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  1. 1. TEM Specimen Preparation By Nibiao Zheng
  2. 2. Introduction <ul><li>Specimen preparation is an important aspect of the transmission electron microscopy (TEM) </li></ul><ul><li>Objective: To make a TEM specimen which is </li></ul><ul><ul><ul><ul><ul><li>representative of the material studied </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>electron transparent </li></ul></ul></ul></ul></ul><ul><li>Methods: depend on both the type of material and the information to obtain. </li></ul>
  3. 3. Tem preparation methods <ul><li>Powder material </li></ul><ul><li>Plan-view specimens: surface study </li></ul><ul><li>Cross-section specimens: interface study,... </li></ul>
  4. 4. Powder specimen <ul><li>Grind the material </li></ul><ul><li>Dissolve the powder into a solution, mix. </li></ul><ul><li>Splash one drop of solution onto a copper grid with carbon supporting film </li></ul><ul><li>Wait until the specimen is dry before observing in TEM </li></ul>
  5. 5. Plan-view specimens <ul><li>Common methods </li></ul><ul><ul><ul><ul><li>Cut a 3mm disk using a ultrasonic disk cutter </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Pre-thin the disk: </li></ul></ul></ul></ul><ul><ul><ul><ul><li>mechanical grinding dimpling </li></ul></ul></ul></ul><ul><ul><ul><ul><li>(electro-polishing) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Ion milling: dual-ion mill (cooling stage) </li></ul></ul></ul></ul><ul><li>2. Special methods: </li></ul><ul><ul><ul><ul><li>Locally electro-polishing </li></ul></ul></ul></ul>
  6. 6. Locally electropolishing <ul><li>Diagram </li></ul>Anode electrolyte Copper wire specimen beaker Good for material that can’t be prepared by mechanical method. But the electrolyte needs H 3 PO 4 , which is easy to explode - need to be in cooling environment. Good for conventional TEM, not quite suitable for HRTEM Cathode
  7. 7. Cross-section specimens <ul><li>Common methods </li></ul><ul><ul><ul><li>Cutting two slices </li></ul></ul></ul><ul><ul><ul><li>Glue these two slices with epoxy or M bond </li></ul></ul></ul><ul><ul><ul><li>Section “the sandwich” </li></ul></ul></ul><ul><ul><ul><li>mechanical grinding, dimpling </li></ul></ul></ul><ul><ul><ul><li>Ion milling: Precision ion polishing system (PIPS) </li></ul></ul></ul><ul><li>2. Other methods </li></ul><ul><ul><ul><li>Focused Ion beam </li></ul></ul></ul><ul><ul><ul><li>Lithography </li></ul></ul></ul><ul><ul><ul><li>Preferential chemical etching </li></ul></ul></ul><ul><ul><ul><li>Other methods </li></ul></ul></ul>
  8. 8. Notes for mechanical thinning <ul><li>Grinding the sample down to 30 microns </li></ul><ul><li>Dimple off up to 10 microns; measure the thickness with a optical microscope </li></ul><ul><li>Disadvantages of thick sample into PIPS: </li></ul><ul><ul><ul><ul><li>Longer ion-milling time </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Contaminations of specimen and PIPS </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Preferential milling in the PIPS </li></ul></ul></ul></ul>
  9. 9. Notes for operation of PIPS <ul><li>Mainly for cross section specimens </li></ul><ul><li>Final thickness of the specimen smaller than 30 microns. Dimpling depth larger than 10 microns. </li></ul><ul><li>Adjust argon gas flow(@80% of maximum current) before putting the specimen into the chamber. </li></ul><ul><li>Mount the specimen in the correction position-check by the camera with the PIPS. </li></ul><ul><li>Use high milling angle, high milling voltage at the beginning: minimize the contamination of the specimen and the chamber. </li></ul>
  10. 10. Focused Ion beam (FIB) <ul><li>Produce cross-section TEM specimens of individual devices (site-specific). </li></ul><ul><li>Can provide ion beams with lateral resolution less than 10nm. </li></ul><ul><li>Provide a large area of uniform thickness; Possible to detect the localized internal stress around features </li></ul><ul><li>Good for materials that are not suitable for mechanical grinding and polishing. </li></ul><ul><li>less preferential milling is observed , enabling the preparation of cross-section specimens from samples composed of different materials </li></ul>
  11. 11. Procedure of FIB a. Select an area of interest, Coat with a layer of metal (Pt) b. Make “trench” using high current ion beam c. Thinning the wall d. Cut the wall and remove
  12. 12. Lithography <ul><li>Draw lines on the layered material using standard lithography </li></ul><ul><li>Etching away material on either side of the line </li></ul><ul><li>Disadvantages: </li></ul><ul><li>Narrow electron transparent region; </li></ul><ul><li>Dimension in the electron </li></ul><ul><li>beam direction fixed by the lithographic capability. </li></ul>
  13. 13. Ultramicrotomy <ul><li>Used for sectioning biological material </li></ul><ul><li>Can create thin film of multiphase material </li></ul><ul><li>Leave the chemistry of the material unchanged </li></ul><ul><li>But introduce deformation structure to the material </li></ul>
  14. 14. Preferential chemical etching <ul><li>Remove part of the sample by chemical etching to leave an area which is electron transparent </li></ul>
  15. 15. Other methods <ul><li>Replication and Extraction </li></ul><ul><li>Cleaving </li></ul><ul><li>The 90 o wedge </li></ul>
  16. 16. Contamination of TEM specimens <ul><li>Contamination can lead to incorrect information of the original specimen. </li></ul><ul><li>Contamination comes from: </li></ul><ul><ul><ul><li>Sample preparation, mounting, storage </li></ul></ul></ul><ul><ul><ul><li>High energy electron beam in TEM analysis. </li></ul></ul></ul><ul><li>Solutions: </li></ul><ul><ul><ul><li>Clean tools and environments, </li></ul></ul></ul><ul><ul><ul><li>Ion plasma cleaner to clean hydrocarbon contamination, </li></ul></ul></ul><ul><ul><ul><li>Re-ion polishing in PIPS with low energy, low angle beam, </li></ul></ul></ul><ul><ul><ul><li>Standard TEM techniques to minimize contamination: 1.Use the largest condenser aperture and let the beam shower the sample for a period of time; 2. liquid nitrogen cool stage. </li></ul></ul></ul><ul><ul><ul><li>Observe the specimen as soon as possible after preparation. </li></ul></ul></ul>
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