SPI Diffraction Standards, TEM

Principal lattice spacings for thallous chloride and aluminum

General Instructions

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 *, the diffraction ring diameter is r where *L = 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 * 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.

SPI #02856-AB Evaporated Thallous Chloride

Thallous chloride has a simple cubic structure with a = 0.3842 nm.


If N = h2+ k2+ l2, the  principal lattice spacings are as follows:

                N               Lattice Spacings (nm)

                1                       0.384
                2                       0.272
                3                       0.249
                4                       0.192
                5                       0.172
                6                       0.157
                8                       0.136
                9                       0.128
                10                      0.121

The thallous chloride is evaporated on to a carbon substrate to form a polycrystalline layer.

SPI #02857-AB Evaporated Aluminium

Aluminium has a face centred cubic structure, with a = 0.4041 nm.

If N = h2+ k2+ l2,  the principal lattice spacings are as follows:

                N               Lattice Spacings (nm)

                3                       0.234
                4                       0.202
                8                       0.143
                11                      0.122
                12                      0.117
                16                      0.101

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