Defect Design of Two Dimensional MoS2 Structures by Using

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C: Surfaces, Interfaces, Porous Materials, and Catalysis 2

Defect Design of Two Dimensional MoS Structures by Using Graphene Layer and Potato Stamp Concept Dundar E Yilmaz, Roghayyeh Lotfi, Chowdhury Ashraf, Sungwook Hong, and Adri C.T. van Duin J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b02991 • Publication Date (Web): 09 May 2018 Downloaded from http://pubs.acs.org on May 10, 2018

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The Journal of Physical Chemistry

Defect Design of Two Dimensional MoS2 Structures by using Graphene Layer and Potato Stamp Concept Dundar E. Yilmaz*1, Roghayyeh Lotfi1, Chowdhury Ashraf1, Sungwook Hong2, and Adri C.T. van Duin1 1

: Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802, USA 2

: Collaboratory for Advanced Computing and Simulations, Department of Chemical

Engineering & Materials Science, University of Southern California, Los Angeles, California 90089-0242, United States

KEYWORDS: graphene, MoS2, defects, vacancy, surface functionalization

ABSTRACT: We propose a novel method to create vacancy defects on MoS2 structures. The method is similar to a potato stamp process, which involves creating vacancy defects on graphene layer and stamping to the MoS2 surface. Based on nudged elastic band and Density Functional Theory calculations, we predict that sulfur atoms on the surface will diffuse into the vacancy sites of the graphene layer. Separation of graphene layer will carry away diffused sulfur

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atoms, leaving the MoS2 surface with sulfur vacancy defects. We carried molecular dynamics simulations with the ReaxFF reactive force field to test the potato stamp concept and then functionalized the MoS2 surface defects with epoxy molecules. We observed dissociation of epoxy molecules at the vacancy site, in which the exposed metal atoms performed catalytic activity.

Introduction MoS2, a transition-metal dichalcogenide (TMD), draws much attention due to its distinctive optical, electronic and catalytic properties. It is a semiconductor with an indirect band gap of 1.23 eV.1 Surface defects play crucial role on electrochemical properties. In particular, vacancy defects decrease thermal and electrical conductivity of single layer MoS2. Moreover, MoS2 surface can be functionalized via sulfur vacancy sites. In this study, we propose a novel method to create sulfur vacancy defects on the surface of MoS2 structure in a controllable manner. The bulk MoS2 structure consists of hexagonal planes of S and Mo atoms. Planes bond together via van der Waals bonds. The weak nature of inter-plane van der Waals interactions make mechanical exfoliation of these layers possible.2 MoS2 can disperse into single layers by reaction of LixMoS2 with water.3 Due to quantum confinement, single layer MoS2 has a direct bandgap of 1.9 eV.4 Single layer transistors2, photo-transistors5 and field effect transistors6-7 based on MoS2, has been reported previously. The unique electronic and chemical properties of MoS2 offer more potential applications than similar two-dimensional materials. Defects have critical effects on electric and magnetic properties of single layer MoS2 structures. Moreover, vacancy defects alter the transport mechanism. It has been showed that electrons are localized at the defect sites and transport occurs through hopping.8 Sulfur vacancies


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are predominant defects in mechanically exfoliated and chemical vapor deposition grown samples.9 Defects are usually result of unwanted phenomena (i.e. contaminations, lattice mismatch etc.) during fabrication or growth process and often lead to undesirable effects on the device. However, precise control of their creation may open new dimensions to materials engineering. Sulfur vacancy energy has been calculated as 5.89 eV with first principles calculations.10 This corresponds to a 90 keV electron beam energy for the displacement threshold of an electron irradiation process.11 At these levels of energy, electrons cause structural damages to the sample apart from the difficulty of focusing them on the particular spot.11 MoS2 is a suitable material for surface functionalization with potential applications such as hydrodesulphurization, hydrogen production. Also, adsorption of nonmetal elements on the surfaces of similar materials can induce local magnetic moment.12 Rayboud et al calculated adsorption energy of thiophene, a relatively less reactive sulfur containing molecule found in crude oil, on the catalytically active MoS2 surfaces.13 Sulfur vacancies on the single layer MoS2 increase catalytic activity by exposing metal atoms to the reactants. Ataca et al. predicted dissociation of H2O molecules on sulfur vacancy sites of single layer MoS2.14 In this study we compare energies of sulfur atoms, at the MoS2 surface and at the vacancy sites of single layer graphene. Later, we perform dynamical simulations to test our hypothesis. Furthermore, we show as a proof of concept, the newly created sulfur vacancy sites can be functionalized with organic molecules. Results and Discussion: Re-training Force Field. We merged two recently published ReaxFF15-16 parameter set for the MoS2 systems17 and C/H/O system18 and trained the C-S interactions. To construct a quantum mechanics (QM) training set for sulfur/graphene interactions, we performed density functional


