Supplementary Information
Supplementary Information Synthesis and Characterizations of Lateral Heterostructures of Semiconducting Atomic Layers Xin-Quan Zhang1+, Chin-Hao Lin1+, Yu-Wen Tseng,1 Kuan-Hua Huang1,Yi-Hsien Lee*1 1
Materials Science and Engineering, National Tsing-Hua University, Hsinchu, 20013, Taiwan +These authors contribute equally.
*Corresponding author E-mail: (Yi-Hsien Lee) [email protected]
Summary
S1 Experimental Setup and Detailed Parameters for the Synthesis S2 Preparation of samples and aromatic seeding promoters S3 Scalable synthesis of in-plane heterostructure of monolayer WS2-MoS2 S4 Influence of starting materials on the CVD growth of the S- and Se-based heterostructure S5 Lateral heterostructure with 1D hetero-interface S6 Characterizations - Cs-corrected STEM-HAADF - Polarization-resolved Second Harmonic Generation (SHG) S7 Raman vibration mode frequencies of the lateral heterostructures
S1. Experimental Setup and Detailed Parameters for the Synthesis A one inch diameter furnace and a homemade quartz reactor were designed for precise control of the gas flow and the reactions of starting reactants. Sulfur and Se powders were placed in the crucible upstream and heated with a temperature of 200 and 300 ℃, respectively. For a high evaporation temperature of WO3, the WO3 powders were filled in the homemade quartz reactor with a transfer tube having a tunable length to enable a stable vapor flow of the WO3-x reactant evaporating from the high temperature zone to react with S or Se on the substrate surfaces in specific temperature range and separated by specific distances. After the growth, 100 sccm Ar flow was introduced to remove the residual reactants and the entire system was rapidly cooled down to room temperature by taking the quartz tube out of the furnace.
Figure S1. Schematic illustration of the synthesis setup and various modes of hetero-epitaxial growth of TMD atomic layers (a) Schematic diagram of the synthesis setup for growing CVD-TMD atomic layers and diverse heterostructures. Initial-grown MoS2 and MoSe2 for further TMD heterostructures could be achieved with three different Mo starting materials: (b) MoO3 powders, (c) MoO3-x thin layers (d) MoX2 (X=S, Se) powders Table T1. Detailed parameters of the synthetic process Distance d1
Unit
d3
10
MoSe2
10
3
Weight of powders
Ar
Mixture
(Inner-tube)
of Ar / H2
Cm
MoS2 -WS2
-WSe2
d2
Gas flow
WO3
9
MoS2
or S or MoSe2
Sccm 30
Se
Size of patterned MoO3 layers
mg 5
2
1500
25
0.8
10 nm thick 0.2*0.2 cm
8
29
9
4
1
1500
50
0.8
2
10 nm thick 0.2*0.2 cm
2
S2 Preparation of samples and aromatic seeding promoters Diverse substrates, including 300 nm SiO2/Si, sapphire, and quartz, were treated by piranha solution and cleaned using sonication in acetone, ethanol and D.I. water for 30 minutes. More details on the cleaning treatment of substrates treatments and on the preparation of the seeding promoters were presented in previous papers1,2. Diverse aromatic molecules have been shown to enhance the growth of diverse TMD monolayers using various forms of CVD processes1,2. In this work, perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt (PTAS) was selected as a seeding promoters for its high temperature stability2. The seeding promoter (PTAS) was prepared from the starting material using alkaline hydrolysis of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA). PTCDA was mixed with ethanol and KOH solution, and the mixtures were refluxed for more than 20 hours. PTAS would be filtrated out by adding ethyl ether to the solution. The precipitated PTAS can be dissolved in DI water for different concentrations for the synthesis of diverse TMD monolayers. A typical concentration of the PTAS solution for the synthesis is 100 M. A droplet (~2 μL) of PTAS solution was dropped on a clean 300 nm SiO2/Si substrate. The PTAS solution was spread out to cover the whole surface. Then the salt-like PTAS aggregations were precipitated as seeding promoters by rapidly drying with a gas flow of N2. The dependence between seed concentration and domain size of as-grown layers is similar to our previous work2. A higher seeding promoter concentration may result in higher density of nucleation sites and smaller domains.
