Carbon Grating Replicas

Calculating the Magnification

Calculate the electron microscope magnification using the diffraction grating replica pattern as follows; measure (in millimetres) between the limiting lines of as many squares of the replica pattern as possible and apply the following formula:

Distance in mm between limiting lines x 2,160
Magnification = Number of spaces between limiting lines

Note: Limiting lines are chosen arbitrarily by the viewer. Statistical significance increases with the distance between the 2 limiting lines due to the increased size of the sample; i.e., the more "lines or spaces" included in the measurement, the more accurate the calibration.

Care of Grating Replica Specimens:

When not in use, the replica should be kept in a dust‐free atmosphere (as the same vial in which it is supplied). The replica surface can be damaged if it is touched with any hard object.

NEVER TRY TO CLEAN IT.

Care should be taken with the TEM specimen to avoid bending the grid, which can cause cracking of the replica. When viewing a replica specimen in the TEM always begin at low magnification, with one square of the supporting copper grid filling the EM screen, slowly increase the illumination to near maximum intensity (but not to cross‐over) then reduce the level of the illumination and go to the desired magnification. Repeat this procedure every time a new area of the replica is to be viewed.

Low Magnification Grating Replica

Gratings are germanium shadowed carbon replicas made from a 15,240 line per inch diffraction grating. The actual grating spacing is 1667 millimicrons. They are supplied mounted on grids as required by the customer. For accurate work, the microscope should be calibrated at each high voltage separately. For each magnification run, the objective current should be set at a suitable reading and the image is brought into focus using the specimen "z" screw.

Photographs of the grating should be taken at the magnifications used for the specimen. The negative of the grating is placed in the enlarger and the enlarger moved up or down until the distance between the lines on the easel is that given by the chart. For example, at 7,500 magnification, the distance between the lines on the easel should be 12.5mm. For accuracy, five lines should be measured or a distance of 62.5mm. Note in measuring lines, the distance from one point to where the pattern is repeated (e.g. left side of line to left side of line or centre to centre) should be taken.

There are several advantages in the use of the grating. It makes an accurate record of the magnification used to be filed with your micrographs. It gives convenient round number magnifications (e.g. 10,000 not 9,879). It makes dark‐room enlarging easy and convenient.

Actual spacing of grating is 1667µm (15,240LPI)

Intermediate Magnification Grating Replica

Gratings are germanium shadowed carbon replicas made from a 28,800 line per inch diffraction grating. The actual grating spacing is 882 millimicrons. They are supplied mounted on grids as required by the customer. For accurate work, the microscope should be calibrated at each high voltage separately. For each magnification run, the objective current should be set at a suitable reading and the image is brought into focus using the specimen "z" screw.

Photographs of the grating should be taken at the magnifications used for the specimen. The negative of the grating is placed in the enlarger and the enlarger moved up or down until the distance between the lines on the easel is that given by the chart. For example, at 25,000 magnification, the distance between the lines on the easel should be 22.1mm. For accuracy, six lines should be measured or a distance of 132.5mm. Note in measuring lines, the distance from one point to where the pattern is repeated (e.g. left side of line to left side of line or centre to centre) should be taken.

There are several advantages in the use of the grating. It makes an accurate record of the magnification used to be filed with your micrographs. It gives convenient round number magnifications (e.g. 25,000 not 24,485). It makes dark‐room enlarging easy and convenient.

Actual spacing of grating is 882µm (28,800LPI)