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Metallic contact between MoS2 and Ni via Au nanoglue

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González, Sebastiaan van Dijken, Matti Alatalo, Wei Cao* 36 38 40 42 44 46 48 50 52 Au(200) Ni(200) Ni(111) Au(111) MoS2(105) MoS2(006) MoS2(103) Intensity (a.u.) 2T(degree) MoS2(102)

Figure S1. Powder X-ray diffraction of sample (MoS2)92.9Ni4.2Au2.9.

XRD patterns are indexed to phases of MoS2 (102), (103), (006), (105), and Ni (111), (200).

The Au (111) and (200) were also identified. A mean crystal size of AuNPs in the product was calculated to ~16 nm by fitting the Scherrer equation via the Rietveld method. It is worth

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Figure S2. TEM-EDS line-scan results.

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1200 1000 800 600 400 200 0

In

te

nsity (a.u.)

Binding Energy (eV)

Ni3p3 Au 4f Si 2p Ni3s S 2p3 S 2s Mo 3d5 C 1s Au 4d Mo 3p3 Mo 3s O 1s Ni 2p3 O KLL Ni 2s 880 875 870 865 860 855 850 845 In te nsity (a.u.)

Binding Energy (eV) Ni, sat NiOOH NiO Ni metal 240 235 230 225 In te nsity (a.u.)

Binding Energy (eV) Mo4+ oxides Mo6+ oxides MoS2 S 2s 172 170 168 166 164 162 160 158 In te nsity (a.u.)

Binding Energy (eV) Sulfate MoS2 92 90 88 86 84 82 In te nsity (a.u.)

Binding Energy (eV)

d c e f Au3+ Au metal 540 535 530 525 In te nsity (a.u.)

Binding Energy (eV)

Survey Ni 2p S 2p O 1s Au 4f Mo 3d Oxides Hydroxides Oxyhydroxides

Figure S3. XPS analysis of the synthesized MoS2-Au-Ni complex. (a) survey scan, (b) Ni 2p,

(c) Mo 3d, (d) S 2s, (e) Au 4f, (f) O 1s. In panel b - e, experimental spectra (scatter plots) are deconvoluted into multi-peaks, and doublet peaks are shaded with identical colors. Plots in grey and wine colors are the baselines and fitting envelopes, respectively.

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Figure S4. Synthesis and characterization of samples in control group. (a) List of synthesized samples and comparative ones in control group. The molar ratios of MoS2, Ni and Cl- were

kept the same in each group, and converted to weight percentages listed in the table. (b) SEM image of sample (MoS2)93.6Ni4.3Cl2.1, which was designed to make comparison with sample

(MoS2)92.9Ni4.2Au2.9. In the figure, most MoS2 flakes are in multilayer form, and well

separated from NiNPs. Even in the case that NiNPs appeared in the surrounding of MoS2,

NiNPs are more likely to aggregate together rather than joining to the MoS2 flakes.

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Figure S5. Introduce NiNPs onto large-scale MoS2 and MoSe2 crystals. (a) NiNPs decorated

on MoS2 crystals. (b) A zoomed-in region marked in (a). (c) EDS spectrum of the interface

region marked in (b). (d) NiNPs decorated on MoSe2 crystals. (e) A zoomed-in region shown

in (d). (f) EDS spectrum of the interface region shown in (e). A strong peak at 1.7 keV comes from the Si substrate.

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Figure S6. EDS determination. Before conductive-AFM measurements, samples were first investigated under SEM for efficient locating on candidate flakes. Then EDS was employed for elemental confirmation. Silicon signals come from the Si substrates.

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0 1 2 3 4 5 10 100 1000 U(Ni-MoS2) U(Ni-Au-MoS2) Resistivity ( :˜ mm) Voltage (V)

Figure S7. Estimation of electrical resistivity of Ni-Au-MoS2 and Ni-MoS2 contacts.

The electrical resistivity of the two contacts are calculated by Equation S1:

U = Rc·A/L (1)

where U, Rc, A, and L represent electrical resistivity, contact resistance, contact area and

contact length, respectively. For a rough estimation, Rc is approximately replaced by Rt1 and

Rt2. Taking the tip area as the contact area and the distance between tip and Au substrate film

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Figure S8. Full view of (a) original and (b) rotated PEEM images.

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Figure S9. SEM image taken before and after synchrotron radiation based PEEM experiments. (a) Before PEEM, taken on 21 Jan. 2015. (b) After PEEM, taken on 25 Feb. 2015. Both images were taken at the Center of Microscopy and Nanotechnology, Oulu, Finland. PEEM experiments were carried out on 15 Feb. 2015, at Max IV laboratory, Lund, Sweden. The joint regions between MoS2 and Ni are kept stable and intact after the exposure to synchrotron

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the MoS2 (100) surface without contact is plotted with red curves, while gray curves represent

band structure of Mo24S48Au46Ni92 supercell. The silver, orange, purple and yellow spheres

represent the Ni, Au, Mo and S atoms, respectively.

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Figure S11. Geometric structures and charge density difference for both models. The red region shows the charge accumulation, while the blue region represents the charge depletion. Panel (a) and (b) present optimized geometry of the Mo24S48Au30 supercell (type-I contact).

Panel (c) and (d) are optimized geometry of the Mo24S48Au6Ni72 supercell (type-II contact).

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-30 0 30 60 90 120 0.0

Time (min)

MoS2-Au

MoS2-Au-Ni

Figure S12. Photodegradation of methylene blue (MB) under UV light irradiation. During photolysis process (without catalyst, see the blank curve), the concentration of MB iskept nearly unchanged, suggesting that the self-degradation is slow even when exposed under UV irradiation. Commercial MoS2 and Au-decorated MoS2 show weak photocatalytic ability. In

the case of synthesized MoS2-Au-Ni ternary complex, the concentration of MB reduces

drastically during the first 30 min, and is almost degraded after 90 min.

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0 100 200 300 400 500 600 700 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 Cantilever Deflection (V) Z position (nm) Piezo Retraction 'V Setpoint 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 10 20 30 40 Contact Force (nN) Setpoint (V)

Figure S13. Investigation of the reliability of C-AFM measurements. (a) Cantilever performance under the setpoint of 1.0 V. (b) Contact force under different setpoint voltages.

The contact force can be calculated by Hooke’s Law: F = k·d, where k is the spring constant of the cantilever (0.18 N/m for the tip used in this work) and d is deflection. The deflection can be obtained by the relation: d = 'V·S, where 'V is the difference between the

minimum cantilever deflection and the deflection in the original state, S is deflection sensitivity which can be calculated by the slope of Piezo Retraction curve.

-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 -400 -200 0 200 400 Experimental Fitting

C-AFM current (nA)

Voltage (V) Equation y = a + b*x Plot B Weight No Weighting Intercept 22.89125 ± 6.97889 Slope 2087.86476 ± 57.28164

Residual Sum of Squares 14027.01766

Pearson's r 0.99403

R-Square(COD) 0.9881

Figure

Figure S1. Powder X-ray diffraction of sample (MoS 2 ) 92.9 Ni 4.2 Au 2.9 .
Figure S2. TEM-EDS line-scan results.
Figure S3. XPS analysis of the synthesized MoS 2 -Au-Ni complex. (a) survey scan, (b) Ni 2p,  (c) Mo 3d, (d) S 2s, (e) Au 4f, (f) O 1s
Figure S4. Synthesis and characterization of samples in control group. (a) List of synthesized  samples and comparative ones in control group
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