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Alexandria, VA, United States

Woodka M.D.,U.S. Army | Schnee V.P.,U.S. Army | Polcha M.P.,Corbin Company
Analytical Chemistry | Year: 2010

A fluorescent polymer sensor array (FPSA) was made from commercially available fluorescent polymers coated onto glass beads and was tested to assess the ability of the array to discriminate between different analytes in aqueous solution. The array was challenged with exposures to 17 different analytes, including the explosives trinitrotoluene (TNT), tetryl, and RDX, various explosive-related compounds (ERCs), and nonexplosive electron-withdrawing compounds (EWCs). The array exhibited a natural selectivity toward EWCs, while the non-electron-withdrawing explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) produced no response. Response signatures were visualized by principal component analysis (PCA), and classified by linear discriminant analysis (LDA). RDX produced the same response signature as the sampled blanks and was classified accordingly. The array exhibited excellent discrimination toward all other compounds, with the exception of the isomers of nitrotoluene and aminodinitrotoluene. Of particular note was the ability of the array to discriminate between the three isomers of dinitrobenzene. The natural selectivity of the FPSA toward EWCs, plus the ability of the FPSA to discriminate between different EWCs, could be used to design a sensor with a low false alarm rate and an excellent ability to discriminate between explosives and explosive-related compounds. © 2010 American Chemical Society. Source


Nallon E.C.,U.S. Army | Polcha M.P.,Corbin Company | Schnee V.P.,U.S. Army
Sensors and Actuators, B: Chemical | Year: 2014

In this paper, we present an organic light emitting diode (OLED) used as a sensor for the detection of 1,4-dinitrobenzene (1,4-DNB). The detection method relies on the attenuation of the emitted light due to interactions between the 1,4-DNB and the active organic layer. The mechanism responsible for this attenuation involves an electron transfer from the electron donating organic layer to the electron deficient nitroaromatic 1,4-DNB. Devices were fabricated and tested against various concentrations of 1,4-DNB to determine if a dependence on concentration exists and to reveal more detail about the internal quenching mechanism.© 2013 Published by Elsevier B.V. Source


Woodka M.D.,U.S. Army | Shpil J.C.,U.S. Army | Schnee V.P.,U.S. Army | Polcha J.M.P.,Corbin Company
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

A sensor system has been constructed that is capable of detecting and discriminating between various explosives presented in ocean water with detection limits at the 10-100 parts per trillion level. The sensor discriminates between different compounds using a biologically-inspired fluorescent polymer sensor array, which responds with a unique fluorescence quenching pattern during exposure to different analytes. The sensor array was made from commercially available fluorescent polymers coated onto glass beads, and was demonstrated to discriminate between different electron-withdrawing analytes delivered in salt water solutions, including the explosives 2,4,6-trinitrotoluene (TNT) and tetryl, the explosive hydrolysis products 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene, as well as other explosive-related compounds and explosive simulants. Sensitivities of 10-100 parts per trillion were achieved by employing a preconcentrator (PC) upstream of the sensor inlet. The PC consists of the porous polymer Tenax, which captures explosives from contaminated water as it passes through the PC. As the concentration of explosives in water decreased, longer loading times were required to concentrate a detectable amount of explosives within the PC. Explosives accumulated within the PC were released to the sensor array by heating the PC to 190 C. This approach yielded preconcentration factors of up to 100-1000x, however this increased sensitivity towards lower concentrations of explosives was achieved at the expense of proportionally longer sampling times. Strategies for decreasing this sampling time are discussed. © 2012 SPIE. Source


Lennon C.M.,Corbin Company | Almeida L.A.,U.S. Army | Jacobs R.N.,U.S. Army | Benson J.D.,U.S. Army | And 5 more authors.
Journal of Electronic Materials | Year: 2013

The surface kinetics of CdTe (211)B grown by molecular beam epitaxy (MBE) is investigated using spectroscopic ellipsometry (SE) during in situ cyclic annealing. A method of measuring sublimation rates from high-index surfaces without use of reflection high-energy electron diffraction is presented. The effect of Te2 overpressure on the activation energy of sublimation for the CdTe (211)B surface is reported. The sensitivity of SE to surface temperature and film thickness was leveraged to monitor sublimation rates of CdTe stabilized by a Te2 overpressure. The sublimation activation energy was found to increase from 0.45 eV to 2.94 eV under the Te2 beam pressure regime investigated. © 2013 TMS (outside the USA). Source


Jacobs R.N.,U.S. Army | Nozaki C.,U.S. Army | Almeida L.A.,U.S. Army | Jaime-Vasquez M.,U.S. Army | And 9 more authors.
Journal of Electronic Materials | Year: 2012

Large-area, low-cost substrates are envisioned for next-generation HgCdTe infrared focal-plane arrays (IRFPA). Si, GaAs, Ge, and InSb have been previously examined as potential candidates. Fabrication of IRFPAs based on these substrates is limited by fundamental materials properties that potentially lead to lower detector performance and operability. Lattice and thermal mismatch between the substrate and epilayer are just two of several material factors that must be considered. We have reviewed these factors in the context of more recent data, and determined it worthwhile to revisit the use of GaAs substrates for epitaxial growth of HgCdTe. Our study starts with an evaluation of the surface quality (epireadiness) of commercially available (211) B-oriented GaAs substrates. Molecular beam epitaxial growth of CdTe buffer layers and subsequent HgCdTe absorber layers are performed in separate vacuum-interconnected chambers. The importance of optimization of the CdTe buffer layer growth for high-quality HgCdTe is detailed through surface morphology and x-ray studies. x-Ray diffraction rocking-curve full-width at half-maximum values as low as 52 arcsec have been obtained. Long-wave infrared Hg 1-xCd xTe (x = 0.23) has been grown on these buffer layers, producing cross-hatch- dominated surface morphologies, with dislocation densities as low as ∼3 × 10 6 cm -2. We have also obtained (for optimized layers), 80-K Hall-effect n-type carrier concentration and electron mobility of approximately ∼1.5 × 10 15 cm -3 and 1 × 10 5 cm 2 V -1 s -1, respectively. Finally, we briefly compare GaAs and Si in light of our preliminary investigation. © 2012 TMS (outside the USA). Source

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