S3 Scalable synthesis of in-plane heterostructure of monolayer WS2-MoS2 Continuous in-plane heterostructure of monolayer WS2-MoS2 was reached with a longer growth time (15 min) and a reduced Mo sources (half pieces of the patterned MoO3 layer). Figure 1 (j) shows the Raman mapping of large area in-plane WS2-MoS2 hetero-junctions. Domain boundaries across different triangular single-crystalline domains can be visualized with Raman and PL mapping. The PL mapping of the WS2 area shows a uniform and strong intensity, indicating a high crystalinity, uniformity and a single layer signature.
Figure S2. Characterizations of large area in-plane heterostructure of monolayer WS2-MoS2 (a) OM image and (b) schematic diagram of the in-plane heterostructure of monolayer MoS2-WS2; Raman mapping of (c) WS2 - E2g mode (d) MoS2 - A1g mode, and PL mapping of (e) WS2 (f) MoS2 over the marked area with a black dash line in fig. S2(a).
S4 Influence of starting materials on the CVD growth of the S- and Se-based heterostructure After coating of the PTAS seeding promoters, the substrates were placed facing up on a quartz plate next to a homemade reactor filled with WO3 and a small piece of Si with different Mo starting materials, including MoO3 powders, a thermally evaporated 10 nm-MoO3-x thin layer on a small piece of Si (2x2 mm2), and 0.8 mg stoichiometric MoX2 (X=S, Se) powders, as shown in supporting information S1. The small quartz reactor is homemade and filled with 1.5 g WO3 (99+ % Acros) in the high temperature region (900°C) for a higher vapor pressure of the WO3 reactants. Another crucible for containing sulfur or selenium is located upstream in the quartz tube. The heating temperature for the sulfur and the selenium vapor is 200 and 300°C, respectively. Ar and H2 were mixed in a ratio of 20~30% and introduced into the system as carrier gases. Another Ar flow was introduced into the homemade reactor to enable better reactants transport of WO3-x. The hot zone of the furnace was heated to 900 °C at a rate of 30 °C /min, and the diverse vdw heterostructures were grown at a temperature ranging from 650 to 780 °C for 10 min under ambient pressure.
Figure S3. Influence of starting materials on the CVD growth of the heterostructure Initially-grown MoS2 and MoSe2 atomic layers were used for further growth of diverse heterostructures and this could be achieved with three different Molybdenum starting materials: (a,b) MoO3 powders, (c,d) thermal evaporated MoO3-x thin layer, and (e,f) stoichiometric powders of MoX2 (X=S, Se). Scalar bar: 20 m
S5 Lateral heterostructure with 1D hetero-interface The domain shape is sensitive to the thickness of the single-crystalline domain. The in-plane heterostructure based on single layer atomic layers usually exhibits a triangular domain shape, while a star-like domain shapes of the in-plane heterostructure of WSe2-MoSe2 appeared for samples with an increased thickness.
Figure S4 Shapes and thickness of the WSe2-MoSe2 and WS2-MoS2 in-plane heterostructures OM images, AFM images, AFM line profile, and Raman mapping of following lateral heterostructures: (a) triangular domain of the monolayer WSe2-MoSe2, (b) star-like domain of the bilayer WSe2-MoSe2, (c) triangular domain of the monolayer WS2-MoS2, (d) triangular domain of the monolayer WS2-MoS2, with twisting of the centered MoS2 (e) triangular domain of the monolayer WS2-MoS2, with the centered hexagonal domain of MoS2
S6 Characterizations An Atomic Force Microscope (AFM, Bruker, Dimension Icon.) was adopted to verify the thickness and surface morphology of the samples. Raman and photoluminescence (PL) spectra and the mapping of the samples were examined with using Raman/PL spectrometer (Witec alpha 300). The wavelength of the laser used for the PL and Raman measurement was 532 nm with a laser power of ~0.15 mW. (A 100X objective was used to focus the laser beam.) The PL and Raman spectra were normalized with the intensity of the Raman A1g mode.
