Workshop on low-energy, high-resolution spectroscopy
LUND, SEPTEMBER 25, 1996
REPORT ON THE WORKSHOP
CONTENTS
INTRODUCTION AND BACKGROUND
The workshop on low-energy spectroscopy was planned in connection with the recent FRN application entitled "Application for a low-energy monochromator for MAX II". There were fifty five participants at the workshop. The workshop was motivated by a need for a high-resolution monochromator ((1-2 meV) in the valence-electron region with a flux of at least 10E12 photons/sec.mrad.100 mA.0.1%bw. Such a beam line would be of great use to solid-state physicists and atomic/molecular physicists. Using MAX II as a source this performance is very realistic for a bending magnet beam line. The workshop was organized in order to formally present the project to the community of prospective users in a forum where the scientific motivation for such a project is discussed and the future scientific goals for the beam line would be outlined. We feel that the workshop was a great success in many ways. The questions presented by the MAX Lab PAC were addressed and very strong interest was shown by the user community.
GOALS OF THE WORKSHOP
The goals of the workshop were both to gather information about state-of-the art low-energy monochromator design and to quantify the needs of the community. The MAX program advisory committee specified several areas which needed clarification and these were brought up during the discussion period. The material covered at the workshop should lead to evaluation of a low-energy monochromator at MAX II and outlining of a design strategy. Major questions to be approached include energy region, resolution, bending magnet vs. undulator source among others. We intended to bring up the question of the complementary properties of laser light vs. synchrotron light and the issue of end stations compatible with a high-resolution light source.
WORKSHOP PROGRAM
12.30 Ingolf Lindau, Director of MAX-Lab: Opening of Workshop
12.40 Ruben Reininger, Synchrotron Radiation Center, University of Wisconsin-Madison: Normal-incidence monochromators at the SRC
13.30 Dr. Changyoung Kim, Stanford University: Angle-resolved photoemission on highly correlated electron systems
14.40 Hans Starnberg, Chalmers University of Technology: Studies of layered intercalation systems by synchrotron radiation.
15.00 Lars Walldén, Chalmers University of Technology: High-resolution photoemission from metal overlayer quantum well states.
15.20 Leif Karlsson, University of Uppsala: UV and synchrotron radiation photoelectron spectra of small molecules in the gas phase
15.40 Mats Qvarford, Lund University: Photoelectron spectroscopy on high-Tc superconductors: The need for high resolution
16.00 Peter Baltzer, Uppsala University: Very high resolution gas phase PES: Experiences from a visit to the ALS
16.40 Presentation and Discussion
18.30 Dinner at IDEON
SUMMARY OF WORKSHOP MATERIAL
Dr. Ruben Reininger presented information about the monochromators at the SRC . which are relevant for low-energy spectroscopy. The 4-m NIM designed in 1979 has become very popular during the last five years for both gas-phase spectroscopy and for solid-state physics and is the basis for further developments at the SRC. Some very important research has been completed based upon the high quality of this beam line.
The second speaker was Changyoung Kim from the Stanford Synchrotron Radiation Center in Palo Alto, California, USA. Dr. Kim is responsible for the new 6.65m NIM to be installed at the SSRL electron storage ring, SPEAR. He presented state-of-the art studies on SrCuO2 in which evidence is found form the separation of the charge and spin excitations during photoexcitation. This interpretation is important for the understanding of superconductivity. Dr. Kim gave a very informative talk describing the spin-charge separation and the origin of this, its relation to dimensionality and the implications of this model. Future progress is dependent on the NIM being implemented at SSRL.
Hans Starnberg from Chalmers University of Technology presented a brief summary of layered materials in which the layers are bonded by van der Waals bonds. The mechanical properties of such systems are mirrored by the electronic properties. The presentation focused upon systems in which an alkali metal is intercalated in a layered system and the intercalation is studied as a function of temperature and of the thickness of the overlayer.
