Giant Pockels effect of polar organic solvents and water in the electric double layer on a transparent electrode

Kanemaru, H.; Yukita, Shunpei; Namiki, Hajime; Nosaka, Yugo; Kobayashi, Takayoshi; Tokunaga, Eiji

doi:10.1039/c7ra05875f

Cited by 13 publications

(29 citation statements)

References 35 publications

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“…This phenomenon would not be observable in pure molecular liquids such as glycerol, in which such an ordering near an electrode is absent. However, the Pockels effect in the liquid phase has indeed been reported by Tokunaga and co-workers for water and other polar organic solvents containing electrolytes (NaCl, NaF, and LiCl) at both low (0.1 M) and high (3–4 M) concentrations. − …”

Section: Resultssupporting

confidence: 59%

“…If the coefficient a 1 in eq 5 is assumed to be similar between ILs and molecular liquids because both are liquids, the difference in |Δn| will then be ascribable to the electric field strength, F, that the layer displaying the Pockels effect experiences. The Pockels coefficients of liquids differ only by at most an order of magnitude from those of typical electro-optic crystals such as LiNbO 3 and KH 2 PO 4 (r 13 = 230 pm V −1 for water 52 and r 33 ≈ 30 pm V −1 for LiNbO 3 56 ). In the previous study, 52 it was assumed that a voltage of 2 V, which is nearly the same as that applied in the present study (1.5 V), is effectively applied across an electrical double layer 2 nm thick.…”

Section: ■ Results and Discussionmentioning

confidence: 93%

“…The Pockels coefficients of liquids differ only by at most an order of magnitude from those of typical electro-optic crystals such as LiNbO 3 and KH 2 PO 4 (r 13 = 230 pm V −1 for water 52 and r 33 ≈ 30 pm V −1 for LiNbO 3 56 ). In the previous study, 52 it was assumed that a voltage of 2 V, which is nearly the same as that applied in the present study (1.5 V), is effectively applied across an electrical double layer 2 nm thick. For the |Δn| of the ILs to be 10 to 10 2 times smaller, the thickness of the intermediate layer needs to be 10 to 10 2 times larger than the typical thickness of the electrical double layer.…”

Section: ■ Results and Discussionmentioning

confidence: 93%

“… a Values measured in the liquid in contact with a positively charged electrode. b 0.1 M NaCl was dissolved. c 0.1 M LiCl was dissolved. d Ref . …”

Section: Resultsmentioning

confidence: 99%

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Observation of the Pockels Effect in Ionic Liquids and Insights into the Length Scale of Potential-Induced Ordering

et al. 2021

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Ionic liquids (ILs) under electric fields play essential roles in the electrochemical utilization of ILs. Recently, long-range organization of ILs in the vicinity of charged (and even neutral) surfaces has been revealed, but experimental evidence for such an ordering is still limited and its spatial length scale remains controversial. Here, we use confocal Raman microspectroscopy to investigate the effect of an applied electric potential on the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and its analogues in a space-resolved manner. Much to our surprise, the observed Raman difference spectra of the ILs obtained with and without an applied potential exhibit uniform intensity changes independent of vibrational modes of cations and anions, a finding in sharp contrast with the electric field effects on molecular liquids that we have previously observed. We interpret this unexpected finding in terms of the Pockels effect that occurs as a result of a potential-induced ordering of the IL near an IL–electrode interface. The refractive index changes due to the applied potential are estimated using the experimental Raman intensity changes. The results allow us to deduce that the length scale of the ordering in the ILs is tens to hundreds of nanometers, extending more than would be expected for the electrical double layer but not as far as a micrometer scale.

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Section: Resultssupporting

confidence: 59%

Section: ■ Results and Discussionmentioning

confidence: 93%

Section: ■ Results and Discussionmentioning

confidence: 93%

“… a Values measured in the liquid in contact with a positively charged electrode. b 0.1 M NaCl was dissolved. c 0.1 M LiCl was dissolved. d Ref . …”

Section: Resultsmentioning

confidence: 99%

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Observation of the Pockels Effect in Ionic Liquids and Insights into the Length Scale of Potential-Induced Ordering

et al. 2021

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“…ΔIPD FM and ΔIPD AM are respectively ~1.2 times and ~1.5 times higher in presence of a glycerol (c0) droplet as compared to in air. A mismatch in the gain in AM and FM is likely due to electrostatic effects on glycerol refractive index [33] at different VLED applied in AM (~19 V) and FM (~1 V) operation. Further, at a given ILED, both ΔIPD FM and ΔIPD AM is higher for D2 than for D1 due to the higher external quantum efficiency of D2.…”

Section: Results and Analysismentioning

confidence: 99%

Optical absorption sensing with dual-spectrum silicon LEDs in SOI-CMOS technology

2020

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Silicon p-n junction diodes emit low-intensity, broad-spectrum light near 1120 nm in forward bias and between 400-900 nm in reverse bias (avalanche). For the first time, we experimentally achieve optical absorption sensing of pigment in solution with silicon micro LEDs designed in a standard silicon-on-insulator CMOS technology. By driving a single LED in both forward and avalanche modes of operation, we steer it's electroluminescent spectrum between visible and near-infrared (NIR). We then characterize the vertical optical transmission of both visible and NIR light from the LED through the same micro-droplet specimen to a vertically mounted discrete silicon photodiode. The effective absorption coefficient of carmine solution in glycerol at varying concentrations were extracted from the color ratio in optical coupling. By computing the LED-specific molar absorption coefficient of carmine, we estimate the concentration (~0.040 mol L -1 ) and validate the same with a commercial spectrophotometer (~0.030 mol L -1 ). With a maximum observed sensitivity of ~1260 cm -1 mol -1 L, the sensor is a significant step forward towards low-cost CMOS-integrated optical sensors with silicon LED as the light source intended for biochemical analyses in food sector and plant/human health.

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Mechanisms of the anomalous Pockels effect in bulk water

Yukita

Suzuki

Shiokawa

et al. 2018

Opt Rev

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Giant Pockels effect of polar organic solvents and water in the electric double layer on a transparent electrode

Abstract: The Pockels effect of polar organic solvents and water within the electric double layer on an ITO electrode is studied to find that water has the largest Pockels coefficient, followed in order by methanol, ethanol, and dimethyl sulfoxide.

Cited by 13 publications

References 35 publications

Observation of the Pockels Effect in Ionic Liquids and Insights into the Length Scale of Potential-Induced Ordering

Observation of the Pockels Effect in Ionic Liquids and Insights into the Length Scale of Potential-Induced Ordering

Optical absorption sensing with dual-spectrum silicon LEDs in SOI-CMOS technology

Mechanisms of the anomalous Pockels effect in bulk water

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