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Physical Chemistry Chemical Physics
Cite this: DOI: 10.1039/c0xx00000x
ARTICLE TYPE
Published on 26 November 2014. Downloaded by Northeastern University on 26/11/2014 14:35:50.
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Effects of 3d transition-metal doping on electronic and magnetic properties of MoS2 nanoribbons Xiaoqing Tian,a Lin Liu,a Yu Du,*a Juan Gu,a Jian-bin Xu,c and Boris I. Yakobson*b Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5 DOI: 10.1039/b000000x
The electronic and magnetic properties of MoS2 nanoribbons doped with 3d transitional metals (TMs) were investigated using firstprinciples calculations. Clean armchair MoS2 nanoribbons (AMoS2NRs) are nonmagnetic semiconductors whereas clean zigzag MoS2 nanoribbons (ZMoS2NRs) are metallic magnets. The 3d TM impurities tend to substitute the outermost cations of AMoS2NRs and ZMoS2NRs, which are in agreement with the experimental results reported. The magnetization of the 3d-TM-impurity-doped AMoS2NRs
10 and ZMoS2NRs is configuration
dependent. The band gap and carrier concentration of AMoS2NRs can be tuned by 3d-TM doping.
Fedoped AMoS2NRs exhibit ferromagnetic characteristics and the Curie temperature (TC) can be tuned using different impurity concentrations. Co-doped ZMoS2NRs are strongly ferromagnetic with a TC above room temperature.
and magnetic properties of 3d TMs (including Mn, Fe, and Co)-
15 Introduction
doped MoS2 nanoribbons with armchair- and zigzag-shaped
The MoS2 monolayer is composed of three covalently bonded
edges.
hexagonal atomic layers (S–Mo–S). Weak van der Waals interactions exist between adjacent MoS2 monolayers. One important advantage of MoS2 is that the electronic and optical
20 properties can be tuned by varying the number of layers. The bulk MoS2 crystal is an indirect gap semiconductor with a band gap of 1.29 eV, whereas the MoS2 monolayer layer is a direct gap semiconductor with a band gap of 1.90 eV.
1,2
One-dimensional
MoS2 has been synthesized in recent experiments.
3,4
40 Computational methods Theoretical calculations were performed with the Quantum Espresso
package,
15
correlation functional.
employing 16
GGA-PBE
exchange
The on-site Coulomb interaction
GGA+U for 3d TMs is used.
45 Coulomb
the
17
The U and J are the on-site
repulsion and exchange interaction parameters,
Quasi-1D
respectively. Typical values of U and J are 4.0 and 1.0 eV,
and nanoribbons of MoS2 share the honeycomb
respectively, for both Mn and Fe;18,19 for Co, U and J are 3.3 and
structure and are expected to display interesting electronic and
1.0 eV. 40 Ry is used as the plane-wave basis set cutoff. The
5,6
structural models of MoS2 nanoribbons are constructed by cutting
Defects and strain are expected to modify the electronic
50 a single-layered MoS2 with the desired edges and widths. The 1-
properties and magnetic of MoS2 monolayer and nanoribbons.
7–10
D periodic boundary condition was applied along the growth
30 MoS2 nanostructures are doped with 3d TMs such as Fe, Co, and
direction of the nanoribbons to simulate infinitely long
Ni to increase its catalytic activities in hydrodesulfurization
nanoribbon systems; the length scales for the MoS2 nanoribbons
processes in the oil industry.11,12 The magnetic and electronic
are defined in Ref. 5. Specifically, the width of AMoS2NRs is
25 nanotubes
magnetic properties arising from quantum confinement effects.
properties of MoS2 nanoribbons could be tuned by 3d TMs doping. Either 3d TM substrates or 3d TM nanoclusters could
35 alter
55 defined
by the number of dimmer columns whereas for
ZMoS2NRs it is defined by the number of Mo columns. A 1.6-
the electronic structures of MoS2 monolayer.13,14 We used
nm-thick vacuum layer was used to eliminate longitudinal
state-of-the-art first-principles technique to study the electronic
interactions between the super cells. For the 14-AMoS2NR, the
This journal is © The Royal Society of Chemistry [year]
[Phys. Chem. Chem. Phys.], [year], [vol], 00–00 | 1
Physical Chemistry Chemical Physics Accepted Manuscript
PCCP
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Physical Chemistry Chemical Physics
View Article Online
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DOI: 10.1039/C4CP04579C
around 3.5 nm (width)×2.2 nm, which is large enough to avoid lateral image interactions. For 10-ZMoS2NR, the super cell contains in total 120 atoms, and its in-plane size is around 4.0 nm
5 (width)×0.7 nm, which is also large enough to avoid lateral image Published on 26 November 2014. Downloaded by Northeastern University on 26/11/2014 14:35:50.
interactions. A sampling of 12 uniformly distributed k-points along the 1-D Brillouin zone is employed for the MoS2 nanoribbons for both the zigzag and armchair shaped edges.
