Mössbauer Spectroscopy E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 1584

Veröffentlichungsjahr: 2013

Beschreibung

Providing a modern update of the field, Mossbauer Spectroscopy focuses on applications across a broad range of fields, including analysis of inorganic elements, nanoparticles, metalloenzymyes, biomolecules (including proteins), glass, coal, and iron. Ideal for a broad range of scientists, this one-stop reference presents advances gained in the field over past two decades, including a detailed theoretical description of Mossbauer spectroscopy, an extensive treatment of Mossbauer spectroscopy in applied areas, and challenges and future opportunities for the further development of this technique.

Leseprobe

Contents

Cover

Title Page

Copyright

Dedication

Preface

Contributors

Part I: Instrumentation

Chapter 1: In Situ Mössbauer Spectroscopy with Synchrotron Radiation on Thin Films

1.1 Introduction

1.2 Instrumentation

1.3 Synchrotron Radiation-Based Mössbauer techniques

1.4 Conclusions

Acknowledgments

References

Chapter 2: Mössbauer Spectroscopy in Studying Electronic Spin and Valence States of Iron in the Earth's Lower Mantle

2.1 Introduction

2.2 Synchrotron Mössbauer Spectroscopy at High Pressures and Temperatures

2.4 Conclusions

Acknowledgments

References

Chapter 3: In-Beam Mössbauer Spectroscopy Using a Radioisotope Beam and a Neutron Capture Reaction

3.1 Introduction

3.2 57Mn (→57Fe) Implantation Mössbauer Spectroscopy

3.3 Neutron In-Beam Mössbauer Spectroscopy

3.4 Summary

References

Part II: Radionuclides

Chapter 4: Lanthanides (151Eu and 155Gd) Mössbauer Spectroscopic Study of Defect-Fluorite Oxides Coupled With New Defect Crystal Chemistry Model

4.1 Introduction

4.2 Defect Crystal Chemistry (DCC) Lattice Parameter Model

4.3 Lns-Mössbauer and Lattice Parameter Data of DF Oxides

4.4 DCC Model Lattice Parameter and Lns-Mössbauer Data Analysis

4.5 Conclusions

References

Chapter 5: Mössbauer and Magnetic Study of Neptunyl(+1) Complexes

5.1 Introduction

5.2 237Np Mössbauer Spectroscopy

5.3 Magnetic Property of Neptunyl Monocation (NpO2+)

5.4 Mössbauer and Magnetic Study of Neptunyl(+1) Complexes

5.5 Discussion

5.6 Conclusion

Acknowledgment

References

Chapter 6: Mössbauer Spectroscopy of 161 Dy in Dysprosium Dicarboxylates

6.1 Introduction

6.2 Experimental Methods

6.3 Results and Discussion

Acknowledgment

References

Chapter 7: Study of Exotic Uranium Compounds Using 238U Mössbauer Spectroscopy

7.1 Introduction

7.2 Determination of Nuclear g-Factor in the Excited State of 238U Nuclei

7.3 Application of 238U Mössbauer Spectroscopy to Heavy Fermion Superconductors

7.4 Application to Two-Dimensional (2D) Fermi Surface System of Uranium Dipnictides

7.5 Summary

Acknowledgments

References

Part III: Spin Dynamics

Chapter 8: Reversible Spin-State Switching Involving a Structural Change

8.1 Introduction

8.2 Three Assembled Structures of Fe(NCX)2(bpa)2 (X = S, Se) and their Structural Change by Desorption of Propanol Molecules [23]

8.3 Occurrence of Spin-Crossover Phenomenon in Assembled Complexes Fe(NCX)2(bpa)2 (X = S, Se, BH3) by Enclathrating Guest Molecules [25–27]

8.4 Reversible Structural Change of Host Framework of Fe(NCS)2(bpp)2·2(Benzene) Triggered by Sorption of Benzene Molecules [29]

8.5 Reversible Spin-State Switching Involving a Structural Change of Fe(NCX)2(bpp)2·2(Benzene) (X = Se, BH3) Triggered by Sorption of Benzene Molecules [30]

8.6 Conclusions

References

Chapter 9: Spin-Crossover and Related Phenomena Coupled with Spin, Photon, and Charge

9.1 Introduction

9.2 Photoinduced Spin-Crossover Phenomena

9.3 Charge Transfer Phase Transition

9.4 Spin Equilibrium and Succeeding Phenomena

References

Chapter 10: Spin Crossover in Iron(III) Porphyrins Involving the Intermediate-Spin State

10.1 Introduction

10.2 Methodology to Obtain Pure Intermediate-Spin Complexes

10.3 Spin Crossover Involving the Intermediate-Spin State

10.4 Spin-Crossover Triangle in Iron(III) Porphyrin Complexes

10.5 Conclusions

Acknowledgments

References

Chapter 11: Tin(II) Lone Pair Stereoactivity: Influence on Structures and Properties and Mössbauer Spectroscopic Properties

11.1 Introduction

11.2 Experimental Aspects

11.3 Crystal Structures

11.4 Tin Electronic Structure and Mössbauer Spectroscopy

11.5 Application to the Structural Determination of α-SnF2

11.6 Application to the Structural Determination of the Highly Layered Structures of α-PbSnF4 and BaSnF4

11.7 Application to the Structural Study of Disordered Phases

11.8 Lone Pair Stereoactivity and Material Properties

11.9 Conclusions

Acknowledgments

References

Part IV: Biological Applications

Chapter 12: Synchrotron Radiation-Based Nuclear Resonant Scattering: Applications to Bioinorganic Chemistry

12.1 Introduction

12.2 Technical Background

12.3 Applications in Bioinorganic Chemistry

12.4 Summary and Prospects

Acknowledgments

References

Chapter 13: MöSsbauer Spectroscopy in Biological and Biomedical Research

13.1 Introduction

13.2 Microorganisms-Related Studies

13.3 Plants

13.4 Enzymes

13.5 Hemoglobin

13.6 Ferritin and Hemosiderin

13.7 Tissues

13.8 Pharmaceutical Products

13.9 Conclusions

Acknowledgments

References

Chapter 14: Controlled Spontaneous Decay of Mössbauer Nuclei (Theory and Experiments)

14.1 Introduction to the Problem of Controlled Spontaneous Gamma Decay

14.2 The Theory of Controlled Radiative Gamma Decay

14.3 Controlled Spontaneous Gamma Decay of Excited Nucleus in the System of Mutually Uncorrelated Modes of Electromagnetic Vacuum

14.4 Spontaneous Gamma Decay in the System of Synchronized Modes of Electromagnetic Vacuum

14.5 Experimental Study of the Phenomenon of Controlled Gamma Decay of Mössbauer Nuclei

14.6 Experimental Study of the Phenomenon of Controlled Gamma Decay by Investigation of Space Anisotropy and Self-Focusing of Mössbauer Radiation

14.7 Direct Experimental Observation and Study of the Process of Controlled Radioactive and Excited Nuclei Radiative Gamma Decay by the Delayed Gamma–Gamma Coincidence Method

14.8 Conclusions

References

Chapter 15: Nature's Strategy for Oxidizing Tryptophan: EPR and Mössbauer Characterization of the Unusual High-Valent Heme Fe Intermediates

