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The Advanced Light Source: Technical Design

Description: The Advanced Light Source (ALS) is a synchrotron radiation source consisting of a 50-MeV linear accelerator, a 1.3-GeV 'booster' synchrotron, a 1.3-GeV electron storage ring, and a number of photon beam lines, as shown in Figure 1. As an introduction to a detailed description of the Advanced Light Source, this section provides brief discussions on the characteristics of synchrotron radiation and on the theory of storage rings. Appendix A contents: Introduction to Synchrotron-Radiation Sources; Storage Ring; Injection System; Control System; Insertion Devices; Photon Beam Lines; and References.
Date: May 1, 1984
Partner: UNT Libraries Government Documents Department

Magnetic spectroscopy and microscopy of functional materials

Description: Heusler intermetallics Mn{sub 2}Y Ga and X{sub 2}MnGa (X; Y =Fe, Co, Ni) undergo tetragonal magnetostructural transitions that can result in half metallicity, magnetic shape memory, or the magnetocaloric effect. Understanding the magnetism and magnetic behavior in functional materials is often the most direct route to being able to optimize current materials for todays applications and to design novel ones for tomorrow. Synchrotron soft x-ray magnetic spectromicroscopy techniques are well suited to explore the the competing effects from the magnetization and the lattice parameters in these materials as they provide detailed element-, valence-, and site-specifc information on the coupling of crystallographic ordering and electronic structure as well as external parameters like temperature and pressure on the bonding and exchange. Fundamental work preparing the model systems of spintronic, multiferroic, and energy-related compositions is presented for context. The methodology of synchrotron spectroscopy is presented and applied to not only magnetic characterization but also of developing a systematic screening method for future examples of materials exhibiting any of the above effects. The chapter progression is as follows: an introduction to the concepts and materials under consideration (Chapter 1); an overview of sample preparation techniques and results, and the kinds of characterization methods employed (Chapter 2); spectro- and microscopic explorations of X{sub 2}MnGa/Ge (Chapter 3); spectroscopic investigations of the composition series Mn{sub 2}Y Ga to the logical Mn{sub 3}Ga endpoint (Chapter 4); and a summary and overview of upcoming work (Chapter 5). Appendices include the results of a Think Tank for the Graduate School of Excellence MAINZ (Appendix A) and details of an imaging project now in progress on magnetic reversal and domain wall observation in the classical Heusler material Co{sub 2}FeSi (Appendix B).
Date: January 28, 2011
Creator: Jenkins, C.A.
Partner: UNT Libraries Government Documents Department

ALSNews 2009

Description: Compilation of Advanced Light Source newsletter, ALSNews, for 2009, Volumes 294-304.
Date: November 25, 2009
Creator: Tamura (Ed.), Lori
Partner: UNT Libraries Government Documents Department

Electronic Properties of Hydrogen Storage Materials with Photon-in/Photon-out Soft-X-Ray Spectroscopy

Description: The applications of resonant soft X-ray emission spectroscopy on a variety of carbon systems have yielded characteristic fingerprints. With high-resolution monochromatized synchrotron radiation excitation, resonant inelastic X-ray scattering has emerged as a new source of information about electronic structure and excitation dynamics. Photon-in/photon-out soft-X-ray spectroscopy is used to study the electronic properties of fundamental materials, nanostructure, and complex hydrides and will offer potential in-depth understanding of chemisorption and/or physisorption mechanisms of hydrogen adsorption/desorption capacity and kinetics.
Date: September 22, 2008
Creator: Guo, Jinghua
Partner: UNT Libraries Government Documents Department

Optimal measurement strategies for effective suppression of drift errors

Description: Drifting of experimental set-ups with change of temperature or other environmental conditions is the limiting factor of many, if not all, precision measurements. The measurement error due to a drift is, in some sense, in-between random noise and systematic error. In the general case, the error contribution of a drift cannot be averaged out using a number of measurements identically carried out over a reasonable time. In contrast to systematic errors, drifts are usually not stable enough for a precise calibration. Here a rather general method for effective suppression of the spurious effects caused by slow drifts in a large variety of instruments and experimental set-ups is described. An analytical derivation of an identity, describing the optimal measurement strategies suitable for suppressing the contribution of a slow drift described with a certain order polynomial function, is presented. A recursion rule as well as a general mathematical proof of the identity is given. The effectiveness of the discussed method is illustrated with an application of the derived optimal scanning strategies to precise surface slope measurements with a surface profiler.
Date: April 16, 2009
Creator: Yashchuk, Valeriy V.
Partner: UNT Libraries Government Documents Department

