angle-resolved xps

**AR-XPS** (Angle-Resolved XPS) is a **non-destructive depth profiling technique that varies the photoelectron take-off angle to change the sampling depth** — at grazing angles, only the topmost layers contribute to the signal, while at normal emission, deeper layers are also sampled. **How Does AR-XPS Work?** - **Tilt**: Vary the sample tilt (or detector angle) from 0° (normal) to ~80° (grazing). - **Sampling Depth**: Effective depth $d = 3lambdacos heta$, where $lambda$ is the inelastic mean free path. - **Depth Profile**: Plot relative peak intensities vs. angle to reconstruct the depth distribution. - **Maximum Entropy**: Advanced reconstruction methods (Maximum Entropy, regularization) extract quantitative depth profiles. **Why It Matters** - **Non-Destructive**: No sputter damage — unlike sputter depth profiling, AR-XPS preserves chemical states. - **Ultra-Thin Films**: Ideal for characterizing films < 10 nm (gate oxides, interface layers, surface treatments). - **Chemical Depth**: Provides chemical state information as a function of depth (not just composition). **AR-XPS** is **XPS depth profiling without sputtering** — tilting the sample to see different depths non-destructively.