15.1 Two Oxidizing Equivalents Stored at a Ferric Heme

15.2 Oxidation of L-Tryptophan by Heme-Based Enzymes

15.3 The Chemical Reaction Catalyzed by MauG

15.4 A High-Valent Bis-Fe(IV) Intermediate in MauG

15.5 A High-Valent Fe Intermediate of Tryptophan 2,3-Dioxygenase

15.6 Concluding Remarks

References

Chapter 16: Iron in Neurodegeneration

16.1 Introduction

16.2 Neurodegeneration and Oxidative Stress

16.3 Mössbauer Studies of Healthy Brain Tissue

16.4 Properties of Ferritin and Hemosiderin Present in Healthy Brain Tissue

16.5 Concentration of Iron Present in Healthy and Diseased Brain Tissue: Labile Iron

16.6 Asymmetry of the Mössbauer Spectra of Healthy and Diseased Brain Tissue

16.7 Conclusion: The Possible Role of Iron in Neurodegeneration

References

Chapter 17: Emission (57Co) Mössbauer Spectroscopy: Biology-Related Applications, Potentials, and Prospects

17.1 Introduction

17.2 Methodology

17.3 Microbiological Applications

17.4 Enzymological Applications

17.5 Conclusions and Outlook

Acknowledgments

References

Part V: Iron Oxides

Chapter 18: Mössbauer Spectroscopy in Study of Nanocrystalline Iron Oxides from Thermal Processes

18.1 Introduction

18.2 Polymorphs of Iron(III) Oxide, Their Crystal Structures, Magnetic Properties, and Polymorphous Phase Transformations

18.3 Use of 57Fe mössbauer Spectroscopy in Monitoring Solid-State Reaction Mechanisms Toward Iron Oxides

18.4 Various Mössbauer Spectroscopy Techniques in Study of Applications Related to Nanocrystalline Iron Oxides

18.5 Conclusions

Acknowledgments

References

Chapter 19: Transmission and Emission 57Fe MöSsbauer Studies on Perovskites and Related Oxide Systems

19.1 Introduction

19.2 Study of High-Tc Superconductors

19.3 Study of Strontium Ferrate and Its Substituted Analogues

19.4 Pursuing Colossal Magnetoresistance in Doped Lanthanum Cobaltates

References

Chapter 20: Enhancing the Possibilities of 57Fe Mössbauer Spectrometry to Study the Inherent Properties of Rust Layers

20.1 Introduction

20.2 Mössbauer Characterization of Some Iron Phases Presented in the Rust Layers

20.3 Determining Inherent Properties of Rust Layers by Mössbauer Spectrometry

20.4 Final Remarks

Acknowledgments

References

Chapter 21: Application of Mössbauer Spectroscopy to Nanomagnetics

21.1 Introduction

21.2 Spinel Ferrites

21.3 Nanosized Fe–Al Alloys Synthesized by High-Energy Ball Milling

21.4 Magnetic Thin Films/Multilayer Systems: 57Fe/AI MLS

21.5 Conclusions

Acknowledgments

References

Chapter 22: Mössbauer Spectroscopy and Surface Analysis

22.1 Introduction

22.2 The Physical Basis: How and Why Electrons Appear in Mössbauer Spectroscopy

22.3 Increasing Surface Sensitivity in Electron Mössbauer Spectroscopy

22.4 The Practical Way: Experimental Low-Energy Electron Mössbauer Spectroscopy

22.5 Mössbauer Surface Imaging Techniques

5.6 Recent Surface Mössbauer Studies in an “Ancient” Material: Fe3O4

Acknowledgment

References

Chapter 23: 57Fe Mössbauer Spectroscopy in the Investigation of the Precipitation of Iron Oxides

23.1 Introduction

23.2 Complexation of Iron Ions by Hydrolysis

23.3 Precipitation of Iron Oxides by Hydrolysis Reactions

23.4 Precipitation of Iron Oxides from Dense β-FeOOH Suspensions

23.5 Precipitation and Properties of Some Other Iron Oxides

23.6 Influence of Cations on the Precipitation of Iron Oxides

Acknowledgment

References

Chapter 24: Ferrates(IV, V, AND VI): Mössbauer Spectroscopy Characterization

24.1 Introduction

24.2 Spectroscopic Characterization

24.3 Mössbauer Spectroscopy Characterization

Acknowledgments

References

Chapter 25: Characterization of Dilute Iron-Doped Yttrium Aluminum Garnets by Mössbauer Spectrometry

25.1 Introduction

25.2 Sample Preparations by the Sol–Gel Method

25.3 X-Ray Diffraction and Exafs Analysis

25.4 Magnetic Properties

25.5 Mössbauer Analysis of Yag Doped with Dilute Iron

25.6 Microdischarge Treatment of Iron-Doped Yag

25.7 Conclusions

Acknowledgments

References

Part VI: Industrial Applications

Chapter 26: Some Mössbauer Studies of Fe–As-Based High-Temperature Superconductors

26.1 Introduction

26.2 Experimental Procedure

26.3 Where do the Injected Electrons Go?

26.4 New Electron-Rich Species in Ni-Doped Single Crystals: is it Superconducting?

26.5 Can O2 Play an Important Role?

Acknowledgment

References

Chapter 27: Mössbauer Study of New Electrically Conductive Oxide Glass

27.1 Introduction

27.2 Structural Relaxation of Electrically Conductive Vanadate Glass

27.3 Summary

Acknowledgments

References

Chapter 28: Applications of Mössbauer Spectroscopy in the Study of Lithium Battery Materials

28.1 Introduction

28.2 Cathode Materials for Li-Ion Batteries

28.3 Anode Materials for Li-Ion Batteries

28.4 Conclusions

Acknowledgments

References

Chapter 29: Mössbauer Spectroscopic Investigations of Novel Bimetal Catalysts for Preferential CO Oxidation in H2

29.1 Introduction

29.2 Experimental Section

29.3 Results and Discussion

29.4 Conclusions

Acknowledgments

References

Chapter 30: The Use of Mössbauer Spectroscopy in Coal Research: is it Relevant or Not?

30.1 Introduction

30.2 Experimental Procedures

30.3 Results and Discussion

30.4 Conclusions

Acknowledgments

References

Part VII: Environmental Applications

Chapter 31: Water Purification and Characterization of Recycled Iron-Silicate Glass

31.1 Introduction

31.2 Properties and Structure of Recycled Silicate Glasses

31.3 Summary

References

Chapter 32: Mössbauer Spectroscopy in the Study of Laterite Mineral Processing

32.1 Introduction

32.2 Conventional Processing

32.3 Microwave Processing

References

Index

Copyright © 2013 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.

Published simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data:

Mössbauer spectroscopy: applications in chemistry, biology, industry, and nanotechnology / [edited by] Virender K. Sharma, Ph.D., Göstar Klingelhöfer, Tetsuaki Nishida.

pages cm

Includes bibliographical references and index.

ISBN 978-1-118-05724-7 (hardback)

1. Mössbauer spectroscopy. I. Sharma, Virender K., editor of compilation. II. Klingelhöfer, Göstar, 1956- editor of compilation. III. Nishida, Tetsuaki, 1950- editor of compilation.

QD96.M6M638 2014

543′.6–dc23

2013011056

We dedicate this book to the late Professor Attila Vertez, Eötvös Loránd University, Budapest, Hungary

Preface

Five decades ago, the Mössbauer concept was invented. Since then the Mössbauer spectroscopy has been applied in a wide range of fields including physics, chemistry, biology, and nanotechnology. The Mössbauer spectroscopy is still being applied vigorously in understanding the hyperfine interactions of electromagnetic nature. This is evident from a similar number of publications on the Mössbauer concept (∼14,000/decade) in the last three decades. This book presents the current knowledge on the applications of Mössbauer spectroscopy. With this theme in the minds of editors, many experts were invited to contribute to the book on the use of the Mössbauer effect in a number of subject areas. The editors also made sure that the contributors were from almost every region of the world (i.e., North America, South America, Europe, Africa, and Asia) in order to cover different aspects of the Mössbauer spectroscopy.

