Publications

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Optical remote sensing has become a valuable tool in many application spaces because it can be unobtrusive, search large areas efficiently, and is increasingly accessible through commercially available products and systems. In the application space of chemical, biological, radiological, nuclear, and explosives (CBRNE) sensing, optical remote sensing can be an especially valuable tool because it enables data to be collected from a safe standoff distance. Data products and results from remote sensing collections can be combined with results from other methods to offer an integrated understanding of the nature of activities in an area of interest and may be used to inform in-situ verification techniques. This work will overview several independent research efforts focused on developing and leveraging spectral and polarimetric sensing techniques for CBRNE applications, including system development efforts, field deployment campaigns, and data exploitation and analysis results. While this body of work has primarily focused on the application spaces of chemical and underground nuclear explosion detection and characterization, the developed tools and techniques may have applicability to the broader CBRNE domain.

Exposure to chemicals in everyday life is now more prevalent than ever. Air and water pollution can be delivery mechanisms for toxins, carcinogens, and other chemicals of interest (COI). A compact, multiplexed, chemical sensor with high responsivity and selectivity is desperately needed. We demonstrate the integration of unique Zr-based metal organic frameworks (MOFs) with a plasmonic transducer to demonstrate a nanoscale optical sensor that is both highly sensitive and selective to the presence of COI. MOFs are a product of coordination chemistry where a central ion is surrounded by a group of ligands resulting in a thin-film with nano-to micro-porosity, ultra-high surface area, and precise structural tunability. These properties make MOFs an ideal candidate for gaseous chemical sensing, however, transduction of a signal which probes changes in MOF films has been difficult. Plasmonic sensors have performed well in many sensing environments, but have had limited success detecting gaseous chemical analytes at low levels. This is due, in part, to the volume of molecules required to interact with the functionalized surface and produce a detectable shift in plasmonic resonance frequency. The fusion of a highly porous thin-film layer with an efficient plasmonic transduction platform is investigated and summarized. We will discuss the integration and characterization of the MOF/plasmonic sensor and summarize our results which show, upon exposure to COI, small changes in optical characteristics of the MOF layer are effectively transduced by observing shifts in plasmonic resonance.

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The permittivity, dielectric loss, and DC dielectric breakdown strength of additively manufactured, solvent-cast, and commercial polyimide films are reported As expected, commercial films performed better than both AM and solvent-cast lab-made films. Solvent-cast films generally performed better than AM films, although performance depended on the optimization of the material for the specific deposition technique. The most significant degradation of performance in all the lab-made films was in the dispersion of both the x/Df measurements and the dielectric breakdown strength (Weibull β). Commercial films had a breakdown strength of 4891 kV/cm and β = 13.0 whereas the highest performing lab-made films had a breakdown strength of 4072 kV/cm and β = 3.8. Furthermore, this increase in dispersion in all the lab-made samples is attributed to higher variability in the preparation, a higher defect level related to fabrication in the lab environment and, for some AM samples, to morphology/topology features resulting from the deposition technique.

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We examined amorphous titania thin films for use as the active material in a polarimetry based HF sensor. The amorphous titania films were found to be sensitive to vapor phase HF and the reaction product was identified as a hydronium oxofluorotitanate phase, which has previously only been synthesized in aqueous solution. The extent of reaction varied both with vapor phase HF concentration, relative humidity, and the exposure time. HF concentrations as low as 1 ppm could be detected for exposure times of 120 h.

Optical fluorescence-based DNA assays are commonly used for pathogen detection and consist of an optical substrate containing DNA capture molecules, binding of target RNA or DNA sequences, followed by detection of the hybridization event with a fluorescent probe. Though fluorescence detection can offer exquisite signal-to-background ratios, with high specificity, vast opportunities exist to improve current optical-based genomic sensing approaches. For these reasons, there is a clear need to explore alternative optical sensing paradigms to alleviate these restrictions. Bio-templated nanomaterial synthesis has become a powerful concept for developing new platforms for bio-sensing, as the biomolecule of interest can act as part of the sensing transducer mechanism. We explored the use of DNA origami structures to immobilize gold nanoparticles in very precise localized arrangements producing unique optical absorption properties with implications in novel DNA sensing schemes. We also explored the use of in-situ TEM as a novel characterization method for DNA-nanoparticle assemblies.

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Methods for the testing of the dielectric breakdown strength of insulation on metal wires under variable humidity conditions were developed. Two methods, an ASTM method and the twisted pair method, were compared to determine if the twisted pair method could be used for determination of breakdown strength under variable humidity conditions. It was concluded that, although there were small differences in outcomes between the two testing methods, the non-standard method (twisted pair) would be appropriate to use for further testing of the effects of humidity on breakdown performance. The dielectric breakdown strength of 34G copper wire insulated with double layer Poly-Thermaleze/Polyamide-imide insulation was measured using the twisted pair method under a variety of relative humidity (RH) conditions and exposure times. Humidity at 50% RH and below was not found to affect the dielectric breakdown strength. At 80% RH the dielectric breakdown strength was significantly diminished. No effect for exposure time up to 140 hours was observed at 50 or 80%RH.