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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.


Crystal structure of monolayer MoS2(blue: Mo, yellow: S).
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Fig1: Crystal structure of monolayer MoS2(blue: Mo, yellow: S).

Mentions: Ultrasoft pseudopotentials are chosen for our simulations, which are carried out for a 5 × 5 × 1 hexagonal supercell (lateral dimension fixed to 15.83 × 15.83 Å2) with 25 Mo atoms and 50 S atoms (Figure 1). At the beginning, 3 × 3 × 1, 5 × 5 × 1, and 7 × 7 × 1 supercells are all taken into consideration. However, after some calculations, we find the calculated impurity states and formation energies stabilize at 5 × 5 × 1 cell size; therefore, it is chosen for the balance between calculation accuracy and computational costs. A 12-Å vacuum layer is introduced in our slab model to prevent the interaction between neighboring supercells and mimicking the realistic condition of monolayer MoS2, and periodic boundary conditions are adopted. Doping (defects) in MoS2 is introduced by replacing (removing) a single host atom in the system. The resulting doping or defect concentration is 4% (2%) as Mo (S) atom is replaced or removed. A high cut-off energy of 816 eV for wave functions and a dense 5 × 5 × 1 Monkhorst-Pack k-point mesh over Brillouin zone are used for the geometric optimization with the generalized gradient approximations (GGAs) in the Perdew-Burke-Ernzerhof parameterization [20]. The relaxation is going on until all components of all forces in the system are smaller than 1.03 × 10−2 eV/Å and the total energy of the supercell converges to less than 1.36 × 10−5 eV. With spin information acquired in the geometric optimization, spin-polarized density of states (DOS) calculations are continued on the structures obtained by GGAs using Perdew-Zunger parameterization [21] of the local density approximation (LDA) for exchange and correlation potential. As a result of this procedure, our theoretical band gap achieves a value very close to the experimental data.Figure 1


Electronic structures of defects and magnetic impurities in MoS2 monolayers.

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

Crystal structure of monolayer MoS2(blue: Mo, yellow: S).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Crystal structure of monolayer MoS2(blue: Mo, yellow: S).
Mentions: Ultrasoft pseudopotentials are chosen for our simulations, which are carried out for a 5 × 5 × 1 hexagonal supercell (lateral dimension fixed to 15.83 × 15.83 Å2) with 25 Mo atoms and 50 S atoms (Figure 1). At the beginning, 3 × 3 × 1, 5 × 5 × 1, and 7 × 7 × 1 supercells are all taken into consideration. However, after some calculations, we find the calculated impurity states and formation energies stabilize at 5 × 5 × 1 cell size; therefore, it is chosen for the balance between calculation accuracy and computational costs. A 12-Å vacuum layer is introduced in our slab model to prevent the interaction between neighboring supercells and mimicking the realistic condition of monolayer MoS2, and periodic boundary conditions are adopted. Doping (defects) in MoS2 is introduced by replacing (removing) a single host atom in the system. The resulting doping or defect concentration is 4% (2%) as Mo (S) atom is replaced or removed. A high cut-off energy of 816 eV for wave functions and a dense 5 × 5 × 1 Monkhorst-Pack k-point mesh over Brillouin zone are used for the geometric optimization with the generalized gradient approximations (GGAs) in the Perdew-Burke-Ernzerhof parameterization [20]. The relaxation is going on until all components of all forces in the system are smaller than 1.03 × 10−2 eV/Å and the total energy of the supercell converges to less than 1.36 × 10−5 eV. With spin information acquired in the geometric optimization, spin-polarized density of states (DOS) calculations are continued on the structures obtained by GGAs using Perdew-Zunger parameterization [21] of the local density approximation (LDA) for exchange and correlation potential. As a result of this procedure, our theoretical band gap achieves a value very close to the experimental data.Figure 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.