Fig. 1 HAADF-STEM and STEM-EDS mapping of an ultrathin gold nanorod with a silver shell.74In high-resolution electron microscopy of molecular materials and nanomaterials, sample damage caused by electron irradiation hinders atomically precise imaging and electron beam analysis. In this study, based on new sample preparation methods for TEM and high-speed TEM/STEM imaging and analysis technologies, we have achieved structural and elemental mapping of single molecules, molecular assemblies, and nanomaterials by minimizing sample damage from electron beams. For example, using single-walled carbon nanotubes as single-molecule specimen support, we succeeded in tracking structural changes of a single polymer chain during heating of carbon fibers produced by the heat treatment of polyacrylonitrile, capturing the conversion process in atomic resolution images. In another example, utilizing STEM-EDS analysis, we characterized a single atomic silver shell formed on the surface of ultra-thin gold nanorods synthesized via a wet process, revealing a hierarchical structure at nanoscale (Fig 1).Recently, scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) have enabled the measurement of phonons with high spatial resolution. Through energy and momentum transfers between incident electrons and phonons, we measured phonon dispersion relations at the nanometer scale and detected vibrational modes localized at heterointerfaces [1]. Based on the principle of detailed balancing of phonon creation and annihilation, we also demonstrated the measurement of local temperature [2]. By using acoustic phonons, we found that temperature can be evaluated more precisely at low temperatures [2]. In this study, as an application of phonon spectroscopy based on the STEM–EELS method, we measured the local temperature of a diamond nanowire (DNW) during Joule heating [2]. Applying a voltage of 20 V to both ends of the DNW, we obtained EELS spectra along the DNW. EELS intensities located on both sides of the zero-loss peak were assigned to phonon modes, i.e., transverse acoustic (TA), longitudinal acoustic, transverse optical (TO), and longitudinal optical (LO) modes. Based on the intensity ratio of TA phonon creation and annihilation, we evaluated the temperature gradient along the DNW axis. The center of the DNW was determined to be 613 ± 5 K [2]. We also discuss the Joule heating mechanism in the DNW.Poster Award NomineeApplication of Nanometric Thermometry Based on Electron Spectroscopy of Phonons P4-05Real-Time Electron Microscopic Imaging and Analysis for Single Molecules and Atomically-Precise NanomaterialsKoji Harano, Jun Kikkawa, and Koji KimotoCenter for Basic Research on Materials, National Institute for Materials Science (NIMS)[1] T. Ishikawa et al., J. Am. Chem. Soc., 145, 12244–12254 (2023). [2] S. Maity et al., Nano Lett., ASAP Article. DOI: 10.1021/acs.nanolett.4c03159P4-06Jun Kikkawa and Koji Kimoto Center for Basic Research on Materials, National Institute for Materials Science (NIMS) [1] J. Kikkawa, T. Taniguchi and K. Kimoto, Phys. Rev. B, 104, L201402 (2021). [2] J. Kikkawa and K. Kimoto, Phys. Rev. B, 106, 95431 (2022).
元のページ ../index.html#74