Negatively stained catalase crystals show lattice plane spacings of approximately 8.75nm and 6.85nm very clearly (using TEM and STEM). They are valuable for high magnification calibration.
Negatively stained catalase crystals show lattice plane spacings of approximately 8.75nm and 6.85nm very clearly (using TEM and STEM). (Figures determined by Wrigley. J. Ultrastructure Res. 24, 454. 1968).
They are valuable for high magnification calibration.
For higher magnifications, one of the crystal lattice plane specimens can be used. Diffraction pattern ring diameters can be simply related to the lattice plane spacings in the crystal used as the specimen. For a lattice spacing d, in a microscope of effective camera length L and operating at an accelerating voltage corresponding to a wavelength l, the diffraction ring diameter is r where lL = dr.
It is not easy to measure the actual value of L or know the precise value of accelerating voltage. However, without knowing the exact values of l and L, one can determine an unknown lattice spacing by measurement of r, if the instrument has first been calibrated with a known substance. This can best be done by using a polycrystalline material of known lattice spacings, so that continuous diffraction rings are available for measurement. The ring diameters must all be measured in the same plane relative to the microscope (to avoid any errors due to ellipticity of the pattern).
Furthermore, the calibrating ring diameter chosen should be similar to that required to be calibrated since there may be distortion of the relative ring diameters due to residual barrel or pincushion distortion in the projector lens system.
The main lattice spacings of catalase crystals (8.75nm and 6.85nm) may be used to calibrate the camera length of a transmission microscope operating in high dispersion diffraction; that is, with the objective switched off and with illumination focused by condenser 2 on to the object plane of the intermediate lens.
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