TRANSMISSION ELECTRON MICROSCOPY (TEM) ANALYSIS SERVICES
Transmission electron microscopy (TEM) is the highest-resolution imaging technique available today. It takes advantage of the fact that trajectories of electrons within an applied beam passing through a specimen will be altered by interactions with the atoms in the sample. By analyzing and imaging the electrons that transmit through very thin slices of materials, it is possible to generate both chemical/compositional information and high-resolution visualizations — down to individual atomic columns in a lattice.
Covalent provides services in 6 major areas of TEM:
|TEM TECHNIQUE||TYPICAL APPLICATIONS|
|Bright-Field (BF) Dark-Field (DF) Imaging||Standard imaging techniques in TEM mode for visualizing nanoscale objects|
BF-TEM can be used to identify alignment to zone axes in crystalline materials
DF-TEM produces differently contrasted images to BF-TEM where elements nonobvious in the standard BF experiment can become more apparent.
|High-Resolution (HR) Imaging||Yields phase-contrast images where pixel intensity is correlated to the phase relationship between direct & diffracted beams|
Enables direct measurement of lattice spacing between atomic planes in crystalline samples
|Scanning Transmission Electron Microscopy (STEM) Imaging||Generates images more sensitive to the mean atomic number of different phases in a sample (High-angle Annular Dark-Field Imaging: HAADF)|
Chemical composition analysis via composition mapping or line profiling (often performed in conjunction with EDX, see below)
|Diffraction Pattern Imaging||Characterizes crystallinity of a material|
Determines crystal structure & orientation
Identifies defects in single crystals
|Electron Energy Loss Spectroscopy (EELS)||Characterizes the chemistry and electronic structure of atoms in the sample|
Better analytical sensitivity to chemical composition & lower detection threshold for lighter elements
Better spatial resolution compared to EDX/EDS
|Energy-dispersive X-ray Spectroscopy (EDX or EDS)||Identifying and mapping the spatial distribution of elements throughout a specimen in 1 or 2 dimensions.|
By analyzing and imaging the electrons that transmit through very thin slices of materials, it is possible to generate both chemical/compositional information and high-resolution visualizations — down to individual atomic columns in a lattice.
MEASUREMENTS COMMON WITH TEM:
- Morphological and structural characterization
- Dimensional measurements of nanostructures, atomic lattice spacings, cell diameter, (resolution as low as a fraction of an Angstrom)
- Line profiling
- Elemental mapping
- Electrochemical properties assays: bonding/valence state characterization, nearest-neighbor bonding information, measurement of dielectric response, free electron density, and energetic band gap) across and between different phases in nanostructures
USES & LIMITATIONS OF TEM:
- What it is great for:
- Highest resolution imaging service for nanoscale components or materials
- Compositional and chemical analysis
- Defect analysis
- Pathology & medical diagnostics, viral load monitoring
- Toxicology & drug delivery
- Single-particle / single-crystal analysis
- Requires extensive sample prep
- Specimen damage possible due to high voltage + current of the applied electron beam
- No surface information; minimal topographical sensitivity
INSTRUMENTS WE USE FOR TEM
Titan 80-300 TEM / STEM
This instrument is outfitted with a field-emission electron source capable of 0.8 Å resolution in TEM mode and 1.4 Å resolution in STEM over a range of applied energies from 80-300 kV. The system has been equipped with an image corrector which can minimize spherical distortions in the beam front; enabling both stage- and beam-tilt for optimized nano-scale alignments. A Gatan GIF facilitates energy-filtered imaging and high-precision electron energy loss spectroscopy (EELS), and an EDAX EDS detector is used for x-ray analysis of elemental composition assays and lateral mapping of chemical presence. Multiple stage holders provide for high-angle tomography stage control, and a Gatan 2k x 2k CCD camera is used to acquire images.
FEI Tecnai G2 Spirit TEM
The Tecnai system produces excellent 2D and 3D images with automated functionality and is configured with twin lenses for high-contrast studies specialized for biological samples, or like materials visualized more easily under high-contrast settings. This instrument utilizes a tungsten filament electron source capable of emitting at 20-120 kV and is EDX-enabled with an attached Bruker SDD EDX detector. Images are acquired using an FEI Eagle 4k CCD camera, and variety of single- and double-tilt stage holders facilitate electron tomography and crystallographic diffraction analysis.