1
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Boggiano HD, Nan L, Grinblat G, Maier SA, Cortés E, Bragas AV. Focusing Surface Acoustic Waves with a Plasmonic Hypersonic Lens. NANO LETTERS 2024; 24:6362-6368. [PMID: 38752764 DOI: 10.1021/acs.nanolett.4c01251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2024]
Abstract
Plasmonic nanoantennas have proven to be efficient transducers of electromagnetic to mechanical energy and vice versa. The sudden thermal expansion of these structures after an ultrafast optical pulsed excitation leads to the emission of hypersonic acoustic waves to the supporting substrate, which can be detected by another antenna that acts as a high-sensitivity mechanical probe due to the strong modulation of its optical response. Here, we propose and experimentally demonstrate a nanoscale acoustic lens comprised of 11 gold nanodisks whose collective oscillation at gigahertz frequencies gives rise to an interference pattern that results in a diffraction-limited surface acoustic beam of about 340 nm width, with an amplitude contrast of 60%. Via spatially decoupled pump-probe experiments, we were able to map the radiated acoustic energy in the proximity of the focal area, obtaining a very good agreement with the continuum elastic theory.
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Affiliation(s)
- Hilario D Boggiano
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física, 1428 Buenos Aires, Argentina
| | - Lin Nan
- Chair in Hybrid Nanosystems, Nanoinstitute Munich, Faculty of Physics, Ludwig-Maximilians-Universität München, 80539 München, Germany
| | - Gustavo Grinblat
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física, 1428 Buenos Aires, Argentina
- CONICET - Universidad de Buenos Aires, Instituto de Física de Buenos Aires (IFIBA), 1428 Buenos Aires, Argentina
| | - Stefan A Maier
- School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
- Department of Physics, Imperial College London, London SW7 2AZ, U.K
| | - Emiliano Cortés
- Chair in Hybrid Nanosystems, Nanoinstitute Munich, Faculty of Physics, Ludwig-Maximilians-Universität München, 80539 München, Germany
| | - Andrea V Bragas
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física, 1428 Buenos Aires, Argentina
- CONICET - Universidad de Buenos Aires, Instituto de Física de Buenos Aires (IFIBA), 1428 Buenos Aires, Argentina
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2
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Imaeda K, Shikama Y, Ushikoshi S, Sakai S, Ryuzaki S, Ueno K. Coherent acoustic vibrations of Au nanoblocks and their modulation by Al2O3 layer deposition. J Chem Phys 2024; 160:144702. [PMID: 38587227 DOI: 10.1063/5.0202690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2024] [Accepted: 03/20/2024] [Indexed: 04/09/2024] Open
Abstract
Coherent acoustic phonons induced in metallic nanostructures have attracted tremendous attention owing to their unique optomechanical characteristics. The frequency of the acoustic phonon vibration is highly sensitive to the material adsorption on metallic nanostructures and, therefore, the acoustic phonon offers a promising platform for ultrasensitive mass sensors. However, the physical origin of acoustic frequency modulation by material adsorption has been partially unexplored so far. In this study, we prepared Al2O3-deposited Au nanoblocks and measured their acoustic phonon frequencies using time-resolved pump-probe measurements. By precisely controlling the thickness of the Al2O3 layer, we systematically investigated the relation between the acoustic phonon frequency and the deposited Al2O3 amounts. The time-resolved measurements revealed that the acoustic breathing modes were predominantly excited in the Au nanoblocks, and their frequencies increased with the increment of the Al2O3 thickness. From the relationship between the acoustic phonon frequency and the Al2O3 thickness, we revealed that the acoustic phonon frequency modulation is attributed to the density change of the whole sample. Our results would provide fruitful information for developing quantitative mass sensing devices based on metallic nanostructures.
