Direct Detection Electron Energy-Loss Spectroscopy: A Method to Push the Limits of Resolution and Sensitivity

TLDR

Electron counting with direct detection sensors offers improved resolution, lower noise, and higher pixel density compared to conventional indirect sensors, and while it has succeeded in imaging and diffraction, its potential for spectroscopy has not yet been explored. The study compares the performance of a direct detection sensor in counting mode with an indirect detection sensor for electron energy‑loss spectroscopy. The authors evaluate the two sensor types by measuring detective quantum efficiency, energy resolution, and field‑of‑view during EELS acquisition. Counting‑mode direct detection yields higher detective quantum efficiency and better energy resolution/field‑of‑view, enabling efficient spectrum imaging, low‑dose mapping, trace element analysis, and time‑resolved spectroscopy, and despite limited counting rate, both core‑loss and low‑loss spectra can be acquired, benefiting a broad range of scientists.

Abstract

In many cases, electron counting with direct detection sensors offers improved resolution, lower noise, and higher pixel density compared to conventional, indirect detection sensors for electron microscopy applications. Direct detection technology has previously been utilized, with great success, for imaging and diffraction, but potential advantages for spectroscopy remain unexplored. Here we compare the performance of a direct detection sensor operated in counting mode and an indirect detection sensor (scintillator/fiber-optic/CCD) for electron energy-loss spectroscopy. Clear improvements in measured detective quantum efficiency and combined energy resolution/energy field-of-view are offered by counting mode direct detection, showing promise for efficient spectrum imaging, low-dose mapping of beam-sensitive specimens, trace element analysis, and time-resolved spectroscopy. Despite the limited counting rate imposed by the readout electronics, we show that both core-loss and low-loss spectral acquisition are practical. These developments will benefit biologists, chemists, physicists, and materials scientists alike.