Lars Walldén, also of Chalmers Institute of Technology presented Li overlayer quantum well states as studied by UV laser based spectroscopy. The Li/Cu(111) system was chosen since it is a two-phase system. The copper substrate provides free electrons which should fill the band upon addition of alkali layers. The well structure on the surface will then contain discrete electronic states. HREELS spectra were measured with a He-Cd laser (3.82 eV, r=5 meV) for which the thickness of the layer was varied. The need for a tunable source with comparable resolution characteristics was emphasized.
Leif Karlsson of Uppsala University spoke about molecular photoionization based upon electron spectroscopy at the Daresbury Synchrotron and using a high-resolution helium resonance lamp. Studies of sulfur based molecules were performed with a focus on the Cooper minimum is the S 2s orbital. Using the high resolution vibrational structure in the inner valence of H2S (4a1-1 orbital) was seen and is attributed to Rydberg (atomic) excitation. Karlsson emphasized that we have only entered infancy in terms of what can be learned from high-resolution molecular spectroscopy.
Mats Qvarford of Lund University presented a talk on photoelectron spectroscopy on high-Tc superconductors with a focus on the need for high resolution. Presently angle-integrated core-level studies provide information about the change in gap as a function of doping. LDA calculations can, in some cases, agree surprisingly well despite the high correlation in such systems. The gap is, however, anisotropic, so that the gap may differ depending upon where in k space the measurement is made. Thus the measured gap is very sensitive to the exact energy, and in turn the width of the excitation. The Fermi peak also shows evidence of broadening depending upon the development of the interface state. This could be studied in greater detail with high-resolution photons.
Peter Baltzer from Uppsala University described measurements made at the Advanced Light Source in Berkeley, California using the spherical-grating monochromator on beam line 9.0.1. The goal of the project was to study the inner valence in O2, N2, CO and NO molecules at very high resolution, hopefully at better than 1 meV in order to extract vibrational branching ratios. This experiment is possible because Peter’s gas-phase electron spectrometer operates at a comparably high resolution. Among other measurements presented here were very high resolution spectra of hydrogen were measured revealing the entire Q-branch rotational manifold.
Scientific interest for the project was expressed by many different research groups working in both gas-phase spectroscopy and solid-state physics. The interests of both of these groups showed that there is a great need for high resolution in the low-energy region specifically 5-30 eV. The discussion at the workshop indicated that there is also interest for the photon energy region 20 eV - 150 eV and beyond; but combining this region with the low energy one would compromise too much. Interest was expressed for a separate project concerning this higher photon-energy region.
CONCLUSIONS
One important point which the discussion made clear is that the project should focus upon getting the greatest performance at low energies and that this would be compromised by trying to cover a larger energy region. A possible scenario would be to plan for two separate beam lines and it would be reasonable to organize a workshop to discuss an instrument working from bout 20 eV up to 120 eV. One of the presentations was, in fact, based upon measurements using laser light. It was pointed out that the usefulness of lasers is limited to the fixed wavelength of the light and that it in effect limits the type of experiments which can be made. It was pointed out during discussion that two end stations for such a beam line are being planned by both the ‘solid-state’ community and the ‘gas-phase’ community.
