Titan Environmental Transmission Electron Microscope (ETEM) Laboratory

Titan photoThe FEI Titan 80-300 Environmental Transmission Electron Microscope has the following capabilities:

The Titan's specifications are as follows (at 300 kV):

Standard Mode
ETEM mode (< 0.5 mbar nitrogen)
uncorrected
Cs image corrected
uncorrected
Cs image corrected
TEM information limit (nm)
< 0.1
< 0.1
< 0.12
< 0.12
TEM point resolution (nm)
0.20
< 0.1
< 0.12
Probe current @ 1nm (nA)
> 0.6
> 0.6
> 0.6
> 0.6

System energy resolution (eV)
– with monochromator on

0.7
< 0.20
0.8
< 0.25
STEM resolution (nm)
< 0.27
< 0.27

 

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 about 1nm) 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 Å 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.

Titan Training Modules:

Pre-requisites for Titan training:

  1. Titan Basics, alignments + Cs image corrector tuning
  2. STEM:
  3. EELS (STEM and/or TEM mode)
  4. Monochromator
  5. Energy-filtered TEM/ Elemental Mapping
  6. Tomography (TEM mode)
  7. Tomography (STEM mode)
  8. Lorentz imaging
  9. Electron holography
  10. High-resolution imaging and through-focal series acquisition and reconstruction
  11. EDS analysis
  12. Environmental TEM (Available Q3 2011)
Ann Marshall Ai Leen Koh
TEM Lab Director Research Scientist
afm@stanford.edu alkoh@stanford.edu
(650) 723-3572 (office) (650) 723-1686 (office)
(650) 725-4684 (lab)
McCullough Room 229 McCullough Room 315