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SEM TEM in Polymer Characterization

Scanning Electron Microscopy (SEM)UsesSample PreparationInstrumentPrinciplesMicrographsTransmission Electron Microscopy (TEM)UsesSample PreparationInstrumentPrinciplesMicrographs. Outline. TopographyTexture/surface of a sampleMorphologySize, shape, order of particlesCompositionElem

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SEM TEM in Polymer Characterization

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    1. SEM & TEM in Polymer Characterization EMAC 403 Matt Fullana

    2. Scanning Electron Microscopy (SEM) Uses Sample Preparation Instrument Principles Micrographs Transmission Electron Microscopy (TEM) Uses Sample Preparation Instrument Principles Micrographs Outline

    3. Topography Texture/surface of a sample Morphology Size, shape, order of particles Composition Elemental composition of sample Crystalline Structure Arrangement present within sample What can you see with an SEM?

    4. Samples must be small enough to fit in sample chamber Most modern microscopes can safely accommodate samples up to 15cm in height Samples must be electrically conductive Polymer samples typically need to be sputter coated to make sample conductive Ultra-thin metal coating Usually gold or gold/palladium alloy Coating helps to improve image resolution SEM Sample Preparation

    5. Once sample is properly prepared, it is placed inside the sample chamber Once chamber is under vacuum, a high voltage is placed across a tungsten filament to generate a beam of high energy electrons (electron gun) and serves as the cathode The position of the anode allows for the generated electrons to accelerate downward towards the sample Condensing lenses “condense” the electrons into a beam and objective lenses focus the beam to a fine point on the sample Scanning Electron Microscopy

    6. Scanning Electron Microscopy

    7. Scanning coils move the focused beam across the sample in a raster scan pattern Same principle used in televisions Scan speed is controllable Scanning Electron Microscopy

    8. As electron beam strikes sample, secondary electrons are emitted from the sample In addition, backscattered electrons are also emitted from the sample Scanning Electron Microscopy

    9. SEM Sample Interactions

    10. Secondary Electrons Back-Scattered Electrons SEM Signals / Detectors

    11. Electrons strike the sample surface As a result, some electrons “splash” out from the sample (secondary electrons) A detector with a strong positive charge attracts these electrons, however depending on the surface topography, not all electrons will be attracted Electrons on high “peaks” will be attracted to the positively charged detector Electrons in low “valleys” will not be attracted to the detector Secondary Electron Detector

    12. SEM Micrographs

    13. SEM Micrographs

    14. Electrons from high-energy beam strike the sample Some electrons pass close to a nucleus and are deflected by the positive charge These back-scattered electrons return to the sample surface moving at high speed Back-scattered electrons is dependent on atomic number of sample Can provide elemental composition information about a sample Back-Scattered Electron Detector

    15. Back-Scattered Electron Detector

    16. Morphology Shape, size, order of particles in sample Crystalline Structure Arrangement of atoms in the sample Imperfections in crystalline structure (defects) Composition Elemental composition of the sample What can we see with a TEM?

    17. Samples need to be extremely thin to be electron transparent so electron beam can penetrate Ultramicrotomy is a method used for slicing samples Slices need to be 50-100nm thick for effective TEM analysis with good resolution TEM Sample Preparation

    18. Instrument setup is similar to SEM Instead of employing a raster scan across the sample surface, the electron beam is “transmitted” through the sample Material density determines darkening of micrograph Darker areas on micrograph indicate a denser packing of atoms which correlates to less electrons reaching the fluorescent screen Electrons which penetrate the sample are collected on a screen/detector and converted into an image Transmission Electron Microscopy

    19. Transmission Electron Microscopy

    20. TEM Micrographs

    21. TEM Micrographs

    22. TEM Micrographs

    23. Pros Easier sample preparation Ability to image larger samples Ability to view a larger sample area SEM Pros and Cons

    24. Pros Higher magnifications are possible (50,000,000x) Resolution is higher (below 0.5Ĺ) Possible to image individual atoms TEM Pros and Cons

    25. Questions?

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