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Electronic properties of substitutional impurities in graphenelike C2N, tg−C3N4, and hg−C3N4

Saif Ullah, Pablo A. Denis, Marcos G. Menezes, Fernando Sato, and Rodrigo B. Capaz
Phys. Rev. B 102, 134112 – Published 19 October 2020
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  • INTRODUCTION
  • METHODS
  • RESULTS
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
    • Supplemental Material
    References

    Abstract

    We study the electronic and structural properties of substitutional impurities of graphenelike nanoporous materials C2N, tg-, and hg−C3N4 by means of density functional theory calculations. We consider four types of impurities; boron substitution on carbon sites [B(C)], carbon substitution on nitrogen sites [C(N)], nitrogen substitution on carbon sites [N(C)], and sulfur substitution on nitrogen sites [S(N)]. From cohesive energy calculations, we find that the C(N) and B(C) substitutions are the most energetically favorable and induce small bond modifications in the vicinity of the impurity, while the S(N) induces strong lattice distortions. Though all of the studied impurities induce defect levels inside the band gap of these materials, their electronic properties are poles apart depending on the behavior of the impurity as an acceptor [B(C) and C(N)] or a donor [N(C) and S(N)]. It is also observed that acceptor (donor) wave functions are composed only of σ (π) orbitals from the impurity itself and/or neighboring sites, closely following the orbital composition of the valence (conduction) band wave functions of the pure materials. Consequently, acceptor wave functions are directed towards the pores and donor wave functions are more extended throughout the neighboring atoms, a property that could further be explored to modify the interaction between these materials and adsorbates. Moreover, impurity properties display a strong site sensitivity and ground state binding energies ranging from 0.03 to 1.13 eV in nonmagnetic calculations, thus offering an interesting route for tuning the optical properties of these materials. Finally, spin-polarized calculations reveal that all impurity configurations have a magnetic ground state with a total moment of 1.0μB per unit supercell, which rises from the spin splitting of the impurity levels. In a few configurations, more than one impurity level can be found inside the gap and two of them could potentially be explored as two-level systems for single-photon emission, following similar proposals recently made on defect complexes on TMDCs.

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    • Received 10 July 2020
    • Revised 28 September 2020
    • Accepted 29 September 2020

    DOI:https://doi.org/10.1103/PhysRevB.102.134112

    ©2020 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    DefectsDopantsStructural properties
    1. Physical Systems
    2-dimensional systems
    1. Techniques
    Band structure methodsDensity functional theory
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Saif Ullah1,*, Pablo A. Denis2, Marcos G. Menezes3,†, Fernando Sato1, and Rodrigo B. Capaz3

    • 1Departamento de Física, Instituto de Ciências Exatas, Campus Universitário, Universidade Federal de Juiz de Fora, 36036-900 Juiz de Fora, MG, Brazil
    • 2Computational Nanotechnology, DETEMA, Facultad de Química, UDELAR, CC 1157, 11800 Montevideo, Uruguay
    • 3Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21941-972 Rio de Janeiro, RJ, Brazil

    • *sullah@fisica.ufjf.br
    • †marcosgm@if.ufrj.br

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    Issue

    Vol. 102, Iss. 13 — 1 October 2020

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    Images

    • Figure 1
      Figure 1

      Top: crystal structures of C2N (left), tg−C3N4 (middle), and hg−C3N4 (right). The green areas represent the unit cells and the nonequivalent nitrogen atoms are labeled as h (hole), l (link), and c (center) in each structure. The hg−C3N4 structure has two nonequivalent carbon atoms, labeled according to the neighboring Nl or Nc sites. Bottom: band structures and projected density of states (PDOS) for selected atoms in the corresponding structures. The contributions from σ and π orbitals from all nonequivalent atoms are included, as specified in the color codes.

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    • Figure 2
      Figure 2

      Band structure and projected density of states (PDOS) for different substitutional impurities in C2N (nonpolarized calculations). See the text and Fig. 1 for a description of the nonequivalent sites. The Fermi energy is set to zero in all cases and the PDOS color code is indicated in each panel. The labels ‘1st’ and ‘2nd’ label atoms which are first and second neighbors to the impurity, respectively.

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    • Figure 3
      Figure 3

      Band structure and projected density of states (PDOS) for different substitutional impurities in tg−C3N4 (nonpolarized calculations). The PDOS labels follow the same notations as in Fig. 2.

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    • Figure 4
      Figure 4

      Band structure and projected density of states (PDOS) for different substitutional impurities in hg−C3N4 (nonpolarized calculations). The PDOS labels follow the same rules as in Fig. 2.

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    • Figure 5
      Figure 5

      Local density of states (LDOS) for the ground state impurity level found in each case. When the ground state is nearly degenerate, the sum over the corresponding levels is shown. Gray, blue, pink, and yellow spheres represent carbon, nitrogen, boron, and sulfur atoms, respectively. In each case, the position of the impurity is indicated by an orange circle. The density is higher (lower) in violet (red) regions.

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    • Figure 6
      Figure 6

      Band structure and total density of states (DOS) for each impurity case in the C2N structure (spin-polarized calculations). Blue (red) lines correspond to spin up (spin down) states. In the DOS plots, the black curve corresponds to the difference between the spin up and down components.

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    • Figure 7
      Figure 7

      Band structure and total density of states (DOS) for each impurity case in the tg−C3N4 structure (spin-polarized calculations). The color code is the same of Fig. 6.

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    • Figure 8
      Figure 8

      Band structure and total density of states (DOS) for each impurity case in the hg−C3N4 structure (spin-polarized calculations). The color code is the same as Fig. 6.

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