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Abstract Experimental synchrotron radiation induced electron- and ion spectroscopies together with electron-ion and ion-ion coincidence techniques as well as electron energy loss spectroscopy have been used to study the electronic properties of several vapor phase samples. In this thesis studies of the electronic structure and fragmentation of Sb4 clusters, photo- and Auger electron spectroscopy of atomic Si and Pb as well as ultra high resolution VUV absorption of vapor phase KF molecules have been performed. The instrumentation and techniques used in the studies, especially the electron energy loss apparatus and the newly built ultra high resolution FINEST beamline branch, are presented.

Abstract In this thesis, different spectroscopic methods are used for studying metals. Electron spectroscopy is applied for the study of binding energy shifts between atomic vapor and solid metals. Photoionization and Auger decay of high temperature aluminum vapors are investigated. Ionization of atomic chromium metal vapor by light absorption is studied with synchrotron radiation and time-of-flight ion mass spectroscopy. Optical spectroscopy is used for studying light emission from electric arc furnace plasma in experimental apparatuses developed during this work. Experimental techniques and sample preparation methods are presented.

Abstract The present thesis investigates the electronic structure of selected atoms and molecules in vapor phase. Electron spectroscopy is applied for studying the electronic transitions following excitation and ionization with electron and photon bombardment. The work focuses on the photoionization and Auger decay of selected noble gasses, and on the photoionization and Auger decay of core ionized or resonant excited alkali halide molecules. The experimental results are compared with theoretical predictions.

We study multi-photon ionization of rare gas atoms and small molecules by infrared femtosecond laser pulses. We demonstrate that ionization is accurately described by a tunnelling model when many infrared photons are absorbed. By measuring photo-electron and photo-ion spectra, we show how the sub-Ångstrom spatial resolution of tunnelling gives information about electron densities in the valence shell of atoms and molecules. The photo-electron and photo-ion momentum distributions are recorded with a velocity map imaging (VMI) spectrometer. We describe a tomographic method for imaging a 3-D momentum distribution of arbitrary symmetry using a 2-D VMI detector. We apply the method to measure the 3-D photo-electron distribution in elliptically polarized light. Using circularly polarized light, we show how the photo-electron momentum distribution can be used to measure the focused laser intensity with high precision. We demonstrate that the gradient of intensities present in a focused femtosecond pulse can be replaced by a single average intensity for a highly nonlinear process like multi-photon ionization. By studying photo-electron angular distributions over a range of laser parameters, we determine experimentally how the photon linear momentum is shared between the photo-electron, photo-ion and light field. We find the photo-electron carries only a portion of the total linear momentum absorbed. In addition we consider how angular momentum is shared in multi-photon ionization, and find the photo-electron receives all of the angular momentum absorbed. Our results demonstrate how optical and material properties influence the photo-electron spectrum in multi-photon ionization. These will have implications for molecular imaging using femtosecond laser pulses, and controlling the initial conditions of laser generated plasmas.

