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

<strong>Tecnai</strong> on-line help Alignments 37<strong>Tecnai</strong> 12 Software version 27 Beam LM Procedure7.1 Preparation Beam LM alignmentPurpose: Set up microscope for aligning the upper part of the column (illumination system) in LM.Importance: ESSENTIAL to make sure that the alignment is done for the correct conditions: centeredC2 aperture, eucentric height and specimen in focus.Method:C2 aperture centering:• Focus spot and center it on the screen• Turn INTENSITY overfocus (clockwise)• Center aperture until illuminated area is symmetrical around the screen centerEucentric height: with the CompuStage switch on the Alpha wobbler and minimize image movement bychanging the Z height.7.2 Pivot point beam shift LMPurpose: Align beam shift pivot point = make sure that the beam does not tilt when it is shifted.Importance: ESSENTIAL for keeping the beam parallel to the optical axis when shifting.Method: Shifting a beam parallel to itself means that it must always go through the front-focal point (=shift pivot point) of the diffraction lens (the 'objective' lens in LM). This plane is conjugate to the backfocal(LAD diffraction) plane and the alignment of the pivot point can thus be seen in LAD diffraction. Theshift 'wobble' done by the microscope should give no beam tilt, so the two central spots in the diffractionpattern should overlap.ProcedureThe alignment procedure consists of four steps:• Two preparation steps for setting up the image and diffraction pattern, respectively.• Two steps in which the X and Y pivot points are aligned.Notes:• The shift 'wobble' may have one beam position blocked by the specimen. If no second beam isvisible when turning MF-X, then (re)move the specimen.• Diffraction focus: in LAD the objective lens (which is here the focusing lens) is switched to fixedsetting. To focus the diffraction pattern to a spot pattern the Intensity should be used, not the Focus.Only if the pattern cannot be focused with the Intensity should the Focus knob (objective lens) beused. In the latter case, turn the Intensity completely overfocus (clockwise), then focus the LADpattern with the Focus knob.7.3 Pivot point beam tilt LMPurpose: Align beam tilt pivot point = make sure that the beam does not shift when it is tilted.Importance: ESSENTIAL for keeping the beam centered during rotation-center alignment and focusingusing the wobbler.Method: A tilting beam must remain centered on the specimen (so the tilt pivot point coincides with thespecimen). The tilt wobble done by the microscope should give no beam shift, so only one spot shouldbe visible in the image.