stem

**STEM** (Scanning Transmission Electron Microscopy) is a **TEM mode where a focused electron probe is scanned across the sample** — detecting transmitted electrons at each point to form images with multiple simultaneous contrast mechanisms (BF, ADF, HAADF) and enable spectroscopy (EELS, EDS) at each pixel. **How Does STEM Work?** - **Probe**: Focus the electron beam to a sub-angstrom probe (aberration-corrected). - **Scan**: Raster the probe across the sample point by point. - **Detectors**: Collect transmitted electrons at different angular ranges simultaneously. - **Spectroscopy**: At each pixel, collect EELS and/or EDS signals for composition mapping. **Why It Matters** - **Z-Contrast (HAADF)**: Image intensity proportional to $Z^{1.7}$ — heavy atoms appear bright. Directly interpretable. - **Simultaneous Signals**: BF, ADF, HAADF images + EELS + EDS all collected simultaneously from one scan. - **Atomic-Scale Composition**: With EELS/EDS, determine chemical composition at atomic-column resolution. **STEM** is **the scanning spotlight for atoms** — focusing electrons to a point and scanning to build atomic-resolution images with simultaneous chemical analysis.