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Sample records for pt da muta

  1. Rapid Purification and Procoagulant and Platelet Aggregating Activities of Rhombeobin: A Thrombin-Like/Gyroxin-Like Enzyme from Lachesis muta rhombeata Snake Venom

    PubMed Central

    Torres-Huaco, Frank Denis; Werneck, Cláudio C.; Vicente, Cristina Pontes; Vassequi-Silva, Talita; Nery-Diez, Ana Cláudia Coelho; Mendes, Camila B.; Antunes, Edson; Marangoni, Sérgio; Damico, Daniela C. S.

    2013-01-01

    We report a rapid purification method using one-step chromatography of SVSP Rhombeobin (LMR-47) from Lachesis muta rhombeata venom and its procoagulant activities and effects on platelet aggregation. The venom was fractionated by a single chromatographic step in RP-HPLC on a C8 Discovery BIO Wide Pore, showing high degree of molecular homogeneity with molecular mass of 47035.49 Da. Rhombeobin showed amidolytic activity upon BAρNA, with a broad optimum pH (7–10) and was stable in solution up to 60°C. The amidolytic activity was inhibited by serine proteinase inhibitors and reducing agents, but not chelating agents. Rhombeobin showed high coagulant activity on mice plasma and bovine fibrinogen. The deduced amino acid sequence of Rhombeobin showed homology with other SVSPs, especially with LM-TL (L. m. muta) and Gyroxin (C. d. terrificus). Rhombeobin acts, in vitro, as a strong procoagulant enzyme on mice citrated plasma, shortening the APTT and PT tests in adose-dependent manner. The protein showed, “ex vivo”, a strong defibrinogenating effect with 1 µg/animal. Lower doses activated the intrinsic and extrinsic coagulation pathways and impaired the platelet aggregation induced by ADP. Thus, this is the first report of a venom component that produces a venom-induced consumptive coagulopathy (VICC). PMID:24058917

  2. Isolation of a proteinase with plasminogen-activating activity from Lachesis muta muta (bushmaster) snake venom.

    PubMed

    Sanchez, E F; Santos, C I; Magalhaes, A; Diniz, C R; Figueiredo, S; Gilroy, J; Richardson, M

    2000-06-01

    A plasminogen activator enzyme (LV-PA) from Lachesis muta muta venom was purified to homogeneity using gel filtration and anion exchange chromatography. SDS-PAGE under reducing conditions showed a single protein band with an Mr of 33,000 Da. It is an acidic glycoprotein which activates plasminogen to plasmin indirectly, functioning via prior formation of a molecular complex, known as plasminogen activator. The purified preparation catalyzes the hydrolysis of several p-nitroanilide peptide substrates containing Lys at the scissile bond. In contrast, no hydrolysis was detected on the synthetic substrates TAME and BAPNA, which contain arginine. By the use of the plasmin-specific chromogenic substrate Tos-Gly-Pro-Lys-pNA, the preparation had a plasmin-like activity of 0.68 U/mg, which was 35.8-fold higher than that of the crude venom from which it was prepared. In vitro, fibrin hydrolysis using LV-PA as plasminogen activator displayed more similarity with the effect produced by streptokinase (SK). SDS-PAGE (10%) analysis showed a 115-kDa complex formation after incubation of plasminogen with either LV-PA or SK. At a molar ratio of 50:1 (fibrinogen:enzyme), the preparation exhibited weakly fibrinogenolytic activity. However, LV-PA is distinguished from thrombin in that it does not clot fibrinogen. After incubation of LV-PA with platelet-rich plasma, the enzyme (2 microM) showed no effect on platelet aggregation induced by ADP, epinephrine, or collagen. Comparison of the N-terminal sequence of LV-PA with other snake venom plasminogen activators revealed that LV-PA exhibits a high degree of sequence identity with the TsVPA from Trimeresurus stejnegeri (90%) and with the Haly-PA from Agkistrodon halys (85%). LV-PA also has homology with other snake venom serine proteinases such as the thrombin-like/gyroxin analogue (38%) from bushmaster venom and with other coagulation serine proteases. The proteinase was readily inhibited by treatment with p-nitrophenyl p

  3. Specific identification of Lachesis muta muta snake venom using antibodies against the plasminogen activator enzyme, LV-PA.

    PubMed

    Felicori, Liza F; Chávez-Olórtegui, Carlos; Sánchez, Eladio F

    2005-05-01

    Sandwich-type enzyme linked immunosorbent assays (ELISA) were developed to detect Lachesis muta muta (bushmaster) snake venom using antibodies against the plasminogen activator enzyme (LV-PA). Antibodies to LV-PA were obtained by immunization of one rabbit with the purified enzyme. The IgG fraction was purified from rabbit blood in a single step on a column of Sepharose-L. m. muta venom and used to coat the microtiter plates. The specificity of the assay was demonstrated by its capacity to correctly discriminate between the circulating antigens in mice that were experimentally inoculated with L. m. muta venom from those in mice inoculated with venoms from Bothrops atrox, B. brazili, B. castelnaudi, Bothriopsis taeniata, B. bilineata, Crotalus durissus ruruima and the antigenic Bothrops (AgB) and Crotalus (AgC) pools venoms used to produce Bothropic and Crotalic antivenoms at Fundacao Ezequiel Dias (FUNED). Measurable absorbance signals were obtained with 1.5 ng of venom per assay. The ELISA was used to follow the kinetic distribution of antigens in experimentally envenomed mice. PMID:15804530

  4. Snake venomics of the South and Central American Bushmasters. Comparison of the toxin composition of Lachesis muta gathered from proteomic versus transcriptomic analysis.

    PubMed

    Sanz, Libia; Escolano, José; Ferretti, Massimo; Biscoglio, Mirtha J; Rivera, Elena; Crescenti, Ernesto J; Angulo, Yamileth; Lomonte, Bruno; Gutiérrez, José María; Calvete, Juan J

    2008-04-30

    We report the proteomic characterization of the venoms of two closely related pit vipers of the genus Lachesis, L. muta (South American Bushmaster) and L. stenophrys (Central American Bushmaster), and compare the toxin repertoire of the former revealed through a proteomic versus a transcriptomic approach. The protein composition of the venoms of Lachesis muta and L. stenophrys were analyzed by RP-HPLC, N-terminal sequencing, MALDI-TOF peptide mass fingerprinting and CID-MS/MS. Around 30-40 proteins of molecular masses in the range of 13-110 kDa and belonging, respectively, to only 8 and 7 toxin families were identified in L. muta and L. stenophrys venoms. In addition, both venoms contained a large number of bradykinin-potentiating peptides (BPP) and a C-type natriuretic peptide (C-NP). BPPs and C-NP comprised around 15% of the total venom proteins. In both species, the most abundant proteins were Zn(2+)-metalloproteinases (32-38%) and serine proteinases (25-31%), followed by PLA(2)s (9-12%), galactose-specific C-type lectin (4-8%), l-amino acid oxidase (LAO, 3-5%), CRISP (1.8%; found in L. muta but not in L. stenophrys), and NGF (0.6%). On the other hand, only six L. muta venom-secreted proteins matched any of the previously reported 11 partial or full-length venom gland transcripts, and venom proteome and transcriptome depart in their relative abundances of different toxin families. As expected from their close phylogenetic relationship, the venoms of L. muta and L. stenophrys share (or contain highly similar) proteins, in particular BPPs, serine proteinases, a galactose-specific C-type lectin, and LAO. However, they dramatically depart in their respective PLA(2) complement. Intraspecific quantitative and qualitative differences in the expression of PLA(2) molecules were found when the venoms of five L. muta specimens (3 from Bolivia and 2 from Peru) and the venom of the same species purchased from Sigma were compared. These observations indicate that these class

  5. MutaBind estimates and interprets the effects of sequence variants on protein-protein interactions.

    PubMed

    Li, Minghui; Simonetti, Franco L; Goncearenco, Alexander; Panchenko, Anna R

    2016-07-01

    Proteins engage in highly selective interactions with their macromolecular partners. Sequence variants that alter protein binding affinity may cause significant perturbations or complete abolishment of function, potentially leading to diseases. There exists a persistent need to develop a mechanistic understanding of impacts of variants on proteins. To address this need we introduce a new computational method MutaBind to evaluate the effects of sequence variants and disease mutations on protein interactions and calculate the quantitative changes in binding affinity. The MutaBind method uses molecular mechanics force fields, statistical potentials and fast side-chain optimization algorithms. The MutaBind server maps mutations on a structural protein complex, calculates the associated changes in binding affinity, determines the deleterious effect of a mutation, estimates the confidence of this prediction and produces a mutant structural model for download. MutaBind can be applied to a large number of problems, including determination of potential driver mutations in cancer and other diseases, elucidation of the effects of sequence variants on protein fitness in evolution and protein design. MutaBind is available at http://www.ncbi.nlm.nih.gov/projects/mutabind/. PMID:27150810

  6. Inhibitory effect of plant Manilkara subsericea against biological activities of Lachesis muta snake venom.

    PubMed

    De Oliveira, Eduardo Coriolano; Fernandes, Caio Pinho; Sanchez, Eladio Flores; Rocha, Leandro; Fuly, André Lopes

    2014-01-01

    Snake venom is composed of a mixture of substances that caused in victims a variety of pathophysiological effects. Besides antivenom, literature has described plants able to inhibit injuries and lethal activities induced by snake venoms. This work describes the inhibitory potential of ethanol, hexane, ethyl acetate, or dichloromethane extracts and fractions from stem and leaves of Manilkara subsericea against in vivo (hemorrhagic and edema) and in vitro (clotting, hemolysis, and proteolysis) activities caused by Lachesis muta venom. All the tested activities were totally or at least partially reduced by M. subsericea. However, when L. muta venom was injected into mice 15 min first or after the materials, hemorrhage and edema were not inhibited. Thus, M. subsericea could be used as antivenom in snakebites of L. muta. And, this work also highlights Brazilian flora as a rich source of molecules with antivenom properties.

  7. Inhibitory Effect of Plant Manilkara subsericea against Biological Activities of Lachesis muta Snake Venom

    PubMed Central

    De Oliveira, Eduardo Coriolano; Fernandes, Caio Pinho; Sanchez, Eladio Flores; Fuly, André Lopes

    2014-01-01

    Snake venom is composed of a mixture of substances that caused in victims a variety of pathophysiological effects. Besides antivenom, literature has described plants able to inhibit injuries and lethal activities induced by snake venoms. This work describes the inhibitory potential of ethanol, hexane, ethyl acetate, or dichloromethane extracts and fractions from stem and leaves of Manilkara subsericea against in vivo (hemorrhagic and edema) and in vitro (clotting, hemolysis, and proteolysis) activities caused by Lachesis muta venom. All the tested activities were totally or at least partially reduced by M. subsericea. However, when L. muta venom was injected into mice 15 min first or after the materials, hemorrhage and edema were not inhibited. Thus, M. subsericea could be used as antivenom in snakebites of L. muta. And, this work also highlights Brazilian flora as a rich source of molecules with antivenom properties. PMID:24511532

  8. The pathology of sponge orange band disease affecting the Caribbean barrel sponge Xestospongia muta.

    PubMed

    Angermeier, Hilde; Kamke, Janine; Abdelmohsen, Usama R; Krohne, Georg; Pawlik, Joseph R; Lindquist, Niels L; Hentschel, Ute

    2011-02-01

    The aim of this study was to examine sponge orange band (SOB) disease affecting the prominent Caribbean sponge Xestospongia muta. Scanning and transmission electron microscopy revealed that SOB is accompanied by the massive destruction of the pinacoderm. Chlorophyll a content and the main secondary metabolites, tetrahydrofurans, characteristic of X. muta, were significantly lower in bleached than in healthy tissues. Denaturing gradient gel electrophoresis using cyanobacteria-specific 16S rRNA gene primers revealed a distinct shift from the Synechococcus/Prochlorococcus clade of sponge symbionts towards several clades of unspecific cyanobacteria, including lineages associated with coral disease (i.e. Leptolyngbya sp.). Underwater infection experiments were conducted by transplanting bleached cores into healthy individuals, but revealed no signs of SOB development. This study provided no evidence for the involvement of a specific microbial pathogen as an etiologic agent of disease; hence, the cause of SOB disease in X. muta remains unidentified.

  9. Sulfated Galactan from Palisada flagellifera Inhibits Toxic Effects of Lachesis muta Snake Venom

    PubMed Central

    da Silva, Ana Cláudia Rodrigues; Ferreira, Luciana Garcia; Duarte, Maria Eugênia Rabello; Noseda, Miguel Daniel; Sanchez, Eladio Flores; Fuly, André Lopes

    2015-01-01

    In Brazil, snakebites are a public health problem and accidents caused by Lachesis muta have the highest mortality index. Envenomation by L. muta is characterized by systemic (hypotension, bleeding and renal failure) and local effects (necrosis, pain and edema). The treatment to reverse the evolution of all the toxic effects is performed by injection of antivenom. However, such therapy does not effectively neutralize tissue damage or any other local effect, since in most cases victims delay seeking appropriate medical care. In this way, alternative therapies are in demand, and molecules from natural sources have been exhaustively tested. In this paper, we analyzed the inhibitory effect of a sulfated galactan obtained from the red seaweed Palisada flagellifera against some toxic activities of L. muta venom. Incubation of sulfated galactan with venom resulted in inhibition of hemolysis, coagulation, proteolysis, edema and hemorrhage. Neutralization of hemorrhage was also observed when the galactan was administered after or before the venom injection; thus mimicking a real in vivo situation. Moreover, the galactan blocked the edema caused by a phospholipase A2 isolated from the same venom. Therefore, the galactan from P. flagellifera may represent a promising tool to treat envenomation by L. muta as a coadjuvant for the conventional antivenom. PMID:26110897

  10. Sulfated Galactan from Palisada flagellifera Inhibits Toxic Effects of Lachesis muta Snake Venom.

    PubMed

    da Silva, Ana Cláudia Rodrigues; Ferreira, Luciana Garcia; Duarte, Maria Eugênia Rabello; Noseda, Miguel Daniel; Sanchez, Eladio Flores; Fuly, André Lopes

    2015-06-11

    In Brazil, snakebites are a public health problem and accidents caused by Lachesis muta have the highest mortality index. Envenomation by L. muta is characterized by systemic (hypotension, bleeding and renal failure) and local effects (necrosis, pain and edema). The treatment to reverse the evolution of all the toxic effects is performed by injection of antivenom. However, such therapy does not effectively neutralize tissue damage or any other local effect, since in most cases victims delay seeking appropriate medical care. In this way, alternative therapies are in demand, and molecules from natural sources have been exhaustively tested. In this paper, we analyzed the inhibitory effect of a sulfated galactan obtained from the red seaweed Palisada flagellifera against some toxic activities of L. muta venom. Incubation of sulfated galactan with venom resulted in inhibition of hemolysis, coagulation, proteolysis, edema and hemorrhage. Neutralization of hemorrhage was also observed when the galactan was administered after or before the venom injection; thus mimicking a real in vivo situation. Moreover, the galactan blocked the edema caused by a phospholipase A2 isolated from the same venom. Therefore, the galactan from P. flagellifera may represent a promising tool to treat envenomation by L. muta as a coadjuvant for the conventional antivenom.

  11. Demographics of increasing populations of the giant barrel sponge Xestospongia muta in the Florida Keys.

    PubMed

    McMurray, Steven E; Henkel, Timothy P; Pawlik, Joseph R

    2010-02-01

    The structure of Caribbean coral reef communities has been altered by numerous anthropogenic and natural stressors. Demographic studies of key functional groups have furthered efforts to describe and understand these changes. Little is known, however, about the demographics of sponges on coral reefs, despite their abundance and the important functions they perform (e.g., increased habitat complexity, water filtration). We have monitored permanent plots on reefs off Key Largo, Florida, USA, to study the demography of a particularly important species, the giant barrel sponge, Xestospongia muta. From 2000 to 2006, population densities of X. muta significantly increased at sites on Conch Reef by a mean of 46% (range = 16-108%) and on Pickles Reef by a mean of 33%. In 2006, densities of X. muta on Conch Reef ranged from 0.134 to 0.277 sponges/m2, and mean sponge volume was 1488 cm3/m2, with the largest size class of sponges constituting 75% of the total volume. Increased population density resulted from a significant increase in the number of sponges in the smallest size class. Recruit survival did not significantly change through time; however, a significant interaction between season and year on recruitment suggests that large recruitment pulses are driving population increases. Mean yearly recruitment rates ranged from 0.011 to 0.025 recruits x m(-2) x yr(-1), with pulses as high as 0.036 recruits/m2. To explore the demographic processes behind the population increase and determine future population growth of X. muta under present reef conditions, a stage-based matrix modeling approach was used. Variable recruitment pulses and mortality events were hypothesized to be large determinants of the demographic patterns observed for X. muta. Elasticity and life table response analysis revealed that survival of individuals in the largest size class has the greatest effect on population growth. Projections indicate that populations of X. muta will continue to increase under

  12. Demographics of increasing populations of the giant barrel sponge Xestospongia muta in the Florida Keys.

    PubMed

    McMurray, Steven E; Henkel, Timothy P; Pawlik, Joseph R

    2010-02-01

    The structure of Caribbean coral reef communities has been altered by numerous anthropogenic and natural stressors. Demographic studies of key functional groups have furthered efforts to describe and understand these changes. Little is known, however, about the demographics of sponges on coral reefs, despite their abundance and the important functions they perform (e.g., increased habitat complexity, water filtration). We have monitored permanent plots on reefs off Key Largo, Florida, USA, to study the demography of a particularly important species, the giant barrel sponge, Xestospongia muta. From 2000 to 2006, population densities of X. muta significantly increased at sites on Conch Reef by a mean of 46% (range = 16-108%) and on Pickles Reef by a mean of 33%. In 2006, densities of X. muta on Conch Reef ranged from 0.134 to 0.277 sponges/m2, and mean sponge volume was 1488 cm3/m2, with the largest size class of sponges constituting 75% of the total volume. Increased population density resulted from a significant increase in the number of sponges in the smallest size class. Recruit survival did not significantly change through time; however, a significant interaction between season and year on recruitment suggests that large recruitment pulses are driving population increases. Mean yearly recruitment rates ranged from 0.011 to 0.025 recruits x m(-2) x yr(-1), with pulses as high as 0.036 recruits/m2. To explore the demographic processes behind the population increase and determine future population growth of X. muta under present reef conditions, a stage-based matrix modeling approach was used. Variable recruitment pulses and mortality events were hypothesized to be large determinants of the demographic patterns observed for X. muta. Elasticity and life table response analysis revealed that survival of individuals in the largest size class has the greatest effect on population growth. Projections indicate that populations of X. muta will continue to increase under

  13. Appraisal of Antiophidic Potential of Marine Sponges against Bothrops jararaca and Lachesis muta Venom

    PubMed Central

    Faioli, Camila Nunes; Domingos, Thaisa Francielle Souza; de Oliveira, Eduardo Coriolano; Sanchez, Eládio Flores; Ribeiro, Suzi; Muricy, Guilherme; Fuly, Andre Lopes

    2013-01-01

    Snakebites are a health problem in many countries due to the high incidence of such accidents. Antivenom treatment has regularly been used for more than a century, however, this does not neutralize tissue damage and may even increase the severity and morbidity of accidents. Thus, it has been relevant to search for new strategies to improve antiserum therapy, and a variety of molecules from natural sources with antiophidian properties have been reported. In this paper, we analyzed the ability of ten extracts from marine sponges (Amphimedon viridis, Aplysina fulva, Chondrosia collectrix, Desmapsamma anchorata, Dysidea etheria, Hymeniacidon heliophila, Mycale angulosa, Petromica citrina, Polymastia janeirensis, and Tedania ignis) to inhibit the effects caused by Bothrops jararaca and Lachesis muta venom. All sponge extracts inhibited proteolysis and hemolysis induced by both snake venoms, except H. heliophila, which failed to inhibit any biological activity. P. citrina inhibited lethality, hemorrhage, plasma clotting, and hemolysis induced by B. jararaca or L. muta. Moreover, other sponges inhibited hemorrhage induced only by B. jararaca. We conclude that Brazilian sponges may be a useful aid in the treatment of snakebites caused by L. muta and B. jararaca and therefore have potential for the discovery of molecules with antiophidian properties. PMID:24141284

  14. Symbiotic prokaryotic communities from different populations of the giant barrel sponge, Xestospongia muta

    PubMed Central

    Fiore, Cara L; Jarett, Jessica K; Lesser, Michael P

    2013-01-01

    The prokaryotic community composition of the ecologically dominant sponge, Xestospongia muta, and the variability of this community across in different populations of sponges from the Caribbean and Bahamas were quantified using 454 pyrosequencing of the 16S rRNA gene. The symbiotic prokaryotic communities of X. muta were significantly different than the surrounding bacterioplankton communities while an analysis of similarity (ANOSIM) of the sponge prokaryotic symbionts from three geographically distant sites showed that both symbiont and bacterioplankton populations were significantly different between locations. Comparisons of individual sponges based on the UniFrac P-test also revealed significant differences in community composition between individual sponges. The sponges harbored a variety of phylum level operational taxonomic units (OTUs) common to many sponges, including Cyanobacteria, Poribacteria, Acidobacteria, Chloroflexi, and Gemmatimonadetes, but four additional symbiotic phyla, previously not reported for this sponge, were observed. Additionally, a diverse archaeal community was also recovered from X. muta including sequences representing the phyla Euryarchaeota and Thaumarchaeota. These results have important ecological implications for the understanding of host–microbe associations, and provide a foundation for future studies addressing the functional roles these symbiotic prokaryotes have in the biology of the host sponge and the nutrient biogeochemistry of coral reefs. PMID:24124112

  15. Transcriptional activity of the giant barrel sponge, Xestospongia muta Holobiont: molecular evidence for metabolic interchange

    PubMed Central

    Fiore, Cara L.; Labrie, Micheline; Jarett, Jessica K.; Lesser, Michael P.

    2015-01-01

    Compared to our understanding of the taxonomic composition of the symbiotic microbes in marine sponges, the functional diversity of these symbionts is largely unknown. Furthermore, the application of genomic, transcriptomic, and proteomic techniques to functional questions on sponge host-symbiont interactions is in its infancy. In this study, we generated a transcriptome for the host and a metatranscriptome of its microbial symbionts for the giant barrel sponge, Xestospongia muta, from the Caribbean. In combination with a gene-specific approach, our goals were to (1) characterize genetic evidence for nitrogen cycling in X. muta, an important limiting nutrient on coral reefs (2) identify which prokaryotic symbiont lineages are metabolically active and, (3) characterize the metabolic potential of the prokaryotic community. Xestospongia muta expresses genes from multiple nitrogen transformation pathways that when combined with the abundance of this sponge, and previous data on dissolved inorganic nitrogen fluxes, shows that this sponge is an important contributor to nitrogen cycling biogeochemistry on coral reefs. Additionally, we observed significant differences in gene expression of the archaeal amoA gene, which is involved in ammonia oxidation, between coral reef locations consistent with differences in the fluxes of dissolved inorganic nitrogen previously reported. In regards to symbiont metabolic potential, the genes in the biosynthetic pathways of several amino acids were present in the prokaryotic metatranscriptome dataset but in the host-derived transcripts only the catabolic reactions for these amino acids were present. A similar pattern was observed for the B vitamins (riboflavin, biotin, thiamin, cobalamin). These results expand our understanding of biogeochemical cycling in sponges, and the metabolic interchange highlighted here advances the field of symbiont physiology by elucidating specific metabolic pathways where there is high potential for host

  16. Hypermutagenesis in mutA cells is mediated by mistranslational corruption of polymerase, and is accompanied by replication fork collapse.

    PubMed

    Al Mamun, Abu Amar M; Gautam, Satyendra; Humayun, M Zafri

    2006-12-01

    Elevated mistranslation induces a mutator response termed translational stress-induced mutagenesis (TSM) that is mediated by an unidentified modification of DNA polymerase III. Here we address two questions: (i) does TSM result from direct polymerase corruption, or from an indirect pathway triggered by increased protein turnover? (ii) Why are homologous recombination functions required for the expression of TSM under certain conditions, but not others? We show that replication of bacteriophage T4 in cells expressing the mutA allele of the glyVtRNA gene (Asp-Gly mistranslation), leads to both increased mutagenesis, and to an altered mutational specificity, results that strongly support mistranslational corruption of DNA polymerase. We also show that expression of mutA, which confers a recA-dependent mutator phenotype, leads to increased lambdoid prophage induction (selectable in vivo expression technology assay), suggesting that replication fork collapse occurs more frequently in mutA cells relative to control cells. No such increase in prophage induction is seen in cells expressing alaVGlu tRNA (Glu-->Ala mistranslation), in which the mutator phenotype is recA-independent. We propose that replication fork collapse accompanies episodic hypermutagenic replication cycles in mutA cells, requiring homologous recombination functions for fork recovery, and therefore, for mutation recovery. These findings highlight hitherto under-appreciated links among translation, replication and recombination, and suggest that translational fidelity, which is affected by genetic and environmental signals, is a key modulator of replication fidelity.

  17. Biochemical characterization of two hemorrhagic proteases from the venom of Lachesis muta (bushmaster).

    PubMed

    Ran, Y L; Zheng, S D; Tu, A T

    1988-01-01

    Two hemorrhagic proteases, Lachesis hemorrhagic toxins a and b (LHTa and LHTb), were isolated from the venom of Lachesis muta, which is distributed in Central and South America. One protease showed strong hemorrhagic action, while the other showed weak hemorrhagic activity even though the two enzymes are very similar in their chemical properties. Neither enzyme hydrolyzed arginine esters, but both hydrolyzed casein and reduced fibrinogen. The A alpha chain of fibrinogen was hydrolyzed first, and the B beta chain was hydrolyzed later. The gamma chain of fibrinogen was resistant to hydrolysis. The molecular weights of LHTa and LHTb were very similar, 22,000 and 23,000, respectively. The amino acid composition of LHTa was also similar to that of LHTb. The secondary structure of LHTa as determined by Lippert's equation was 52% alpha helix, 17% beta sheet, and 31% random coil; that of LHTb was 47% alpha helix, 13% beta sheet, and 40% random coil. PMID:2979750

  18. Requirement for homologous recombination functions for expression of the mutA mistranslator tRNA-induced mutator phenotype in Escherichia coli.

    PubMed

    Ren, L; Al Mamun, A A; Humayun, M Z

    2000-03-01

    Expression of the Escherichia coli mutA mutator phenotype requires recA, recB, recC, ruvA, and ruvC gene, but not recD, recF, recO, or recR genes. Thus, the recBCD-dependent homologous recombination system is a component of the signal pathway that activates an error-prone DNA polymerase in mutA cells. PMID:10671469

  19. Islamic Education Philosophy Development (Study Analysis on Ta'lim Al-Kitab Al-Zarnuji Muta'allim Works)

    ERIC Educational Resources Information Center

    Asrori, H. Achmad

    2016-01-01

    "Ta'lim Muta'allim" is one of the monumental works of Shaykh Tajuddin Nu'man ibn Ibrahim ibn al-Khalil al-Zarnuji, who lived in the 6th century H/13-14 M. The reason for writing this study ie: (1) it is very rich with the basic values of Islamic education, (2) the values are already widely practiced in the world of education, especially…

  20. Morphological characteristics of Mesocestoides canislagopodis (Krabbe 1865) tetrathyridia found in rock ptarmigan (Lagopus muta) in Iceland.

    PubMed

    Skirnisson, Karl; Sigurðardóttir, Ólöf G; Nielsen, Ólafur K

    2016-08-01

    Necropsies of 1010 rock ptarmigans (Lagopus muta) sampled in autumn 2006-2015 in northeast Iceland revealed Mesocestoides canislagopodis tetrathyridia infections in six birds (0.6 %), two juvenile birds (3 month old), and four adult birds (15 months or older). Four birds had tetrathyridia in the body cavity, one bird in the liver, and one bird both in the body cavity and the liver. There were more tetrathyridia in the body cavity of the two juveniles (c. 50 in each) than in three adults (10-40), possibly indicating a host-age-related tetrathyridia mortality. Approximately, half of tetrathyridia in the body cavity were free or loosely attached to the serosa, the other half were encapsulated in a thin, loose connective tissue stroma, frequently attached to the lungs and the liver. Tetrathyridia in the liver parenchyma incited variably intense inflammation. Tetrathyridia from the juvenile hosts were whitish, heart-shaped, and flattened, with unsegmented bodies with a slightly pointed posterior end. In the adult hosts, tetrathyridia were sometimes almost rectangular-shaped, slightly wider compared to those in the juveniles, but more than twice as long as the younger-aged tetrathyridia. Tetrathyridia infections are most likely acquired during the brief insectivorous feeding phase of ptarmigan chicks, and the tetrathyridia persist throughout the lifespan of the birds. PMID:27117162

  1. MUTA calculations of a laser-produced Mg hollow atom spectrum

    NASA Astrophysics Data System (ADS)

    Colgan, J.; Abdallah, J., Jr.; Faenov, A.; Pikuz, T. A.; Skobelev, I. Yu

    2008-07-01

    A study is made of the spectra produced from a short-wavelength long-pulse (nanosecond) laser incident on a Mg plasma. A very complex experimental spectrum is analyzed in detail by comparison with large-scale atomic kinetics calculations using the recently developed mixed-UTA (MUTA) model. We find that the experimental spectrum appears to contain lines from many inner-shell transitions from ions ranging from neutral Mg to Li-like Mg. Lines from transitions such as 1s-3l, 1s-4l, and from hollow atoms (where in this context hollow atoms refer to ions with an empty 1s shell) are observed. The inclusion of very small fractions of hot electrons is demonstrated to make significant differences to the spectra. Although it is found that the calculations do not match perfectly the experimental spectra, reasonable agreement between the experiment and the theory can be obtained if temperature and density gradients are assumed present in the experimental conditions.

  2. Reduced Metabolic Cost of Locomotion in Svalbard Rock Ptarmigan (Lagopus muta hyperborea) during Winter

    PubMed Central

    Lees, John; Nudds, Robert; Stokkan, Karl-Arne; Folkow, Lars; Codd, Jonathan

    2010-01-01

    The Svalbard rock ptarmigan, Lagopus muta hyperborea experiences extreme photoperiodic and climatic conditions on the Arctic archipelago of Svalbard. This species, however, is highly adapted to live in this harsh environment. One of the most striking adaptations found in these birds is the deposition, prior to onset of winter, of fat stores which may comprise up to 32% of body mass and are located primarily around the sternum and abdominal region. This fat, while crucial to the birds' survival, also presents a challenge in that the bird must maintain normal physiological function with this additional mass. In particular these stores are likely to constrain the respiratory system, as the sternum and pelvic region must be moved during ventilation and carrying this extra load may also impact upon the energetic cost of locomotion. Here we demonstrate that winter birds have a reduced cost of locomotion when compared to summer birds. A remarkable finding given that during winter these birds have almost twice the body mass of those in summer. These results suggest that Svalbard ptarmigan are able to carry the additional winter fat without incurring any energetic cost. As energy conservation is paramount to these birds, minimising the costs of moving around when resources are limited would appear to be a key adaptation crucial for their survival in the barren Arctic environment. PMID:21125015

  3. Morphological characteristics of Mesocestoides canislagopodis (Krabbe 1865) tetrathyridia found in rock ptarmigan (Lagopus muta) in Iceland.

    PubMed

    Skirnisson, Karl; Sigurðardóttir, Ólöf G; Nielsen, Ólafur K

    2016-08-01

    Necropsies of 1010 rock ptarmigans (Lagopus muta) sampled in autumn 2006-2015 in northeast Iceland revealed Mesocestoides canislagopodis tetrathyridia infections in six birds (0.6 %), two juvenile birds (3 month old), and four adult birds (15 months or older). Four birds had tetrathyridia in the body cavity, one bird in the liver, and one bird both in the body cavity and the liver. There were more tetrathyridia in the body cavity of the two juveniles (c. 50 in each) than in three adults (10-40), possibly indicating a host-age-related tetrathyridia mortality. Approximately, half of tetrathyridia in the body cavity were free or loosely attached to the serosa, the other half were encapsulated in a thin, loose connective tissue stroma, frequently attached to the lungs and the liver. Tetrathyridia in the liver parenchyma incited variably intense inflammation. Tetrathyridia from the juvenile hosts were whitish, heart-shaped, and flattened, with unsegmented bodies with a slightly pointed posterior end. In the adult hosts, tetrathyridia were sometimes almost rectangular-shaped, slightly wider compared to those in the juveniles, but more than twice as long as the younger-aged tetrathyridia. Tetrathyridia infections are most likely acquired during the brief insectivorous feeding phase of ptarmigan chicks, and the tetrathyridia persist throughout the lifespan of the birds.

  4. Factors Affecting Diet Variation in the Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Conservation Implications

    PubMed Central

    García-González, Ricardo; Aldezabal, Arantza; Laskurain, Nere Amaia; Margalida, Antoni; Novoa, Claude

    2016-01-01

    The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) lives at one of the southernmost limits of the ptarmigan range. Their small population sizes and the impacts of global changes are limiting factors in the conservation of this threatened subspecies. An effective conservation policy requires precise basic knowledge of a species' food and habitat requirements, information that is practically non-existent for this Pyrenean population. Here, we describe the diet of a ptarmigan population in the Eastern Pyrenees, the environmental factors influencing its variability and the relationship between diet floristic composition and quality. Diet composition was determined by microhistological analysis of faeces and diet quality was estimated from free-urate faecal N content. Our results show that grouse diet is based mainly on arctic-alpine shrubs of the Ericaceae family, as well as dwarf willows (Salix spp.) and Dryas octopetala. The most frequently consumed plant species was Rhododendron ferrugineum, but its abundance in the diet was negatively related to the diet nitrogen content. Conversely, the abundance of Salix spp., grass leaves and arthropods increased the nitrogen content of the diet. Seasonality associated with snow-melting contributed the most to variability in the Pyrenean ptarmigan diet, differentiating winter from spring/summer diets. The latter was characterised by a high consumption of dwarf willows, flowers, arthropods and tender forb leaves. Geographic area and sex-age class influenced diet variability to a lesser extent. Current temperature increases in the Pyrenees due to global warming may reduce the persistence and surface area of snow-packs where preferred plants for rock ptarmigan usually grow, thus reducing food availability. The high consumption of Rh. ferrugineum characterised the diet of the Pyrenean population. Given the toxicity of this plant for most herbivores, its potential negative effect on Pyrenean ptarmigan populations should be

  5. Factors Affecting Diet Variation in the Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Conservation Implications.

    PubMed

    García-González, Ricardo; Aldezabal, Arantza; Laskurain, Nere Amaia; Margalida, Antoni; Novoa, Claude

    2016-01-01

    The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) lives at one of the southernmost limits of the ptarmigan range. Their small population sizes and the impacts of global changes are limiting factors in the conservation of this threatened subspecies. An effective conservation policy requires precise basic knowledge of a species' food and habitat requirements, information that is practically non-existent for this Pyrenean population. Here, we describe the diet of a ptarmigan population in the Eastern Pyrenees, the environmental factors influencing its variability and the relationship between diet floristic composition and quality. Diet composition was determined by microhistological analysis of faeces and diet quality was estimated from free-urate faecal N content. Our results show that grouse diet is based mainly on arctic-alpine shrubs of the Ericaceae family, as well as dwarf willows (Salix spp.) and Dryas octopetala. The most frequently consumed plant species was Rhododendron ferrugineum, but its abundance in the diet was negatively related to the diet nitrogen content. Conversely, the abundance of Salix spp., grass leaves and arthropods increased the nitrogen content of the diet. Seasonality associated with snow-melting contributed the most to variability in the Pyrenean ptarmigan diet, differentiating winter from spring/summer diets. The latter was characterised by a high consumption of dwarf willows, flowers, arthropods and tender forb leaves. Geographic area and sex-age class influenced diet variability to a lesser extent. Current temperature increases in the Pyrenees due to global warming may reduce the persistence and surface area of snow-packs where preferred plants for rock ptarmigan usually grow, thus reducing food availability. The high consumption of Rh. ferrugineum characterised the diet of the Pyrenean population. Given the toxicity of this plant for most herbivores, its potential negative effect on Pyrenean ptarmigan populations should be

  6. Bleaching and stress in coral reef ecosystems: hsp70 expression by the giant barrel sponge Xestospongia muta.

    PubMed

    López-Legentil, Susanna; Song, Bongkeun; McMurray, Steven E; Pawlik, Joseph R

    2008-04-01

    Sponges are a prominent component of coral reef ecosystems. Like reef-building corals, some sponges have been reported to bleach and die. The giant barrel sponge Xestospongia muta is one of the largest and most important components of Caribbean coral reef communities. Tissues of X. muta contain cyanobacterial symbionts of the Synechococcus group. Two types of bleaching have been described: cyclic bleaching, from which sponges recover, and fatal bleaching, which usually results in sponge death. We quantified hsp70 gene expression as an indicator of stress in X. muta undergoing cyclic and fatal bleaching and in response to thermal and salinity variability in both field and laboratory settings. Chlorophyll a content of sponge tissue was estimated to determine whether hsp70 expression was related to cyanobacterial abundance. We found that fatally bleached sponge tissue presented significantly higher hsp70 gene expression, but cyclically bleached tissue did not, yet both cyclic and fatally bleached tissues had lower chlorophyll a concentrations than nonbleached tissue. These results corroborate field observations suggesting that cyclic bleaching is a temporary, nonstressful state, while fatal bleaching causes significant levels of stress, leading to mortality. Our results support the hypothesis that Synechococcus symbionts are commensals that provide no clear advantage to their sponge host. In laboratory experiments, sponge pieces incubated at 30 degrees C exhibited significantly higher hsp70 expression than control pieces after 1.5 h, with sponge mortality after less than 15 h. In contrast, sponges at different salinities were not significantly stressed after the same period of time. Stress associated with increasing seawater temperatures may result in declining sponge populations in coral reef ecosystems.

  7. A snakebite caused by a bushmaster (Lachesis muta): report of a confirmed case in State of Pernambuco, Brazil.

    PubMed

    Lima, Pedro Henrique Santana de; Haddad Junior, Vidal

    2015-01-01

    We report a case of envenomation caused by a bushmaster ( Lachesis muta) in a male child in State of Pernambuco, Brazil. The victim showed discrete local manifestations, but presented altered blood coagulation 2 hours after the bite. Ten ampoules of bothropic-lachetic antivenom therapy were administered, and 48 hours later, the patient showed discrete edema, pain, and ecchymosis around the bite and normal blood coagulation. The patient was discharged 5 days after the envenomation. The prompt administration of specific treatment was important for the favorable outcomes observed. PMID:26516981

  8. Prothrombin time (PT)

    MedlinePlus

    PT; Pro-time; Anticoagulant-prothrombin time; Clotting time: protime; INR; International normalized ratio ... PT is measured in seconds. Most of the time, results are given as what is called INR ( ...

  9. Crystallization and preliminary X-ray diffraction studies of an l-amino-acid oxidase from Lachesis muta venom

    PubMed Central

    Ullah, Anwar; Masood, Rehana; Spencer, Patrick Jack; Murakami, Mário Tyago; Arni, Raghuvir Krishnaswamy

    2014-01-01

    Snake-venom proteins form multi-component defence systems by the recruitment and rapid evolution of nonvenomous proteins and hence serve as model systems to understand the structural modifications that result in toxicity. l-Amino-acid oxidases (LAAOs) are encountered in a number of snake venoms and have been implicated in the inhibition of platelet aggregation, cytotoxicity, haemolysis, apoptosis and haemorrhage. An l-amino-acid oxidase from Lachesis muta venom has been purified and crystallized. The crystals belonged to space group P21, with unit-cell parameters a = 66.05, b = 79.41, c = 100.52 Å, β = 96.55°. The asymmetric unit contained two molecules and the structure has been determined and partially refined at 3.0 Å resolution. PMID:25372830

  10. Genetic structure of the Caribbean giant barrel sponge Xestospongia muta using the I3-M11 partition of COI

    NASA Astrophysics Data System (ADS)

    López-Legentil, S.; Pawlik, J. R.

    2009-03-01

    In recent years, reports of sponge bleaching, disease, and subsequent mortality have increased alarmingly. Population recovery may depend strongly on colonization capabilities of the affected species. The giant barrel sponge Xestospongia muta is a dominant reef constituent in the Caribbean. However, little is known about its population structure and gene flow. The 5'-end fragment of the mitochondrial gene cytochrome oxidase subunit I is often used to address these kinds of questions, but it presents very low intraspecific nucleotide variability in sponges. In this study, the usefulness of the I3-M11 partition of COI to determine the genetic structure of X. muta was tested for seven populations from Florida, the Bahamas and Belize. A total of 116 sequences of 544 bp were obtained for the I3-M11 partition corresponding to four haplotypes. In order to make a comparison with the 5'-end partition, 10 sequences per haplotype were analyzed for this fragment. The 40 resulting sequences were of 569 bp and corresponded to two haplotypes. The nucleotide diversity of the I3-M11 partition (π = 0.00386) was higher than that of the 5'-end partition (π = 0.00058), indicating better resolution at the intraspecific level. Sponges with the most divergent external morphologies (smooth vs. digitate surface) had different haplotypes, while those with the most common external morphology (rough surface) presented a mixture of haplotypes. Pairwise tests for genetic differentiation among geographic locations based on F ST values showed significant genetic divergence between most populations, but this genetic differentiation was not due to isolation by distance. While limited larval dispersal may have led to differentiation among some of the populations, the patterns of genetic structure appear to be most strongly related to patterns of ocean currents. Therefore, hydrological features may play a major role in sponge colonization and need to be considered in future plans for management and

  11. p53MutaGene: an online tool to estimate the effect of p53 mutational status on gene regulation in cancer.

    PubMed

    Amelio, I; Knight, R A; Lisitsa, A; Melino, G; Antonov, A V

    2016-01-01

    p53MutaGene is the first online tool for statistical validation of hypotheses regarding the effect of p53 mutational status on gene regulation in cancer. This tool is based on several large-scale clinical gene expression data sets and currently covers breast, colon and lung cancers. The tool detects differential co-expression patterns in expression data between p53 mutated versus p53 normal samples for the user-specified genes. Statistically significant differential co-expression for a gene pair is indicative that regulation of two genes is sensitive to the presence of p53 mutations. p53MutaGene can be used in 'single mode' where the user can test a specific pair of genes or in 'discovery mode' designed for analysis of several genes. Using several examples, we demonstrate that p53MutaGene is a useful tool for fast statistical validation in clinical data of p53-dependent gene regulation patterns. The tool is freely available at http://www.bioprofiling.de/tp53.

  12. Population Genetic Structure, Abundance, and Health Status of Two Dominant Benthic Species in the Saba Bank National Park, Caribbean Netherlands: Montastraea cavernosa and Xestospongia muta.

    PubMed

    de Bakker, Didier M; Meesters, Erik H W G; van Bleijswijk, Judith D L; Luttikhuizen, Pieternella C; Breeuwer, Hans J A J; Becking, Leontine E

    2016-01-01

    Saba Bank, a submerged atoll in the Caribbean Sea with an area of 2,200 km2, has attained international conservation status due to the rich diversity of species that reside on the bank. In order to assess the role of Saba Bank as a potential reservoir of diversity for the surrounding reefs, we examined the population genetic structure, abundance and health status of two prominent benthic species, the coral Montastraea cavernosa and the sponge Xestospongia muta. Sequence data were collected from 34 colonies of M. cavernosa (nDNA ITS1-5.8S-ITS2; 892 bp) and 68 X. muta sponges (mtDNA I3-M11 partition of COI; 544 bp) on Saba Bank and around Saba Island, and compared with published data across the wider Caribbean. Our data indicate that there is genetic connectivity between populations on Saba Bank and the nearby Saba Island as well as multiple locations in the wider Caribbean, ranging in distance from 100s-1000s km. The genetic diversity of Saba Bank populations of M. cavernosa (π = 0.055) and X. muta (π = 0.0010) was comparable to those in other regions in the western Atlantic. Densities and health status were determined along 11 transects of 50 m2 along the south-eastern rim of Saba Bank. The densities of M. cavernosa (0.27 ind. m-2, 95% CI: 0.12-0.52) were average, while the densities of X. muta (0.09 ind. m-2, 95% CI: 0.02-0.32) were generally higher with respect to other Caribbean locations. No disease or bleaching was present in any of the specimens of the coral M. cavernosa, however, we did observe partial tissue loss (77.9% of samples) as well as overgrowth (48.1%), predominantly by cyanobacteria. In contrast, the majority of observed X. muta (83.5%) showed signs of presumed bleaching. The combined results of apparent gene flow among populations on Saba Bank and surrounding reefs, the high abundance and unique genetic diversity, indicate that Saba Bank could function as an important buffer for the region. Either as a natural source of larvae to replenish

  13. Population Genetic Structure, Abundance, and Health Status of Two Dominant Benthic Species in the Saba Bank National Park, Caribbean Netherlands: Montastraea cavernosa and Xestospongia muta

    PubMed Central

    de Bakker, Didier M.; Meesters, Erik H. W. G.; van Bleijswijk, Judith D. L.; Luttikhuizen, Pieternella C.; Breeuwer, Hans J. A. J.; Becking, Leontine E.

    2016-01-01

    Saba Bank, a submerged atoll in the Caribbean Sea with an area of 2,200 km2, has attained international conservation status due to the rich diversity of species that reside on the bank. In order to assess the role of Saba Bank as a potential reservoir of diversity for the surrounding reefs, we examined the population genetic structure, abundance and health status of two prominent benthic species, the coral Montastraea cavernosa and the sponge Xestospongia muta. Sequence data were collected from 34 colonies of M. cavernosa (nDNA ITS1-5.8S-ITS2; 892 bp) and 68 X. muta sponges (mtDNA I3-M11 partition of COI; 544 bp) on Saba Bank and around Saba Island, and compared with published data across the wider Caribbean. Our data indicate that there is genetic connectivity between populations on Saba Bank and the nearby Saba Island as well as multiple locations in the wider Caribbean, ranging in distance from 100s–1000s km. The genetic diversity of Saba Bank populations of M. cavernosa (π = 0.055) and X. muta (π = 0.0010) was comparable to those in other regions in the western Atlantic. Densities and health status were determined along 11 transects of 50 m2 along the south-eastern rim of Saba Bank. The densities of M. cavernosa (0.27 ind. m-2, 95% CI: 0.12–0.52) were average, while the densities of X. muta (0.09 ind. m-2, 95% CI: 0.02–0.32) were generally higher with respect to other Caribbean locations. No disease or bleaching was present in any of the specimens of the coral M. cavernosa, however, we did observe partial tissue loss (77.9% of samples) as well as overgrowth (48.1%), predominantly by cyanobacteria. In contrast, the majority of observed X. muta (83.5%) showed signs of presumed bleaching. The combined results of apparent gene flow among populations on Saba Bank and surrounding reefs, the high abundance and unique genetic diversity, indicate that Saba Bank could function as an important buffer for the region. Either as a natural source of larvae to

  14. Population Genetic Structure, Abundance, and Health Status of Two Dominant Benthic Species in the Saba Bank National Park, Caribbean Netherlands: Montastraea cavernosa and Xestospongia muta.

    PubMed

    de Bakker, Didier M; Meesters, Erik H W G; van Bleijswijk, Judith D L; Luttikhuizen, Pieternella C; Breeuwer, Hans J A J; Becking, Leontine E

    2016-01-01

    Saba Bank, a submerged atoll in the Caribbean Sea with an area of 2,200 km2, has attained international conservation status due to the rich diversity of species that reside on the bank. In order to assess the role of Saba Bank as a potential reservoir of diversity for the surrounding reefs, we examined the population genetic structure, abundance and health status of two prominent benthic species, the coral Montastraea cavernosa and the sponge Xestospongia muta. Sequence data were collected from 34 colonies of M. cavernosa (nDNA ITS1-5.8S-ITS2; 892 bp) and 68 X. muta sponges (mtDNA I3-M11 partition of COI; 544 bp) on Saba Bank and around Saba Island, and compared with published data across the wider Caribbean. Our data indicate that there is genetic connectivity between populations on Saba Bank and the nearby Saba Island as well as multiple locations in the wider Caribbean, ranging in distance from 100s-1000s km. The genetic diversity of Saba Bank populations of M. cavernosa (π = 0.055) and X. muta (π = 0.0010) was comparable to those in other regions in the western Atlantic. Densities and health status were determined along 11 transects of 50 m2 along the south-eastern rim of Saba Bank. The densities of M. cavernosa (0.27 ind. m-2, 95% CI: 0.12-0.52) were average, while the densities of X. muta (0.09 ind. m-2, 95% CI: 0.02-0.32) were generally higher with respect to other Caribbean locations. No disease or bleaching was present in any of the specimens of the coral M. cavernosa, however, we did observe partial tissue loss (77.9% of samples) as well as overgrowth (48.1%), predominantly by cyanobacteria. In contrast, the majority of observed X. muta (83.5%) showed signs of presumed bleaching. The combined results of apparent gene flow among populations on Saba Bank and surrounding reefs, the high abundance and unique genetic diversity, indicate that Saba Bank could function as an important buffer for the region. Either as a natural source of larvae to replenish

  15. A phospholipase A₂ isolated from Lachesis muta snake venom increases the survival of retinal ganglion cells in vitro.

    PubMed

    da Silva Cunha, Karinne Cristinne; Fuly, André Lopes; de Araujo, Elizabeth Giestal

    2011-03-15

    We have previously showed that a phospholipase A₂ isolated from Lachesis muta snake venom and named LM-PLA₂-I displayed particular biological activities, as hemolysis, inhibition on platelet aggregation, edema induction and myotoxicity. In the present work, we evaluated the effect of LM-PLA₂-I on the survival of axotomized rat retinal ganglion cells kept in vitro, as well as its mechanism of action. Our results clearly showed that treatment with LM-PLA₂-I increased the survival of ganglion cells (100% when compared to control cultures) and the treatment of LM-PLA₂-I with p-bromophenacyl bromide abolished this effect. This result indicates that the effect of LM-PLA₂-I on ganglion cell survival is entirely dependent on its enzymatic activity and the generation of lysophosphatidylcholine (LPC) may be a prerequisite to the observed survival. In fact, commercial LPC mimicked the effect of LM-PLA₂-I upon ganglion cell survival. To investigate the mechanism of action of LM-PLA₂-I, cultures were treated with chelerythrine chloride, BAPTA-AM, rottlerin and also with an inhibitor of c-junc kinase (JNKi). Our results showed that rottlerin and JNK inhibitor abolished the LM-PLA₂-I on ganglion cell survival. Taken together, our results showed that LM-PLA₂-I and its enzymatic product, LPC promoted survival of retinal ganglion cells through the protein kinase C pathway and strongly suggest a possible role of the PLA₂ enzyme and LPC in controlling the survival of axotomized neuronal cells. PMID:21223976

  16. Unique Pt5 metallacycle: [Pt(II)Cl(pyrrolidinedithiocarbamate)]5.

    PubMed

    Montagner, Diego; Sanz Miguel, Pablo J

    2011-11-01

    The neutral complex [PtCl(PyDT)](5) (PyDT = (CH(2))(4)NCS(2)(-)) represents the first example of a Pt(5) metallacycle. This unique architecture based on chiral S-bridged Pt(II) monomers was prepared by thermal degradation of the reaction product of PtCl(2) and a pyrrolidinedithioester. PMID:21901224

  17. PT-symmetric strings

    SciTech Connect

    Amore, Paolo; Fernández, Francisco M.; Garcia, Javier; Gutierrez, German

    2014-04-15

    We study both analytically and numerically the spectrum of inhomogeneous strings with PT-symmetric density. We discuss an exactly solvable model of PT-symmetric string which is isospectral to the uniform string; for more general strings, we calculate exactly the sum rules Z(p)≡∑{sub n=1}{sup ∞}1/E{sub n}{sup p}, with p=1,2,… and find explicit expressions which can be used to obtain bounds on the lowest eigenvalue. A detailed numerical calculation is carried out for two non-solvable models depending on a parameter, obtaining precise estimates of the critical values where pair of real eigenvalues become complex. -- Highlights: •PT-symmetric Hamiltonians exhibit real eigenvalues when PT symmetry is unbroken. •We study PT-symmetric strings with complex density. •They exhibit regions of unbroken PT symmetry. •We calculate the critical parameters at the boundaries of those regions. •There are exact real sum rules for some particular complex densities.

  18. Influence of Snowmelt Timing on the Diet Quality of Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Implications for Reproductive Success

    PubMed Central

    García-González, Ricardo; Aldezabal, Arantza; Laskurain, Nere Amaia; Margalida, Antoni; Novoa, Claude

    2016-01-01

    The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) is the southernmost subspecies of the species in Europe and is considered threatened as a consequence of changes in landscape, human pressure, climate change, and low genetic diversity. Previous studies have shown a relationship between the date of snowmelt and reproductive success in the Pyrenean ptarmigan. It is well established that birds laying early in the breeding season have higher reproductive success, but the specific mechanism for this relationship is debated. We present an explicative model of the relationship between snowmelt date and breeding success mediated by food quality for grouse in alpine environments. From microhistological analyses of 121 faecal samples collected during three years in the Canigou Massif (Eastern Pyrenees), and the assessment of the chemical composition of the main dietary components, we estimated the potential quality of individual diets. Potential dietary quality was correlated with free-urate faecal N, a proxy of the digestible protein content ingested by ptarmigan, and both were correlated with phenological stage of consumed plants, which in turn depends on snowmelt date. Our findings suggest that the average snowmelt date is subject to a strong interannual variability influencing laying date. In years of early snowmelt, hens benefit from a longer period of high quality food resources potentially leading to a higher breeding success. On the contrary, in years of late snowmelt, hens begin their breeding period in poorer nutrient condition because the peaks of protein content of their main food items are delayed with respect to laying date, hence reducing breeding performance. We discuss the possible mismatch between breeding and snowmelt timing. PMID:26849356

  19. Influence of Snowmelt Timing on the Diet Quality of Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Implications for Reproductive Success.

    PubMed

    García-González, Ricardo; Aldezabal, Arantza; Laskurain, Nere Amaia; Margalida, Antoni; Novoa, Claude

    2016-01-01

    The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) is the southernmost subspecies of the species in Europe and is considered threatened as a consequence of changes in landscape, human pressure, climate change, and low genetic diversity. Previous studies have shown a relationship between the date of snowmelt and reproductive success in the Pyrenean ptarmigan. It is well established that birds laying early in the breeding season have higher reproductive success, but the specific mechanism for this relationship is debated. We present an explicative model of the relationship between snowmelt date and breeding success mediated by food quality for grouse in alpine environments. From microhistological analyses of 121 faecal samples collected during three years in the Canigou Massif (Eastern Pyrenees), and the assessment of the chemical composition of the main dietary components, we estimated the potential quality of individual diets. Potential dietary quality was correlated with free-urate faecal N, a proxy of the digestible protein content ingested by ptarmigan, and both were correlated with phenological stage of consumed plants, which in turn depends on snowmelt date. Our findings suggest that the average snowmelt date is subject to a strong interannual variability influencing laying date. In years of early snowmelt, hens benefit from a longer period of high quality food resources potentially leading to a higher breeding success. On the contrary, in years of late snowmelt, hens begin their breeding period in poorer nutrient condition because the peaks of protein content of their main food items are delayed with respect to laying date, hence reducing breeding performance. We discuss the possible mismatch between breeding and snowmelt timing. PMID:26849356

  20. Influence of Snowmelt Timing on the Diet Quality of Pyrenean Rock Ptarmigan (Lagopus muta pyrenaica): Implications for Reproductive Success.

    PubMed

    García-González, Ricardo; Aldezabal, Arantza; Laskurain, Nere Amaia; Margalida, Antoni; Novoa, Claude

    2016-01-01

    The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) is the southernmost subspecies of the species in Europe and is considered threatened as a consequence of changes in landscape, human pressure, climate change, and low genetic diversity. Previous studies have shown a relationship between the date of snowmelt and reproductive success in the Pyrenean ptarmigan. It is well established that birds laying early in the breeding season have higher reproductive success, but the specific mechanism for this relationship is debated. We present an explicative model of the relationship between snowmelt date and breeding success mediated by food quality for grouse in alpine environments. From microhistological analyses of 121 faecal samples collected during three years in the Canigou Massif (Eastern Pyrenees), and the assessment of the chemical composition of the main dietary components, we estimated the potential quality of individual diets. Potential dietary quality was correlated with free-urate faecal N, a proxy of the digestible protein content ingested by ptarmigan, and both were correlated with phenological stage of consumed plants, which in turn depends on snowmelt date. Our findings suggest that the average snowmelt date is subject to a strong interannual variability influencing laying date. In years of early snowmelt, hens benefit from a longer period of high quality food resources potentially leading to a higher breeding success. On the contrary, in years of late snowmelt, hens begin their breeding period in poorer nutrient condition because the peaks of protein content of their main food items are delayed with respect to laying date, hence reducing breeding performance. We discuss the possible mismatch between breeding and snowmelt timing.