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theory (DFT) calculations of sulfur binding energies on pristine and mono-vacancy graphene sheets using the Vienna Ab Initio simulation package (VASP).19 For C and S atoms, the projector-augmented-wave (PAW) potentials20 were used to describe the core and valence electrons, and the GGA-PBE functional21 was employed for exchange correlation. In addition, previous DFT studies suggested that the GGA-PBE type van der Waals correction could be employed for adatom/molecules on graphene-like systems because of their weak binding energies.22-25 As such, we used the van der Waals correction term for all calculations using DFTD2 method26 to accurately calculate sulfur atoms/molecules’ binding energies on the graphene sheets. A cut off energy of 520 eV was chosen and 4 × 4 × 1 Gamma centered k-point mesh was used. For system configurations, we used a 6 × 6 × 1 graphene supercell (72 atoms) with vacuum layers of 15 Å. Note that we performed a convergence test using different super cell sizes and cut off values, and the supercell size and cut-off energy that we used lied in acceptable error ranges (~ 0.05 eV). To study effects of different types of sulfur adsorbates as well as surface defects on binding behaviors, we placed S/S2/S8 adsorbates on the pristine and mono-vacancy graphene sheets, and evaluated S/S2/S8 binding energies defined as: (1)

where Etotal, Egraphene, and ES are the energy of the pristine/mono-vacancy graphene sheet with adsorbed S/S2/S8, the energy of the pristine/mono-vacancy graphene sheet, and the energy of isolated S/S2/S8 adsorbate, respectively. Table 1 summarizes results of the binding energies obtained by our DFT calculations and previous DFT studies.


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Table 1 Binding energies of S/S2/S8 on the pristine and mono-vacancy graphene sheets Binding energy (kcal/mol) LDA

GGA-PBE with DFT-D2 GGA-PBE (this work) S atom on pristine graphene (2-fold site)

-28.22

S atom on pristine graphene (3-fold site)

-18.72

S atom on pristine graphene (6-fold site)

-0.37

S2 molecule on pristine graphene

-5.82

S8 molecule on pristine graphene

-12.31

S atom on mono-vacancy graphene

-178.68

S2 molecule on mono-vacancy graphene

-132.56

S8 molecule on mono-vacancy graphene

-19.55 27

-47.84 28

-166.75 27

-70.13

Please note that a 2-fold binding site on the pristine graphene was found to be the lowest binding site for a S adatom, and thus, we initially placed S2 and S8 molecules on the 2-fold site. For the mono-vacancy graphene sheet, a S8 molecule was initially placed parallel to the graphene sheet (see Figure 1), but we found that the S8 molecule was preferably bound to the mono-vacancy site when it is placed perpendicular to the graphene sheet. Thus, the S8 binding energy on the monovacancy graphene in Table 1 corresponds to the S8 molecule perpendicular to the graphene sheet. All the binding energies in Table 1 were included in our QM training set to optimize ReaxFF reactive force field parameters for S/C interactions. A comparison between QM and ReaxFF distances and energies are shown in Figure 1 and Figure 2 respectively.


