Search

US-12625298-B2 - Method of manufacture of a metasurface

US12625298B2US 12625298 B2US12625298 B2US 12625298B2US-12625298-B2

Abstract

The present invention relates to a new method for making metasurfaces comprising liquid gating. VO 2 is an exemplary substrate for use in the present invention. The inventive metasurfaces can be used as a planar lens, vortex generator, beam deflector, and axicon, inter alia. The inventive methods allow metasurfaces to be formed readily on curved or flexible surfaces.

Inventors

  • Stuart S.P. Parkin

Assignees

  • Max Planck Gesellschaft Zur Förderung Der Wissenschaften eV

Dates

Publication Date
20260512
Application Date
20201112
Priority Date
20191112

Claims (20)

  1. 1 . A method for chemically transforming a surface of a substrate into a metasurface which is a plasmonic array comprising the steps of: I. providing a surface on a substrate which exhibits at least two distinct measurable states of an optical property and which can stably but reversibly be transitioned from i. a first state of the optical property into at least ii. one second state of the optical property which is measurably distinct from the first state, by a change in a chemical composition of the surface of the substrate II. creating on the surface of the substrate at least one area i. outside of which the substrate is in the first state of the optical property, and ii. inside of which the substrate is in one of the at least one second state of the optical property, or iii. wherein the states of the optical property of the inside area and the outside area are inverted, and III. wherein step II further comprises defining and delineating a desired-to-be inside area on the surface of the substrate which is in the first state of the optical property via a resist cover layer and subsequently contacting the surface in the defined and delineated inside area with a liquid which reacts with the surface of the substrate material to form a chemical product that yields or brings about the transition into the at least one second state of the optical property within the inside area only, or wherein in step III the states of the optical property of the surface and the inside area are inverted and the substrate is VO 2 , and the metasurface comprises a metallic VO 2 antennae array within an insulating VO 2 matrix, and IV. removing the resist cover layer after completion of the transition.
  2. 2 . The method of claim 1 , wherein the optical property is selected from one or more of refraction, diffraction, extinction, scattering, absorption, reflection, polarization or transmittance.
  3. 3 . The method of claim 1 , wherein the substrate has a thickness in the range of 1-100 nm.
  4. 4 . The method of claim 3 , wherein the thickness is in the range of 5-50 nm.
  5. 5 . The method of claim 3 , wherein the thickness is in the range of 7-15 nm.
  6. 6 . The method of claim 1 , wherein the liquid brings about a change in the chemical composition of the substrate material.
  7. 7 . The method of claim 1 , wherein the transition is instigated by applying an electric potential to the liquid.
  8. 8 . The method of claim 7 , wherein the electric potential is 0.1-10 Volts.
  9. 9 . The method of claim 8 , wherein the electric potential is 1-5 Volts.
  10. 10 . The method of claim 8 , wherein the electric potential is 2-4 Volts.
  11. 11 . The method of claim 1 , wherein the liquid is selected from one or more of water, an alcohol, a hydrocarbon or a halogen containing hydrocarbon.
  12. 12 . The method of claim 11 , wherein the alcohol is ethanol or methanol; the hydrocarbon is pentane or hexane, and the halogen containing hydrocarbon is chloroform.
  13. 13 . The method of claim 1 , wherein the liquid is an ionic liquid.
  14. 14 . The method of claim 13 , wherein the ionic liquid is selected from one or more of 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), 1-Propyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, 1-Butyl-3-methylimidazolium bis(tri-fluoromethylsulfonyl)imide and 1-Hexyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide.
  15. 15 . A substrate comprising a metasurface whose composition is contained entirely within a chemically transitioned surface layer of a substrate manufactured according to the method of claim 1 , wherein said metasurface controls a wavefront of electromagnetic waves.
  16. 16 . The substrate of claim 15 , wherein the substrate has a thickness of up to about 1 μm and the change in optical property is present through the entire thickness of the substrate.
  17. 17 . The substrate of claim 15 , wherein the second state of the optical property remains unchanged at conditions ranging from between 1° and 30° C. and between 950 and 1100 hPa for at least 100 days.
  18. 18 . A planar lens, vortex generator, beam deflector, axicon, electromagnetic absorber, polarization converter or spectrum filters, for wireless communications, energy harvesting, imaging, or cloaking comprising the substrate metasurface of claim 15 .
  19. 19 . The method of claim 1 , wherein the step of defining and delineating a desired-to-be inside area on the surface of the substrate comprises applying a removeable lithographic resist as the cover layer on the surface of the substrate and cutting out the desired forms that define and delineate the desired-to-be inside area.
