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

<strong>Tecnai</strong> on-line help Options 119Options Software version 29.1.2 The Mi plus SA magnification calibration procedureThe calibrations procedure consists of a calibration for each magnification of the series. The followingprocedure is used:• Direct cross-grating calibration of the lowermost SA magnification.• Calibration of the image shift at the lowermost SA magnification (this does not calibrate amagnification, but the image shift itself, used later).• Calibration of the Mi magnifications with the cross-grating method.• Calibration of the remaining SA magnifications, going up in magnification up to the point where themagnification on the CCD camera is larger than 250kx. The software detects the magnification atwhich the cross-grating method does not work anymore and displays a warning in that sense. Thenthe software automatically switches to the image shift method which will be used for the remainingSA magnifications.9.1.3 The LM magnification calibration procedureThe calibrations procedure consists of a calibration for each magnification of the series down to amagnification of 200x on the CCD. The procedure uses an analysis of the FFT of the cross-grating todetermine the magnifications.9.1.4 The D camera length calibration procedureThe calibrations procedure consists of a calibration for the camera lengths of the series (in the case ofEFTEM the lowermost camera lengths are excluded from the calibration because they often are notusable - the projection system reduction is so strong that it becomes impossible to get the electron beamthrough the differential pumping aperture). The following procedure is used:• Direct calibration of the diffraction rings of a cross-grating at a camera length selected by software onthe basis of CCD camera size and high tension.• Calibration of the diffraction shift at that camera length (this does not calibrate a camera length, butthe diffraction shift itself, used later).• Calibration of the lowermost camera lengths with the diffraction shift (the rings are too close to thecenter of the diffraction pattern).• Calibration of the rings for the camera lengths where the rings are well enough separated from thecenter but not so large that they are no longer visible on the CCD.• Calibration of the higher camera lengths with the diffraction shift (the rings are too large to fit on theCCD).If possible, the procedure will be run in the Nanoprobe mode, because the large illuminated area forparallel illumination in Microprobe is so large that it often leads to the appearance of severe distortions inthe center of the pattern. It is important to focus the pattern so the rings becomes as sharp as possible.The focusing in Nanoprobe should be done with the Intensity - provided the camera lengths are focusedprior, which should have been done in the Image HM-TEM Camera Length alignment procedure.Note: The software is not suitable for calibration of the LAD (LM) camera lengths nor for the Lorentzmode camera lengths.