Transcript Document
Synchrotron Radiation for Material Analysis M. Aslam Baig National Center for Physics Quaid-i-Azam University Campus, Islamabad Pakistan [email protected] [email protected] 1 X-ray ray tubes Vacuum tube K HV X-rays Cathode Electrons Intensity (a. u.) Anode Characteristic radiation min 0.02 Filament supply K 0.04 0.06 Bremsstrahlung radiation 0.08 0.10 Wavelength (nm) The spectrum from an X-ray tube has discrete fluorescent lines superimposed on the continuous bremsstrahlung radiation Energy Dissipation 4 How a Storage Ring Works How does it work? Electrons are generated here And initially accelerated in the LINAC BAIG, Karachi, 7th. January, 2005 Synchrotron radiation angular distribution Electron orbit Electron orbit Acceleration v Acceleration e- e- v << c m0 = electron mass v = electron velocity E = electron energy c = velocity of light Q m0c2/E = 1/g rad vc v Radiation angular distribution (a) electrons travelling at low speed (b) electrons travelling at relativistic speed (g = (1-v2/c2)-1/2 10000 at ESRF) Time structure Light pulses e - e - e- e- I 100 ps t 1ms Time pulsed emission is interesting for studying rapid reactions From the magnetic device to the experimental station Synchrotron storage ring 300 m 5m Spectrometer Focusing device Undulator Monochromator 30 m 2m 10 m Als-Nielsen Introduction to Modern X-ray Physics Why is it special? Why is wavelength important? sample sample Visible light X-rays To penetrate a sample, you need a wavelength of similar, or smaller magnitude. Fluorescence Elemental analysis I Detector X-rays Sample wavelength Absorption m 2.0 1.0 X-rays Sample Detector 0.0 8800 9000 9200 9400 9600 E (eV) Energy Imaging X-rays Detector 9800 10000 The absorption coefficient μ t I0 I I = I0 exp(-μt) linear absorption coefficient α = μt = ln ( I0/I ) 12 X-ray Absorption Fine Structure Zinc K-edge 3.0 mt(E) (arb. units.) 2.5 2.0 1.5 1.0 0.5 9.4 9.6 9.8 10.0 10.2 10.4 10.6 Energy (keV) 13 Extended X-ray absorption fine structure (EXAFS) In condensed matter the ejected photoelectron (wave) will be scattered by neighbouring atoms. It is the interference between the outgoing electron and the back-scattered ones which leads to oscillations visible in the absorption spectrum above the edge. Extended X-ray absorption fine structure (EXAFS) Lab data took over 12 hours to collect. Synchrotron data took 25 minutes and could have been collected in about 3. Taken from: “Introduction to Powder Diffraction” By: R J Cernik Powder Diffraction Fe compounds XANES can be used simply as a fingerprint of phases and oxidation state. 18 FLASH – Light Source 19 Photoionization of Neon Richter et al PRL 102, 163002, 2009 20 Xenon Ions 21 Rel. Signal Intensity (arb. units) Surface analysis of superconducting materials Sr Ca 6.0 Bi1.7 Pb0.4 Sr2 Ca2 Cu2 O4 Cu2O Mg 3.0 SrO CaO Ca2CuO3 SrCaO2 Pb/Bi 0.0 0 100 200 300 Mass / charge (m/q) Baig et al J.Appl. Phys. 2009 22 Future……. • Prospects for Pakistan SESAME • Synchrotron Radiation Facility being built in Amman, Jordan