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Generation and Applications Indus Synchrotrons Utilization Division
Focused X-Ray Beams : Generation and Applications G S Lodha Indus Synchrotrons Utilization Division RRCAT, Indore I thank the organizer of this prestigious colloquium series for asking we to give a talk. There is a significant difference in the theme of this talk from the talks delivered earlier as the audience were from my research field or students. Here I am before distinguished experts in very many fields of science and technology and I need to communicate how bright x-ray beams available from Indus-1 and Indus-2 synchrotron sources can be used in their specific realms of research. The objective is to put forward a case for having Indus synchrotrons facilities as a scientific hub for multidisciplinary research. Communicating the strength of x-ray beams to a set of experts, who already are aware of most of the information , is a rather difficult proposition, but I venture to make a modest effort. I may please be excused, if some of the projections are too elementary, but I thought of including these for building up a base for what I want to drive home. The talk will cover the essential ingredients towards generation of focused x-ray beams and the type of science which can be done using these beam. Then I will give a broad introduction to the Indus synchrotron sources available Raja Rammana Centre for Advanced Technology, Indore and the beamlines available as national facilities. I am glad to share an important milestone at RRCAT, “Indus -1 and Indus-2 synchrotron sources are now available to the users on a round the clock basis, week after week”. With this introduction, in the next 40 minutes, I take you to journey of introducing the topic of generation of focused x-ray beams of micro m to nm and the type of science on can do using these beams. Advances in Science, Engineering and Technology Colloquium TIFR, August 20, 2010
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X-ray Interaction with Matter
Let me start, by refreshing our knowledge of how x-ray interact with matter. Some of the projected figures are taken from the WEB. I have tried to put the required acknowledgements, but I sincerely apologize if I have missed to this at some places. source: Spring-8 web site
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Focused X-ray Beams W.C. Roentgen : Refractive index of all materials ≈ unity Difficult to make an x-ray lens. With the recent availability of extremely bright x-ray sources (synchrotron storage rings, x-ray free electron lasers, …), R&D efforts towards focusing x-rays to smaller and smaller size have become intense. At present it is possible to generate focused x-ray beam of <30 nm, using the reflection, diffraction and refraction phenomena in the x-ray region. When Roentgen realized that the high energy beams had no charge, he immediately concluded that these may be high light beams and started experiments towards reflection and refraction. By measuring the transmission of single crystal rock salt and powdered salt, he concluded that multiple scattering was insignificant, implying that refractive index of all materials was very near to unity. With the significant improvement in technology towards generating brighter x-ray sources and fabrication of optical components, it is now possible to focus beams to <30 nm, with ongoing efforts towards reaching diffraction limited resolution in the x-ray region of the e-m spectrum.
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Optics for X-ray (~10 keV)
Complex refractive index: n=1-δ+iβ Refraction is small: Re(n)=1-δ with δ=10-6 ….10-5 Focal length: f=R/2 (n-1) = R/2δ Absorption is high: absorption lengths 1μm … 10μm Figure of merit: β/δ = 10-5 (Li,Be) …10-3 (C,Al,Si) … (Au,Pt,W) Dilemma smaller f smaller R more flux larger aperture larger R Refractive index very near to unity for all materials. Refraction is very small. Further absorption is very high. For soft x-ray/ VUV region, air also becomes absorbing. Experiments needs to be done in windowless UHV mode. Extremely rich region of the em spectrum as K, L, M photo absorption edges lie in this region.
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Why focus x-ray to sub micron size?
X-ray microscopy: Most materials are heterogeneous at length scale of micron to nm (transmission microscopy, scanning microscopy…). Increased flux: Higher sensitivity due to reduced background. Small samples or samples in different environment (pressure, temperature, magnetic field …) The question is “Why one wants to focus x-ray beams to finer and finer spot size?” One wants to see objects with features that cannot be observed in visible light because of diffraction limited resolution constraints. One can do some of the imaging at much higher resolution using electron beams (TEM, SEM…), but significant limitations due to multiple complex scattering processes.
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General Terminology in X-Ray Optics
Magnification Numerical Aperture Resolution Depth of focus Astigmatism Chromatic Aberration Before I get towards putting the projections of various devices used for focusing x-rays, please permit me to reintroduce a few terminologies which all of you are aware while dealing with visible light optics but looking with a prospective of x-ray beam instead of visible beam.
