Multimode objective lens for momentum microscopy and x-ray photoemission electron microscopy: Experiments

Area of Science:

• * Surface science and nanoscience
• * Advanced electron microscopy techniques

Background:

• * Conventional objective lenses in X-ray photoemission electron microscopes (XPEEMs) and momentum microscopes face limitations due to high field strengths at the sample surface.
• * High field strengths can induce field emission, especially from sharp sample edges, and contribute to space-charge interactions, limiting resolution and sample compatibility.
• * Existing designs restrict working distances and fields of view, hindering the study of delicate or complex samples.

Purpose of the Study:

• * To experimentally investigate the performance of a newly proposed objective lens design for XPEEMs and momentum microscopes.
• * To evaluate the impact of the new lens on field emission, space-charge effects, resolution, and working distance across a range of photon energies.
• * To explore the capabilities of the new lens in different operational modes (zero-field and repeller) for advanced imaging applications.

Main Methods:

• * Experimental characterization of the new objective lens using photon energies from extreme ultraviolet (XUV) to soft and hard X-rays.
• * Testing at synchrotron facilities and with a high-harmonic generation source.
• * Evaluation in zero-field and repeller modes, and in time-of-flight XPEEM mode.

Main Results:

• * The new lens significantly reduces field strength at the sample (by up to an order of magnitude), mitigating field emission risks.
• * It enables larger working distances (up to 23 mm) and fields of view with resolutions comparable to conventional lenses, but at much lower field strengths.
• * Zero-field mode facilitates the study of 3D objects and operando devices; repeller mode reduces space-charge effects but decreases the k-field diameter and usable energy interval.
• * Time-of-flight XPEEM mode achieved raw data resolution of 250 nm, improvable to better than 100 nm with data processing.

Conclusions:

• * The novel objective lens design offers significant advantages for XPEEM and momentum microscopy, including reduced field emission and enhanced imaging capabilities.
• * Its flexibility in different operational modes makes it suitable for studying a wider range of samples, including delicate cleaved samples and operando devices.
• * The lens represents a substantial advancement for high-resolution electron microscopy, enabling new scientific investigations in surface science and materials analysis.