TEM: FEI Titan Environmental Transmission Electron Microscope
The Stanford Nano Shared Facilities houses a state-of-the-art FEI 80-300 environmental (scanning) transmission electron microscope with the following capabilities:
- Accelerating voltages 80, 200 and 300 kV
- High brightness field emission gun (X-FEG)
- Spherical aberration corrector in image-forming (objective) lens
- Lorentz lens for imaging magnetic samples
- Low-dose exposure technique
- TEM and STEM tomography
- Biprism for electron holography
- Energy-dispersive X-ray spectroscopy (EDS) with Oxford Xmax SDD Detector
- Electron-energy loss spectroscopy (EELS) and Dual EELS with Gatan Quantum 966 EEL spectrometer
- Energy-Filtered TEM imaging
- Environmental mode which allows gases to be introduced into the otherwise high vacuum of the TEM column (Guidelines on gases and gas pressures available)
- Image resolution (TEM mode): 0.07 nm
- Probe resolution (STEM mode): 0.14 nm (at 300kV)
- Energy resolution: ~ 1 eV (monochromator off), 0.1 eV (monochromator on)
Principles of Operation: The transmission electron microscope uses a high-energy electron beam transmitted through a very thin specimen to image and analyze the microstructure of materials with atomic scale resolution. The TEM can be employed in two different technical variants. In conventional TEM, the sample is illuminated by a near-parallel beam of electrons and the image is formed by a series of electromagnetic lenses. In scanning TEM (STEM), a fine probe (of less than 0.2 nm) is formed by optically focusing the incident electrons and is then scanned across the sample. The transmitted electrons are registered by detectors, and the resulting signal is displayed and captured by a CCD camera or spectrometer. In addition, interactions between electrons and the specimen can result in some of the incident electrons losing energies, or in the generation of X-rays, both with energies that are characteristic of the chemical composition of the specimen. Thus, by fitting the (S)TEM with an electron energy-loss (EEL) spectrometer or an energy-dispersive X-ray spectrometer, chemical information about the sample on the nanometer scale can be obtained. The information limit in a TEM is limited by aberrations in the electromagnetic lenses. Now, systems that are largely free of aberrations can be constructed with aberration compensation ("correctors") brought about by adding optical elements to a lens that exhibit the same aberrations as the lens but of the opposite sign.
Restrictions on Samples: Sample preparation for TEM generally requires more time and experience than for most other characterization techniques. A TEM specimen must be approximately 1000 Ã… or less in thickness in the area of interest. The entire specimen must fit into a 3mm diameter cup and be less than about 100 microns in thickness. A thin, disc shaped sample with a hole in the middle, the edges of the hole being thin enough for TEM viewing, is typical. The initial disk is usually formed by cutting and grinding from bulk or thin film/substrate material, and the final thinning done by ion milling. Other specimen preparation possibilities include direct deposition onto a TEM-thin substrate (Si3N4, carbon); direct dispersion of powders on such a substrate; grinding and polishing using special devices (t-tool, tripod); chemical etching and electropolishing; lithographic patterning of walls and pillars for cross-section viewing; and focused ion beam (FIB) sectioning for site specific samples.
Artifacts are common in TEM samples, due both to the thinning process and to changing the form of the original material. For example surface oxide films may be introduced during ion milling and the strain state of a thin film may change if the substrate is removed. Most artifacts can either be minimized by appropriate preparation techniques or be systematically identified and separated from real information.
In order to become a qualified user on the FEI Titan TEM, 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 SNSF COVID-19 Authorization protocol and receive notification of authorization.
- Complete the training process for the FEI Tecnai TEM. Before being considered for training on the FEI Titan TEM, you must first be a fully qualified and proficient user of the Tecnai. An hour-long driving test on the Tecnai will be given.
- Contact email@example.com to coordinate subsequent training. Basic Titan training consists of Titan microscope alignments and aberration (image corrector) tuning, which will be completed in two 4-hour sessions and a 3-hour final, plus observations during start-up in your first three sessions with your own samples.
- Further training on specific techniques can be requested following basic training, which includes the following:
- STEM imaging
- Monochromator training (imaging or EELS)
- Energy-filtered TEM imaging
- TEM tomography
- STEM tomography
- Lorentz imaging
- Electron holography
- EDS analysis
- Environmental TEM: Guidelines on gases and gas pressures available, please contact firstname.lastname@example.org for more information.
The Materials Science and Engineering Department at Stanford also offers accredited courses on TEM theory and TEM laboratory.