Conceptual design of a monochromated scanning electron microscopy-based reflection electron energy loss spectroscopy system for surface nanospectroscopy.

This study presents a monochromated scanning electron microscopy-based reflection electron energy loss spectroscopy (MC-SEM-REELS) system using cylindrical lenses as energy dispersive units for surface spectroscopy at the nanoscale. After examining the validity of the theory through comparisons with the experimental results in our previous studies, we estimated the theoretical performance and limitations of the MC-SEM-REELS system based on electron-optical simulation. The results reveal that the MC, when used with a Schottky field emission gun, improves the spatial resolution of the SEM under low-energy conditions. However, if the highest performance is pursued for spatial and energy resolutions, the MC-SEM-REELS system suffers from a trade-off relationship between the two due to the limitation of source brightness. We also assessed the energy resolution of the spectrometer under the serial and parallel detection modes. In the serial detection mode, the system's spatial resolution is estimated at 3.9 nm when the energy resolution is 10 meV at a landing energy of 800 eV on a sample. In the parallel detection mode, the total energy resolution is limited to 100 meV; however, the spatial resolution improves to 2.6 nm at the same energy condition, with offering the additional advantage of shorter measurement times. The findings of this study could provide guidelines for using spectroscopic imaging tools under a low-energy electron probe by establishing the limits of spatial and energy resolutions. Furthermore, this study proposes a new analysis tool with high spatial and energy resolution for surface nanospectroscopy.