J.S. Melinger

United States Naval Research Laboratory, Washington, Washington, D.C., United States

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Publications (166)321.82 Total impact

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    ABSTRACT: The growing maturity of DNA-based architectures has raised considerable interest in applying them to create photoactive light harvesting and sensing devices. Towards optimizing efficiency in such structures, resonant energy transfer was systematically examined in a series of dye-labeled DNA duplexes where donor-acceptor separation was incrementally changed from 0 - 16 base pairs. Cyanine dyes were localized on the DNA using double phosphoramidite attachment chemistry. Steady state spectroscopy, single-pair fluorescence, time-resolved fluorescence, and ultrafast two-color pump-probe methods were utilized to examine the energy transfer processes. Energy transfer rates were found to be more sensitive to the distance between the Cy3 donor and Cy5 acceptor dye molecules than efficiency measurements. Picosecond energy transfer and near unity efficiencies were observed for the closest separations. Comparison between our measurements and the predictions of Förster theory based on structural modeling of the dye-labeled DNA duplex suggest that the double phosphoramidite linkage leads to a distribution of intercalated and non-intercalated dye orientations. Deviations from the predictions of Förster theory point to a failure of the point-dipole approximation for separations less than 10 base pairs. Interactions between the dyes that alter their optical properties and violate the weak coupling assumption of Förster theory were observed for separations less than 4 base pairs, sug-gesting the removal of nucleobases causes DNA deformation and leads to enhanced dye-dye interaction.
    The journal of physical chemistry. B. 11/2014;
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    ABSTRACT: Structural DNA nanotechnology has developed profoundly in the last several years allowing for the creation of increasingly sophisticated devices capable of discrete sensing, locomotion, and molecular logic. The latter research field is particularly attractive as it provides information processing capabilities that may eventually be applied in situ, for example in cells, with potential for even further coupling to an active response such as drug delivery. Rather than design a new DNA assembly for each intended logic application, it would be useful to have one generalized design that could provide multiple different logic gates or states for a targeted use. In pursuit of this goal, we demonstrate a switchable, triangular dye-labeled three-arm DNA scaffold where the individual arms can be assembled in different combinations and the linkage between each arm can be physically removed using toehold-mediated strand displacement and then replaced by a rapid anneal. Rearranging this core structure alters the rates of Förster resonance energy transfer (FRET) between each of the two or three pendant dyes giving rise to a rich library of unique spectral signatures that ultimately form the basis for molecular photonic logic gates. The DNA scaffold is designed such that different linker lengths joining each arm, and which are used as the inputs here, can also be used independently of one another thus enhancing the range of molecular gates. The functionality of this platform structure is highlighted by easily configuring it into a series of one-, two- and three-input photonic Boolean logic gates such as OR, AND, INHIBIT, etc., along with a photonic keypad lock. Different gates can be realized in the same structure by altering which dyes are interrogated and implementation of toehold-mediated strand displacement and/or annealing allows reconfigurable switching between input states within a single logic gate as well as between two different gating devices.
    RSC Advances 10/2014; 4(90). · 3.71 Impact Factor
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    SPIE Organic Photovoltaics XV; 10/2014
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    ABSTRACT: DNA demonstrates a remarkable capacity for creating designer nanostructures and devices. A growing number of these structures utilize Förster resonance energy transfer (FRET) as part of the device's functionality, readout or characterization, and, as device sophistication increases so do the concomitant FRET requirements. Here we create multi-dye FRET cascades and assess how well DNA can marshal organic dyes into nanoantennae that focus excitonic energy. We evaluate 36 increasingly complex designs including linear, bifurcated, Holliday junction, 8-arm star and dendrimers involving up to five different dyes engaging in four-consecutive FRET steps, while systematically varying fluorophore spacing by Förster distance (R0). Decreasing R0 while augmenting cross-sectional collection area with multiple donors significantly increases terminal exciton delivery efficiency within dendrimers compared with the first linear constructs. Förster modelling confirms that best results are obtained when there are multiple interacting FRET pathways rather than independent channels by which excitons travel from initial donor(s) to final acceptor.
    Nature Communications 01/2014; 5:5615. · 10.74 Impact Factor