X-ray photon-in/photon-out methods for chemical imaging

Description: Most interesting materials in nature are heterogeneous, so it is useful to have analytical techniques with spatial resolution sufficient to resolve these heterogeneities.This article presents the basics of X-ray photon-in/photon-out chemical imaging. This family of methods allows one to derive images reflectingthe chemical state of a given element in a complex sample, at micron or deep sub-micron scale. X-ray chemical imaging is relatively non-destructiveand element-selective, and requires minimal sample preparation. The article presents the basic concepts and some considerations of data takingand data analysis, along with some examples.
Date: March 24, 2010
Creator: Marcus, Matthew A.
Partner: UNT Libraries Government Documents Department

Analysis of ultra-narrow ferromagnetic domain walls

Description: New materials with high magnetic anisotropy will have domains separated by ultra-narrow ferromagnetic walls with widths on the order of a few unit cells, approaching the limit where the elastic continuum approximation often used in micromagnetic simulations is accurate. The limits of this approximation are explored, and the static and dynamic interactions with intrinsic crystalline defects and external driving #12;elds are modeled. The results developed here will be important when considering the stability of ultra-high-density storage media.
Date: January 10, 2012
Creator: Jenkins, Catherine & Paul, David
Partner: UNT Libraries Government Documents Department

Preface to International Workshop on X-ray Mirror Design, Fabrication, and Metrology

Description: The International Workshop on X-Ray Mirror Design, Fabrication, and Metrology (IWXM), Osaka, Japan, was held as a satellite meeting of the Conference on Synchrotron Radiation Instrumentation (SRI) 2009, Melbourne, Australia, in October, 2009. The workshop was organized by a collaboration of scientists from a number of leading synchrotron institutions and universities around the World, such as Osaka University, SPring-8, KEK (Japan), ALS, APS and NSLS (USA), ELETTRA (Italy), ESRF, Synchrotron SOLEIL (France), BESSY (Germany), Diamond (UK), SSRF (China), NSRRC (Taiwan) and PAL (Korea). The workshop followed a series of parallel workshops focused on metrology (1st, 2nd and 3rd International Workshop on Metrology for X-ray and Neutron Optics) and on active X-ray optics (1st and 2nd X-ray and XUV Active Optics Workshop, ACTOP06 and ACTOP08) and included the 3rd workshop on X-ray and EUV active optics (ACTOP09). The workshop brought together more than 100 participants: manufacturers, optical and mechanical engineers, designers, and users of X-ray optics; allowing for free exchange of ideas, highlighting of existing problems and challenges, and searching for ways to improve existing instrumentation for sub-microradian and sub-nanometer accuracy. A visit to the Osaka University mirror fabrication laboratory, SPring-8, and the X-ray free electron laser (XFEL) facility was included in the workshop.
Date: April 20, 2010
Creator: Yamauchi, Kazuto; Yashchuk, Valeriy V. & Cocco, Daniele
Partner: UNT Libraries Government Documents Department

Versatile assembly of p-carboxylatocalix[4]arene-O-alkyl ethers

Description: Crystallisation of lower-rim tetra-O-alkylated p-carboxylatocalix[4]arenes from pyridine results in the formation of both bi-layer and pillar type supramolecular motifs. Full alkylation at the calixarene lower rim has significant influence over the supramolecular self-assembly motif, including preclusion of pyridine guest molecules from the calixarene cavity in the solid state.
Date: July 8, 2009
Creator: Kennedy, Stuart; Teat, Simon J. & Dalgarno, Scott J.
Partner: UNT Libraries Government Documents Department

