Joseph S. Melinger

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

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Publications (171)409.81 Total impact

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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.
    Chemistry of Materials 09/2015; 27(18):150909124212009. DOI:10.1021/acs.chemmater.5b03181 · 8.35 Impact Factor
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    Paul A Lane · Paul D Cunningham · Joseph S Melinger · Okan Esenturk · Edwin J Heilweil ·
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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.
    Nature Communications 07/2015; 6:7558. DOI:10.1038/ncomms8558 · 11.47 Impact Factor
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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.
    IEEE Transactions on Nuclear Science 12/2014; 61(6):3218-3225. DOI:10.1109/TNS.2014.2363631 · 1.28 Impact Factor
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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 12/2014; 5:5615. DOI:10.1038/ncomms6615 · 11.47 Impact Factor
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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; 118(50). DOI:10.1021/jp5065006 · 3.30 Impact Factor
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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). DOI:10.1039/C4RA10580J · 3.84 Impact Factor
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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.
    SPIE Organic Photovoltaics XV; 10/2014
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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.
    IEEE Transactions on Nuclear Science 12/2013; 60(6):4184-4191. DOI:10.1109/TNS.2013.2290307 · 1.28 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. DOI:10.1021/nl401525k · 13.59 Impact Factor
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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.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; 8476. DOI:10.1117/12.930055 · 0.20 Impact Factor
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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. DOI:10.1021/nn301177h · 12.88 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). DOI:10.1063/1.4709385 · 2.18 Impact Factor
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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.
    Optics Express 03/2012; 20(6):6788-807. DOI:10.1364/OE.20.006788 · 3.49 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. DOI:10.1103/PhysRevLett.108.077402 · 7.51 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). DOI:10.1063/1.3678000 · 2.18 Impact Factor
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    ABSTRACT: The laser pulse energy thresholds for single-event upset measured by single photon and two photon absorption are measured and compared for Sandia SRAMs and DPSRAMs, and IBM 45-nm SRAMs for devices with and without the back substrate removed. These results are also compared to heavy-ion results taken on the same devices. Sandia SRAM data taken on different test dates resulted in considerably different TPA laser pulse energy thresholds even though the TPA system was calibrated using standard techniques each test date. These differences are believed to be due to changes in laser spot size. This shows that it is imperative to develop a calibration procedure that monitors all relevant laser parameters if TPA is to be used as a routine quantitative tool. Removing the back substrate makes a very large difference in TPA laser pulse energy threshold. This large difference is likely due to either displacement currents generated in the back substrate by TPA and/or nonlinear optical effects which can reduce the laser pulse irradiance in the active region. Nevertheless, the mechanism does not appear to affect the qualitative nature of TPA measurements. Both SPA and TPA laser measurements were used to estimate the heavy-ion threshold LETs of the Sandia DPSRAMs and 45-nm IBM SRAMs. Both SPA and TPA overestimated the heavy-ion threshold LET of the IBM 45-nm SRAMs (likely due to the large laser spot size compared to the size of the SRAM cell), but reasonably estimated the threshold LETs of the Sandia DPSRAMs. For the first time, TPA laser pulse energy (squared) is directly compared to SPA laser pulse energy at threshold. There is reasonable quantitative agreement between the charge required to induce upsets by TPA and SPA with the back substrate removed.
    IEEE Transactions on Nuclear Science 12/2011; 58(6):2968-2975. DOI:10.1109/TNS.2011.2171006 · 1.28 Impact Factor
  • Dalemcmorrow · Joseph S.melinger · Alvin R.knudson ·
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    ABSTRACT: Single-event effects are a serious concern for high-speed III-V semiconductor devices operating in radiation-intense environments. GaAs integrated circuits (ICs) based on field effect transistor technology exhibit single-event upset sensitivity to protons and very low linear energy transfer (LET) particles. The current understanding of single-event effects in III-V circuits and devices, and approaches for mitigating their impact, are discussed.
    International Journal of High Speed Electronics and Systems 11/2011; 14(02). DOI:10.1142/S0129156404002375
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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. DOI:10.1007/s10762-011-9816-3 · 1.94 Impact Factor

Publication Stats

4k Citations
409.81 Total Impact Points


  • 1998-2013
    • 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
  • 1997
    • Institute of Geophysics, China Earthquake Administration
      Peping, Beijing, China
  • 1996
    • Sandia National Laboratories
      Albuquerque, New Mexico, United States
  • 1991-1995
    • Princeton University
      • Department of Chemistry
      Princeton, New Jersey, United States