Metal-based negative refractive index materials have been extensively studied in the microwave region. However, negative-index metamaterials have not been realized at near-IR or visible frequencies due to difficulties of fabrication and to the generally poorer optical properties of metals at these wavelengths. In this paper, we report the first fabrication and experimental verification of a transversely structured metal-dielectric-metal multilayer exhibiting a negative refractive index around 2 µm. Both the amplitude and the phase of the transmission and reflection were measured experimentally, and are in good agreement with a rigorous coupled wave analysis. PACS: 78.20.Ci; 42.25.Bs; 42.79.Dj Negative refractive-index materials are of great interest for a variety of potential applications. 1 Because natural negative refractive index materials do not exist, artificial structures have been proposed and fabricated that exhibit an effective negative index over limited frequency ranges. 2 The two principal approaches to the realization of negative refraction are metamaterials and photonic crystals. Metamaterials typically use metallic structures to provide a negative permittivity and use resonant structures (inductor-capacitor tank circuits) with a scale much smaller than the wavelength to provide a negative permeability leading to negative refraction, while § Email: brueck@chtm.unm.edu photonic crystals exhibit negative refraction as a consequence of band-folding effects. In the microwave region, negative index materials have been demonstrated using both approaches, while in the visible spectral region, negative refraction has been recently predicted. 3 In recent work, magnetically resonant structures exhibiting negative permeability have been demonstrated in the mid-infrared. 4,5 Despite theoretical studies and numerical modeling, 6,7 demonstration of negative refraction at near-infrared (near-IR) and visible wavelengths is as yet missing and, therefore, the experimental demonstration of a negative refractive index around 2 µm presented here represents an important milestone.Extension of metamaterials based on split ring resonators 8 to near-IR and visible wavelengths necessarily involves complicated and often difficult fabrication for the nanoscale metallic structures used to generate the requisite resonances. On the other hand, much of the photonic crystal literature has focused on all-dielectric structures because of their low-loss characteristics.Recent related work has used periodic metallic structures to couple incident radiation to surface plasma waves giving enhanced optical transmission through arrays of sub-wavelength holes in a metal film. 9,10 In this work, a hybrid approach is introduced which uses a pair of metal layers separated by a dielectric to provide resonant interactions (e. g. distributed inductance/capacitance) along with a periodic array of holes through the film stack to facilitate interaction with the surface plasma waves of the composite structure.The structure consists of a glass subs...

We numerically demonstrate a metamaterial with both negative epsilon and negative mu over an overlapping near-infrared wavelength range resulting in a low loss negative-index material. Parametric studies optimizing this negative index are presented. This structure can be easily fabricated with standard semiconductor processing techniques.

This report presents a study of electrokinetic transport in a series of integrated macro- to nano-fluidic chips that allow for controlled injection of molecular mixtures into high-density arrays of nanochannels. The high-aspect-ratio nanochannels were fabricated on a Si wafer using interferometric lithography and standard semiconductor industry processes, and are capped with a transparent Pyrex cover slip to allow for experimental observations. Confocal laser scanning microscopy was used to examine the electrokinetic transport of a negatively charged dye (Alexa 488) and a neutral dye (rhodamine B) within nanochannels that varied in width from 35 to 200 nm with electric field strengths equal to or below 2000 V m-1. In the negatively charged channels, nanoconfinement and interactions between the respective solutes and channel walls give rise to higher electroosmotic velocities for the negatively charged dye than for the neutral dye, towards the negative electrode, resulting in an anomalous separation that occurs over a relatively short distance (<1 mm). Increasing the channel widths leads to a switch in the electroosmotic transport behavior observed in microscale channels, where neutral molecules move faster because the negatively charged molecules are slowed by the electrophoretic drag. Thus a clear distinction between "nano-" and "microfluidic" regimes is established. We present an analytical model that accounts for the electrokinetic transport and adsorption (of the neutral dye) at the channel walls, and is in good agreement with the experimental data. The observed effects have potential for use in new nano-separation technologies.

This communication reports strongly anisotropic wetting behavior on one-dimensional nanopatterned surfaces. Contact angles, degree of anisotropy, and droplet distortion are measured on micro- and nanopatterned surfaces fabricated with interference lithography. Both the degree of anisotropy and the droplet distortion are extremely high as compared with previous reports because of the well-defined nanostructural morphology. The surface is manipulated to tune with the wetting from hydrophobic to hydrophilic while retaining the structural wetting anisotropy with a simple silica nanoparticle overcoat. The wetting mechanisms are discussed. Potential applications in microfluidic devices and evaporation-induced pattern formation are demonstrated.

Interferometric lithography (IL) is a powerful technique for the definition of large-area, nanometer-scale, periodically patterned structures. Patterns are recorded in a light-sensitive medium, such as a photoresist, that responds nonlinearly to the intensity distribution associated with the interference of two or more coherent beams of light. The photoresist patterns produced with IL are a platform for further fabrication of nanostructures and growth of functional materials and are building blocks for devices. This article provides a brief review of IL technologies and focuses on various applications for nanostructures and functional materials based on IL including directed self-assembly of colloidal nanoparticles, nanophotonics, semiconductor materials growth, and nanofluidic devices. Perspectives on future directions for IL and emerging applications in other fields are presented.