Surface sensitivity of Auger-electron spectroscopy and X-ray photoelectron spectroscopy |
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| Institution: | 1. Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA;2. Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warsaw, Poland;3. Materials Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA;4. Japan Energy ARC Co. Ltd., 3-17-35 Niizo-Minami, Toda-shi, Saitama 335, Japan;5. Electron and Optical Physics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA;1. Department of Physics, Hasanuddin University, Makassar 90245, Indonesia;2. Department of Physics, Chungbuk National University, Cheongju 362-763, Korea;3. Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense M, Odense DK-5230, Denmark;1. Institute of Radiation Medicine, Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH), Ingolstädter Landstr. 1, 85764 Neuherberg, Germany;2. Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela LRS, Portugal;3. Institut de Physique Nucléaire de Lyon, Université de Lyon, Université Claude Bernard Lyon 1, CNRS/IN2P3 UMR 5822, Villeurbanne, France;4. Department of Engineering Physics, Tsinghua University, Beijing, China;5. Normandie University, ENSICAEN, UNICAEN, CEA, CNRS, CIMAP, UMR 6252, BP 5133, F-14070 Caen Cedex 05, France;6. Karlsruhe Institute of Technology, Karlsruhe, Germany;7. Institut de Radioprotection et de Sûreté Nucléaire, Fontenay-Aux-Roses, France;8. Alferov Federal State Budgetary Institution of Higher Education and Science Saint Petersburg National Research Academic University of the Russian Academy of Sciences, St. Petersburg, Russia;9. TranslaTUM, Klinikum rechts der Isar, Technische Universität München, Munich, Germany;10. Nuctech Company Limited, Beijing, China;11. Physikalisch-Technische Bundesanstalt, Braunschweig, Germany;12. Massachusetts General Hospital & Harvard Medical School, Department of Radiation Oncology, Boston, MA, USA;13. Peking University Cancer Hospital, Beijing, China;1. Department of Physics, University of Science and Technology of China, Hefei 230026, Anhui, China;2. Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, China;3. Data Science Group, Center for Materials Research by Information Integration, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan;4. Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Debrecen, Hungary;5. ELI-ALPS, ELI-HU Non-profit Ltd., Dugonics tér 13, H-6720 Szeged, Hungary;1. Department of Physics and Astronomy, Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Denmark;2. Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland;3. Elettra – Sincrotrone Trieste S.C.p.A., 34149 Basovizza, Trieste, Italy;4. IOM-CNR Laboratorio TASC, Area Science Park, Trieste, Italy;5. Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell, United Kingdom;6. Institut für Physik, Technische Universität Chemnitz, Germany;7. SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, United Kingdom;8. Department of Physics, Universitá degli Studi di Trieste, 34127 Trieste, Italy;9. International Faculty – University of Köln, Germany;1. Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei 230026, Anhui, PR China;2. Key Laboratory of Strong-Coupled Quantum Matter Physics, Chinese Academy of Sciences, PR China;3. Institute for Technical Physics and Materials Science Centre for Energy Research, Hungarian Academy of Sciences, H-1121 Budapest, Hungary;4. Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), P.O. Box 51, Debrecen, Hungary;5. ELI-ALPS, ELI-HU Non-Profit, Ltd., Dugonics tér 13, H-6720 Szeged, Hungary;1. National Research Center “Kurchatov Institute” Petersburg Nuclear Physics Institute, Gatchina 188300, Russian Federation;2. Kurnakov Institute of General and Inorganic Chemistry, Moscow 119991, Russian Federation;3. Moscow Institute of Physics and Technology, Dolgoprudny 141701, Russian Federation |
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| Abstract: | A convenient measure of surface sensitivity in Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) is the mean escape depth (MED). If the effects of elastic-electron scattering are neglected, the MED is equal to the electron inelastic mean free path (IMFP) multiplied by the cosine of the emission angle with respect to the surface normal, and depends on the material and electron energy of interest. An overview is given here of recent calculations of IMFPs for 50–2000 eV electrons in a range of materials. This work has led to the development of a predictive formula based on the Bethe equation for inelastic electron scattering in matter from which IMFPs can be determined. Estimates show, however, that elastic-electron scattering can significantly modify the MED. Thus, for AES, the MED will be reduced by up to about 35%. For XPS, however, the MED can be changed by up to ±30% for common measurement conditions although it can be much larger (by up to a factor of 2) for near-grazing emission angles. Ratios of MED values, calculated with elastic scattering considered and neglected for XPS from the 3s, 3p, and 3d subshells of silver with Mg Kα X-rays are approximately constant (to about 10%) over a range of emission angles that varies from 40° to 60° depending on the subshell and the angle of X-ray incidence. Recommendations are given on how to determine the optimum range of emission angles for satisfactory analysis of angle-resolved XPS (ARXPS) data. Definitions are included of three terms often used for describing surface sensitivity (IMFP, MED, and effective attenuation length (EAL)), and examples are given of the varying magnitudes of these quantities for different analytical conditions. |
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