Atomic-scale Phonon Transport at Heterogeneities in 2D Materials

Phonons play a critical role in thermal and electronic properties in 2D materials, leading to unique points of degeneracy in the phonon spectrum, and a quadratic dispersion of acoustic phonons where the group velocity is no longer constant. While this has emerged as an understanding of phonon behavior in 2D materials using global techniques, we have yet to make correlations to the atomic arrangements of the lattice and the associated phonon transport in the presence of intrinsic and extrinsic structural defects. In this talk, we detail how non-equilibrium processing techniques with ion beam irradiation and large area growth with alloying modify the global structure of our film with bulk characterization techniques. Next, we provide an avenue to measure phonon distributions in the lattice with monochromated electron energy loss spectroscopy (EELS) inside an aberration-corrected scanning transmission electron microscope (STEM), yielding insight into the infrared excitations in the film beyond the diffraction limit set by optical probes. This is accompanied by advanced techniques like off-axis EELS so neutron selection rules dominate our acquisition to produce a localized signal and suppress long-range modes, and momentum-resolved EELS for mapping phononic density of states along a dispersion curve. We round out our discussion by providing milestones that will enable the scientific community to build materials with single-atom selectivity. Ultimately, this work not only pushes boundaries in electron microscopy, but also provides avenues to the entire scientific landscape on decoupling the structure-property relationship in solids for the better and more efficient design of next-generation nanoelectronics.