Scanning Electron Microsocpy

SEM It B a type of e microscope that produces images of a sample by scanning it with a focussed beam of es Pauerful magnification tool that utilizes focussed been of IS to obtain information The IS interact with atoms in the sample, producing various Signal that can be detected and that contain the Information about the sample's suface topography and composition The I beam is generally scanned in a rater Scan Pattern and the beam's position is wmbine with the detected Signal to Produce an Image SEM can achieve resolution better than 1nm The most common mode of detection PS by 2° electrons smitted by atoms exuted by the l beam The no: of 20 electron is a function of the angle b/w the Surface and the beam. On a flat Surface, the Plume of 2°T is mostly contained

by the sample / but on titted surface the Plume is partially exposed and more es are emitted. By scanning the sample and detecting the 2 is, an image displaying the tilt of the surface Ps created. Principle A normal SEM e minoscope operates at high vacuum The basic principle is that a beam of IS is generated by a suitable source, typically a tungsten filament / field emission gun The e beam is accelerated through a high voltage (eg 20KV and pass through a System of aportures and electromagnetic lenses to produce a thin beam of electrons. Then the beam Scans of the surface of the spacimen by means of Scan oils. Electrons are emitted from the specimen by the action of the scanning beam and collected by suitably -positioned detector. The microscope operator is watching the image on a Screen Imagine a spot. on the Screen scanning across the screen from left to right. At the end of

the Screen, it drops dow a line and Scans across again, the process of being repeated down to the both of the screen. Component of SEM Electron source Thermionic gun. field emission gun. Electromagnate or electrostatic lenser. Vacuum chamber. Sample chamber and stage. Detectors 2°nd e dedkctor. Back scatter detector Diffracted back slatter detector. X-ray Detector Instrumentation 1 An electron optical System. 2 A Specimen stage 3 A a° electron Detector 4 Image Display and Rewording unit 5 Vacuum System.