Half-Metallicity in Co-Doped WSe2 Nanoribbons

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Half-Metallicity in Co-Doped WSe Nanoribbons Runzhang Xu, Bilu Liu, Xiaolong Zou, and Hui-Ming Cheng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b12196 • Publication Date (Web): 16 Oct 2017 Downloaded from http://pubs.acs.org on October 18, 2017

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ACS Applied Materials & Interfaces

Half-Metallicity in Co-Doped WSe2 Nanoribbons Runzhang Xu1, Bilu Liu1, Xiaolong Zou1*, Hui-Ming Cheng1,2

1 The Low-Dimensional Materials and Devices Laboratory, Tsinghua-Berkeley Shenzhen Institute, Tsinghua University, Shenzhen, Guangdong 518055, PR China 2 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, PR China

KEYWORDS Half-metal, Transition-metal dichalcogenides, Doping, Spintronics, Density functional theory calculations

ABSTRACT Recent development of two-dimensional transition-metal dichalcogenides in electronics and optoelelectronics has triggered the exploration in spintronics, with high demand in search for half-metallicity in these systems. Here, through density functional theory (DFT) calculations, we predict robust half-metallic behaviors in Co edge-doped WSe2 nanoribbons. With electrons partially occupying the anti-bonding state consisting of Co 3dyz and Se 4pz orbitals, the system becomes spin-polarized due to the defect-state induced Stoner effect, and the strong exchange splitting eventually 1 ACS Paragon Plus Environment


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gives rise to the half-metallicity. The half-metal gap reaches 0.15 eV on the DFT generalized gradient approximation level, and increases significantly to 0.67 eV using hybrid functional. Furthermore, we find that the half-metallicity sustains even under large external strain and relatively low edge doping concentration, which promises the potential of such Co edge-doped WSe2 nanoribbon in spintronics applications.

INTRODUCTION Due to their intriguing electronic, valleytronic, and optical properties,1,

2

two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have received great interest recently. Benefitting from their direct energy band gaps3 and high carrier mobility,4 TMDCs have been showcased in various high-performance device prototypes, including field-effect transistors,4-6 photodetectors,7, 8 memory devices,9 integrated circuits,10, 11 and many others. Along with recently developed large-scale chemical vapor deposition (CVD) growth12,

13

and controlled doping,14-17 TMDCs

offer attractive potential for future electronics and optoelectronics applications. More recently, coupled spin and valley transport18 have been demonstrated in the MoS2 FETs under illumination of polarized light,19, 20 with spin lifetime longer than 1 ns.21 These findings have ignited the search for 2D TMDC-based half-metallic materials, which could introduce spin-polarized electrons without the delicate setup in optical operation. Transition-metal (TM) doping has been suggested to be an effective way to induce ferromagnetism in various 2D materials, including semimetallic WTe2,22 antimonene,23 g-C2N,24 phosphorene,25 and semiconducting TMDCs.26, 27 However, 2 ACS Paragon Plus Environment

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for TMDCs, spin-polarized energy is smaller than 4 meV,27 which rules out their practical operation. On the other hand, wetting deposition of TMs on MoS2 leads to the localization of spin density on TMs rather than inside the channel materials.28 Moreover, the negligible half-metal gap (defined as the difference between valence band maximum and the Fermi level) makes the spin transport easily destroyed by the spin-flip scattering. Therefore, the search for suitable 2D TMDC-based half-metallic materials is urgently called for.

Here we report the prediction of half-metallicity in cobalt (Co) edge-doped WSe2 nanoribbons (NRs) using first-principles calculations. The edge energies of various configurations with different edge selenium (Se) coverages, the formation energies for Co doping at different sites and their thermal stabilities were investigated, demonstrating good stabilities of these systems for experimental realization. The energy band gap and half-metal gap as large as 1.27 and 0.67 eV are obtained, making Co doped WSe2 NRs a good candidate for half-metals. Through partial density of states (PDOS) and molecular orbital analysis, we reveal that the half-metallicity originates from the defect-state induced Stoner effect. Further, the influences of ribbon width, dopant concentration, and external strain on the half-metallicity in our proposed system were also explored, manifesting the robustness of such spin-polarized systems. Our strategy can be easily extended to other TMDC systems with similar structural and electronic characteristics.

