Publications

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We have developed and characterized novel in-situ corrosion sensors to monitor and quantify the corrosive potential and history of localized environments. Embedded corrosion sensors can provide information to aid health assessments of internal electrical components including connectors, microelectronics, wires, and other susceptible parts. When combined with other data (e.g. temperature and humidity), theory, and computational simulation, the reliability of monitored systems can be predicted with higher fidelity.

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After years in the field, many materials suffer degradation, off-gassing, and chemical changes causing build-up of measurable chemical atmospheres. Stand-alone embedded chemical sensors are typically limited in specificity, require electrical lines, and/or calibration drift makes data reliability questionable. Along with size, these "Achilles' heels" have prevented incorporation of gas sensing into sealed, hazardous locations which would highly benefit from in-situ analysis. We report on development of an all-optical, mid-IR, fiber-optic based MEMS Photoacoustic Spectroscopy solution to address these limitations. Concurrent modeling and computational simulation are used to guide hardware design and implementation.

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Metal Organic Frameworks (MOFs) are a rapidly developing class of nanoporous materials with numerous applications in diverse fields such as chemical detection, hazardous gas detection, and carbon capture. Even though numerous articles have been written emphasizing the adsorption properties of these MOFs, their compatibility with respect to the sensing device has not been explored. While there are numerous types of sensing devices that could benefit from the use of MOF-based coatings to enhance sensitivity and selectivity, we are particularly interested in microcantilevers because of the high sensitivity they can provide within a compact, lower-power architecture. In this paper, we address this need by analyzing the effect of the mechanical properties of MOFs on the sensor response. In particular, we are interested in the structural flexibility of MOFs, because this unique guest-induced property can be used for strain-induced sensing attribute of the microcantilever. In this regard we examined the effects of important MOF mechanical properties such as the Young's Modulus, Poisson's ratio, and density on the sensor response for a range of values representative of the MOFs available in the literature. From our analysis we determined that increasing the Young's Modulus and Poisson's ratio improve the response, while the density of the MOF has a negligible effect on the cantilever response. In addition, we also examined the influence on cantilever response of the intermediate layer used to bind the MOF, from which we observe that SiO 2 provides the best sensor response for a given MOF layer. © 2012 Elsevier B.V.

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Significant deformation of thin films occurs when measuring thickness by mechanical means. This source of measurement error can lead to underestimating film thickness if proper corrections are not made. Analytical solutions exist for Hertzian contact deformation, but these solutions assume relatively large geometries. If the film being measured is thin, the analytical Hertzian assumptions are not appropriate. ANSYS is used to model the contact deformation of a 48 gauge Mylar film under bearing load, supported by a stiffer material. Simulation results are presented and compared to other correction estimates. Ideal, semi-infinite, and constrained properties of the film and the measurement tools are considered.

Metal organic framework (MOF) materials are a class of hybrid organic-inorganic crystalline materials whose pore structures and chemical properties can be tailored by the selection of component chemical moieties. Many MOFs have extraordinary intrinsic surface areas, capable of adsorbing large quantities of other chemicals, such as volatile organic compounds or moisture. Upon absorption of guest molecules, many MOFs undergo reversible changes in the dimensions of their unit cells. These properties suggest several routes to chemical sensing in which the transduction mechanisms are: 1) the stress induced at an interface between a flexible MOF layer and a static microcantilever fabricated with a built-in piezoresistive stress sensor; 2) the change in the resonant frequency of an oscillating microcantilever induced by mass adsorption; and 3) the change in the resonant frequency of a acoustic sensor, such as a surface acoustic wave (SAW) sensor through changes in mass loading and film moduli. This paper focuses on humidity sensing by SAWs coated with Cu 3(BTC) 2 (HKUST-1) over a very broad concentration range. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. © 2011 Materials Research Society.

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