Lateral and Vertical MoSe2âMoS2 Heterostructures via Epitaxial

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Surfaces, Interfaces, and Catalysis; Physical Properties of Nanomaterials and Materials

Lateral and Vertical MoSe2-MoS2 Heterostructures via Epitaxial Growth: Triggered by High Temperature Annealing and Precursor Concentration Tao Chen, Degong Ding, Jia Shi, Guang Wang, Liangzhi Kou, Xiaoming Zheng, Xibiao Ren, Xinfeng Liu, Chuanhong Jin, Jianxin Zhong, and Guolin Hao J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b01961 • Publication Date (Web): 30 Jul 2019 Downloaded from pubs.acs.org on July 31, 2019

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The Journal of Physical Chemistry Letters

Lateral and Vertical MoSe2-MoS2 Heterostructures via Epitaxial Growth: Triggered by High Temperature Annealing and Precursor Concentration Tao Chen1, 2#, Degong Ding3#, Jia Shi4, 5#, Guang Wang6, Liangzhi Kou7, Xiaoming Zheng6, Xibiao Ren3, Xinfeng Liu4, Chuanhong Jin2, 3, Jianxin Zhong1 and Guolin Hao1, 2* 1. School of Physics and Optoelectronics and Hunan Key Laboratory for Micro-Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, P. R. China 2. Hunan Institute of Advanced Sensing and Information Technology, Xiangtan University, Xiangtan 411105, P. R. China 3. State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, P. R. China 4. Division of Nanophotonics, CAS Key Laboratory of Standardization and Measurement

for

Nanotechnology,

CAS

Center

for

Excellence

in

Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, P. R. China 5. University of Chinese Academy of Sciences 19 A Yuquan Rd, Shijingshan District, Beijing 100049, P. R. China 6. Department of Physics, College of Liberal Arts and Sciences, National University of Defense Technology, Changsha 410073, P. R. China 7. School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Gardens Point Campus, Brisbane, QLD 4001, Australia # These authors contribute equally to this work. *Corresponding author. Tel.: +86 0731-58293749; fax: +86 0731-58298612. E-mail: [email protected]

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Abstract: Atomically thin transition-metal dichalcogenide (TMDC) heterostructures have attracted increasing attention due to their unprecedented opportunities in the fields of electronics and optoelectronics. However, selective growth of either lateral or vertical TMDC heterostructure remains challenging. Here, we report that lateral and vertical MoS2/MoSe2 epitaxial heterostructures can be successfully fabricated via one-step growth strategy, which are triggered by the concentration of sulfur precursor vapor and

high

temperature

annealing

process.

Vertically

stacked

MoS2/MoSe2

heterostructures can be synthesized via control of the nucleation and growth kinetics, which is induced by high sulfur vapor concentration. High temperature annealing process results in the formation of fractured MoSe2 and in situ epitaxial growth of lateral MoSe2-MoS2 heterostructures. This study has unveiled the importance of sulfur vapor concentration and high temperature annealing process on the controllable growth of MoSe2-MoS2 heterostructures, which paves a new route for fabricating two-dimensional TMDC heterostructures. TOC Graphic.


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As

the

essential

building

blocks

of

modern

semiconductor

industry,

heterostructures play a key role in the realm of electronics and optoelectronics.1,

2

Recently, two-dimensional (2D) materials have shown intriguing optical and electronic properties, which are distinct from their bulk counterparts and could be complementary to conventional semiconductors.3-6 Monolayer transition-metal dichalcogenides (TMDCs), such as MX2 (M:Mo, W; X:S, Se), are direct band-gap semiconductors possessing broken inversion symmetry and high photoelectric conversion efficiency, which have attracted considerable attention in recent years.7-10 Moreover, different atomically thin TMDC materials can be stacked vertically to create van der Waals (vdW) heterostructures or in-plane seamlessly stitched to form lateral heterostructures.11-13 Beyond single-component atomically thin TMDC materials, many new physical phenomena and optoelectronic functionalities have been realized in TMDC heterostructures,14-16 which are considered to be the essential building blocks for next-generation optoelectronic and light-harvest applications including field effect transistors, light-emitting diodes as well as photodetectors.12, 13, 17-20

An effectively synthesized route has been proven to be far more challenging and highly desired to design and fabricate TMDC heterostructures.11,

21

Although

mechanical transfer techniques could create vdW heterostructures by stacking different TMDC materials,13, 22-24 the quality of heterostructures was affected due to the contaminant residues and uncontrolled stacking orientation during the fabrication



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process. Many efforts have been focused on chemical vapor deposition (CVD) method due to the possibility of well-defined interlayer orientations, atomically sharp and clean interlayer interfaces as well as reproducible production, which has proven to be the most effective growth technique to synthesize TMDC heterostructures.11, 25, 26

Vertical and in-plane heterostructures of two different MX2, such as WS2-WSe2,

MoSe2-MoS2, MoS2-WS2, WS2-MoS2 with exciting optical and electrical properties have been fabricated by employing one-step or two-step CVD synthetic technique.27-34 However, the controllable synthesis of TMDC heterostructures with different shell sizes and selectively lateral and vertical growth remains a considerable challenge.30, 34 Corresponding growth mechanism is still unclear, although it is highly desirable and essential for device fabrication and integration.

Here, selective growth of highly crystalline in-plane interconnected and vertically stacked MoS2/MoSe2 heterostructures was achieved by one-step ambient pressure chemical vapor deposition (APCVD) synthesized strategy. Both in-plane and vertically stacked MoSe2-MoS2 heterostructures were systematically investigated. The nucleation and growth kinetics for the fabrication of MoS2/MoSe2 heterostructures have been effectively manipulated via tuning the sulfur vapor concentration. Meanwhile, the space-confined MoS2 nanoribbons with different widths can be epitaxially grown within monolayer MoSe2 plane by controlling the high-temperature annealing

process.