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(c)

(b)

(a) 1.90 1.89

1.90 1.89

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3.39 3.61

2.60 2.83

2.60 2.83

3.39 3.61

3.39 3.61

1.94 1.89

DFT = -28.22 kcal/mol



ReaxFF = -22.52 kcal/mol



(e)

(d) 3.96 4.37

3.55 3.57

3.55 3.71

3.43 3.33

3.39 3.27 4.42 4.52





Figure 1 Binding energies and distances of (a) S on 2-fold site, (b) 3-fold site, (c) 6-fold site, (d) S2 and (e) S8 in pristine graphene. DFT numbers are in red while ReaxFF numbers are in black. (C atoms are in cyan and S atoms are in yellow)


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1.72 1.71

(b)

(a)

1.72 1.71

1.75 1.82

1.75 1.82

1.75 1.82

1.72 1.71





(c)

1.74 1.82 1.74 1.82

1.74 1.82

DFT = -70.13 kcal/mol ReaxFF = -121.15 kcal/mol

Figure 2. Binding energies and distances of (a) S, (b) S2 and (c) S8 in mono-vacancy graphene. DFT numbers are in red while ReaxFF numbers are in black. (C atoms are in cyan and S atoms are in yellow)


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d

Figure 3 Comparison of Binding energies between DFT (Ma et al.29) and ReaxFF for graphene per C as a function of the interlayer distance (d) between graphene and the bottommost S atom of MoS2. Ma et al. predicted an equilibrium distance of 3.32 Å. In a separate DFT study, Miwa et al.30 predicted an equilibrium distance of 3.66 Å. ReaxFF predicted equilibrium distance is 3.57 Å, which is between these two DFT numbers


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(a)

(b)

Figure 4 Comparison between DFT and ReaxFF energies for S-O bond dissociation and Mo-S-O angle distortion. Pink, yellow, red and white spheres represent Mo, S, O and H atoms respectively. According to our density functional theory (DFT) calculations, S binds strongly to the defected graphene in comparison to the pristine one, and it is important that our force field can capture this trend. Thus, we started with force field optimization to capture the appropriate binding energies of S atom, S2 and S8 on both pristine and mono-vacancy graphene. We took the C/H/O parameters from Ashraf et al.18 in which C parameters are taken from Srinivasan et al.31 These C parameters are already trained for predicting reasonable mechanical properties of graphene. Next, we merged the C/H/O force field with the latest MoS2 force field17 and trained the C and S interactions to reproduce S binding energies on graphene in ReaxFF. During the training, only CS bond, off-diagonal, angle and torsion parameters were trained, so other interactions remain unchanged. Figure 1 and Figure 2 shows the comparison of distances and binding energies of S atom, S2 and S8 on pristine and mono-vacancy graphene respectively between DFT and ReaxFF, which are in reasonable agreement.


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Another aim of the training was to reproduce the correct interlayer distance between MoS2 and graphene founded in the DFT study. Miwa et al.30 and Ma et al.29 calculated that the equilibrium spacing between MoS2-graphene layers to be 3.66 Å and 3.32 Å respectively, while ReaxFF predicted a spacing of 3.57 Å (Figure 3). Additionally, in order to obtain accurate interaction of S and O atoms in the system, we trained S-O bond and Mo-S-O angle parameters to reproduce the bond dissociation and angle distortion of MoS4OH2 structure around its equilibrium values (Figure 4). Equilibrium DFT values for S-O bond and Mo-S-O angle are 1.71 Å and 99.83 degree, respectively and as it can be seen from Figure 4, there is a good agreement between DFT and ReaxFF data. ‘Potato stamp’ simulations. The proposed method is similar to potato stamping concept that we all did once in kindergarten. One would carve figures on a cleaved potato surface and paint and stamp it to a piece of paper. Similarly, implementing this method for grabbing S atoms will consist of three steps: • Create vacancy defects on single layer graphene. • Stamp graphene layer onto the MoS2 surface at elevated temperatures. Sulfur atoms will diffuse to vacancy sites on the graphene layer. • Separate graphene with sulfur atoms diffused. While not completely straightforward, creating vacancy defects on a graphene layer is much more manageable compared to creating those defects directly on the MoS2 surface; i. e. one does not need to worry about sublayer atoms; since there is only one layer of atoms. To verify the applicability of the second step of the potato stamp procedure outlined above, we calculated energies of sulfur atom at the MoS2 surface, at the defect site of graphene and through the reaction path (Figure 5). Based on reaction energy barrier calculations, we predict that for


