xanes

**XANES** (X-Ray Absorption Near-Edge Structure) is the **near-edge region (±50 eV) of an XAS spectrum** — providing a fingerprint of the absorbing atom's oxidation state, coordination geometry, and electronic structure through the shape and position of the absorption edge. **What Does XANES Reveal?** - **Edge Position**: Shifts to higher energy with increasing oxidation state (~1-3 eV per formal charge unit). - **Pre-Edge Features**: Transitions to empty $d$ orbitals reveal coordination geometry (tetrahedral vs. octahedral). - **White Line**: Intense near-edge peak related to empty density of states above the Fermi level. - **Fingerprinting**: Compare to reference spectra for phase/oxidation state identification. **Why It Matters** - **Oxidation State**: The most reliable method for determining the oxidation state of an element in a complex material. - **High-k Dielectrics**: Identifies the phase and bonding of Hf in HfO$_2$ gate dielectrics. - **Catalysis**: Determines the active oxidation state of catalytic species under operating conditions. **XANES** is **the oxidation state ruler** — reading chemical state and coordination from the shape of the X-ray absorption edge.