576 Matching Results

Search Results

Advanced search parameters have been applied.

Device Engineering for Enhanced Efficiency from Platinum(II) Phosphorescent OLEDs

Description: Phosphorescent organic light emitting diodes (PHOLEDs) based on efficient electrophosphorescent dopant, platinum(II)-pyridyltriazolate complex, bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) (Pt(ptp)2) have been studied and improved with respect to power efficiency, external efficiency, chromacity and efficiency roll-off. By studying the electrical and optical behavior of the doped devices and functionality of the various constituent layers, devices with a maximum EQE of 20.8±0.2 % and power efficiency of 45.1±0.9 lm/W (77lm/W with luminaries) have been engineered. This improvement compares to devices whose emission initially could only be detected by a photomultiplier tube in a darkened environment. These devices consisted of a 65 % bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) (Pt(ptp)2) doped into 4,4'-bis(carbazol-9-yl)triphenylamine (CBP) an EML layer, a hole transporting layer/electron blocker of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), an electron transport layer of 1,3,5-tris(phenyl-2-benzimidazolyl)-benzene (TPBI), and a LiF/Al cathode. These devices show the acceptable range for warm white light quadrants and qualify to be called "warm white" even w/o adding another emissive layer. Dual EML devices composed of neat Pt(ptp)2 films emitting orange and CBP: Pt(ptp)2 film emitting blue-green produced a color rendering index (CRI) of 59 and color coordinates (CIE) of (0.47,0.49) at 1000Cd/m² with power efficiency of 12.6±0.2 lm/W and EQE of 10.8±0.2 %. Devices with two blue fluorescent emission layers as singlet filters and one broad yellow emission layer from CBP: Pt(ptp)2 displayed a CRI of 78 and CIE of (0.28,0.31) at 100Cd/m² with maximum power efficiency of 6.7±0.3 lm/W and EQE of 5.7±0.2 %.
Date: August 2010
Creator: Li, Minghang
Partner: UNT Libraries

Platinum Group Thiophenoxyimine Complexes: Syntheses,Crystallographic and Computational Studies of Structural Properties

Description: Monomeric thiosalicylaldiminate complexes of rhodium(I) and iridium(I) were prepared by ligand transfer from the homoleptic zinc(II) species. In the presence of strongly donating ligands, the iridium complexes undergo insertion of the metal into the imine carbon-hydrogen bond. Thiophenoxyketimines were prepared by non-templated reaction of o-mercaptoacetophenone with anilines, and were complexed with rhodium(I), iridium(I), nickel(II) and platinum(II). X-ray crystallographic studies showed that while the thiosalicylaldiminate complexes display planar ligand conformations, those of the thiophenoxyketiminates are strongly distorted. Results of a computational study were consistent with a steric-strain interpretation of the difference in preferred ligand geometries.
Date: October 3, 2006
Creator: Krinsky, Jamin L.; Arnold, John & Bergman, Robert G.
Partner: UNT Libraries Government Documents Department

Thistle

Description: No Description Available.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: 1898/1907
Creator: Lincoln, Edwin Hale
Partner: UNT College of Visual Arts + Design

Surface structure of MX-chains studied by atomic force microscopy

Description: The surfaces of mixed-valence halogen-bridged transition metal linear chain compounds [[Pt(en){sub 2}][Pt(en)]{sub 2}(X{sub 1-y}X{prime}{sub y}){sub 2}](ClO{sub 4}){sub 4} (X, X{prime} = Cl, Br, or I; en = C{sub 2}H{sub 8}N{sub 2}; y = 0.0 - 1.0) were examined by atomic force microscopy (AFM). The AFM images are consistent with the surfaces expected from the bulk crystal structure. The surface unit cell parameters of the images correspond to the lattice constants of the bulk crystals. The patterns of the atomic-scale AFM images are dominated by the most protruded H atoms of the en ligands and the most protruded O atoms of the ClO{sub 4}{sup -} anions.
Date: March 1, 1995
Creator: Bar, G.; Scott, B.; Johnson, S.R.; Kanner, G.S. & Swanson, B.I.
Partner: UNT Libraries Government Documents Department

