Joseph S. Melinger

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

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Publications (181)419.01 Total impact

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    ABSTRACT: Molecular photonic wires (MPWs) precisely position dyes using structural DNA methodologies where they exploit Förster resonance energy transfer (FRET) to direct photonic energy over nm distances with potential applications in light harvesting, biosensing, and molecular electronics. Although versatile, the number of donor-acceptor dye pairs available and the downhill nature of FRET combine to limit the size and efficiency of current MPWs. HomoFRET between identical dyes should provide zero energy loss but at the cost of random transfer directionality. Here, it has been investigated what HomoFRET has to offer as a means to extend MPWs. Steady-state-, lifetime-, and fluorescence anisotropy measurements along with mathematical models are utilized to experimentally examine various 3-, 4-, and 5-dye MPW constructs containing from 1 to 6 HomoFRET repeat sections. Results show that HomoFRET can be extended up to 6 repeat dyes/5 steps with only a ≈55% energy transfer efficiency decrease while doubling the longest MPW length to a remarkable 30 nm. Critically, analogous constructs lacking the HomoFRET portion are unable to deliver any energy over the same lengths. Even with nondirectionality, the introduction of a repeated-optimized HomoFRET transfer dye is preferable compared to additional less efficient dye species. HomoFRET further provides the benefit of having a higher energy output.
    No preview · Article · Jan 2016 · Advanced Optical Materials
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    ABSTRACT: The rigidity and defined length of the polyproline type II helix (PPII) have made it the structural basis of a nanoscopic ruler, which has been widely applied in Förster resonance energy transfer (FRET) studies. A growing body of data, however, has questioned the foundation for this and has provided evidence for structural perturbations to the PPII caused by temperature, salt content, solvent polarity, and even Pro repeat length. Here, we examine the polyproline ruler in the context of semiconductor quantum dots (QDs) and FRET. For this study, a series of polyproline peptides (Pron, n = 0, 3, 6, 9, 12, 15, 18) displaying a C-terminal hexahistidine sequence (His6) and an N-terminal cysteine for site-specific labeling with Cy3 dye were synthesized. Peptide rigidity was first examined with ATTO 647 Ni2+-nitrilotriacetic acid acceptor dye coordinated to the His6-termini of the Cy3 donor-labeled peptides. These conditions provided a steady-state fluorescent response that closely followed FRET predictions derived from the expected donor–acceptor distances; this confirmed the PPII conformation and nanoscopic ruler in the context of our sequences. Peptides were next assembled to negatively charged dihydrolipoic acid functionalized 530 nm emitting QDs, which then acted as a donor to the Cy3 acceptor. These data revealed decreases in FRET efficiency E but at significantly less than the magnitude predicted. Lastly, peptides were assembled to neutral poly(ethylene glycol) or PEG-appended dihydrolipoic acid functionalized 530 nm QDs, and here FRET E did not change as peptide length increased. The latter observations were confirmed with excited-state lifetime measurements and single-pair FRET analysis. Circular dichroism spectroscopy was performed on select peptides both free in solution and as assembled to the PEGylated QDs along with physical characterization by dynamic light scattering and electrophoretic mobility. Overall, analysis confirms the initial validity of the rigid polyproline ruler, while it also suggests that peptide subpopulations adopt a different conformation when attached to QDs. Rather than a gross structural rearrangement, this change is consistent with a trans to cis bond reversion in some of the Pro–Pro peptidyl bond(s), which alters persistence length. This suggests that the PPII is highly context dependent and can be strongly influenced by microenvironments or interfacial effects and thus requires careful consideration of experimental format and related factors before being implemented with nanoparticles.
    No preview · Article · Sep 2015 · Chemistry of Materials
