Magellan Scanning Electron Microscope (SEM) Laboratory

The instrument is an FEI Magellan 400 XHR Scanning Electron Microscope with FEG source, EDAX Pegasus integrated EDS and EBSD system located in the basement of Spilker, room 008 A.

Principles of operation:

In a scanning electron microscope (SEM), a fine beam of electrons is scanned across the surface of a specimen in synchronism with a spot on the display screen. A detector monitors the intensity of a chosen secondary signal from the specimen (for example, secondary electrons) and the brightness of the display spots controlled by an amplified version of the detected signal. If, for any reason, the intensity of the emitted secondary signal changes across the specimen then contrast will be seen in the image on the display screen. The resulting image is strikingly similar to what would be seen through an optical microscope; the illumination and shadowing show a natural-seeming topography.

It is important to remember that the image formed in an SEM is not necessarily that of the surface. As the electron beam penetrates the sample, the interaction causes excitation of secondary, backscatter, and Auger electrons; characteristic and Bremsstrahlung x-rays; and photons. It is possible, by choosing the electron energy, to control the depth to which the electrons penetrate and the type of emitted signal used to form the image. While this gives the microscopist a great deal of control over the nature of the final image, an understanding of how the image is formed is required to interpret it sensibly.

Electron beam resolution:

At optimum working distance (SE mode)
  15 kV 0.8 nm
  2 kV 0.8 nm
  1 kV 0.9 nm
  200 V 1.5 nm

Advanced techniques:

Energy Dispersive Spectroscopy (EDS)
Electron Backscatter Diffraction/Orientation Imaging Microscopy (EBSD/OIM)

Restrictions on samples:

The sample material must be able to withstand a high vacuum environment without outgassing. It must be clean. It may be attached to the sample holder using any suitable SEM vacuum-quality adhesive. The sample must be electrically grounded to the sample holder to minimize sample charging. If the sample is nonconductive (plastic, fiber, polymer, or other substance with an electrical resistance greater than 1E10 ohms), the sample may be coated with a 200 – 300 Å layer of carbon or other conductor. Rough surfaced samples must be evenly coated from every direction. Biological, cloth and powder samples may require carbon or other conductive painting on portions of the sample that are hard to coat. The workstation can accommodate up to 100 mm (4") wafers.

Training and Service:

Before being considered for training on the FEI Magellan SEM, you must first be a fully qualified user of the FEI Sirion SEM or the FEI DB235 Dual-Beam FIB/SEM.

Service requests will be considered on a case-by basis. However, our normal mode of operation is to train users to perform the characterization experiments themselves.