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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 MoS2doped with (a) V (b) Nb, and (c) Ta (solid line). Positive (negative) dotted lines: up-spin (down-spin) states. Pristine MoS2 (dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.
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Fig6: DOS of MoS2doped with (a) V (b) Nb, and (c) Ta (solid line). Positive (negative) dotted lines: up-spin (down-spin) states. Pristine MoS2 (dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.

Mentions: Next, we study the substitution of a Mo atom by different transition metal (TM) atoms. To start with, we consider the VB group elements that have one valence electron less than Mo and a magnetic moment of 1 μB (0.52 μB for Nb), which suggests the possibility for p-type doping. The DOS plots for MoS2 doped with three different elements V, Nb, and Ta are shown in Figure 6a,b,c. The impurity states originating from the three dopants are sitting at less than 0.1 eV away from the VBM, all of them characterized by a small spin-splitting. The formation energies for this type of dopants are also very low, decreasing with increasing atomic number. The most interesting feature is that under Mo-rich condition, i.e., when the Mo chemical potential is equal to its bulk Mo value, the formation energies become negative with Nb and Ta down in the VB column. As displayed in Table 1, Ta doping shows the lowest formation energy ever in our study, i.e., Eform ≈ −0.35 eV, whereas the formation energy of Nb is slightly higher, i.e., Eform ≈ −0.28 eV but is lower than the previous calculation [28], thanks to our larger cell size. Our model also shows that these values can be even lower in the S-rich limit [30]. Contrary to the case of S replacement, now the formation energies gets lower as atom size gets bigger, which results from the more significant size difference between these dopants and S atom. And all three elements induce very similar valence band structures to that of pristine MoS2, especially Ta. Not only are our findings in agreement with the previous work of Dolui et al. [28] but they also predict the VB group elements are optimal candidates for achieving p-type doping in MoS2.Figure 6


Electronic structures of defects and magnetic impurities in MoS2 monolayers.

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

DOS of MoS2doped with (a) V (b) Nb, and (c) Ta (solid line). Positive (negative) dotted lines: up-spin (down-spin) states. 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

Fig6: DOS of MoS2doped with (a) V (b) Nb, and (c) Ta (solid line). Positive (negative) dotted lines: up-spin (down-spin) states. Pristine MoS2 (dashed blue line). E = 0 is the VBM. The vertical grey dashed line stands for Fermi level.
Mentions: Next, we study the substitution of a Mo atom by different transition metal (TM) atoms. To start with, we consider the VB group elements that have one valence electron less than Mo and a magnetic moment of 1 μB (0.52 μB for Nb), which suggests the possibility for p-type doping. The DOS plots for MoS2 doped with three different elements V, Nb, and Ta are shown in Figure 6a,b,c. The impurity states originating from the three dopants are sitting at less than 0.1 eV away from the VBM, all of them characterized by a small spin-splitting. The formation energies for this type of dopants are also very low, decreasing with increasing atomic number. The most interesting feature is that under Mo-rich condition, i.e., when the Mo chemical potential is equal to its bulk Mo value, the formation energies become negative with Nb and Ta down in the VB column. As displayed in Table 1, Ta doping shows the lowest formation energy ever in our study, i.e., Eform ≈ −0.35 eV, whereas the formation energy of Nb is slightly higher, i.e., Eform ≈ −0.28 eV but is lower than the previous calculation [28], thanks to our larger cell size. Our model also shows that these values can be even lower in the S-rich limit [30]. Contrary to the case of S replacement, now the formation energies gets lower as atom size gets bigger, which results from the more significant size difference between these dopants and S atom. And all three elements induce very similar valence band structures to that of pristine MoS2, especially Ta. Not only are our findings in agreement with the previous work of Dolui et al. [28] but they also predict the VB group elements are optimal candidates for achieving p-type doping in MoS2.Figure 6

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.