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

<strong>Tecnai</strong> on-line help Alignments 34<strong>Tecnai</strong> 12 Software version 2DescriptionThe image shift calibration provides the conversion factor for the image shift used in measuring and forthe beam shift - image shift.6.15 Diffraction shift calibration HMPurpose: Calibrate the diffraction shift to physically meaningful values.Importance: ESSENTIAL for meaningful diffraction measurement results.Method: Move the diffraction pattern and adjust the displayed value of the diffraction shift usingMultifunction Y.ProcedureThe alignment procedure consists of five steps:• The first step is a preparation step for the diffraction mode.• In the second step the diffraction pattern must be centered accurately (on the center of the viewingscreen or the tip of the beam stop).• In the third step, the diffraction pattern is shifted with Multifunction X to bring a ring to the center andthe diffraction shift (nm value or angle) is adjusted with Multifunction Y to the correct value.• The fourth step repeats the procedure of the third step for the Y diffraction shift.DescriptionThe diffraction shift is converted through the calibration procedure into to physically meaningful unitssuch as Bragg angles and d spacings (in the latter case the Bragg Law formula is used). The diffractionshift can be read off in the flap-out of the Alignment Control Panel and is used in the Measuring ControlPanel.6.16 Beam shift - image shift calibration HMPurpose: Define the beam shift compensation for the image shift.Importance: CONVENIENCE for keeping the beam on the screen when the image is shifted. The beamshift - image shift is used in the Image shift Control Panel and in Low Dose.Method: Move the image off-axis and recenter the beam using Multifunction X,Y.Note: This procedure is complicated by the fact that it is not easy to tell how far the beam-shift/imageshiftshould be changed. The on-line help file therefore contains a control that indicates the status of thebeam-shift/image-shift, beam coils and image coils.Using this you change the beam shift-image shift until either:• the beam is at the screen edge.• the beam shift-image shift is more than 50% (barbecomes green) OR one of the coils is more than 80%(bar becomes red).The microscope will sound a beep when the beam shift-imageshift is at its limit but also when one of the coils is at its limit.In the former case you can continue with the calibration, butwhen a coil is limited very likely you cannot. The control in thehelp file which is directly linked to the microscope displays thesituation.