Design, Synthesis and Screening of Homoleptic and Heteroleptic Platinum(ii) Pyridylazolate Complexes for N-type Semiconducting and Light-emitting Devices

Description: A series of heteroleptic and homoleptic platinum(II) complexes has been synthesized and characterized towards their use in thin film devices such as organic light-emitting diodes (OLEDs) and organic thin film transistors (OTFTs). Pyridylpyrazolate- and pyridyltetrazolate-containing ligands were selected due to their structural rigidity and ease of functionalization. Single-crystal x-ray diffraction studies of two selected heteroleptic complexes show strong aggregation with preferential stacking into vertical columns with a varying degree of overlap of the neighboring square planar molecular units. It is shown that the close proximity of the molecules to one another in the stack increases semiconducting character, phosphorescence quantum yields, and shorter radiative lifetimes. The potential for these materials towards incorporation into high-efficiency doping free white OLEDs (DFW-OLEDs) for solid-state lighting and display applications has been realized and will be expanded upon by present and future embodiments of materials in this thesis.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: August 2012
Creator: Oswald, Iain William Herbert
Partner: UNT Libraries

Examination of the platinum effect on the oxidation behavior ofnickel-aluminide coatings

Description: Oxidation resistant nickel-aluminide coatings are designed to develop a protective alumina scale during high temperature exposure. It is well established that platinum additions, typically about 6-8 at%, provide substantial improvements in oxidation resistance of such coatings, yet the nature of the platinum effect is still not fully understood. In this work, the oxidation behavior of two commercial NiAl and NiPtAl coatings deposited on the same Ni-base single crystal alloy CMSX-4 was analyzed. Cyclic and isothermal oxidation tests were conducted at 1150 C in air. Microstructure development and alumina/coating interface chemistry were studied as a function of oxidation time. Numerous voids developed at the Al{sub 2}O{sub 3}/NiAl interface, and sulfur was found to segregate at the void surfaces and at the contact interface, leading to spallation of the scale over the convex areas along ridges on the coating surface. The presence of platinum prevented sulfur segregation and void formation at the Al{sub 2}O{sub 3}/NiPtAl interface. As a result, the Al{sub 2}O{sub 3} scale on the NiPtAl coating remained adherent and virtually no spallation was observed even after prolonged cyclic oxidation.
Date: May 15, 2007
Creator: Hou, Peggy Y. & Tolpygo, V.K.
Partner: UNT Libraries Government Documents Department

Synthesis and Characterization of Platinum(II)(2-(9-anthracenylylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione)(dichloride), Platinum(II)(2-(9-anthracenylylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione(maleonitriledithiolate), and Platinum(II)(4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione)(4-Methyl-1,2-benzene dithiol)

Description: Substitution of the 1,5-cyclooctadiene (cod) ligand in PtCl2(cod) (1) by the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) yields PtCl2(bpcd) (2). Knoevenagel condensation of 2 with 9-anthracenecarboxaldehyde leads to the functionalization of the bpcd ligand and formation of the corresponding 2-(9-anthracenylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (abpcd) substituted compound PtCl2(abpcd) (3), which is also obtained from the direct reaction of 1 with the abpcd ligand in near quantitative yield. The reaction of 3 with disodium maleonitriledithiolate (Na2mnt) affords the chelating dithiolate compound Pt(mnt)(abpcd) (4). The reaction of PtCl2(bpcd) (2) with 4-methyl-1,2-benzene dithiol under basic conditions affords Pt(tdt)(bpcd) (5). Compounds 2-5 have been fully characterized in solution by IR and NMR spectroscopies (1H and 31P), and their molecular structures established by X-ray crystallography. The electrochemical properties of 2‑5 have examined by cyclic voltammetry, and the nature of the HOMO and LUMO levels in systems 2-4 has been established by MO calculations at the extended Hückel level, the results of which are discussed with respect to electrochemical data and related diphosphine derivatives. In addition the new compounds 2-5 have been isolated by column chromatography and characterized by IR, UV-Vis spectroscopy.
Date: December 2009
Creator: Hunt, Sean W.
Partner: UNT Libraries

Step- vs. kink-formation energies on Pt(111)

