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Xrd

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introduction of XRD

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Xrd

  1. 1. NANOSAINS DAN NANOMATERIAL X-RAY DIFFRACTIONS (XRD) Evi Fitri (3325122134) Universitas Negeri Jakarta 2015
  2. 2. Introduction  X-ray diffraction is used to obtain structural information about crystalline solids.  Useful in biochemistry to solve the 3D structures of complex bio- molecules.  Bridge between physics, chemistry, and biology. X-raydiffractionis important for  Solid-state physics  Biophysics  Medical physics  Chemistry and Biochemistry
  3. 3.  Mostuseful in the characterisation of crystalline materials; Ceramics, metals, intermetallics, minerals, inorganic compounds  Rapid and nondestructive techniques  Provide information on unit cell dimension Structural Analysis  X-ray diffraction provides most definitive structural information  Interatomic distances and bond angles What is XRD ?
  4. 4. Electromagnetic Spectrum  Beams of electromagnetic radiation  *smallerwavelength than visible light,  *higher energy  *more penetrative What Is X-Rays ?
  5. 5. History of X-Ray Diffraction Wilhelm Conrad Röntgen discovered 1895 the X-rays. 1901 he was honoured by the Noble prize for physics. In 1995 the German Post edited a stamp, dedicated to W.C. Röntgen.
  6. 6. History of X-Ray Diffraction  (1895) X-rays discovered by Roentgen  (1914) First diffraction pattern of a crystal made by Knippingand von Laue  (1915) Theory to determine crystal structure from diffraction pattern developed by Bragg.  (1953) DNA structure solved by Watson and Crick  Now Diffraction improved by computer technology; methods used to determine atomic structures and in medical applications The First X-Ray
  7. 7. X-Ray Production • The prime componen in X-Ray tube are filamen (catode), vacum room, anode, and high voltage • When high energy electrons strike an anodein a sealed vacuum, x-raysare generated. Anodes are often made of copper, iron or molybdenum. • High energy electron come from heated filamen in X-Ray tube. • X-rays are electromagnetic radiation. • They have enough energy to cause ionization.
  8. 8. Generation of X-Rays
  9. 9. Bragg’s Law n λ = 2d sin θ English physicists Sir W.H. Bragg and his son Sir W.L. Bragg developed a relationship in 1913 to explain why the cleavage faces of crystals appear to reflect X-ray beams at certain angles of incidence (theta, θ). The variable d is the distance between atomic layers in a crystal, and the variable lambda l is the wavelength of the incident X-ray beam; n is an integer. This observation is an example of X-ray wave interference (Roentgen strahl interferenzen), commonly known as X- ray diffraction (XRD), and was direct evidence for the periodic atomic structure of crystals postulated for several centuries.
  10. 10. Bragg’s Law The Braggs were awarded the Nobel Prize in physics in 1915 for their work in determining crystal structures beginning with NaCl, ZnS and diamond.
  11. 11. Bragg’s Law Constructive interference occurs only when  n λ = AB + BC  AB=BC  n λ = 2AB  Sin θ =AB/d  AB=d sin θ  n λ = 2 d sin θ  λ = 2 d sin θ
  12. 12. How Diffraction Works ?  Wave Interacting with a Single Particle  Incident beams scattered uniformly in all directions  Wave Interacting with a Solid  Scattered beams interfere constructively in some directions, producing diffracted beams  Random arrangements cause beams to randomly interfere and no distinctive pattern is produced  Crystalline Material  Regular pattern of crystalline atoms produces regular diffraction pattern.  Diffraction pattern gives information on crystal structure
  13. 13. Components XRD  X-ray source  Device for restricting wavelength range “goniometer”  Sample holder  Radiation detector  Signal processor and readout
  14. 14. How XRD works ?  A continuous beam of X-rays is incident on the crystal  The diffracted radiation is very intense in certain directions These directions correspond to constructive interference from waves reflected from the layers of the crystal  The diffraction pattern is detected by photographic film
  15. 15. How XRD works: Bragg’s Law  The beam reflected from the lower surface travels farther than the one reflected from the upper surface  If the path difference equals some integral multiple of the wavelength, constructive interference occurs  Bragg’s Law gives the conditions for constructive interference
  16. 16. How Diffraction Works: Schematic
  17. 17. Single Crystal Diffraction Used to determine  crystal structure  orientation  degree of crystalline perfection/imperfections (twinning, mozaicity, etc.) Sample is illuminated with monochromatic radiation  Easier to index and solve the crystal structure because it diffraction peak is uniquely resolved
  18. 18. Single Crystal Diffraction A single crystal at random orientations and its corresponding diffraction pattern. Just as the crystal is rotated by a random angle, the diffraction pattern calculated for this crystal is rotated by the same angle
  19. 19. Single Crystal Diffraction
  20. 20. X-ray Powder Diffraction  More appropriately called polycrystalline X-ray diffraction, because it can also be used for sintered samples, metal foils, coatings and films, finished parts, etc.  Used to determine  phase composition (commonly called phase ID)-what phases are present?  quantitative phase analysis-how much of each phase is present?  unit cell lattice parameters, crystal structure  average crystallite size of nanocrystallinesamples  crystallite microstrainandtexture  residual stress (really residual strain)
  21. 21. X-ray Powder Diffraction A 'powder' composed from 4 single crystals in random orientation (left) and the corresponding diffraction pattern (middle). The individual diffraction patterns plotted in the same color as the corresponding crystal start to add up to rings of reflections. With just four reflection its difficult though to recognize the rings. The right image shows a diffraction pattern of 40 single crystal grains (black). The colored spots are the peaks from the 4 grain 'powder' shown in the middle image.
  22. 22. Applications of X-Ray Diffraction  Determinationof Crystalstructure  Phaseidentification/ transition  Grainsize / micro-strain  Texture/stress( i.e.polymer, fiber )  Determination of thin film composition  Industry Identification of archeological materials
  23. 23. Advantages of XRD  Fastidentification of materials,  Easysample preparation,  Computer-aidedmaterial identification,  Large library of known crystalline structures.
  24. 24. Safetyin XRD  Exposure types o Short-term high-dose o Long-term low-dose  Invisible, odorless,colorless (most exposures undetectable)  Lab users must understand radiation safety issues and pass an exam to use lab  Safeguards present in lab do not substitute for knowledge and following safe procedures
  25. 25. What are the dangerousareas?
  26. 26. Thank you

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