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COMPUTATIONAL METHODS The spin-polarized calculations were performed using Vienna Ab-initio Simulation Package (VASP)29,

30

based on the density functional theory (DFT). The

projector-augmented wave (PAW) potentials31,

32

and the Perdew-Burke-Ernzerhof

(PBE) functional33 were used to treat the ion-electron interactions and the exchange-correlations, respectively. Based on periodic boundary conditions, a vacuum layer larger than 10 Å was applied to keep interactions between the corresponding nearest surface layers negligible. The plane wave energy cutoff of 400 eV and the 11ⅹ1ⅹ1 k-point sampling were adopted for structural optimization, with energy and force convergence criteria set to10-5 eV and 0.01 eV/Å, respectively. The supercell of WSe2 NRs was constructed from the most stable 2H phase34 with zigzag termination on both edges. The choice of zigzag rather than armchair termination is based on the experimental observations on the morphology of CVD-grown TMDC samples.13, 35

RESULTS AND DISCUSSION Due to the heteroelemental composition of WSe2, the zigzag NRs have two different edges, W- and Se-edge. Both edges could have different Se coverages, brought by the unique bonding characteristics of Se atoms in WSe2.36 Following the same notation introduced by Schweiger et al.,37 W0, W50, and W100 describe W-edges with 0 %, 50 %, and 100 % Se coverage, while Se100, Se50, and Se0 represent Se-edges with 100 %, 50 %, and 0 % Se coverage, respectively. These structures are shown in Figure 4 ACS Paragon Plus Environment

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1a. Taking W0 and Se100 as references, the relative energies of other edges (including the reconstructed ones of W- and Se-edge) are calculated as a function of Se chemical potential µSe in the thermodynamic equilibrium range of -4.33 eV < µSe < -3.49 eV, where WSe2 remains stable against the segregation of bulk W (µSe = -4.33 eV) or bulk Se (µSe = -3.49 eV) (Figure 1b). It can be seen that in a wide range of the Se chemical potential, W50 and Se100 are respectively the most stable W- and Se-edge. Hereafter, we take W50-Se100 as our prototype model, as shown in the inset of Figure 1c.

Figure 1. (a) Top (left) and side (right) views of WSe2 NRs with various edge Se coverages. (b) The energies of different W- (blue) and S-edges (red) relative to



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references (W0 and Se100, black) as a function of Se chemical potential µSe. The blue dashed line (W50 and Se100) denotes the most stable edges in almost the whole range of µSe. (c) The formation energy of Co doping as a function of doping site (N). The inset, as an example, denotes the doping of one Co atom at site 1 (the first zigzag line from W-edge).

For the most stable W50-Se100 structure, W atoms around Se100 edge are fully saturated, and thus the doping would have little effects on its magnetic properties. Therefore, we mainly consider the Co doping around W50 edge. The doping formation energy is calculated as, Ef = Edoped – Epure - (µCo – µW), where Edoped and Epure are the total energies of Co doped and undoped pure systems, respectively, µCo and µW are the chemical potentials of bulk Co and W. The calculated formation energy as a function of doping site (N) is presented in Figure 1c, in which N is defined as the index of zigzag lines starting from W-edge and denoted by the numbers (1 to 8) at the bottom. The doping formation energy has the lowest (negative) value when doping at site 1 and increases significantly when substitution happens in the middle of the ribbon, indicating the Co dopants preferably locate at W-edge. Further, the stability of these NRs can be verified by performing molecular dynamics (MD) simulations at 500 K (details presented in Figure S2). The well-preserved structures of Co-doped WSe2 NRs suggest their good thermal stability at high temperatures. Therefore, it is highly possible to synthesize Co edge-doped WSe2 NRs 6 ACS Paragon Plus Environment

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in experiments from thermodynamic point of view.

