Spectrally Tunable, Large Raman

Spectrally Tunable, Large Raman

Enhancement from Nonradiative Energy Transfer in van der Waals Heterostructure

Medha Dandu,

Kenji Watanabe,

Takashi Taniguchi,

Ajay K. Sood,

and Kausik Majumdar

†Department of Electrical Communication Engineering, Indian Institute of Science, Bangalore 560012, India

‡National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-044, Japan

¶Department of Physics,

Indian Institute of Science, Bangalore 560012, India E-mail: kausikm@iisc.ac.in

3 6 9 12 0

10 20 30

Thickness (nm)

Distance (mm)

1 2 3

0 3 6 9 12

Thickness (nm)

Distance (mm)

11 nm

11 nm

(a) (b)

(c) (d)

J

J

Figure S1: Optical images and AFM of samples J1 and J2. (a,b) Optical images of WS₂/SnSe₂ sample, J₁ and MoS₂/SnSe₂ sample, J₂. Dashed lines highlight 1L-TMD (pink) and SnSe2 (green) regions. Scale bar is 5 µm. (c,d) Step height proles of SnSe2 along the white arrows in (a,b) obtained from AFM scans.

1 2 3 4 5 6

0 3 6 9

Thickness (nm)

Distance (m)

0.5 1.0 1.5

0 10 20 30 40

Thickness (nm)

Distance (m) 1 2 3 4 5 6 7 8

0 3 6 9 12

Thickness (nm)

Distance (m)

5.5 nm

8 nm

(b)

40 nm

(a)

(c)

40 nm

Figure S2: Optical images and AFM of MoS2/SnSe2 samples. Optical images of MoS2/SnSe2 samples and corresponding AFM step height proles along the white arrows in optical images depicting the thickness of SnSe₂. Scale bar is5 µm.

0.5 1.0 1.5 2.0 2.5 3.0 3.5 0

3 6 9

Thickness (nm)

Distance (m)

1 2 3 4 5 6

0 10 20 30

Thickness (nm)

Distance (m)

B A B

A

hBN on top

15 nm 9 nm

0.2 0.4 0.6 0.8 1.0 0

3 6 9 12

Thickness (nm)

Distance (m) 9.8 nm

1 2 3 4

0 3 6 9

Thickness (nm)

Distance (m) 1 2 3

0 3 6 9 12 15

Thickness (nm)

Distance (m) 9 nm

13.2 nm

B A

A B

(b)

(c)

9 nm

Figure S3: Optical images and AFM of MoS2/hBN/SnSe2 samples. Left panel shows the optical images of MoS2/hBN/SnSe2 samples. Scale bar is 5 µm. Dashed lines highlight the regions of MoS₂ (pink), hBN (yellow) and SnSe₂ (green) regions. Middle panel shows the corresponding AFM step height proles of hBN along the yellow arrow in optical images. Right panel shows the corresponding AFM step height proles along the white arrow in optical images from which SnSe₂ thickness is extracted.

1 2 3 0

10 20

Thickness (nm)

Distance (mm)

0.5 1.0 1.5

0 3 6 9

Thickness (nm)

Distance (mm) 18 nm

8.5 nm

1 2 3 4 5 6 7

0 10 20 30 40 50 60

Thickness (nm)

Distance (mm) 35nm

25nm

(c) (b) (a)

Figure S4: Optical images and AFM of MoS2/hBN samples. Optical images of MoS₂/hBN samples (left panel) with the corresponding AFM step height proles of hBN (right panel) along the yellow arrow in optical images. Scale bar is 5 µm. Region of hBN (MoS2) is marked with yellow (pink) dashed line in optical images.

5 10 15 20 25 30 35 40 0

3 6 9 12 15

0 1 2 3 4

PL intensity ratio Raman intensity ratio

5 10 15

404.5 405.0 405.5 406.0

1L-MoS2/SnSe2

1L-MoS2

A1g peak position (cm-1)

5 10 15

4 5 6

A1g FWHM (cm-1)

5 10 15

405.25 405.50 405.75

A1g peak position (cm-1)

Thickness of SnSe₂ (nm)

5 10 15

5.0 5.5 6.0 6.5 7.0

A1g FWHM (cm-1)

Thickness of SnSe₂ (nm) 633 nm

633 nm 633 nm

532 nm 532 nm

(d) (e)

5 10 15

384.5 385.0

E1 2g peak position (cm-1)

Thickness of SnSe₂ (nm) 532 nm

(f)

Figure S5: Raman characterization from MoS2/SnSe2 samples. (a,b) MoS2 A_1g peak position and FWHM with 633 nm excitation from isolated (blue) and junction (green) regions. (c) PL intensity ratio versus Raman intensity ratio across dierent MoS₂/SnSe₂ samples under 633 nm excitation emphasizing contribution of NRET and dierence in their enhancement factors. (d,e) Peak position and FWHM of MoS₂ A_1g with532 nm excitation.

