Supporting Information Large Work Function Modulation of Monolayer MoS 2 by Ambient Gases Si Young Lee, 1 Un Jeong Kim, 3,, * JaeGwan Chung, 4 Honggi Nam, 1,2 Hye Yun Jeong, 1,2 Gang Hee Han, 1 Hyun Kim, 1,2 Hye Min Oh, 1,2 Hyangsook Lee, 4 Hyochul Kim, 3 Young-Geun Roh, 3 Jineun Kim, 3 Sung Woo Hwang, 3 Yeonsang Park, 3, * Young Hee Lee 1,2, * 1 Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Sungkyunkwan University, Suwon 440-746, Republic of Korea. 2 Department of Energy Science, Department of Physics, Sungkyunkwan University, Suwon 440-746. Republic of Korea. 3 Device Lab., Samsung Advanced Institute of Technology, Suwon 443-803, Republic of Korea. 4 AE group, Platform Technology Laboratory, Samsung Advanced Institute of Technology, Suwon 443-803, Republic of Korea. S. Y. L. and U. J. K. contributed equally. *Corresponding authors. E-mail: (Y. H. Lee) leeyoung@skku.edu, (U. J. Kim) ujjane.kim@samsung.com, and (Y. Park) yeonsang.park@samsung.com
Figure S1. (a) Optical image of the CVD-grown monolayer MoS 2 on SiO 2 (300 nm)/si wafer. Scale bar, 30 µm. Inset: Optical image of centimeter-scale monolayer MoS 2 film on SiO 2 /Si wafer. Scale bar, 1 cm. (b) Transmission electron microscope image of the CVD-grown MoS 2. The green and yellow dots indicate the Mo and S atoms, respectively. Scale bar, 1 nm. Inset: electron diffraction pattern. (c) PL intensity mapping of the MoS 2 flake with a 532-nm laser (power ~ 3.8 mw). Scale bar, 3 µm. Inset: single PL spectrum of the monolayer MoS 2. (d) Raman spectra of exfoliated and CVD-grown monolayer MoS 2 on SiO 2. XPS core level spectra of (e) Mo3d and (f) S2p from the bulk and monolayer MoS 2.
Figure S2. (a) The time evolution of work function change under O 2 gas flow (~3 Torr). (b) KP measurement of CVD-grown monolayer MoS 2 in N 2 gas environment. Figure S3. Valence-band spectrum from the UPS measurement. (a) Bulk and CVD-grown monolayer MoS 2 measured in UHV. (b) CVD-grown monolayer MoS 2 measured in UHV and O 2 gas environment.
Figure S4. PL spectra of the CVD-grown monolayer MoS 2 on SiO 2 /Si wafer in ambient and vacuum. Laser wavelength of 473 nm was used.
Figure S5. (a) I DS V DS transfer curves of the CVD-grown monolayer MoS 2 with V GS from 20 to -20 V measured in ambient. (b) Average mobilities of MoS 2 transistor in ambient, LV, and HV. (c) Time dependent transfer curve (I DS -V GS ) measured at V DS =1 V with 10 minutes span under O 2 exposure. Inset: On-current and threshold voltage (V th ) as a function time under O 2 environment. (d) Time dependent transfer curve (I DS -V GS ) measured at V DS =1 V with 30 minutes span under H 2 O exposure.
Figure S6. I V characteristics of exfoliated monolayer MoS 2. (a) I DS V GS curves of the MoS 2 transistor in ambient, LV, and HV at V DS = 1 V. I DS V DS curves of the MoS 2 transistor in (b) ambient, (c) LV, and (d) HV.
Figure S7. I V characteristics of the exfoliated monolayer MoS 2 under different gas environments. (a) I DS V GS transfer curves measured in ambient, HV (~10-6 Torr after annealing) and O 2 environment. I DS V GS transfer curve measured in (b) H 2 O, (c) N 2 and (d) H 2 gas environments in the vacuum chamber. Figure S8. Electrical properties of the half-covered monolayer MoS 2 transistor with symmetric Pd source/pd drain contact. I DS V DS transfer curves in (a) linear and (b) log scale.
MoS 2 Secondary edge [ev] Valence band edge [ev] Work function [ev] Bulk (our work) 36.271 1.266 4.542 Bulk 2 4.92 Solution processed 1L MoS 2 3 4.36 CVD 1 L (our work) 36.84 1.779 4.023 CVD 1 L 1 1.7 4.20 CVD 1 L with O 2 exposure (3 Torr, 2 h) + pumping (our work) 36.53 4.28 Table S1. UPS measurement data of the bulk and CVD-grown monolayer MoS 2 under UHV from previous works. References 1. Tsai, M.-L.; Su, S.-H.; Chang, J.-K.; Tsai, D.-S.; Chen, C.-H.; Wu, C.-I.; Li, L.-J.; Chen, L.-J.; He, J.-H. Monolayer MoS 2 Heterojunction Solar Cells. ACS Nano 2014, 8, 8317-8322. 2. Lin, J.; Zhong, J.; Zhong, S.; Li, H.; Zhang, H.; Chen, W. Modulating Electronic Transport Properties of MoS 2 Field Effect Transistors by Surface Overlayers. App. Phys. Lett. 2013, 103, 063109. 3. Yun, J.-M.; Noh, Y.-J.; Yeo, J.-S.; Go, Y.-J.; Na, S.-I.; Jeong, H.-G.; Kim, J.; Lee, S.; Kim, S.-S.; Koo, H. Y.; Kim, T.-W.; Kim, D.-Y. Efficient Work-Function Engineering of Solution-Processed MoS 2 Thin Films for Novel Hole and Electron Transport Layers Leading to High-Performance Polymer Solar Cells. J. Mat. Chem. C. 2013, 1, 3777-3783.