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

Gluchko, Sergei; Anufriev, Roman; Yanagisawa, Ryoto; Volz, Sébastian; Nomura, Masahiro

doi:10.1063/1.5079931

Cited by 24 publications

(20 citation statements)

References 21 publications

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“…The carrier scattering becomes strongly energy dependent, which increases the Seebeck coefficient. Another nano-feature that has been widely explored are nanopores, which drastically reduce thermal conductivity [26,28,141,142,143,144,145,146,147,148,149]. Porosity could lead to an increase in the Seebeck coefficient due to the increase of the entropy per charge carrier due to energy filtering at the pore boundaries, but as we will show later on, this improvement is not significant.…”

Section: Nanostructuring: Materials Methods and State-of-the-artmentioning

confidence: 99%

Hierarchically nanostructured thermoelectric materials: challenges and opportunities for improved power factors

et al. 2020

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The field of thermoelectric materials has undergone a revolutionary transformation over the last couple of decades as a result of the ability to nanostructure and synthesize myriads of materials and their alloys. The ZT figure of merit, which quantifies the performance of a thermoelectric material has more than doubled after decades of inactivity, reaching values larger than two, consistently across materials and temperatures. Central to this ZT improvement is the drastic reduction in the material thermal conductivity due to the scattering of phonons on the numerous interfaces, boundaries, dislocations, point defects, phases, etc., which are purposely included. In these new generation of nanostructured materials, phonon scattering centers of different sizes and geometrical configurations (atomic, nano- and macro-scale) are formed, which are able to scatter phonons of mean-free-paths across the spectrum. Beyond thermal conductivity reductions, ideas are beginning to emerge on how to use similar hierarchical nanostructuring to achieve power factor improvements. Ways that relax the adverse interdependence of the electrical conductivity and Seebeck coefficient are targeted, which allows power factor improvements. For this, elegant designs are required, that utilize for instance non-uniformities in the underlying nanostructured geometry, non-uniformities in the dopant distribution, or potential barriers that form at boundaries between materials. A few recent reports, both theoretical and experimental, indicate that extremely high power factor values can be achieved, even for the same geometries that also provide ultra-low thermal conductivities. Despite the experimental complications that can arise in having the required control in nanostructure realization, in this colloquium, we aim to demonstrate, mostly theoretically, that it is a very promising path worth exploring. We review the most promising recent developments for nanostructures that target power factor improvements and present a series of design ‘ingredients’ necessary to reach high power factors. Finally, we emphasize the importance of theory and transport simulations for materialoptimization, and elaborate on the insight one can obtain from computational tools routinely used in the electronic device communities. Graphical abstract

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Section: Nanostructuring: Materials Methods and State-of-the-artmentioning

confidence: 99%

Hierarchically nanostructured thermoelectric materials: challenges and opportunities for improved power factors

et al. 2020

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“…Nanophononics and nanomechanics deal with vibrations in solids where the typical frequencies are in the range spanning from few GHz up to THz. [1][2][3][4][5][6][7][8][9][10][11][12] These frequencies have associated wavelengths in the 1-100 nm range, making them interesting for high-resolution acoustic imaging and sensing applications. Ultrasound imaging in the kHz-MHz has revolutionized medical applications; a similar impact can be predicted for nanoacoustic waves for non-destructive testing at the nanoscale.…”

Section: Introductionmentioning

confidence: 99%

Mesoporous Thin Films for Acoustic Devices in the Gigahertz Range

et al. 2020

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The coherent manipulation of acoustic waves on the nanoscale usually requires multilayers with thicknesses and interface roughness defined down to the atomic monolayer. This results in expensive devices with predetermined functionality. Nanoscale mesoporous materials present high surface-to-volume ratio and tailorable mesopores, which allow the incorporation of chemical functionalization to nanoacoustics. However, the presence of pores with sizes comparable to the acoustic wavelength is intuitively perceived as a major roadblock in nanoacoustics. Here we present multilayered nanoacoustic resonators based on mesoporous SiO 2 thin-films showing acoustic resonances in the 5-100 GHz range. We characterize the acoustic response of the system using coherent phonon generation experiments. Despite resonance wavelengths comparable to the pore size, we observe for the first time well-defined acoustic resonances. Our results open the path to a promising platform for nanoacoustic sensing and reconfigurable acoustic nanodevices based on soft, inexpensive fabrication methods.

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“…Rectification values of up to 350% were theoretically predicted in graphene nanoribbons [22], while experiments showed that graphene junctions could provide even higher values of up to 800% rectification [12]. In the more technologically placed silicon, theoretical studies suggest that geometrically asymmetric structures can enhance thermal rectification effects [14][15][16][17][18][19], verified by some experimental works as well [10,15,23]. Rectification is achieved when the structure is separated into regions in which the mean-free-path (MFP) is controlled by two mechanismsthe temperature-dependent Umklapp scattering, and a mechanism much less temperature dependent such as boundary scattering.…”

Section: Introductionmentioning

confidence: 85%

Thermal rectification optimization in nanoporous Si using Monte Carlo simulations

Chakraborty

Brooke

Hulse

et al. 2019

Journal of Applied Physics

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We investigate thermal rectification in nanoporous silicon using a semi-classical Monte Carlo (MC) simulation method. We consider geometrically asymmetric nanoporous structures, and investigate the combined effects of porosity, inter-pore distance, and pore position relative to the device boundaries. Two basis geometries are considered, one in which the pores are arranged in rectangular arrays, and ones in which they form triangular arrangements. We show that systems: i) with denser, compressed pore arrangements (i.e with smaller inter-pore distances), ii) with pores positioned closer to the device edge/contact, and iii) with pores in a triangular arrangement, can achieve rectification of over 55%. Introducing smaller pores into existing porous geometries in a hierarchical fashion increases rectification even further to over 60%. Importantly, for the structures we simulate, we show that sharp rectifying junctions, separating regions of long from short phonon mean-free-paths are more beneficial for rectification than spreading the asymmetry throughout the material along the heat direction in a graded fashion.

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

Cited by 24 publications

References 21 publications

Hierarchically nanostructured thermoelectric materials: challenges and opportunities for improved power factors

Hierarchically nanostructured thermoelectric materials: challenges and opportunities for improved power factors

Mesoporous Thin Films for Acoustic Devices in the Gigahertz Range

Thermal rectification optimization in nanoporous Si using Monte Carlo simulations

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