-Cs-corrected STEM-HAADF An analytic spherical aberration-corrected scanning transmission electron microscope High-Angle Annular Dark-Field (Cs-corrected STEM-HAADF) has been widely adopted for nano-materials characterization because of its sub-atomic resolution and capabilities on chemical mappings of light elements. The atomic and chemical configurations of the TMD monolayers (MX2, M=Mo, W; X= S, Se) were identified with a Cs-corrected STEM-HAADF (JEOL, JEM-ARM200F) at an acceleration voltage of 200 kV.) Z-contrast STEM images were post-processed by an HREM filter using Gatan Digital Micrograph software to de-noise and improve the images. Image processing was used to effectively filter HR-ADF images in frequency space. Rotational averaging of the FFT was utilized to separate the discrete spots (crystalline phases) from the continuum (amorphous phases). Then the average amorphous component was subtracted to yield the pure crystalline component. As-grown TMD monolayers or their heterostructures could be transferred on carbon-support Cu grids for TEM analysis using poly (methyl methacrylate) (PMMA). After spin-coating of PMMA on as-grown layers, baking at 60°C for 10 minutes, the PMMA-coated samples were immersed in a 2 M KOH solution at 60°C. Then the PMMA-as grown layers were lifted off from the substrate. The PMMA could be removed by rinsing with acetone, isopropyl alcohol, and deionized (DI) water.
- Polarization-resolved Second Harmonic Generation (SHG) Polarized second harmonic generation (SHG) imaging has been considered a promising characterization on the crystalline orientations and the symmetry of materials. SHG occurs due to a second-order nonlinear effect in crystal structures having non-centrosymmetry, providing an excellent contrast agent in non-invasive optical imaging3-11. The polarization-resolved SHG imaging on the lateral and the vertical heterostructures of different semiconducting TMD monolayers were obtained using a Leica SP5 MP confocal microscope operated in nondescan mode. The laser pulse was provided by a mode-locked Ti:Sapphire laser (Chameleon, Coherent) and the optimized wavelength for the analysis was 810 nm. An objective lens with a magnification of 10X was used to allow laser pulses focused onto the sample and to collect the reflected SH signals from the sample. A short pass dichroic mirror (680 SP, Semrock) and a band pass filter (400/40, Semrock) were adopted to distinguish the scattered laser light from the SH signals in the backward direction. In
addition, a polarizer was set in front of the photomultiplier tube (PMT) and parallel to the polarization of the excitation beam. The angular dependence of the SHG signal was measured by rotating the samples with steps of 5 degrees
S7 Raman vibration mode frequencies of the lateral heterostructures S-based heterostructure: (Laser: 532 nm) Exfoliated
CVD
Lateral
[12,13]
[1,2]
(1D-interface)
@ SiO2
@ SiO2
@ MoS2
@ WS2
E2g
384.0
384.7
-
384.4
A1g
403.0
401.9
-
402.4
2LA(M)
351.0
351.8
349.4
-
A1g
417.5
417.7
418.4
-
TMD MoS2
WS2
Se-based heterostructure: (Laser: 532 nm) Exfoliated
CVD
[14-16]
[17,18]
@ SiO2
@ SiO2
@ MoSe2
@ WSe2
E2g
287.5
286.7
-
286.7
A1g
240.6
241.9
-
241.6
E2g
247.0
249.6
249.6
-
A1g
257.0
259.7
259.7
-
TMD MoSe2
WSe2
Lateral (1D)
