CHEMICAL VAPOR DEPOSITION OF THIN FILM MATERIALS FOR ...

1.2.3.3 X-ray Diffraction (XRD)
X-ray diffraction is a classic technique for crystal structure characterization. X-rays that
can be used to probe the material structures in atomic scale (few angstroms) have wavelengths in
the same order. They usually possess much larger energies than those used for XPS analysis and
are thus called hard X-rays. Generation of these X-rays starts from the bombardment of anode
source materials, such as Cu, Co, Ag, Cr, or Fe etc., with a focused high energy (tens to hundreds
of keV) electron beam. When electrons strike these materials, they are decelerated and a
continuous spectrum of X-ray is emitted known as Bremsstrahlung radiation. High energy
electrons can also knock inner shell electrons out of the atoms and leave vacancies in those shells.
When an outer shell electron falls into the inner shell to fill the vacancy, the excessive energies
left will be relieved by emission of characteristic X-ray photons. The as emitted X-ray possess
the energy (wavelength) characteristic of the shell energy gap of atoms of the source material.
For example, Cu Kα X-ray frequently used in XRD measurement has a wavelength of ~1.5418Å
(~8.04 keV) and Kα here represents the X-ray originating from the action of filling up a vacancy
in K shell by a L shell electron.
Fig. 6. Geometric derivation of Bragg's law.
nλ 2d sin θ (1.12)
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