A First Principles Approach to Thermal Transport in Nanomaterials (original) (raw)
Thermal transport in nanostructures
AIP Advances, 2012
This review summarizes recent studies of thermal transport in nanoscaled semiconductors. Different from bulk materials, new physics and novel thermal properties arise in low dimensional nanostructures, such as the abnormal heat conduction, the size dependence of thermal conductivity, phonon boundary/edge scatterings. It is also demonstrated that phonons transport super-diffusively in low dimensional structures, in other words, Fourier's law is not applicable. Based on manipulating phonons, we also discuss envisioned applications of nanostructures in a broad area, ranging from thermoelectrics, heat dissipation to phononic devices.
Materials Science-poland, 2008
New physical phenomena connected with heat transport in structures with dimensions comparable with characteristic lengths of energy carriers are briefly reviewed. Problems with basic physical understanding of mechanisms responsible for energy transport in such structures are considered. In particular, the role of boundaries is discussed. Thermal properties of a few structures which dimensions influence heat transport, namely: superlattices and multilayered systems, nanoporous materials and nanotubes are analyzed. Problem of hot spots in electronic devices is also mentioned. The last part of the paper is devoted to methods of experimental investigation of thermal properties of nanostructures. Capabilities and shortcomings of two relatively new experimental techniques: picosecond reflectance thermometry and scanning thermal microscopy have been discussed.
Nanoscale thermal transport. II. 2003–2012
Applied Physics Reviews, 2014
A diverse spectrum of technology drivers such as improved thermal barriers, higher efficiency thermoelectric energy conversion, phase-change memory, heat-assisted magnetic recording, thermal management of nanoscale electronics, and nanoparticles for thermal medical therapies are motivating studies of the applied physics of thermal transport at the nanoscale. This review emphasizes developments in experiment, theory, and computation in the past ten years and summarizes the present status of the field. Interfaces become increasingly important on small length scales. Research during the past decade has extended studies of interfaces between simple metals and inorganic crystals to interfaces with molecular materials and liquids with systematic control of interface chemistry and physics. At separations on the order of $1 nm, the science of radiative transport through nanoscale gaps overlaps with thermal conduction by the coupling of electronic and vibrational excitations across weakly bonded or rough interfaces between materials. Major advances in the physics of phonons include first principles calculation of the phonon lifetimes of simple crystals and application of the predicted scattering rates in parameter-free calculations of the thermal conductivity. Progress in the control of thermal transport at the nanoscale is critical to continued advances in the density of information that can be stored in phase change memory devices and new generations of magnetic storage that will use highly localized heat sources to reduce the coercivity of magnetic media. Ultralow thermal conductivity-thermal conductivity below the conventionally predicted minimum thermal conductivity-has been observed in nanolaminates and disordered crystals with strong anisotropy. Advances in metrology by time-domain thermoreflectance have made measurements of the thermal conductivity of a thin layer with micron-scale spatial resolution relatively routine. Scanning thermal microscopy and thermal analysis using proximal probes has achieved spatial resolution of 10 nm, temperature precision of 50 mK, sensitivity to heat flows of 10 pW, and the capability for thermal analysis of sub-femtogram samples. V
Journal of Applied Physics, 2003
Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid-solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime-experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3 method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.
Thermal Conductivity of Nanoscale Materials: A Review
Journal of Ultra Scientist of Physical Sciences Section B, 2017
Nanoscale materials are being widely used in science and technology. Rapid development in synthesis and fabrication of Nanoscale materials has created a great demand for scientific understanding of thermal conductivity in nanoscale materials. The thermal conductivity in low dimensional has been obtained by using different theoretical and numerical approaches. The low dimensional structures such as quantum well, wires and dots confined in extremely small region and have novel transport properties. Measurement methods e.g. reducing grain size, multiple Phonon scattering, BTE in 2D nanoribbons, source of coherent Phonons etc open new way for nanoscale thermal transport study. This review summarizes the development in experiments, theory and computation that have occurred in thermal transport of nanoscale materials.
