Practical Electron Microscopy and Database

Chapter/Index: Introduction | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Appendix

Coherence in EM Measurements

Table 1218. Coherency of scattered electrons from a specimen in EM (electron microscope) measurements. Coherency Property Coherent In phase: preserves the relative phases of the wavelets scattered from different locations in a material; namely, well-defined phase relationship between incident and scattered radiation Fixed wavelength The resolution for coherent imaging is much worse than that for incoherent imaging Useful for diffraction experiments Incoherent No phase relationship: does not preserve a phase relationship between the incident wave and the scattered wavelets Not useful for diffraction experiments The spatial distribution of the scattered intensity is obtained by summing up the intensities from independent scattering events Incoherent elastic scattering follows the Rutherford scattering law The resolution for incoherent imaging is much greater than that for coherent imaging due to squaring an amplitude distribution Incoherent cases: e.g. difference in wavelength More coherent beam Sharper diffraction pattern can be obtained * When the electrons are treated as waves, their coherency becomes important.