Different heat treatments were applied to commercial Pd77Ag23 membranes to promote surface segregation. X-ray photoelectron spectroscopy (XPS) analysis indicates that the membrane surface composition changed after heat treatment. The surface area of all membranes increased after heat treatment. The higher the surface Pd/(Pd+Ag) ratio, the higher the hydrogen permeability. Surface carbon removal and surface area increase cannot explain the observed permeability differences.
Previous computational modeling predicted that Cu54Zr46 would have high hydrogen permeability. Amorphous metallic Cu-Zr (Zr=37, 54, 60 at. %) membranes were synthesized and investigated. The surface oxides may result in the lower experimental hydrogen permeability lower than that predicted by the simulations. The permeability decrease indicates that the Cu-Zr alloys crystallized in less than two hours during the test (performed at 300 °C) at temperatures below the glass transition temperature. This original experimental results show that thermal stability of amorphous metallic membranes is critical for hydrogen separation applications.
The hydrogen permeability of Ni60Nb35M5 (M=Sn, Ti and Zr) amorphous metallic membranes was investigated. Nanoindentation shows that the Young’s modulus and hardness increased after hydrogen permeability test. The structure is maintained amorphous after 24 hours of hydrogen permeability testing at 400°C. The maximum hydrogen permeability of three alloys is 10-10 mol m-1 s-1 Pa-0.5. Though these alloys exhibited a slight hydrogen permeability decreased during the test, the amorphous metallic membranes were thermally stable and did not crystalize.
Optical simulation and optimization of light extraction efficiency for organic light emitting diodes
Worldwide energy demand is increasing as the population grows and the standard of living in developing countries improves. Some studies estimate as much as 20% of annual energy usage is consumed by lighting. Improvements are being made in lightweight, flexible, rugged panels that use organic light emitting diodes (OLEDs), which are particularly useful in developing regions with limited energy availability and harsh environments.
Displays also benefit from more efficient materials as well as the lighter weight and ruggedness enabled by flexible substrates. Displays may require different emission characteristics compared with solid-state lighting. Some display technologies use a white OLED (WOLED) backlight with a color filter, but these are more complex and less efficient than displays that use separate emissive materials that produce the saturated colors needed to reproduce the entire color gamut. Saturated colors require narrow-band emitters. Full-color OLED displays up to and including television size are now commercially available from several suppliers, but research continues to develop more efficient and more stable materials.
This research program investigates several topics relevant to solid-state lighting and display applications. One project is development of a device structure to optimize performance of a new stable Pt-based red emitter developed in Prof Jian Li's group. Another project investigates new Pt-based red, green and blue emitters for lighting applications and compares a red/blue structure with a red/green/blue structure to produce light with high color rendering index. Another part of this work describes the fabrication of a 14.7" diagonal full color active-matrix OLED display on plastic substrate. The backplanes were designed and fabricated in the ASU Flexible Display Center and required significant engineering to develop; a discussion of that process is also included.
Photocurrent Enhancements of Organic Solar Cells by Altering Dewetting of Plasmonic Ag Nanoparticles
Incorporation of metal nanoparticles into active layers of organic solar cells is one of the promising light trapping approaches. The size of metal nanoparticles is one of key factors to strong light trapping, and the size of thermally evaporated metal nanoparticles can be tuned by either post heat treatment or surface modification of substrates. We deposited Ag nanoparticles on ITO by varying nominal thicknesses, and post annealing was carried out to increase their size in radius. PEDOT:PSS was employed onto the ITO substrates as a buffer layer to alter the dewetting behavior of Ag nanoparticles. The size of Ag nanoparticles on PEDOT:PSS were dramatically increased by more than three times compared to those on the ITO substrates. Organic solar cells were fabricated on the ITO and PEDOT:PSS coated ITO substrates with incorporation of those Ag nanoparticles, and their performances were compared. The photocurrents of the cells with the active layers on PEDOT:PSS with an optimal choice of the Ag nanoparticles were greatly enhanced whereas the Ag nanoparticles on the ITO substrates did not lead to the photocurrent enhancements. The origin of the photocurrent enhancements with introducing the Ag nanoparticles on PEDOT:PSS are discussed.
