Submitted to
Supporting Information
for
Ultrafine and Smooth Full Metal Nanostructures for Plasmonics
By Xinli Zhu, Yang Zhang, Jiasen Zhang*, Jun Xu, Yue Ma, Zhi-Yuan Li and Dapeng Yu*
[*]
X. L. Zhu, Y. Zhang, Prof. J. S. Zhang, J. Xu, Y. Ma, Prof. D. P. Yu
State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University,
Beijing 100871 (P. R. China)
E-mail: [email protected]; [email protected];
Prof. Z. Y. Li
Institute of Physics, Chinese Academy of Sciences,
Beijing 100190 (P. R. China)
*Email: [email protected]; [email protected]
Contents
1. Atomic force microscopy (AFM) characterization………………………………………2
2. Various patterned silver structures with 60 nm and 600 nm height……………………...3
3. CL spectra of nanocavities with different side length……………………………………4
4. FDTD simulation and analytical results………………………………………………….5
5. Fabrication of patterned metals and CL characterization………………………………...6
A. Focused ion beam (FIB) milling and CL characterization…………………………..6
B. EBL/RIE/metal deposition and CL characterization………………………………...8
C. EBL/metal deposition and CL characterization……………………………………...11
D. Metal deposition/EBL/metal deposition/lift off and CL characterization…………...13
E. TS method combined with PMMA as a template (our technique), CL characterization,
and simulated reflectivity of different height metal reflectors……………………….16
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1. Atomic force microscopy (AFM) characterization
Figure S1. Typical AFM images of different surfaces. (a) A silicon wafer. (b) PMMA layer
on a silicon substrate. (c) Silver film which is stripped off the silicon wafer corresponding to
the exposed region in our experiment. (d) Silver film which is stripped off the PMMA
corresponding to the unexposed region in our experiment. (e) Top surface of 1 μm thick silver
film which is directly deposited on the silicon wafer. (f) Top surface of 1 μm thick silver film
which directly deposited on the PMMA layer. RMS roughnesses are indicated on each image.
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2. Various patterned silver structures with 60 nm and 600 nm height
Figure S2. Typical SEM images of various silver nanostructures. The height of all the
patterns is 60 nm. (a) A grating with a 375 nm pitch and a 70-nm-width groove. (b) A grating
with a 360 nm period and 76-nm-width ridges. (c) A coaxial cylinders separated by a 115 nm
annular-shaped groove and the diameter of the center cylinder is 145 nm (inset is the top view
SEM); (d) A equilateral-hexagonal cavity with a 435 nm side length, which consists of six
cuboids (inset is the top view SEM); (e) A bull’s eye with 350-nm-wide circular grooves
spaced every 560 nm, the diameter of the center hole is 155 nm; (f) A hexagonal array of 220
nm-diameter nano-pillars spaced by 375 nm (center to center); (g) English letters and Arabic
numerals.
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Figure S3. Typical SEM images of various silver nanostructures. The height of all the
patterns is 600 nm. (a) A equilateral-triangle cavity with a 1570 nm side length; (b) A
cylinder with a 1980 nm diameter. (c) A square-shaped plateau with a 1990 nm side length.
(d) A 1820 nm-side length equilateral-triangle bump pair with a 125 nm gap; (e) A 925 nmdiameter cylinder pair with a 48 nm gap; (f-h) Magnified images of (c-e), respectively; (i) A
tapered structure with gap down to 18 nm.
3. CL spectra of nanocavities with different side length.
Figure S4. CL spectra of four plasmonic nanocavities. The height of all the cavities is 300 nm.
CL spectra of nanocavities with cavity length 430, 500, 610 and 720 nm. The marked
resonant wavelengths correspond to the lowest plasmonic mode (1, 3).
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4. FDTD simulation and analytical results
Figure S5. Numerical simulations of the mode patterns and the characteristics of the
plasmonic reflector with a 300 nm height by FDTD. (a, b) Simulated mode patterns of the inplane and out-of-plane field components of SPPs at a vacuum wavelength of 818 nm for the
cavity that is the same as the 935-nm side length cavity in the experiment, respectively. In the
calculation, a focused wave is incident upon a side from the top of the cavity to excite SPPs.
