Anyone wishing to understand how charges move within high-tech materials – and, in particular, at their interfaces – will, in future, have to visit a new measurement facility at the BESSY II synchrotron radiation source in Berlin. The facility was designed as part of a research project at the TU Bergakademie Freiberg and has now been fully installed at BESSY II following around four years of development work. The project, funded by the Federal Ministry of Research, Technology and Space (BMFTR) as part of the ErUM-Pro programme, was led by physicist Dr Friedrich Roth. The new setup thus expands the measurement and analysis options available to scientists: International teams can use the facility to investigate how electronic charges move after a material has been excited – and to do so with significantly increased measurement efficiency. The first user experiments are planned for February 2027.
“This means that a new experimental facility for time-resolved X-ray photoelectron spectroscopy (tr-XPS) is now available at the BESSY II synchrotron radiation source in Berlin. Ultrafast processes at material surfaces and interfaces can now be investigated with high temporal resolution,” explains PD Dr. habil. Friedrich Roth, project leader at the TU Bergakademie Freiberg. “The focus here is on the question of how electronic charges move after a material has been excited, and which processes take place at functional interfaces on timescales of picoseconds. Such processes play a crucial role, for example, in semiconductors, photocatalysts and novel energy materials.” Physicist Friedrich Roth coordinated the construction of the new facility in close collaboration with the Helmholtz Centre Berlin (HZB), the Fritz Haber Institute of the Max Planck Society (FHI), the German Electron Synchrotron (DESY) and the European XFEL.
High-efficiency time-resolved experiments
A distinctive feature of the new system is the combination of a highly efficient time-of-flight electron analyser with a powerful optical laser source and the synchrotron radiation from BESSY II. This enables the efficiency of time-resolved tr-XPS measurements to be significantly increased. For users, the higher measurement efficiency means, above all, that considerably more information can be obtained within the limited measurement time available at a synchrotron radiation source. For example, different materials or experimental conditions can be systematically compared with one another, and changes over time can be tracked in detail. The new infrastructure thus expands the existing capabilities at BESSY II to include experiments in which both high temporal resolution and efficient data acquisition are crucial.
Following extensive installation and commissioning work, the system is now ready for the first user experiments. “There is already international interest: research groups from Sweden, the UK, France and the USA intend to carry out experiments using the new setup in future,” said Roth.
For me, it is particularly important that we have not simply set up yet another measuring instrument here, but have worked with our partners to create a novel experimental facility for the national and international user community. Research groups can bring their own material systems to BESSY II and investigate there how electronic processes develop on extremely short time scales following optical excitation. The combination of high temporal resolution and high measurement efficiency gives us the opportunity to investigate ultra-fast charge transfer processes at complex material interfaces much more systematically in future. The fact that we are already receiving enquiries from several countries even before regular user operations begin shows just how great the demand is for such experimental opportunities.
Research across institutional boundaries
The facility also serves as an example of the close links between research at Freiberg and Germany’s major research infrastructures. Scientists from the TU Bergakademie Freiberg collaborated closely on the project with the Helmholtz Centre Berlin, the Fritz Haber Institute in Berlin, DESY and the European XFEL. The partners contributed their respective expertise in synchrotron and free-electron laser research, photoelectron spectroscopy, detector technology and time-resolved measurement methods.
The resulting infrastructure thus combines experience gained from experiments at various large-scale research facilities and applies this to a permanently available user facility at BESSY II.
“Modern experimental research increasingly operates within networks. No single university and no single large-scale research facility could cover the necessary expertise on its own. For us in Freiberg, this close collaboration with HZB, FHI, DESY and the European XFEL is therefore of central importance. At the same time, we can contribute our own expertise in photoelectron spectroscopy and time-resolved experiments to these networks,” explains Roth.
From development to international user operations
With the commissioning phase now complete, the next phase of the project is set to begin. The system is to be opened up to scientific user groups and utilised to address various research questions in the fields of materials, surfaces and energy research. In doing so, the project not only strengthens the experimental capabilities at BESSY II, but also enhances the international profile of TU Bergakademie Freiberg in the field of time-resolved photoelectron spectroscopy and research at large-scale research facilities.
The project was funded by the Federal Ministry of Research, Technology and Space (BMFTR) as part of the ErUM-Pro programme (grant reference 05K22OF2).
