X-ray Diffraction (XRD)






Historical Perspective
1912: Maxwell von Laue first discovered X-ray diffraction
- determined that X-rays would be scattered by atoms in a crystalline solid if there was similarity in the wavelength of X-rays and the interatomic distances of the crystalline material. 
1913: Sir William H. Bragg and and his son Sir W. Lawrence Bragg derived the equation known as Bragg’s Law to define diffraction as a function of the angle of incidence

2d sinq = nl

l = wavelength of the x-ray
q = scattering angle
n = integer representing the order of the diffraction peak
d = inter-plane distance of (i.e atoms, ions, molecules)

-determined why the cleavage faces of crystals appeared to reflect X-ray beams at certain angles of incidence (q).  This is due to constructive interference.   
- simulated the experiment, using visible light and tiny arrays of dots and pinholes to mimic atomic arrangements on a much larger scale.  These experiments provided similar patterns to X-rays but were safer to work with than X-rays. 
1914: von Laue awarded Nobel Prize for discovery of X-ray diffraction by crystals and showing X-rays are electromagnetic waves
1915: Braggs awarded Nobel Prize for their work determining the crystal structure of diamond, NaCl and ZnS.


Celeste Morris, Bradley Sieve and Heather Bullen, Department of Chemistry, Northern Kentucky University, Highland Heights, KY 41099