis. The Boltzmann Transport Equation (BTE) is a powerful tool to treat non-equilibrium heat transport in thin films. The BTE describes the evolution of the number density (or energy) distribution for phonons as a result of transport (or drift) and inter-phonon collisions. Drift causes the phonon energy distribution to deviate from equilibrium, while collisions tend to restore equilibrium. Prior to solution of the BTE, it is necessary to compute the lifetimes (or scattering rates) for phonons of all wave-vector and polarization. The lifetime of a phonon is the net result of its collisions with other phonons, which in turn is governed by the conservation of energy and momentum during the underlying collision processes. This research project contributed to the state-of-the-art in two ways: (1) by developing and demonstrating a calibration-free simple methodology to compute intrinsic phonon scattering (Normal and Umklapp processes) time scales with the inclusion of optical phonons, and (2) by developing a suite of numerical algorithms for solution of the BTE for phonons. The suite of numerical algorithms includes Monte Carlo techniques and deterministic techniques based on the Discrete Ordinates Method and the Ballistic-Diffusive approximation of the BTE. These methods were applied to calculation of thermal conductivity of silicon thin films, and to simulate heat conduction in multi-dimensional structures. In addition, thermal transport in silicon nanowires was investigated using two different first principles methods. One was to apply the Green-Kubo formulation to an equilibrium system. The other was to use Non-Equilibrium Molecular Dynamics (NEMD). Results of MD simulations showed that the nanowire cross-sectional shape and size significantly affects the thermal conductivity, as has been found experimentally. In summary, the project clarified the role of various phonon modes - in particular, optical phonon - in non-equilibrium transport in silicon. It laid the foundation for the solution of the BTE in complex three-dimensional structures using deterministic techniques, paving the way for the development of robust numerical tools that could be coupled to existing device simulation tools to enable coupled electro-thermal modeling of practical electronic/optoelectronic devices. Finally, it shed light on why the thermal conductivity of silicon nanowires is so sensitive to its cross-sectional shape.

Download or read book Nanoscale Energy Transport and Conversion written by Gang Chen and published by Oxford University Press. This book was released on 2005-03-03 with total page 570 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is a graduate level textbook in nanoscale heat transfer and energy conversion that can also be used as a reference for researchers in the developing field of nanoengineering. It provides a comprehensive overview of microscale heat transfer, focusing on thermal energy storage and transport. Chen broadens the readership by incorporating results from related disciplines, from the point of view of thermal energy storage and transport, and presents related topics on the transport of electrons, phonons, photons, and molecules. This book is part of the MIT-Pappalardo Series in Mechanical Engineering.

Download or read book Phonon Focusing and Phonon Transport written by Igor Gaynitdinovich Kuleyev and published by Walter de Gruyter GmbH & Co KG. This book was released on 2020-06-08 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: The series Texts and Monographs in Theoretical Physics collects advanced texts on selected topics from the broad and varied field of Theoretical Physics. The works in the series will enable the readers to get a deep understanding of current topics in Theoretical Physics, with a special emphasis on recent developments. They are aimed at advanced students and researchers in theoretical and mathematical physics, and can also serve as secondary reading for lectures and seminars at post-graduate levels.

