Position and momentum mapping of vibrations in graphene nanostructures in the electron microscope
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TLDR
In this article, the authors provide a new pathway to determine the phonon dispersions down to the scale of an individual freestanding graphene monolayer by mapping the distinct vibration modes for a large momentum transfer.Abstract:
Propagating atomic vibrational waves, phonons, rule important thermal, mechanical, optoelectronic and transport characteristics of materials. Thus the knowledge of phonon dispersion, namely the dependence of vibrational energy on momentum is a key ingredient to understand and optimize the material's behavior. However, despite its scientific importance in the last decade, the phonon dispersion of a freestanding monolayer of two dimensional (2D) materials such as graphene and its local variations has still remained elusive because of experimental limitations of vibrational spectroscopy. Even though electron energy loss spectroscopy (EELS) in transmission has recently been shown to probe the local vibrational charge responses, these studies are yet limited to polar materials like boron nitride or oxides, in which huge signals induced by strong dipole moments are present. On the other hand, measurements on graphene performed by inelastic x-ray (neutron) scattering spectroscopy or EELS in reflection do not have any spatial resolution and require large microcrystals. Here we provide a new pathway to determine the phonon dispersions down to the scale of an individual freestanding graphene monolayer by mapping the distinct vibration modes for a large momentum transfer. The measured scattering intensities are accurately reproduced and interpreted with density functional perturbation theory (DFPT). Additionally, a nanometre-scale mapping of selected momentum (q) resolved vibration modes using graphene nanoribbon structures has enabled us to spatially disentangle bulk, edge and surface vibrations.read more
Citations
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Single-atom vibrational spectroscopy in the scanning transmission electron microscope.
TL;DR: Using high-resolution electron energy-loss spectroscopy in the electron microscope, it is shown that a single substitutional silicon impurity in graphene induces a characteristic, localized modification of the vibrational response.
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Optical Excitations with Electron Beams: Challenges and Opportunities
TL;DR: Free electron beams such as those employed in electron microscopes have evolved into powerful tools to investigate photonic nanostructures with an unrivaled combination of spatial and spectral preciseness as discussed by the authors.
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Single-defect phonons imaged by electron microscopy.
Xingxu Yan,Chengyan Liu,Chengyan Liu,Chaitanya Gadre,Lei Gu,Toshihiro Aoki,Tracy C. Lovejoy,Niklas Dellby,Ondrej L. Krivanek,Darrell G. Schlom,Darrell G. Schlom,Ruqian Wu,Xiaoqing Pan +12 more
TL;DR: In this paper, the authors demonstrate that the capabilities of a transmission electron microscope open the door to direct mapping of phonon propagation around defects, which is expected to provide useful guidance for engineering thermal properties of materials.
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Direct observation of highly confined phonon polaritons in suspended monolayer hexagonal boron nitride.
Ning Li,Xiangdong Guo,Xiaoxia Yang,Xiaoxia Yang,Ruishi Qi,Tianyu Qiao,Yifei Li,Ruochen Shi,Yuehui Li,Kaihui Liu,Zhi Xu,Lei Liu,F. Javier García de Abajo,F. Javier García de Abajo,Qing Dai,Qing Dai,Enge Wang,Peng Gao +17 more
TL;DR: Monochromatic electron energy-loss spectroscopy enables the observation of highly confined and ultraslow hyperbolic phonon polaritons in suspended monolayer hexagonal boron nitride, expanding the potential of van der Waals materials for nanophotonic applications.
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Hybrid pixel direct detector for electron energy loss spectroscopy.
Benjamin Plotkin-Swing,G.J. Corbin,Sacha De Carlo,Niklas Dellby,Christoph Hoermann,M.V. Hoffman,Tracy C. Lovejoy,C.E. Meyer,Andreas Mittelberger,Radosav S. Pantelic,Luca Piazza,Ondrej L. Krivanek +11 more
TL;DR: A hybrid pixel direct detector is characterized and its suitability for electron energy loss spectroscopy (EELS) is demonstrated, including EELS of boron nitride in which an unsaturated zero loss peak is recorded at the same time as inner shell loss edges.
References
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