Transcript SEM
SEM (SCANNING ELECTRON MICROSCOPE) 20823856 Özgen Buğdaycı 20824336 Elif Topçuoğlu 20823985 Yavuz Duran Hacettepe University 12.04.2012 OUTLINE Definiton of scanning electron microscope History Usage Area Instrumentation Sample preparation Working principles Limitations Advantages & disadvantages Conclusion 2 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 3 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 4 USAGE AREA Morphology Topology Microstructure studies Solid state physic Geology Biology diamond-crystal structure - worldscheaper.com 5 microstructure of a 15Mo3 steel - emeraldinsight.com SEM ELECTRONIC CONSOLE focus magnification brightness contrast Console of SEM - www.chems.msu.edu 6 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 7 INSTRUMENTATION COMPONENTS Electron gun Electromagnetic lenses Scanning Detectors Sample stage Vacuum system Components of SEM - www.purdue.edu 8 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 9 INSTRUMENTATION LENSES; is used to produce clear and detail images Lens - ammrf.org.au Condenser lens reduces the diameter of the electron beam Objective lens focuses electron beam Working principle of the lens - ammrf.org.au 10 INSTRUMENTATION SCANNING COILS are used to raster the beam across the sample surface are able to move the beam Scanning coils - freudlabs.com 11 INSTRUMENTATION SAMPLE CHAMBER is where the sample is placed can manipulate and move the sample Sample chamber - jenkins.ucdavis.edu DETECTORS is used the detect the secondary and backscattered electrons Detector - www.geos.ed.ac.uk 12 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 13 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 14 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 15 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 16 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 17 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 18 ADVANTAGES High resolution and magnification 3-D Topographical imaging Compatible with PC technologies and softwares A peacock’s head front wiev - www.nanosmo.com Fast Analysing Store data in digital form Easier sample preparation techniques SEM adapted with pc equipments - www.lnnano.org 19 DISADVANTAGES Can not analys fluid or gas compounds Expensive Instrumentation Wasting time on sample preparation Constant voltage during analysing 20 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 21 CONCLUSION SEM; provides detailed surface data of solid samples informs external morphology, chemical composition, crystalline structure SAMPLE; must be prepared before placed 22 REFERENCES www.iaszoology.com/sem www.phy.cuhk.edu.hk www.fy.chalmers.se/microscopy www.materials.ac.uk www.microscopemaster.com 23 Thanks for your attention Any Questions?