Raman

and

photoluminescence

(PL)

spectroscopy

characterizations demonstrate that in-plane and vertical MoSe2-MoS2 heterostructures


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exhibit clearly spacial distribution and optical modulation. Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) investigations reveal structure and surface potential distributions of as-prepared MoSe2-MoS2 heterostructures. Annular dark field

scanning transmission electron microscopy (ADF-STEM), fast

Fourier transform (FFT) pattern, and second harmonic generation (SHG) characterizations have demonstrated the single crystalline structure, epitaxial growth property as well as atomically sharp interfaces of synthesized heterostructures. Our experimental

results

highlighted

the

roles

of

sulfur

concentration

and

high-temperature annealing process paving the way for controllable fabrication of 2D lateral and vertical TMDC heterostructures, which is an essential step towards construction of electronic and optoelectronic devices. Figure 1a schematically illustrates the experimental setup for the targeted growth of 2D stacked and stitched MoSe2-MoS2 heterostructures through one-step APCVD growth process. Both MoSe2 and MoS2 monolayer or few-layer crystals can be well fabricated on SiO2/Si, sapphire as well as mica substrates, respectively. Corresponding morphologies, crystal structures as well as electrostatic properties of as-prepared products were systematically investigated (Figure S1-S3). Briefly, high purity MoO3 powder (20 mg) in the quartz boat was located in the heating center of 1 in. horizontal tube furnace. Silicon wafers with 300 nm SiO2 top layer were placed face down on the quartz boat. Se powder (400 mg) in another quartz boat was placed upstream 23 cm away from the center of quartz tube. Prior to heating, the quartz tube



was purged with high flow of Argon gas (500 standard cubic centimeters per minute (sccm)) for 20 min. Then the furnace was ramped to 730 °C at a speed rate of 30 °C min-1 and held for 10 min with a mixture argon (150 sccm) and hydrogen (4 sccm) gas. The successful growth of monolayer MoSe2 serves as the first step for the whole synthesized procedure. Then the lateral-stitching and vertical-stacking growth were accomplished by heating sulfur powder at given temperatures. It should be highlighted that the formation of vertical or lateral MoSe2-MoS2 heterostructures strongly depends on the thermal evaporation temperatures of sulfur powder, which could modify the nucleation and growth kinetics during the growth process and more details will be discussed later. In situ epitaxial growth of MoS2 was grown for 10 min by introduction of S powder (400 mg) with 150 sccm argon flow without exposing the MoSe2 domains to the ambient environment. On one hand, when the synthesized MoSe2 samples were in situ annealed at 730 °C for 5 min, the fractures were generated within the monolayer MoSe2 crystals and films. And then in situ epitaxial growth MoS2 along these one-dimensional (1D) fractures will be accomplished forming MoSe2-MoS2 lateral heterostructures as schematically shown in Figure 1b. In contrast, in-plane lateral heterostructures without fractures dominate when the sulfur powder is in situ mechanically transferred into precise position 10 cm away from the center of quartz tube (~ 500 °C) after the growth of MoSe2 without annealing process (Figure1d). On the other hand, vertical MoS2/MoSe2 heterostructures are preferred when the sulfur is transferred into the quartz tube 5 cm away from the heating center


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(~ 730 °C) with high sulfur vapor concentration as schematically shown in Figure 1f. The morphologies, crystal structure as well as atomically sharp interfaces of diverse MoSe2-MoS2 heterostructures are systematically characterized by employing optical microscopy (Olympus BX53), SEM (SU5000), AFM (Seiko, SPI3800N + 300 HV and Bruker, Dimension Icon), ADF-STEM (Nion UltraSTEM-100). Surface potential distributions are performed by KPFM (Bruker, Dimension Icon) under ambient conditions with humidity ~40%. Raman and photoluminescence spectra of the MoSe2-MoS2 in-plane and vertical heterostructures were performed by using Witec Alpha 300R confocal system with a 532 nm laser excitation (~ 1 mW) at room temperature in ambient environment. The output from a mode locked Ti: sapphire laser (output wavelength: 800 nm and repetition rate: 76 MHz) was filtered, attenuated, and focused on a sample by microscope objective lens (100X, NA=0.95, with spot size ~1.6 m at fundamental wavelength). The SHG signal was then back collected by the same lens, and filtered by a 650 nm short pass filter before entering the spectrometer (PI Acton 2500i with a liquid nitrogen cooled charge coupled device camera). Fracture behavior is a widespread phenomenon and has been widely investigated in 2D materials providing some support for the design of nanodevices and nanomaterials.35, 36 In general, the fractures are mainly produced by means of external load, high-temperature annealing and electron beam irradiation as demonstrated in 2D materials.37-39 Accordingly, it will be much more meaningful if we can construct



heterostructures or superlattices on the basis of controllable fabrication of 1D fractures within 2D plane. The concept of this construction was systematically conducted by one-step APCVD growth method to fabricate monolayer or few-layer MoSe2 films followed by 5 min high-temperature annealing process (730 °C), which leads to the formation of fractured MoSe2 and has been systematically investigated by optical microscopy SEM, TEM as well as AFM (Figure S4). It is worth noting that these fractures prefer to origin from grain boundaries of monolayer polycrystalline MoSe2 films. This result is in good accordance with the Griffith’s criterion,40 which describes that fracture strength will be reduced in the presence of defects or grain boundaries promoting the fracture generation at these positions. Defect sites within the monolayer MoSe2 single crystal can also result in the formation of fractured monolayer MoSe2 nanoplates or films, which will be illuminated according to our ADF-STEM results. Fractures within monolayer MoSe2 with fresh and unpassivated edges can be viewed as 1D confined channel for in situ epitaxial growth of MoS2 nanoribbons. Figure 1c shows optical image of synthesized MoSe2-MoS2 heterostructures, where MoS2 nanoribbons prefer to grow along the pre-existing fractures within monolayer MoSe2. Special MoSe2-MoS2 lateral superlattices with Y-shaped MoS2 nanoribbons were obtained and can be clearly distinguished from optical image as shown in Figure S5. Systematical investigations demonstrated that the widths of MoS2 nanoribbons within the monolayer MoSe2 nanoplates or films can be effectively tuned by controlling the high-temperature annealing time (Figure S6).