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certain defect types on the graphene sheet, if graphene layer was close enough, then diffusion of sulfur atoms on the MoS2 surface to these sites is energetically favorable. We calculated energy barrier using nudged elastic band (NEB)32-33 method with the ReaxFF reactive force field implemented in open source LAMMPS framework34. The simulation box contains a single layer MoS2 with dimensions of 64.6 Å x 55.3 Å and a layer of graphene positioned 2 Å above it. MoS2 slab and graphene layer contains 1200 and 1320 atoms respectively. We calculated energy barriers of five common defects observed in graphene structures: Mono vacancy (Figure 5-a), di-vacancy (Figure 5-b), Stone-Wales defect (Figure 5-c), and two reconstructed di-vacancy defects (Figure 5-d). The Stone-Wales defect does not involve any missing atom, instead, four hexagons formed into two pentagons and two heptagons.35 Mono vacancy defect is created by removing one carbon atom. We considered three different divacancy cases: In the first case two neighboring carbon atoms are missing. To distinguish this defect from other reconstructed di-vacancies, we will dub this as ‘simple’. Second and third cases also have two missing carbon atoms, but atoms nearby the defect sites form two pentagons and one octagon for the 585 type and three pentagons and three heptagons for the 555777-type.36 For each case, one defect is created on the graphene layer. During the NEB calculation, the S atom beneath the vacancy site moved along the path to the defect site. At each point on the path, while S atom are fixed, we calculated the total energy after relaxing the system (Figure 5-e). As Figure 5 indicates, sulfur migration to the mono and di-vacancy defect sites of graphene is energetically favorable. However, it is endothermic for Stone-Wales35 and di-vacancy (555777-type and 585type) defects with energy barriers 13.4 eV, 7.6 eV and 6.7 eV respectively. We calculated energy barriers for diffusion of sulfur atom to mono and di-vacancy (simple) sites of graphene as 2.5 eV


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and 1.6 eV, respectively. Based on these calculations we predict that diffusion of S atoms to mono and di-vacancy sites can occur under certain circumstances.

a)

b)

c)

d)

e)

Figure 5. Reaction barrier energies for diffusion of S atom at the MoS2 top layer to the graphene defect sites: a) Mono vacancy, b) di-vacancy, c) Stone-Wales d) di-vacancy (585-type, triangles) and di-vacancy (555777-type, circles). e) Reaction path of sulfur atom diffusing into the vacancy site. Color code: Carbon: cyan, Sulfur: yellow, Molybdenum: pink After calculating reaction barrier energies, we further tested the second step of potato stamping with dynamical simulations. We built MoS2 slab with dimensions 129.32 Å x 110.60 Å and a


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single layer graphene with the same dimensions. To match graphene and MoS2 lattices we compressed graphene lattice in x (0.83 %) and y (0.94 %) directions and stretched the MoS2 lattice in y direction (1.26 %). We simulated the potato stamp process with mono and di-vacancies (simple). Density of sulfur vacancy defects in chemical vapor deposition grown samples has been measured previously in the order of 1013cm-2.8 Along with this observation, we built systems with 10, 20, 40 and 100 mono vacancies and 10, 20, 30, 40 and 50 di-vacancies. These samples span vacancy densities up to 1014 cm-2. For each case we generated three replicas of the system with different initial configurations. We created vacancy defects on the graphene layer by randomly deleting carbon atoms. Initially, graphene layer was placed 10 Å above the MoS2 surface (Figure 6-a). Subsequently, we lowered graphene layer to the surface until it was 2 Å away from the MoS2 surface. We applied opposite forces on graphene layer and S atoms in the bottom layer to mimic the stamping process. This step of the simulation took for 5 ps. To increase the diffusion rate, we ran the simulation at 700 K (Figure 6-b). In the last step, we reversed forces to separate graphene and MoS2 layers. At this stage, we gradually increased the forces until the layers were separated (Figure 6-c).


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Figure 6. Snapshots of the stamping process. (a) Graphene layer positioned above the MoS2 slab (b) and lowered kept intact for 5 ps. (c) Layers separated. Color code: Carbon: cyan, Sulfur: yellow, Molybdenum: grey Figure 7 demonstrates the efficiency of the potato stamp process, i.e. number of captured S atoms per defect on the graphene. For the mono vacancy cases, approximately one sulfur atom is captured for every two vacancies. This ratio is similar for the di-vacancy case, but if we consider number of missing carbon atoms, the efficiency would be higher in mono vacancy case. This is in good agreement with the energy barrier calculations (Figure 5).


