Highly conformable terahertz metasurface absorbers via two-photon polymerization on polymeric ultra-thin films

Abstract

The continuously increasing interest in flexible and integrated photonics requires new strategies for device manufacturing on arbitrary complex surfaces and with smallest possible size, respectively. Terahertz (THz) technology can particularly benefit from this achievement to make compact systems for emission, detection and on-demand manipulation of THz radiation. Here, we present a novel fabrication method to realize conformable terahertz metasurfaces. The flexible and versatile character of polymeric nanomembranes is combined with direct laser writing via two-photon polymerization to develop free-standing ultra-thin quasi-perfect plasmonic absorbers with an unprecedentedly high level of conformability. Moreover, revealing new flexible dielectric materials presenting low absorption and permittivity in the THz range, this work paves the way for the realization of ultra-thin, conformable hybrid or all-dielectric devices to enhance and enlarge the application of THz technologies, and flexible photonics in general.

Novel fabrication method for highly conformable THz metasurfaces

“…Through a single deposition of a gold layer, two complementary metal patterns displaced by the thickness of the 2PP printed metasurface are created. This two-plane metal resonator distribution already presents absorption resonances at THz frequencies [5] due to the excitation of the LC-mode. By coupling a second metallized PVF film via Van der Waals adhesion to the bottom of the device a double-metal structure is created.…”

“…A novel fabrication method for the realization of conformable metasurfaces is reported. In particular, as a demonstrator of the developed technique, ultra-sub-wavelength free-standing plasmonic metasurface THz absorbers with high degree of conformability were fabricated [5]. The proposed technique exploits the combination between direct laser writing via two-photon polymerization (2PP) and transfer printing using ultra-thin polymeric membranes.…”

“…In this particular work, the 2PP process is performed to realize the metasurface geometry − the in-plane meta-molecules arrangements and the corresponding thickness − while the enhanced spontaneous delamination of a few nanometers thin polyvinyl-formal layer (PVF) via substrate functionalization allows to detach and handle the entire structure after previous metallization. The whole device can be thus straightforwardly suspended or transferred onto a final target using different techniques [5,6]. A graphic description of the fabrication steps of the conformable metasurfaces is shown in Figure1.…”

“…The experimental absorption spectra measured with unpolarized light at 45 degree of incidence is shown to be in good agreement with simulations. Thanks to the ultra-thin thickness and high elasticity of the polymeric materials, objects with curvature down to few tens micrometers can be easily wrapped with the fabricated metasurfaces [5], as also shown in Figure 2e. The response of the same metasurface of both flat and conformed configurations is reported in Figure 2f.…”

Facile Handling of 3D Two‐Photon Polymerized Microstructures by Ultra‐Conformable Freestanding Polymeric Membranes

“…Examples of ultra‐thin polymeric films (with thickness < 1 µm) comprise a variety of applications that span the fields of polymer science, [ 39 ] biomedics, [ 40 ] tissue engineering, [ 41,42 ] sensing, [ 43 ] and, more recently, wearable/flexible electronics [ 44–46 ] and photonics. [ 28,47 ] Accordingly, in these latter demonstrations, polymeric nano‐films were used as free‐standing supports to achieve device adhesion on nonplanar surfaces owing to their few nanometer thicknesses, which maximizes the adhesion by dispersion forces and minimize the strain forces originating from bending phenomena (which might induce damage). This is because, for a thin plate, as the film thickness ( t ) decreases the bending stiffness of the film ( D ), given by the product of the film Young's modulus ( E ) and the second‐moment area ( I ), approximately varies according to Equation 1: [ 27,35 ] $$\[ \begin{array}{*{20}{c}}{D\; = \;E\cdotI\; = \;E\frac{{{t^3}}}{{12\left( {1 - {\nu ^2}} \right)}}}\end{array} \]$$where ν is the film Poisson ratio.…”