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Ideal focusing lens: Converts plane wave to a spherical wave, with the conservation of the coherence
In-coherent source Geometric Optics Refraction 1/F = (n-1) (1/Do + 1/Di) Coherent source Wave Optics Phase shift along the optical path For generating x-ray micro/ nano focused beam M~10-2 to 10-4 in synchrotron beamline. Unlike laser sources, most of the x-ray sources are in-coherent. With bright x-ray sources and devices for generating beams with high monocromaticity, one can now generate x-ray beams with high spatial and temporal coherence. With the quality of beams available, the source can be de-magnified by almost This will further improve significantly with the availability forth generation light sources (free electron x-ray lasers), in advanced stage of development in synchrotron light source laboratories. Magnification: M=Di/Do
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Numerical Aperture NA= n Sin θmax NA ~ 0.5 (D/f)
Measure of light collection power NA= n Sin θmax NA ~ 0.5 (D/f) NA is very closely related to performance of the optics (e.g. depth of focus, diffraction limited resolution, flux etc.). Low NA is one of the major constraint for x-ray optics. Improvement of light collection power of the x-ray optical elements is one of the major technological challenge. With significant improvement in micro/ nano fabrication technology availability, it is now possible to overcome this constraint to a great extent.
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Focusing increases the angular spread. Brightness: B= P/ (ΔAs . ΔΩs)
For high photon flux at the focus: High brightness and large numerical aperture Focusing increases the angular spread. Brightness: B= P/ (ΔAs . ΔΩs) P : radiated power; ΔAs :source area ; ΔΩs : source divergence The photon flux at the focus is ~ B. 2 . NA2. η is spot size and η is the efficiency of the optics. Thus the high photon flux at the focus requires high source brightness and large numerical aperture optics. Requirement of high brightness in x-ray region can be meet with third and fourth generation light sources and large numerical aperture by improvement in technology towards fabrication of x-ray optics.
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Rayleigh’s Criterion: Resolution Limit
Point sources are spatially coherent Mutally incoherent Intensities add Rayleigh criterion (26.5% dip) Conclusion : With spatially coherent illumination, objects are “just resolavable” when For higher diffraction limited resolution one needs to use shorter wavelength. source: D. Attwood
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Resolution improves with smaller λ
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Depth of focus Where is a spot size
Depth of focus increases with energy and decreases with focal spot size. This parameter becomes important for 2D and 3D imaging, as this depends on the depth from which x-rays are scattered in the sample and reaching the detector for constructing the image. source: Xradia
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Astigmatism Horizontal and vertical focusing are separated at grazing incidence. fm = (R Sin θ)/2 fs = R/(2Sinθ) Reflection Crossed mirror pair (Kirkpatrick-Baez system) Synchrotron radiation sources or Source Focus or For x-ray reflecting optics, many a times, one is forced to use extreme grazing incidence optics, where astigmatism become a major constraint, thus requiring aspheric grazing incidence optics of very large size (~1.5 m) with very low figure errors and rms roughness. SR sources are usually asymmetric in shape, but for many experiments there is a requirement of symmetric x-ray beams. One of the major breakthrough came about by decoupling the merridonal and sagittal focusing elements, the technique first proposed by Krapatric and Benz in 50’s but has now become extremely powerfull for nano focusing reflecting optics with high NA.
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Chromatic aberration Reflective Optics: Can focus pink beams using grazing incidence optics. Grazing angles can be higher by using x-ray multilayer reflector, but at the cost of limited energy Diffractive Optics : f ~ E , small NA Refractive Optics : f ~ E2
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X-ray Micro focussing optics
Reflective optics Diffractive optics Refractive optics
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X-ray Reflectivity: Single and Multilayer
Single Layer Total external reflection when θ<θc (a few mrad) c = √2 = λ√Z Multilayer Large θ leads to larger acceptance or shorter mirror length. Spectral bandwidth ~ a few %
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X-ray Multilayer Optics
Advantages Layer thicknesses can be tailored Can be deposited on figured surfaces
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Reflective optics Schwarzschild objective Wolter microscope Capillary optics Kirkpatrick-Baez mirrors
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Schwarzschild objective
Near normal incidence with multilayer coating (126 eV) N.A. > 0.1 Imaging microscope source: F. Cerrina (UW-Madison), J. Underwood (LBNL)
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Wolter microscope Use 2 coaxial conical mirrors with hyperbolic and elliptical profile Imaging microscope Difficult to polish for the right figures and roughness Conical optics (hyperbolic and elliptical profile). Parabolic profile can be used under relaxed spot requirements. If spot size requirements are further relaxed, one can use cylindrical approximation SXT planned aboard ASTROSAT.
