Thermoelectric Metamaterials: Nano‐Waveguides for Thermoelectric Energy Conversion and Heat Management at the Nanoscale

Abstract

are heterostructures, electronic and phononic superlattices that have been extensively studied since their discovery nearly 100 years ago. [2][3][4][5][6][7][8][9] Electrons and phonons in geometry-modulated nanostructures, nano-waveguides (nWVGs), have attracted extended research interest since the 1980s. [10][11][12][13][14] In 2010, we proposed nWVGs for thermoelectric efficiency enhancement by geometrical control of electron and phonon properties. [15][16][17] Thermoelectric (TE) energy conversion could ideally serve the need of our society for low-cost green energy production, reduction of CO 2 emissions and waste-heat recycling. Low efficiencies of traditional thermoelectric materials prohibited for long widespread thermoelectric applications. In the last 20 years, the efforts of the thermoelectric community concentrated to alternative approaches, such as using low-dimensional and nanostructured materials, to enhance the TE efficiency. Much progress has been achieved and research is continuing along these lines. Currently, another dimension has been added by that thermoelectric materials could power the Internet of things (IoT). [18] Already-achieved record efficiencies should be sufficient for this purpose. Nevertheless, traditional thermoelectric materials are not suitable for integration into the microelectronics industrial processes. Novel strategies to enhance the TE efficiency of technologically important materials are of predominant importance and interest. Thermoelectric metamaterials (THEMMs), nWVGs with enhanced TE properties, can contribute to this task. Their operation is based on the same principles as low-dimensional and nanostructured materials.The discovery of low-dimensional materials revolutionized science and technology provide the fascinating ability to engineer the energy bandstructure and properties of matter with superlattices of different materials. [19][20][21] Superlattices made of low-dimensional constituent materials exhibited improved properties and novel functionalities due to quantum confinement. Shrinking dimensions to the nanoscale and forming low-dimensional nanostructures and nanocomposite materials opened-up new horizons in science and led to the era of nanotechnology.Low-dimensional materials have one or more dimensions small enough (typically in the nanometric range) so that carriers The idea of using metamaterials for thermoelectrics was proposed 10 years ago. Enhanced thermoelectric effects and decreased thermal conduction are theoretically demonstrated due to modification of electrons and phonons by quantum interference between propagating and scattered waves at geometrical discontinuities. These structures are now considered promising for breakthrough in thermoelectric energy conversion and heat management at the nanoscale. They could ideally power the Internet of things. This review is devoted to electron and phonon transport properties of thermoelectric metamaterials in the quantum confinement regime. Enhanced thermoelectric effects and decreased thermal conductiv...

Bonding Heterogeneity Inducing Low Lattice Thermal Conductivity and High Thermoelectric Performance in 2D CdTe2

“…The κ L as a function of the phonon mean free path (MFP) is an important parameter to estimate the size effects and design nanostructures with optimized κ L . , As shown in Figure f, almost all phonons have an MFP below 1 μm in 2D CdTe. Notably, phonons in CdTe with MFPs below 20 nm contribute 3/4 of the κ L , implying that the κ L of CdTe can decrease sharply with a sample of less than 20 nm.…”

“…Thus, a reduced κ L can effectively improve thermoelectric performance. Defect engineering or nanostructuring is usually used to increase phonon scattering, inducing low thermal transport properties. − However, these strategies sometimes lead to a degradation of the electronic transport properties. Thus, exploring compounds with intrinsic low κ L has been of great interest because the electronic transport properties can be optimized with a small effect on the κ L .…”

Low-Grade Thermal Energy Harvesting and Self-Powered Sensing Based on Thermogalvanic Hydrogels

“…In the past few years, thermogalvanic hydrogels have made significant advances in both thermoelectric conversion and thermoelectric sensing [ 138 , 139 , 140 , 141 ]. Compared with other energy devices, such as chemical batteries, supercapacitors, and solar cells, first of all, thermogalvanic hydrogels can directly convert heat into electricity, enabling the recovery and utilization of applied waste heat, thus contributing to the development of green energy.…”

A brief review of metamaterials for opening low-frequency band gaps

“…The term metamaterial is a composite word of meta and materia. The word meta stems from Greek, carrying a meaning of beyond, and the word materia stems from the Latin word material, carrying a meaning of matter or material [1] . From the wording components of this term metamaterial, it is clear that metamaterials denote a type of man-made materials capable of achieving properties that are not found in natural materials.…”