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Seeing single silicon atom vibrations
Vibrational spectroscopy can achieve high energy resolution, but spatial resolution of unperturbed vibrations is more difficult to realize. Hage et al. show that a single-atom impurity in a solid (a silicon atom in graphene) can give rise to distinctive localized vibrational signatures. They used high-resolution electron energy-loss spectroscopy in a scanning transmission electron microscope to detect this signal. An experimental geometry was chosen that reduced the relative elastic scattering contribution, and repeated scanning near the silicon impurity enhanced the signal. The experimental vibration frequencies are in agreement with ab initio calculations.
Science, this issue p. 1124
Abstract
Single-atom impurities and other atomic-scale defects can notably alter the local vibrational responses of solids and, ultimately, their macroscopic properties. Using high-resolution electron energy-loss spectroscopy in the electron microscope, we show that a single substitutional silicon impurity in graphene induces a characteristic, localized modification of the vibrational response. Extensive ab initio calculations reveal that the measured spectroscopic signature arises from defect-induced pseudo-localized phonon modes—that is, resonant states resulting from the hybridization of the defect modes and the bulk continuum—with energies that can be directly matched to the experiments. This finding realizes the promise of vibrational spectroscopy in the electron microscope with single-atom sensitivity and has broad implications across the fields of physics, chemistry, and materials science.
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