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    ABSTRACT: Photocurrent in an organic solar cell is generated by a charge transfer reaction between electron donors and acceptors. Charge transfer is expected to proceed from thermalized states, but this picture has been challenged by recent studies that have investigated the role of hot excitons. Here we show a direct link between excess excitation energy and photocarrier mobility. Charge transfer from excited donor molecules generates hot photocarriers with excess energy coming from the offset between the lowest unoccupied molecular orbital of the donor and that of the acceptor. Hot photocarriers manifest themselves through a short-lived spike in terahertz photoconductivity that decays on a picosecond timescale as carriers thermalize. Different dynamics are observed when exciting the acceptor at its absorption edge to a thermalized state. Charge transfer in this case generates thermalized carriers described by terahertz photoconductivity dynamics consisting of an instrument-limited rise to a long-lived signal.
    Full-text · Article · Jul 2015 · Nature Communications
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    ABSTRACT: The single-event effect sensitivity of three different commonly employed current mirror circuits, as well as an unconventional inverse-mode current mirror, all implemented in C-SiGe (NPN + PNP) HBT on SOI technology are investigated. Comparisons of the measured data of the basic NPN and PNP current mirror circuits show higher single-event radiation tolerance of PNP SiGe HBTs compared with NPN SiGe HBTs. The concept of utilizing inverse-mode SiGe HBTs in current mirror circuits is investigated. Measurement results validate the feasibility of employing inverse-mode PNP SiGe HBTs in current mirrors and show an excellent resilience against ion-strikes. Full 3-D NanoTCAD models of the SiGe HBTs are developed and used in mixed-mode TCAD simulations (within Cadence) to validate the measurement results. Finally, based on the measurement data and analysis of the four current mirrors, some practical suggestions and observations are offered for operation of such circuits in extreme environments.
    No preview · Article · Dec 2014 · IEEE Transactions on Nuclear Science
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    ABSTRACT: A SiGe RF low-noise amplifier (LNA) with built-in tolerance to single-event transients is proposed. The LNA utilizes an inverse-mode SiGe HBT for the common-base transistor in a cascode core. This new cascode configuration exhibits reduced transient peaks and shorter transient durations compared to the conventional cascode one. The improved SET response was verified with through-wafer two-photon absorption pulsed-laser experiments and supported via mixed-mode TCAD simulations. In addition, analysis of the RF performance and the reliability issues associated with the inverse-mode operation further suggests this new cascode structure can be a strong contender for space-based applications. The LNA with the inverse-mode-based cascode core was fabricated in a 130 nm SiGe BiCMOS platform and has similar RF performance to the conventional schematic-based LNA, further validating the proposed approach.
    No preview · Article · Dec 2014 · IEEE Transactions on Nuclear Science
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    ABSTRACT: The single-event transient (SET) response of a third-generation bulk C-SiGe ( npn + pnp) BiCMOS platform is investigated for the first time. Pulsed-laser, two-photon absorption experiments show that the pnp SiGe heterojunction bipolar transistor (SiGe HBT) exhibits a significant reduction in sensitive area as well as an improved transient response compared with the npn SiGe HBT. Ion-strike simulations on 3-D TCAD, C-SiGe HBT models agree with experimental findings, showing a reduction in overall transient duration and collected charge for the pnp SiGe HBT. These improvements in device-level SETs are attributed to the n-well isolation layer present in the vertical material stack of the pnp HBT. These results suggest that precision analog, RF/mm-wave, and high-speed digital applications utilizing unhardened, high-performance bulk pnp SiGe HBTs should benefit from an inherently improved SEE response.
    No preview · Article · Dec 2014 · IEEE Transactions on Nuclear Science
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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.
    Full-text · Article · Dec 2014 · Nature Communications
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    ABSTRACT: Nonlinear beam propagation software is used to calculate quantitatively the two-photon absorption (TPA)-induced charge-density profiles generated in silicon by focused femtosecond laser pulses under conditions that are experimentally relevant for single-event effects studies. The described approach permits simulation and prediction of the impact of various optical nonlinearities on the beam propagation through, and generation of free carriers in silicon for F/#s approaching one. It is found that, even at moderate incident laser pulse energies, the nonlinear-optical processes of nonlinear refraction, free-carrier absorption, and free-carrier refraction all contribute, and must be considered in describing the TPA-induced charge generation in silicon. Free-carrier refraction is found to play the dominant role in distorting the charge density profile at larger pulse energies. The simulation results are validated with experimentally measured beam sizes for different focusing conditions.