(f) MoS₂ E_2g¹ peak position from isolated and junction regions from532 nm Raman spectra.

1.8 2.0 2.2



R/R of SnSe

Energy (eV) 12 nm SnSe₂ at 4 K

Figure S6: Dierential reectance spectroscopy on SnSe₂. Broad ^∆R_R spectra of12 nm SnSe2 from dierential reectance spectroscopy at 4K.

1.8 2.0 2.2 2.4 2.6 Energy (eV)

1.83702 1.9291 2.03255 2.14939 273

313 353 393 433

Energy (eV)

Temperature (K)

0.000 0.2500 0.5000 0.7500 1.000

250 300 350 400 450 -0.4

-0.3 -0.2 -0.1

DR/R minima

Temperature (K)

250 300 350 400 450 1.94

1.96 1.98 2.00 2.02

2.04 DR/R minima

532 nm PL

A1s peak position (eV)

Temperature (K)

243 K 453 K

(a) (b) (c)

(d)

Figure S7: Temperature dependent Dierential reectance spectroscopy on WS₂ in sample J1. (a)^∆R_R spectra from isolated WS2at dierent temperatures from243K to453 K which represent shift ofA_1sexciton peak. (b) Temperature versusA_1speak energy contour plot from WS₂ ^∆R_R spectra where blue region depicts the ^∆R_R minima. (c)A_1s peak position as a function of temperature extracted from ^∆R_R minima and 532nm PL. (d) Strength of ^∆R_R minima as a function of temperature which shows relative similar oscillator strength of WS2

from243 K to 453 K.

250 300 350 400 450 5

6 7 8 9

WS2/SnSe2 WS2

A1g Total FWHM (cm-1)

Temperature(K)

250 300 350 400 450 416

417 418 419 420

421 ^WS _WS^2/SnSe2

2

A1g peak position (cm-1)

Temperature(K)

250 300 350 400 450 0

1 2 3

PL Intensity Ratio at 1.9426 eV

Temperature(K)

250 300 350 400 450 0.00

0.25 0.50 0.75

1.00 WS2/SnSe2

Normalized PL Intensity at 1.96 eV

Temperature(K) 633 nm

250 300 350 400 450 5

10 15 ^{WS2 X}

WS2 T

PL intensity (x103 counts)

Temperature(K) 250 300 350 400 450 25

30 35 40 45

50 WS2 532 nm A1s peak Linear fit

Total FWHM (meV)

Temperature (K)

532 nm

532 nm

(d) (e) (f)

Figure S8: Temperature dependent Raman and PL characterization of WS2/SnSe2 sample, J1. (a,b) Temperature versus WS2 A_1g FWHM and position on isolated (blue) and junction (green) regions from 633 nm excitation. (c) FWHM of WS₂ A1s exciton as a function of temperature and the corresponding linear t. (d) 633 nm PL intensity ratio (at 1.9426 eV) of WS2/SnSe2 which exhibits modulation with temperature similar to η_{N RET} discussed in the main text. (e) Normalized532 nm PL intensity at 1.96 eV exhibiting maximum at the temperature close to 633 nm excitation resonance. (f) Exciton (X) and Trion (T) peak intensities as a function of temperature with 532 nm excitation.

1.94 1.96 1.98 2.00 2.02 2.04 1

2 3 4 ^J1

J₃

Raman intensity Ratio

Exciton peak position (eV) 0.5 1.0 1.5 2.0 2.5

0 3 6 9 12

Thickness (nm)

Distance (mm) 10.5 nm

J₃

(a) (b) (c)

Figure S9: Raman enhancement characteristics of another WS2/SnSe2 sample, J3. (a) Optical image of J3 with WS2 and SnSe2 marked by pink and green dashed lines respectively. Scale bar is5µm. (b) SnSe₂ thickness prole from AFM along the white arrow in (a). (c) 633 nm WS2 Raman intensity ratio as a function of exciton peak position from

1.80 1.85 1.90 1.95 2.00 2.05 2.10 Energy (eV)

1.80 1.85 1.90 1.95 2.00 2.05 2.10 Energy (eV)

1.80 1.85 1.90 1.95 2.00 2.05 2.10 Energy (eV)

1.80 1.85 1.90 1.95 2.00 2.05 2.10 Energy (eV)

T = 293 K

T = 423 K

T = 453 K

T

T

T

X

X

X

1.96 eV

T X

T = 243 K

Figure S10: Temperature dependent PL spectra of isolated WS₂ from WS2/SnSe2 sample, J1. PL spectra obtained from 532 nm excitation of isolated WS2

at four dierent temperatures with corresponding tting of exciton (X) and trion (T) peaks.