X-Ray Spectroscopy.pptx

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1. X-Ray Spectroscopy

2. INTRODUCTION GENERATION OF X-RAYS X-RAY TECHNIQUES PRINCIPLE INSTRUMENTATION APPLICATIONS CONCLUSIONS ACHIEVEMENTS REFERENCES CONTENTS

3. INTRODUCTION: X-rays are discovered by Wilhelm Roentgen who called them x-rays because the nature at first was unknown so, x-rays are also called Roentgen rays. X-ray diffraction was discovered by Max. The wavelength range is 10 -7 to about 10 -15 m. 3

4. The penetrating power of x-rays depends on energy also, there are two types of x-rays. i ) Hard x-rays : which have high frequency and have more energy. ii) soft x-rays : which have less penetrating and have low energy

5. X-ray spectroscopy is based on the measurement of emission, absorption, scattering, fluorescence and diffraction of electromagnetic radiation. X-ray fluorescence and X-ray absorption widely used for qualitative determination.

6. X-RAYS 1 .X-rays are short wave length electromagnetic radiations produced by the deceleration of high energy electrons or by electronic transitions of electrons in the inner orbital of atoms 2 .X-ray region 0.1to100 A ˚ 3 .Analytical purpose 0.7 to 2 A ˚ (0.1-25) 6

7. GENERATION OF X-RAYS By bombarding matter by High energy electrons X-ray photons (secondary beam of X-Ray fluorescence) By use of radioactive source From synchrotron radiation Cornell-high-energy synchrotron radiation laboratory Stanford synchrotron radiation laboratory Brookhaven national laboratory 7

8. Source of X-rays as vacancy filled by cascade of electrons from lower energy levels 8

9. Characteristic Radiation 9

10. 10

11. Continuous Radiation 11

12. Tube Spectrum X-ray sources often produce both continuous and discontinuous (line) spectra. Both are of use in analysis. Bremsstrahlung Characteristic Spectrum (target dependent) l min 12

13. Continum results from collision between electrons of the beam and atoms of target metal. At each collision, electron is decelerated and aphoton of X-ray is produced. Energy is equal to the difference in kinetic energy of electron before and after. Max. X-ray energy = Max. electron energy

14. X-RAY TECHNIQUES X-RAY FLOURESCENCE METHOD X-RAY DIFFRACTION METHOD X-RAY ABSORPTION METHOD 14

15. X-ray fluorescence spectrometry relies on characteristic secondary radiation emitted by materials when excited by a high-energy x-ray source and is used primarily to determine amounts of particular elements in materials. X-ray crystallography relies on the dual wave/particle nature of x-rays to discover information about the structure of crystalline materials. X-ray radiography is used for creating images of light-opaque materials relies on the relationship between density of materials and absorption of x-rays. Applications include a variety of medical and industrial applications.

16. X-Ray Fluorescences The absorption of X-rays produces electronically excited ions that return to their ground state by transitions involving electrons from highier energy levels.

17. RAY DIFFRACTION

18.   Max Theodor Felix von Laue (9 October 1879 – 24 April 1960) was a German physicist who won the Nobel Prize in Physics in 1914 for his discovery of the diffraction of X-rays by crystals . 18

19. Diffraction of X-Rays The electric vector of the radiation interacts with the electrons in the atoms of the matter to produce scattering. When X-rays are scattered by the ordered environment in a crystal, constructive and destructive interference occurs among the scattered rays because the distance between the scattering centers are of the same order of magnitude as the wave length of the radiation. Diffraction results.

20. PRINCIPLE X-ray diffraction is based on constructive interference of monochromatic x-rays and a crystalline sample. These x-rays are generated by a cathode ray tube, filtered to produce monochromatic radiation ,collimated to concentrate and directed towards the sample. The interaction of incident rays with the sample produces constructive interference when conditions satisfy Bragg’s law. 20

21. Bragg’s law When an X-ray beam strikes a crystal surface at some angel θ . Part of the beam is scattered by the layer of atoms at the surface. The unscattered part of the beam penetrates to the second layer of the atoms where again a fraction is scattered. The remainder passes on to the third layer and so on. Cumulative effect of the scattering results diffraction.

22. The requirements for diffraction are Spacing between layers of atoms must be roughly the same as the wave length of the radiation The scattering centers must be spatially distributed in a highly regular way. In 1912, W. L. Bragg treated the diffraction of X-rays by crystal. A narrow beam of radiation strikes the crystal surface at angle θ . Scattering results as a result of interaction of radiation with atom located at O, P and R.

