Supporting Information
The Effect of Dielectric Constants on Noble Metal/Semiconductor SERS Enhancement:
FDTD Simulation and Experiment Validation of Ag/Ge and Ag/Si Substrates
Tao Wang1,2, Zhaoshun Zhang1, Fan Liao1, Qian Cai1, Yanqing Li1,*, Shuit-Tong Lee1 & Mingwang
Shao1,*
1
Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-based
Functional Materials and Devices& Collaborative Innovation Center of Suzhou Nano Science and
Technology, Soochow University, Suzhou, Jiangsu 215123, P. R. China
2
Anhui Key Laboratory of Functional Coordination Compounds, Anqing Normal University, Anqing
246011, People’s Republic of China
1
1. Finite-Difference Time Domain (FDTD) Simulations:
The 3D finite-difference time-domain method was used to calculate the electric field by the
Lumerical FDTD Solutions software. A schematic illustration of the model was showed in
Figure S1. Briefly, two noble metal spheres (Au or Ag) with a diameter of 40 nm were placed
on a Ge or Si substrate, with a gap of 5nm between them. A linearly polarized plane wave of a
certain wavelength (514nm or 633 nm) was incident perpendicularly to the substrate from the
top of the dimeric noble metal spheres. A non-uniform grid size was used for the overall
simulation volume, which varies with the refractive index of each material. In order to best
capture the electric field in the vicinity of noble metal-dielectric material interfaces, a small
region of 110 nm × 70 nm × 70 nm containing the two noble metal spheres and part of the
substrate was set with a grid of 0.5 nm. The simulation time was set at 500 fs to ensure the
fields to decay completely before termination of the simulation. To obtain the electric field
distribution, a plane monitor was placed parallel to the substrate with the same height of the
centre of the noble metal spheres.
Figure S1. Schematic representation of noble metal/semiconductor substrate in the FDTD
calculation.
2
2. Intensity (  E  ) distributions of one silver nanoparticle on Ge wafer
2
Figure S2. Intensity (  E  ) distributions obtained from 3D FDTD calculations at wavelength
2
633nm of one silver nanoparticle with 40 nm diameter on Ge wafer.
3. XRD pattern of Ag NPs on Ge wafer
Figure S3. The XRD pattern of Ag NPs on Ge wafer: In addition to the diffraction peaks of
Ge and GeO2, the others may be indexed as (111) and (200) crystal planes of silver (JCPDS.
04-0783).
3
4. The SEM images of Ag NPs grown on Ge wafer
Figure S4. The SEM images of Ag NPs on Ge wafer prepared by AgNO3 with different
concentration for different reaction time: 1 × 10-5 M AgNO3 for 20 min (a); 1 × 10-4 M
AgNO3 for 20 min (b); 1 × 10-3 M AgNO3 for 10 min (c) and 1 × 10-2 M AgNO3 for 10 min
(d).
5. The size distribution histogram of Ag NPs grown on Ge wafer
Figure S5. The size distribution histogram of Ag NPs grown on Ge wafer from SEM image
(Fig. 2b) based on 300 particles
4
6. Schematic to illustrate the process of the SERS detection
Figure S6. Schematic to illustrate the process of the SERS detection
5
7. The normal Raman spectrum of 0.01 M R6G methanol solution
Figure S7 shows the characteristics of the Raman spectra of 0.01 M R6G methanol solution.
The band at 1130 cm-1 was assigned to C-H in-plane bending modes. The C-C stretching
vibration bending mode is 1181 cm-1. The bands at 1366, 1515, 1580, and 1654cm-1 are
assigned to the aromatic C-C stretching modes.
Figure S7. The normal Raman spectrum of 0.01 M R6G methanol solution.
8. Histograms of normalized Raman intensities of R6G (1 × 10-10 M) on the as-prepared
Ag/Ge substrate.
Figure S8. Histograms of normalized Raman intensities of R6G (1 × 10-10 M) on the asprepared Ag/Ge substrate.
6
9. EF calculation of the as-prepared Ag/Ge substrate:
The average SERS EF was calculated according to the formula:
EF=
I SERS N 0
I 0 NSERS
where I0 and ISERS are the peak intensity of the Raman measurement with 0.01 M R6G
solution and SERS measurement with 1×10-10 M R6G solution, respectively; N0 and NSERS are
the number of R6G molecules in the scattering volume for the Raman measurement and
SERS measurement, respectively.
N0  n0 N A  C0V0 N A ;
N SERS  nSERS N A  CSERSVSERS N A ;
I SERS N 0
I SERS C0V0 N A
I SERS C0 59111102
So, EF 
=
= 1.3 × 109;


I 0 N SERS I 0CSERSVSERS N A I 0CSERS 454 11010
where n0 and nSERS are the amount substance of R6G molecules in the scattering volume; V0
and VSERS are the scattering volume (V0 = VSERS); C0 and CSERS are the concentration of R6G
solution. The subscripts 0 and SERS represent Raman measurement and SERS measurement,
respectively. A is the area of laser spot; h is the laser spot depth of focus; NA is Avogadro
constant.
7
10. The SEM images of Ag NPs growing on Si wafer
Figure S9. The SEM images of Ag NPs growing on Si wafer
11. The size distribution histogram of Ag NPs grown on Si wafer
Figure S10. The size distribution histogram of Ag NPs grown on Ge wafer from SEM image
(Fig. S8) based on 300 particles
8
12. The Raman spectrum of R6G aqueous solution (1 × 10-9 M) on the as-prepared Ag/Si
substrate (upper part), and the SERS contour (lower part)
Figure S11. The Raman spectrum of R6G aqueous solution (1 × 10-9 M) on the as-prepared
Ag/Si substrate (upper part), and the SERS contour (lower part).
9
13. The intensities of the main Raman vibrations of R6G aqueous solution (at 1 × 10-9
M) in the 200 spots SERS line-scan spectra collected on the as-prepared Ag/Si substrate.
Figure S12. The intensities of the main Raman vibrations of R6G aqueous solution (at 1 × 109
M) in the 200 spots SERS line-scan spectra collected on the as-prepared Ag/Si substrate.
14. Histograms of normalized Raman intensities of R6G (1 × 10-9 M) on the as-prepared
Ag/Si substrate.
Figure S13. Histograms of normalized Raman intensities of R6G (1 × 10-9 M) on the asprepared Ag/Si substrate.
10
15. The normal Raman spectrum of MBA powder.
Figure S14. The normal Raman spectrum of MBA powder.
16. Histograms of normalized Raman intensities of MBA (1 × 10-9 M) on the as-prepared
Ag/Ge substrate.
Figure S15. Histograms of normalized Raman intensities of MBA (1 × 10-9 M) on the asprepared Ag/Ge substrate.
11
17. UV-Vis spectrum of the as-prepared Ag/Ge substrate.
The extinction spectrum of the as-prepared Ag/Ge substrate was recorded on a Thermo
Scientific Evolution 220 UV–visible spectrophotometer. As shown in Figure S12, there is a
peak at 365 nm, which is the surface plasmon resonance caused by Ag nanoparticles.
Figure S16. The extinction spectrum of the as-prepared Ag/Ge substrate.
12