Reference: (1) Lee, Y.-H.; Yu, L.; Wang, H.; Fang, W.; Ling, X.; Shi, Y.; Lin, C.-T.; Huang, J.-K.; Chang, M.-T.; Chang, C.-S.; et al. Nano Lett. 2013, 13, 1852-1857. (2) Ling, X.; Lee, Y. H.; Lin, Y. X.; Fang, W. J.; Yu, L. L.; Dresselhaus, M. S.; Kong, J. Nano Lett. 2014, 14, 464-472. (3) van der Zande, A. M.; Kunstrnann, J.; Chernikov, A.; Chenet, D. A.; You, Y.; Zhang, X.; Huang, P. Y.; Berkelbach, T. C.; Wang, L.; Zhang, F.; et al. Nano Lett. 2014, 14, 3869-3875. (4) Kumar, N.; Najmaei, S.; Cui, Q. N.; Ceballos, F.; Ajayan, P. M.; Lou, J.; Zhao, H. Phys. Rev. B 2013, 87, 161403. (5) Malard, L. M.; Alencar, T. V.; Barboza, A. P. M.; Mak, K. F.; de Paula, A. M. Phys. Rev. B 2013, 87, 201401. (6) Li, Y. L.; Rao, Y.; Mak, K. F.; You, Y. M.; Wang, S. Y.; Dean, C. R.; Heinz, T. F. Nano Lett. 2013, 13, 3329-3333. (7) Kim, C. J.; Brown, L.; Graham, M. W.; Hovden, R.; Havener, R. W.; McEuen, P. L.; Muller, D. A.; Park, J. Nano Lett. 2013, 1, 5660-5665. (8) Shen, Y. R. The Principles of Nonlinear Optics; Wiley-Interscience: New York, 2003. (9) van der Veen, M. A.; Vermoortele, F.; De Vos, D. E.; Thierry, V. Anal. Chem. 2012, 84, 6378-6385. (10) Hsu, W. T.; Zhao, Z. A.; Li, L. J.; Chen, C. H.; Chiu, M. H.; Chang, P. S.; Chou, Y. C.; Chang, W. H. ACS Nano 2014, 8, 2951-2958. (11) Yin, X. B.; Ye, Z. L.; Chenet, D. A.; Ye, Y.; O'Brien, K.; Hone, J. C.; Zhang, X. Science 2014, 344, 488-490. (12) Lee, C., Yan, H., Brus, L.E., Heinz, T. F., Hone, J., Ryu, S., 2010 ACS Nano, 4, 2695–2700 (13) Zhao, W., Ghorannevis, Z., Amara, K. K., Pang, J. R., Toh, M., Zhang, X., Kloc, C., Tan, P. H., Eda, G., Nanoscale, 2013, 5, 9677-9683 (14) Terrones, H.; Del Corro, E.; Feng, S.; Poumirol, J. M.; Rhodes, D.; Smirnov, D.; Pradhan, N. R.; Lin, Z.; Nguyen, M. A. T.; Elias, A. L.;et al. Sci. Rep. 2014, 4, 4215. (15) Tonndorf, P.; Schmidt, R.; Böttger, P.; Zhang, X.; Börner, J.; Liebig, A.; Albrecht, M.; Kloc, C.; Gordan, O.; Zahn, D. R. T.; et al., 2013 Opt. Exp., 21, 4908-4916 (16) Berkdemir, A., Gutiérrez, H. R., Botello-Méndez, A. R., PereaLópez, N., Elías, A. L., Chen-Ing (17) Chia, C.-I., Wang, B., Crespi, V. H., López-Urías, F., Charlier, J.-C. et al, 2012 Sci. Rep. 3, 1755 (18) Lu, X.; Utama, M. I. B.; Lin, J.; Gong, X.; Zhang, J.; Zhao, Y.; Pantelides, S. T.; Wang, J.; Dong, Z.; Liu, Z.; et al. Nano Lett. 2014, 14, 2419-2425.
Materials Science and Engineering, National Tsing-Hua University, Hsinchu, 20013, Taiwan +These authors contribute equally.
*Corresponding author E-mail: (Yi-Hsien Lee) [email protected]
Summary
S1 Experimental Setup and Detailed Parameters for the Synthesis S2 Preparation of samples and aromatic seeding promoters S3 Scalable synthesis of in-plane heterostructure of monolayer WS2-MoS2 S4 Influence of starting materials on the CVD growth of the S- and Se-based heterostructure S5 Lateral heterostructure with 1D hetero-interface S6 Characterizations - Cs-corrected STEM-HAADF - Polarization-resolved Second Harmonic Generation (SHG) S7 Raman vibration mode frequencies of the lateral heterostructures
S1. Experimental Setup and Detailed Parameters for the Synthesis A one inch diameter furnace and a homemade quartz reactor were designed for precise control of the gas flow and the reactions of starting reactants. Sulfur and Se powders were placed in the crucible upstream and heated with a temperature of 200 and 300 ℃, respectively. For a high evaporation temperature of WO3, the WO3 powders were filled in the homemade quartz reactor with a transfer tube having a tunable length to enable a stable vapor flow of the WO3-x reactant evaporating from the high temperature zone to react with S or Se on the substrate surfaces in specific temperature range and separated by specific distances. After the growth, 100 sccm Ar flow was introduced to remove the residual reactants and the entire system was rapidly cooled down to room temperature by taking the quartz tube out of the furnace.
