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Nanoscale
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Du, C. Xia, W.
Xiong, T. Wang, Y. Jia and J. Li, Nanoscale, 2017, DOI: 10.1039/C7NR06473J.
Volume 8 Number 1 7 January 2016 Pages 1?660
Nanoscale
www.rsc.org/nanoscale
This is an Accepted Manuscript, which has been through the
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ISSN 2040-3364
PAPER
Qian Wang et al.
TiC2: a new two-dimensional sheet beyond MXenes
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Page 1 of 28
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Two-Dimensional Transition-Metal Dichalcogenides-Based
Ferromagnetic van der Waals Heterostructures
The lacking of ferromagnetic (FM) van der Waals (vdW) heterostructures
hinders the application of two-dimensional (2D) materials in spintronics,
information memories and storage devices. Here, we find theoretically
that the 2D transition-metal dichalcogenides-based vdW heterostructures,
such as MoS2/VS2 and WS2/VS2, possess the excellent characteristics of
stable stacking configurations, FM semiconducting ground states, high
Curie temperature, staggered band alignment and large band offset.
Fortunately, 100% spin-polarized currents at the Fermi level can be
achieved under certain positive external electric field, which can filter the
current into a single spin channel. Also, the majority channel undergoes
the transition from type-II to type-I (type-III) band alignment under the
negative (positive) electric field; while the band alignment of the minority
channel is robust to the electric field. Our results provide a feasible way
to realize the 2D TMDs-based FM semiconducting heterostructures for
the spintronic devices.
______________________
a
Department of physics, Henan Normal University, Xinxiang 453007, China. E-mail:
xiacongxin@htu.edu.cn
b
Key Laboratory for Special Functional Materials of Ministry of Education, Henan
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Juan Du, Congxin Xia,a,* Wenqi Xiong,a Tianxing Wang,a Yu Jia,b and Jingbo Lic,*
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DOI: 10.1039/C7NR06473J
University, Kaifeng 475004, China
c
Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China.
Introduction
Recently, two-dimensional (2D) materials-based van der Waals (vdW)
heterostructures have attracted tremendous research attentions due to their
novel properties and potential applications for the future nano-devices.1-6
By forming heterostructures, many promising features can be achieved,
such as high carrier mobility, tunable band gap, broad spectrum, which
are ideal for fabricating high-performance optoelectronic and electronic
devices. Nevertheless, there are rare studies about ferromagnetic (FM)
vdW heterostructures to date,7 which hinders the application of
heterostructures in spintronics, information memories and storage
devices.
According to previous studies, vdW heterostructures have the
advantage of integrating the characteristics of their stacked 2D materials,
thus, the explorations and studies of 2D magnetic materials are necessary
to design the magnetic vdW heterostructures. However, most of the 2D
materials are nonmagnetic. Initial efforts to induce magnetic ordering into
the nonmagnetic materials are focused on the structural modulation, such
as transition metal (TM) doping,8 defects,9 strain engineering,10 interface
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E-mail: jbli@semi.ac.cn
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dangling bonds,11 and surface functionalization.12,13 However, these
structural modulation inevitably lead to complex implication with the
disulfde (VS2) is identified to be a FM semiconducting material by
theoretical and experimental methods, which holds great potential for
further application in nextgeneration spintronic devices.14 Very recently,
Xiong et al. reported the Mg(OH)2/VS2 heterobilayer has the FM
properties with high Curie temperature.7 However, experimental
fabrications of 2D Mg(OH)2 material are still challenging. Thus, to
further understand the physical mechanism and extend the spintronic
device applications, more research works will be required to explore new
FM heterostructures.
