Injection Molding of Free‐Standing, Three‐Dimensional, All‐Metal Terahertz Metamaterials

Abstract

Fabrication of free‐standing two‐ and three‐dimensional terahertz meta­materials is demonstrated via injection molding of gallium, a metal that melts at temperatures just slightly above room temperature. Molds are created by inscribing the desired microchannel geometries in one or two polydimethylsiloxane (PDMS) films using conventional soft lithography techniques and then reversibly bonding the two films together using van der Waals forces. After heating gallium above its melting point (∼30 °C), the liquid metal is injected into the mold. Surprisingly, the metal does not solidify even after cooling the filled mold at −16 °C for 24 h. However, when the liquid metal comes into contact with solid gallium at room temperature, the entire metal device solidifies within the mold immediately. The PDMS films can then be peeled away, yielding a free‐standing solid gallium structure. A 2D split ring resonator‐based metamaterial is fabricated and three different approaches for creating 3D metamaterials are demonstrated: a multilayer stack, a manually folded structure that maintains its shape after folding, and a directly injection molded 3D structure. The transmission properties of these devices are measured using terahertz time‐domain spectroscopy and are shown to not suffer from limitations imposed by substrates.

Three dimensional printing of metamaterial embedded geometrical optics (MEGO)

“…So far, we have shown disk and split ring resonators which are planar and can be fabricated by photolithography but there are some truly three dimensional resonators that cannot be fabricated by conventional photolithography or may require multiple steps (>10) of photolithography. Even injection molding may not be possible due to discontinuities, sharp curvatures and higher aspect ratios in some 3D designs 60 . In Fig.…”

Direct Writing of Microfluidic Three-Dimensional Photonic Crystal Structures for Terahertz Technology Applications

“…Metallic photonic crystals in terahertz range have small losses and big gaps compared with their dielectric counterparts and thus can be applied in various technical applications . Although metallic two-dimensional TPCs were reported in literature, , there are few studies on metallic 3D-TPCs due to the lack of feasible creation methods . Our microfluidic 3D-TPCSs made the creation of metallic 3D-TPCs relatively easily.…”

“…28 Although metallic two-dimensional TPCs were reported in literature, 29,30 there are few studies on metallic 3D-TPCs due to the lack of feasible creation methods. 31 Our microfluidic 3D-TPCSs made the creation of metallic 3D-TPCs relatively easily. With a simple injection of a liquid alloy into our microfluidic 3D-TPCSs, metallic 3D-TPCs could be created due to the formation of reverse woodpile metallic structures in their microstructured channels.…”

Gallium platinum alloys – a new material system for UV plasmonics

“…Gallium is another attractive plasmonic material that has an added advantage of allowing for changes in its dielectric properties via thermally-driven phase transitions at close to room temperature [20][21][22]. In bulk form, the metal can be easily melted and reshaped to yield the desired geometry [23]. However, Ga does not easily wet most common substrates, including Si and a variety of glasses, making vacuum deposition of thin, continuous Ga films extremely challenging.…”