  1. PT quantum mechanics.

    PubMed

    Bender, Carl M; DeKieviet, Maarten; Klevansky, S P

    2013-04-28

    PT-symmetric quantum mechanics (PTQM) has become a hot area of research and investigation. Since its beginnings in 1998, there have been over 1000 published papers and more than 15 international conferences entirely devoted to this research topic. Originally, PTQM was studied at a highly mathematical level and the techniques of complex variables, asymptotics, differential equations and perturbation theory were used to understand the subtleties associated with the analytic continuation of eigenvalue problems. However, as experiments on PT-symmetric physical systems have been performed, a simple and beautiful physical picture has emerged, and a PT-symmetric system can be understood as one that has a balanced loss and gain. Furthermore, the PT phase transition can now be understood intuitively without resorting to sophisticated mathematics. Research on PTQM is following two different paths: at a fundamental level, physicists are attempting to understand the underlying mathematical structure of these theories with the long-range objective of applying the techniques of PTQM to understanding some of the outstanding problems in physics today, such as the nature of the Higgs particle, the properties of dark matter, the matter-antimatter asymmetry in the universe, neutrino oscillations and the cosmological constant; at an applied level, new kinds of PT-synthetic materials are being developed, and the PT phase transition is being observed in many physical contexts, such as lasers, optical wave guides, microwave cavities, superconducting wires and electronic circuits. The purpose of this Theme Issue is to acquaint the reader with the latest developments in PTQM. The articles in this volume are written in the style of mini-reviews and address diverse areas of the emerging and exciting new area of PT-symmetric quantum mechanics.

  2. PT-symmetric kinks

    SciTech Connect

    Souza Dutra, A. de; Santos, V. G. C. S. dos; Amaro de Faria, A. C. Jr.

    2007-06-15

    Some kinks for non-Hermitian quantum field theories in 1+1 dimensions are constructed. A class of models where the soliton energies are stable and real are found. Although these kinks are not Hermitian, they are symmetric under PT transformations.

  3. Pt, Co-Pt and Fe-Pt alloy nanoclusters encapsulated in virus capsids

    NASA Astrophysics Data System (ADS)

    Okuda, M.; Eloi, J.-C.; Jones, S. E. Ward; Verwegen, M.; Cornelissen, J. J. L. M.; Schwarzacher, W.

    2016-03-01

    Nanostructured Pt-based alloys show great promise, not only for catalysis but also in medical and magnetic applications. To extend the properties of this class of materials, we have developed a means of synthesizing Pt and Pt-based alloy nanoclusters in the capsid of a virus. Pure Pt and Pt-alloy nanoclusters are formed through the chemical reduction of [PtCl4]- by NaBH4 with/without additional metal ions (Co or Fe). The opening and closing of the ion channels in the virus capsid were controlled by changing the pH and ionic strength of the solution. The size of the nanoclusters is limited to 18 nm by the internal diameter of the capsid. Their magnetic properties suggest potential applications in hyperthermia for the Co-Pt and Fe-Pt magnetic alloy nanoclusters. This study introduces a new way to fabricate size-restricted nanoclusters using virus capsid.

  4. PT symmetry in optics

    NASA Astrophysics Data System (ADS)

    Christodoulides, Demetrios

    2015-03-01

    Interest in complex Hamiltonians has been rekindled after the realization that a wide class of non-Hermitian Hamiltonians can have entirely real spectra as long as they simultaneously respect parity and time reversal operators. In non-relativistic quantum mechanics, governed by the Schrödinger equation, a necessary but not sufficient condition for PT symmetry to hold is that the complex potential should involve real and imaginary parts which are even and odd functions of position respectively. As recently indicated, optics provides a fertile ground to observe and utilize notions of PT symmetry. In optics, the refractive index and gain/loss profiles play the role of the real and imaginary parts of the aforementioned complex potentials. As it has been demonstrated in several studies, PT-symmetric optical structures can exhibit peculiar properties that are otherwise unattainable in traditional Hermitian (conservative) optical settings. Among them, is the possibility for breaking this symmetry through an abrupt phase transition, band merging effects and unidirectional invisibility. Here we review recent developments in the field of -symmetric optics.

  5. Thermodynamic Modeling of the Pt-Te and Pt-Sb-Te Systems

    NASA Astrophysics Data System (ADS)

    Guo, Cuiping; Huang, Liang; Li, Changrong; Shang, Shunli; Du, Zhenmin

    2015-08-01

    The Pt-Te and the Pt-Sb-Te systems are modeled using the calculation of phase diagram (CALPHAD) technique. In the Pt-Te system, the liquid phase is modeled as (Pt, PtTe2, Te) using the associate model, and four intermediates, PtTe2, Pt2Te3, Pt3Te4 and PtTe, are treated as stoichiometric compounds and their enthalpies of formation are obtained by means of first-principles calculations. The solution phases, fcc(Pt) and hex(Te), are described as substitutional solutions. Combined with the thermodynamic models of the liquid phase in the Pt-Sb and Sb-Te systems in the literature, the liquid phase of the Pt-Sb-Te ternary system is modeled as (Pt, Sb, Te, Sb2Te3, PtTe2) also using the associate model. The compounds, PtTe2, Pt2Te3, Pt3Te4 and PtTe in the Pt-Te system and PtSb2, PtSb, Pt3Sb2 and Pt7Sb in the Pt-Sb system are treated as line compounds Pt m (Sb,Te) n in the Pt-Sb-Te system, and the compound Pt5Sb is treated as (Pt,Sb)5(Pt,Sb,Te). A set of self-consistent thermodynamic parameters is obtained. Using these thermodynamic parameters, the experimental Pt-Te phase diagram, the experimental heat capacities of PtTe and PtTe2, the enthalpies of formation from first-principles calculations for PtTe2, Pt2Te3, Pt3Te4, and PtTe, and the ternary isothermal sections at 873 K, 923 K, 1073 K and 1273 K are well reproduced.

  6. Growth of Pt Clusters from Mixture Film of Pt-C and Dynamics of Pt Clusters

    NASA Astrophysics Data System (ADS)

    Shintaku, Masayuki; Kumamoto, Akihito; Suzuki, Hitoshi; Kaito, Chihiro

    2007-06-01

    A complete mixture film of carbon and platinum produced by coevaporation in a vacuum was directly heated in a transmission electron microscope. It was found that the diffusion and crystal growth of Pt clusters in the mixture film take place at approximately 500 °C. Pt clusters with a size of 2-5 nm were connected with each other in a parallel orientation or twin-crystal configuration in the mixture film. The growth of onion-like carbon with a hole at the center also occurred. The grown Pt clusters with twin-crystal structures appeared on and in the carbon film. The diffusion of Pt atoms in carbon was discussed as the problem of elusion in fuel cells. Direct observation of the movement of Pt clusters on and in the carbon film was carried out. The movement difference of Pt clusters in and on carbon film has been directly presented.

  7. {PT}-symmetric optical superlattices

    NASA Astrophysics Data System (ADS)

    Longhi, Stefano

    2014-04-01

    The spectral and localization properties of {PT}-symmetric optical superlattices, either infinitely extended or truncated at one side, are theoretically investigated, and the criteria that ensure a real energy spectrum are derived. The analysis is applied to the case of superlattices describing a complex ( {PT}-symmetric) extension of the Harper Hamiltonian in the rational case.

  8. Homogeneous Pt-bimetallic Electrocatalysts

    SciTech Connect

    Wang, Chao; Chi, Miaofang; More, Karren Leslie; Markovic, Nenad; Stamenkovic, Vojislav

    2011-01-01

    Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt{sub 3}M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2-3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt{sub 3}M nanocatalysts validated the volcano curve established on extended surfaces, with Pt{sub 3}Co being the most active alloy.

  9. Lifetime measurements in 180Pt

    NASA Astrophysics Data System (ADS)

    Chen, Q. M.; Wu, X. G.; Chen, Y. S.; Li, C. B.; Gao, Z. C.; Li, G. S.; Chen, F. Q.; He, C. Y.; Zheng, Y.; Hu, S. P.; Zhong, J.; Wu, Y. H.; Li, H. W.; Luo, P. W.

    2016-04-01

    Lifetimes of the yrast states in 180Pt have been measured from 4+ to 8+ using the recoil distance Doppler-shift technique in the coincidence mode. These states were populated by the reaction 156Gd(28Si,4 n )180Pt at a beam energy of 144 MeV. The differential decay curve method was applied to determine the lifetimes from experimental coincidence data. The B (E 2 ) values extracted from lifetimes increase with increasing spin, implying rotor behavior, but do not show the typical shape coexistence where the B (E 2 ) values present a rapid increase at very low spins. Calculations based on the triaxial projected shell model were performed for the yrast states in 180Pt and the results of both energies and E 2 transition probabilities reproduce the experimental data very well. The result also shows that a better description of the yrast band in 180Pt requires consideration of the γ degree of freedom.

  10. Patterns of population structure and dispersal in the long-lived "redwood" of the coral reef, the giant barrel sponge ( Xestospongia muta)

    NASA Astrophysics Data System (ADS)

    Richards, Vincent P.; Bernard, Andrea M.; Feldheim, Kevin A.; Shivji, Mahmood S.

    2016-09-01

    Sponges are one of the dominant fauna on Florida and Caribbean coral reefs, with species diversity often exceeding that of scleractinian corals. Despite the key role of sponges as structural components, habitat providers, and nutrient recyclers in reef ecosystems, their dispersal dynamics are little understood. We used ten microsatellite markers to study the population structure and dispersal patterns of a prominent reef species, the giant barrel sponge ( Xestospongia muta), the long-lived "redwood" of the reef, throughout Florida and the Caribbean. F-statistics, exact tests of population differentiation, and Bayesian multi-locus genotype analyses revealed high levels of overall genetic partitioning ( F ST = 0.12, P = 0.001) and grouped 363 individuals collected from the Bahamas, Honduras, US Virgin Islands, Key Largo (Florida), and the remainder of the Florida reef tract into at minimum five genetic clusters ( K = 5). Exact tests, however, revealed further differentiation, grouping sponges sampled from five locations across the Florida reef tract (~250 km) into three populations, suggesting a total of six genetic populations across the eight locations sampled. Assignment tests showed dispersal over ecological timescales to be limited to relatively short distances, as the only migration detected among populations was within the Florida reef tract. Consequently, populations of this major coral reef benthic constituent appear largely self-recruiting. A combination of levels of genetic differentiation, genetic distance, and assignment tests support the important role of the Caribbean and Florida currents in shaping patterns of contemporary and historical gene flow in this widespread coral reef species.

  11. Description of the life stages of quill mite Mironovia lagopus sp. nov. (Acari: Syringophilidae) parasitizing the rock ptarmigan Lagopus muta (Phasianidae) from Iceland.

    PubMed

    Bochkov, Andre V; Skirnisson, Karl

    2011-03-01

    A new species of syringophilid mites, Mironovia lagopus sp. nov. (Acari: Syringophilidae) is described from feather quills of the rock ptarigman Lagopus muta (Montin) (Phasianidae) from Iceland. Females of this new species differ from the closely related Mironovia rouloul Skoracki and Sikora by setae d2, which are subequal or 1.1-1.2 times shorter than setae e2 (vs. d2 1.4-1.5 times longer than e2 in Mironovia rouloul) and by setae ag1, which are 1.3-1.5 times shorter than ag2 (vs. ag1 1.7-1.8 times shorter than ag2). The postembryonic stages of this new species are figured and described in details. In ontogeny of Mironovia spp., the observed pattern of setal appearance is not different from the pattern in other galliform-associated genera such as Syringophilus and Colinophilus, with exception for tarsal setae p'I, II which are absent in protonymphs. The key to all four species of the genus Mironovia is also provided.

  12. Integrable discrete PT symmetric model.

    PubMed

    Ablowitz, Mark J; Musslimani, Ziad H

    2014-09-01

    An exactly solvable discrete PT invariant nonlinear Schrödinger-like model is introduced. It is an integrable Hamiltonian system that exhibits a nontrivial nonlinear PT symmetry. A discrete one-soliton solution is constructed using a left-right Riemann-Hilbert formulation. It is shown that this pure soliton exhibits unique features such as power oscillations and singularity formation. The proposed model can be viewed as a discretization of a recently obtained integrable nonlocal nonlinear Schrödinger equation.

  13. PT quantum mechanics - Recent results

    NASA Astrophysics Data System (ADS)

    Bender, Carl M.

    2012-09-01

    Most quantum physicists believe that a quantum-mechanical Hamiltonian must be Dirac Hermitian (invariant under matrix transposition and complex conjugation) to be sure that the energy eigenvalues are real and that time evolution is unitary. However, the non-Dirac-hermitian Hamiltonian H = p2+ix3 has a real positive discrete spectrum and generates unitary time evolution and defines a fully consistent and physical quantum theory. Evidently, Dirac Hermiticity is too restrictive. While H = p2+ix3 is not Dirac Hermitian, it is PT symmetric (invariant under combined space reflection P and time reversal T). Another PT-symmetric Hamiltonian whose energy levels are real, positive and discrete is H = p2-x4, which contains an upside-down potential. The quantum mechanics defined by a PT-symmetric Hamiltonian is a complex generalization of ordinary quantum mechanics. When quantum mechanics and quantum field theory are extended into the complex domain, new kinds of theories having strange and remarkable properties emerge. In the past two years some of these properties have been verified in laboratory experiments. Here, we first discuss PT-symmetric Hamiltonians at a simple intuitive level and explain why the energy levels of such Hamiltonians may be real, positive, and discrete. Second, we describe a recent experiment in which the PT phase transition was observed. Third, we briefly mention that PT-symmetric theories can be useful at a fundamental level. While the double-scaling limit of an O(N)-symmetric gφ4 quantum field theory appears to be inconsistent because the critical value of g is negative, this limit is in fact not inconsistent because the critical theory is PT symmetric.

  14. Pt···Pt vs Pt···S contacts between Pt-containing heterobimetallic lantern complexes.

    PubMed

    Baddour, Frederick G; Fiedler, Stephanie R; Shores, Matthew P; Bacon, Jeffrey W; Golen, James A; Rheingold, Arnold L; Doerrer, Linda H

    2013-12-01

    A trio of Pt-based heterobimetallic lantern complexes of the form [(py)PtM(SAc)4(py)] (M = Co, 1; Ni, 2; Zn, 3) with unusual octahedral coordination of Pt(II) was prepared from a reaction of [PtM(SAc)4] with excess pyridine. These dipyridine lantern complexes could be converted to monopyridine derivatives with gentle heat to give the series [PtM(SAc)4(py)] (M = Co, 4; Ni, 5; Zn, 6). An additional family of the form [PtM(SAc)4(pyNH2)] (M = Co, 7; Ni, 8; Zn, 9) was synthesized from reaction of [PtM(SAc)4(OH2)] or [PtM(SAc)4] with 4-aminopyridine. Dimethylsulfoxide and N,N-dimethylformamide were also determined to react with [PtM(SAc)4] (M = Co, Ni), respectively, to give [PtCo(SAc)4(DMSO)](DMSO), 10, and [PtNi(SAc)4(DMF)](DMF), 11. Structural and magnetic data for these compounds and those for two other previously published families, [PtM(tba)4(OH2)] and [PtM(SAc)4(L)], L = OH2, pyNO2, are used to divide the structures among three distinct categories based on Pt···Pt and Pt···S distances. In general, the weaker donors H2O and pyNO2 seem to favor metallophilicity and antiferromagnetic coupling between 3d metal centers. When Pt···S interactions are favored over Pt···Pt ones, no coupling is observed and the pKa of the pyridine donor correlates with the interlantern S···S distance. UV-vis-NIR electronic and (1)H NMR spectra provide complementary characterization as well.

  15. Transcriptional Profiling of Dibenzo[def,p]chrysene-induced Spleen Atrophy Provides Mechanistic Insights into its Immunotoxicity in MutaMouse.

    PubMed

    Chepelev, Nikolai L; Long, Alexandra S; Williams, Andrew; Kuo, Byron; Gagné, Rémi; Kennedy, Dean A; Phillips, David H; Arlt, Volker M; White, Paul A; Yauk, Carole L

    2016-01-01

    Dibenzo[def,p]chrysene (DBC) is the most carcinogenic polycyclic aromatic hydrocarbon (PAH) examined to date. We investigated the immunotoxicity of DBC, manifested as spleen atrophy, following acute exposure of adult MutaMouse males by oral gavage. Mice were exposed to 0, 2.0, 6.2, or 20.0 mg DBC /kg-bw per day, for 3 days. Genotoxic endpoints (DBC-DNA adducts and lacZ mutant frequency in spleen and bone marrow, and red blood cell micronucleus frequency) and global gene expression changes were measured. All of the genotoxicity measures increased in a dose-dependent manner in spleen and bone marrow. Gene expression analysis showed that DBC activates p53 signaling pathways related to cellular growth and proliferation, which was evident even at the low dose. Strikingly, the expression profiles of DBC exposed mouse spleens were highly inversely correlated with the expression profiles of the only published toxicogenomics dataset of enlarged mouse spleen. This analysis suggested a central role for Bnip3l, a pro-apoptotic protein involved in negative regulation of erythroid maturation. RT-PCR confirmed expression changes in several genes related to apoptosis, iron metabolism, and aryl hydrocarbon receptor signaling that are regulated in the opposite direction during spleen atrophy versus benzo[a]pyrene-mediated splenomegaly. In addition, benchmark dose modeling of toxicogenomics data yielded toxicity estimates that are very close to traditional toxicity endpoints. This work illustrates the power of toxicogenomics to reveal rich mechanistic information for immunotoxic compounds and its ability to provide information that is quantitatively similar to that derived from standard toxicity methods in health risk assessment.

  16. Transcriptional Profiling of Dibenzo[def,p]chrysene-induced Spleen Atrophy Provides Mechanistic Insights into its Immunotoxicity in MutaMouse.

    PubMed

    Chepelev, Nikolai L; Long, Alexandra S; Williams, Andrew; Kuo, Byron; Gagné, Rémi; Kennedy, Dean A; Phillips, David H; Arlt, Volker M; White, Paul A; Yauk, Carole L

    2016-01-01

    Dibenzo[def,p]chrysene (DBC) is the most carcinogenic polycyclic aromatic hydrocarbon (PAH) examined to date. We investigated the immunotoxicity of DBC, manifested as spleen atrophy, following acute exposure of adult MutaMouse males by oral gavage. Mice were exposed to 0, 2.0, 6.2, or 20.0 mg DBC /kg-bw per day, for 3 days. Genotoxic endpoints (DBC-DNA adducts and lacZ mutant frequency in spleen and bone marrow, and red blood cell micronucleus frequency) and global gene expression changes were measured. All of the genotoxicity measures increased in a dose-dependent manner in spleen and bone marrow. Gene expression analysis showed that DBC activates p53 signaling pathways related to cellular growth and proliferation, which was evident even at the low dose. Strikingly, the expression profiles of DBC exposed mouse spleens were highly inversely correlated with the expression profiles of the only published toxicogenomics dataset of enlarged mouse spleen. This analysis suggested a central role for Bnip3l, a pro-apoptotic protein involved in negative regulation of erythroid maturation. RT-PCR confirmed expression changes in several genes related to apoptosis, iron metabolism, and aryl hydrocarbon receptor signaling that are regulated in the opposite direction during spleen atrophy versus benzo[a]pyrene-mediated splenomegaly. In addition, benchmark dose modeling of toxicogenomics data yielded toxicity estimates that are very close to traditional toxicity endpoints. This work illustrates the power of toxicogenomics to reveal rich mechanistic information for immunotoxic compounds and its ability to provide information that is quantitatively similar to that derived from standard toxicity methods in health risk assessment. PMID:26496743

  17. Characterization of NiPt, FePt, and NiFePt nanoparticles

    NASA Astrophysics Data System (ADS)

    Sutherland, Greg; Wood, Darren; Jackson, Amy; Warren, Andrew; Coffey, Kevin; Vanfleet, Richard

    2012-10-01

    Many metal alloys can form in chemically ordered structures, often resulting in significant changes in properties. The ordered structures are preferred at low temperatures and will go through an order-disorder phase transition at a critical temperature. The formation and stability of these ordered structures in alloy nanoparticles is not well understood but may give insight into the role size plays in phase transitions. To this end we are studying FePt, NiPt, and FeNiPt alloy nanoparticles. We will focus this presentation on the characterization of these nanoparticles in a Transmission Electron Microscope (TEM) for composition, size, and structure. These nanoparticles are made by co-sputtering the constituents and annealing at different temperatures in various gas mixtures. The nanoparticle samples are prepared for TEM viewing by wedge polishing. We find FePt to be ``well behaved'' meaning this alloy forms particles, retains the as deposited composition, and chemically orders as expected. However, the order-disorder temperature is too high for the desired further studies. NiPt, which has a lower order-disorder temperature, is not ``well behaved'' in that the nanoparticle compositions are not good matches to the as deposited conditions and no chemical ordering has been achieved even under conditions that should be sufficient based on bulk processing. We will discuss these results and possible implications.

  18. PT-symmetric quantum theory

    NASA Astrophysics Data System (ADS)

    Bender, Carl M.

    2015-07-01

    The average quantum physicist on the street would say that a quantum-mechanical Hamiltonian must be Dirac Hermitian (invariant under combined matrix transposition and complex conjugation) in order to guarantee that the energy eigenvalues are real and that time evolution is unitary. However, the Hamiltonian H = p2 + ix3, which is obviously not Dirac Hermitian, has a positive real discrete spectrum and generates unitary time evolution, and thus it defines a fully consistent and physical quantum theory. Evidently, the axiom of Dirac Hermiticity is too restrictive. While H = p2 + ix3 is not Dirac Hermitian, it is PT symmetric; that is, invariant under combined parity P (space reflection) and time reversal T. The quantum mechanics defined by a PT-symmetric Hamiltonian is a complex generalization of ordinary quantum mechanics. When quantum mechanics is extended into the complex domain, new kinds of theories having strange and remarkable properties emerge. In the past few years, some of these properties have been verified in laboratory experiments. A particularly interesting PT-symmetric Hamiltonian is H = p2 - x4, which contains an upside-down potential. This potential is discussed in detail, and it is explained in intuitive as well as in rigorous terms why the energy levels of this potential are real, positive, and discrete. Applications of PT-symmetry in quantum field theory are also discussed.

  19. PT3. [SITE 2002 Section].

    ERIC Educational Resources Information Center

    Thompson, Mary, Ed.; Price, Jerry, Ed.

    This document contains 142 papers on PT3 (Preparing Tomorrow's Teachers to use Technology) from the SITE (Society for Information Technology & Teacher Education) 2002 conference. Topics covered include: a technology in urban education summit; student professional development; meeting NCATE (National Council of Teachers of English) standards;…

  20. Surface termination of CePt5/Pt (111 ): The key to chemical inertness

    NASA Astrophysics Data System (ADS)

    Praetorius, C.; Zinner, M.; Held, G.; Fauth, K.

    2015-11-01

    The surface termination of CePt5/Pt (111 ) is determined experimentally by LEED-IV. In accordance with recent theoretical predictions, a dense Pt terminated surface is being found. Whereas the CePt5 volume lattice comprises Pt kagome layers, additional Pt atoms occupy the associated hole positions at the surface. This finding provides a natural explanation for the remarkable inertness of the CePt5 intermetallic. Implications of the structural relaxations determined by LEED-IV analysis are discussed with regard to observations by scanning tunneling microscopy and electron spectroscopies.

  1. Electrochemical Co-Reduction Synthesis of AuPt Bimetallic Nanoparticles-Graphene Nanocomposites for Selective Detection of Dopamine in the Presence of Ascorbic Acid and Uric Acid.

    PubMed

    Zhao, Zongya; Zhang, Mingming; Chen, Xiang; Li, Youjun; Wang, Jue

    2015-07-09

    In this paper, AuPt bimetallic nanoparticles-graphene nanocomposites were obtained by electrochemical co-reduction of graphene oxide (GO), HAuCl4 and H2PtCl6. The as-prepared AuPt bimetallic nanoparticles-graphene nanocomposites were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and other electrochemical methods. The morphology and composition of the nanocomposite could be easily controlled by adjusting the HAuCl4/H2PtCl6 concentration ratio. The electrochemical experiments showed that when the concentration ratio of HAuCl4/H2PtCl6 was 1:1, the obtained AuPt bimetallic nanoparticles-graphene nanocomposite (denoted as Au1Pt1NPs-GR) possessed the highest electrocatalytic activity toward dopamine (DA). As such, Au1Pt1NPs-GR nanocomposites were used to detect DA in the presence of ascorbic acid (AA) and uric acid (UA) using the differential pulse voltammetry (DPV) technique and on the modified electrode, there were three separate DPV oxidation peaks with the peak potential separations of 177 mV, 130 mV and 307 mV for DA and AA, DA and UA, AA and UA, respectively. The linear range of the constructed DA sensor was from 1.6 μM to 39.7 μM with a detection limit of 0.1 μM (S/N = 3). The obtained DA sensor with good stability, high reproducibility and excellent selectivity made it possible to detect DA in human urine samples.

  2. Electrochemical Co-Reduction Synthesis of AuPt Bimetallic Nanoparticles-Graphene Nanocomposites for Selective Detection of Dopamine in the Presence of Ascorbic Acid and Uric Acid

    PubMed Central

    Zhao, Zongya; Zhang, Mingming; Chen, Xiang; Li, Youjun; Wang, Jue

    2015-01-01

    In this paper, AuPt bimetallic nanoparticles-graphene nanocomposites were obtained by electrochemical co-reduction of graphene oxide (GO), HAuCl4 and H2PtCl6. The as-prepared AuPt bimetallic nanoparticles-graphene nanocomposites were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and other electrochemical methods. The morphology and composition of the nanocomposite could be easily controlled by adjusting the HAuCl4/H2PtCl6 concentration ratio. The electrochemical experiments showed that when the concentration ratio of HAuCl4/H2PtCl6 was 1:1, the obtained AuPt bimetallic nanoparticles-graphene nanocomposite (denoted as Au1Pt1NPs-GR) possessed the highest electrocatalytic activity toward dopamine (DA). As such, Au1Pt1NPs-GR nanocomposites were used to detect DA in the presence of ascorbic acid (AA) and uric acid (UA) using the differential pulse voltammetry (DPV) technique and on the modified electrode, there were three separate DPV oxidation peaks with the peak potential separations of 177 mV, 130 mV and 307 mV for DA and AA, DA and UA, AA and UA, respectively. The linear range of the constructed DA sensor was from 1.6 μM to 39.7 μM with a detection limit of 0.1 μM (S/N = 3). The obtained DA sensor with good stability, high reproducibility and excellent selectivity made it possible to detect DA in human urine samples. PMID:26184200

  3. Effect of Pt layers on chemical ordering in FePt thin films

    NASA Astrophysics Data System (ADS)

    Gupta, R.; Medwal, R.; Sharma, P.; Mahapatro, A. K.; Annapoorni, S.

    2013-12-01

    The tunability in the structural and magnetic phases present in RF-sputtered Fe3Pt thin films over Si (1 0 0) substrates have been studied by introducing thin films of platinum (Pt) as an underlayer and/or overlayers. Annealing of the Fe3Pt thin films with Pt underlayers (Pt/Fe3Pt) structures at 600 °C for 1 h, indicates well organized nanostructured grains as imaged through an atomic force microscope (AFM). The evolution of superstructure peaks as well as the preferred orientation along (0 0 1) plane observed in the X-ray diffraction (XRD) study is well supported by the magnetic measurements. These annealed Pt/Fe3Pt structures show high magnetocrystalline anisotropy and the presence of hard phase with a coercivity of 8.5 kOe. Here, the annealing process allows the adjacent Pt atoms to diffuse into the Fe3Pt unit cells and triggers the structural transformation to chemically ordered L10 phase. An additional L12 phase is observed in the annealed Fe3Pt thin films with Pt overlayer and underlayer (Pt/Fe3Pt/Pt) tri-layered structures.

  4. PT AND PT/NI "NEEDLE" ELETROCATALYSTS ON CARBON NANOTUBES WITH HIGH ACTIVITY FOR THE ORR

    SciTech Connect

    Colon-Mercado, H.

    2011-11-10

    Platinum and platinum/nickel alloy electrocatalysts supported on graphitized (gCNT) or nitrogen doped carbon nanotubes (nCNT) are prepared and characterized. Pt deposition onto carbon nanotubes results in Pt 'needle' formations that are 3.5 nm in diameter and {approx}100 nm in length. Subsequent Ni deposition and heat treatment results in PtNi 'needles' with an increased diameter. All Pt and Pt/Ni materials were tested as electrocatalysts for the oxygen reduction reaction (ORR). The Pt and Pt/Ni catalysts showed excellent performance for the ORR, with the heat treated PtNi/gCNT (1.06 mA/cm{sup 2}) and PtNi/nCNT (0.664 mA/cm{sup 2}) showing the highest activity.

  5. The Role of Pt Complex on the Synthesis of FePt by Polyol Process

    SciTech Connect

    Aizawa, S.; Tohji, K.; Jeyadevan, B.

    2008-02-25

    Target materials in this experiment were FePt alloy nanoparticles with face-centered tetragonal structure, narrow size distribution, and the size of 6-8 nm. This type of materials was expected to have high recording-density of 1 Tbit/inch{sup 2} with high magnetic anisotropy. In this study, a detailed investigation was carried out to understand the reduction characteristics of Pt complexes, and FePt alloy nanoparticles with diameters larger than 6 nm was try to synthesize. For the synthesis of Pt nanoparticles by using polyol process, three kinds of Pt complexes, namely, H{sub 2}PtCl{sub 6}, Pt(EDTA), and Pt(acac){sub 2} was used. The size of Pt metal nanoparticles was only few nm in the case of single Pt complex, while it was increased to 7-10 nm in the case of mixed Pt complex and adjusting the reaction temperature increasing ratio. FePt alloy nanoparticles with the diameter of 7-8 nm, distorted shape, and narrow size distribution were successfully synthesized. However, composition ratio of the particle was Fe{sub 12-21}Pt{sub 79-88}, nevertheless the ratio of a Fe:Pt in the original solution was 2:1.

  6. Low Pt content direct methanol fuel cell anode catalyst: nanophase PtRuNiZr

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram R. (Inventor); Whitacre, Jay F. (Inventor)

    2010-01-01

    A method for the preparation of a metallic material having catalytic activity that includes synthesizing a material composition comprising a metal content with a lower Pt content than a binary alloy containing Pt but that displays at least a comparable catalytic activity on a per mole Pt basis as the binary alloy containing Pt; and evaluating a representative sample of the material composition to ensure that the material composition displays a property of at least a comparable catalytic activity on a per mole Pt basis as a representative binary alloy containing Pt. Furthermore, metallic compositions are disclosed that possess substantial resistance to corrosive acids.

  7. Direct Determination of the Ionization Energies of PtC, PtO, and PtO2 with VUVRadiation

    SciTech Connect

    Citir, Murat; Metz, Ricardo B.; Belau, Leonid; Ahmed, Musahid

    2008-07-21

    Photoionization efficiency curves were measured for gas-phase PtC, PtO, and PtO2 using tunable vacuum ultraviolet (VUV) radiation at the Advanced Light Source. The molecules were prepared by laser ablation of a platinum tube, followed by reaction with CH4 or N2O and supersonic expansion. These measurements providethe first directly measured ionization energy for PtC, IE(PtC) = 9.45 +- 0.05 eV. The direct measurement also gives greatly improved ionization energies for the platinum oxides, IE(PtO) = 10.0 +- 0.1 eV and IE(PtO2) = 11.35 +- 0.05 eV. The ionization energy connects the dissociation energies of the neutral and cation, leading to greatly improved 0 K bond dissociation energies for the neutrals: D0(Pt-C) = 5.95 +- 0.07 eV, D0(Pt-O)= 4.30 +- 0.12 eV, and D0(OPt-O) = 4.41 +- 0.13 eV, as well as enthalpies of formation for the gas-phase molecules Delta H0 f,0(PtC(g)) = 701 +- 7 kJ/mol, Delta H0f,0(PtO(g)) = 396 +- 12 kJ/mol, and Delta H0f,0(PtO2(g)) = 218 +- 11 kJ/mol. Much of the error in previous Knudsen cell measurements of platinum oxide bond dissociation energies is due to the use of thermodynamic second law extrapolations. Third law values calculated using statistical mechanical thermodynamic functions are in much better agreement with values obtained from ionization energies and ion energetics. These experiments demonstrate that laser ablation production with direct VUV ionization measurements is a versatile tool to measure ionization energies and bond dissociation energies for catalytically interesting species such as metal oxides and carbides.

  8. Guiding SPPs with PT-symmetry

    PubMed Central

    Yang, Fan; Lei Mei, Zhong

    2015-01-01

    The concept of parity-time (PT) symmetry in SPPs is proposed and confirmed for the first time in this work. By introducing periodic modulation of the effective refractive index in SPP system, the asymmetric propagation is theoretically predicted and numerically demonstrated. After validation of this concept, we apply it in two applications: PT-waveguide and PT-cloak. Both two applications further illustrate the wide applicability of this concept in SPP system. PMID:26446520

  9. High-performance core-shell PdPt@Pt/C catalysts via decorating PdPt alloy cores with Pt

    NASA Astrophysics Data System (ADS)

    Wu, Yan-Ni; Liao, Shi-Jun; Liang, Zhen-Xing; Yang, Li-Jun; Wang, Rong-Fang

    A core-shell structured low-Pt catalyst, PdPt@Pt/C, with high performance towards both methanol anodic oxidation and oxygen cathodic reduction, as well as in a single hydrogen/air fuel cell, is prepared by a novel two-step colloidal approach. For the anodic oxidation of methanol, the catalyst shows three times higher activity than commercial Tanaka 50 wt% Pt/C catalyst; furthermore, the ratio of forward current I f to backward current I b is high up to 1.04, whereas for general platinum catalysts the ratio is only ca. 0.70, indicating that this PdPt@Pt/C catalyst has high activity towards methanol anodic oxidation and good tolerance to the intermediates of methanol oxidation. The catalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The core-shell structure of the catalyst is revealed by XRD and TEM, and is also supported by underpotential deposition of hydrogen (UPDH). The high performance of the PdPt@Pt/C catalyst may make it a promising and competitive low-Pt catalyst for hydrogen fueled polymer electrolyte membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC) applications.

  10. Polyol-synthesized PtRu/C and PtRu black for direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Guo, Junsong; Sun, Gongquan; Shiguo, Sun; Shiyou, Yan; Weiqian, Yang; Jing, Qi; Yushan, Yan; Qin, Xin

    PtRu/C and PtRu black catalysts with nominal Pt:Ru atomic ratio of 1:1 are prepared by a modified polyol process (co-reduction of metal precursor salts) as anode catalysts for direct methanol fuel cells (DMFCs). Without the carbon support, PtRu nanoparticles tend to agglomerate, while the PtRu nanoparticles in PtRu/C have a good dispersion as shown by TEM. Both PtRu black and PtRu/C have the almost same alloy degree indicated by XRD, but PtRu supported on carbon could improve the influence of Ru on Pt toward methanol oxidization as shown by cyclic voltammetry. The microstructure of PtRu/C is further studied by high-resolution transmission electron microscopy (HRTEM), and the results indicate that the lattice constant of Pt in PtRu electrocatalyst has contracted despite a few parts of Pt not alloyed with Ru due to the lattice constant of Pt without contracting, which is further proved by the results of temperature-programmed reduction (TPR). Such parts of unalloyed Ru are further proved to have ability to reduce the methanol oxidation potential on Pt by comparing the catalytic behaviors of Pt/C and Pt + Ru/C prepared by mixing carbon with separately prepared Pt and Ru colloids. Moreover, the catalytic behaviors of PtRu black and PtRu/C are also compared with those of commercial ones.

  11. AN ANIMAL MODEL OF PLATINUM (PT) HYPERSENSITIVITY

    EPA Science Inventory

    Exposure to Pt salts has been associated with occupational asthma. Pt, the most active component and widely used metal in catalytic converters, is released in automobile exhaust and is a proposed diesel fuel additive. Thus, with the potential for widespread environmental distrib...

  12. Shape-Controlled Synthesis of Pt Nanopeanuts

    NASA Astrophysics Data System (ADS)

    Zhang, Xuemei; Xia, Zengzilu; Huang, Yingzhou; Jia, Yunpeng; Sun, Xiaonan; Li, Yu; Li, Xueming; Wu, Rui; Liu, Anping; Qi, Xueqiang; Wang, Shuxia; Wen, Weijia

    2016-08-01

    Exploring the novel shape of Pt nanoparticles is one of the most useful ways to improve the electrocatalytic performance of Pt in fuel cells. In this work, the Pt nanopeanuts consisting of two nanospheres grown together have been fabricated through a two-step polyol method. The high resolution scanning electron microscope (SEM) images and energy dispersive x-ray (EDX) spectrum collected at adjacent part point out the Pt nanopeanut is apparently different from the two physical attached nanospheres. To understand the growth mechanism of this nanopeanut, the final products in different synthesis situations are studied. The results indicate the interesting morphology of Pt nanopeanuts mainly benefit from the chemical reagent (FeCl3) while the size and homogeneity are greatly affected by the temperature. Furthermore, the electrocatalytic activity of the Pt nanopeanuts has also been demonstrated here. Our two-step synthesis of Pt nanopeanuts not only enlarges the group of Pt nanoparticles, but also provides a beneficial strategy for the synthesis of novel metal nanoparticles.

  13. Nonlinear waves in PT -symmetric systems

    NASA Astrophysics Data System (ADS)

    Konotop, Vladimir V.; Yang, Jianke; Zezyulin, Dmitry A.

    2016-07-01

    Recent progress on nonlinear properties of parity-time (PT )-symmetric systems is comprehensively reviewed in this article. PT symmetry started out in non-Hermitian quantum mechanics, where complex potentials obeying PT symmetry could exhibit all-real spectra. This concept later spread out to optics, Bose-Einstein condensates, electronic circuits, and many other physical fields, where a judicious balancing of gain and loss constitutes a PT -symmetric system. The natural inclusion of nonlinearity into these PT systems then gave rise to a wide array of new phenomena which have no counterparts in traditional dissipative systems. Examples include the existence of continuous families of nonlinear modes and integrals of motion, stabilization of nonlinear modes above PT -symmetry phase transition, symmetry breaking of nonlinear modes, distinctive soliton dynamics, and many others. In this article, nonlinear PT -symmetric systems arising from various physical disciplines are presented, nonlinear properties of these systems are thoroughly elucidated, and relevant experimental results are described. In addition, emerging applications of PT symmetry are pointed out.

  14. Shape-Controlled Synthesis of Pt Nanopeanuts

    PubMed Central

    Zhang, Xuemei; Xia, Zengzilu; Huang, Yingzhou; Jia, Yunpeng; Sun, Xiaonan; Li, Yu; Li, Xueming; Wu, Rui; Liu, Anping; Qi, Xueqiang; Wang, Shuxia; Wen, Weijia

    2016-01-01

    Exploring the novel shape of Pt nanoparticles is one of the most useful ways to improve the electrocatalytic performance of Pt in fuel cells. In this work, the Pt nanopeanuts consisting of two nanospheres grown together have been fabricated through a two-step polyol method. The high resolution scanning electron microscope (SEM) images and energy dispersive x-ray (EDX) spectrum collected at adjacent part point out the Pt nanopeanut is apparently different from the two physical attached nanospheres. To understand the growth mechanism of this nanopeanut, the final products in different synthesis situations are studied. The results indicate the interesting morphology of Pt nanopeanuts mainly benefit from the chemical reagent (FeCl3) while the size and homogeneity are greatly affected by the temperature. Furthermore, the electrocatalytic activity of the Pt nanopeanuts has also been demonstrated here. Our two-step synthesis of Pt nanopeanuts not only enlarges the group of Pt nanoparticles, but also provides a beneficial strategy for the synthesis of novel metal nanoparticles. PMID:27528078

  15. Shape-Controlled Synthesis of Pt Nanopeanuts.

    PubMed

    Zhang, Xuemei; Xia, Zengzilu; Huang, Yingzhou; Jia, Yunpeng; Sun, Xiaonan; Li, Yu; Li, Xueming; Wu, Rui; Liu, Anping; Qi, Xueqiang; Wang, Shuxia; Wen, Weijia

    2016-01-01

    Exploring the novel shape of Pt nanoparticles is one of the most useful ways to improve the electrocatalytic performance of Pt in fuel cells. In this work, the Pt nanopeanuts consisting of two nanospheres grown together have been fabricated through a two-step polyol method. The high resolution scanning electron microscope (SEM) images and energy dispersive x-ray (EDX) spectrum collected at adjacent part point out the Pt nanopeanut is apparently different from the two physical attached nanospheres. To understand the growth mechanism of this nanopeanut, the final products in different synthesis situations are studied. The results indicate the interesting morphology of Pt nanopeanuts mainly benefit from the chemical reagent (FeCl3) while the size and homogeneity are greatly affected by the temperature. Furthermore, the electrocatalytic activity of the Pt nanopeanuts has also been demonstrated here. Our two-step synthesis of Pt nanopeanuts not only enlarges the group of Pt nanoparticles, but also provides a beneficial strategy for the synthesis of novel metal nanoparticles. PMID:27528078

  16. Metrology with PT-Symmetric Cavities: Enhanced Sensitivity near the PT-Phase Transition.

    PubMed

    Liu, Zhong-Peng; Zhang, Jing; Özdemir, Şahin Kaya; Peng, Bo; Jing, Hui; Lü, Xin-You; Li, Chun-Wen; Yang, Lan; Nori, Franco; Liu, Yu-Xi

    2016-09-01

    We propose and analyze a new approach based on parity-time (PT) symmetric microcavities with balanced gain and loss to enhance the performance of cavity-assisted metrology. We identify the conditions under which PT-symmetric microcavities allow us to improve sensitivity beyond what is achievable in loss-only systems. We discuss the application of PT-symmetric microcavities to the detection of mechanical motion, and show that the sensitivity is significantly enhanced near the transition point from unbroken- to broken-PT regimes. Our results open a new direction for PT-symmetric physical systems and it may find use in ultrahigh precision metrology and sensing. PMID:27661674

  17. Metrology with PT -Symmetric Cavities: Enhanced Sensitivity near the PT -Phase Transition

    NASA Astrophysics Data System (ADS)

    Liu, Zhong-Peng; Zhang, Jing; Özdemir, Şahin Kaya; Peng, Bo; Jing, Hui; Lü, Xin-You; Li, Chun-Wen; Yang, Lan; Nori, Franco; Liu, Yu-xi

    2016-09-01

    We propose and analyze a new approach based on parity-time (PT ) symmetric microcavities with balanced gain and loss to enhance the performance of cavity-assisted metrology. We identify the conditions under which PT -symmetric microcavities allow us to improve sensitivity beyond what is achievable in loss-only systems. We discuss the application of PT -symmetric microcavities to the detection of mechanical motion, and show that the sensitivity is significantly enhanced near the transition point from unbroken- to broken-PT regimes. Our results open a new direction for PT -symmetric physical systems and it may find use in ultrahigh precision metrology and sensing.

  18. PT-Symmetric Quantum Field Theory

    NASA Astrophysics Data System (ADS)

    Bender, Carl M.

    2011-09-01

    In 1998 it was discovered that the requirement that a Hamiltonian be Dirac Hermitian (H = H†) can be weakened and generalized to the requirement that a Hamiltonian be PT symmetric ([H,PT] = 0); that is, invariant under combined space reflection and time reversal. Weakening the constraint of Hermiticity allows one to consider new kinds of physically acceptable Hamiltonians and, in effect, it amounts to extending quantum mechanics from the real (Hermitian) domain into the complex domain. Much work has been done on the analysis of various PT-symmetric quantum-mechanical models. However, only very little analysis has been done on PT-symmetric quantum-field-theoretic models. Here, we describe some of what has been done in the context of PT-symmetric quantum field theory and describe some possible fundamental applications.

  19. Architecturally designed Pt-MoS2 and Pt-graphene composites for electrocatalytic methanol oxidation.

    PubMed

    Patil, Sagar H; Anothumakkool, Bihag; Sathaye, Shivaram D; Patil, Kashinath R

    2015-10-21

    Thin films consisting of platinum nanoparticles (Pt NPs) with uniform size and distribution have been successfully prepared at a liquid-liquid interface. Apart from the usual substrates like glass, Si etc. the films were also deposited on the surfaces of MoS2 thin films and graphene nanosheets (GNS) respectively, by using a layer-by-layer (LbL) deposition technique to form Pt-MoS2 and Pt-GNS composites. The loading concentration of Pt NPs on MoS2 and GNS can be adjusted by selecting the number and sequence of the component layers during LbL deposition. The Pt thin films, Pt-MoS2 and Pt-GNS nanocomposite thin films are characterized using transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). TEM results of the composites show that Pt NPs with sizes in the range of 1 to 3 nm are uniformly dispersed on the MoS2/GNS surface. The catalytic activities of Pt and Pt-composites for the reaction of methanol oxidation are studied using cyclic voltammetry and chronoamperometry. Electrochemical studies reveal that both the Pt-MoS2 and Pt-GNS nanocomposites show excellent electrocatalytic activity towards methanol oxidation. Pt-MoS2 and Pt-GNS nanocomposite electrodes show excellent stability for reuse of the catalyst. A probable mechanism of catalysis has been discussed. We propose that the similar architecture reported here would be promising for the synthesis of high performance catalysts for fuel cells, gas phase reactions, and other applications such as sensors. PMID:26377752

  20. Reduction of Pt2+ species in model Pt-CeO2 fuel cell catalysts upon reaction with methanol

    NASA Astrophysics Data System (ADS)

    Neitzel, Armin; Johánek, Viktor; Lykhach, Yaroslava; Skála, Tomáš; Tsud, Nataliya; Vorokhta, Mykhailo; Matolín, Vladimír; Libuda, Jörg

    2016-11-01

    The stability of atomically dispersed Pt2+ species on the surface of nanostructured CeO2 films during the reaction with methanol has been investigated by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy. The isolated Pt2+ species were prepared at low Pt concentration in Pt-CeO2 film. Additionally, Pt2+ species coexisting with metallic Pt particles were prepared at high Pt concentration. We found that adsorption of methanol yields similar decomposition products regardless of Pt concentration in Pt-CeO2 films. A small number of oxygen vacancies formed during the methanol decomposition can be replenished in the Pt-CeO2 film with low Pt concentration by diffusion of oxygen from the bulk. In the presence of supported Pt particles, a higher number of oxygen vacancies leads to a partial reduction of the Pt2+ species. The isolated Pt2+ species are reduced under rather strongly reducing conditions only, i.e. during annealing under continuous exposure to methanol. Reduction of isolated Pt2+ species results in the formation of ultra-small Pt particles containing around 25 atoms per particle or less. Such ultra-small Pt particles demonstrate excellent stability against sintering during annealing of Pt-CeO2 film with low Pt concentration under reducing conditions.

  1. Highly Active Pt(3)Pb and Core-Shell Pt(3)Pb-Pt Electrocatalysts for Formic Acid Oxidation

    SciTech Connect

    Kang Y.; Stach E.; Qi L.; Li M.; Diaz R.E.; Su D.; Adzic R.R.; Li J.; Murray C.B.

    2012-03-27

    Formic acid is a promising chemical fuel for fuel cell applications. However, due to the dominance of the indirect reaction pathway and strong poisoning effects, the development of direct formic acid fuel cells has been impeded by the low activity of existing electrocatalysts at desirable operating voltage. We report the first synthesis of Pt{sub 3}Pb nanocrystals through solution phase synthesis and show they are highly efficient formic acid oxidation electrocatalysts. The activity can be further improved by manipulating the Pt{sub 3}Pb-Pt core-shell structure. Combined experimental and theoretical studies suggest that the high activity from Pt{sub 3}Pb and the Pt-Pb core-shell nanocrystals results from the elimination of CO poisoning and decreased barriers for the dehydrogenation steps. Therefore, the Pt{sub 3}Pb and Pt-Pb core-shell nanocrystals can improve the performance of direct formic acid fuel cells at desired operating voltage to enable their practical application.

  2. Experimental and theoretical studies of ammonia decomposition activity on Fe-Pt, Co-Pt, and Cu-Pt bimetallic surfaces

    NASA Astrophysics Data System (ADS)

    Hansgen, Danielle A.; Thomanek, Lisa M.; Chen, Jingguang G.; Vlachos, Dionisios G.

    2011-05-01

    We investigate the decomposition of ammonia on bimetallic surfaces prepared by the deposition of a monolayer of Fe, Co, or Cu on a Pt(111) surface computationally and experimentally. We explore the correlation between predicted activities based on the nitrogen binding energies with experimental decomposition activity on these bimetallic and corresponding monometallic surfaces. Through density functional theory calculations and microkinetic modeling, it is predicted that the Fe-Pt-Pt(111) and Co-Pt-Pt(111) surfaces, with a monolayer of Fe or Co on top of Pt(111), are active toward decomposing ammonia. In contrast, the corresponding subsurface configurations, Pt-Fe-Pt(111) and Pt-Co-Pt(111) are inactive. These predictions were confirmed experimentally through temperature programmed desorption experiments. Decomposition was seen at temperatures below 350 K for the Fe-Pt-Pt(111) and Co-Pt-Pt(111) surfaces. For the Cu/Pt(111) system, the surface, subsurface and parent metals were each predicted to be inactive, consistent with experiments, further validating the model predictions. The stability of these bimetallic surfaces in the presence of adsorbed nitrogen is also discussed.

  3. Microstructure and electronic behavior of PtPd@Pt core-shell nanowires

    SciTech Connect

    Han, Wei-Qiang; Su, Dong; Murphy, Michael; Ward, Matthew; Sham, Tsun-Kong; Wu, Lijun; Zhu, Yimei; Hu, Yongfeng; Aoki, Toshihiro

    2010-07-19

    PtPd{at}Pt core-shell ultrathin nanowires were prepared using a one-step phase-transfer approach. The diameters of the nanowires range from 2 to 3 nm, and their lengths are up to hundreds of nanometers. Line scanning electron energy loss spectra showed that PtPd bimetallic nanowires have a core-shell structure, with a PtPd alloy core and a Pt monolayer shell. X-ray absorption near edge structure (XANES) spectra reveal that a strong Pt-Pd interaction exists in this nanowire system in that there is PtPd alloying and/or interfacial interaction. Extended x-ray absorption fine structures (EXAFS) further confirms the PtPd@Pt core-shell structure. The bimetallic nanowires were determined to be face-centered cubic structures. The long-chain organic molecules of n-dodecyl trimethylammonium bromide and octadecylamine, used as surfactants during synthesis, were clearly observed using aberration-corrected TEM operated at 80 KV. The interaction of Pt and surfactants was also revealed by EXAFS.

  4. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 32 National Defense 3 2014-07-01 2014-07-01 false Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form...

  5. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 32 National Defense 3 2013-07-01 2013-07-01 false Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form...

  6. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 32 National Defense 3 2012-07-01 2009-07-01 true Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form...

  7. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 3 2010-07-01 2010-07-01 true Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form...

  8. 32 CFR Appendix F to Part 623 - Power of Attorney (DA Form 4881-4-R)

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 3 2010-07-01 2010-07-01 true Power of Attorney (DA Form 4881-4-R) F Appendix F to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. F Appendix F to Part 623—Power of Attorney (DA Form...

  9. 32 CFR Appendix E to Part 623 - Surety Bond (DA Form 4881-3-R)

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 32 National Defense 3 2011-07-01 2009-07-01 true Surety Bond (DA Form 4881-3-R) E Appendix E to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. E Appendix E to Part 623—Surety Bond (DA Form...

  10. \\cal{PT} -symmetry in Rydberg atoms

    NASA Astrophysics Data System (ADS)

    Ziauddin; Chuang, You-Lin; Lee, Ray-Kuang

    2016-07-01

    We propose a scheme to realize parity-time ( {PT} )-symmetry in an ensemble of strongly interacting Rydberg atoms, which act as superatoms due to the dipole blockade mechanism. We show that Rydberg-dressed 87Rb atoms in a four-level inverted Y-type configuration is highly efficient to generate the refractive index for a probe field, with a symmetric (antisymmetric) profile spatially in the corresponding real (imaginary) part. Comparing with earlier investigations, the present scheme provides a versatile platform to control the system from {PT} -symmetry to non-PT -symmetry via different external parameters, i.e., coupling field detuning, probe field intensity and control field intensity.

  11. Adsorption of formaldehyde and formyl intermediates on Pt, PtRu-, and PtRuMo-alloy surfaces: A density functional study

    NASA Astrophysics Data System (ADS)

    Cahyanto, Wahyu Tri; Shukri, Ganes; Agusta, Mohammad Kemal; Kasai, Hideaki

    2013-02-01

    Stable binding configuration for formaldehyde (H2CO) and formyl (HCO) adsorption on Pt, PtRu, and PtRuMo are studied within the frame of density functional theory (DFT). We address this study to investigate the role of Ru and Mo on the binding characteristic of formaldehyde and formyl adsorption with respect to interaction strength and charge analysis. Several binding conformation on all possible surface adsorption sites are considered in determining the most stable adsorption geometry on three surfaces. Our results show that the presence of Ru in PtRu and Mo in PtRuMo stabilize the formaldehyde and formyl, which are indicated by stronger bond strength. Further electronic structure analysis shows that the addition of Ru in PtRu and Mo in PtRuMo modifies the electronic structure of Pt's surface significantly. The presence of both impurities shifted the derived anti-bonding state - which is originally located below the fermi level in pure Pt surface - to be above the fermi level in PtRu and PtRuMo systems. This fact explains the stronger adsorption found on PtRu & PtRuMo as compared to pure Pt surface.

  12. Synthesis and optical property characterization of elongated AuPt and Pt@Au metal nanoframes

    NASA Astrophysics Data System (ADS)

    Lee, Sangji; Jang, Hee-Jeong; Jang, Ho Young; Hong, Soonchang; Moh, Sang Hyun; Park, Sungho

    2016-02-01

    We report a facile method to synthesize elongated nanoframes consisting of Pt and Au in solution. Pentagonal Au nanorods served as templates and successfully led to an elongated AuPt nanoframe after etching the core Au. Subsequently, the coating of Au around Pt ridges resulted in Pt@Au metal nanoframes. The resulting elongated nanostructure exhibited 5 well-defined ridges continuously connected along the long axis. During the shape evolution from pure Au nanorods to elongated Pt@Au metal nanoframes, their corresponding localized surface plasmon resonance bands were monitored. Especially, unique surface plasmon features were observed for elongated Pt@Au nanoframes where the short-axis oscillation of surface free electrons is strongly coupled but the long-axis oscillation is not coupled among the ridges.We report a facile method to synthesize elongated nanoframes consisting of Pt and Au in solution. Pentagonal Au nanorods served as templates and successfully led to an elongated AuPt nanoframe after etching the core Au. Subsequently, the coating of Au around Pt ridges resulted in Pt@Au metal nanoframes. The resulting elongated nanostructure exhibited 5 well-defined ridges continuously connected along the long axis. During the shape evolution from pure Au nanorods to elongated Pt@Au metal nanoframes, their corresponding localized surface plasmon resonance bands were monitored. Especially, unique surface plasmon features were observed for elongated Pt@Au nanoframes where the short-axis oscillation of surface free electrons is strongly coupled but the long-axis oscillation is not coupled among the ridges. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08200e

  13. Epitaxial oxide bilayer on Pt (001) nanofacets

    NASA Astrophysics Data System (ADS)

    Hennessy, Daniel; Komanicky, Vladimir; Iddir, Hakim; Pierce, Michael S.; Menzel, Andreas; Chang, Kee-Chul; Barbour, Andi; Zapol, Peter; You, Hoydoo

    2012-01-01

    We observed an epitaxial, air-stable, partially registered (2 × 1) oxide bilayer on Pt (001) nanofacets [V. Komanicky, A. Menzel, K.-C. Chang, and H. You, J. Phys. Chem. 109, 23543 (2005)]. The bilayer is made of two half Pt layers; the top layer has four oxygen bonds and the second layer two. The positions and oxidation states of the Pt atoms are determined by analyzing crystal truncation rods and resonance scattering data. The positions of oxygen atoms are determined by density functional theory (DFT) calculations. Partial registry on the nanofacets and the absence of such registry on the extended Pt (001) surface prepared similarly are explained in DFT calculations by strain relief that can be accommodated only by nanoscale facets.