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Figure 7. Efficiency of stamping process for three statistical replicas. Number of S atoms diffused to mono (squares) and di-vacancy (circles) sites in the graphene. Functionalization of the MoS2 Surface. Controlling vacancy defects on the MoS2 should have numerous applications such as biological, organo-metallic systems, catalysis and opto-electronic systems. In this study, to provide an example, we functionalized the MoS2 surface with S defects –that is created by using the potato stamp procedure, described previously- by letting epoxy molecules adsorb to the vacancy sites. We built a single layer of MoS2 with same dimensions used in the above-mentioned simulation and added the vacancy defects on the MoS2 structure by randomly deleting sulfur atoms. Thereafter, we included 100 Epoxybutane molecules (C4H8O) into the system (Figure 8-a) randomly with a minimum distance of 3 Å to the MoS2 surface.


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Figure 8 a) Initial configuration of system: MoS2 slab with sulfur vacancies and 100 Epoxybutane molecules (C4H8O) randomly distributed in the simulation box with a minimum distance of 3 Å to the MoS2 surface. After 2.5 ns simulation time all of the epoxy molecules bonded to the MoS2 surface: b) cross sectional view, c, d) perspective views of surfaces. Color code: Carbon: cyan, Sulfur: yellow, Molybdenum: pink, Oxygen: red. We ran the simulation for 2 ns at 700 K. At the end of the simulation we observed that all defect sites were filled with epoxy molecules via formation of O-Mo bonds. Figure 8 presents a snapshot of the system at the end of the simulation. Figure 9 focuses on two defect sites at the start (Figure 9-a, c) and end (Figure 9-b, d) of the simulation. It is visible in both Figure 9-b and Figure 9-d that epoxy molecules are bonded to the defect sites for both cases via O-Mo bonds.


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Figure 9 Snapshots of two defect sites (a, c). Epoxybutane molecules attach to the vacancy sites via O-Mo bonds (b, d). Vacancy sites are highlighted with dashed circles. Color code: Carbon: cyan, Sulfur: yellow, Molybdenum: silver, Oxygen: red. During the molecular dynamics simulation, we observed an interesting reaction which involves dissociation of an epoxy molecule. We captured consecutive snapshots focused on the defect site during the reaction. Dissociation starts with Epoxybutane molecule approaching to the vacancy site (Figure 10-a). The oxygen atom of the epoxy molecule makes a strong ionic bond with Mo atom underneath the vacancy site (Figure 10-b). This strong ionic bonding weakens the covalent C-O bonds in the Epoxybutane. The S atom next to the defect site, with a dangling bond due to vacancy, captures one of two carbon atoms bonded to O (Figure 10-c). Next, another S neighbor


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of the vacancy site captures the second C atom bonded to the oxygen (Figure 10-d). This reaction is similar to an earlier prediction of dissociation of water molecules on vacancy defects of MoS214 and indicates that sulfur vacancies in MoS2 can be used for functionalization of the surface.

Figure 10 Epoxy dissociation: epoxy molecule approaches to defect site (a), O atom of the epoxy molecule bonds to Mo (b), the epoxy loses one of its C atoms (c), the epoxy loses its second C atom (d). Color code: Carbon: cyan, Sulfur: yellow, Molybdenum: silver, Oxygen: red