As is well known, TMDs have been identified to be promising
components of heterostructures for their unique electronic properties. For
example, due to the quantum confinement, an indirect to direct band gap
transition can be observed when the materials are thinned into
monolayers, resulting in strong photoluminescence and absorption.15-19
Additionally, TMDs have many potential applications in various fields
including
hydrogen
storage,20
catalysis,21
Li-ion
battery,22
and
optoelectronic devices like photonics and transistors.17,19,23,24 Moreover,
type-II band alignment is always found in the TMDs heterostructures,
where electrons and holes are inclined to spatially separate to different
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lattice, orbital and spin degrees of freedom. More recently, 2D vanadium
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layers as demonstrated by the photoluminescence (PL) quenching and
time resolved measurements.25-27 The optoelectronic properties of MoS2
Based on the above analysis, in this work, we construct the MoS2/VS2
and WS2/VS2 heterostructures and perform theoretical calculations on
their electronic and magnetic properties, considering the electric field
effects. Our first-principles results show that both MoS2/VS2 and
WS2/VS2 heterostructures exhibit FM semiconducting ground states with
high Curie temperature and staggered band alignment. Particularly,
half-metallic FM properties and multi-band alignment transitions (type-I,
II and III) can be achieved under certain electric field modulation. These
will be very interesting to the studies of spintronic device in the future.
Calculation methods
In this work, all the calculations are performed based on the
spin-polarized density functional theory (DFT) as implemented in the
Vienna Ab-initio simulation package (VASP).29-31 The exchange
correlation potential is described with the Perdew-Burke-Ernzerhof (PBE)
of the generalized gradient approximation (GGA).32 The electron-ion
potential is modeled with projected augmented wave (PAW) potential. In
order to obtain a more accurate description of the electronic states, all the
electronic properties are calculated using the hybrid functional (HSE06).
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and WS2 monolayers can be tuned by quantum confinement of carriers.28
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The spin-orbit coupling (SOC) effects33 is explicitly included in the
calculations. The kinetic energy cutoff of plane wave is set to be 400 eV
carried out using 11��Monkhorst-Pack k-point meshes for geometry
optimization of the system.34 The geometry structures are relaxed until
the force on each atom is less than 0.01eV/� and the total energy
convergence criteria is chosen as 10-5 eV. Meanwhile, the DFT-D2
method of Grimme is used to describe the vdW interaction in the
TMDs-based heterostructures.35,36
Results and discussions
We firstly calculate the structural parameters, electronic and
magnetic properties of 2D MoS2, WS2 and VS2 monolayer unit cells. For
the convenience, we denote the MoS2 and WS2 as XS2 (X = Mo, W). The
VS2 monolayer occurs in two polymorphs, i.e., octahedral (tVS2) and
trigonal prismatic (hVS2) with D3d and D3h point groups, respectively.37
Also, hVS2 monolayer is proved to be the most stable one with the
highest magnetic moment at and below room temperature.38 Therefore,
only the 2D hVS2 phase is considered in this work. Here, as shown in Fig.
1, MoS2, WS2, and VS2 monolayers share the same hexagonal structure
with the lattice constants of 3.183�, 3.182�, and 3.170�, respectively.
The calculated band structures (See Fig. S1 (supplementary information))
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for the plane wave expansion. The Brillouin zone (BZ) integration is
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indicate that all the three monolayers exhibit semiconducting properties.
In addition, the band gap values of the monolayers calculated using
which are close to the experimental values. Generally speaking, HSE
methods give lower band gaps than GW calculations for semiconducting
materials.39,40 However, in this work, we do not adopt the GW method
because it was found that GW tends to overestimate the band gaps of the
MoS2 and WS2.41,42 Such discrepancies come from the different
theoretical methods. For the HSE06 method used in this work, a
percentage 25% of exact nonlocal Hartree-Fock exchange is added to the
PBE functional, while GW calculations are based on the many-body
Green?s function theory. Moreover, MoS2 and WS2 monolayers own
non-magnetic ground state, while VS2 monolayer possesses ferromagnetic
ordering with the magnetic moment per unit cell of 1.0 礏. Furthermore,
strong SOC effects can be found in MoS2 (WS2) monolayer with strongly
spin-split bands at K point, and this splitting can reach the order of 24
meV (23 meV) in the CB and 166 meV (449 meV) in the VB, which are
in accordance with the reported values.43 However, it seems that the SOC
effects make no difference to the VS2 monolayer, as the band structures
calculated with the SOC is more or less the same as those without SOC.
