<p>Two-dimensional (2D) titanium dioxide (TiO<InlineEquation ID="IEq1"> <EquationSource Format="TEX">$_2$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mn>2</mn> <mrow /> </mmultiscripts> </math></EquationSource> </InlineEquation>) derivatives are promising candidates for optoelectronic and catalytic applications; however, their wide band gaps and limited tunability restrict practical implementation. In this work, we propose a novel 2D tetragonal TiOSe material in which the substitution of selenium improves structural flexibility and diversifies the electronic response. Using first-principles density functional theory (DFT) with hybrid functionals, we systematically studied explore the effects of substitutional doping, replacing selenium with boron (B), fluorine (F), nitrogen (N), nickel (Ni), sulfur (S), and silicon (Si) on the structural, electronic, and optical properties. Phonon calculations and ab initio molecular dynamics (AIMD) simulations confirm the dynamic and thermal stability of all doped systems. Structural optimizations reveal dopant-specific lattice distortions, with sulfur inducing minimal strain, while nickel and silicon cause significant bond rearrangements. Our cohesive energy calculations reveal the thermodynamic stability of doped TiOSe systems, with values ranging from − 5.65 eV/atom (fluorine doped) to − 9.85 eV/atom (boron doped). The pristine TiOSe monolayer shows strong stability (− 6.45 eV/atom), while covalent dopants like boron and nitrogen enhance cohesion through stronger bonding. All configurations exceed the 4 eV/atom stability threshold, confirming their potential for practical device applications under ambient conditions. Electronic structure analysis reveals that sulfur substitution creates an indirect band gap of 0.67 eV, whereas doping with B, F, N, Ni, and Si yields a metallic state characterized by a finite density of states at the Fermi level. Comprehensive optical characterization reveals strong absorption coefficients exceeding <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$6 \times 10^{5}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>6</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>5</mn> </msup> </mrow> </math></EquationSource> </InlineEquation> cm<InlineEquation ID="IEq6"> <EquationSource Format="TEX">$^{-1}$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow /> <mrow /> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation> in the UV–visible range, with tunable dielectric functions and refractive indices spanning from 1 to 6 across different doping configurations. The S-doped system exhibits a distinct absorption edge at 1.8 eV (corresponding to near-infrared wavelengths), while Ni doping induces broadband optical conductivity suitable for transparent electrode applications. These results demonstrate that substitutional doping is an effective approach to tailor the electronic and optical characteristics of 2D TiOSe, offering design guidelines for multifunctional materials in applications such as photovoltaics, photocatalysis, and transparent conductors.</p>

Tailoring electronic and optical properties of 2D tetragonal TiOSe through substitutional doping: first-principles insights for optoelectronic applications

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发表日期：

2025年11月29日

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Mohamed Barhoumi

摘要

Two-dimensional (2D) titanium dioxide (TiO $_2$ $_{2}$ ) derivatives are promising candidates for optoelectronic and catalytic applications; however, their wide band gaps and limited tunability restrict practical implementation. In this work, we propose a novel 2D tetragonal TiOSe material in which the substitution of selenium improves structural flexibility and diversifies the electronic response. Using first-principles density functional theory (DFT) with hybrid functionals, we systematically studied explore the effects of substitutional doping, replacing selenium with boron (B), fluorine (F), nitrogen (N), nickel (Ni), sulfur (S), and silicon (Si) on the structural, electronic, and optical properties. Phonon calculations and ab initio molecular dynamics (AIMD) simulations confirm the dynamic and thermal stability of all doped systems. Structural optimizations reveal dopant-specific lattice distortions, with sulfur inducing minimal strain, while nickel and silicon cause significant bond rearrangements. Our cohesive energy calculations reveal the thermodynamic stability of doped TiOSe systems, with values ranging from − 5.65 eV/atom (fluorine doped) to − 9.85 eV/atom (boron doped). The pristine TiOSe monolayer shows strong stability (− 6.45 eV/atom), while covalent dopants like boron and nitrogen enhance cohesion through stronger bonding. All configurations exceed the 4 eV/atom stability threshold, confirming their potential for practical device applications under ambient conditions. Electronic structure analysis reveals that sulfur substitution creates an indirect band gap of 0.67 eV, whereas doping with B, F, N, Ni, and Si yields a metallic state characterized by a finite density of states at the Fermi level. Comprehensive optical characterization reveals strong absorption coefficients exceeding $6 \times 10^{5}$ $6 \times 10^{5}$ cm $^{-1}$ $^{- 1}$ in the UV–visible range, with tunable dielectric functions and refractive indices spanning from 1 to 6 across different doping configurations. The S-doped system exhibits a distinct absorption edge at 1.8 eV (corresponding to near-infrared wavelengths), while Ni doping induces broadband optical conductivity suitable for transparent electrode applications. These results demonstrate that substitutional doping is an effective approach to tailor the electronic and optical characteristics of 2D TiOSe, offering design guidelines for multifunctional materials in applications such as photovoltaics, photocatalysis, and transparent conductors.