We have used surface plasmon resonant metal gratings to induce and probe the dielectric response (i.e., electro-optic modulation) of ionic liquids (ILs) at electrode interfaces. Here, the cross-plane electric field at the electrode surface modulates the refractive index of the IL due to the Pockels effect. This is observed as a shift in the resonant angle of the grating (i.e., Δϕ), which can be related to the change in the local index of refraction of the electrolyte (i.e., Δnlocal). The reflection modulation of the IL is compared against a polar (D2O) and a non-polar solvent (benzene) to confirm the electro-optic origin of resonance shift. The electrostatic accumulation of ions from the IL induces local index changes to the gratings over the extent of electrical double layer (EDL) thickness. Finite difference time domain simulations are used to relate the observed shifts in the plasmon resonance and change in reflection to the change in the local index of refraction of the electrolyte and the thickness of the EDL. Simultaneously using the wavelength and intensity shift of the resonance enables us to determine both the effective thickness and Δn of the double layer. We believe that this technique can be used more broadly, allowing the dynamics associated with the potential-induced ordering and rearrangement of ionic species in electrode–solution interfaces.
REFERENCES
1.
K. S.
Panse
, H.
Wu
, S.
Zhou
, F.
Zhao
, N. R.
Aluru
, and Y.
Zhang
, “Innermost ion association configuration is a key structural descriptor of ionic liquids at electrified interfaces
,” J. Phys. Chem. Lett.
13
, 9464
–9472
(2022
).2.
L. K. S.
Bonagiri
, K. S.
Panse
, S.
Zhou
, H.
Wu
, N. R.
Aluru
, and Y.
Zhang
, “Real-space charge density profiling of electrode–electrolyte interfaces with angstrom depth resolution
,” ACS Nano
16
, 19594
–19604
(2022
).3.
Y.
Wang
, G. M.
Swain
, and G. J.
Blanchard
, “Charge-induced birefringence in a room-temperature ionic liquid
,” J. Phys. Chem. B
125
, 950
–955
(2021
).4.
Y.
Wang
, F.
Parvis
, M. I.
Hossain
, K.
Ma
, R.
Jarošová
, G. M.
Swain
, and G. J.
Blanchard
, “Local and long-range organization in room temperature ionic liquids
,” Langmuir
37
, 605
–615
(2021
).5.
K.
Ma
, R.
Jarosova
, G. M.
Swain
, and G. J.
Blanchard
, “Modulation of an induced charge density gradient in the room-temperature ionic liquid BMIM+BF4–
,” J. Phys. Chem. C
122
, 7361
–7367
(2018
).6.
Y.
Wang
, L.
Adhikari
, G. A.
Baker
, and G. J.
Blanchard
, “Cation structure-dependence of the Pockels effect in aprotic ionic liquids
,” Phys. Chem. Chem. Phys.
24
, 18067
–18072
(2022
).7.
K.
Ma
, R.
Jarosova
, G. M.
Swain
, and G. J.
Blanchard
, “Charge-induced long-range order in a room-temperature ionic liquid
,” Langmuir
32
, 9507
–9512
(2016
).8.
A.
Montenegro
, A. E.
Vaughn
, M.
Mammetkuliyev
, B.
Zhao
, B.
Zhang
, H.
Shi
, D.
Bhattacharyya
, A. V.
Benderskii
, and S. B.
Cronin
, “Field-dependent orientation and free energy of D2O at an electrode surface observed via SFG spectroscopy
,” J. Phys. Chem. C
126
, 20831
–20839
(2022
).9.
A.
Montenegro
, C.
Dutta
, M.
Mammetkuliev
, H.
Shi
, B.
Hou
, D.
Bhattacharyya
, B.
Zhao
, S. B.
Cronin
, and A. V.
Benderskii
, “Asymmetric response of interfacial water to applied electric fields
,” Nature
594
, 62
–65
(2021
).10.
H.
Kanemaru
, S.
Yukita
, H.
Namiki
, Y.
Nosaka
, T.
Kobayashi
, and E.
Tokunaga
, “Giant Pockels effect of polar organic solvents and water in the electric double layer on a transparent electrode
,” RSC Adv.
7
, 45682
–45690
(2017
).11.
S.
Toda
, R.
Clark
, T.
Welton
, and S.
Shigeto
, “Observation of the Pockels effect in ionic liquids and insights into the length scale of potential-induced ordering
,” Langmuir
37
, 5193
–5201
(2021
).12.
B. V.
Merinov
, S. V.
Zybin
, S.
Naserifar
, S.