Description: Ab-initio kink-formation energies are about 0.25 and 0.18 eV on the (100)- and (111)-microfacet steps of Pt(111), while the sum of the step-formation energies is 0.75 eV/atom. These results imply a specific ratio of formation energies for the two step types, namely 1.14, in excellent agreement with experiment. If kink-formation costs the same energy on the two step types, an inference recently drawn from scanning probe observations of step wandering, this ratio ought to be 1.
Date: May 1, 2000
Creator: FEIBELMAN,PETER J.
Partner: UNT Libraries Government Documents Department

Reactivity of hydrogen with uranium in the presence of Pt

Description: The surface-reaction of di-hydrogen with uranium in the presence of Pt clusters has been studied using scanning tunneling microscopy (STM). Uranium was deposited on highly oriented pyrolytic graphite (HOPG) and annealed at temperatures up to 1200{degrees}C to obtain atomically pyrolytic flat surfaces. Pt clusters were then formed using evaporation from a Pt source onto the surface and subsequent annealing. Hydrogen mainly attacked uranium in the vicinity of Pt clusters and formed hydride. The hydride formation probability is almost constant at 2.3x10{sup -4} over the range of exposures studied.
Date: July 1, 1997
Creator: Balooch, M. & Siekhaus, W.J.
Partner: UNT Libraries Government Documents Department

Hydrogen Oxidation-Driven Hot Electron Flow Detected by Catalytic Nanodiodes

Description: Hydrogen oxidation on platinum is shown to be a surface catalytic chemical reaction that generates a steady state flux of hot (>1 eV) conduction electrons. These hot electrons are detected as a steady-state chemicurrent across Pt/TiO{sub 2} Schottky diodes whose Pt surface is exposed to hydrogen and oxygen. Kinetic studies establish that the chemicurrent is proportional to turnover frequency for temperatures ranging from 298 to 373 K for P{sub H2} between 1 and 8 Torr and P{sub O2} at 760 Torr. Both chemicurrent and turnover frequency exhibit a first order dependence on P{sub H2}.
Date: July 20, 2009
Creator: Hervier, Antoine; Renzas, J. Russell; Park, Jeong Y. & Somorjai, Gabor A.
Partner: UNT Libraries Government Documents Department

Converting Homogeneous to Heterogeneous in Electrophilic Catalysis using Monodisperse Metal Nanoparticles

Description: A continuing goal in catalysis is the transformation of processes from homogeneous to heterogeneous. To this end, nanoparticles represent a new frontier in heterogeneous catalysis, where this conversion is supplemented by the ability to obtain new or divergent reactivity and selectivity. We report a novel method for applying heterogeneous catalysts to known homogeneous catalytic reactions through the design and synthesis of electrophilic platinum nanoparticles. These nanoparticles are selectively oxidized by the hypervalent iodine species PhICl{sub 2}, and catalyze a range of {pi}-bond activation reactions previously only homogeneously catalyzed. Multiple experimental methods are utilized to unambiguously verify the heterogeneity of the catalytic process. The discovery of treatments for nanoparticles that induce the desired homogeneous catalytic activity should lead to the further development of reactions previously inaccessible in heterogeneous catalysis. Furthermore, our size and capping agent study revealed that Pt PAMAM dendrimer-capped nanoparticles demonstrate superior activity and recyclability compared to larger, polymer-capped analogues.
Date: October 15, 2009
Creator: Witham, Cole A.; Huang, Wenyu; Tsung, Chia-Kuang; Kuhn, John N.; Somorjai, Gabor A. & Toste, F. Dean
Partner: UNT Libraries Government Documents Department

The effect of specific chloride adsorption on the electrochemicalbehavior of ultrathin Pd films deposited on Pt(111) in acidsolution