In Chapters 1 and 2, an introduction is made to the synchrotron Mössbauer spectroscopy with examples. Examples include the in situ Mössbauer spectroscopy with synchrotron radiation on thin films and the study of deep-earth minerals. Investigations of in-beam Mössbauer spectroscopy using a beam at the RIKEN RIBF is presented in Chapter 3. This chapter demonstrates innovative experimental setup for online Mössbauer spectroscopy using the thermal neutron capture reaction, (n, γ) . The Mössbauer spectroscopy of radionuclides is described in Chapters 4–7. Chapter 4 gives full description of the latest analysis results of lanthanides ( and ) Mössbauer structure and powder X-ray diffraction (XRD) lattice parameter (a0) data of defect fluorite (DF) oxides with the new defect crystal chemistry (DCC) a0 model. Chapter 5 reviews the Mössbauer and magnetic study of neptunyl(+1) complexes, while Chapter 6 describes the Mössbauer spectroscopy of organic complexes of europium and dysprosium. Mössbauer spectroscopy is presented in Chapter 7. There are three chapters on spin-state switching/spin-crossover phenomena (Chapter 8–10). Examples in these chapters are mainly on iron compounds, such as iron(III) porphyrins. The use of Mössbauer spectroscopy of physical properties of Sn(II) is discussed in Chapter 11.

Chapters 12–17 are devoted to applications of the Mössbauer spectroscopy to the biological chemistry. Chapter 12 details the recent progress on the application of NFS, SRPAC, and SRPAC to bioinorganic chemistry. The future prospect of these techniques is also given. The role of Mössbauer spectroscopy in biological and biomedical research is described in Chapters 13 and 17. These chapters demonstrate how Mössbauer spectroscopy can be applied to study microorganisms, plants, tissues, enzymes, hemoglobin, ferritin, and hemosiderin. Chapter 15 deals with the Mössbauer characterization of high-valent iron intermediates in the oxidation of L-tryptophan by heme-based enzymes. Chapter 16 is focused on the use of Mössbauer spectroscopy to study iron in neurodegenerative diseases.

Recent advances on studying iron and iron oxides using Mössbauer spectroscopy are described in Chapters 18–25. Chapter 18 discusses the nanocrystalline iron oxides, while Chapter 19 presents perovskite-related systems where emission Mössbauer spectroscopy contributes to exploring the structure and electronic or magnetic behavior of these materials. The use of Mössbauer spectrometry to study iron phases in rust layers is described in Chapter 20. The progress made on understanding bulk magnetic properties of nanosized powders of ferrites, mechanically alloyed/milled Fe–Cr–Al intermetallics, and a Fe–Al multilayer system is presented in Chapter 21. The application of surface Mössbauer spectroscopy to study very thin layers (a few atomic layers thick) of iron oxides is discussed in Chapter 22. Chapter 23 describes in detail the precipitation of iron oxides from aqueous iron salt solutions using Mössbauer spectroscopy. Chapter 24 is focused on the spectroscopic characterization of ferrates in high-valent oxidation states (+4, +5, and +6). Chapter 25 deals with dilute iron-doped yttrium aluminum garnets.

Mössbauer spectroscopy of materials of industrial interest is discussed in Chapters 26–30. Chapter 26 deals with Fe–As-based high-temperature superconductors. Mössbauer study of cathode active material for lithium-ion battery (LIB) and electrically conductive vanadate glass is presented in Chapter 27. More details on the applications of Mössbauer spectroscopy to LIB are given in Chapter 28. Chapter 29 is the example of applying Mössbauer spectroscopy to develop novel bimetal heterogeneous catalysts for preferential CO oxidation in H2. Chapter 30 shows the successful use of Mössbauer spectroscopy to identify and quantify the iron mineral phases of South African coal fractions. The last two chapters are mainly on the applications of Mössbauer spectroscopy to the environmental field, for example, describing the recycling process of iron-containing “waste ” of silicate glasses, which is related to purification of polluted water (Chapter 31). The variables control in the laterite mineral processing using Mössbauer spectroscopy is another example (Chapter 32).

Finally, the editors of the book would like to acknowledge contributions by late Professor Attila Vertez, Eötvös Loránd University. In addition to studying fundamentals of Mössbauer spectroscopy, Attila applied the Mössbauer effect to various fields. One of the coeditors, Virender K. Sharma, met Attila in fall 2002 when he was visiting Budapest under the sustainability grant, received by Florida Tech, from the U.S. Department of States. During the visit, Attila was very kind to accept him in his group. Since then Virender had several interactions in Budapest and on one occasion in Melbourne, Florida. Because of the admiration for Attila, the Mössbauer community organized a special symposium titled “Chemical Applications of Mössbauer Spectroscopy,” honoring him at the American Chemical Society Spring Meeting at San Francisco in March 2010. In the summer 2010, Virender traveled to Budapest to present the “Salute of Excellence” from the American Chemical Society. It was heartening to see that leading chemists from Hungary, including the president of the chemistry division of the Hungarian Academy of Science and president of Eötvös Loránd University, were present at that occasion. Attila will always be known as a great scientist with a gentleman touch and we will miss him dearly. This book is dedicated to late Professor Attila Vertez for his many accomplishments in Mössbauer spectroscopy.

Virender K. Sharma

Göstar Klingelhöfer

Tetsuaki Nishida

Contributors

Ricardo Alcántara, Laboratorio de Química Inorgánica, Universidad de Córdoba, Córdoba, Spain

Irina V. Alenkina, Faculty of Physical Techniques and Devices for Quality Control, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation

Ercan E. Alp, Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA

César A. Barrero, Grupo de Estado Sólido, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia, Medellín, Colombia

Erika R. Bauminger, Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem, Israel

Edward Brown, Chemistry Department, Nassau Community College, Garden City, NY

Stephen P. Cramer, Department of Applied Science, University of California-Davis, Davis, CA, USA

Juan de la Figuera, Instituto de Química Física “Rocasolano”, CSIC, Madrid, Spain

Georges Dénès, Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada

Eamonn Devlin, Institute of Materials Science, N.C.S.R. “Demokritos”, Attiki, Athens, Greece

Kednerlin Dornevil, Department of Chemistry, Georgia State University, Atlanta, GA, USA

Andrzej Friedman, Department of Neurology, Faculty of Health Science, Medical University of Warsaw, Warsaw, Poland

Jií Frydrych, Regional Center of Advanced Technologies and Materials, Olomouc, Czech Republic

Jolanta Gałzka-Friedman, Faculty of Physics, Warsaw University of Technology, Warsaw, Poland

José Ramón Gancedo, Instituto de Química Física “Rocasolano”, CSIC, Madrid, Spain

Karen E. García, Grupo de Estado Sólido, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia, Medellín, Colombia

Jean-Marc Greneche, LUNAM, Université du Maine, Institut des Molécules et Matériaux du Mans, Le Mans Cedex, France

Yisong Guo, Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, USA

Barbara R. Hillery, Chemistry Department, Nassau Community College, Garden City, NY

Yukio Hinatsu, Department of Chemistry, Hokkaido University, Sapporo, Hokkaido, Japan

Zoltán Homonnay, Faculty of Science, Eotvos Lorand University, Budapest, Hungary

Naoki Igawa, Quantum Bean Science Directorate, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki, Japan

Jie Jin, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China

Alexander A. Kamnev, Laboratory of Biochemistry, Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences, Saratov, Russian Federation

Airat Khasanov, Department of Chemistry, University of North Carolina at Asheville, Asheville, NC, USA

Yoshio Kobayashi, Department of Engineering Science, The University of Electro-Communications, Tokyo, Japan

