The history of our group dates back to the 1960's when such pioneers as Timo Paakkari and Pekka Suortti started systematic x-ray crystallographic studies at the Department of Physics (then located near Helsinki downtown, at Siltavuorenpenger). In the 1970's, Seppo Manninen spent a post-doc period at the lab of Prof. Malcolm Cooper, Warwick (UK) and brought the knowhow of x-ray Compton scattering spectroscopy to Helsinki.
Our group's location before and now. Left: Siltavuorenpenger campus (1959-2001). Right: Kumpula campus (2001- )
Our group has been utilizing synchrotron radiation already since the 1970's since the work of Pekka Suortti at Brookhaven National Synchrotron Light Source. He worked with synchrotron radiation techniques including designs of beamlines and their application to spectroscopy, x-ray diffraction, including the resonance phenomena, and medical imaging. In the 1980-1990 period many important researcher visits were made to Daresbury and HASYLAB as well. Important turning points took place in the early 1990's with Ritva Serimaa's post-doc period at Stanford Synchrotron Radiation Laboratory (SSRL) and Keijo Hämäläinen's post-doc at Brookhaven's National Synchrotron Light Source (NSLS). Both of them became later professors in our laboratory. Notably, Serimaa was the first female physics professor in the University of Helsinki. Her research field is small-angle and wide-angle x-ray scattering from nanomaterials and polymers such as cellulose. Hämäläinen developed the field of inelastic x-ray scattering spectroscopy at under the supervision of Dr. Jerry Hastings. Hämäläinen is best known in the field of x-ray spectroscopy from his utilization of resonant x-ray emission spectroscopy to yield much more information on the electronic structure than regular x-ray absorption spectroscopy can yield. The Hämäläinen method was based on the recording of resonant x-ray emission peak intensity when incident photon energy is tuned across an x-ray absorption edge. The variations of the intensity could be interpreted as x-ray absorption spectra with an elimination of the deep core-hole lifetime broadening. Resonant x-ray emission spectroscopy is even nowadays a hypermodern tool for x-ray spectroscopy.
Nowadays we are an integral part of the Finnish Synchrotron Radiation Users' Organization.
Helsinki and light sources
In the end of 1980's Pekka Suortti, amongst others, proposed that Finland should become a member of the then-yet-to-be European Synchrotron Radiation Facility already at its planning phase together with other Nordic countries. At that time there were only few synchrotron radiation users in Finland and it wasn’t clear to many people that it would become such an important research tool for many people worldwide. Currently, roughly 7000 researcher visits are made to ESRF annually.
ESRF is still one of our most important experimental facilities. Annually we perform nearly 10 synchrotron radiation experiments on average, majority of them at ESRF and MAX-Lab.
Helsinki and computational materials physics
Today an important factor of our work is based on the interplay of computational and experimental materials physics. Spectroscopy yields indirect information on the underlying function and structure of materials. Interpretation and prediction of experimental results can only be done through computations. This is an important challenge in our frontier and has been attacked by our group in the early days of our existence. Starting from developing corrections to x-ray powder intensities, calculations of Compon profiles, the interpretation of resonant and non-resonant IXS spectra has been very close to our hearts. One important advance was when J. Aleksi Soininen spent a post-doc period with Eric Shirley (US) in the early 2000's and developed advanced methods to take electron-hole interaction into account in various spectra including valence- and core-excited states. His work includes as well the methodology to extract symmetry-projected densities of states from core-level IXS spectra. Nowadays various kinds of software is routinely used in the group, both locally and at supercomputers, for calculating atomic structures and molecular dynamics, electronic properties, x-ray observables and dielectric properties in general.
Helsinki and x-ray microtomography
In 2008 a microtomography (uCT) laboratory was built around a state-of-the-art uCT scanner nanotom(R) supplied by Phoenix|x-ray Systems + Services GmbH. The scanner enables sub-micrometer resolution with sample diameter below 20 mm. The maximum sample diameter is 120 mm.
The uCT facility includes also other x-ray applications such as diffraction and scattering. For these purposes, a complementary system with a microfocus x-ray source (device IµS supplied by Incoatec GmbH) and dedicated detectors has been designed. The special design of the µCT scanner with a room-size shielded cabinet enables the use of the complementary system without removing the sample from the scanner.
In 2015, the laboratory was extended with another high-resolution uCT scanner: a Bruker SkyScan. Other lower-resolution experimental x-ray imaging devices exist and are widely used in collaboration with the Department of Mathematics for instance.
The uCT laboratory has been very successful and multidisciplinary facility that serves cultural heritage, biosciences, industry, and materials physics alike.
X-ray physics and medical physics
Want to know where we are doing today?
Please visit our Research Topics page.
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