Abstract:We investigate experimentally and theoretically the acoustic phonon propagation in two-dimensional phononic crystal membranes. Solid-air and solid-solid phononic crystals were made of square lattices of holes and Au pillars in and on 250 nm thick single crystalline Si membrane, respectively. The hypersonic phonon dispersion was investigated using Brillouin light scattering. Volume reduction (holes) or mass loading (pillars) accompanied with second-order periodicity and local resonances are shown to significant… Show more
“…In the past few years, this idea expanded beyond the phononic bandgaps and researchers began dreaming about the suppression of phonons in the terahertz frequency range thus reducing the thermal conductivity of materials [30,32,33,55]. However, the Brillouin light scattering experiments could confirm changes in phonon dispersion only up to a few tens of gigahertz [31,48], which affects only a negligible part of the thermal phonon spectrum at room temperature.…”
Section: Discussionmentioning
confidence: 99%
“…This mode flattening is often described as hybridization between the membrane modes and the resonant frequencies of the pillars. Analyzing the relative height of the mode location (ξ) [30,31], we find that the states corresponding to the flattened regions are localized inside the pillars (green color) [30,32–34]. Such localized states at the resonant frequencies are called local resonances.10.1080/14686996.2018.1542524-F0001Figure 1.Phonon dispersion of a pillar-based PnC (solid lines), a silicon membrane (dashed lines), and resonant frequencies of a pillar (horizontal dash-dotted lines).…”
Section: Physics Of Local Resonances and Phononic Bandgapsmentioning
confidence: 99%
“…To measure the phonon dispersion directly, Trzaskowska et al [47] applied the Brillouin light scattering technique and demonstrated that nickel pillars, deposited on a silicon substrate, strongly flatten the dispersion relation for the surface acoustic wave at the frequencies below 6 GHz. Later Brillouin light scattering experiments [31,48] demonstrated that pillars made of aluminum or gold could flatten phonon dispersion at even higher frequencies (up to 30 GHz), similarly to the hole-based PnCs.…”
Section: Measurements Of Phononic Bandgaps and Phonon Dispersionmentioning
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.
“…In the past few years, this idea expanded beyond the phononic bandgaps and researchers began dreaming about the suppression of phonons in the terahertz frequency range thus reducing the thermal conductivity of materials [30,32,33,55]. However, the Brillouin light scattering experiments could confirm changes in phonon dispersion only up to a few tens of gigahertz [31,48], which affects only a negligible part of the thermal phonon spectrum at room temperature.…”
Section: Discussionmentioning
confidence: 99%
“…This mode flattening is often described as hybridization between the membrane modes and the resonant frequencies of the pillars. Analyzing the relative height of the mode location (ξ) [30,31], we find that the states corresponding to the flattened regions are localized inside the pillars (green color) [30,32–34]. Such localized states at the resonant frequencies are called local resonances.10.1080/14686996.2018.1542524-F0001Figure 1.Phonon dispersion of a pillar-based PnC (solid lines), a silicon membrane (dashed lines), and resonant frequencies of a pillar (horizontal dash-dotted lines).…”
Section: Physics Of Local Resonances and Phononic Bandgapsmentioning
confidence: 99%
“…To measure the phonon dispersion directly, Trzaskowska et al [47] applied the Brillouin light scattering technique and demonstrated that nickel pillars, deposited on a silicon substrate, strongly flatten the dispersion relation for the surface acoustic wave at the frequencies below 6 GHz. Later Brillouin light scattering experiments [31,48] demonstrated that pillars made of aluminum or gold could flatten phonon dispersion at even higher frequencies (up to 30 GHz), similarly to the hole-based PnCs.…”
Section: Measurements Of Phononic Bandgaps and Phonon Dispersionmentioning
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.
“…26 There are few reports on cavity-type hPnCs with cylindrical nanopores, e.g., with a single crystalline epoxy/air sample, 18 anodic porous alumina containing hexagonal arrays of aligned nanopores oriented normal to the film surface, 27,28 and square arrays of holes of Si-membranes. 29 Using Brillouin light scattering spectroscopy (BLS) in transmission geometry (see Fig. 2(d)), the phonon dispersion relation has been recorded for a square lattice hPnC with filled spherical nanopores 6 and hexagonal lattice with both air-and filled spherical nanopores.…”
mentioning
confidence: 99%
“…30 In the former case, there was no direct comparison with the theoretical band diagram, while in the latter this comparison was restricted on the observed phononic branches. For the semi-or non-transparent hPnCs, 28,29 BLS was employed in backscattering geometry where the ripple mechanism dominated the scattering from the surface. For a fundamental understanding, however, the theoretical representation of the full BLS spectrum, frequencies, and intensities is necessary.…”
The phononic band diagram of a periodic square structure fabricated by femtosecond laser pulse-induced two photon polymerization is recorded by Brillouin light scattering (BLS) at hypersonic (GHz) frequencies and computed by finite element method. The theoretical calculations along the two main symmetry directions quantitatively capture the band diagrams of the air- and liquid-filled structure and moreover represent the BLS intensities. The theory helps identify the observed modes, reveals the origin of the observed bandgaps at the Brillouin zone boundaries, and unravels direction dependent effective medium behavior.
The central concept in phononics is the tuning of the phonon dispersion relation, or phonon engineering, which provides a means of controlling related properties such as group velocity or phonon interactions and, therefore, phonon propagation, in a wide range of frequencies depending on the geometries and sizes of the materials. Phononics exploits the present state of the art in nanofabrication to tailor dispersion relations in the range of GHz for the control of elastic waves/phonons propagation with applications toward new information technology concepts with phonons as state variable. Moreover, phonons provide an adaptable approach for supporting a coherent coupling between different state variables, and the development of nanoscale optomechanical systems during the last decade attests this prospect. The most extended approach to manipulate the phonon dispersion relation is introducing an artificial periodic modulation of the elastic properties, which is referred to as phononic crystal (PnC). Herein, the focus is on the recent experimental achievements in the fabrication and application of 2D PnCs enabling the modification of the dispersion relation of surface and membrane modes, and presenting phononic bandgaps, waveguiding, and confinement in the hypersonic regime. Furthermore, these artificial materials offer the potential of modifying and controlling the heat flow to enable new schemes in thermal management.
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