Figure 2. (a) The spin-polarized DOS and energy bands of 4-Co-W50-Se100 NR in the energy range from -1.0 eV to 1.0 eV. The black and red curves in the left panel represent respectively the DOS of spin-up and -down channels. In the middle and right panels, the squares and circles indicate the contributions of the W- and Se-edges, respectively, and their sizes represent the relative weight of such contributions. The Fermi-level is denoted by dashed lines. (b) Top view and (c) side view of the partial charge density distribution (transparent red isosurfaces) of electronic states in the energy range from -0.12 eV to 0.26 eV.

For MoS2 NRs, it is well known that both Mo and S zigzag edges are metallic and ferromagnetic, with the spin contribution mainly from d and p orbitals of edge Mo and S atoms.48 Similarly, undoped WSe2 zigzag NRs have metallic and ferromagnetic ground state with the spin contribution from d and p orbitals of edge W and Se atoms. Interestingly, the introduction of Co dopants leads to half-metallicity. The spin



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polarization energy, defined as the energy difference between nonmagnetic and ferromagnetic states, reaches 30 meV per unit length. Figure 2a shows the density of states (DOS) of Co doped WSe2 NR with a width of 4 and W50 and Se100 edges (named as 4-Co-W50-Se100 NR), together with its spin-up and -down energy bands. The band structures clearly show half-metallicity, with semiconducting and metallic behaviors observed respectively in the spin-up and spin-down channels. The band gap in spin-up channel is calculated as 0.38 eV, while the half-metal gap reaches 0.12 eV. Given the inaccuracy of DFT simulations on determining the position of energy levels, we have further carried out the HSE hybrid functional calculations,38-40 yielding a half-metal gap of 0.67 eV (see Figure S3 in the Supporting Information), comparable to those in La(Mn,Zn)AsO alloy,41 organic porous sheets,42 and 2D Cr2C.43 Such a large gap is enough for room-temperature operation, which makes Co doped WSe2 NRs a good candidate for spintronics applications. We have further performed Hubbard U (DFT+U) and spin-orbit coupling (SOC) calculations to check the half-metallicity, they all show no qualitative influence on the half-metallic band structure (details presented in Figure S4 and S5).

The half-metallic characteristics of 4-Co-W50-Se100 NR were further elucidated by the projected wave function character analysis. Figure 2a displays the weight decomposition of the contribution for each band into W (squares) or Se (circles) edges, respectively. Two bands from W and Se edges cross each other near Fermi-level in the spin-down channel, while they are pushed downward in the spin-up channel due to the 8 ACS Paragon Plus Environment

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exchange interaction. The partial charge density distribution of the electronic states in the energy range from -0.12 eV to 0.26 eV relative to Fermi-level (namely the semiconducting gap) was further calculated to demonstrate the edge contribution to the half-metallicity. Figure 2b and 2c show the top- and side-view of partial charge density distribution isosurfaces, respectively. They are mainly located at the edge atoms of the ribbon, in agreement with the weight decomposition of energy bands shown in Figure 2a. From Figure 2c, it can be seen that the metallic behavior in spin-down energy band at the W-edge is contributed by an anti-bonding state between Co 3dyz orbitals and the Se 4pz orbitals. Similar anti-bonding state is also found around the Se-edge.

Figure 3. Schematics of spin-polarized PDOS of dyz, dxy, and dxz orbitals for (a) Fe, (b) Co, and (c) Ni. For simplicity, we neglect contribution from Se p orbitals and use d



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and d* to represent the corresponding bonding and anti-bonding molecular levels. The black (up and down) arrows stands for (spin-up and -down) electrons occupying the energy levels, and the dashed lines represent the Fermi-level. The spin-down dyz* state in (b) crosses the Fermi-level and is partially occupied.