Norimichi Kojima, Graduate School of Arts and Sciences, The University of Tokyo, Meguro-ku, Tokyo, Japan

Józef Korecki, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Alla A. Kornilova, Moscow State University, Moscow, Russia

Krisztina Kovács, Laboratory of Nuclear Chemistry, Institute of Chemistry, Eötvös Loránd University, Budapest, Hungary

Stjepko Krehula, Division of Materials Chemistry, Rudjer Boškovi Institute, Zagreb, Croatia

Shiro Kubuki, Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji, Japan

Pedro Lavela, Laboratorio de Química Inorgánica, Universidad de Córdoba, Córdoba, Spain

Jan łaewski, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Jung-Fu Lin, Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, USA

Aimin Liu, Department of Chemistry, Georgia State University, Atlanta, GA, USA

Kuo Liu, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China

Libor Machala, Regional Center of Advanced Technologies and Materials, Olomouc, Czech Republic

M. Cecilia Madamba, Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada

Zhu Mao, Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, USA

José F. Marco, Instituto de Química Física “Rocasolano”, CSIC, Madrid, Spain

Leopold May, Chemistry Department, Nassau Community College, Garden City, NY

Hocine Merazig, Laboratoire de Chimie Moléculaire, du Contrôle de l'Environnement et de Mesures Physico-Chimiques, Département de Chimie, Faculté des Sciences, Université Mentouri, Constantine, Algeria

Toshiyuki Misu, Department of Chemistry, Faculty of Science, Toho University, Funabashi, Chiba, Japan

Matteo Monti, Instituto de Química Física “Rocasolano”, CSIC, Madrid, Spain

Alvaro L. Morales, Grupo de Estado Sólido, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia, Medellín, Colombia

Abdualhafed Muntasar, Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada

Svetozar Musi, Division of Materials Chemistry, Rugjer Boškovi Institute, Zagreb, Croatia

Masami Nakada, Advanced Science Research Center, Japan Atomic Energy Agency, Ibaraki, Japan

Tadahiro Nakamoto, Department of Materials Characterization, Toray Research Center, Inc., Otsu, Shiga, Japan

Akio Nakamura, Advanced Science Research Center, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki, Japan

Mikio Nakamura, Department of Chemistry, Faculty of Science, Toho University, Funabashi, Chiba, Japan

Satoru Nakashima, Natural Science Center for Basic Research and Development, Hiroshima University, Higashi-Hiroshima, Japan

Lakshmi Nambakkat, Department of Physics, University College of Science, Mohanlal Sukhadia University, Udaipur, Rajasthan, India

Amar Nath, Department of Chemistry, University of North Carolina at Asheville, Asheville, NC, USA

Zoltán Németh, Faculty of Science, Eotvos Lorand University, Budapest, Hungary

Tetsuaki Nishida, Department of Biological and Environmental Chemistry, Faculty of Humanity-Oriented Science and Engineering, Kinki University, Iizuka, Japan

Kiyoshi Nomura, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan

Yoshihiro Okamoto, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki, Japan

Michael I. Oshtrakh, Faculty of Physical Techniques and Devices for Quality Control, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation

Krzysztof Parliski, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Jií Pechoušek, Regional Center of Advanced Technologies and Materials, Olomouc, Czech Republic

Carlos Pérez Vicente, Laboratorio de Química Inorgánica, Universidad de Córdoba, Córdoba, Spain

Yurii D. Perfiliev, Chemistry Department, Florida Institute of Technology, Melbourne, FL, USA

Duncan Quarless, Chemistry Department, Nassau Community College, Garden City, NY

Mira Risti, Division of Materials Chemistry, Rugjer Boškovi Institute, Zagreb, Croatia

Ralf Röhlsberger, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Michail Samouhos, School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, Greece

Bogdan Sepiol, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Virender K. Sharma, Chemistry Department, Florida Institute of Technology, Melbourne, Florida, USA

Marcel Sladecek, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Michał lzak, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Tomasz lzak, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Sabrina G. Sobel, Chemistry Department, Nassau Community College, Garden City, NY

Nika Spiridis, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Svetoslav Stankov, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Akira Sugahara, Graduate School of Arts and Sciences, The University of Tokyo, Meguro-ku, Tokyo, Japan

Masashi Takahashi, Department of Chemistry, Faculty of Science, Toho University, Funabashi, Chiba, Japan

Masuo Takeda, Department of Chemistry, Faculty of Science, Toho University, Funabashi, Chiba, Japan

José L. Tirado, Laboratorio de Química Inorgánica, Universidad de Córdoba, Córdoba, Spain

Satoshi Tsutsui, Research and Utilization Division, SPring-8/JASRI, Sayo-cho, Sayo-gun, Hyogo, Japan; Advanced Science Research Center, Japan Atomic Energy Agency, Ibaraki, Japan

Jií Tuek, Regional Center of Advanced Technologies and Materials, Olomouc, Czech Republic

Gero Vogl, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Vladimir I. Vysotskii, Mathematics and Theoretical Radiophysics Department, Kiev National Shevchenko University, Kiev, Ukraine

Frans B. Waanders, School of Chemical and Minerals Engineering, North West University, Potchefstroom, South Africa

Junhu Wang, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China

Clive I. Wynter, Chemistry Department, Nassau Community College, Garden City, NY

Yuming Xiao, HPCAT, Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA

Yoshitaka Yoda, Research and Utilization Division, SPring-8/JASRI, Kouto, Sayo, Hyogo, Japan

Marcin Zajc, Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

Radek Zboil, Regional Center of Advanced Technologies and Materials, Olomouc, Czech Republic; Chemistry Department, Florida Institute of Technology, Melbourne, FL, USA

Tao Zhang, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China

Wansheng Zhang, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China

Xiaowei Zhang, Photon Factory, KEK, 1-1 Oho, Tsukuba, Ibaraki, Japan

Charalabos Zografidis, School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, Greece

Part I

Instrumentation

Chapter 1

In Situ Mössbauer Spectroscopy with Synchrotron Radiation on Thin Films

Svetoslav Stankov, Tomasz lzak, Marcin Zajc, Michał lzak, Marcel Sladecek, Ralf Röhlsberger, Bogdan Sepiol, Gero Vogl, Nika Spiridis, Jan Łaewski, Krzysztof Parliski, and Józef Korecki

Institute for Synchrotron Radiation, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Karlsruhe, Germany

1.1 Introduction

Soon after the first observation [1–3] by Rudolf Mössbauer in 1958 of nuclear resonant recoilless absorption and emission of γ-rays from nuclei of , the Mössbauer effect became a well-established spectroscopic method for probing the electronic, magnetic, and dynamic properties of solids, liquids, and even gases [4]. The unprecedentedly high intrinsic energy resolving power on the order of 10−13 offered by the Mössbauer effect is determined by the natural linewidth of the nuclear resonant exited state. The relatively simple and easily accessible experimental setup, and the observation of the effect in isotopes of widely spread and technologically relevant elements such as iron and tin and their compounds stimulated the explosion of applications of the Mössbauer spectroscopy not only in solid state physics but also in fundamental physics [5], chemistry [6], geology [7], biology [8], industry [9], and many other fields.