Ferrimagnetism and disorder of epitaxial Mn2-xCoxVAl Heusler compound thin films

Description: The quaternary full Heusler compound Mn{sub 2-x}Co{sub x}VAl with x = 1 is predicted to be a half-metallic antiferromagnet. Thin films of the quaternary compounds with x = 0-2 were prepared by dc and RF magnetron co-sputtering on heated MgO (0 0 1) substrates. The magnetic structure was examined by x-ray magnetic circular dichroism and the chemical disorder was characterized by x-ray diffraction. Ferrimagnetic coupling of V to Mn was observed for Mn{sub 2}VAl (x = 0). For x = 0.5, we also found ferrimagnetic order with V and Co antiparallel to Mn. The observed reduced magnetic moments are interpreted with the help of band structure calculations in the coherent potential approximation. Mn{sub 2}VAl is very sensitive to disorder involving Mn, because nearest-neighbour Mn atoms couple antiferromagnetically. Co{sub 2}VAl has B2 order and has reduced magnetization. In the cases with x {ge} 0.9 conventional ferromagnetism was observed, closely related to the atomic disorder in these compounds.
Date: January 29, 2011
Creator: Meinert, Markus; Schmalhorst, Jan-Michael; Reiss, Gunter & Arenholz, Elke
Partner: UNT Libraries Government Documents Department

Hole doping in high temperature superconductors using the XANES technique

Description: Superconducting and physical properties of F-doped HgPb-1223 and Ce-doped Tl-1223 systems were considerably improved through adjusting the hole content of the two systems. In this study, we have used the x-ray absorption near-edge structure (XANES) technique to investigate the electronic structure of the two systems by probing the unoccupied electronic states. For the F-doped Hg-1223 system, the O K-edge, Ca L{sub 2,3} and Cu L{sub 2,3}-edge structures were thoroughly investigated. The pre-edge features of O K-edge spectra, as a function of doping, reveal important information about the projected local density of unoccupied states on the O sites in the region close to the absorption edge, which is a measure of O 2p hole concentration in the valence band. In the originally under-doped Hg-1223, the results indicate that the number of O 2p holes in the CuO{sub 2} planes increases as fluorine was introduced up to an optimal value, after which it decreases. Furthermore, the Cu L{sub 2,3} absorption edge provides useful information about the valence state of Cu which is also related to the hole density in the CuO{sub 2} planes and confirms the same previous conclusion. The Ca L{sub 2,3}-edge shows the presence crystal field splitting in HgPb1223/F{sub x} which is similar to CaF{sub 2} and CaO in addition to the spin-orbit splitting of the Ca 2p core level electrons. These results ensure that fluorine goes into the structure of HgPb-1223/F{sub x} and it occupies the vacant interstitial oxygen site in the Hg-O plane, as was expected. In Ce-substituted Tl-1223, similar measurements were perfonned for samples with different Ce content. The pre-edge feature of the O K-edge spectra shows clearly the drastic decrease of the hole content in CuO{sub 2} planes of this originally over-doped system with increasing Ce content. This result is also confirmed from the chemical state ...
Date: September 1, 2008
Creator: Hamdan, Nasser & Hussain, Zahid
Partner: UNT Libraries Government Documents Department

IKNO, a user facility for coherent terahertz and UV synchrotron radiation

Description: IKNO (Innovation and KNOwledge) is a proposal for a multi-user facility based on an electron storage ring optimized for the generation of coherent synchrotron radiation (CSR) in the terahertz frequency range, and of broadband incoherent synchrotron radiation (SR) ranging from the IR to the VUV. IKNO can be operated in an ultra-stable CSR mode with photon flux in the terahertz frequency region up to nine orders of magnitude higher than in existing 3rd generation light sources. Simultaneously to the CSR operation, broadband incoherent SR up to VUV frequencies is available at the beamline ports. The main characteristics of the IKNO storage and its performance in terms of CSR and incoherent SR are described in this paper. The proposed location for the infrastructure facility is in Sardinia, Italy.
Date: April 26, 2008
Creator: Sannibale, Fernando; Marcelli, Augusto & Innocenzi, Plinio
Partner: UNT Libraries Government Documents Department

In-situ early stage electromigration study in Al line using synchrotron polychromatic X-ray microdiffraction

Description: Electromigration is a phenomenon that has attracted much attention in the semiconductor industry because of its deleterious effects on electronic devices (such as interconnects) as they become smaller and current density passing through them increases. However, the effect of the electric current on the microstructure of interconnect lines during the very early stage of electromigration is not well documented. In the present report, we used synchrotron radiation based polychromatic X-ray microdiffraction for the in-situ study of the electromigration induced plasticity effects on individual grains of an Al (Cu) interconnect test structure. Dislocation slips which are activated by the electric current stressing are analyzed by the shape change of the diffraction peaks. The study shows polygonization of the grains due to the rearrangement of geometrically necessary dislocations (GND) in the direction of the current. Consequences of these findings are discussed.
Date: October 31, 2007
Creator: Chen, Kai; Tamura, Nobumichi & Tu, King-Ning
Partner: UNT Libraries Government Documents Department