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    ABSTRACT: We show how THz time-domain spectroscopy can be used for the remote detection of an evolving gas phase mixture containing D2O and HDO and to characterize the reaction kinetics of: H2O + D2O -> 2HDO.
    CLEO: Science and Innovations; 06/2013
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    Nano Letters 04/2013; 13(6):3003. · 13.03 Impact Factor
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    ABSTRACT: Ultraviolet optical pulses with a full-width-at-half-maximum diameter focused spot size of $0.32~muhbox{m}$ are generated, characterized, and used to produce SEUs in a 90 nm CMOS/SOI SRAM. The results provide unequivocal experimental evidence for cell-to-cell variations in SEU sensitivity that can be identified with process variations at the individual transistor level.
    IEEE Transactions on Nuclear Science 01/2013; 60(6):4184-4191. · 1.22 Impact Factor
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    ABSTRACT: Energy transfer plays a key role in various applications of organic semiconductors such as electroluminescence, photovoltaics, and sensors. We have carried out a study combining transient and continuous wave (CW) optical spectroscopy with modeling. The fluorescence spectra and dynamics of a functionalized pentacene doped into a fluorescent host (Alq3) were measured and simulated by a Monte Carlo model incorporating distributed dopants and exciton migration. For nonluminescent materials, transient absorption spectroscopy provides insight into excitation migration. Singlet diffusion rates in C60 were determined by probing delayed charge transfer to ZnPc in films with a layered nanostructure.
    Proc SPIE 09/2012;
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    ABSTRACT: The ability of luminescent semiconductor quantum dots (QDs) to engage in diverse energy transfer processes with organic dyes, light-harvesting proteins, metal complexes, and redox-active labels continues to stimulate interest in developing them for biosensing and light-harvesting applications. Within biosensing configurations, changes in the rate of energy transfer between the QD and the proximal donor, or acceptor, based upon some external (biological) event form the principle basis for signal transduction. However, designing QD sensors to function optimally is predicated on a full understanding of all relevant energy transfer mechanisms. In this report, we examine energy transfer between a range of CdSe-ZnS core-shell QDs and a redox-active osmium(II) polypyridyl complex. To facilitate this, the Os complex was synthesized as a reactive isothiocyanate and used to label a hexahistidine-terminated peptide. The Os-labeled peptide was ratiometrically self-assembled to the QDs via metal affinity coordination, bringing the Os complex into close proximity of the nanocrystal surface. QDs displaying different emission maxima were assembled with increasing ratios of Os-peptide complex and subjected to detailed steady-state, ultrafast transient absorption, and luminescence lifetime decay analyses. Although the possibility exists for charge transfer quenching interactions, we find that the QD donors engage in relatively efficient Förster resonance energy transfer with the Os complex acceptor despite relatively low overall spectral overlap. These results are in contrast to other similar QD donor-redox-active acceptor systems with similar separation distances, but displaying far higher spectral overlap, where charge transfer processes were reported to be the dominant QD quenching mechanism.
    ACS Nano 06/2012; 6(6):5330-47. · 12.03 Impact Factor
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    Ani Khachatrian, Joseph S. Melinger, Syed B. Qadri
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    ABSTRACT: We report temperature-dependent measurements of the terahertz (THz) vibrational spectrum of ammonium nitrate (AN) films and mixed potassium nitrate (KN)–ammonium nitrate films using waveguide THz time domain spectroscopy. The experiments were performed on polycrystalline films on the metal surface of a parallel plate waveguide. At cryogenic temperature and with frequency resolution as high as 7 GHz, our measurements produce a complex vibrational spectrum for AN, and show vibrational resonances not observed in previous far infrared and Raman measurements. We investigate potential interactions between AN and the metal surface by measuring THz spectra of films on aluminum, gold, and a gold surface coated with an organic self-assembled monolayer. Measurements are also performed on a deuterated AN film and indicate that the observed THz modes are due largely to the motion of the nitrate ions in the AN crystal. Finally, the effect of introducing small amounts of an impurity into the AN lattice is examined. We find that introduction of as little as 1%-2% by weight of potassium nitrate into the AN lattice causes line broadening of the THz modes, which is consistent with increased disorder introduced by the impurity.
    Journal of Applied Physics 05/2012; 111(9). · 2.21 Impact Factor
