Supporting Information

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1 Supporting Information Observation of Charge Transfer in Heterostructures Composed of MoSe 2 Quantum Dots and a Monolayer of MoS 2 or WSe 2 Shrawan Roy, a,b Guru P. Neupane, a,b Krishna P. Dhakal, a,b Jubok Lee, a,b Seok Joon Yun, a,b Gang Hee Han, a and Jeongyong Kim a,b* a Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea b Department of Energy Science, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea * j.kim@skku.edu. S1

2 a b c Fig. S1. (a) UV/visible spectra of MoSe 2 nanosheets synthesized with varying sonication times in the range 6 to 24 h. The inset clearly shows that the excitonic peaks A and B due to MoSe 2 are produced by the nanosheet samples for all sonication times. TEM images of the MoSe 2 nanosheets obtained with sonication for (b) 20 h and (c) 24 h, which show that the MoSe 2 nanosheets are a few layers in thickness and that they are thinner for the longer sonication time. S2

3 PL intensity (arb. unit) 300 nm 320 nm 340 nm 350 nm 360 nm 380 nm 400 nm 420 nm 440 nm 460 nm 480 nm 500 nm 520 nm Wavelength (nm) Fig. S2. PL spectra of MoSe 2 QDs dispersed in NMP under excitation range 300 nm to 520 nm. S3

4 a b 15.8 ev 1.3 ev Fig. S3. (a) and (b) are ultra-violet photoemission spectra (UPS) and X-ray photoemission spectra (XPS) of synthesized MoSe 2 QDs, respectively. The photoemission spectra were excited by Helium I with a photon energy of 21.2 ev. From the tangent of the off-set curve in UPS spectrum in Fig. S3(a), we estimated the cutoff value as ~15.8 ev that would correspond to the kinetic energy (K.E.) of photoemitted electrons. Using the binding energy (E b ) measured from the XPS spectrum in Fig. S3(b) we estimated the position of valence band maximum (VBM) at 1.3 ev below from the Fermi level. 1 The work function (Φ) of MoSe 2 QDs was estimated to be 4.1 ev by using the equation 1. The estimated value of Φ of the MoSe 2 QD was similar to 2, 3, 4 reported values of MoSe 2 monolayers and nanosheets. Φ = hν (21.2 ev) - K.E.- E b (1) S4

5 1 Fig. S4. Raman spectra of pristine 1L-WSe 2 with two characteristic Raman modes, the E 2g mode at 249 cm 1 and the A 1g mode at 260 cm 1. The difference between the positions of the peaks of the E 1 2g and A 1g modes, 11 cm 1 and the absence of the B 1 2g mode, which normally appears for multilayer WSe 2 at ~309 cm 1 (indicated by the arrow), confirm the 1L thickness of our sample. 5 S5

6 1L-TMD Peak position (nm) Spectral weight (%) A 0 A - B A 0 A - Pristine 1L-MoS MoSe 2 QDs/MoS B 8 12 A 0 A + A 0 A + Pristine 1L-WSe MoSe 2 QDs/WSe Table 1. Fit parameters (peak position and spectral weight) of neutral exciton and trions of pristine 1L-TMDs and MoSe 2 QDs/TMDs. S6

7 REFERENCES (1) Nguyen, E. P.; Carey, B. J.; Ou, J. Z.; Embden, J. v.; Gaspera E. D.; Chrimes, A. F.; Spencer, M. J. S.; Zhuiykov, S.; Kalantar-Zadeh, K.; Daeneke T. Electronic Tuning of 2D MoS 2 through Surface Functionalization. Adv. Mater. 2015, 27, (2) Chang, Y.-H.; Zhang, W.; Zhu, Y.; Han, Y.; Pu, J.; Chang, J.-K.; Hsu, W.-T.; Huang, J.-K.; Hsu, C.-L.; Chiu, M.-H.; et al. Monolayer MoSe 2 Grown by Chemical Vapor Deposition for Fast Photodetection. ACS Nano 2014, 8, (3) Mao, J.; Yu, Y.; Wang, L.; Zhang, X.; Wang,Y.; Shao, Z.; Jie, J. Ultrafast, Broadband Photodetector Based on MoSe 2 /Silicon Heterojunction with Vertically Standing Layered Structure Using Graphene as Transparent Electrode. Adv. Sci. 2016, 3, (4) Peng, Q.; Wang, Z.; Sa, B.; Wu, B.; Sun, Z. Electronic Structures and Enhanced Optical Properties of Blue Phosphorene/Transition Metal Dichalcogenides van der Waals Heterostructures. Sci. Rep. 2016, 6, (5) Tonndorf, P.; Schmidt, R.; Böttger, P.; Zhang, X.; Börner, J.; Liebig, A.; Albrecht, M.; Kloc, C.; Gordan, O.; Zahn, D. R. T.; et al. Photoluminescence Emission and Raman Response of Monolayer MoS 2, MoSe 2 and WSe 2. Opt. Express 2013, 21, S7

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