All these obtained results are quite consistent with previous experimental
and theoretical researches.14,44
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HSE06 method are presented in Table S1 (supplementary information),
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Fig. 1 The structures of (a) MoS2, (b) VS2, and (c) WS2 monolayers from the side and
top views, (d) MoS2/VS2 and (e) WS2/VS2 heterostructures from the side view. The
black rectangular and rhombic frame represent the unit cells.
Structural stability of the XS2/VS2 heterostructures
Due to the close lattice constants of XS2 and VS2 monolayers, we
can construct the XS2/VS2 heterostructures via combing the unit cells of
XS2 monolayer with that of the VS2 monolayer, which induce very small
lattice mismatch as shown in Fig. 1. Also, the lattice mismatch is
calculated using the formula ? =
2(a1 ? a 2 )
, where a1, a2 are the lattice
a1 + a 2
constants of the two isolated monolayers, respectively. The lattice
mismatch of the two heterostructures are < 1%. Moreover, in Fig. S1
(supplementary information), we have compared the band structures of
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the MoS2, WS2, and VS2 monolayers with and without strain induced by
the lattice mismatch, showing that the strain introduced to accommodate
corresponding monolayers. After optimization, the equilibrium interlayer
distance of the heterostructure is calculated to be 3.085� for MoS2/VS2
heterostructure and 3.043� for WS2/VS2 heterostructure.
In order to check whether the 2D XS2/VS2 vdW heterostructures is
stable, we firstly perform the spin-polarized ab initio molecular dynamics
(AIMD) under the canonical (NVT) ensemble, using a 4�supercell
containing 96 atoms. The simulations are carried out using a Nos�
thermostat at 300 K for 3 picoseconds. Fig. 2 shows the fluctuation of
temperature and total energy as a function of the simulation time. After 3
picoseconds, no structure distortion is found in the XS2/VS2
heterostructures. Moreover, the amplitude of fluctuation for both
temperature and total energy is small and regular during the process of
MD, which confirms that the two heterostructures are thermally stable at
room temperature. Besides, the fluctuation of magnetic moment as a
function of the MD simulation time shown in Fig. 2 will be discussed
later to assess the stability of the magnetic states at room temperature.
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the lattice mismatch has little effect on the electronic properties of the
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Fig. 2 The fluctuations of temperature, total energy and ferromagnetic moment as a
function of the molecular dynamic simulation step (a-c) for MoS2/VS2 heterostructure
and (d-f) for WS2/VS2 heterostructure at 300 K, respectively.
Additionally, to quantificationally assess the stability of XS2/VS2
heterostructures, we carry out the calculation of the binding energy Eb
using the following formula,
Eb =
where E XS
2
E XS 2 / VS 2 ? E XS 2 ? EV S2
(1)
A
/ VS 2
, E XS and EVS represent the total energies of the
2
2
XS2/VS2 heterostructures, the XS2 and VS2 monolayers, respectively. A is
the interfacial area. The binding energy is calculated to be -84.589
meV/�for MoS2/VS2 heterostructure and -119.766 meV/�for WS2/VS2
heterostructure. These values are lower than that of the graphite (-12
meV/�45 and bulk MoS2 (-26 meV/�,46 which also indicate that they
can form stable structure patterns in practice. Thus, according to the
above obtained theoretical results, we can conclude that the 2D MoS2/VS2
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and WS2/VS2 heterostructures can be fabricated in practice. However, we
would like to point out that there have not any experimental publications
on the MoS2/VS2 and WS2/VS2 heterostructures to date.
For a new material, it is important to study its electronic structures.