Download or read book Simulation of Thermal Transport in Semiconductor Nanostructures written by Song Mei and published by . This book was released on 2017 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: With the advancement of nanofabrication techniques, the sizes of semiconductor electronic and optoelectronic devices keep decreasing while the operating speeds keep increasing. High-speed operation leads to more heat generation and puts more thermal stress on the devices. Since the heat conduction in semiconductors is dominated by the lattice (i.e., phonons), understanding phonon transport in nanostructures is essential to addressing and alleviating the thermal-stress problem in these modern devices. In addition to the increased thermal stress, the advanced techniques that have allowed for the shrinking of the devices routinely rely on heterostructuring, doping, alloying, and the growth of intentionally strained layers to achieve the desired electronic and optical properties. These introduce impediments to phonon transport such as boundaries, interfaces, point defects (alloy atoms or dopants), and strain. Phonon transport is strongly affected by this nanoscale disorder. This dissertation examines how different types of disorder interact with phonons and degrade phonon transport. First, we study thermal transport in graphene nanoribbons (GNRs). GNRs are quasi-one-dimensional (quasi-1D) systems where the edges (boundaries) play an important role in reducing thermal conductivity. Additionally, the thermal transport in GNRs is anisotropic and depend on the GNR's chirality (GNR orientation and edge termination). We use phonon Monte Carlo (PMC) with full phonon dispersions to describe two highly-symmetric types of GNRs: the armchair GNR (AGNR) and the zigzag GNR (ZGNR). PMC tracks phonon in real space and we can explicitly include non-trivial edge structures. Moreover, the relatively low computational burden of PMC allows us to simulate samples up to 100 $\mu$m in length and predict an upper limit for thermal conductivity in graphene. We then investigate the thermal conductivity in III-V superlattices (SLs). SLs consist of alternating thin layers of different materials and III-V SLs are widely used in nanoscale thermoelectric and optoelectronic devices. The key feature in SLs is that it contains many interfaces, which dictates thermal transport. As III-V SLs are often fabricated using well-controlled techniques and have high-quality interfaces, we develop a model with only one free parameter---the effective rms roughness of the interfaces---to describe its twofold influence: reducing the in-plane layer thermal conductivity and introducing thermal boundary resistance (TBR) in the cross-plane direction. Both the calculated in-plane and cross-plane thermal conductivity of SLs agree with a number of different experiments. Finally, we study thermal conductivity of ternary III-V alloys. In modern optoelectronic devices, ternary III-V alloys are used more often than binary compounds because one can use composition engineering to achieve different effective masses, electron/hole barrier heights, and strain levels. Ternary alloys are usually treated under the virtual crystal approximation (VCA) where cation atoms are assumed to be randomly distributed and possess an averaged mass. This assumption is challenged by a discrepancy between different experiments, as well as the discrepancy between experiments and calculations. We use molecular dynamics (MD) to study the ternary alloy system as both atom masses and atom locations are explicitly tracked in MD. We discover that the thermal conductivity is determined by a competition between mass-difference scattering and the short-range ordering of the cations.

Download or read book Effect of Phonon Transport on the Seebeck Coefficient and Thermal Conductivity of Silicon Nanowire Arrays written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Anderson Localization of Thermal Phonons written by Jonathan Michael Mendoza and published by . This book was released on 2017 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: In semiconductor devices, thermal energy is carried by phonons, the quantized excitation of atomic vibrations. These phonons scatter with impurities, electrons, grain boundaries, and other phonons. At a sufficiently large scale, phonon dynamics can be approximated as a Brownian random walk, leading to ordinary diffusion described by the heat equation. However, such approximations fail at the scale of the phonon mean free path. In this regime, a proper wave description encoding phonon scattering is required. For sufficiently short thermal systems, the thermal conductivity becomes extrinsic and exhibits linear scaling with system size. This scale is known as the ballistic transport regime. As the system size grows beyond this scale, the thermal conductivity asymptotes into the intrinsic, ordinary diffusive regime. However, there are special circumstances where this transition does not occur. In this Thesis, we demonstrate the anomalous scaling of thermal conductivity. The source of this anomaly is the Anderson localization of thermal phonons. Anderson localization is the spatial trapping of waves due to extreme levels of elastic disorder. The hallmark of Anderson localization is an exponential decay law of conductance with increasing system size. Since thermal transport is a broadband process, this exponential suppression leads to a thermal conductivity maximum as a function of system size. Our numerical study of GaAs/AlAs superlattices with ErAs nanoparticles exhibits this thermal conductivity maximum, yielding quantitative agreement to experiments. We then generalize our elastic model to allow for the incorporation of finite-temperature effects. The inclusion of phonon-phonon scattering decoheres phonons, resulting in phonon delocalization. Counterintuitively, the additional inelastic scattering increases conductance for originally localized phonons. This localization to diffusive transition as a function of temperature is captured in our model at low temperatures (~20K).

