Research#
Aims at a fundamental understanding of physical and chemical transformations
Towards applications for a sustainable future
Enabled by method and instrument development
X-ray studies of chemical reactions on surfaces#
X-ray photoelectron spectroscopy in operando
We operate the POLARIS instrument at P22, PETRA, DESY, Hamburg, Germany together with DESY
Hard X-ray photoelectron spectroscopy at pressures up to 1 bar and temperatures up to 700°C
Much closer to industrial applications then typical for photoelectron spectroscopy
Focus on hydrogenation reactions and reactions of small molecules on well-defined catalysts (Haber-Bosch, Fischer-Tropsch, water-gas shift, …)
Study (slow) temporal evolution through quick gas pressure or temperature changes
X-ray studies of electrochemistry
In-house developed cells for soft and hard X-ray absorption spectroscopy, also with laser-excitation, under operating conditions
Successful use of HAXPES during electrochemistry in POLARIS
Focus on CO2 reduction and oxygen evolution reactions
X-ray studies of laser-induced chemical reactions
TITAN instrument at the LCLS, SLAC, Stanford, USA operated together with SLAC and Stanford University
Free-electron lasers resolve processes of bond formation and breaking on the femtosecond timescale
Focus on reactions of small molecules in ultra-high vacuum on well-defined catalyst surfaces
X-ray studies of phase transitions#
Real-space images of domains in quantum materials
Inhomogeneity is probably ubiquitous
Use resonant soft X-ray scattering as contrast mechanism
Image domain ordering with Fresnel zone plates
Focus on chemical inhomogeneity and structural defects from surface treatment
3d transition metal oxides
Domain dynamics across phase transitions
Use X-ray photon correlation spectroscopy
Use resonant soft X-ray scattering as contrast mechanism
Access domain wall motion
Elemental rare-earth antiferromagnets
3d transition metal oxides
Dissect phase transitions through femtosecond laser excitation
Electron or lattice driven dynamics have characteristic timescales
Ultrafast studies can disentangle driving forces
Use soft X-ray spectroscopy and scattering as contrast mechanism
3d transition metal oxides
Semiconductors
Phase change materials
Method and instrument development#
Non-linear X-ray methods
Free-electron lasers deliver X-ray pulses that enable non-linear methods
Optical laser spectroscopy has developed many powerful techniques that can be ported over
The combination of non-linear processes with X-ray selectivity holds great promises
Concurrent processes are a severe challenge and complicate the adaptation
Transient grating methods have been implemented
X-ray optical wave-mixing has been demonstrated and has great potential for surface sensitive applications
Development also inside an international collaboration, the WavemiX network as well as the NEXT COST action
MUSIX
Multi-dimensional spectroscopy and (in-)elastic X-ray scattering instrument
Located at FLASH, DESY, Hamburg, Germany
Ultra-high vacuum diffractometer
Liquid Helium cryostat down to 25 K
Photon spectrometer with first grating order from 50-600 eV, resolving power better than 2000, CCD detector
TITAN
Surface science endstation at the LCLS
Standard ultra-high vacuum surface science preparation capabilities
Photon spectrometer and photoelectron spectrometer
To be used at the third interaction point of the LCLS soft X-ray branch
POLARIS
Hard X-ray photoelectron spectroscopy up to 1 bar and 700°C
Located at P22, PETRA, DESY, Hamburg, Germany
Versatile gas dosing and sample cleaning and heating system
Pump laser under development
UOPS
Under development
Funded as a research technology platform within the WISE program: Wallenberg Initiative Materials Science for Sustainability by the Knut and Alice Wallenberg Foundation
Aims to combine high gas-pressure HAXPES capabilities of POLARIS with femtosecond temporal resolution of free-electron laser pulses and ultrashort optical pulses
ResScatt
Ultra-high vacuum diffractometer
Located at SoftiMax, MAX IV, Lund, Sweden
Interferometric sample position tracking
Integrated CCD, but also additional detectors and optics (zone plates) can be flexibly accomodated
Liquid Helium cryostat
Can host a Timepix detector, provided by University of California, Berkeley through a Röntgen-Ångström cluster project for soft X-ray XPCS with nanosecond resolution
PAX
Photoelectron analysis of X-rays
Alternative concept to measure photons generated through resonant inelastic X-ray scattering (RIXS)
Measurement of photoelectrons emitted from a converter and deconvolution of the converter spectrum
High resolution in compact instruments
Parallel acquisition of a range in q-space through photoelectron microscopy
Implemented in a dedicated instrument at P04, PETRA, DESY, Hamburg, Germany