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 |
