Tecnai on-line help manual -- Options - UT Southwestern

<strong>Tecnai</strong> on-line help Options 80Options Software version 26 TEM Compucentricity (FP5455/00)6.1 IntroductionThe β tilt of the double-tilt holder is not eucentric. Its motion therefore results (in the ideal case) in achange in the X and Z values. (In non-ideal cases also Y and α are changed a little.) This non-eucentricbehaviour can make it hard to keep track of a feature of interest in the specimen during tilting. TEMCompucentricity makes it possible to reduce these non-eucentric motions and thereby makes it easier touse the β tilt.Schematic diagram of the effect of the β tilt. The thick black lines show the locations of the X and Z stageaxes, while the dotted black line indicates the eucentric height. The central blue circle is the β tilt axis,which is displaced from its 'ideal' X 0, Z 0 location. The dotted blue circles indicate the path traveled by apoint when tilted around β. Tilting around β for the point lying on the smaller dotted blue circle requires asmall correction to X and Z (red arrow lines) to bring the area back to the same position in space (but adifferent stage position). For the point lying on the larger dotted blue circle the correction (red arrowlines) is much larger because it is further away from the tilt axis itself. The corrections are appliedautomatically when compucentric tilting is used.Compucentricity consists of:• Establishing the current stage position and the required new tilts.• Calculating what corrections should be made to the stage axes to keep the feature of interestcentered on the screen.• Moving the CompuStage to the new position.Since specimen holders deviate from the 'ideal' model, a correction can (and for good results should) bemade for this 'non-ideal' behaviour through a calibration procedure. Data are stored for each specimenholder separately. Prior to calibration holders must therefore be identified by name.