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Apparently, this growth procedure doesn’t introduce contaminants, which exhibits advantages compared to patterned TMDC islands or nanoribbons embedded into another kind TMDC material by using etching-regrowth technique always with unavoidable photoresist residues on the surface or interface of heterostructures.41, 42 Raman and PL spectra were employed to further characterize the structure and quality of MoSe2-MoS2 heterostructures collected from the squared area of optical image as shown in Figure 2a. Corresponding Raman intensity mappings using A1g oscillation mode (405.2 cm-1) and the in-plane E12g oscillation mode (380.5 cm-1) of MoS2 are shown in Figure 2b, c confirming the uniformity of Y-shaped MoS2 nanoribbon, which corresponds to monolayer MoS2. However, we observe a remarkable red shift of E12g phonon mode (~ 4 cm-1) compared to pristine monolayer MoS2. This red shift could be attributed to the localized tensile strain in MoS2 nanoribbon within MoSe2 due to the lattice mismatch between MoS2 and MoSe2 (~ 2 %). In contrast, the A1g mode is insensitive to strain and shows a very small shift. Previously theoretical and experimental studies have systematically investigated the Raman shift of MoS2 by applying strain, which could further support our observations.43,

44

In order to study the band structure of space-confined MoS2

nanoribbon within MoSe2, we have also carried out the PL measurements. The PL peak of MoS2 in this in-plane junction is located at 700 nm (Figure S7), which exhibits a red shift compared to as-prepared individual MoS2 monolayers. Although MoS2 nanoribbons may be slightly doped by selenium, we propose that this variation



could be mainly attributed to strain effect induced by the lattice mismatch between MoSe2 and MoS2. In addition, Raman intensity mapping corresponding to the A1g oscillation mode of MoSe2 (Figure 2d) verifies the successful synthesis of monolayer MoSe2. Clear contrast from Raman intensity mappings of MoS2 and MoSe2 as shown in Figure 2b-d confirms the formation of this lateral MoSe2-MoS2 junction. Figure 2e shows typical AFM image of lateral MoSe2-MoS2 junction exhibiting a flat surface with sharp heterointerface over the whole area. Figure 2f shows corresponding surface potential image of this area with remarkable contrast, which gives further evidence of successful fabrication of lateral heterostructures. The surface potential difference is around 96 mV between monolayer MoSe2 and MoS2, which further demonstrates that the work function of monolayer MoS2 is higher than monolayer MoSe2. After the growth of MoSe2, the sulfur powders were immediately shifting into the heating zone (~ 500 °C) leading to the formation of in-plane MoSe2-MoS2 heterostructures. Without high temperature annealing process, the MoSe2 nanoplates remain intact without embedded MoS2 nanoribbons. As shown in Figure 1e, it can be clearly seen that monolayer MoS2 epitaxially grows along the peripheral edges of monolayer MoSe2 domain. SEM was also employed to further characterize the synthesized lateral heterostructure exhibiting clear contrast between MoSe2 (bright region) and MoS2 (dark region) (Figure S8). Figure 3a depicts distinct features of Raman spectra, which are taken from the points in the central and surrounding regions of a triangular MoSe2-MoS2 domain as marked in the optical image (Figure 3b). The

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Raman spectrum from the peripheral region exhibits the out of plane A1g and in-plane E12g oscillation peaks of monolayer MoS2 (Figure 3c, d), respectively, while Raman spectrum from the core region shows the out of plane A1g oscillation mode at 241.8 cm-1 corresponding to monolayer MoSe2 (Figure 3e). Raman mapping results demonstrate the spatial distribution of the in-plane MoSe2-MoS2 heterostructure with triangular MoSe2 domain located in the centre triangle, while MoS2 is only present in the outer region. The detailed crystal structure of as-grown in-plane MoSe2-MoS2 junction was further investigated by STEM. Figure 3f shows a low-magnification ADF-STEM image of lateral MoSe2-MoS2 heterostructure. The contrast difference can be observed corresponding to different chemical composition. Elemental mapping was obtained using energy-dispersize spectroscopy (EDS) across lateral MoSe2-MoS2 junction. The maps of Se, S, and Mo exhibit spatial distribution across the interface as shown in Figure 3g-i. The atomically resolved ADF-STEM image of MoSe2-MoS2 lateral heterostructures demonstrates the atomically sharp interface between MoSe2 and MoS2 (Figure 3j, k). One hexagonal structure of synthesized lateral MoSe2-MoS2 heterostructure was observed from the FFT pattern of the ADF-STEM image (Figure 3j) as shown in Figure 3l. Corresponding magnified FFT image (Figure 3(m)) reveals that each diffraction spot consists of two diffraction peaks corresponding to MoSe2 and MoS2, respectively. The orientation of FFT pattern of monolayer MoS2 is the same as monolayer MoSe2 further demonstrating the epitaxial growth of MoS2 along MoSe2 edges. Meanwhile, dislocations in monolayer MoSe2 nearby the junction were