Fig. 3 presents the band structures and projected band structures of the
XS2/VS2 heterostructures with and without SOC effects. We can find that
the behaviors of the majority (spin-up) and minority (spin-down) bands
are different, suggesting that they possess the magnetic ground states. The
results are in accordance with the calculations of magnetic moments for
the heterostructures (0.9053 礏 for MoS2/VS2 and 0.8980 礏 for WS2/VS2
heterostructures), which will be discussed later. Moreover, compared with
the magnetic moment of the 2D VS2 unitcell (1 礏), the magnetic
moments of heterostructures are reduced slightly due to the weak
magnetization of Mo (W) atoms. In addition, Fig. 3 also shows that for
the majority channel of the XS2/VS2 heterostructures, the valence band
maximum (VBM) lies at the ?point and the conduction band minimum
(CBM) lies at the K point; while for the minority channel, the VBM also
lies at the ? point and the CBM lies near to the M point along the M-?
line. Thus, the XS2/VS2 heterostructures possess the indirect band
structures for both the majority and minority channels. Interestingly, for
the MoS2/VS2 heterostructure, the majority and minority channels exhibit
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Electronic structures and band alignment of the XS2/VS2 heterostructures
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semiconducting properties with the band gaps of 0.41 eV and 0.94 eV,
respectively; while for the WS2/VS2 case, the majority and minority
Considering the SOC effects, we find a spin-splitting of 163 meV (458
meV) at the K point in the VB of the XS2/VS2 heterostructures. Moreover,
the intrinsic magnetic moments remain almost that same as that without
SOC and the band gap seems insensitive to the SOC effects.
Fig. 3 The band structures and projected band structures of (a) MoS2/VS2 and (b)
WS2/VS2 heterostructures with and without SOC effects, and the majority and
minority bands are marked with upward arrows and downward arrows, respectively.
Additionally, Fig. 3 also shows clearly that in the XS2/VS2
heterostructures, the states of the CBM and VBM are contributed by the
XS2 layer and VS2 layer, respectively, indicating a staggered (type-II)
band alignment occurs in the semiconducting heterostructures. Moreover,
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channels have the band gap values of 0.19eV and 0.73 eV, respectively.
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we can also find from our obtained data that the CBM is absolutely
contributed by the VS2 layer in both the majority and minority channels;
(21%) VS2 in the majority channel, and 92% (93%) MoS2 (WS2) and 8%
(7%) VS2 in the minority channel. Furthermore, the states in CBM and
VBM share the same spin channel. The results obtained above can be
proved by the projected density of states (PDOS) shown in Fig. S2
(supplementary information). Therefore, we can conclude that the
XS2/VS2 heterostructures own the semiconducting nature and type-II
band alignment, facilitating the effective separation of photogenerated
holes and electrons.
Notably, band alignment is significantly important in designing
heterostructure-based devices, therefore, in Fig. 4(a), we show the band
edges of XS2/VS2 heterostructures relative to the vacuum level (Evacuum).
This band alignment further prove the type-II nature of XS2/VS2
heterostructures in both majority and minority channels. In particular, we
can find that both the majority and minority channels of the XS2/VS2
heterostructures exhibit large conduction band offset ? Ec and valence
band offset ? Ev , as shown in Table S1 (supplementary information),
which can help to confine the electrons and holes in separated layers and
further prolong the lifetime of indirect excitons. Note that this large band
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while the VBM is composed of about 71% (79%) MoS2 (WS2) and 29%
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offset and type-II band alignment won?t be affected by the SOC effects
although large spin-splitting occur at the K point in the VB of the two
offsets can help the XS2/VS2 heterostructures to be well-behaved
electron-hole separators, and pave the way for the application in related
optoelectronic devices.
Fig. 4 (a) Band edges and work functions of MoS2/VS2 and WS2/VS2 heterostructures,
referring to the vacuum level (Evacuum). (b) The plane-averaged charge density
difference of MoS2/VS2 and WS2/VS2 heterostructures. The inset is the 3D surface of
the charge density difference, the green and pink areas represent electrons
accumulation and depletion, respectively.
