SEM (SCANNING ELECTRON MICROSCOPE) Özgen Buğdaycı Elif Topçuoğlu Yavuz Duran Hacettepe University

2 OUTLINE Definiton of scanning electron microscope History Usage Area Instrumentation Sample preparation Working principles Limitations Advantages & disadvantages Conclusion

3 What is SEM? SEM = Scanning Electron Microscope Is a type of electron microscope. Uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens. Scanning electron microscope -

4 HISTORY The first SEM image was obtained by Max Knoll in Further pioneering work on SEM was performed by Manfred von Ardenne (1937) Further developed by Prof. Sir Charles Oatley and his student Gary Stewart and first time marketed by Cambridge Scientific Instrument Company in first successful SEM –

5 USAGE AREA MorphologyTopology Microstructure studies Solid state physic GeologyBiology microstructure of a 15Mo3 steel - emeraldinsight.com diamond-crystal structure - worldscheaper.com

6 SEM SEM ELECTRONIC CONSOLE  focus  magnification  brightness  contrast Console of SEM -

7 SEM SEM ELECTRONIC COLUMN generated under vacuum focused to a small diameter scanned across the surface of a specimen. Electronic column of SEM -

8 INSTRUMENTATION COMPONENTS Electron gun Electromagnetic lenses ScanningDetectors Sample stage Vacuum system Components of SEM -

9 INSTRUMENTATION ELECTRON GUN; is used for producing an intense beam of electron  Thermionic gun  thermal energy  Field emission gun  electric field ANODE; accelarates the free electrons Electron gun - academic.udayton.edu

10 INSTRUMENTATION LENSES; is used to produce clear and detail images  Condenser lens  reduces the diameter of the electron beam  Objective lens  focuses electron beam Lens - ammrf.org.au Working principle of the lens - ammrf.org.au

11 INSTRUMENTATION SCANNING COILS are used to raster the beam across the sample surface are able to move the beam Scanning coils - freudlabs.com

12 INSTRUMENTATION SAMPLE CHAMBER is where the sample is placed can manipulate and move the sampleDETECTORS is used the detect the secondary and backscattered electrons Sample chamber - jenkins.ucdavis.edu Detector -

13 INSTRUMENTATION VACUUM CHAMBER Absence of vacuum chamber; electron gun’s filament would be damaged other gas molecules would cause collisions with electrons sample would react with gases Electron column - iaszoology.com

14 SAMPLE PREPARATION For organic materials; fixation  to preserve structure drying  moisture must be removed coating  to conductive the sample A spider coated with Au - thenallyblog.com Preparation - For metals; no need for preparation no need for preparation For non-metallics; need to be coated need to be coated

15 SAMPLE PREPARATION SPUTTER COATING; Makes non metallic samples conductive Uses Ar and electric field to tear off metal from cathode Metal fall onto sample and coat the material Sputter coating device - microscopy.ca

16 SAMPLE PREPARATION The coating material; commonly carbon, gold, or some other metal or alloy  carbon  elemental analysis  metal coatings  high resolution imaging applications must be vacuum compatible dependent on material properties (beam sensitivity, hardness, etc.) must be appropriate thickness

17 WORKING PRINCIPLE Beam is; generated by electron gun collimated and focused by lenses rastered across the sample surface Secondary or backscattered electrons are; collected by detector formed the specimen image in the microscope Working principle - ammrf.org.au

18 LIMITATIONS Samples must be solid Size of analyte  vertically  <40mm  horizontally  <100mm Stable in a vacuum Designed to prevent any electrical and magnetic interference Can not detect low elements (Lighter than Na-11) like most of analys microscopy

19 ADVANTAGES ADVANTAGES High resolution and magnification 3-D Topographical imaging Compatible with PC technologies and softwares Fast Analysing Store data in digital form Easier sample preparation techniques A peacock’s head front wiev - SEM adapted with pc equipments -

20 DISADVANTAGES Can not analys fluid or gas compounds Expensive Instrumentation Wasting time on sample preparation Constant voltage during analysing

21 RESULT SEM uses electrons instead of light to form an image. developed new areas of study & still helping. popular among researchers due to their wide range of applications

22 CONCLUSION SEM; SEM; provides detailed surface data of solid samples informs external morphology, chemical composition, crystalline structure SAMPLE; SAMPLE; must be prepared before placed

23 REFERENCES

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