  14. Heavy Lift & Propulsion Technology (HL&PT)

    NASA Video Gallery

    Cris Guidi delivers a presentation from the Heavy Lift & Propulsion Technology (HL&PT) study team on May 25, 2010, at the NASA Exploration Enterprise Workshop held in Galveston, TX. The purpose of ...

  15. Sintering behavior of spin-coated FePt and FePtAu nanoparticles

    NASA Astrophysics Data System (ADS)

    Kang, Shishou; Jia, Zhiyong; Zoto, I.; Reed, D.; Nikles, David E.; Harrell, J. W.; Thompson, Gregory; Mankey, Gary; Krishnamurthy, Vemuru V.; Porcar, L.

    2006-04-01

    FePt and [FePt]95Au5 nanoparticles with an average size of about 4 nm were chemically synthesized and spin coated onto silicon substrates. Samples were subsequently thermally annealed at temperatures ranging from 250 to 500 °C for 30 min. Three-dimensional structural characterization was carried out with small-angle neutron scattering (SANS) and small-angle x-ray diffraction (SAXRD) measurements. For both FePt and [FePt]95Au5 particles before annealing, SANS measurements gave an in-plane coherence length parameter a=7.3 nm, while SAXRD measurements gave a perpendicular coherence length parameter c=12.0 nm. The ratio of c/a is about 1.64, indicating the as-made particle array has a hexagonal close-packed superstructure. For both FePt and FePtAu nanoparticles, the diffraction peaks shifted to higher angles and broadened with increasing annealing temperature. This effect corresponds to a shrinking of the nanoparticle array, followed by agglomeration and sintering of the nanoparticles, resulting in the eventual loss of positional order with increasing annealing temperature. The effect is more pronounced for FePtAu than for FePt. Dynamic coercivity measurements show that the FePtAu nanoparticles have both higher intrinsic coercivity and higher switching volume at the same annealing temperature. These results are consistent with previous studies that show that additive Au both lowers the chemical ordering temperature and promotes sintering.

  16. Facile synthesis of Pt-Pd alloy nanocages and Pt nanorings by templating with Pd nanoplates

    DOE PAGESBeta

    Wang, Xue; Luo, Ming; Huang, Hongwen; Chi, Miaofang; Howe, Jane; Xie, Zhaoxiong; Xia, Younan

    2016-09-06

    We report a facile method for the synthesis of Pt-Pd nanocages and Pt nanorings by conformally coating Pd nanoplates with Pt-based shells using polyol- and water-based protocols, respectively, followed by selective removal of the Pd cores. For the polyol-based system, Pd nanoplates were conformally coated with Pt-Pd alloy shells due to the use of a high reaction temperature of 200 °C and a slow injection rate for the Pt precursor. In comparison, Pt shells were formed on Pd nanoplates (with a larger thickness on the side face than on the top/bottom face) in the water-based system due to the usemore » of a low reaction temperature of 80 °C and the presence of twin boundaries on the side face. As such, the Pd@Pt nanoplates prepared using the polyol- and water-based protocols evolved into Pt-Pd nanocages and Pt nanorings, respectively, when the Pd templates in the cores were selectively removed by wet etching. As a result, the wall thickness of the nanocages and the ridge thickness of the nanorings could be reduced down to 1.1 nm and 1.8 nm, respectively, without breaking the hollow structures.« less

  17. Coating Pt-Ni Octahedra with Ultrathin Pt Shells to Enhance the Durability without Compromising the Activity toward Oxygen Reduction.

    PubMed

    Park, Jinho; Liu, Jingyue; Peng, Hsin-Chieh; Figueroa-Cosme, Legna; Miao, Shu; Choi, Sang-Il; Bao, Shixiong; Yang, Xuan; Xia, Younan

    2016-08-23

    We describe a new strategy to enhance the catalytic durability of Pt-Ni octahedral nanocrystals in the oxygen reduction reaction (ORR) by conformally depositing an ultrathin Pt shell on the surface. The Pt-Ni octahedra were synthesized according to a protocol reported previously and then employed directly as seeds for the conformal deposition of ultrathin Pt shells by introducing a Pt precursor dropwise at 200 °C. The amount of Pt precursor was adjusted relative to the number of Pt-Ni octahedra involved to obtain Pt-Ni@Pt1.5L octahedra of 12 nm in edge length for the systematic evaluation of their chemical stability and catalytic durability compared to Pt-Ni octahedra. Specifically, we compared the elemental compositions of the octahedra before and after treatment with acetic and sulfuric acids. We also examined their electrocatalytic stability toward the ORR through an accelerated durability test by using a rotating disk electrode method. Even after treatment with sulfuric acid for 24 h, the Pt-Ni@Pt1.5L octahedra maintained their original Ni content, whereas 11 % of the Ni was lost from the Pt-Ni octahedra. After 10 000 cycles of ORR, the mass activity of the Pt-Ni octahedra decreased by 75 %, whereas the Pt-Ni@Pt1.5L octahedra only showed a 25 % reduction. PMID:27460459

  18. Copper dusting effects on perpendicular magnetic anisotropy in Pt/Co/Pt tri-layers

    NASA Astrophysics Data System (ADS)

    Parakkat, Vineeth Mohanan; Ganesh, K. R.; Anil Kumar, P. S.

    2016-05-01

    The effect of Cu dusting on perpendicular magnetic anisotropy of sputter grown Pt/Co/Pt stack in which the Cu layer is in proximity with that of Co is investigated in this work. We used magneto optic Kerr effect microscopy measurements to study the variation in the reversal mechanisms in films with Co thicknesses below 0.8nm by systematically varying their perpendicular magnetic anisotropy using controlled Cu dusting. Cu dusting was done separately above and below the cobalt layer in order to understand the role of bottom and top Pt layers in magnetization reversal mechanisms of sputtered Pt/Co/Pt stack. The introduction of even 0.3nm thick Cu layer below the cobalt layer drastically affected the perpendicular magnetic anisotropy as evident from the nucleation behavior. On the contrary, even a 4nm thick top Cu layer had little effect on the reversal mechanism. These observations along with magnetization data was used to estimate the role of top and bottom Pt in the origin of perpendicular magnetic anisotropy as well as magnetization switching mechanism in Pt/Co/Pt thin films. Also, with an increase in the bottom Cu dusting from 0.2 to 0.4nm there was an increase in the number of nucleation sites resulting in the transformation of domain wall patterns from a smooth interface type to a finger like one and finally to maze type.

  19. Atomic Processes in Low Temperature Growth of Pt on Pt(111)

    NASA Astrophysics Data System (ADS)

    Michely, Thomas

    1996-03-01

    STM measurements performed in the temperature range from 20 - 265 K and kinetic Monte Carlo simulations were used to investigate atomic processes during Pt deposition on Pt(111). This approach allows the determination of the activation energy and attempt frequency of Pt-adatom migration on Pt(111) with only a minimum of assumptions and independent of nucleation theory. Moreover, by analysis of the shape and branch thickness of dendritic Pt adatom islands, it is found that atoms attached to just one atom of an island have an asymmetric jump probability towards higher coordinated sites. This asymmetry, which results from non-equivalent hopping paths, gives rise to the preferential growth directions of the dendrites and of the aggregation at preexistent step edges.(The contributions of Michael Hohage, Michael Bott, Markus Morgenstern, Zhengyu Zhang and George Comsa to this work are acknowledged.)

  20. Effects of culture supernatant from Lactobacillus pentosus strain S-PT84 on autonomic nerve activity in rats.

    PubMed

    Beppu, Yoshinori; Izumo, Takayuki; Horii, Yuko; Shen, Jiao; Fujisaki, Yoshiyuki; Nakashima, Toshihiro; Tsuruoka, Nobuo; Nagai, Katsuya

    2012-01-01

    Intestinal administration of various lactobacilli has been reported to affect autonomic neurotransmission, blood pressure, blood glucose, and body weight in rats, however, the mechanisms of action of the lactobacilli remain to be clarified. Therefore, the effect of the culture supernatant of Lactobacillus pentosus strain S-PT84 on the autonomic nerve activity in urethane-anesthetized rats was investigated. Intraduodenal injection of the low-molecular-weight (LMW) fraction (molecules less than 10,000 Da) of the S-PT84 culture supernatant elevated the brown adipose tissue sympathetic nerve activity and reduced the gastric vagal nerve activity. Moreover, intraoral administration of this LMW fraction increased the body temperature of rats above the interscapular brown adipose tissue. These results suggest that the LMW fraction of the S-PT84 culture supernatant affects the autonomic nerve activity and thermogenesis, and that the change in thermogenesis may be caused by the change in the sympathetic nerve activity of brown adipose tissue.

  1. Multifunctional Pt(II) Reagents: Covalent Modifications of Pt Complexes Enable Diverse Structural Variation and In-Cell Detection.

    PubMed

    White, Jonathan D; Haley, Michael M; DeRose, Victoria J

    2016-01-19

    To enhance the functionality of Pt-based reagents, several strategies have been developed that utilize Pt compounds modified with small, reactive handles. This Account encapsulates work done by us and other groups regarding the use of Pt(II) compounds with reactive handles for subsequent elaboration with fluorophores or other functional moieties. Described strategies include the incorporation of substituents for well-known condensation or nucleophilic displacement-type reactions and their use, for example, to tether spectroscopic handles to Pt reagents for in vivo investigation. Other chief uses of displacement-type reactions have included tethering various small molecules exhibiting pharmacological activity directly to Pt, thus adding synergistic effects. Click chemistry-based ligation techniques have also been applied, primarily with azide- and alkyne-appended Pt complexes. Orthogonally reactive click chemistry reactions have proven invaluable when more traditional nucleophilic displacement reactions induce side-reactivity with the Pt center or when systematic functionalization of a larger number of Pt complexes is desired. Additionally, a diverse assortment of Pt-fluorophore conjugates have been tethered via click chemistry conjugation. In addition to providing a convenient synthetic path for diversifying Pt compounds, the use of click-capable Pt complexes has proved a powerful strategy for postbinding covalent modification and detection with fluorescent probes. This strategy bypasses undesirable influences of the fluorophore camouflaged as reactivity due to Pt that may be present when detecting preattached Pt-fluorophore conjugates. Using postbinding strategies, Pt reagent distributions in HeLa and lung carcinoma (NCI-H460) cell cultures were observed with two different azide-modified Pt compounds, a monofunctional Pt(II)-acridine type and a difunctional Pt(II)-neutral complex. In addition, cellular distribution was observed with an alkyne-appended difunctional

  2. CoPt nanoparticles by chemical reduction

    NASA Astrophysics Data System (ADS)

    Wang, H. L.; Zhang, Y.; Huang, Y.; Zeng, Q.; Hadjipanayis, George C.

    2004-05-01

    CoPt nanoparticles with a size of 1-2nm were synthesized by chemical reduction using the solvents of water and alcohol. A phase transformation from the originally disordered face centered cubic (FCC) structure to an ordered face centered tetragonal L10 structure occurred after annealing, which results in the coercivity up to 9kOe because of the high anisotropy of the tetragonal phase (K~2-4×107erg/cm3) (Philos. Mag. 13 (1966) 567; IEEE Trans. Magn. 20 (1984) 1625). HREM images of as-grow Co48Pt52 shows the single-crystalline FCC structure with the shape of columnar and spherical.

  3. Nuclear Data Sheets for {sup 170}Pt

    SciTech Connect

    Baglin, Coral M.

    1999-02-22

    Nuclear structure data pertaining to 170Pt have been compiled and evaluated, and incorporated into the ENSDF data file. This evaluation of170Pt supersedes the previous publication (Coral M. Baglin,Nuclear Data Sheets 77,125 (1996) (literature cutoff date October 1995)), and includes literature available by 17 February 1999. The newly incorporated references are: 98Se20, 98Ki20, 97Ju04, 96Bi07 and 95Au04. Three new data sets have been added, as follows:174Hg ? decay,171Au p decay (1.02 ms), (HI,xn?).

  4. Ion-irradiation induced chemical ordering of FePt and FePtAu nanoparticles

    NASA Astrophysics Data System (ADS)

    Seetala, Naidu V.; Harrell, J. W.; Lawson, Jeremy; Nikles, David E.; Williams, John R.; Isaacs-Smith, Tamara

    2005-12-01

    We have studied the effect of ion-beam irradiation on reducing the ordering temperature of FePt and FePtAu nanoparticles. FePt and FePt(Au14%) 4 nm particles dispersed on a Si-substrate were irradiated by 300 keV Al-ions with a dose of 1 × 1016 ions/cm2 at 43 °C using a water-cooled flange in order to minimize the vacancy migration and voids formation within the collision cascades. Partial chemical ordering has been observed in as-irradiated particles with coercivity of 60-130 Oe. Post-irradiation annealing at 220 °C enhanced chemical ordering in FePt nanoparticles with coercivity of 3500 Oe, magnetic anisotropy of 1.5 × 107 erg/cc, and thermal stability factor of 130. A much higher 375 °C post-irradiation annealing was required in FePtAu, presumably because Au atoms were trapped at Fe/Pt lattice sites at lower temperatures. As the annealing temperature increased, anomalous features in the magnetization reversal curves were observed that disappeared at higher annealing temperatures.

  5. Discovery of the Pt-Based Superconductor LaPt5As.

    PubMed

    Fujioka, Masaya; Ishimaru, Manabu; Shibuya, Taizo; Kamihara, Yoichi; Tabata, Chihiro; Amitsuka, Hiroshi; Miura, Akira; Tanaka, Masashi; Takano, Yoshihiko; Kaiju, Hideo; Nishii, Junji

    2016-08-10

    A novel superconductor, LaPt5As, which exhibits a new crystal structure was discovered by high-pressure synthesis using a Kawai-type apparatus. A superconducting transition temperature was observed at 2.6 K. Depending on the sintering pressure, LaPt5As has superconducting and non-superconducting phases with different crystal structures. A sintering pressure of around 10 GPa is effective to form single-phase superconducting LaPt5As. This material has a very unique crystal structure with an extremely long c lattice parameter of over 60 Å and corner-sharing tetrahedrons composed of network-like Pt layers. Density functional theory calculations have suggested that the superconducting current flows through these Pt layers. Also, this unique layered structure characteristic of LaPt5As is thought to play a key role in the emergence of superconductivity. Furthermore, due to a stacking structure which makes up layers, various structural modifications for the LaPt5As family are conceivable. Since such a high-pressure synthesis using a Kawai-type apparatus is not common in the field of materials science, there is large room for further exploration of unknown phases which are induced by high pressure in various materials. PMID:27461965

  6. Tailoring Curie temperature and magnetic anisotropy in ultrathin Pt/Co/Pt films

    NASA Astrophysics Data System (ADS)

    Parakkat, Vineeth Mohanan; Ganesh, K. R.; Anil Kumar, P. S.

    2016-05-01

    The dependence of perpendicular magnetization and Curie temperature (Tc) of Pt/Co/Pt thin films on the thicknesses of Pt seed (Pts) and presence of Ta buffer layer has been investigated in this work. Pt and Co thicknesses were varied between 2 to 8 nm and 0.35 to 1.31 nm (across the spin reorientation transition thickness) respectively and the Tc was measured using SQUID magnetometer. We have observed a systematic dependence of Tc on the thickness of Pts. For 8nm thickness of Pts the Co layer of 0.35nm showed ferromagnetism with perpendicular anisotropy at room temperature. As the thickness of the Pts was decreased to 2nm, the Tc went down below 250K. XRD data indicated polycrystalline growth of Pts on SiO2. On the contrary Ta buffer layer promoted the growth of Pt(111). As a consequence Ta(5nm)/Pt(3nm)/Co(0.35nm)/Pt(2nm) had much higher Tc (above 300K) with perpendicular anisotropy when compared to the same stack without the Ta layer. Thus we could tune the ferromagnetic Tc and anisotropy by varying the Pts thickness and also by introducing Ta buffer layer. We attribute these observations to the micro-structural evolution of Pts layer which hosts the Co layer.

  7. Discovery of the Pt-Based Superconductor LaPt5As.

    PubMed

    Fujioka, Masaya; Ishimaru, Manabu; Shibuya, Taizo; Kamihara, Yoichi; Tabata, Chihiro; Amitsuka, Hiroshi; Miura, Akira; Tanaka, Masashi; Takano, Yoshihiko; Kaiju, Hideo; Nishii, Junji

    2016-08-10

    A novel superconductor, LaPt5As, which exhibits a new crystal structure was discovered by high-pressure synthesis using a Kawai-type apparatus. A superconducting transition temperature was observed at 2.6 K. Depending on the sintering pressure, LaPt5As has superconducting and non-superconducting phases with different crystal structures. A sintering pressure of around 10 GPa is effective to form single-phase superconducting LaPt5As. This material has a very unique crystal structure with an extremely long c lattice parameter of over 60 Å and corner-sharing tetrahedrons composed of network-like Pt layers. Density functional theory calculations have suggested that the superconducting current flows through these Pt layers. Also, this unique layered structure characteristic of LaPt5As is thought to play a key role in the emergence of superconductivity. Furthermore, due to a stacking structure which makes up layers, various structural modifications for the LaPt5As family are conceivable. Since such a high-pressure synthesis using a Kawai-type apparatus is not common in the field of materials science, there is large room for further exploration of unknown phases which are induced by high pressure in various materials.

  8. Heterobimetallic lantern complexes that couple antiferromagnetically through noncovalent Pt···Pt interactions.

    PubMed

    Baddour, Frederick G; Fiedler, Stephanie R; Shores, Matthew P; Golen, James A; Rheingold, Arnold L; Doerrer, Linda H

    2013-05-01

    A series of Pt-based heterobimetallic lantern complexes of the form [PtM(SAc)4(OH2)] (M = Co, 1; Ni, 2; Zn, 3) were prepared using a facile, single-step procedure. These hydrated species were reacted with 3-nitropyridine (3-NO2py) to prepare three additional lantern complexes, [PtM(SAc)4(3-NO2py)] (M = Co, 4; Ni, 5; Zn, 6), or alternatively dried in vacuo to the dehydrated species [PtM(SAc)4] (M = Co, 7; Ni, 8; Zn, 9). The Co- and Ni-containing species exhibit Pt-M bonding in solution and the solid state. In the structurally characterized compounds 1-6, the lantern units form dimers in the solid state via a short Pt···Pt metallophilic interaction. Antiferromagnetic coupling between 3d metal ions in the solid state through noncovalent metallophilic interactions was observed for all the paramagnetic lantern complexes prepared, with J-coupling values of -12.7 cm(-1) (1), -50.8 cm(-1) (2), -6.0 cm(-1) (4), and -12.6 cm(-1) (5). The Zn complexes 3 and 6 also form solid-state dimers, indicating that the formation of short Pt···Pt interactions in these complexes is not predicated on the presence of a paramagnetic 3d metal ion. These contacts and the resultant antiferromagnetic coupling are also not unique to heterobimetallic lantern complexes with axially coordinated H2O or the previously reported thiobenzoate supporting ligand.

  9. Pt-Ni and Pt-Co Catalyst Synthesis Route for Fuel Cell Applications

    NASA Technical Reports Server (NTRS)

    Firdosy, Samad A.; Ravi, Vilupanur A.; Valdez, Thomas I.; Kisor, Adam; Narayan, Sri R.

    2013-01-01

    Oxygen reduction reactions (ORRs) at the cathode are the rate-limiting step in fuel cell performance. The ORR is 100 times slower than the corresponding hydrogen oxidation at the anode. Speeding up the reaction at the cathode will improve fuel cell efficiency. The cathode material is generally Pt powder painted onto a substrate (e.g., graphite paper). Recent efforts in the fuel cell area have focused on replacing Pt with Pt-X alloys (where X = Co, Ni, Zr, etc.) in order to (a) reduce cost, and (b) increase ORR rates. One of these strategies is to increase ORR rates by reducing the powder size, which would result in an increase in the surface area, thereby facilitating faster reaction rates. In this work, a process has been developed that creates Pt-Ni or Pt-Co alloys that are finely divided (on the nano scale) and provide equivalent performance at lower Pt loadings. Lower Pt loadings will translate to lower cost. Precursor salts of the metals are dissolved in water and mixed. Next, the salt mixtures are dried on a hot plate. Finally, the dried salt mixture is heattreated in a furnace under flowing reducing gas. The catalyst powder is then used to fabricate a membrane electrode assembly (MEA) for electrochemical performance testing. The Pt- Co catalyst-based MEA showed comparable performance to an MEA fabri cated using a standard Pt black fuel cell catalyst. The main objective of this program has been to increase the overall efficiencies of fuel cell systems to support power for manned lunar bases. This work may also have an impact on terrestrial programs, possibly to support the effort to develop a carbon-free energy source. This catalyst can be used to fabricate high-efficiency fuel cell units that can be used in space as regenerative fuel cell systems, and terrestrially as primary fuel cells. Terrestrially, this technology will become increasingly important when transition to a hydrogen economy occurs.

  10. Sintering Behavior of Spin-coated FePt and FePtAu Nanoparticles

    SciTech Connect

    Kang, Shishou; Jia, Zhiyong; Zoto, Ilir; Reed, R. C.; Nikles, David E.; Harrell, J. W.; Vemuru, Krishnamurthy V; Porcar, L.

    2006-01-01

    FePt and [FePt]{sub 95}Au{sub 5} nanoparticles with an average size of about 4 nm were chemically synthesized and spin coated onto silicon substrates. Samples were subsequently thermally annealed at temperatures ranging from 250 to 500 C for 30 min. Three-dimensional structural characterization was carried out with small-angle neutron scattering (SANS) and small-angle x-ray diffraction (SAXRD) measurements. For both FePt and [FePt]{sub 95}Au{sub 5} particles before annealing, SANS measurements gave an in-plane coherence length parameter a = 7.3 nm, while SAXRD measurements gave a perpendicular coherence length parameter c = 12.0 nm. The ratio of c/a is about 1.64, indicating the as-made particle array has a hexagonal close-packed superstructure. For both FePt and FePtAu nanoparticles, the diffraction peaks shifted to higher angles and broadened with increasing annealing temperature. This effect corresponds to a shrinking of the nanoparticle array, followed by agglomeration and sintering of the nanoparticles, resulting in the eventual loss of positional order with increasing annealing temperature. The effect is more pronounced for FePtAu than for FePt. Dynamic coercivity measurements show that the FePtAu nanoparticles have both higher intrinsic coercivity and higher switching volume at the same annealing temperature. These results are consistent with previous studies that show that additive Au both lowers the chemical ordering temperature and promotes sintering.

  11. Preparation of onion-like Pt-terminated Pt-Cu bimetallic nano-sized electrocatalysts for oxygen reduction reaction in fuel cells

    NASA Astrophysics Data System (ADS)

    Lim, Taeho; Kim, Ok-Hee; Sung, Yung-Eun; Kim, Hyun-Jong; Lee, Ho-Nyun; Cho, Yong-Hun; Kwon, Oh Joong

    2016-06-01

    Onion-like Pt-terminated Pt-Cu bimetallic nano-sized electrocatalysts (Pt/Cu/Pt/C) were synthesized by using an electroless deposition method. The synthesized Pt/Cu/Pt/C consisted of a Pt-enriched shell, a sandwiched Pt-Cu alloy layer, and a Pt core. The Pt/Cu/Pt/C showed higher electrocatalytic activity toward oxygen reduction reaction in half-cell test than that of commercial Pt/C due to an electronic structure change in the Pt-enriched shell, resulting from the sandwiched Pt-Cu alloy layer underneath. The stability of the Pt/Cu/Pt/C was examined by using both half-cell and single-cell degradation tests. In both tests, the Pt/Cu/Pt/C exhibited stronger resistance to catalyst degradation than that of the commercial Pt/C. It is notable that cell performance with the Pt/Cu/Pt/C was fully recovered by N2 purging after single-cell degradation testing, indicating there was no permanent damage to the electrocatalyst during the test. It is suggested that thermodynamically-stable structure of the Pt/Cu/Pt/C contributed to the improved stability.

  12. Efficient Pt catalysts for polymer electrolyte fuel cells

    SciTech Connect

    Fournier, J.; Gaubert, G.; Tilquin, J.Y.

    1996-12-31

    Commercialization of polymer electrolyte fuel cells (PEFCs) requires an important decrease in their production cost. Cost reduction for the electrodes principally concerns the decrease in the amount of Pt catalyst necessary for the functioning of the PEFC without affecting cell performance. The first PEFCs used in the Gemini Space Program had a loading of 4-10 mg pt/cm{sup 2}. The cost of the electrodes was drastically reduced when pure colloidal Pt was replaced by Pt supported on carbon (Pt/C) with a Pt content of 0.4 Mg/cm{sup 2}. Since the occurrence of that breakthrough, many studies have been aimed at further lowering the Pt loading. Today, the lowest loadings reported for oxygen reduction are of the order of 0.05 mg pt/cm{sup 2}. The carbon support of commercial catalysts is Vulcan XC-72 from Cabot, a carbon black with a specific area of 254 m{sup 2}/g. Graphites with specific areas ranging from 20 to 305 m{sup 2}/g are now available from Lonza. The first aim of the present study was to determine the catalytic properties for 02 reduction of Pt supported on these high specific area graphites. The second aim was to use Pt inclusion synthesis on these high area graphites, and to measure the catalytic performances of these materials. Lastly, this same Pt-inclusion synthesis was extended even for use with Vulcan and Black Pearls as substrates (two carbon blacks from Cabot). All these catalysts have been labelled Pt-included materials to distinguish them from the Pt-supported ones. It will be shown that the reduced Pt content Pt-included materials obtained with high specific area substrates a are excellent catalysts for oxygen reduction, especially at high currents. Therefore, Pt inclusion synthesis appears to be a new method to decrease the cathodic Pt loading.

  13. Effect of ferroelectricity on electron transport in Pt/BaTiO3/Pt tunnel junctions.

    PubMed

    Velev, J P; Duan, Chun-Gang; Belashchenko, K D; Jaswal, S S; Tsymbal, E Y

    2007-03-30

    Based on first-principles calculations, we demonstrate the impact of the electric polarization on electron transport in ferroelectric tunnel junctions (FTJs). Using a Pt/BaTiO3/Pt FTJ as a model system, we show that the polarization of the BaTiO3 barrier leads to a substantial drop in the tunneling conductance due to changes in the electronic structure driven by ferroelectric displacements. We find a sizable change in the transmission probability across the Pt/BaTiO3 interface with polarization reversal, a signature of the electroresistance effect. These results reveal exciting prospects that FTJs offer as resistive switches in nanoscale electronic devices. PMID:17501233

  14. Sulfonate group-modified FePtCu nanoparticles as a selective probe for LDI-MS analysis of oligopeptides from a peptide mixture and human serum proteins.

    PubMed

    Kawasaki, Hideya; Akira, Tarui; Watanabe, Takehiro; Nozaki, Kazuyoshi; Yonezawa, Tetsu; Arakawa, Ryuichi

    2009-11-01

    Bare FePtCu nanoparticles (NPs) are first prepared for laser desorption/ionization mass spectroscopy (LDI-MS) analysis as affinity probes to selectively trap oppositely charged analytes from a sample solution. Our present results demonstrate bare FePtCu NPs to be a potentially useful matrix for surface-assisted laser desorption/ionization mass spectroscopy (SALDI-MS), for the analysis of small proteins and peptides. The upper detectable mass range of peptides was approximately 5 kDa, and the detection limit for peptides approximately 5 fmol. Sulfonate group-modified FePtCu nanoparticles (FePtCu-SO(3)(-) NPs), with ionization being independent of the solution pH, can interact with a positively charged analyte, and the analyte-bound NPs can be separated from the reaction supernatant by centrifugation or an external magnetic field. An oligopeptide, Gly-Gly-Tyr-Arg (GGYR) from an oligopeptide mixture containing Asp-Asp-Asp-Asp (DDDD), Gly-Gly-Gly-Gly (GGGG) and GGYR, was detected using SALDI-MS with FePtCu-SO(3)(-) NPs employing electrostatic interaction. Furthermore, FePtCu-SO(3)(-) NPs can detect lysozyme (Lyz) in human serum through the electrostatic attraction between positively charged Lyz and FePtCu-SO(3)(-) NPs at pH 8, while detection of negatively charged albumin in human serum is not possible.

  15. PT3 Papers. [SITE 2001 Section].

    ERIC Educational Resources Information Center

    Pierson, Melissa, Ed.; Thompson, Mary, Ed.; Adams, Angelle, Ed.; Beyer, Evelyn, Ed.; Cheriyan, Saru, Ed.; Starke, Leslie, Ed.

    This document contains the papers on the PT3 (Preparing Tomorrow's Teachers to use Technology) program from the SITE (Society for Information Technology & Teacher Education) 2001 conference. Topics covered include: modeling instruction with modern information and communications technology; transforming computer coursework for preservice teachers;…

  16. PT-symmetric quantum electrodynamics and unitarity.

    PubMed

    Milton, Kimball A; Abalo, E K; Parashar, Prachi; Pourtolami, Nima; Wagner, J

    2013-04-28

    More than 15 years ago, a new approach to quantum mechanics was suggested, in which Hermiticity of the Hamiltonian was to be replaced by invariance under a discrete symmetry, the product of parity and time-reversal symmetry, PT. It was shown that, if PT is unbroken, energies were, in fact, positive, and unitarity was satisfied. Since quantum mechanics is quantum field theory in one dimension--time--it was natural to extend this idea to higher-dimensional field theory, and in fact an apparently viable version of PT-invariant quantum electrodynamics (QED) was proposed. However, it has proved difficult to establish that the unitarity of the scattering matrix, for example, the Källén spectral representation for the photon propagator, can be maintained in this theory. This has led to questions of whether, in fact, even quantum mechanical systems are consistent with probability conservation when Green's functions are examined, since the latter have to possess physical requirements of analyticity. The status of PT QED will be reviewed in this paper, as well as the general issue of unitarity.

  17. New candidates for the Pt8Ti structures in intermetallics

    NASA Astrophysics Data System (ADS)

    Gilmartin, Erin; Corbitt, Jacqueline; Hart, Gus

    2008-03-01

    The only known intermetallic structure with an 8:1 stoichiometry is that of Pt8Ti. Because of its uniqueness, this structure has been studied in Pt, Pd, and Ni rich systems. However, these metals have only been paired with a handful of other elements. Are there more elements that when alloyed with Pt, Pd, or Ni order with the Pt8Ti structure? We explored 40 different Pd- and Pt-based binary systems. We calculated their formation enthalpies for the Pt8Ti structure, compared the value to the tie line between pure Pd/Pt and experimentally-observed ground states. We find that there are other (beyond those experimentally observed) possible alloys with this structure. These new Pt/Pd-rich alloys could fin application in the jewelry and catalysis industries.

  18. Surface structure and chemistry of Pt/Cu/Pt(1 1 1) near surface alloy model catalyst in CO

    NASA Astrophysics Data System (ADS)

    Zeng, Shibi; Nguyen, Luan; Cheng, Fang; Liu, Lacheng; Yu, Ying; Tao, Franklin (Feng)

    2014-11-01

    Near surface alloy (NSA) model catalyst Pt/Cu/Pt(1 1 1) was prepared on Pt(1 1 1) through a controlled vapor deposition of Cu atoms. Different coordination environments of Pt atoms of the topmost Pt layer with the underneath Cu atoms in the subsurface result in different local electronic structures of surface Pt atoms. Surface structure and chemistry of the NAS model catalyst in Torr pressure of CO were studied with high pressure scanning tunneling microscopy (HP-STM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In Torr pressure of CO, the topmost Pt layer of Pt/Cu/Pt(1 1 1) is restructured to thin nanoclusters with size of about 1 nm. Photoemission feature of O 1s of CO on Pt/Cu/Pt(1 1 1) suggests CO adsorbed on both edge and surface of these formed nanoclusters. This surface is active for CO oxidation. Atomic layers of carbon are formed on Pt/Cu/Pt(1 1 1) at 573 K in 2 Torr of CO.

  19. Reactivity of Two-Dimensional Au9, Pt9, and Au18Pt18 against Common Molecules.

    PubMed

    Takahashi, Lauren; Takahashi, Keisuke

    2016-09-19

    Adsorption of common molecules over two-dimensional Au9, Pt9, and Au18Pt18 is investigated with implementation of first-principles calculations. In general, it is found that Pt9 and Au18Pt18 exhibit low adsorption energies where Au18Pt18 preserves the structural integrity of the molecule and surface. In particular, adsorption of molecules onto Au18Pt18 frequently results in low adsorption energies and high reactivity with minor surface reconstruction of Au18Pt18 and average bond lengths of molecules. The decrease in adsorption energy can be attributed to the presence of platinum, while gold can be considered responsible for structural stability. In addition, molecule dissociation is observed in the cases of H2, HCl, CH4, SO, and SO2 when Pt atoms are involved. Thus, two-dimensional Au9, Pt9, and Au18Pt18 show low adsorption energies against common molecules, reflecting adsorption energies observed in small Au and Pt clusters. These results demonstrate that Au18Pt18 can successfully utilize the low adsorption energies associated with platinum while preserving the integrity of the surface structure using gold atoms, making it possible to adsorb desired molecules using select areas of the Au18Pt18 surface. PMID:27608367

  20. Hydrogen-induced ferromagnetism in two-dimensional Pt dichalcogenides

    NASA Astrophysics Data System (ADS)

    Manchanda, P.; Enders, A.; Sellmyer, D. J.; Skomski, R.

    2016-09-01

    Electronic, structural, and magnetic properties of Pt dichalcogenide monolayers are investigated using first-principle calculations. We find that hydrogenation lifts the spin degeneracy in narrow antibonding Pt 5 d subband electrons and transforms the nonmagnetic semiconductors Pt X2(X =S ,Se ,Te ) into ferromagnetic metals, Pt X2 -1H; neither strain nor thin-film edges are necessary to support the transition. The trend towards ferromagnetism is most pronounced for X =S , decreasing with increasing atomic weight of the chalcogens.

  1. Surface diffusion modes for Pt dimers and trimers on Pt(001)

    SciTech Connect

    Kellogg, G.L.; Voter, A.F. Los Alamos National Laboratory, Los Alamos, New Mexico )

    1991-07-29

    Field-ion-microscope observations and molecular statics calculations using embedded-atom-method potentials have identified the surface diffusion modes for Pt dimers and trimers on Pt(001). Dimers migrate by a series of displacements involving exchange between one of the dimer atoms and a substrate atom and have a lower activation barrier for diffusion than monomers. Trimer diffusion involves both exchange and hopping displacements and has an activation barrier comparable to monomers.

  2. Unusual cluster shapes and directional bonding of an fcc metal: Pt/Pt(111).

    PubMed

    Schmid, Michael; Garhofer, Andreas; Redinger, Josef; Wimmer, Florian; Scheiber, Philipp; Varga, Peter

    2011-07-01

    Small clusters of Pt adatoms grown on Pt(111) exhibit a preference for the formation of linear chains, which cannot be explained by simple diffusion-limited aggregation. Density functional theory calculations show that short chains are energetically favorable to more compact configurations due to strong directional bonding by d(z)(2)-like orbitals, explaining the stability of the chains. The formation of the chains is governed by substrate distortions, leading to funneling towards the chain ends. PMID:21797553

  3. Simulation of electroforming of the Pt/NiO/Pt switching memory structure

    NASA Astrophysics Data System (ADS)

    Sysun, V. I.; Sysun, I. V.; Boriskov, P. P.

    2016-05-01

    We analyze experimental data on a transient thermal electroforming of a Pt/NiO/Pt unipolar memory switching structure. Numerical simulation of this process shows that the channel can be identified with the melting region of nickel oxide, in which its cross section is determined by the maximal breakdown current, a considerable contribution to which can come from a parasitic capacitance. Rough analytic approximations are given for estimating the channel formation parameters.

  4. Structural and magnetic properties of the ordered FePt{sub 3}, FePt and Fe{sub 3}Pt nanoparticles

    SciTech Connect

    Liu, Yang; Jiang, Yuhong; Zhang, Xiaolong; Wang, Yaxin; Zhang, Yongjun; Liu, Huilian; Zhai, Hongju; Liu, Yanqing; Yang, Jinghai; Yan, Yongsheng

    2014-01-15

    The Fe{sub x}Pt{sub 100−x} nanoparticles (NPs) with different nominal atomic rations (30≤x≤80) were synthesized at 700 °C by the sol–gel method. The structure, morphology and magnetic properties of the samples were investigated. When the Fe content in the Fe–Pt alloy NPs was 30 at%, FePt{sub 3} NPs were successfully synthesized. With the increase in Fe content up to 50 at%, it was found that the superlattice reflections (0 0 1) and (1 1 0) appeared, which indicated the formation of the L1{sub 0}-FePt phase. Meanwhile, the FePt{sub 3} fraction was reduced. When the Fe content increased to 60 at%, single-phase L1{sub 0}-FePt NPs were synthesized. The coercivity (Hc), saturation magnetization (Ms) and chemical order parameter S for Fe{sub 60}Pt{sub 40} NPs were as high as 10,200 Oe, 17.567 emu/g and 0.928, respectively. With the further increase of the Fe content to 80 at%, only Fe{sub 3}Pt phase existed and the Hc of the Fe{sub 3}Pt NPs decreased drastically to 360 Oe. - Graphical abstract: Fe{sub 3}Pt, FePt and FePt{sub 3} nanoparticles was obtained by sol–gel method. The effect of iron and platinum content on structural and magnetic properties of the FePt nanoparticles was investigated. Display Omitted - Highlights: • L1{sub 2}-FePt{sub 3}, L1{sub 0}-FePt and L1{sub 2}-Fe{sub 3}Pt NPs were synthesized by sol–gel method. • The chemical order parameter S affects the magnetic properties of the Fe–Pt alloy. • Structural and magnetic properties of the Fe–Pt alloy NPs were studied. • The synthetic route in this study will open up the possibilities of practical use.

  5. Magnetism in single-crystalline CePtSn.

    SciTech Connect

    Bordallo, H. N.; Chang, S.; Lacerda, A. H.; Nakotte, H.; Takabatake, T.; Torikachvili, M. S.

    1999-08-04

    CePtSn exhibits two antiferromagnetic transitions at low temperatures. We report on magnetoresistance and in magnetization studies of single-crystalline CePtSn in magnetic fields up to 18 T. The data were taken to establish the magnetic phase diagrams for CePtSn in fields applied along the principal directions.

  6. Effects of thermal magnetic fluctuations on spin transport in Pt

    NASA Astrophysics Data System (ADS)

    Freeman, Ryan; Zholud, Andrei; Cao, Rongxing; Urazhdin, Sergei

    Despite extensive studies and applications of Pt as a spin Hall material in spintronic devices, its spin-dependent transport properties are still debated. We present a comprehensive experimental study of spin transport in Pt, utilizing measurements of giant magnetoresistance (GMR) in nanoscale Permalloy (Py)-based spin valves with Pt inserted in the nonmagnetic spacer. The spin diffusion length and the interfacial spin flipping coefficients are extracted from the dependence of MR on the Pt thickness. For samples with Pt separated from Py by Cu spacers, the spin diffusion length is 6 nm at 7K, and decreases to 3 nm at room temperature. The interfacial spin flipping decreases with increasing temperature, resulting in nonmonotonic temperature dependence of MR in samples with thin Pt. In contrast, in samples with Pt in direct contact with Py, we do not observe such a nonmonotonic dependence, and the spin diffusion length is significantly larger than in samples with Pt surrounded by Cu spacers. Our results indicate a large effect of the giant paramagnetic fluctuations in the nearly ferromagnetic Pt. These fluctuations are suppressed due to the proximity magnetism when Pt is in contact with Py, resulting in enhanced spin diffusion length and reduced spin flipping at the Pt interfaces. These observations indicate the need for a critical revision of spin transport and spin Hall-related properties of Pt-based structures. Supported by NSF ECCS-1305586.

  7. Probing the solvent shell with 195Pt chemical shifts: density functional theory molecular dynamics study of Pt(II) and Pt(IV) anionic complexes in aqueous solution.

    PubMed

    Truflandier, Lionel A; Autschbach, Jochen

    2010-03-17

    Ab initio molecular dynamics (aiMD) simulations based on density functional theory (DFT) were performed on a set of five anionic platinum complexes in aqueous solution. (195)Pt nuclear magnetic shielding constants were computed with DFT as averages over the aiMD trajectories, using the two-component relativistic zeroth-order regular approximation (ZORA) in order to treat relativistic effects on the Pt shielding tensors. The chemical shifts obtained from the aiMD averages are in good agreement with experimental data. For Pt(II) and Pt(IV) halide complexes we found an intermediate solvent shell interacting with the complexes that causes pronounced solvent effects on the Pt chemical shifts. For these complexes, the magnitude of solvent effects on the Pt shielding constant can be correlated with the surface charge density. For square-planar Pt complexes the aiMD simulations also clearly demonstrate the influence of closely coordinated non-equatorial water molecules on the Pt chemical shift, relating the structure of the solution around the complex to the solvent effects on the metal NMR chemical shift. For the complex [Pt(CN)(4)](2-), the solvent effects on the Pt shielding constant are surprisingly small.

  8. Modification of Pt/Co/Pt film properties by ion irradiation

    NASA Astrophysics Data System (ADS)

    Avchaciov, K. A.; Ren, W.; Djurabekova, F.; Nordlund, K.; Sveklo, I.; Maziewski, A.

    2015-09-01

    We studied the structural modifications of a Pt/Co/Pt trilayer epitaxial film under Ga+ 30-keV ion irradiation by means of classical molecular dynamics and Monte Carlo simulations. The semiclassical tight-binding second-moment approximation potential was adjusted to reproduce the enthalpies of formation, the lattice constants, and the order-disorder transition temperatures for Co-Pt alloys. We found that during irradiation, the sandwich-type Pt(fcc)/Co(hcp)/Pt(fcc) film structure underwent a transition to the new solid solution α -Co /Pt (fcc ) phase. Our analysis of the short-range order indicates the formation, within a nanosecond time scale, of a homogeneous chemically disordered solution. The longer time-scale simulations employing a Monte Carlo algorithm demonstrated that the transition from the disordered phase to the ordered L 10 and L 12 phases was also possible but not significant for the changes in perpendicular magnetic anisotropy (PMA) observed experimentally. The strain analysis showed that the Co layer was under tensile strain in the lateral direction at the fluences of 1.5 ×1014-3.5 ×1014ionscm -2 ; this range of fluences corresponds to the appearance of PMA. This strain was induced in the initially relaxed hcp Co layer due to its partial transformation to the fcc phase and to the influence of atomic layers with larger lattice constants at upper/lower interfaces.

  9. Alternative alloys for platinum jewelry? New structures in Pt-Hf and Pt-Mo

    NASA Astrophysics Data System (ADS)

    Gilmartin, Erin; Corbitt, Jacqueline; Hart, Gus

    2008-10-01

    The only known intermetallic structure with an 8:1 stoichiometry is that of Pt8Ti. It is intriguing that an ordered compound would occur at such low concentrations of the minority atom. But this structure occurs in about a dozen binary intermetallic systems. The formation of an ordered structure can significantly enhance the performance of the material, particularly the hardness. Pt- and Pd-rich ordered structures have been experimentally studied in the systems Pt/Pd-X where X is Ti, V, Cr, Zr, Nb, M, Hf, Ta, and W. We took a broader look at 80 Pt/Pd rich alloys to find new candidates for the 8:1 structure and have found about 20. In order to verify our predictions, we used the cluster expansion to find the stable structures. We first applied the cluster expansion to Pt-Hf and Pt-Mo because these two candidates are the most likely to form the 8:1 structure. These new candidates can have applications in the jewelry and catalysis industries.

  10. An evaluation of Pt sulfite acid (PSA) as precursor for supported Pt catalysts

    SciTech Connect

    Regalbuto, J.R.; Ansel, O.; Miller, J.T.

    2010-11-12

    As a catalyst precursor, platinum sulfite acid (PSA) is easy to use and not relatively expensive, and is a potentially attractive precursor for many types of supported catalysts. The ultimate usefulness for many catalyst applications will depend on the extent that Pt can be dispersed and sulfur eliminated. To our knowledge, there exists no detailed characterization in the catalysis literature of PSA and the nanoparticulate Pt phases derived from it during catalyst pretreatment. To this end a series of supports including alumina, silica, magnesia, niobia, titania, magnesia and carbon were contacted with PSA solutions and subsequently analyzed with extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) analysis, and x-ray photoelectron spectroscopy (XPS) to characterize the Pt species formed upon impregnation, calcination, and reduction. While all catalysts show retention of some S, reasonably small particle sizes with relatively little Pt-S can in some instances be produced using PSA. The amount of retained sulfur appears to decrease with decreasing surface acidity, although even the most acidic supports (niobia and silica) display some storage of S even while only Pt-O bands are observed after calcination or reoxidation. More sulfur was eliminated by high temperature calcinations followed by reduction in hydrogen, at the expense of increasing Pt particle size.

  11. Alloy Cu3Pt nanoframes through the structure evolution in Cu-Pt nanoparticles with a core-shell construction

    PubMed Central

    Han, Lin; Liu, Hui; Cui, Penglei; Peng, Zhijian; Zhang, Suojiang; Yang, Jun

    2014-01-01

    Noble metal nanoparticles with hollow interiors and customizable shell compositions have immense potential for catalysis. Herein, we present an unique structure transformation phenomenon for the fabrication of alloy Cu3Pt nanoframes with polyhedral morphology. This strategy starts with the preparation of polyhedral Cu-Pt nanoparticles with a core-shell construction upon the anisotropic growth of Pt on multiply twinned Cu seed particles, which are subsequently transformed into alloy Cu3Pt nanoframes due to the Kirkendall effect between the Cu core and Pt shell. The as-prepared alloy Cu3Pt nanoframes possess the rhombic dodecahedral morphology of their core-shell parents after the structural evolution. In particular, the resulting alloy Cu3Pt nanoframes are more effective for oxygen reduction reaction but ineffective for methanol oxidation reaction in comparison with their original Cu-Pt core-shell precursors. PMID:25231376

  12. Dealloying of mesoporous PtCu alloy film for the synthesis of mesoporous Pt films with high electrocatalytic activity.

    PubMed

    Li, Cuiling; Malgras, Victor; Aldalbahi, Ali; Yamauchi, Yusuke

    2015-02-01

    Mesoporous Pt film with highly electrocatalytic activity is successfully synthesized by dealloying of mesoporous PtCu alloy film prepared through electrochemical micelle assembly. The resulting mesoporous electrode exhibits high current density and superior stability toward the methanol oxidation reaction.

  13. Monofunctional Platinum (PtII) Compounds - Shifting the Paradigm in Designing New Pt-based Anticancer Agents.

    PubMed

    Chong, Shu Xian; Au-Yeung, Steve Chik Fun; To, Kenneth Kin Wah

    2016-01-01

    Platinum (Pt)-based anticancer drugs, exemplified by cisplatin, are key components in combination chemotherapy. However, their effective use is hindered by toxicity and emergence of drug resistance. They bind to DNA and mainly form the Pt-GG diadduct, subsequently leading to apoptosis to mediate cell death. On the other hand, the Pt drug -proteins and -metabolites interactions, which involve the reaction between Pt and sulfur sites located in protein side chains and important bionucleophiles (e.g., glutathione), are responsible for the toxicity and drug resistance problem. Therefore, carefully designed coordinating ligands may provide the means of fine tuning the electronic environment around the core Pt atom and allow the resulting Pt compounds to bind with the DNA in a different manner. This may produce alternative cell death mechanisms in cancer cells, thereby circumventing Pt resistance. This article reviewed the recent development in monofunctional Pt complexes and their prospects in becoming a new generation of anticancer drugs.

  14. Preparation of Pt Nanocatalyst on Carbon Materials via a Reduction Reaction of a Pt Precursor in a Drying Process.

    PubMed

    Lee, Jae-Young; Lee, Woo-Kum; Rim, Hyung-Ryul; Joung, Gyu-Bum; Weidner, John W; Lee, Hong-Ki

    2016-06-01

    Platinum (Pt) nanocatalyst for a proton-exchange membrane fuel cell (PEMFC) was prepared on a carbon black particle or a graphite particle coated with a nafion polymer via a reduction of platinum(II) bis(acetylacetonate) denoted as Pt(acac)2 as a Pt precursor in a drying process. Sublimed Pt(acac)2 adsorbed on the nafion-coated carbon materials was reduced to Pt nanoparticles in a glass reactor at 180 degrees C of N2 atmosphere. The morphology of Pt nanoparticles on carbon materials was observed by scanning electron microscopy (SEM) and the distribution of Pt nanoparticles was done by transmission electron microscopy (TEM). The particle size was estimated by analyzing the TEM image using an image analyzer. It was found that nano-sized Pt particles were deposited on the surface of carbon materials, and the number density and the average particle size increased with increasing reduction time. PMID:27427723

  15. Alloy Cu3Pt nanoframes through the structure evolution in Cu-Pt nanoparticles with a core-shell construction

    NASA Astrophysics Data System (ADS)

    Han, Lin; Liu, Hui; Cui, Penglei; Peng, Zhijian; Zhang, Suojiang; Yang, Jun

    2014-09-01

    Noble metal nanoparticles with hollow interiors and customizable shell compositions have immense potential for catalysis. Herein, we present an unique structure transformation phenomenon for the fabrication of alloy Cu3Pt nanoframes with polyhedral morphology. This strategy starts with the preparation of polyhedral Cu-Pt nanoparticles with a core-shell construction upon the anisotropic growth of Pt on multiply twinned Cu seed particles, which are subsequently transformed into alloy Cu3Pt nanoframes due to the Kirkendall effect between the Cu core and Pt shell. The as-prepared alloy Cu3Pt nanoframes possess the rhombic dodecahedral morphology of their core-shell parents after the structural evolution. In particular, the resulting alloy Cu3Pt nanoframes are more effective for oxygen reduction reaction but ineffective for methanol oxidation reaction in comparison with their original Cu-Pt core-shell precursors.

  16. One-Step Synthesis of Pt/Graphene Composites from Pt Acid Dissolved Ethanol via Microwave Plasma Spray Pyrolysis

    NASA Astrophysics Data System (ADS)

    Jo, Eun Hee; Chang, Hankwon; Kim, Sun Kyung; Choi, Ji-Hyuk; Park, Su-Ryeon; Lee, Chong Min; Jang, Hee Dong

    2016-09-01

    Pt nanoparticles-laden graphene (Pt/GR) composites were synthesized in the gas phase from a mixture of ethanol and Pt precursor by microwave plasma spray pyrolysis. The morphology of Pt/GR composites has the shape of wrinkled sheets of paper, while Pt nanoparticles (Pt NPs) that are less than 2.6 nm in the mean diameter are uniformly well deposited on the surface of GR sheets stacked in only three layers. The Pt/GR composite prepared with 20 wt% of Pt had the highest specific surface area and electrochemical surface area of up to 402 m2 g‑1 and 77 m2 g‑1 (Pt), respectively. In addition, the composite showed superior electrocatalytic activity compared with commercial Pt-carbon black. The excellent electrocatalytic activity was attributed to the high specific surface area and electrochemical surface area of the Pt/GR composite directly produced by microwave plasma spray pyrolysis. Thus, it is clearly expected that the Pt/GR composite is a promising material for DMFC catalysts.

  17. One-Step Synthesis of Pt/Graphene Composites from Pt Acid Dissolved Ethanol via Microwave Plasma Spray Pyrolysis.

    PubMed

    Jo, Eun Hee; Chang, Hankwon; Kim, Sun Kyung; Choi, Ji-Hyuk; Park, Su-Ryeon; Lee, Chong Min; Jang, Hee Dong

    2016-09-13

    Pt nanoparticles-laden graphene (Pt/GR) composites were synthesized in the gas phase from a mixture of ethanol and Pt precursor by microwave plasma spray pyrolysis. The morphology of Pt/GR composites has the shape of wrinkled sheets of paper, while Pt nanoparticles (Pt NPs) that are less than 2.6 nm in the mean diameter are uniformly well deposited on the surface of GR sheets stacked in only three layers. The Pt/GR composite prepared with 20 wt% of Pt had the highest specific surface area and electrochemical surface area of up to 402 m(2) g(-1) and 77 m(2) g(-1) (Pt), respectively. In addition, the composite showed superior electrocatalytic activity compared with commercial Pt-carbon black. The excellent electrocatalytic activity was attributed to the high specific surface area and electrochemical surface area of the Pt/GR composite directly produced by microwave plasma spray pyrolysis. Thus, it is clearly expected that the Pt/GR composite is a promising material for DMFC catalysts.

  18. One-Step Synthesis of Pt/Graphene Composites from Pt Acid Dissolved Ethanol via Microwave Plasma Spray Pyrolysis

    PubMed Central

    Jo, Eun Hee; Chang, Hankwon; Kim, Sun Kyung; Choi, Ji-Hyuk; Park, Su-Ryeon; Lee, Chong Min; Jang, Hee Dong

    2016-01-01

    Pt nanoparticles-laden graphene (Pt/GR) composites were synthesized in the gas phase from a mixture of ethanol and Pt precursor by microwave plasma spray pyrolysis. The morphology of Pt/GR composites has the shape of wrinkled sheets of paper, while Pt nanoparticles (Pt NPs) that are less than 2.6 nm in the mean diameter are uniformly well deposited on the surface of GR sheets stacked in only three layers. The Pt/GR composite prepared with 20 wt% of Pt had the highest specific surface area and electrochemical surface area of up to 402 m2 g−1 and 77 m2 g−1 (Pt), respectively. In addition, the composite showed superior electrocatalytic activity compared with commercial Pt-carbon black. The excellent electrocatalytic activity was attributed to the high specific surface area and electrochemical surface area of the Pt/GR composite directly produced by microwave plasma spray pyrolysis. Thus, it is clearly expected that the Pt/GR composite is a promising material for DMFC catalysts. PMID:27622908

  19. Investigation of the electrocatalysis for oxygen reduction reaction by Pt and binary Pt alloys: an XRD, XAS and electrochemical study

    SciTech Connect

    Mukerjee, S.; McBreen, J.; Srinivasan, S.

    1995-12-31

    Electrocatalysis for the oxygen reduction reaction (ORR) on five binary Pt alloy electrocatalysts (PtCr/C, PtMn/C, PtFe/C, PtCo/C and PtNi/C) supported on carbon have been investigated. The electrochemical characteristics for ORR in a proton conducting fuel cell environment has been correlated with the electronic and structural parameters determined under in situ conditions using XANES and EXAFS technique respectively. Results indicate that all the alloys possess higher Pt 5d band vacancies as compared to Pt/C. There is also evidence of lattice contraction in the alloys (supported by XRD results). Further, the Pt/C shows increase in Pt 5 d band vacancies during potential transitions from 0.54 to 0.84 V vs. RHE, which has been ration@ on the basis of OH type adsorption. In contrast to this, the alloys do not exhibit such an enhancement. Detailed EXAFS analysis supports the presence of OH species on Pt/C and its relative absence in the alloys. Correlation of the electrochemical results with bond distances and d-band vacancies show a volcano type behavior with the PtCr/C on top of the curve.

  20. Surface enrichment of Pt in Ga2O3 films grown on liquid Pt/Ga alloys

    NASA Astrophysics Data System (ADS)

    Grabau, Mathias; Krick Calderón, Sandra; Rietzler, Florian; Niedermaier, Inga; Taccardi, Nicola; Wasserscheid, Peter; Maier, Florian; Steinrück, Hans-Peter; Papp, Christian

    2016-09-01

    The formation of surface Ga2O3 films on liquid samples of Ga, and Pt-Ga alloys with 0.7 and 1.8 at.% Pt was examined using near-ambient pressure (NAP) X-ray photoelectron spectroscopy (XPS). Thickness, composition and growth of the oxide films were deduced as a function of temperature and Pt content of the alloys, in ultra-high vacuum and at oxygen pressures of 3 × 10- 7, 3 × 10- 3 and 1 mbar. We examined oxide layers up to a thickness of 37 Å. Different growth modes were found for oxidation at low and high pressures. The formed Ga2O3 oxide films showed an increased Pt content, while the pristine GaPt alloy showed a surface depletion of Pt at the examined temperatures. Upon growth of Ga2O3 on Pt/Ga alloys a linear increase of Pt content was observed, due to the incorporation of 3.6 at.% Pt in the Ga2O3. The Pt content in Ga2O3, at the examined temperatures and bulk Pt concentrations is found to be independent of pressure, temperature and the nominal Pt content of the metallic alloy.

