Voltage-controlled optical devices
Achieving precise, localized reversible control of optical material properties is challenging. Fortunately, electrochemical reactions and proton pumping in a solid-state system provide reversible electrical control of the solid-state system's optical properties. Applying a voltage to a thin solid electrolyte layer, such as GdO x , splits water into O 2 and H + (with charge conservation ensured by electron transfer at the electrodes) at the interface between the solid electrolyte and an electrode. The voltage drives the protons into the solid electrolyte, changing the solid electrolyte's refractive index. Reversing the polarity of the applied voltage drives the protons out of the solid electrolyte, reversing the refractive index change. This reversible electrical control can be used to implement interference color modulation, transmission modulation, and switchable plasmonics. Because the solid electrolyte can be less than 10 nanometers thick, this electrochemical control enables highly localized control of optical properties active plasmonic devices and reconfigurable metamaterials.
1. A device comprising:
a first electrode;
a second electrode;
a solid electrolyte disposed between the first electrode and the second electrode; and
a voltage source, in electrical communication with the first electrode and the second electrode, to apply a voltage across the first electrode and the second electrode, the voltage splitting water into oxygen and protons at an interface between the first electrode and the solid electrolyte, the voltage generating an electric field that drives the protons toward the second electrode, the protons causing a change in an optical property of the solid electrolyte.
2. The device of claim 1 , wherein the first electrode is permeable enough to pass the water to the interface between the first electrode and the solid electrolyte.
3. The device of claim 1 , wherein the first electrode comprises a conductive nanostructure and wherein the change in the optical property of the solid electrolyte shifts a wavelength of a plasmonic resonance of the conductive nanostructure.
4. The device of claim 1 , wherein the solid electrolyte comprises a rare earth oxide RE 2 O 3-δ , where RE is at least one of La, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Yb, or Y and δ is between 0.01 and 0.5.
5. The device of claim 1 , wherein the solid electrolyte has a thickness of about 4 nm to about 80 nm.
6. The device of claim 1 , wherein the solid electrolyte has a proton conductivity of about 10 −11 siemens/meter to about 10 −7 siemens/meter at room temperature.
7. The device of claim 1 , wherein the change in the optical property of the solid electrolyte occurs in less than about 100 seconds.
8. The device of claim 1 , wherein the second electrode comprises at least one of magnesium, yttrium, lanthanum, or an alloy thereof, the protons causing the second electrode to change from a reflective state to a dielectric state.
9. The device of claim 1 , further comprising:
a water storage layer, disposed on the first electrode, to provide the water via the first electrode.
10. The device of claim 1 , further comprising:
a substrate; and
a dielectric layer disposed between the substrate and the second electrode and having a refractive index different than a refractive index of the solid electrolyte.
11. The device of claim 1 , further comprising:
a plasmonic nanostructure formed in or next to the solid electrolyte, the change in the optical property of the solid electrolyte shifting a wavelength of a plasmonic resonance of the plasmonic nanostructure.
12. The device of claim 11 , further comprising:
a metal layer disposed over at least a portion of the plasmonic nanostructure.
13. The device of claim 11 , wherein the protons cause the second electrode to change from a conductive reflective state to a dielectric transparent state.
14. The device of claim 11 , wherein the protons cause a change in an optical property of the plasmonic nanostructure.
15. A method comprising:
applying an electric field across a solid electrolyte with a first electrode and a second electrode, the electric field splitting water into oxygen ions and protons at an interface between the first electrode and the solid electrolyte, the electric field driving the protons toward the second electrode, the protons causing a change in an optical property of the solid electrolyte.
16. The method of claim 15 , further comprising:
absorbing the water from a surrounding atmosphere via the first electrode.
17. The method of claim 15 , further comprising:
absorbing the water from a water storage layer disposed on the first electrode.
18. The method of claim 15 , wherein the change in the optical property of the solid electrolyte shifts a wavelength of a plasmonic resonance of a conductive nanostructure.
19. The method of claim 15 , wherein the protons cause the second electrode to change from a reflective state to a dielectric state.
20. The method of claim 15 , further comprising:
detecting the change in the optical property of the solid electrolyte.
21. The method of claim 15 , wherein the second electrode is disposed on a dielectric layer and the change in the optical property is a change in a refractive index of the solid electrolyte.
22. The method of claim 15 , wherein the solid electrolyte contains a plasmonic nanostructure formed in the solid electrolyte and the change in the optical property of the solid electrolyte shifts a wavelength of a plasmonic resonance of the plasmonic nanostructure.
23. A device comprising:
a layer of noble metal;
a layer of magnesium;
a layer of gadolinium oxide disposed between the layer of noble metal and the layer of magnesium; and
a voltage source, in electrical communication with the layer of noble metal and the layer of magnesium, to apply an electric field across the gadolinium oxide, the electric field splitting water into oxygen ions and protons at an interface between the layer of noble metal and the gadolinium oxide, the electric field driving the protons toward the layer of magnesium, the protons changing the layer of magnesium from a reflective state to a non-reflective state.