2013
Materials at the nanoscale show properties uniquely different from the bulk scale which when controlled can be utilized for variety of thermal management applications. Different applications require reduction, increase or directional control of thermal conductivity. This thesis focuses on investigating thermal transport in two such application areas, viz., 1) thermoelectric energy conversion and 2) thermal rectification. Using molecular dynamics simulations, several methods for reducing of thermal conductivity in polyaniline and polyacetylene are investigated. The reduction in thermal conductivity leads to improvement in thermoelectric figure of merit. Thermal diodes allow heat transfer in one direction and prevents in the opposite direction. These Professor Ishwar K. Puri is my thesis advisor. He mentored me throughout my PhD. He provided new ideas, research directions and key technical inputs at all the stages. He also provided critical feedback while preparing manuscripts. He is a co-author in all my scientific publications during this PhD. Dr. Ganesh Balasubramanian introduced me to molecular dynamics simulations and the field of nanoscale thermal transport. He helped me with research ideas in the beginning phases of my PhD. He also provided critical reviews in manuscript preparation. He is a co-author in two of my published journal papers. viii
Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid-solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime-experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3 method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.
Thermoelectric Transport in Nanocomposites
Materials (Basel, Switzerland), 2017
Thermoelectric materials which can convert energies directly between heat and electricity are used for solid state cooling and power generation. There is a big challenge to improve the efficiency of energy conversion which can be characterized by the figure of merit (ZT). In the past two decades, the introduction of nanostructures into bulk materials was believed to possibly enhance ZT. Nanocomposites is one kind of nanostructured material system which includes nanoconstituents in a matrix material or is a mixture of different nanoconstituents. Recently, nanocomposites have been theoretically proposed and experimentally synthesized to be high efficiency thermoelectric materials by reducing the lattice thermal conductivity due to phonon-interface scattering and enhancing the electronic performance due to manipulation of electron scattering and band structures. In this review, we summarize the latest progress in both theoretical and experimental works in the field of nanocomposite the...
Anomalous Thermal Transport in Nanostructures
Fluctuation Relations and Beyond, 2013
Thermal transport in nanoscale structures has attracted an increasing attention in last two decades. Here we give a brief review of the recent developments in experimental and theoretical studies of heat transport in nano materials such as nanotube and nanowire. In particular, we will demonstrate that the phonons in nanotube and nanowires transport super-diffusively, which leads to a length dependent thermal conductivity. In other words, heat conduction in low dimensional nanostructures does not obey the Fourier's law.
Thermal Conductivity of a Nano-Structured Material
2005
In this paper, the phonon Boltzmann equation is solved numerically to study the phonon thermal conductivity of nano-structured thin films opened a nano-hole in a host material. We focused on effects of hole size on the reduction of thermal conductivity. The simulation shows that the temperature profiles in nano-structures are very different from those in conventional bulk materials, due to ballistic phonon transport at nanoscale. The conventional heat conduction equations cannot be applied to solve the heat transfer in solids at nanoscale. The effective thermal conductivity of nano-structures are calculated from temperature gradient. We predict the thermal conductivity dependence on the size of a nano-hole. At constant thin film thickness the larger the hole size, the smaller is the thermal conductivity of two-dimensional nano-structured thin film. The results of this study can be used to the development of thermal management of heat conduction by using artificial physical property.
