Supporting Information Tuning Local Electronic Structure of Single Layer MoS2 through Defect Engineering

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1 Supporting Information Tuning Local Electronic Structure of Single Layer MoS2 through Defect Engineering Yan Chen, 1,2,,$, * Shengxi Huang, 3,6, Xiang Ji, 2 Kiran Adepalli, 2 Kedi Yin, 8 Xi Ling, 3,9 Xinwei Wang, 8 Jianmin Xue, 7 Mildred Dresselhaus, 3,4 Jing Kong, 2,3, * Bilge Yildiz 1,5, * 1 Department of Nuclear Science and Engineering, 2 Research Laboratory of Electronics, 3 Department of Electrical Engineering and Computer Science, 4 Department of Physics, 5 Department of Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 6 Department of Electrical Engineering, The Pennsylvania State University, University Park, PA State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing , P. R. China 8 School of Advanced Materials, Shenzhen Graduate School, Peking University, Shenzhen , P. R. China 9 Department of Chemistry, Division of Materials Science and Engineering, and The Photonics Center, Boston University, Boston, MA, 02215, USA These authors contribute equally to this work. * Corresponding Authors: Prof. Yan Chen Emai: escheny@scut.edu.cn Prof. Jing Kong jingkong@mit.edu Prof. Bilge Yildiz byildiz@mit.edu Calculation Methods Modeling Molecular dynamics simulations were performed on the large-scale/molecular massively parallel simulator (LAMMPS). 1 The Stillinger-Weber potential developed by Jiang s group was used to describe the interatomic interactions within singer-layer MoS2 for stable molecular dynamics simulations. 2,3 Ziegler Biersack Littmark (ZBL) 4,5 universal repulsive potentials at short 1

2 interatomic separations was joined to the SW potential to model the energetic collisions process. Ion irradiations were conducted on a free-standing single layer MoS2 consisting of 576 Mo atoms and 1152 S atoms, with a lateral size of Å 2. Periodic boundary conditions (PBCs) were used during the dynamical simulations. The incident Ar + ion was initially placed at 20 Å above the MoS2 sheet, and the incident direction was perpendicular to the MoS2 sheet. The incident energies were varied from 50 ev to 1000 kev, and 100 independent simulations were carried out for each specific energy. During the irradiation process, NVE ensemble was employed with a time step of 0.1 fs and was used to guarantee energy conservation. The first principles calculations were carried out based on the spin-polarized DFT 6 employing periodic boundary conditions as implemented in the Vienna ab initio simulation package (VASP). 7,8 The projector augmented wave (PAW) 9,10 pseudopotentials and the generalized gradient approximation (GGA) 11 functional of Perdew, Burke and Ernzerhof (PBE) 11 were used. The optpbe method was also employed to account for the influence of the van der Waals (vdw) interaction All calculations were performed with a supercell of singer-layer MoS2 containing 108 atoms with a vacuum layer of 15 Å to avoid the interlayer interactions. The total energy was converged to be better than 10 mev for a plane wave cutoff of 500 ev and Monkhorst Pack 15 k-point sampling for the Brillouin zone. For geometry relaxation, we used the method of conjugate gradient energy minimization, and the energy convergence criterion was 10-5 ev between two consecutive steps. The maximal force exerted on each atom was less than 0.02 ev Å upon ionic relaxation. Supporting Figures 2

3 Intensity (a.u) (a) (b) (c) Quartz Quartz (d) Quartz (e) Quartz (f) Mo S Au 4f Au 4d Mo 3p C 1s Mo 3d S 2p Au E Binding Energy (ev) Figure S1. MoS2 structures and the optical microscope images of the samples used in this work. (a-e) The illustrations of the structures studied in this work: CVD MoS2 on Si/SiO2 substrate, MoS2/Au, MoS2/SLG/Au, MoS2/BN/Au and MoS2/CeO2/Au. The latter four structures are supported by quartz substrates. The optical microscope images of the samples after MoS2 transfer are shown. (f) XPS spectrum of MoS2/Au. All peaks of Mo 3p, Au 4d, C 1s, Mo 3d, S 2p and Au 4f are labeled. E, the binding energy difference between Au 4f7/2 and Mo 3d5/2, is labeled. The inset shows the optical microscope image of MoS2 transferred on Au substrate. The red dashed triangles indicate the crystalline MoS2. The inset shows the atomic structure of MoS2 from the top view. 3

