Zeiss GeminiSEM Series Instruction Manual

Also see for GeminiSEM Series: Instruction manual

3 Product and Functional Description | 3.2 Main Components ZEISSImaging gun mode is especially useful at low kV or at high magnifications to reduce chromaticaberration and to achieve a better resolution. Switching from Normal gun mode to Imaging gunmode is useful for reducing the probe current without any need for beam adjustments.Analytic Gun Mode In Analytic gun mode, the temperature of the Schottky emitter and the extraction voltage are in-creased. This leads to a higher probe current. Overall, the probe current in Analytic gun mode isabout twice the probe current in Normal gun mode.The Analytic gun mode is especially useful for applications which require high intensities (e.g.WDX).3.2.7 Detectors3.2.7.1 Principle of Signal DetectionThe interaction products most frequently used for the generation of images in scanning electronmicroscopy are secondary electrons (SEs) and backscattered electrons (BSEs).Primary Electrons Primary Electrons (PEs) are electrons forming the scanning beam before hitting the specimen.SecondaryElectronsSecondary electrons are emitted from the topmost layer of the specimen.§ SE1 ElectronsElectrons emitted at the point of impact between the beam and the specimen are known asSE1 type electrons. The amount of electrons emitted at the point of impact is related to theshape of the specimen.Secondary electron detectors, such as the InLens SE detector, collect SE1 type electrons fromthe surface layer of the specimen and are thus ideal for displaying surface structures.§ SE2 ElectronsThe emergence of backscattered electrons from the specimen excites further emission of sec-ondary electrons. These are known as SE2 type electrons.Detectors that collect SE2 type electrons are especially suitable where the working distance islarge. Surface detail as the effect of “lateral illumination” emphasizes the topography of thespecimen.BackscatteredElectronsBackscattered electrons (BSEs) emerge from below the surface of the specimen (up to an orderof μm). The number of electrons emitted at the point of impact is highly dependent on the meanatomic number of the specimen material. This means that a BSE image provides depth informa-tion and atomic number contrast.BSE detectors are used to display the materials contrast because the backscatter coefficient is de-pendent on the mean atomic number of the material under investigation.TransmittedElectronsThis comprises primary electrons that are transmitted through an ultrathin specimen and weaklyscattered primary electrons with a small range of angles. Depending on the material, primary elec-trons are scattered under different angles and can be detected by a STEM detector placed belowthe specimen. Unscattered electrons are detected in the center of the STEM detector and give abright field image. Electrons scattered under higher angles are detected by outer areas of theSTEM detector and produce dark field images.CathodoluminescenceElectrons impacting on luminescent materials cause the emission of photons (Cathodolumines-cence, CL) which may have wavelengths in the visible spectrum and can be imaged by specializeddetectors.3.2.7.2 Detectors OverviewThe beam scans the specimen and initiates particles to be emitted. A detector collects the emis-sion and produces an electric signal with an amplitude proportional to the number of particles atany given time.40 Instruction Manual ZEISS GeminiSEM series | en-US | Rev. 2 | 349500-8138-000