Abstract In this thesis, different spectroscopic methods are used for studying metals. Electron spectroscopy is applied for the study of binding energy shifts between atomic vapor and solid metals. Photoionization and Auger decay of high temperature aluminum vapors are investigated. Ionization of atomic chromium metal vapor by light absorption is studied with synchrotron radiation and time-of-flight ion mass spectroscopy. Optical spectroscopy is used for studying light emission from electric arc furnace plasma in experimental apparatuses developed during this work. Experimental techniques and sample preparation methods are presented. / Original papers The original publications are not included in the electronic version of the dissertation. Huttula, M., Jänkälä, K., Mäkinen, A., Aksela, H., & Aksela, S. (2008). Core shell electron spectroscopy on high temperature vapors: 2s photoionization and Auger decay of atomic aluminium. New Journal of Physics, 10(1), 13009. https://doi.org/10.1088/1367-2630/10/1/013009 Huttula, M., Partanen, L., Mäkinen, A., Kantia, T., Aksela, H., & Aksela, S. (2009). KLL Auger decay in free aluminum atoms. Physical Review A, 79(2). https://doi.org/10.1103/physreva.79.023412 Aksela, S., Kantia, T., Patanen, M., Mäkinen, A., Urpelainen, S., & Aksela, H. (2012). Accurate free atom–solid binding energy shifts for Au and Ag. Journal of Electron Spectroscopy and Related Phenomena, 185(8–9), 273–277. https://doi.org/10.1016/j.elspec.2012.05.007 Mäkinen, A., Patanen, M., Aksela, S., & Aksela, H. (2012). Atom-solid 3p level binding energy shift of transition metals Cr, Mn, Fe, Co, and Ni. Journal of Electron Spectroscopy and Related Phenomena, 185(12), 573–577. https://doi.org/10.1016/j.elspec.2012.12.006 Mäkinen, A., Niskanen, J., & Aksela, H. (2012). Relative photoionization cross section of Cr atoms in the valence region. Physical Review A, 85(5). https://doi.org/10.1103/physreva.85.053411 Mäkinen, A., Niskanen, J., Tikkala, H., & Aksela, H. (2013). Optical emission from a small scale model electric arc furnace in 250–600 nm region. Review of Scientific Instruments, 84(4), 43111. https://doi.org/10.1063/1.4802833

Malgré les rapides progrès technologiques dans les nitrures, les propriétés intrinsèques des alliages de nitrures et les processus physiques qui gouvernent la physique de ces dispositifs sont encore mal connus. Au cours de mon travail de thèse, de nouvelles approches expérimentales et théoriques ont été développées pour aborder l’étude des mécanismes microscopiques qui gouvernent les propriétés électroniques des dispositifs à base de nitrures semi-conducteurs. Une nouvelle technique expérimentale permettant de mesurer directement la distribution en énergie des électrons de conduction d’une LED en fonctionnement est explorée. Cette approche permet l’observation directe de populations d’électrons chauds excités dans le dispositif optoélectronique sous injection électrique et émis dans l’ultravide. Une théorie récente de la localisation dans les systèmes désordonnés est appliquée aux matériaux et dispositifs optoélectroniques à base de nitrures. Cette méthode permet pour la première fois la détermination du paysage de localisation induit par le désordre d’alliage sans résoudre l’équation de Schrödinger. Expérimentalement, une signature claire du désordre d’alliage est observée par des mesures de spectroscopie de photocourant dans des puits quantiques d’InGaN sous forme d’une queue d’Urbach pour des excitations d’énergie inférieure à la largeur de la bande interdite. Ceci permet de définir une énergie caractéristique du désordre qui est en excellent accord avec les prédictions fournies par la nouvelle théorie de la localisation. / In spite of the rapid technological progress in nitrides, the intrinsic properties of nitride alloys and the physics of III-N devices are still not well understood. In the course of my thesis work, novel experimental and theoretical approaches to tackle the study of the microscopic mechanisms governing the electronic properties of nitride semiconductors have been developed. A new experimental technique allowing to directly measure the energy distribution of conduction electrons of an operating LED is explored. This approach allows the direct observation of hot electron populations excited in the optoelectronic device under electrical operation and emitted in ultra-high vacuum. A recent theory of localization in disordered systems is applied to nitride materials and optoelectronic devices. This method allows for the first time the determination of the localization landscape induced by alloy disorder without resorting to the Schrödinger equation. Experimentally, a clear signature of alloy disorder is observed by biased photocurrent spectroscopy of InGaN quantum wells in the form of an Urbach tail for below-gap excitation and is found to be in excellent agreement with the predictions given by the novel localization theory.