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Affiliation(s)
- Keisuke Imaeda
- Faculty of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan
| | - Yuto Shikama
- Graduate School of Chemical Sciences and Engineering, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan
| | - Shimba Ushikoshi
- Graduate School of Chemical Sciences and Engineering, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan
| | - Satoshi Sakai
- Graduate School of Chemical Sciences and Engineering, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan
| | - Sou Ryuzaki
- Faculty of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan
| | - Kosei Ueno
- Faculty of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan
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3
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Audoin B. Principles and advances in ultrafast photoacoustics; applications to imaging cell mechanics and to probing cell nanostructure. PHOTOACOUSTICS 2023; 31:100496. [PMID: 37159813 PMCID: PMC10163675 DOI: 10.1016/j.pacs.2023.100496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 03/29/2023] [Accepted: 04/12/2023] [Indexed: 05/11/2023]
Abstract
In this article we first present the foundations of ultrafast photoacoustics, a technique where the acoustic wavelength in play can be considerably shorter than the optical wavelength. The physics primarily involved in the conversion of short light pulses into high frequency sound is described. The mechanical disturbances following the relaxation of hot electrons in metals and other processes leading to the breaking of the mechanical balance are presented, and the generation of bulk shear-waves, of surface and interface waves and of guided waves is discussed. Then, efforts to overcome the limitations imposed by optical diffraction are described. Next, the principles behind the detection of the so generated coherent acoustic phonons with short light pulses are introduced for both opaque and transparent materials. The striking instrumental advances, in the detection of acoustic displacements, ultrafast acquisition, frequency and space resolution are discussed. Then secondly, we introduce picosecond opto-acoustics as a remote and label-free novel modality with an excellent capacity for quantitative evaluation and imaging of the cell's mechanical properties, currently with micron in-plane and sub-optical in depth resolution. We present the methods for time domain Brillouin spectroscopy in cells and for cell ultrasonography. The current applications of this unconventional means of addressing biological questions are presented. This microscopy of the nanoscale intra-cell mechanics, based on the optical monitoring of coherent phonons, is currently emerging as a breakthrough method offering new insights into the supra-molecular structural changes that accompany cell response to a myriad of biological events.
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4
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Sun T, Zhou C, Guo H, Meng Z, Liu X, Wang Z, Zhou H, Fei Y, Qiu K, Zhang F, Li B, Zhu X, Yang F, Zhao J, Guo J, Zhao J, Sheng Z. Coherent Phonon-Induced Gigahertz Optical Birefringence and Its Manipulation in SrTiO 3. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2205707. [PMID: 36646514 PMCID: PMC9982545 DOI: 10.1002/advs.202205707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/01/2022] [Revised: 11/30/2022] [Indexed: 06/17/2023]
Abstract
Birefringence, which modulates the polarization of electromagnetic wave, has been commercially developed and widely used in modern photonics. Fostered by high-frequency signal processing and communications, feasible birefringence technologies operating in gigahertz (GHz) range are highly desired. Here, a coherent phonon-induced GHz optical birefringence and its manipulation in SrTiO3 (STO) crystals are demonsrated. With ultrafast laser pumping, the coherent acoustic phonons with low damping are created in the transducer/STO structures. A series of transducer layers are examined and the optimized one with relatively high photon-phonon conversion efficiency, i.e., semiconducting LaRhO3 film, is obtained. The most intriguing finding here is that, by virtue of high sensitivity to strain perturbation of STO, GHz optical birefringence can be induced by the coherent acoustic phonons and the birefringent amplitudes possess crystal orientation dependence. Optical manipulation of both coherent phonons and its induced GHz birefringence by double pump technique are also realized. These findings reveal an alternative mechanism of ultrafast optical birefringence control, and offer prospects for applications in high-frequency acoustic-optics devices.