  1. Granular nanostructures and magnetic characteristics of FePt-TiO{sub 2}/FePt-C stacked granular films

    SciTech Connect

    Ono, Takuya Moriya, Tomohiro; Hatayama, Masatoshi; Kikuchi, Nobuaki; Okamoto, Satoshi; Kitakami, Osamu; Shimatsu, Takehito

    2014-05-07

    To realize a granular film composed of L1{sub 0}-FePt grains with high uniaxial magnetic anisotropy energy, K{sub u}, and segregants for heat-assisted magnetic recording, the FePt-TiO{sub 2}/FePt-C stacked film was investigated. The FePt-TiO{sub 2}/FePt-C stacked film has well-isolated granular structure with average grain size of 6.7 nm because the FePt-TiO{sub 2} film follows the FePt-C template film in microstructural growth. However, the K{sub u} value is quite low for total thickness of 9 nm: 5 × 10{sup 6} erg/cm{sup 3}. Exploration of the thickness dependence of L1{sub 0}-FePt(001) peaks in XRD spectra and cross-sectional TEM images suggest that degradation of the L1{sub 0} ordering appears near the middle of the FePt-TiO{sub 2} layer. The EDX-STEM mapping reveals that Ti atoms exist within the FePt grains in addition to the grain boundary. This indicates the possibility that TiO{sub 2} tends to be incorporated into the FePt grains and that it prevents L1{sub 0}-ordering of the FePt grains along the normal-to-plane direction.

  2. One-Step Synthesis of Pt/Graphene Composites from Pt Acid Dissolved Ethanol via Microwave Plasma Spray Pyrolysis.

    PubMed

    Jo, Eun Hee; Chang, Hankwon; Kim, Sun Kyung; Choi, Ji-Hyuk; Park, Su-Ryeon; Lee, Chong Min; Jang, Hee Dong

    2016-01-01

    Pt nanoparticles-laden graphene (Pt/GR) composites were synthesized in the gas phase from a mixture of ethanol and Pt precursor by microwave plasma spray pyrolysis. The morphology of Pt/GR composites has the shape of wrinkled sheets of paper, while Pt nanoparticles (Pt NPs) that are less than 2.6 nm in the mean diameter are uniformly well deposited on the surface of GR sheets stacked in only three layers. The Pt/GR composite prepared with 20 wt% of Pt had the highest specific surface area and electrochemical surface area of up to 402 m(2) g(-1) and 77 m(2) g(-1) (Pt), respectively. In addition, the composite showed superior electrocatalytic activity compared with commercial Pt-carbon black. The excellent electrocatalytic activity was attributed to the high specific surface area and electrochemical surface area of the Pt/GR composite directly produced by microwave plasma spray pyrolysis. Thus, it is clearly expected that the Pt/GR composite is a promising material for DMFC catalysts. PMID:27622908

  3. Determination of intrinsic spin Hall angle in Pt

    SciTech Connect

    Wang, Yi; Deorani, Praveen; Qiu, Xuepeng; Kwon, Jae Hyun; Yang, Hyunsoo

    2014-10-13

    The spin Hall angle in Pt is evaluated in Pt/NiFe bilayers by spin torque ferromagnetic resonance measurements and is found to increase with increasing the NiFe thickness. To extract the intrinsic spin Hall angle in Pt by estimating the total spin current injected into NiFe from Pt, the NiFe thickness dependent measurements are performed and the spin diffusion in the NiFe layer is taken into account. The intrinsic spin Hall angle of Pt is determined to be 0.068 at room temperature and is found to be almost constant in the temperature range of 13–300 K.

  4. Exactly solvable PT -symmetric models in two dimensions

    NASA Astrophysics Data System (ADS)

    Agarwal, Kaustubh S.; Pathak, Rajeev K.; Joglekar, Yogesh N.

    2015-11-01

    Non-Hermitian, PT -symmetric Hamiltonians, experimentally realized in optical systems, accurately model the properties of open, bosonic systems with balanced, spatially separated gain and loss. We present a family of exactly solvable, two-dimensional, PT potentials for a non-relativistic particle confined in a circular geometry. We show that the PT -symmetry threshold can be tuned by introducing a second gain-loss potential or its Hermitian counterpart. Our results explicitly demonstrate that PT breaking in two dimensions has a rich phase diagram, with multiple re-entrant PT -symmetric phases.

  5. Pt skin on Pd-Co-Zn/C ternary nanoparticles with enhanced Pt efficiency toward ORR

    NASA Astrophysics Data System (ADS)

    Xiao, Weiping; Zhu, Jing; Han, Lili; Liu, Sufen; Wang, Jie; Wu, Zexing; Lei, Wen; Xuan, Cuijuan; Xin, Huolin L.; Wang, Deli

    2016-08-01

    Exploring highly active, stable and relatively low-cost nanomaterials for the oxygen reduction reaction (ORR) is of vital importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Herein, a highly active, durable, carbon supported, and monolayer Pt coated Pd-Co-Zn nanoparticle is synthesized via a simple impregnation-reduction method, followed by spontaneous displacement of Pt. By tuning the atomic ratios, we obtain the composition-activity volcano curve for the Pd-Co-Zn nanoparticles and determined that Pd : Co : Zn = 8 : 1 : 1 is the optimal composition. Compared with pure Pd/C, the Pd8CoZn/C nanoparticles show a substantial enhancement in both the catalytic activity and the durability toward the ORR. Moreover, the durability and activity are further enhanced by forming a Pt skin on Pd8CoZn/C nanocatalysts. Interestingly, after 10 000 potential cycles in N2-saturated 0.1 M HClO4 solution, Pd8CoZn@Pt/C shows improved mass activity (2.62 A mg-1Pt) and specific activity (4.76 A m-2total), which are about 1.4 and 4.4 times higher than the initial values, and 37.4 and 5.5 times higher than those of Pt/C catalysts, respectively. After accelerated stability testing in O2-saturated 0.1 M HClO4 solution for 30 000 potential cycles, the half-wave potential negatively shifts about 6 mV. The results show that the Pt skin plays an important role in enhancing the activity as well as preventing degradation.Exploring highly active, stable and relatively low-cost nanomaterials for the oxygen reduction reaction (ORR) is of vital importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Herein, a highly active, durable, carbon supported, and monolayer Pt coated Pd-Co-Zn nanoparticle is synthesized via a simple impregnation-reduction method, followed by spontaneous displacement of Pt. By tuning the atomic ratios, we obtain the composition-activity volcano curve for the Pd-Co-Zn nanoparticles and determined that Pd : Co : Zn = 8

  6. Experimental measurements of the heats of formation of Fe{sub 3}Pt, FePt, and FePt{sub 3} using differential scanning calorimetry

    SciTech Connect

    Wang, B.; Berry, D. C.; Chiari, Y.; Barmak, K.

    2011-07-01

    Using differential scanning calorimetry (DSC), the heats of formation of Fe{sub 3}Pt, FePt, and FePt{sub 3} were determined from the reaction of sputter deposited Fe/Pt multilayer thin-films with a periodicity of 200 nm but different overall compositions. Film compositions were measured by energy dispersive x-ray spectrometry. The phases present along the reaction path were identified by x-ray diffraction. For the most Fe-rich phase, namely, Fe{sub 3}Pt, the measured enthalpy of formation was -9.3 {+-} 1.3 kJ/mol in a film with a composition of 70.4:29.6 ({+-}0.2 at. %) Fe:Pt. For FePt, the measured enthalpy of formation was -27.2 {+-} 2.2 kJ/g-atom in a 49.0:51.0 ({+-}0.5 at. %) Fe:Pt film. For FePt{sub 3}, which is the most Pt rich intermetallic phase, the measured enthalpy of formation was -23.7 {+-} 2.2 in a film with a composition of 22.2:77.8 ({+-}0.6 at. %) Fe:Pt. The reaction enthalpies for films with Fe:Pt compositions of 44.5:55.5 ({+-}0.3 at. %) and 38.5:61.5 ({+-}0.4 at. %) were -26.9 {+-} 1.0 and -26.6 {+-} 0.6 kJ/g-atom, respectively, which taken together with the value for the 49.0:51.0 film demonstrate the relative insensitivity of the reaction enthalpy to film composition over a broad composition range in the vicinity of the equiatomic composition. The experimental heats of formation are compared with two sets of reported first-principles calculated values for each of the three phases at exact stoichiometry.

  7. Pt skin on Pd-Co-Zn/C ternary nanoparticles with enhanced Pt efficiency toward ORR.

    PubMed

    Xiao, Weiping; Zhu, Jing; Han, Lili; Liu, Sufen; Wang, Jie; Wu, Zexing; Lei, Wen; Xuan, Cuijuan; Xin, Huolin L; Wang, Deli

    2016-08-21

    Exploring highly active, stable and relatively low-cost nanomaterials for the oxygen reduction reaction (ORR) is of vital importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Herein, a highly active, durable, carbon supported, and monolayer Pt coated Pd-Co-Zn nanoparticle is synthesized via a simple impregnation-reduction method, followed by spontaneous displacement of Pt. By tuning the atomic ratios, we obtain the composition-activity volcano curve for the Pd-Co-Zn nanoparticles and determined that Pd : Co : Zn = 8 : 1 : 1 is the optimal composition. Compared with pure Pd/C, the Pd8CoZn/C nanoparticles show a substantial enhancement in both the catalytic activity and the durability toward the ORR. Moreover, the durability and activity are further enhanced by forming a Pt skin on Pd8CoZn/C nanocatalysts. Interestingly, after 10 000 potential cycles in N2-saturated 0.1 M HClO4 solution, Pd8CoZn@Pt/C shows improved mass activity (2.62 A mg(-1)Pt) and specific activity (4.76 A m(-2)total), which are about 1.4 and 4.4 times higher than the initial values, and 37.4 and 5.5 times higher than those of Pt/C catalysts, respectively. After accelerated stability testing in O2-saturated 0.1 M HClO4 solution for 30 000 potential cycles, the half-wave potential negatively shifts about 6 mV. The results show that the Pt skin plays an important role in enhancing the activity as well as preventing degradation. PMID:27445114

  8. Synthesis And Characterization of Pt Clusters in Aqueous Solutions

    SciTech Connect

    Siani, A.; Wigal, K.R.; Alexeev, O.S.; Amiridis, M.D.

    2009-05-26

    Extended X-ray absorption fine structure (EXAFS) and UV-visible (UV-vis) spectroscopies were used to monitor the various steps involved in the synthesis of unprotected and poly(vinyl alcohol) (PVA)-protected aqueous colloidal Pt suspensions. The results indicate that on hydrolysis of the H{sub 2}PtCl{sub 6} precursor, the Cl{sup -} ligands were partially replaced by aquo ligands in the first coordination shell of Pt to form [PtCl{sub 2}(H{sub 2}O){sub 4}]{sup 2+}. Treatment of these species with NaBH{sub 4} under controlled pH conditions led to the formation of nearly uniform Pt{sub 4} and Pt{sub 6} clusters in the absence and presence of PVA, respectively. These highly dispersed colloidal Pt suspensions were stable for several months. The addition of 2-propanol (IPA) to both types of Pt suspensions led to some sintering of the Pt clusters, although both suspensions retained their colloidal nature. Less sintering was evident in the PVA-protected Pt suspension. Both the unprotected and the PVA-protected colloidal Pt suspensions were catalytically active for the liquid-phase selective oxidation of 2-propanol to acetone, with the unprotected suspension exhibiting the highest activity.

  9. Spin Hall effects in mesoscopic Pt films with high resistivity

    NASA Astrophysics Data System (ADS)

    Qin, Chuan; Luo, Yongming; Zhou, Chao; Cai, Yunjiao; Jia, Mengwen; Chen, Shuhan; Wu, Yizheng; Ji, Yi

    2016-10-01

    The energy efficiency of the spin Hall effects (SHE) can be enhanced if the electrical conductivity is decreased without sacrificing the spin Hall conductivity. The resistivity of Pt films can be increased to 150-300 µΩ · cm by mesoscopic lateral confinement, thereby decreasing the conductivity. The SHE and inverse spin Hall effects (ISHE) in these mesoscopic Pt films are explored at 10 K by using the nonlocal spin injection/detection method. All relevant physical quantities are determined in situ on the same substrate, and a quantitative approach is developed to characterize all processes effectively. Extensive measurements with various Pt thickness values reveal an upper limit for the Pt spin diffusion length: {λ\\text{pt}}   ⩽  0.8 nm. The average product of {λ\\text{pt}} and the Pt spin Hall angle {α\\text{H}} is substantial: {α\\text{H}}{λ\\text{pt}}   =  (0.142  ±  0.040) nm for 4 nm thick Pt, though a gradual decrease is observed at larger Pt thickness. The results suggest enhanced spin Hall effects in resistive mesoscopic Pt films.

  10. Gaseous NH3 Confers Porous Pt Nanodendrites Assisted by Halides

    PubMed Central

    Lu, Shuanglong; Eid, Kamel; Li, Weifeng; Cao, Xueqin; Pan, Yue; Guo, Jun; Wang, Liang; Wang, Hongjing; Gu, Hongwei

    2016-01-01

    Tailoring the morphology of Pt nanocrystals (NCs) is of great concern for their enhancement in catalytic activity and durability. In this article, a novel synthetic strategy is developed to selectively prepare porous dendritic Pt NCs with different structures for oxygen reduction reaction (ORR) assisted by NH3 gas and halides (F−, Cl−, Br−). The NH3 gas plays critical roles on tuning the morphology. Previously, H2 and CO gas are reported to assist the shape control of metallic nanocrystals. This is the first demonstration that NH3 gas assists the Pt anisotropic growth. The halides also play important role in the synthetic strategy to regulate the formation of Pt NCs. As-made porous dendritic Pt NCs, especially when NH4F is used as a regulating reagent, show superior catalytic activity for ORR compared with commercial Pt/C catalyst and other previously reported Pt-based NCs. PMID:27184228

  11. Gaseous NH3 Confers Porous Pt Nanodendrites Assisted by Halides

    NASA Astrophysics Data System (ADS)

    Lu, Shuanglong; Eid, Kamel; Li, Weifeng; Cao, Xueqin; Pan, Yue; Guo, Jun; Wang, Liang; Wang, Hongjing; Gu, Hongwei

    2016-05-01

    Tailoring the morphology of Pt nanocrystals (NCs) is of great concern for their enhancement in catalytic activity and durability. In this article, a novel synthetic strategy is developed to selectively prepare porous dendritic Pt NCs with different structures for oxygen reduction reaction (ORR) assisted by NH3 gas and halides (F‑, Cl‑, Br‑). The NH3 gas plays critical roles on tuning the morphology. Previously, H2 and CO gas are reported to assist the shape control of metallic nanocrystals. This is the first demonstration that NH3 gas assists the Pt anisotropic growth. The halides also play important role in the synthetic strategy to regulate the formation of Pt NCs. As-made porous dendritic Pt NCs, especially when NH4F is used as a regulating reagent, show superior catalytic activity for ORR compared with commercial Pt/C catalyst and other previously reported Pt-based NCs.

  12. Transforming AdaPT to Ada

    NASA Technical Reports Server (NTRS)

    Goldsack, Stephen J.; Holzbach-Valero, A. A.; Waldrop, Raymond S.; Volz, Richard A.

    1991-01-01

    This paper describes how the main features of the proposed Ada language extensions intended to support distribution, and offered as possible solutions for Ada9X can be implemented by transformation into standard Ada83. We start by summarizing the features proposed in a paper (Gargaro et al, 1990) which constitutes the definition of the extensions. For convenience we have called the language in its modified form AdaPT which might be interpreted as Ada with partitions. These features were carefully chosen to provide support for the construction of executable modules for execution in nodes of a network of loosely coupled computers, but flexibly configurable for different network architectures and for recovery following failure, or adapting to mode changes. The intention in their design was to provide extensions which would not impact adversely on the normal use of Ada, and would fit well in style and feel with the existing standard. We begin by summarizing the features introduced in AdaPT.

  13. Integrability of PT-symmetric dimers

    NASA Astrophysics Data System (ADS)

    Pickton, J.; Susanto, H.

    2013-12-01

    The coupled discrete linear and Kerr nonlinear Schrödinger equations with gain and loss describing transport on dimers with parity-time (PT)-symmetric potentials are considered. The model is relevant among others to experiments in optical couplers and proposals on Bose-Einstein condensates in PT-symmetric double-well potentials. It is known that the models are integrable. Here, the integrability is exploited further to construct the phase portraits of the system. A pendulum equation with a linear potential and a constant force for the phase difference between the fields is obtained, which explains the presence of unbounded solutions above a critical threshold parameter. The behavior of all solutions of the system, including changes in the topological structure of the phase plane, is then discussed.

  14. Magnetic properties of ordered NiPt

    NASA Astrophysics Data System (ADS)

    Brommer, P. E.; Franse, J. J. M.

    1988-04-01

    Thermal expansion, forced volume magnetostriction and high magnetic field data are presented on the ordered equiatomic NiPt compound. Values are derived for the magnetovolume parameter κC (≃3 × 10 -6kg2A-2m-4), and for the electronic and lattice Grüneisen parameters (Γ e ≊ 5.6; Γ latt ≊ 2.5) . Ordering effects on the magnetoelastic properties are studied for alloys containing 40-60 at % Ni.

  15. Solitons in PT-symmetric nonlinear lattices

    SciTech Connect

    Abdullaev, Fatkhulla Kh.; Konotop, Vladimir V.; Zezyulin, Dmitry A.; Kartashov, Yaroslav V.

    2011-04-15

    The existence of localized modes supported by the PT-symmetric nonlinear lattices is reported. The system considered reveals unusual properties: unlike other typical dissipative systems, it possesses families (branches) of solutions, which can be parametrized by the propagation constant; relatively narrow localized modes appear to be stable, even when the conservative nonlinear lattice potential is absent; and finally, the system supports stable multipole solutions.

  16. Effect of nitrogen upon structural and magnetic properties of FePt in FePt/AlN multilayer structures

    SciTech Connect

    Gao, Tenghua Zhang, Cong; Sannomiya, Takumi; Muraishi, Shinji; Nakamura, Yoshio; Shi, Ji

    2014-09-01

    This paper investigates the effect of the addition of nitrogen in FePt layers for ultrathin FePt/AlN multilayer structures. X-ray diffraction results reveal that a compressive stress relaxation occurs after annealing owing to the release of interstitial nitrogen atoms in the FePt layers. The introduction of nitrogen also induces a large in-plane compressive strain during grain growth not seen in FePt deposited without nitrogen. This strain is considered to decrease the driving force for (111) grain growth and FePt ordering.

  17. Pt skin on AuCu intermetallic substrate: a strategy to maximize Pt utilization for fuel cells.

    PubMed

    Wang, Gongwei; Huang, Bing; Xiao, Li; Ren, Zhandong; Chen, Hao; Wang, Deli; Abruña, Héctor D; Lu, Juntao; Zhuang, Lin

    2014-07-01

    The dependence on Pt catalysts has been a major issue of proton-exchange membrane (PEM) fuel cells. Strategies to maximize the Pt utilization in catalysts include two main approaches: to put Pt atoms only at the catalyst surface and to further enhance the surface-specific catalytic activity (SA) of Pt. Thus far there has been no practical design that combines these two features into one single catalyst. Here we report a combined computational and experimental study on the design and implementation of Pt-skin catalysts with significantly improved SA toward the oxygen reduction reaction (ORR). Through screening, using density functional theory (DFT) calculations, a Pt-skin structure on AuCu(111) substrate, consisting of 1.5 monolayers of Pt, is found to have an appropriately weakened oxygen affinity, in comparison to that on Pt(111), which would be ideal for ORR catalysis. Such a structure is then realized by substituting the Cu atoms in three surface layers of AuCu intermetallic nanoparticles (AuCu iNPs) with Pt. The resulting Pt-skinned catalyst (denoted as Pt(S)AuCu iNPs) has been characterized in depth using synchrotron XRD, XPS, HRTEM, and HAADF-STEM/EDX, such that the Pt-skin structure is unambiguously identified. The thickness of the Pt skin was determined to be less than two atomic layers. Finally the catalytic activity of Pt(S)AuCu iNPs toward the ORR was measured via rotating disk electrode (RDE) voltammetry through which it was established that the SA was more than 2 times that of a commercial Pt/C catalyst. Taking into account the ultralow Pt loading in Pt(S)AuCu iNPs, the mass-specific catalytic activity (MA) was determined to be 0.56 A/mg(Pt)@0.9 V, a value that is well beyond the DOE 2017 target for ORR catalysts (0.44 A/mg(Pt)@0.9 V). These findings provide a strategic design and a realizable approach to high-performance and Pt-efficient catalysts for fuel cells.

  18. The role of the cationic Pt sites in the adsorption properties of water and ethanol on the Pt4/Pt(111) and Pt4/CeO2(111) substrates: A density functional theory investigation

    NASA Astrophysics Data System (ADS)

    Seminovski, Yohanna; Tereshchuk, Polina; Kiejna, Adam; Da Silva, Juarez L. F.

    2016-09-01

    Finite site platinum particles, Ptn, supported on reduced or unreduced cerium oxide surfaces, i.e., CeO2-x(111) ( 0 < x < /1 2 ), have been employed and studied as catalysts for a wide range of applications, which includes hydrogen production using the ethanol steam reforming processes. Our atomic-level understanding of the interaction of Pt with CeO2-x has been improved in the last years; however, the identification of the active sites on the Ptn/CeO2-x(111) substrates is still far from complete. In this work, we applied density functional theory based calculations with the addition of the on-site Coulomb interactions (DFT+U) for the investigation of the active sites and the role of the Pt oxidation state on the adsorption properties of water and ethanol (probe molecules) on four selected substrates, namely, Pt(111), Pt4/Pt(111), CeO2(111), and Pt4/CeO2(111). Our results show that water and ethanol preferentially bind in the cationic sites of the base of the tetrahedron Pt4 cluster instead of the anionic lower-coordinated Pt atoms located on the cluster-top or in the surface Ce (cationic) and O (anionic) sites. The presence of the Pt4 cluster contributes to increase the adsorption energy of both molecules on Pt(111) and CeO2(111) surfaces; however, its magnitude increases less for the case of Pt4/CeO2(111). Thus, the cationic Pt sites play a crucial role in the adsorption properties of water and ethanol. Both water and ethanol bind to on-top sites via the O atom and adopt parallel and perpendicular configurations on the Pt(111) and CeO2(111) substrates, respectively, while their orientation is changed once the Pt4 cluster is involved, favoring H binding with the surface sites.

  19. Crystallisation of ice in charged Pt nanochannel

    NASA Astrophysics Data System (ADS)

    Zhang, X. X.; Lü, Y. J.; Chen, M.

    2013-12-01

    Using molecular dynamics simulations, we examine the crystallisation process of the extended simple point charge model (SPC/E) water confined in a charged Pt nanochannel. The presence of the external electric field enhances the surface layering of water and promotes the super-cooled water to crystallise into Ic ice within tens of nanoseconds. Ic ice is found to nucleate from the interior of the water lamina, and the Pt(111) surfaces do not show a remarkable promotion of Ic ice nucleation. Structural analysis reveals that a two-dimensional hydrogen-bond network is built among the water molecules absorbed on the charged Pt surfaces, which influences the bonding of the molecules between the first and the second layers, and disturbs the formation of tetrahedral structures that match Ic ice, finally resulting in the nucleation-free near the walls. Such arrangements of water molecules remain in the subsequent growth of Ic ice and cause the slowdown of growth velocity while approaching surfaces.

  20. Atomic-scale redistribution of Pt during reactive diffusion in Ni (5% Pt)-Si contacts.

    PubMed

    Cojocaru-Mirédin, O; Cadel, E; Blavette, D; Mangelinck, D; Hoummada, K; Genevois, C; Deconihout, B

    2009-06-01

    The NiSi silicide that forms by reactive diffusion between Ni and Si active regions of nanotransistors is used nowadays as contacts in nanoelectronics because of its low resistivity. Pt is added to the Ni film in order to stabilise the NiSi phase against the formation of the high-resistivity NiSi(2) phase and agglomeration. In situ X-ray diffraction (XRD) experiments performed on material aged at 350 degrees C (under vacuum) showed the complete consumption of the Ni (5 at% Pt) phase, the regression of Ni(2)Si phase as well as the growth of the NiSi phase after 48 min. Pt distribution for this heat treatment has been analysed by laser-assisted tomographic atom probe (LATAP). An enrichment of platinum in the middle of the NiSi phase suggests that Pt is almost immobile during the growth of NiSi at the two interfaces: Ni(2)Si/NiSi and NiSi/Si. In the peak, platinum was found to substitute for Ni in the NiSi phase. Very small amounts of Pt were also found in the Ni(2)Si phase close to the surface and at the NiSi/Si interface. PMID:19339118

  1. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys

    NASA Astrophysics Data System (ADS)

    De Clercq, A.; Giorgio, S.; Mottet, C.

    2016-02-01

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher.

  2. Atomic-scale redistribution of Pt during reactive diffusion in Ni (5% Pt)-Si contacts.

    PubMed

    Cojocaru-Mirédin, O; Cadel, E; Blavette, D; Mangelinck, D; Hoummada, K; Genevois, C; Deconihout, B

    2009-06-01

    The NiSi silicide that forms by reactive diffusion between Ni and Si active regions of nanotransistors is used nowadays as contacts in nanoelectronics because of its low resistivity. Pt is added to the Ni film in order to stabilise the NiSi phase against the formation of the high-resistivity NiSi(2) phase and agglomeration. In situ X-ray diffraction (XRD) experiments performed on material aged at 350 degrees C (under vacuum) showed the complete consumption of the Ni (5 at% Pt) phase, the regression of Ni(2)Si phase as well as the growth of the NiSi phase after 48 min. Pt distribution for this heat treatment has been analysed by laser-assisted tomographic atom probe (LATAP). An enrichment of platinum in the middle of the NiSi phase suggests that Pt is almost immobile during the growth of NiSi at the two interfaces: Ni(2)Si/NiSi and NiSi/Si. In the peak, platinum was found to substitute for Ni in the NiSi phase. Very small amounts of Pt were also found in the Ni(2)Si phase close to the surface and at the NiSi/Si interface.

  3. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys.

    PubMed

    De Clercq, A; Giorgio, S; Mottet, C

    2016-02-17

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher. PMID:26795206

  4. A comparative theoretical study for the methanol dehydrogenation to CO over Pt3 and PtAu2 clusters.

    PubMed

    Zhong, Wenhui; Liu, Yuxia; Zhang, Dongju

    2012-07-01

    The density functional theory (DFT) calculations are carried out to study the mechanism details and the ensemble effect of methanol dehydrogenation over Pt(3) and PtAu(2) clusters, which present the smallest models of pure Pt clusters and bimetallic PtAu clusters. The energy diagrams are drawn out along both the initial O-H and C-H bond scission pathways via the four sequential dehydrogenation processes, respectively, i.e., CH(3)OH → CH(2)OH → CH(2)O → CHO → CO and CH(3)OH → CH(3)O → CH(2)O → CHO → CO, respectively. It is revealed that the reaction kinetics over PtAu(2) is significantly different from that over Pt(3). For the Pt(3)-mediated reaction, the C-H bond scission pathway, where an ensemble composed of two Pt atoms is required to complete methanol dehydrogenation, is energetically more favorable than the O-H bond scission pathway, and the maximum barrier along this pathway is calculated to be 12.99 kcal mol(-1). In contrast, PtAu(2) cluster facilitates the reaction starting from the O-H bond scission, where the Pt atom acts as the active center throughout each elementary step of methanol dehydrogenation, and the initial O-H bond scission with a barrier of 21.42 kcal mol(-1) is the bottom-neck step of methanol decomposition. Importantly, it is shown that the complete dehydrogenation product of methanol, CO, can more easily dissociate from PtAu(2) cluster than from Pt(3) cluster. The calculated results over the model clusters provide assistance to some extent for understanding the improved catalytic activity of bimetal PtAu catalysts toward methanol oxidation in comparison with pure Pt catalysts. PMID:22160734

  5. 32 CFR Appendix F to Part 623 - Power of Attorney (DA Form 4881-4-R)

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 32 National Defense 3 2012-07-01 2009-07-01 true Power of Attorney (DA Form 4881-4-R) F Appendix F to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. F Appendix F to Part 623—Power of Attorney (DA Form 4881-4-R) EC24OC91.024...

  6. 32 CFR Appendix F to Part 623 - Power of Attorney (DA Form 4881-4-R)

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 32 National Defense 3 2013-07-01 2013-07-01 false Power of Attorney (DA Form 4881-4-R) F Appendix F to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. F Appendix F to Part 623—Power of Attorney (DA Form 4881-4-R) EC24OC91.024...

  7. 32 CFR Appendix F to Part 623 - Power of Attorney (DA Form 4881-4-R)

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 32 National Defense 3 2011-07-01 2009-07-01 true Power of Attorney (DA Form 4881-4-R) F Appendix F to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. F Appendix F to Part 623—Power of Attorney (DA Form 4881-4-R) EC24OC91.024...

  8. 32 CFR Appendix F to Part 623 - Power of Attorney (DA Form 4881-4-R)

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 32 National Defense 3 2014-07-01 2014-07-01 false Power of Attorney (DA Form 4881-4-R) F Appendix F to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. F Appendix F to Part 623—Power of Attorney (DA Form 4881-4-R) EC24OC91.024...

  9. Patterning self-assembled FePt nanoparticles

    NASA Astrophysics Data System (ADS)

    Chen, Min; Nikles, David E.; Yin, Huaqin; Wang, Shoutao; Harrell, J. W.; Majetich, Sara A.

    2003-10-01

    We describe a potential way to extend the ordered domain of self-assembled FePt nanoparticles. The FePt particles, with an average diameter of 3 nm, were prepared by simultaneous thermal decomposition of Fe(CO) 5 and chemical reduction of Pt(acac) 2 and then were dispersed in a mixture of hexane and octane. When self-assembling on a plain silicon wafer, FePt nanoparticles formed ordered hexagonal arrays in a range of tens to a few hundred nanometers. A silicon wafer with patterned holes of a photoresist film, made using UV-lithographing technique, was used as a template to direct the stacking direction of the FePt nanoparticles. The FePt dispersion was dropped on the patterned holes of the photoresist film. After being heat-treated at 100°C for 30 min under vacuum condition, the photoresist was stripped out by dipping the sample in acetone. The patterned disks, with an average diameter of 2.0 μm and a height of 250 nm, of self-assembled FePt nanoparticles were examined using SEM and Auger mapping. Their magnetic properties were measured using AGM. The Auger electrons of neither Fe LMM nor Pt MNN could be detected from the sample, which indicated the adsorption of oleic acid and oleylamine on the surface of FePt nanoparticles. The coercivity of patterned FePt significantly increased with the annealing temperature above 600°C.

  10. The mechanism of charge density wave in Pt-based layered superconductors: SrPt2As2 and LaPt2Si2.

    PubMed

    Kim, Sooran; Kim, Kyoo; Min, B I

    2015-01-01

    The intriguing coexistence of the charge density wave (CDW) and superconductivity in SrPt2As2 and LaPt2Si2 has been investigated based on the ab initio density functional theory band structure and phonon calculations. We have found that the CDW instabilities for both cases arise from the q-dependent electron-phonon coupling with quasi-nesting feature of the Fermi surface. The band structure obtained by the band-unfolding technique reveals the sizable q-dependent electron-phonon coupling responsible for the CDW instability. The local split distortions of Pt atoms in the [As-Pt-As] layers play an essential role in driving the five-fold supercell CDW instability as well as the phonon softening instability in SrPt2As2. By contrast, the CDW and phonon softening instabilities in LaPt2Si2 occur without split distortions of Pt atoms. The phonon calculations suggest that the CDW and the superconductivity coexist in [X-Pt-X] layers (X = As or Si) for both cases. PMID:26449877

  11. The mechanism of charge density wave in Pt-based layered superconductors: SrPt2As2 and LaPt2Si2

    PubMed Central

    Kim, Sooran; Kim, Kyoo; Min, B. I.

    2015-01-01

    The intriguing coexistence of the charge density wave (CDW) and superconductivity in SrPt2As2 and LaPt2Si2 has been investigated based on the ab initio density functional theory band structure and phonon calculations. We have found that the CDW instabilities for both cases arise from the q-dependent electron-phonon coupling with quasi-nesting feature of the Fermi surface. The band structure obtained by the band-unfolding technique reveals the sizable q-dependent electron-phonon coupling responsible for the CDW instability. The local split distortions of Pt atoms in the [As-Pt-As] layers play an essential role in driving the five-fold supercell CDW instability as well as the phonon softening instability in SrPt2As2. By contrast, the CDW and phonon softening instabilities in LaPt2Si2 occur without split distortions of Pt atoms. The phonon calculations suggest that the CDW and the superconductivity coexist in [X-Pt-X] layers (X = As or Si) for both cases. PMID:26449877

  12. Pt-content-controlled synthesis of Pd nanohollows/Pt nanorods core/shell composites with enhanced electrocatalytic activities for the methanol oxidation reaction

    NASA Astrophysics Data System (ADS)

    Lai, Shiqin; Fu, Chenglin; Chen, Yongxiang; Yu, Xiang; Lai, Xuandi; Ye, Cui; Hu, Jianqiang

    2015-01-01

    Pd nanohollows/Pt nanorods (PdNHs/PtNRs) core/shell composites have been synthesized by a multistep crystalline growth method, in which Pt NRs grow on the exterior surface of hollow Pd nanospheres in order. Moreover, the size and quantity of the Pt NRs in the PdNHs/PtNRs can be easily tailored and thus ameliorate Pt utilization efficiency through varying H2PtCl6 concentrations. By comparing with Pt NPs and commercial Pt/C (JM), the PdNHs/PtNRs prepared using 2.50 mL 0.02 M H2PtCl6 have larger surface area, better anti-CO poisoning ability and more excellent catalytic performance. Moreover, the catalytic properties of the PdNHs/PtNRs can be well tunable by modifying the Pt contents. Our studies indicate that the PdNHs/PtNRs prepared using 2.50 mL 0.02 M H2PtCl6, in which Pd NHs are nearly completely covered with Pt NRs, have the largest surface area, best antitoxic ability and most excellent catalytic performance, indicative of high Pt utilization efficiency of the PdNHs/PtNRs relative to Pt/C (JM), Pt NPs and other PdNHs/PtNRs prepared using other H2PtCl6 concentrations. Therefore, the strategy to the size and content control of the PdNHs/PtNRs nanocomposites can facilitate optimized design of Pt-based catalysts for direct methanol fuel cells.

  13. Nanoporous PtAg and PtCu alloys with hollow ligaments for enhanced electrocatalysis and glucose biosensing.

    PubMed

    Xu, Caixia; Liu, Yunqing; Su, Fa; Liu, Aihua; Qiu, Huajun

    2011-09-15

    Nanoporous silver (NPS) and copper (NPC) obtained by dealloying AgAl and CuAl alloys, respectively, were used as both three-dimensional templates and reducing agents for the fabrication of nanoporous PtAg (NPS-Pt) and PtCu (NPC-Pt) alloys with hollow ligaments by a simple galvanic replacement reaction with H(2)PtCl(6). Electron microscopy and X-ray diffraction characterizations demonstrate that NPS and NPC with similar ligament sizes (30-50 nm) have different effects on the formed hollow nanostructures. For NPS-Pt, the shell of the hollow ligament is seamless. However, the shell of NPC-Pt is comprised of small pores and alloy nanoparticles with a size of ∼3 nm. The as-prepared NPS-Pt and NPC-Pt exhibit remarkably improved electrocatalytic activities towards the oxidation of ethanol and H(2)O(2) compared with state-of-the-art Pt/C catalyst, and can be used for sensitive electrochemical sensing applications. The hierarchical nanoporous structure also provides a good microenvironment for enzymes. After immobilization of glucose oxidase (GOx), the enzyme modified nanoporous electrode can sensitively detect glucose in a wide linear range (0.6-20 mM). PMID:21778046

  14. Degrees and signatures of broken PT symmetry in nonuniform lattices

    SciTech Connect

    Scott, Derek D.; Joglekar, Yogesh N.

    2011-05-15

    We investigate the robustness of the parity- and time-reversal (PT) symmetric phase in an N-site lattice with a position-dependent, parity-symmetric hopping function and a pair of imaginary, PT-symmetric impurities. We find that the ''fragile''PT-symmetric phase in these lattices is stronger than its counterpart in a lattice with constant hopping. With an open system in mind, we explore the degrees of broken PT symmetry and their signatures in single-particle wave-packet evolution. We predict that, when the PT-symmetric impurities are closest to each other, the time evolution of a wave packet in an even-N lattice is remarkably different from that in an odd-N lattice. Our results suggest that PT symmetry breaking in such lattices is accompanied by rich, hitherto unanticipated, phenomena.

  15. Superior CO catalytic oxidation on novel Pt/clay nanocomposites.

    PubMed

    Varade, Dharmesh; Abe, Hideki; Yamauchi, Yusuke; Haraguchi, Kazutoshi

    2013-11-27

    Nanostructured novel Pt/Clay nanocomposites consisting of well-defined Pt nanoparticles prepared by clay-mediated in situ reduction displays very high thermal stability, large BET surface area and superior catalytic activity for CO oxidation as compared to a model reference Pt/SiO2 catalysts. CO oxidation has attracted renewed attention because of its technological importance in the area of pollution control. The Pt/Clay system consisting of Pt nanoparticles strongly immobilized between the atomic layers of clay inhibits nanoparticle sintering and loss of catalytic activity even after prolonged heating at high temperatures. At elevated temperatures (300 °C), the Pt/Clay system demonstrates significant enhancement of catalytic activity, with almost 100% CO conversion in less than 5 min. Emphasis is given to the role played by the clay supporting material which is chemically and thermally stable under the catalytic conditions of exhaust purification.

  16. Superconductivity in Pd, Ir, and Pt chalcogenide

    NASA Astrophysics Data System (ADS)

    Oh, Yoon Seok; Yang, Junjie; Choi, Y. J.; Hogan, A.; Horibe, Y.; Cheong, S.-W.

    2012-02-01

    Large spin-orbit coupling in materials with heavy chalcogens can result in unique quantum states or functional properties such as topological insulator, giant thermoelectric power, and superconductivity. When materials contain heavy cations in addition to heavy chalcogens, spin-orbit coupling can be further enhanced. For these reasons, we have studied the superconductivity of Pd, Ir, and Pt tellurides and selenides. In the exploration of these chalcogenides, we have focused on the competition between superconductivity and charge density wave that is associated with superlattice reflections.

  17. Laser cleanup of Pt group metals

    SciTech Connect

    Chen, H.L.

    1980-10-28

    Due to increasing interest in chemical and fuel synthesis from syngas, the feasibility and practicality of purifying Pt group metals (Pd, Ru, Rh) using LIS technologies have been re-evaluated. Findings for the selective removal of /sup 107/Pd from Pd metal are described here. The selectivity of this technique is based on the angular momentum selection rules for atomic absorption of circularly polarized light. In principle, it is possible to selectively excite isotopes with non-zero nuclear spin, using two circularly polarized laser pulses, while leaving the isotopes with zero nuclear spin unexcited. The excited atom can then be ionized using a third photon of appropriate energy.

  18. Factors affecting the spontaneous adsorption of Bi(III) onto Pt and PtRu nanoparticles

    NASA Astrophysics Data System (ADS)

    Sawy, Ehab N. El; Khan, M. Akhtar; Pickup, Peter G.

    2016-02-01

    The influence of Bi(III) concentration and pH on the spontaneous adsorption of Bi species onto Pt nanoparticles has been systematically investigated in order to identify the adsorbing species, determine whether the nature of the adsorbing species changes, and investigate whether the activities of the resulting Bi decorated particles for formic acid oxidation can be influenced. The adsorption of Bi follows a Temkin-type isotherm, with a pH dependence indicating that the adsorbing species is [Bi6O4(OH)4]6+. Activities of Bi decorated Pt nanoparticles for formic acid oxidation are strongly influenced by the Bi coverage, with a maximum enhancement of a factor of ca. 60 at a coverage of 70%, but not by the Bi(III) concentration or pH used to adsorb the Bi species, other than through their influence on Bi coverage. These results support the conclusion that the adsorbing species is [Bi6O4(OH)4]6+ under all conditions investigated. Adsorbed Bi also activates PtRu nanoparticles for formic acid oxidation, although the effect is not as strong as for Pt. The maximum enhancement observed was only a factor of ca. 7. This has been attributed to attenuation of the effects of Bi adatoms that are adsorbed at Ru sites.

  19. Layer-Resolved Magnetic Moments in Ni/Pt Multilayers

    NASA Astrophysics Data System (ADS)

    Wilhelm, F.; Poulopoulos, P.; Ceballos, G.; Wende, H.; Baberschke, K.; Srivastava, P.; Benea, D.; Ebert, H.; Angelakeris, M.; Flevaris, N. K.; Niarchos, D.; Rogalev, A.; Brookes, N. B.

    2000-07-01

    The magnetic moments in Ni/Pt multilayers are thoroughly studied by combining experimental and ab initio theoretical techniques. SQUID magnetometry probes the samples' magnetizations. X-ray magnetic circular dichroism separates the contribution of Ni and Pt and provides a layer-resolved magnetic moment profile for the whole system. The results are compared to band-structure calculations. Induced Pt magnetic moments localized mostly at the interface are revealed. No magnetically ``dead'' Ni layers are found. The magnetization per Ni volume is slightly enhanced compared to bulk NiPt alloys.

  20. Jarzynski Equality in PT-Symmetric Quantum Mechanics.

    PubMed

    Deffner, Sebastian; Saxena, Avadh

    2015-04-17

    We show that the quantum Jarzynski equality generalizes to PT-symmetric quantum mechanics with unbroken PT symmetry. In the regime of broken PT symmetry, the Jarzynski equality does not hold as also the CPT norm is not preserved during the dynamics. These findings are illustrated for an experimentally relevant system-two coupled optical waveguides. It turns out that for these systems the phase transition between the regimes of unbroken and broken PT symmetry is thermodynamically inhibited as the irreversible work diverges at the critical point.

  1. Thermochemistry of Pt-fullerene complexes: semiempirical study.

    PubMed

    Voityuk, Alexander A

    2009-10-29

    Modified Neglect of Differential Overlap (MNDO) and MNDO/d based semiempirical methods are widely employed to explore structure and thermochemistry of molecular systems. In this work, the AM1/d method has been parametrized for systems containing platinum. The proposed scheme delivers excellent performance for binding energies of Pt complexes with ethylene and large pi conjugated hydrocarbons. The estimated bond energies accurately reproduce the results of MP4(SDQ) calculations and show significant improvement over DFT (B3LYP and M05) data. We apply the AM1/d scheme to explore the structure and thermochemistry of several Pt compounds with C(60) and C(70). The calculated binding energies of bare Pt atoms and [Pt(PH(3))(2)] units to the fullerenes are 75 and 45 kcal/mol, respectively. We find that coordination of a single metal center to C(60) activates the fullerene cage making subsequent coordination of Pt more favorable. The bond energy [C(60)-PtC(60)] is calculated to be 65 kcal/mol. The estimated reaction enthalpies are useful for exploring the stability of Pt(x)C(60) polymer systems and their interaction with phosphines. AM1/d predicts a very low barrier to rotation of the coordinated fullerenes in [Pt(C(60))(2)]. The AM1/d scheme is computationally very efficient and can be employed to obtain fast quantitative estimates for binding energies and structural parameters of Pt complexes with large pi conjugated systems like fullerenes and carbon nanotubes.

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

    SciTech Connect

    Feibelman, P.J.

    1999-04-05

    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).

  3. A novel method to evaluate spin diffusion length of Pt

    NASA Astrophysics Data System (ADS)

    Zhang, Yan-qing; Sun, Niu-yi; Che, Wen-ru; Shan, Rong; Zhu, Zhen-gang

    2016-05-01

    Spin diffusion length of Pt is evaluated via proximity effect of spin orbit coupling (SOC) and anomalous Hall effect (AHE) in Pt/Co2FeAl bilayers. By varying the thicknesses of Pt and Co2FeAl layer, the thickness dependences of AHE parameters can be obtained, which are theoretically predicted to be proportional to the square of the SOC strength. According to the physical image of the SOC proximity effect, the spin diffusion length of Pt can easily be identified from these thickness dependences. This work provides a novel method to evaluate spin diffusion length in a material with a small value.

  4. Nanoscale PtSi Tips for Conducting Probe Technologies

    NASA Astrophysics Data System (ADS)

    Bhaskaran, Harish; Sebastian, Abu; Despont, Michel

    2009-01-01

    A method to improve the conduction and wear properties of nanometric conducting tips by forming silicides of Pt at the tip apex is presented. Tips with PtSi apexes are fabricated in conjunction with standard Si tips. Wear measurements are carried out on both tip types of similar geometries, and a one-on-one comparison between Si and PtSi at the nanoscale is shown for the first time. Both the wear properties on tetrahedral amorphous carbon and the conduction on Au of the PtSi tip apexes are shown to be superior to the Si tips.

  5. Jarzynski equality in PT-symmetric quantum mechanics

    SciTech Connect

    Deffner, Sebastian; Saxena, Avadh

    2015-04-13

    We show that the quantum Jarzynski equality generalizes to PT -symmetric quantum mechanics with unbroken PT -symmetry. In the regime of broken PT -symmetry the Jarzynski equality does not hold as also the CPT -norm is not preserved during the dynamics. These findings are illustrated for an experimentally relevant system – two coupled optical waveguides. It turns out that for these systems the phase transition between the regimes of unbroken and broken PT -symmetry is thermodynamically inhibited as the irreversible work diverges at the critical point.

  6. Local PT symmetry violates the no-signaling principle.

    PubMed

    Lee, Yi-Chan; Hsieh, Min-Hsiu; Flammia, Steven T; Lee, Ray-Kuang

    2014-04-01

    Bender et al. [Phys. Rev. Lett. 80, 5243 (1998)] have developed PT-symmetric quantum theory as an extension of quantum theory to non-Hermitian Hamiltonians. We show that when this model has a local PT symmetry acting on composite systems, it violates the nonsignaling principle of relativity. Since the case of global PT symmetry is known to reduce to standard quantum mechanics A. Mostafazadeh [J. Math. Phys. 43, 205 (2001)], this shows that the PT-symmetric theory is either a trivial extension or likely false as a fundamental theory. PMID:24745396

  7. Cyclometalated heteronuclear Pt/Ag and Pt/Tl complexes: a structural and photophysical study.

    PubMed

    Jamali, Sirous; Ghazfar, Reza; Lalinde, Elena; Jamshidi, Zahra; Samouei, Hamidreza; Shahsavari, Hamid R; Moreno, M Teresa; Escudero-Adán, Eduardo; Benet-Buchholz, Jordi; Milic, Dalibor

    2014-01-21

    To investigate the factors influencing the luminescent properties of polymetallic cycloplatinated complexes a detailed study of the photophysical and structural properties of the heteronuclear complexes [Pt2Me2(bhq)2(μ-dppy)2Ag2(μ-acetone)](BF4)2, 2, [PtMe(bhq)(dppy)Tl]PF6, 3, and [Pt2Me2(bhq)2(dppy)2Tl]PF6, 4, [bhq = benzo[h]quinoline, dppy = 2-(diphenylphosphino)pyridine] was conducted. Complexes 3 and 4 synthesized by the reaction of [PtMe(bhq)(dppy)], 1, with TlPF6 (1 or 1/2 equiv.) and stabilized by unsupported Pt-Tl bonds as revealed by multinuclear NMR spectroscopy and confirmed by X-ray crystallography for 3. DFT calculations for the previously reported butterfly Pt2Ag2 cluster 2 reveal that in the optimized geometry the bridging acetone molecule is removed and the metal core displays a planar-shaped geometry in which according to a QTAIM calculation and natural bond orbital (NBO) analysis the Ag···Ag metallophilic interaction is strengthened. In contrast to the precursor 1, which is only emissive in glassy solutions ((3)MLCT 485 nm), all 2-4 heteropolynuclear complexes display intense emissions in the solid state and in glassy solutions. Time-dependent density functional theory (TD-DFT) is used to elucidate the origin of the electronic transitions in the heteronuclear complexes 2 and 3. The low energy absorption and intense orange emission for cluster 2 (solid 77 K and glass) are attributed to metal-metal to ligand charge transfer (MM'LCT) with a minor L'LCT contribution. For 3 and 4 two different bands are developed: the high energy band (602-630 nm) observed for 4 at 77 K (solid, glass) and in diluted glasses for 3 is ascribed to emission from discrete Pt2Tl units of mixed (3)L'LCT/(3)LM'CT origin. However, the low energy band (670-690 nm) observed at room temperature (solid) for both complexes and also in concentrated glasses for 3 is assigned to (3)ππ excited states arising from intermolecular interactions. PMID:24165802

  8. Spin Hall magnetoresistance in Co2FeSi/Pt thin films: dependence on Pt thickness and temperature

    NASA Astrophysics Data System (ADS)

    Huang, Xiufeng; Dai, Zhiwen; Huang, Lin; Lu, Guangduo; Liu, Min; Piao, Hongguang; Kim, Dong-Hyun; Yu, Seong-cho; Pan, Liqing

    2016-11-01

    We have investigated the temperature and the Pt layer thickness dependence of the magnetoresistances (MRs) in Co2FeSi/Pt thin films. Based on the field dependent measurements, it can be seen that the spin-current-induced spin Hall magnetoresistance (SMR) plays the dominant role in the MRs in the Co2FeSi/Pt bilayers in the whole temperature range. Meanwhile, a quite small part of anisotropic magnetoresistance (AMR) existed in the MRs. It proved to be originated from magnetic proximity effect (MPE) by measuring the Pt thickness and temperature dependence of the AMR. Moreover, the Co2FeSi layer thickness has much weaker effect on the SMR and AMR compared to the Pt layer thickness. These results indicate that the Co2FeSi/Pt interface is beneficial to be used in the spin-current-induced physical phenomena.

  9. The role of surface Pt on the coadsorption of hydrogen and CO on Pt monolayer film modified Ru(0001) surfaces

    NASA Astrophysics Data System (ADS)

    Diemant, T.; Hartmann, H.; Bansmann, J.; Behm, R. J.

    2016-10-01

    We have investigated the impact and role of the Pt surface modification on the coadsorption of hydrogen and CO on structurally well defined bimetallic Pt monolayer island/film modified Ru(0001) surfaces with Pt contents up to a complete Pt layer, employing temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS). Kinetic limitations in the surface diffusion are shown to play an important role for adsorption at 90 K, and lead to profound effects of the dosing sequence on the adsorption and desorption characteristics. Furthermore, they are responsible for spill-over effects during the TPD measurements, where COad becomes mobile and can spill-over from weakly bonding Pt monolayer areas to strongly bonding Pt-free Ru(0001) areas, which displaces Dad from these surface areas. The present findings are discussed in comparison with previous results on related metallic and bimetallic adsorption and coadsorption systems.

  10. Resolving Sulfur Oxidation and Removal from Pt and Pt3Co Electrocatalysts Using in Situ X-ray Absorption Spectroscopy

    SciTech Connect

    Ramaker, D.; Gatewood, D; Korovina, A; Garsany, Y; Swider-Lyons, K

    2010-01-01

    Adsorbed sulfur is a poison to the Pt catalysts used in proton exchange membrane fuel cells, but it can be removed by potential cycling. This process is studied for S{sub x}-poisoned nanoscale Pt- and Pt{sub 3}Co- on Vulcan carbon (Pt/VC and Pt{sub 3}Co/VC) in perchloric acid electrolyte using the {Delta}{mu} adsorbate isolation technique for in situ X-ray absorption spectroscopy. The {Delta}{mu} technique is modified to better distinguish the {Delta}{mu} signatures for H, O, and Sx on Pt. The resulting {Delta}{mu} analysis suggests that SO{sub 2} on nanoscale Pt is oxidized to bisulfate or sulfate species in two regions, near 1.05 V on the cluster edges of the Pt nanoparticle, and at higher potentials from the Pt(111) faces where oxygen is less strongly bound. The bisulfate or sulfate species desorb from the Pt surface at high potentials due to O(OH) adsorption/replacement and at low potentials due to loss of the Coulomb attraction between the bisulfate anion and the Pt. A similar oxidation process occurs for S{sub x}-poisoned Pt{sub 3}Co/VC, but at lower potentials because a ligand effect coming from Co shifts the oxidization potential of adsorbed SO{sub 2} to lower potentials while pushing OH adsorption to higher potentials. The spectroscopic results give insights into cyclic voltammetry data and are consistent with electrochemical cycling procedures for removing the sulfur.

  11. Adsorption of aromatics on the (111) surface of PtM and PtM3 (M = Fe, Ni) alloys

    SciTech Connect

    Hensley, Alyssa; Schneider, Sebastian; Wang, Yong; McEwen, Jean-Sabin

    2015-09-18

    The adsorption of benzene and phenol was studied on PtM and PtM3 (111) surfaces, with M being either Ni or Fe. Under vacuum, the most favorable near surface structures showed an enrichment in Pt over the M species. An analysis of the electronic structure of the metal species in the clean surfaces with different near surface structures was done with the d-band model and showed that the Pt's d-states are significantly shifted away from the Fermi level due to the Pt-M interactions while the M species' d-states were less affected, with Ni's d-band shifting closer to the Fermi level and Fe's d-band shifting away from the Fermi level. The adsorption of aromatics, benzene and phenol, on several near surface structures for the PtM and PtM3 (111) surfaces showed that higher surface M concentrations resulted in a stronger adsorption due to the larger amount of charge transferred between the adsorbate and surface. However, compared to the adsorption of benzene and phenol on monometallic surfaces, the adsorption of these species on the PtM and PtM3 (111) surfaces was significantly weakened. Overall, our results show that the observed behavior of these Pt/Fe and Pt/Ni alloys is similar to that seen for the previously studied Pd/Fe surfaces. Furthermore, balancing the weakly adsorbing Pt surface species with the more strongly interacting Fe or Ni species can lead to the tailored adsorption of aromatics with applications in both hydrodeoxygenation and hydrogenation reactions by increasing the desorption rate of wanted aromatic products.

  12. Pt and Pt-Ru/Carbon Nanotube Nanocomposites Synthesized in Supercritical Fluid as Electrocatalysts for Low-Temperature Fuel Cells

    SciTech Connect

    Lin, Yuehe; Cui, Xiaoli; Wang, Jun; Yen, Clive; Wai, Chien M.

    2006-06-01

    In recent years, the use of supercritical fluids (SCFs) for the synthesis and processing of nanomaterials has proven to be a rapid, direct, and clean approach to develop nanomaterials and nanocomposites. The application of supercritical fluid technology can result in products (and processes) that are cleaner, less expensive, and of higher quality than those that are produced using conventional technologies and solvents. In this work, carbon nanotube (CNT)-supported Pt and Pt-Ru nanoparticles catalysts have been synthesized in supercritical carbon dioxide (scCO2). The experimental results demonstrate that Pt, Pt-Ru/CNT nanocomposites synthesized in supercritical carbon dioxide are effective electrocatalysts for low-temperature fuel cells.

  13. Electrocatalytical study of carbon supported Pt, Ru and bimetallic Pt-Ru nanoparticles for oxygen reduction reaction in alkaline media

    NASA Astrophysics Data System (ADS)

    Hosseini, M. G.; Zardari, P.

    2015-08-01

    Carbon supported Pt, Ru and bimetallic Pt-Ru nanoparticles (Pt/C, Ru/C and Pt.Ru/C) have been prepared by the chemical reduction method. Particle morphology, composition and structure of nanoparticles have been investigated by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. SEM results showed a uniform dispersion of nanoparticles with rough and porous structure into carbon supports with the average particle size of 30-64 nm. EDX analysis demonstrated the presence of both Pt and Ru nanoparticles in each gas diffusion electrode. The Pt/C, Ru/C and Pt.Ru/C composites were used as electrocatalyst for oxygen reduction reaction (ORR) in alkaline media. The ORR activities of cathodes were characterized using cyclic voltammetry (CV), polarization technique, AC impedance spectroscopy (EIS) and chronoamperometry. CV and polarization curves showed significantly higher activity on Pt.Ru/C electrocatalyst than observed on Pt/C and Ru/C catalysts, which can be related to synergistic effect, which is playing a critical role in ORR activity. The Tafel slope values of 120 mV/dec showed that the first electron transfer is the rate determining step. The EIS results of cathodes under different polarization potentials indicated two different behaviours which depend on the applied dc potentials and reveal different electrochemical processes occurring on the electrodes.

  14. Activation of Homolytic Si-Zn and Si-Hg Bond Cleavage, Mediated by a Pt(0) Complex, via Novel Pt-Zn and Pt-Hg Compounds.