The filiform-like corrosion of Magnesium (Mg) alloys AZ31B and AM30 was investigated with electrochemical and microanalytical techniques. Potentiodynamic polarization testing and scanning vibrating electrode technique (SVET) measurements confirmed the “differential electrocatalytic” mechanism previously reported for filiform and filiform-like corrosion on pure Mg and AZ31B. Transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) revealed that the MgO corrosion filaments on both alloys were likely a product of the direct reaction of Mg and water (H2O), responsible for the rapid hydrogen (H2) evolution observed at the propagating corrosion fronts. TEM analysis also revealed through-thickness cracks and noble intermetallic particles within the corrosion filaments and noble metal enrichment at the corrosion filament/metal interfaces, which were proposed to play significant roles in the cathodic activation of the corrosion filaments. The higher susceptibility of the AZ31B alloy to cathodic activation versus AM30 suggested that Zinc (Zn) has a detrimental effect on the resistance of Magnesium-Aluminum-Zinc (Mg-Al-Zn) alloys to filiform and filiform-like corrosion. / Thesis / Master of Applied Science (MASc)

In this thesis, the electronic properties of two-dimensional magnetic materials, transition metal trichlorides and transition metal phosphorus trichalcogenides, are studied by means of various spectroscopic techniques including photoelectron spectroscopy (PES), electron energy-loss spectroscopy (EELS) and optical spectroscopy. The experiments on transition metal trichlorides mainly focus on manipulating the electronic structure of α−RuCl3 — a Kitaev spin liquid candidate material that, however, hosts an antiferromagnetic ground state at temperatures below 7 K. Such manipulation attempts include transition metal substitution by Cr, Ar+ sputtering of exfoliated flakes and the creation of an interface of α−RuCl3 with the organic semiconductor manganese (II) phtalocyanine (MnPc). To study the influence of transition metal substitution by Cr, the parent compounds α−RuCl3 and CrCl3, and the mixed compound Cr0.5Ru0.5Cl3 were studied by PES and EELS. The mixed compound preserves the +III oxidation state of Cr and Ru. The valence band resembles a superposition of the parent compounds and EELS reveals the appearance of a new optical absorption channel assigned to a Cr-Ru charge transfer. Ar+ sputtering decreases the chlorine content of exfoliated α−RuCl3 flakes. However, the properties of the sputtered film, namely the rate of chlorine loss and the work function, depend heavily on the initial flake thickness. The work function spans a remarkable range from Φ = 4.6 eV to 6.1 eV. The interface of α−RuCl3 with MnPc demonstrates the potential of α−RuCl3 as a strong electron acceptor. The work function and electron affinity of α−RuCl3 are characterized and the charge transfer from MnPc to α−RuCl3 is experimentally verified. In the second part of the thesis, two transition metal phosphorus trichalcogenide compounds are studied: FePS3 and NiPS3. Both are antiferromagnetic materials with FePS3 being of Ising-type and NiPS3 of anisotropic Heisenberg-type. Their electronic structure is spectroscopically investigated and the results are used as input for advanced density functional theory calculations (DFT+U) characterizing FePS3 as a Mott insulator and NiPS3 as a charge-transfer insulator. In the magnetically ordered state, magnetism and electronic properties are intertwined with the giant linear dichroism (LD) of FePS3 measured in optical transmission being the most impressive example. A microscopic understanding of the LD is provided with the DFT+U results giving confidence to the described model. For NiPS3, the origin of an extremely sharp magnetic exciton is studied bearing some analogy to the famous Zhang-Rice singlet state initially proposed for cuprates.:Contents iii List of Figures v Acronyms ix 1. Introduction 1 2. Experimental Techniques 3 2.1. Photoelectron Spectroscopy (PES) . . . . . . . . . . . . . . . . . . . 3 2.2. Three-step-model of Photoemission . . . . . . . . . . . . . . . . . . . 4 2.2.1. Photoabsorption . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.2. Propagation to the Surface . . . . . . . . . . . . . . . . . . . 