of 19
Supporting Information
for
Adv. Mater.,
DOI: 10.1002/adma.202104863
Electrically Tunable and Dramatically Enhanced
Valley-Polarized Emission of Monolayer WS
2
at Room
Temperature with Plasmonic Archimedes Spiral
Nanostructures
Wei-Hsiang Lin,* Pin Chieh Wu
, Hamidreza Akbari
,
George R. Rossman
,
Nai-Chang Yeh,* and
Harry A.
Atwater
*
1
Supporting Information
Electrically Tunable and Dramatically En
hanced Valley-Polarized Emission of
Monolayer WS
2
at Room Temperature with Plasmonic Archimedes Spiral
Nanostructures
Wei-Hsiang Lin*, Pin Chieh Wu, Hamidreza Akbari, George. R. Rossman, Nai-Chang Yeh*
and Harry A. Atwater*
Wei-Hsiang Lin, Hamidreza Akbari, Prof. Harry A. Atwater
Department of Applied Physics, California Institute of Technology, Pasadena, CA 91125,
USA
E-mail:
haa@caltech.edu
and whlin@alumni.caltech.edu
Prof. Pin Chieh Wu
Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan
Prof. George. R. Rossman
Department of Geological and Planetary Scie
nces, California Institute of Technology,
Pasadena, CA 91125, USA
Prof. Nai-Chang Yeh
Department of Physics, California Institu
te of Technology, Pasadena, CA 91125, USA
E-mail: ncyeh@caltech.edu
2
Supporting Information 1.
We have characterized our single crystalline WS
2
samples using Raman spectroscopy and X-
ray photoelectron spectroscopy (XPS), and the re
presentative data are summarized below.
To demonstrate the crystallinity of single crystalline WS
2
, we performed Raman spectroscopic
studies of the
1
g
A
and
1
2
g
E
modes using a 514.3 nm laser (2.41 eV) as the excitation source, and
a representative spectrum is shown in Figure S1.
Figure S1.
Raman spectrum of a monolayer WS
2
, showing the
1
g
A
and
1
2
g
E
optical phonon
modes, and the LA (M) mode associated with the longitudinal acoustic phonon at the M point
of the Brillouin zone, which may be considered as an indicator of the sample quality.
X-ray photoelectron spectroscopy (XPS) was also conducted to examine the chemical
composition and valence
states of monolayer WS
2
transferred to Au (111) / mica substrates.
The core level spectra were calibrated via
fitting adventitious carbon at 284.8 eV. The high-
resolution spectra of W 4f and S 2p peaks are shown in Figure S2. For 2H-phase WS
2
, the
corresponding binding energies of the W 4f
7/2
and W 4f
5/2
peaks were found to locate at 32.15
3
and 34.31 eV, respectively, and the binding energies for the S 2p
3/2
and S 2p
1/2
peaks were
located at 162.87 and 163.07 eV, respectively. These values are all consistent with those
reported previously in literature.
Figure S2.
XPS of a monolayer WS
2
, showing the W 4f
7/2
and W 4f
5/2
peaks in the left spectrum
and the S 2p
3/2
and S 2p
1/2
peaks in the right spectrum.
4
Supporting Information 2.
The total decay rate of the as-grown monolayer WS
2
without coupling to the plasmonic
nanostructures is:
off
R
NR


, (1)
where
R
and
NR
are the radiative and nonradiative decay rates, respectively. The coupling to
plasmonic nano-cavities enhances the radiative ra
te by the Purcell effect and induces a new
decay channel through metallic losses with a rate
M
. Therefore, the total decay rate of the
coupled monolayer WS
2
can be expressed as:
(1)
on
p
R
NR
M
F
 
 
, (2)
where
p
F
is the Purcell factor that enhances the radiative decay rate. Therefore,
(1)
p
RNRM
on
off
R
NR
F



. (3)
In order to determine the underlying Purcell factor
from the measured rates, we note that the
quantum yield
is defined as the ratio of the number of photons emitted to the number of
photons absorbed:
R
off
RNR
, (4)
(1)
p
R
on
RNR
F

, (5)
on
off
p R
M
F

 
. (6)
Therefore, the metallic-loss corrected Purcell factor
p
F
is given by:
1
1
 





pR
on
p
off
pR
M
off
F
F
F
. (7)
5
Figure S3.
Time-resolved PL decay profile of a) WS
2
and b) WS
2
-2TRHPAS.