Ultrafast Low-Energy Electron Microscopy for Surface Structural Dynamics

The technology offered provides the possibility to observe dynamical processes and structures in a highly time resolved manner in combination with a fully functional low energy electron microscope (LEEM). It is an advanced ultrafast low-energy electron microscope (ULEEM).

Challenge

Surface and interface phenomena represent a central aspect within the field of contemporary nanotechnology and condensed matter physics, exerting a profound influence on diverse fields such as catalysis, electronics, and the study of quantum materials. Conventional low-energy electron microscopy (LEEM) and low-energy electron diffraction (LEED) techniques offer high surface sensitivity but are deficient in temporal resolution when it comes to capturing ultrafast dynamics. Conversely, ultrafast transmission electron microscopy (UTEM) and time-resolved photoemission techniques offer high temporal resolution but are limited in surface specificity or spatial imaging. Recent research in charge-density waves and structural phase transitions in materials has demonstrated the necessity for an instrument combining real-space imaging, surface sensitivity, and ultrafast temporal resolution.

Our Solution

The presented ULEEM system addresses this gap by integrating low-energy electron optics with laser-driven ultrafast excitation and detection, enabling novel insights into transient surface phenomena. The invention introduces a modular ULEEM system that utilizes a tip-shaped photoemitter for generating linearly modulated electron pulses. Unlike conventional ultrafast sources based on nonlinear multiphoton emission, this design enables direct, proportional control of the electron emission via the intensity of the excitation laser. This approach simplifies the setup, reduces thermal stress on the emitter, and supports a wider range of laser types-including continous-wave and modulated sources. Electrons are emitted with high spatial coherence and low energy spread, ideal for surface-sensitive imaging. 

The electron pulses can be synchronized with optical, electrical, or magnetic sample excitation using a delay control stage, enabling femtosecond-resolved pump-probe experiments. Optional integration of static electron mirror allows for temporal pulse compression down to approx. 100-200 fs.

The system is compatible with existing LEEM architectures, offering an upgrade path for time-resolved studies of surface phenomena with enhanced energy and temporal resolution.

Figure 1: Schematic of the ULEEM setup. A femtosecond laser pulse is split and delayed via a delay line before illuminating a photocathode to generate pulsed electron bunches. These electrons are injected into a low-energy electron microscope via an added pulsed electron source. Prisms and electron optics guide the beam toward the sample. Reflected or emitted electrons are detected to reconstruct ultrafast changes in the sample surface structure.

Advantages 

• Real-space surface imaging with nanometer resolution and picosecond temporal precision.
• Surface-specific sensitivity due to low electron energies and high coherence.
• Pump-probe integration for dynamic studies of photo-induced phase transitions.
• Compact and modular design for laboratory-scale ultrafast experiments.
• Versatility in sample environments, supporting variable temperature and materials.

Applications

• Time-resolved studies of surface phase transitions
• Real-space imaging of topological defect dynamics at surfaces and interfaces.
• Ultrafast catalysis and reaction pathway analysis on functional surfaces.
• Development of ultrafast electronic and memory devices using non-equilibrium states.
• Educational and research instrumentation for advanced surface science laboratories.

Patent Status

WO2024188471 (A1) (filed)
Patent Applicant: Max Planck Society for the Advancement of Science e. V. and Georg-August University of Goettingen e. V.

Contact

Dr. Maria Kamper
Patent Manager (Physics, Technology and Software)
E-Mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Tel.: +49 (0) 551 30724 159
Ref: MM-2394-SUG

(image source Max Planck Society for Advancement of Science e. V.)