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Conventional SEM

Conventional SEM. Specimen at high vacuum – requires sample fixation and dehydration or freezing. Charging is minimized by coating sample with metal or carbon or lowering the operating kV. Variable Pressure Scanning Electron Microscope. Variable Pressure Scanning Electron Microscope.

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Conventional SEM

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  1. Conventional SEM Specimen at high vacuum – requires sample fixation and dehydration or freezing. Charging is minimized by coating sample with metal or carbon or lowering the operating kV.

  2. Variable Pressure Scanning Electron Microscope

  3. Variable Pressure Scanning Electron Microscope • - Vacuum in the sample chamber can range from high vacuum (< 10-6 Pascals) up to 3,000 Pa. • - Gas in the sample chamber allows uncoated and unfixed samples to be imaged. • Detectors used at higher pressures are backscatter or special secondary detectors. • - Moisture on the sample can be controlled by cooling/heating stage and water injection system.

  4. LV SEM – High Vacuum Mode

  5. LV SEM - Low Vacuum Mode

  6. SEM Electron/Specimen Interactions When the electron beam strikes a sample, both photon and electron signals are emitted. Incident Beam Backscattered electrons X-rays - composition info - Atomic number and topographical Cathodoluminescence - Electrical Secondary electrons Auger electrons - Surface sensitive compositional - Topographical Specimen Specimen Current Electrical

  7. Secondary Electron Detector

  8. Backscatter electron detector

  9. Signal Detection with Variable Pressure Mode

  10. VPSE Detector, Light Pipe and PMT. Incident Electron Beam Zeiss VPSE Detector Principle Photons BSE’s The photons are detected and amplified to provide the final image. Specimen

  11. Peltier stage Heats to 50 C Cools to - 25 C

  12. Dual Magnification Imaging

  13. SEM Control Interface

  14. Control of Water vapor and temperature

  15. Applications Live centipede Bacteria on rock

  16. Fresh moss with liquid water

  17. Pattern produced in silica gel

  18. Skyscan 1072 Micro-CT X-Ray Tomography Scanner

  19. MicroCT X-ray imaging that reconstructs images to form cross-sections and volumetric information. Resolution to 5 mm, 3D reconstruction, density measurements. Any sample works having differential density within sample (e.g. bone vs. tissue, or addition of x-ray contrast agents) Applications – Bone, insects, food science, material science, substrate/cell distribution.

  20. Sasov and van Dyck, 1998, J. Microsc. Object is rotated 180 degrees. Images captured at one degree increments. Reconstructions done on aligned images to create volume data.

  21. Oak Ridge Natl Lab

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