TEM

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 Thickness determination 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 spatial distribution of elements throughout a specimen in 1 or 2 dimensions.

TEM, STEM

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 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 analyses
  • Limitations:
    • Requires extensive sample prep
    • Specimen damage possible due to high voltage + current of the applied electron beam
    • No surface information; minimal topographical sensitivity
    • Volatile or insulating materials are often difficult / impossible to image

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 Technai G2 Spirit TEM

The Technai 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.