Subsurface depth dependence of nitrogen doping in TiO₂anatase: a DFT study

Area of Science:

• Materials Science
• Solid State Physics
• Computational Chemistry

Background:

• Titanium dioxide (TiO2) is a crucial semiconductor material with applications in photocatalysis and solar cells.
• Nitrogen doping is a common strategy to enhance TiO2's visible light absorption and photocatalytic activity.
• Understanding dopant behavior at the atomic level is key to optimizing material properties.

Purpose of the Study:

• To investigate the structural and electronic properties of nitrogen-doped TiO2 anatase.
• To determine the influence of nitrogen dopant depth and site (substitutional vs. interstitial) on formation energy.
• To analyze the electronic structure modifications, including intragap states and spin magnetization.

Main Methods:

• First-principles calculations based on density functional theory (DFT).
• Simulation of nitrogen (N) impurity at various depths below the TiO2 anatase (101) surface.
• Evaluation of formation energies for both substitutional and interstitial N sites.
• Analysis of local atomic structure and electronic band structure.

Main Results:

• Interstitial nitrogen sites exhibit a lower formation energy compared to substitutional sites in TiO2 anatase.
• The formation energy shows a mild dependence on the dopant's depth below the surface.
• Bond lengths around the nitrogen impurity vary smoothly with depth.
• Nitrogen doping introduces intragap impurity states and localized hole-related spin magnetization density.

Conclusions:

• Interstitial nitrogen doping is energetically favorable in TiO2 anatase.
• Dopant depth has a minor but discernible effect on the formation energy and local structure.
• Nitrogen doping significantly alters the electronic and magnetic properties of TiO2, creating localized spin states.