23. BRAGG’s EQUATION William Henry Bragg 1862 – 1942 Nobel Prize in Physics 1915

24. d     dSin  The path difference between ray 1 and ray 2 = 2d Sin For constructive interference: n = 2d Sin Ray 1 Ray 2  Deviation = 2  24 A B O P R C D

25. If AP+PC=n λ Where n is an integer, The scattered radiation will be in phase at OCD, and the crystal will appear to reflect the X-radiation. But AP=PC=d sin θ Where d is the interplaner distance of the crystal. Thus, the conditions for consructive interference of the beam at angle θ are n λ =2d sin θ . X-rays appear to be reflected from the crystal only if the angle of incidence satisfies the condition sin θ = n λ /2d. At other angles, destructive interference occurs.

26. “ Constructive interference of the reflected beams emerging from two different planes will take place if the path lengths of two rays is equal to whole number of wavelengths”. for constructive interference, n λ =2dsin Ф this is called as BRAGG’S LAW 26

27. The Bragg Equation where n is an integer  is the wavelength of the x-rays d is the interplanar spacing in the specimen  is the diffraction angle (discussed later!) The Bragg equation is the fundamental equation, valid only for monochromatic X-rays, that is used to calculate interplanar spacings used in XRD analysis.

28. Diffractometer Components and Geometry

29. Our Scintag Diffractometer (Pt. 1)

30. Scintag Diffractometer Geometry

31. Spellman DF 3 Solid State High-voltage generator power supply Scintag Diffractometer HV Power Supply

32. Bicron Scintillation Detector and Monochromator Scintag Diffractometer Detector

33. From right to left: Power module Bias Power Supply Signal Amplifier Ratemeter (counter) Scintag Diffractometer Detector Power Supply

34. Instrument components Absorption, emission, fluorescence and diffraction of X-rays. Instruments for these application contain components that are analogous in function to the five components of instruments for optical spectroscopicmeasurements .

35. A source A device for restricting the wavelength range of incident radiation A sample holder A radiation detector/ transducer A signal processor and readout Components differ considerably in detail from the corresponding optical components. However functions are the same. The ways they combine to form instruments are often similar to optical spectrophotometer. First using filter Second using monochromator - to transmit desired wavelength In addition a third method is available for obtaining information about isolated portions of an X-ray spectrum. Isolation is achieved by electronically with devices that discriminate among various parts of a spectrum based on energy rather than wavelength of radiation

36. Thus, X-ray instruments are often described as wavelength-dispersive instruments Or energy-dispersive instruments depending on the method which the resolve the spectra.

37. INSTRUMENTATION Production of x-rays Collimator Monochromator a.Filter b.Crystal monochromator Detectors a.Photographic methods b.Counter methods Geiger muller tube counter Proportional counter Scintillation counter Solid state semi-conductor detector Semi-conductor detectors 37

38. Instrumentation of XRD 38

39. PRODUCTION OF X-RAYS: X-rays are generated when high velocity electrons impinge on a metal target. Approximately 1% of the total energy of the electron beam is converted into x-radiation. The remainder being dissipated as heat. Many types of x-ray tubes are available which are used for producing x-rays. 39

40. Source Tubes ( coolidge tube) Radio isotopes Secondary fluorescences

41. X-ray tube  Filament (Tungsten)  Target metal (Cu, Cr) Electrons are accelerated by a potential of about 55,000 Volts Typical wavelengths used for X-ray experiments lie between 0.6 and 1.9Å. X-ray Tube 41

42. X-rays are generated by directing an electron beam on to a cooled metal target. Beryllium is transparent to X-rays (on account of the small number of electrons in each atom) and is used for the windows. X-ray Tube ( Continue ) 42

43. X-ray production at instrumental level 16

44. Coolidge tube   It consists of a Cathode which is a filament of tungsten metal heated by a battery B to emit the thermoionic electrons . This beam of electrons constitutes the cathode ray stream . The anode consists of a heavy block of copper with a metal target plated on or embedded in the surface of copper. The target metals as tungsten, chromium, copper, molybdenum, rhodium scandium, silver, iron and cobalt If a positive voltage in the form of an anode(target) is kept near these electrons , the electrons are accelerated towards anode . On striking the anode, electrons transfer their energy to its metallic surface which then gives off X-rays . 15

45. Radio isotopes 55 Fe 26 , 57 Co 27 , 109 Cd 48 , 125 I 53 , 147 Pb 82 Secondary fluorescent sources: X-rays with a tungsten target could be used to excite the k α and K β lines of molybdenum.

46. X-ray monochromators Consists of a pair of beam collimators, which serve the same purpose as the slits in an optical instrument and a dispersing element mounted on a gonimeter or rotatable table. Permits variation and precise determination of angle between crystal face and the collimated incident beam. According to bragg’s law wave lengths are diffracted.