found as shown Figure S9a, b. The dislocations within MoSe2 must contain strain due to the bond mismatch, which may reduce the fracture strength and promote the fracture formation. The nonuniform strain distribution around the dislocation has been elucidated as shown in Figure S9c, which is obtained by applying a geometric phase analysis (GPA) to the ADF-STEM image in Figure S9a, which can further confirm the red shift of Raman active mode and PL peak in the MoS2-MoSe2 heterostructures. Generally, the shell sizes of TMDC heterostructures synthesized from previous methods are relatively small. Meanwhile, the shell size (MoS2) and the domain size in the core are difficult to control, which restricts corresponding applications. Our experimental results demonstrate that the size of MoSe2 in the core and MoS2 in the shell can be effectively tuned from several micrometers to several hundred micrometers by controlling the growth time, and large-scale uniform MoSe2-MoS2 heterostructure films are also obtained (Figure S10), which is beneficial for the device fabrication ensuring their promising application in future electronic and optoelectronic devices. When we put sulfur powders (400 mg) from room temperature zone into the quartz tube 5 cm away from the heating center (~ 730 °C) immediately after the growth of MoSe2, high sulfur vapor concentration environment will be created in a very short time. It is worth noting that MoS2 not only grows along peripheral MoSe2 edges but also on the top surface of MoSe2 forming vertical MoS2/MoSe2 heterostructures. Figure 1g shows optical image of monolayer MoSe2-MoS2


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heterostructures sitting on top of another monolayer MoSe2. The vertically stacked structure was characterized by using Raman spectroscopy. Figure 4a shows corresponding Raman spectra of vertical MoS2/MoSe2 heterostructure obtained from the black and red points as shown in Figure 4b. The black line represents the out of plane A1g oscillation mode of bilayer MoSe2 in the centre region. And red line corresponds to bilayer MoS2/MoSe2 vertical heterostructures in the edge region, which possesses out of plane A1g active mode, the in-plane E12g oscillation mode of MoS2 as well as out of plane A1g oscillation mode of MoSe2 demonstrating successful formation of vertical MoS2/MoSe2 heterostructures. The ADF-STEM image of vertical MoS2/MoSe2 heterostructure with low-magnification is shown in Figure 4f. The interface between MoSe2 and MoS2 is visible exhibiting a low contrast. Figure 4g shows a magnified image of the dotted red square in Figure 4f, which exhibits clearly contrast between MoSe2 and MoS2. The darker region (left) shown in Figure 4g is MoS2 and the bright region (middle) corresponds to monolayer MoSe2, whereas the brighter region (right) represents the epitaxial growth monolayer MoS2 on top of the monolayer MoSe2, which is epitaxially grown from the edges of bilayer MoSe2 island with the same stacking orientation. The morphologies and surface potential distributions of vertical heterostructures were also characterized by AFM and KPFM. Surface potential distribution and remarkable built-in potential difference between MoS2 and MoSe2 further confirm the synthesized vertical heterostructures as shown in Figure 4h, i. When we increased the mass of sulfur powder (up to 800 mg) generating



much higher sulfur concentration environment, full coverage of monolayer MoS2 on the top surface of monolayer MoSe2 can be fabricated via epitaxial growth. It can be clearly seen that the monolayer MoSe2 was severely alloyed, which was demonstrated by PL measurement (Figure S11). It is critical to obtain well defined vertically stacked MoS2/MoSe2 heterostructures with precisely controlled growth parameters. The structure symmetry of lateral and vertical MoS2/MoSe2 heterostructures was further determined by analyzing polarization-dependent SHG intensity. One typical optical image of MoSe2-MoS2 lateral heterostructures is shown in Figure 5a. Figure 5b-d exhibits the corresponding SHG signals of MoSe2, MoS2 and the interface in MoSe2-MoS2 lateral heterostructures. Due to the threefold symmetry of monolayer MoSe2 and MoS2 crystal structure, sixfold rotational symmetry of SHG intensity can be clearly observed through polarization-dependent SHG spectra. There were not obviously suppressed SHG signals along the interface of MoSe2-MoS2 lateral heterostructures demonstrating a single crystal signature of seamlessly stitched in-plane heterostructures. The intensity of SHG can be described as I|| = I0sin (3θ)2, where I0 is the maximum SHG intensity and θ is the angle between the polarization of incident beam and the armchair direction. Furthermore, the interface with the same angle direction between MoSe2 and MoS2 was illuminated by the SHG measurements (Figure 5d), which can be confirmed by our STEM characterization. The SHG measurements of monolayer MoSe2, bilayer MoSe2 and the vertically stacking MoS2/MoSe2 heterostructures were further investigated as shown in Figure


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5f-h, respectively. Figure 5e is the corresponding optical image of MoS2/MoSe2 vertical heterostructures. The orientation of SHG signal of bilayer MoSe2 generates a variation about 15° compared to the SHG signal of monolayer MoSe2 due to the vertically stacking MoSe2 structures (Figure 5g). It can be observed that vertically stacked MoS2/MoSe2 heterostructures and bilayer MoSe2 have the same SHG signal as shown in Figure 5g, which further confirms vdW epitaxy growth with well-aligned lattice orientation between MoSe2 and MoS2 layers. Moreover, we found that the SHG intensity of vertical MoS2/MoSe2 is larger than bilayer MoSe2 indicating the preservation of broken inversion symmetry structure. Compared to vertical TMDC heterostructures obtained by increasing the growth temperature, we paved a new way to successfully synthesized vertical MoS2/MoSe2 heterostructures by increasing the concentration of sulfur vapors. We believe that the growth of vertical MoS2/MoSe2 is kinetically determined. As demonstrated from previous studies,45 the ratio of deposition to the diffusion rate for reaction precursors plays a key role in the growth process. The precursor molecule concentration determines the average distance of adsorbed molecules travelling to meet another adsorbate, either for nucleation of new aggregates or attachment to previously formed island. At low sulfur vapor concentration during the growth process, we propose that the diffusion rate of MoS2 molecules are faster than the deposition rate, which is required for the lateral MoSe2-MoS2 heterostructures under near-equilibrium environment as schematically shown in Figure 6a. However, when the sulfur vapor



