Asymmetric electrostatic dodecapole: compact bandpass filter with low aberrations for momentum microscopy

Area of Science:

• Physics
• Materials Science
• Spectroscopy

Background:

• Traditional energy filters in microscopy often use spherical fields, leading to aberrations at high transmission.
• Optimizing for high energy resolution can compromise image quality when high transmission is needed.

Purpose of the Study:

• To introduce a new electrostatic dodecapole for bandpass-filtered imaging in real or reciprocal space.
• To demonstrate aberration correction up to the third order using this multipole.
• To implement the dodecapole as a prefilter in a time-of-flight momentum microscope.

Main Methods:

• Utilized an electrostatic dodecapole with an asymmetric electrode array for energy-dispersive beam deflection and aberration correction.
• Integrated the dodecapole into a time-of-flight momentum microscope at the PETRA III hard X-ray beamline.
• Employed transfer lenses and adjustable apertures for precise bandpass selection.

Main Results:

• Achieved a small deflection angle (4°) and minimal beam displacement (∼8 mm), allowing for a compact instrument design.
• Successfully filtered kinetic energy intervals from 10 eV to hundreds of electronvolts (FWHM) for pass energies of 100–1400 eV.
• Significantly improved the signal-to-background ratio by eliminating unwanted energy signals.

Conclusions:

• The electrostatic dodecapole provides an effective solution for aberration-corrected bandpass imaging in advanced microscopy.
• This technology enhances the performance of time-of-flight momentum microscopes by improving spectral purity.
• The compact design and precise filtering capabilities open new avenues for high-resolution imaging experiments.