Supporting Information Rotationally Commensurate Growth of MoS2 ...
Supporting Information Rotationally Commensurate Growth of MoS2 on Epitaxial Graphene Xiaolong Liu1†, Itamar Balla2†, Hadallia Bergeron2, Gavin P. Campbell2, Michael J. Bedzyk1,2,3*, and Mark C. Hersam1,2,4,5* 1
Graduate Program in Applied Physics, 2Department of Materials Science and Engineering, 3
Department of Physics, 4Department of Chemistry, 5Department of Medicine Northwestern University, Evanston, IL 60208, USA
*Correspondence should be addressed to: [email protected] [email protected] † These authors (X.L. and I.B.) contributed equally. Contents:
Figure S1. Additional AFM images of van der Waals epitaxy of MoS2 on EG
Figure S2. STM and STS mappings of EG wrinkles and cracks
Figure S3. Optical and AFM images of monolayer MoS2/SiO2
Figure S4. High-resolution grazing-incidence X-ray scattering of MoS2/EG and diffraction of single crystal bulk
Figure S5. Bandgap measurements from 80 STS spectra of monolayer MoS2
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Supplementary Figures
Figure S1. Additional AFM images of van der Waals epitaxy of MoS2 on EG grown at 43 Torr. MoS2 flakes are mostly monolayers and have aligned edges as a result of being in registry with the underlying EG.
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Figure S2. STM and STS mappings of EG wrinkles and cracks. (a) A crack in EG possibly resulting from the growth of MoS2 due to the negative coefficient of thermal expansion of EG (Vsample = -0.3 V, Itunneling = 50 pA).1 (b) A zoomed-in image of a flower-shaped graphene wrinkle found on the cracked EG region (Vsample = -0.3 V, Itunneling = 50 pA). STS mappings of the topography images in (a) and (b) are shown in (c) and (d), respectively. Although EG wrinkles are not obvious in the topography images, STS mappings reveal different electronic properties at wrinkles2 and edges of a graphene sheet at the crack. These differences in electronic properties may lead to higher reactivity that underlies the preferred nucleation of MoS2 on SiC step edges covered with curved EG and EG edges as seen in Figure 1 and Figure S1.
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Figure S3. Optical and AFM images of monolayer MoS2/SiO2. (a) Optical image and (b) AFM image of a MoS2 crystal domain on SiO2 from which the Raman spectra were taken in Figure 2b. The measured thickness is ~0.88 nm, slightly larger than the standard monolayer thickness of 0.7 nm, which may be due to the non-atomically flat substrate.
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Figure S4. High-resolution grazing-incidence X-ray scattering of MoS2/EG and diffraction of single crystal bulk MoS2. The lattice constants of bulk MoS2 and MoS2/EG obtained from these peaks are 3.159 ± 0.006 Å and 3.160 ± 0.005 Å, respectively.
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Figure S5. Bandgap measurements from 80 STS spectra on multiple monolayer MoS2 domains. These measurements imply that the bandgap is 2.01 ± 0.08 eV. The standard deviation of 0.08 eV represents the experimental variability in bandgap measurements in this work.
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References (1) (2)
Yoon, D.; Son, Y.-W.; Cheong, H. Negative Thermal Expansion Coefficient of Graphene Measured by Raman Spectroscopy. Nano Lett. 2011, 11, 3227–3231. Lalmi, B.; Girard, J. C.; Pallecchi, E.; Silly, M.; David, C.; Latil, S.; Sirotti, F.; Ouerghi, A. Flower-Shaped Domains and Wrinkles in Trilayer Epitaxial Graphene on Silicon Carbide. Sci. Rep. 2014, 4, 4066.
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Graduate Program in Applied Physics, 2Department of Materials Science and Engineering, 3
Department of Physics, 4Department of Chemistry, 5Department of Medicine Northwestern University, Evanston, IL 60208, USA
*Correspondence should be addressed to: [email protected] [email protected] † These authors (X.L. and I.B.) contributed equally. Contents:
Figure S1. Additional AFM images of van der Waals epitaxy of MoS2 on EG
Figure S2. STM and STS mappings of EG wrinkles and cracks
Figure S3. Optical and AFM images of monolayer MoS2/SiO2
Figure S4. High-resolution grazing-incidence X-ray scattering of MoS2/EG and diffraction of single crystal bulk
Figure S5. Bandgap measurements from 80 STS spectra of monolayer MoS2
S1
Supplementary Figures
Figure S1. Additional AFM images of van der Waals epitaxy of MoS2 on EG grown at 43 Torr. MoS2 flakes are mostly monolayers and have aligned edges as a result of being in registry with the underlying EG.
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Figure S2. STM and STS mappings of EG wrinkles and cracks. (a) A crack in EG possibly resulting from the growth of MoS2 due to the negative coefficient of thermal expansion of EG (Vsample = -0.3 V, Itunneling = 50 pA).1 (b) A zoomed-in image of a flower-shaped graphene wrinkle found on the cracked EG region (Vsample = -0.3 V, Itunneling = 50 pA). STS mappings of the topography images in (a) and (b) are shown in (c) and (d), respectively. Although EG wrinkles are not obvious in the topography images, STS mappings reveal different electronic properties at wrinkles2 and edges of a graphene sheet at the crack. These differences in electronic properties may lead to higher reactivity that underlies the preferred nucleation of MoS2 on SiC step edges covered with curved EG and EG edges as seen in Figure 1 and Figure S1.
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Figure S3. Optical and AFM images of monolayer MoS2/SiO2. (a) Optical image and (b) AFM image of a MoS2 crystal domain on SiO2 from which the Raman spectra were taken in Figure 2b. The measured thickness is ~0.88 nm, slightly larger than the standard monolayer thickness of 0.7 nm, which may be due to the non-atomically flat substrate.
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Figure S4. High-resolution grazing-incidence X-ray scattering of MoS2/EG and diffraction of single crystal bulk MoS2. The lattice constants of bulk MoS2 and MoS2/EG obtained from these peaks are 3.159 ± 0.006 Å and 3.160 ± 0.005 Å, respectively.
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Figure S5. Bandgap measurements from 80 STS spectra on multiple monolayer MoS2 domains. These measurements imply that the bandgap is 2.01 ± 0.08 eV. The standard deviation of 0.08 eV represents the experimental variability in bandgap measurements in this work.
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References (1) (2)
Yoon, D.; Son, Y.-W.; Cheong, H. Negative Thermal Expansion Coefficient of Graphene Measured by Raman Spectroscopy. Nano Lett. 2011, 11, 3227–3231. Lalmi, B.; Girard, J. C.; Pallecchi, E.; Silly, M.; David, C.; Latil, S.; Sirotti, F.; Ouerghi, A. Flower-Shaped Domains and Wrinkles in Trilayer Epitaxial Graphene on Silicon Carbide. Sci. Rep. 2014, 4, 4066.
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