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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Modeling of threshold and dynamics behavior of organic nanostructured lasers

Organic dye molecules offer significant potential as gain media in the emerging field of optical amplification and lasing at subwavelength scales. In this article, we investigate the laser dynamics in systems comprising subwavelength-structured cavities that incorporate organic dyes. To this end, we have developed a comprehensive theoretical framework able to accurately describe the interaction of organic molecules with any arbitrary photonic structure to produce single-mode lasing. The model provides explicit analytic expressions of the threshold and slope efficiency that characterize this class of lasers, and also the duration over which lasing action can be sustained before the dye photobleaches. Both the physical properties of the dyes and the optical properties of the cavities are considered. We also systematically studied the feasibility of achieving lasing action under continuous-wave excitation in optically pumped monolithic organic dye lasers. This study suggests routes to realize an organic laser that can potentially lase with a threshold of only a few W cm -2 . In conclusion, our work puts forward a theoretical formalism that could enable the advancement of nanostructured organic-based light emitting and sensing devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Graphitization Behavior of Loblolly Pine Wood Investigated by in Situ High Temperature X-ray Diffraction

Graphitization is a complex process involving chemical and morphological changes, although the detailed mechanism for different starting materials is not well understood. In this work, in situ high temperature X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to examine the phase transition occurring between 1000 and 1500 °C in loblolly pine wood-derived carbon materials. Electron energy loss spectroscopy (EELS) was also used to study these wood-derived carbon materials. XRD data showed the disappearance of a disordered carbon phase between 1300 and 1400 °C, followed by the formation of a crystalline graphitic phase between 1400 and 1500 °C. Here, lattice parameters and the crystal structure of the loblolly pine wood-derived graphite were systematically calculated from the empirical data. The presence of a large endothermic peak at 1500 °C in the DSC thermogram supported this observation. Selected area electron diffraction patterns showed the growth of graphitic crystallites after heat treatment. EELS spectra also supported the presence of a well-developed graphite structure.

Anode materials↗
DOE OSTI2012

Ternary behavior and systematic nanoscale manipulation of domain structures in P3HT/PCBM/P3HT-b-PEO films

Nanophase separation plays a critical role in the performance of donor acceptor based organic photovoltaic (OPV) devices. Although post-fabrication annealing is often used to enhance OPV efficiency, the ability to exert precise control over phase separated domains and connectivity remains elusive. In this work, we use a diblock copolymer to systematically manipulate the domain sizes of an organic solar cell active layer at the nanoscale. More specifically, a poly(3-hexylthiophene)-bpoly( ethylene oxide) (P3HT-b-PEO) diblock copolymer with a low polydispersity index (PDI 1.3) is added to a binary blend of P3HT and 6,6-phenyl C61-butyric acid methyl ester (PCBM) at different concentrations (0 20 wt%). Energy-filtered TEM (EFTEM) results suggest systematic changes of P3HT distribution as a function of block copolymer compatibilizer concentration and thermal annealing. X-ray scattering and microscopy techniques are used to show that prior to annealing, active layer domain sizes do not change substantially as compatibilizer is added; however after thermal annealing, the domain sizes are significantly reduced as the amount of P3HT-b-PEO compatibilizer increases. The impact of compatibilizer is further rationalized through quantum density functional theory calculations. Overall, this work demonstrates the possibility of block copolymers to systematically manipulate the nanoscale domain-structure of blends used for organic photovoltaic devices. Furthermore, if coupled with efficient charge transport and collection (through judicious choice of block copolymer type and composition), this approach may contribute to further optimization of OPV devices.

14 SOLAR ENERGY↗
DOE OSTI2019

Hardware MPI message matching: Insights into MPI matching behavior to inform design: Hardware MPI message matching

Here, this paper explores key differences of MPI match lists for several important United States Department of Energy (DOE) applications and proxy applications. This understanding is critical in determining the most promising hardware matching design for any given high-speed network. The results of MPI match list studies for the major open-source MPI implementations, MPICH and Open MPI, are presented, and we modify an MPI simulator, LogGOPSim, to provide match list statistics. These results are discussed in the context of several different potential design approaches to MPI matching–capable hardware. The data illustrate the requirements for different hardware designs in terms of performance and memory capacity. Finally, this paper's contributions are the collection and analysis of data to help inform hardware designers of common MPI requirements and highlight the difficulties in determining these requirements by only examining a single MPI implementation.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Redox Behavior of 2,3-Diamino-1,4-naphthoquinone and its N-Alkylated Derivatives

Electrochemical reduction and oxidation potentials and standard heterogeneous electron transfer rate constants are reported for 2,3-diamino-1,4-naphthoquinone and two of its N-alkylated derivatives in acetonitrile. For two of the compounds, spectroelectrochemistry was used to obtain the absorption spectra of the radical cation and the radical anion. The compounds can be viewed as captodative biradicaloids and as such are of interest for photophysical studies of singlet fission.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