Author: 李海鵬Publisher:
ISBN:
Category : Low-dimensional semiconductors
Languages : en
Pages : 256
Book Description
Molecular Dynamics Simulations of Phonon Thermal Transport in Low-dimensional Silicon Structures
Author: 李海鵬Publisher:
ISBN:
Category : Low-dimensional semiconductors
Languages : en
Pages : 256
Book Description
Phonon Thermal Transport in Silicon-Based Nanomaterials
Author: Hai-Peng LiPublisher: Springer
ISBN: 9811326371
Category : Science
Languages : en
Pages : 86
Book Description
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.
Phonons in Low Dimensional Structures
Author: Vasilios N. StavrouPublisher: BoD – Books on Demand
ISBN: 1789846269
Category : Science
Languages : en
Pages : 176
Book Description
The field of low-dimensional structures has been experiencing rapid development in both theoretical and experimental research. Phonons in Low Dimensional Structures is a collection of chapters related to the properties of solid-state structures dependent on lattice vibrations. The book is divided into two parts. In the first part, research topics such as interface phonons and polaron states, carrier-phonon non-equilibrium dynamics, directional projection of elastic waves in parallel array of N elastically coupled waveguides, collective dynamics for longitudinal and transverse phonon modes, and elastic properties for bulk metallic glasses are related to semiconductor devices and metallic glasses devices. The second part of the book contains, among others, topics related to superconductor, phononic crystal carbon nanotube devices such as phonon dispersion calculations using density functional theory for a range of superconducting materials, phononic crystal-based MEMS resonators, absorption of acoustic phonons in the hyper-sound regime in fluorine-modified carbon nanotubes and single-walled nanotubes, phonon transport in carbon nanotubes, quantization of phonon thermal conductance, and phonon Anderson localization.
First Principles Modeling of Phonon Heat Conduction in Nanoscale Crystalline Structures
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
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.
Phonon Transport in Molecular Dynamics Simulations
Author: Alan J. H. McGaugheyPublisher: Ann Arbor, Mich. : University Microfilms International
ISBN: 9780496850648
Category :
Languages : en
Pages :
Book Description
Phonon Dynamics and Thermal Transport in Surface-disordered Nanostructures
Author: Leon Nathaniel MaurerPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
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.
Nanoscale Energy Transport and Harvesting
Author: Zhang GangPublisher: CRC Press
ISBN: 9814463035
Category : Science
Languages : en
Pages : 222
Book Description
Energy transport and conversion in nanoscale structures is a rapidly expanding area of science. It looks set to make a significant impact on human life and, with numerous commercial developments emerging, will become a major academic topic over the coming years. Owing to the difficulty in experimental measurement, computational simulation has becom
Two-dimensional Materials
Author: Pramoda Kumar NayakPublisher: BoD – Books on Demand
ISBN: 9535125540
Category : Technology & Engineering
Languages : en
Pages : 282
Book Description
There are only a few discoveries and new technologies in materials science that have the potential to dramatically alter and revolutionize our material world. Discovery of two-dimensional (2D) materials, the thinnest form of materials to ever occur in nature, is one of them. After isolation of graphene from graphite in 2004, a whole other class of atomically thin materials, dominated by surface effects and showing completely unexpected and extraordinary properties, has been created. This book provides a comprehensive view and state-of-the-art knowledge about 2D materials such as graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMD) and so on. It consists of 11 chapters contributed by a team of experts in this exciting field and provides latest synthesis techniques of 2D materials, characterization and their potential applications in energy conservation, electronics, optoelectronics and biotechnology.
Phonon Dynamics and Thermal Transport in Surface-disordered Nanostructures
Author: Leon Nathaniel MaurerPublisher:
ISBN:
Category :
Languages : en
Pages : 286
Book Description
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.
Author: Xinjiang Wang