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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.


Spin density of (a) Mn (b) Fe, and (c) Co-doped MoS2.
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Fig7: Spin density of (a) Mn (b) Fe, and (c) Co-doped MoS2.

Mentions: Lastly, we consider magnetic TM elements, such as Mn, Fe, and Co, as representative of the VIB, VIIB, and VIIIB group elements that have, respectively, one, two, and three electrons in excess to Mo atoms. In Figure 7a, the spin density plot shows the most localized distribution around the Mn atom with a total magnetic moment of 1 μB. For Fe and Co (Figure 7b,c), although the total magnetic moment is stronger, i.e., 2 and 3 μB, respectively, the distribution of spin density becomes less localized and broader with the spins spreading to the neighboring atoms in both cases. Despite the broadened spin distribution, all three elements still have higher spin density than that of V, Nb, and Ta. The DOSs of these doped systems are shown in Figure 8a,b,c, where we find another noticeable effect of the Mn atom, as its impurity level is the nearest to the conduction band, whereas Fe and Co dopants induce impurity levels much farther away from the CBM. Because of the use of a 5 × 5 cell, the impurity levels of all three elements are closer to the CBM than the recent reports using 4 × 4 cell [17, 18]. Moreover, for Mn, Fe, and Co dopant atoms, the separation between Fermi level and the conduction band is 0.48, 0.77, and 0.78 eV, respectively, which is also narrower than the previous calculation, making Mn dopant more attractive for n-type doping. The Mn doping is also the most energetically favorable (Eform ≈ 1.78 eV) among these magnetic impurities, as the formation energy increases with the atomic number, which is due to the smaller size difference between dopants and S, consistent with our prediction. As a result, Mn shows the highest potential for spintronics applications among those possible candidates as well as the capability of obtaining n-type doping in MoS2.Figure 7


Electronic structures of defects and magnetic impurities in MoS2 monolayers.

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

Spin density of (a) Mn (b) Fe, and (c) Co-doped MoS2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4494037&req=5

Fig7: Spin density of (a) Mn (b) Fe, and (c) Co-doped MoS2.
Mentions: Lastly, we consider magnetic TM elements, such as Mn, Fe, and Co, as representative of the VIB, VIIB, and VIIIB group elements that have, respectively, one, two, and three electrons in excess to Mo atoms. In Figure 7a, the spin density plot shows the most localized distribution around the Mn atom with a total magnetic moment of 1 μB. For Fe and Co (Figure 7b,c), although the total magnetic moment is stronger, i.e., 2 and 3 μB, respectively, the distribution of spin density becomes less localized and broader with the spins spreading to the neighboring atoms in both cases. Despite the broadened spin distribution, all three elements still have higher spin density than that of V, Nb, and Ta. The DOSs of these doped systems are shown in Figure 8a,b,c, where we find another noticeable effect of the Mn atom, as its impurity level is the nearest to the conduction band, whereas Fe and Co dopants induce impurity levels much farther away from the CBM. Because of the use of a 5 × 5 cell, the impurity levels of all three elements are closer to the CBM than the recent reports using 4 × 4 cell [17, 18]. Moreover, for Mn, Fe, and Co dopant atoms, the separation between Fermi level and the conduction band is 0.48, 0.77, and 0.78 eV, respectively, which is also narrower than the previous calculation, making Mn dopant more attractive for n-type doping. The Mn doping is also the most energetically favorable (Eform ≈ 1.78 eV) among these magnetic impurities, as the formation energy increases with the atomic number, which is due to the smaller size difference between dopants and S, consistent with our prediction. As a result, Mn shows the highest potential for spintronics applications among those possible candidates as well as the capability of obtaining n-type doping in MoS2.Figure 7

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.