To gain a deeper understanding of the origin of the half-metallicity, we analyze the change in the electronic structures of TM doped W50-Se100 NRs, by considering three different magnetic TM dopants of Fe, Co, and Ni. The contribution of five 3d orbitals, namely dxy, dyz, dxz, dz2, and dx2-y2, for each dopant were respectively calculated. Due to the interactions between TMs and Se, all five 3d orbitals split into bonding and anti-bonding molecular states, denoted as d and d* with p orbitals from Se atoms neglected. We exclude the dz2 and dx2-y2 orbitals in the following analysis since their occupations barely change in three doping cases. For W50-edge, the overlap between TM dxz and Se (especially the second-row Se atoms) p orbitals is most efficient, resulting in largest splitting between bonding and anti-bonding states. On the other hand, dyz orbital has the weakest interaction with Se p orbitals, leading to the smallest splitting. Accordingly, the arrangement of dyz, dxy, and dxz orbital (including bonding and anti-bonding states) for each dopant and their electron state occupation are schematically illustrated in Figure 3, with the full PDOS plots shown in Figure S6 in the Supporting Information. In the case of Fe doping, all bonding states are occupied and dyz* orbital locates right above the Fermi-level. The Fe atom displays no spin-polarization, as shown in Figure 3a. Substituting Fe with Co 10 ACS Paragon Plus Environment

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introduces one additional 3d electron that occupies the dyz* state. According to the Stoner model for defect states,44 as long as the DOS of dyz* is large enough, it becomes spin-polarized. The spin polarization lowers the energy of the system, and eventually creates an energy gap in spin-up channel, leaving the spin-down dyz* states partially occupied (across Fermi-level), as shown in Figure 3b. Further replacing Co with Ni brings in another 3d electron which occupies the unfilled spin-down dyz* orbital, as shown in Figure 3c. This change again leads to the disappearance of spin-polarization of Ni atom and the half-metallicity of the system.

Figure 4. (a) The width dependence of half-metal gaps and semiconducting gaps of Co doped WSe2 (W50-Se100) and MoS2 (Mo50-S100) NRs. The red solid-triangles represent the semiconducting gap values of Co doped WSe2, while the red hallow-triangles are its half-metal gap values. The black solid- and hallow-circles denote the semiconducting and half-metal gap of Co doped MoS2, respectively. (b) The Co edge doping concentration dependence of half-metal gaps of the 4-Co-W50-Se100 NRs. Inset shows the doping configurations at edge Co concentrations of 100%, 75%, 66%, and 60%. No half-metallicity is observed below 60% Co edge doping. (c) The energy bands of spin-up and -down channels of 11 ACS Paragon Plus Environment


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4-Co-W50-Se100 NRs under +5% tensile strain along the periodic direction.

The robustness of the half-metallicity is quite important, since it determines whether such intriguing properties can be realized experimentally. Here, we consider the influences of ribbon width, edge doping concentration, and external strain on the half-metallicity. First, we examine NRs with different widths of 6, 8, 10, and 14. The half-metallicity and its width dependence of another similar TMDC NRs (MoS2 Mo50-S100) were also calculated for comparison. The obtained half-metal and semiconducting gaps as functions of ribbon width are shown in Figure 4a. Both the half-metal and semiconducting gaps of Co doped WSe2 are found to slightly increase along with the ribbon width and quickly converge at the width of 8. The largest measured half-metal and semiconducting gaps are respectively 0.15 eV and 0.42 eV for WSe2. The picture for Co doped MoS2 differs slightly, with maximum obtained at the width of 6. Nevertheless, the overall trend of Co doped WSe2 and MoS2 can be considered the same, suggesting the possibility of extending the TM edge doping strategy to induce half-metallicity in other TMDC systems. Second, in experimental synthesis of Co doped WSe2 NRs, the perfect configuration of 100 % Co doping at edge W atoms is barely achievable, which brings up the necessity for exploring the influence of dopant concentration on half-metallicity. An edge-Co concentration as low as 60 % at W-edge (100 % corresponds to full edge doping) is found to sustain a half-metal gap of 0.08 eV (band structure shown in Figure S7) in spin-up channel, as shown in Figure 4b. Third, the external strain acting on the ribbon plays a vital role in 12 ACS Paragon Plus Environment

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practical applications, especially for flexible electronics. Since the compressive strain would lead to the buckling of NRs for releasing the stress, we are only interested in tensile strain here. When applied a high-level external stretch of +5 % along its periodic direction, the half-metallicity still survives, with the energy bands (shown in Figure 4c) slightly different from the strain-free case. The half-metal and semiconducting gaps are only reduced by about 0.01 eV and 0.11 eV.

