Size-dependent Auger spectra and two-hole Coulomb interaction of small supported Cu-clusters

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Auger (L3M4,5M4,5) and X-ray photoionization spectra (2p, 3d) of mass-selected CuN-clusters supported by a thin natural silica layer are presented in the size range N = 8–55 atoms per cluster. The Auger spectra of all clusters are shifted to a lower kinetic energy with respect to the spectrum of the bulk. Furthermore the Auger energy decreases systematically with decreasing cluster size. The binding energies of the 2p and 3d valence states are higher than the corresponding bulk values. Using the energy of the Auger main line, the corresponding core hole peak and the centroid of the self-convoluted 3d valence band the on-site Coulomb interaction energy Udd of the two-hole final state as a function of cluster size has been determined

Modern X-ray spectroscopy:XAS and XES in the laboratory

X-ray spectroscopy is an important tool for scientific analysis. While the earliest demonstration experiments were realised in the laboratory, with the advent of synchrotron light sources most of the experiments shifted to large scale synchrotron facilities. In the recent past there is an increased interest to perform X-ray experiments also with in-house laboratory sources, to simplify access to X-ray absorption and X-ray emission spectroscopy, in particular for routine measurements. Here we summarise the recent developments and comment on the most representative example experiments in the field of in-house laboratory X-ray spectroscopy. We first give an introduction and some historic background on X-ray spectroscopy. This is followed by an overview of the detection techniques used for X-ray absorption and X-ray emission measurements. A short paragraph also puts related high energy resolution and resonant techniques into context, though they are not yet feasible in the laboratory. At the end of this section the opportunities using wavelength dispersive X-ray spectroscopy in the laboratory are discussed. Then we summarise the relevant details of the recent experimental laboratory setups split into two separate sections, one for the recent von Hamos setups, and one for the recent Johann/Johansson type setups. Following that, focussing on chemistry and catalysis, we then summarise some of the notable X-ray absorption and X-ray emission experiments and the results accomplished with in-house setups. In a third part we then discuss some applications of laboratory X-ray spectroscopy with a particular focus on chemistry and catalysis.</p

Depth dependent magnetization profiles of hybrid exchange springs

We report on the magnetization depth profile of a hybrid exchange spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant, and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element specific x-ray magnetic circular dichroism (XMCD) of the Co, Fe, and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations

Chemical Bonding of Transition-metal Co13_{13} Clusters with Graphene

We carried out density functional calculation to study Co$_{13}$ clusters on graphene. We deposit several free isomers in different disposition respect to hexagonal lattice nodes, studying even the $hcp$ $2d$ isomer recently obtained as the most stable one. Surprisingly, Co$_{13}$ clusters bonded to graphene prefer $icosahedron-like$ structures where the low lying isomer is much distorted, because it is linked with more bonds than in previous works. For any isomer the most stable position binds to graphene by the Co atoms that can lose electrons. We find that the charge transfers between graphene and clusters are small enough to conclude that the Co-graphene binding is not ionic-like but chemical. Besides, the same order of stability among the different isomers on doped graphene is well kept. These findings could also be of interest for magnetic clusters on graphenic nanostructures such as ribbons and nanotubes.Comment: 12 pages, 6 figure

EMIL The energy materials in situ laboratory Berlin a novel characterization facility for photovoltaic and energy materials

A knowledge based approach towards developing a new generation of solar energy conversion devices requires a fast and direct feedback between sophisticated analytics and state of the art processing test facilities for all relevant material classes. A promising approach is the coupling of synchrotron based X ray characterization techniques, providing the unique possibility to map the electronic and chemical structure of thin layers and interface regions with relevant in system in situ sample preparation or in operando analysis capabilities in one dedicated laboratory. EMIL, the Energy Materials In situ Laboratory Berlin, is a unique facility at the BESSY II synchrotron light source. EMIL will be dedicated to the in system, in situ, and in operando X ray analysis of materials and devices for energy conversion and energy storage technologies including photovoltaic applications and photo electrochemical processes. EMIL comprises up to five experimental end stations, three of them can access X rays in an energy range of 80 eV 10 keV. For example, one key setup of EMIL combines a suite of advanced spectroscopic characterization tools with industry relevant deposition facilities in one integrated ultra high vacuum system. These deposition tools allow the growth of PV devices based on silicon, compound semiconductors, hybrid heterojunctions, and organo metal halide perovskites on up to 6 sized substrates. EMIL will serve as a research platform for national and international collaboration in the field of photovoltaic photocatalytic energy conversion and beyond. In this paper, we will provide an overview of the analytic and material capabilities at EMIL

Free Clusters Studied by Synchrotron-Based X-ray Spectroscopy: From Rare Gases to Metals

