Iodine-Mediated Chemical Vapor Deposition Growth of Metastable Transition Metal

Transcription

1 Supporting Information Iodine-Mediated Chemical Vapor Deposition Growth of Metastable Transition Metal Dichalcogenides Qiqi Zhang,, Yao Xiao, #, Tao Zhang,, Zheng Weng, Mengqi Zeng, Shuanglin Yue, ± Rafael G. Mendes, Lingxiang Wang, Shengli Chen, Mark H. Rümmeli, Lianmao Peng ± and Lei Fu*,#, # The Institute for Advanced Studies (IAS), Wuhan University, Wuhan , China College of Chemistry and Molecular Sciences, Wuhan University, Wuhan , China ± Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing , China IFW Dresden, 20 Helmholtz Strasse, Dresden 01069, Germany *Address correspondence to leifu@whu.edu.cn These authors contributed equally to this work. 1

2 1. Methods and Characterizations Methods: To achieve the synthesis of few-layered and monolayer highly crystalline 1T -MoTe 2 flakes, we used silicon covered by 300-nm-thick SiO 2 as the substrate, tellurium (Te) powder and molybdenum dioxide (MoO 2 ) powder as the Te and Mo sources, and potassium iodide (KI) as catalyst, respectively. All the reactants were placed into a quartz boat and the substrate was placed over a mixture of MoO 2 and KI. The quartz boat was then put into the quartz tube of the chemical vapor deposition (CVD) furnace. It was heated to 700 C and held for 80 min in an atmosphere of 20 sccm Ar and 5 sccm H 2. Then we could obtain highly crystalline 1T -MoTe 2 flakes on the surface of SiO 2 /Si substrate. Characterizations: Optical images were performed with an optical microscope (OM) (Olympus DX51), and Raman spectroscopy was taken with a laser micro-raman spectrometer (Renishaw in Via, 532 nm excitation wavelength). Atomic force microscopy (AFM) images were taken with a NT-MDT Ntegra Spectra. Scanning electron microscopy (SEM) images were obtained using a ZEISS Merlin Compact scanning electron microscope. Transmission electron microscopy (TEM) images and selected-area electron diffraction (SAED) images were taken with an aberration corrected, high-resolution TEM (AC-HRTEM, FEI Titan3) operating at 80 kv. X-ray diffraction (XRD) measurement was conducted with a PANalytical X pert Pro system. X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Fisher, ESCALAB 250Xi, using Al-Kα radiation. The electrical properties containing current voltage curves were collected via four-probe measurement in a probe station under ambient conditions using a Keithley 4200-SCS. Electrical Measurements: Samples were loaded onto a rotating insert in a Quantum Design Physical Property Measurement System (PPMS). Temperature-dependent electrical measurements were taken using a 1.0 mv source-drain bias using a Keithley 237 Source-Measure Unit. Current was measured at temperatures from 9 to 300 K in order to determine the temperature-dependent resistance of the sample. Calculations: The density functional theory (DFT) calculations were performed using the CASTEP (Zeitschrift für Kristallographie, 2005, 220(5 6), ) module in the Materials Studio software (Bio Accelrys). The exchange-correlation functional was on the basis of Perdew-Burke-Ernzerh (PBE) within the generalized gradient approximation (GGA). To optimize the structure of 1T -MoTe 2 monolayer, a supercell with a vacuum region of ~40 Å was used, respectively, using a k-point mesh. In the geometry optimization, significant self-consistent-field (SCF) convergence criterions were adopted. More detailedly, the energy convergence was set to be lower than ev per atom and the force convergence was < ev Å 1. The energy cutoff was set to be 270 ev. As for 2H-MoTe 2, the vacuum region, k-point, energy cutoff and SCF convergence criterions were all the same except a supercell used. 2

3 2. The synthesis process and the OM images of highly crystalline 1T -MoTe 2 flakes Figure S1. (a) Schematic illustration of the CVD synthesis process of highly crystalline 1T -MoTe 2 flake. (b) Control of temperature and gas flow rate of H 2 and Ar during the CVD synthesis process. (c) The Optical image of a ribbon-shaped 1T -MoTe 2 flake. (d) The OM image of ribbon-pieced shape of highly crystalline 1T -MoTe 2 flake. 3

4 3. Large-area uniformity of 1T -MoTe 2 flakes Figure S2. The OM image of the large area uniform 1T -MoTe 2 flakes. 4

5 4. TEM and SAED images of highly crystalline 1T -MoTe 2 flake Figure S3. (a, b) Typical TEM images of highly crystalline 1T -MoTe 2 flake. (c, d) SAED taken from marked regions in (b), which suggest a highly crystallinity due to the consistent crystallographic structures. 5

6 5. The effect of iodide on growth of 1T -MoTe 2 flake Figure S4. The statistical analysis for (a) the connection between size and coverage ratio, (b) length/width ratio (for evaluating the regulation of the flakes) and (c) layer numbers (via RGB color analysis) of the 1T -MoTe 2 flake and iodide contents. (d) XRD result of the residual after the reaction of the synthesis of 1T -MoTe 2 flakes. 6

7 6. OM images and RGB color analysis for the influence of iodide content on the regulation and thickness of 1T -MoTe 2 Figure S5. The influence of iodide content on the regulation and thickness of 1T -MoTe 2. (a) to (c) The OM images of different samples towards different intermediate contents, and scale bars are 10 µm. (d) to (f) RGB analysis of the layer numbers of different samples towards different intermediate contents, the scale bars of which are all 1 µm. 7

8 7. XRD result of the intermediates during the reaction of the synthesis of 1T -MoTe 2 flakes The possible total reaction between reactants speculated from Figure 3d might be 6MoO KI + 2Te MoTe 2 + Mo + 4K 0.30 MoO I 2. According to Figure S4d, the generation of volatile intermediate MoO 2 I 2 might involve the reaction: 17MoO 2 + 2KI + 3Te 2TeO 3 (g) + K 2 Mo 4 O 13 + MoO 2 I 2 (g) + TeMo 4 O Mo. Figure S6. XRD analysis of the intermediates during the reaction of the synthesis of 1T -MoTe 2 flakes. 8

9 8. XPS results of 1T -MoTe 2 sample on SiO 2 /Si substrate and a blank one Figure S7. XPS of 1T -MoTe 2 sample on SiO 2 /Si substrate and pure SiO 2 /Si substrate, which could show the existence of I on the sample substrate to indirectly prove the reaction between the catalyst and precursor. 9

10 9. OM image of four electrodes deposited on 1T -MoTe 2 flake Figure S8. OM image of four electrodes deposited on 1T -MoTe 2 flake. The channel between probe II and III is marked out and the average length and the width are 4.6 and 20.2 µm, respectively. 10