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SESAME and a consortium of five Helmholtz Centers are designing and installing a state-of-the-art soft X-Ray undulator beamline at the SESAME light source in Amman, Jordan. Funding is provided by the Helmholtz Association over a four year project cycle that started in January 2019. This is an interim report covering the first 36 months of the project where the construction and installation has been almost completed and commissioning and characterization of the beamline is about to start. Additionally, seminars, workshops, and a training program are part of the project aimed at establishing a broad user community.

Physical review / B 97(3), 035110 (2018). doi:10.1103/PhysRevB.97.035110, We present a detailed study of the Ti $3d$ carriers at the interface of $LaAlO_{3}/SrTiO_3$ heterostructures by high-resolution resonant inelastic soft x-ray scattering (RIXS), with special focus on the roles of overlayer thickness and oxygen vacancies. Our measurements show the existence of interfacial Ti $3d$ electrons already below the critical thickness for conductivity. The (total) interface charge carrier density increases up to a $LaAlO_3$ overlayer thickness of 6 unit cells before it levels out. Furthermore, we observe strong Ti $3d$ charge carrier doping by oxygen vacancies. The RIXS data combined with photoelectron spectroscopy and transport measurements indicate the simultaneous presence of localized and itinerant charge carriers. At variance with previous interpretations, we show that in our excitation energy dependent RIXS measurements the amounts of localized and itinerant Ti $3d$ electrons in the ground state do not scale with the intensities of the Raman and fluorescence peaks, respectively. Rather, we attribute the observation of either Raman components or fluorescence signal to the specific nature of the intermediate state reached in the RIXS excitation process., Published by APS, Woodbury, NY

The interfaces between two condensed phases often exhibit emergent physical properties that can lead to new physics and novel device applications and are the subject of intense study in many disciplines. We here apply experimental and theoretical techniques to the characterization of one such interesting interface system: the two-dimensional electron gas (2DEG) formed in multilayers consisting of SrTiO3 (STO) and GdTiO3 (GTO). This system has been the subject of multiple studies recently and shown to exhibit very high carrier charge densities and ferromagnetic effects, among other intriguing properties. We have studied a 2DEG-forming multilayer of the form [6 unit cells (u.c.) STO/3 u.c. of GTO](20) using a unique array of photoemission techniques including soft and hard x-ray excitation, soft x-ray angle-resolved photoemission, core-level spectroscopy, resonant excitation, and standing-wave effects, as well as theoretical calculations of the electronic structure at several levels and of the actual photoemission process. Standing-wave measurements below and above a strong resonance have been exploited as a powerful method for studying the 2DEG depth distribution. We have thus characterized the spatial and momentum properties of this 2DEG in detail, determining via depth-distribution measurements that it is spread throughout the 6 u.c. layer of STO and measuring the momentum dispersion of its states. The experimental results are supported in several ways by theory, leading to a much more complete picture of the nature of this 2DEG and suggesting that oxygen vacancies are not the origin of it. Similar multitechnique photoemission studies of such states at buried interfaces, combined with comparable theory, will be a very fruitful future approach for exploring and modifying the fascinating world of buried-interface physics and chemistry.

Integrating epitaxial and ferromagnetic Europium Oxide (EuO) directly on silicon is a perfect route to enrich silicon nanotechnology with spin filter functionality. To date, the inherent chemical reactivity between EuO and Si has prevented a heteroepitaxial integration without significant contaminations of the interface with Eu silicides and Si oxides. We present a solution to this long-standing problem by applying two complementary passivation techniques for the reactive EuO/Si interface: ($i$) an $in\:situ$ hydrogen-Si $(001)$ passivation and ($ii$) the application of oxygen-protective Eu monolayers --- without using any additional buffer layers. By careful chemical depth profiling of the oxide-semiconductor interface via hard x-ray photoemission spectroscopy, we show how to systematically minimize both Eu silicide and Si oxide formation to the sub-monolayer regime --- and how to ultimately interface-engineer chemically clean, heteroepitaxial and ferromagnetic EuO/Si $(001)$ in order to create a strong spin filter contact to silicon., 11 pages of scientific paper, 10 high-resolution color figures. Supplemental information on the thermodynamic problem available (PDF). High-resolution abstract graphic available (PNG). Original research (2016)

Applied physics letters 102, 062907 (2013). doi:10.1063/1.4792525, Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostaticpotential profile across the junction upon polarization reversal of the ultrathin ferroelectricbarrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electricpotential barrier profile in as-grown Cr/BaTiO3(001)/Pt(001) heterostructures. Transportproperties of Cr/BaTiO3/Pt junctions with a sub-lm Cr top electrode are interpreted in terms oftunneling electroresistance with resistance changes of a factor of 30 upon polarization reversal.By fitting the I-V characteristics with the model employing an experimentally determined electricpotential barrier we derive the step height changes at the BaTiO3/Pt (Cr/BaTiO3) interfaceþ0.42(0.03) eV following downward to upward polarization reversal., Published by American Institute of Physics, Melville, NY

We present a detailed study of the electronic structure and band alignment in LaAlO3/SrTiO3 oxide heterostructures by hard x-ray photoelectron spectroscopy. Our spectroscopic measurements find no evidence for the strong potential gradient within the polar LaAlO3 film predicted by band theory. Due to the high interface sensitivity of the method, we are further able to determine the valence band offset between the LaAlO3 film and the SrTiO3 substrate, which is found to be independent of the number of LAO overlayers. Finally, we discuss several explanations for the apparent absence of the built-in field in ex situ prepared LaAlO3/SrTiO3 heterostructures.

