A. Robert Ellis

Micrometer‐Scale Cubic Unit Cell 3D Metamaterial Layers

www.MaterialsViews.com C O M Micrometer-Scale Cubic Unit Cell 3D Metamaterial Layers M U N I By D. Bruce Burckel , * Joel R. Wendt , Gregory A. Ten Eyck , James C. Ginn , A. Robert Ellis , Igal Brener , and Michael B. Sinclair C A IO N The electromagnetic (EM) behavior of most bulk materials can be summarized by two frequency dependent tensors, the dielectric permittivity ( ε ) and the magnetic permeability ( μ ). The fi eld of metamaterials is predicated upon the possibility that man-made materials can exhibit absolute control over the magnitude and sign of both ε and μ within a specifi ed spectral band through the use of designed inclusions with specifi c engineered EM properties to create a new class of devices with enhanced functionality. For non-chiral, artifi cially structured materials, exotic EM behaviors such as perfect lensing [ 1 ] and negative refraction [ 2 ] are possible where ε and μ are simultaneously negative while cloaking requires the ability to spatially vary the permittivity and/or permeability over a wide range of values according to prescriptions from transformation optics. [ 3 ] In practice, achieving simultaneous negative ε and μ is diffi cult. The permittivity of metals below the bulk plasma frequency is inherently negative, and can be large; [ 4 ] however, naturally occurring negative permeability is quite rare, being presently limited to ferromagnetic materials at RF frequencies and lower. Furthermore, at high frequencies (optical and infrared) the response of materials to incident electromagnetic fi elds is dominated by the permittivity of the material, since the magnetic susceptibility is typically 4 orders of magnitude smaller in bulk materials than the electric susceptibility, [ 5 ] making μ r ≈ 1. In 1999 Pendry proposed an isotropic cubic unit cell with split ring resonators (SRR) located on its faces as a method for creating an artifi cially magnetic material in the microwave frequency range. [ 6 ] Shortly after Pendry proposed using SRRs to achieve magnetic permeability tuning of the resulting material, a negative index material was demonstrated with design wavelength λ = 30 mm (microwave) using a combination of SRRs and wires. [ 7 ] The individual SRRs measured 2.6 mm/side, were printed on circuit board material and then assembled into a macroscopic 2D array. One might expect that straightforward extension of the design, fabrication and characterization aspects of microwave metamaterials would lead to analog IR and visible metamaterials merely scaled to the wavelength of interest. In practice, however, translation of metamaterials

Fabrication of 3D Metamaterial Resonators Using Self-Aligned Membrane Projection Lithography

Fabrication of composite materials with designed constituent elements of sub-micrometer size typically requires cutting edge lithography techniques such as immersion lithography, [ 4 ] nanoimprint lithography, [ 5 ] or e-beam lithography. [ 6 ] While these techniques are capable of printing features with the requisite lateral dimensions, they are all planar patterning approaches, and hence offer limited options for creation of 3D structures, or structures with out-of-plane components. Other patterning techniques such as interferometric lithography are capable of creating 3D structures, [ 7 ] but are typically limited to periodic patterns, while direct write approaches are serial, [ 8 ] and hence do not scale well, severely limiting the design space. We introduce a fabrication technique called membrane projection lithography (MPL) which combines planar lithography with a sequence of processing steps to create micrometer-scale structures with out-of-plane components. The method is general, and can be repeated in a layer-by-layer fashion to create 3D volumetric materials with engineered inclusions. The basic premise behind MPL is to create a patterned membrane positioned over a cavity, and then use directional evaporation through the membrane to deposit instances of the membrane pattern on the interior face of the cavity. We fabricate micrometerscale metallic resonators using two separate MPL process fl ows: self-aligned MPL (SAMPL), and single-evaporation MPL (SEMPL). MPL is somewhat related to microstencil fabrication used in micro electromechanical systems (MEMS) fabrication, although the size scale, and linewidths of the patterns we present here are typically at least a factor of 10 smaller than those reported elsewhere. [ 9 ]

Doping-tunable thermal emission from plasmon polaritons in semiconductor epsilon-near-zero thin films