ELECTRIC CURRENT, THERMOCURRENT, AND HEAT FLUX IN NANO- AND MICROELECTRONICS: TRANSPORT MODEL
The Landauer – Datta – Lundstrom modern electron and heat transport model is briefly summarized. If a band structure is chosen analytically or numerically, the number of conduction modes can be evaluated and, if a model for a mean-free-path for backscattering can be established, then the near-equilibrium thermoelectric transport coefficients can be calculated for 1D, 2D, and 3D resistors of any size in ballistic, quasi-ballistic, and diffusive linear response regimes when there are differences in both voltage and/or temperature across the device. Modes of conduction and transmission concepts are introduced. New expression for a specific resistivity is suggested providing a different view of resistivity in terms of the specific number of modes (per unit cross-sectional area) and the mean-free-path for backscattering. Fermi conduction window functions for electrons and phonons are formulated and compared. Whether a conductor is good or bad is determined only by the availability of the conductor energy states in an energy window ~ around the equilibrium electrochemical potential, which can vary widely from one material to another. Special attention is given to the near-equilibrium transport. General expression for thermocurrent is introduced which is suitable for analysis of conductivity of any materials from metals and semiconductors up to modern nanoresistors and nanocomposites. This general expression is simplified for the case of the linear response regime. Thermocurrent is derived through three transport coefficients – conductivity, the Soret electro-thermal diffusion coefficient, and the electronic heat conductance under the short circuit conditions. Heat transfer by phonons is treated in details. Basic equation for the heat current is formulated. Electrical and thermal conductances are similar in structure, namely: both are proportional to corresponding quantum of conductance, times an integral over the transmission, times the number of modes, times a window function. Moreover, the thermal broadening functions for electrons and phonons have similar shapes and each has a width of a few kT. Along with the number of modes determined by the dispersion relation, these two window functions play a key role in quantitative determination of the electrical and thermal conductivities.
19th International Conference on Ultrafast Phenomena, 2014
Understanding thermal transport from nanoscale heat sources is important for a fundamental description of energy flow in materials, as well as for many technological applications including thermal management in nanoelectronics, thermoelectric devices, nano-enhanced photovoltaics and nanoparticle-mediated thermal therapies. Thermal transport at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of carrier mean free paths in a material, the length scales of the heat sources, and the distance over which heat is transported. Past work has shown that Fourier's law for heat conduction dramatically over-predicts the rate of heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale thermal transport that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interplay between neighboring heat sources can facilitate efficient, diffusive-like heat dissipation, even from the smallest nanoscale heat sources. This finding suggests that thermal management in nanoscale systems including integrated circuits might not be as challenging as projected. Finally, we demonstrate a unique and new capability to extract mean free path distributions of phonons in materials, allowing the first experimental validation of differential conductivity predictions from first-principles calculations.
A Theoretical and Numerical Study of Nanoscale Heat Transfer
2020
In order to continue the progress of nanotechnology in producing effective and efficient mechanical, electrical, and optical nanostructure devices, the physics of the devices in micro and nanoscale need to be understood and accurately modeled. For instance, the demand for high areal density data storage devices such as hard disk drives (HDDs) has led to heatassisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR) technologies. These technologies require layered nanostructures with thicknesses of a few nanometers and a high temperature difference across the layers. These technologies introduce thermo-mechanical design challenges since the nanoscale heat transfer mechanics do not follow the classical heat transfer theories. In this work, the mechanisms of heat transfer in the nanoscale are studied. are like siblings to me. I also immensely thank Shahin Tabrizi, a father figure to me, for his selfless mentorship, which significantly improved my academic and personal life. Finally, this accomplishment would not be possible without the unconditional love, support, and encouragement of my family. My parents have never had the chance to pursue their dreams as students. However, their endless encouragement and support always fueled my passion and resilience in pursuing my dreams. Their kind attitude and care for the family and me have taught me how to be selfless while aiming and striving for the best. Growing up, my beloved brother and sister have always been there for me, and they taught me how to be a better and kinder person.
Universal effective medium theory to predict the thermal conductivity in nanostructured materials
International Journal of Heat and Mass Transfer, 2022
Nanostructured materials enable high thermal transport tunability, holding promises for thermal management and heat harvesting applications. Predicting the effect that nanostructuring has on thermal conductivity requires models, such as the Boltzmann transport equation (BTE), that capture the non-diffusive transport of phonons. Although the BTE has been well validated against several key experiments, notably those on nanoporous materials, its applicability is computationally expensive. Several effective model theories have been put forward to estimate the effective thermal conductivity; however, most of them are either based on simple geometries, e.g., thin films, or simplified material descriptions such as the gray-model approximation. To fill this gap, we propose a model that takes into account the whole mean-free-path (MFP) distribution as well as the complexity of the material's boundaries in infinitely thick films with extruded porosity using uniparameter logistic regression. We validate our approach, which is called the "Ballistic Correction Model" (BCM), against full BTE simulations of a selection of three base materials (GaAs, InAs, and Si) with nanoscale porosity, obtaining excellent agreement. While the key parameters of our method, associated with the geometry of the bulk material, are obtained from the BTE, they can be decoupled and used in arbitrary combinations and scales. We tabulated these parameters for a few cases, enabling the exploration of systems that are beyond those considered in this work. Providing a simple yet accurate estimation of thermal transport in nanostructures, our work sets out to accelerate the discovery of materials for thermal-related applications.
