Getting the most out of a post-column EELS spectrometer on a TEM/STEM by optimising the optical coupling

Area of Science:

• Electron Microscopy
• Spectroscopy
• Materials Science

Background:

• Coupling transmission electron microscopy/scanning transmission electron microscopy (TEM/STEM) systems with electron energy loss spectroscopy (EELS) requires precise optical setups.
• JEOL ARM 200CF TEM/STEM with a probe aberration corrector but no image corrector presents specific challenges for EELS integration.

Purpose of the Study:

• To optimize the projector system of a JEOL ARM 200CF TEM/STEM for seamless integration with a Gatan 965 Quantum ER EELS system.
• To explain the performance improvements achieved through optimized setups using ray tracing.

Main Methods:

• Utilized ray tracing simulations to determine improved configurations for the TEM/STEM projector system.
• Validated simulation results through experimental measurements of system performance.

Main Results:

• Significantly increased the energy range for stable collection angle (within 5% of zero-loss value) from 1.2keV to 4.7keV at 200kV with a 2.5mm Quantum entrance aperture.
• Observed lower energy ranges at reduced accelerating voltages (e.g., 0.5keV to 2.0keV at 80kV).
• Reduced spectrum artifacts and minimized diffraction pattern motion for low-loss electrons at low STEM magnification.

Conclusions:

• Optimized projector system setups enhance the performance of TEM/STEM-EELS coupling.
• Key improvements stem from adjusting energy-loss for projector crossover and reducing lens stack aberrations.
• De-scanning the probe post-objective lens is recommended for accurate spectrum imaging of low-loss electrons.