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concentration is increased, the deposition rate is larger than the diffusion rate, and the growth of MoS2 crystals will be determined by kinetics. MoS2 molecules grown along the edge of pre-depositing MoSe2 islands on the monolayer MoSe2 and more nucleation sites on the surface of MoSe2 will be promoted resulting in the formation of vertical MoS2/MoSe2 heterostructures (Figure 6b). In summary, we have demonstrated the selective growth of in-plane and vertically stacking MoSe2-MoS2 heterostructure via vdW epitaxial growth. The concentration of sulfur precursor vapor and high-temperature annealing process have been demonstrated to be essential for obtaining lateral and vertical MoS2/MoSe2 heterostructures. This study paves a new way for controllable synthesis of new 2D vdW heterostructures, which enriches the library of 2D family towards electronic and optoelectronic applications.

ACKNOWLEDGEMENTS This work was supported by Grants from the Science and Technology Project of Hunan Province (2019JJ30021) and Education Commission of Hunan Province (18B084), National Natural Science Foundation of China (Nos. 11404274, 11574935), Degree

and

Postgraduate

Education

Reform

Project

of

Hunan

Province

(JG2018B045), the Program for Changjiang Scholars and Innovative Research Team in University (IRT13093). X. F. Liu thanks the support from Beijing Municipal Natural Science Foundation (4182076 and 4184109).


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Supporting Information Available: Figure S1, characterizations of MoS2 nanoplates by optical microscopy, SEM, AFM, Raman and photoluminescence measurements; Figure S2, MoSe2 nanostructures measured by optical microscopy, AFM, SEM and HRTEM; Figure S3, optical, AFM and KPFM images of bilayer MoSe2; Figure S4, characterizations of fractured MoSe2 nanostructures by optical, SEM, AFM, TEM; Figure S5, optical images of lateral MoSe2-MoS2 junctions; Figure S6, optical images of MoSe2-MoS2 lateral heterostructures and corresponding width analysis of MoS2 nanoribbons; Figure S7, PL spectroscopy of MoS2 nanoribbons within MoSe2 plane and corresponding PL intensity mapping of MoS2 nanoribbons; Figure S8, SEM image of lateral MoSe2-MoS2 heterostructures; Figure S9, ADF-STEM image of MoSe2-MoS2 junction and GPA analysis; Figure S10, optical images of MoSe2-MoS2 lateral heterostructures with controllable shell width under different growth time; Figure S11, optical image of vertical MoS2/MoSe2 heterostructures and PL spectroscopy of MoS2 indicating alloyed nature by selenium.



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REFERENCES (1) Kroemer, H. Heterostructure Bipolar Transistors and Integrated Circuits. Proc. IEEE. 1982, 70, 13-25. (2) Geim, A. K.; Grigorieva, I. V. Van der Waals Heterostructures. Nature 2013, 499, 419-425. (3) Chen, P.; Zhang, Z.; Duan, X.; Duan, X. Chemical Synthesis of Two-Dimensional Atomic Crystals, Heterostructures and Superlattices. Chem. Soc. Rev. 2018, 47, 3129-3151. (4) Xu, M.; Liang, T.; Shi, M.; Chen, H. Graphene-Like Two-Dimensional Materials. Chem. Rev. 2013, 113, 3766-3798. (5) Novoselov, K. S.; Jiang, D.; Schedin, F.; Booth, T. J.; Khotkevich, V. V.; Morozov, S. V.; Geim, A. K. Two-Dimensional Atomic Crystals. Proc. Nati. Acad. Sci. U. S. A. 2005, 102, 10451-10453. (6) Koppens, F. H. L.; Mueller, T.; Avouris, Ph.; Ferrari, A. C.; Vitiello, M. S.; Polini, M. Photodetectors Based on Graphene, Other Two-Dimensional Materials and Hybrid Systems. Nat. Nanotechnol. 2014, 9, 780-793. (7) 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, 699-712. (8) Manzeli, S.; Ovchinnikov, D.; Pasquier, D.; Yazyev, O. V.; Kis, A. 2D Transition Metal Dichalcogenides. Nat. Rev. Mater. 2017, 2, 17


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(9) 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, 136805. (10)Chen, T.; Hao, G.; Wang, G.; Li, B.; Kou, L.; Yang, H.; Zheng, X.; Zhong, J. Controlled Growth of Atomically Thin MoSe2 Films and Nanoribbons by Chemical Vapor Deposition. 2D Mater. 2019, 6, 025002. (11)Zhang, T.; Fu, L. Controllable Chemical Vapor Deposition Growth of Two-Dimensional Heterostructures. Chem. 2018, 4, 671-689. (12)Yu, W. J.; Li, Z.; Zhou, H.; Chen, Y.; Wang, Y.; Huang, Y.; Duan, X. Vertically Stacked Multi-Heterostructures of Layered Materials for Logic Transistors and Complementary Inverters. Nat. Mater. 2012, 12, 246-252. (13)Liu, Y.; Weiss, N. O.; Duan, X.; Cheng, H-C.; Huang, Y.; Duan, X. Van der Waals Heterostructures and Devices. Nat. Rev. Mater. 2016, 1, 16042. (14)Jin, C.; Regan, E. C.; Yan, A.; Utama, M. I. B.; Wang, D.; Zhao, S.; Qin Y.; Yang, S.; Zheng, Z.; Shi, S.; et al. Observation of Moiré Excitons in WSe2/WS2 Heterostructure Superlattices. Nature 2019, 567, 76-80. (15)Xu, X.; Yao, W.; Xiao, D.; Heinz, T. F. Spin and Pseudospins in Layered Transition Metal Dichalcogenides. Nat. Phys. 2014, 10, 343-350. (16)Amin, B.; Singh, N.; Schwingenschlögl, U. Heterostructures of Transition Metal Dichalcogenides. Phys. Rev. B 2015, 92, 075439. (17)Cheng, R.; Li, D.; Zhou, H.; Wang, C.; Yinl, A.; Jiang, S.; Liu,Y.; Chen, Y.; Huang, Y.; Duan, X. Electroluminescence and Photocurrent Generation from



