In transmission electron microscopy (TEM), a thin sample, typically less than 200 nm, is bombarded by a highly focused beam of single-energy electrons. The beam has enough energy for the electrons to be transmitted through the sample, and the transmitted or scattered electron signal is greatly magnified by a series of electromagnetic lenses. The magnified signal may be observed by electron diffraction, amplitude-contrast imaging such as diffraction contrast, or phase-contrast imaging such as high resolution TEM.
Transmission electron diffraction patterns help to determine the crystallographic structure of a material. Amplitude-contrast images yield information about the chemistry and microstructure of a material and its defects. Phase-contrast imaging or high-resolution (HR) TEM imaging gives information about the microstructure of a material and its defects at an atomic resolution.
With scanning transmission electron microscopy (STEM), a highly-focused electron probe is raster-scanned across the material, and various types of scattering are collected as a function of position. The transmitted electrons at high scattering angle can be collected to form high-resolution, chemically sensitive, atomic number (Z-) contrast images. The x-rays generated can be collected using an energy-dispersive X-ray spectroscopy (EDS) detector and used to form high spatial resolution compositional maps. Electron energy losses can be detected using a Gatan image filter (GIF) to map the compositional and electronic properties of materials.
Our Analytical Microscopy group is equipped with several highly advanced instruments:
Electron diffraction is used to determine the crystallographic structure of materials on a fine scale.
Diffraction-contrast and high-resolution TEM yields information on the composition, microstructure, and atomic structure of materials and defects. High-resolution STEM Z-contrast imaging provides directly interpretable, chemically sensitive images of the structure of materials, defects, and interfaces in samples with atomic resolution.
EDS and EELS provide quantitative and qualitative compositional analysis of materials to sub-nm spatial resolution for almost any element. STEM EDS and EELS enable elemental mapping with nm-scale resolution. EELS also provides information on the electronic properties of materials. A GIF enables elemental mapping by energy-filtered TEM with high-spatial resolution.
Investigates the structure, composition, and perfection of multilayer films and interfaces.
The following table is a condensed listing of equipment, techniques, applications, and properties of instrumentation for Transmission/Scanning Transmission Electron Microscopy.
| System | Analytical Techniques | Typical Applications | Lateral Resolution | Special Features |
|---|---|---|---|---|
| Phillips CM30 | TEM | Structural and compositional analysis and lattice imaging | 0.23 nm | High-resolution, EDS |
| FEI F20 (UT) | Field-emission STEM | Structural, electronic, and compositional analysis; elemental mapping; lattice imaging | 0.19 nm for HRTEM; 0.14 nm for Z-contrast STEM |
High-resolution, Z-contrast, EDS, EELS, Energy filtering, Field-emission electron source |
| FEI NOVA 2000 | Field-emission scanning electron (SEM) and ion microscopy | Preparation of TEM and SEM samples. Fabrication of nano-structures | 1.1 nm @15 kV for SEM 7 nm for SIM |
THERMO EDS FIB etch and deposition High-resolution SEM |
For additional information, contact Mowafak Al-Jassim, 303-384-6602.