If a photon with an energy equal to the resonant energy impinges on the Mössbauer nucleus in its ground state, the photon may, with a probability given by the Lamb–Mössbauer factor fLM, excite the nuclear resonant level without an energy loss due to recoil. After the mean lifetime of this state, the nucleus returns back into its ground state either by emitting a photon or by ejecting an electron with probabilities 1/(1 + α) and α /(1 + α), respectively, where α is the coefficient of total internal conversion. For most of the Mössbauer isotopes, α is significantly greater that 1; therefore, the dominant mechanism for the de-excitation is internal conversion. The limited mean-free path of ejected electrons defines an escape depth of only few nanometers. By detecting the conversion electrons (conversion electron Mössbauer spectroscopy, CEMS), information about the electronic and magnetic properties of the materials' surface can be derived. The high values of the cross section for nuclear resonant absorption and the small escape depths of the conversion electrons established CEMS as a standard technique for investigating surface layers of materials [10]. Moreover, by analyzing the energy of the ejected electrons depth-selective information can be retrieved [11,12]. This determined the vast range of applications of this technique to surface science and nanotechnology already soon after the first observation of the Mössbauer effect.

The feasibility for in situ experiments on ultrathin films consisting of only one atomic layer of iron by the CEMS technique has been successfully demonstrated [13] in the mid-1980s. However, the relatively long data acquisition times (∼15 h) needed for accumulating spectra with reasonable statistics by using a conventional radioactive source have limited further applications.

A new era in the Mössbauer spectroscopy emerged in the year 1985 from the first observation of coherent elastic nuclear resonant scattering (NRS) of synchrotron radiation by the group of Erich Gerdau in Hamburg [14]. The demonstration that nuclear resonant experiments are indeed feasible by using synchrotron radiation instead of radioactive source was a tremendous success. However, only the advent of the third-generation synchrotron radiation sources in the middle 1990s along with the rapid development of high-resolution X-ray optics [15–19] and fast avalanche photodiode detectors (APDs) [20] established Mössbauer spectroscopy with synchrotron radiation as a standard technique for probing electronic, magnetic, and dynamic properties of materials [21]. The enormous brilliance of the X-ray beams provided by insertion devices such as wigglers and undulators, which is by more than 10 orders of magnitude larger in comparison with that of the conventional radioactive sources, allowed for the investigation of samples containing very small quantities of the resonant isotope. This resulted in a significant expansion of applications to layered systems (thin- and ultrathin films, and multilayers), nanostructures (islands, clusters), and samples under extreme conditions, for example, very high pressures and temperatures [22].

The possibility to finely tune the energy of the photons using high-resolution monochromators (HRMs) has resulted in a new technique for direct determination of the phonon density of states of the resonant element—the nuclear inelastic scattering (NIS) [23–25]. Thus, in the same experimental setup, one is able to probe simultaneously hyperfine interactions and lattice dynamics of the sample.

Investigation of well-defined nanostructures often requires that the preparation, characterization, and maintenance of the samples during experiments are performed under controlled, in most cases ultrahigh vacuum (UHV), conditions. Corresponding instrumentation [26,27] has been constructed and permanently installed at the nuclear resonance beamline ID18 [28] of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. This opened up new perspectives for in situ investigations of electronic and magnetic properties, vibrational dynamics, and diffusion phenomena by several nuclear resonant scattering-based techniques such as coherent elastic nuclear resonant scattering, coherent quasielastic nuclear resonant scattering, and incoherent inelastic nuclear resonant scattering/absorption.

The aim of this chapter is to report on recent advances in the in situ Mössbauer spectroscopy with synchrotron radiation on thin films that became possible due to the instrumentation developments at the nuclear resonance beamline ID18 of the ESRF. After a detailed description of the beamline and of the UHV system for in situ experiments, a brief introduction into the basic NRS techniques is given. Finally, the application of these techniques to investigate magnetic, diffusion, and lattice dynamics phenomena in ultrathin epitaxial films deposited on a W(110) substrate is presented and discussed.

1.2 Instrumentation

The Classical Mössbauer spectroscopy with a standard radioactive source has been performed in the energy domain, whereas the nuclear resonant scattering using synchrotron radiation measures the time-domain spectra. This implies fundamental differences in the experimental approach and the associated instrumentation. The Synchrotron radiation at third-generation sources is produced by insertion devices (wigglers or undulators) installed in the straight sections of the storage ring, where relativistic electrons (positrons) circulate the ring [29]. One of the prerequisites for performing NRS experiments is the timing mode of the storage ring operation. For nuclear resonant scattering applications, the storage ring is filled with equidistant electron (positron) bunches that produce intensive X-ray pulses having a width of about 100 ps. Especially suitable for NRS applications at the ESRF is the 16-bunch mode providing a time spacing of 176 ns between the bunches.

The second condition that has to be fulfilled is the utilization of fast detectors and associated timing electronics. Avalanche photodiodes have been successfully introduced [20] for NRS applications due to their quick time response, high dynamic range, and relatively high quantum efficiency. The time resolution ranges from 0.1 to 1.0 ns and the efficiency from several percent to about 50% depending on the energy of the X-rays. The timing electronics is based on standard NIM modules, including constant fraction discriminators, gate generators, fast ADCs (analog digital converters), and MCAs (multichannel analyzers). A reference timing signal from the radio frequency system of the storage ring provides a synchronization of the electronics with the photon pulse arrival time.

To further improve the performance of the APD detectors for nuclear resonant scattering applications, the high-degree suppression of the nonresonant radiation is essential. This is achieved by using high-resolution monochromators based on asymmetrically cut Si single crystals with high-order reflections [19,30]. The role of the HRM in nuclear resonant scattering techniques is twofold: (1) it filters out a significant part of the nonresonant photons, thus preventing the detector in forward direction from overload during the intense X-ray pulses; and (2) the HRM provides the necessary instrumental energy resolution in the range of few millielectron volts to submillielectron volts for the purposes of the nuclear inelastic scattering experiments. A separate HRM has to be developed for each Mössbauer transition in order to provide the highest energy resolution, flux, and/or degree of polarization. Table 1.1 summarizes the isotopes that are currently accessible at ID18 of the ESRF for nuclear resonant scattering experiments with the natural lifetime and energy of the nuclear resonant level and the energy resolution of the corresponding high-resolution monochromator.

Table 1.1 Mössbauer Isotopes with the Natural Lifetime and Energy of the Nuclear Resonant Level, and Energy Resolution Provided by the Corresponding High-Resolution Monochromator at ID18 of the ESRF.

1.2.1 Nuclear Resonance Beamline ID18 at the ESRF

A layout of the beamline for nuclear resonant scattering experiments ID18 of the ESRF in Grenoble is schematically shown in Fig. 1.1. It consists of a front end, two optical and three experimental hutches with adjacent control cabins. The front end accommodates three revolver-type undulators that allow one to switch between magnetic structures with 20 or 27 mm period. While the former provides photons with energy 14.413 keV on its fundamental, the latter is optimized for Mössbauer isotopes with lower/higher energies (Table 1.1). The first optics hutch (OH1) accommodates the primary slit system that shapes the synchrotron beam and defines its size, the high heat load monochromator (HHLM), further collimating optics, and beam intensity monitors (not shown in the figure). The HHLM [31] is a fixed exit double-crystal Si(111) monochromator with a bandwidth of few electron volts. A cryogenic cooling allows for handling the heat load and ensures short- and long-term stability of the crystals positions. The second optics hutch (OH2) hosts various exchangeable high-resolution monochromators. For the resonant energy transition of 14.413 keV in , several possibilities exist offering various energy resolution and beam flux. The most suitable one has to be selected according to the needs of the particular experiment. A bending focusing monochromator (FM) for reducing the horizontal beam size to ∼100 μm is also available in OH2.

Figure 1.1 A layout of the nuclear resonance beamline ID18 of the European Synchrotron Radiation Facility in Grenoble, France. u27 and u20 stand for the revolver-type undulators with 27 mm period for one structure and 20 mm period for the other. OH1 and OH2 are the first and second optics hutches devoted to the accommodation of HHLM, slit systems (S1, S2), CRL, HRMs, and FM. EH1, EH2, and EH3 stand for the experimental hutches, while CC1–CC3 denote the control cabins. DIFF is the six-circle diffractometer, UHV: the ultrahigh-vacuum system for in situ experiments, and CRYO: the cryomagnet system. X-ray beam monitors and attenuators are not shown.