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    ABSTRACT: Using a low power beam of ultrashort THz pulses that propagate in the ambient laboratory environment we have measured the rotational signatures of small molecule vapors at frequencies within the atmospheric transmission windows. We investigate two types of apparatus. In the first type the THz beam propagates along a 6.7 meter round trip path that is external to the spectrometer, and which contains a long sample tube (5.4 meter round trip path) that holds the analyte vapor. The environment of the tube is controlled to simulate dry or humid conditions. In the second apparatus the THz beam propagates over a much longer 170 meter round trip path with analyte vapor contained in a relatively short 1.2 meter round trip path sample chamber. We describe the rotational signatures for each apparatus in the presence of the strong interference from water vapor absorption. For the shorter path long-tube apparatus we find that the peak detection sensitivity is sufficient to resolve a 1% absorption feature. For the more challenging 170 meter path apparatus we find that the peak detection sensitivity is sufficient to resolve a 3-5% absorption feature. The experiments presented here represent a first step towards using ultrashort THz pulses for coherent broad band detection of small molecule gases and vapors under ambient conditions.
    Optics Express 03/2012; 20(6):6788-807. · 3.55 Impact Factor
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    ABSTRACT: We elucidate photoexcitation dynamics in C(60) and zinc phthalocyanine (ZnPc) from picoseconds to milliseconds by transient absorption and time-resolved terahertz spectroscopy. Autoionization of C(60) is a precursor to photocarrier generation. Decay of the terahertz signal is due to decreasing photocarrier mobility over the first 20 ps and thereafter reflects recombination dynamics. Singlet diffusion rates in C(60) are determined by modeling the rise of ground state bleaching of ZnPc absorption following C(60) excitation. Recombination dynamics transform from bimolecular to monomolecular as the layer thickness is reduced, revealing a metastable exciplex at the C(60)/ZnPc interface with a lifetime of 150 μs.
    Physical Review Letters 02/2012; 108(7):077402. · 7.73 Impact Factor
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    ABSTRACT: While multiple exciton generation (MEG) is known to occur more efficiently in semiconductor nanocrystals than in the bulk, the required energy threshold prevents visible photons from being utilized. We report two-color pump-probe measurements demonstrating a two-fold increase in the MEG efficiency of solution samples of PbSe quasi onedimensional nanorods over zero-dimensional nanocrystals to a value of 0.78, where 1 is the largest efficiency possible. This improvement is accompanied by a reduction of the MEG threshold energy to 2.28Eg, which allows visible photons to participate in MEG. This approaches the theoretical limit for the threshold energy of 2Eg imposed by energy conservation. Detailed balance calculations show that, unlike nanocrystals, photovoltaic cells based on PbSe nanorods can use MEG to improve power conversion efficiencies, particularly when used in conjunction with solar concentrators.
    SPIE Photonics West: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices, San Francisco; 01/2012
  • S. Sree Harsha, Joseph. S. Melinger, S. B. Qadri, D. Grischkowsky
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    ABSTRACT: The influence of the metal substrate on the measurement of high resolution THz vibrational modes of molecular solids with the waveguide THz-TDS technique is investigated. The sample film of salicylic acid is studied using waveguide THz-TDS on three different metal substrates and two-surface passivated substrates. The independence of the observed THz vibrational modes to the metal substrate is demonstrated. Independently, surface passivation is presented as a viable experimental addition to the waveguide THz-TDS technique to aid the characterization of samples with known reactivity to metal surfaces.
    Journal of Applied Physics 01/2012; 111(2). · 2.21 Impact Factor
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    Michael Theuer, Joseph S. Melinger
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    ABSTRACT: Terahertz time-domain spectroscopy accesses the frequency range between 100GHz and 5 THz by using the coherent generation and detection based on femtosecond laser sources. On the way to obtain fingerprint absorption spectra of molecular solids, terahertz waveguides have proven to be a valuable tool to extend the results to narrow and high resolution linewidths of crystalline solids. We will discuss the development, properties and applications of terahertz waveguide geometries for spectroscopic applications, in particular high-resolution measurements using parallel-plate waveguides. KeywordsTerahertz–Far infrared–Waveguide–Spectroscopy
    Journal of infrared, millimeter and terahertz waves 11/2011; 32(11):1267-1284. · 1.12 Impact Factor
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    ABSTRACT: The creation of a single electron-hole pair (i.e., exciton) per incident photon is a fundamental limitation for current optoelectronic devices including photodetectors and photovoltaic cells. The prospect of multiple exciton generation per incident photon is of great interest to fundamental science and the improvement of solar cell technology. Multiple exciton generation is known to occur in semiconductor nanostructures with increased efficiency and reduced threshold energy compared to their bulk counterparts. Here we report a significant enhancement of multiple exciton generation in PbSe quasi-one-dimensional semiconductors (nanorods) over zero-dimensional nanostructures (nanocrystals), characterized by a 2-fold increase in efficiency and reduction of the threshold energy to (2.23 ± 0.03)E(g), which approaches the theoretical limit of 2E(g). Photovoltaic cells based on PbSe nanorods are capable of improved power conversion efficiencies, in particular when operated in conjunction with solar concentrators.
