Momentum resolved band gap measurement by high energy resolution electron energy loss spectroscopy

BIO Web of Conferences 129, 24012 (2024) EMC 2024 https://doi.org/10.1051/bioconf/202412924012 Momentum resolved band gap measurement by high energy resolution electron energy loss spectroscopy Dr Dileep Krishnan1, Dr. Ioannis Iatrakkis 1 Thermofisher Scientific, Eindhoven, Netherlands Techniques based on light optics have been traditionally used for studying optical properties of semiconductors. But there are 2 fundamental limitations of photon sources – 1. Its spatial resolutions are limited to μm range and 2. Photons cannot transfer any momentum (q) to the material. Electron energy loss spectroscopy (EELS) has been used to measure optical band gap for a few decades which compensates the aforementioned two shortcomings of UVvisible spectroscopy with nanometer range resolution and momentum transfer. But the limitation of EELS has been the energy resolution of the electron source; an X-FEG without mono was only 1 eV of resolution. With improvements of monochromator design on Thermo Fisher Scientific Spectra platform microscopes, energy resolution < 20 meV is now possible. Also, the 3-condensor lens system allows for a large range of momentum resolution possible with an upper limit <200 μrad in STEM mode. In this report, momentum resolved band gap measurement has been performed with an excited monochromator (energy resolution < 25 meV) with a momentum resolution of < 800 μrad using the Thermofisher Scientific EELS filter and spectrometer. Effort is put to automate the acquisition of EELS across the momentum space. In the literature, the modelling of EELS in the low-loss region has been commonly done by simplistic free electron gas model [1 ].We are developing an effective tight binding model approach to approximate the band gap and extract the low loss spectral function. The final state in the double differential scattering cross section formula has been described suing mixed dynamic form factor (MDFF) [2]. Figure caption: Figure 1. (a) The CBED pattern and the positions where the low-loss EELS measurements have been made. (b) The corresponding EELS spectra. Graphic: Keywords: Extreme low-loss, band gap, q-resolved-EELS Reference: [1] Korneychuk, S., Guzzinati, G. & Verbeeck, J., Phys. Status Solidi A 215, 1800318 (2018). [2] Schattschneider, P., Nelhiebel, M., Souchay, H., Jouffrey, B., Micron 31, 333 (2000) © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (https://creativecommons.org/licenses/by/4.0/).  (...truncated)