ALSNews 2007

Description: Compilation of Advanced Light Source newsletter, ALSNews, for 2007, Volumes 272-282.
Date: November 28, 2007
Creator: McCullough (Ed.), Julie & Tamura (Ed.), Lori
Partner: UNT Libraries Government Documents Department

ALSNews 2008

Description: Compilation of Advanced Light Source newsletter, ALSNews, for 2008, Volumes 283-293.
Date: November 26, 2008
Creator: McCullough (Ed.), Julie & Tamura (Ed.), Lori
Partner: UNT Libraries Government Documents Department

Anisotropic x ray magnetic linear dichroism - Its importance for the analysis of soft x ray spectra of magnetic oxides

Description: Using spectroscopic information for x ray magnetometry and magnetic microscopy requires detailed theoretical understanding of spectral shape and magnitude of dichroism signals. We have shown unambiguously that--contrary to common belief--spectral shape and magnitude of x ray magnetic linear dichroism (XMLD) are not only determined by the relative orientation of magnetic moments and x ray polarization, but also their orientations relative to the crystallographic axes must be taken into account for accurate interpretation of XMLD data.
Date: July 2, 2008
Creator: van der Laan, G. & Arenholz, Elke
Partner: UNT Libraries Government Documents Department

Autocollimators for Deflectometry: Current Status and Future Progress

Description: The proliferation of autocollimator-based surface profilometers at synchrotron metrology laboratories worldwide necessitates a detailed understanding of the parameters influencing their angular response. A comprehensive overview of the current status of autocollimator characterization and calibration at the Physikalisch-Technische Bundesanstalt (PTB) and its implications for their optimal application are provided, as well as information on future challenges and expected progress. Autocollimator-based deflectometric profilometers are in operation at the PTB, the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, USA, the BESSY II, Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Germany, and the Diamond Light Source Ltd (DLS), UK. A continuous topic of research at the PTB is to investigate the factors influencing the angular response of autocollimators and to provide the most accurate calibration of the instruments to aid users in their application and manufacturers in their improvements [1-3]. At the PTB, the calibration of autocollimators is realized by a direct comparison of the devices with the primary angle reference standard [1]. With highly stable autocollimators, calibrations with standard measurement uncertainties of u = 0.003 arcsec (15 nrad) have been achieved [2,3]. The influence of a number of parameters on the angle measurement with autocollimators have been investigated in detail, such as the reflectivity of the surface under test (SUT), the diameter and shape of the aperture stop, its position both along the autocollimator's optical axis and perpendicular to it [2], as well as the optical path length of the autocollimator beam [3]. Extensive information on these errors and their minimization will be presented.
Date: June 15, 2009
Creator: Geckeler, Ralf; Just, Andreas; Krause, Michael & Yashchuk, Valeriy V.
Partner: UNT Libraries Government Documents Department

Calibration of Modulation Transfer Function of Surface Profilometers with 1D and 2D Binary Pseudo-random Array Standards

Description: We suggest and describe the use of a binary pseudo-random grating as a standard test surface for calibration of the modulation transfer function of microscopes. Results from calibration of a MicromapTM-570 interferometric microscope are presented.
Date: May 19, 2008
Creator: Yashchuk, Valeriy V.; McKinney, Wayne R. & Takacs, Peter Z.
Partner: UNT Libraries Government Documents Department

Chemical Analysis of Impurity Boron Atoms in Diamond Using Soft X-ray Emission Spectroscopy

Description: To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.
Date: March 29, 2008
Creator: Muramatsu, Yasuji; Iihara, Junji; Takebe, Toshihiko & Denlinger, Jonathan D.
Partner: UNT Libraries Government Documents Department

Correlation between Crystallographic and Magnetic Domains at Co/NiO(001) Interfaces

Description: Using soft x-ray spectromicroscopy we show that NiO(001) exhibits a crystallographic and magnetic domain structure near the surface identical to that of the bulk. Upon Co deposition a perpendicular coupling between the Ni and Co moments is observed that persists even after formation of uncompensated Ni spins at the interface through annealing. The chemical composition at the interface alters its crystallographic structure and leads to a reorientation of the Ni moments from the <112> to the <110> direction. We show that this reorientation is driven by changes in the magnetocrystalline anisotropy rather than exchange coupling mediated by residual uncompensated spins.
Date: December 18, 2008
Creator: Ohldag, H.; van der Laan, G. & Arenholz, E.
Partner: UNT Libraries Government Documents Department

