IM1-P-7 Quantum state secondary electron emission spectroscopy in low voltage scanning electron microscope for probing Valence band

Introduction Probing the surface and near-surface valence band (VB) with nanoscale lateral resolution is essential for advancing surface science and related technologies. However, conventional spectroscopic tools lack the resolution to achieve this goal. Scanning Electron Microscopy (SEM), known for its nanoscale imaging capabilities, can be paired with Secondary Electron Emission Spectroscopy (SEES) in the low-energy range (below 50 eV). When operated under low-voltage excitation conditions (<3 kV), the approach offers high signal yield and rapid data collection, making it suitable for nanoscale material mapping and VB analysis [1]. Despite these advantages, analyzing spectral data at low kinetic energies remains challenging due to a strong background signal from secondary electron cascades. Currently, no comprehensive model describes the full secondary electron (SE) emission process and its fine energy structure. Objectives This work aims to develop an experimental approach for characterizing the valence band of materials using SEM equipped with a specialized electron energy analyzer. It explores how the detailed features in experimental spectra relate to the occupied and unoccupied quantum states of the VB and introduces a theoretical model connecting the valence band Density of States (DOS) to the observed SE spectral response. Materials & Methods An ultra-high vacuum scanning Auger microscope (SAM) integrated with a Cylindrical Mirror Analyzer (CMA) was modified with custom entrance optics for detecting low-energy electrons. Experiments were conducted on highly oriented pyrolytic graphite and various metals at primary beam energies below 3 kV. To minimize surface contamination, we performed measurements in an ultra-high vacuum (UHV) environment with controlled electron exposure. Data interpretation was guided by the Fermi Golden Rule and perturbation theory, using ab initio calculated DOS as input. Results The acquired spectral data demonstrated high reproducibility. Spectra recorded at various primary electron (PE) energies retained consistent fine structures, indicating robustness across conditions. The energy positions and intensity patterns of spectral features closely matched predictions from the proposed model, showing promising agreement. Conclusion This study confirms that SEES measurements can be reliably reproduced and semi-quantitatively modeled, offering insight into the quantum states of the valence band under UHV conditions. The approach opens new possibilities for examining valence band DOS in complex materials and devices. References [1] Han, W., et al. "Quantitative material analysis using secondary electron energy spectromicroscopy." Sci Rep 10, 22144 (2020).