Atomically Sharp WSe2/MoS2 Heterojunction p–n Diodes. Nano Lett. 2014, 14, 5590-5597. (18)Ross, J. S.; Klement, P.; Jones, A. M.; Ghimire, N. J.; Yan, J.; Mandrus, D. G.; Taniguchi, T.; Watanabe, K.; Kitamura, K.; Yao, W.; Cobden, D. H.; Xu, X. D. Electrically Tunable Excitonic Light-Emitting Diodes Based on Monolayer WSe2 p–n Junctions. Nat. Nanotechnol. 2014, 9, 268-272. (19)

Li, M. Y.; Su, S. K.; Wong, H. S.; Li, L. J. How 2D Semiconductors Could

Extend Moor's Law. Nature. 2019, 567, 169-170. (20)

Cheng, R.; Wang, F.; Yin, L.; Wang, Z.; Wen, Y.; Shifa, T.; He, J.

High-Performance, Multifunctional Devices Based on Asymmetric Van der Waals Heterostructures, Nat. Electron. 2018, 1, 356-361. (21)Duan, X.; Wang, C.; Pan, A.; Yu, R.; Duan, X. Two-Dimensional Transition Metal Dichalcogenides as Atomically Thin Semiconductors: Opportunities and Challenges. Chem. Soc. Rev. 2015, 44, 8859-8876. (22)Lee, C-H.; Lee, G-H.; Van. der. Zande, A. M.; Chen, W.; Li, Y.; Han, M.; Cui, X.; Arefe, G.; Nuckolls, C.; Heinz, T. F.; Guo J.; Hone, J.; Kim P. Atomically Thin p–n Junctions with Van der Waals Heterointerfaces. Nat. Nanotechnol. 2014, 9, 676-681. (23)Zhang, K.; Zhang, T.; Cheng, G.; Li, T.; Wang, S.; Wei, W.; Sun, Y.; Wang, P.; Zhang, D.; Zeng, C.; Wang, X.; Hu, W.; Fan, H.; Shen, G.; Chen, X.; Duan, X.; Chang, K.; Dai, N. Interlayer Transition and Infrared Photodetection in Atomically Thin Type-II MoTe2/MoS2 Van der Waals Heterostructures. ACS Nano 2016, 10,


Page 20 of 33

Page 21 of 33 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


3852-3858. (24)Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro, Neto. A. H. 2D Materials and Van der Waals Heterostructures. Science 2016, 353, aac9439. (25)Yoo, Y.; Degregorio, Z. P.; Johns, J. E. Seed Crystal Homogeneity Controls Lateral and Vertical Heteroepitaxy of Monolayer MoS2 and WS2. J. Am. Chem. Soc. 2015, 137, 14281-14287. (26)Chen, J.; Zhou, W.; Tang, W.; Tian, B.; Zhao, X.; Xu, H.; Liu, Y.; Geng, D.; Tan, S. J. R.; Fu, W.; Loh, K. P. Lateral Epitaxy of Atomically Sharp WSe2/WS2 Heterojunctions on Silicon Dioxide Substrates. Chem. Mater. 2016, 28, 7194-7197. (27)Duan, X.; Wang, C.; Shaw, J. C.; Cheng, R.; Chen, Y.; Li, H.; Wu, X.; Tang, Y.; Zhang, Q.; Pan, A.; Jiang, J.; Yu, R.; Huang, Y.; Duan, X. Lateral Epitaxial Growth of Two-Dimensional Layered Semiconductor Heterojunctions. Nat. Nanotechnol 2014, 9, 1024-1030. (28)Huang, C.; Wu, S.; Sanchez, A. M.; Peters, Jonathan. J. P.; Beanland, R.; Ross, Jason. S.; Rivera, P.; Yao, W.; Cobden, D. H.; Xu, X. Lateral Heterojunctions within Monolayer MoSe2–WSe2 Semiconductors. Nat. Mater. 2014, 13, 1096-1101. (29)Sahoo, P. K.; Memaram, S.; Xin, Y.; Balicas, L.; Gutiérrezne, H. R. One-Pot Growth of Two-Dimensional Lateral Heterostructures via Sequential Edge-Epitaxy. Nature 2018, 553, 63-67. (30)Gong, Y.; Lin, J.; Wang, X.; Shi, G.; Lei, S.; Lin, Z.; Zou, X.; Ye, G.; Vajtai, R.; Yakobson, B. I.; Terrones, M.; Tay, B. K.; Lou, J.; Pantelides, S. T.; Liu, Z.; Zhou,



W.; Ajayan, P. M. Vertical and in-Plane Heterostructures from WS2/MoS2 Monolayers. Nat. Mater. 2014, 13, 1135-1142. (31)Chen, K.; Wan, X.; Wen, J.; Xie, W.; Kang, Z.; Zeng, X.; Chen, H.; Xu, J-B. Electronic Properties of MoS2–WS2 Heterostructures Synthesized with Two-Step Lateral Epitaxial Strategy. ACS Nano 2015, 9, 9868-9876. (32)Chen, T.; Hao, G.; Kou, L.; Wang, C.; Zhong, J. Controllable Epitaxial Growth of MoSe2–MoS2 Lateral Heterostructures with Tunable Electrostatic Properties. Nanotechnology 2018, 29, 484003. (33)

