Nanoscale phonon spectroscopy reveals emergent interface vibrational structure of superlattices

作     者：Hoglund, Eric R. Bao, De-Liang O'Hara, Andrew Makarem, Sara Piontkowski, Zachary T. Matson, Joseph R. Yadav, Ajay K. Haisimaier, Ryan C. Engel-Herbert, Roman Ihlefeld, Jon F. Ravichandran, Jayakanth Ramesh, Ramamoorthy Caldwell, Joshua D. Beechem, Thomas E. Tomko, John A. Hachtel, Jordan A. Pantelides, Sokrates T. Hopkins, Patrick E. Howe, James M. 

作者机构：Dept. of Materials Science and Engineering University of Virginia CharlottesvilleVA22904 United States Dept. of Physics and Astronomy Vanderbilt University NashvilleTN37235 United States Sandia National Laboratories AlbuquerqueNM87123 United States Dept. of Mechanical Engineering and Electrical Engineering Vanderbilt University NashvilleTN37235 United States Dept. of Materials Science and Engineering University of California Berkley BerkleyCA94720 United States Dept. of Materials Science and Engineering Pennsylvania State University University ParkPA16802 United States Dept. of Chemical Engineering and Materials Science University of Southern California Los AngelesCA90089 United States Center for Integrated Nanotechnologies Sandia National Laboratories AlbuquerqueNM87123 United States School of Mechanical Engineering Birck Nanotechnology Center Purdue University West LafayetteIN47907 United States Dept. of Mechanical and Aerospace Engineering University of Virginia CharlottesvilleVA22904 United States Center for Nanophase Materials Sciences Oak Ridge National Laboratory Oak RidgeTN37830 United States Dept. of Electrical and Computer Engineering Vanderbilt University NashvilleTN37235 United States Dept. of Physics University of Virginia CharlottesvilleVA22904 United States 

出 版 物：《arXiv》 (arXiv)

年 卷 期：2021年

核心收录：

主　　题：Phonons 

摘      要：As the length-scales of materials decrease, heterogeneities associated with interfaces approach the importance of the surrounding materials. This has led to extensive studies of emergent electronic and magnetic interface properties in superlattices.1-9However, the interfacial vibrations that impact phonon-mediated properties, like thermal conductivity10,11, are measured using macroscopic techniques that lack spatial resolution. While it is accepted that intrinsic phonons change near boundaries12,13, the physical mechanisms and length-scales through which interfacial effects influence materials remain unclear. Herein, we demonstrate the localized vibrational response of interfaces in SrTiO3-CaTiO3superlattices by combining advanced scanning transmission electron microscopy imaging and spectroscopy, density-functional-theory calculations, and ultrafast optical spectroscopy. Structurally diffuse interfaces are observed that bridge the bounding materials. The local symmetries create phonon modes that determine the global response of the superlattice once the spacing of the interfaces approaches the phonon spatial extent. Our results provide direct visualization of the progression of the local atomic structure and interface vibrations as they come to determine the vibrational response of an entire superlattice. Direct observation of such local atomic and vibrational phenomena demonstrates that their spatial extent needs to be quantified to understand macroscopic behavior. Tailoring interfaces, and knowing their local vibrational response, provides a means of pursuing designer solids having emergent infrared and thermal responses. © 2021, CC BY.