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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) N (b) P, and (c) As (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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Fig4: DOS of MoS2doped with (a) N (b) P, and (c) As (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 turn our analysis to the properties of dopants substituted at the S site, beginning with the replacement of an S atom with VA group elements, such as N, P, and As. As shown in Figure 4a for N-doping, we can see that the impurity states are near the valence band edge with two spin states separated by nearly 0.2 eV and a magnetic moment of 1 μB. For P-doped MoS2 (Figure 4b), the similarity with N impurity can be observed as the system is again magnetic, and the gap states move even closer to the valence band. Going down the periodic table further, the DOS of MoS2 with As impurity shows acceptor states in the gap almost merging with the valence band states of pristine MoS2 (Figure 4c), it therefore indicates that As can be a suitable p-dopant in MoS2. The formation energies for all three elements, all around 2 eV, are rather large, i.e., those elements are unlikely to be stable dopants at thermal equilibrium, therefore the technique of creating S vacancies may be a better option [24]. Here, we observe the impurity states shift to the valence band as atomic number increases, which is consistent with previous theoretical work by Dolui et al. [28]. Also the formation energies in our two works are in good agreement (approximately 5%). However, we also find MoS2 systems doped with an As atom exhibits a magnetic moment of 1 μB, as with N and P dopants, which was not reported previously. This is possibly due to the slightly larger lattice constant of our MoS2 model.Figure 4


Electronic structures of defects and magnetic impurities in MoS2 monolayers.

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

DOS of MoS2doped with (a) N (b) P, and (c) As (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
Show All Figures
getmorefigures.php?uid=PMC4494037&req=5

Fig4: DOS of MoS2doped with (a) N (b) P, and (c) As (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 turn our analysis to the properties of dopants substituted at the S site, beginning with the replacement of an S atom with VA group elements, such as N, P, and As. As shown in Figure 4a for N-doping, we can see that the impurity states are near the valence band edge with two spin states separated by nearly 0.2 eV and a magnetic moment of 1 μB. For P-doped MoS2 (Figure 4b), the similarity with N impurity can be observed as the system is again magnetic, and the gap states move even closer to the valence band. Going down the periodic table further, the DOS of MoS2 with As impurity shows acceptor states in the gap almost merging with the valence band states of pristine MoS2 (Figure 4c), it therefore indicates that As can be a suitable p-dopant in MoS2. The formation energies for all three elements, all around 2 eV, are rather large, i.e., those elements are unlikely to be stable dopants at thermal equilibrium, therefore the technique of creating S vacancies may be a better option [24]. Here, we observe the impurity states shift to the valence band as atomic number increases, which is consistent with previous theoretical work by Dolui et al. [28]. Also the formation energies in our two works are in good agreement (approximately 5%). However, we also find MoS2 systems doped with an As atom exhibits a magnetic moment of 1 μB, as with N and P dopants, which was not reported previously. This is possibly due to the slightly larger lattice constant of our MoS2 model.Figure 4

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.