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

<strong>Tecnai</strong> on-line help Alignments 19<strong>Tecnai</strong> 12 Software version 24 Gun procedure4.1 Gun tiltPurpose: The gun tilt makes sure that the electron beam from the gun comes down parallel to theoptical axis, so that no electrons from the beam are lost before they can be used for imaging, etc.Importance: ESSENTIAL for having sufficient beam intensity.Method: Obtain maximum intensity.ProcedureThe gun tilt alignment consists of two steps:• A step for preparation and finding light.• A step to set the gun tilt itself.DescriptionGun alignment consists of two parts: gun tilt and gun shift. The gun tilt alignment makes sure that theelectron beam enters the microscope (that is, the C1 - spot size - lens) parallel to the optical axis, whilegun shift ensures that the beam goes through the center of the C1 lens.The gun tilt is aligned simply by maximizing the intensity (with a useful guide often being the exposuretime measured on the screen). For fine-tuning at high magnifications use the direct alignments and thecriteria outlined under FEG alignment.Since gun tilt alignment implies no gun shift (which would be visible as a beam shift), it should bepossible to align the gun tilt without movement of the beam. If this is not the case, the gun tilt pivot pointsare not aligned properly.4.2 Gun tilt pivot pointsPurpose: Minimize movement of the beam during gun tilt alignment.Importance: CONVENIENCE for not having to correct beam position while doing the gun tilt alignment.Method: Minimize beam movement.