Transmission/Scanning Transmission Electron Microscopy
NREL investigates the structure and chemistry of materials with particular emphasis on defects and interfaces using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM).
This is particularly useful for determining how the microstructure affects derived material properties. Our microscopes are equipped to perform diffraction contrast, higher-resolution phase-contrast microscopy, high-angle annular dark-field microscopy, nanodiffraction, convergent beam electron diffraction, energy-dispersive X-ray spectroscopy, and electron energy-loss spectroscopy.
How They Work
Transmission Electron Microscopy
In TEM, a thin sample, typically less than 200 nanometers, 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 TEM imaging gives information about the microstructure of a material and its defects at an atomic resolution.
Scanning Transmission Electron Microscopy
With 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.
Equipment and Instruments
We're equipped with several highly advanced instruments:
- FEI 200 kV field emitting gun F20 UT ultra-high resolution STEM fitted with a high-angle angular dark field STEM detector for high-resolution (~0.14 nm) STEM Z-contrast microscopy. This provides directly interpretable, chemically sensitive, atomic resolution images. The F20 UT has a 0.17 nm point-to-point resolution in the high-resolution TEM mode. This instrument is also equipped with a GIF that enables electron energy loss spectroscopy and elemental mapping for a wide range of elements and energy-filtered electron diffraction and imaging, and an EDS system for compositional analysis and elemental mapping with high spatial resolution.
- 300 kV Philips CM30 TEM for amplitude-contrast and high-resolutionTEM imaging with an EDS system for compositional analysis
- A wide range of specimen preparation equipment including a low-energy, low-temperature ion milling system to reduce damage during sample preparation
- A dual-beam focused-ion-beam workstation that enables site-specific preparation of TEM samples.
The following table is a condensed listing of equipment, techniques, applications, and properties of instrumentation for Transmission/Scanning Transmission Electron Microscopy.
Major Instrumentation for 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
FIB etch and deposition
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.