Synchrotron soft X-ray and field-emission electron sources: a comparison

Area of Science:

• Physics, Applied
• Materials Science
• Spectroscopy

Background:

• The soft X-ray spectral region (100-1000 eV) overlaps significantly with the useful range of electron energy-loss spectroscopy.
• Both techniques utilize well-developed monochromators and parallel detection devices with comparable resolution.
• Complementary experiments in imaging, spectroscopy, and diffraction have been successfully performed using both electrons and photons.

Purpose of the Study:

• To compare the brightness, degeneracy, monochromaticity, beam size, source size, spatial, and temporal coherence of field-emission electron beams and soft X-ray synchrotron radiation.
• To provide recent brightness values for nanotip field emitters and undulators, including measured and calculated data.
• To discuss the quantum mechanical upper limit on source brightness and relationships among beam brightness, coherence, and degeneracy.

Main Methods:

• Comparative analysis of beam and source properties.
• Review of factors limiting brightness and coherence.
• Discussion of measurement methods for these parameters.

Main Results:

• Presentation of recent brightness values for field emitters and undulators, with examples from the Advanced Light Source.
• Discussion of the theoretical limits and practical considerations for source brightness and coherence.
• Comparison of electron and photon beam characteristics relevant to experimental applications.

Conclusions:

• Field-emission electron beams and soft X-ray synchrotron radiation are highly comparable in spectral range and instrumental resolution.
• Understanding and comparing their fundamental beam properties (brightness, coherence) is crucial for optimizing diffraction, imaging, and spectroscopic experiments.
• The choice between techniques may depend on specific experimental requirements and potential radiation damage considerations.