Evidence for residual elastic strain in deformed natural quartz

Description: Residual elastic strain in naturally deformed, quartz-containing rocks can be measured quantitatively in a petrographic thin section with high spatial resolution using Laue microdiffraction with white synchrotron x-rays. The measurements with a resolution of one micrometer allow the quantitative determination of the deviatoric strain tensor as a function of position within the crystal investigated. The observed equivalent strain values of 800-1200 microstrains represent a lower bound of the actual preserved residual strain in the rock, since the stress component perpendicular to the cut sample surface plane is released. The measured equivalent strain translates into an equivalent stress in the order of {approx} 50 MPa.
Date: January 30, 2009
Creator: Kunz, Martin; Chen, Kai; Tamura,Nobumichi & Wenk, Hans-Rudolf
Partner: UNT Libraries Government Documents Department

Paraxial SGM beamlines for coherence experiments at the Advanced Light Source

Description: Beamlines have been designed for coherence experiments at the ALS based on brightness preserving spherical grating monochromators. The operation is almost paraxial so that a very simple scheme can deliver the modest spectral resolution required, with just two focusing optics, one of which is the spherical grating.
Date: July 24, 2008
Creator: Warwick, Anthony I; Warwick, Anthony I & Howells, Malcolm
Partner: UNT Libraries Government Documents Department

Magnetic order and interfacial coupling in oxide thin films and heterostructures probed with soft x-ray dichroism

Description: The combination of novel magnetic properties induced by reduced dimensionality and strong magnetic interactions across interfaces leads to intriguing new properties in magnetic hetero- and nanostructures not observed in the constituent materials in bulk form. It is the careful optimization of the characteristics of the individual layers as well as the magnetic coupling across the interface that allows us to control the magnetic properties and tailor them for devices, e.g., in information storage and processing technology. Soft x-ray magnetic spectroscopies can make unique contributions to improving our understanding of complex magnetic nanostructures since these techniques provide elemental, valence- and site-symmetry specific information with high sensitivity and tunable probing depth. X-ray magnetic circular dichroism (XMCD) is sensitive to (unidirectional) ferromagnetic order, while x-ray magnetic linear dichroism (XMLD) can also detect (uniaxial) antiferromagnetic order. A crystalline electric field with cubic symmetry induces only a weak angular dependence in XMCD spectra [1] but can cause a very pronounced anisotropy in XMLD spectra [2]. Furthermore, non-magnetic sites with a distorted local cubic symmetry can give rise to an x-ray linear dichroism (XLD). In this presentation, we discuss how to distinguish between the individual contributions to soft x-ray dichroism spectra in order to extract the wealth of information about magnetic thin films, interfaces and hetero- and nanostructures contained in the data [3, 4, 5] We determined the magnetic structure of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO)/La{sub 0.7}Sr{sub 0.3}FeO{sub 3} (LSFO) superlattices with 6 unit cell thick sublayers using soft x-ray magnetic dichroism [5]. Circular dichroism was employed to study the characteristics of the ferromagnetic LSMO layer indicating a reduced magnetic ordering temperature of 200 K compared to the bulk value of 360 K. Linear dichroism is used to analyze the antiferromagnetic order in the LSFO layers which persists up to the bulk Neel temperature near 400 ...
Date: February 1, 2009
Creator: Arenholz, Elke & van der Laan, G.
Partner: UNT Libraries Government Documents Department

Magnetic structure near the Co/NiO(001) interface

Description: We investigate the magnetic coupling at the Co/NiO interface using soft x-ray magnetic linear dichroism (XMLD) and circular dichroism taking explicitly into account the recently observed angular dependence of the XMLD with respect to the crystallographic axes. We find that the Co moments are aligned perpendicular to the NiO moments. We discuss the impact of the anisotropic XMLD on the intensity ratio of the two peaks at the Ni L{sub 2} edge, which is commonly employed to determine the spin orientation in antiferromagnets using XMLD.
Date: August 29, 2008
Creator: Arenholz, Elke; van der Laan, Gerrit & Nolting, Frithjof
Partner: UNT Libraries Government Documents Department