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Capillary optics One-bounce capillary
Large working distance (cm) Compact: may fit into space too small for K-B Nearly 100% transmission N.A. ~ 2-4 mrad (¡Ü 2θc) Difficult to make submicron spot Multi- bounce condensing capillary Easy to make with small opening (submicron) Short working distance (100 μm) Low transmission Limited acceptance. X-ray beam can be pre focused followed by a capillary reflecting optics for further focusing to micron size. source: D. Bilderback (Cornell)
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Kirkpatrick-Baez mirrors
A horizontal and a vertical mirror arranged to have a common focus Achromatic: can focus pink beam (but not with multilayer coating) Can be used to produce ~ round focal spot Very popular for focusing in the 1-10 μm APS 85x90 nm2 ESRF 45 nm, Spring8 25x30 nm2 (diffraction limit ~ 17 nm)
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Diffractive optics Fresnel zone plates (FZP)
Multilayer Laue Lens (MLL)
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Fresnel zone plates (Phase ZP and Amplitude ZP)
Efficiency of an amplitude ZP with opaque zones ~ 10% Efficiency of a phase ZP with π-phase shift ~ 40% Phase For a phase shift of For phase zone plates, the thickness of the material in the material should be such that it introduces a phase difference of phi, between the blocked and unblocked portion. The resolution is dependent the smallest zone width one can make, with the required aspect ratio. As delta decreases (hard x-rays), deta t increases, thus one needs zone plates with very high aspect ratio. One uses x-ray lithography to fabricate high aspect ratio zone plates required for hard x-ray focusing.
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Fabrication Fresnel zone plates
E Anderson, A Liddle, W Chao, D Olynick and B Harteneck (LBNL)
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Hard X-ray ZP: recently available
W. Yun (Xradia) Δr = 24 nm, 300 nm thick, Aspect Ratio = 12.5 (Xradia) Aspect ratio > 100 is probably difficult to achieve with lithographic zone plates!
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Multilayer Laue Lens (MLL)
For high aspect ratio Aspect ratio > 1000 (Δr = 5-10 nm, 10 μm thick) demonstrated Source : A. Macrander (APS)
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Refractive optics Compound refractive lens (CRL) f = R/2N
Small aperture Small focusing strength Strong absorption E>20keV f = R/2N R radius (~200 m) N number of lenses (10 …300) real part of refractive index (10-5 to 10-6) 2R0 800 m m d 10 m -50 m Parabolic profile : No spherical aberration Refractive index in x-ray region slightly less than unity. For focusing x-ray beam, one needs to use concave lens instead of convex lens. As refraction term is very small (10(-6)), R should be small and N should be large (compound refractive lens). For reduction of spherical aberration, parabolic profile required. Modern micro fabrication technology has allowed development of refracting optics for the generation of nano focused hard x-ray beams (Major development efforts at ESRF). Source : Achen Univ., APL 74, 3924 (1999)
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What is Synchrotron Radiation?
Synchrotron radiation is emitted from an electron traveling at almost the speed of light ( C) and its path is bent by a magnetic field. It was first observed in a synchrotron in Thus the name "synchrotron radiation".
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Generation of Synchrotron Radiation
Synchrotron radiation is emitted at a bending magnet or at an insertion device. Corresponding to the weak and strong magnetic field, there are two types of insertion devices: an undulator and a wiggler.
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General Properties of Synchrotron Radiation
Ultra-bright Highly directional Spectrally continuous (Bending Magnet /Wiggler) or quasi-monochromatic (Undulator) Linearly or circularly polarized Pulsed with controlled intervals Temporally and spatially stable
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Synchrotron Radiation Spectrum
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Brightness of synchrotron sources
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X-ray Sources: Peak Brilliance
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Synchrotron Radiation(SR) Sources…
America: 18 Asia: 25 Europe: 22 Oceania: 1 IV generation light sources under construction/ planning stage.