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According to the concept presented here, organic molecules can be utilized for different applications. As an example, one can create vacancy sites and attach a large organic molecule such as DNA on the surface to design biosensor applications. Moreover, controlling location and density of vacancy site may lead the design of efficient catalytic surfaces. Conclusion: In this work, based on Nudged Elastic Band and molecular dynamics calculations using the ReaxFF reactive force field, we showed that mechanical stamping of graphene layer with vacancy sites to the MoS2 structure will result diffusion of S atoms to these sites. Our simulations with ReaxFF force field show that this method provides an attractive way to create sulfur vacancies on the surface with a precise control. Furthermore, we demonstrated that subsequent exposure of the newly created vacancy sites to a reactive gas atmosphere – epoxides, in our case, can provide highly controlled functionalization of the MoS2 material. Such engineering of the surface with atomistic resolution is crucial to develop advanced materials. Acknowledgements: This work was supported by NSF grant MIP/DMR 1539916. References: 1. Kam, K. K.; Parkinson, B. A., Detailed Photocurrent Spectroscopy of the Semiconducting Group-Vi Transition-Metal Dichalcogenides. J Phys Chem-Us 1982, 86, 463467. 2. Radisavljevic, B.; Radenovic, A.; Brivio, J.; Giacometti, V.; Kis, A., Single-Layer Mos2 Transistors. Nat Nanotechnol 2011, 6, 147-150. 3. Bissessur, R.; Heising, J.; Hirpo, W.; Kanatzidis, M., Toward Pillared Layered Metal Sulfides. Intercalation of the Chalcogenide Clusters Co(6)Q(8)(Pr(3))(6) (Q=S, Se, and Te and R=Alkyl) into Mos2. Chem Mater 1996, 8, 318-&. 4. Kuc, A.; Zibouche, N.; Heine, T., Influence of Quantum Confinement on the Electronic Structure of the Transition Metal Sulfide Ts2. Phys Rev B 2011, 83. 5. Yin, Z. Y.; Li, H.; Li, H.; Jiang, L.; Shi, Y. M.; Sun, Y. H.; Lu, G.; Zhang, Q.; Chen, X. D.; Zhang, H., Single-Layer Mos2 Phototransistors. Acs Nano 2012, 6, 74-80.


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6. Zhang, Y. J.; Ye, J. T.; Matsuhashi, Y.; Iwasa, Y., Ambipolar Mos2 Thin Flake Transistors. Nano Lett 2012, 12, 1136-1140. 7. Qiu, H.; Pan, L. J.; Yao, Z. N.; Li, J. J.; Shi, Y.; Wang, X. R., Electrical Characterization of Back-Gated Bi-Layer Mos2 Field-Effect Transistors and the Effect of Ambient on Their Performances. Appl Phys Lett 2012, 100. 8. Qiu, H., et al., Hopping Transport through Defect-Induced Localized States in Molybdenum Disulphide. Nat Commun 2013, 4. 9. Hong, J. H., et al., Exploring Atomic Defects in Molybdenum Disulphide Monolayers. Nat Commun 2015, 6. 10. Ataca, C.; Ciraci, S., Functionalization of Single-Layer Mos2 Honeycomb Structures. J Phys Chem C 2011, 115, 13303-13311. 11. Komsa, H. P.; Kotakoski, J.; Kurasch, S.; Lehtinen, O.; Kaiser, U.; Krasheninnikov, A. V., Two-Dimensional Transition Metal Dichalcogenides under Electron Irradiation: Defect Production and Doping. Phys Rev Lett 2012, 109. 12. Ma, Y. D.; Dai, Y.; Guo, M.; Niu, C. W.; Lu, J. B.; Huang, B. B., Electronic and Magnetic Properties of Perfect, Vacancy-Doped, and Nonmetal Adsorbed Mose2, Mote2 and Ws2 Monolayers. Physical Chemistry Chemical Physics 2011, 13, 15546-15553. 13. Raybaud, P.; Hafner, J.; Kresse, G.; Toulhoat, H., Adsorption of Thiophene on the Catalytically Active Surface of Mos2: An Ab Initio Local-Density-Functional Study. Phys Rev Lett 1998, 80, 1481-1484. 14. Ataca, C.; Ciraci, S., Dissociation of H2o at the Vacancies of Single-Layer Mos2. Phys Rev B 2012, 85. 15. Senftle, T. P., et al., The Reaxff Reactive Force-Field: Development, Applications and Future Directions. Npj Comput Mater 2016, 2. 16. van Duin, A. C. T.; Dasgupta, S.; Lorant, F.; Goddard, W. A., Reaxff: A Reactive Force Field for Hydrocarbons. Journal of Physical Chemistry A 2001, 105, 9396-9409. 17. Ostadhossein, A.; Rahnamoun, A.; Wang, Y. X.; Zhao, P.; Zhang, S. L.; Crespi, V. H.; van Duin, A. C. T., Reaxff Reactive Force-Field Study of Molybdenum Disulfide (Mos2). J Phys Chem Lett 2017, 8, 631-640. 18. Ashraf, C.; van Duin, A. C. T., Extension of the Reaxff Combustion Force Field toward Syngas Combustion and Initial Oxidation Kinetics. Journal of Physical Chemistry A 2017, 121, 1051-1068. 19. Kresse, G.; Furthmüller, J., Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169. 20. Blöchl, P. E., Projector Augmented-Wave Method. Phys. Rev. B 1994, 50, 17953. 21. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. 22. Hardcastle, T.; Seabourne, C.; Zan, R.; Brydson, R.; Bangert, U.; Ramasse, Q.; Novoselov, K.; Scott, A., Mobile Metal Adatoms on Single Layer, Bilayer, and Trilayer Graphene: An Ab Initio Dft Study with Van Der Waals Corrections Correlated with Electron Microscopy Data. Phys. Rev. B 2013, 87, 195430. 23. Ambrosetti, A.; Silvestrelli, P., Adsorption of Rare-Gas Atoms and Water on Graphite and Graphene by Van Der Waals-Corrected Density Functional Theory. The Journal of Physical Chemistry C 2011, 115, 3695-3702.


