Publications

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The magnetostatic response of a variety of 3D metallic loop traces are studied numerically by evaluating the Biot- Savart law as a first step in understanding the radiative behavior of such structures. These numerical studies confirm that the magnetostatic behavior of localized planar and non-planar current distributions are equivalent to magnetic dipoles in the far field, however the near-field behavior of these traces can be quite different. © 2012 SPIE.

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The advancement of materials technology towards the development of novel 3D nanostructures for energy applications has been a long-standing challenge. The purpose of this project was to explore photolithographically defineable pyrolyzed photoresist carbon films for possible energy applications. The key attributes that we explored were as follows: (1) Photo-interferometric fabrication methods to produce highly porous (meso, micro, and nano) 3-D electrode structures, and (2) conducting polymer and nanoparticle-modification strategies on these structures to provide enhanced catalytic capabilities and increase conductivity. The resulting electrodes were then explored for specific applications towards possible use in battery and energy platforms.

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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.

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.

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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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This senior council Tier 1 LDRD was focused on exploring the use of porous growth masks as a method for defect reduction during heteroepitaxial crystal growth. Initially our goal was to investigate porous silica as a growth mask, however, we expanded the scope of the research to include several other porous growth masks on various size scales, including mesoporous carbon, photolithographically patterned SU-8 and carbonized SU-8 structures. Use of photolithographically defined growth templates represents a new direction, unique in the extensive literature of patterned epitaxial growth, and presents the possibility of providing a single step growth mask. Additional research included investigation of pore viability via electrochemical deposition into high aspect ratio photoresist. This project was a small footprint research effort which, nonetheless, produced significant progress towards both the stated goal as well as unanticipated research directions.

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This one-year out-of-the-box LDRD was focused on exploring the use of porous growth masks as a method for defect reduction during heteroepitaxial crystal growth. Initially our goal was to investigate porous silica as a growth mask, however, we expanded the scope of the research to include several other porous growth masks on various size scales, including mesoporous carbon, and the UV curable epoxy, SU-8. Use of SU-8 as a growth mask represents a new direction, unique in the extensive literature of patterned epitaxial growth, and presents the possibility of providing a single step growth mask. Additional research included investigation of pore viability via electrochemical deposition into high aspect ratio photoresist patterns and pilot work on using SU-8 as a DUV negative resist, another significant potential result. While the late start nature of this project pushed some of the initial research goals out of the time table, significant progress was made. 3 Acknowledgements This work was performed in part at the Nanoscience @ UNM facility, a member of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation (Grant ECS 03-35765). Sandia is multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United Stated Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. This work was supported under the Sandia LDRD program (Project 99405). 4

A gecko's extraordinary ability to suspend itself from walls and ceilings of varied surface roughness has interested humans for hundreds of years. Many theories and possible explanations describing this phenomenon have been proposed including sticky secretions, microsuckers, and electrostatic forces; however, today it is widely accepted that van der Waals forces play the most important role in this type of dry adhesion. Inarguably, the vital feature that allows a gecko's suspension is the presence of billions 3 of tiny hairs on the pad of its foot called spatula. These features are small enough to reach within van der Waals distances of any surface (spatula radius %7E100 nm); thus, the combined effect of billions of van der Waals interactions is more than sufficient to hold a gecko's weight to surfaces such as smooth ceilings or wet glass. Two lithographic approaches were used to make hierarchal structures with dimensions similar to the gecko foot dimensions noted above. One approach combined photo-lithography with soft lithography (micro-molding). In this fabrication scheme the fiber feature size, defined by the alumina micromold was 0.2 um in diameter and 60 um in height. The second approach followed more conventional photolithography-based patterning. Patterned features with dimensions %7E0.3 mm in diameter by 0.5 mm tall were produced. We used interfacial force microscopy employing a parabolic diamond tip with a diameter of 200 nm to measure the surface adhesion of these structures. The measured adhesive forces ranged from 0.3 uN - 0.6 uN, yielding an average bonding stress between 50 N/cm2 to 100 N/cm2. By comparison the reported literature value for the average stress of a Tokay gecko foot is 10 N/cm2. Acknowledgements This work was funded by Sandia National Laboratory's Laboratory Directed Research & Development program (LDRD). All coating processes were conducted in the cleanroom facility located at the University of New Mexico's Center for High Technology Materials (CHTM). SEM images were performed at UNM's Center for Micro-Engineering on equipment funded by a NSF New Mexico EPSCoR grant. 4

Our discovery that the introduction of living cells (Saccharomyces cerevisiae) alters dramatically the evaporation driven self-assembly of lipid-silica nanostructures suggested the formation of novel bio/nano interfaces useful for cellular interrogation at the nanoscale. This one year ''out of the box'' LDRD focused on the localization of metallic and semi-conducting nanocrystals at the fluid, lipid-rich interface between S. cerevisiae and the surrounding phospholipid-templated silica nanostructure with the primary goal of creating Surface Enhanced Raman Spectroscopy (SERS)-active nanostructures and platforms for cellular integration into electrode arrays. Such structures are of interest for probing cellular responses to the onset of disease, understanding of cell-cell communication, and the development of cell-based bio-sensors. As SERS is known to be sensitive to the size and shape of metallic (principally gold and silver) nanocrystals, various sizes and shapes of nanocrystals were synthesized, functionalized and localized at the cellular surface by our ''cell-directed assembly'' approach. Laser scanning confocal microscopy, SEM, and in situ grazing incidence small angle x-ray scattering (GISAXS) experiments were performed to study metallic nanocrystal localization. Preliminary Raman spectroscopy studies were conducted to test for SERS activity. Interferometric lithography was used to construct high aspect ratio cylindrical holes on patterned gold substrates and electro-deposition experiments were performed in a preliminary attempt to create electrode arrays. A new printing procedure was also developed for cellular integration into nanostructured platforms that avoids solvent exposure and may mitigate osmotic stress. Using a different approach, substrates comprised of self-assembled nanoparticles in a phospholipid templated silica film were also developed. When printed on top of these substrates, the cells integrate themselves into the mesoporous silica film and direct organization of the nanoparticles to the cell surface for integration into the cell.