Supporting Information

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1 Copyright WILEY VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, Supporting Information for Small, DOI: /smll Large-Area Vapor-Phase Growth and Characterization of MoS 2 Atomic Layers on a SiO 2 Substrate Yongjie Zhan, Zheng Liu, Sina Najmaei, Pulickel M. Ajayan, * and Jun Lou *

2 Supporting Information for Large Area Vapor Phase Growth and Characterization of MoS 2 Atomic Layers on SiO 2 Substrate Yongjie Zhan, Zheng Liu, Sina Najmaei, Pulickel M. Ajayan*, and Jun Lou* 1. Optical and SEM images of CVD MoS 2 Figure S1. (a) and (b), Optical images of CVD-grown MoS2. Inset in a: An zoom-out area marked by a white arrow. (c) and (d), SEM images of MoS 2. The MoS 2 size can be easily scalable to the order of millimeters

3 2. Schematic of the chemical vapor deposition (CVD) system. Figure S2. The CVD system to prepare MoS 2 samples Mo thin films deposited on SiO 2 substrates were placed in a ceramic boat and then loaded into the center of a tube furnace. Pure sulfur in another boat was placed at the upwind low temperature zone in the same quartz tube. During the reaction, the temperature surrounding sulfur was kept to be slightly above its melting point ~113 o C. The quartz tube was first kept in a flowing protective atmosphere of high purity N 2, the flow rate of was ~ sccm (standard cubic centimeters per minute). After 15 minutes of N 2 purging, the furnace temperature was gradually increased from room temperature to 500 o C in 30 minutes. Then the temperature was increased from 500 o C to 750 o C in 90minutes and was kept at 750 o C for 10 minutes before cooled down to room temperature in 120 minutes. Figure S2 shows an illustration of the reaction condition of this CVD process

4 3. Raman spectra of CVD MoS 2 grown on various substrates Intensity (a.u.) pre-deposition thickness & substrates. 6nm Mo on SiO 2. 10nm Mo on Al 2 O 3. 6nm Mo on Si Raman Shift (cm -1 ) Figure S3. Raman spectra of MoS 2 samples grown on different substrates. Raman spectroscopy is used to identify the quality of CVD MoS 2 films grown on 3 different substrates with a cm -1 laser. The peaks locate ~385 cm -1 correspond the E 1 2g vibration mode of MoS 2, and peaks at ~408 cm -1 correspond to the A 1g mode. 1 It can be found that thin MoS 2 samples can be grown on various substrates including SiO 2, Au, Si et al. The Raman signal is weak for MoS 2 on Si

5 4. AFM image of CVD MoS 2 Figure S4. AFM image of MoS 2 on SiO 2 substrates showing thicknesses of 0.7nm (corresponding to single-layer MoS 2, Fig. a) and 4.5nm (corresponding to ~6 to 7 layered MoS 2 )

6 Submitted to 5. High resolution TEM images of MoS2 Figure S5. (a) and (c) High resolution TEM images of MoS2 with Moiré patterns. Insets are corresponding FFT patterns showing a few atomic layers. (b) and (d) Corresponding reconstructed images by masking the FFT pattern from insets of (a) and (c). -5-

7 6. XPS spectra of CVD MoS 2 Figure S6. XPS spectra of the MoS 2 thin film showing the typical Mo and S peaks from MoS 2. The XPS spectra of the as-grown MoS 2 film for the Mo and S edges are shown in Figure S6. Sulfur is in brown color. It shows 2p1/2 and 2p3/2 core levels at ev and ev, respectively, marked by the arrows, close to the previous reports (2p1/2: ev, 2, 2p3/2: ev ~ ev 2-4 ). The spectrum Molybdenum is in black. The Mo 3d3/2 and 3d5/2 peaks are around ~231.3 ev and ~228.2 ev, indicated by the black arrows, which is almost identify to the bulk MoS 2 samples (3d3/2: ev ~ ev, 3d5/2: ev ~ ev) 2,5,6 The calculated atomic concentration of S and Mo are 68.49% and 31.51%, with a ratio close to 2:

8 7. XRD spectra of MoS 2 powder and CVD MoS 2 Figure S7. XRD spectra of MoS 2 powder (top) and CVD MoS 2 film (bottom, on SiO 2 ). Due to the CVD MoS 2 film is only few layers, its XRD signal is much lower than that from the bulk MoS 2 powder. According to the Scherrer formula τ = Kλ / β cosθ (θ~28.3; β~0.256; λ~0.154 and K~0.9), the grain size of CVD MoS2 can be estimated to be ~ 32nm, close to the value from dark filed TEM image

9 8. Syntheses of MoS 2 films on Au substrate and Raman Spectrum Figure S8. (a) and (b). Optical images of CVD MoS 2 films on Au substrates. The yellow parts are Au particles. (c) and (d) SEM image of MoS 2 films marked by the red arrows. (f) Raman spectrum of MoS 2 on Au films. Au is an inert metal and does not react with sulfur in during synthesis of MoS 2. The thicknesses of gold films are proved to be a key factor in our experiments. Thickness below100 nm was not thick enough and would shrink - 8 -

10 into isolated micro-balls on silicon substrate after the annealing process during synthesis. Au films with a thickness of ~350nm are finally determined. Figure S6 shows optical, SEM images and Raman spectrum of typical MoS 2 samples grown on Au substrate with a thickness of 350nm. The Mo thickness is ~ 3 nm. After high temperature annealing, Au substrate shrank into particles (Figure S8b). The MoS 2 films can be found on most of areas marked by the red arrows (Figure S8c and S8d). Raman spectra show the E 1 2g and A 1 g mode of MoS 2. As shown in SEM images, red arrows reveal more details of these films surrounding Au islands and on Au substrate. Also, the suspended MoS 2 film in Figure S8d seems like very thin as they are transparent. Thanks to the highly conductive Au substrate, the MoS 2 films are much clearer under SEM than those grown on SiO 2 substrate

11 9. Formation of suspended MoS 2 film. Figure S9. Illustrations of the formation of suspended MoS 2 film. The Au and Mo layers are deposited by sputtering and E-beam evaporator, respectively. The MoS 2 film is formed before the Au film shrinks into particles. During the annealing process (750 o C for 10min), the MoS 2 films are deformed when the gold film shrink into particles, forming a suspended MoS 2 film (Fig. S8d)

12 References: 1 Jiménez Sandoval, S., Yang, D., Frindt, R. F. & Irwin, J. C. Raman study and lattice dynamics of single molecular layers of MoS2. Phys. Rev. B: Condens. Matter Mater. Phys. 44, 3955 (1991). 2 Turner, N. H. & Single, A. M. Determination of peak positions and areas from wide-scan XPS spectra. Surface and Interface Analysis 15, (1990). 3 Yu, X.-R., Liu, F., Wang, Z.-Y. & Chen, Y. Auger parameters for sulfurcontaining compounds using a mixed aluminum-silver excitation source. Journal of Electron Spectroscopy and Related Phenomena 50, (1990). 4 Lince, J. R., Carre, D. J. & Fleischauer, P. D. Effects of argon-ion bombardment on the basal plane surface of molybdenum disulfide. Langmuir 2, (1986). 5 Alstrup, I., Chorkendorff, I., Candia, R., Clausen, B. S. & Topsøe, H. A combined X-Ray photoelectron and Mössbauer emission spectroscopy study of the state of cobalt in sulfided, supported, and unsupported Co--- Mo catalysts. Journal of Catalysis 77, (1982). 6 Seifert, G., Finster, J. & Müller, H. SW X[alpha] calculations and x-ray photoelectron spectra of molybdenum(ii) chloride cluster compounds. Chemical Physics Letters 75, (1980). 7 Mott, S. N. Electrons in glass. Reviews of Modern Physics 50, 203 (1978). 8 Miller, A. & Abrahams, E. Impurity Conduction at Low Concentrations. Physical Review 120, 745 (1960)