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Affiliation(s)
- Tao Sun
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
- University of Science and Technology of ChinaHefei230026P. R. China
- Present address:
Institute of Plasma PhysicsHFIPSChinese Academy of SciencesHefei230031P. R. China
| | - Chun Zhou
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
- Present address:
Institute of Plasma PhysicsHFIPSChinese Academy of SciencesHefei230031P. R. China
| | - Hongli Guo
- ICQD/Hefei National Laboratory for Physical Sciences at Microscaleand CAS Key Laboratory of Strongly‐Coupled Quantum Matter Physicsand Department of PhysicsUniversity of Science and Technology of ChinaHefei230026P. R. China
| | - Zhi Meng
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
| | - Xinyu Liu
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
| | - Zhou Wang
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
- University of Science and Technology of ChinaHefei230026P. R. China
| | - Han Zhou
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
- University of Science and Technology of ChinaHefei230026P. R. China
| | - Yuming Fei
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
- University of Science and Technology of ChinaHefei230026P. R. China
| | - Kang Qiu
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
| | - Fapei Zhang
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
| | - Bolin Li
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
| | - Xuetao Zhu
- Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of SciencesBeijing100190P. R. China
| | - Fang Yang
- Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of SciencesBeijing100190P. R. China
| | - Jimin Zhao
- Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of SciencesBeijing100190P. R. China
| | - Jiandong Guo
- Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of SciencesBeijing100190P. R. China
| | - Jin Zhao
- ICQD/Hefei National Laboratory for Physical Sciences at Microscaleand CAS Key Laboratory of Strongly‐Coupled Quantum Matter Physicsand Department of PhysicsUniversity of Science and Technology of ChinaHefei230026P. R. China
| | - Zhigao Sheng
- Anhui Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field LaboratoryHFIPSAnhui, Chinese Academy of SciencesHefei230031P. R. China
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5
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Gigahertz optoacoustic vibration in Sub-5 nm tip-supported nano-optomechanical metasurface. Nat Commun 2023; 14:485. [PMID: 36717581 PMCID: PMC9886940 DOI: 10.1038/s41467-023-36127-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 01/18/2023] [Indexed: 01/31/2023] Open
Abstract
The gigahertz acoustic vibration of nano-optomechanical systems plays an indispensable role in all-optical manipulation of light, quantum control of mechanical modes, on-chip data processing, and optomechanical sensing. However, the high optical, thermal, and mechanical energy losses severely limit the development of nano-optomechanical metasurfaces. Here, we demonstrated a high-quality 5 GHz optoacoustic vibration and ultrafast optomechanical all-optical manipulation in a sub-5 nm tip-supported nano-optomechanical metasurface (TSNOMS). The physical rationale is that the design of the semi-suspended metasurface supported by nanotips of <5 nm enhances the optical energy input into the metasurface and closes the mechanical and thermal output loss channels, result in dramatically improvement of the optomechanical conversion efficiency and oscillation quality of the metasurface. The design strategy of a multichannel-loss-mitigating semi-suspended metasurface can be generalized to performance improvements of on-chip processed nano-optomechanical systems. Applications include all-optical operation of nanomechanical systems, reconfigurable nanophotonic devices, optomechanical sensing, and nonlinear and self-adaptive photonic functionalities.
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6
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Vasileiadis T, Noual A, Wang Y, Graczykowski B, Djafari-Rouhani B, Yang S, Fytas G. Optomechanical Hot-Spots in Metallic Nanorod-Polymer Nanocomposites. ACS NANO 2022; 16:20419-20429. [PMID: 36475620 PMCID: PMC9798866 DOI: 10.1021/acsnano.2c06673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Accepted: 11/28/2022] [Indexed: 06/17/2023]
Abstract
Plasmonic coupling between adjacent metallic nanoparticles can be exploited for acousto-plasmonics, single-molecule sensing, and photochemistry. Light absorption or electron probes can be used to study plasmons and their interactions, but their use is challenging for disordered systems and colloids dispersed in insulating matrices. Here, we investigate the effect of plasmonic coupling on optomechanics with Brillouin light spectroscopy (BLS) in a prototypical metal-polymer nanocomposite, gold nanorods (Au NRs) in polyvinyl alcohol. The intensity of the light inelastically scattered on thermal phonons captured by BLS is strongly affected by the wavelength of the probing light. When light is resonant with the transverse plasmons, BLS reveals mostly the normal vibrational modes of single NRs. For lower energy off-resonant light, BLS is dominated by coupled bending modes of NR dimers. The experimental results, supported by optomechanical calculations, document plasmonically enhanced BLS and reveal energy-dependent confinement of coupled plasmons close to the tips of NR dimers, generating BLS hot-spots. Our work establishes BLS as an optomechanical probe of plasmons and promotes nanorod-soft matter nanocomposites for acousto-plasmonic applications.