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A Typical Synchrotron Facility
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A typical Synchrotron source
Creating SR light 7/9/2008 (3) Then they pass into the booster ring accelerated to c (4) And are finally transferred into the storage ring A typical Synchrotron source With BM and ID (1) Electrons are generated here (2) Initially accelerated in the LINAC
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Building a Synchrotron Source…
Magnets RF systems LCW Beam physics Power supplies Survey and alignment Health physics Beam diagnostics Cryogenics etc. UHV Controls Fabrication and metrology shop Chemical Cleaning
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Utilization of the properties of the SR beam: A few examples
Microbeam: Diffractometry, microscopy Pulsed Structure : Time-resolved experiments Energy Tunability: Crystal structure analysis, anomalous dispersion High collimation: Various types of imaging techniques with high spatial resolution Linear / circular polarizion : Magnetic properties of materials. High energy X-ray: High-Q experiments, Compton scattering, Excitation of high-Z atoms High spatial coherence: X-ray phase optics and X-ray interferometry
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Application of SR
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Life Science Atomic structure analysis of protein macromolecules
Elucidation of biological functions
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Materials Science Precise electron distribution in inorganic crystals
Structural phase transition Atomic and electronic structure of advanced materials superconductors, highly correlated electron systems and magnetic substances Local atomic structure of amorphous solids, liquids and melts
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Chemical Science Dynamic behaviors of catalytic reactions
X-ray photochemical process at surface Atomic and molecular spectroscopy Analysis of ultra-trace elements and their chemical states Archeological studies
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Earth and Planetary Science
In situ X-ray observation of phase transformation of earth materials at high pressure and high temperature Mechanism of earthquakes Structure of meteorites and interplanetary dusts
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Environmental Science
Analysis of toxic heavy atoms contained in bio- materials Development of novel catalysts for purifying pollutants in exhaust gases Development of high quality batteries and hydrogen storage alloys
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Industrial Application
Characterization of microelectronic devices and nanometer-scale quantum devices Analysis of chemical composition and chemical state of trace elements X-ray imaging of materials Residual stress analysis of industrial products Pharmaceutical drug design
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Medical Application Application of high spatial resolution imaging techniques to medical diagnosis of cancers
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SR Based Research Methods
X-ray Diffraction and Scattering Spectroscopy and Spectrochemical Analysis X-ray Imaging Radiation Effects
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Indus building complex
7/9/2008 Indus building complex
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Synchrotron Complex at RRCAT housing Indus-1 and Indus-2
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Schematic View of Indus Complex
TL-3 TL-1 TL-2 Indus-2, 2.5 GeV SR Trials to store the beam began in December 2005 Indus-1 (450 MeV, 100 mA) (Working since 1999) Booster Synchrotron (700 MeV) (Started in 1995) Microtron (20 MeV) (Started in 1992)
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Indus-1 Storage Ring
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Schematic representation of experimental hall
Five beamlines have been operational. Several publications (~50) have resulted from utilization of these beamlines. X-ray absorption and Infra red spectroscopy beamlines under installation
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Beamlines operational on Indus-1
Range (nm) Beamline Optics λ/ Δλ Experimental station Pre and Post mirror Monochromator Reflectivity (RRCAT) 4-100 Au coated Toroidal 1.4 m TGM with three gratings ~400 Reflectometer and time of flight mass spectrometer Angle Integrated PES (UGC-DAE-CSR) 6-160 Pt coated Toroidal 2.6 m TGM with three gratings ~600 Hemi-spherical analyzer (HSA) Angle Resolved PES (BARC) 1.4 m TGM with three gratings Angle resolved HSA electron analyzer Photo Physics (BARC) 50-250 1 m Seya-Nomioka ~1000 Absorption cell , sample manipulator High resolution VUV (BARC) 70-200 Au coated cylindrical 6.65 m off plane Eagle mount spectrometer ~70000 High temperature furnace, absorption cell
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Recent studies using Indus -1
Reflectivity near absorption edge energies Hydrogen bond braking near absorption edge energies Interface studies Photo dissociation spectroscopy X-ray multilayer optics and optical response in soft x-ray region X-ray Telescope Calibration
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Indus-2 beamlines Installed being installed/ under construction
BM Beamlines BL# Groups ADXRD (commissioned) BL-12 RRCAT EDXRD (commissioned) BL-11 BARC EXAFS (commissioned) BL- 8 GIMS ( being installed) Bl-13 SINP PES (being installed) BL-14 Under Construction BM MCD/PES BL-1 UGC-DAE-CSR Imaging BL-4 BARC + ARPES/PEEM BL-6 White-beam lithography BL-7 Scanning EXAFS BL-9 XRF-microprobe BL-16 SWAXS BL-18 Protein Crystallography BL-21 X-ray diagnostics BL-23 Visible diagnostics BL-24 Soft X-ray BL-26 being installed/ under construction Installed
