Transmission/Scanning Transmission Electron Microscopy

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:

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 (EELS) 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 HRTEM 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 (FIB) workstation that enables site-specific preparation of TEM samples.

Applications

Crystallography

Electron diffraction is used to determine the crystallographic structure of materials on a fine scale.

Microstructure

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.

Composition

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.

Cross-sectional Analysis

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.

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	THERMO EDS FIB etch and deposition High-resolution SEM

Modes

For additional information, contact Mowafak Al-Jassim, 303-384-6602.

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