Giant Gap-Plasmon Tip-Enhanced Raman Scattering of MoS 2 Monolayers on Au Nanocluster Arrays

Transcription

1 Giant Gap-Plasmon Tip-Enhanced Raman Scattering of MoS Monolayers on Au Nanocluster Arrays M.Rahaman, A.G. Milekhin,,3 E.E. Rodyakina,,3 A.V. Latyshev,,3 V.M. Dzhagan,, and D.R.T. Zahn Semiconductor Physics, Chemnitz University of Technology, D-97, Chemnitz, Germany Novosibirsk State University, Pirogov, 639, Novosibirsk, Russia 3 Rzhanov Institute of Semiconductor Physics RAS, Lavrentiev Ave. 3, 639, Novosibirsk, Russia V. Lashkaryov Institute of Semiconductors Physics, Nat. Acad. of Sci. of Ukraine, 38, Kyiv, Ukraine

2 Introduction/Motivation Tip-Enhanced Raman Spectroscopy Electrical field confinement C 6 CNT GO Limitation of Au conventional λ = Raman spectroscopy Au 785 nm w = (.8 ±.) nm Abbe diffraction limit: Spatial resolution =.6λ NA λ NA E / V m - E y 3 R = nm λ = 785 nm R = nm E fit 6 9 Lateral distance / nm wavelength of the light.5 V m - V m - numerical aperture nm of nmthe objective k Au 5 nm Sheremet et al.; Carbon COMSOL simulation

3 Experimental parameters 65 Sample 8 nm nm 5 nm 5 nm λ = 785 nm; x,.7 NA, 3 mw 3 SEM image

4 Si L-MoS /Nanocylinders heterostructure Optical image 6 nm L-MoS Intensity /cts s - 8 Micro-Raman spectra Exp E g A g Fit 9.9 cm - E g A g 53 nm, l/mm Raman shift /cm - AFM topography Intensity / cts s Au cylinders Photon energy / ev PL on MoS 53 nm Raman spectra of MoS + Si B A Wavelength / nm μm

5 TERS on L-MoS /Nanocylinders heterostructure TERS (39 3) cm -.5 Intenisty / cts 8 E z 65 E E x z A g TERS enhancement, E Electric field, E x TERS spectra y LA (M) + A u E g x Si nm.5 kcts E / V m Fit 8 5 = (..) nm E Raman shift / cm - (V m V m - ) nm, 6 l/mm, 3 mw approx Milekhin et al., Nanoscale, Laterial distance / nm x k y z E 3 nm 5

6 Enhancement factor and spatial resolution TERS (39 3) cm -. Milekhin et al., Nanoscale, Gauss fit to the edge + kcts 5 nm.5 Topography TERS enhancement E y k E Au λ = 785 nm R = nm EF hot spot L-MoS 6.5 X 6 (V m - ) (E / V m - ) x 6 EF = Contrast TERS = Contrast. 5 TERS 3 w = (5.3.) nm = 5. 8 nm 6 8 Au E fit R far R tip R far R hot spot Lateral distance / nm

7 Investigation of local heterogeneities Strain Peak position map Temperature rise Hot electron doping TERS (39 3) cm - 5 nm Milekhin et al., Nanoscale, kcts Normalized intensity cm - cm - / /5 / Raman shift/ cm

8 Investigation of local heterogeneities TERS (36 8) cm - E-6 nm nm E- E-3 E- V E- Topography E-5 kcts s - x cm - nm Rahaman et al., Nano Lett., (7), 7, 67 Raman shift / cm TERS intensity/ a.u Raman shift due to strain A u V E E E3 E E5 E6 cm - 3L-MoS.9 % strain Position Strain induced shift. cm - / /5 / cm Raman shift/ cm - Local heating effect.8 cm

9 Normalized intensity Raman shift / cm - Local heating due to hot spots formation Temperature dependent micro-raman study of 3L-MoS A g E g - C -5 C -5 C C 5 C 5 C 6 C C A g :. cm - /K E g :. cm - /K A g E g Fit Raman shift / cm Temperature / K Temperature rise in the hot spots =.8. 5 C 9

10 Quantifying hot electron doping Doping induced Raman shift = 6.7 cm - Doping gradient of phonon modes TERS intensity/ a.u. 5 5 cm - cm - / Raman shift/ cm /5 Hot electron doping of.6 3 cm - / 3 Lloyd et al.; Nano Lett. (6),6, % strain induced shift for A g.5 cm - Temperature induced shift for A g.8 cm -. Li et al.; ACS Nano (5),9, 58. Yu et al., Adv. Func. Mat. (6), 6, Najmaei et al., ACS Nano (), 8, 68 Chakraborty et al. Phys. Rev. B (), 85, 63(R) Doping gradient for A g mode =.3 3 cm - /cm -

11 Doping induced phase transition Plasmonic hot electron induced phase transition Kang et al. Adv. Mat.(),, 667

12 Doping induced phase transition Plasmonic hot electron induced phase transition 5 nm TERS (39 3) cm kcts Normalized intensity T- MoS Raman shift / cm - Milekhin et al., Nanoscale, 755 8

13 Normalized intensity Summary + 5 nm kcts Gauss fit to the edge TERS cm - EF = TERS 39 3 cm nm T- MoS.5..5 kcts 3 5 Estimated strain of.9 % and temperature rise of 5 C Plasmonic hot electron doping concentration of.6 3 cm Raman shift / cm - 3

14 Thank you for attention