6 2.2.3. Escape into the Vacuum . . . . . . . . . . . . . . . . . . . . . 7 2.3. Spectral Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.4. Energy-filtered Photoemission Electron Microscopy (PEEM) . . . . . 9 2.5. Background Signal of XPS and UPS Measurements . . . . . . . . . . 9 2.6. Electron Energy-loss Spectroscopy (EELS) . . . . . . . . . . . . . . . 10 2.6.1. EELS Cross Section . . . . . . . . . . . . . . . . . . . . . . . 12 2.7. The Dielectric Function . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.7.1. The Drude-Lorentz-model . . . . . . . . . . . . . . . . . . . . 16 2.7.2. Related functions . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.7.3. Kramers-Kronig relations . . . . . . . . . . . . . . . . . . . . 19 2.8. Optical Microscopy and Spectroscopy . . . . . . . . . . . . . . . . . . 20 2.8.1. Optical Microscopy . . . . . . . . . . . . . . . . . . . . . . . . 20 2.8.2. Optical Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 21 2.8.3. Optical Contrast of Thin Films . . . . . . . . . . . . . . . . . 22 2.9. Core Level Spectroscopy of Solids . . . . . . . . . . . . . . . . . . . . 25 2.9.1. Spin-orbit Splitting and Notation . . . . . . . . . . . . . . . . 25 2.9.2. Core Level Spectroscopies: XPS and EELS/XAS . . . . . . . 26 2.9.3. Multiplet and Charge Transfer Effects . . . . . . . . . . . . . 26 2.10. Atomic Force Microscopy (AFM) . . . . . . . . . . . . . . . . . . . . 29 2.11. Details on Spectrometers . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.11.1. nanoARPES . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.11.2. nanoESCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.11.3. Transmission EELS . . . . . . . . . . . . . . . . . . . . . . . . 37 3. Manipulating the Electronic Structure of α−RuCl3 41 3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.2. Tuning the Electronic Structure of the Trichlorine Honeycomb Lattice by Transition Metal Substitution: α−RuCl3, Cr0.5Ru0.5Cl3, CrCl3 . 47 3.2.1. Electron diffraction . . . . . . . . . . . . . . . . . . . . . . . . 48 3.2.2. Core Level Spectroscopy . . . . . . . . . . . . . . . . . . . . . 49 3.2.3. UPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.2.4. EELS Results in the Low Energy Region . . . . . . . . . . . . 52 3.2.5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.3. Work Function Engineering of Atomically Thin α−RuCl3 by Arsputtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.3.1. Characterization . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.3.2. Work Function . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.3.3. XPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.3.4. UPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 3.3.5. Discussion and Summary . . . . . . . . . . . . . . . . . . . . 64 3.4. Charge Transfer at the α−RuCl3/MnPc Interface . . . . . . . . . . . 66 3.4.1. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.4.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.4.3. Discussion and Summary . . . . . . . . . . . . . . . . . . . . 73 4. Spectroscopic Investigation of NiPS3 and FePS3 75 4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4.1.1. Crystal Structure and Magnetic Properties . . . . . . . . . . 76 4.1.2. Electronic Structure . . . . . . . . . . . . . . . . . . . . . . . 79 4.2. FePS3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.2.1. UPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.2.2. XPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.2.3. Electron Diffraction . . . . . . . . . . . . . . . . . . . . . . . 86 4.2.4. EELS Results in the Energy Region between 4 eV and 80 eV . 87 4.2.5. EELS Results in the Low Energy Region . . . . . . . . . . . . 88 4.2.6. Optical Spectroscopy and Linear Dichroism (LD) . . . . . . . 89 4.2.7. Discussion and Conclusion . . . . . . . . . . . . . . . . . . . . 92 4.3. NiPS3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 4.3.1. UPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 4.3.2. Core Level Spectroscopy . . . . . . . . . . . . . . . . . . . . . 98 4.3.3. Electron Diffraction . . . . . . . . . . . . . . . . . . . . . . . 101 4.3.4. EELS Results in the Energy Region between 4 eV and 70 eV . 