Figure S1. Schematic illustration of the synthesis setup and various modes of hetero-epitaxial growth of TMD atomic layers (a) Schematic diagram of the synthesis setup for growing CVD-TMD atomic layers and diverse heterostructures. Initial-grown MoS2 and MoSe2 for further TMD heterostructures could be achieved with three different Mo starting materials: (b) MoO3 powders, (c) MoO3-x thin layers (d) MoX2 (X=S, Se) powders Table T1. Detailed parameters of the synthetic process Distance d1
Unit
d3
10
MoSe2
10
3
Weight of powders
Ar
Mixture
(Inner-tube)
of Ar / H2
Cm
MoS2 -WS2
-WSe2
d2
Gas flow
WO3
9
MoS2
or S or MoSe2
Sccm 30
Se
Size of patterned MoO3 layers
mg 5
2
1500
25
0.8
10 nm thick 0.2*0.2 cm
8
29
9
4
1
1500
50
0.8
2
10 nm thick 0.2*0.2 cm
2
S2 Preparation of samples and aromatic seeding promoters Diverse substrates, including 300 nm SiO2/Si, sapphire, and quartz, were treated by piranha solution and cleaned using sonication in acetone, ethanol and D.I. water for 30 minutes. More details on the cleaning treatment of substrates treatments and on the preparation of the seeding promoters were presented in previous papers1,2. Diverse aromatic molecules have been shown to enhance the growth of diverse TMD monolayers using various forms of CVD processes1,2. In this work, perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt (PTAS) was selected as a seeding promoters for its high temperature stability2. The seeding promoter (PTAS) was prepared from the starting material using alkaline hydrolysis of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA). PTCDA was mixed with ethanol and KOH solution, and the mixtures were refluxed for more than 20 hours. PTAS would be filtrated out by adding ethyl ether to the solution. The precipitated PTAS can be dissolved in DI water for different concentrations for the synthesis of diverse TMD monolayers. A typical concentration of the PTAS solution for the synthesis is 100 M. A droplet (~2 μL) of PTAS solution was dropped on a clean 300 nm SiO2/Si substrate. The PTAS solution was spread out to cover the whole surface. Then the salt-like PTAS aggregations were precipitated as seeding promoters by rapidly drying with a gas flow of N2. The dependence between seed concentration and domain size of as-grown layers is similar to our previous work2. A higher seeding promoter concentration may result in higher density of nucleation sites and smaller domains.
S3 Scalable synthesis of in-plane heterostructure of monolayer WS2-MoS2 Continuous in-plane heterostructure of monolayer WS2-MoS2 was reached with a longer growth time (15 min) and a reduced Mo sources (half pieces of the patterned MoO3 layer). Figure 1 (j) shows the Raman mapping of large area in-plane WS2-MoS2 hetero-junctions. Domain boundaries across different triangular single-crystalline domains can be visualized with Raman and PL mapping. The PL mapping of the WS2 area shows a uniform and strong intensity, indicating a high crystalinity, uniformity and a single layer signature.
Figure S2. Characterizations of large area in-plane heterostructure of monolayer WS2-MoS2 (a) OM image and (b) schematic diagram of the in-plane heterostructure of monolayer MoS2-WS2; Raman mapping of (c) WS2 - E2g mode (d) MoS2 - A1g mode, and PL mapping of (e) WS2 (f) MoS2 over the marked area with a black dash line in fig. S2(a).
S4 Influence of starting materials on the CVD growth of the S- and Se-based heterostructure After coating of the PTAS seeding promoters, the substrates were placed facing up on a quartz plate next to a homemade reactor filled with WO3 and a small piece of Si with different Mo starting materials, including MoO3 powders, a thermally evaporated 10 nm-MoO3-x thin layer on a small piece of Si (2x2 mm2), and 0.8 mg stoichiometric MoX2 (X=S, Se) powders, as shown in supporting information S1. The small quartz reactor is homemade and filled with 1.5 g WO3 (99+ % Acros) in the high temperature region (900°C) for a higher vapor pressure of the WO3 reactants. Another crucible for containing sulfur or selenium is located upstream in the quartz tube. The heating temperature for the sulfur and the selenium vapor is 200 and 300°C, respectively. Ar and H2 were mixed in a ratio of 20~30% and introduced into the system as carrier gases. Another Ar flow was introduced into the homemade reactor to enable better reactants transport of WO3-x. The hot zone of the furnace was heated to 900 °C at a rate of 30 °C /min, and the diverse vdw heterostructures were grown at a temperature ranging from 650 to 780 °C for 10 min under ambient pressure.
Figure S3. Influence of starting materials on the CVD growth of the heterostructure Initially-grown MoS2 and MoSe2 atomic layers were used for further growth of diverse heterostructures and this could be achieved with three different Molybdenum starting materials: (a,b) MoO3 powders, (c,d) thermal evaporated MoO3-x thin layer, and (e,f) stoichiometric powders of MoX2 (X=S, Se). Scalar bar: 20 m
S5 Lateral heterostructure with 1D hetero-interface The domain shape is sensitive to the thickness of the single-crystalline domain. The in-plane heterostructure based on single layer atomic layers usually exhibits a triangular domain shape, while a star-like domain shapes of the in-plane heterostructure of WSe2-MoSe2 appeared for samples with an increased thickness.
