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Hitachi S-900 Field-Emission
Scanning Electron Microscope

The S900 scanning electron microscope with a cold-cathode field-emission emitter. Using a cold field emission source as the electron emitter instead of tungsten wire or LaB6 crystal produces the brightest beam with the smallest electron source and lowest energy spread. This increases the resolution of the SEM, and allows the use of low accelerating voltages, which helps prevent beam damage and penetration and reduces charging artifacts.

The S-900 also has an Autrata high resolution backscattered detector, which allows imaging of backscattered electrons and much lower accelerating voltages and higher resolution than with a semiconductor or Robinson backscattered electron detector. The Autrata detector produces images of as high a resolution as the secondary detector down to 5kV accelerating voltage.

Another unique feature to the S-900 is the ability to accommodate a Gatan cryostage. The cryostage allows the imaging of hydrated frozen samples. Cryo-SEM offers high resolution imaging of hydrated samples without the artifacts of fixation and dehydration associated with conventional sample preparation for SEM.

The Autrata detector makes the S-900 particularly useful for imaging colloidal metals conjugated to antibodies or other ligands attached to cell surface receptors and doing immunoSEM. SEMs are good for immunolabeling of surface structures, as the entire specimen can be examined, instead of simply a narrow slice, as is the usual case with sectioned material. Immunolabeling of internal structures can also be studied in the SEM using colloidal metal conjugates using different techniques to open the specimen to expose the interior. Backscattered electrons can also be used to detect colloidal metals within a sample, as the higher energy of the primary electrons allows them to escape from within the sample. Examples of the use of colloidal gold conjugated antibodies for immunoSEM can be seen on the colloidal metals gallery pages. See the "Colloidal metals and conjugates" page for further information.

Due to the complexity of the instrument, users cannot be trained to operate the S-900 field-emission SEM (FESEM). The microscope must be operated by BBPIC staff.