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Electronic structures of defects and magnetic impurities in MoS2 monolayers.

Lu SC, Leburton JP - Nanoscale Res Lett (2014)

Bottom Line: Specifically, we found VB group impurity elements, such as Ta, substituting Mo to achieve negative formation energy values with impurity states all sitting at less than 0.1 eV from the valence band maximum (VBM), making them the optimal p-type dopant candidates.Among the magnetic impurities such as Mn, Fe, and Co with 1, 2, and 3 magnetic moments/atom, respectively, Mn has the lowest formation energy, the most localized spin distribution, and the nearest impurity level to the conduction band among those elements.Additionally, impurity levels and Fermi level for the above three elements are closer to the conduction band than the previous work (PCCP 16:8990-8996, 2014) which shows the possibility of n-type doping by Mn, thanks to our 5 × 5 cell model.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA, slu18@illinois.edu.

ABSTRACT
We provide a systematic and theoretical study of the electronic properties of a large number of impurities, vacancies, and adatoms in monolayer MoS2, including groups III and IV dopants, as well as magnetic transition metal atoms such as Mn, Fe, Co, V, Nb, and Ta. By using density functional theory over a 5 × 5 atomic cell, we identify the most promising element candidates for p-doping of MoS2. Specifically, we found VB group impurity elements, such as Ta, substituting Mo to achieve negative formation energy values with impurity states all sitting at less than 0.1 eV from the valence band maximum (VBM), making them the optimal p-type dopant candidates. Moreover, our 5 × 5 cell model shows that B, a group III element, can induce impurity states very close to the VBM with a low formation energy around 0.2 eV, which has not been reported previously. Among the magnetic impurities such as Mn, Fe, and Co with 1, 2, and 3 magnetic moments/atom, respectively, Mn has the lowest formation energy, the most localized spin distribution, and the nearest impurity level to the conduction band among those elements. Additionally, impurity levels and Fermi level for the above three elements are closer to the conduction band than the previous work (PCCP 16:8990-8996, 2014) which shows the possibility of n-type doping by Mn, thanks to our 5 × 5 cell model.

No MeSH data available.


DOS of MoS2with (a) S vacancy (b) Mo vacancy, and (c) adsorbate Mo on Mo (solid line). Pristine MoS2 (dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.
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Fig3: DOS of MoS2with (a) S vacancy (b) Mo vacancy, and (c) adsorbate Mo on Mo (solid line). Pristine MoS2 (dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.

Mentions: Before studying the doping effect of substitutional impurities on monolayer MoS2, we first simulate the electronic properties of vacancies in MoS2 by removing a Mo or an S atom from a pristine MoS2 monolayer to identify the corresponding gap states and assess the existence of a resulting magnetic moment. Formation energies are calculated for the purpose of estimating the tendency of vacancy creation and listed in Table 1 with theoretical magnetic moments. The DOSs for two kinds of vacancies are also displayed in Figure 3. As revealed from our formation energy calculation, creating an S vacancy (Eform ≈ 3.36 eV) is more energetically favorable than creating a Mo vacancy (Eform ≈ 7.36 eV), which is in good agreement with the experimental findings [24]. Furthermore, the DOS plots in Figure 3a show the gap states generated by a single S vacancy are close to the conduction band, while the states originating from single Mo vacancy (Figure 3b) are in even closer proximity of the VBM with three peaks of gap states arising from the mixture of the neighboring S p-orbitals. This suggests the possibility of p-type doping if Mo vacancy can be created in an efficient way. However, there is no magnetism induced in monolayer MoS2 by Mo or S vacancy as found in our simulation, showing no reason of using intrinsically defective MoS2 for spintronics applications, unlike the case of graphene and h-BN [25, 26]. In Figure 3c, we show the DOS for a Mo atom adsorbed on Mo site in MoS2 cell. It is seen that the incorporation of the adsorbate Mo creates defect states near the both band edges, VBM, and CBM, with a formation energy of approximately 1.1 eV higher than for an S vacancy, but not as high as for a Mo vacancy. Therefore, in addition to S vacancy, the Mo adsorbate can be a possible source of tail states as observed in the experiment [27].Table 1


Electronic structures of defects and magnetic impurities in MoS2 monolayers.