Description: The electrochemical behavior of thin Pd films supported on a Pt(111) electrode is investigated by cyclic voltammetry (CV) and in-situ Fourier transform infrared (FTIR) spectroscopy. It is demonstrated that in perchloric acid solution underpotential deposition of hydrogen (H{sub upd}) and hydroxyl adsorption (OH{sub ad}) is in strong competition with the adsorption of Cl- anions, the latter being present as a trace impurity in HClO{sub 4}. The interaction of Cl- with Pd is rather strong, controlling the adsorption of H{sub upd} and OH{sub ad} as well as the kinetic rate of CO oxidation. The microscopic insight (the binding sites) of the adsorbed CO (CO{sub ad}) and the rate of CO oxidation (established from CO2 production) on Pt(111) modified with a (sub)monolayer of Pd is elucidated by means of Fourier infrared (FTIR) spectroscopy. The appearance of both the characteristic Pt(111)-CO{sub ad} and Pt(111)1 ML Pd-CO{sub ad} stretching bands on a Pt(111) surface covered by 0.5 ML Pd confirms previous findings that the Pd atoms agglomerate into islands and that the bare Pt areas and the Pd islands behave according to their own surface chemistry. The systematic increase of the Pd surface coverage results in a gradual change in the catalytic properties of Pt(111)-xPd electrodes towards CO oxidation, from those characteristic of bare Pt(111) to those which are characteristic for Pt(111) covered with 1 ML of Pd.
Date: October 1, 2002
Creator: arenz@thch.uni-bonn.de
Partner: UNT Libraries Government Documents Department

Ordering of Self-Diffusion Barrier Energies on Pt(110)-1x2

Description: Bond-counting arguments, supported by ab-initio calculations, predict a lower barrier for "leapfrog" diffusion of Pt addimers on Pt(llO)-lx2 than for adatom dif- fusion or addimer dissociation. This conflicts with experiment, possibly signaling contaminant influence.
Date: June 1, 1999
Creator: Feibelman, Peter J.
Partner: UNT Libraries Government Documents Department

Receptor-targeted metalloradiopharmaceuticals. Final technical report

Description: Copper (II) and platinum (II) coordination complexes were prepared and characterized. These complexes were designed to afford structural homology with steroidal and non-steroidal estrogens for possible use as receptor-targeted radiopharmaceuticals. While weak affinity for the estrogen receptor was detectable, none would appear to have sufficient receptor-affinity for estrogen-receptor-targeted imaging or therapy.
Date: March 22, 2000
Creator: Green, Mark A.
Partner: UNT Libraries Government Documents Department

Self-Diffusion Along Step-Bottoms on Pt(111)

Description: First-principles total energies of periodic vicinals are used to estimate barriers for Pt-adatom diffusion along straight and kinked steps on Pt(111), and around a corner where straight steps intersect. In all cases studied, hopping diffusion has a lower barrier than concerted substitution. In conflict with simulations of dendritic Pt island formation on Pt(111), hopping from a corner site to a step whose riser is a (111)-micro facet is predicted to be more facile than to one whose riser is a (100).
Date: April 5, 1999
Creator: Feibelman, P.J.
Partner: UNT Libraries Government Documents Department

The Role of Organic Capping Layers of Platinum Nanoparticles in Catalytic Activity of CO Oxidation

Description: We report the catalytic activity of colloid platinum nanoparticles synthesized with different organic capping layers. On the molecular scale, the porous organic layers have open spaces that permit the reactant and product molecules to reach the metal surface. We carried out CO oxidation on several platinum nanoparticle systems capped with various organic molecules to investigate the role of the capping agent on catalytic activity. Platinum colloid nanoparticles with four types of capping layer have been used: TTAB (Tetradecyltrimethylammonium Bromide), HDA (hexadecylamine), HDT (hexadecylthiol), and PVP (poly(vinylpyrrolidone)). The reactivity of the Pt nanoparticles varied by 30%, with higher activity on TTAB coated nanoparticles and lower activity on HDT, while the activation energy remained between 27-28 kcal/mol. In separate experiments, the organic capping layers were partially removed using ultraviolet light-ozone generation techniques, which resulted in increased catalytic activity due to the removal of some of the organic layers. These results indicate that the nature of chemical bonding between organic capping layers and nanoparticle surfaces plays a role in determining the catalytic activity of platinum colloid nanoparticles for carbon monoxide oxidation.
Date: December 17, 2008
Creator: Park, Jeong Y.; Aliaga, Cesar; Renzas, J. Russell; Lee, Hyunjoo & Somorjai, Gabor A.
Partner: UNT Libraries Government Documents Department