An optical metamaterial is a composite in which subwavelength features, rather than the constituent materials, control the macroscopic electromagnetic properties of the material. Recently, properly designed metamaterials have garnered much interest because of their unusual interaction with electromagnetic waves. Whereas nature seems to have limits on the type of materials that exist, newly invented metamaterials are not bound by such constraints. These newly accessible electromagnetic properties make these materials an excellent platform for demonstrating unusual optical phenomena and unique applications such as subwavelength imaging and planar lens design. 'Negative-index materials', as first proposed, required the permittivity, epsilon, and permeability, mu, to be simultaneously less than zero, but such materials face limitations. Here, we demonstrate a comparatively low-loss, three-dimensional, all-semiconductor metamaterial that exhibits negative refraction for all incidence angles in the long-wave infrared region and requires only an anisotropic dielectric function with a single resonance. Using reflection and transmission measurements and a comprehensive model of the material, we demonstrate that our material exhibits negative refraction. This is furthermore confirmed through a straightforward beam optics experiment. This work will influence future metamaterial designs and their incorporation into optical semiconductor devices.

We report advances in nanoimprint lithography, its application in nanogap metal contacts, and related fabrication yield. We have demonstrated 5 nm linewidth and 14 nm linepitch in resist using nanoimprint lithography at room temperature with a pressure less than 15 psi. We fabricated gold contacts (for the application of single macromolecule devices) with 5 nm separation by nanoimprint in resist and lift-off of metal. Finally, the uniformity and manufacturability of nanoimprint over a 4 in. wafer were demonstrated.The field of nanotechnology is advancing rapidly. Applications of nanotechnology include subwavelength optical elements, biochemical analysis devices, photonic crystals, high-density single-domain magnetic storage, and singlemolecule devices, to name a few. Yet, key to the commercial success of these nanotechnology applications are low cost and high throughput manufacturing capabilities. State-of-theart manufacturing photolithography patterning tools are both too expensive and incapable of producing the necessary pitch and feature sizes of these applications. Thus, presently, researchers have been largely constrained to using lowthroughput lithography tools, such as electron-beam lithography (EBL), atomic force microscopy (AFM), and ion-beam lithography. For high-throughput and low-cost lithography, various "nanoprinting" technologies have been developed. 1-3 Here, we report our investigation of the resolution limit of nanoimprint lithography, where we demonstrated a nanoimprint record of 5 nm linewidth features and 14 nm pitch over a large area, its applications in nanogap metal contacts, and a study of fabrication yields.In photocurable nanoimprint lithography (P-NIL) (shown in Fig. 1), a mold is pressed into a low viscosity photocurable resist liquid to physically deform the resist shape such that it conforms to the topology of the mold. The resist is cured with exposure to UV light, crosslinking the various components in the resist liquid, producing a uniform, relatively rigid polymer network. The mold is then separated from the cured resist. Finally, an anisotropic reactive ion etch (RIE) removes the residual resist in the compressed area, exposing the substrate surface.In order to explore the performance of P-NIL, a variety of molds were fabricated to test specific attributes, including minimum pitch (maximum density), minimum feature size, and large-area uniformity patterning. Previously, 10 nm dots and 40 nm pitch have been demonstrated by NIL 1 with the resolution limited by our ability to fabricate the mold, as proximity effects inherent with EBL make sub-35 nm pitch patterning very difficult. To produce a mold with a pitch resolution surpassing EBL capabilities, we fabricated a NIL mold by selectively wet etching Al 0.7 Ga 0.3 As from a cleaved edge of a GaAs/ Al 0.7 Ga 0.3 As superlattice [grown by molecular-beam epitaxy (MBE)] with a dilute solution of hydrofluoric acid (HF). 4,5 This mold fabrication process offers many advantages, specifically very dense sub-50 nm pitch topologies can be ...

Infrared absorption spectroscopy of vibro-rotational molecular resonances provides a powerful method for investigation of a wide range of molecules and molecular compounds. However, the wavelength of light required to excite these resonances is often orders of magnitude larger than the absorption cross sections of the molecules under investigation. This mismatch makes infrared detection and identification of nanoscale volumes of material challenging. Here we demonstrate a new type of infrared plasmonic antenna for long-wavelength nanoscale enhanced sensing. The plasmonic materials utilized are epitaxially grown semiconductor engineered metals, which results in high-quality, low-loss infrared plasmonic metals with tunable optical properties. Nanoantennas are fabricated using nanosphere lithography, allowing for cost-effective and large-area fabrication of nanoscale structures. Antenna arrays are optically characterized as a function of both the antenna geometry and the optical properties of the plasmonic semiconductor metals. Thin, weakly absorbing polymer layers are deposited upon the antenna arrays, and we are able to observe very weak molecular absorption signatures when these signatures are in spectral proximity to the antenna resonance. Experimental results are supported with finite element modeling with strong agreement.

Surface plasmon polaritons and their localized counterparts, surface plasmons, are widely used at visible and near-infrared (near-IR) frequencies to confine, enhance, and manipulate light on the subwavelength scale. At these frequencies, surface plasmons serve as enabling mechanisms for future on-chip communications architectures, high-performance sensors, and high-resolution imaging and lithography systems. Successful implementation of plasmonics-inspired solutions at longer wavelengths, in the mid-infrared (mid-IR) frequency range, would benefit a number of highly important technologies in health- and defense-related fields that include trace-gas detection, heat-signature sensing, mimicking, and cloaking, and source and detector development. However, the body of knowledge of visible/near-IR frequency plasmonics cannot be easily transferred to the mid-IR due to the fundamentally different material response of metals in these two frequency ranges. Therefore, mid-IR plasmonic architectures for subwavelength light manipulation require both new materials and new geometries. In this work we attempt to provide a comprehensive review of recent approaches to realize nano-scale plasmonic devices and structures operating at mid-IR wavelengths. We first discuss the motivation for the development of the field of mid-IR plasmonics and the fundamental differences between plasmonics in the mid-IR and at shorter wavelengths. We then discuss early plasmonics work in the mid-IR using traditional plasmonic metals, illuminating both the impressive results of this work, as well as the challenges arising from the very different behavior of metals in the mid-IR, when compared to shorter wavelengths. Finally, we discuss the potential of new classes of mid-IR plasmonic materials, capable of mimicking the behavior of traditional metals at shorter wavelengths, and allowing for true subwavelength, and ultimately, nano-scale confinement at long wavelengths.

We demonstrate thin-film metamaterials with resonances in the mid-infrared wavelength range. Our structures are numerically modeled and experimentally characterized by reflection and angularly-resolved thermal emission spectroscopy. We demonstrate strong and controllable absorption resonances across the mid-infrared wavelength range. In addition, the polarized thermal emission from these samples is shown to be highly selective and largely independent of emission angles from normal to 45 degrees. Experimental results are compared to numerical models with excellent agreement. Such structures hold promise for large-area, low-cost metamaterial coatings for control of gray-or black-body thermal signatures, as well as for possible mid-IR sensing applications.