Subsurface depth dependence of nitrogen doping in TiO₂ anatase: a DFT study

Abstract

We report first-principles calculations of the structure and electronic structure of nitrogen-doped TiO2 anatase as a function of the dopant depth below the (101) surface. Specifically we evaluate the depth dependence of the formation energy for a few positions of the N impurity, considering for both substitutional and interstitial sites. We find a significant advantage of interstitial over substitutional positions, and a mild dependence of this formation energy on depth. The lengths of the bonds surrounding the impurity also evolve smoothly with depth. Regarding the electronic structure, we report the main features of the intragap impurity states and the hole-related spin magnetization density surrounding the N impurity.

Role of N Doping in the Reduction of Titania Nanostructures

“…The formation energy labeled as E f is defined as E normalf , N s = E normalN @ Ti 84 O 167 + 1 2 E normalO 2 − 1 2 E normalN 2 − E Ti 84 O 168 E normalf , N i = E normalN @ Ti 84 O 168 − 1 2 E normalN 2 − E Ti 84 O 168 where E N@Ti 84 O 167 and E N@Ti 84 O 168 correspond to the total energies of substitutional and interstitial doped NPs, respectively; E Ti 84 O 168 is the total energy of the undoped NP; and E N 2 and E O 2 are the total energies of the N 2 and O 2 molecules in their electronic ground state, which for the O 2 molecule is a triplet state. This definition of reference state of element is consistent with previous studies. ,, Consequently, the nitrogen molecule is taken as a convenient reference, and from the energy balance in eqs and , we do not expect any difference when employing a different source of nitrogen. In fact, different nitrogen precursors are used in experimental studies such as ammonium hydroxide or ammonia.…”

“…This definition of reference state of element is consistent with previous studies. 19,26,35 Consequently, the nitrogen molecule is taken as a convenient reference, and from the energy balance in eqs 1 and 2, we do not expect any difference when employing a different source of nitrogen. In fact, different nitrogen precursors are used in experimental studies such as ammonium hydroxide or ammonia.…”

“…They found that N at the (001) side of the interface constitutes the most stable doping arrangement. On the other hand, Kakil et al demonstrated that subsurface N doping in TiO 2 anatase is depth-dependent for both substitutional and interstitial N, and that N location depends on the nanocrystal facet. Moreover, they investigated N-doping of Ti 9 O 18 and Ti 28 O 56 nanoclusters and found that the interstitial N formation energy is lower than that of substitutional N. Additional theoretical calculations predicted a decreasing of the band gap due to the presence of nitrogen, in agreement with results from UV–vis spectroscopy .…”

Theoretical and experimental investigation of the electronic and optical properties of pure and interstitial nitrogen -doped (TiO2)n cluster

“…To 101) Anatase TiO 2 Surfaces and discovered that N001 is the most stable doping arrangement, with the nitrogen atom on the (001) side of the interface. kakil et al (Kakil et al 2020) demonstrated that nitrogen doping in TiO 2 anatase is subsurface depth dependent in substitution and interstitial doped forms, and that nitrogen impurity locations are dependent on nanocrystal facet (Kakil et al 2021). They also investigated the formation of nitrogen impurity in TiO 2 nanoparticles and how the mid-gap state of TiO 2 nanocrystal is generated, as well as how the nitrogen impurity locations depend on facet of nanocrystal.…”

Theoretical and Experimental Investigation of the Electronic and Optical Properties of Pure and Interstitial Nitrogen -Doped (TiO2)n Cluster

“…To 101) Anatase TiO 2 Surfaces and discovered that N001 is the most stable doping arrangement, with the nitrogen atom on the (001) side of the interface. kakil et al (Kakil et al 2020) demonstrated that nitrogen doping in TiO 2 anatase is subsurface depth dependent in substitution and interstitial doped forms, and that nitrogen impurity locations are dependent on nanocrystal facet (Kakil et al 2021). They also investigated the formation of nitrogen impurity in TiO 2 nanoparticles and how the mid-gap state of TiO 2 nanocrystal is generated, as well as how the nitrogen impurity locations depend on facet of nanocrystal.…”