Ultrafast transmission electron microscopy (UTEM) enables the study of structural, electronic, and magnetic dynamics on ultrashort timescales and at nanometer length scales. To extend these capabilities and enable new experiments, the instrumentation and experimental conditions need to be continuously developed and characterized. Our research group therefore focuses on several aspects of instrumental development and characterization, including:
In collaboration with JEOL, a Japanese manufacturer of electron microscopes, we developed a new electron source for UTEM. A conventional cold field emission gun (CFEG) was modified to generate electron pulses by illuminating the emitter tip with a laser pulse. This laser-driven CFEG provides high spatial and temporal coherence, making the electron beam particularly sensitive to small changes in the phase of the electron wave. This opens up new possibilities for investigating complex ultrafast dynamics, including magnetic textures.
When many electrons are emitted within a short time, their Coulomb interaction causes them to influence one another, leading to correlations within the electron pulse. These space-charge effects can be measured and analysed using an event-based electron detector. Understanding the emission process and the resulting electron correlations may enable us to control the properties of electron pulses and optimise them for various applications in ultrafast electron microscopy.
The NeoArm is equipped with an aberration corrector that enables atomic-resolution imaging in scanning transmission electron microscopy (STEM) mode. We are investigating how the aberration corrector affects ultrashort electron pulses and how its performance can be optimised for pulsed-beam applications. The aim is to establish aberration-corrected UTEM for advanced STEM techniques, including differential phase contrast (DPC) STEM and electron ptychography. This would combine the high spatial resolution of aberration-corrected STEM with the temporal resolution of UTEM.