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Affiliation(s)
| | - Adnane Noual
- LPMR,
Département de Physique, Faculté des Sciences, Université Mohammed Premier, Oujda, 60000, Morocco
| | - Yuchen Wang
- Department
of Materials Science and Engineering, University
of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104, United States
| | - Bartlomiej Graczykowski
- Faculty
of Physics, Adam Mickiewicz University, 61-614 Poznan, Poland
- Max
Planck Institute for Polymer Research, 55128 Mainz, Germany
| | - Bahram Djafari-Rouhani
- Département
de Physique, Institut d’Electronique de Microélectonique
et de Nanotechnologie, UMR CNRS 8520, Université
de Lille, Villeneuve
d’Ascq, 59655, France
| | - Shu Yang
- Department
of Materials Science and Engineering, University
of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104, United States
| | - George Fytas
- Max
Planck Institute for Polymer Research, 55128 Mainz, Germany
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7
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Cortés E, Wendisch FJ, Sortino L, Mancini A, Ezendam S, Saris S, de S. Menezes L, Tittl A, Ren H, Maier SA. Optical Metasurfaces for Energy Conversion. Chem Rev 2022; 122:15082-15176. [PMID: 35728004 PMCID: PMC9562288 DOI: 10.1021/acs.chemrev.2c00078] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light-matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.
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Affiliation(s)
- Emiliano Cortés
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany,
| | - Fedja J. Wendisch
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany
| | - Luca Sortino
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany
| | - Andrea Mancini
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany
| | - Simone Ezendam
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany
| | - Seryio Saris
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany
| | - Leonardo de S. Menezes
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany,Departamento
de Física, Universidade Federal de
Pernambuco, 50670-901 Recife, Pernambuco, Brazil
| | - Andreas Tittl
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany
| | - Haoran Ren
- MQ Photonics
Research Centre, Department of Physics and Astronomy, Macquarie University, Macquarie
Park, New South Wales 2109, Australia
| | - Stefan A. Maier
- Chair
in Hybrid Nanosystems, Nano Institute Munich, Faculty of Physics, Ludwig-Maximilians-University Munich, Königinstraße 10, 80539 Munich, Germany,School
of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia,Department
of Phyiscs, Imperial College London, London SW7 2AZ, United Kingdom,
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8
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Ng RC, El Sachat A, Cespedes F, Poblet M, Madiot G, Jaramillo-Fernandez J, Florez O, Xiao P, Sledzinska M, Sotomayor-Torres CM, Chavez-Angel E. Excitation and detection of acoustic phonons in nanoscale systems. NANOSCALE 2022; 14:13428-13451. [PMID: 36082529 PMCID: PMC9520674 DOI: 10.1039/d2nr04100f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Accepted: 08/15/2022] [Indexed: 06/15/2023]
Abstract
Phonons play a key role in the physical properties of materials, and have long been a topic of study in physics. While the effects of phonons had historically been considered to be a hindrance, modern research has shown that phonons can be exploited due to their ability to couple to other excitations and consequently affect the thermal, dielectric, and electronic properties of solid state systems, greatly motivating the engineering of phononic structures. Advances in nanofabrication have allowed for structuring and phonon confinement even down to the nanoscale, drastically changing material properties. Despite developments in fabricating such nanoscale devices, the proper manipulation and characterization of phonons continues to be challenging. However, a fundamental understanding of these processes could enable the realization of key applications in diverse fields such as topological phononics, information technologies, sensing, and quantum electrodynamics, especially when integrated with existing electronic and photonic devices. Here, we highlight seven of the available methods for the excitation and detection of acoustic phonons and vibrations in solid materials, as well as advantages, disadvantages, and additional considerations related to their application. We then provide perspectives towards open challenges in nanophononics and how the additional understanding granted by these techniques could serve to enable the next generation of phononic technological applications.
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Affiliation(s)
- Ryan C Ng
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
| | | | - Francisco Cespedes
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
- Departamento de Física, Universidad Autónoma de Barcelona, Bellaterra, 08193 Barcelona, Spain
| | - Martin Poblet
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
| | - Guilhem Madiot
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
| | - Juliana Jaramillo-Fernandez
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
| | - Omar Florez
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
- Departamento de Física, Universidad Autónoma de Barcelona, Bellaterra, 08193 Barcelona, Spain
| | - Peng Xiao
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
- Departamento de Física, Universidad Autónoma de Barcelona, Bellaterra, 08193 Barcelona, Spain
| | - Marianna Sledzinska
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
| | - Clivia M Sotomayor-Torres
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
- ICREA, Passeig Lluis Companys 23, 08010 Barcelona, Spain
| | - Emigdio Chavez-Angel
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain.
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