SEM: Thermo Fisher Scientific Apreo S LoVac Scanning Electron Microscope
Overview
The instrument is a Thermo Fisher Scientific Apreo S LoVac Scanning Electron Microscope (SEM), located in Spilker Building Room 008I. The microscope is equipped with a NiCol electron column, immersion lens, Trinity detector system, low-vacuum SE detector, retractable backscatter detector, beam deceleration capabilities, Bruker Quantax EBSD 400i integrated system (comprised of an e-Flash(HR) EBSD detector and an XFlash 6 | 60 SDD EDS detector), and Maps 3 for correlative microscopy and large area mapping.
Principles of operation: In a 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.
Restrictions on samples: The sample material must be able to withstand a high vacuum environment without outgassing (even for lower vacuum conditions, the system must get to high vacuum, first). It must be clean. It may be attached to the sample holder using conductive paint or clean clips. The sample should be electrically grounded to the sample holder to minimize charging. If the sample is insulating, there are a number of charge mitigation strategies available in the microscope, or the sample may be coated with a conductive layer (we can provide Au/Pd coating upon request). Note that rough surfaces should be conformally coated. The workstation can accommodate up to 100 mm (4”) wafers. For Au/Pd (60:40 ratio) coating on your samples, please see SEM: Sample Coating Service.
Electron beam resolution (ideal sample, optimal working distance):
| High vacuum, field-free mode | |
| 15 kV | 1.0 nm |
| 2 kV | 0.8 nm |
| 1 kV | 0.9 nm |
| High vacuum, immersion mode | |
| 15 kV | 0.7 nm |
| 1 kV | 1.0 nm |
| High vacuum, immersion mode with beam deceleration | |
| 1 kV | 0.8 nm |
| 500 V | 0.8 nm |
| 100 V | 1.8 nm |
| Low vacuum, field-free mode | |
| 15 kV | 1.2 nm |
| 3 kV | 1.8 nm |
Advanced techniques:
- Energy Dispersive Spectroscopy (EDS)
- Electron Backscatter Diffraction/Orientation Imaging Microscopy (EBSD/OIM)
Getting Started and Training Information
In order to become a qualified user on the Thermo Fisher Apreo SEM, you need to follow each of these steps in the order as listed here:
- Complete the process to become a lab member of SNSF and follow the instructions to activate a Badger account.
- Complete the Online SEM course.
- The course is hosted on the nano@stanford edx.org course. The SEM module is located under Microscopy.
- Fill out the Apreo Intake Form.
- Complete remote and in-person trainings and then a practical final (normally a total of three 2-hour sessions; detailed information provided upon the completion of the intake form above).
- Complete a Beginner’s Permit to gain after-hours access.
- For advanced techniques (i.e., EDS, EBSD, Maps, Low Vacuum):
After you have completed your Beginner’s Permit, you may attend one of the technique sessions. These advanced sessions are offered on an as-needed basis. These are designed to provide a practical introduction to the technique, and further training may be required by the instructor. Note: you will be charged for no-shows if you do not let us know at least 12 hours in advance of your scheduled time.
Any further inquiries may be directed to Richard Chin (rwchin@stanford.edu).