Figure S4 Shapes and thickness of the WSe2-MoSe2 and WS2-MoS2 in-plane heterostructures OM images, AFM images, AFM line profile, and Raman mapping of following lateral heterostructures: (a) triangular domain of the monolayer WSe2-MoSe2, (b) star-like domain of the bilayer WSe2-MoSe2, (c) triangular domain of the monolayer WS2-MoS2, (d) triangular domain of the monolayer WS2-MoS2, with twisting of the centered MoS2 (e) triangular domain of the monolayer WS2-MoS2, with the centered hexagonal domain of MoS2
S6 Characterizations An Atomic Force Microscope (AFM, Bruker, Dimension Icon.) was adopted to verify the thickness and surface morphology of the samples. Raman and photoluminescence (PL) spectra and the mapping of the samples were examined with using Raman/PL spectrometer (Witec alpha 300). The wavelength of the laser used for the PL and Raman measurement was 532 nm with a laser power of ~0.15 mW. (A 100X objective was used to focus the laser beam.) The PL and Raman spectra were normalized with the intensity of the Raman A1g mode.
-Cs-corrected STEM-HAADF An analytic spherical aberration-corrected scanning transmission electron microscope High-Angle Annular Dark-Field (Cs-corrected STEM-HAADF) has been widely adopted for nano-materials characterization because of its sub-atomic resolution and capabilities on chemical mappings of light elements. The atomic and chemical configurations of the TMD monolayers (MX2, M=Mo, W; X= S, Se) were identified with a Cs-corrected STEM-HAADF (JEOL, JEM-ARM200F) at an acceleration voltage of 200 kV.) Z-contrast STEM images were post-processed by an HREM filter using Gatan Digital Micrograph software to de-noise and improve the images. Image processing was used to effectively filter HR-ADF images in frequency space. Rotational averaging of the FFT was utilized to separate the discrete spots (crystalline phases) from the continuum (amorphous phases). Then the average amorphous component was subtracted to yield the pure crystalline component. As-grown TMD monolayers or their heterostructures could be transferred on carbon-support Cu grids for TEM analysis using poly (methyl methacrylate) (PMMA). After spin-coating of PMMA on as-grown layers, baking at 60°C for 10 minutes, the PMMA-coated samples were immersed in a 2 M KOH solution at 60°C. Then the PMMA-as grown layers were lifted off from the substrate. The PMMA could be removed by rinsing with acetone, isopropyl alcohol, and deionized (DI) water.
- Polarization-resolved Second Harmonic Generation (SHG) Polarized second harmonic generation (SHG) imaging has been considered a promising characterization on the crystalline orientations and the symmetry of materials. SHG occurs due to a second-order nonlinear effect in crystal structures having non-centrosymmetry, providing an excellent contrast agent in non-invasive optical imaging3-11. The polarization-resolved SHG imaging on the lateral and the vertical heterostructures of different semiconducting TMD monolayers were obtained using a Leica SP5 MP confocal microscope operated in nondescan mode. The laser pulse was provided by a mode-locked Ti:Sapphire laser (Chameleon, Coherent) and the optimized wavelength for the analysis was 810 nm. An objective lens with a magnification of 10X was used to allow laser pulses focused onto the sample and to collect the reflected SH signals from the sample. A short pass dichroic mirror (680 SP, Semrock) and a band pass filter (400/40, Semrock) were adopted to distinguish the scattered laser light from the SH signals in the backward direction. In