    No preview · Article · Dec 2014 · IEEE Transactions on Nuclear Science
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    ABSTRACT: A pulsed-laser dosimetry approach for two-photon absorption (TPA) single-event effects (SEE) measurements is presented. Development and implementation of three online beam monitors is described. The beam monitors permit characterization of the primary laser beam parameters of interest: the pulse energy delivered to the device under test, the pulse duration, and the focused laser spot size. A direct consequence of this methodology is the ability to monitor continuously the operating point of the TPA SEE pulsed-laser beamline and to make the necessary adjustments when parameters drift, either during an experiment or between experiments.
    No preview · Article · Dec 2014 · IEEE Transactions on Nuclear Science
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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.
    Full-text · Article · Nov 2014 · The Journal of Physical Chemistry B
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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.
    No preview · Article · Oct 2014 · RSC Advances
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    Paul A Lane · Paul D Cunningham · Joseph S Melinger · Edwin J Heilweil
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    ABSTRACT: We present a study of charge transfer and carrier dynamics in films of zinc phthalocyanine (ZnPc) and buckmisnsterfullerene (C60) by investigated by time-resolved terahertz spectroscopy (TRTS). We compare terahertz photoconductivity dynamics in composite and multi-layered films of C60 and ZnPc. The few picosecond terahertz photoconductivity dynamics arise from autoionization and recombination between C60 molecules and cooling of hot photocarriers following from charge transfer between C60 and ZnPc.
    Full-text · Conference Paper · Oct 2014
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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.
    No preview · Article · Dec 2013 · IEEE Transactions on Nuclear Science
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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.
    No preview · Conference Paper · Jun 2013
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    Full-text · Article · Apr 2013 · Nano Letters
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    ABSTRACT: We employ time resolved fluorescence, steady state fluorescence resonance energy transfer (FRET) and single-particle fluorescence resonance energy transfer (spFRET) measurements to study multivalent quantum dot (QD)/dye systems and dermine how inhomogeneity affects the FRET dynamics of the acceptor dye molecules.
    No preview · Article · Jan 2013
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    Paul A. Lane · Mason A. Wolak · Paul D. Cunningham · Joseph S. Melinger
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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.
    Full-text · Article · Sep 2012 · Proceedings of SPIE - The International Society for Optical Engineering
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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.
    No preview · Article · Jun 2012 · ACS Nano
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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.
    Preview · Article · May 2012 · Journal of Applied Physics
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    Joseph S Melinger · Yihong Yang · Mahboubeh Mandehgar · D Grischkowsky
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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.
    Full-text · Article · Mar 2012 · Optics Express

Publication Stats

4k Citations
419.01 Total Impact Points

Institutions

  • 1997-2015
    • United States Naval Research Laboratory
      • Optical Sciences Division
      Washington, Washington, D.C., United States
  • 2003-2009
    • National Institute of Standards and Technology
      • • Materials Science and Engineering Division
      • • National Fire Research Laboratory Group
      GAI, Maryland, United States
  • 2007
    • Oklahoma State University - Stillwater
      • School of Electrical and Computer Engineering
      Stillwater, OK, United States
  • 2002-2003
    • University of Missouri - Kansas City
      • Department of Chemistry
      Kansas City, MO, United States
  • 1998
    • Clemson University
      CEU, South Carolina, United States
  • 1996
    • Sandia National Laboratories
      Albuquerque, New Mexico, United States
  • 1991-1995
    • Princeton University
      • Department of Chemistry
      Princeton, New Jersey, United States