Download or read book Studying Phonon Mean Free Paths at the Nanoscale written by Lingping Zeng and published by . This book was released on 2016 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Measuring Phonon Mean Free Path Distributions by Probing Quasiballistic Phonon Transport in Grating Nanostructures written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Phonon Dynamics and Thermal Transport in Surface disordered Nanostructures written by Leon Nathaniel Maurer and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation examines the effects of surface disorder on phonon dynamics through two different but complementary approaches. First, we use a phonon Monte Carlo (PMC) simulation with random, rough surfaces. PMC is an excellent tool for studying nanostructures of experimentally relevant sizes. We detail our PMC method, including improvements over previous PMC simulations. We investigate why rough silicon nanowires have measured thermal conductivities about two orders of magnitude lower than predicted and comparable to amorphous materials. We show that it can be largely explained through scattering from rough surfaces; extreme roughness causes a qualitative change in how phonons interact with boundaries. During this project, we uncovered the utility of the geometric mean free path (GMFP), which is a concept developed in the study of chaotic billiards. The GMFP is the average distance a particle travels between surface scattering events (in the absence of other scattering mechanisms), and we show that the thermal conductivities obtained from our PMC simulations are a function of the GMFP. Second, we study two-dimensional elastic nanoribbons using finite-difference methods. Elastic materials make good model systems for studying lattice dynamics because elastic materials capture wave behavior, and, in the long-wavelength limit, phonons behave like elastic waves. Our elastic-medium finite-difference time-domain (FDTD) simulation allows us to efficiently model relatively large structures while still treating phonons as waves. We develop a technique to calculate the thermal conductivity of elastic nanoribbons by coupling our FDTD simulation with the Green-Kubo formula. We also employ a time-independent finite-difference (TIFD) method to solve for and study individual modes of our system. We find that rough surfaces can have an outsize impact on phonon dynamics. Surfaces do not simply scatter phonons; rough surfaces can also trap energy and cause all modes throughout the system to localize. The energy trapping and localization coincide with reduced thermal conductivity. We also investigate the effects of Rayleigh waves, a nonbulk mode often ignored in phonon transport simulations. We use TIFD methods to search for signs of wave chaos in nanoribbons. We find an interesting connection between the GMFP and thermal conductivity, which points the way towards future work.

Download or read book Thermal Rectification by Ballistic Phonons in Asymmetric Nanostructures written by John Patrick Miller and published by . This book was released on 2009 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modeling Self Heating Effects in Nanoscale Devices written by Katerina Raleva and published by Morgan & Claypool Publishers. This book was released on 2017-09-13 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is generally acknowledged that modeling and simulation are preferred alternatives to trial and error approaches to semiconductor fabrication in the present environment, where the cost of process runs and associated mask sets is increasing exponentially with successive technology nodes. Hence, accurate physical device simulation tools are essential to accurately predict device and circuit performance. Accurate thermal modelling and the design of microelectronic devices and thin film structures at the micro- and nanoscales poses a challenge to electrical engineers who are less familiar with the basic concepts and ideas in sub-continuum heat transport. This book aims to bridge that gap. Efficient heat removal methods are necessary to increase device performance and device reliability. The authors provide readers with a combination of nanoscale experimental techniques and accurate modelling methods that must be employed in order to determine a device's temperature profile.

Download or read book Phonon Dynamics and Thermal Transport in Surface disordered Nanostructures written by Leon Nathaniel Maurer and published by . This book was released on 2016 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation examines the effects of surface disorder on phonon dynamics through two different but complementary approaches. First, we use a phonon Monte Carlo (PMC) simulation with random, rough surfaces. PMC is an excellent tool for studying nanostructures of experimentally relevant sizes. We detail our PMC method, including improvements over previous PMC simulations. We investigate why rough silicon nanowires have measured thermal conductivities about two orders of magnitude lower than predicted and comparable to amorphous materials. We show that it can be largely explained through scattering from rough surfaces; extreme roughness causes a qualitative change in how phonons interact with boundaries. During this project, we uncovered the utility of the geometric mean free path (GMFP), which is a concept developed in the study of chaotic billiards. The GMFP is the average distance a particle travels between surface scattering events (in the absence of other scattering mechanisms), and we show that the thermal conductivities obtained from our PMC simulations are a function of the GMFP. Second, we study two-dimensional elastic nanoribbons using finite-difference methods. Elastic materials make good model systems for studying lattice dynamics because elastic materials capture wave behavior, and, in the long-wavelength limit, phonons behave like elastic waves. Our elastic-medium finite-difference time-domain (FDTD) simulation allows us to efficiently model relatively large structures while still treating phonons as waves. We develop a technique to calculate the thermal conductivity of elastic nanoribbons by coupling our FDTD simulation with the Green-Kubo formula. We also employ a time-independent finite-difference (TIFD) method to solve for and study individual modes of our system. We find that rough surfaces can have an outsize impact on phonon dynamics. Surfaces do not simply scatter phonons; rough surfaces can also trap energy and cause all modes throughout the system to localize. The energy trapping and localization coincide with reduced thermal conductivity. We also investigate the effects of Rayleigh waves, a nonbulk mode often ignored in phonon transport simulations. We use TIFD methods to search for signs of wave chaos in nanoribbons. We find an interesting connection between the GMFP and thermal conductivity, which points the way towards future work.

Download or read book Phonon Engineering Theory of Crystalline Layered Nanostructures written by Etraj I and published by LAP Lambert Academic Publishing. This book was released on 2015-11-19 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.