47. COLLIMATOR: In order to get a narrow beam of x-rays, the x-rays generated by the target material are allowed to pass through a collimator which consists of two sets of closely packed metal plates separated by a small gap. The collimator absorbs all the x-rays except the narrow beam that passes between the gap. 47

48. TYPES OF MONOCHROMATORS In order to do monochromatization,2 methods are available 1.Filter 2.Crystal monochromator a)Flat crystal monochromator b)Curved crystal monochromator Materials used- Nacl,LiF,quartz etc,. 48

49. DETECTORS The x-ray intensities can be measured and recorded either by photographic or counter methods. Both these types of methods depends upon ability of x-rays to ionize matter and differ only in the subsequent fate of electrons produced by the ionizing process. 49

50. DETECTORS Photographic methods D= logIo /I Counter methods Geiger- muller tube counter Proportional counter Scintillation detector Solid-state semi-conductor detector Semi conductor detectors:si (Li) & Ge (Li) 50

51. A) photographic method: In order to record position and intensity of x-ray beam a plane cylindrical film is used. The film after exposing to x-rays is developed,the blackening of the developed field is expressed in terms of density units D given by D=logIo/I D is related to the total x-ray energy that causes the blackening of the photographic film and measured by densitometer. . 51

52. B) Counter methods: These are of many types, like Geiger-muller tube counter Proportional counter Scintillation counter Solid-state semiconductor detector Semiconductor detector 52

53. a) Geiger- muller tube counter Filled with inert gases like argon. Positive potential of 800-2500 Volts ADVANTAGES: inexpensive,trouble free detector,higher signal. DISADVANTAGES: used only for counting low rates,efficiency falls off rapidly at λ <1A°,cannot be used to measure energy of ionising radiation. 53

54. b) Proportional counter: Construction is similar to Geiger-tube counter only but proportional counter is filled with a heavier gas like xenon or krypton. Heavier gas is preferred because it is easily ionised . 54

55. c) Scintillation counter In this detector, there is a large sodium iodide crystal activated with a small amount of thallium. When x-rays incident upon crystal, the pulses of visible light are emitted which can be detected by photomultiplier tube. 55

56. SCINTILLATION DETECTOR 56

57. d)Solid state semi-conductor detector The electrons produced by X-ray beam are promoted into conduction bands and the current which flows is directly proportional to the incident X-ray energy . Disadvantage: Mainted at very low Temp to minimise the noise and prevent deterioration of the detector. 57

58. e) Semi-conductor detectors When x-ray falls on a semiconductor or a silicon lithium-drifted detector,it generates an electron(-e) and a hole(+e) in a fashion analogous to the formation of a primary ion pair in a proportional counter. The principle is similar to that of gas ionization detector as used in a proportional counter, except that the materials used are in a solid state. 58

59. X-RAY DIFFRACTION METHODS These are generally used for investigating the internal structures and crystal structures of various solid compounds. They are 1.Laue’s photographic method a)Transmission method b)Back reflection method 2.Bragg’s X-ray spectrometer method 3.Rotating crystal method 4.Powder method 59

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61. b)Back-reflection method This method is similar to Transmission method . However, black-reflection is the only method for the study of large and thick specimens. Disadvantage: Big crystals are required 61

62. 2)Bragg’s x-ray spectrometer method : This method is based on Bragg’s law, bragg analysed the structures of Nacl,KaI and ZnS . 62

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65. APPLICATIONS Structure of crystals Polymer characterisation State of anneal in metals Particle size determination Spot counting method Broadening of diffraction lines Low-angle scattering 5.Applications of diffraction methods to complexes Determination of cis-trans isomerism Determination of linkage isomerism 6.Miscellaneous applications 65

66. 1.STRUCTURE OF CRYSTALS a -x-ray pattern of salt Nacl b -x-ray pattern of salt Kcl c -x-ray pattern of mixture of Nacl &Kcl d -x-ray pattern of a powder mixed crystal of Nacl & Kcl 66

67. 2.POLYMER CHARACTERISATION Determine degree of crystanillity Non-crystalline portion scatters x-ray beam to give a continuous background(amorphous materials) Crystalline portion causes diffraction lines that are not continuous.(crystalline materials) 67

68. 3.State of anneal in metals: XRD is used to to test the metals without removing the part from its position and without weakening it. 4.PARTICLE SIZE DETERMINATION Spot counting method: v=V. δθ . cos θ /2n V =volume of individual crystallite V=total volume irradiated n=no. of spots in diffraction ring δθ =divergence of x-ray beam 68