4 (a) MoS 2, 300 o C Anneal E A 1 as grown (b) MoS 2, 300 o C Anneal Au SLG/Au Intensity (a.u.) Au SLG/Au BN/Au CeO 2 /Au Intensity (a.u.) BN/Au CeO 2 /Au as grown Raman Shift (cm -1 ) Energy (ev) Figure S2. Raman (a) and PL (b) spectra of as-grown MoS2 and MoS2 after 300 vacuum annealing on the four substrates. The spectra are all normalized by the corresponding A1 modes. 4

5 (a) Mo 3d (b) 1.2 (c) Intensity (a.u) 300 o C 450 o C Sputtering Sputtering+450 o C Binding Energy (ev) relative S to Mo ratio MoS2/Au 300 O C 450 O C Ar + sputtering Ar + sputtering & 450 O C MoS2/SLG/Au MoS2/BN/Au MoS2/CeO2/Au Intensity (a.u.) as-grown,/200 transfer 300 o C 450 o C sputter Energy (ev) Figure S3. (a) S 2p peaks of XPS spectra of MoS2/BN/Au after 300 and 450 annealing, sputtering and with subsequent 450 annealing. It can be seen that the S 2p peak shape does not change comparing 300 and 450 annealing. (b) The relative XPS intensity ratio of S and Mo peaks for the four samples after thermal annealing and sputtering. It can be seen that compared to 300 annealing, the S to Mo ratio does not change after and 450 annealing, but drops significantly after sputtering. (c) PL spectra of as-grown MoS2 and MoS2/Au after transfer, 300 and 450 annealing, and sputtering. The intensity of the as-grown MoS2 shown is 1/200 of the original value. The red shift of the PL peaks after annealing compared to as-grown samples is probably due to strain. 16 5

6 (a) MoS 2 /BN/Au E A 1 (b) MoS 2 /BN/Au Intensity (a.u.) 300 o C 450 o C Sputter Intensity (a.u.) 300 o C 450 o C Sputter (c) Raman Shift (cm -1 ) Raman Shift (cm -1 ) E' A 1 ' (d) FWHM (cm -1 ) Energy (ev) E' A 1 ' Figure S4. (a) Raman and (b) PL spectra of the MoS2/BN/Au sample after transfer, vacuum annealing at 300 and 450, and sputtering. The MoS2 Raman peaks E and A1 are labeled. All spectra are normalized by the corresponding A1 peaks. (c) Raman shift and (d) FWHM of E and A1 peaks for the MoS2/BN/Au sample after 300 and 450 annealing, and sputtering. 6

7 Figure S5. STS measured from different locations of the sample for sputtered MoS2 on HOPG. The three in-gap defect peaks are labeled, which vary at different locations of the sample. 7

8 DoS (a.u.) Total Mo S 160 Mo S S Mo V MoS3 V MoS Energy (ev) Energy(eV) Figure S6. The density of states (DoS) from the contributions of Mo, S and total of MoS2 with S replaced by Mo (MoS), Mo replaced by S (SMo), Mo and three S vacancy (VMoS3) and Mo and six S valcancy (VMoS6). 8

9 (a) (b) (c) Number of sputtered atoms Ion energy K ion (kev) Ar Figure S7. (a-b) Simulated interstitial defect in MoS2 after Ar+ sputtering. (a) the defect form immediately after the sputtering. (b) the defect form after 10 ps relaxation at room temperature. At 300K with 10 ps relaxation, the interstitial atoms will migrate to other sites and form a stable and regular defect form. (c) The simulated number of sputtered atoms as a function of Ar+ sputtering energy. As seen here, the sputtered atoms reach a peak at ev Ar+ sputtering. 9

10 Figure S8. The possibility for different defect structures to form in single MoS2 after 200 ev, 500 ev, and 2000 ev Ar + sputtering. 10

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