The intensities of the in-plane and out-of-plane components of SPPs on the silver surface are
calculated and recorded. (c) Simulated reflectivity and refection phase shift of the out-ofplane component of SPPs for the cavity reflectors. The refection phase shift of the in-plane
component is near 0 (not shown here). We calculate the reflection phase shift and reflectivity
of SPPs using two-dimensional FDTD. Assuming that a SPP wave propagates along the xaxis at the silver/air interface (x-y plane), the SPP wave is reflected by a silver reflector
normal to the x-y plane with a height of 300 nm.
Figure S6. Analytical mode patterns with the boundary condition E = 0. (a, b) Analytical
mode patterns of (2, 10) and (3, 9) modes, respectively. (c) The mixed pattern of (a) and (b)
which is obtained by adding the intensities of (a) and (b) directly.
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5. Fabrication of patterned metals and CL characterization
A. Focused ion beam (FIB) milling and CL characterization
A 2μm thick silver layer was deposited on a silicon wafer by magnetron sputtering
deposition. Desired patterns were performed on the silver surface using a dual-beam FEI
DB235 FIB workstation. The structures were milled using 30kV Ga+ beam and 10 pA ion
beam current. Figures S7-8 b and c show the silver films have very rough surfaces after the
FIB milling owe to polycrystalline silver. The CL results reveal there is only a very broad
peak, no resonant wavelength and plasmonic mode in the measurement range.
Figure S7. CL spectra and SEM images of the equilateral-triangle cavity with a 1850 nm side
length. The cavity has very rough surface and about 200~400 nm high walls. (a) CL spectra
for the electron beam excited from the vertex to the middle point of opposite side of the cavity
with a step size of 160 nm. Spectra are offset vertically for clarity. (b,c) Top view and 52°
tilted SEM images of the cavity, which is fabricated by FIB milling. (d,e) SEM and
panchromatic CL images, which were obtained simultaneously. The violet dashed arrow
indicates line scan direction. Scale bars are 500 nm.
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Figure S8. CL spectra and SEM images of the equilateral-triangle cavity with a 900 nm side
length. The cavity has very rough surface and about 200~400 nm high walls. (a) CL spectra
for the electron beam excited from the vertex to the middle point of opposite side of the cavity
with a step size of 110 nm. Spectra are offset vertically for clarity. (b,c) Top view and 52°
tilted SEM images of the cavity, which is fabricated by FIB milling. (d,e) SEM and
panchromatic CL images, which were obtained simultaneously. The violet dashed arrow
indicates line scan direction. Scale bars are 300 nm.
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B. EBL/RIE/metal deposition and CL characterization
Figure S9. Schematic diagram of the fabrication process of metal patterns. (a) A silicon wafer
is spin-coated by PMMA. (b) PMMA is patterned by standard EBL. (c) The silicon is etched
in a SF6 plasma. The patterns are transferred to the silicon substrate. (d) The PMMA is rinsed
with acetone. (e) A metal layer is deposited on patterned silicon wafer by magnetron
sputtering deposition.
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Figure S10. CL spectra and SEM images of the equilateral-triangle cavity with a 1950 nm
side length and 300 nm high reflectors. (a) CL spectra for the electron beam excited from the
vertex to the middle point of opposite side of the cavity with a step size of 170 nm. Spectra
are offset vertically for clarity. (b,c) Top view and 30° tilted SEM images of the cavity, which
is fabricated by EBL/RIE/metal deposition. (d,e) SEM and panchromatic CL images, which
were obtained simultaneously. The violet dashed arrow indicates line scan direction. Scale
bars are 500 nm.
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Figure S11. CL spectra and SEM images of the equilateral-triangle cavity with a 900 nm side
length and 300 nm high reflectors. (a) CL spectra for the electron beam excited from the
vertex to the middle point of opposite side of the cavity with a step size of 110 nm. Spectra are
offset vertically for clarity. (b,c) Top view and 30° tilted SEM images of the cavity, which is
fabricated by EBL/RIE/metal deposition. (d,e) SEM and panchromatic CL images, which
were obtained simultaneously. The violet dashed arrow indicates line scan direction. Scale bars are
300 nm.
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C. EBL/metal deposition and CL characterization
Figure S12. Schematic diagram of the fabrication process of metal patterns. (a) A silicon
wafer is spin-coated by PMMA. (b) PMMA is patterned by standard EBL. (c) A metal layer is
deposited on patterned PMMA layer. The patterns are transferred to the metal layer by
magnetron sputtering deposition.