    PubMed

    Kratish, Yosi; Molev, Gregory; Kostenko, Arseni; Sheberla, Dennis; Tumanskii, Boris; Botoshansky, Mark; Shimada, Shigeru; Bravo-Zhivotovskii, Dmitry; Apeloig, Yitzhak

    2015-09-28

    The thermally stable [(tBuMe2 Si)2 M] (M=Zn, Hg) generate R3 Si(.) radicals in the presence of [(dmpe)Pt(PEt3 )2 ] at 60-80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn (2 a and 2 b), M=Hg (3 a and 3 b)) which were isolated and characterized. Mild warming or photolysis of 2 or 3 lead to homolytic dissociation of the Pt-MSiR3 bond generating silyl radicals and novel unstable pentacoordinate platinum paramagnetic complexes (M=Zn (5), Hg (6)) whose structures were determined by EPR spectroscopy and DFT calculations. PMID:26288342

  15. Activation of Homolytic Si-Zn and Si-Hg Bond Cleavage, Mediated by a Pt(0) Complex, via Novel Pt-Zn and Pt-Hg Compounds.

    PubMed

    Kratish, Yosi; Molev, Gregory; Kostenko, Arseni; Sheberla, Dennis; Tumanskii, Boris; Botoshansky, Mark; Shimada, Shigeru; Bravo-Zhivotovskii, Dmitry; Apeloig, Yitzhak

    2015-09-28

    The thermally stable [(tBuMe2 Si)2 M] (M=Zn, Hg) generate R3 Si(.) radicals in the presence of [(dmpe)Pt(PEt3 )2 ] at 60-80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn (2 a and 2 b), M=Hg (3 a and 3 b)) which were isolated and characterized. Mild warming or photolysis of 2 or 3 lead to homolytic dissociation of the Pt-MSiR3 bond generating silyl radicals and novel unstable pentacoordinate platinum paramagnetic complexes (M=Zn (5), Hg (6)) whose structures were determined by EPR spectroscopy and DFT calculations.

  16. Muta-mycosynthesis of naphthalene analogs.

    PubMed

    Tian, Yuan; Jiang, Nan; Zhang, Ai Hua; Chen, Chao Jun; Deng, Xin Zhao; Zhang, Wen Jing; Tan, Ren Xiang

    2015-03-20

    A mutasynthetic strategy is introduced for the mycosynthesis of naphthalene-based molecules (mutadalesols A-F) with directed substitution patterns and new frameworks by generating and using the ΔpksTL mutant strain of Daldinia eschscholzii. (±)-Mutadalesol A and its (+)-enantiomer are cytotoxic, and its (-)-enantiomer inhibits Toll-like receptor 5 (TLR5). The in-culture reactability of fungal oligoketide intermediates with 5-aminonaphthalen-1-ol (ANL) is demonstrated, shedding light on bioorthogonal accesses to unnatural molecule libraries valuable in drug discovery pipelines.

  17. Adsorption of molecular hydrogen on Pd(Pt) decorated graphene

    NASA Astrophysics Data System (ADS)

    Adhikari, Narayan; Khaniya, Asim; Lamichhane, Saran; Pantha, Nurapati

    2015-03-01

    We have performed the first-principles based Density Functional Theory (DFT) calculations to study the stability, geometrical structures, and electronic properties of a Pd(Pt) atom adsorbed graphene to investigate the possibility of using Pd(Pt) decorated graphene as energy storage materials with reference to pristine graphene. The London dispersion forces have been incorporated by the DFT-D2 levels of calculations implemented in Quantum Espresso packages. Our findings show that Pd and Pt both adsorb on graphene at Bridge site. The electronic structures of Pd(Pt) adsorbed graphene possesses band gap opening due to breaking of the symmetry of graphene. Further we have studied the adsorption of moelcular hydrogen ((H 2) n , n = 1-7) on the Pd(Pt)-graphene system. The adatom Pd(Pt) enhances the binding energy per hydrogen molecule in Pd(Pt)-graphene system in comparison to that in the pristine graphene. The binding energy per hydrogen molecule of the adatom-graphene system decreases as the number of H 2 molecules increases and finally it saturates to 0.15 eV (0.16 eV) per hydrogen molecule for Pd-graphene (Pt-graphene) systems respectively. ICTP-NET 56/TWAS.

  18. Limited genetic diversity in Salmonella enterica Serovar Enteritidis PT13

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Salmonella enterica serovar Enteritidis has emerged as a significant foodborne pathogen throughout the world and is commonly characterized by phage typing. In Canada phage types (PT) 4, 8 and 13 predominate and in 2005 a large foodborne PT13 outbreak occurred in the province of Ontario. The ability ...

  19. Positioning Evaluation and Research within PT3 Projects

    ERIC Educational Resources Information Center

    Rockman, Saul

    2004-01-01

    This special issue of JTATE is focused on evaluation and research studies conducted under the PT3 program of the U.S. Department of Education. PT3, Preparing Tomorrow's Teachers to Use Technology, is a program designed to ensure that new teachers are prepared to use computers and other technology when they reach the classroom and, in the effort to…

  20. Modifying exchange-spring behavior of CoPt/NiFe bilayer by inserting a Pt or Ru spacer

    SciTech Connect

    Hsu, Jen-Hwa Tsai, C. L.; Lee, C.-M.; Saravanan, P.

    2015-05-07

    We herein explore the possibility of obtaining tunable tilted magnetic anisotropy in ordered-CoPt (5 nm)/NiFe(t{sub NiFe}) bilayers through modifying their exchange spring behavior by inserting Pt and Ru-spacers. The tuning process of tilt angle magnetization of NiFe-layer was systematically investigated by varying the Pt or Ru thickness (t{sub Pt} or t{sub Ru}) from 0 to 8 nm at different thicknesses of NiFe (t{sub NiFe} = 1.5, 4.0, and 6.0 nm). Polar magneto-optic Kerr effect (p-MOKE) studies reveal that the bilayers grown in absence of spacers exhibit almost a rectangular hysteresis loop. With the insertion of Pt-spacer, the loop becomes more and more tilted as t{sub Pt} increases; whereas, in the case of Ru-spacer, the nature of the loops is not simply changing in one direction. The estimated SQR{sub ⊥} (= θ{sub r}/θ{sub s}) values from the p-MOKE loops are found to monotonically decrease with increasing t{sub Pt} when t{sub Pt} ≦ 4 nm. In contrast, in the case of Ru-spacer, an oscillatory behavior for the SQR{sub ⊥} values is apparent when t{sub Ru} ≦ 4 nm. As a result, an oscillatory tilted angle of NiFe spin configuration was obtained in the case of Ru-spacer; while a decoupling effect was prominent for the Pt-spacer. The results of present study reveal that the insertion of Pt and Ru-spacers as an appropriate means for realizing tunable tilted magnetic anisotropy in the CoPt/NiFe exchange springs.

  1. Fine grains ceramics of PIN-PT, PIN-PMN-PT and PMN-PT systems: drift of the dielectric constant under high electric field.

    PubMed

    Pham-Thi, M; Augier, C; Dammak, H; Gaucher, P

    2006-12-22

    Lead-based ferroelectric ceramics with (1-x)Pb(B1 B2)O3-xPbTiO3 formula have emerged as a group of promising materials for various applications like ultrasonic sonars or medical imaging transducers. (1-x)PMN-xPT, (1-x)PIN-xPT and ternary solutions xPIN-yPMN-zPT ceramics are synthesised using the solid state reaction method. Our objective is to achieve higher structural transition temperatures than those of PMN-PT ceramics with as good dielectric, piezoelectric and electromechanical properties. Ceramics capacitance and loss tangent are measured when the ac field of measurement increases up to E=500 V/mm. Behaviours of these materials under ac field are related to their coercive field and Curie temperature.

  2. Anomalous Hall effect in YIG|Pt bilayers

    SciTech Connect

    Meyer, Sibylle Schlitz, Richard; Geprägs, Stephan; Opel, Matthias; Huebl, Hans; Goennenwein, Sebastian T. B.; Gross, Rudolf

    2015-03-30

    We measure the ordinary and the anomalous Hall effect in a set of yttrium iron garnet|platinum (YIG|Pt) bilayers via magnetization orientation dependent magnetoresistance experiments. Our data show that the presence of the ferrimagnetic insulator YIG leads to an anomalous Hall effect like voltage in Pt, which is sensitive to both Pt thickness and temperature. Interpretation of the experimental findings in terms of the spin Hall anomalous Hall effect indicates that the imaginary part of the spin mixing conductance G{sub i} plays a crucial role in YIG|Pt bilayers. In particular, our data suggest a sign change in G{sub i} between 10 K and 300 K. Additionally, we report a higher order Hall effect contribution, which appears in thin Pt films on YIG at low temperatures.

  3. Strong spin Hall effect in the antiferromagnet PtMn

    NASA Astrophysics Data System (ADS)

    Ou, Yongxi; Shi, Shengjie; Ralph, D. C.; Buhrman, R. A.

    2016-06-01

    Effectively manipulating magnetism in ferromagnet (FM) thin-film nanostructures with an in-plane current has become feasible since the determination of a "giant" spin Hall effect (SHE) in certain heavy metal/FM systems. Recently, both theoretical and experimental reports indicate that metallic antiferromagnet materials can have both a large anomalous Hall effect and a strong SHE. Here we report a systematic study of the SHE in PtMn with several PtMn/FM systems. By using interface engineering to reduce the "spin memory loss" we obtain, in the best instance, a spin-torque efficiency ξDLPtMn≡TintθSHPtMn≃0.24 , where Tint is the effective interface spin transparency. This is more than twice the previously reported spin-torque efficiency for PtMn. We also find that the apparent spin diffusion length in PtMn is surprisingly long, λsPtMn≈2.3 nm .

  4. Point interactions, metamaterials, and PT-symmetry

    NASA Astrophysics Data System (ADS)

    Mostafazadeh, Ali

    2016-05-01

    We express the boundary conditions for TE and TM waves at the interfaces of an infinite planar slab of homogeneous metamaterial as certain point interactions and use them to compute the transfer matrix of the system. This allows us to demonstrate the omnidirectional reflectionlessness of Veselago's slab for waves of arbitrary wavelength, reveal the translational and reflection symmetry of this slab, explore the laser threshold condition and coherent perfect absorption for active negative-index metamaterials, introduce a point interaction modeling phase-conjugation, determine the corresponding antilinear transfer matrix, and offer a simple proof of the equivalence of Veselago's slab with a pair of parallel phase-conjugating plates. We also study the connection between certain optical setups involving metamaterials and a class of PT-symmetric quantum systems defined on wedge-shape contours in the complex plane. This provides a physical interpretation for the latter.

  5. Status of Genesis Mo-Pt Foils

    NASA Technical Reports Server (NTRS)

    Nishiizumi, K.; Allton, J. H.; Burnett, D. S.; Butterworth, A. L.; Caffee, M. W.; Clark, B.; Jurewicz, A. J. G.; Komura, K.; Westphal, A. J.; Welten, K. C.

    2005-01-01

    A total of 8,000 sq cm of Mo-coated Pt foils were exposed to solar wind for 884 days by the Genesis mission. Solar wind ions were captured in the surface of the Mo. Our objective is the measurement of long-lived radionuclides, such as Be-10, Al-26, Cl-36, and Mn-53, and short-lived radionuclides, such as Na-22 and Mn-54, in the captured sample of solar wind. The expected flux of these nuclides in the solar wind is 100 atom/sq cm yr or less. The hard landing of the SRC (Sample Return Capsule) at UTTR (Utah Test and Training Range) has resulted in contaminated and crumpled foils. Here we present a status report and revised plan for processing the foils.

  6. Spin-orbit torque in Pt/CoNiCo/Pt symmetric devices

    PubMed Central

    Yang, Meiyin; Cai, Kaiming; Ju, Hailang; Edmonds, Kevin William; Yang, Guang; Liu, Shuai; Li, Baohe; Zhang, Bao; Sheng, Yu; Wang, Shouguo; Ji, Yang; Wang, Kaiyou

    2016-01-01

    Current induced magnetization switching by spin-orbit torques offers an energy-efficient means of writing information in heavy metal/ferromagnet (FM) multilayer systems. The relative contributions of field-like torques and damping-like torques to the magnetization switching induced by the electrical current are still under debate. Here, we describe a device based on a symmetric Pt/FM/Pt structure, in which we demonstrate a strong damping-like torque from the spin Hall effect and unmeasurable field-like torque from Rashba effect. The spin-orbit effective fields due to the spin Hall effect were investigated quantitatively and were found to be consistent with the switching effective fields after accounting for the switching current reduction due to thermal fluctuations from the current pulse. A non-linear dependence of deterministic switching of average Mz on the in-plane magnetic field was revealed, which could be explained and understood by micromagnetic simulation. PMID:26856379

  7. Spin-orbit torque in Pt/CoNiCo/Pt symmetric devices

    NASA Astrophysics Data System (ADS)

    Yang, Meiyin; Cai, Kaiming; Ju, Hailang; Edmonds, Kevin William; Yang, Guang; Liu, Shuai; Li, Baohe; Zhang, Bao; Sheng, Yu; Wang, Shouguo; Ji, Yang; Wang, Kaiyou

    2016-02-01

    Current induced magnetization switching by spin-orbit torques offers an energy-efficient means of writing information in heavy metal/ferromagnet (FM) multilayer systems. The relative contributions of field-like torques and damping-like torques to the magnetization switching induced by the electrical current are still under debate. Here, we describe a device based on a symmetric Pt/FM/Pt structure, in which we demonstrate a strong damping-like torque from the spin Hall effect and unmeasurable field-like torque from Rashba effect. The spin-orbit effective fields due to the spin Hall effect were investigated quantitatively and were found to be consistent with the switching effective fields after accounting for the switching current reduction due to thermal fluctuations from the current pulse. A non-linear dependence of deterministic switching of average Mz on the in-plane magnetic field was revealed, which could be explained and understood by micromagnetic simulation.

  8. Synthesis of PtCo3 polyhedral nanoparticles and evolution to Pt3Co nanoframes

    NASA Astrophysics Data System (ADS)

    Becknell, Nigel; Zheng, Cindy; Chen, Chen; Yu, Yi; Yang, Peidong

    2016-06-01

    Bimetallic nanoframes have great potential for achieving new levels of catalytic activity in various heterogeneous reactions due to their high surface area dispersion of expensive noble metals on the exterior and interior surfaces of the structure. PtCo3 nanoparticles with polyhedral shapes were synthesized by a hot-injection method. Scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy (EDS) showed that these nanoparticles demonstrated elemental segregation of platinum to the edges of the polyhedron, forming the basis for a framework nanostructure. The process of preferential oxidative leaching which removed cobalt from the interior of the framework was tracked by EDS and inductively coupled plasma optical emission spectroscopy. This evolution procedure left the platinum-rich edges intact to form a Pt3Co nanoframe. This is the first reported synthesis of a platinum-cobalt nanoframe and could have potential applications in catalytic reactions such as oxygen reduction.

  9. Evolution of anomalous Hall behavior in thin Pt/Co/Pt trilayers

    NASA Astrophysics Data System (ADS)

    Sun, Niu-yi; Zhang, Yan-qing; Che, Wen-ru; Shan, Rong; Zhu, Zhen-gang

    2016-05-01

    In this work, through controlling spin scattering mechanisms, anomalous Hall behaviors exhibit a series of evolutions in thin Pt/Co/Pt trilayers. The shape of Hall resistivity over longitudinal resistivity (ρAH /ρxx versus ρxx) curve turns from bending to linear and then bending again in most trilayers. This kind of evolution cannot be explained by the conventional linear scaling of anomalous Hall effect. It should be ascribed to the contribution of spin-phonon skew scattering. Our research may help to understand spin scattering behavior in low-dimensional systems more deeply and build a proper synergy between theory and experiment on the research of anomalous Hall effect.

  10. Spin-orbit torque in Pt/CoNiCo/Pt symmetric devices.

    PubMed

    Yang, Meiyin; Cai, Kaiming; Ju, Hailang; Edmonds, Kevin William; Yang, Guang; Liu, Shuai; Li, Baohe; Zhang, Bao; Sheng, Yu; Wang, Shouguo; Ji, Yang; Wang, Kaiyou

    2016-01-01

    Current induced magnetization switching by spin-orbit torques offers an energy-efficient means of writing information in heavy metal/ferromagnet (FM) multilayer systems. The relative contributions of field-like torques and damping-like torques to the magnetization switching induced by the electrical current are still under debate. Here, we describe a device based on a symmetric Pt/FM/Pt structure, in which we demonstrate a strong damping-like torque from the spin Hall effect and unmeasurable field-like torque from Rashba effect. The spin-orbit effective fields due to the spin Hall effect were investigated quantitatively and were found to be consistent with the switching effective fields after accounting for the switching current reduction due to thermal fluctuations from the current pulse. A non-linear dependence of deterministic switching of average Mz on the in-plane magnetic field was revealed, which could be explained and understood by micromagnetic simulation. PMID:26856379

  11. Electrodeposited Co-Pt thin films for magnetic hard disks

    NASA Astrophysics Data System (ADS)

    Bozzini, B.; De Vita, D.; Sportoletti, A.; Zangari, G.; Cavallotti, P. L.; Terrenzio, E.

    1993-03-01

    ew baths for Co-Pt electrodeposition have been developed and developed and ECD thin films (≤0.3μm) have been prepared and characterized structurally (XRD), morphologically (SEM), chemically (EDS) and magnetically (VSM); their improved corrosion, oxidation and wear resistance have been ascertained. Such alloys appear suitable candidates for magnetic storage systems, from all technological viewpoints. The originally formulated baths contain Co-NH 3-citrate complexes and Pt-p salt (Pt(NH 3) 2(NO 2) 2). Co-Pt thin films of fcc structure are deposited obtaining microcrystallites of definite composition. At Pt ⋍ 30 at% we obtain fcc films with a=0.369 nm, HC=80 kA m, and high squareness; increasing Co and decreasing Pt content in the bath it is possible to reduce the Pt content of the deposit, obtaining fcc structures containing two types of microcrystals with a = 0.3615 nm and a = 0.369 nm deposited simultaneously. NaH 2PO 2 additions to the bath have a stabilizing influence on the fcc structure of a = 0.3615 nm, Pt ⋍ 20 at% and HC as high as 200 kA/m, with hysteresis loops suitable for both longitudinal or perpendicular recording, depending on the thickness. We have prepared 2.5 in. hard disks for magnetic recording with ECD Co-Pt 20 at% with a polished and texturized ACD Ni-P underlayer. Pulse response, 1F & 2F frequency and frequency sweep response behaviour, as well as noise and overwrite characteristics have been measured for both our disks and high-standard sputtered Co-Cr-Ta production disks, showin improved D50 for Co-Pt ECD disks. The signal-to-noise ratio could be improved by pulse electrodeposition and etching post-treatments.

  12. Structural and electronic properties of Ce overlayers and low-dimensional Pt-Ce alloys on Pt\\{111\\}

    NASA Astrophysics Data System (ADS)

    Baddeley, Christopher J.; Stephenson, Andrew W.; Hardacre, Christopher; Tikhov, Mintcho; Lambert, Richard M.

    1997-11-01

    The structural, thermal, chemisorptive, and electronic properties of Ce on Pt\\{111\\} are studied by photoemission, Auger spectroscopy, scanning tunnel microscope (STM), and low-energy electron diffraction (LEED). Stranski-Krastanov-like growth of low-density Ce layers is accompanied by substantial valence charge transfer from Ce to Pt: in line with this, the measured dipole moment and polarizability of adsorbed Ce at low coverages are 7.2×10-30 C m and ~1.3×10-29 m3, respectively. Pt-Ce intermixing commences at ~400 K and with increasing temperature a sequence of five different ordered surface alloys evolves. The symmetry, periodicities, and rotational epitaxy observed by LEED are in good accord with the STM data which reveal the true complexity of the system. The various bimetallic surface phases are based on growth of crystalline Pt5Ce, a hexagonal layer structure consisting of alternating layers of Pt2Ce and Kagomé nets of Pt atoms. This characteristic ABAB layered arrangement of the surface alloys is clearly imaged, and chemisorption data permit a distinction to be made between the more reactive Pt2Ce layer and the less reactive Pt Kagomé net. Either type of layer can appear at the surface as the terminating structure, thicker films exhibiting unit mesh parameters characteristic of the bulk alloy.

  13. Impact of buffer layer and Pt thickness on the interface structure and magnetic properties in (Co/Pt) multilayers

    NASA Astrophysics Data System (ADS)

    Bersweiler, M.; Dumesnil, K.; Lacour, D.; Hehn, M.

    2016-08-01

    The influence of Pt thickness on the interface structure (roughness / intermixing) and magnetic properties has been investigated for (Co / Pt) multilayers sputtered on a Pt or a thin oxide (MgO or AlO x ) buffer layer. When Pt thickness increases from 1.2 nm–2.2 nm, we observe that the effective anisotropy increases with the Pt thickness, simultaneously with the decrease of roughness, i.e. the occurrence of sharper interfaces. Perpendicular magnetic anisotropy (PMA) is still achieved on the oxide buffer layers, but with a lower effective anisotropy correlated to more perturbed interfaces. The detailed analysis of the saturation magnetization shows that: (i) M s is significantly enhanced in the case of rough/intermixed interfaces, which is attributed to and discussed in the framework of Pt induced polarization, (ii) the change in volume dipolar anisotropy is the main factor responsible for the reduction of K eff for systems grown on oxides. Beyond the major role of volume dipolar contribution that reduces PMA, a supplemental positive contribution promoting PMA can be invoked for rough interfaces and large M s (deposit on oxide). This contribution is consistent with a dipolar surface anisotropy term and increases for rough interfaces, in contrast to the Néel surface anisotropy. These opposite variations may interestingly lead to an enhanced anisotropy in (Co / Pt) stackings grown on oxides compared to systems deposited on Pt, i.e. with sharper interfaces.

  14. Investigation of nano Pt and Pt-based alloys electrocatalysts for direct methanol fuel cells and their properties

    NASA Astrophysics Data System (ADS)

    Suo, Chunguang; Zhang, Wenbin; Shi, Xinghua; Ma, Chuxia

    2014-03-01

    The electrocatalysts used in micro direct methanol fuel cell (μDMFC), such as Pt/C and Pt alloy/C, prepared by liquid-phase NaBH4 reduction method have been investigated. XC-72 (Cobalt corp. Company, U.S.A) is chosen as the activated carrier for the electrocatalysts to keep the catalysts powder in the range of several nanometers. The XRD, SEM, EDX analyses indicated that the catalysts had small particle size in several nanometers, in excellent dispersed phase and the molar ratio of the precious metals was found to be optimal. The performances of the DMFCs using cathodic catalyst with Pt percentage of 30wt% and different anodic catalysts (Pt-Ru, Pt-Ru-Mo) were tested. The polarization curves and power density curves of the cells were measured to determine the optimal alloy composition and condition for the electrocatalysts. The results showed that the micro direct methanol fuel cell with 30wt% Pt/C as the cathodic catalyst and n(Pt):n(Ru):n(Mo) = 3:2:2 PtRuMo/C as the anodic catalyst at room temperature using 2.0mol/L methanol solution has the best performances.

  15. Impact of buffer layer and Pt thickness on the interface structure and magnetic properties in (Co/Pt) multilayers

    NASA Astrophysics Data System (ADS)

    Bersweiler, M.; Dumesnil, K.; Lacour, D.; Hehn, M.

    2016-08-01

    The influence of Pt thickness on the interface structure (roughness / intermixing) and magnetic properties has been investigated for (Co / Pt) multilayers sputtered on a Pt or a thin oxide (MgO or AlO x ) buffer layer. When Pt thickness increases from 1.2 nm-2.2 nm, we observe that the effective anisotropy increases with the Pt thickness, simultaneously with the decrease of roughness, i.e. the occurrence of sharper interfaces. Perpendicular magnetic anisotropy (PMA) is still achieved on the oxide buffer layers, but with a lower effective anisotropy correlated to more perturbed interfaces. The detailed analysis of the saturation magnetization shows that: (i) M s is significantly enhanced in the case of rough/intermixed interfaces, which is attributed to and discussed in the framework of Pt induced polarization, (ii) the change in volume dipolar anisotropy is the main factor responsible for the reduction of K eff for systems grown on oxides. Beyond the major role of volume dipolar contribution that reduces PMA, a supplemental positive contribution promoting PMA can be invoked for rough interfaces and large M s (deposit on oxide). This contribution is consistent with a dipolar surface anisotropy term and increases for rough interfaces, in contrast to the Néel surface anisotropy. These opposite variations may interestingly lead to an enhanced anisotropy in (Co / Pt) stackings grown on oxides compared to systems deposited on Pt, i.e. with sharper interfaces.

  16. A Selective Blocking Method To Control the Overgrowth of Pt on Au Nanorods

    PubMed Central

    2013-01-01

    A method for the preparation of smooth deposits of Pt on Au nanorods is described, involving sequential deposition steps with selective blocking of surface sites that reduces Pt-on-Pt deposition. The Au–Pt nanorods prepared by this method have higher long-term stability than those prepared by standard Pt deposition. Electrochemical data show that the resulting structure has more extended regions of Pt surface and enhanced activity toward the carbon monoxide oxidation and oxygen reduction reactions. PMID:23594230

  17. Laser-excited luminescence and absorption study of mixed valence for K 2Pt(CN) 4—K 2Pt(CN) 6 crystals

    NASA Astrophysics Data System (ADS)

    Kasi Viswanath, A.; Smith, Wayne L.; Patterson, H.

    1982-04-01

    Crystals of K 2Pt(CN) 6 doped with Pt(CN) 2-4 show an absorption band at 337 nm which is assigned as a mixed-valence (MV) transition from Pt (II) to Pt(IV). From a Hush model analysis, the absorption band is interpreted to be class II in the Day—Robin scheme. When the MV band is laser excited at 337 nm, emmision is observed from Pt(CN) 2-4 clusters.

  18. Effects of toluene and benzoic acid on the kinetics of ferrous oxidation on Pt and nafion-coated Pt electrodes

    SciTech Connect

    Ye, J.H.; Fedkiw, P.S. . Dept. of Chemical Engineering)

    1994-06-01

    The electrochemical kinetics of Fe[sup 2+] oxidation to Fe[sup 3+] have been investigated by cyclic and ring disk electrode voltammetry in the absence and presence of the contaminants toluene (7 mM, saturated solution) or benzoic acid (16 mM) in 1M H[sub 2]SO[sub 4] electrolyte on (1) smooth Pt electrodes, (2) Nafion-coated smooth Pt electrodes, and (3) Pt electrodes electrodeposited within a Nafion film coated onto a glassy carbon (GC) substrate. On uncoated Pt, the kinetics are adversely affected by these two organics: both the anodic transfer coefficient and the apparent standard rate constant are decreased. A 3.7 [mu]m Nafion coating, however, effectively buffers the smooth Pt electrode from toluene, but, nevertheless, benzoic acid still affects the reaction rate. In contrast, the transfer coefficient and rate constant for Fe[sup 2+] oxidation on the Pt/Nafion/GC electrode are essentially unaffected by either toluene or benzoic acid. Qualitative features of the voltammograms also indicate that the Nafion film protects the Pt from contamination by these aromatics: two current plateaus are observed using an uncoated Pt electrode in the presence of toluene or benzoic acid with a ratio which increased with rotation rate; with the Nafion coating on a smooth Pt electrode and in the presence of toluene, however, there is only one current plateau; in the presence of benzoic acid, two current plateaus remain, but the ratio is nearer unity and less sensitive to rotation rate. In contrast, only a single plateau current is observed using the Pt/Nafion/GC electrode. The Nafion coating is apparently an effective buffer layer against these two aromatics, but concurrently affects a decrease in the mass-transfer limited current due to the diffusional resistance of the film.

  19. 32 CFR Appendix D to Part 623 - Certificate for Signature by an Alternate (DA Form 4881-1-R)

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 32 National Defense 3 2014-07-01 2014-07-01 false Certificate for Signature by an Alternate (DA Form 4881-1-R) D Appendix D to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. D Appendix D to Part 623—Certificate for Signature by an Alternate (DA...

  20. 32 CFR Appendix D to Part 623 - Certificate for Signature by an Alternate (DA Form 4881-1-R)

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 32 National Defense 3 2013-07-01 2013-07-01 false Certificate for Signature by an Alternate (DA Form 4881-1-R) D Appendix D to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. D Appendix D to Part 623—Certificate for Signature by an Alternate (DA...

  1. 32 CFR Appendix C to Part 623 - Agreement for Loan of US Army Materiel (DA Form 4881-R)

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 32 National Defense 3 2012-07-01 2009-07-01 true Agreement for Loan of US Army Materiel (DA Form 4881-R) C Appendix C to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. C Appendix C to Part 623—Agreement for Loan of US Army Materiel (DA Form...

  2. 32 CFR Appendix C to Part 623 - Agreement for Loan of US Army Materiel (DA Form 4881-R)

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 32 National Defense 3 2013-07-01 2013-07-01 false Agreement for Loan of US Army Materiel (DA Form 4881-R) C Appendix C to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. C Appendix C to Part 623—Agreement for Loan of US Army Materiel (DA Form...

  3. 32 CFR Appendix C to Part 623 - Agreement for Loan of US Army Materiel (DA Form 4881-R)

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 32 National Defense 3 2014-07-01 2014-07-01 false Agreement for Loan of US Army Materiel (DA Form 4881-R) C Appendix C to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. C Appendix C to Part 623—Agreement for Loan of US Army Materiel (DA Form...

  4. 32 CFR Appendix D to Part 623 - Certificate for Signature by an Alternate (DA Form 4881-1-R)

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 32 National Defense 3 2012-07-01 2009-07-01 true Certificate for Signature by an Alternate (DA Form 4881-1-R) D Appendix D to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. D Appendix D to Part 623—Certificate for Signature by an Alternate (DA Form...

  5. 32 CFR Appendix C to Part 623 - Agreement for Loan of US Army Materiel (DA Form 4881-R)

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 32 National Defense 3 2011-07-01 2009-07-01 true Agreement for Loan of US Army Materiel (DA Form... ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. C Appendix C to Part 623—Agreement for Loan of US Army Materiel (DA Form 4881-R) EC24OC91.013 EC24OC91.014 EC24OC91.015 EC24OC91.016...

  6. 32 CFR Appendix C to Part 623 - Agreement for Loan of US Army Materiel (DA Form 4881-R)

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 3 2010-07-01 2010-07-01 true Agreement for Loan of US Army Materiel (DA Form... ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. C Appendix C to Part 623—Agreement for Loan of US Army Materiel (DA Form 4881-R) EC24OC91.013 EC24OC91.014 EC24OC91.015 EC24OC91.016...

  7. Design criteria for stable Pt/C fuel cell catalysts

    PubMed Central

    Katsounaros, Ioannis; Witte, Jonathon; Bongard, Hans J; Topalov, Angel A; Baldizzone, Claudio; Mezzavilla, Stefano; Schüth, Ferdi

    2014-01-01

    Summary Platinum and Pt alloy nanoparticles supported on carbon are the state of the art electrocatalysts in proton exchange membrane fuel cells. To develop a better understanding on how material design can influence the degradation processes on the nanoscale, three specific Pt/C catalysts with different structural characteristics were investigated in depth: a conventional Pt/Vulcan catalyst with a particle size of 3–4 nm and two Pt@HGS catalysts with different particle size, 1–2 nm and 3–4 nm. Specifically, Pt@HGS corresponds to platinum nanoparticles incorporated and confined within the pore structure of the nanostructured carbon support, i.e., hollow graphitic spheres (HGS). All three materials are characterized by the same platinum loading, so that the differences in their performance can be correlated to the structural characteristics of each material. The comparison of the activity and stability behavior of the three catalysts, as obtained from thin film rotating disk electrode measurements and identical location electron microscopy, is also extended to commercial materials and used as a basis for a discussion of general fuel cell catalyst design principles. Namely, the effects of particle size, inter-particle distance, certain support characteristics and thermal treatment on the catalyst performance and in particular the catalyst stability are evaluated. Based on our results, a set of design criteria for more stable and active Pt/C and Pt-alloy/C materials is suggested. PMID:24605273

  8. Atomic Layer Deposition of Ir−Pt Alloy Films;

    SciTech Connect

    Christensen, S. T.; Elam, J. W.

    2010-01-01

    Atomic layer deposition (ALD) was used to prepare thin-film mixtures of iridium and platinum. By controlling the ratio between the iridium(III) acetylacetonate/oxygen cycles for Ir ALD and the (trimethyl)methylcyclopentadienyl platinum(IV)/oxygen cycles for Pt ALD, the Ir/Pt ratio in the films could be controlled precisely. We first examined the growth mechanisms for the pure Ir and Pt ALD films, as well as the mixed-metal Ir-Pt ALD films, using in situ quartz crystal microbalance and quadrupole mass spectrometer measurements. These studies revealed that the nucleation and growth of each of the noble metals proceeds smoothly, with negligible perturbation caused by the presence of the other metal. As a consequence of this mutual compatibility, the composition, as well as the growth per cycle for the Ir-Pt films, followed rule-of-mixtures formulas that were based on the ratio of the metal ALD cycles and the growth rates of pure Ir and Pt ALD. X-ray diffraction (XRD) measurements revealed that the films deposit as single-phase alloys in which the lattice parameter varies linearly with the composition. Similar to the pure noble-metal films, the Ir-Pt alloy films grow conformally on high-aspect-ratio trenches. This capability should open up new opportunities in microelectronics, catalysis, and other applications.

  9. Macromolecular Pt(IV) Prodrugs from Poly(organo)phosphazenes.

    PubMed

    Henke, Helena; Kryeziu, Kushtrim; Banfić, Jelena; Theiner, Sarah; Körner, Wilfried; Brüggemann, Oliver; Berger, Walter; Keppler, Bernhard K; Heffeter, Petra; Teasdale, Ian

    2016-08-01

    The preparation of novel macromolecular prodrugs via the conjugation of two platinum(IV) complexes to suitably functionalized poly(organo)phosphazenes is presented. The inorganic/organic polymers provide carriers with controlled dimensions due to the use of living cationic polymerization and allow the preparation of conjugates with excellent aqueous solubility but long-term hydrolytic degradability. The macromolecular Pt(IV) prodrugs are designed to undergo intracellular reduction and simultaneous release from the macromolecular carrier to present the active Pt(II) drug derivatives. In vitro investigations show a significantly enhanced intracellular uptake of Pt for the macromolecular prodrugs when compared to small molecule Pt complexes, which is also reflected in an increase in cytotoxicity. Interestingly, drug-resistant sublines also show a significantly smaller resistance against the conjugates compared to clinically established platinum drugs, indicating that an alternative uptake route of the Pt(IV) conjugates might also be able to overcome acquired resistance against Pt(II) drugs. In vivo studies of a selected conjugate show improved tumor shrinkage compared to the respective Pt(IV) complex. PMID:27169668

  10. Macromolecular Pt(IV) Prodrugs from Poly(organo)phosphazenes.

    PubMed

    Henke, Helena; Kryeziu, Kushtrim; Banfić, Jelena; Theiner, Sarah; Körner, Wilfried; Brüggemann, Oliver; Berger, Walter; Keppler, Bernhard K; Heffeter, Petra; Teasdale, Ian

    2016-08-01

    The preparation of novel macromolecular prodrugs via the conjugation of two platinum(IV) complexes to suitably functionalized poly(organo)phosphazenes is presented. The inorganic/organic polymers provide carriers with controlled dimensions due to the use of living cationic polymerization and allow the preparation of conjugates with excellent aqueous solubility but long-term hydrolytic degradability. The macromolecular Pt(IV) prodrugs are designed to undergo intracellular reduction and simultaneous release from the macromolecular carrier to present the active Pt(II) drug derivatives. In vitro investigations show a significantly enhanced intracellular uptake of Pt for the macromolecular prodrugs when compared to small molecule Pt complexes, which is also reflected in an increase in cytotoxicity. Interestingly, drug-resistant sublines also show a significantly smaller resistance against the conjugates compared to clinically established platinum drugs, indicating that an alternative uptake route of the Pt(IV) conjugates might also be able to overcome acquired resistance against Pt(II) drugs. In vivo studies of a selected conjugate show improved tumor shrinkage compared to the respective Pt(IV) complex.

  11. Nanosized Pt-Co catalysts for the preferential CO oxidation.

    PubMed

    Ko, Eun-Yong; Park, Eun Duck; Seo, Kyung Won; Lee, Hyun Chul; Lee, Doohwan; Kim, Soonho

    2006-11-01

    The preferential CO oxidation in the presence of excess hydrogen was studied over Pt-Co/gamma-Al2O3. CO chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX) and temperature programmed reduction (TPR) were conducted to characterize active catalysts. The catalytic activity for CO oxidation and methanation at low temperatures increased with the amounts of cobalt in Pt-Co/gamma-Al2O3. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Co and Pt was determined to be 10. The co-impregnated Pt-Co/gamma-Al2O3 appeared to be superior to Pt/Co/gamma-Al2O3 and Co/Pt/gamma-Al2O3. The reductive pretreatment at high temperature such as 773 K increased the CO2 selectivity over a wide reaction temperature. The bimetallic phase of Pt-Co seems to give rise to high catalytic activity in selective oxidation of CO in H2-rich stream. PMID:17252813

  12. Macromolecular Pt(IV) Prodrugs from Poly(organo)phosphazenes

    PubMed Central

    Banfić, Jelena; Theiner, Sarah; Körner, Wilfried; Brüggemann, Oliver; Berger, Walter; Keppler, Bernhard K.; Heffeter, Petra; Teasdale, Ian

    2016-01-01

    The preparation of novel macromolecular prodrugs via the conjugation of two platinum(IV) complexes to suitably functionalized poly(organo)phosphazenes is presented. The inorganic/organic polymers provide carriers with controlled dimensions due to the use of living cationic polymerization and allow the preparation of conjugates with excellent aqueous solubility but long-term hydrolytic degradability. The macromolecular Pt(IV) prodrugs are designed to undergo intracellular reduction and simultaneous release from the macromolecular carrier to present the active Pt(II) drug derivatives. In vitro investigations show a significantly enhanced intracellular uptake of Pt for the macromolecular prodrugs when compared to small molecule Pt complexes, which is also reflected in an increase in cytotoxicity. Interestingly, drug-resistant sublines also show a significantly smaller resistance against the conjugates compared to clinically established platinum drugs, indicating that an alternative uptake route of the Pt(IV) conjugates might also be able to overcome acquired resistance against Pt(II) drugs. In vivo studies of a selected conjugate show improved tumor shrinkage compared to the respective Pt(IV) complex. PMID:27169668

  13. Development of a PtSn bimetallic catalyst for direct fuel cells using bio-butanol fuel.

    PubMed

    Puthiyapura, V K; Brett, D J L; Russell, A E; Lin, W F; Hardacre, C

    2015-09-01

    Pt and PtSn catalysts were studied for n-butanol electro-oxidation at various temperatures. PtSn showed a higher activity towards butanol electro-oxidation compared to Pt in acidic media. The onset potential for n-butanol oxidation on PtSn is ∼520 mV lower than that found on Pt, and significantly lower activation energy was found for PtSn compared with that for Pt. PMID:26214283

  14. Purification and Characterization of a Cold-Adapted Lipase from Oceanobacillus Strain PT-11

    PubMed Central

    Jiewei, Tian; Zuchao, Lei; Peng, Qiu; Lei, Wang; Yongqiang, Tian

    2014-01-01

    We isolated a moderately halophilic lipase-producing bacterium from the saline soil. Based on the morphological, physiological, chemotaxonomic and phylogenetic analysis, the isolate PT-11 was postulated to be a novel species identified as Oceanobacillus rekensis PT-11. The lipase was purified 2.50-fold by Q-Sepharose FF and SP-Sepharose FF chromatography and its molecular mass was estimated to be 23.5 kDa by SDS-PAGE. It was highly active over the broad temperature ranging from 10 to 35°C and showed up to 80% of the maximum activity at 10°C indicating the lipase to be a typical cold-adapted enzyme. The enzyme activity was slightly enhanced by Na+, Li+ and K+. Incubation with detergents, such as Tween-20 and Tween-80, slightly inhibited the enzyme activity; while Triton X-100decreased the enzyme activity. The enzyme was fairly stable in the presence of long-chain alcohols but was highly denatured in hydrophilic solvents such as acetone or short-chain alcohols (C1–C3). PMID:24984141

  15. Purification and characterization of a cold-adapted lipase from Oceanobacillus strain PT-11.

    PubMed

    Jiewei, Tian; Zuchao, Lei; Peng, Qiu; Lei, Wang; Yongqiang, Tian

    2014-01-01

    We isolated a moderately halophilic lipase-producing bacterium from the saline soil. Based on the morphological, physiological, chemotaxonomic and phylogenetic analysis, the isolate PT-11 was postulated to be a novel species identified as Oceanobacillus rekensis PT-11. The lipase was purified 2.50-fold by Q-Sepharose FF and SP-Sepharose FF chromatography and its molecular mass was estimated to be 23.5 kDa by SDS-PAGE. It was highly active over the broad temperature ranging from 10 to 35°C and showed up to 80% of the maximum activity at 10°C indicating the lipase to be a typical cold-adapted enzyme. The enzyme activity was slightly enhanced by Na+, Li+ and K+. Incubation with detergents, such as Tween-20 and Tween-80, slightly inhibited the enzyme activity; while Triton X-100decreased the enzyme activity. The enzyme was fairly stable in the presence of long-chain alcohols but was highly denatured in hydrophilic solvents such as acetone or short-chain alcohols (C1-C3). PMID:24984141

  16. Whole body retention in rats of different 191Pt compounds following inhalation exposure.

    PubMed Central

    Moore, W; Malanchuk, M; Crocker, W; Hysell, D; Cohen, A; Stara, J F

    1975-01-01

    The whole body retention, excretion, lung clearance, distribution, and concentration of 191Pt in other tissues was determined in rats following a single inhalation exposure to different chemical forms of 191Pt. The chemical forms of 191Pt used in study were 191PtCl4, 191Pt(SO4)2, 191PtO, and 191Pt metal. Immediately after exposure most of the 191Pt was found in the gastrointestinal and respiratory tract. Movement of the 191Pt through the gastrointestinal tract was rapid, most of the 191Pt being eliminated within 24 hr after exposure. Lung clearance was much slower, with a clearance half-time of about 8 days. In addition to the lungs, kidney and bone contained the highest concentrations of 191Pt. PMID:1227859

  17. Kinetically induced irreversibility in electro-oxidation and reduction of Pt surface.

    PubMed

    Jinnouchi, Ryosuke; Kodama, Kensaku; Suzuki, Takahisa; Morimoto, Yu

    2015-05-14

    A mean field kinetic model was developed for electrochemical oxidations and reductions of Pt(111) on the basis of density functional theory calculations, and the reaction mechanisms were analyzed. The model reasonably describes asymmetric shapes of cyclic voltammograms and small Tafel slopes of relevant redox reactions observed in experiments without assuming any unphysical forms of rate equations. Simulations using the model indicate that the oxidation of Pt(111) proceeds via an electrochemical oxidation from Pt to PtOH and a disproportionation reaction from PtOH to PtO and Pt, while its reduction proceeds via two electrochemical reductions from PtO to PtOH and from PtOH to Pt.

  18. Nanopatterned CoPt alloys with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Makarov, D.; Bermúdez-Ureña, E.; Schmidt, O. G.; Liscio, F.; Maret, M.; Brombacher, C.; Schulze, S.; Hietschold, M.; Albrecht, M.

    2008-10-01

    CoPt alloy films with perpendicular magnetic anisotropy were grown on SiO2 nanoparticle arrays with particle sizes as small as 10 nm. In order to induce perpendicular magnetic anisotropy in the CoPt film, a MgO seed layer was sputter deposited. Despite the fact that neighboring CoPt film caps are interconnected, individual caps appear as single domain and for most of them their magnetization orientation can be reversed individually. This behavior might be caused by domain wall nucleation and pinning preferentially at the rim of each cap. Thus, arrays of magnetic caps with defined pinning sites can be considered as a percolated perpendicular medium.

  19. Non-Hermitian quantum Hamiltonians with PT symmetry

    SciTech Connect

    Jones-Smith, Katherine; Mathur, Harsh

    2010-10-15

    We formulate quantum mechanics for non-Hermitian Hamiltonians that are invariant under PT, where P is the parity and T denotes time reversal, for the case that time-reversal symmetry is odd (T{sup 2}=-1), generalizing prior work for the even case (T{sup 2}=1). We discover an analog of Kramer's theorem for PT quantum mechanics, present a prototypical example of a PT quantum system with odd time reversal, and discuss potential applications of the formalism.

  20. Giant Goos-Hänchen shift using PT symmetry

    NASA Astrophysics Data System (ADS)

    Ziauddin; Chuang, You-Lin; Lee, Ray-Kuang

    2015-07-01

    Influence of PT symmetry on the Goos-Hänchen (GH) shift in the reflected light is presented for an ensemble of atomic medium in a cavity, in the configuration of four-level N -type (87Rb atoms) systems driving by two copropagating strong laser fields and a weak probe field. The atom-field interaction follows the realization of PT symmetry by adjusting the coupling field detunings [J. Shenget al., Phys. Rev. A 88, 041803(R) (2013), 10.1103/PhysRevA.88.041803]. A giant enhancement for the GH shift in the reflected light is revealed when the PT -symmetry condition is satisfied.

  1. Inverse spin Hall effect in Pt/(Ga,Mn)As

    SciTech Connect

    Nakayama, H.; Chen, L.; Chang, H. W.; Ohno, H.; Matsukura, F.

    2015-06-01

    We investigate dc voltages under ferromagnetic resonance in a Pt/(Ga,Mn)As bilayer structure. A part of the observed dc voltage is shown to originate from the inverse spin Hall effect. The sign of the inverse spin Hall voltage is the same as that in Py/Pt bilayer structure, even though the stacking order of ferromagnetic and nonmagnetic layers is opposite to each other. The spin mixing conductance at the Pt/(Ga,Mn)As interface is determined to be of the order of 10{sup 19 }m{sup −2}, which is about ten times greater than that of (Ga,Mn)As/p-GaAs.

  2. Mesoporous Trimetallic PtPdRu Spheres as Superior Electrocatalysts.

    PubMed

    Jiang, Bo; Ataee-Esfahani, Hamed; Li, Cuiling; Alshehri, Saad M; Ahamad, Tansir; Henzie, Joel; Yamauchi, Yusuke

    2016-05-17

    Mesoporous Trimetallic PtPdRu Spheres with well-defined spherical morphology and uniformly sized pores were synthesized in an aqueous solution using ascorbic acid as the reducing agent and triblock copolymer F127 as the pore directing agent. These mesoporous PtPdRu spheres exhibited enhanced electrocatalytic activity compared to commercial Pt black, resulting in a ∼4.9 times improvement in mass activity for the methanol oxidation reaction. The excellent electrocatalytic activity and stability are due to the unique mesoporous architecture and electronic landscape between different elements. PMID:27072776

  3. On stable solitons and interactions of the generalized Gross-Pitaevskii equation with PT- and non- PT-symmetric potentials.

    PubMed

    Yan, Zhenya; Chen, Yong; Wen, Zichao

    2016-08-01

    We report the bright solitons of the generalized Gross-Pitaevskii (GP) equation with some types of physically relevant parity-time- ( PT-) and non- PT-symmetric potentials. We find that the constant momentum coefficient Γ can modulate the linear stability and complicated transverse power-flows (not always from the gain toward loss) of nonlinear modes. However, the varying momentum coefficient Γ(x) can modulate both unbroken linear PT-symmetric phases and stability of nonlinear modes. Particularly, the nonlinearity can excite the unstable linear mode (i.e., broken linear PT-symmetric phase) to stable nonlinear modes. Moreover, we also find stable bright solitons in the presence of non- PT-symmetric harmonic-Gaussian potential. The interactions of two bright solitons are also illustrated in PT-symmetric potentials. Finally, we consider nonlinear modes and transverse power-flows in the three-dimensional (3D) GP equation with the generalized PT-symmetric Scarff-II potential. PMID:27586605

  4. Monolayer PtSe 2 , a New Semiconducting Transition-Metal-Dichalcogenide, Epitaxially Grown by Direct Selenization of Pt

    DOE PAGESBeta

    Wang, Yeliang; Li, Linfei; Yao, Wei; Song, Shiru; Sun, J. T.; Pan, Jinbo; Ren, Xiao; Li, Chen; Okunishi, Eiji; Wang, Yu-Qi; et al

    2015-05-21

    For single-layer transition-metal dichalcogenides (TMDs) receive significant attention due to their intriguing physical properties for both fundamental research and potential applications in electronics, optoelectronics, spintronics, catalysis, and so on. Here, we demonstrate the epitaxial growth of high-quality single-crystal, monolayer platinum diselenide (PtSe2), a new member of the layered TMDs family, by a single step of direct selenization of a Pt(111) substrate. We found that a combination of atomic-resolution experimental characterizations and first-principle theoretic calculations reveals the atomic structure of the monolayer PtSe2/Pt(111). Angle-resolved photoemission spectroscopy measurements confirm for the first time the semiconducting electronic structure of monolayer PtSe2 (in contrastmore » to its semimetallic bulk counterpart). The photocatalytic activity of monolayer PtSe2 film is evaluated by a methylene-blue photodegradation experiment, demonstrating its practical application as a promising photocatalyst. Moreover, circular polarization calculations predict that monolayer PtSe2 has also potential applications in valleytronics.« less

  5. 32 CFR Appendix D to Part 623 - Certificate for Signature by an Alternate (DA Form 4881-1-R)

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 32 National Defense 3 2011-07-01 2009-07-01 true Certificate for Signature by an Alternate (DA Form 4881-1-R) D Appendix D to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. D Appendix D to Part...

  6. 32 CFR Appendix D to Part 623 - Certificate for Signature by an Alternate (DA Form 4881-1-R)

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 3 2010-07-01 2010-07-01 true Certificate for Signature by an Alternate (DA Form 4881-1-R) D Appendix D to Part 623 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY SUPPLIES AND EQUIPMENT LOAN OF ARMY MATERIEL Pt. 623, App. D Appendix D to Part...

  7. Crystallographic parameters of compounds and solid solutions in binary systems Cu-Pt and Ga-Pt

    SciTech Connect

    Potekaev, Alexandr; Probova, Svetlana; Klopotov, Anatolii; Vlasov, Viktor; Markov, Tatiana; Klopotov, Vladimir

    2015-10-27

    The study establishes that the packing index in compounds of the system Cu-Pt is close to the value 0.74 against a slight deviation from the Zen law of atomic volumes. The compounds in the system Ga-Pt have the highest values of the packing index in the range of the equiatomic composition, which greatly exceed ψ for close-packed structures based on FCC and HCP lattices for compounds made of the same kind of atoms. A correlation between singular points on the phase diagram of the system Ga-Pt and high values of the packing index in compounds is established.

  8. Synthesis, structures, and photoluminescence properties of novel lanthanide tetracyanoplatinates lacking Pt-Pt interactions

    SciTech Connect

    Stojanovic, Milorad; Robinson, Nicholas J.; Chen Xi; Smith, Philip A.; Sykora, Richard E.

    2010-04-15

    The synthesis of a series of lanthanide tetracyanoplatinates all incorporating 2,2':6',2''-terpyridine (terpy) have been carried out by reaction of Ln{sup 3+} nitrate salts with terpy and potassium tetracyanoplatinate. The incorporation of different Ln{sup 3+} cations results in the isolation of [Ln(DMF){sub 2}(C{sub 15}H{sub 11}N{sub 3})(H{sub 2}O){sub 2}(NO{sub 3})]Pt(CN){sub 4} (Ln=La-Nd, Sm-Yb) under otherwise identical reaction conditions. These compounds have been isolated as single crystals and X-ray diffraction has been used to investigate their structural features. All of the reported compounds are isostructural. Crystallographic data for the representative Eu{sup 3+} compound (EuPt) are (MoKalpha, lambda=0.71073 A): monoclinic, space group P2{sub 1}/c, a=10.1234(4) A, b=18.7060(7) A, c=17.1642(5) A, beta=97.249(3){sup o}, V=3224.4(2), Z=4, R(F)=2.78% for 426 parameters with 7724 reflections with I>2sigma(I). The structure consists of a zero-dimensional, ionic salt containing complex [Eu(DMF){sub 2}(C{sub 15}H{sub 11}N{sub 3})(H{sub 2}O){sub 2}(NO{sub 3})]{sup 2+} cations and Pt(CN){sub 4}{sup 2-} anions. The complex cations contain the Eu{sup 3+} ions in a tri-capped trigonal prismatic coordination environment with one terdentate 2,2':6',2''-terpyridine molecule, one bidentate nitrate anion, two O-bound dimethylformamide molecules, and two coordinated water molecules. Photoluminescence data illustrate that EuPt displays intramolecular energy transfer from the coordinated terpy molecule to the Eu{sup 3+} cation. The uncoordinated tetracyanoplatinate anion also exhibits visible emission. - Graphical abstract: The synthesis of an isostructural series of lanthanide tetracyanoplatinates incorporating 2,2':6',2''-terpyridine are presented. Solid-state absorption and luminescence properties are discussed for the Eu{sup 3+} and La{sup 3+} compounds.

  9. Glucose sensing based on Pt-MWCNT and MWCNT

    NASA Astrophysics Data System (ADS)

    Aryasomayajula, Lavanya; Xie, Jining; Wang, Shouyan; Varadan, Vijay K.

    2007-04-01

    It is known that multi walled carbon nanotubes (MWCNTs) is an excellent materials for biosensing applications and with the introduction of Pt nanoparticles (Pt-MWCNTs) of about 3nm in diameter in MWCNTs greatly increases the current sensitivity and also the signal to noise ratio. We fabricated the CNT- based glucose sensor by immobilization the bio enzyme, glucose oxidase (GoX), on the Pt-MWCNT and electrode were prepared. The sensor has been tested effectively for both the abnormal blood glucose levels- greater than 6.9 mM and less than 3.5 mM which are the prediabetic and diabetic glucose levels, respectively. The current signal obtained from the Pt-MWCNT was much higher compared to the MWCNT based sensors.

  10. Observation of optical solitons in PT-symmetric lattices

    NASA Astrophysics Data System (ADS)

    Wimmer, Martin; Regensburger, Alois; Miri, Mohammad-Ali; Bersch, Christoph; Christodoulides, Demetrios N.; Peschel, Ulf

    2015-07-01

    Controlling light transport in nonlinear active environments is a topic of considerable interest in the field of optics. In such complex arrangements, of particular importance is to devise strategies to subdue chaotic behaviour even in the presence of gain/loss and nonlinearity, which often assume adversarial roles. Quite recently, notions of parity-time (PT) symmetry have been suggested in photonic settings as a means to enforce stable energy flow in platforms that simultaneously employ both amplification and attenuation. Here we report the experimental observation of optical solitons in PT-symmetric lattices. Unlike other non-conservative nonlinear arrangements where self-trapped states appear as fixed points in the parameter space of the governing equations, discrete PT solitons form a continuous parametric family of solutions. The possibility of synthesizing PT-symmetric saturable absorbers, where a nonlinear wave finds a lossless path through an otherwise absorptive system is also demonstrated.

  11. Tunable topological states in electron-doped HTT-Pt

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoming; Wang, Zhenhai; Zhao, Mingwen; Liu, Feng

    2016-04-01

    Modulating topologically nontrivial states in trivial materials is of both scientific and technological interest. Using first-principles calculations, we propose a demonstration of electron-doping- (or gate-voltage-) induced multiple quantum states; namely, quantum spin Hall (QSH) and quantum anomalous Hall (QAH) states, in a single material of the organometallic framework (HTT-Pt) synthesized from triphenylene hexathiol molecules (HTT) and PtC l2 . At a low doping level, the trivial HTT-Pt converts to a QSH insulator protected by time-reversal symmetry (TRS). When the electronic doping concentration is further increased, TRS will be broken, making the HTT-Pt a QAH insulator. The band gaps of these topologically nontrivial states can be as large as 42.5 meV, suggesting robustness at high temperatures. The possibility of switching between the QSH and QAH states offers an intriguing platform for a different device paradigm by interfacing between QSH and QAH states.