LIST OF PARTICIPANTS
Dr. Akane Agui Uppsala University Dept. of Physics Box 530 751 21 UPPSALA Sweden
Doc. Jesper Andersen Lund University Institute of physics Dept. of synchrotron radiation research Sölvegatan 14 223 62 LUND Sweden
Dr. Anders Arner Lund University Dept. of physiology and neuroscience Sölvegatan 19 223 62 LUND Sweden
Dr. Dimitri Arvanitis Uppsala University Dept. of physics Box 530 751 21 UPPSALA Sweden
Doc. Peter Baltzer Uppsala University Department of physics Box 530 751 21 UPPSALA Sweden
Dr. Andreas Beutler Lund University Institute of physics Dept. of synchrotron radiation research Sölvegatan 14 223 62 LUND Sweden
PhD Student Jonas Birgersson Linköping University IFM 581 83 LINKÖPING Sweden
Dr. Sergei Butorin Lund University MAX-lab Box 118 221 00 LUND Sweden
Dr. Yu-Cheng Chao Linköping University IFM 581 83 LINKÖPING Sweden
Dr. Gualtiero Chiaia Royal Institute of Technology Dept. of Materials Science 100 44 STOCKHOLM Sweden
Dipl. Miner. Benyam Estifanos Lund University Institute of geology Sölvegatan 13 223 62 LUND Sweden
1:e fo.ing. Jan-Olof Forsell Uppsala University Dept. of physics Box 530 751 21 UPPSALA Sweden
Civ.ing. Ken Yoshiki Franzén Royal Institute of Technology Physics I 100 44 STOCKHOLM Sweden
Dr. Struan Gray Lund University Institute of physics Dept. of synchrotron radiation research Sölvegatan 14 223 62 LUND Sweden
Karin Heister Tunavägen 39 B 223 63 LUND Sweden
PhD Student Niklas Johansson Linköping University IFM 581 83 LINKÖPING Sweden
Mr. Jonathan Hunter-Dunn Uppsala University Dept. of physics Box 530 751 21 UPPSALA Sweden
Dr. Andrzej Karawajczyk Royal Institute of Technology Institue of physics I 100 44 STOCKHOLM Sweden
Doc. Leif Karlsson Uppsala University Dept. of physics Box 530 751 21 UPPSALA Sweden
Dr. Ulf Karlsson Royal Institute of Technology Dept. of Materials Science 100 44 STOCKHOLM Sweden
MSc Ilmar Kink Lund university Institute of physics Dept. of Atomic Spectroscopy Sölvegatan 14 223 62 LUND Sweden
Dr. Rein Kink Institute of physics Riia 142 EE 2400 TARTU Estonia
Ph.D. Marco Kirm Institute of physics Riia 142 EE 2400 TARTU Estonia
Ass.Res.Sc. Ku-Ding Tsuei Synchr. Radiation Research Center Hsinchu Science-Based Ind. Park Hsinchu Taiwan 300, R.O.C.
Prof. Ingolf Lindau Lund University MAX-lab Box 118 221 00 LUND Sweden
Prof. Per-Olof Nilsson Chalmers University of Technology Dept. of physics 412 96 GÖTEBORG Sweden
Doc. Ralf Nyholm Lund University MAX-lab Box 118 221 00 LUND Sweden
Henrik Nylén Lund University Institute of physics Dept. of synchrotron radiation research Sölvegatan 14 223 62 LUND Sweden
Doc. Ergo Nõmmiste University of Oulu Dept. of Physical Sciences FIN-90570 Oulu Finland
Dr. Luc Patthey Uppsala University Dept. of physics Box 530 751 21 UPPSALA Sweden
Dr. Mats Qvarford Lund University Institute of physics Dept. of synchrotron radiation research Sölvegatan 14 223 62 LUND Sweden
Dr. Anders Sandell Lund University Institute of physics Sölvegatan 14 223 62 LUND Sweden
Doc. Stacey Sorensen Lund University Institute of physics Dept. of synchrotron radiation research Sölvegatan 14 223 62 LUND Sweden
Dr. Marek Stankiewicz Royal Institute of Techynology Physics I 100 44 STOCKHOLM Sweden
Doc. Hans Starnberg CTH/GU Dept. of Physics 412 96 GÖTEBORG Sweden
Dr. Frode Strisland Lund University Institute of physics Dept. of synchrotron radiation research Sölvegatan 14 223 62 LUND Sweden
Dr. Svante Svensson Uppsala University Dept. of physics Box 530 751 21 UPPSALA Sweden
Doc. Roger Uhrberg Linköping University IFM 581 83 LINKÖPING Sweden
Dr. Lars Walldén Chalmers University of Technology Dept. of physics 412 96 GÖTEBORG Sweden
Prof. Juhani Väyrynen University of Turku Dept. of Applied Physics Verilinnantie 5 FIN-200 14 TURKU Finland
Dr. Alexander Zakharov Lund University Institute of physics Dept. of synchrotron radiation research Sölvegatan 14 223 62 LUND Sweden
Last modified: 1996-12-10
Friday, 15-Sep-2006 12:23:21 CEST
telephone: 046/222 72 65;046/222 76 62
E-post stacey.sorensen@maxlab.lu.se