Discover how Scanning Transmission Electron Microscopy (STEM) reveals morphology, elemental and phase composition, crystallinity, atomic structure as well as functional physical properties such as strain or electric fields inside materials and semiconductor devices. Learn the principles behind TEM and STEM, how the image contrast is formed, and why advanced 4D STEM and electron diffraction techniques are extending the conventional analytical STEM and transforming material science characterisation.
Scanning Transmission Electron Microscopy (STEM) is one of the most powerful analytical techniques available today. It allows scientists to visualize internal structure, map chemical composition, measure strain, determine grain orientation, and even solve unknown crystal structures down to sub-ångström resolution de novo.
In this guide, you will learn:
If you are exploring advanced microscopy for materials science or semiconductor applications, this overview will help you to understand the fundamentals and the latest analytical STEM capabilities.
Transmission Electron Microscopy is a technique where an electron beam passes through an ultra-thin specimen. The transmitted electrons carry information about the internal structure of the material.
Unlike Scanning Electron Microscopy, which mainly provides surface information, TEM allows imaging of the interior of a sample at nanometer and atomic resolution.
TEM uses a parallel electron beam and forms images from scattered and unscattered electrons by the objective lens that are magnified by several projection lenses.
STEM is a mode of transmission electron microscopy where a highly focused, convergent electron probe is scanned point by point across the sample. At each pixel, signals are generated from the interaction of electrons with the sample and collected by various detectors.
These signals may include:
This pixel-by-pixel signal collection makes STEM a powerful platform for imaging, compositional analysis, structural analysis, and advanced difraction techniques.
What is the difference between SEM, TEM, and STEM?
SEM detects scattered (BSE) and emitted (SE) elecrons from the surface of a specimen and is primarily used for surface imaging and characterization.
TEM uses a parallel beam transmitted through a thin specimen to form high resolution, phase contrast images of internal structure.
STEM also uses transmitted electrons, but scans a focused electron probe across the sample, enabling simultaneous imaging, elemental mapping, diffraction, and analytical measurements.
Contrast in TEM imaging is created mainly by two mechanisms:
1. Scattering contrast
Areas that scatter electrons strongly appear darker because more electrons are blocked by the objective aperture.
2. Phase contrast
Electron waves passing through the sample experience phase shifts depending on the material structure. These waves interfere and create high resolution lattice images.
The final image depends on factors such as spherical aberration, defocus, and contrast transfer function, which ultimately limit achievable resolution.
Acceleration voltage mainly influences resolution and penetration depth.
Lower voltages:
Higher voltages:
Analytical STEM combines imaging at each scanned position with chemical and structural analysis.
Key analytical techniques include:
This allows detailed characterization of alloys, nanoparticles, semiconductor devices, and complex multilayer architectures in additive manufacturing and functional materials.
STEM/EDX tomography enables three-dimensional characterisation of materials and their morphology.
In this technique, the sample is tilted across a defined angular range while images or analytical data are collected at each tilt step. Using 3D reconstruction algorithms, a 3D volume of the sample is generated. This allows for segmentation of the key features in the sample architecture.
Applications include:
4D-STEM refers to scanning a 2D region of interest while recording 2D diffraction pattern at every pixel. This produces a four-dimensional dataset with two spatial dimensions and two diffraction dimensions.
4D-STEM enables:
This techniques significantly improves the spatial resolution compared to SEM-based diffraction techniques (EBSD, TKD).
Beam precession tilts and rotates the electron beam during diffraction data acquisition, effectivelly minimizing the dynamical scattering effects.
This technique facilitates:
Beam precession is especially critical for high quality 4D-STEM datasets, resulting in accurate and precise analytical results.
Electron diffraction tomography collects diffraction patterns while tilting the sample (stepwise or continuously) across a defined angular range.
Combined with beam precession and dedicated refinement software, this technique allows for:
This transforms electron diffraction tomography for atomic structure determination for otherwise challenging samples. Crystal twinning or too small crystals do not prevent atomic structure determination anymore.
Modern materials and semiconductor devices are becoming:
Analytical STEM enables:
All these capabilities are essential for the characterization of strucutral (critical dimensions) and physical properties of advanced nodes, functional materials, complex alloys, and nanoparticles.
Dr. Daniel Nemecek, Tescan STEM expert