In order to further understand the charge transfer of the XS2/VS2
heterostructures and its underlying mechanism, we perform the
calculations of work function and the charge density difference (CDD).
We can see from Table S1 (supplementary information) that the work
function of XS2/VS2 heterostructure is between that of the XS2 and VS2
monolayers. This can be easily understood that charges tend to transfer
from the material with smaller work function to that with larger one when
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heterostructures. The typical staggered band alignment and large band
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forming heterostructure. The charge transfer will align the Fermi level to
a certain value, and therefore obtain a certain work function. Moreover,
tend to transfer from XS2 to VS2 layer when forming the heterostructure.
Also, Bader charge analysis further verifies the direction of the charge
transfer and gives the specific quantity, where 0.009 electrons are found
to transfer from the MoS2 layer to the VS2 layer, 0.013 electrons transfer
from the WS2 layer to the VS2 layer. The transferred electrons (0.009 and
0.013) are calculated in the single cell of the heterostructures. Thus,
negative charge are accumulated in the VS2 layer, and the XS2 layer
become the center of the positive charge. Furthermore, a built-in electric
field is formed in the heterostructure, pointing from the XS2 layer to the
VS2 layer.
To visualize the charge transfer in the XS2/VS2 heterostructures more
intuitive, we calculate the charge density difference (CDD) and the
corresponding
plane-averaged
CDD
using
the
formula
?? = ? XS 2 / VS 2 ? ? XS 2 ? ?VS 2 , where ? XS 2 / VS 2 , ? XS 2 and ? VS 2 represent the charge
density of the XS2/VS2 heterostructures, the XS2 monolayer and the VS2
monolayer, respectively. As shown in Fig. 4(b), charges are depleted in
the XS2 layer (marked in pink), while accumulated in the VS2 layer
(marked in green), causing the charge redistribution and further resulting
in the formation of interface dipole. Moreover, obviously charge
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the smaller work function of the XS2 monolayer indicates that charges
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depletion is found in the interface, which results from the surface charge
repulsion effect and can result in the surface orbital rehybridization.
Magnetic properties of XS2/VS2 heterostructures
plot the spin density of the heterostructures in Fig. 5, showing that the
magnetic moment is mainly contributed by the V atoms. In the following,
we explore the ground-state magnetic properties of the heterostructures.
The non-magnetic (NM), ferromagnetic (FM), and anti-ferromagnetic
(AFM), are considered by using a (2� supercell. Fig. 5(c)-(e) present
the optimized configurations, local magnetic arrangements, magnetic
moments and energy relative to that of the FM configuration (the energy
of FM configuration is set to 0) for NM, FM, and AFM states,
respectively. Obviously, the FM state is the most stable one for the two
heterostructures, with energy 171.62 meV and 167.51 meV lower than
that of the NM and AFM states in the MoS2/VS2 heterostructure, and
169.81 meV and 168.14 meV lower than that of the NM and AFM states
in the WS2/VS2 heterostructure. Thus, we can conclude that the XS2/VS2
heterostructures own the FM ground states, which are promising
candidates for the development of next-generation spintronic and
optoelectronic devices.
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To explore the magnetic properties of the XS2/VS2 heterostructures, we
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Fig. 5 The spin density of the XS2/VS2 heterostructure with (a) side and (b) top view.
The black dashed rectangular and rhombic frame represent the primitive cells. The
NM, FM and AFM magnetic configurations of XS2/VS2 heterostructure, their
magnetic moments and relative energies with respect to the FM states are shown in (c),
(d) and (e), respectively.
Curie temperature (TC), also known as the magnetic transition point, is
an important temperature parameter for a FM material. In order to clarify
the stability of FM at finite temperatures, we estimate the Curie
temperature (TC) of the XS2/VS2 heterostructures using the following
formula
?k BTc 2 = E AFM ? EFM ,
(2)
where ? is the dimension of the system, kB is the Boltzmann constant,
EAFM and EFM are the total energies of the unit-cell system with AFM and
FM coupling, respectively. Interestingly, we find high Curie temperatures
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of 485 K for the MoS2/VS2 heterostructure, and 487 K for the WS2/VS2
heterostructure. These rather high Curie temperatures make XS2/VS2
spintronics devices.