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X-ray Multilayer Deposition Laboratory
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Reflectivity Beamline Indus-1
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Normal incidence soft x-ray reflector: Mo/Si multilayer
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X-ray calibration: Soft X-ray Telescope
ASTROSAT :One of the most ambitious space astronomy programme initiated by Space Science Community in India. Payload of soft x-ray imaging telescope (SXT) sensitive to 0.3 to 8 keV is planned. Performance of SXT grazing incidence foil mirrors evaluated using Indus-1 soft x-ray reflectivity beamline Archana et al Experimental Astronomy (2010) 28:11-23
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Soft & Deep X-ray Lithography (SDXRL) beamline -BL7
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SDXRL beamline - Applications
MEMS (Micro-Gears, …) Zone Plate Ø Fabrication of Hard x-rays optics Ø Small periodicity gratings Ø Micro Electro Mechanical Systems (MEMS) Ø Photonic band gap crystals (for visible radiation) Ø Quantum wires and quantum dots devices (high density pattering over large areas) Ø Fabrication of high density hetrostructures for nano devices High aspect ratio micro-structures
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SDXRL beamline – Present Status
Primary slits Installed beamline inside hutch X-ray mirrors with manipulators X-ray Scanner
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BL16 Beamline Front End Beamline optics KB mirror Pre-DCM section DCM
Indus-2 beamlines BL16 Beamline Front End Beamline optics DCM Beam transport pipes and vacuum components Front end exit KB mirror Pre-DCM section
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X-ray Microprobe beamline
Indus-2 beamlines X-ray Microprobe beamline Beamline optics Post-DCM section DCM Optics table Beam transport pipes and vacuum components
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Road Ahead…. A modest start has been done at RRCAT with the availability of synchrotron radiation sources Indus-1 and Indus-2. These sources are being operated on a round the clock basis, week after week. Few x-ray beamlines have become operational, with many more in implementation stage. These are national science facilities. Users from various fields are welcome to plan research using these facilities, which will significantly help us to improve the performance further. It will be our endeavor to support all users of this national facility.
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All are welcome to Indus SR Facility
Thank you
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Acknowledgements:
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X-ray Diffraction and Scattering
Research Methods Typical Examples of Research Subjects Macromolecular crystallography ( I-2) Atomic structure and function of proteins. X-ray diffraction under extreme conditions (I-2) Structural phase transition at high pressure / high or low temperature X-ray powder diffraction (I-2) Precise electron distribution in inorganic crystals Surface diffraction (I-2) Atomic structure of surfaces and interfaces. Phase transition, melting, roughening, morphology and catalytic reactions on surfaces Small angle scattering (I-2) Shape of protein molecules and biopolymers. Dynamics of muscle fibers X-ray magnetic scattering Magnetic structure. Bulk and surface magnetic properties X-ray Optics X-ray interferometry. Coherent X-ray optics. X-ray quantum optics
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Spectroscopy and Spectrochemical Analysis
Research Methods Typical Examples of Research Subjects Photoelectron spectroscopy (I-1) Electronic structure of advanced materials such as superconductors, magnetic substances, and highly correlated electron systems. Atomic and molecular spectroscopy (I-1) Photoionization spectra, photoabsorption spectra and photoelectron spectra of neutral , atoms and simple molecules. Spectra of multicharged ions. X-ray fluorescence spectroscopy (I-2) Ultra-trace element analysis. Chemical states of trace elements. Archeological and geological studies. X-ray absorption fine structure (I-2) Atomic structure and electronic state around a specific atom in amorphous materials, thin films, catalysts, metal proteins and liquids. X-ray magnetic circular dichroism (I-2) Magnetic properties of solids, thin films and surfaces. Orbital and spin magnetic moments. Infrared spectroscopy (I-2) Infrared microspectroscopy. Infrared reflection and absorption spectroscopy. X-ray inelastic scattering Electronic excitation. Electron correlations in the ground state. Phonon excitation.
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X-ray Imaging Research Methods Typical Examples of Research Subjects
Refraction-contrast imaging (I-2) lmaging of low absorbing specimens. X-ray fluorescence microscopy (I-2) Imaging of trace elemental distribution with a scanning X-ray microprobe. X-ray microscopy (I-2) Imaging of materials by magnifying with microfocusing elements. X-ray topography (I-2) Static and dynamic processes of crystal growth, phase transition and plastic deformation in crystals. Crystal lattice imperfections. Photoelectron emission microscopy (I-2) Element-specific surface morphology. Chemical reaction at surface. Magnetic domains.
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Radiation Effects Research Methods
Typical Examples of Research Subjects Material processing (I-2) Soft X-ray CVD. Microfabrication. Radiation biology (I-2) Radiation damage of biological substances.
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Mo/Si soft x-ray Polarizer multilayer
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