102 4.3.5. EELS in the Low Energy Region . . . . . . . . . . . . . . . . 103 4.3.6. Multiplet theory and RIXS . . . . . . . . . . . . . . . . . . . 105 4.3.7. Discussion and Conclusion . . . . . . . . . . . . . . . . . . . . 107 5. Summary and Outlook 109 A. Appendix 111 A.1. The Pseudo-Voigt Profile . . . . . . . . . . . . . . . . . . . . . . . . . 111 A.2. Calculation of Reciprocal Lattice Vectors . . . . . . . . . . . . . . . . 111 Bibliography 113 / In dieser Arbeit wurden die elektronischen Eigenschaften von zweidimensionalen magnetischen Materialien, Übergangsmetall-Trichloriden und Übergangsmetall-Phosphor-Trichalkogeniden, untersucht. Dabei kamen verschiedene Spektroskopie-Techniken zum Einsatz: Photoelektronenspektroskopie (PES), Elektronen-Energieverlust-Spektroskopie (EELS) und optische Spektroskopie. Die Experimente an Übergangsmetall-Trichloriden zielen hauptsächlich auf die Manipulation der elektronischen Eigenschaften von α−RuCl3 ab. α−RuCl3 ist ein Kandidat für eine Kitaev Quantenspinflüssigkeit, das jedoch bei tiefen Temperaturen unter 7K einen antiferromagnetischen Grundzustand besitzt. Die Manipulationsversuche beinhalten die Substitution des Übergangsmetalls durch Cr, Ar+ sputtern von exfolierten Kristallflocken und die Erzeugung einer Grenzfläche zwischen α−RuCl3 und dem organischen Halbleiter Mangan (II) Phthalocyanin (MnPc). Um den Einfluss der Substitution des Übergangsmetalls durch Cr zu untersuchen, wurden die Ausgangsverbindungen α−RuCl3 und CrCl3, und die gemischte Verbindung Cr0.5Ru0.5Cl3 mittels PES und EELS untersucht. In der gemischten Verbindung liegen Cr und Ru weiterhin mit Oxidationszahl +III vor. Das Valenzband lässt sich als Überlagung der Ausgangsverbindungen darstellen und EELS Daten zeigen einen neuen optischen Absorptionskanal durch Ladungstransfer von Cr zu Ru. Ar+ sputtern reduziert den Chloranteil von exfolierten α−RuCl3-Flocken. Die Eigenschaften der gesputterten Filme, insbesondere Austrittsarbeit und Chlorverlust, hängen jedoch stark von der ursprünglichen Dicke der exfolierten Flocke ab. Die Austrittsarbeit zeigt eine beachtliche Spanne von Φ = 4.6 eV bis 6.1 eV. Die Grenzfläche von α−RuCl3 mit MnPc demonstriert das Potential von α−RuCl3 als starken Elektronenakzeptor. Die Austrittsarbeit und die Elektronenaffinität von α−RuCl3 wurden charakterisiert und der Ladungstransfer von MnPc zu α−RuCl3 wurde experimentell bestätigt. Im zweiten Teil der Arbeit werden zwei Vertreter der Übergangsmetall-Phosphor-Trichalkogeniden untersucht: FePS3 und NiPS3. Beide Materialien sind antiferromagnetisch, wobei FePS3 dem Ising-Typ entspricht und NiPS3 einem anisotropen Heisenberg-Modell. Die elektronische Struktur der beiden Materialien wurde durch spektroskopische Methoden untersucht und als Grundlage für DFT+U Rechnungen verwendet, wodurch FePS3 als Mott-Isolator und NiPS3 als Ladungstransfer-Isolator charakterisiert wurden. Im magnetisch geordneten Zustand sind elektronische und magnetische Eigenschaften verflochten, das sich am eindrucksvollsten im großen linearen dichroismus (LD) Effekt von FePS3 gemessen in optischer Transmission zeigt. Ein mikroskopisches Modell zur Erklärung des LD wird beschrieben und durch Ergebnisse aus DFT+U Rechnungen unterlegt. Bei NiPS3 wurde die Ursache für ein energetisch extrem scharfes, magnetisches Exziton untersucht, das Analogien zum bekannten Zhang-Rice-Singulett aufweist, welches ursprünglich für Kuprate vorgeschlagen wurde.:Contents iii List of Figures v Acronyms ix 1. Introduction 1 2. Experimental Techniques 3 2.1. Photoelectron Spectroscopy (PES) . . . . . . . . . . . . . . . . . . . 3 2.2. Three-step-model of Photoemission . . . . . . . . . . . . . . . . . . . 4 2.2.1. Photoabsorption . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.2. Propagation to the Surface . . . . . . . . . . . . . . . . . . . 6 2.2.3. Escape into the Vacuum . . . . . . . . . . . . . . . . . . . . . 7 2.3. Spectral Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.4. Energy-filtered Photoemission Electron Microscopy (PEEM) . . . . . 9 2.5. Background Signal of XPS and UPS Measurements . . . . . . . . . . 9 2.6. Electron Energy-loss Spectroscopy (EELS) . . . . . . . . . . . . . . . 10 2.6.1. EELS Cross Section . . . . . . . . . . . . . . . . . . . . . . . 