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Fall River, MA, United States

Levitsky I.A.,Emitech, Inc
Sensors (Switzerland) | Year: 2015

We present a short review of recent progress in the field of optical gas sensors based on porous silicon (PSi) and PSi composites, which are separate from PSi optochemical and biological sensors for a liquid medium. Different periodical and nonperiodical PSi photonic structures (bares, modified by functional groups or infiltrated with sensory polymers) are described for gas sensing with an emphasis on the device specificity, sensitivity and stability to the environment. Special attention is paid to multiparametric sensing and sensor array platforms as effective trends for the improvement of analyte classification and quantification. Mechanisms of gas physical and chemical sorption inside PSi mesopores and pores of PSi functional composites are discussed. © 2015 by the authors; licensee MDPI, Basel, Switzerland. Source

Tokranova N.A.,University at Albany | Novak S.W.,University at Albany | Castracane J.,University at Albany | Levitsky I.A.,University of Rhode Island | Levitsky I.A.,Emitech, Inc
Journal of Physical Chemistry C | Year: 2013

We present the study of a nanohybrid composite with superior sensing performance consisting of an emissive sensory polymer infiltrated into a mesoporous Si one-dimensional (1D) photonic crystal with a microcavity (MC). It was found that the critical condition for deep polymer infiltration is the presence of an initial low porosity layer (porosity of 45%) in contrast to shallow infiltration governed by an initial high porosity layer (porosity of 58%). This results in a narrow fluorescence peak (due to deep infiltration) or a spectral "hole" in the fluorescence band (shallow infiltration). Such a unique effect is in agreement with the model based on capillary filling and confirmed by secondary ion mass spectrometry (SIMS) data analyzing the profile of polymer infiltration along the MC depth. In the case of deep infiltration, the characteristic filling length exceeds 2 μm, allowing the polymer to impregnate the MC layer. The infiltrated polymer is spatially confined and exists as quasi-isolated chains without pore clogging as can be concluded from the "blue" spectral shift of up to 10 nm as compared with a nonspatially confined film. Polymer isolation over a large surface area along with sufficient pore openings makes this porous Si (PSi) MC/polymer nanohybrid an ideal material for gas sensing applications. This is due to the high sensitivity in conjunction with a strong fluorescence signal which is not possible with solid polymer films or bare PSi. These results are confirmed by direct observation of higher sensitivity, enhanced specificity, and partial recovery of the optical signal for the nanohybrid composite upon exposure to trinitrotoluene vapors as compared with a conventional polymer film deposited on a flat substrate. © 2013 American Chemical Society. Source

Glamazda A.Y.,Ukrainian Academy of Sciences | Karachevtsev V.A.,Ukrainian Academy of Sciences | Euler W.B.,University of Rhode Island | Levitsky I.A.,University of Rhode Island | Levitsky I.A.,Emitech, Inc
Advanced Functional Materials | Year: 2012

An anisotropic carbon nanotube (CNT)-polymer composite for bolometric applications in the mid-IR spectral range (2.5-20 μm) is studied. Composite alignment in conjunction with non-uniform distribution of CNTs in the polymer matrix allows for a significant enhancement of the temperature coefficient of resistance (0.82% K -1) with respect to uniform composite (0.24% K -1). As a result a responsivity of ≈ 500 V W -1 is reached, which is the highest for CNT-based bolometers reported to date. Such remarkable optical and thermal characteristics are explained in terms of fluctuation tunneling theory taking into account the composite anisotropy and the gradient of the CNT concentration. Flatness of the photoresponse in the broad spectral mid-IR range and enhanced responsivity provide a great potential for the use of such novel composite for applications in IR spectroscopy and thermal imaging. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

An optochemical detector for detecting various chemical compounds and comprising a flow cell incorporating the sensory element constructed of an organic-inorganic emissive nanocomposite which luminescence spectral response is specific to exposed target vapors and particulates. The change in the luminescent spectral response is measured during this exposure. The detector is equipped with air-jet sampling system functioning in real-time mode for delivery of vapors and particulates to sensory element.

Agency: Department of Defense | Branch: Army | Program: SBIR | Phase: Phase I | Award Amount: 69.45K | Year: 2009

We propose to study and develop a novel, highly sensitive and selective optochemical portable detection system for stand-off detection (more than 300 m) of IED hazard. In Phase-I, the feasibility of the concept will be demonstrated at a distance of 150 m for major nitro-explosives (TNT, RDX, PETN) deposited on the surface with concentration ~ ng/mm2. The two main transduction mechanisms will be tested: polymer fluorescence quenching and spectral shift of resonance peak of nanoporous Si microcavity infiltrated with imprinted silica. The unique nanodevice structure provides a large surface area between the sensory material and the analytes leading to the highest sensitivity, which is critical for fast detection (response time is about several seconds) of low vapor pressure explosives. Stand-off sensing will be provided by ballistic delivery in conjunction with laser excitation/interrogation followed by the signal processing. The proposed technology is highly innovative and promising for future developments. We have demonstrated some of the key issues for its implementation, thus the successful completion of Phase-I is highly possible. In Phase-II, the developed prototype will be capable of detecting IEDs from the stand-odd distance of more than 300 meters in the presence of common operational interferences.

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