To further assess whether the magnetic states can survive at room
temperature, Fig. 2(c) and (f) present the fluctuation of magnetic moment
as a function of the MD simulation time at 300K. It is shown that the
magnetic moment retain the value of 14 礏 in the first 500 fs and then
begin to oscillate periodically during the simulation. The reason is that
the atoms will move in some way during the simulation, resulting in
relatively displacement between the two layers, which has certain
influence on the magnetic moment. In the first 500 fs of the simulation,
the movement of the atoms are too small that can be ignored, thus the
magnetic moment remains almost unchanged. Moreover, the system
retains the magnetic ground state with the average magnetic moment of
14.6 礏 for the MoS2/VS2 heterostructure and 14.7 礏 for the WS2/VS2
heterostructure at room temperature. Our results simply proved the
stability of the magnetic state for the heterostructures at room temperature.
In this work, our calculations show that for XS2/VS2 heterostructures, the
magnetic properties are mainly contributed by VS2, and the X element is
slightly magnetized and carry a very small magnetic moment in the
heterostructures. We may conclude from these calculations that the
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heterostructures become promising materials for applications in
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elements other than W and Mo-based 2D non-magnetic metal sulfides
might have the similar property in the heterostructures composed of 2D
nonmagnetic and ferromagnetic semiconducting materials.
In practice, when the materials are considered as building block in the
electronic devices, it is always subjected to the electrostatic gating
influences. Thus, it is useful to study how the external electric filed
affects the band structures of the XS2/VS2 FM heterostructures. Here, we
apply the external electric field to XS2/VS2 heterostructures along the
direction perpendicular to the stacking layers, and define the positive
direction as pointing from the XS2 layer to VS2 layer.
Fig. 6 (a) The majority and minority band gaps, and (b) band alignment types of
MoS2/VS2 and WS2/VS2 heterostructures as a function of the external electric field.
The type-I (II, III) represents the type-I (II, III) band alignments in the heterostructure.
Firstly, Fig. 6(a) gives the variation of band gap as a function of the
external electric field, showing that the band gap is sensitive to not only
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Electric field effects on band structures of the XS2/VS2 FM heterostructures
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the intensity but also the direction of external electric field. When the
external electric field is applied along the negative direction (from the
minority channels exhibit monotonically increasing trend with the
increasing strength of the external electric field. However, an opposite
changing trend can be found when the external electric field is applied
along the positive direction. The band gaps of the two spin channels
decrease with the increasing strength of the positive external electric field.
As demonstrated by the band structures of the XS2/VS2 heterostructures
under selected external electric field shown in Fig. S3 (supplementary
information). Interestingly, a semiconductor-metal transition occur at the
majority channel when the strength exceeds 0.2 V/� for WS2/VS2
heterostructure and 0.3 V/� for MoS2/VS2 case. The minority channel
retain the semiconducting properties when the external electric field is
applied under the range of -0.7 V/� ~ 0.7 V/�. That?s to say, certain
positive external electric filed can induce the semiconductor to half-metal
transition in the XS2/VS2 FM heterostructures. Therefore, applying
positive electric field to the XS2/VS2 FM heterostructures is excepted to
achieve the 100% spin-polarized currents, which can pave a way for the
potential application in high performance spintronics devices.47,48
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VS2 layer to the XS2 layer), the band gaps of both the majority and
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Fig. 7 Band alignments under external electric fields of -0.4 V/�, 0 V/�, 0.3 V/�, 0.6
V/� for MoS2/VS2 heterostructure and -0.7 V/�, 0 V/�, 0.2 V/�, 0.3 V/� for
WS2/VS2 heterostructure referring to the vacuum level (Evacuum).