12 2.7. The Dielectric Function . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.7.1. The Drude-Lorentz-model . . . . . . . . . . . . . . . . . . . . 16 2.7.2. Related functions . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.7.3. Kramers-Kronig relations . . . . . . . . . . . . . . . . . . . . 19 2.8. Optical Microscopy and Spectroscopy . . . . . . . . . . . . . . . . . . 20 2.8.1. Optical Microscopy . . . . . . . . . . . . . . . . . . . . . . . . 20 2.8.2. Optical Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 21 2.8.3. Optical Contrast of Thin Films . . . . . . . . . . . . . . . . . 22 2.9. Core Level Spectroscopy of Solids . . . . . . . . . . . . . . . . . . . . 25 2.9.1. Spin-orbit Splitting and Notation . . . . . . . . . . . . . . . . 25 2.9.2. Core Level Spectroscopies: XPS and EELS/XAS . . . . . . . 26 2.9.3. Multiplet and Charge Transfer Effects . . . . . . . . . . . . . 26 2.10. Atomic Force Microscopy (AFM) . . . . . . . . . . . . . . . . . . . . 29 2.11. Details on Spectrometers . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.11.1. nanoARPES . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.11.2. nanoESCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.11.3. Transmission EELS . . . . . . . . . . . . . . . . . . . . . . . . 37 3. Manipulating the Electronic Structure of α−RuCl3 41 3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.2. Tuning the Electronic Structure of the Trichlorine Honeycomb Lattice by Transition Metal Substitution: α−RuCl3, Cr0.5Ru0.5Cl3, CrCl3 . 47 3.2.1. Electron diffraction . . . . . . . . . . . . . . . . . . . . . . . . 48 3.2.2. Core Level Spectroscopy . . . . . . . . . . . . . . . . . . . . . 49 3.2.3. UPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.2.4. EELS Results in the Low Energy Region . . . . . . . . . . . . 52 3.2.5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.3. Work Function Engineering of Atomically Thin α−RuCl3 by Arsputtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.3.1. Characterization . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.3.2. Work Function . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.3.3. XPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.3.4. UPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 3.3.5. Discussion and Summary . . . . . . . . . . . . . . . . . . . . 64 3.4. Charge Transfer at the α−RuCl3/MnPc Interface . . . . . . . . . . . 66 3.4.1. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.4.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.4.3. Discussion and Summary . . . . . . . . . . . . . . . . . . . . 73 4. Spectroscopic Investigation of NiPS3 and FePS3 75 4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4.1.1. Crystal Structure and Magnetic Properties . . . . . . . . . . 76 4.1.2. Electronic Structure . . . . . . . . . . . . . . . . . . . . . . . 79 4.2. FePS3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.2.1. UPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.2.2. XPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.2.3. Electron Diffraction . . . . . . . . . . . . . . . . . . . . . . . 86 4.2.4. EELS Results in the Energy Region between 4 eV and 80 eV . 87 4.2.5. EELS Results in the Low Energy Region . . . . . . . . . . . . 88 4.2.6. Optical Spectroscopy and Linear Dichroism (LD) . . . . . . . 89 4.2.7. Discussion and Conclusion . . . . . . . . . . . . . . . . . . . . 92 4.3. NiPS3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 4.3.1. UPS Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 4.3.2. Core Level Spectroscopy . . . . . . . . . . . . . . . . . . . . . 98 4.3.3. Electron Diffraction . . . . . . . . . . . . . . . . . . . . . . . 101 4.3.4. EELS Results in the Energy Region between 4 eV and 70 eV . 102 4.3.5. EELS in the Low Energy Region . . . . . . . . . . . . . . . . 103 4.3.6. Multiplet theory and RIXS . . . . . . . . . . . . . . . . . . . 105 4.3.7. Discussion and Conclusion . . . . . . . . . . . . . . . . . . . . 107 5. Summary and Outlook 109 A. Appendix 111 A.1. The Pseudo-Voigt Profile . . . . . . . . . . . . . . . . . . . . . . . . . 111 A.2. Calculation of Reciprocal Lattice Vectors . . . . . . . . . . . . . . . . 111 Bibliography 113