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24. Le, D.; Kara, A.; Schröder, E.; Hyldgaard, P.; Rahman, T. S., Physisorption of Nucleobases on Graphene: A Comparative Van Der Waals Study. J. Phys.: Condens. Matter 2012, 24, 424210. 25. Quiroga, M. A.; Cabeza, G. F., Role of Van Der Waals Forces in Graphene Adsorption over Pd, Pt, and Ni. Brazilian Journal of Physics 2013, 43, 126-129. 26. Grimme, S., Semiempirical Gga‐Type Density Functional Constructed with a Long‐Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787-1799. 27. Yun, Y. S.; Le, V.-D.; Kim, H.; Chang, S.-J.; Baek, S. J.; Park, S.; Kim, B. H.; Kim, Y.H.; Kang, K.; Jin, H.-J., Effects of Sulfur Doping on Graphene-Based Nanosheets for Use as Anode Materials in Lithium-Ion Batteries. J. Power Sources 2014, 262, 79-85. 28. Nakada, K.; Ishii, A., Migration of Adatom Adsorption on Graphene Using Dft Calculation. Solid State Commun. 2011, 151, 13-16. 29. Ma, Y. D.; Dai, Y.; Guo, M.; Niu, C. W.; Huang, B. B., Graphene Adhesion on Mos2 Monolayer: An Ab Initio Study. Nanoscale 2011, 3, 3883-3887. 30. Miwa, R. H.; Scopel, W. L., Lithium Incorporation at the Mos2/Graphene Interface: An Ab Initio Investigation. J Phys-Condens Mat 2013, 25. 31. Srinivasan, S. G.; van Duin, A. C. T.; Ganesh, P., Development of a Reaxff Potential for Carbon Condensed Phases and Its Application to the Thermal Fragmentation of a Large Fullerene. J Phys Chem A 2015, 119, 571-580. 32. Henkelman, G.; Jonsson, H., Improved Tangent Estimate in the Nudged Elastic Band Method for Finding Minimum Energy Paths and Saddle Points. J Chem Phys 2000, 113, 99789985. 33. Henkelman, G.; Uberuaga, B. P.; Jonsson, H., A Climbing Image Nudged Elastic Band Method for Finding Saddle Points and Minimum Energy Paths. J Chem Phys 2000, 113, 99019904. 34. Plimpton, S., Fast Parallel Algorithms for Short-Range Molecular-Dynamics. J Comput Phys 1995, 117, 1-19. 35. Stone, A. J.; Wales, D. J., Theoretical-Studies of Icosahedral C60 and Some Related Species. Chem Phys Lett 1986, 128, 501-503. 36. Banhart, F.; Kotakoski, J.; Krasheninnikov, A. V., Structural Defects in Graphene. Acs Nano 2011, 5, 26-41.


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Potato stamp concept: We all did once those beautiful potato stamps when we were kids. Carve your design on potato surface. Paint and stamp it on paper!

Same concept may work on nanoscale! Create vacancy defects on graphene sheet, stamp it on MoS2 surface. Sulfur atoms will diffuse to vacancy sites on graphene layer.

Lift the graphene layer with sulfur atoms diffused.


Defect Design of Two Dimensional MoS2 Structures by Using

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