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

<strong>Tecnai</strong> on-line help Alignments 47<strong>Tecnai</strong> 12 Software version 29 Beam Nanoprobe procedure9.1 Preparation Beam Nanoprobe alignmentPurpose: Set up microscope for aligning the upper part of the column (condenser system) inNanoprobe.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.9.2 Pivot point beam shift NanoprobePurpose: 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 objective lens. This plane is conjugate to the back-focal (diffraction) plane and thealignment of the pivot point can thus be seen in diffraction. The shift 'wobble' done by the microscopeshould give no beam tilt, so the two central spots in the diffraction pattern 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: the Intensity setting is preset to a fixed value that should give a (nearly) parallelincident beam which in turn should give a spot diffraction pattern. In order to keep the diffractionfocus the same as in the microprobe mode (where it can be set more reliably), the pattern should befocused (after it has been focused properly in microprobe) with the Intensity, not Focus.9.3 Pivot point beam tilt NanoprobePurpose: 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, focusing withthe wobbler and dark-field operation.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.