A standard six-circle diffractometer for diffraction experiments in horizontal and vertical scattering geometries at ambient conditions is operational in the first experimental hutch (EH1). In addition, it can accommodate a furnace (300–1200 K) and continuous flow cryostat (10–300 K) allowing for NRS experiments in a large temperature range.

The second experimental hutch (EH2) is devoted to experiments on samples at extreme conditions. It accommodates the UHV system [26] devoted to in situ experiments on thin films and nanostructures that is described in detail in the next section. A cryomagnet system offers external magnetic fields up to 8 T in horizontal direction, either perpendicular or parallel to the X-ray beam and a temperature range between 1.5 and 297 K. It is mounted on a two-circle heavy-duty goniometer used for sample tilting to an angular range of ±5° both parallel and perpendicular to the direction of propagation of the X-ray beam. The setup is particularly suitable for experiments on surfaces, thin films, and multilayers. The sample holder is capable of carrying up to six samples.

The third experimental hutch (EH3) offers enough space for user equipment, for example, portable ultrahigh-vacuum chambers. It is also used for setting up a high-resolution backscattering monochromator [32]. This type of HRM is used for Mössbauer isotopes with resonant energies above ca. 30 keV, that is, (35.493 keV) and (37.1298 keV) [33,34].

An interlock system allows for carrying out an experiment in any of the experimental hutches while enabling free access to the others. The beam inside these hutches is either transported in shielded vacuum tubes or blocked by the upstream beam shutter. By this means, the experiment in one hutch can be performed in parallel with the preparation work in others. Computers and electronics to run the experiment are located in three separated control cabins (CC1–CC3) adjacent to the corresponding experimental hutches.

Depending on the X-ray energy used in the experiments, compound refractive lenses (CRL), made of either Be, plastic, or Al [35], are employed for collimating the beam in order to match the beam divergence to the angular acceptance of the monochromators. In addition, CRLs serve to focus the beam to approximately 15 × 250 μm2 for the needs of particular experiments. These comprise, for example, high-pressure applications by using diamond anvil cells, or investigations of nanostructured samples deposited on a substrates where grazing incidence geometry has to be utilized. Alternatively, focusing of the X-ray beam down to about 5 × 10 μm2 is achieved by bending multilayer mirrors arranged in Kirkpatrick–Baez geometry.

1.2.2 The UHV System for In Situ Nuclear Resonant Scattering Experiments at ID18 of the ESRF

The UHV instrument is permanently installed in the second experimental hutch of ID18 of the ESRF, which requires remote control of the entire system. Figure 1.2 presents schematically the instrument, while Fig. 1.3 displays a top-view photograph. The UHV setup with a base pressure of 1 × 10−10 mbar consists of a central distribution chamber equipped with a sample transfer mechanism and peripherally attached chambers as described in detail below.

Figure 1.2 A schematic view of the UHV system with the preparation 1, NRS 2, distribution 3, storage 4, and load-lock 5 chambers (for simplicity all bypasses and evaporation sources are omitted). Number 6 shows the CF63 port where the portable chambers can be connected to the system. (Reproduced from Ref. 26 with permission of the American Institute of Physics.)

Figure 1.3 A top-side photograph of the UHV system with the preparation 1, NRS 2, distribution 3, storage 4, and load-lock 5 chambers. Chamber 6 shows the portable chamber for XRD, GISAXS, and XPCS experiments connected to the system. (Reproduced from Ref. 26 with permission of the American Institute of Physics.)

The preparation chamber, number 1 in Figs. 1.2 and 1.3, is equipped with two electron beam evaporators and an effusion cell. A four-pocket mini electron beam evaporator serves for deposition of metals from rods and crucibles from each pocket separately, as well as for codeposition of different combinations of the evaporants. A single-pocket e-beam source is used for deposition of the Mössbauer isotope . An effusion cell is available for evaporation of rare-earth metals. A precise calibration of the deposition rate with a thickness reproducibility of 1 Å is done by a quartz-balance monitor. The deposited structures can be characterized by low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). In this chamber, the samples can be cooled down to about 90 K and heated up to 2300 K by a multifunctional manipulator.

The chamber for NRS experiments, number 2 in Figs. 1.2 and 1.3, is mounted on a two-circle goniometer that serves to align the sample and perform experiments with the focused synchrotron beam in grazing incidence scattering geometry. The manipulator provides contacts for temperature measurement, resistive and electron-bombardment heating, and feedthrough for cooling the sample down to 90 K by flow of liquid nitrogen. In addition, the sample holder can be rotated in the range of ±180 degrees about an axis perpendicular to the sample surface, allowing for angular resolved studies. For the purpose of nuclear inelastic scattering experiments, an avalanche photodiode detector is brought close to the sample via a tube reaching into the chamber with a Be window at its end, as shown on the photograph in Fig. 1.4. The figure also shows the entrance and exit Be windows for the focused synchrotron radiation beam that impinges on the sample under grazing angles of few milliradians. It further shows the sample mounted on the sample station, and the Z-stage for the APD detector used for nuclear inelastic scattering experiments as well as the APDs for detecting the nuclear forward scattered radiation.

Figure 1.4 A site photograph of the sample station in the NRS chamber 2. Shown are the detectors (APD) for the nuclear forward scattering and the nuclear inelastic scattering experiments, sample, entrance and exit Be windows for the grazing incidence scattering geometry with the focused X-ray beam. During the nuclear inelastic scattering experiment, the distance between the APD (above the sample) and the sample is reduced to about 2 mm.

The distribution chamber, number 3 in Figs. 1.2 and 1.3, connects the above-described chambers and serves for transferring the sample holders between them. In addition, a sample storage chamber, number 4 in Figs. 1.2 and 1.3, with the capacity to store up to six sample holders, is an integrated part of the distribution chamber. The lowest position provides electrical contacts for resistive heating and temperature control allowing for annealing of the sample holders. The load-lock chamber, number 5 in Figs. 1.2 and 1.3, serves for introducing the sample holder into the UHV system.

Two additional portable chambers are available for transferring samples to other beamlines of the ESRF. The portable chamber for NRS experiments (Fig. 1.5) was constructed in order to extend the in situ NRS experiments to thin films and nanostructures of noniron isotopes. (Formerly the end-station ID22N of the ESRF was optimized for the nuclear resonances of , , and ). This chamber is based on two crossed CF100 tubes with a sample station. The station provides electrical contacts to the sample holder for temperature control (K- or C-type thermocouples), resistive or electron-bombardment heating, and feedthroughs for sample cooling down to 90 K by flow of liquid nitrogen. The sample holder can be rotated in the range of ±180 degrees around an axis perpendicular to the surface normal. This chamber is pumped by a double-flanged 100 l s−1 ion getter pump ending with a viewport. Entrance and exit windows for the X-ray beam are made out of a 100 μm thick Be foil diffusion bonded to CF63 flanges. Additional CF40 flanges are used for a viewport and a vacuum gauge. Similarly to the main NRS chamber, a CF63 tube with welded Be window on the bottom is mounted above the sample station on a stage with a linear transfer in order to reduce the distance between the APD detector and the sample. This chamber was employed to study magnetic properties and lattice dynamics of the extremely reactive Sm and Eu metallic films at the end-station ID22N.

Figure 1.5 A schematic view of the portable UHV chamber for NRS experiments. (Reproduced from Ref. 26 with permission of the American Institute of Physics.)