A double‐crystal, UHV‐compatible monochromator for XAFS applications at bending magnet beamlines has been designed. It uses two crystal sets, Si(111) and (311), on a common central rotation axis driven by an ex‐vacuo goniometer. All mechanical and electrical components are mounted on a 400 mm UHV flange which is attached to a compact vacuum chamber. The first crystals are water cooled using connector‐ and bellowless tubing through the fluidic sealed feedthrough of the central rotation. The first crystal set is mounted off‐axis and can be translated vertically to keep the fixed exit condition. The second crystal set uses small crystals of the same size as the first. In order to accept the reflected beam of the first crystal at small Bragg angles, it is tangentially translated along the beam. The angle can be varied from 5° to 55.5° resulting in a total energy range 2.4 – 43.4 keV for Si(111)/(311). Crystal sets are interchangeable by translating the vacuum chamber. Angle encoding is achieved by a Renishaw incremental optical encoder in vacuo.

Physical review / B 67(3), 035122 (2003). doi:10.1103/PhysRevB.67.035122, Published by APS, Woodbury, NY

Physical review / B 57(11), 6422 - 6426 (1998). doi:10.1103/PhysRevB.57.6422, The evolution of the Pd Auger electron emission resulting in an open 3d and 4d shell, respectively, was experimentally studied as a function of photon energy across the L3 threshold. Both for the core-core-core (L3−M4,5M4,5) and the core-valence-valence (L3−N4,5N4,5) processes the observed resonance behavior is interpreted in terms of radiationless resonant Raman scattering. In the threshold regime the Auger electron emission traces the photon energy and the linewidth exhibits a sublifetime narrowing. Around the L3 threshold the L3−N4,5N4,5 emission partly overlaps with the valence-band satellite. The accurate intensity normalized constant initial state data reveal a Fano-type modulation for the main valence band. However, no such behavior is obtained for the satellite region if the resonant threshold process in the L3−N4,5N4,5 Auger channel is taken properly into account., Published by Inst., Woodbury, NY

Physical review / B 45(7), 4682 - 4687 (1992). doi:10.1103/PhysRevA.45.4682, The x-ray absorption of transition metals from Cr to Zn is examined in the energy region of K+L double photoabsorption. A variational procedure is developed to extract correlated components from pairs of spectra. Applied to absorption spectra taken at different sample temperatures, the procedure is used to suppress the extended x-ray-absorption fine-structure oscillations that pervade the K+L region in this range of elements. A relative sensitivity of 2×10$^{−3}$ to 3×10$^{−4}$ of the absorption coefficient, depending on the sample quality, is achieved. No significant features attributable to multiple photoexcitation are found in the spectra on that level, so that previous reports of K+L edges for Co, Ni, and Zn are not confirmed., Published by Inst.8644, Woodbury, NY

Physical review / B 41(8), 4887 - 4890 (1990). doi:10.1103/PhysRevB.41.4887, Coincidence measurements between the energy spectrum of inelastically scattered 151-keV photons and the recoil electrons for a 0.12-μm-thick Al foil are reported. For fixed scattering angles the coincidence count rate is proportional to the electron momentum density with momentum components parallel to the momentum-transfer vector. The experiment was performed with use of the synchrotron radiation from a bending magnet of the DORIS storage ring at Deutsches Elektronen-Synchrotron (DESY), Hamburg., Published by Inst., Woodbury, NY

Physical review / B 58(11), 6871 - 6876 (1998). doi:10.1103/PhysRevB.58.6871, High-resolution Ag L3-edge XANES for a series of Au-Ag alloys, AuAg3, AuAg, and Au3Ag, have been obtained by monitoring the intensity of the highly energy-resolved Ag L3M4,5M4,5(1G4) Auger line. The experimental results reveal features that were previously unresolved with total electron yield techniques and confirm previous observations that Ag gains d charge and Au loses d in Au-Ag alloys. Full-scale multiple scattering calculations for the Ag L3-edge XANES of Ag and AuAg yield semiquantitative agreement with the experiment. The results show that in the case of wide band metals, the Auger yield of a well-separated narrow final state can indeed be used to improve the resolution of XANES near the threshold. The implication of the results to electron charge redistribution upon alloying is discussed., Published by Inst., Woodbury, NY