A First Principles Approach to Thermal Transport in Nanomaterials (original) (raw)
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AIP Advances, 2012
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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.
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.