  12. Electrical oscillation in Pt/VO{sub 2} bilayer strips

    SciTech Connect

    Wang, Ying; Qi, Long; Xu, Yanjun; Wu, Yihong; Chai, Jianwei; Wang, Shijie; Yang, Yumeng; Tanaka, Hidekazu

    2015-02-14

    We report on the observation of stable electrical oscillation in Pt/vanadium dioxide (VO{sub 2}) bilayer strips, in which the Pt overlayer serves the dual purposes of heating up the VO{sub 2} and weakening the electric field in the VO{sub 2} layer. Systematic measurements in an ultrahigh vacuum nanoprobe system show that the oscillation frequency increases with the bias current and/or with decreasing device dimension. In contrast to most VO{sub 2}-based oscillators reported to date, which are electrically triggered, current-induced Joule heating in the Pt overlayer is found to play a dominant role in the generation of oscillation in Pt/VO{sub 2} bilayers. A simple model involving thermally triggered transition of VO{sub 2} on a heat sink is able to account for the experimental observations. The results in this work provide an alternative view of the triggering mechanism in VO{sub 2}-based oscillators.

  13. Controlling magnetic anisotropy in epitaxial FePt(001) films

    SciTech Connect

    Lu Zhihong; Walock, M. J.; LeClair, P.; Butler, W. H.; Mankey, G. J.

    2009-07-15

    Epitaxial equiatomic Fe{sub 50}Pt{sub 50} thin films with a variable order parameter ranging from 0 to 0.9 and Fe{sub 100-x}Pt{sub x} thin films with x ranging from 33 to 50 were deposited on MgO (001) substrates by dc sputtering. A seed layer consisting of nonmagnetic Cr (4 nm)/Pt (12 nm) was used to promote the crystallinity of the magnetic films. The crystal structure and magnetic properties were gauged using x-ray diffraction and magnetometry. The magnetic anisotropy can be controlled by changing the order parameter. For Fe{sub 100-x}Pt{sub x} films, the increase in Fe composition leads to an increase in coercivity in the hard axis loop and causes a loss of perpendicular anisotropy.

  14. Mixed-Metal Pt Monolayer Electrocatalysts with Improved CO Tolerance

    SciTech Connect

    Nilekar, Anand U.; Sasaki, Kotaro; Farberow, Carrie A.; Adzic, Radoslav R.; Mavrikakis, Manos

    2011-11-23

    Using a combination of periodic, self-consistent, density functional theory (DFT) calculations and COstripping voltammetry experiments, we have designed a new class of Pt-M bimetallic monolayer catalysts supported on a non-Pt metal, which exhibit improved stability against CO poisoning and might be suitable for proton-exchange membrane fuel cell anodes. These surfaces help in reducing the overpotential associated with anodic CO oxidation and minimize the amount of Pt used, thereby reducing materials cost. DFT calculations predict highly repulsive interactions between adsorbed CO molecules on these surfaces, leading to weaker binding and lower coverage of CO than on pure Pt, which in turn facilitates oxidative removal of CO from these catalytic surfaces.

  15. Mixed-Metal Pt Monolayer Electrocatalysts with Improved CO Tolerance

    SciTech Connect

    Sasaki K.; Nilekar A.U.; Farberow C.A.; Adzic R.R.; Mavrikakis M.

    2011-11-23

    Using a combination of periodic, self-consistent, density functional theory (DFT) calculations and CO-stripping voltammetry experiments, we have designed a new class of Pt-M bimetallic monolayer catalysts supported on a non-Pt metal, which exhibit improved stability against CO poisoning and might be suitable for proton-exchange membrane fuel cell anodes. These surfaces help in reducing the overpotential associated with anodic CO oxidation and minimize the amount of Pt used, thereby reducing materials cost. DFT calculations predict highly repulsive interactions between adsorbed CO molecules on these surfaces, leading to weaker binding and lower coverage of CO than on pure Pt, which in turn facilitates oxidative removal of CO from these catalytic surfaces.

  16. Anomalous surface phase formation on Pt sub 3 Sn <110>

    SciTech Connect

    Haner, A.N.; Ross, P.N. ); Bardi, U. . Dipt. di Chimica)

    1990-06-01

    LEED analysis of the clean annealed surface of a {l angle}110{r angle} oriented Pt{sub 3}Sn single crystal surface indicates the formation of a multilayer surface phase which does not have the L1{sub 2} bulk structure. LEISS analysis indicates a surface stoichiometry of ca. 1:1 with Sn atoms displaced ca. 1.4 above the plane of Pt atoms. The surface phase is hypothesized to be a rhombic distortion of the {l angle}0001{r angle} plant of PtSn, which has a B8{sub 1} (NiAs-type) bulk structure. It is not clear whether the phase forms by precipitation of PtSn due to a slight (0.5%) stoichiometric excess of Sn in the bulk, or due to multilayer reconstruction driven by surface segregation. 20 refs., 3 figs.

  17. Observation of optical solitons in PT-symmetric lattices

    PubMed Central

    Wimmer, Martin; Regensburger, Alois; Miri, Mohammad-Ali; Bersch, Christoph; Christodoulides, Demetrios N.; Peschel, Ulf

    2015-01-01

    Controlling light transport in nonlinear active environments is a topic of considerable interest in the field of optics. In such complex arrangements, of particular importance is to devise strategies to subdue chaotic behaviour even in the presence of gain/loss and nonlinearity, which often assume adversarial roles. Quite recently, notions of parity-time (PT) symmetry have been suggested in photonic settings as a means to enforce stable energy flow in platforms that simultaneously employ both amplification and attenuation. Here we report the experimental observation of optical solitons in PT-symmetric lattices. Unlike other non-conservative nonlinear arrangements where self-trapped states appear as fixed points in the parameter space of the governing equations, discrete PT solitons form a continuous parametric family of solutions. The possibility of synthesizing PT-symmetric saturable absorbers, where a nonlinear wave finds a lossless path through an otherwise absorptive system is also demonstrated. PMID:26215165

  18. Single Pt nanowire electrode: preparation, electrochemistry, and electrocatalysis.

    PubMed

    Li, Yongxin; Wu, Qingqing; Jiao, Shoufeng; Xu, Chaodi; Wang, Lun

    2013-04-16

    A single Pt nanowire electrode (SPNE) was fabricated through HF etching process from Pt disk nanoelectrode and an underpotential deposition (UPD) redox replacement technique. The electrochemical experiments showed that SPNE had steady-state electrochemical responses at redox species solution and the mass transfer rates were affected by the lengths and radii of SPNEs. The prepared SPNEs were utilized to examine the oxygen-reduction reaction in a KOH solution to explore the feasibility of electrocatalytic activity of single Pt nanowire and the results showed that the electrocatalytic activity of SPNE was dependent on the surface position of single Pt nanowire: the tip end position is more active than the sidewall position. Meanwhile, the electrocatalytic activity of SPNE was related to the radius of nanowire. These observations are not only important to understand the structure-function relationship in single nanowire level but have significant implications for the synthesis and selection of novel catalysts with high efficiency used in electrochemistry, energy, bioanalysis, etc.

  19. Formation of FePt nanoparticles by organometallic synthesis

    SciTech Connect

    Bagaria, H. G.; Johnson, D. T.; Srivastava, C.; Thompson, G. B.; Shamsuzzoha, M.; Nikles, D. E.

    2007-05-15

    Our interest in determining the mechanism of FePt nanoparticle formation has led to this study of the evolution of particle size and composition during synthesis. FePt nanoparticles were prepared by the simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl. During the course of the reaction, samples were removed and the particle structure, size, and composition were determined using x-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy-energy dispersive x-ray spectrometry. Early in the reaction the particles were Pt rich (greater than 95 at. % Pt) and as the reaction proceeded the Fe content increased to the target of 50%. The particle diameter increased from 3.1 to 4.6 nm during the reaction. Energy dispersive x-ray spectrometry measurements of individual particle compositions using a high resolution TEM showed a broad distribution of particle compositions with a standard deviation greater than 15% of the average composition.

  20. Synthesis, Characterization, and Cytotoxicity of the First Oxaliplatin Pt(IV) Derivative Having a TSPO Ligand in the Axial Position

    PubMed Central

    Savino, Salvatore; Denora, Nunzio; Iacobazzi, Rosa Maria; Porcelli, Letizia; Azzariti, Amalia; Natile, Giovanni; Margiotta, Nicola

    2016-01-01

    The first Pt(IV) derivative of oxaliplatin carrying a ligand for TSPO (the 18-kDa mitochondrial translocator protein) has been developed. The expression of the translocator protein in the brain and liver of healthy humans is usually low, oppositely to steroid-synthesizing and rapidly proliferating tissues, where TSPO is much more abundant. The novel Pt(IV) complex, cis,trans,cis-[Pt(ethanedioato)Cl{2-(2-(4-(6,8-dichloro-3-(2-(dipropylamino)-2-oxoethyl)imidazo[1,2-a]pyridin-2-yl)phenoxy)acetate)-ethanolato}(1R,2R-DACH)] (DACH = diaminocyclohexane), has been fully characterized by spectroscopic and spectrometric techniques and tested in vitro against human MCF7 breast carcinoma, U87 glioblastoma, and LoVo colon adenocarcinoma cell lines. In addition, affinity for TSPO (IC50 = 18.64 nM), cellular uptake (ca. 2 times greater than that of oxaliplatin in LoVo cancer cells, after 24 h treatment), and perturbation of cell cycle progression were investigated. Although the new compound was less active than oxaliplatin and did not exploit a synergistic proapoptotic effect due to the presence of the TSPO ligand, it appears to be promising in a receptor-mediated drug targeting context towards TSPO-overexpressing tumors, in particular colorectal cancer (IC50 = 2.31 μM after 72 h treatment). PMID:27347942

  1. Synthesis, Characterization, and Cytotoxicity of the First Oxaliplatin Pt(IV) Derivative Having a TSPO Ligand in the Axial Position.

    PubMed

    Savino, Salvatore; Denora, Nunzio; Iacobazzi, Rosa Maria; Porcelli, Letizia; Azzariti, Amalia; Natile, Giovanni; Margiotta, Nicola

    2016-06-25

    The first Pt(IV) derivative of oxaliplatin carrying a ligand for TSPO (the 18-kDa mitochondrial translocator protein) has been developed. The expression of the translocator protein in the brain and liver of healthy humans is usually low, oppositely to steroid-synthesizing and rapidly proliferating tissues, where TSPO is much more abundant. The novel Pt(IV) complex, cis,trans,cis-[Pt(ethanedioato)Cl{2-(2-(4-(6,8-dichloro-3-(2-(dipropylamino)-2-oxoethyl)imidazo[1,2-a]pyridin-2-yl)phenoxy)acetate)-ethanolato}(1R,2R-DACH)] (DACH = diaminocyclohexane), has been fully characterized by spectroscopic and spectrometric techniques and tested in vitro against human MCF7 breast carcinoma, U87 glioblastoma, and LoVo colon adenocarcinoma cell lines. In addition, affinity for TSPO (IC50 = 18.64 nM), cellular uptake (ca. 2 times greater than that of oxaliplatin in LoVo cancer cells, after 24 h treatment), and perturbation of cell cycle progression were investigated. Although the new compound was less active than oxaliplatin and did not exploit a synergistic proapoptotic effect due to the presence of the TSPO ligand, it appears to be promising in a receptor-mediated drug targeting context towards TSPO-overexpressing tumors, in particular colorectal cancer (IC50 = 2.31 μM after 72 h treatment).

  2. Thermal Fluctuations in the Structure of Naturally Chiral Pt Surfaces

    SciTech Connect

    ASTHAGIRI,ARAVIND; FEIBELMAN,PETER J.; SHOLL,DAVID S.

    2000-07-20

    The intrinsic chirality of metal surfaces with kinked steps (e.g. Pt(643)) endows them with enantiospecific adsorption properties (D. S. Shell, Langmuir, 14, 1998, 862). To understand these properties quantitatively the impact of thermally-driven step wandering must be assessed. The authors derive a lattice-gas model of step motion on Pt(111) surfaces using diffusion barriers from Density Functional Theory. This model is used to examine thermal fluctuations of straight and kinked steps.

  3. FePt/BN granular films with texture

    NASA Astrophysics Data System (ADS)

    Daniil, M.; Farber, P.; Okumura, H.; Hadjipanayis, G. C.

    2001-03-01

    The driving force for higher magnetic recording density leads to future materials with very small sizes, below 10 nm. At these sizes thermal fluctuations lead to the superparamagnetic effect, resulting in unstable magnetization. This obstacle can be overcome by using materials with higher anisotropy, such as CoPt and FePt, which have magnetocrystalline anisotropy above 10^7 erg/cc. Another vital requirement for low noise recording media is the isolation of the grains, to reduce the intergrain interactions. This can be succeeded by growing the FePt/CoPt nanoparticles in a non magnetic matrix. In the present work we report on the effect of BN matrix in the structure, microstructure and magnetic properties of FePt nanoparticles. FePt particles with the highly anisotropic L10 structure were obtained by annealing the as-deposited multilayers at temperatures above 600^oC. Films with thicker bilayer thickness were found to have a strong [111] texture, which is less developed in thinner bilayer films. For special bilayer thickness (FePt(20 ÅBN(40 Åa special type of ordering is observed, in which the c-axis of all particles has an out of plane component, that makes these materials promising for both perpendicular and longitudinal recording. Magnetic measurements showed that a wide range of coercivities (2-18 kOe) can be obtained by varying the annealing temperature and time and the layer thickness. The coercivity increases with the annealing temperature and time, due to the increase of average grain size, which according to TEM studies it was ranged from 3 to 15 nm. The amount of BN was found to control the intergrain interactions, which for higher concentrations lead to decoupling of the FePt grains. This work has been supported by NSF-DMR 9972035.

  4. The role of hydrogen during Pt-Ga nanocatalyst formation.

    PubMed

    Filez, Matthias; Redekop, Evgeniy A; Galvita, Vladimir V; Poelman, Hilde; Meledina, Maria; Turner, Stuart; Van Tendeloo, Gustaaf; Bell, Alexis T; Marin, Guy B

    2016-01-28

    Hydrogen plays an essential role during the in situ assembly of tailored catalytic materials, and serves as key ingredient in multifarious chemical reactions promoted by these catalysts. Despite intensive debate for several decades, the existence and nature of hydrogen-involved mechanisms - such as hydrogen-spillover, surface migration - have not been unambiguously proven and elucidated up to date. Here, Pt-Ga alloy formation is used as a probe reaction to study the behavior and atomic transport of H and Ga, starting from Pt nanoparticles on hydrotalcite-derived Mg(Ga)(Al)Ox supports. In situ XANES spectroscopy, time-resolved TAP kinetic experiments, HAADF-STEM imaging and EDX mapping are combined to probe Pt, Ga and H in a series of H2 reduction experiments up to 650 °C. Mg(Ga)(Al)Ox by itself dissociates hydrogen, but these dissociated hydrogen species do not induce significant reduction of Ga(3+) cations in the support. Only in the presence of Pt, partial reduction of Ga(3+) into Ga(δ+) is observed, suggesting that different reaction mechanisms dominate for Pt- and Mg(Ga)(Al)Ox-dissociated hydrogen species. This partial reduction of Ga(3+) is made possible by Pt-dissociated H species which spillover onto non-reducible Mg(Al)Ox or partially reducible Mg(Ga)(Al)Ox and undergo long-range transport over the support surface. Moderately mobile Ga(δ+)Ox migrates towards Pt clusters, where Ga(δ+) is only fully reduced to Ga(0) on condition of immediate stabilization inside Pt-Ga alloyed nanoparticles. PMID:26742561

  5. FAST-PT: Convolution integrals in cosmological perturbation theory calculator

    NASA Astrophysics Data System (ADS)

    McEwen, Joseph E.; Fang, Xiao; Hirata, Christopher M.; Blazek, Jonathan A.

    2016-03-01

    FAST-PT calculates 1-loop corrections to the matter power spectrum in cosmology. The code utilizes Fourier methods combined with analytic expressions to reduce the computation time down to scale as N log N, where N is the number of grid point in the input linear power spectrum. FAST-PT is extremely fast, enabling mode-coupling integral computations fast enough to embed in Monte Carlo Markov Chain parameter estimation.

  6. Construction of modified embedded atom method potentials for Cu, Pt and Cu-Pt and modelling surface segregation in Cu 3Pt alloys

    NASA Astrophysics Data System (ADS)

    Luyten, Jan; Schurmans, Maarten; Creemers, Claude; Bunnik, Bouke S.; Kramer, Gert Jan

    2007-07-01

    In this work, surface segregation to Cu 3Pt surfaces is studied with the modified embedded atom method (MEAM). This work is triggered by the catalytic importance of Cu-Pt alloys, together with the contradictory experimental results for the surface segregation in Cu 3Pt(1 1 1) alloys based on low energy ion scattering (LEIS) [Y.G. Shen, D.J. O'Connor, K. Wandelt, R.J. MacDonald, Surf. Sci. 328 (1995) 21] and low energy electron diffraction (LEED) [Y. Gauthier, A. Senhaji, B. Legrand, G. Tréglia, C. Becker, K. Wandelt, Surf. Sci. 527 (2003) 71]. In order to accurately describe the segregation behaviour in the Cu 3Pt system, a reliable potential, that is also applicable to surface phenomena, is indispensable. Therefore, first, new MEAM parameters are derived, consistently based on ab initio density functional theory (DFT) calculations, according to a method that is a modification of previous work [P. van Beurden, G.J. Kramer, Phys. Rev. B 63 (2001) 165106]. Upon testing, these parameters prove to reproduce very well various surface properties of this system. Next, Monte Carlo (MC) simulations combined with the newly derived MEAM potentials are set up to investigate surface segregation to low index single crystal surfaces. For the Cu 3Pt(1 1 1) surface, our MC/MEAM simulations agree completely with the available LEIS evidence and contradict the unusual depth profile based on LEED. However, the slight Pt enrichment observed in the LEED experiments can be reproduced by assuming a slight Pt excess in the bulk of the sample. The simulated composition depth profile, on the other hand, does not agree with the LEED evidence. Also, for the Cu 3Pt(1 0 0) surface, the MC/MEAM results agree completely with LEIS experiments. For the Cu 3Pt(1 1 0) surface, finally, the MC/MEAM simulations show a somewhat deviating behaviour with respect to the experimental LEIS evidence. The possibility of a missing-row reconstruction is evaluated, but cannot explain the discrepancy for the Cu 3Pt

  7. Atomic layer deposition synthesis and evaluation of core–shell Pt-WC electrocatalysts

    SciTech Connect

    Hsu, Irene J.; Chen, Jingguang G. E-mail: bgwillis@engr.uconn.edu; Jiang, Xiaoqiang; Willis, Brian G. E-mail: bgwillis@engr.uconn.edu

    2015-01-15

    Pt-WC core shell particles were produced using atomic layer deposition (ALD) to deposit Pt layers onto WC particle substrates. A range of Pt depositions were used to determine the growth mechanism for the Pt-WC powder system. TEM imaging and Cu stripping voltammetry found that Pt ALD growth on WC powder substrates was similar to that on WC thin films. However, excess free carbon was found to affect Pt ALD by blocking adsorption sites on WC. The Pt-WC samples were evaluated for the oxygen reduction reaction using a rotating disk electrode to obtain quantitative activity information. The mass and specific activities for the 30 and 50 ALD cycle samples were found to be comparable to a 10 wt. % Pt/C catalyst. However, higher overpotentials and lower limiting currents were observed with ALD Pt-WC compared to Pt/C catalysts, indicating that the oxygen reduction mechanism is not as efficient on Pt-WC as on bulk Pt. Additionally, these Pt-WC catalysts were used to demonstrate hydrogen evolution reaction activity and were found to perform as well as bulk Pt catalyst but with a fraction of the Pt loading, in agreement with the previous work on Pt-WC thin film catalysts.

  8. The nature of the cataclysmic variable PT Per

    NASA Astrophysics Data System (ADS)

    Watson, M. G.; Bruce, A.; MacLeod, C.; Osborne, J. P.; Schwope, A. D.

    2016-08-01

    We present a study of the cataclysmic variable star PT Per based on archival XMM-Newton X-ray data and new optical spectroscopy from the William Herschel Telescope (WHT) with Intermediate dispersion Spectrograph and Imaging System (ISIS). The X-ray data show deep minima which recur at a period of 82 min and a hard, unabsorbed X-ray spectrum. The optical spectra of PT Per show a relatively featureless blue continuum. From an analysis of the X-ray and optical data we conclude that PT Per is likely to be a magnetic cataclysmic variable of the polar class in which the minima correspond to those phase intervals when the accretion column rotates out of the field of view of the observer. We suggest that the optical spectrum, obtained around 4 yr after the X-ray coverage, is dominated by the white dwarf in the system, implying that PT Per was in a low accretion state at the time of the observations. An analysis of the likely system parameters for PT Per suggests a distance of ≈90 pc and a very low mass secondary, consistent with the idea that PT Per is a `period-bounce' binary. Matching the observed absorption features in the optical spectrum with the expected Zeeman components constrains the white dwarf polar field to be Bp ≈ 25-27 MG.

  9. Design of Low Pt Concentration Electrocatalyst Surfaces with High Oxygen Reduction Reaction Activity Promoted by Formation of a Heterogeneous Interface between Pt and CeO(x) Nanowire.

    PubMed

    Chauhan, Shipra; Mori, Toshiyuki; Masuda, Takuya; Ueda, Shigenori; Richards, Gary J; Hill, Jonathan P; Ariga, Katsuhiko; Isaka, Noriko; Auchterlonie, Graeme; Drennan, John

    2016-04-13

    Pt-CeO(x) nanowire (NW)/C electrocatalysts for the improvement of oxygen reduction reaction (ORR) activity on Pt were prepared by a combined process involving precipitation and coimpregnation. A low, 5 wt % Pt-loaded CeO(x) NW/C electrocatalyst, pretreated by an optimized electrochemical conditioning process, exhibited high ORR activity over a commercially available 20 wt % Pt/C electrocatalyst although the ORR activity observed for a 5 wt % Pt-loaded CeO(x) nanoparticle (NP)/C was similar to that of 20 wt % Pt/C. To investigate the role of a CeO(x) NW promotor on the enhancement of ORR activity on Pt, the Pt-CeO(x) NW interface was characterized by using hard X-ray photoelectron spectroscopy (HXPS), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). Microanalytical data obtained by these methods were discussed in relation to atomistic simulation performed on the interface structures. The combined techniques of HXPS, TEM-EELS, and atomistic simulation indicate that the Pt-CeO(x) NW interface in the electrocatalyst contains two different defect clusters: Frenkel defect clusters (i.e., 2Pt(i)(••) - 4O(i)″ - 4V(o)(••) - V(Ce)″″) formed in the surface around the Pt-CeO(x) NW interface and Schottky defect clusters (i.e., (Pt(Ce)″ - 2V(O)(••) - 2Ce(Ce)') and (Pt(Ce)″ - V(O)(••))) which appear in the bulk of the Pt-CeO(x) NW interface similarly to Pt-CeO(x) NP/C. It is concluded that the formation of both Frenkel defect clusters and Schottky defect clusters at the Pt-CeO(x) NW heterointerface contributes to the promotion of ORR activity and permits the use of lower Pt-loadings in these electrocatalysts.

  10. Activity of dealloyed PtCo 3 and PtCu 3 nanoparticle electrocatalyst for oxygen reduction reaction in polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Oezaslan, Mehtap; Strasser, Peter

    We report a comparative study of the alloy formation and electrochemical activity of dealloyed PtCo 3 and PtCu 3 nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). For the Pt-Co system the maximum annealing temperatures were 650 °C, 800 °C and 900 °C for 7 h to drive the Pt-Co alloy formation and the particle growth. EDS and XRD were employed for the characterization of catalyst powders. The RDE and RRDE experiments were conducted in 0.1 M HClO 4 at room temperature. We demonstrate that the mass and surface area specific ORR activities of Pt-Co and Pt-Cu alloys after voltammetric activation exhibit a considerable improvement compared to those of pure Pt/C. The dealloyed PtCo 3 (800 °C/7 h) electrocatalyst performs 3 times higher in terms of Pt-based mass activity and 4-5 times higher in terms of ECSA-based specific activity than a 28.2 wt.% Pt/C. Dealloyed Pt-Co catalysts (800 °C/7 h) show the most favorable balance between mass and specific ORR activity with a particle size of 2.2 ± 0.1 nm. We hypothesize that geometric strain effects of the dealloyed Pt-Co nanoparticles, similar to those found in dealloyed PtCu 3 nanoparticles, are responsible for the improvement in ORR activity [1].

  11. Effects of Alloyed Metal on the Catalysis Activity of Pt for Ethanol Partial Oxidation: Adsorption and Dehydrogenation on Pt3M (M=Pt, Ru, Sn, Re, Rh, and Pd)

    PubMed Central

    Xu, Zhen-Feng; Wang, Yixuan

    2011-01-01

    The adsorption and dehydrogenation reactions of ethanol over bimetallic clusters, Pt3M (M = Pt, Ru, Sn, Re, Rh, and Pd), have been extensively investigated with density functional theory. Both the α-hydrogen and hydroxyl adsorptions on Pt as well as on the alloyed transition metal M sites of PtM were considered as initial reaction steps. The adsorptions of ethanol on Pt and M sites of some PtM via the α-hydrogen were well established. Although the α-hydrogen adsorption on Pt site is weaker than the hydroxyl, the potential energy profiles show that the dehydrogenation via the α-hydrogen path has much lower energy barrier than that via the hydroxyl path. Generally for the α-hydrogen path the adsorption is a rate-determining-step because of rather low dehydrogenation barrier for the α-hydrogen adsorption complex (thermodynamic control), while the hydroxyl path is determined by its dehydrogenation step (kinetic control). The effects of alloyed metal on the catalysis activity of Pt for ethanol partial oxidation, including adsorption energy, energy barrier, electronic structure, and eventually rate constant were discussed. Among all of the alloyed metals only Sn enhances the rate constant of the dehydrogenation via the α-hydrogen path on the Pt site of Pt3Sn as compared with Pt alone, which interprets why the PtSn is the most active to the oxidation of ethanol. PMID:22102920

  12. Effects of Alloyed Metal on the Catalysis Activity of Pt for Ethanol Partial Oxidation: Adsorption and Dehydrogenation on Pt(3)M (M=Pt, Ru, Sn, Re, Rh, and Pd).

    PubMed

    Xu, Zhen-Feng; Wang, Yixuan

    2011-10-27

    The adsorption and dehydrogenation reactions of ethanol over bimetallic clusters, Pt(3)M (M = Pt, Ru, Sn, Re, Rh, and Pd), have been extensively investigated with density functional theory. Both the α-hydrogen and hydroxyl adsorptions on Pt as well as on the alloyed transition metal M sites of PtM were considered as initial reaction steps. The adsorptions of ethanol on Pt and M sites of some PtM via the α-hydrogen were well established. Although the α-hydrogen adsorption on Pt site is weaker than the hydroxyl, the potential energy profiles show that the dehydrogenation via the α-hydrogen path has much lower energy barrier than that via the hydroxyl path. Generally for the α-hydrogen path the adsorption is a rate-determining-step because of rather low dehydrogenation barrier for the α-hydrogen adsorption complex (thermodynamic control), while the hydroxyl path is determined by its dehydrogenation step (kinetic control). The effects of alloyed metal on the catalysis activity of Pt for ethanol partial oxidation, including adsorption energy, energy barrier, electronic structure, and eventually rate constant were discussed. Among all of the alloyed metals only Sn enhances the rate constant of the dehydrogenation via the α-hydrogen path on the Pt site of Pt(3)Sn as compared with Pt alone, which interprets why the PtSn is the most active to the oxidation of ethanol. PMID:22102920

  13. Surface segregation effects in electrocatalysis: Kinetics ofoxygen reduction reaction on polycrystalline Pt3Ni alloy surfaces

    SciTech Connect

    Stamenkovic, V.; Schmidt, T.J.; Ross, P.N.; Markovic, N.M.

    2002-11-01

    Effects of surface segregation on the oxygen reduction reaction (ORR) have been studied on a polycrystalline Pt3Ni alloy in acid electrolyte using ultra high vacuum (UHV) surface sensitive probes and the rotating ring disk electrode (RRDE) method. Preparation, modification and characterization of alloy surfaces were done in ultra high vacuum (UHV). Depending on the preparation method, two different surface compositions of the Pt3Ni alloy are produced: a sputtered surface with 75 % Pt and an annealed surface (950 K ) with 100 % Pt. The latter surface is designated as the 'Pt-skin' structure, and is a consequence of surface segregation, i.e., replacement of Ni with Pt atoms in the first few atomic layers. Definitive surface compositions were established by low energy ion scattering spectroscopy (LEISS). The cyclic voltammetry of the 'Pt-skin' surface as well as the pseudocapacitance in the hydrogen adsorption/desorption potential region is similar to a polycrystalline Pt electrode. Activities of ORR on Pt3Ni alloy surfaces were compared to polycrystalline Pt in 0.1M HClO4 electrolyte for the observed temperature range of 293 < T < 333 K. The order of activities at 333 K was: 'Pt-skin' > Pt3Ni (75% Pt) > Pt with the maximum catalytic enhancement obtained for the 'Pt-skin' being 4 times that for pure Pt. Catalytic improvement of the ORR on Pt3Ni and 'Pt-skin' surfaces was assigned to the inhibition of Pt-OHad formation (on Pt sites) versus polycrystalline Pt. Production of H2O2 on both surfaces were similar compared to the pure Pt. Kinetic analyses of RRDE data confirmed that kinetic parameters for the ORR on the Pt3Ni and 'Pt-skin' surfaces are the same as on pure Pt: reaction order, m=1, two identical Tafel slopes, activation energy, {approx} 21-25 kJ/mol. Therefore the reaction mechanism on both Pt3Ni and 'Pt-skin' surfaces is the same as one proposed for pure Pt i.e. 4e{sup -} reduction pathway.

  14. Interfacial oxygen migration and its effect on the magnetic anisotropy in Pt/Co/MgO/Pt films

    SciTech Connect

    Chen, Xi; Feng, Chun E-mail: ghyu@mater.ustb.edu.cn; Liu, Yang; Jiang, Shaolong; Hua Li, Ming; Hua Yu, Guang E-mail: ghyu@mater.ustb.edu.cn; Long Wu, Zheng; Yang, Feng

    2014-02-03

    This paper reports the interfacial oxygen migration effect and its induced magnetic anisotropy evolution in Pt/Co/MgO/Pt films. During depositing the MgO layer, oxygen atoms from the MgO combine with the neighboring Co atoms, leading to the formation of CoO at the Co/MgO interface. Meanwhile, the films show in-plane magnetic anisotropy (IMA). After annealing, most of the oxygen atoms in CoO migrate back to the MgO layer, resulting in obvious improvement of Co/MgO interface and the enhancement of effective Co-O orbital hybridization. These favor the evolution of magnetic anisotropy from IMA to perpendicular magnetic anisotropy (PMA). The oxygen migration effect is achieved by the redox reaction at the Co/MgO interface. On the contrary, the transfer from IMA to PMA cannot be observed in Pt/Co/Pt films due to the lack of interfacial oxygen migration.

  15. The PtAl{sup −} and PtAl{sub 2}{sup −} anions: Theoretical and photoelectron spectroscopic characterization

    SciTech Connect

    Zhang, Xinxing; Ganteför, Gerd; Bowen, Kit H. E-mail: ana@chem.ucla.edu; Alexandrova, Anastassia N. E-mail: ana@chem.ucla.edu

    2014-04-28

    We report a joint photoelectron spectroscopic and theoretical study of the PtAl{sup −} and PtAl{sub 2}{sup −} anions. The ground state structures and electronic configurations of these species were identified to be C{sub ∞v}, {sup 1}Σ{sup +} for PtAl{sup −}, and C{sub 2v}, {sup 2}B{sub 1} for PtAl{sub 2}{sup −}. Structured anion photoelectron spectra of these clusters were recorded and interpreted using ab initio calculations. Good agreement between theory and experiment was found. All experimental features were successfully assigned to one-electron transitions from the ground state of the anions to the ground or excited states of the corresponding neutral species.

  16. New tests to detect antiphospholipid antibodies: antiprothrombin (aPT) and anti-phosphatidylserine/prothrombin (aPS/PT) antibodies.

    PubMed

    Sciascia, Savino; Khamashta, Munther A; Bertolaccini, Maria Laura

    2014-05-01

    Antiprothrombin antibodies have been proposed as potential new biomarkers for thrombosis and/or pregnancy morbidity in the setting of the antiphospholipid syndrome (APS). Antiprothrombin antibodies are commonly detected by ELISA, using prothrombin coated onto irradiated plates (aPT), or prothrombin in complex with phosphatidylserine (aPS/PT), as antigen. Although these antibodies can co-exist in the same patient, aPT and aPS/PT seem to belong to different populations of autoantibodies. Early research explored the role of antibodies to prothrombin as potential antigenic targets for the lupus anticoagulant (LA). To date their clinical significance is being investigated and their potential role in identifying patients at higher risk of developing thrombotic events or pregnancy morbidity is being probed.

  17. Lack of support for adaptive superstructure NiPt7 : Experiment and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Schönfeld, B.; Engelke, M.; Ruban, A. V.

    2009-02-01

    Order and effective interaction parameters on the Pt-rich side of solid Ni-Pt alloys have been investigated by experimental and first-principles theoretical techniques. Diffuse x-ray scattering was taken from single-crystalline Ni-87.8at.%Pt aged at 603 K to set up a state of thermal equilibrium. From the separated short-range order scattering, effective pair interaction parameters were determined. These experimentally deduced values do not produce the suggested NiPt7 superstructure at lower temperatures. Instead of that, phase separation into NiPt3 regions with L12 structure and a Pt-rich matrix is observed in Monte Carlo simulations and supported by x-ray scattering of Ni-75.2at.%Pt . First-principles calculations at 0 K also show that the suggested NiPt7 phase is unstable against decomposition into NiPt3 and Pt.

  18. Spectroscopic in situ Measurements of the Relative Pt Skin Thicknesses and Porosities of Dealloyed PtMn (Ni, Co) Electrocatalysts

    PubMed Central

    Caldwell, Keegan M.; Ramaker, David E.; Jia, Qingying; Mukerjee, Sanjeev; Ziegelbauer, Joseph M.; Kukreja, Ratandeep S.; Kongkanand, Anusorn

    2015-01-01

    X-ray adsorption near edge structure (XANES) data at the Co or Ni K-edge, analyzed using the Δμ difference procedure, are reported for dealloyed PtCox and PtNix catalysts (six different catalysts at different stages of life). All catalysts meet the 2017 DOE beginning of life target Pt mass activity target (>0.44 A mgPt−1), but exhibit varying activities and durabilities. The variance factors include different initial precursors, dealloying in HNO3 vs H2SO4, if a postdealloying thermal annealing step was performed, and different morphologies (some with a multi PtMx core and porous Pt skin, some single core with nonporous skin). Data are obtained at the initial beginning of life (BOL, ~200 voltage cycles) and after 10k and 30k (end of life, EOL) voltage cycles following DOE protocol (0.6–1.0 V vs reversible hydrogen electrode). The Δμ data are used to determine at what potential (Vpen) the Pt skin is penetrated by O. The durability, related to a drop in the electrochemical surface areas (ECSAs) after extensive voltage cycling, directly correlates with the Vpen at BOL. The data indicate that cycling produces a “characteristic” Pt skin robustness (porosity or thickness). When the Pt skin at BOL is “thin” (Vpen < 0.9 V) it grows to a “characteristic” thickness consistent with a Vpen of ≈1.1 V, and if it begins very thick, it thins to the same “characteristic” thickness. Particles dealloyed in H2SO4 appear to have a thicker Pt skin at BOL than those dealloyed in HNO3, and a postdealloying annealing procedure appears to produce a particularly nonporous skin with high Vpen, but not necessarily thicker. Furthermore, the PtM3 catalysts exhibited a fast skin “healing” process whereby the initial porous skin appears to become more nonporous after holding the potential at 0.9 V. This work is believed to be the first in situ XAS study to shed light on the nature of the Pt skin, its thickness, and/or porosity, and how it changes with respect to

  19. FMR studies of exchange-coupled multiferroic polycrystalline Pt/BiFeO3/Ni81Fe19/Pt heterostructures

    NASA Astrophysics Data System (ADS)

    Ben Youssef, Jamal; Richy, Jérôme; Beaulieu, Nathan; Hauguel, Tony; Dekadjevi, David T.; Jay, Jean-Philippe; Spenato, David; Pogossian, Souren P.

    2016-09-01

    An experimental study of the in-plane azimuthal behaviour and frequency dependence of the ferromagnetic resonance field and the resonance linewidth as a function of BiFeO3 thickness is carried out in a polycrystalline exchange-biased BiFeO3/Ni81Fe19 system. The magnetization decrease of the Pt/BiFeO3/Ni81Fe19/Pt heterostructure with BiFeO3 thickness deduced from static measurements has been confirmed by dynamic investigations. Ferromagnetic resonance measurements have shown lower gyromagnetic ratio in a perpendicular geometry compared with that of parallel geometry. The monotonous decrease of gyromagnetic ratio in perpendicular geometry as a function of the BiFeO3 film thickness seems to be related to the spin-orbit interactions due to the neighbouring Pt film at its interface with Ni81Fe19 film. The enhancement of gyromagnetic ratio in Pt/Ni81Fe19/Pt is attributed to the Pt. The in-plane azimuthal shape of the total linewidth of the uniform mode shows isotropic behaviour that increases with BiFeO3 thickness. The study of the frequency dependence of the resonance linewidth in a broad band of 3-35 GHz has allowed the determination of intrinsic and extrinsic contributions to the relaxation as a function of BiFeO3 thickness in perpendicular geometry. In our system the magnetic relaxation is dominated by the spin-pumping mechanism due to the presence of Pt. The insertion of BiFeO3 between Pt and Ni81Fe19 attenuates the spin-pumping damping at one interface.

  20. Visible light photoactivity of TiO2 loaded with monometallic (Au or Pt) and bimetallic (Au/Pt) nanoparticles

    NASA Astrophysics Data System (ADS)

    Gołąbiewska, Anna; Lisowski, Wojciech; Jarek, Marcin; Nowaczyk, Grzegorz; Zielińska-Jurek, Anna; Zaleska, Adriana

    2014-10-01

    TiO2 modified with monometallic (Au or Pt) and bimetallic (Au/Pt) nanoparticles have been prepared using a water-in-oil microemulsion system (water/AOT/cyclohexane) followed by calcination step. The effect of metal ratio, reducing agent type (NaBH4 or N2H4), TiO2 matrix type (P-25, ST-01, TiO-5, TiO2 nanotubes or TiO2 obtained by TIP hydrolysis) as well as calcination temperature (from 350 to 650 °C) were systematically investigated. Obtained photocatalysts were characterized by UV-vis diffuse-reflectance spectroscopy (DRS), BET surface area measurements, scanning transmission microscopy (STEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity under visible light (λ > 420 nm) has been estimated in phenol degradation reaction in aqueous phase. The results showed that phenol degradation rate under visible light in the presence of TiO2 loaded with Au/Pt nanoparticles differed from 0.7 to 2.2 μmol dm-3 min-1 for samples prepared using different reducing agent. Sodium borohydride (NaBH4) favors formation of smaller Au/Pt nanoparticles and higher amount gold in Au/Pt is in the form of electronegative species (Auδ-) resulted in higher photoactivity. TiO2 obtained by TIP hydrolysis in microemulsion system seems to be the best support for Au/Pt nanoparticles from all among investigated matrix. It was also observed that enhancement of calcination temperature from 450 to 650 °C resulted in rapid drop of Au/Pt-TiO2 photoactivity under visible light due to surface area shrinkage, crystal structure change and probably change in Au/Pt nanoparticles morphology.

  1. Electric field mediated non-volatile tuning magnetism in CoPt/PMN-PT heterostructure for magnetoelectric memory devices

    NASA Astrophysics Data System (ADS)

    Yang, Y. T.; Li, J.; Peng, X. L.; Wang, X. Q.; Wang, D. H.; Cao, Q. Q.; Du, Y. W.

    2016-02-01

    We report a power efficient non-volatile magnetoelectric memory in the CoPt/(011)PMN-PT heterostructure. Two reversible and stable electric field induced coercivity states (i.e., high-HC or low-HC) are obtained due to the strain mediated converse magnetoelectric effect. The reading process of the different coercive field information written by electric fields is demonstrated by using a magnetoresistance read head. This result shows good prospects in the application of novel multiferroic devices.

  2. Spatiospectral separation of exceptional points in PT-symmetric optical potentials

    NASA Astrophysics Data System (ADS)

    Yu, Sunkyu; Piao, Xianji; Mason, Daniel R.; In, Sungjun; Park, Namkyoo

    2012-09-01

    Non-Hermitian Hamiltonians satisfying parity-time (PT) symmetry reveal unusual physical phenomena related to exceptional points, where the onset of PT symmetry breaking occurs. Here, by permitting dispersive variations in the PT-symmetric potential along the propagation axis of a wave, we show that it is possible to obtain PT-induced exceptional points of spatiospectral separation. As an example, we demonstrate “rainbow nonreciprocity” using a PT-symmetric chirped optical potential.

  3. Combining voltammetry and ion chromatography: application to the selective reduction of nitrate on Pt and PtSn electrodes.

    PubMed

    Yang, Jian; Kwon, Youngkook; Duca, Matteo; Koper, Marc T M

    2013-08-20

    To overcome the shortcomings of electroanalytical methods in analyzing the ionic reaction products that are either electrochemically inert or lack distinct electrochemical/spectroscopic fingerprints, we suggest combining voltammetry with ion chromatography by applying online sample collection to the electrochemical cell and offline ion chromatographic analysis. This combination allows a quantitative analysis including the potential dependence of the product distribution in a straightforward way. As a proof-of-concept example, we discuss the formation of ionic reaction products from nitrate reduction on Pt and Sn-modified Pt electrode in acid. On the Pt electrode, ammonia was the only identifiable product. After Sn modification of the Pt electrode, a change in selectivity was observed to hydroxylamine as the dominant product. Moreover, the rate determining step of nitrate reduction (reduction to nitrite) was enhanced by Sn modification of the Pt electrode, and a significant concentration of nitrite was evidenced on a Pt electrode with a high coverage of Sn species. The suggested combination of voltammetry and online ion chromatography hence proves very useful in the quantitative elucidation of electrocatalytic reactions with different ionic products.

  4. First-principles study of nitric oxide oxidation on Pt(111) versus Pt overlayer on 3d transition metals

    SciTech Connect

    Arevalo, Ryan Lacdao; Escaño, Mary Clare Sison; Kasai, Hideaki

    2015-03-15

    Catalytic oxidation of NO to NO{sub 2} is a significant research interest for improving the quality of air through exhaust gas purification systems. In this paper, the authors studied this reaction on pure Pt and Pt overlayer on 3d transition metals using kinetic Monte Carlo simulations coupled with density functional theory based first principles calculations. The authors found that on the Pt(111) surface, NO oxidation proceeds via the Eley–Rideal mechanism, with O{sub 2} dissociative adsorption as the rate-determining step. The oxidation path via the Langmuir–Hinshelwood mechanism is very slow and does not significantly contribute to the overall reaction. However, in the Pt overlayer systems, the oxidation of NO on the surface is more thermodynamically and kinetically favorable compared to pure Pt. These findings are attributed to the weaker binding of O and NO on the Pt overlayer systems and the binding configuration of NO{sub 2} that promotes easier N-O bond formation. These results present insights for designing affordable and efficient catalysts for NO oxidation.

  5. New potential structure for jewelry application. Does it exist in Pt-Mo, Pt-Hf, or other systems?

    NASA Astrophysics Data System (ADS)

    Gilmartin, Erin; Corbitt, Jacqueline; Hart, Gus

    2009-10-01

    The only known intermetallic structure with an 8:1 stoichiometry is that of Pt8Ti. It is intriguing that an ordered phase would occur at such low concentrations of the minority atom, but this structure occurs in about a dozen binary intermetallic systems. The formation of an ordered phase in an alloy can significantly enhance the performance of the material, particularly the hardness. We have taken a broad look at possible systems where this phase forms. Using first-principles, we calculated the stability of this structure relative to experimentally known phases for more than 70 Pt/Pd binary systems. We find the Pt8Ti structure is a possible ground state in more than 20 cases. Our experimental collaborators have verified our prediction in Pt-Mo and observed order-hardening in Pt-Hf. We discuss the discovery of new ground states via the cluster expansion that are likely to be verified experimentally and their impact on Pt- and Pd-based jewelry and catalysts.

  6. Alternative alloys for catalysts and platinum jewelry? New structures in Pt-Hf and Pt-Mo

    NASA Astrophysics Data System (ADS)

    Gilmartin, Erin; Corbitt, Jacqueline; Hart, Gus

    2009-03-01

    The only known intermetallic structure with an 8:1 stoichiometry is that of Pt8Ti. It is intriguing that an ordered phase would occur at such low concentrations of the minority atom, but this structure occurs in about a dozen binary intermetallic systems. The formation of an ordered phase in an alloy can significantly enhance the performance of the material, particularly the hardness. We have taken a broad look at possible systems where this phase forms. Using first-principles, we calculated the stability of this structure relative to experimentally known phases for more than 80 Pt/Pd binary systems. We find the Pt8Ti structure is a possible ground state in more than 20 cases. Our experimental collaborators have verified our prediction in Pt-Mo and observed order-hardening in Pt-Hf. We discuss the discovery of new ground states that are likely to be verified experimentally and their impact on materials for Pt- and Pd-based catalysts and jewelry.

  7. Microscopic evidence of strain-mediated magnetoelectric coupling in Co/Pt multilayers/PMN-PT(011) heterostructures

    NASA Astrophysics Data System (ADS)

    Sun, Ying; Wang, Wenbo; Wu, Weida; Zheng, Xiaoli; Cai, Jianwang; Zhao, Yonggang; Liu, Ming

    A promising way to control magnetization(M) via an electric field(E-field) is using magnetoelectric(ME) effect in FM/FE heterostructures. We use magnetic(electric) force microscopy(M(e)FM) to study the strain-mediated E-field modulation of M in (Co/Pt)n with perpendicular magnetic anisotropy(PMA) or in-plane anisotropy on PMN-PT(011) substrates. MFM were performed on (Co/Pt)n with an DC E-field applied to PMN-PT. In MeFM, we superimpose an AC modulation on a DC one and utilize lock-in technique to detect weak ME effect. For (Co/Pt)n with PMA, MFM images show stripe domains with no obvious changes at varied DC E-fields. However, MeFM shows interesting structures and the image contrast reverses sign at opposite strain slopes of the PMN-PT substrate. For sample with in-plane anisotropy, both MFM and MeFM images show dipole-like domains. Interestingly, the MeFM image contrast reverses sign at opposite strain slopes of the substrate. The sign reversal of MeFM contrast indicates that features revealed by MeFM are intrinsic local ME effect. Our MeFM data are consistent with the ferromagnetic resonance results showing that strain-induced anisotropy change will cause part of M switching to the in-plane direction. Possible scenarios will be discussed.

  8. Dynamic linear electro-optic frequency dependence in PMN-32%PT and PZN-8%PT for RF microwave photonics

    NASA Astrophysics Data System (ADS)

    Johnson, Shikik T.

    The electrooptic effect (at lambda = 633nm) in both PMN-32%PT and PZN-8%PT relaxor ferroelectric single crystals was investigated as a function of small signal modulation frequencies. Piezo-resonance measurements were also conducted to examine piezooptic coupling in these materials for selected resonance modes to observe the influence of piezoelectric activity on the electro-optic behavior. The electrooptic rC coefficient in PMN-32PT and PZN-8%PT crystals were found to have strong frequency dependence at frequencies below 100s Hz apparently due to space charge effects. Anomalous electrooptic properties near piezoelectric resonance frequencies are reported to be attributed to a synchronization of the low frequency piezoelectric resonance and high frequency transverse lattice vibrations near 4th harmonics. Also reported is enhanced electrooptic properties near piezoelectric resonant frequencies that may be attributed to synchronization of the low frequency fundamental modes and up to their 5th order harmonics accompanied by nonlinear extrinsic activity in the form of lateral domain region motion. A constructive interaction with overlapping high order piezoelectric and electrooptic resonances can be engineered, using PMN-32%PT rhombohedral and PZN-8%PT crystals as an example, so that a small signal (.25V/mm) amplified electro-optic detector in the RF frequency region may be envisaged.

  9. Atomic structure of PtCu nanoparticles in PtCu/C catalysts prepared by simultaneous and sequential deposition of components on carbon support

    NASA Astrophysics Data System (ADS)

    Bugaev, L. A.; Srabionyan, V. V.; Pryadchenko, V. V.; Bugaev, A. L.; Avakyan, L. A.; Belenov, S. V.; Guterman, V. E.

    2016-05-01

    Nanocatalysts PtCu/C with different distribution of components in bimetallic PtCu nanoparticles (NPs) were synthesized by simultaneous and sequential deposition of Cu and Pt on carbon support. Electrochemical stability of the obtained samples PtCu/C was studied using the cyclic voltammetry. Characterization of atomic structure of as prepared PtCu NPs and obtained after acid treatment was performed by Pt L 3- and Cu K-edge EXAFS using the technique for determining local structure parameters of the absorbing atom under strong correlations among them. EXAFS derived parameters were used for generation of structural models of PtCu NPs by the method of cluster simulations. Within this approach, the models of atomic structure of PtCu NPs obtained by the two methods of synthesis, before and after post treatment and after two months from their preparation were revealed.

  10. Oxidation of Half-Lantern Pt2(II,II) Compounds by Halocarbons. Evidence of Dioxygen Insertion into a Pt(III)-CH3 Bond.

    PubMed

    Sicilia, V; Baya, M; Borja, P; Martín, A

    2015-08-01

    The half-lantern compound [{Pt(bzq)(μ-N^S)}2] (1) [bzq = benzo[h]quinoline, HN^S = 2-mercaptopyrimidine (C4H3N2HS)] reacts with CH3I and haloforms CHX3 (X = Cl, Br, I) to give the corresponding oxidized diplatinum(III) derivatives [{Pt(bzq)(μ-N^S)X}2] (X = Cl 2a, Br 2b, I 2c). These compounds exhibit half-lantern structures with short intermetallic distances (∼2.6 Å) due to Pt-Pt bond formation. The halogen abstraction mechanisms from the halocarbon molecules by the Pt2(II,II) compound 1 were investigated. NMR spectroscopic evidence using labeled reagents support that in the case of (13)CH3I the reaction initiates with an oxidative addition through an SN2 mechanism giving rise to the intermediate species [I(bzq)Pt(μ-N^S)2Pt(bzq)((13)CH3)}]. However, with haloforms the reactions proceed through a radical-like mechanism, thermally (CHBr3, CHI3) or photochemically (CHCl3) activated, giving rise to mixtures of species [X(bzq)Pt(μ-N^S)2Pt(bzq)R] (3a-c) and [X(bzq)Pt(μ-N^S)2Pt(bzq)X] (2a-c). In these cases the presence of O2 favors the formation of species 2 over 3. Transformation of 3 into 2 was possible upon irradiation with UV light. In the case of [I(bzq)Pt(μ-N^S)2Pt(bzq)((13)CH3)}] (3d), in the presence of O2 the formation of the unusual methylperoxo derivative [I(bzq)Pt(μ-N^S)2Pt(bzq)(O-O(13)CH3)}] (4d) was detected, which in the presence of (13)CH3I rendered the final product [{Pt(bzq)(μ-N^S)I}2] (2c) and (13)CH3OH.

  11. Oxidation of Half-Lantern Pt2(II,II) Compounds by Halocarbons. Evidence of Dioxygen Insertion into a Pt(III)-CH3 Bond.

    PubMed

    Sicilia, V; Baya, M; Borja, P; Martín, A

    2015-08-01

    The half-lantern compound [{Pt(bzq)(μ-N^S)}2] (1) [bzq = benzo[h]quinoline, HN^S = 2-mercaptopyrimidine (C4H3N2HS)] reacts with CH3I and haloforms CHX3 (X = Cl, Br, I) to give the corresponding oxidized diplatinum(III) derivatives [{Pt(bzq)(μ-N^S)X}2] (X = Cl 2a, Br 2b, I 2c). These compounds exhibit half-lantern structures with short intermetallic distances (∼2.6 Å) due to Pt-Pt bond formation. The halogen abstraction mechanisms from the halocarbon molecules by the Pt2(II,II) compound 1 were investigated. NMR spectroscopic evidence using labeled reagents support that in the case of (13)CH3I the reaction initiates with an oxidative addition through an SN2 mechanism giving rise to the intermediate species [I(bzq)Pt(μ-N^S)2Pt(bzq)((13)CH3)}]. However, with haloforms the reactions proceed through a radical-like mechanism, thermally (CHBr3, CHI3) or photochemically (CHCl3) activated, giving rise to mixtures of species [X(bzq)Pt(μ-N^S)2Pt(bzq)R] (3a-c) and [X(bzq)Pt(μ-N^S)2Pt(bzq)X] (2a-c). In these cases the presence of O2 favors the formation of species 2 over 3. Transformation of 3 into 2 was possible upon irradiation with UV light. In the case of [I(bzq)Pt(μ-N^S)2Pt(bzq)((13)CH3)}] (3d), in the presence of O2 the formation of the unusual methylperoxo derivative [I(bzq)Pt(μ-N^S)2Pt(bzq)(O-O(13)CH3)}] (4d) was detected, which in the presence of (13)CH3I rendered the final product [{Pt(bzq)(μ-N^S)I}2] (2c) and (13)CH3OH. PMID:26197039

  12. Anti-prothrombin (aPT) and anti-phosphatidylserine/prothrombin (aPS/PT) antibodies and the risk of thrombosis in the antiphospholipid syndrome. A systematic review.

    PubMed

    Sciascia, Savino; Sanna, Giovanni; Murru, Veronica; Roccatello, Dario; Khamashta, Munther A; Bertolaccini, Maria Laura

    2014-02-01

    Antibodies to prothrombin are detected by directly coating prothrombin on irradiated ELISA plates (aPT) or by using the phosphatidylserine/prothrombin complex as antigen (aPS/PT). Although these antibodies have both been associated with antiphospholipid syndrome (APS) and a correlation between the two assays have been reported, it seems that aPT and aPS/PT belong to different populations of autoantibodies. It was our objective to systematically review the available evidence on aPT and aPS/PT antibodies and the risk of thrombosis in APS. Medline-reports published between 1988 and 2013 investigating aPT and aPS/PT as a risk factor for thrombosis were included. Whenever possible, antibody isotype(s) and site of thrombosis were analysed. This systematic review is based on available data from more than 7,000 patients and controls from 38 studies analysing aPT and 10 aPS/PT. Antibodies to prothrombin (both aPT and aPS/PT) increased the risk of thrombosis (odds ratio [OR] 2.3; 95% confidence interval [CI] 1.72-3.5). aPS/PT seemed to represent a stronger risk factor for thrombosis, both arterial and/or venous than aPT (OR 5.11; 95%CI 4.2-6.3 and OR 1.82; 95%CI 1.44-2.75, respectively). In conclusion, routine measurement of aPS/PT (but not aPT) might be useful in establishing the thrombotic risk of patients with previous thrombosis and/or systemic lupus erythematosus. Their inclusion as laboratory criteria for the APS should be indisputably further explored.

  13. Spectroelectrochemical Study of Carbon Monoxide and Ethanol Oxidation on Pt/C, PtSn(3:1)/C and PtSn(1:1)/C Catalysts.

    PubMed

    Rizo, Rubén; Lázaro, María Jesús; Pastor, Elena; García, Gonzalo

    2016-09-12

    PtSn-based catalysts are one of the most active materials toward that contribute ethanol oxidation reaction (EOR). In order to gain a better understanding of the Sn influence on the carbon monoxide (principal catalyst poison) and ethanol oxidation reactions in acidic media, a systematic spectroelectrochemical study was carried out. With this end, carbon-supported PtSnx (x = 0, 1/3 and 1) materials were synthesized and employed as anodic catalysts for both reactions. In situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) indicate that Sn diminishes the amount of bridge bonded CO (COB) and greatly improves the CO tolerance of Pt-based catalysts. Regarding the effect of Sn loading on the EOR, it enhances the catalytic activity and decreases the onset potential. FTIRS and DEMS analysis indicate that the C-C bond scission occurs at low overpotentials and at the same potential values regardless of the Sn loading, although the amount of C-C bond breaking decreases with the rise of Sn in the catalytic material. Therefore, the elevated catalytic activity toward the EOR at PtSn-based electrodes is mainly associated with the improved CO tolerance and the incomplete oxidation of ethanol to form acetic acid and acetaldehyde species, causing the formation of a higher amount of both C2 products with the rise of Sn loading.

  14. Ag on Pt(111): Changes in Electronic and CO Adsorption Properties upon PtAg/Pt(111) Monolayer Surface Alloy Formation.

