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Professor Svante Svensson joins PLEIADES team
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Since mid-September and for the next two years, an additional scientist has joined the PLEIADES beamline research group at SOLEIL. Professor Svante Svensson continues a history of collaboration, first with LURE then with SOLEIL that has existed for … a quarter of a century!
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Svante Svensson knows the region well. He arrived at LURE in 1982, on the Orsay campus, for a year’s sabbatical with Paul Morin, Marie-Yvonne Adam and Irène Nenner. A specialist in high resolution electron spectroscopy, he did his thesis at Uppsala University in the laboratory of Kai Siegbahn, Nobel laureate in physics in 1981. The Nobel Prize was given for research on electron spectroscopy for chemical analysis (ESCA), commonly known as photoelectron spectroscopy.
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 What is photoelectron spectroscopy?
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When light, in the form of photons, hits an atom, this creates a disturbance in the electron cloud. If the photons have enough energy (in the ultraviolet or X-ray range), they will eject one or more electrons positioned near the nucleus – referred to as core electrons1. A study of the core electrons thus ejected then gives information on the atom to which they were attached. To do this, the kinetic energy of the ejected electrons has to be measured.
Photons transmit their energy as follows:
Incident photon energy = energy of electron emitted + energy required to withdraw the electron from the atom (i.e. binding energy)
This “binding energy” corresponds to the force binding the electron to the atomic nucleus, and it characterises the atom under study. For example the energy required to tear a core electron from a heavy atom, whose nucleus contains several dozen protons and therefore has a strong positive charge that will attract the electron, requires more energy than in the case of say helium, whose nucleus only consists of 2 protons.
In addition, these measurements provide information on the local environment of the atom under study, as the binding energy values will vary slightly depending on the nature of the atoms surrounding the absorber atom. One can, for example, distinguish several carbon atoms from the same molecule, as they are surrounded by different atoms.
Areas of research such as the study of reactions that occur on the surface of solids, notably those involving catalytic phenomena2, have benefited a great deal from the development of this spectroscopic technique.
From left to right: Mrs Valérie Pécresse, Research Minister, MM. Paul Morin, Svante Svensson and Catalin Miron, during the Opening Ceremony of the RTRA – Triangle of Physics in June 2008.
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Synchrotron apprenticeship at LURE
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In Sweden, in the nineteen seventies, Svante Svensson had the spectroscopists Joseph Nordgren and Nils Mårtensson among his colleagues, now Chairman of the Nobel Physics Committee and Director of the “MAX-lab”, the Swedish synchrotron, respectively. A generation of clearly productive research scientists, although with little experience of synchrotron technology. Indeed, when he arrived at LURE, although Prof. Svensson knew of their importance, he had never yet had the opportunity to work with synchrotron radiation. The X-rays that he had used up to then for his research had been produced by rotating anode tubes cooled by high pressure water.
This first Franco-Swedish collaborative venture will give him some training in this field and he will return to Sweden with the necessary know-how to start basing his research on the use of synchrotron radiation.
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MAX I, MAX II…
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Prof. Svensson has started by working at the 2nd generation MAX I synchrotron, where he is already obtaining, (with BM51, the first MAX I undulator beamline), better results than with ALS, the Californian synchrotron, despite this being the newer 3rd generation.
He will then transfer this beamline to MAX II, the third synchrotron of the 3rd generation to be constructed, in the nineteen nineties (after ALS in the USA and Elettra in Italy). It is at this point that the second phase of the collaboration will take place: Catalin Miron, who was a PhD student in Paul Morin’s lab, and now responsible for the PLEIADES beamline, will rejoin Dr. Svensson’s team as a post-doc. Catalin will therefore get to know the Swedish synchrotron, which, in a few years time, will temporarily receive some of the PLEIADES instruments until the line is up and running at SOLEIL.
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Improving the resolution
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Dr. Svensson’ research advances came about in parallel with technological developments, especially due to custom-made adaptations to the spectrometers marketed by Scienta. This Swedish company was created in the great Swedish tradition of high resolution electron spectroscopy, with the aim of developing instruments to keep up with advances made by M. Siegbahn in photoemission spectroscopy. Interactions between Scienta and its neighbour Uppsala University continue as ever, resulting in numerous transfers of technology.
Thus, it is naturally a Scienta spectrometer that has been installed, as well as the EPICEAAA mounting of the PLEIADES beamline (see Rayon de SOLEIL n°10), perfected to detect several charged particles simultaneously (electrons, ions) and analyse their mass, energy and emission direction. The aim is to obtain a very complete image of the processes resulting from a photon/molecule “shock”. The most recent model of Scienta spectrometer was chosen (R4000), with a resolution3 of 380 µeV – a record for this type of instrument. Svante Svensson’s work at SOLEIL might well include a test of another spectrometer on PLEIADES, which is still being developed in Uppsala at the moment and will have a resolution of 200 µeV.
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A chair funded by the “Réseau thématique de recherche avancé (RTRA) Triangle of Physics ”
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Dr. Svensson has expressed “his gratitude” for being able to benefit from the funding of the ECMACSE project: studies on complex matter with extreme sources, by the RTRA – Triangle of Physics network – funding which has also allowed Ms Oksana Travnikovaqui to come to SOLEIL as a post-doc.
This project involves SOLEIL and the IRAMIS/SPAM4 teams at Saclay AEC. The aim is to develop studies of spectroscopy crossed with extreme sources: soft X-rays on PLEIADES and lasers at the AEC. Two complimentary techniques, with the same objective: to observe and understand matter. For the samples under study, molecules but also “clusters” and liquid microjets, the aim is to follow their rapid fragmentation dynamics (in the order of a few femtoseconds, 10-15 sec: one millionth of one billionth of a sec…).
For some studies, experimental chambers will be brought to SOLEIL from Dr. Svensson’s laboratory in Uppsala, a case of “not re-inventing the wheel”, when the material already exists over there!
The third phase of Franco-Swedish collaboration will begin… 
Catalin Miron installs the Scienta R4000 spectrometer on PLEIADES,
in September 2007
1 Core electrons: close to the nucleus composed of protons/neutrons, they can be distinguished from valence electrons, located further away from the nucleus and that intervene in the formation of chemical links (covalent) between atoms, notably in the creation of molecules.
2 Catalysis: initiation or acceleration of a chemical reaction by a substance – the catalyst – that is present but does not participate in the reaction: It is not consumed and remains unchanged at the end of the reaction.
3 Resolution limit: minimum perceptible difference between two values of a measurement taken by an instrument. The resolution is the inverse of the resolution limit. In the case of emission spectroscopy, the energy of electrons is measured.
4 IRAMIS/SPAM: Institut Rayonnement Matière de Saclay / Service des Photons, Atomes et Molécules
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