69. APPLICATIONS OF DIFFRACTION METHODS TO COMPLEXES a)Determination of cis -Trans Isomerism : Bis (pyridine-2-carboxamido) nickle (II) chloride b)Determination of linkage isomerism : Biuret+copper (II)= pottassiumbis ( biureto ) cuprate (II) tetrahydrate 69

70. MISCELLANEOUS APPLICATIONS Soil classification based on crystallinity Analysis of industrial dusts Assessment of weathering & degradation of minerals & polymers Study of corrosion products Examination of tooth enamel & dentine Examination of bone state & tissue state Structure of DNA&RNA 70

71. CONCLUSIONS For materials including metals, minerals, plastics, pharmaceuticals and semiconductors XRD apparatus provide highly accurate tools for non-destructive analysis. The diffraction systems are also supported by an extensive range of application software 71

72. X-ray diffraction pattern for a single alum crystal.  Image by Dr H. J. Milledge , Department of Geology,   University College, London

73. X-ray diffraction image of a crystal of lysozyme 73

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76. θ - 2 θ Scan The θ - 2 θ scan maintains these angles with the sample, detector and X-ray source Normal to surface Only planes of atoms that share this normal will be seen in the θ - 2 θ Scan 76

77. Sample Type Single Crystal Sample is placed in a beam and the reflections are observed for specific orientations Time consuming and difficult to orient the crystal Powder Sample Many small crystallites with random orientations Much easier to prepare and one can see reflections in all directions 77

78. X-ray diffraction by a single crystal 78

79. This is the principle behind X-ray diffraction (XRD) in which an X-ray of known wavelength is focussed onto a crystal that can be aligned until a diffraction pattern is created. A blanker on the optical access blocks the transmitted wavelengths. 79

80. An XRD pattern of silicon crystal 80

81. Analyzing a powder sample 81

82. If multiple minicrystals are diffracted the resultant pattern will be a set of distinct concentric rings, not discreet spots. 82

83. Formation of a powder pattern 83

84. A powder pattern of a crystalline is its “fingerprint” 84

85. Smaller Crystals Produce Broader XRD Peaks

86. A modern Diffractometer 86

87. XRD 3003 PTS 87

88. /2 Example Polycrystalline sample has a number of peaks due to mixture of crystal orientations. 10 20 30 40 50 60 70 80 90 100 2000 4000 6000 Polycrystalline Silicon Powder Intensity (counts/sec) 2Q 88

89. Diffraction Pattern Diffraction patterns are a plot of intensity vs  89

90. Analytical applications of PXRD Identification of unknowns. Phase purity. Determination of lattice parameters. Determination of crystalline size. Quantitative Analysis Structure determination and refinement. Residual stress Texture analysis 90

91. Analytica Chimica Acta 538 (2005) 291–296 91

92. Bruker's X-ray Diffraction D8-Discover instrument

93. 1895 W.C. Roentgen discoversed X-rays ( Nobel Prize 1901 ) 1910 Max von Laue: Diffraction Theory ( Nobel Prize: 1912 ) 1915 W.L. Bragg & W.H. Bragg: NaCl , KCl ( Nobel Prize Physics ) 2 • d • sin Θ = n • λ 1934 D. Bernal & D. Crowfoot examine first Proteins 1950 DNA double helix structure: Watson, Crick, Wilkins ( Nobel Prize 1963 ) 1958 Myoglobin Structure ( Nobel Prize 1962 Kendrew, Perutz) 1971 Insulin (Blundell) 1978 First Virus Structure (S.C Harrison) 1988 Nobel Prize : Photosynthetic reaction center (Huber, Michel, Deisenhofer) 1997 Nobel Prize : ATP- synthase structure (Walker) 1997 Nucleosome core particle (T. Richmond) 1999 Ribosome Structures ( Steitz , …) 2000 Reovirus core structure (S.C. Harrison) 2000 Rhodopsin structure, GPCR ( Palczewski et al.) 2002 ABC-Transporter (D. Rees et al.) 2003 R.MacKinnon : structures of ion channel ( Nobel Prize Chemistry 2003 ) X-Ray diffraction achievements 48

94. REFERENCES 1)Instrumental methods of chemical analysis ,B.K.sharma,17 th edition 1997-1998,GOEL publishing house.page no:329-359 2)Principles of instrumental analysis,5 th edition ,by Dougles a.skoog,f.James holles,Timothy A.Niemen.page no:277-298 3)Instrumental methods of chemical analysis , Gurudeep R.chatwal,sham k.anand,Himalaya publications page no:2.303-2.332 4) Instrumental Methods Of Chemical Analysis – H. Kaur pg.no:727-729,737 5) http://www.scienceiscool.org/solids/intro.html 6) http://en.wikipedia.org/wiki/X-ray_crystallography 94