    PubMed

    Diemant, Thomas; Schüttler, Konstantin M; Behm, R Jürgen

    2015-10-01

    The electronic and chemical (adsorption) properties of bimetallic Ag/Pt(111) surfaces and their modification upon surface alloy formation, that is, during intermixing of Ag and Pt atoms in the top atomic layer upon annealing, were studied by X-ray photoelectron spectroscopy (XPS) and, using CO as probe molecule, by temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), respectively. The surface alloys are prepared by deposition of sub-monolayer Ag amounts on a Pt(111) surface at room temperature, leading to extended Ag monolayer islands on the substrate, and subsequent annealing of these surfaces. Surface alloy formation starts at ≈600-650 K, which is evidenced by core-level shifts (CLSs) of the Ag(3d5/2 ) signal. A distinct change of the CO adsorption properties is observed when going to the intermixed PtAg surface alloys. Most prominently, we find the growth of a new desorption feature at higher temperature (≈550 K) in the TPD spectra upon surface alloy formation. This goes along with a shift of the COad -related IR bands to lower wave number. Surface alloy formation is almost completed after heating to 700 K.

  15. Spectroelectrochemical Study of Carbon Monoxide and Ethanol Oxidation on Pt/C, PtSn(3:1)/C and PtSn(1:1)/C Catalysts.

    PubMed

    Rizo, Rubén; Lázaro, María Jesús; Pastor, Elena; García, Gonzalo

    2016-01-01

    PtSn-based catalysts are one of the most active materials toward that contribute ethanol oxidation reaction (EOR). In order to gain a better understanding of the Sn influence on the carbon monoxide (principal catalyst poison) and ethanol oxidation reactions in acidic media, a systematic spectroelectrochemical study was carried out. With this end, carbon-supported PtSnx (x = 0, 1/3 and 1) materials were synthesized and employed as anodic catalysts for both reactions. In situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) indicate that Sn diminishes the amount of bridge bonded CO (COB) and greatly improves the CO tolerance of Pt-based catalysts. Regarding the effect of Sn loading on the EOR, it enhances the catalytic activity and decreases the onset potential. FTIRS and DEMS analysis indicate that the C-C bond scission occurs at low overpotentials and at the same potential values regardless of the Sn loading, although the amount of C-C bond breaking decreases with the rise of Sn in the catalytic material. Therefore, the elevated catalytic activity toward the EOR at PtSn-based electrodes is mainly associated with the improved CO tolerance and the incomplete oxidation of ethanol to form acetic acid and acetaldehyde species, causing the formation of a higher amount of both C2 products with the rise of Sn loading. PMID:27626404

  16. Effect of the structural characteristics of binary Pt-Ru and ternary Pt-Ru-M fuel cell catalysts on the activity of ethanol electrooxidation in acid medium.

    PubMed

    Antolini, Ermete

    2013-06-01

    In view of their possible use as anode materials in acid direct ethanol fuel cells, the electrocatalytic activity of Pt-Ru and Pt-Ru-M catalysts for ethanol oxidation has been investigated. This minireview examines the effects of the structural characteristics of Pt-Ru, such as the degree of alloying and Ru oxidation state, on the electrocatalytic activity for ethanol oxidation.

  17. Low Temperature Hydrogenation of Benzene and Cyclohexene: A Comparative Study Between gamma-Al2O3 Supported PtCo and PtNi Bimetallic Catalysts

    SciTech Connect

    Lu, S.; Lonergan, W; Bosco, J; Wang, S; Zhu, Y; Xie, Y; Chen, J

    2008-01-01

    Supported PtCo and PtNi bimetallic and Co, Ni, Pt monometallic catalysts were prepared by impregnation method on ?-Al2O3 and evaluated for the hydrogenation of benzene and cyclohexene at low temperatures (273-343 K) and atmospheric pressure. Results from batch reactor studies with Fourier transform infrared spectroscopy (FTIR) and flow reactor studies both showed that PtCo bimetallic catalysts exhibited significantly higher activity than PtNi and monometallic Co, Ni, and Pt catalysts for benzene hydrogenation, while PtNi catalysts showed higher activity for cyclohexene hydrogenation. Results from H2 chemisorption and H2-temperature-programmed reduction (H2-TPR) studies showed that a small amount of Pt addition could increase the chemisorption capacity and make the reduction of Co or Ni much easier, especially for Co-based catalysts. Extended X-ray absorption fine structure (EXAFS) results confirmed the formation of Pt-Co and Pt-Ni bimetallic bonds in the PtCo and PtNi bimetallic catalysts, supporting the argument from previous surface science and theoretical predictions that these two bimetallic catalysts would have higher hydrogenation activity than the corresponding monometallic catalysts.

  18. CdpC2PT, a reverse prenyltransferase from Neosartorya fischeri with a distinct substrate preference from known C2-prenyltransferases.

    PubMed

    Mundt, Kathrin; Li, Shu-Ming

    2013-10-01

    A putative prenyltransferase gene, NFIA_043650, was amplified from Neosartorya fischeri NRRL 181 and cloned into the expression vector pQE60. The deduced polypeptide consisting of 445 amino acids with a molecular mass of 51 kDa was overproduced in Escherichia coli and purified as His6-tagged protein to near homogeneity. The purified soluble protein was subsequently assayed with potential aromatic substrates in the presence of dimethylallyl diphosphate. HPLC analysis of the reaction mixtures revealed acceptance of all tested tryptophan-containing cyclic dipeptides. Isolation and structural elucidation of enzyme products of five selected substrates indicated a reverse C2-prenylation on the indole nucleus, proving the enzyme to be a cyclic dipeptide C2-prenyltransferase (CdpC2PT). Differing significantly from two known brevianamide F reverse C2-prenyltransferases NotF and BrePT which use cyclo-l-Trp-l-Pro as their preferred substrate, CdpC2PT showed a clear substrate preference for (S)-benzodiazepinedinone and cyclo-l-Trp-l-Trp with KM values of 84.1 and 165.2 µM and turnover numbers at 0.63 and 0.30 s(-1), respectively. A possible role of CdpC2PT in the biosynthesis of fellutanines is discussed.

  19. Insight into the Reaction Mechanisms of Methanol on PtRu/Pt(111): A Density Functional Study

    NASA Astrophysics Data System (ADS)

    Ding, Qiuyue; Xu, Wenbin; Sang, Pengpeng; Xu, Jing; Zhao, Lianming; He, Xiaoli; Guo, Wenyue

    2016-04-01

    Periodic DFT calculations have been performed to systematically investigate the mechanisms of methanol decomposition and oxidation on the PtRu/Pt(111) surface. Geometries and energies for the primary species involved are analyzed and the reaction network has been mapped out. The calculation shows that among three initial Csbnd H, Osbnd H, and Csbnd O bond scissions of methanol, the Osbnd H bond scission is found to be the most favorable and bears a lower energy barrier than the desorption of methanol. The decomposition of CH3O occurs via the path CH3O → CH2O → CHO → CO with the limiting step of the first dehydrogenation. Although the oxidation of CO is hindered by a high barrier, the CHO oxidation to CHOOH could occur facilely. Further decomposition of formic acid to CO2 and/or CO could occur via four possible pathways, that is, initial Csbnd H, Osbnd H, and Csbnd O bond activations as well as simultaneous activation of Csbnd H and Csbnd O bonds, where the first pathway, HCOOH → COOH → CO2, is the most favorable from a kinetic point of view. Compared to that on Pt(111), methanol on PtRu/Pt(111) prefers to decomposition rather than desorption and then oxidation via the favorable non-CO path with a lower rate-determining energy barrier of CH3O → CH2O for the whole reaction, which indicates that PtRu alloy can improved tolerance toward CO poisoning compared with pure Pt.

  20. The Changing Roles of P&T Committees

    PubMed Central

    Vogenberg, F. Randy; Gomes, Judith

    2014-01-01

    Market and regulatory changes in the last 10 years, as well as the Affordable Care Act, have resulted in significant modifications to health care delivery models. Traditionally, P&T committees limited the impact of their decisions to the populations associated with their hospital or health plan; however, as hospitals have begun to transform into larger health systems and even integrated payer organizations, P&T committees must consider both inpatient and outpatient needs of patients in multiple hospitals and ambulatory care settings. The function of the P&T committee has not necessarily changed, but its scope has expanded. Considerations of quality, cost (reimbursement), and access (accreditation) affecting P&T committees over the past decade will become even more important as new drugs and biotech therapies enter the market and the shortage of primary care physicians intensifies. Pharmacists, physical therapists, nurses, and physicians are assuming new leadership responsibilities, making them partners with P&T committees in improving clinical care and cost performance for health systems. PMID:25395819

  1. DFT Study of Optical Properties of Pt-based Complexes

    NASA Astrophysics Data System (ADS)

    Oprea, Corneliu I.; Dumbravǎ, Anca; Moscalu, Florin; Nicolaides, Atnanassios; Gîrţu, Mihai A.

    2010-01-01

    We report Density Functional Theory (DFT) calculations providing the geometrical and electronic structures, as well as the vibrational and optical properties of the homologous series of Pt-pyramidalized olefin complexes (CH2)n-(C8H10)Pt(PH3)2, where n = 0, 1, and 2, in their neutral and oxidized states. All complexes were geometry optimized for the singlet ground state in vacuum using DFT methods with B3LYP exchange-correlation functional and the Effective Core Potential LANL2DZ basis set, within the frame of Gaussian03 quantum chemistry package. We find the coordination geometry of Pt to be distorted square planar, with dihedral angles ranging from 0°, for n = 0 and 1, which have C2V symmetry to 3.4°, for n = 2 with C2 symmetry. The Mulliken charge analysis allows a discussion of the oxidation state of the Pt ion. Electronic transitions were calculated at the same level of theory by means of Time Dependant-DFT. For n = 2 the electronic absorption bands are located in the UV region of the spectrum, the transitions being assigned to metal to ligand charge transfers. The relevance of these Pt-based compounds as possible pigments for dye-sensitized solar cells is discussed.

  2. Thermal stability of Pt/Co multilayered films

    NASA Astrophysics Data System (ADS)

    Sumi, S.; Kusumoto, Y.; Teragaki, Y.; Torazawa, K.; Tsunashima, S.; Uchiyama, S.

    1993-05-01

    The thermal stability of Pt/Co multilayered films with various underlayers has been studied by annealing up to 400 °C. In Pt/Co films sputtered on glass or amorphous AlN underlayers, their coercivity and the squareness of magnetic hysteresis loops are degraded by annealing above 300 °C. In contrast, in films sputtered on ZnO or Pt underlayers, the coercivity is remarkably increased by annealing at 300 °C. The film with the ZnO underlayer shows a hysteresis loop with perfect squareness even after annealing at 400 °C. The results of x-ray diffraction indicate that the ZnO underlayer not only enhances the fcc Pt/Co(111) orientation but also prevents the decay of the multilayered structure during annealing. The results of laser microannealing using a conventional disk drive system also indicate that the Pt/Co films with ZnO underlayers have superior resistance to laser damage.

  3. Surfactant-Assisted Hydrothermal Synthesis of PMN-PT Nanorods.

    PubMed

    Li, Chuan; Liu, Xingzhao; Luo, Wenbo; Xu, Dong; He, Kai

    2016-12-01

    The effects of surfactant polyacrylate acid (PAA) on shape evolution of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (0.7PMN-0.3PT) nanorods were studied. The results revealed that the polyacrylic acid content had great influence on the morphology of 0.7PMN-0.3PT. With increasing PAA concentration from 0.45 to 0.82 g/ml, the ratio of perovskite phase (PMN-PT nanorod) increased, while the ratio of pyrochlore phase decreased. When the PAA concentration was 0.82 g/ml, pure 0.7PMN-0.3PT nanorods were obtained. However, when PAA concentration was higher than 0.82 g/ml, the excess of PAA would hindered their [100] orientation growth. The piezoelectric coefficient d 33 of 0.7PMN-0.3PT nanorod was obtained by linear fitting, and the d 33 value was 409 pm/V. PMID:26831687

  4. Surfactant-Assisted Hydrothermal Synthesis of PMN-PT Nanorods

    NASA Astrophysics Data System (ADS)

    Li, Chuan; Liu, Xingzhao; Luo, Wenbo; Xu, Dong; He, Kai

    2016-02-01

    The effects of surfactant polyacrylate acid (PAA) on shape evolution of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (0.7PMN-0.3PT) nanorods were studied. The results revealed that the polyacrylic acid content had great influence on the morphology of 0.7PMN-0.3PT. With increasing PAA concentration from 0.45 to 0.82 g/ml, the ratio of perovskite phase (PMN-PT nanorod) increased, while the ratio of pyrochlore phase decreased. When the PAA concentration was 0.82 g/ml, pure 0.7PMN-0.3PT nanorods were obtained. However, when PAA concentration was higher than 0.82 g/ml, the excess of PAA would hindered their [100] orientation growth. The piezoelectric coefficient d 33 of 0.7PMN-0.3PT nanorod was obtained by linear fitting, and the d 33 value was 409 pm/V.

  5. Strong Spin Hall effect in PtMn

    NASA Astrophysics Data System (ADS)

    Ou, Yongxi; Shi, Shengjie; Ralph, Daniel; Buhrman, Robert

    Recent reports indicate that certain metallic antiferromagnets (AFM) can exhibit a significant spin Hall effect. Here we report a large damping-like spin torque efficiency (ξDL) in PtMn/ferromagnet(FM) bilayer structures, determined from both FM-thickness-dependent spin-torque ferromagnetic resonance (ST-FMR), and harmonic response (HR) measurements of layers with perpendicular magnetic anisotropy (PMA). We find that ξDL can vary from <0.1 to >0.15, depending on the thickness of PtMn, the stacking order of the samples, and the choice of the FM material. The field-like spin torque efficiency (ξFL) is also quite variable, 0<|ξFL|<0.5. The large broadening of the ST-FMR linewidth suggests extra spin attenuation at the AFM/FM interface that is possibly due to intermixing. The PtMn/FeCoB/MgO structures that exhibit PMA have a comparatively low switching current density and an unusual asymmetric switching phase diagram. These results indicate that AFM PtMn has significant potential both for advancing the understanding the physics of the spin Hall effect in Pt alloys, and for enabling new spintronics functionality.

  6. PT -symmetric Hamiltonians and their application in quantum information

    NASA Astrophysics Data System (ADS)

    Croke, Sarah

    2015-05-01

    We discuss the prospect of PT -symmetric Hamiltonians finding applications in quantum information science, and conclude that such evolution is unlikely to provide any benefit over existing techniques. Although it has been known for some time that PT -symmetric quantum theory, when viewed as a unitary theory, is exactly equivalent to standard quantum mechanics, proposals continue to be put forward for schemes in which PT -symmetric quantum theory can outperform standard quantum theory. The most recent of these is the suggestion to use PT -symmetric Hamiltonians to perform an exponentially fast database search, a task known to be impossible with a quantum computer. Further, such a scheme has been shown to apparently produce effects in conflict with fundamental information-theoretic principles, such as the impossibility of superluminal information transfer, and the invariance of entanglement under local operations. In this paper we propose three inequivalent experimental implementations of PT -symmetric Hamiltonians, with careful attention to the resources required to realize each such evolution. Such an operational approach allows us to resolve these apparent conflicts, and evaluate fully schemes proposed in the literature for faster time evolution and state discrimination.

  7. Thiolate bridging and metal exchange in adducts of a zinc finger model and Pt(II) complexes: biomimetic studies of protein/Pt/DNA interactions.

    PubMed

    Almaraz, Elky; de Paula, Queite A; Liu, Qin; Reibenspies, Joseph H; Darensbourg, Marcetta Y; Farrell, Nicholas P

    2008-05-14

    To provide precedents for the possible interactions of platinum DNA adducts with zinc finger proteins, the complexes [Pt(dien)Cl]Cl (dien = diethylenetriamine) and [Pt(terpy)Cl]Cl (terpy = 2,2':6',2''-terpyridine) were exposed to the N,N'-bis(2-mercaptoethyl)-1,4-diazacycloheptanezinc(II) dimer, [Zn(bme-dach)]2, and the products defined by electrospray ionization mass spectrometry (ESI-MS), X-ray crystallography and (195)Pt NMR spectroscopy. The presence of a leaving chloride in both platinum(II) complexes facilitates electrophilic substitution involving sulfur-containing zinc finger synthetic models or, as in previous studies, zinc finger peptidic sequences. Monitored via ESI-MS, both reactants yielded evidence for Zn-(mu-SR)-Pt bridges followed by zinc ejection from the N2S2 coordination sphere and subsequent formation of a trimetallic Zn-(mu-SR)2-Pt-(mu-SR)2-Zn-bridged species. The isolation of Zn-(mu-SR)-Pt-bridged species [(Zn(bme-dach)Cl)(Pt(dien))]Cl is, to our knowledge, the first Zn-Pt bimetallic thiolate-bridged model demonstrating the interaction between Zn-bound thiolates and Pt(2+). In the case of the [Pt(terpy)Cl]Cl reaction with the [Zn(bme-dach)]2, ESI-MS analysis further suggests metal exchange by formation of [Zn(terpy)Cl](+), whereas the [Pt(dien)Cl]Cl reaction does not yield the corresponding [Zn(dien)Cl](+) ion. Direct synthesis of the Zn-Pt thiolate-bridged species and the Pt(N2S2) chelate, where Pt has displaced the Zn from the chelate core, permitted the isolation of X-ray-quality crystals to confirm the bridging and metal-exchanged structures. The ESI-MS, (195)Pt NMR spectroscopy, and molecular structures of the di- and trinuclear complexes will be discussed, as they provide insight into the metal-exchange mechanism.

  8. Facile synthesis of PtAu alloy nanoparticles with high activity for formic acid oxidation

    SciTech Connect

    Zhang, Sheng; Shao, Yuyan; Yin, Geping; Lin, Yuehe

    2010-02-15

    We report the facile synthesis of carbon supported PtAu alloy nanoparticles with high electrocatalytic activity as the anode catalyst for direct formic acid fuel cells (DFAFCs). PtAu alloy nanopaticles are synthesized by co-reducing HAuCl4 and H2PtCl6 with NaBH4 in the presence of sodium citrate and then the nanoparticles are deposited on Vulcan XC-72R carbon support (PtAu/C). The obtained catalysts are characterized with X-ray diffraction (XRD) and transmission electron microscope (TEM), which reveal PtAu alloy formation with an average diameter of 4.6 nm. PtAu/C exhibits 8 times higher catalytic activity toward formic acid oxidation than Pt/C. The enhanced activity of PtAu/C catalyst is attributed to noncontinuous Pt sites formed in the presence of the neighbored Au sites, which promotes direct oxidation of formic acid by avoiding poison CO.

  9. A pathway for the growth of core-shell Pt-Pd nanoparticles

    SciTech Connect

    Narula, Chaitanya Kumar; Yang, Xiaofan; Li, Chen; Pennycook, Stephen J; Lupini, Andrew R

    2015-10-12

    In this study, the aging of both Pt-Pd nanoparticles and core-shell Pt-Pd nanoparticles has been reported to result in alloying of Pt with Pd. In comparison to monometallic Pt catalysts, the growth of Pd-Pt bimetallics is slower; however, the mechanism of growth of particles and the mechanism by which Pd improves the hydrothermal durability of bimetallic Pd-Pt particles remains uncertain. In our work on hydrothermal aging of core-shell Pt-Pd nanoparticles, synthesized by solution methods, with varying Pd:Pt ratio of 1:4, 1:1, and 4:1, we compare the growth of core-shell Pt-Pd nanoparticles and find that particles grow by migrating and joining together. The unique feature of the observed growth is that Pd shells from both particles open up and join, allowing the cores to merge. At high temperatures, alloying occurs in good agreement with reports by other workers.

  10. Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction

    SciTech Connect

    Lim, B.; Tao, J.; Jiang, M.; Camargo, P.H.C.; Cho, E.C.; Lu, X.; Zhu, Y.; Xia, Y.

    2009-06-05

    Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. We synthesized Pd-Pt bimetallic nanodendrites consisting of a dense array of Pt branches on a Pd core by reducing K{sub 2}PtCl{sub 4} with L-ascorbic acid in the presence of uniform Pd nanocrystal seeds in an aqueous solution. The Pt branches supported on faceted Pd nanocrystals exhibited relatively large surface areas and particularly active facets toward the oxygen reduction reaction (ORR), the rate-determining step in a proton-exchange membrane fuel cell. The Pd-Pt nanodendrites were two and a half times more active on the basis of equivalent Pt mass for the ORR than the state-of-the-art Pt/C catalyst and five times more active than the first-generation supportless Pt-black catalyst.

  11. Tailoring the morphology of Pt3Cu1 nanocrystals supported on graphene nanoplates for ethanol oxidation.

    PubMed

    Zhang, Genlei; Yang, Zhenzhen; Zhang, Wen; Hu, Hongwei; Wang, Chunzhen; Huang, Chengde; Wang, Yuxin

    2016-02-01

    In the search for alternatives to conventional Pt electrocatalysts, we synthesized a series of graphene nanoplate (GNP)-supported Pt3Cu1 nanocrystals (NCs), possessing almost the same composition but different morphologies to probe their electrochemical properties as a function of morphology for the ethanol oxidation reaction. The morphology of the Pt3Cu1 catalysts could be systematically evolved from dendritic (D-Pt3Cu1/GNPs) to wire-like (W-Pt3Cu1/GNPs) and spherical (Pt3Cu1/GNPs) by only varying pH of the reaction solution. The as-prepared Pt3Cu1 catalysts were subsequently characterized using a suite of techniques including transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS) and X-ray photoelectron spectroscopy (XPS) to verify not only their morphologies and chemical compositions but also the incorporation of Cu into the Pt lattice, as well as physical structure and integrity. Gratifyingly, the three Pt3Cu1 catalysts exhibited superior electrocatalytic properties for the ethanol oxidation compared to the monometallic Pt/GNPs and Pt/C-JM (Johnson Matthey), with the activities, durabilities and anti-poisonous abilities following the order Pt3Cu1/GNPs < W-Pt3Cu1/GNPs < D-Pt3Cu1/GNPs.

  12. Self-supported Pt nanoclusters via galvanic replacement from Cu2O nanocubes as efficient electrocatalysts

    NASA Astrophysics Data System (ADS)

    Li, Qing; Xu, Ping; Zhang, Bin; Wu, Gang; Zhao, Hongtao; Fu, Engang; Wang, Hsing-Lin

    2013-07-01

    A novel synthesis method for self-supported Pt nanoclusters (Pt NCs) comprised of interconnected 2-3 nm Pt nanoparticles was developed by employing the galvanic replacement process between Cu2O nanocubes and PtCl42- ions. This discovered synthesis procedure eliminates the use of any polymer capping agents and enables a catalytically clean Pt surface. It is determined that the presence of H+ ions is crucial for initializing the galvanic replacement reaction. The electrocatalytic performances of the Pt NCs were tested for both oxygen reduction and methanol oxidation reactions, which showed higher electrochemical activity and greater long-term durability as compared with commercial Pt materials.A novel synthesis method for self-supported Pt nanoclusters (Pt NCs) comprised of interconnected 2-3 nm Pt nanoparticles was developed by employing the galvanic replacement process between Cu2O nanocubes and PtCl42- ions. This discovered synthesis procedure eliminates the use of any polymer capping agents and enables a catalytically clean Pt surface. It is determined that the presence of H+ ions is crucial for initializing the galvanic replacement reaction. The electrocatalytic performances of the Pt NCs were tested for both oxygen reduction and methanol oxidation reactions, which showed higher electrochemical activity and greater long-term durability as compared with commercial Pt materials. Electronic supplementary information (ESI) available: Fig. S1-S9. See DOI: 10.1039/c3nr02243a

  13. Reducing Pt use in the catalysts for formic acid electrooxidation via nanoengineered surface structure

    NASA Astrophysics Data System (ADS)

    Liao, Mengyin; Wang, Yulu; Chen, Guoqin; Zhou, Hua; Li, Yunhua; Zhong, Chuan-Jian; Chen, Bing H.

    2014-07-01

    The design of active and durable catalysts for formic acid (FA) electrooxidation requires controlling the amount of three neighboring platinum atoms in the surface of Pt-based catalysts. Such requirement is studied by preparing Pt decorated Pd/C (donated as Pt-Pd/C) with various Pt:Pd molar ratios via galvanic displacement making the amount of three neighboring Pt atoms in the surface of Pt-Pd/C tunable. The decorated nanostructures are confirmed by XPS, HS-LEIS, cyclic voltammetry and chronoamperometric measurements, demonstrating that Pt-Pd/C (the optimal molar ratio, Pt:Pd = 1:250) exhibits superior activity and durability than Pd/C and commercial Pt/C (J-M, 20%) catalysts for FA electrooxidation. The mass activity of Pt-Pd/C (Pt:Pd = 1:250) (3.91 A mg-1) is about 98 and 6 times higher than that of commercial Pt/C (0.04 A mg-1) and Pd/C (0.63 A mg-1) at a given potential of 0.1 V vs SCE, respectively. The controlled synthesis of Pt-Pd/C lead to the formation of largely discontinuous Pd and Pt sites and inhibition of CO formation, exhibiting unprecedented electrocatalytic performance toward FA electrooxidation while the cost of the catalyst almost the same as Pd/C. These findings have profound implications to the design and nanoengineering of decorated surfaces of catalysts for FA electrooxidation.

  14. Tailoring the morphology of Pt3Cu1 nanocrystals supported on graphene nanoplates for ethanol oxidation.

    PubMed

    Zhang, Genlei; Yang, Zhenzhen; Zhang, Wen; Hu, Hongwei; Wang, Chunzhen; Huang, Chengde; Wang, Yuxin

    2016-02-01

    In the search for alternatives to conventional Pt electrocatalysts, we synthesized a series of graphene nanoplate (GNP)-supported Pt3Cu1 nanocrystals (NCs), possessing almost the same composition but different morphologies to probe their electrochemical properties as a function of morphology for the ethanol oxidation reaction. The morphology of the Pt3Cu1 catalysts could be systematically evolved from dendritic (D-Pt3Cu1/GNPs) to wire-like (W-Pt3Cu1/GNPs) and spherical (Pt3Cu1/GNPs) by only varying pH of the reaction solution. The as-prepared Pt3Cu1 catalysts were subsequently characterized using a suite of techniques including transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS) and X-ray photoelectron spectroscopy (XPS) to verify not only their morphologies and chemical compositions but also the incorporation of Cu into the Pt lattice, as well as physical structure and integrity. Gratifyingly, the three Pt3Cu1 catalysts exhibited superior electrocatalytic properties for the ethanol oxidation compared to the monometallic Pt/GNPs and Pt/C-JM (Johnson Matthey), with the activities, durabilities and anti-poisonous abilities following the order Pt3Cu1/GNPs < W-Pt3Cu1/GNPs < D-Pt3Cu1/GNPs. PMID:26785816

  15. SIMS and FAB-MS surface studies of Pt-Sn/Al 2O 3 and Pt 3Pb model catalysts

    NASA Astrophysics Data System (ADS)

    Unger, W.; Lietz, G.; Lieske, H.; Völter, J.

    1990-08-01

    SIMS and FAB-MS methods have been applied to study surface complexes in chloride containing Pt-Sn/Al 2O 3 and Pt 3Pb in dependence on the temperature of treatment in oxygen. The existence and the limited (700 to ˜850 K) thermal stability of a (PtO xCl y) surface complex was confirmed. Pt-Sn/Al 2O 3, air treated (calcined) at 770 K, contains already neighbouring Pt and Sn species being precursors of alloy clusters formed during subsequent reduction.

  16. Monte carlo simulations of segregation in Pt-Re catalyst nanoparticles

    SciTech Connect

    Wang, Guofeng; Van Hove, M.A.; Ross, P.N.; Baskes, M.I.

    2004-04-01

    We have investigated the segregation of Pt atoms to the surfaces of Pt-Re nanoparticles using the Monte Carlo method and Modified Embedded Atom Method potentials that we have developed for Pt-Re alloys. The Pt75Re25 nanoparticles (containing from 586 to 4033 atoms) are assumed to have disordered fcc configurations and cubo-octahedral shapes (terminated by {l_brace}111{r_brace} and {l_brace}100{r_brace} facets), while the Pt50Re50 and Pt25Re75 nanoparticles (containing from 587 to 4061 atoms) are assumed to have disordered hcp configurations and truncated hexagonal bipyramidal shapes (terminated by {l_brace}0001{r_brace} and {l_brace}101 {bar 1}{r_brace} facets). We predict that due to the segregation process the equilibrium Pt-Re nanoparticles would achieve a core-shell structure, with a Pt-enriched shell surrounding a Pt-deficient core. For fcc cubo-octahedral Pt75Re25 nanoparticles, the shells consist of almost 100 at. percent of Pt atoms. Even in the shells of hcp truncated hexagonal bipyramidal Pt50Re50 nanoparticles, the concentrations of Pt atoms exceed 85 at. percent (35 at. percent higher than the overall concentration of Pt atoms in these nanoparticles). Most prominently, all Pt atoms will segregate to the surfaces in the hcp truncated hexagonal bipyramidal Pt25Re75 nanoparticles containing less than 1000 atoms. We also find that the Pt atoms segregate preferentially to the vertex sites, less to edge sites, and least to facet sites on the shell of Pt-Re nanoparticles.

  17. Ternary Pt-Ru-Ni catalytic layers for methanol electrooxidation prepared by electrodeposition and galvanic replacement

    PubMed Central

    Papaderakis, Athanasios; Pliatsikas, Nikolaos; Prochaska, Chara; Papazisi, Kalliopi M.; Balomenou, Stella P.; Tsiplakides, Dimitrios; Patsalas, Panagiotis; Sotiropoulos, Sotiris

    2014-01-01

    Ternary Pt-Ru-Ni deposits on glassy carbon substrates, Pt-Ru(Ni)/GC, have been formed by initial electrodeposition of Ni layers onto glassy carbon electrodes, followed by their partial exchange for Pt and Ru, upon their immersion into equimolar solutions containing complex ions of the precious metals. The overall morphology and composition of the deposits has been studied by SEM microscopy and EDS spectroscopy. Continuous but nodular films have been confirmed, with a Pt ÷ Ru ÷ Ni % bulk atomic composition ratio of 37 ÷ 12 ÷ 51 (and for binary Pt-Ni control systems of 47 ÷ 53). Fine topographical details as well as film thickness have been directly recorded using AFM microscopy. The composition of the outer layers as well as the interactions of the three metals present have been studied by XPS spectroscopy and a Pt ÷ Ru ÷ Ni % surface atomic composition ratio of 61 ÷ 12 ÷ 27 (and for binary Pt-Ni control systems of 85 ÷ 15) has been found, indicating the enrichment of the outer layers in Pt; a shift of the Pt binding energy peaks to higher values was only observed in the presence of Ru and points to an electronic effect of Ru on Pt. The surface electrochemistry of the thus prepared Pt-Ru(Ni)/GC and Pt(Ni)/GC electrodes in deaerated acid solutions (studied by cyclic voltammetry) proves the existence of a shell consisting exclusively of Pt-Ru or Pt. The activity of the Pt-Ru(Ni) deposits toward methanol oxidation (studied by slow potential sweep voltammetry) is higher from that of the Pt(Ni) deposit and of pure Pt; this enhancement is attributed both to the well-known Ru synergistic effect due to the presence of its oxides but also (based on the XPS findings) to a modification effect of Pt electronic properties. PMID:24959530

  18. Bulk ordering and surface segregation in Ni50Pt50

    NASA Astrophysics Data System (ADS)

    Pourovskii, L. V.; Ruban, A. V.; Abrikosov, I. A.; Vekilov, Y. Kh.; Johansson, B.

    2001-07-01

    Interatomic interactions obtained from the effective screened generalized-perturbation method have been applied in Monte Carlo simulations to derive the bulk and surface-alloy configurations for Ni50Pt50. The calculated order-disorder transition temperature and short-range order parameters in the bulk compare well with experimental data. The surface-alloy compositions for the (111) and (110) facets above the ordering transition temperature are also found to be in a good agreement with experiments. It is demonstrated that the segregation profile at the (110) surface of NiPt is mainly caused by the unusually strong segregation of Pt into the second layer and the interlayer ordering due to large chemical nearest-neighbor interactions.

  19. Level densities and thermodynamical properties of Pt and Au isotopes

    NASA Astrophysics Data System (ADS)

    Giacoppo, F.; Bello Garrote, F. L.; Bernstein, L. A.; Bleuel, D. L.; Eriksen, T. K.; Firestone, R. B.; Görgen, A.; Guttormsen, M.; Hagen, T. W.; Kheswa, B. V.; Klintefjord, M.; Koehler, P. E.; Larsen, A. C.; Nyhus, H. T.; Renstrøm, T.; Sahin, E.; Siem, S.; Tornyi, T.

    2014-11-01

    The nuclear level densities of Pt-196194 and Au,198197 below the neutron separation energy have been measured using transfer and scattering reactions. All the level density distributions follow the constant-temperature description. Each group of isotopes is characterized by the same temperature above the energy threshold corresponding to the breaking of the first Cooper pair. A constant entropy excess Δ S =1.9 kB and 1.1 kB is observed in 195Pt and 198Au with respect to 196Pt and 197Au, respectively, giving information on the available single-particle level space for the last unpaired valence neutron. The breaking of nucleon Cooper pairs is revealed by sequential peaks in the microcanonical caloric curve.

  20. Equiatomic CoPt thin films with extremely high coercivity

    SciTech Connect

    Varghese, Binni; Piramanayagam, S. N. Yang, Yi; Kai Wong, Seng; Khume Tan, Hang; Kiat Lee, Wee; Okamoto, Iwao

    2014-05-07

    In this paper, magnetic and structural properties of near-equiatomic CoPt thin films, which exhibited a high coercivity in the film-normal direction—suitable for perpendicular magnetic recording media applications—are reported. The films exhibited a larger coercivity of about 6.5 kOe at 8 nm. The coercivity showed a monotonous decrease as the film thickness was increased. The transmission electron microscopy images indicated that the as fabricated CoPt film generally consists of a stack of magnetically hard hexagonal-close-packed phase, followed by stacking faults and face-centred-cubic phase. The thickness dependent magnetic properties are explained on the basis of exchange-coupled composite media. Epitaxial growth on Ru layers is a possible factor leading to the unusual observation of magnetically hard hcp-phase at high concentrations of Pt.

  1. Pt- and Au-induced monodirectional nanowires on Ge(110)

    NASA Astrophysics Data System (ADS)

    Watanabe, T.; Yamada, Y.; Sasaki, M.; Sakai, S.; Yamauchi, Y.

    2016-11-01

    The adsorption of Pt or Au on Ge(110) and subsequent annealing resulted in formation of well-ordered monodirectional nanowires (NWs) throughout the surface over a cm-scale. The NWs were aligned along the [ 1 1 bar 0] direction, independent of the surface reconstruction of Ge(110). Metastable-atom deexcitation spectroscopy of Pt-NWs revealed that the topmost part of the NWs comprised Ge atoms, suggesting the exchange of the Ge and metal atoms, leaving an ultrathin Ge layer on top of the NWs. The increase in the electronic density of state near the Fermi energy was observed from both the MDS and UPS spectra of the Pt-NWs, suggesting a metallicity of the NWs.

  2. Intracavity laser absorption spectroscopy of platinum fluoride, PtF

    NASA Astrophysics Data System (ADS)

    Handler, Kimberly G.; Harris, Rachel A.; O'Brien, Leah C.; O'Brien, James J.

    2011-01-01

    Two vibrational bands of an electronic transition of PtF occurring at 11 940 cm -1 and 12 496 cm -1 were recorded and analyzed. These transitions are identified as the (0,0) and (1,0) bands of an [11.9] Ω = 3/2 - XΩ = 3/2 electronic transition. Gas phase PtF was produced in a copper hollow cathode lined with platinum foil using a trace amount of SF 6, and the spectrum was recorded at Doppler resolution by intracavity laser absorption spectroscopy. This work represents the first published spectroscopic data on PtF. Molecular constants for the ground and excited electronic states are presented.

  3. Zero index metamaterials with PT symmetry in a waveguide system.

    PubMed

    Fu, Yangyang; Xu, Yadong; Chen, Huanyang

    2016-01-25

    Inspired by the concept of parity-time symmetry, we propose a new waveguide system consisting of zero index metamaterials with an air gap. Based on analytical calculations and numerical simulations, we demonstrate that there are two exceptional points in such a system, which can induce unidirectional transparency. However, the introduced air gap could effectively manipulate the property of the waveguide system with PT symmetry. In particular, coherent perfect absorber-laser modes could be excited in PT broken phase, if a specific phase difference in the air gap is obtained. More interestingly, when Fabry-Pérot resonances take place in the air gap, the PT symmetry property will be suppressed, i.e., the value of loss/gain could not affect transmission and reflection of the waveguide. As a result, perfect bidirectional transmission without reflection can occur in the waveguide system.

  4. Misfit strain phase diagrams of epitaxial PMN–PT films

    SciTech Connect

    Khakpash, N.; Khassaf, H.; Rossetti, G. A.; Alpay, S. P.

    2015-02-23

    Misfit strain–temperature phase diagrams of three compositions of (001) pseudocubic (1 − x)·Pb (Mg{sub l/3}Nb{sub 2/3})O{sub 3} − x·PbTiO{sub 3} (PMN–PT) thin films are computed using a phenomenological model. Two (x = 0.30, 0.42) are located near the morphotropic phase boundary (MPB) of bulk PMN–PT at room temperature (RT) and one (x = 0.70) is located far from the MPB. The results show that it is possible to stabilize an adaptive monoclinic phase over a wide range of misfit strains. At RT, the stability region of this phase is much larger for PMN–PT compared to barium strontium titanate and lead zirconate titanate films.

  5. Anatomy of Dzyaloshinskii-Moriya Interaction at Co /Pt Interfaces

    NASA Astrophysics Data System (ADS)

    Yang, Hongxin; Thiaville, André; Rohart, Stanislas; Fert, Albert; Chshiev, Mairbek

    2015-12-01

    The Dzyaloshinskii-Moriya interaction (DMI) has been recently recognized to play a crucial role in allowing fast domain wall dynamics driven by spin-orbit torques and the generation of magnetic Skyrmions. Here, we unveil the main features and microscopic mechanisms of DMI in Co /Pt bilayers via first principles calculations. We find that the large DMI of the bilayers has a dominant contribution from the spins of the interfacial Co layer. This DMI between the interfacical Co spins extends very weakly away from the interface and is associated with a spin-orbit coupling in the adjacent atomic layer of Pt. Furthermore, no direct correlation is found between DMI and proximity induced magnetism in Pt. These results clarify the underlying mechanisms of DMI at interfaces between ferromagnetic and heavy metals and should help optimizing material combinations for domain wall and Skyrmion-based devices.

  6. Bimetallic Wiregauze Supported Pt-Ru Nanocatalysts for Hydrogen Mitigation.

    PubMed

    Sanap, Kiran K; Varma, S; Waghmode, S B; Sharma, P; Manoj, N; Vatsa, R K; Bharadwaj, S R

    2015-05-01

    Passive autocatalytic recombiner (PAR) is one of the most suitable devices for mitigation of hydrogen, generated in nuclear power plant under accidental conditions. For this purpose we report development of stainless steel wire gauze supported Pt-Ru nanoparticles as catalysts. Simultaneous electroless deposition has been employed for the synthesis of the catalysts. Pt-Ru based bimetallic catalysts were characterized for their rate of coating kinetics, noble metal loading, phase purity by XRD and surface morphology by SEM, TEM and elemental analysis by SIMS. Developed catalysts were found to be active for efficient recombination of hydrogen and oxygen in air as well as in presence of various prospective poisons like CO2, CH4, CO and relative humidity. Pt-Ru based bimetallic catalyst with 0.9% loading was found to be active for CO poisoning up to 400 ppm of CO. PMID:26504972

  7. Unbreakable PT symmetry of solitons supported by inhomogeneous defocusing nonlinearity.

    PubMed

    Kartashov, Yaroslav V; Malomed, Boris A; Torner, Lluis

    2014-10-01

    We consider bright solitons supported by a symmetric inhomogeneous defocusing nonlinearity growing rapidly enough toward the periphery of the medium, combined with an antisymmetric gain-loss profile. Despite the absence of any symmetric modulation of the linear refractive index, which is usually required to establish a parity-time (PT) symmetry in the form of a purely real spectrum of modes, we show that the PT symmetry is never broken in the present system, and that the system always supports stable bright solitons, i.e., fundamental and multi-pole ones. This fact is connected to the nonlinearizability of the underlying evolution equation. The increase of the gain-loss strength results, in lieu of the PT symmetry breaking, in merger of pairs of different soliton branches, such as fundamental and dipole, or tripole and quadrupole ones. The fundamental and dipole solitons remain stable at arbitrarily large values of the gain-loss coefficient. PMID:25360948

  8. Misfit strain phase diagrams of epitaxial PMN-PT films

    NASA Astrophysics Data System (ADS)

    Khakpash, N.; Khassaf, H.; Rossetti, G. A.; Alpay, S. P.

    2015-02-01

    Misfit strain-temperature phase diagrams of three compositions of (001) pseudocubic (1 - x).Pb (Mgl/3Nb2/3)O3 - x.PbTiO3 (PMN-PT) thin films are computed using a phenomenological model. Two (x = 0.30, 0.42) are located near the morphotropic phase boundary (MPB) of bulk PMN-PT at room temperature (RT) and one (x = 0.70) is located far from the MPB. The results show that it is possible to stabilize an adaptive monoclinic phase over a wide range of misfit strains. At RT, the stability region of this phase is much larger for PMN-PT compared to barium strontium titanate and lead zirconate titanate films.

  9. Twofold PT symmetry in doubly exponential optical lattices

    NASA Astrophysics Data System (ADS)

    Cole, J. T.; Makris, K. G.; Musslimani, Z. H.; Christodoulides, D. N.; Rotter, S.

    2016-01-01

    We introduce a family of non-Hermitian optical potentials that are given in terms of double-exponential periodic functions. The center of PT symmetry is not around zero and the potential satisfies a shifted PT -symmetry relation at two distinct locations. Motivated by wave transmission through thin phase screens and gratings, we examine these refractive index modulations from the perspective of optical lattices that are homogeneous along the propagation direction. The diffraction dynamics, abrupt phase transitions in the eigenvalue spectrum, and exceptional points in the band structure are examined in detail. In addition, the nonlinear properties of wave propagation in Kerr nonlinearity media are studied. In particular, coherent structures such as lattice solitons are numerically identified by applying the spectral renormalization method. The spatial symmetries of such lattice solitons follow the shifted PT -symmetric relations. Furthermore, such lattice solitons have a power threshold and their linear and nonlinear stabilities are critically dependent on their spatial symmetry point.

  10. Determination of geometric orientation of adsorbed cinchonidine on Pt and Fe and quiphos on Pt nanoclusters via DRIFTS.

    PubMed

    Kraynov, A; Suchopar, A; D'Souza, L; Richards, R

    2006-03-21

    Platinum nanoclusters modified with cinchonidine have been employed as 'quasi-homogeneous' catalysts for the hydrogenation of ethyl pyruvate and have demonstrated exceptional activities while the ee's of these systems are currently inferior to the traditional Pt/Al2O3 heterogeneous system. For the bulk systems it has been shown that the orientation of the modifier on the metal surface is a critical parameter influencing catalytically induced enantioselectivity. It has been speculated that the lower observed ee's for the nanocluster systems are a result of the modifier assuming an orientation unfavorable for inducing enantioselectivity due to the lack of large numbers of planar metal atoms. Using DRIFTS (diffuse reflectance infra-red Fourier transform spectroscopy) analysis of samples together with geometry optimization and IR modelling we have studied the orientation of cinchonidine on Pt and Fe nanoclusters and additionally the man-made ligand quiphos on Pt nanoclusters. It has been determined that cinchonidine can adsorb on Pt and Fe nanoclusters in both 'flat' and 'tilted' modes, while quiphos can be adsorbed on Pt only via the 'pi-bonded' mode. These studies thus provide an insight into modifier orientation on nanocluster surfaces that can be extended to a wide range of potential modifiers and facilitate a better understanding of the origin of enantioselectivity with these 'quasi-homogeneous' catalyst systems.

  11. Isomerization and hydrocracking of heptane over bimetallic bifunctional PtPd/H-Beta and PtPd/USY zeolite catalysts

    SciTech Connect

    Blomsma, E.; Martens, J.A.; Jacobs, P.A.

    1997-01-15

    Bifunctional catalysts are prepared by loading NH{sub 4}-Beta zeolites with platinum, palladium, and platinum-palladium metal combinations via cation exchange and incipient wetness impregnation with Pt(NH{sub 3}){sub 4}Cl{sub 2} and Pd(NH{sub 3}){sub 4}Cl{sub 2} complexes, followed by calcination and reduction. In comparison to the Pt and Pd loaded acid zeolites, the bimetallic Pd-Pt zeolites are found to be more active and selective in the isomerization of heptane. The noble metal phases are characterized with temperature programmed reduction and hydrogen chemisorption. The dispersion of platinum is significantly improved in presence of as little as 20 mole% of palladium. The improved Pt dispersion leads to a better intimacy and balance of the acid and hydrogenation-dehydrogenation functions in these bi-functional catalysts and suppression of undesirable hydrogenolysis and dimerization-cracking activity. On Pt/USY zeolite, the addition of palladium has similar beneficial effects on the catalytic performances. 34 refs., 4 figs., 3 tabs.

  12. Magnetic-field-induced Crystallographic Texture Enhancement in Cold-deformed FePt/Fe3Pt Nanocomposites

    NASA Astrophysics Data System (ADS)

    Cui, B. Z.; Li, D. S.; Han, K.; Schneider-Muntau, H. J.; Liu, J. P.; Garmestani, H.; Dempsey, N. M.

    2005-03-01

    We introduce a unique approach to obtaining anisotropic FePt/Fe3Pt nanocomposites with crystallographic texture of the hard phase: roll-bonding and magnetic annealing. Magnetic-field- induced crystallographic texture and magnetic property enhancement in cold-deformed Fe62Pt38 nanostructured magnets have been studied. Compared with the samples annealed without a magnetic field, the annealing in the presence of both out-of- plane and in-plane 19 T fields enhances texture of the hard FePt phase by about 50 %. Consequently, annealing samples in a 19 T field improves iHc, Br, and (BH)max. Especially, (BH)max was increased by 21 - 25 %. Additionally, magnetically anisotropic behavior and better squareness of the demagnetization curves were observed in the magnetically annealed samples. It is suggested that cold-rolling-induced textures in both Fe and Pt phases and magnetic-field-assisted phase transformation should be responsible for the notice improvement of the crystallographic texture and magnetic properties in the magnetically annealed samples.

  13. Transmission electron microscopy characterization of Au/Pt/Ti/Pt/GaAs ohmic contacts for high power GaAs/InGaAs semiconductor lasers.

    PubMed

    Łaszcz, A; Czerwinski, A; Ratajczak, J; Szerling, A; Phillipp, F; Van Aken, P A; Katcki, J

    2010-03-01

    We report on transmission electron microscopy studies of Au/Pt/Ti/Pt(10-30 nm) contact structures for high power GaAs/InGaAs semiconductor lasers. The studies showed that annealing at 450 degrees C of contact structures causes the reaction of whole Pt with substrate components (Ga and As) and the formation of Pt-GaAs interlayers with smooth interfaces as required for such structures. Annealing of the structures at 470 and 490 degrees C unfavourably affects the contact structure. At this condition, the strong downward diffusion of Au and Pt from the top layers causes a formation of Au-Pt pits, which break the Ti barrier. Transmission electron microscopy observation revealed that Au/Pt/Ti/Pt(10-30 nm) system annealed at 450 degrees C is appropriate for practical applications. The EDS technique used to identify the phase composition in the Pt(30 nm)/GaAs structure (specially produced for the EDS analysis) annealed at 450 degrees C showed that two layers were formed as a result of the reaction of the whole Pt layer with GaAs, and they consist of Ga, Pt and As. The top layer has the highest concentration of Ga. However, the bottom layer, which is close to the substrate, has the highest concentration of As.

  14. Monodisperse core/shell Ni/FePt nanoparticles and their con-version to Ni/Pt to catalyze oxygen reduction

    DOE PAGESBeta

    Zhang, Sen; Hao, Yizhou; Su, Dong; Doan-Nguyen, Vicky V. T.; Wu, Yaoting; Li, Jing; Sun, Shouheng; Murray, Christopher B.

    2014-10-28

    We report a size-controllable synthesis of monodisperse core/shell Ni/FePt nanoparticles (NPs) via a seed-mediated growth and their subsequent conversion to Ni/Pt NPs. Preventing surface oxidation of the Ni seeds is essential for the growth of uniform FePt shells. These Ni/FePt NPs have a thin (≈ 1 nm) FePt shell, and can be converted to Ni/Pt by acetic acid wash to yield active catalysts for oxygen reduction reaction (ORR). Tuning the core size allow for optimization of their electrocatalytic activity. The specific activity and mass activity of 4.2 nm/0.8 nm core/shell Ni/FePt reach 1.95 mA/cm² and 490 mA/mgPt at 0.9 Vmore » (vs. reversible hydrogen electrode, RHE), which are much higher than those of benchmark commercial Pt catalyst (0.34 mA/cm² and 92 mA/mgPt at 0.9 V). Our studies provide a robust approach to monodisperse core/shell NPs with non-precious metal core, making it possible to develop advanced NP catalysts with ultralow Pt content for ORR and many other heterogeneous reactions.« less

  15. Monodisperse core/shell Ni/FePt nanoparticles and their con-version to Ni/Pt to catalyze oxygen reduction

    SciTech Connect

    Zhang, Sen; Hao, Yizhou; Su, Dong; Doan-Nguyen, Vicky V. T.; Wu, Yaoting; Li, Jing; Sun, Shouheng; Murray, Christopher B.

    2014-10-28

    We report a size-controllable synthesis of monodisperse core/shell Ni/FePt nanoparticles (NPs) via a seed-mediated growth and their subsequent conversion to Ni/Pt NPs. Preventing surface oxidation of the Ni seeds is essential for the growth of uniform FePt shells. These Ni/FePt NPs have a thin (≈ 1 nm) FePt shell, and can be converted to Ni/Pt by acetic acid wash to yield active catalysts for oxygen reduction reaction (ORR). Tuning the core size allow for optimization of their electrocatalytic activity. The specific activity and mass activity of 4.2 nm/0.8 nm core/shell Ni/FePt reach 1.95 mA/cm² and 490 mA/mgPt at 0.9 V (vs. reversible hydrogen electrode, RHE), which are much higher than those of benchmark commercial Pt catalyst (0.34 mA/cm² and 92 mA/mgPt at 0.9 V). Our studies provide a robust approach to monodisperse core/shell NPs with non-precious metal core, making it possible to develop advanced NP catalysts with ultralow Pt content for ORR and many other heterogeneous reactions.

  16. Magnetism of FePt nanoparticles and nanodot arrays.

    NASA Astrophysics Data System (ADS)

    Zeng, Hao

    2008-03-01

    L10 structured FePt materials show great potential for magnetic data storage media applications.^1 The first part of this talk concerns the magnetism in chemically synthesized FePt nanoparticles. Discrete FePt nanoparticles with L10 structure have recently been realized by salt annealing, making it possible to study their size dependent magnetic properties.^2 We have discovered a strong reduction of magnetization with decreasing FePt particle size and an unusual temperature dependent magnetization that deviates from the Bloch's T^3/2 law at low temperatures. A model based on competing exchange interactions is proposed to explain the unusual behavior, considering explicitly the nanoparticle shape. FePt system has complicated exchange interactions, with interaction in the (100) plane being strongly ferromagnetic and inter-plane much weaker. The ferromagnetic and antiferromagnetic exchange interactions contribute differently at the nanoparticle surface and interior, leading to reduced ferromagnetic order at the surface terminated by certain facets. The model correctly explains the magnetization reduction with decreasing particle size, a surface paramagnetic phase as evidenced by Mossbauer spectroscopy and the unusual temperature dependent magnetization behaviors. The second part of this talk will report our recent efforts in developing ordered FePt nanodot arrays using self-assembled porous templates as evaporation masks. The arrays possess perpendicular anisotropy, large coercivity and extremely high density, all of which are desirable features for future data storage media. ^1S. Sun et al., Science, 287, 1989 (2000). ^2C. Rong, et al., Adv. Mater. 18, 2984 (2006).

  17. Co-Pt core-shell nanostructured catalyst prepared by selective chemical vapor pulse deposition of Pt on Co as a cathode in polymer electrolyte fuel cells

    SciTech Connect

    Seo, Sang-Joon; Chung, Ho-Kyoon; Yoo, Ji-Beom; Chae, Heeyeop; Seo, Seung-Woo; Min Cho, Sung

    2014-01-15

    A new type of PtCo/C catalyst for use as a cathode in polymer electrolyte fuel cells was prepared by selective chemical vapor pulse deposition (CVPD) of Pt on the surface of Co. The activity of the prepared catalyst for oxygen reduction was higher than that of a catalyst prepared by sequential impregnation (IMP) with the two metallic components. This catalytic activity difference occurs because the former catalyst has smaller Pt crystallites that produce stronger Pt-Co interactions and have a larger Pt surface area. Consequently, the CVPD catalyst has a great number of Co particles that are in close contact with the added Pt. The Pt surface was also electronically modified by interactions with Co, which were stronger in the CVPD catalyst than in the IMP catalyst, as indicated by X-ray diffraction, X-ray photoemission spectroscopy, and cyclic voltammetry measurements of the catalysts.

  18. Same-View Nano-XAFS/STEM-EDS Imagings of Pt Chemical Species in Pt/C Cathode Catalyst Layers of a Polymer Electrolyte Fuel Cell.

    PubMed

    Takao, Shinobu; Sekizawa, Oki; Samjeské, Gabor; Nagamatsu, Shin-ichi; Kaneko, Takuma; Yamamoto, Takashi; Higashi, Kotaro; Nagasawa, Kensaku; Uruga, Tomoya; Iwasawa, Yasuhiro

    2015-06-01

    We have made the first success in the same-view imagings of 2D nano-XAFS and TEM/STEM-EDS under a humid N2 atmosphere for Pt/C cathode catalyst layers in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells (PEFCs) with Nafion membrane to examine the degradation of Pt/C cathodes by anode gas exchange cycles (start-up/shut-down simulations of PEFC vehicles). The same-view imaging under the humid N2 atmosphere provided unprecedented spatial information on the distribution of Pt nanoparticles and oxidation states in the Pt/C cathode catalyst layer as well as Nafion ionomer-filled nanoholes of carbon support in the wet MEA, which evidence the origin of the formation of Pt oxidation species and isolated Pt nanoparticles in the nanohole areas of the cathode layer with different Pt/ionomer ratios, relevant to the degradation of PEFC catalysts.

  19. Novel Sol-Gel Based Pt Nanocluster Catalysts for Propane Dehydrogenation

    SciTech Connect

    Boespflug, Elaine; Kawola, Jeffrey S.; Martino, Anthony; Sault, Allen G.

    1999-08-09

    We report propane dehydrogenation behavior of catalysts prepared using two novel synthesis strategies that combine inverse micelle Pt nanocluster technology with silica and alumina sol-gel processing. Unlike some other sol-gel catalyst preparations. Pt particles in these catalysts are not encapsulated in the support structure and the entire Pt particle surface is accessible for reaction. Turnover frequencies (TOF) for these catalysts are comparable to those obtained over Pt catalysts prepared by traditional techniques such as impregnation, yet the resistance to deactivation by carbon poisoning is much greater in our catalysts. The deactivation behavior is more typical of traditionally prepared PtSn catalysts than of pure Pt catalysts.

  20. Improved oxygen reduction activity on the Ih Cu@Pt core-shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Yang, Zongxian; Geng, Zhixia; Zhang, Yanxing; Wang, Jinlong; Ma, Shuhong

    2011-09-01

    The minimum energy path (MEP) for the dissociation of O 2 on the Ih Cu@Pt12 core-shell nanoparticle. Ih Cu@Pt12 is the most stable among the symmetric Cu@Pt12 core-shell isomers. O 2 prefers to be adsorbed on the Ih Cu@Pt12 with the t-b-t configuration. The Ih Cu@Pt12 has enhanced activity for O 2 dissociation and O diffusion. Ih Cu@Pt12 nanoparticle is a good candidate for being the ORR catalyst.

  1. Theoretical determination of the structure of acetylene on Pt(111)

    NASA Astrophysics Data System (ADS)

    Anderson, Alfred B.; Hubbard, Arthur T.