Results and discussion
10
The structures of relaxed 14-AMoS2NRs (Fig. 1(a)) give a width of around 2.1 nm. After structural optimization, the width of 14-AMoS2NR is increased by around 1.5 percent. There is obvious structural reconstruction to mitigate the truncation of chemical bonds at the edges. The S–Mo bonds in MoS2 are
15 composed of partial covalent and ionic bonds similar to the bonds of ZnO. The oxidation state of the edgiest Mo is +1.63, which is 0.1 smaller than that of the interior Mo using the Bader analysis method.20
The edgiest Mo atom is moved by 0.3 Å inwards
relative to the edgiest S atom. The bond length of S–Mo bond is
20 about 0.1 Å smaller than that of the interior bond. The calculated spin-polarized density of states (SPDOS) of 14-AMoS2NR (Fig.
Fig. 1 (a) Top view of relaxed 14-AMoS2NR and seven substitutional sites. (b) SPDOS of relaxed 14-AMoS2NRs. (c) Formation energy of the 3d TM-doped 14-AMoS2NRs for the seven configurations. (d) Configuration-dependent
45 magnetic
moment (M) of the 3d TM impurities in 14-AMoS2NRs. 14-
AMoS2NRs are extended periodically along the y direction. Mo atoms are blue, S atoms are orange, and Fe atoms are red. For S and Mo, the SPDOS presented here is the averaged value of each atomic species (total SPDOS of S or Mo atoms divided by the number of atoms). This notion is used throughout
50 the paper.
1(b)). The 14-AMoS2NR is a nonmagnetic semiconductor with band gaps of 0.56 eV and this is in good agreement with Ref. 5.
For 3d TM-doped 14-AMoS2NR, configuration 1 has the lowest
The band gap value is determined by the difference in the on-site
formation energy (Fig. 1(c)), and hence is the most favored.
25 energies
of two edges, and intra- and inter-edge hopping
parameters of the tight-binding
models.21
Because clean 14-
Configuration 4 has the highest formation energy, so is the least
55 favored.
The 3d TM impurities tend to replace the outermost
AMoS2NR is a nonmagnetic semiconductor, 3d TMs (Mn, Fe,
cations. The order of the formation energies is Hf (Mn )< Hf (Fe)
Co) are used as dopants to achieve magnetic properties. Seven
PCCP Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: X. Tian, L. Liu, Y. Du, J. Gu, J. Xu and B. I. Yakobson, Phys. Chem. Chem. Phys., 2014, DOI: 10.1039/C4CP04579C.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
www.rsc.org/pccp
View Article Online DynamicDOI: Article Links ► 10.1039/C4CP04579C
Physical Chemistry Chemical Physics
Cite this: DOI: 10.1039/c0xx00000x
ARTICLE TYPE
Published on 26 November 2014. Downloaded by Northeastern University on 26/11/2014 14:35:50.
www.rsc.org/xxxxxx
Effects of 3d transition-metal doping on electronic and magnetic properties of MoS2 nanoribbons Xiaoqing Tian,a Lin Liu,a Yu Du,*a Juan Gu,a Jian-bin Xu,c and Boris I. Yakobson*b Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5 DOI: 10.1039/b000000x
The electronic and magnetic properties of MoS2 nanoribbons doped with 3d transitional metals (TMs) were investigated using firstprinciples calculations. Clean armchair MoS2 nanoribbons (AMoS2NRs) are nonmagnetic semiconductors whereas clean zigzag MoS2 nanoribbons (ZMoS2NRs) are metallic magnets. The 3d TM impurities tend to substitute the outermost cations of AMoS2NRs and ZMoS2NRs, which are in agreement with the experimental results reported. The magnetization of the 3d-TM-impurity-doped AMoS2NRs
10 and ZMoS2NRs is configuration
dependent. The band gap and carrier concentration of AMoS2NRs can be tuned by 3d-TM doping.
Fedoped AMoS2NRs exhibit ferromagnetic characteristics and the Curie temperature (TC) can be tuned using different impurity concentrations. Co-doped ZMoS2NRs are strongly ferromagnetic with a TC above room temperature.
and magnetic properties of 3d TMs (including Mn, Fe, and Co)-
15 Introduction
doped MoS2 nanoribbons with armchair- and zigzag-shaped
The MoS2 monolayer is composed of three covalently bonded
edges.
hexagonal atomic layers (S–Mo–S). Weak van der Waals interactions exist between adjacent MoS2 monolayers. One important advantage of MoS2 is that the electronic and optical
20 properties can be tuned by varying the number of layers. The bulk MoS2 crystal is an indirect gap semiconductor with a band gap of 1.29 eV, whereas the MoS2 monolayer layer is a direct gap semiconductor with a band gap of 1.90 eV.
1,2
One-dimensional
MoS2 has been synthesized in recent experiments.
3,4
40 Computational methods Theoretical calculations were performed with the Quantum Espresso
package,
15
correlation functional.
employing 16
GGA-PBE
exchange
The on-site Coulomb interaction
GGA+U for 3d TMs is used.