A portable chamber for wide-angle XRD, GISAXS, and XPCS experiments, shown in Fig. 1.6, is constructed to transfer the already prepared and characterized samples to other beamlines at the ESRF in order to apply these techniques in situ. The chamber is based on CF100 tubes including three CF40 flanges for a vacuum gauge, a viewport, and a simple evaporation source, allowing one to perform in situ deposition. Two diametrically mounted entrance and exit X-ray Be windows with thickness of 200 μm are specially polished in order to minimize the small-angle X-ray scattering from the windows, which is an important issue for the XPCS spectroscopy. A Be dome for wide-angle X-ray diffraction (XRD) can be mounted on the top CF100 flange. By a linear manipulator, the sample holder is vertically transferred between the positions for small- and wide-angle X-ray scattering. Resistive heating and temperature control of the sample are provided via electrical feedthroughs on the manipulator. The chamber is pumped by a 75 l s−1 ion getter pump. By using this chamber, the morphology of ultrathin Fe films on MgO (001) [36,37] was systematically investigated employing GISAXS at beamline ID10A of the ESRF.

Figure 1.6 A schematic view of the portable UHV chamber for wide-angle XRD, GISAXS, and XPCS experiments. (Reproduced from Ref. 26 with permission of the American Institute of Physics.)

The entire UHV setup is mounted on a support table with horizontal (2 × 102 steps mm−1) and vertical (2 × 105 steps mm−1) motorized movements to allow for precise adjustment of the sample to the synchrotron beam. The chamber for in-situ NRS experiments at grazing incidence geometry and for X-ray reflectivity measurements is mounted on a two-circle goniometer (1 × 105 steps deg−1 for an angular range of ±5°). The synchrotron beam can be conditioned to a sample spot size as small as 15 × 250 μm2 by compound refractive lenses or by 5 × 10 μm2 by Kirkpatrick–Baez focusing mirrors.

1.3 Synchrotron Radiation-Based Mössbauer techniques

In this section, an introduction into the most common synchrotron radiation Mössbauer techniques is given emphasizing on the applications to thin films. A detailed elaboration of the methods can be found elsewhere [21,22,38].

In the following, atoms of the Mössbauer isotopes bound in a crystal lattice with single-line resonances (vanishing hyperfine interactions) are considered. If a photon with an energy matching that of the nuclear resonant transition impinges on a nucleus, the following absorption processes could take place: (i) the photon is resonantly absorbed by the nucleus without energy and momentum exchange with the crystal lattice, that is, elastic absorption. The probability for an elastic absorption is given by the Lamb–Mössbauer factor fLM. (ii) The photon is resonantly absorbed by the nucleus involving energy and momentum transfers with the crystal lattice, that is, inelastic absorption. The probability for this process is defined as 1 − fLM. After the mean lifetime of the excited state the nucleus returns into the ground state. When a resonant photon is emitted (without energy and momentum exchange with the crystal lattice) and the system returns into a state that is indistinguishable from the state before the resonant absorption, this process is coherent scattering. The emission of conversion electrons or the fluorescent radiation leads to incoherent scattering since the system is moved back into a state that differs from the initial state.

Each of these processes is considered separately below. Selected examples of relevant in situ experiments on thin films illustrating the capabilities of the techniques are presented and discussed.

1.3.1 Coherent Elastic Nuclear Resonant Scattering

1.3.1.1 Brief Theoretical Background

In the case of coherent elastic scattering, a macroscopic ensemble of scattering atoms can be replaced by a continuous medium characterized by an index of refraction n [39]:

(1.1)

where Mi is the coherent forward scattering length of the i th atom and ρi is the number density of atoms in the material. The sum runs over all atoms within the scattering volume. k0 is the wave number of the radiation. The wave amplitude in depth z of a slab of material is given by

(1.2)

For anisotropic media, the index of refraction depends on the polarization state of light and is represented by a 2 × 2 matrix [40]. In that case, the propagation of light in forward direction is described by the propagation matrix: , with being the forward scattering matrix. Then (1.2) can be written in more general form:

(1.3)

From (1.2) and (1.3) directly follows the relation between the index of refraction n and the forward scattering matrix f: .

The propagation matrix F describes the modification of the wave field A upon propagation from coordinate z to coordinate z + dz. It is a multidimensional matrix with dimension given by the number of the open scattering channels. This formalism is successfully applied not only to describe the propagation of light in forward direction but also in case of X-ray diffraction from single crystals, and reflection from surfaces, thin films, and multilayers.

While the structural arrangement of the scattering centers determines the dimension and the symmetries of F that are of importance for calculating the matrix exponential in (1.3), the interaction of the photons with the atoms is given by the atomic scattering length M. In order to account for its energy dependence and the polarization mixing M (ω) is described by 2 × 2 matrix: . E (ω) represents the nonresonant contribution of the electronic charge scattering, and N (ω) contains the contributions from the resonant nuclear scattering processes. The electronic scattering length is then given by

(1.4)

where ν and μ are the polarization vectors, Z is the atomic number, r0 is the classical electron radius, and σt is the total absorption cross section.

For the case of 2L -pole resonance, the resonant scattering length is given by [41]

(1.5)

fR< 1 describes the degree of elasticity of the scattering process, expressed by the Debye–Waller factor in the fast-relaxation limit and by the Lamb–Mössbauer factor in the slow-relaxation limit. The two dot products between the polarization basis vectors (ν, μ) and the vector spherical harmonics YLM(k0) describe the anisotropy of photon absorption and reemission, respectively. The energy dependence of the scattering process is contained in the functions FLM(ω). These functions are the energy-dependent resonant strengths for transitions with a change of M in the magnetic quantum number. In the general case they are given by [41]

(1.6)

where the sum runs over all initial (ground) states labeled by α and the intermediate excited states labeled by η. pα is the probability that the initial state α is occupied and pα(η) is the probability that the state η is initially unoccupied. E (α) and E (η) are the energies of the ground-state and excited-state levels, respectively. Γx(αMη; L) is the partial resonance width of the transition between α and η with a change of M in the magnetic quantum number, Γ (η) denotes the full resonance width. Since Γ (η) ≈ 1–10 eV for electronic resonances, the scattering takes place on a timescale of ≈ 10− 16 s that is essentially prompt. In contrast, the width of nuclear resonances is in the range of 10− 6–10− 12 eV; therefore, the scattering proceeds on comparatively long timescales. This is essential for separating both contributions one from another and for establishing the nuclear resonant scattering of synchrotron radiation as a time-domain spectroscopy.

The expression (1.5) for the resonant scattering length can be expanded in powers of the unit vector m that defines the magnetic quantization axis of the atom in the sample. The resonant scattering length for an electric dipole transition (L = 1) gets the form [42]

(1.7)

For convenience, the subscript L is omitted.

For the case of a magnetic dipole transition the role of the electric and magnetic fields of the radiation are interchanged and polarization vectors in Eq. (1.7) have to be transformed according to the rule , where k0 is a unit vector of the photon wave vector. The three terms in Eq. (1.7) represent different polarization dependences. The first term is not sensitive to the sample magnetization. Its polarization dependence given by is that of nonresonant charge scattering. The second term describes circular dichroism because it depends on the difference between the resonant scattering amplitudes F+1 and F− 1. Since its polarization dependence is , it describes orthogonal scattering, for example, and . The third term is proportional to and describes linear magnetic dichroism. Its polarization dependence allows for all scattering processes within the given polarization basis.

