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.