XRD/SAED for a single elemental material has more than one peak/circle. Since the angles obtained from XRD can be converted to d-spacing by Bragg` s Law, does this mean I can also measure several d-space values in HRTEM?
Dear Bryan
Indeed you can visualize several sets of lattice fringes by HRTEM and thus measure their corresponding interplaner spacing. The limitation is the resolution limit of the TEM: New corrected microscopes provide a limit of below 1 Angström. On the other hand it depends on the material , in other words which lattice planes in the crystal posses a spacing that is larger than the resolution limit.
Additionally, you can only image the lattice fringes of planes that fulfill the Bragg condition, means the grain/crystal you observe should be in (or close to) a special orientation. Grains with a size>1µm are easy to tilt in a low indexed zone axis orientation. The alignment of nanograins is very challenging, but not necessary - statistics will help: You will find several nanograins close to zone axis orientation just by chance.
You should first calculate d-spacings by XRD as Martin mentioned and then compare with the HRTEM resolution. If you can see a numeric result in Å level, you can prove it by measuring in an HRTEM image. This result avoids you to make mistake.
Basically, if your microscope has been correctly calibrated, you can calculate d-spacing for each reflection order in SAED, but the error will increase while the diffraction spots becoming far away from center (000), the higher the reflection order, the more excitation error, this can be demonstrated in the reciprocal space by intersecting Ewald sphere into the reciprocal-lattice of material.
Usually you can measure two d-spacings close to the (000) point (depending on symmetry, you may measure only one or need to measure three d-spacing s), then calculate the lattice parameters, according to which, calculate the d-spacings of high reflection orders.
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