Reconfigurable nanomechanical photonic metamaterials

Abstract

Video file:FIB_Fabrication.mov Title:Focused ion beam fabrication of an array of metamaterial samples Description:Prototyping membrane reconfigurable metamaterial. Focused ion beam (FIB) milling is used to pattern a 4 x 4 array of metamaterial samples on pre-fabricated gold patches supported by a silicon nitride membrane of 50 nm thickness. Milling includes patterning of the gold film and cutting through the silicon nitride membrane, where appropriate. The video, which has been recorded by scanning electron microscopy (SEM), is compressed to a few seconds while the total FIB milling time is about 22 minutes. Video courtesy of Jun-Yu Ou.Video file: Actuating_Chevron_Metamaterial.mov Title:Actuating nanomembrane chevron metamaterial Description:Chevron nanowire array fabricated on a silicon nitride nanomembrane. To show reconfiguration of the metamaterial every second chevron nanowire is heated by electrical current running through the nanowire and heated nanowires bend due to differential thermal expansion of the gold and silicon nitride layers that make up the nanowires. The SEM video shows the central part of the array with alternating nanowires moving from the plane of the array. Actuation of the metamaterial is seen at a viewing angle of 30° while the total applied current is increased from zero to +7 mA and then reduced via zero to -7 mA and finally returned to zero. The same structure can also be driven by the magnetic Lorentz force acting on current-carrying nanowires when an external magnetic field that is oriented perpendicular to the current flow is applied. Note that SEM imaging of nanowire actuation driven by the Lorentz force is impossible, as the required static magnetic field would interfere with the scanning electron microscope. Video courtesy of João P. Valente.Video file: Electrostatic_Metamaterial_Switch.mov Title:Switching nanomembrane electro-optical metamaterial with the Coulomb force Description:Irreversible switching transition of an electrostatically reconfigurable plasmonic metamaterial fabricated on a silicon nitride nanomembrane. When the driving voltage is less than the switching threshold voltage of about 3 V, the structure can be modulated in a reversible fashion. The SEM video shows that when the applied voltage increases above the threshold voltage, the plasmonic nanostructure switches irreversibly into a string-pair configuration, resulting in a dramatic change of the metamaterial's optical properties. The image drift is caused by the applied voltage. Video courtesy of Jun-Yu Ou.Video file: Random_Access_Metamaterial.mov Title:Actuating individual wires in randomly reconfigurable nanomembrane metamaterial Description:Random access reconfigurable metamaterial. An array of nanowires on a silicon nitride nanomembrane allows independent electrical actuation of each nanowire of the array. The SEM video shows how electrical current supplied to individual nanowires by a computer-controlled multi-channel digital-to-analog converter actuates the nanostructure. In this way the optical resp...

Nano‐ and Micro‐Auxetic Plasmonic Materials

“…However, the plasmonic response and thus the optical properties of metamaterials have been shown to be highly sensitive to the geometry of the structure. [ 28 ] We argue that also actuation of micro-and nanoscale auxetic metamaterials will lead to pronounced changes of their optical properties, such as changes of strength and spectral position of plasmonic resonances.…”

“…[ 18 ] Careful design of the auxetic scaffold that supports plasmonic or high-index dielectric resonators enables unique combinations of mechanical and optical properties that may be controlled through actuation with sub-microsecond response times. [ 28 ] Recent advances in MEMS and NEMS reconfi gurable metamaterials [ 30,31,33 ] provide solutions for electrical actuation of micro-and nano-auxetic metamaterials, enabling applications in optoelectronic devices, e.g., tunable wave plates based on anisotropic auxetics, and polarization insensitive nano mechanical light modulators and variable fi lters based on isotropic auxetics. Miniaturization of such structures drives up achievable modulation speeds, which are expected to reach gigahertz on the nanoscale, [ 28 ] and, in contrast to conventional reconfi gurable metamaterials, auxetic devices could also benefi t from enhanced mechanical properties such as fatigue and indentation resistance.…”

“…Our nano-auxetic metamaterials are based on the re-entrant honeycomb design, which is known for auxetic properties for a wide range of beam thicknesses, sizes, and angles. [ 11 ] Inspired by recent work in the fi eld of nanomechanical photonic devices, [ 28 ] nanomembrane technology was used to fabricate auxetics with lattice parameters in the range from a few micrometers to hundreds of nanometers. Nanomembrane technology has already provided simple and effi cient solutions for reconfi guration of nanoscale structures that are not auxetic, enabling nanomechanical devices and sensors.…”

Metamaterials at the University of Southampton and beyond

“…At the submicrometre dimensions of metamolecules, Coulomb, Ampère and Lorentz forces, compete with elastic forces and can thus be used to reconfigure the shape of individual metamolecules, or their mutual arrangement. We have identified that nanomembranes are the ideal platform for such nano-optomechanical reconfigurable metamaterials [65]. Metamaterials on structured membranes can be reconfigured thermoelastically [66], mechanically [67], electrically [68] and magnetically [69].…”

Photomechanical meta-molecule array for real-time terahertz imaging

“…Because the performance of the metamaterial absorber is primarily determined by the designed structure of the meta-atom rather than its composites, the microfabrication friendly materials, typically demonstrate low loss in the THz regime, can convert the THz energy to heat with high efficiency. Recently, several researchers have attempted to combine the metamaterial with micromechanical structures 21 . By mechanically changing the geometry of the metamaterials, the optical properties can be modulated effectively, and several novel phenomena have been realized, such as state switching, anisotropy control, and resonance shifting [22][23][24] .…”