    Nano Letters 08/2011; 11(8):3476-81. · 13.03 Impact Factor
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    ABSTRACT: We demonstrate the first phase of a long path THz-TDS apparatus to remotely detect the THz spectrum of small vapor phase molecules with rotational transitions that fall within the atmospheric transparency windows.
    04/2011;
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    ABSTRACT: A donor-acceptor charge transfer system based on two discotic mesogens has been synthesized. The donor is either a triphenylene (POG0) or a triphenylene-based conjugated dendron (POG1), while the acceptor is a perylene diimide (PDI) core. The donors are covalently linked to the bay positions of the PDI core through an ether linkage. In chloroform, due to the short donor-acceptor distance and the matching frontier orbital levels, photoinduced charge transfer from either the donor excitation or the acceptor excitation are both thermodynamically and kinetically favored, resulting in efficient quenching of both donor and acceptor fluorescence. In a less polar solvent, hexane, while charge transfer is still the dominant mechanism for decay of the excited electronic state of POG1, photoinduced charge transfer is no longer energetically favorable for POG0 when the acceptor PDI core is excited, making the PDI core of POG0 weakly fluorescent in chloroform but strongly so in hexane. In solid film, POG0 is highly aggregated through both PDI-PDI and triphenylene-triphenylene homotopic stacking. POG1, on the other hand, aggregates through triphenylene dendrons with limited PDI-PDI core stacking, presumably due to the steric hindrance caused by bulky triphenylene moieties which block the access to the PDI core. The efficient photoinduced charge transfer, coupled with the homotopic stacking that forms separated electron-transporting PDI-stacked columns and hole transporting triphenylene-stacked columns, suggests that the reported donor-acceptor systems based on dual-discotic mesogens are potentially new efficient photovoltaic materials.
    The Journal of Physical Chemistry A 02/2011; 115(9):1579-92. · 2.77 Impact Factor
  • Ani Khachatrian, Syed Qadri, Joseph S. Melinger
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    ABSTRACT: We have performed high resolution terahertz vibrational spectroscopy of ammonium nitrate and potassium nitrate crystalline films and their mixtures employing waveguide terahertz time domain spectroscopy. Measurements were conducted on films that were drop cast from solution onto aluminum and gold surfaces. The terahertz spectra of the films were compared with more traditional terahertz time domain measurements of ammonium nitrate and potassium nitrate pellets. Temperature dependence studies indicate that as samples were cooled to cryogenic temperatures the vibrational lines become significantly narrower and more intense, more so in the case of films than pellets. We also investigate line broadening caused by impurities by measuring terahertz spectra ammonium films containing small amounts of potassium nitrate.
    01/2011;
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    ABSTRACT: We describe the initial phase of a long path terahertz time-domain spectroscopy apparatus to detect THz rotational spectra of small vapor phase molecules within the atmospheric transparency windows. We discuss the measurements first for a relatively short path THz propagation path of 6.2 meters, and then for a much longer path of 170 meters.
    Infrared, Millimeter and Terahertz Waves (IRMMW-THz), 2011 36th International Conference on; 01/2011

Publication Stats

2k Citations
321.82 Total Impact Points

Institutions

  • 1998–2012
    • United States Naval Research Laboratory
      • • Electronics Science and Technology Division
      • • Center for Biomolecular Science and Engineering
      • • Institute for Nanoscience
      Washington, Washington, D.C., United States
  • 2003–2011
    • University of Missouri - Kansas City
      • Department of Chemistry
      Kansas City, MO, United States
  • 2007–2010
    • Vanderbilt University
      • Department of Electrical Engineering and Computer Science
      Nashville, MI, United States
    • University of Maryland, College Park
      • Department of Chemistry and Biochemistry
      College Park, MD, United States
  • 2007–2009
    • Oklahoma State University - Stillwater
      • School of Electrical and Computer Engineering
      Stillwater, OK, United States
  • 1997
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 1996
    • Sandia National Laboratories
      Albuquerque, New Mexico, United States
  • 1995–1996
    • Naval Postgraduate School
      • Department of Electrical and Computer Engineering
      Monterey, CA, United States
  • 1991
    • Princeton University
      • Department of Chemistry
      Princeton, NJ, United States