Heat conduction tuning using the wave nature of phonons

The world communicates to our senses of vision, hearing and touch in the language of waves, as the light, sound, and even heat essentially consist of microscopic vibrations of different media. The wave nature of light and sound has been extensively investigated over the past century and is now widely used in modern technology. But the wave nature of heat has been the subject of mostly theoretical studies, as its experimental demonstration, let alone practical use, remains challenging due to the extremely short wavelengths of these waves. Here we show a possibility to use the wave nature of heat for thermal conductivity tuning via spatial short-range order in phononic crystal nanostructures. Our experimental and theoretical results suggest that interference of thermal phonons occurs in strictly periodic nanostructures and slows the propagation of heat. This finding broadens the methodology of heat transfer engineering by expanding its territory to the wave nature of heat

Materials Today Physics

Thermal transport at the nanoscale level is attracting attention not only because of its physically interesting features such as the peculiar behavior of phonons due to their pronounced ballistic and wave-like properties but also because of its potential applications in alleviating heat dissipation problems in electronic and optical devices and thermoelectric energy harvesting. In the last quarter-century, researchers have elucidated the thermal transport properties of various nanostructured materials, including phononic crystals (PnCs): artificial periodic structures for phonons. PnCs are excellent platforms for investigating thermal transport owing to their well-defined structural parameters. In addition, it is interesting to control thermal transport by interference, as demonstrated in the low-frequency regime with elastic waves and sounds. In this article, we focus on high-frequency phonons and review the thermal transport in semiconductor PnCs. This comprehensive review provides an understanding of recent studies and trends, organized as theoretical and experimental, in terms of the quasiparticle and wave aspects

Planar-type silicon thermoelectric generator with phononic nanostructures for 100 {\mu}W energy harvesting

Energy harvesting is essential for the internet-of-things networks where a tremendous number of sensors require power. Thermoelectric generators (TEGs), especially those based on silicon (Si), are a promising source of clean and sustainable energy for these sensors. However, the reported performance of planar-type Si TEGs never exceeded power factors of 0.1 ${\mu} Wcm^{-2} K^{-2}$ due to the poor thermoelectric performance of Si and the suboptimal design of the devices. Here, we report a planar-type Si TEG with a power factor of 1.3 ${\mu} Wcm^{-2} K^{-2}$ around room temperature. The increase in thermoelectric performance of Si by nanostructuring based on the phonon-glass electron-crystal concept and optimized three-dimensional heat-guiding structures resulted in a significant power factor. In-field testing demonstrated that our Si TEG functions as a 100-${\mu}W$-class harvester. This result is an essential step toward energy harvesting with a low-environmental load and cost-effective material with high throughput, a necessary condition for energy-autonomous sensor nodes for the trillion sensors universe

On the reduction and rectification of thermal conduction using phononic crystals with pacman-shaped holes

International audienc

Review of thermal transport in phononic crystals

International audienceThermal transport at the nanoscale level is attracting attention not only because of its physically interesting features such as the peculiar behavior of phonons due to their pronounced ballistic and wave-like properties but also because of its potential applications in alleviating heat dissipation problems in electronic and optical devices and thermoelectric energy harvesting. In the last quarter-century, researchers have elucidated the thermal transport properties of various nanostructured materials, including phononic crystals (PnCs): artificial periodic structures for phonons. PnCs are excellent platforms for investigating thermal transport owing to their well-defined structural parameters. In addition, it is interesting to control thermal transport by interference, as demonstrated in the low-frequency regime with elastic waves and sounds. In this article, we focus on high-frequency phonons and review the thermal transport in semiconductor PnCs. This comprehensive review provides an understanding of recent studies and trends, organized as theoretical and experimental, in terms of the quasiparticle and wave aspects

Imbalance in fatty-acid-chain length of gangliosides triggers Alzheimer amyloid deposition in the precuneus.

Amyloid deposition, a crucial event of Alzheimer's disease (AD), emerges in distinct brain regions. A key question is what triggers the assembly of the monomeric amyloid ß-protein (Aß) into fibrils in the regions. On the basis of our previous findings that gangliosides facilitate the initiation of Aß assembly at presynaptic neuritic terminals, we investigated how lipids, including gangliosides, cholesterol and sphingomyelin, extracted from synaptic plasma membranes (SPMs) isolated from autopsy brains were involved in the Aß assembly. We focused on two regions of the cerebral cortex; precuneus and calcarine cortex, one of the most vulnerable and one of the most resistant regions to amyloid deposition, respectively. Here, we show that lipids extracted from SPMs isolated from the amyloid-bearing precuneus, but neither the amyloid-free precuneus nor the calcarine cortex, markedly accelerate the Aß assembly in vitro. Through liquid chromatography-mass spectrometry of the lipids, we identified an increase in the ratio of the level of GD1b-ganglioside containing C20:0 fatty acid to that containing C18:0 as a cause of the enhanced Aß assembly in the precuneus. Our results suggest that the local glycolipid environment play a critical role in the initiation of Alzheimer amyloid deposition

Increased ratio of level of (d20:1–20:0) to that of (d20:1–18:0) in GD1b-ganglioside in the amyloid-bearing precuneus.

<p>Ratios of the level of (d20:1–20:0) to that of (d20:1–18:0) in GD1a- and GD1b-gangliosides were calculated from the levels of <i>a</i>- and <i>b</i>-series of gangliosides obtained by normal-phase LC-MS using an NH₂ column. The ratio is expressed as mean ± SEM. *, <i>p</i><0.05. <i>P1</i>, <i>C1</i>, <i>P2</i> and <i>C2</i> indicate lipid samples extracted from SPMs of the amyloid-free precuneus, the calcarine cortex of the brain with the amyloid-free precuneus, the amyloid-bearing precuneus, and the calcarine cortex of the brain with the amyloid-bearing precuneus, respectively.</p

Effect of the alteration in the ratio of level of (d20:1–20:0) to that of (d20:1–18:0) in GD1b-ganglioside on Aß assembly.

<p>A, Addition of GD1b(d20:1–20:0) ganglioside to the lipids extracted from the amyloid-free precuneus significantly enhanced Aß assembly as determined by AFM. B, Addition of GD1b(d20:1–18:0) ganglioside to the lipids extracted from the amyloid-bearing precuneus significantly inhibited Aß assembly as determined by AFM. The subspecies of GD1b-ganglioside was purified from commercially available GD1b-gangliosides and added to the extent that its ratio equaled (<i>center</i>, × 1) or exceeded by four-fold (<i>right</i>, × 5) the original ratio in the lipids extracted from the amyloid-bearing precuneus. Scale bar, 500 nm.</p