45 Coulomb
the
17
The U and J are the on-site
repulsion and exchange interaction parameters,
Quasi-1D
respectively. Typical values of U and J are 4.0 and 1.0 eV,
and nanoribbons of MoS2 share the honeycomb
respectively, for both Mn and Fe;18,19 for Co, U and J are 3.3 and
structure and are expected to display interesting electronic and
1.0 eV. 40 Ry is used as the plane-wave basis set cutoff. The
5,6
structural models of MoS2 nanoribbons are constructed by cutting
Defects and strain are expected to modify the electronic
50 a single-layered MoS2 with the desired edges and widths. The 1-
properties and magnetic of MoS2 monolayer and nanoribbons.
7–10
D periodic boundary condition was applied along the growth
30 MoS2 nanostructures are doped with 3d TMs such as Fe, Co, and
direction of the nanoribbons to simulate infinitely long
Ni to increase its catalytic activities in hydrodesulfurization
nanoribbon systems; the length scales for the MoS2 nanoribbons
processes in the oil industry.11,12 The magnetic and electronic
are defined in Ref. 5. Specifically, the width of AMoS2NRs is
25 nanotubes
magnetic properties arising from quantum confinement effects.
properties of MoS2 nanoribbons could be tuned by 3d TMs doping. Either 3d TM substrates or 3d TM nanoclusters could
35 alter
55 defined
by the number of dimmer columns whereas for
ZMoS2NRs it is defined by the number of Mo columns. A 1.6-
the electronic structures of MoS2 monolayer.13,14 We used
nm-thick vacuum layer was used to eliminate longitudinal
state-of-the-art first-principles technique to study the electronic
interactions between the super cells. For the 14-AMoS2NR, the
This journal is © The Royal Society of Chemistry [year]
[Phys. Chem. Chem. Phys.], [year], [vol], 00–00 | 1
Physical Chemistry Chemical Physics Accepted Manuscript
PCCP
Page 1 of 7
Physical Chemistry Chemical Physics
View Article Online
Page 2 of 7
DOI: 10.1039/C4CP04579C
around 3.5 nm (width)×2.2 nm, which is large enough to avoid lateral image interactions. For 10-ZMoS2NR, the super cell contains in total 120 atoms, and its in-plane size is around 4.0 nm
5 (width)×0.7 nm, which is also large enough to avoid lateral image Published on 26 November 2014. Downloaded by Northeastern University on 26/11/2014 14:35:50.
interactions. A sampling of 12 uniformly distributed k-points along the 1-D Brillouin zone is employed for the MoS2 nanoribbons for both the zigzag and armchair shaped edges.
Results and discussion
10
The structures of relaxed 14-AMoS2NRs (Fig. 1(a)) give a width of around 2.1 nm. After structural optimization, the width of 14-AMoS2NR is increased by around 1.5 percent. There is obvious structural reconstruction to mitigate the truncation of chemical bonds at the edges. The S–Mo bonds in MoS2 are
15 composed of partial covalent and ionic bonds similar to the bonds of ZnO. The oxidation state of the edgiest Mo is +1.63, which is 0.1 smaller than that of the interior Mo using the Bader analysis method.20
The edgiest Mo atom is moved by 0.3 Å inwards
relative to the edgiest S atom. The bond length of S–Mo bond is
20 about 0.1 Å smaller than that of the interior bond. The calculated spin-polarized density of states (SPDOS) of 14-AMoS2NR (Fig.
Fig. 1 (a) Top view of relaxed 14-AMoS2NR and seven substitutional sites. (b) SPDOS of relaxed 14-AMoS2NRs. (c) Formation energy of the 3d TM-doped 14-AMoS2NRs for the seven configurations. (d) Configuration-dependent
45 magnetic
moment (M) of the 3d TM impurities in 14-AMoS2NRs. 14-
AMoS2NRs are extended periodically along the y direction. Mo atoms are blue, S atoms are orange, and Fe atoms are red. For S and Mo, the SPDOS presented here is the averaged value of each atomic species (total SPDOS of S or Mo atoms divided by the number of atoms). This notion is used throughout
50 the paper.
1(b)). The 14-AMoS2NR is a nonmagnetic semiconductor with band gaps of 0.56 eV and this is in good agreement with Ref. 5.
For 3d TM-doped 14-AMoS2NR, configuration 1 has the lowest
The band gap value is determined by the difference in the on-site
formation energy (Fig. 1(c)), and hence is the most favored.
25 energies
of two edges, and intra- and inter-edge hopping
parameters of the tight-binding
models.21
Because clean 14-
Configuration 4 has the highest formation energy, so is the least
55 favored.
The 3d TM impurities tend to replace the outermost
AMoS2NR is a nonmagnetic semiconductor, 3d TMs (Mn, Fe,
cations. The order of the formation energies is Hf (Mn )< Hf (Fe)
Co) are used as dopants to achieve magnetic properties. Seven
