Post on 22-Dec-2015
X-Ray Diffraction as a Materials Characterization Technique
By: Omar AlshehriWaterloo, ONSpring 2010
oalshehri@ksu.edu.sa
Outlines
• History.• Must-have basics.• How x-rays are generated?• How characterization is done?• Applications.• The $1 x-ray source.• Conclusion.
History
• Discovered accidently in November 8th
1895 by Wilhelm Roentgen.• He was awarded the 1st Nobel Prize in
physics [1].• In 1912 Max von Laue invents x-ray
diffraction.• William Lawrence Bragg figured out how
to use x-rays to determine the crystal structures of materials.
Source: [8]
Source: [7]
Source: [7]
Must-Have Basics
• X-ray is a form of electromagneticradiation.
• The energy associated with x-ray is as follows: eV/photon.
• The wavelengths range is0.001<λ<10 nm. NO HARD RULESFOR DETERMINING THIS RANGE [2].
• Therefore, if we plug in λ=0.1 nmwe will get an energy of12,400 eV/photon. How huge is it?
Must-Have Basics (cont.)
Inner shell electron.Nitrogen atom
n=1
n=α
The ionization energy=668 eV.
The ionization energy, the energy to nock out an electron to the vacuum level, for the inner most electrons of nitrogen is 668 eV. Compare it with the 12,400 eV/photon for the 0.1 nm wavelength’s x-ray!!! Very huge [2].
How X-Rays are Generated
• There are three methods to generate x-ray [3]:1- X-ray tube.2- Synchrotron radiation.3- 1 dollar source [4].
Most common in laboratories.
How X-Rays are Generated (cont.)
Filament (Cathode)
Electrons
Target (Anode)
Vacuum Chamber
X-ray
The efficiency of energy conversion from thermoelectrons to x-rays is exteremely low 0.1%
Current
How X-Rays are Generated (cont.)
Filament (Cathode)
X-ray
Target atom: Cu or Mo atom
Emitted electron
Ray or Rays?
How Characterization is Done [5,7]
?
Image Plate~$350K
Benzene Snowflake
Isolated“Benzenes”
Look for e-density onevenly spaced planes.
(or near)
Benzene Snowflake
Isolated“Benzenes”
Closer-spacedplanes give
higher angles.
Look for e-density on (or near)evenly spaced planes.
“Direct” or “Diffraction” or “Real” Space “Reciprocal” Space
Crystal Diffraction Photo
“Unit Cell” Structure Fuzzy Pattern
Crystal Lattice Viewing Holes
Decreasing Spacing Increasing Spacing
How Characterization is Done? (cont.) [5]
How Characterization is Done? (cont.) [6]
Conclusions
• X-ray diffraction is a powerful technique but with many precautions as has harmful radiations.
• As x-ray diffraction has many capabilities, it has limitations that prevent its application.
• Day by day, science is proving it self to be simpler and cheaper than we pretend it!
References• 1- nobelprize.org• 2- Donald Sadoway, 3.091 Introduction to Solid State Chemistry, Fall 2004. (Massachusetts Institute of
Technology: MIT OpenCourseWare). http://ocw.mit.edu (accessed 07, 20, 2010). License: Creative Commons Attribution-Noncommercial-Share Alike.
• 3- Materials Characterization Techniques. By: Zhang, Sam, Li, Lin, and Kumar Ashok. CRC press, 2008.• 4- http://www.nature.com/nature/videoarchive/x-rays/• 5- https://webspace.yale.edu/chem125_oyc/125/LectureSlides/Lect06timed.ppt• 6- http://www.eserc.stonybrook.edu/ProjectJava/Bragg/• 7- https://webspace.yale.edu/chem125_oyc/125/LectureSlides/Lect05timed.ppt• 8- Wikipedia.com