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Becauseof thehighdielectricstrengthofwater, it isextremelydifficult todischargeplasmainacontrollablewayin the aqueous phase. By using lithographically defined electrodes andmetal/dielectric nanoparticles, we create electric field enhancementthatenablesplasmadischargeinliquidelectrolytesatsignificantlyreducedappliedvoltages.Here,weusehighvoltage (10−30kV)nanosecondpulse(20ns)dischargestogenerateatransientplasmaintheaqueousphase.Anelectrodegeometrywitha radiusofcurvatureofapproximately10μm,agapdistanceof300μm,andanestimatedfieldstrengthof5×106V/cmresultedina reductionintheplasmadischargethresholdfrom28to23kV.Asecondstructurehadaradiusofcurvatureofaround5μmanda gapdistanceof100μmhadanestimatedfieldstrengthof9×106V/cmbutdidnotperformaswellasthelargergapelectrodes. Addinggoldnanoparticles(20nmdiameter) insolutionfurther reducedthethresholdforplasmadischargeto17kVduetothe electricfieldenhancementatthewater/goldinterface,withanestimatedE-fieldenhancementof4×.Addingaluminananoparticles decoratedwithPtreducedtheplasmadischargethresholdto14kV. Inthisscenario, theemergenceofatriplepointatthejuncture ofalumina,Pt,andwaterresultsinthecoexistenceofthreedistinctdielectricconstantsatasingularlocation.Thisleadstoanotable concentrationof electric field, effectively aiding in the initiationof plasma discharge at a reduced voltage. To gain amore comprehensive and detailed understanding of the electric field enhancement mechanism, we performed rigorous numerical simulations.Thesesimulationsprovidevaluableinsights intotheintricateinterplaybetweenthelithographicallydefinedelectrodes, thenanoparticles, andthe resultingelectricfielddistribution, enablingus toextract crucial informationandoptimize thedesign parameters forenhancedperformance. 

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. 

We demonstrate a free-space optical communication link with an optical transmitter that harvests naturally occurring Planck radiation from a warm body and modulates the emitted intensity. The transmitter exploits an electro-thermo-optic effect in a multilayer graphene device that electrically controls the surface emissivity of the device resulting in control of the intensity of the emitted Planck radiation. We design an amplitude-modulated optical communication scheme and provide a link budget for communications data rate and range based on our experimental electro-optic characterization of the transmitter. Finally, we present an experimental demonstration achieving error-free communications at 100 bits per second over laboratory scales. 

We demonstrate a substantial modulation of the optical properties of multilayer graphene (∼100 layers) using a simple device consisting of a multilayer graphene/polymer electrolyte membrane/gold film stack. Applying a voltage of 3–4 V drives the intercalation of anion [TFSI]− [ion liquid diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide [DEME][TFSI]] resulting in the reversible modulation of the properties of this optically dense material. Upon intercalation, we observe an abrupt shift of 35 cm−1 in the G band Raman mode, an abrupt increase in FTIR reflectance over the wavelength range from 1.67 to 5 μm (2000–6000 cm−1), and an abrupt increase in luminescent background observed in the Raman spectra of graphene. All of these abrupt changes in the optical properties of this material arise from the intercalation of the TFSI− ion and the associated change in the free carrier density (Δn = 1020 cm−3). Suppression of the 2D band Raman mode observed around 3 V corresponds to Pauli blocking of the double resonance Raman process and indicates a modulation of the Fermi energy of ΔEF = 1.1 eV.