It should be emphasized that the half metallicity in Co-doped TMDC NRs can only be achieved in the thermodynamically stable M50 (M = Mo or W) edges considered here. Figure S8 shows the calculated band structures and DOS for 50% and 100% Co edge doped Mo0 and W0 edges. For Mo0 case, although robust FM states can be achieved through Co doping, consistent with previous report,45 neither spin-up nor -down channels show energy gap near the Fermi level (Figure S8a and S8b). Similar FM states are realized in W0 case, however, 50% and 100% Co doping result in either semiconducting (Figure S8c) or metallic (Figure S8d) band structure. Therefore, the fully spin-polarized transport cannot be realized merely through doping in Mo0 and W0 edge, and additional measure should be taken to induce the half-metallicity, for example, the combination of external exchange field and transverse electric field, as suggested by Peeters et al.46 Another key characteristic of Co-doped WSe2 is that the magnetic interaction between Co is mediated by the dispersive edge states, which is different from the d0 magnetism realized in Mg- or Cu-doped SnO2,47, 48 where the exchange interaction is mainly mediated by the localized donor/acceptor states. 13 ACS Paragon Plus Environment


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Different characteristics would render them suitable for different applications. While Co-doped WSe2 is fit for spin filter or injection, doped SnO2 is suited to the channel materials for spintronic applications.

Based on the above discussion, half-metallic Co-doped WSe2 NRs can in principle be adopted as key components for spin field effect transistor (spin-FET).49-52 The nanostructured spin-FET can be fabricated by cutting the zigzag edges at the two opposite ends of WSe2 monolayer followed by subsequent Co doping. The NRs and the sandwiched 2D sheet therefore serve as two spin filters and semiconductor, respectively. Assuming both NRs are spin-down polarized, the electric current becomes spin-down polarized after passing through the first spin filter and subsequently goes into semiconductor where its spin orientation can be switched by gating bias through spin orbit coupling.51, 52 When the spin of the electric current is parallelly aligned to the second filter (namely, spin-down), the electric current can pass through (on state), however, the current is blocked (off state) when its spin is antiaparallelly aligned to the filter.

CONCLUSION In summary, we have predicted the half-metallicity in Co doped WSe2 NRs with W50-Se100 edges and systematically studied its physical origins using DFT calculations. The calculated maximum values of half-metal and semiconducting gap are respectively 0.42 eV and 0.15 eV, which promises its potential applications in 14 ACS Paragon Plus Environment

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spintronics. The half-metallicity is found to result from the asymmetric Co 3d-electron state occupation, in which the spin-up dyz orbital is fully occupied while the spin-down dyz is not. Our further analyses indicate that the half-metallic properties are rather robust against the influences of ribbon width, dopant concentration, and external strain. Given the similar structural and electronic characteristics among various TMDCs, the TM edge doping strategy for inducing half-metallicity can be extended to other TMDC systems. Combined with the recent progress in controlled growth and doping in TMDCs, our work suggests a high feasibility of 2D TMDC-based spintronics.

ASSOCIATED CONTENT Supporting Information The following files are available free of charge. Formation energy of Co edge doping as a function of ribbon width, molecular dynamics simulations for 4×4 and 6×8 superlattice, spin-polarized energy bands for 4and 6-Co-W50-Se100 NRs calculated by HSE06, spin-polarized energy bands for 4and 6-Co-W50-Se100 NRs by DFT+U, spin-orbit coupled energy bands of 4-Co-W50-Se100 NRs calculated by SOC, partial DOS for 3d electrons of Fe, Co, and Ni dopants, spin-polarized energy bands for 4-Co-W50-Se100 NRs with 60% Co edge doping, and spin-polarized DOS and energy bands of Co edge doped Mo0 and W0 edges.



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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT This work was supported by the Development and Reform Commission of Shenzhen Municipality under the “Low-Dimensional Materials and Devices Discipline”, the Youth 1000-Talent Program of China, and the Tsinghua-Berkeley Shenzhen Institute (TBSI). The calculations were carried out on Tianhe-1 (A) at National Supercomputer Center in Tianjin.