For a linear polarization basis, as it is frequently used in case of scattering experiments with synchrotron radiation, the matrix elements can be explicitly written as

(1.8)

These matrix elements express the strong polarization-mixing effects that are observed in resonant scattering from magnetized samples. The occurrence of optical activity crucially depends on the orientation of m relative to the incident wave vector and its polarization state. The off-diagonal elements describe the orthogonal scattering that turns incident σ -polarization into π - polarization and vice versa. Equation (1.8) is often used to describe the polarization effects in nuclear resonant scattering experiments with synchrotron radiation.

Figure 1.7 sketches the grazing incidence scattering geometry used for studies of thin films and surfaces. The set of polarization vectors (σ, π), the polar and azimuthal angles (Θ, ϕ) describing the relative orientation of the wave vector k0 of the incident photons to the direction of the magnetization vector m of the sample are indicated.

Figure 1.7 Experimental geometry used in nuclear resonant scattering of synchrotron radiation from thin films and surfaces. Θ and ϕ define the relative orientation of the incident wave vector k0 to the direction of a unidirectional magnetization m of the sample. σ and π are the linear polarization basis vectors, and φ is the incidence angle. (Reproduced from Ref. 22 with permission of Springer.)

1.3.1.2 Time Spectra of the Nuclear Resonant Scattering

In the following discussion, the case of the nuclear resonant scattering from the 14.413 keV resonance of is considered. Due to its large absorption cross section, large Lamb–Mössbauer factor, and its relevance in many fields of natural sciences, this resonance is one of the most widely applied Mössbauer transitions. It is a magnetic dipole transition with spins , , magnetic moments , of the ground and excited states, respectively, and a natural lifetime . In magnetic materials the spin-polarized 3d electrons create a spin polarization of the s-electrons via the exchange interaction that leads to a strong magnetic field at the nucleus with a magnitude of 33.3 T in the case of ferromagnetic α-Fe. This magnetic field lifts the degeneracy of ground and excited states, resulting in a Zeeman splitting of the nuclear energy levels. According to the dipole selection rule , six allowed energy transitions, corresponding to six separated resonances, are observed, as depicted in Fig. 1.8a. In the case of a pure magnetic hyperfine interaction, the energetic positions of the resonances are given by

(1.9)

with and being the magnetic quantum numbers and and the g -factors of the ground and excited states, respectively.

Figure 1.8 Energy dependence of the functions FM in the case of nuclear resonant scattering from a magnetic dipole resonance between nuclear spins Ig = 1/2 and Ie = 3/2. (a) Pure magnetic hyperfine interaction. The energetic positions apply to the case of α- with a magnetic hyperfine field of 33.3 T. The six dipole-allowed transitions decompose into three different polarization dependencies: the functions F−1, F0, and F+1 describe the scattering of right-circular, linear, and left-circular polarization, respectively. (b) Pure electric hyperfine interaction. (Reproduced from Ref. 22 with permission of Springer.)

In nonmagnetic materials the degeneracy of the ground and excited states could, in general, be partly lifted as a result of an electric field gradient (EFG) acting on the nucleus. The sources of the EFG are the distributed electric charges around the Mössbauer nuclei. These could be either charges of the neighboring ions or ligands surrounding the resonant atom (lattice/ligand contribution), or charges in partially filled valence orbitals of the Mössbauer atom (valence electron contribution). The EFG is a second-rank symmetrical tensor and in a coordinate system related to its principal axes , , and , selected so that . It is fully determined by the z -component and by the asymmetry parameter . From the definition of the asymmetry parameter, and the fact that the Laplace equation holds, that is, since the sources of the EFG are fully external for the nucleus, for η applies: . Assuming a purely electric quadrupole interaction the energy levels of the excited state splits to two levels, resulting in two resonances (Fig. 1.8b) with energy positions given by

(1.10)

with Q being the quadrupole moment of the nucleus.

For the particular case of nuclear resonant scattering, the functions FM defined by Eq. (1.6) with L = 1 are given by the following expression [22,43]:

(1.11)

where K is defined as

(1.12)

with Γ0 being the natural linewidth of the transition. The sum runs over all ground-state levels with magnetic quantum numbers mi. is the resonant energy of the transition with the quantum numbers mi and M. The Clebsch–Gordan coefficients describe the relative strength of the transitions.

Since the nuclear resonant scattering is a coherent elastic process it is impossible to identify the scattering atom in the sample. Instead, for each individual resonant nucleus there is a small probability that this nucleus is excited. The summation of all these small amplitudes gives the total probability amplitude for a photon to interact resonantly with the nuclei. If the incident radiation pulse is short compared to the nuclear lifetime τ0, these probability amplitudes exhibit the same temporal phase. As a result, a collectively excited state is created, where a single excitation is coherently distributed over the resonant atoms of the sample [44]. The wave function of this collectively excited state is given by a coherent superposition of states:

(1.13)

where denotes the state in which the i th resonant atom at the position ri is in its excited state . This collectively excited state is named nuclear exciton and exhibits remarkable optical properties resulting from the coherent superposition of states. Below some important implications of the nuclear exciton concept on the time spectrum of nuclear resonant scattering is given. A detailed elaboration of the formalism can be found elsewhere [42,45].

In a nuclear resonant scattering experiment all resonant levels of the Mössbauer nuclei in the sample are simultaneously excited by a short pulse of synchrotron radiation, creating the nuclear exciton. The time dependence of the delayed intensity emitted upon de-excitation of the nuclear exciton in forward direction is the time spectrum of nuclear forward scattering (NFS).

In the absence of magnetic and electric fields in the sample, the Mössbauer spectrum consists of a single resonant line. The NFS time spectrum in this case is determined by an exponential decay of the nuclear exciton consisting of only one resonant frequency. In a semilogarithmic scale, the decay is a straight line with a slope defined by the lifetime of the excited state. Figure 1.9 illustrates a comparison between the Mössbauer transmission spectrum (a), NFS spectra in energy (b) and in time (c) domain, calculated for 0.2 μm thick stainless steel absorber (thin approximation holds, that is, self-absorption and multiple scattering effects are neglected) [46].

Figure 1.9 Calculated Mössbauer transmission spectra (a), nuclear forward scattering spectra in energy (b) and in time (c) domain for the case of single resonance in a 0.2 μm thick stainless steel foil 100% enriched in . (d), (e), and (f) are the corresponding spectra for a 3.0 μm thick stainless steel foil 100% enriched in . (Reproduced from Ref. 46 with permission of Kluwer Academic Publishers.)

If hyperfine fields are acting on the nucleus, the degeneracy of the nuclear levels is lifted, leading to a splitting of the nuclear transition into six (magnetic hyperfine interaction, Fig. 1.8a) or two (electric hyperfine interaction, Fig. 1.8b) resonances. The superposition of wave's amplitudes with frequency differences corresponding to the various resonant transitions leads to oscillations of the intensity in the temporal evolution of the exciton decay. These oscillations are referred to as quantum beats that contain information about the magnitude and orientation of the hyperfine fields. Figure 1.10 illustrates a comparison between the Mössbauer transmission spectrum (a), NFS spectra in energy (b) and in time (c) domain, calculated for the case of electric quadrupole interaction in 0.2 μm thick stainless steel absorber [46]. The time spectrum of NFS consists of quantum beats that result from coherent superposition of waves corresponding to the two possible resonant transitions. The quantum beat period is inversely proportional to the energy splitting of the resonant level, implying that small energy differences result in large quantum beat periods.

Figure 1.10 Calculated Mössbauer transmission spectra (a), nuclear forward scattering spectra in energy (b) and in time (c) domain for the case of a quadrupole doublet in a 0.2 μm thick stainless steel foil 100% enriched in . (d), (e), and (f) are the corresponding spectra for a 3.0 μm thick stainless steel foil 100% enriched in . (Reproduced from Ref. 46 with permission of Kluwer Academic Publishers.)