I got my PhD degree in 2010 from University of Oulu. My topic was “Electron spectroscopic studies of the electronic structure of some metal atoms and alkali halide molecules”. From 2011 to 2015 I worked as a researcher at Synchrotron SOLEIL, focusing on photoelectron and photoabsorption studies of gas-phase clusters and nanoparticles. In September 2015 I moved back to University of Oulu, and I am currently working as an Academy Research Fellow with a project title of “Characterization of free-standing nanomaterials using novel light sources”.
My PhD works was all about photoelectron and Auger spectroscopies of gas phase atoms and molecules. I have carried out both computational and experimental work. It is like the music from one's teenage years: molecular spectroscopy is still my favorite topic, there is nothing better to see a high-resolution photoelectron spectrum with a matching calculation! I am still somewhat active in this field also, especially through collaborations with different experimental and theoretical groups in UK, Sweden, and France.
The same experimental techniques applied to gas phase molecules can be applied to study clusters and nanoparticles. The main topic in my Academy of Finland research fellow project is to benefit from the extreme surface sensitivity of X-ray photoelectron spectroscopy and extremely brilliant light sources (synchrotrons and free electron lasers) to learn from the geometrical and electronic structure of these gas phase species. The surface properties of clusters and nanoparticles and their chemical reactivity are of fundamental relevance interdisciplinarily and intersectorially. The role of surface chemistry of nano-objects is of utmost importance in catalysis and its industrial applications. Compared to bulk materials, nanoparticles provide enormous surface and carry unique surface properties which can be designed to enhance materials’ efficiency in energy conversion and storage technologies. We are exposed daily also to naturally made agglomerates of atoms and molecules. Important environmental issues like climate evolution and global warming have been related to the physicochemical properties and reactivity of small molecular agglomerates. For example water-salt clusters serve as seeds for cloud formation above seas and bring reactive ions up to the atmosphere contributing to ozone depletion.
Recently, I have been involved in several collaborative projects where synchrotron radiation based techniques are applied to studies of biomaterials. With University of Oulu's Fibre and particle engineering research unit we have studied nanocellulose-nanosilica hybrid films, with researchers from Natural Resources Institute of Finland (Luke) we have analysed cells of Norway spruce, and with PEDEGO research unit and Biocenter Oulu, we have started a project called SoftXMed (http://www.oulu.fi/biocenter/projects/emerging/patanen).
The common factor for these biomaterial projects is the techniques used, scanning transmission soft X-ray microscopy (STXM). It utilises electromagnetic radiation in soft X-ray energy regime to irradiate the samples, and collects the transmitted light. Soft X-rays are used because this radiation has suitable energy to cause excitations of inner-shell electrons in atoms. The energy of the radiation has to be exactly matching the energy difference between the so-called ground state and excited state in order the core-excitation to happen. Each element has its own characteristic energies at which these excitations can take place, furthermore, the energies of the excitations are modified when the atom interacts with its neighbours (i.e. forms chemical bonds). Thus, in the heart of the STXM technique is to continuously tune the energy of the radiation to locate these excited states in the specific sample in question: this energy will give information about the chemical substances present in the sample. The size of the irradiating beam is very small, less than 50 nm, which means that the sample can be studied with a spatial resolution of < 50 nm. In practice, the sample is place on a scanning stage, and a raster scanned image of the sample can be formed at each energy. Compared to transmission microscopies in which only one energy of radiation is used, STXM is like a colour photos compared to black and with photographs. The spectral information provided by STXM may help to identify unknown substances that seem to accumulate inside the cells, and thus find possible biomarkers of diseases.
STXM can be carried out at synchrotron radiation facilities, and the team is a long-term user of these large-scale infrastructures in Sweden, France and Japan. The technique itself is still evolving and a lot of progress is foreseen regarding e.g. sample preparation techniques and sample environments. As the STXM itself would not require ultra-high vacuum conditions, conductive or stained samples, the aim is also to investigate possibilities for less processed samples.