Analytical insights into thermophysical properties of nanomaterials
The European Physical Journal Applied Physics, 2014
Using the discrete ordinate method, we solve the equations of phonon radiative transfer for thin films analytically, and deduce closed-form expressions for three thermophysical properties including the phonon intensity, heat flux density and effective phonon thermal conductivity. These analytical expressions provide a fast and convenient way to analyze heat conduction behavior in thin films, and thus allowing us to comprehend how the film thickness and bulk phonon mean free path affects the thermophysical properties. Also we extend these expressions from thin films to one period of superlattices, and demonstrate that adjusting the thickness ratio of two layers can control its effective phonon thermal conductivity.
Conceptual analysis of heat transfer and its modification at the nano scale
Development of technology in the fields of heavy machinery demands the use of materials which have low thermal conductivity for various reasons like heat loss, failure of components due to thermal expansion, etc.. Hence nano engineered materials are naturally a better choice given that the cost of production and other convenience factors are favourable. In any crystal , heat transfer from one end of the crystal to another occurs by the transfer of momentum from one molecule to another. The desired requirements can be met by nano-structuring the material accordingly. The concept lies in how the atoms are arranged within the crystal lattice. Taking into account the concept of slip systems and other structural configurations, a microscopic model for a carbon nanotube was developed in which the strength is enhanced and thermal conductivity is lowered.
Phonon Transport at the Nanoscale with Applications to Batteries and Advanced Thermal Insulation
International Heat Transfer Conference 16
It has been almost three decades since Nanoscale Thermal Science and Engineering became a wellestablished research field. Various major breakthroughs in fundamental understanding of thermal transport (phonons, photons, and electrons) at the nanoscale have been achieved in these three decades; however, the impact of these fundamental insights has been primarily targeted toward microelectronics and thermoelectrics applications. In this paper we provide examples of other applications such as Lithium ion battery thermal management and building thermal insulation, where nanoscale thermal science has a significant role to play. We have used time domain thermoreflectance (TDTR) to measure thermal conductivity of Lithium ion battery cathode material. To understand the fundamentals of thermal transport in the cathode material we created a model cathode system as compared engineered samples using pulsed laser deposition technique. We also used 3-omega technique for the engineered system. We have also made highly insulating material using functionalized nanoparticles for building applications. Results show that surface functionalization has a huge impact on thermal conductivity of an assembly of nanoparticle.
Low-temperature thermal transport in nanowires
Journal of Experimental and Theoretical Physics Letters, 2005
We propose a theory of low temperature thermal transport in nano-wires in the regime where a competition between phonon and flexural modes governs the relaxation processes. Starting with the standard kinetic equations for two different types of quasiparticles we derive a general expression for the coefficient of thermal conductivity. The underlying physics of thermal conductance is completely determined by the corresponding relaxation times, which can be calculated directly for any dispersion of quasiparticles depending on the size of a system. We show that if the considered relaxation mechanism is dominant, then at small wire diameters the temperature dependence of thermal conductivity experiences a crossover from T 1/2 to T 3-dependence. Quantitative analysis shows reasonable agreement with resent experimental results.
Heat Transport Control and Thermal Characterization of Low-Dimensional Materials: A Review
Nanomaterials, 2021
Heat dissipation and thermal management are central challenges in various areas of science and technology and are critical issues for the majority of nanoelectronic devices. In this review, we focus on experimental advances in thermal characterization and phonon engineering that have drastically increased the understanding of heat transport and demonstrated efficient ways to control heat propagation in nanomaterials. We summarize the latest device-relevant methodologies of phonon engineering in semiconductor nanostructures and 2D materials, including graphene and transition metal dichalcogenides. Then, we review recent advances in thermal characterization techniques, and discuss their main challenges and limitations.