Fall River, MA, United States
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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.


Ong P.-L.,Emitech, Inc | Levitsky I.A.,Emitech, Inc
IEEE Sensors Journal | Year: 2011

In this contribution, we report fluorescent gas chemosensors for detection of nitroaromatic vapors and other classes of volatile organic compounds based on porous silicon (PSi) microcavity (MC) infiltrated with sensory emissive polymers. Such hybrid functional sensors have several advantages over traditional fluorescent chemosensors, where the sensory polymers are deposited on flat substrate. This includes a high interfacial area of nanoporous Si (high sensitivity), narrow fluorescent band due to photon confinement, dependence of the spectral peak position on nature of analyte (enhanced selectivity), and fast recovery time. We demonstrated that deep and uniform polymer infiltration is critical for effective gas sensing and investigated the experimental conditions required for preparation of high-quality hybrid sensors. In the case of deep infiltration, the broad polymer fluorescence (FWHM ∼ 100m ) shows a narrowing to the resonance peak (FWHM ∼ 100m) with narrow intensity angle diagram. In addition, the potential of the sensor array platform and sensor recovery under ultrasound power is discussed. © 2006 IEEE.


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.


Viola E.A.,University of Rhode Island | Levitsky I.A.,University of Rhode Island | Levitsky I.A.,Emitech, Inc | Euler W.B.,University of Rhode Island
Journal of Physical Chemistry C | Year: 2010

Cantilevers made of a bilayer composite of single walled carbon nanotubes (SWNTs) deposited onto Nafion exhibit substantial mechanical motion upon exposure to visible or near-infrared light. The kinetics of the tip displacement are studied as a function of SWNT thickness, mass loading, and humidity level. The rate constants strongly depend upon the SWNT layer thickness. During the light-on cycle the absorption of the light by the SWNTs drives the motion while in the light-off cycle the stiffness of the SWNTs retards the relaxation. At low humidity levels a second, fast, but small, response in the opposite direction of the net major displacement is observed. The kinetics of the photoactuation was also monitored by IR spectroscopy with similar kinetic parameters. The primary mechanism responsible for the actuation appears to be migration of water and hydrated hydrogen ions in the Nafion film toward the interface and into the SWNT layer. © 2010 American Chemical Society.


Ong P.-L.,Emitech, Inc | Euler W.B.,Emitech, Inc | Levitsky I.A.,Emitech, Inc | Levitsky I.A.,University of Rhode Island
Nanotechnology | Year: 2010

Photovoltaic devices based on single-walled carbon nanotubes (SWNTs) and n-silicon heterojunctions have been fabricated by a spray deposition process. We provide direct evidence that nanotubes serve as an active photosensing material involved directly in the photon absorption process as well as contributing to charge separation, transport and collection. The characteristic band of the SWNT band in the photoconductivity spectrum matches the S11 absorption band of semiconducting SWNTs of 7,6 chirality. Centrifugation of the SWNTs provides two fractions. The sediment fraction exhibits a conversion efficiency (∼1.7%) higher by a factor of eight compared to the supernatant fraction. SEM images and conductivity measurements show that the SWNT network morphology of the sediment fraction has longer and thicker nanotube bundles forming highly porous films, accounting for the enhanced conductivity and higher transparency. © 2010 IOP Publishing Ltd.


Ong P.-L.,Emitech, Inc | Levitsky I.A.,Emitech, Inc | Levitsky I.A.,University of Rhode Island
Energies | Year: 2010

We present a review of the emerging class of hybrid solar cells based on organic-semiconductor (Group IV, III-V), nanocomposites, which states separately from dye synthesized, polymer-metal oxides and organic-inorganic (Group II-VI) nanocomposite photovoltaics. The structure of such hybrid cell comprises of an organic active material (p-type) deposited by coating, printing or spraying technique on the surface of bulk or nanostructured semiconductor (n-type) forming a heterojunction between the two materials. Organic components include various photosensitive monomers (e.g., phtalocyanines or porphyrines), conjugated polymers, and carbon nanotubes. Mechanisms of the charge separation at the interface and their transport are discussed. Also, perspectives on the future development of such hybrid cells and comparative analysis with other classes of photovoltaics of third generation are presented. © 2010 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.


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.


Ong P.-L.,Emitech, Inc | Euler W.B.,University of Rhode Island | Levitsky I.A.,Emitech, Inc | Levitsky I.A.,University of Rhode Island
Applied Physics Letters | Year: 2010

We report a room temperature mid-infrared photodetector based on a carbon nanotube-silicon heterojunction nanostructure. The observed mid-infrared band (8-12μm) in the photocurrent spectrum is consistent with the estimated band gap energy of semiconducting multiwall nanotubes (15 to 30 nm diameter). The fast response time (16 ms) and small temperature change (∼ 10-8 K) upon infrared light suggest that the photocurrent response is not due to bolometric effect. We determined that the primary mechanism of the photocurrent in this spectral range is associated with photon absorption of semiconducting multiwalled carbon nanotubes followed by charge separation at the interface, their transport, and collection at the external electrodes. © 2010 American Institute of Physics.


Grant
Agency: Department of Defense | Branch: Army | Program: SBIR | Phase: Phase II | Award Amount: 729.75K | Year: 2011

We propose to develop a novel, highly efficient, soldier-borne system for real-time detection and neutralization of IED hazards at a stand-off distance of 150 meters and more. The proposed approach is a significant advance in stand-off explosive detector technologies, combining image processing with chemical detection signature and ballistic delivery of the sensory material to inspected objects. This allows fast identification of major explosives contained in IEDs (less than 2-3 second) followed by IED neutralization. In Phase I, the feasibility of the explosive detection concept was demonstrated using fluorescence imaging (FLIM) approach. In Phase II, major efforts will be focused on the improvement of the fluorescence imaging method such as stand-off distance extension; enhancement of the fluorescence quenching contrast by the lock-in imaging and using narrow band-pass filtering; image processing/pattern recognition and integration ballistic delivery means with recording/ processing equipment in one portable package (less than 20 pound). The neutralization system will be identified and designed to work in conjunction with the IED detector. In Phase II, two developed prototypes (FLIM-I and FLIM-II) will be tested at stand-off distance of 150 m and more and test results will be compared with modeling efforts. The Phase II prototype will prove to be an essential link between the accomplishments of Phase I and the development of a commercially viable technology in Phase III which have a wide variety application in the military and commercial sectors.


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.

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