REFERENCES (1) Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S. Electronics

and

Optoelectronics

of

Two-Dimensional

Transition

Metal

Dichalcogenides. Nat. Nanotechnol. 2012, 7 (11), 699-712. (2) Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H. The Chemistry of Two-Dimensional Layered Transition Metal Dichalcogenide Nanosheets. Nat. Chem. 2013, 5 (4), 263-275. (3) Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105 (13), 136805. 16 ACS Paragon Plus Environment

Page 17 of 22

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(4) Radisavljevic, B.; Radenovic, A.; Brivio, J.; Giacometti, i. V.; Kis, A. Single-Layer MoS2 Transistors. Nat. Nanotechnol. 2011, 6 (3), 147-150. (5) Zhang, Y.; Ye, J.; Matsuhashi, Y.; Iwasa, Y. Ambipolar MoS2 Thin Flake Transistors. Nano Lett. 2012, 12 (3), 1136-1140. (6) Liu, B.; Ma, Y.; Zhang, A.; Chen, L.; Abbas, A. N.; Liu, Y.; Shen, C.; Wan, H.; Zhou, C. High-Performance WSe2 Field-Effect Transistors Via Controlled Formation of in-Plane Heterojunctions. ACS Nano 2016, 10 (5), 5153-5160. (7) Lopez-Sanchez, O.; Lembke, D.; Kayci, M.; Radenovic, A.; Kis, A. Ultrasensitive Photodetectors Based on Monolayer MoS2. Nat. Nanotechnol. 2013, 8 (7), 497-501. (8) Yin, Z.; Li, H.; Li, H.; Jiang, L.; Shi, Y.; Sun, Y.; Lu, G.; Zhang, Q.; Chen, X.; Zhang, H. Single-Layer MoS2 Phototransistors. ACS Nano 2011, 6 (1), 74-80. (9) Choi, M. S.; Lee, G.-H.; Yu, Y.-J.; Lee, D.-Y.; Lee, S. H.; Kim, P.; Hone, J.; Yoo, W. J. Controlled Charge Trapping by Molybdenum Disulphide and Graphene in Ultrathin Heterostructured Memory Devices. Nat. Commun. 2013, 4, 1624. (10) Yu, L.; Zubair, A.; Santos, E. J.; Zhang, X.; Lin, Y.; Zhang, Y.; Palacios, T. s. High-Performance WSe2 Complementary Metal Oxide Semiconductor Technology and Integrated Circuits. Nano Lett. 2015, 15 (8), 4928-4934. (11) Radisavljevic, B.; Whitwick, M. B.; Kis, A. Integrated Circuits and Logic Operations Based on Single-Layer MoS2. ACS Nano 2011, 5 (12), 9934-9938. (12) Najmaei, S.; Liu, Z.; Zhou, W.; Zou, X.; Shi, G.; Lei, S.; Yakobson, B. I.; Idrobo, J.-C.; Ajayan, P. M.; Lou, J. Vapour Phase Growth and Grain Boundary Structure of Molybdenum Disulphide Atomic Layers. Nat. Mater. 2013, 12 (8), 754-759. 17 ACS Paragon Plus Environment


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(13) Van Der Zande, A. M.; Huang, P. Y.; Chenet, D. A.; Berkelbach, T. C.; You, Y.; Lee, G.-H.; Heinz, T. F.; Reichman, D. R.; Muller, D. A.; Hone, J. C. Grains and Grain Boundaries in Highly Crystalline Monolayer Molybdenum Disulphide. Nat. Mater. 2013, 12 (6), 554-561. (14) Pham, V. P.; Yeom, G. Y. Recent Advances in Doping of Molybdenum Disulfide: Industrial Applications and Future Prospects. Adv. Mater. 2016, 28 (41), 9024-9059. (15) Tedstone, A. A.; Lewis, D. J.; O’Brien, P. Synthesis, Properties, and Applications of Transition Metal-Doped Layered Transition Metal Dichalcogenides. Chem. Mater. 2016, 28 (7), 1965-1974. (16) Yang, L.; Majumdar, K.; Liu, H.; Du, Y.; Wu, H.; Hatzistergos, M.; Hung, P.; Tieckelmann, R.; Tsai, W.; Hobbs, C. Chloride Molecular Doping Technique on 2D Materials: WS2 and MoS2. Nano Lett. 2014, 14 (11), 6275-6280. (17) Suh, J.; Park, T.-E.; Lin, D.-Y.; Fu, D.; Park, J.; Jung, H. J.; Chen, Y.; Ko, C.; Jang, C.; Sun, Y. Doping against the Native Propensity of MoS2: Degenerate Hole Doping by Cation Substitution. Nano Lett. 2014, 14 (12), 6976-6982. (18) Xiao, D.; Liu, G.-B.; Feng, W.; Xu, X.; Yao, W. Coupled Spin and Valley Physics in Monolayers of MoS2 and Other Group-VI Dichalcogenides. Phys. Rev. Lett. 2012, 108 (19), 196802. (19) Mak, K. F.; McGill, K. L.; Park, J.; McEuen, P. L. The Valley Hall Effect in MoS2 Transistors. Science 2014, 344 (6191), 1489-1492. (20) Lee, J.; Mak, K. F.; Shan, J. Electrical Control of the Valley Hall Effect in Bilayer MoS2 Transistors. Nat. Nanotechnol. 2016, 11 (5), 421-425. 18 ACS Paragon Plus Environment

