Back - scattered electrons Back scattered electrons are those scattered backwood and emitted out of the specimen, when the incident is are Scattered in the. specimens. They are sometimes Called reflected electrons. Since backscattered IS possess higher energy than 2° electrons , information from a relatively deep region is contained in the backscattered electrons. The backsuttered electrons are sensitive to the compositi of the Specimen. As the atomic no: of the constituent atoms in the specim is large , the backscattered to yield is larger That is an area that consists of a heavy atom appears bright in the backscattered I image. This this image is Scirtal for observing a compositional difference B Moderials Investigated by SEM Metals ,glass and Ceramics Semiconductors Plastics and Polymere. Powders and dust. Composite materials.
Advantages It gives detailed and topographical Imaging and versatib info garnered from different detectors. - The instrument works very fast - Moden SEM samples require minimal preparation actions - Require characterization of Solid materials - SEM'S are composatively easy to operate, with user-friendly intuitive Interfaces - Data acquisition is rapid (less than 5 minutes /image). - Modern SEMS generate data in digital formats, which are highly Portable Disadvantages SEM PS expensive and large Special training is required to Operate The Preparation of samples can result in artifacts - H is limited to Solid sample - H (essy a small risk of radiation exposure associated with the electrons that Slatter from beneath the sample surjan. - Sputter wating can disturb delicate Samples.
Applications It is ability to examine detail on a wide range of made in an easily interpreted manner. High to low magnification with an exceptional depth y fours The ability to analyse the elemental composition of lum the smallert features on specimens H becomes possible to make conclusive identifications of origin of Some materials and thus contribute to the Chain of evidence - Particle contamination of identification and elimination - Identification and elimination of corrosion and oxidisat problems - To study the fracture Section through sputtered layer Conclusion SEM has been a Valiable tool in the dvpt of Scientific theory. H has contributed greatly to biology, medicine and material Science. - Although SEM are large / expensive equipment ,it
remain popular among researchers due to high resolution and detailed images H produce Summary SEM Scans the surjace of the sample by releasing is and making the is bounce or Scatter upon Impact The ts are emitted when the metallic filament is heated - The T bean makes its way through the electromagnetic lens towards the sample. - Once it hits the sample the back Scattered IS are collected , wn verted to signal producing an image.