Intensity of diffraction • Scattering by a unit cell Atomic scattering factor Structure factor Interpretation of diffracted intensities The Lorentz polarization factor The structure factor The multiplicity of the reflecting planes The sampling geometry Absorption effects -Temperature ●Software 6
Intensity of diffraction • Scattering by a unit cell – Atomic scattering factor – Structure factor • Interpretation of diffracted intensities – The Lorentz polarization factor – The structure factor – The multiplicity of the reflecting planes – The sampling geometry – Absorption effects – Temperature • Software 6
An electron scatters the incident X-ray beam to all directions in space. (p.59 of textbook) (Thomson equation) 2 Scattered spherical K=7.94x0-30m2 wave Lorentz polarization factor Incident wave 7
An electron scatters the incident X-ray beam to all directions in space. 7 K = 7.94x10-30 m 2 (Thomson equation) Lorentz polarization factor (p.59 of textbook)
Scattering by an atom (p.59 of textbook) Atomic scattering factor ()describes how efficiently an atom is scattering in a given direction. I= amplitude of the wave scattered by one atom amplitude of the wave scatter by one electron 80.0 70.0E (Z,0,) 60.0E 50.0f f0) 40.0F 30.0f Fe 20.0 Al 10.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Sin()/A-] 8
8 Scattering by an atom Atomic scattering factor (f): describes how efficiently an atom is scattering in a given direction. (p.59 of textbook) (~Z, , )
Scattering by the unit cell The type of unit cell influences the intensity of the diffracted beam but not the direction of the diffracted beam. Base-centered Body-centered 9
Scattering by the unit cell • The type of unit cell influences the intensity of the diffracted beam but not the direction of the diffracted beam. 9 Base-centered Body-centered
doo1 B Diffracted waves from the(001)and(002)crystal planes are 180 out of phase and will cancel each other out for body-centered cell. 10
10 Diffracted waves from the (001) and (002) crystal planes are 18 0 o out of phase and will cancel each other out for body-centered cell