Li, F.; Feng, X.; Li, Z.; Ma, C.; Qu, J.; Wu, X.; Li, D.; Zhang, X.; Yang, T.; He,

Y.; Li, H.; Hu, X.; Fan, P.; Chen, Y.; Zheng, B.; Zhu, X.; Wang, X.; Duan, X.; Pan, A. Rational Kinetics Control toward Universal Growth of 2D Vertically Stacked Heterostructures. Adv. Mater. 2019, 31, 1901351. (34)Zhou, J.; Tang, B.; Lin, J.; Lv, D.; Shi, J.; Sun, L.; Zeng, Q.; Niu, L.; Liu, F.; Wang, X.; Liu, X.; Suenaga, K.; Jin, C.; Liu, Z. Morphology Engineering in Monolayer MoS2-WS2 Lateral Heterostructures. Adv. Funct. Mater. 2018, 28, 1801568. (35)Taghinejad, H.; Eftekhar, A. A.; Campbell, P. M.; Beatty, B.; Taghinejad, M.; Zhou, Y.; Perini, C. J.; Moradinejad, H.; Henderson, W. E.; Woods, E. V.; Zhang, X.; Ajayan, P. M.; Reed, E. J.; Vogel, E. M.; Adibi, A. Strain Relaxation via Formation of Cracks in Compositionally Modulated Two-Dimensional Semiconductor Alloys. npj 2D Mater. Appl. 2018, 2, 10.


Page 22 of 33

Page 23 of 33 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


(36)Yin, H.; Qi, H. J.; Fan, F.; Zhu, T.; Wang, B.; Wei, Y. Griffith Criterion for Brittle Fracture in Graphene. Nano Lett. 2015, 15, 1918-1924. (37)Hao, S.; Yang, B.; Gao, Y. Orientation-Specific Transgranular Fracture Behavior of CVD-Grown Monolayer MoS2 Single Crystal. Appl. Phys. Lett. 2017, 110, 153105. (38)Ly, T. H.; Zhao, J.; Cichocka, M. O.; Li, L-J.; Lee, Y. H. Dynamical Observations on the Crack Tip Zone and Stress Corrosion of Two-Dimensional MoS2. Nat. Commun. 2017, 8, 14116. (39)Yang, Y.; Li, X.; Wen, M.; Hacopian, E.; Chen, W.; Gong, Y.; Zhang, J.; Li, B.; Zhou,W.; Ajayan, P. M.; Chen, Q.; Zhu, T.; Lou, J. Brittle Fracture of 2D MoSe2. Adv. Mater. 2017, 29, 1604201. (40)Griffith, A. A. The Phenomena of Rupture and Flow in Solids. Philos. Trans. R. Soc. London 1921, A221, 163-198. (41)Mahjouri-Samani, M.; Lin, M-W.; Wang, K.; Lupini, A. R.; Lee, J.; Basile, L.; Boulesbaa, A.; Rouleau, C. M.; Puretzky, A. A.; Ivanov, I. N.; Xiao, K.; Yoon, M.; Geohegan, D. B. Patterned Arrays of Lateral Heterojunctions within Monolayer Two-Dimensional Semiconductors. Nat. Commun. 2015, 6, 7749. (42)Ling, X.; Lin, Y.; Ma, Q.; Wang, Z.; Song, Y.; Yu, L.; Huang, S.; Fang, W.; Zhang, X.; Hsu, A. L.; Bie, Y.; Lee, Y. H.; Zhu, Y.; Wu, L.; Jarillo-Herrero, P.; Dresselhaus, M.; Palacios, T.; Kong, J. Parallel Stitching of 2D Materials. Adv. Mater. 2016, 28, 2322-2329. (43)Wang, Y.; Cong, C.; Qiu, C.; Yu, T. Raman Spectroscopy Study of Lattice



Vibration and Crystallographic Orientation of Monolayer MoS2 under Uniaxial Strain. Small 2013, 9, 2857-2861. (44)Castellanos-Gomez, A.; Roldán, R.; Cappelluti, E.; Buscema, M.; Guinea, F.; van der Zant, H. S. J.; Steele, G. A. Local Strain Engineering in Atomically Thin MoS2. Nano Lett. 2013, 13, 5361-5366. (45)Battaile, C. C.; Srolovitz, D. J. Kinetic Monte Carlo Simulation of Chemical Vapor Deposition. Annu. Rev. Mater. Res. 2002, 32, 297-319.


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Figure Capations Figure 1. (a) The schematic of synthesis process for both in-plane and vertical MoS2/MoSe2 heterostructures. (b, c) Schematic crystal structure and optical images of in-plane MoSe2-MoS2 heterostructures induced by high tempeature annealing process. (d, e) Schematic crystal structure and optical images of the lateral MoSe2-MoS2 heterostructures by using conventional growth procedure. (f, g) Schematic and optical MoS2/MoSe2 vertical heterostructures triggered by high sulfur vapor concentration.

Figure 2. (a) Optical image of the MoSe2-MoS2 lateral heterostructure used for Raman characterizations. (b, c) Raman intensity mapping at E12g, A1g oscillation peaks of MoS2, respectively. (d) Raman intensity mapping at A1g oscillation peak corresponding to MoSe2. (e, f) Corresponding AFM and KPFM images of lateral MoSe2-MoS2 heterostructure.

Figure 3. (a) Raman spectra taken from the red and black points marked in (b), showing characteristic peaks of MoSe2 and MoS2 in the inner and outer regions. (b) Optical image of MoSe2-MoS2 lateral heterostructures. (c, d) Raman intensity mapping

of MoS2 corresponding to E12g, A1g oscillation modes, respectively. (e)

Raman intensity mapping of MoSe2 corresponding to A1g oscillation modes. (f) Low magnification ADF-STEM image of MoSe2-MoS2 heterostructure. (g-i) EDS mapping image of Se, S, Mo for the heterostructure. (j) ADF-STEM image of lateral



MoSe2-MoS2 heterostructure with atomically sharp interface. (k) Amplified ADF-STEM image corresponding to yellow square area as marked in (j) exhibiting clearly atomic distribution. (l) FFT pattern taken across the heterostructure. (m) Amplified one pot from FFT consisting of a pair diffraction peaks with the same orientation.