Figure S13. CL spectra and SEM images of the equilateral-triangle cavity with a 2000 nm
side length and 300 nm high reflectors. (a) CL spectra for the electron beam excited from the
vertex to the middle point of opposite side of the cavity with a step size of 170 nm. Spectra
are offset vertically for clarity. (b,c) Top view and 30° tilted SEM images of the cavity, which
is fabricated by EBL/metal deposition. The grain size is about 100 nm. (d,e) SEM and
panchromatic CL images, which were obtained simultaneously. The violet dashed arrow
indicates line scan direction. Scale bars are 500 nm.
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Figure S14. CL spectra and SEM images of the equilateral-triangle cavity with a 1100 nm
side length and 300 nm high reflectors. (a) CL spectra for the electron beam excited from the
vertex to the middle point of opposite side of the cavity with a step size of 140 nm. Spectra
are offset vertically for clarity. (b,c) Top view and 30° tilted SEM images of the cavity, which
is fabricated by EBL/metal deposition. The grain size is about 100 nm. (d,e) SEM and
panchromatic CL images, which were obtained simultaneously. The violet dashed arrow
indicates line scan direction. Scale bars are 500 nm.
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D. Metal deposition/EBL/metal deposition/lift off and CL characterization
Figure S15. Schematic diagram of the fabrication process of metal patterns. (a) A metal layer
is deposited on a silicon wafer by magnetron sputtering deposition. (b) The wafer is spincoated by PMMA. (c) PMMA is patterned by standard EBL. (d) A metal layer is deposited on
patterned PMMA by magnetron sputtering deposition. (e) A standard lift-off process.
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Figure S16. CL spectra and SEM images of the equilateral-triangle cavity with a 1450 nm
side length and 250 nm high reflectors. (a) CL spectra for the electron beam excited from the
vertex to the middle point of opposite side of the cavity with a step size of 130 nm. Spectra
are offset vertically for clarity. (b,c) Top view and 30° tilted SEM images of the cavity, which
is fabricated by metal deposition/EBL/metal deposition/lift off. (d,e) SEM and panchromatic
CL images, which were obtained simultaneously. The violet dashed arrow indicates line scan
direction. Scale bars are 500 nm.
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Figure S17. CL spectra and SEM images of the equilateral-triangle cavity with a 950 nm side
length and 250 nm high reflectors. (a) CL spectra for the electron beam excited from the
vertex to the middle point of opposite side of the cavity with a step size of 120 nm. Spectra
are offset vertically for clarity. (b,c) Top view and 30° tilted SEM images of the cavity, which
is fabricated by metal deposition/EBL/metal deposition/lift off. (d,e) SEM and panchromatic
CL images, which were obtained simultaneously. The violet dashed arrow indicates line scan
direction. Scale bars are 500 nm.
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E. TS method combined with PMMA as a template (our technique) and CL
characterization
Figure S18. CL spectra and mode patterns of the equilateral-triangle cavity with a 1900 nm
side length and 80 nm high reflectors. (a) CL spectra for the electron beam excited from the
vertex to the middle point of opposite side of the cavity with a step size of 170 nm. Inset is the
SEM image of the cavity. The violet dashed arrow indicates line scan direction. Spectra are
offset vertically for clarity. (b-h) Monochromatic CL images at the indicated wavelengths.
There are only faint patterns in wavelengths shorter than 500 nm and no patterns in
wavelengths longer than 500 nm. Scale bars are 500 nm.
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Figure S18. CL spectra and mode patterns of the equilateral-triangle cavity with a 1900 nm
side length and 160 nm high reflectors. (a) CL spectra for the electron beam excited from the
vertex to the middle point of opposite side of the cavity with a step size of 170 nm. Inset is the
SEM image of the cavity. The violet dashed arrow indicates line scan direction. Spectra are
offset vertically for clarity. (b-h) Monochromatic CL images at the indicated wavelengths.
There are faint patterns in wavelengths shorter than 650 nm and no patterns in wavelengths
longer than 650 nm. Scale bars are 500 nm.
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Figure S20. Simulated reflectivity of the out-of-plane component of SPPs for the cavity
reflectors with different height. We calculate the reflectivity of SPPs using two-dimensional
FDTD. Assuming that a SPP wave propagates along the x-axis at the silver/air interface (x-y
plane), the SPP wave is reflected by a silver reflector normal to the x-y plane.
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