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Supporting Information
Tip-enhanced Raman Spectroscopy: Bridging the Gap between Experiments and Theory
Mahfujur Rahaman,1 Alexander G. Milekhin,2,3 Ashutosh Mukherjeee,1 Ekaterina E. Rodyakina,2,3 Alexander
V. Latyshev,2,3 Volodymyr M. Dzhagan,1 and Dietrich R. T. Zahn1
1. Semiconductor Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany
2. Rzhanov Institute of Semiconductor Physics RAS, Lavrentiev Ave. 13, 630090 Novosibirsk, Russia
3. Novosibirsk State University, Pirogov 2, 630090 Novosibirsk, Russia
4. Lashkaryov Institute of Semiconductors Physics, National Academy of Sciences of Ukraine, 03028 Kyiv, Ukraine
Email: [email protected]
Figure S1:
Figure S2:
Figure S2: (a) Typical SEM and (b) AFM images of the Au nanodisks prepared by electron beam lithography.
The diameter and the height of each disk are 110 nm and 50 nm, respectively. A height profile between the
two disks is shown in the inset of figure (b).
200 nm
110 nm
Au nano cylinders
0
50
nm
0.0 0.1 0.20
10
20
30
40
50
Z / n
m
X / m
46 0.5 nm
(a) (b)
Figure S1: (a) A typical SEM image of a TERS tip prepared by evaporating Au on a silicon cantilever. (b) A magnified SEM image of a TERS tip revealing the formation of Au nanoclusters at and around the tip.
(a) (b)
100 nm2 μm
Electronic Supplementary Material (ESI) for Faraday Discussions.This journal is © The Royal Society of Chemistry 2018
Figure S3:
Figure S4:
Figure S3: Optical (a) and AFM (b) images of the sample after 1L-MoS2 flake transfer onto the plasmonic substrate (a). 1L-MoS2 is marked by a circle in optical image and a black dotted line is made along the
border of the flake as the guide for the sight.
0
60
nm
1l-MoS2
10 μm
MoS2
Au nanoclusters
(a) (b)
Au cylinders 2 μm
Figure S4: (a) Micro-Raman and (b) the photoluminescence spectra of MoS2 sample shown in figure S2.
The frequency difference and the high PL yield confirm the presence of monolayer MoS2.
550 600 650 7000
200
400
600
800
1000 A
Inte
nsity / c
tss
-1
Wave length / nm
PL on MoS2
Raman spectra of
MoS2 + Si
B
300 350 400 450 5000
40
80
120
Inte
nsity /ctss
-1
Raman shift /cm-1
Exp
E2g
A1g
Fit19.9 cm
-1
E2g
A1g
(a) (b)
Figure S5:
Figure S5: FEM simulation of TERS sensitivity on different substrate. TERS enhancement image of (a) Au – Au, (b) Au – (2 nm SiO2) – Si, and (c) Au – SiO2 tip – sample system; whereas (d) Au tip alone. The excitation energy and tip radius used I the calculation are 785 nm and 40 nm. The tip – substrate distance is kept at 1 nm for the simulation. Interestingly, even on SiO2 substrate there is a small enhancement compared to tip alone due to slight reflective nature of the substrate originated from the change in refractive index at the air/SiO2 interface and in agreement to the literature.1 The electric field enhancement ratio between Au – Au and Au – SiO2 is 9 at 1 nm tip – substrate distance. In order to determine the lateral confinement of the field, cross sections are taken along the surface line of the substrates in (a) – (c) and presented in (e) – (g) respectively.The line the shape of the lateral distribution of the fields changes from substrate to substrate and also getting narrower with increasing plasmonic interaction between the tip and substrate. Each field profile is fitted to determine the FWHM of the individual system. Compared to Au – SiO2 system in (g), Au – (2 nm SiO2) – Si in (f) has higher enhancement and also FWHM due to strong contribution from Si. The FWHM of Au – Au system is 13.7 nm, a very good agreement to equation
4 in the main text.
80 90 100 110 1200
10
20
30
40
E / Vm
-1
Laterial distance / nm
Eloc
Fit
Au - Au
FWHM = 13.7 nm
30 60 90 120 150 180
1
2
3
4
5
Eloc
Fit
E / Vm
-1
Laterial distance / nm
Au - SiO2
FWHM = 84.2 nm
50 100 150
0
3
6
9
12
E / Vm
-1
Laterial distance / nm
Eloc
Fit
Au - Si/SiO2
FWHM = 26.2 nm
λ = 785 nm
R = 40 nm
Au
Au
E
k
Au
Si
SiO2
2 nm
SiO2
Au Au
40 nm0
2.5
E / V
·m-1
0
4.5
0
12
0
42
E / V
·m-1
E / V
·m-1
E / V
·m-1
(a) (b) (c) (d)
(e) (f) (g)
Figure S6:
Reference
1. S. Trautmann, J. Aizpurua, I. Go ̈tz, A. Undisz, J. Dellith, H. Schneidewind, M. Rettenmayr and V. Deckert, Nano-
scale, 2016, 9, 391
Figure S6: Influence of plasmonic substrate on spatial resolution. (a) Normalized E4 profiles taken along the tip radius when tip is at the center and when tip is at the edge as shown in Figure 5 in main text. (b) PseudoVoigt fitting of the E4 at the center, and (c) asymmetric Voigt fitting at the edge. As can be seen, the FWHM of the E4 is smaller at the edge than at the center. Which implies that the spatial resolution not
only depends on the product of √(𝑅𝑑) in equation 4 in the main text but also on the size and shape of the substrate.
0 10 20 30 40 50
Norm
aliz
ed E
4
Lateral distance / nm
Center
Edge
0 10 20 30 40 50 60
Center
fit
FWHM = (7.1 0.1) nm
Norm
aliz
ed E
4
Laterial distance / nm0 10 20 30 40 50 60
Norm
aliz
ed E
4
FWHM = (5.7 0.1) nm
Edge
fit
Laterial distance / nm
(a) (b) (c)