addition, a polarizer was set in front of the photomultiplier tube (PMT) and parallel to the polarization of the excitation beam. The angular dependence of the SHG signal was measured by rotating the samples with steps of 5 degrees
S7 Raman vibration mode frequencies of the lateral heterostructures S-based heterostructure: (Laser: 532 nm) Exfoliated
CVD
Lateral
[12,13]
[1,2]
(1D-interface)
@ SiO2
@ SiO2
@ MoS2
@ WS2
E2g
384.0
384.7
-
384.4
A1g
403.0
401.9
-
402.4
2LA(M)
351.0
351.8
349.4
-
A1g
417.5
417.7
418.4
-
TMD MoS2
WS2
Se-based heterostructure: (Laser: 532 nm) Exfoliated
CVD
[14-16]
[17,18]
@ SiO2
@ SiO2
@ MoSe2
@ WSe2
E2g
287.5
286.7
-
286.7
A1g
240.6
241.9
-
241.6
E2g
247.0
249.6
249.6
-
A1g
257.0
259.7
259.7
-
TMD MoSe2
WSe2
Lateral (1D)
Reference: (1) Lee, Y.-H.; Yu, L.; Wang, H.; Fang, W.; Ling, X.; Shi, Y.; Lin, C.-T.; Huang, J.-K.; Chang, M.-T.; Chang, C.-S.; et al. Nano Lett. 2013, 13, 1852-1857. (2) Ling, X.; Lee, Y. H.; Lin, Y. X.; Fang, W. J.; Yu, L. L.; Dresselhaus, M. S.; Kong, J. Nano Lett. 2014, 14, 464-472. (3) van der Zande, A. M.; Kunstrnann, J.; Chernikov, A.; Chenet, D. A.; You, Y.; Zhang, X.; Huang, P. Y.; Berkelbach, T. C.; Wang, L.; Zhang, F.; et al. Nano Lett. 2014, 14, 3869-3875. (4) Kumar, N.; Najmaei, S.; Cui, Q. N.; Ceballos, F.; Ajayan, P. M.; Lou, J.; Zhao, H. Phys. Rev. B 2013, 87, 161403. (5) Malard, L. M.; Alencar, T. V.; Barboza, A. P. M.; Mak, K. F.; de Paula, A. M. Phys. Rev. B 2013, 87, 201401. (6) Li, Y. L.; Rao, Y.; Mak, K. F.; You, Y. M.; Wang, S. Y.; Dean, C. R.; Heinz, T. F. Nano Lett. 2013, 13, 3329-3333. (7) Kim, C. J.; Brown, L.; Graham, M. W.; Hovden, R.; Havener, R. W.; McEuen, P. L.; Muller, D. A.; Park, J. Nano Lett. 2013, 1, 5660-5665. (8) Shen, Y. R. The Principles of Nonlinear Optics; Wiley-Interscience: New York, 2003. (9) van der Veen, M. A.; Vermoortele, F.; De Vos, D. E.; Thierry, V. Anal. Chem. 2012, 84, 6378-6385. (10) Hsu, W. T.; Zhao, Z. A.; Li, L. J.; Chen, C. H.; Chiu, M. H.; Chang, P. S.; Chou, Y. C.; Chang, W. H. ACS Nano 2014, 8, 2951-2958. (11) Yin, X. B.; Ye, Z. L.; Chenet, D. A.; Ye, Y.; O'Brien, K.; Hone, J. C.; Zhang, X. Science 2014, 344, 488-490. (12) Lee, C., Yan, H., Brus, L.E., Heinz, T. F., Hone, J., Ryu, S., 2010 ACS Nano, 4, 2695–2700 (13) Zhao, W., Ghorannevis, Z., Amara, K. K., Pang, J. R., Toh, M., Zhang, X., Kloc, C., Tan, P. H., Eda, G., Nanoscale, 2013, 5, 9677-9683 (14) Terrones, H.; Del Corro, E.; Feng, S.; Poumirol, J. M.; Rhodes, D.; Smirnov, D.; Pradhan, N. R.; Lin, Z.; Nguyen, M. A. T.; Elias, A. L.;et al. Sci. Rep. 2014, 4, 4215. (15) Tonndorf, P.; Schmidt, R.; Böttger, P.; Zhang, X.; Börner, J.; Liebig, A.; Albrecht, M.; Kloc, C.; Gordan, O.; Zahn, D. R. T.; et al., 2013 Opt. Exp., 21, 4908-4916 (16) Berkdemir, A., Gutiérrez, H. R., Botello-Méndez, A. R., PereaLópez, N., Elías, A. L., Chen-Ing (17) Chia, C.-I., Wang, B., Crespi, V. H., López-Urías, F., Charlier, J.-C. et al, 2012 Sci. Rep. 3, 1755 (18) Lu, X.; Utama, M. I. B.; Lin, J.; Gong, X.; Zhang, J.; Zhao, Y.; Pantelides, S. T.; Wang, J.; Dong, Z.; Liu, Z.; et al. Nano Lett. 2014, 14, 2419-2425.
