Nanoscale Interface Phonon Dynamics Imaged by Electron Microscopy*

Thermal transport mechanisms are drastically altered by the inclusion of alloys, nanostructures, and superlattice interfaces in materials. To understand the dynamics at these nanoscale structures, a high-resolution technique capable of probing phonons at the nanoscale is essential. Recent developments in electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) have made it possible to study phonons at nanometer resolution¹. Additionally, vibrational EELS allows for nanoscale temperature imaging using principle of detailed balance². Here we demonstrate the two-dimensional nanoscale vibrational mapping of a single SiGe quantum dot (QD) using an atom-sized probe in the electron microscope. We develop a novel technique to map propagating phonon modes that allows for the imaging of real space interface specularity and use principle of detailed balance to investigate ultra-high temperature gradients in the presence of nanostructures and interfaces.

 

Experimental work was supported by the Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Grant No. DESC0014430, and partially by National Science Foundation (NSF) under Grant No. DMR-1506535 and DMR-1629270.