Multimode objective lens for momentum microscopy and XPEEM: Theory.

Area of Science:

• Electron microscopy
• Surface science
• Optics

Background:

• Strong electric fields in cathode lenses are crucial for high resolution but can cause field emission and flashovers.
• Microscopic sample features and slow background electrons lead to complications like space charge effects.
• Existing lens configurations struggle to mitigate these issues effectively.

Purpose of the Study:

• To develop and analyze a novel objective lens configuration that reduces the electric field at the sample.
• To investigate the performance of this new 'gaplens' configuration using ray-tracing simulations.
• To assess the impact of reduced electric fields on aberration coefficients and imaging capabilities.

Main Methods:

• Ray-tracing simulations were performed for energies ranging from eV to 6 keV.
• A novel objective configuration with annular electrodes was designed to shape the electric field.
• Aberration coefficients (spherical and chromatic) were determined for different lens modes.

Main Results:

• The 'gaplens' configuration reduces the electric field at the sample to below 1 kV/mm.
• This new mode exhibits smaller aberrations and enables larger fields of view compared to the extractor mode.
• The accessible solid angle is three times larger in the gaplens mode, and 25 nm resolution is predicted for XPEEM.
• Retarding fields effectively suppress space charge effects.

Conclusions:

• The novel 'gaplens' objective configuration significantly improves cathode lens performance by lowering electric fields.
• This design mitigates field emission and space charge effects, leading to enhanced imaging resolution and field of view.
• The 'gaplens' mode offers a promising advancement for high-resolution electron microscopy, particularly for 3D structured samples.