S. Virasawmy

All-metal self-supported THz metamaterial--the meta-foil.

Modern metamaterials face functional constraints as they are commonly embedded in or deposited on dielectric materials. We provide a new solution by microfabricating a completely free-standing all-metal self-supported metamaterial. Using upright S-string architecture with the distinctive feature of metallic transverse interconnects, we form a locally stiff, globally flexible space-grid. Infrared Fourier transform interferometry reveals the typical double-peak structure of a magnetically excited left-handed and an electrically excited right-handed pass-band that is maintained under strong bending and heating, and is sensitive to dielectrics. Exploiting UV/X-ray lithography and ultimately plastic moulding, meta-foils can be mass manufactured cost-effectively to serve as optical elements.

THz meta-foil – a platform for practical applications of metamaterials

The meta-foil, an all-metal fully self-supported locally stiff and globally flexible metamaterial, is presented. Its architecture is based on an array of parallel S-strings interconnected by transverse metal rods that are periodically repeated along the strings. For the present samples, this period is about once or twice the length of an S, which is 31 µm. The resonance frequency of the left-handed pass-band is 3.2 THz or somewhat higher depending on geometry. The meta-foil is manufactured by UV or X-ray lithography-based microfabrication. In the end, it may be produced cost-effectively by plastic moulding. The physical function is explained by numerical simulation and equivalent circuit theory. The spectra are measured by Fourier transform infrared spectroscopy. Maximum transmission is achieved at normal incidence with a cosine-square-like decrease with incidence angle. A change of geometrical parameters alters the resonance frequency as expected. The spectra are also rather sensitive to surrounding dielectrics, indicating a sensor capability. As the meta-foil can be bent, a cylindrical hyperlens set-up is discussed as a forthcoming application to sub-wavelength resolution imaging.

Micro/nanomanufactured THz electromagnetic metamaterials as a base for applications in transportation

Micro/nanomanufactured electromagnetic metamaterials in the THz spectral range may help extending the use of metamaterials in transportation. S-string based THz metamaterials as manufactured by SSLS, in particular, the meta-foil, provide a promising platform for applications. Special emphasis may be given to antennas being conformal or quickly steerable or tunable for inter-traffic communication. Achievements by SSLS in co-operation with MIT and Zhejiang University are discussed and potential applications outlined.

Self-supported all-metal THz metamaterials

Ideal metamaterials would consist of metal conductors only that are necessary for negative ε and μ. However, most of present-day metamaterials include dielectrics for various support functions. Overcoming dielectrics, we manufactured free-standing THz metamaterials as bi-layer chips of S-string arrays suspended by window-frames at a small gap that controls the resonance frequency. Remaining problems concerning their useful range of incidence angles and the possibility of stacking have been solved by manufacturing the first self-supported free-standing all-metal metamaterials featuring upright S-strings interconnected by metal rods. Large-area slabs show maximum magnetic coupling at normal incidence with left-handed resonances between 3.2 - 4.0 THz. Such metamaterials which we dub the meta-foil represent an ideal platform for including index-gradient optics to achieve optical functionalities like beam deflection and imaging.

Manufacturing Metamaterials Using Synchrotron Lithography

The function of metamaterials relies on their resonant response to electromagnetic waves in characteristic spectral bands. To make metamaterials homogeneous, the size of the basic resonant element should be less than 10% of the wavelength. For the THz range up to the visible, structure details of 50 nm to 30 μm are required as are high aspect ratios, tall heights, and large areas. For such specifications, lithography, in particular, synchrotron radiation deep X-ray lithography, is the method of choice. X-ray masks are made via primary pattern generation by means of electron or laser writing. Several different X-ray masks and accurate mask-substrate alignment are necessary for architectures requiring multi-level lithography. Lithography is commonly followed by electroplating of metallic replica. The process can also yield mould inserts for cost-effective manufacture by plastic moulding. We made metamaterials based on rod-split-rings, split-cylinders, S-string bi-layer chips, and S-string meta-foils. Left-handed resonance bands range from 2.4 to 216 THz. Latest is the all-metal self-supported flexible meta-foil with pass-bands of 45% up to 70% transmission at 3.4 to 4.5 THz depending on geometrical parameters.

Design and fabrication of gold nanostructures with nanosphere lithography for LSPR applications

This paper reports the details regarding the design and fabrication of gold nanostructures on glass substrates through nanosphere lithography (NSL) for the application of localized surface plasmon resonance (LSPR), which can be used for biosensors. It is realized through gold film deposition on nanospheres dispersed on a surface and subsequent anisotropic etching. Depending on the gold deposition and etching conditions, a variety of gold nanostructure shapes can be obtained. So far through this method, only 2D nanocrescents are reported. In this paper it is pointed out that both 2D and 3D non-conformal nanostructures can be fabricated, and some 2D and 3D profiles of the obtainable nanostructures are simulated by our programs under various deposition and etching conditions. The fabrication processes of the nanostructures on glass substrates are also reported, and the simulated profiles of such nanostructures coincide well with the experimental results. These results prove that our profile simulation program can realize the design of 2D and 3D nanostructures obtainable by nanosphere lithography, and reduce the effort and cost for achieving optimized nanostructures by experiments in the trial and error stage.