We utilize the unique dispersion properties of leaky plasmon polaritons in epsilon-near-zero (ENZ) thin films to demonstrate thermal radiation control. Owing to its highly flat dispersion above the light line, a thermally excited leaky wave at the ENZ frequency out-couples into free space without any scattering structures, resulting in a narrowband, wide-angle, p-polarized thermal emission spectrum. We demonstrate this idea by measuring angle- and polarization-resolved thermal emission spectra from a single layer of unpatterned, doped semiconductors with deep-subwavelength film thickness ( d/λ0 ∼ 6×10−3, where d is the film thickness and  λ0 is the free space wavelength). We show that this semiconductor ENZ film effectively works as a leaky wave thermal radiation antenna, which generates far-field radiation from a thermally excited mode. The use of semiconductors makes the radiation frequency highly tunable by controlling doping densities and also facilitates device integration with other components. Ther...

Directional and monochromatic thermal emitter from epsilon-near-zero conditions in semiconductor hyperbolic metamaterials.

The development of novel thermal sources that control the emission spectrum and the angular emission pattern is of fundamental importance. In this paper, we investigate the thermal emission properties of semiconductor hyperbolic metamaterials (SHMs). Our structure does not require the use of any periodic corrugation to provide monochromatic and directional emission properties. We show that these properties arise because of epsilon-near-zero conditions in SHMs. The thermal emission is dominated by the epsilon-near-zero effect in the doped quantum wells composing the SHM. Furthermore, different properties are observed for s and p polarizations, following the characteristics of the strong anisotropy of hyperbolic metamaterials.

Highly directional thermal emission from two-dimensional silicon structures

We simulate, fabricate, and characterize near perfectly absorbing two-dimensional grating structures in the thermal infrared using heavily doped silicon (HdSi) that supports long wave infrared surface plasmon polaritons (LWIR SPPs). The devices were designed and optimized using both finite difference time domain (FDTD) and rigorous coupled wave analysis (RCWA) simulation techniques to satisfy stringent requirements for thermal management applications requiring high thermal radiation absorption over a narrow angular range and low visible radiation absorption over a broad angular range. After optimization and fabrication, characterization was performed using reflection spectroscopy and normal incidence emissivity measurements. Excellent agreement between simulation and experiment was obtained.

Miniaturized UV Fluorescence Collection Optics Integrated with Ion Trap Chips

For practical quantum computing, it will be necessary to detect the fluorescence from trapped ions using microscale ion trap chips. We describe the first design, fabrication and assembly of a set of diffractive optics for intimate integration into the trap chip and for coupling this fluorescence into multimode fibers. The design is complicated by the constraints of the ion trap environment. In addition, the choice of available materials is restricted to those compatible with ultrahigh vacuum. The completed optics-ion trap assembly has successfully demonstrated ion trapping, as well as ion shuttling, with no necessary modifications to the trapping and shuttling voltage levels.

Precision alignment of integrated optics in surface electrode ion traps for quantum information processing.

The integration of optics for efficient light delivery and the collection of fluorescence from trapped ions in surface electrode ion traps is a key component to achieving scalability for quantum information processing. Diffractive optical elements (DOEs) present a promising approach as compared to bulk optics because of their small physical profile and their flexibility in tailoring the optical wavefront. The precise alignment of the optics for coupling fluorescence to and from the ions, however, poses a particular challenge. Excitation and manipulation of the ions requires a high degree of optical access, significantly restricting the area available for mounting components. The ion traps, DOEs, and other components are compact, constraining the manipulation of various elements. For efficient fluorescence collection from the ions the DOE must be have a large numerical aperture (NA), which results in greater sensitivity to misalignment. The ion traps are sensitive devices, a mechanical approach to alignment such as contacting the trap and using precision motors to back-off a set distance not only cannot achieve the desired alignment precision, but risks damage to the ion trap. We have developed a non-contact precision optical alignment technique. We use line foci produced by off-axis linear Fresnel zone plates (FZPs) projected on alignment targets etched in the top metal layer of the ion trap and demonstrate micron-level alignment accuracy.