San Francisco State University Electron Microscopy Facility

Image: Hensill Hall and Microscopy pictures

Specimen Preparation

Specimens must be oil-free (e.g., free of finger prints), dry, stable under vacuum, and conductive. Provided the first three requirements are met, insulating specimens can be coated with a thin, conductive layer of carbon or metal. Specimens may be mounted on Zeiss specimen stubs (12mm or 25mm diameter) using a thin layer of carbon or silver paint as needed. The specimens should be gently heated for 24 hrs to drive-off solvent vapor from the carbon or silver paint prior to imaging or coating.

 

Non-conductive specimens may be coated with an appropriate thin metal film for high-resolution imaging, or with carbon if chemical analysis or EBSD is to be performed. Specimens exposed to the air will become coated by airborne molecular contamination - essentially hydrocarbons. Airborne molecular contamination on conductive specimens, or those already coated with a thin metal film, may be removed by plasma cleaning prior to analysis in the Ultra 55.

 

Specimen preparation equipment includes:

1. Cressington-C high-vacuum carbon evaporation coater: Used primarily for coating insulators prior to EDS and EBSD analysis.

2. Cressington-HR sputter coater for the deposition of Au, Au/Pd, or Ir: Used primarily for high-resolution imaging.

3. Tousimis Critical Point Dryer: The fully automated critical point dryer gently completes the final stage of biological specimen dehydration.

4. Struers RotoPol-35 polishing system with SiC grits, diamond suspensions, and colloidal silica.

5. Buehler VibroMet 2 vibratory polisher with colloidal silica for EBSD-suitable final polish.

6. Gatan Model 682 Precision Etching Coating System (PECS) with targets for depositing C, Au/Pd, Pt, and Ir.

7. XEI plasma cleaner: Used to remove airborne contamination from conductive samples and those insulating specimens already coated with a thin layer of metal. The plasma cleaner cannot be used on uncoated biological specimens.

8. Reichert glass knife maker and ultra-microtome for the preparation of biological thin sections.

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