Pumping, Measuring and Modeling Atomic Vibrations in the Electron Microscope

• Applicant: Dr. Benedikt Haas
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530143441

The PuMMAVi project will build and utilize a low-cost setup for focusing long wavelength infrared (LWIR) radiation onto a sample inside an electron microscope to resonantly pump and probe phonons with high spatial resolution. Together with dedicated nanowire (NW) samples and cutting-edge modeling, this will enable a deep understanding of phonon-dominated thermal transport in quasi one-dimensional systems with direct implications for heat dissipation in nanowire-based light emitting diodes and the role of defects in this process. PuMMAVi will explore vibrational phenomena in GaN and AlN-based NWs that are of current interest in the framework of NW-based visible and ultraviolet (UV) light emitting diode (LED) applications, but are also a model system to better understand phonon transport and interaction in general. To this end, instrumental development yielding a prototype in-situ polarized LWIR (and visible light) injection system integrated into a NION HERMES microscope will be carried out. The spectral resolution of electron energy loss spectroscopy (EELS) in such an electron microscope has recently reached 5meV, opening novel possibilities for probing atomic vibrations in materials with unprecedented spatial resolution. To achieve a fundamental understanding of phonon physics at the nanoscale, we will employ and further develop state-of-the-art computational tools based on first-principles methods to quantitatively model experimental EEL spectra. Different aspects of lattice dynamics in these systems will be investigated experimentally and theoretically within PuMMAVi, ranging from phonon dispersions in bulk nitrides to surface phonon-polaritons occurring in pristine nanowires and localized vibrational modes associated with structural defects, such as Mg, Si or Eu dopants, p-n junctions, stacking faults or inversion domain boundaries. The PuMMAVi project will benefit from the synergistic interaction between cutting-edge experiments performed on the unique instrument installed in Berlin (AG SEM), high-quality pristine and defect-containing nanowires grown in Grenoble (IRIG) and the cutting-edge expertise in vibrational EELS modeling in Paris (IMPMC).

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partners: Dr. Bruno Daudin; Dr. Guillaume Radtke