  20. 20 . The method of claim 19 , wherein the lithographic resist is removed after completing the transition into the at least one second state by washing with a solvent and the obtained metasurface dried.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is being filed under 35 U.S.C. § 371 as a National Stage Application of pending International Application No. PCT/EP2020/081852 filed Nov. 12, 2020, which claims priority to the following parent application: European Patent Application No. 19208484.6, filed Nov. 12, 2019. Both International Application No. PCT/EP2020/081852 and European Patent Application No. 19208484.6 are hereby incorporated by reference herein in their entirety. FIELD OF THE INVENTION Metasurfaces can be described as one- and two-dimensional plasmonic arrays (scattering elements) with a periodicity which is small compared to the length of the operating wavelength (subwavelength periodicity). Due to the negligible thickness of these surfaces (ultrathin films) compared to the wavelength of operation, metasurfaces can be considered as an interface of discontinuity enforcing an abrupt change in both the amplitude and phase of the impinging electromagnetic wave. BACKGROUND OF THE INVENTION Early examples of metasurface properties are the dark areas in the reflection spectra of subwavelength metallic grating. This unusual phenomenon was named Wood's anomaly and led to the discovery of the surface plasmon polariton (SPP), a particular electromagnetic wave excited at metal surfaces. Subsequently, another important phenomenon, the Levi-Civita relation, was introduced, which states that a subwave-length-thick film can result in a dramatic change in electromagnetic boundary conditions. Recently, some novel phenomena such as ultra-broadband coherent perfect absorption were demonstrated, where a 0.3 nm thick film could absorb all electromagnetic waves across the RF, microwave, and terahertz frequencies. In optical applications, an anti-reflective coating can be regarded as a simple metasurface, as it was first observed by Lord Rayleigh. In recent years, several new metasurfaces have been developed, including plasmonic metasurfaces, metasurfaces based on geometric phases, and metasurfaces based on impedance sheets. One of the most important applications of metasurfaces is to control a wavefront of electromagnetic waves by imparting local, gradient phase shifts to the incoming waves, which leads to a generalization of the well known laws of reflection and refraction. In this way, a metasurface can be used as a planar lens, vortex generator, beam deflector, axicon and so on. In addition, metasurfaces are also applied in electromagnetic absorbers, polarization converters, and spectrum filters, for wireless communications, energy harvesting, imaging, and cloaking. Besides the gradient metasurface lenses, metasurface-based superlenses offer another degree of control of the wavefront by using evanescent waves. With surface plasmons in the ultrathin metallic layers, perfect imaging and super-resolution lithography could be possible, which breaks the common assumption that all optical lens systems are limited by diffraction, a phenomenon called the diffraction limit. Classical metasurfaces are artificial sheet materials composed of periodic subwavelength metal/dielectric structures in the horizontal dimensions, which can produce a desired optical wavefront transformation and thereby allows the control of direction, polarization, phase, and amplitude for reflected and transmitted optical fields. Metasurface properties require a strong spatial modulation of the light matter interaction strength. This modulation is either achieved using the plasmonic response in metallic antenna structures or with the aid of Mie resonances in dielectric nanostructures (dielectric metamaterials). OBJECT OF THE INVENTION For the fabrication of optical metasurfaces, two main approaches were used so far: i) top-down methods which rely on photolithography or electron-beam lithography and following etching, deposition, and lift-off processes,ii) bottom-up approaches that include laser/ion-beam printing, or self-assembly methods. Thus, most reported metasurfaces need an additive or subtractive fabrication process and have static functionalities that depend on their fixed geometrical parameters and cannot be changed after fabrication. As a consequence, these techniques lead to irreversible modifications of the metasurface material thereby excluding dynamic adaptations/modifications of the metasurface. Moreover, most of these methods are limited to be applied to planar surfaces only, thereby excluding its application to 3D objects. It was, therefore, an object of the present invention to avoid the above-mentioned disadvantages and to provide for an easier (less process steps) and more flexible method of manufacture of metasurfaces, allowing for a dynamic modification of the metasurface, which inter alia means that the surface modifications are reversible. BRIEF DESCRIPTION OF THE INVENTION This object is achieved with a method for making metasurfaces comprising the steps of: I. Providing a substrate which exhibits at least two dist