Abstract:In this paper, we present experimental evidence on the change of the phonon spectrum and vibrational properties of a bulk material through phonon hybridization mechanisms. The phonon spectrum in a finite material is strongly affected by the presence of free surfaces, which is the addition of a contribution from an essentially two-dimensional crystal. The phonon spectrum of a bulk material can hence be altered by a hybridization mechanism between confined phonon modes in nanostructures introduced on the surface… Show more
“…However, the existing theoretical literature cannot explain why some samples would show an increase whereas other would show a decrease in the heat capacity. Moreover, the measured temperature dependence does not reveal any significant changes of the relative heat capacity, although theoretically one may expect a stronger impact of the phonon interference at low temperatures [18] as phonon wavelengths and mean free paths become longer.10.1080/14686996.2018.1542524-F0005Figure 5.(a) Relative heat capacity of bulk silicon samples with pillars on the surface measured by Iskandar et al [62] at room temperature. The inset shows one of the samples (the shape and size are different for every sample).…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
confidence: 99%
“…Iskandar et al [62] studied thermal properties of bulk silicon with arrays of periodic pillars on the surface. Using the reactive ion etching, they created eight samples with different dimensions of the pillars and measured changes in the heat capacity of these samples as compared to the original silicon wafer.…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
confidence: 99%
“…Nor does the heat capacity seem to correlate with any other geometrical parameter of the pillars. Iskandar et al [62] attributed the observed changes in heat capacity to the impact of local resonance. However, the existing theoretical literature cannot explain why some samples would show an increase whereas other would show a decrease in the heat capacity.…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
confidence: 99%
“…The inset shows one of the samples (the shape and size are different for every sample). Reprinted from [62], with the permission of AIP Publishing. (b) The thermal conductivity of the nanobeams with pillars of different diameters measured by Anufriev et al [63] at room temperature.…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
confidence: 99%
“…(a) Relative heat capacity of bulk silicon samples with pillars on the surface measured by Iskandar et al [62] at room temperature. The inset shows one of the samples (the shape and size are different for every sample).…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
Phononic crystals have been studied for the past decades as a tool to control the propagation of acoustic and mechanical waves. Recently, researchers proposed that nanosized phononic crystals can also control heat conduction and improve the thermoelectric efficiency of silicon by phonon dispersion engineering. In this review, we focus on recent theoretical and experimental advances in phonon and thermal transport engineering using pillar-based phononic crystals. First, we explain the principles of the phonon dispersion engineering and summarize early proof-of-concept experiments. Next, we review recent simulations of thermal transport in pillar-based phononic crystals and seek to uncover the origin of the observed reduction in the thermal conductivity. Finally, we discuss first experimental attempts to observe the predicted thermal conductivity reduction and suggest the directions for future research.
“…However, the existing theoretical literature cannot explain why some samples would show an increase whereas other would show a decrease in the heat capacity. Moreover, the measured temperature dependence does not reveal any significant changes of the relative heat capacity, although theoretically one may expect a stronger impact of the phonon interference at low temperatures [18] as phonon wavelengths and mean free paths become longer.10.1080/14686996.2018.1542524-F0005Figure 5.(a) Relative heat capacity of bulk silicon samples with pillars on the surface measured by Iskandar et al [62] at room temperature. The inset shows one of the samples (the shape and size are different for every sample).…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
confidence: 99%
“…Iskandar et al [62] studied thermal properties of bulk silicon with arrays of periodic pillars on the surface. Using the reactive ion etching, they created eight samples with different dimensions of the pillars and measured changes in the heat capacity of these samples as compared to the original silicon wafer.…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
confidence: 99%
“…Nor does the heat capacity seem to correlate with any other geometrical parameter of the pillars. Iskandar et al [62] attributed the observed changes in heat capacity to the impact of local resonance. However, the existing theoretical literature cannot explain why some samples would show an increase whereas other would show a decrease in the heat capacity.…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
confidence: 99%
“…The inset shows one of the samples (the shape and size are different for every sample). Reprinted from [62], with the permission of AIP Publishing. (b) The thermal conductivity of the nanobeams with pillars of different diameters measured by Anufriev et al [63] at room temperature.…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
confidence: 99%
“…(a) Relative heat capacity of bulk silicon samples with pillars on the surface measured by Iskandar et al [62] at room temperature. The inset shows one of the samples (the shape and size are different for every sample).…”
Section: Experimental Measurements Of the Thermal Propertiesmentioning
Phononic crystals have been studied for the past decades as a tool to control the propagation of acoustic and mechanical waves. Recently, researchers proposed that nanosized phononic crystals can also control heat conduction and improve the thermoelectric efficiency of silicon by phonon dispersion engineering. In this review, we focus on recent theoretical and experimental advances in phonon and thermal transport engineering using pillar-based phononic crystals. First, we explain the principles of the phonon dispersion engineering and summarize early proof-of-concept experiments. Next, we review recent simulations of thermal transport in pillar-based phononic crystals and seek to uncover the origin of the observed reduction in the thermal conductivity. Finally, we discuss first experimental attempts to observe the predicted thermal conductivity reduction and suggest the directions for future research.
The notion of a locally resonant metamaterial—widely applied to light and sound—has recently been introduced to heat, whereby the thermal conductivity is reduced primarily by intrinsic localized atomic vibrations rather than scattering mechanisms. This article reviews and analyzes this new emerging concept, termed nanophononic metamaterial (NPM), and contrasts it with the competing concept of a nanophononic crystal (NPC) in which thermal conductivity reduction is realized primarily via nanoscale Bragg scattering. Both the NPM and NPC core mechanisms require the presence of a sufficient level of wave behavior, which is possible when there is a relatively wide distribution of the phonon mean free path (MFP). Silicon serves as a perfect material to form NPMs and NPCs given its relatively large average phonon MFP. This offers a unique opportunity considering silicon's abundance and mature fabrication technology. It is shown in this comparative study that while both the NPM and NPC nanosystems may be rendered to serve as extreme insulators of heat, an NPM may do so without excessive reduction in the minimum feature size–which is key to keeping the electrical properties intact. This trait makes a silicon‐based NPM poised to serve as a low‐cost thermoelectric material with exceptional performance.
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...
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