SEM (SCANNING ELECTRON MICROSCOPE)

1. SEM(SCANNING ELECTRON MICROSCOPE) 20823856 Özgen Buğdaycı 20824336 Elif Topçuoğlu 20823985 Yavuz Duran Hacettepe University 12.04.2012

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 - www.directindustry.com

4. HISTORY • The first SEM image was obtained by Max Knoll in 1935. • 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 1965.  first successful SEM – www.science.howstuffworks.com

5. USAGE AREA • Morphology • Topology • Microstructure studies • Solid state physic • Geology • Biology diamond-crystal structure - worldscheaper.com microstructureof a 15Mo3 steel - emeraldinsight.com

6. SEM ELECTRONIC CONSOLE • focus • magnification • brightness • contrast Console of SEM - www.chems.msu.edu

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

8. INSTRUMENTATION COMPONENTS • Electron gun • Electromagnetic lenses • Scanning • Detectors • Sample stage • Vacuum system Components of SEM - www.purdue.edu

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 • sample DETECTORS • is used the detect the secondary and backscattered electrons Sample chamber - jenkins.ucdavis.edu Detector - www.geos.ed.ac.uk

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 • For metals; • no need for preparation • For non-metallics; • need to be coated Preparation - www.mos.org

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 • 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 - www.nanosmo.com SEM adapted with pc equipments - www.lnnano.org

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

23. REFERENCES • www.iaszoology.com/sem • www.phy.cuhk.edu.hk • www.fy.chalmers.se/microscopy • www.materials.ac.uk • www.microscopemaster.com

24. Thanks for your attention Any Questions?