The main topic of this Thesis is the x-ray spectroscopic studies of free nano-clusters with size more than 10^3 atoms. The photoelectron spectroscopy experiments on rare gas and metal clusters were performed at beamline I411 at MAX-lab National Swedish synchrotron radiation facility. Free rare-gas clusters are simplest objects in cluster research. However their electronic structure springs a lot of surprises. In the x-ray absorption spectra of free Kr clusters the positions of the related cluster and atomic states of the higher 3d^{-1}6p and 3d^{-1}7p excited states in bulk and surface atoms are reversed compared to the 3d^{-1}5p state. The energy shifts of the higher core-excited states in cluster atoms grow towards the limiting values of the core-ionized states. The knowledge of the final cluster states reached after Auger decay of the resonantly excited core states threw a new light on this phenomenon. We explain these experimental findings by a spatial spread of the excited orbitals over the cluster lattice. The interplay of the two main effects - confinement and polarization - leads to qualitatively different situations. When the excited orbital radius is less than the interatomic distance in clusters (3d^{-1}5p state in Kr), confinement dominates. If the excited orbital radius exceeds the nearest neighbour distance (3d^{-1}np, n>5 states in Kr), polarization takes over and the energy-level structure becomes ion-like. Interest in studies of more complex than rare gas clusters systems determined the construction of the gas-aggregation metal cluster source. For the vaporisation of low melting point metals (Na) an oven was used. Vapours of higher melting point metals (Ag, Cu, Pb) were produced with a magnetron sputtering source. The design of the gas-aggregation source and description of the experimental setup are presented in this Thesis. Using this source we performed the first core-level photoemission (XPS) experiments on free metal clusters. The recorded spectra have shown that synchrotron-based x-ray core-level photoelectron spectroscopy can be efficiently implemented to free metal clusters. The evolution of the electronic structure with size has been studied by valence ionization, XPS and Auger techniques. These measurements have shown a close similarity between large clusters and solids. The difference between the established ionization potential of metal clusters and the solid has been used for the cluster size estimation for Na, Cu and Ag clusters. The presence of neutral and charged metal clusters in the Pb cluster beam created by magnetron-based source has offered an independent method for estimating cluster dimensions from core-level spectra, in which the charge states are resolved

Concept, construction and commissioning of an alignment system for deep X-ray lithography

An in-house-made alignment system for deep X-ray lithography is presented that features low costs, low weight and little demand in space. Synchrotron radiation illuminates alignment marks on mask and substrate. The radiation transmitted through these alignment marks is detected by X-ray-sensitive diodes. The mask is fixed to the vacuum chamber, whereas the substrate is mounted on a six-axis kinematic stage. The information about the degree of alignment is the obtained photocurrent, which reaches its maximum at the best alignment position. Variation of the photocurrent is an error signal in a feedback loop. A slit screen protects the resist in the pattern area from irradiation during the alignment procedure. The features of the alignment system offer guidelines for research groups interested in upgrading their system as well

Phosphorus K beta X ray emission spectroscopy detects non covalent interactions of phosphate biomolecules in situ

Phosphorus is ubiquitous in biochemistry, being found in the phosphate groups of nucleic acids and the energy transferring system of adenine nucleotides e.g. ATP . K amp; 946; X ray emission spectroscopy XES of phosphorus has been largely unexplored, with no previous applications to biomolecules. Here, the potential of P K amp; 946; XES to study phosphate containing biomolecules, including ATP and NADPH, is evaluated, as is the application of the technique to aqueous solution samples. P K amp; 946; spectra offer a detailed picture of phosphate valence electronic structure, reporting on subtle non covalent effects, such as hydrogen bonding and ionic interactions, that are key to enzymatic catalysis. Spectral features are interpreted using density functional theory DFT calculations, and potential applications to the study of biological energy conversion are highlighte

Ray-tracing analysis of diffractive-refractive X-ray optics

Ray-tracing simulations of mistuned sagittal diffractive - refractive X-ray lenses (DRXL) are presented. In this article, firstly the characteristic aberrations for various types of crystal misalignments within one-crystal and four-crystal DRXLs are considered, and the sensitivity of such an optical system to the mutual misalignment of its components is discussed. The simulations reveal that a DRXL is not too sensitive to the adjustment of its components. In the second part of this article the performance of such lenses with ideal and approximate profiles is examined. Comparative analysis of parabolic and cylindrical DRXLs showed that, in the case when the linear source size is comparable with the acceptance of the lens, the performances of parabolic and cylindrical DRXLs are practically the same

THERMOELECTRIC HEAT REMOVAL SYSTEM FOR THE OPERATIONAL STABILISATION OF HEAT PIPES IN A SYSTEM FOR PROVIDING THE THERMAL REGIME OF RADIO ELECTRONIC EQUIPMENT

Objectives. The aim of the study is to conduct an analysis of thermophysical processes in a thermoelectric system used for  providing the thermal regime of electronic equipment located in a cabinet. A cabinet design and thermoelectric system for efficient  heat removal from the condensing part of the heat pipe are  proposed. An additional advantage of the proposed design is the  obviation of significant additional power consumption requirement  for regulating the temperature of radio electronic equipment stored  in the cabinet.A distinctive feature of the constructive realisation is  the presence of an intermediate heat removal.Methods. The three-dimensionality of the problem and mixed boundary conditions lead to the need to develop a calculation  of heat transfer in the elements of the construction of the  thermoelectric system. The numerical calculation method is based on the method of energy balances. The analysis of the heat regimes of  the intermediate heat removal is performed on the basis of a mathematical model for a locally-heated and -cooled restricted plate.Results. A cabinet design and a thermoelectric system for efficient  heat removal from the condensing part of the heat pipe are  proposed. A distinctive feature of the constructive realisation is the  presence of an intermediate heat removal.Conclusion.The capacity of the intermediate heat removal for given dimensions and temperature of the source is weakly affected by its  thickness (in constructively reasonable limits), as well as the  temperature and area of the absorbing side of the thermoelectric  module; the total heat output from the heat source is determined by the dimensions and heat exchange conditions on the free surface of the intermediate heat removal, as well as by the temperature and dimensions of the heat absorbing side of the thermoelectric module. The use of an intermediate heat removal can significantly reduce the thermal load on the thermoelectric module with a slight decrease in the temperature driving force