SEM: Thermo Fisher Scientific Apreo S LoVac Scanning Electron Microscope
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|
- Energy Dispersive Spectroscopy (EDS)
- Electron Backscatter Diffraction/Orientation Imaging Microscopy (EBSD/OIM)
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 Axess STARS EHS-2470-WEB: COVID-19 Hygiene Best Practices.
- Complete the Online SEM course.
- The course is hosted in edx.org Nano @ Stanford. The SEM module is located under Microscopy.
- Basic practical training for inexperienced SEM users generally requires 2 two-hour regular trainings followed by a final, which is similarly up to 2 hours. All prospective users must pass the practical final to earn the Beginner’s Permit. The final may be attempted multiple times.
- Training #1
- Via RemotePC Meeting. Max 4 people per session. Usually offered Monday mornings; please read the "To be scheduled for training section" below.
- Trainees are expected to know the material presented in the online course/quiz.
- Training #2
- One-on-one with a trainer. Trainer will be coaching the trainee through the use of the instrument as previously demonstrated in Training Session 1.
- The room allows for > 6’ separation between people. This will be maintained as much as possible, although there will be several instances where the trainer and trainee will need to be in closer proximity to allow both to see the screen properly.
- Training #3 (final)
- One-on-one with a trainer.
- This is an open-note practical exam at the system. Trainee is expected to be able to run the system independently, making proper adjustments as required to meet specifications as presented by the trainer.
- This session may need to be repeated until the trainee passes.
- Passing the final earns the trainee a “beginner’s permit.”
- In the same email scheduling the previous trainings, the request for scheduling the final training may be made.
- Startup instructions for the instruments available here. It can be helpful for you to bring them to your sessions.
- To be scheduled for training:
- Send an email to Rich Chin with your regular daytime calendar conflicts. You will be placed in the queue according to the time your email is received, pending your completion of all the pre-requisites. Please note each of these sessions will block off 2 hours of your time during the day (8:30am - 5pm). You can look at the Apreo calendar to get an idea of when training sessions are normally booked, although times are subject to change.
- Due to the popularity of this system, it is common that there is a backlog of people in the queue to be trained. Do not expect to be scheduled within the next couple weeks of your request.
- To be notified about any changes to training protocol or instrument issues, subscribe to email@example.com by going to http://mailman.stanford.edu and request subscription to: apreo-training. (Note: it is not searchable on the public lists.)
- Training #1
- Complete a Beginner's Permit.
- To complete a Beginner's Permit, the trainee must complete three sessions, scheduled by the trainee, with their own sample(s).
- The sessions are to be wholly within business hours (8:30a-5p), but on different days.
- The sessions will require a trainer to be present at the very least at the beginning of the session, maintaining > 6’ separation while in the room.
- The trainee must demonstrate safety and competence in instrument operation to the satisfaction of the trainer to earn a “sign-off”.
- The trainers are available for some consult/troubleshooting via remote access.
- For advanced techniques (i.e., EDS, EBSD, Maps, Low Vacuum):
- After you have passed your final training, you may sign up for one of the technique sessions. These advanced sessions are offered on an as-needed basis. These are designed to provide a basic 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 (firstname.lastname@example.org).