Figure 4. (a) Raman spectra taken from the red and black points marked in (b), showing characteristic peaks of vertical MoS2/MoSe2 heterostructure and bilayer MoSe2. (b) Optical image of MoS2/MoSe2 vertical heterostructures. (c, d) Raman intensity mapping of MoS2 corresponding to E12g, A1g oscillation modes, respectively. (e) Raman intensity mapping of MoSe2 corresponding to A1g oscillation modes. (f) Low magnification ADF-STEM image of vertical MoS2/MoSe2 heterostructure. (g) Atomic resolution ADF-STEM image of vertical MoS2/MoSe2 heterostructure. (h) AFM image of vertical MoS2/MoSe2 heterostructure. (i) Corresponding surface potential image of vertical MoS2/MoSe2 heterostructure.

Figure 5. (a) Optical image of MoSe2-MoS2 lateral heterostructure. (b) The polarization-resolved SHG intensity of MoSe2 monolayer corresponding to core region as shown in (a). (c) The polarization-dependent SHG intensity of monolayer MoS2 corresponding to shell region in (a). (d) The polarization-resolved SHG intensity obtained from the interface of MoSe2-MoS2 lateral heterostructure. (e)


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Optical image of vertical MoS2/MoSe2 heterostructures. (f) The polarization-resolved SHG intensity of monolayer MoSe2 in (e). (g) The polarization-resolved SHG intensity of bilayer MoSe2. (h) The polarization-resolved SHG intensity of MoS2/MoSe2 vertical heterostructure.

Figure 6. (a, b) Schematic growth mechanism of lateral and vertical MoS2/MoSe2 heterostructures.



Figure 1 (a) The schematic of synthesis process for both in-plane and vertical MoS2/MoSe2 heterostructures. (b, c) Schematic crystal structure and optical images of in-plane MoSe2-MoS2 heterostructures induced by high tempeature annealing process. (d, e) Schematic crystal structure and optical images of the lateral MoSe2-MoS2 heterostructures by using conventional growth procedure. (f, g) Schematic and optical MoS2/MoSe2 vertical heterostructures triggered by high sulfur vapor concentration. 358x200mm (115 x 115 DPI)

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Figure 2 (a) Optical image of the MoSe2-MoS2 lateral heterostructure used for Raman characterizations. (b, c) Raman intensity mapping at E12g, A1g oscillation peaks of MoS2, respectively. (d) Raman intensity mapping at A1g oscillation peak corresponding to MoSe2. (e, f) Corresponding AFM and KPFM images of lateral MoSe2-MoS2 heterostructure. 331x207mm (96 x 96 DPI)



Figure 3 (a) Raman spectra taken from the red and black points marked in (b), showing characteristic peaks of MoSe2 and MoS2 in the inner and outer regions. (b) Optical image of MoSe2-MoS2 lateral heterostructures. (c, d) Raman intensity mapping of MoS2 corresponding to E12g, A1g oscillation modes, respectively. (e) Raman intensity mapping of MoSe2 corresponding to A1g oscillation modes. (f) Low magnification ADF-STEM image of MoSe2-MoS2 heterostructure. (g-i) EDS mapping image of Se, S, Mo for the heterostructure. (j) ADF-STEM image of lateral MoSe2-MoS2 heterostructure with atomically sharp interface. (k) Amplified ADF-STEM image corresponding to yellow square area as marked in (j) exhibiting clearly atomic distribution. (l) FFT pattern taken across the heterostructure. (m) Amplified one pot from FFT consisting of a pair diffraction peaks with the same orientation. 239x200mm (150 x 150 DPI)


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Figure 4 (a) Raman spectra taken from the red and black points marked in (b), showing characteristic peaks of vertical MoS2/MoSe2 heterostructure and bilayer MoSe2. (b) Optical image of MoS2/MoSe2 vertical heterostructures. (c, d) Raman intensity mapping of MoS2 corresponding to E12g, A1g oscillation modes, respectively. (e) Raman intensity mapping of MoSe2 corresponding to A1g oscillation modes. (f) Low magnification ADF-STEM image of vertical MoS2/MoSe2 heterostructure. (g) Atomic resolution ADF-STEM image of vertical MoS2/MoSe2 heterostructure. (h) AFM image of vertical MoS2/MoSe2 heterostructure. (i) Corresponding surface potential image of vertical MoS2/MoSe2 heterostructure. 1157x698mm (38 x 38 DPI)



Figure 5 (a) Optical image of MoSe2-MoS2 lateral heterostructure. (b) The polarization-resolved SHG intensity of MoSe2 monolayer corresponding to core region as shown in (a). (c) The polarization-dependent SHG intensity of monolayer MoS2 corresponding to shell region in (a). (d) The polarization-resolved SHG intensity obtained from the interface of MoSe2-MoS2 lateral heterostructure. (e) Optical image of vertical MoS2/MoSe2 heterostructures. (f) The polarization-resolved SHG intensity of monolayer MoSe2 in (e). (g) The polarization-resolved SHG intensity of bilayer MoSe2. (h) The polarization-resolved SHG intensity of MoS2/MoSe2 vertical heterostructure. 473x200mm (93 x 93 DPI)


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Figure 6 (a, b) Schematic growth mechanism of lateral and vertical MoS2/MoSe2 heterostructures. 537x200mm (90 x 90 DPI)


Lateral and Vertical MoSe2âMoS2 Heterostructures via Epitaxial

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