© Copyright 2016 Devon R. Mortensen Understanding near Fermi-level electronic structure through x-ray emission spectroscopy Devon R. Mortensen A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2016 Reading Committee: Gerald T. Seidler, Chair Marjorie Olmstead Xiaodong Xu Program Authorized to Offer Degree: Physics University of Washington Abstract Understanding near Fermi-level electronic structure through x-ray emission spectroscopy Devon R. Mortensen Chair of the Supervisory Committee: Professor Gerald T. Seidler Physics Atomic and molecular chemical properties are largely determined by the electronic structure of near Fermi-level states. Determining this structure is therefore one of the central tasks in materials characterization and development. In the work of this dissertation I explore the capabilities and limitations of non-resonant x-ray emission spectroscopy (NXES) as an analytical technique aimed at addressing these issues. To this end, I report the development of novel laboratory- and synchrotron-based instrumentation for the study of transition metal and lanthanide compounds. One of the primary results of this research thrust is increased accessibility and throughput, making NXES measurements a more viable option in routine and research-grade materials study. Using experimental data obtained from these spectrometers, I evaluate current state-of-the-art theory in terms of modeling valence structure in ambient transition-metal complexes. Additionally, I use NXES to elucidate the evolving 4f-electronic structure in the early light lanthanides under pressure. In particular these results show a persistent 4f-moment across certain volume collapse transitions in Cerium and Praseodymium, thus helping settle a long-standing debate about the nature of volume collapse. TABLE OF CONTENTS List of Figures ................................................................................................................................ xi List of Tables ............................................................................................................................... xxi Chapter 1. Introduction ................................................................................................................... 1 1.1 Outline of dissertation ..................................................................................................... 1 1.2 Overview of x-ray spectroscopy ..................................................................................... 2 1.3 X-ray Absorption Fine Structure .................................................................................... 3 1.3.1 X-ray Absorption Near Edge Structure....................................................................... 5 1.3.2 Extended X-ray Absorption Fine Structure ................................................................ 6 1.4 Non-resonant X-ray Emission Spectroscopy .................................................................. 6 1.4.1 Kα emission ................................................................................................................ 8 1.4.2 Kβ emission ................................................................................................................ 8 1.4.3 Valence-to-core emission............................................................................................ 9 Chapter 2. Survey of instrumentation ........................................................................................... 11 2.1 Background ................................................................................................................... 11 2.1.1 Bragg diffraction ....................................................................................................... 12 2.1.2 Curved crystals.......................................................................................................... 13 2.2 Focusing crystal spectrometers ..................................................................................... 14 2.2.1 The Rowland circle ................................................................................................... 14 2.2.2 Bragg geometries ...................................................................................................... 15 2.2.3 Laue geometries ........................................................................................................ 17 vi 2.3 Dispersive crystal spectrometers................................................................................... 19 2.3.1 von Hamos geometry ................................................................................................ 19 2.3.2 Off-circle Bragg geometry ........................................................................................ 20 2.3.3 Dispersive Laue geometry ........................................................................................ 21 2.4 Synchrotron implementations ....................................................................................... 23 2.4.1 Multi-analyzer Rowland spectrometers .................................................................... 23 2.4.2 A miniature von Hamos spectrometer ...................................................................... 25 2.5 Laboratory implementations ......................................................................................... 26 2.5.1 A conventional von Hamos spectrometer ................................................................. 27 2.5.2 A novel von Hamos spectrometer ............................................................................. 28 2.5.3 A DuMond-type Laue spectrometer ........................................................................ 30 2.5.4 A dispersive Laue EXAFS spectrometer .................................................................. 32 Chapter 3. Valence-to-core x-ray emission spectroscopy ............................................................. 34 3.1 Background ................................................................................................................... 34 3.2 Recent applications ....................................................................................................... 36 3.2.1 Catalysis .................................................................................................................... 36 3.2.2 Environmental science .............................................................................................. 40 3.3 Theory ........................................................................................................................... 42 Chapter 4. A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure ................................................................ 46 4.1 Introduction ................................................................................................................... 47 4.2 Prior work in laboratory-based x-ray spectroscopy ...................................................... 50 vii 4.2.1 X-ray Absorption Fine Structure .............................................................................. 50 4.2.2 X-ray Emission Spectroscopy ................................................................................... 53 4.3 Monochromator Design ................................................................................................ 54 4.4 Results and Discussion ................................................................................................. 65 4.4.1 Laboratory XANES .................................................................................................. 65 4.4.2 Laboratory Nonresonant XES ................................................................................... 70 4.5 Conclusions ................................................................................................................... 75 Chapter 5. Benchtop nonresonant x-ray emission spectroscopy .................................................. 77 5.1 Introduction ................................................................................................................... 77 5.2 Experimental Details ..................................................................................................... 78 5.3 Results and Discussion ................................................................................................. 81 5.4 Conclusion .................................................................................................................... 83 Chapter 6. Robust optic alignment in a tilt-free implementation of the Rowland circle spectrometer .................................................................................................................................. 85 6.1 Introduction ................................................................................................................... 86 6.2 Compensating for wafer miscut in SBCA alignment ................................................... 87 6.3 Symmetric Rowland configuration ............................................................................... 90 6.4 Asymmetric Rowland configuration ............................................................................. 94 6.5 The effect of wafer miscut on SBCA performance .................................................... 100 6.6 Conclusion .................................................................................................................