Morozov
, J.
Oppenheim
, W. A.
Goddard
III, J.
Lee
, J. H.
Lee
, H. E.
Han
, Y. C.
Choi
, and S. H.
Kim
, “Interface structure in Li-metal/[Pyr14] [TFSI]-ionic liquid system from ab initio molecular dynamics simulations
,” J. Phys. Chem. Lett.
10
, 4577
–4586
(2019
).13.
M. Y.
Yang
, B. V.
Merinov
, S. V.
Zybin
, W. A.
Goddard Iii
, E. K.
Mok
, H. J.
Hah
, H. E.
Han
, Y. C.
Choi
, and S. H.
Kim
, “Transport properties of imidazolium based ionic liquid electrolytes from molecular dynamics simulations
,” Electrochem. Sci. Adv.
2
, e2100007
(2022
).14.
G.
Feng
, S.
Li
, V.
Presser
, and P. T.
Cummings
, “Molecular insights into carbon supercapacitors based on room-temperature ionic liquids
,” J. Phys. Chem. Lett.
4
, 3367
–3376
(2013
).15.
E.
Heid
, S.
Boresch
, and C.
Schröder
, “Polarizable molecular dynamics simulations of ionic liquids: Influence of temperature control
,” J. Chem. Phys.
152
, 094105
(2020
).16.
H.
Zhang
, M.
Zhu
, W.
Zhao
, S.
Li
, and G.
Feng
, “Molecular dynamics study of room temperature ionic liquids with water at mica surface
,” Green Energy Environ.
3
, 120
–128
(2018
).17.
P.
Ray
, A.
Balducci
, and B.
Kirchner
, “Molecular dynamics simulations of lithium-doped ionic-liquid electrolytes
,” J. Phys. Chem. B
122
, 10535
–10547
(2018
).18.
Z.
Yan
, D.
Meng
, X.
Wu
, X.
Zhang
, W.
Liu
, and K.
He
, “Two-dimensional ordering of ionic liquids confined by layered silicate plates via molecular dynamics simulation
,” J. Phys. Chem. C
119
, 19244
–19252
(2015
).19.
F.
Federici Canova
, M.
Mizukami
, T.
Imamura
, K.
Kurihara
, and A. L.
Shluger
, “Structural stability and polarisation of ionic liquid films on silica surfaces
,” Phys. Chem. Chem. Phys.
17
, 17661
–17669
(2015
).20.
J.
Homola
, I.
Koudela
, and S. S.
Yee
, “Surface plasmon resonance sensors based on diffraction gratings and prism couplers: Sensitivity comparison
,” Sens. Actuators, B
54
, 16
–24
(1999
).21.
P. S.
Vukusic
, G. P.
Bryan-Brown
, and J. R.
Sambles
, “Surface plasmon resonance on gratings as a novel means for gas sensing
,” Sens. Actuators, B
8
, 155
–160
(1992
).22.
S.
Long
, J.
Cao
, Y.
Wang
, S.
Gao
, N.
Xu
, J.
Gao
, and W.
Wan
, “Grating coupled SPR sensors using off the shelf compact discs and sensitivity dependence on grating period
,” Sens. Actuators Rep.
2
, 100016
(2020
).23.
J. S.
Yuk
, E. F.
Guignon
, and M. A.
Lynes
, “Sensitivity enhancement of a grating-based surface plasmon-coupled emission (SPCE) biosensor chip using gold thickness
,” Chem. Phys. Lett.
591
, 5
–9
(2014
).24.
S.
Roh
, T.
Chung
, and B.
Lee
, “Overview of the characteristics of micro- and nano-structured surface plasmon resonance sensors
,” Sensors
11
, 1565
–1588
(2011
).25.
D.
Hayama
, K.
Seto
, K.
Yamashita
, S.
Yukita
, T.
Kobayashi
, and E.
Tokunaga
, “Giant Pockels effect in an electrode-water interface for a ‘liquid’ light modulator
,” OSA Continuum
2
, 3358
–3373
(2019
).26.
A.
Okada
, T.
Kobayashi
, and E.
Tokunaga
, “Interfacial Pockels effect of solvents with a larger static dielectric constant than water and an ionic liquid on the surface of a transparent oxide electrode
,” Appl. Sci.
12
, 2454
(2022
).27.
S.
Zhang
, N.
Nishi
, and T.
Sakka
, “Electrochemical surface plasmon resonance measurements of camel-shaped static capacitance and slow dynamics of electric double layer structure at the ionic liquid/electrode interface
,” J. Chem. Phys.