Lu SC, Leburton JP - Nanoscale Res Lett (2014)

DOS of MoS2with (a) S vacancy (b) Mo vacancy, and (c) adsorbate Mo on Mo (solid line). Pristine MoS2 (dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4494037&req=5

Fig3: DOS of MoS2with (a) S vacancy (b) Mo vacancy, and (c) adsorbate Mo on Mo (solid line). Pristine MoS2 (dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.
Mentions: Before studying the doping effect of substitutional impurities on monolayer MoS2, we first simulate the electronic properties of vacancies in MoS2 by removing a Mo or an S atom from a pristine MoS2 monolayer to identify the corresponding gap states and assess the existence of a resulting magnetic moment. Formation energies are calculated for the purpose of estimating the tendency of vacancy creation and listed in Table 1 with theoretical magnetic moments. The DOSs for two kinds of vacancies are also displayed in Figure 3. As revealed from our formation energy calculation, creating an S vacancy (Eform ≈ 3.36 eV) is more energetically favorable than creating a Mo vacancy (Eform ≈ 7.36 eV), which is in good agreement with the experimental findings [24]. Furthermore, the DOS plots in Figure 3a show the gap states generated by a single S vacancy are close to the conduction band, while the states originating from single Mo vacancy (Figure 3b) are in even closer proximity of the VBM with three peaks of gap states arising from the mixture of the neighboring S p-orbitals. This suggests the possibility of p-type doping if Mo vacancy can be created in an efficient way. However, there is no magnetism induced in monolayer MoS2 by Mo or S vacancy as found in our simulation, showing no reason of using intrinsically defective MoS2 for spintronics applications, unlike the case of graphene and h-BN [25, 26]. In Figure 3c, we show the DOS for a Mo atom adsorbed on Mo site in MoS2 cell. It is seen that the incorporation of the adsorbate Mo creates defect states near the both band edges, VBM, and CBM, with a formation energy of approximately 1.1 eV higher than for an S vacancy, but not as high as for a Mo vacancy. Therefore, in addition to S vacancy, the Mo adsorbate can be a possible source of tail states as observed in the experiment [27].Table 1

Bottom Line: Specifically, we found VB group impurity elements, such as Ta, substituting Mo to achieve negative formation energy values with impurity states all sitting at less than 0.1 eV from the valence band maximum (VBM), making them the optimal p-type dopant candidates.Among the magnetic impurities such as Mn, Fe, and Co with 1, 2, and 3 magnetic moments/atom, respectively, Mn has the lowest formation energy, the most localized spin distribution, and the nearest impurity level to the conduction band among those elements.Additionally, impurity levels and Fermi level for the above three elements are closer to the conduction band than the previous work (PCCP 16:8990-8996, 2014) which shows the possibility of n-type doping by Mn, thanks to our 5 × 5 cell model.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA, slu18@illinois.edu.

ABSTRACT
We provide a systematic and theoretical study of the electronic properties of a large number of impurities, vacancies, and adatoms in monolayer MoS2, including groups III and IV dopants, as well as magnetic transition metal atoms such as Mn, Fe, Co, V, Nb, and Ta. By using density functional theory over a 5 × 5 atomic cell, we identify the most promising element candidates for p-doping of MoS2. Specifically, we found VB group impurity elements, such as Ta, substituting Mo to achieve negative formation energy values with impurity states all sitting at less than 0.1 eV from the valence band maximum (VBM), making them the optimal p-type dopant candidates. Moreover, our 5 × 5 cell model shows that B, a group III element, can induce impurity states very close to the VBM with a low formation energy around 0.2 eV, which has not been reported previously. Among the magnetic impurities such as Mn, Fe, and Co with 1, 2, and 3 magnetic moments/atom, respectively, Mn has the lowest formation energy, the most localized spin distribution, and the nearest impurity level to the conduction band among those elements. Additionally, impurity levels and Fermi level for the above three elements are closer to the conduction band than the previous work (PCCP 16:8990-8996, 2014) which shows the possibility of n-type doping by Mn, thanks to our 5 × 5 cell model.

No MeSH data available.