Gregory A. Ten Eyck

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 ]

Coherent coupling between a quantum dot and a donor in silicon

Individual donors in silicon chips are used as quantum bits with extremely low error rates. However, physical realizations have been limited to one donor because their atomic size causes fabrication challenges. Quantum dot qubits, in contrast, are highly adjustable using electrical gate voltages. This adjustability could be leveraged to deterministically couple donors to quantum dots in arrays of qubits. In this work, we demonstrate the coherent interaction of a 31P donor electron with the electron of a metal-oxide-semiconductor quantum dot. We form a logical qubit encoded in the spin singlet and triplet states of the two-electron system. We show that the donor nuclear spin drives coherent rotations between the electronic qubit states through the contact hyperfine interaction. This provides every key element for compact two-electron spin qubits requiring only a single dot and no additional magnetic field gradients, as well as a means to interact with the nuclear spin qubit.In silicon, quantum information can be stored in donors or quantum dots, each with its advantages and limitations—particularly in terms of fabrication. Here the authors coherently couple a phosphorous donor’s electron spin to a quantum dot, encoding information in the hybrid two-electron system’s state.

All-dielectric metamaterials: Path to low losses and high spectral selectivity

Ohmic losses severely limit the performance of metamaterials. High-index semiconductors offer an attractive alternative. We review several meta-surfaces based on silicon and silicon carbide enabling infrared applications such as polarization manipulation and thermal emission.

Waveguide sensor for detection of HNS degradation

Hexanitrostilbene (HNS) is a secondary explosive widely used in a variety of commercial and military applications, due in part to its high heat resistivity. Degradation of HNS is known to occur through exposure to a variety of sources including heat, UV radiation, and certain chemical compounds, all of which may lead to reduced performance. Detecting the degradation of HNS within a device, however, has required destructive analyses of the entire device while probing the HNS in only an indirect fashion. Specifically, the common methods of investigating this degradation include wet chemical, surface area and performance testing of the devices incorporating HNS rather than a direct interrogation of the material itself. For example, chemical tests frequently utilized, such as volatility, conductivity, and contaminant trapping, provide information on contaminants present in the system rather than the chemical stability of the HNS. To instead probe the material directly, we have pursued the use of optical methods, in particular infrared (IR) spectroscopy, in order to assess changes within the HNS itself. In addition, by successfully implementing miniature silicon (Si) waveguides fabricated at Sandia National Laboratories to facilitate this spectroscopic approach, we have demonstrated that HNS degradation monitoring may take place in a non-destructive, in-situ fashion. Furthermore, as these waveguides may be manufactured in a variety of configurations, this direct, non-destructive, approach holds promise for incorporation into a variety of devices.

Electrostatic microvalves utilizing conductive nanoparticles for improved speed, lower power, and higher force actuation.

We have designed and built electrostatically actuated microvalves compatible with integration into a PDMS based microfluidic system. The key innovation for electrostatic actuation was the incorporation of carbon nanotubes into the PDMS valve membrane, allowing for electrostatic charging of the PDMS layer and subsequent discharging, while still allowing for significant distention of the valveseat for low voltage control of the system. Nanoparticles were applied to semi-cured PDMS using a stamp transfer method, and then cured fully to make the valve seats. DC actuation in air of these valves yielded operational voltages as low as 15V, by using a supporting structure above the valve seat that allowed sufficient restoring forces to be applied while not enhancing actuation forces to raise the valve actuation potential. Both actuate to open and actuate to close valves have been demonstrated, and integrated into a microfluidic platform, and demonstrated fluidic control using electrostatic valves.

Vibrational Spectroscopy of HNS Degradation

Hexanitrostilbene (HNS) is a widely used explosive, due in part to its high thermal stability. Degradation of HNS is known to occur through UV, chemical exposure, and heat exposure, which can lead to reduced performance of the material. Common methods of testing for HNS degradation include wet chemical and surface area testing of the material itself, and performance testing of devices that use HNS. The commonly used chemical tests, such as volatility, conductivity and contaminant trapping provide information on contaminants rather than the chemical stability of the HNS itself. Additionally, these tests are destructive in nature. As an alternative to these methods, we have been exploring the use of vibrational spectroscopy as a means of monitoring HNS degradation non-destructively. In particular, infrared (IR) spectroscopy lends itself well to non-destructive analysis. Molecular variations in the material can be identified and compared to pure samples. The utility of IR spectroscopy was evaluated using pressed pellets of HNS exposed to DETA (diethylaminetriamine). Amines are known to degrade HNS, with the proposed product being a σ-adduct. We have followed these changes as a function of time using various IR sampling techniques including photoacoustic and attenuated total reflectance (ATR).