153
, 044707
(2020
).28.
N.
Nishi
, Y.
Hirano
, T.
Motokawa
, and T.
Kakiuchi
, “Ultraslow relaxation of the structure at the ionic liquid|gold electrode interface to a potential step probed by electrochemical surface plasmon resonance measurements: Asymmetry of the relaxation time to the potential-step direction
,” Phys. Chem. Chem. Phys.
15
, 11615
–11619
(2013
).29.
Y.
Wang
, I.
Aravind
, Z.
Cai
, L.
Shen
, G. N.
Gibson
, J.
Chen
, B.
Wang
, H.
Shi
, B.
Song
, E.
Guignon
, N. C.
Cady
, W. D.
Page
, A.
Pilar
, and S. B.
Cronin
, “Hot electron driven photocatalysis on plasmon-resonant grating nanostructures
,” ACS Appl. Mater. Interfaces
12
, 17459
–17465
(2020
).30.
I.
Aravind
, Y.
Wang
, Z.
Cai
, L.
Shen
, B.
Zhao
, S.
Yang
, Y.
Wang
, J. M.
Dawlaty
, G. N.
Gibson
, E.
Guignon
, N. C.
Cady
, W. D.
Page
, A.
Pilar
, and S. B.
Cronin
, “Hot electron plasmon-resonant grating structures for enhanced photochemistry: A theoretical study
,” Crystals
11
, 118
(2021
).31.
J.
Homola
, “Electromagnetic theory of surface plasmons
,” in Surface Plasmon Resonance Based Sensors
, edited by J.
Homola
(Springer
, Berlin, Heidelberg
, 2006
), pp. 3
–44
.32.
L.
Shen
, G. N.
Gibson
, N.
Poudel
, B.
Hou
, J.
Chen
, H.
Shi
, E.
Guignon
, N. C.
Cady
, W. D.
Page
, A.
Pilar
, and S. B.
Cronin
, “Plasmon resonant amplification of hot electron-driven photocatalysis
,” Appl. Phys. Lett.
113
, 113104
(2018
).33.
L.
Shen
, N.
Poudel
, G. N.
Gibson
, B.
Hou
, J.
Chen
, H.
Shi
, E.
Guignon
, W. D.
Page
, A.
Pilar
, and S. B.
Cronin
, “Plasmon resonant amplification of a hot electron-driven photodiode
,” Nano Res.
11
, 2310
–2314
(2018
).34.
Y.
Wang
, L.
Shen
, Y.
Wang
, B.
Hou
, G. N.
Gibson
, N.
Poudel
, J.
Chen
, H.
Shi
, E.
Guignon
, N. C.
Cady
, W. D.
Page
, A.
Pilar
, J.
Dawlaty
, and S. B.
Cronin
, “Hot electron-driven photocatalysis and transient absorption spectroscopy in plasmon resonant grating structures
,” Faraday Discuss.
214
, 325
–339
(2019
).35.
Y.
Wang
, H.
Shi
, L.
Shen
, Y.
Wang
, S. B.
Cronin
, and J. M.
Dawlaty
, “Ultrafast dynamics of hot electrons in nanostructures: Distinguishing the influence on interband and plasmon resonances
,” ACS Photonics
6
, 2295
–2302
(2019
).36.
Y.
Wang
, Y.
Wang
, I.
Aravind
, Z.
Cai
, L.
Shen
, B.
Zhang
, B.
Wang
, J.
Chen
, B.
Zhao
, H.
Shi
, J. M.
Dawlaty
, and S. B.
Cronin
, “In situ investigation of ultrafast dynamics of hot electron-driven photocatalysis in plasmon-resonant grating structures
,” J. Am. Chem. Soc.
144
, 3517
–3526
(2022
).37.
T.
Douglas
, S.
Yoo
, and P.
Dutta
, “Ionic liquid solutions show anomalous crowding behavior at an electrode surface
,” Langmuir
38
, 6322
–6329
(2022
).38.
J.
Homola
and M.
Piliarik
, “Surface plasmon resonance (SPR) sensors
,” in Surface Plasmon Resonance Based Sensors
, edited by J.
Homola
(Springer
, Berlin, Heidelberg
, 2006
), pp. 45
–67
.39.
X.
Luo
, S.
Deng
, and P.
Wang
, “Temporal–spatial-resolved mapping of the electrical double layer changes by surface plasmon resonance imaging
,” RSC Adv.
8
, 28266
–28274
(2018
).© 2024 Author(s). Published under an exclusive license by AIP Publishing.
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