Page 19 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(21) Mak, K. F.; He, K.; Shan, J.; Heinz, T. F. Control of Valley Polarization in Monolayer MoS2 by Optical Helicity. Nat. Nanotechnol. 2012, 7 (8), 494-498. (22) Song, Y.; Wang, X.; Mi, W. Spin Splitting and Reemergence of Charge Compensation in Monolayer WTe2 by 3d Transition-Metal Adsorption. Phys. Chem. Chem. Phys. 2017, 19 (11), 7721-7727. (23) Yang, L. F.; Song, Y.; Mi, W. B.; Wang, X. C. Prediction of Spin-Dependent Electronic Structure in 3d-Transition-Metal Doped Antimonene. Appl. Phys. Lett. 2016, 109 (2), 022103. (24) Zheng, Z. D.; Wang, X. C.; Mi, W. B. Tunable Electronic Structure of Monolayer Semiconductor g-C2N by Adsorbing Transition Metals: A First-Principles Study. Carbon 2016, 109 (Supplement C), 764-770. (25) Sui, X.; Si, C.; Shao, B.; Zou, X.; Wu, J.; Gu, B.-L.; Duan, W. Tunable Magnetism in Transition-Metal-Decorated Phosphorene. J. Phys. Chem. C 2015, 119 (18), 10059-10063. (26) Ramasubramaniam, A.; Naveh, D. Mn-Doped Monolayer MoS2: An Atomically Thin Dilute Magnetic Semiconductor. Phys. Rev. B 2013, 87 (19), 195201. (27) Cheng, Y.; Zhu, Z.; Mi, W.; Guo, Z.; Schwingenschlögl, U. Prediction of Two-Dimensional Diluted Magnetic Semiconductors: Doped Monolayer MoS2 Systems. Phys. Rev. B 2013, 87 (10), 100401. (28) Chen, Q.; Ouyang, Y.; Yuan, S.; Li, R.; Wang, J. Uniformly Wetting Deposition of Co Atoms on MoS2 Monolayer: A Promising Two-Dimensional Robust Half-Metallic Ferromagnet. ACS Appl. Mater. Interfaces 2014, 6 (19), 16835-16840. 19 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 22

(29) Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6 (1), 15-50. (30) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54 (16), 11169. (31) Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50 (24), 17953. (32) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B 1999, 59 (3), 1758. (33) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865. (34) Ataca, C.; Sahin, H.; Ciraci, S. Stable, Single-Layer MX2 Transition-Metal Oxides and Dichalcogenides in a Honeycomb-Like Structure. J. Phys. Chem. C 2012, 116 (16), 8983-8999. (35) Zhou, W.; Zou, X.; Najmaei, S.; Liu, Z.; Shi, Y.; Kong, J.; Lou, J.; Ajayan, P. M.; Yakobson, B. I.; Idrobo, J.-C. Intrinsic Structural Defects in Monolayer Molybdenum Disulfide. Nano Lett. 2013, 13 (6), 2615-2622. (36) Zou, X.; Yakobson, B. I. An Open Canvas 2D Materials with Defects, Disorder, and Functionality. Acc. Chem. Res. 2014, 48 (1), 73-80. (37) Schweiger, H.; Raybaud, P.; Kresse, G.; Toulhoat, H. Shape and Edge Sites Modifications of MoS2 Catalytic Nanoparticles Induced by Working Conditions: A Theoretical Study. J. Catal. 2002, 207 (1), 76-87. 20 ACS Paragon Plus Environment

