Charging phenomena in PEEM imaging and spectroscopy.

Area of Science:

• Materials Science
• Surface Science
• Analytical Chemistry

Background:

• X-ray photoelectron emission microscopy (X-PEEM) is a powerful microchemical analytical tool used in synchrotron laboratories.
• X-ray absorption spectroscopy (XAS) is often employed with X-PEEM, with sample charging being a known issue, particularly for insulators.

Purpose of the Study:

• To investigate and model the impact of surface charge formation on X-PEEM imaging and XAS spectra.
• To explain the origin of artifacts like reduced signal, distorted imaging, and unusual spectral lineshapes, including negative spectra.

Main Methods:

• Modeling the effect of surface charge on secondary electron yield from uniform samples.
• Analyzing the influence of localized charge centers on imaging and resolution in non-uniform insulating samples.
• Investigating the impact of non-uniform surface charge on XAS spectral lineshapes.

Main Results:

• Surface charge primarily reduces the secondary electron yield contributing to the detected signal.
• Localized charge on non-uniform insulators distorts the surface electrostatic field, affecting microscope imaging and resolution.
• Non-uniform surface charge can lead to unexpected spectral lineshapes, including negative spectra in extreme cases.

Conclusions:

• Sample charging effects in X-PEEM, even for insulators, cannot be neglected and can significantly impact data quality.
• Understanding and modeling charging phenomena are crucial for accurate interpretation of X-PEEM and XAS data.
• Strategies to minimize the impact of sample charging are essential for analyzing poorly conducting samples effectively.