Publications

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A tandem interferometer system measuring the absolute phase and amplitude of planar split-ring resonators fabricated on a BaF2 substrate with a designed resonance at 10.5 μm is presented. © 2010 Optical Society of America.

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We report low-temperature transport measurements of a silicon metal-oxide-semiconductor (MOS) double quantum dot (DQD). In contrast to previously reported measurements of DQD's in Si MOS structures, our device has a lateral gate geometry very similar to that used by Petta et al. to demonstrate coherent manipulation of single electron spins. This gate design provides a high degree of tunability, allowing for independent control over individual dot occupation and tunnel barriers, as well as the ability to use nearby constrictions to sense dot charge occupation. Comparison of experimentally extracted capacitances between the dot and nearby gates with electrostatic modeling demonstrates the presence of disorder and the ability to partially compensate for this disorder by adjustment of gate voltages. We experimentally show gate-controlled tuning of the interdot coupling over a wide range of energies, an important step towards potential quantum computing applications.

We fabricated a split-gate defined point contact in a double gate enhancement mode Si-MOS device, and implanted Sb donor atoms using a self-aligned process. E-beam lithography in combination with a timed implant gives us excellent control over the placement of dopant atoms, and acts as a stepping stone to focused ion beam implantation of single donors. Our approach allows us considerable latitude in experimental design in-situ. We have identified two resonance conditions in the point contact conductance as a function of split gate voltage. Using tunneling spectroscopy, we probed their electronic structure as a function of temperature and magnetic field. We also determine the capacitive coupling between the resonant feature and several gates. Comparison between experimental values and extensive quasi-classical simulations constrain the location and energy of the resonant level. We discuss our results and how they may apply to resonant tunneling through a single donor.

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Metamaterials form a new class of artificial electromagnetic materials that provides the device designer with the ability to manipulate the flow of electromagnetic energy in ways that are not achievable with naturally occurring materials. However, progress toward practical implementation of metamaterials, particularly at infrared and visible frequencies, has been hampered by a combination of absorptive losses; the narrow band nature of the resonant metamaterial response; and the difficulty in fabricating fully 3-dimensional structures. They describe the progress of a recently initiated program at Sandia National Laboratories directed toward the development of practical 3D metamaterials operating in the thermal infrared. They discuss their analysis of fundamental loss limits for different classes of metamaterials. In addition, they discuss new design approaches that they are pursuing which reduce the reliance on metallic structures in an effort to minimize ohmic losses.

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We present a new fabrication technique called Membrane Projection Lithography for the production of three-dimensional metamaterials at infrared wavelengths. Using this technique, multilayer infrared metamaterials that include both in-plane and out-of-plane resonators can be fabricated.

Dielectric resonators are an effective means to realize isotropic, low-loss optical metamaterials. As proof of this concept, a cubic resonator is analytically designed and then tested in the long-wave infrared.

The authors have developed two versions of a flexible fabrication technique known as membrane projection lithography that can produce nearly arbitrary patterns in '212 D' and fully three-dimensional (3D) structures. The authors have applied this new technique to the fabrication of split ring resonator-based metamaterials in the midinfrared. The technique utilizes electron beam lithography for resolution, pattern design flexibility, and alignment. The resulting structures are nearly three orders of magnitude smaller than equivalent microwave structures that were first used to demonstrate a negative index material. The fully 3D structures are highly isotropic and exhibit both electrically and magnetically excited resonances for incident transverse electromagnetic waves.

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3-D cubic unit cell arrays containing split ring resonators were fabricated and characterized. The unit cells are {approx}3 orders-of-magnitude smaller than microwave SRR-based metamaterials and exhibit both electrically and magnetically excited resonances for normally incident TEM waves in addition to showing improved isotropic response.

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We describe a time-domain spectroscopy system in the thermal infrared used for complete transmission and reflection characterization of metamaterials in amplitude and phase. The system uses a triple-output near-infrared ultrafast fiber laser, phase-locked difference frequency generation and phase-matched electro-optic sampling. We will present measurements of several metamaterials designs.