To further explore the underlying mechanism of external electric
field effects on the band structures of the XS2/VS2 FM heterostructures,
we present the variation of the band edge in Fig. 7. It is clearly shown
that the majority and minority channels exhibit similar changing trend
under the external electric field in the WS2/VS2 and MoS2/VS2
heterostructures. The positive electric field can shift the bands of VS2
downward, and the negative electric field shifts the VS2 bands upward.
However, the external electric field exerts an opposite effect on the bands
of the XS2 layer. This can be explained as follows. The direction of the
built-in electric field is the same as that of the positive external electric
field. Thus, when the positive electric field is applied, the total electric
field is enhanced in the heterostructures, strengthening the drift of charges.
Thus, the positive external electric field can facilitate the electrons
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DOI: 10.1039/C7NR06473J
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transfer from the VS2 layer to the XS2 layer, shifting the bands of XS2
upward and the bands of VS2 downward. On the contrary, a negative
Therefore, negative external electric field can promote the electrons
transfer from the XS2 layer to the VS2 layer, shifting the bands of VS2
upward and the bands of XS2 downward. Note that the heterostructures
are relaxed for each setting of the electric field, and no obvious structural
changes are observed, as shown in Table S2 (supplementary information).
Interestingly, we can find from Fig. 7 that in the majority channel of
the heterostructures, a type-II to type-I band alignment transition can be
found when a certain negative external electric field is applied; and a
transition from type-II to type-III occurs under certain positive external
electric field. However, the minority channel of the heterostructures retain
the type-II band alignment under different external electric field. Detailed
transition point and band alignment of the heterostructures under different
external electric field are shown in Fig. 6(b). Furthermore, in Fig. S4
(supplementary information), the projected band structures of the
XS2/VS2 heterostructure under selected external electric field also prove
the band alignment transition. As is known, type-I heterostructure
contribute to the fast recombination of electrons and holes, thus it can be
used in luminescent devices, such as light-emitting diodes (LEDs).49,50
Type-II heterostructure can facilitate the effective separation of electrons
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external electric field will weaken the effects of the total electric field.
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and holes, thus prolong the lifetime of interlayer exciton, making it good
candidate for the application in electron-hole separators, and related
carriers, and further allows the operation of a tunnel field effect
transistors (FET).52,53 All the three types of band alignment (type-I,
type-II and type-III) can be achieved in the XS2/VS2 heterostructures
under different external electric field, realizing multi-band alignment
modulations in a single heterostructure but in different spin channel,
which offer an effective way for high-performance optoelectronic and
spintronic devices.
Conclusion
In conclusion, through the first-principles calculations, we predict two
stable FM heterostructures, MoS2/VS2 and WS2/VS2, which own type-II
band alignment and high Curie temperature, 485 K for MoS2/VS2
heterostructure and 487 K for WS2/VS2 heterostructure. Interestingly, a
semiconductor to half-metal transition can be obtained under certain
positive external electric filed, which imply that external electric filed can
be expected to induce 100% spin-polarized currents and further pave a
way for the potential application in high performance spintronics devices.
Particularly, negative and positive external electric filed can also induce
type-II to type-I and type-II to type-III band alignment transitions,
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optoelectronic devices.2,51 Type-III heterostructure allows tunneling of
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respectively, in the majority channel of the heterostructure. However, the
minority channel of the heterostructure retain the type-II band alignment
stable FM type-II vdW heterostructures with high Curie temperature, but
also pave a way for the realization of semiconductor to half-metal
transition and band alignment transition under external electric field,
which provide a feasible way toward multifunctional spintronic and
optoelectronic devices.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This research was supported by the National Natural Science Foundation
of China under Grant No.11674084, 61622406, 11674310, 61571415.
And
Natural
Science
Foundation
of
Henan
under
Grant
No.162300410169. The calculations are also supported by The High
Performance Computing Center of Henan Normal University.
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