Page 21 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(38) Li, Y.; Zhou, Z.; Zhang, S.; Chen, Z. MoS2 Nanoribbons: High Stability and Unusual Electronic and Magnetic Properties. J. Am. Chem. Soc. 2008, 130 (49), 16739-16744. (39) Heyd, J.; Scuseria, G. E.; Ernzerhof, M. Hybrid Functionals Based on a Screened Coulomb Potential. J. Chem. Phys. 2003, 118 (18), 8207-8215. (40) Heyd, J.; Scuseria, G. E. Efficient Hybrid Density Functional Calculations in Solids: Assessment of the Heyd–Scuseria–Ernzerhof Screened Coulomb Hybrid Functional. J. Chem. Phys. 2004, 121 (3), 1187-1192. (41) Li, X.; Wu, X.; Yang, J. Room-Temperature Half-Metallicity in La(Mn,Zn)AsO Alloy Via Element Substitutions. J. Am. Chem. Soc. 2014, 136 (15), 5664-5669. (42) Kan, E.-J.; Hu, W.; Xiao, C.; Lu, R.; Deng, K.; Yang, J.; Su, H. Half-Metallicity in Organic Single Porous Sheets. J. Am. Chem. Soc. 2012, 134 (13), 5718-5721. (43) Si, C.; Zhou, J.; Sun, Z. Half-Metallic Ferromagnetism and Surface Functionalization-Induced

Metal-Insulator

Transition

in

Graphene-Like

Two-Dimensional Cr2C Crystals. ACS Appl. Mater. Interfaces 2015, 7 (31), 17510-17515. (44) Yazyev, O. V.; Helm, L. Defect-Induced Magnetism in Graphene. Phys. Rev. B 2007, 75 (12), 125408. (45) Tian, X.; Liu, L.; Du, Y.; Gu, J.; Xu, J.-B.; Yakobson, B. I. Effects of 3d Transition-Metal Doping on Electronic and Magnetic Properties of MoS2 Nanoribbons. Phys. Chem. Chem. Phys. 2015, 17 (3), 1831-1836. (46) Khoeini, F.; Shakouri, K.; Peeters, F. M. Peculiar Half-Metallic State in Zigzag 21 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 22

Nanoribbons of MoS2: Spin Filtering. Phys. Rev. B 2016, 94 (12), 125412. (47) Zhang, C.-W.; Yan, S.-S. First-Principles Study on Ferromagnetism in Mg-Doped SnO2. Appl. Phys. Lett. 2009, 95 (23), 232108. (48) Li, Y.; Deng, R.; Tian, Y.; Yao, B.; Wu, T. Role of Donor-Acceptor Complexes and Impurity Band in Stabilizing Ferromagnetic Order in Cu-Doped SnO2 Thin Films. Appl. Phys. Lett. 2012, 100 (17), 172402. (49) Wolf, S.; Awschalom, D.; Buhrman, R.; Daughton, J.; Von Molnar, S.; Roukes, M.; Chtchelkanova, A. Y.; Treger, D. Spintronics: A Spin-Based Electronics Vision for the Future. Science 2001, 294 (5546), 1488-1495. (50) Datta, S.; Das, B. Electronic Analog of the Electro-Optic Modulator. Appl. Phys. Lett. 1990, 56 (7), 665-667. (51) Schliemann, J.; Egues, J. C.; Loss, D. Nonballistic Spin-Field-Effect Transistor. Phys. Rev. Lett. 2003, 90 (14), 146801. (52) Awschalom, D. D.; Flatté, M. E. Challenges for Semiconductor Spintronics. Nat. Phys. 2007, 3 (3), 153-159.

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Half-Metallicity in Co-Doped WSe2 Nanoribbons

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