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

<strong>Tecnai</strong> on-line help Alignments 60<strong>Tecnai</strong> 12 Software version 2Important:• The specimen must be at the eucentric height. To do this properly, go to the Nanoprobe mode andpress the Eucentric Focus button. The objective lens current is now set to the proper value forNanoprobe (provided the SA objective preset has been aligned properly). Then bring the specimeninto focus with the Z height of the specimen stage. (By doing it this way you will attain a morereproducible setting than by using the alpha wobbler.)• During STEM alignment TIA (Tem Imaging & Analysis) must be running.ProcedureThe alignment procedure consists of four steps:• In the first step the normal TEM is focused and the beam is centered.• In the second step the normal TEM diffraction pattern is focused properly (focus the diffractionpattern to a spot pattern on the basis of a preset intensity setting).• In the third step, the microscope is switched to STEM and the STEM diffraction pattern (now a diskpattern) is centered.• In the fourth step, each camera length is centered on the screen and focused.Notes:• This alignment affects the same diffraction alignment parameter as the diffraction alignment fornanoprobe. The focusing of the individual camera lengths is the same as in the HM Image cameralengths procedure. These alignments are repeated in this HM-STEM alignment subprocedure forconvenience.• The focusing of the camera lengths is repeated here because it can be done more accurately inSTEM. Once we know that the beam-shift pivot points are correct, we know that any movement ofthe diffraction pattern must be due to a diffraction focus that is away from the back-focal plane.Focusing can thus be done by minimizing movement.• For the movement of the diffraction pattern in STEM, it is important to make a distinction betweenany movement seen during the 'normal' scan and during the flyback (the rapid beam movement backto the beginning of the next scan line). During the flyback the beam often cannot keep up due to theinertia in the optics and the diffraction pattern may make an irregular swing. During the flyback thediffraction pattern typically has much less intensity than during the normal scan, producing anirregular line of lower intensity. The flyback should be ignored when it comes to minimizingmovement.12.7 HM-STEM Detector alignmentPurpose: Make sure the diffraction pattern is centered properly on the STEM Bright-Field/Dark-Fielddetector.Importance: ESSENTIAL for obtaining correct STEM Bright-Field and Dark-Field images.Method: First center the diffraction pattern on the screen, then define the off-axis shift necessary to havethe pattern centered on the bright-field/dark-field detectors. Since the latter shift is reproducible (notaffected by hysteresis), the only requirement later is to make sure the diffraction pattern is centered inthe screen center (with the off-axis shift not active) and then switch the off-axis shift on in order to havethe pattern properly centered again.Important:• The specimen must be at the eucentric height. To do this properly, go to the Nanoprobe mode andpress the Eucentric Focus button. The objective lens current is now set to the proper value forNanoprobe (provided the SA objective preset has been aligned properly). Then bring the specimeninto focus with the Z height of the specimen stage. (By doing it this way you will attain a morereproducible setting than by using the alpha wobbler.)• During STEM alignment TIA (Tem Imaging & Analysis) must be running.