Mof4 family associated protein 1 (MRFAP1) is a 14 kDa nuclear protein, which involves in maintaining normal histone modification levels by negatively regulating recruitment of the NuA4 (nucleosome acetyltransferase of H4) histone acetyltransferase complex to chromatin. MRFAP1 has been identified as one of the most up-regulated proteins after NEDD8 (neural precursor cell expressed developmentally down- regulated 8) inhibition in multiple human cell lines. However, the biological function of MRFAP1 and the E3 ligase that targets MRFAP1 for destruction remain mysterious. Here we show, by using an immunoprecipitation-based proteomics screen, that MRFAP1 is an interactor of the F-box protein FBXW8. MRFAP1 is degraded by means of the ubiquitin ligase Cul7/FBXW8 during mitotic anaphase-telophase transition and accumulated in mitotic metaphase. Overexpression of FBXW8 increased the polyubiquitination and decreased the stability of MRFAP1, whereas knockdown of FBXW8 prolonged the half-life of MRFAP1. Moreover, forced expression of MRFAP1 in HeLa cells caused growth retardation and genomic instability, leading to severe mitotic cell death. Thus, Cul7/FBXW8-mediated destruction of MRFAP1 is a regulatory component monitoring the anaphase-telophase transition and preventing genomic instability.
A tetradentate Pd(II) complex, Pd3O3, which exhibits highly efficient excimer emission is synthesized and characterized. Pd3O3 can achieve blue emission despite using phenyl-pyridine emissive ligands which have been a mainstay of stable green and red phosphorescent emitter designs, making Pd3O3 a good candidate for stable blue or white OLEDs. Pd3O3 exhibits strong and efficient phosphorescent excimer emission expanding the excimer based white OLEDs beyond the sole class of Pt complexes. Devices of Pd3O3 demonstrate peak external quantum efficiencies as high as 24.2% and power efficiencies of 67.9 Lm per W for warm white devices. Furthermore, Pd3O3 devices in a carefully designed stable structure achieved a device operational lifetime of nearly 3000 h at 1000 cd m-2 without any outcoupling enhancement while simultaneously achieving peak external quantum efficiencies of 27.3% and power efficiencies over 81 Lm per W.
The electronic structure of eight zinc-centered porphyrin macrocyclic molecules are investigated using density functional theory for ground-state properties, time-dependent density functional theory (TDDFT) for excited states, and Franck-Condon (FC) analysis for further characterization of the UV-vis spectrum. Symmetry breaking was utilized to find the lowest energy of the excited states for many states in the spectra. To confirm the theoretical modeling, the spectroscopic result from zinc phthalocyanine (ZnPc) is used to compare to the TDDFT and FC result. After confirmation of the modeling, five more planar molecules are investigated: zinc tetrabenzoporphyrin (ZnTBP), zinc tetrabenzomonoazaporphyrin (ZnTBMAP), zinc tetrabenzocisdiazaporphyrin (ZnTBcisDAP), zinc tetrabenzotransdiazaporphyrin (ZnTBtransDAP), and zinc tetrabenzotriazaporphyrin (ZnTBTrAP). The two latter molecules are then compared to their phenylated sister molecules: zinc monophenyltetrabenzotriazaporphyrin (ZnMPTBTrAP) and zinc diphenyltetrabenzotransdiazaporphyrin (ZnDPTBtransDAP). The spectroscopic results from the synthesis of ZnMPTBTrAP and ZnDPTBtransDAP are then compared to their theoretical models and non-phenylated pairs. While the Franck-Condon results were not as illuminating for every B-band, the Q-band results were successful in all eight molecules, with a considerable amount of spectral analysis in the range of interest between 300 and 750 nm. The π-π* transitions are evident in the results for all of the Q bands, while satellite vibrations are also visible in the spectra. In particular, this investigation finds that, while ZnPc has a D4h symmetry at ground state, a C4v symmetry is predicted in the excited-state Q band region. The theoretical results for ZnPc found an excitation energy at the Q-band 0-0 transition of 1.88 eV in vacuum, which is in remarkable agreement with published gas-phase spectroscopy, as well as our own results of ZnPc in solution with Tetrahydrofuran that are provided in this paper.