![]() ![]() This always has the index 000.Ĭaution 1: systematic (kinetic) absences appear in electron diffraction patterns just as in X-ray diffraction patterns,įor the same reason: the various features of the lattice or motif diffract electrons in the same direction but the phase factorsįrom the various features cancel, leaving an absence.Ĭaution 2: sometimes where there should be a systematic absence, the spot appears to be still there. Note that the large (strong) spot in the middle is the straight-through beam (the beam which has passed through the sample These make the Ewald sphere diagram look like this so that whole layers of the reciprocal lattice end up projected onto The small electron wavelength also makes the diffraction angles θ small (1-2°) thisĬan be seen by substituting a wavelength of 2.51 x 10 -12 m into the Bragg equation (see Bragg's law in the X-ray Diffraction TLP). The small electron wavelength makes the radius of the Ewald sphere very large (recall its radius is 1/ λ). Lattice direction, as this makes the electron diffraction pattern easier to interpret. Identification of crystalline phases in a sample to orient the sample so that the electron beam is parallel to a low index It should be noted that there is not necessarily always a particular plane oriented like this. The thin sample makes the reciprocal lattice points longer in the reciprocal direction corresponding to the real-space These factors conspire to have a fortunate effect on the Ewald sphere construction (see TheĮwald sphere in the Reciprocal Space TLP) and diffraction pattern: Or less) - it has to be thin so that enough electrons can get through to form a diffraction pattern without being absorbed. Than X-rays, and (2) the sample is very thin in the direction of the electron beam (of the order of 100 nm The two important differences between electron and X-ray diffraction are that (1) electrons have a much smaller wavelength A series of electrons hittingĪn object is exactly equivalent to a beam of electron waves hitting the object and it produces a diffraction pattern in the IntroductionĮlectrons can act as waves as well as particles this is a consequence of quantum mechanics. It is strongly recommended that you read through the TLPs on Diffraction and ImagingĪnd X-ray Diffraction before reading this TLP. Know how to index a diffraction pattern from a sample with a known lattice.Understand why the spots on an electron diffraction pattern appear where they do.Example of indexing with an unknown electron beam orientation.Indexing with the orientation of the electron beam unknown.Example of indexing with a known electron beam orientation.Indexing with the orientation of the electron beam known. ![]()
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