    1980-09-01

    An atom superposition and electron delocalization technique applied to acetylene chemisorption on small cluster models for the Pt(111) surface shows preference for the triangular site as deduced from electron energy loss analyses by Ibach and Lehwald. This confirms the applicability of Badger's and related rules in this instance. Calculations on CCH 3 produce a structure in agreement with a dynamic LEED analysis at 400 K by Kesmodel, Dubois and Somorjai. Structures of CCH 2 and CHCH 2 are calculated and these species are found to be less stable than acetylene and CCH 3, respectively, when chemisorbed on Pt(111).

  2. Velocity-dependent fatigue crack paths in nanograined Pt films.

    PubMed

    Meirom, R A; Clark, T; Polcawich, R; Pulskamp, J; Dubey, M; Muhlstein, C L

    2008-08-22

    Studies of crack growth in nanograined films assert that mechanical damage accumulates at grain boundaries irrespective of the crack velocity and loading conditions. This work shows that crack advance in nanograined Pt films involves a dislocation-slip mechanism that is a function of the crack growth rate and mode of loading. Crack paths in Pt were initially intergranular, but transitioned to a transgranular mode that persisted until catastrophic failure. This research demonstrates that crack growth mechanisms modeled for nanograined Ni cannot be generalized to other pure, metallic systems.

  3. Accurate energy levels for singly ionized platinum (Pt II)

    NASA Technical Reports Server (NTRS)

    Reader, Joseph; Acquista, Nicolo; Sansonetti, Craig J.; Engleman, Rolf, Jr.

    1988-01-01

    New observations of the spectrum of Pt II have been made with hollow-cathode lamps. The region from 1032 to 4101 A was observed photographically with a 10.7-m normal-incidence spectrograph. The region from 2245 to 5223 A was observed with a Fourier-transform spectrometer. Wavelength measurements were made for 558 lines. The uncertainties vary from 0.0005 to 0.004 A. From these measurements and three parity-forbidden transitions in the infrared, accurate values were determined for 28 even and 72 odd energy levels of Pt II.

  4. Structural and Electronic Transformations of Pt/C, Pd@Pt(1 ML)/C and Pd@Pt(2 ML)/C Cathode Catalysts in Polymer Electrolyte Fuel Cells during Potential-step Operating Processes Characterized by In-situ Time-resolved XAFS

    NASA Astrophysics Data System (ADS)

    Nagamatsu, Shin-ichi; Takao, Shinobu; Samjeské, Gabor; Nagasawa, Kensaku; Sekizawa, Oki; Kaneko, Takuma; Higashi, Kotaro; Uruga, Tomoya; Gayen, Sirshendu; Velaga, Srihari; Saniyal, Milan K.; Iwasawa, Yasuhiro

    2016-06-01

    The dynamic structural and electronic transformations of Pt/C, Pd@Pt(1 ML)/C, Pd@Pt(2 ML)/C cathode catalysts in polymer electrolyte fuel cells (PEFCs) during the potential-step operating processes between 0.4 and 1.4 VRHE (potential vs RHE) were characterized by in-situ (operando) time-resolved Pt LIII-edge quick-XAFS at 100 ms time-resolution. Potential-dependent surface structures and oxidation states of Pt, Pd@Pt(1 ML) and Pd@Pt(2 ML) nanoparticles on carbon at 0.4 and 1.4 VRHE were also analyzed by in-situ Pt LIII-edge and Pd K-edge quick-XAFS. The Pt, Pd@Pt(1 ML) and Pd@Pt(2 ML) nanoparticle surfaces were restructured and disordered at 1.4 VRHE, which were induced by strong Pt-O bonds as well as alloying effects. The rate constants for the changes of Pt valence, CN(Pt-Pt), CN(Pt-Pd) and CN(Pt-O) (CN: coordination number) in the potential-step operating processes were also determined and discussed in relation to the origin of oxygen reduction reaction (ORR) activities of the Pt/C, Pd@Pt(1 ML)/C and Pd@Pt(2 ML)/C cathode catalysts.

  5. Single-Crystalline cooperite (PtS): Crystal-Chemical characterization, ESR spectroscopy, and {sup 195}Pt NMR spectroscopy

    SciTech Connect

    Rozhdestvina, V. I. Ivanov, A. V.; Zaremba, M. A.; Antsutkin, O. N.; Forsling, W.

    2008-05-15

    Single-crystalline cooperite (PtS) with a nearly stoichiometric composition was characterized in detail by X-ray diffraction, electron-probe X-ray microanalysis, and high-resolution scanning electron microscopy. For the first time it was demonstrated that {sup 195}Pt static and MAS NMR spectroscopy can be used for studying natural platinum minerals. The {sup 195}Pt chemical-shift tensor of cooperite was found to be consistent with the axial symmetry and is characterized by the following principal values: {delta}{sub xx} = -5920 ppm, {delta}{sub yy} = -3734 ppm, {delta}{sub zz} = +4023 ppm, and {delta}{sub iso} = -1850 ppm. According to the ESR data, the samples of cooperite contain copper(II), which is adsorbed on the surface during the layer-by-layer crystal growth and is not involved in the crystal lattice.

  6. Selective hydrogenation of m-chloronitrobenzene to m-chloroaniline over polyvinylpyrrolidone-stabilized Pt and Pt/Sn catalysts

    NASA Astrophysics Data System (ADS)

    Li, Feng; Ma, Rui; Song, Hualin; Song, Hua; Yu, Dezhi

    2015-05-01

    A Pt-polyvinylpyrrolidone (PVP) catalyst was synthesized via chemical reduction of platinum ions with hydrazine hydrate in a PVP/ n-butanol/H2PtCl6 aqueous solution. Its catalytic activity was evaluated by the liquid-phase hydrogenation of m-chloronitrobenzene ( m-CNB) to m-chloroaniline ( m-CAN) under mild conditions ( T = 303 K, p = 0.1 MPa). The as prepared catalyst exhibited higher activity and selectivity than prepared via conventional ethanol reduction with the same platinum load. The catalytic performance of PVP-Pt catalyst was remarkably improved by addition of 0.2 wt % Sn4+. The modification mechanism may be related with the interaction of Sn4+ with nitro group of m-CNB and -NH2 in m-CAN.

  7. Study of coordination environments around Pd and Pt in a Pd-core Pt-shell nanoparticle during heating

    NASA Astrophysics Data System (ADS)

    Nishimura, Y. F.; Hamaguchi, T.; Yamaguchi, S.; Takagi, H.; Dohmae, K.; Nonaka, T.; Nagai, Y.

    2016-05-01

    Local coordination environments around Pd and Pt in a Pd-core Pt-shell nanoparticle (NP) at temperatures ranging from 473 to 873 K was evaluated by utilizing in situ XAFS measurement technique to investigate the temperature range in which a core-shell structure is preserved. The core-shell structure was considered to be kept up to 673 K and start to change at about 773 K. Heating to 873 K accelerated atomic mixing in the core-shell NPs. Catalytic properties of the present Pd-core Pt-shell NP are available in the stoichiometric C3H6-O2 atmosphere at temperatures less than 773 K at most.

  8. Insight into the active phase of CO oxidation on Ni/Pt and NiO1 - x/Pt model catalysts from a first principles investigation

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Lv, Yong-kang; Wang, Gui-Chang

    2013-08-01

    CO oxidation on bimetallic and metal oxide has drawn much attention in the past years due to its importance both technologically and theoretically, but the active phase as well as the detailed reaction mechanism on the bimetallic surface oxide (i.e., a sandwich-like surface structure) are still unclear. In this work, the CO oxidation on the various Pt-Ni model catalysts [including Pt(111), Pt/Ni/Pt(111), Ni/Pt(111), NiO1 - x/Pt(111) and NiO1 - x/Pt/Ni/Pt(111)] was studied by performing the density functional theory calculations. It was found that the CO oxidation reaction would process with a higher reaction barrier on metals at lower oxygen coverage via the Langmuir-Hinshelwood (L-H) mechanism, whereas CO oxidation reaction would take place with a lower barrier at higher oxygen coverage on metals or in the presence of molecular oxygen/CO (on NiO1 - x-like systems) via the Eley-Rideal mechanism. The calculation results show that the activation energy of CO oxidation follows the order: Pt(111) (0.75 eV) > Pt/Ni/Pt(111) (0.69 eV) > Ni/Pt(111) (0.47 eV at 1 ML oxygen), which is in general agreement with the experimental observations. On the surface oxide NiO1 - x/Pt(111) and NiO1 - x/Pt/Ni/Pt(111) systems, it was found that the molecular CO can subtract the surface lattice oxygen to form CO2 spontaneously through the Eley-Rideal mechanism on NiO1 - x/Pt/Ni/Pt(111), whereas such kinetic behavior cannot occur on the NiO1 - x/Pt(111) system, suggesting the high reactivity of CO oxidation on NiO1 - x/Pt/Ni/Pt(111). The possible reason was analyzed by the magnitude of surface oxygen vacancy formation energy, namely NiO1 - x/Pt/M/Pt(111) with relatively low vacancy formation energy as compared to that of NiO1 - x/Pt(111) (3.46 vs 4.51 eV). Moreover, we extend the above study to a more general case in which the subsurface metals in NiO1 - x/Pt/M/Pt(111) system including VIII group metals like Fe/Co/Ni and the IB group metals like Cu, and it was found that the molecular CO

  9. Shape and Composition Effects on Photocatalytic Hydrogen Production for Pt-Pd Alloy Cocatalysts.

    PubMed

    Luo, Muhua; Lu, Pan; Yao, Weifeng; Huang, Cunping; Xu, Qunjie; Wu, Qiang; Kuwahara, Yasutaka; Yamashita, Hiromi

    2016-08-17

    The shape and composition effects of platinum-palladium (Pt-Pd) alloy nanoparticle cocatalysts on visible-light photocatalytic hydrogen evolution from an aqueous ammonium sulphite solution have been reported and discussed. The activity of Pt-Pd nanoparticles loaded Pt-Pd/CdS photocatalysts are affected based on both the Pt-Pd alloy nanoparticles' shape and their compositions. In this research, two shapes of Pt-Pd nanoparticles have been studied. One is Pt-Pd nanocubes enclosed by {100} crystal planes and the other is nano-octahedra covered with {111} crystal facets. Results show that the photocatalytic turnover frequency (TOF), defined as moles of hydrogen produced per surface mole of Pt-Pd metal atom per second, for Pt-Pd nanocubes/CdS (Pt-Pd NCs/CdS) photocatalyst can be 3.4 times more effective than Pt-Pd nano-octahedra/CdS (Pt-Pd NOTa/CdS) nanocomposite photocatalyst. Along with the shape effect, the atomic ratio of Pt to Pd can also impact the efficiency of Pt-Pd/CdS photocatalysts. When the Pt to Pd atomic ratio changes from 1:0 to about 2:1, the rate of hydrogen production increases from 900 μmol/h for Pt NCs/CdS catalyst to 1837 μmol/h for Pt-Pd (2:1) NCs/CdS photocatalyst-a 104% rate increase. This result suggests that the 33 mol % of more expensive Pt can be replaced with less costly Pd, resulting in a more than 100% hydrogen production rate increase. The finding of this research will lead to the research and development of highly effective catalysts for photocatalytic hydrogen production using solar photonic energy. PMID:27439590

  10. Optical characterization of the PtSi/Si by using spectroscopic ellipsometry

    NASA Astrophysics Data System (ADS)

    Le, Van Long; Kim, Tae Jung; Park, Han Gyeol; Kim, Hwa Seob; Yoo, Chang Hyun; Kim, Hyoung Uk; Kim, Young Dong; Kim, Junsoo; Im, Solyee; Choi, Won Chul; Moon, Seung Eon; Nam, Eun Soo

    2016-08-01

    We report an optical characterization of PtSi films for thermoelectric device applications which was done by using nondestructive spectroscopic ellipsometry (SE). A Pt monolayer and a Pt-Si multilayer which consisted of three pairs of Pt and Si layers were deposited on p-doped-silicon substrates by using sputtering method; then, rapid annealing process was done to form PtSi films through intermixing of Pt and Si atoms at the interface. Pseudodielectric function data < ɛ > = < ɛ 1 > + i < ɛ 2 > for the PtSi/Si samples were obtained from 1.12 to 6.52 eV by using spectroscopic ellipsometry. Employing the Tauc-Lorentz and the Drude models, determined the dielectric function ( ɛ) of the PtSi films. We found that the composition ratio of Pt:Si was nearly 1:1 for the PtSi monolayer and we observed transitions between occupied and unoccupied states in the Pt 5 d states. We also observed the formation of PtSi layers in the Pt-Si multilayer sample. The SE results were confirmed by the transmission electron microscopy and energy dispersive X-ray spectroscopy.

  11. Electro-oxidation of ethanol on ternary non-alloyed Pt-Sn-Pr/C catalysts

    NASA Astrophysics Data System (ADS)

    Corradini, Patricia G.; Antolini, Ermete; Perez, Joelma

    2015-02-01

    Ternary Pt-Sn-Pr/C (70:10:20), (70:15:15) and (45:45:10) electro-catalysts were prepared by a modified formic acid method, and their activity for the ethanol oxidation reaction (EOR) was compared with that of Pt-Pr/C catalysts prepared by the same methods and that of commercial Pt-Sn/C (75:25) and Pt/C catalysts. Among all the catalysts, the Pt-Sn-Pr/C (45:45:10) catalyst presented both the highest mass activity and the highest specific activity. The steady state electrochemical stability of ternary Pt-Sn-Pr catalysts increased with the surface Sn/Pt atomic ratio. Following repetitive potential cycling (RPC), the activity for ethanol oxidation of Pt-Sn-Pr/C catalysts with high surface Sn/Pt atomic ratio was considerably higher than that of the corresponding as-prepared catalysts, and increased with increasing the Sn/Pt ratio. The increase of the EOR mass activity following RPC was ascribed to the increase of either the specific activity (for the Pt-Sn-Pr/C (70:15:15) catalyst) or the electrochemically active surface area (for the Pt-Sn-Pr/C (45:45:10) catalyst). Dissolution of Sn and Pr oxides from Pt-Sn-Pr/C catalyst surface was observed following RPC.

  12. Effect of interlayer interaction on domain structure of CoPt stacked films with perpendicular anisotropy

    NASA Astrophysics Data System (ADS)

    Kawamura, H.; Hayakawa, K.; Nomiya, N.; Sugita, R.

    2015-05-01

    The effect of interlayer magnetostatic interaction on the domain structure of CoPt (3 nm)/PtPt nm)/CoPt (10 nm) stacked films having perpendicular anisotropy is investigated. The domain structure of the demagnetized CoPt stacked films is observed using magnetic force microscope. The Co80Pt20 stacked films with Pt interlayer thickness δPt less than about 20 nm have the maze domain similar to that of the film with δPt of 0 nm. This is because the top and bottom layers are connected by the magnetostatic interaction and the magnetization distribution of both layers is integrated. The domain structure of the films with δPt around 25 nm is mixture of the maze and irregular domains. For the films with δPt over about 30 nm, because the interaction between the top and bottom layers decreases, the irregular domain which is observed in the 3 nm thick CoPt single layer film appears. In the region where the domain structure changes from the maze domain to the irregular one, domain size steeply increases with increase of δPt.

  13. Methanol and ethanol electroxidation using Pt electrodes prepared by the polymeric precursor method

    NASA Astrophysics Data System (ADS)

    Freitas, R. G.; Santos, M. C.; Oliveira, R. T. S.; Bulhões, L. O. S.; Pereira, E. C.

    The results of methanol and ethanol oxidation in acidic medium on Pt electrodes deposited on Ti substrate using the Pechini method are presented. In this route the metallic salts were dissolved in a mixture of ethylene glycol (EG) and citric acid (CA) forming a polyester network, which is painted onto a Ti substrate and then heat treated at 600 °C in order to obtain the metallic Pt thin films. The X-ray diffraction analysis showed the presence of Pt pattern peaks. The presence of the (4 2 0) plane in a higher amount compared to bulk Pt was observed and the peak position of the planes (2 0 0) and (4 2 0) were displaced by approximately -0.3°. The roughness data presented almost the same values for Ti and Ti/Pt. The electrochemical characterization of the electrodes in 0.1 M HClO 4 showed a typical Pt voltammetric profile. Although the voltammetric profiles of Ti/Pt and bulk Pt were the same, the electrocatalytical behavior for methanol oxidation showed an enhancement of the oxidation current density peak, which increased by 170% compared to bulk platinum. Although, the current density peak for ethanol oxidation on Ti/Pt is smaller than for Pt, it began at 0.11 V less positive than the same process on bulk Pt. The chronoamperometric experiments for methanol and ethanol oxidation on Ti/Pt increased by almost 934% and 440%, respectively, compared with Pt bulk.

  14. High loading of uniformly dispersed Pt nanoparticles on polydopamine coated carbon nanotubes and its application in simultaneous determination of dopamine and uric acid

    NASA Astrophysics Data System (ADS)

    Lin, Mouhong; Huang, Haoliang; Liu, Yingju; Liang, Canjian; Fei, Shidong; Chen, Xiaofen; Ni, Chunlin

    2013-02-01

    Multiwalled carbon nanotubes (MWCNT) were homogeneously covered with a bio-functional polydopamine (PDOP) by a simple dip-coating approach in mild basic solution. Then, uniformly dispersed and highly loaded platinum nanoparticles (PtNPs) were deposited on MWCNT@PDOP by a mild reductant, and were characterized by transmission electron microscopy and x-ray photoelectron spectroscopy. Afterwards, this nanocomposite was modified on the glass carbon electrode and applied to simultaneously determine dopamine (DA) and uric acid (UA) by differential pulse voltammetry (DPV). Results showed that a linear electro-oxidation response was found for DA and UA in the range of 0.25-20 μM and 0.3-13 μM with the detection limit (S/N = 3) of 0.08 μM and 0.12 μM, respectively. In addition, the detection sensitivities for DA and UA by DPV were 1.03 μA μM-1 and 2.09 μA μM-1, respectively, which were much higher than those from a cyclic voltammogram. Finally, the reproducibility and stability of the nanocomposite were also evaluated, demonstrating that such MWCNT@PDOP@PtNPs can be a promising candidate for advanced electrode material in electrochemical sensing and other electrocatalytic applications.

  15. Syntheses and structural analyses of variable-stoichiometric Au-Pt-Ni carbonyl/phosphine clusters, Pt3(Pt(1-x)Ni(x))(AuPPh3)2(mu2-CO)4(CO)(PPh3)3 and Pt2(Pt(2-y)Ni(y))(AuPPh3)2(mu2-CO)4(CO)2(PPh3)2, with ligation-induced site-specific Pt/Ni substitutional disorder within butterfly-based Pt3(Pt(1-x)Ni(x))Au2 and Pt2(Pt(2-y)Ni(y))Au2 core-geometries.

    PubMed

    de Silva, Namal; Nichiporuk, Rita V; Dahl, Lawrence F

    2006-05-21

    In ongoing attempts of directed synthesis of high-nuclearity Au-Pt carbonyl/phosphine clusters with [Ni6(CO)12]2- used as reducing agent and CO source, we have isolated and characterized two new closely related variable-stoichiometric trimetallic clusters, Pt3(Pt(1-x)Ni(x))(AuPPh3)2(mu2-CO)4(CO)(PPh3)3 (1) and Pt2(Pt(2-y)Ni(y))(AuPPh3)2(mu2-CO)4(CO)2(PPh3)2 (2). Their M4Au2 cores may be envisioned as substitutional disordered butterfly-based M4Au2 frameworks (M = Pt/Ni) formed by connections of the two basal M(B) atoms with both (Au-Au)-linked Au(PPh3) moieties. Based upon low-temperature CCD X-ray diffraction studies of eight crystals obtained from different samples, ligation-induced site-specific Pt/Ni substitutional disorder (involving formal insertion of Ni in place of Pt) in a given crystal was found to occur only at the one OC-attached basal M(B) site in 1 or at both OC-attached basal M(B) sites in 2 corresponding to a crystal composite of the Pt3(Pt(1-x)Ni(x))Au2 core in 1 or of the Pt2(Pt(2-y)Ni(y))Au2 core in 2; the Ph3P-attached M(B) site (M(B) = Pt) in 1 and two wingtip M(w) sites (M(w) = Pt) in 1 and 2 were not substitutionally disordered. The resulting variable stoichiometry of the M4Au2 core in 1 may be viewed as a crystal composite of two superimposed individual stereoisomers, Pt4(AuPPh3)2(mu2-CO)4(CO)(PPh3)3 (1a) and Pt3Ni(AuPPh3)2(mu2-CO)4(CO)(PPh3)3 (1b), in the averaged unit cell of a given crystal. Likewise, 2 represents the crystal-averaged composite of three individual stereoisomers, Pt4(AuPPh3)2(mu2-CO)4(CO)2(PPh3)2 (2a), Pt3Ni(AuPPh3)2(mu2-CO)4(CO)2(PPh3)2 (2b), and Pt2Ni2(AuPPh3)2(mu2-CO)4(CO)2(PPh3)2 (2c). Formal Ni substitution for Pt at only the basal M(B) site(s) in the four crystal composites each of 1 and 2 was found to vary widely from 17% to 79% Ni in 1 and from 21% to 95% Ni in 2. Nevertheless, reasonably close Pt/Ni occupancy factors were found within each of the four pairs of composite crystals selected from samples obtained from

  16. Abnormal bipolar resistive switching behavior in a Pt/GaO{sub 1.3}/Pt structure

    SciTech Connect

    Guo, D. Y.; Wu, Z. P.; Zhang, L. J.; Yang, T.; Hu, Q. R.; Lei, M.; Tang, W. H. E-mail: pgli@zstu.edu.cn; Li, P. G. E-mail: pgli@zstu.edu.cn; Li, L. H.

    2015-07-20

    A stable and repeatable abnormal bipolar resistive switching behavior was observed in a Pt/GaO{sub 1.3}/Pt sandwich structure without an electroforming process. The low resistance state (LRS) and the high resistance state (HRS) of the device can be distinguished clearly and be switched reversibly under a train of the voltage pulses. The LRS exhibits a conduction of electron tunneling, while the HRS shows a conduction of Schottky-type. The observed phenomena are considered to be related to the migration of oxygen vacancies which changes the space charge region width of the metal/semiconductor interface and results in a different electron transport mechanism.

  17. High pressure Raman spectroscopic studies of Pt(II) complex trans-PtCl2(PEt3)2

    NASA Astrophysics Data System (ADS)

    Bajaj, Naini; Poswal, H. K.; Bhatt, Himal; Deo, M. N.; Sharma, Surinder M.

    2016-05-01

    We report here the high pressure Raman spectroscopy of the Pt(II) complex trans-PtCl2(P(C2H5)3)2 up to 5 GPa. We have analyzed the metal-ligand stretching modes as well as ligand internal vibrational modes of the complex under pressure. Many characteristic Raman modes show pressure induced splitting at pressures as low as 1 GPa. On careful analysis of the skeletal region, the new modes appeared could be corroborated with the position of corresponding modes in the infrared spectrum, thus indicating a loss of inversion symmetry in the trans- isomer.

  18. Creep and Flow Regimes of Magnetic Domain-Wall Motion in Ultrathin Pt/Co/Pt Films with Perpendicular Anisotropy

    NASA Astrophysics Data System (ADS)

    Metaxas, P. J.; Jamet, J. P.; Mougin, A.; Cormier, M.; Ferré, J.; Baltz, V.; Rodmacq, B.; Dieny, B.; Stamps, R. L.

    2007-11-01

    We report on magnetic domain-wall velocity measurements in ultrathin Pt/Co(0.5 0.8nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, α.

  19. Cluster Chemistry in Electron-Poor Ae-Pt-Cd Systems (Ae=Ca, Sr, Ba): (Sr,Ba)Pt2Cd4, Ca6Pt8Cd16, and Its Known Antitype Er6Pd16Sb8

    SciTech Connect

    Samal, Saroj L.; Gulo, Fakhili; Corbett, John D.

    2013-02-18

    Three new ternary polar intermetallic compounds, cubic Ca6Pt8Cd16, and tetragonal (Sr, Ba)Pt2Cd4 have been discovered during explorations of the Ae–Pt–Cd systems. Cubic Ca6Pt8Cd16 (Fm-3m, Z = 4, a = 13.513(1) Å) contains a 3D array of separate Cd8 tetrahedral stars (TS) that are both face capped along the axes and diagonally bridged by Pt atoms to generate the 3D anionic network Cd8[Pt(1)]6/2[Pt(2)]4/8. The complementary cationic surface of the cell consists of a face-centered cube of Pt(3)@Ca6 octahedra. This structure is an ordered ternary variant of Sc11Ir4 (Sc6Ir8Sc16), a stuffed version of the close relative Na6Au7Cd16, and a network inverse of the recent Er6Sb8Pd16 (compare Ca6Pt8Cd16). The three groups of elements each occur in only one structural version. The new AePt2Cd4, Ae = Sr, Ba, are tetragonal (P42/mnm,Z = 2, a ≈ 8.30 Å, c ≈ 4.47 Å) and contain chains of edge-sharing Cd4 tetrahedra along c that are bridged by four-bonded Ba/Sr. LMTO-ASA and ICOHP calculation results and comparisons show that the major bonding (Hamilton) populations in Ca6Pt8Cd16 and Er6Sb8Pd16 come from polar Pt–Cd and Pd–Sb interactions, that Pt exhibits larger relativistic contributions than Pd, that characteristic size and orbital differences are most evident for Sb 5s, Pt8, and Pd16, and that some terms remain incomparable, Ca–Cd versus Er–Pd.

  20. The effect of support on the characteristics of Pt Nanoparticles

    NASA Astrophysics Data System (ADS)

    Shafai Erfani, Ghazal; Rahman, Talat S.

    2013-03-01

    We have carried out density functional theory calculations within the projector augmented wave scheme (PAW) and the pseudopotential approach to evaluate the effect of the support (γ-alumina and titania) on geometric and electronic structural properties of Pt22, Pt33, Pt44, Pt55 nanoparticles (NPs) with the shape previously characterized by extended X-ray absorption fine structure spectroscopy (EXAFS). We are in particular interested in the electronic structural changes of the perimeter atoms, as we expect them to play a major role in catalysis. We find stabilization of the NP on the substrate to depend critically on the existence of oxygen vacancies on the surface and the effect to be more prominent for titania than for alumina. On both substrates the average bond-length (first nearest-neighbor distance) expands (1 to 3%) as compared to that of unsupported NPs. We present results for the charge transfer and local density of states of the atoms at the interface and make comparisons with available experimental data on the propensity of these atoms to be chemically active. Work supported in part by DOE Grant DE-FG02-07ER46354

  1. Bloch oscillations in complex crystals with PT symmetry.

    PubMed

    Longhi, S

    2009-09-18

    Bloch oscillations in complex lattices with PT symmetry are theoretically investigated with specific reference to optical Bloch oscillations in photonic lattices with gain or loss regions. Novel dynamical phenomena with no counterpart in ordinary lattices, such as nonreciprocal Bloch oscillations related to violation of the Friedel's law of Bragg scattering in complex potentials, are highlighted.

  2. Ultralow Pt-loading bimetallic nanoflowers: fabrication and sensing applications

    NASA Astrophysics Data System (ADS)

    Wu, Qingqing; Li, Yongxin; Xian, Hongying; Xu, Chaodi; Wang, Lun; Chen, Zhibing

    2013-01-01

    Ultralow Pt-loading Au nanoflowers (AuNFs) were synthesized on a glassy carbon electrode surface by the underpotential deposition (UPD) monolayer redox replacement technique, which involves redox replacement of a copper UPD monolayer by PtCl42- that can be reduced and deposited simultaneously. Field-emission scanning electron microscopy, energy dispersive spectroscopy, x-ray photoelectron spectroscopy and the electrochemical method were utilized to characterize the ultralow Pt-loading AuNFs. Cyclic voltammogram results showed that the ultralow Pt-loading AuNFs exhibited excellent electrocatalytic activity towards the reduction of hydrogen peroxide and the oxidation of glucose in neutral media, and the reaction pathway of glucose oxidation was changed from an intermediate process based on the electrosorption of glucose to a direct oxidation process. From chronoamperometric results, it could be obtained that this prepared biosensor had wide linear ranges and very low detection limits (DLs) for H2O2 (0.025-94.3 μM DL = 0.006 μM) and glucose (0.0028-8.0 mM DL = 0.8 μM), which were much better than previous results.

  3. Thermodynamic properties and phase equilibria for Pt-Rh alloys

    SciTech Connect

    Jacob, K.T.; Priya, S.; Waseda, Yoshio

    1998-06-01

    The activity of rhodium in solid Pt-Rh alloys is measured in the temperature range from 900 to 1,300 K using the solid-state cell Pt-Rh, Rh + Rh{sub 2}O{sub 3}/(Y{sub 2}O{sub 3})ZrO{sub 2}/Pt{sub 1{minus}x}Rh{sub x} + Rh{sub 2}O{sub 3}, Pt-Rh. The activity of platinum and the free energy, enthalpy, and entropy of mixing are derived. Activities exhibit moderate negative deviation from Raoult`s law. The mixing properties can be represented by a pseudosubregular solution model in which excess entropy has the same type of functional dependence on composition as the enthalpy of mixing, {Delta}H = X{sub Rh} (1 {minus} X{sub Rh})[{minus}10,970 + 45X{sub Rh}] J/mol, {Delta}S{sup E} = X{sub Rh} (1 {minus} X{sub Rh})[{minus}3.80 + 1.55 {times} 10{sup {minus}2} X{sub Rh}] J/mol{center_dot}K. The negative enthalpy of mixing obtained in this study is in qualitative agreement with predictions of semiempirical models of Miedema and co-workers and Colinet et al. The results of this study do not support the solid-state miscibility gap suggested in the literature, but are consistent with liquidus data within experimental uncertainty limits.

  4. Desorption of oxygen from alloyed Ag/Pt(111)

    SciTech Connect

    Jankowski, Maciej; Wormeester, Herbert Zandvliet, Harold J. W.; Poelsema, Bene

    2014-06-21

    We have investigated the interaction of oxygen with the Ag/Pt(111) surface alloy by thermal desorption spectroscopy (TDS). The surface alloy was formed during the deposition of sub-monolayer amounts of silver on Pt(111) at 800 K and subsequent cooling to 300 K. The low-temperature phase of the surface alloy is composed of nanometer-sized silver rich stripes, embedded within platinum-rich domains, which were characterized with spot profile analysis low energy electron diffraction. The TDS measurements show that oxygen adsorption is blocked on Ag sites: the saturation coverage of oxygen decreases with increasing Ag coverage. Also, the activation energy for desorption (E{sub des}) decreases with Ag coverage. The analysis of the desorption spectra from clean Pt(111) shows a linear decay of E{sub des} with oxygen coverage, which indicates repulsive interactions between the adsorbed oxygen atoms. In contrast, adsorption on alloyed Ag/Pt(111) leads to an attractive interaction between adsorbed oxygen atoms.

  5. Reactivity of FeO(111)/Pt(111)with Alcohols

    SciTech Connect

    Kim, Yu Kwon; Zhang, Zhenrong; Parkinson, Gareth S.; Li, Shao-Chun; Kay, Bruce D.; Dohnalek, Zdenek

    2009-11-19

    We report on the reactivity of a FeO(111) monolayer grown on Pt(111) toward aliphatic alcohols. Using a combination of temperature programmed desorption, infrared reflection-absorption spectroscopy, and scanning tunneling microscopy techniques we show that the alcohols dissociate primarily at FeO(111) step edges and their oxidation leads to the removal of the FeO(111) film. Upon annealing, FeO(111) lattice oxygen is incorporated into the reaction products and reduced iron left behind dissolves into the underlying Pt(111) substrate. Ethanol is employed in a more detailed spectroscopic study to follow the reaction products and surface intermediates as the removal of FeO(111) proceeds. The ethoxy species formed upon dissociative adsorption of ethanol at the FeO(111) step edges undergo partial oxidation to acetaldehyde and a complete oxidation to CO and H2O. Other products, CH4 and H2, associated with the reactions occurring on Pt(111) are also observed as the bare Pt(111) surface appears. A similar etching process was also observed for n-decane.

  6. An Examination of Faculty Beliefs Concerning P&T Decisions

    ERIC Educational Resources Information Center

    Luchs, Chris; Seymoure, Suzanne; Smith, Walter

    2011-01-01

    According to Schuster and Finkelstein (2006) faculty workloads have been increasing dramatically. Besides the additional hours worked by faculty the composition of work has changed as well (Schultz et al., 1989). Studies on research, teaching and service components of promotion and tenure (P&T) decisions at colleges and universities have…

  7. Synthesis and Magnetic Properties of CoPt Nanoparticles

    NASA Astrophysics Data System (ADS)

    Trung, Truong Thanh; Nhung, Do Thi; Nam, Nguyen Hoang; Luong, Nguyen Hoang

    2016-07-01

    Magnetic nanoparticles CoPt were prepared by the chemical reduction of cobalt (II) chloride and chloroplatinic acid, then the samples were ultrasonicated for 2 h. After annealing at various temperatures from 400°C to 700°C for 1 h, the samples showed hard magnetic properties with coercivity up to 1.15 kOe at room temperature.

  8. Kinetic modeling of Pt-catalyzed glycolaldehyde decomposition to syngas.

    PubMed

    Salciccioli, Michael; Vlachos, Dionisios G

    2012-05-10

    Fundamental knowledge of the elementary reaction mechanisms involved in oxygenate decomposition on transition metal catalysts can facilitate the optimization of future catalyst and reactor systems for biomass upgrade to fuels and chemicals. Pt-catalyzed decomposition of glycolaldehyde, as the smallest oxygenate with alcohol and aldehyde functionality, was studied via a DFT-based microkinetic model. It was found that two decomposition pathways exist. Under conditions of low hydrogen surface coverage, the initial C-H bond breaking reaction to HOCH(2)CO* is prevalent, while under conditions of high hydrogen coverage, the rather unexpected O-H bond forming reaction to HOCH(2)CHOH* is more active (subsequent decomposition is energetically favorable from HOCH(2)CHOH*). Our results indicate the possibility that (de)hydrogenation chemistry is rate-controlling in many small polyoxygenate biomass derivatives, and suitable catalysts are needed. Finally, DFT was used to understand the increased decomposition activity observed on the surface segregated Ni-Pt-Pt bimetallic catalyst. It was found that the initial O-H bond breaking of glycolaldehyde to OCH(2)CHO* has an activation barrier of just 0.21 eV. This barrier is lower than that of any glycolaldehyde consuming reaction on Pt. These computational predictions are in qualitative agreement with experimental results. PMID:22483365

  9. Bloch Oscillations in Complex Crystals with PT Symmetry

    SciTech Connect

    Longhi, S.

    2009-09-18

    Bloch oscillations in complex lattices with PT symmetry are theoretically investigated with specific reference to optical Bloch oscillations in photonic lattices with gain or loss regions. Novel dynamical phenomena with no counterpart in ordinary lattices, such as nonreciprocal Bloch oscillations related to violation of the Friedel's law of Bragg scattering in complex potentials, are highlighted.

  10. New Pt(II)(dithiolate) Compounds Possessing an Energetically Accessible Diphosphine-Based LUMO: Syntheses, Redox Properties, and Solid-State Structures of PtCl2(pbpcd), Pt(tdt)(pbpcd), and Pt(tdt)(bpcd)

    SciTech Connect

    Hunt, Sean W; Yang, Li; Wang, Xiaoping; Nesterov, Vladimir; Richmond, Michael G.

    2010-01-01

    The new ligand 2-(pyren-1-ylidene)-4,5-bis- (diphenylphosphino)-4-cyclopenten-1,3-dione (pbpcd) has been synthesized from the Knoevenagel condensation using 1-pyrenecarboxaldehyde with 4,5-bis(diphenylphosphino)- 4-cyclopenten-1,3-dione (bpcd). Displacement of the cod ligand in PtCl2(cod) by pbpcd furnishes PtCl2 (pbpcd) (2) in near quantitative yield. Treatment of 2 with the dipotassium salt of toluene-3,4-dithiol (K2tdt) affords the dithiolate compound Pt(tdt)(pbpcd) (3) as a 1:1 mixture of diastereomers. An alternative synthesis of 3 from Pt(tdt)(bpcd) (5) and 1-pyrenecarboxaldehyde also affords 3 in 23% yield. The pbpcd ligand and all new diphosphinesubstituted compounds have been isolated and fully characterized in solution by IR and NMR spectroscopies, and the solid-state structures of 2_CH2Cl2, 3_toluene, and 5_CH2Cl2 established by X-ray diffraction analyses. The solid-state structure of each product exhibits a square-planar architecture at the metal center. The redox properties of the pbpcd ligand and the tdt-substituted compound 3 have been explored by cyclic and differential-pulse voltammetry, and these data are discussed with respect to extended Huckel MO calculations and the nature of the HOMO and LUMO levels in each compound.

  11. Science in Action Series: AGATE ( pt 4/5 )

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This show was made for the Office of Education at NASA Langley. The objective is to make math and science appealing to a middle school audience. This clip (pt 1/5 ) What will stop everybody from crashing into each other? And what would happen if they did?

  12. Science in Action Series: AGATE ( pt 1/5 )

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This show was made for the Office of Education at NASA Langley. The objective is to make math and science appealing to a middle school audience. This clip (pt 1/5 ) introduces the AGATE concept as a future alternative to cars.

  13. Science in Action Series: AGATE (pt 2/5 )

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This show was made for the Office of Education at NASA Langley. The objective is to make math and science appealing to a middle school audience. This clip (pt 2/5 ) is an animation which tells us a little about the plane itself: including capacity, speed and range.

  14. Science in Action Series: AGATE ( pt 3/5 )

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This show was made for the Office of Education at NASA Langley. The objective is to make math and science appealing to a middle school audience. This clip (pt 3/5 ) tells us more about the plane. How much will it cost to run, and how will we learn to fly?

  15. Science in Action Series: AGATE ( pt5/5 )

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This show was made for the Office of Education at NASA Langley. The objective is to make math and science appealing to a middle school audience. This clip (pt 5/5 ) answers more FAQ's: How will this be different from flying a normal aircraft? How will the cockpit be different? What will the next generation of computer controlled flight managemnt offer?

  16. Self-suspended permanent magnetic FePt ferrofluids.

    PubMed

    Dallas, Panagiotis; Kelarakis, Antonios; Sahore, Ritu; DiSalvo, Francis J; Livi, Sebastien; Giannelis, Emmanuel P

    2013-10-01

    We present the synthesis and characterization of a new class of self-suspended ferrofluids that exhibit remanent magnetization at room temperature. Our system relies on the chemisorption of a thiol-terminated ionic liquid with very low melting point on the surface of L10 FePt nanoparticles. In contrast, all types of ferrofluids previously reported employ either volatile solvents as the suspending media or superparamagnetic iron oxide nanoparticles (that lacks permanent magnetization) as the inorganic component. The ferrofluids do not show any sign of flocculation or phase separation, despite the strong interactions between the magnetic nanoparticles due to the strong chemisorption of the ionic liquid as evidenced by Raman spectroscopy and thermal analysis. Composites with high FePt loading (40 and 70 wt%) exhibit a pseudo solid-like rheological behavior and high remanent magnetization values (10.1 and 12.8 emu/g respectively). At lower FePt loading (12 wt%) a liquid like behavior is observed and the remanent and saturation magnetization values are 3.5 and 6.2 emu/g, respectively. The magnetic and flow properties of the materials can be easily fine tuned by controlling the type and amount of FePt nanoparticles used. PMID:23859815

  17. Nonlinearity-induced PT-symmetry without material gain

    NASA Astrophysics Data System (ADS)

    Miri, Mohammad-Ali; Alù, Andrea

    2016-06-01

    Parity-time symmetry has raised a great deal of attention in optics in recent years, yet its application has been so far hindered by the stringent requirements on coherent gain balanced with loss. In this paper, we show that the conditions to enable parity and time symmetry can be simultaneously satisfied for a pair of modes with mixed frequencies interacting in a nonlinear medium, without requiring the presence of material gain. First, we consider a guided wave structure with second order nonlinearity and we derive the PT-symmetric Hamiltonian that governs the interaction of two waves of mixed frequencies when accompanied by a high intensity pump beam at the sum frequency. We also extend the results to an array of coupled nonlinear waveguide channels. It is shown that the evolution dynamics of the low-frequency waves is associated with a periodic PT-symmetric lattice while the phase of the pump beams can be utilized as a control parameter to modify the gain and loss distribution, thus realizing different PT lattices by design. Our results suggest that nonlinear wave mixing processes can form a rich platform to realize PT-symmetric Hamiltonians of arbitrary dimensions in optical systems, without requiring material gain.

  18. Ultrafast magnetization dynamics in heterogeneous granular FePt media

    NASA Astrophysics Data System (ADS)

    Granitzka, Patrick; Reid, Alexander; Jal, Emmanuelle; Liu, Tianmin; Schlotter, William; Shafer, Padraic; Metha, Virat; Hellwig, Olav; Tahakashi, Yukiko; Fullerton, Eric; Stohr, Joachim; Durr, Hermann

    Granular FePt in the L10 phase is a key material for future magnetic data storage devices, supporting stable magnetic domains less than 10 nm in diameter. To switch the magnetization of magnetically hard materials like FePt, new writing techniques are needed such as Heat Assisted Magnetic Recording (HAMR). However, it is not known how HAMR works on the fundamental length and time scales of magnetization in FePt. Here we investigate the nanoscale aspects of magnetization dynamics in FePt HAMR with fs X-ray pulses from the Linac Coherent Light Source at Stanford using resonant X-ray diffraction. We show that while many spins display switching in a magnetic field following a fs duration optical excitation. The remaining spins do not switch. Surprisingly the ratio of spins that switch to spins that do not, stays constant over a large fluence range. Furthermore we observe that the spin reservoir which displays heat assisted magnetic recording is quenched homogeneously over the size distribution of grains, while the spins that do not follow the field display a length-scale dependent quenching.

  19. Observation of inverse spin Hall effect in ferromagnetic FePt alloys using spin Seebeck effect

    SciTech Connect

    Seki, Takeshi Takanashi, Koki; Uchida, Ken-ichi; Kikkawa, Takashi; Qiu, Zhiyong; Saitoh, Eiji

    2015-08-31

    We experimentally observed the inverse spin Hall effect (ISHE) of ferromagnetic FePt alloys. Spin Seebeck effect due to the temperature gradient generated the spin current (J{sub s}) in the FePt|Y{sub 3}Fe{sub 5}O{sub 12} (YIG) structure, and J{sub s} was injected from YIG to FePt and converted to the charge current through ISHE of FePt. The significant difference in magnetization switching fields for FePt and YIG led to the clear separation of the voltage of ISHE from that of anomalous Nernst effect in FePt. We also investigated the effect of ordering of FePt crystal structure on the magnitude of ISHE voltage in FePt.

  20. Perpendicular magnetic anisotropy and spin reorientation transition in L1{sub 0} FePt films

    SciTech Connect

    Ahn, Jae Young; Lee, Nyun Jong; Kim, Tae Hee; Lee, J.-H.; Michel, Anny; Eyidi, Dominique

    2011-04-01

    We investigated the thickness and composition dependence of perpendicular magnetic anisotropy (PMA) in L1{sub 0} Fe{sub 1-x}Pt{sub x} (x = 0.4, 0.5, and 0.55) films. The FePt films with different thicknesses of 35 and 70 A were grown at the substrate temperature T{sub s} = 300 deg. C by molecular beam epitaxy coevaporation technique. A (001)-oriented epitaxial L1{sub 0} FePt film was grown on the thin (001)-oriented fcc Pt layer, while a poorly crystallized FePt film was formed on the (111)-textured Pt layer. Our results showed that, at a fixed thickness of 70 A, the PMA of FePt alloy films is enhanced as Pt content increases from 40% to 55%.

  1. Structural and magnetic properties of L1(0)/A1, FePt nanocomposites

    SciTech Connect

    Giannopoulos, G; Speliotis, T; Li, WF; Hadjipanayis, G; Niarchos, D

    2013-01-01

    In this work structural and magnetic properties of (L1(0)-FePt/A1-FePt) exchange coupled nanocomposites are presented. Semi spherical "dome-like" nanocomposites with L1(0) FePt isolated nanoparticles and A1 FePt (fcc) cap layers were obtained by depositing A1-FePt on type L1(0) FePt nanoparticles in order to understand the influence of the soft magnetic layer thickness on the magnetic properties of the system. Epitaxial growth is confirmed by X-ray diffraction and TEM, while the coercivity decreases dramatically for the L1(0)/A1-FePt system when the thickness of the A1-FePt cap layers is increased. This result can be used to realize ultrahigh magnetic recording media with tunable coercivity, suitable for conventional write heads. (C) 2012 Elsevier B.V. All rights reserved.

  2. First-principles computation of surface segregation in L10 CoPt magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Zhenyu; Lei, Yinkai; Wang, Guofeng

    2016-07-01

    In this study, we have employed the first-principles density functional theory (DFT) computational method to predict the influence of surface segregation on the magnetic properties of small L10 CoPt nanoparticles. For both the modelled cuboidal (with a chemical formula of Co26Pt12) and cuboctahedral (with a chemical formula of Co18Pt20) CoPt nanoparticles, the DFT calculations predict that Pt surface segregation should occur thermodynamically. Associated with this Pt surface segregation, the surface-segregated CoPt magnetic nanoparticles are predicted to have significantly reduced magnetic moments and magnetic anisotropy energies than those of the corresponding bulk-terminated (i.e. non-segregated) nanoparticles. Hence, our study suggests that surface segregation could deteriorate the magnetic properties of CoPt nanoparticles.

  3. One-step synthesis of graphene-Pt nanocomposites by gamma-ray irradiation

    NASA Astrophysics Data System (ADS)

    Tokai, Akihiro; Okitsu, Kenji; Hori, Fuminobu; Mizukoshi, Yoshiteru; Iwase, Akihiro

    2016-06-01

    We developed a one-step gamma-ray irradiation method to synthesize nanocomposites composed of graphene and Pt nanoparticles from aqueous solution containing graphene and Pt(IV) complex ions in the presence of 2-propanol (IPA) or sodium dodecyl sulfate (SDS). It was confirmed that gamma-ray irradiation provided carbonyl groups on graphene and Pt nanoparticles formed from the radiolytic reduction of Pt(IV) complex ions were deposited onto the carbonyl modified graphene. In the presence of IPA, small Pt nanoparticles were deposited on graphene, but large Pt nanoparticles were deposited in the presence of SDS: the size of Pt nanoparticles formed was larger in the presence of SDS than IPA. Based on the results, formation and deposition mechanisms of Pt nanoparticles were proposed.

  4. Development of a ReaxFF potential for Pt-O systems describing the energetics and dynamics of Pt-oxide formation.

    PubMed

    Fantauzzi, Donato; Bandlow, Jochen; Sabo, Lehel; Mueller, Jonathan E; van Duin, Adri C T; Jacob, Timo

    2014-11-14

    ReaxFF force field parameters describing Pt-Pt and Pt-O interactions have been developed and tested. The Pt-Pt parameters are shown to accurately account for the chemical nature, atomic structures and other materials properties of bulk platinum phases, low and high-index platinum surfaces and nanoclusters. The Pt-O parameters reliably describe bulk platinum oxides, as well as oxygen adsorption and oxide formation on Pt(111) terraces and the {111} and {100} steps connecting them. Good agreement between the force field and both density functional theory (DFT) calculations and experimental observations is demonstrated in the relative surface free energies of high symmetry Pt-O surface phases as a function of the oxygen chemical potential, making ReaxFF an ideal tool for more detailed investigations of more complex Pt-O surface structures. Validation for its application to studies of the kinetics and dynamics of surface oxide formation in the context of either molecular dynamics (MD) or Monte Carlo simulations are provided in part by a two-part investigation of oxygen diffusion on Pt(111), in which nudged elastic band (NEB) calculations and MD simulations are used to characterize diffusion processes and to determine the relevant diffusion coefficients and barriers. Finally, the power of the ReaxFF reactive force field approach in addressing surface structures well beyond the reach of routine DFT calculations is exhibited in a brief proof-of-concept study of oxygen adsorbate displacement within ordered overlayers.

  5. Screening of electrocatalysts for direct ammonia fuel cell: Ammonia oxidation on PtMe (Me: Ir, Rh, Pd, Ru) and preferentially oriented Pt(1 0 0) nanoparticles

    NASA Astrophysics Data System (ADS)

    Vidal-Iglesias, F. J.; Solla-Gullón, J.; Montiel, V.; Feliu, J. M.; Aldaz, A.

    Ammonia has attracted attention as a possible fuel for direct fuel cells since it is easy to handle and to transport as liquid or as concentrated aqueous solution. However, on noble metal electrodes ammonia oxidation is a sluggish reaction and the electrocatalyst needs to be improved for developing efficient ammonia fuel cells. In this work, ammonia electrooxidation reaction on 3-4-nm bimetallic PtMe (Ir, Rh, Pd, Ru) and on preferentially oriented Pt(1 0 0) nanoparticles is reported. PtMe nanoparticles have been prepared by using water-in-oil microemulsions to obtain a narrow size distribution whereas preferentially oriented Pt nanoparticles have been prepared through colloidal routes. Among all the bimetallic samples tested, only Pt 75Ir 25 and Pt 75Rh 25 nanoparticles show, at the low potential range, an enhancement of the oxidation density current with respect to the behaviour found for pure platinum nanoparticles prepared by the same method. In addition, two Pt(1 0 0) preferentially oriented nanoparticles of different particle size (4 and 9 nm) have been also studied. These oriented nanoparticles show higher current densities than polycrystalline Pt nanoparticles due to the sensitivity of ammonia oxidation toward the presence of surface sites with square symmetry. The reactivity of the different 4-nm nanoparticles parallels well with that expected from bulk PtMe alloys and Pt single crystal electrodes.

  6. Oxygen vacancy promoted CO oxidation over Pt/CeO2 catalysts: A reaction at Pt-CeO2 interface

    NASA Astrophysics Data System (ADS)

    Liu, Huan-Huan; Wang, Yu; Jia, Ai-Pin; Wang, Shu-Yuan; Luo, Meng-Fei; Lu, Ji-Qing

    2014-09-01

    A series of Pt/CeO2 catalysts with different Pt contents were prepared using an incipient wetness impregnation method and tested for CO oxidation. Kinetic study on the catalysts indicated that the reaction rate was independent of the partial pressures of CO and O2 (r = kapp[CO]0[O2]0). The derived reaction pathways involved chemisorption of CO on surface Pt atoms and reacting with lattice oxygen provided by the CeO2 support at the Pt-CeO2 interface, suggesting a Mars van-Krevelen type reaction on these catalysts and the interfacial Pt-O-Ce ensembles being the active sites. Also, turnover frequencies (TOFs) calculated based on Pt dispersion and periphery Pt atoms were found to be proportional to the Pt particle size, with the large Pt particles possessing higher TOF than the small ones. Such a trend was interpreted by the important role of the oxygen vacancies via the formation of Pt-Ce-O solid solution, which could accelerate the mobility of lattice oxygen and consequently the activity.

  7. The molecular, electronic, bonding, and photophysical features of the [(c-Pt3)Tl(c-Pt3)]+ inorganic metallocenes.

    PubMed

    Tsipis, Athanassios C; Gkekas, George N

    2013-06-21

    The molecular, electronic, bonding and photophysical properties of a series of inorganic metallocenes with the general formula {[Pt3(μ2-L)3(L')3]2(μ6-Tl)}(+) (L = CO, CH3CN, PH2, C6F5, or SO2 and L' = CO, PH3, CH3CN, C6F5) have been studied by means of DFT electronic structure calculations. The estimated Tl-cd distances between Tl(+) cations and the centroids (cd) of the trimetallic Pt3(μ2-L)3(L')3 {3 : 3 : 3} decks were found in the range 2.932-3.397 Å. The predicted bond dissociation energy, D0, of the (c-Pt3)···Tl(+) bonds was found to lie within the range -31.5 up to -77.5 kcal mol(-1) at the B3LYP/LANL2TZ(f)(Pt) ∪ 6-31G(d,p)(E) ∪ SRLC(Tl) level of theory. Most of the [(c-Pt3)Tl(c-Pt3)](+) inorganic metallocenes adopt a bend titanocene-like structure. The Localized Orbital Locator (LOL) contour maps along with the 3D contour plots of the Reduced Gradient Density (RDG) mirror the composite nature of the interaction of Tl(+) with the triangular Pt3 metallic ring cores consisting of electrostatic, covalent and dispersion interaction components. The Pt3···Tl(+)···Pt3 bonding mode was further validated by Energy Decomposition Analysis (EDA) calculations which demonstrated that the electrostatic and covalent components of the interaction contribute almost equally to the bonding interactions. Furthermore, Charge Decomposition Analysis (CDA) and Natural Bond Orbital Analysis (NBO) calculations indicated that charge transfer from the Tl(+) cation to the Pt3(0) {3 : 3 : 3} decks also occurs. The {[Pt3(μ2-L)3(L')3]2(μ6-Tl)}(+) sandwiches absorb in the UV-Vis region (300-500 nm) and emit in the visible-near IR region (600-1000 nm). The absorption bands are mainly of MLCT/MC character while phosphorescence is predicted to occur via the first triplet excited state, T1, since the spin density of this excited state could be described as a SOMO - 1/SOMO combination. Generally, no significant distortions occur upon excitation of these systems

  8. Ba3Pt4Al4-Structure, Properties, and Theoretical and NMR Spectroscopic Investigations of a Complex Platinide Featuring Heterocubane [Pt4Al4] Units.

    PubMed

    Stegemann, Frank; Benndorf, Christopher; Bartsch, Timo; Touzani, Rachid St; Bartsch, Manfred; Zacharias, Helmut; Fokwa, Boniface P T; Eckert, Hellmut; Janka, Oliver

    2015-11-16

    Ba3Pt4Al4 was prepared from the elements in niobium ampules and crystallizes in an orthorhombic structure, space group Cmcm (oP44, a = 1073.07(3), b = 812.30(3), c = 1182.69(3) pm) isopointal to the Zintl phase A2Zn5As4 (A = K, Rb). The structure features strands of distorted [Pt4Al4] heterocubane-like units connected by condensation over Pt/Al edges. These are arranged in a hexagonal rod packing by further condensation over Pt and Al atoms with the barium atoms located inside cavities of the [Pt4Al4](δ-) framework. Structural relaxation confirmed the electronic stability of the new phase, while band structure calculations indicate metallic behavior. Crystal orbital Hamilton bonding analysis coupled with Bader effective charge analysis suggest a polar intermetallic phase in which strong Al-Pt covalent bonds are present, while a significant electron transfer from Ba to the [Pt4Al4](δ-) network is found. By X-ray photoelectron spectroscopy measurements the Pt 4f5/2 and 4f7/2 energies for Ba3Pt4Al4 were found in the range of those of elemental Pt due to the electron transfer of Ba, while PtAl and PtAl2 show a pronounced shift toward a more cationic platinum state. (27)Al magic-angle spinning NMR investigations verified the two independent crystallographic Al sites with differently distorted tetrahedrally coordinated [AlPt4] units. Peak assignments could be made based on both geometrical considerations and in relation to electric field gradient calculations. PMID:26536164

  9. Quantitative Prediction of Surface Segregation in Bimetallic Pt-MAlloy Nanoparticles (M=Ni, Re, Mo)

    SciTech Connect

    Wang, Guofeng; Van Hove, Michel A.; Ross, Phil N.; Baskes,Michael I.

    2005-06-20

    This review addresses the issue of surface segregation inbimetallic alloy nanoparticles, which are relevant to heterogeneouscatalysis, in particular for electro-catalysts of fuel cells. We describeand discuss a theoretical approach to predicting surface segregation insuch nanoparticles by using the Modified Embedded Atom Method and MonteCarlo simulations. In this manner it is possible to systematicallyexplore the behavior of such nanoparticles as a function of componentmetals, composition, and particle size, among other variables. We choseto compare Pt75Ni25, Pt75Re25, and Pt80Mo20 alloys as example systems forthis discussion, due to the importance of Pt in catalytic processes andits high-cost. It is assumed that the equilibrium nanoparticles of thesealloys have a cubo-octahedral shape, the face-centered cubic lattice, andsizes ranging from 2.5 nm to 5.0 nm. By investigating the segregation ofPt atoms to the surfaces of the nanoparticles, we draw the followingconclusions from our simulations at T= 600 K. (1) Pt75Ni25 nanoparticlesform a surface-sandwich structure in which the Pt atoms are stronglyenriched in the outermost and third layers while the Ni atoms areenriched in the second layer. In particular, a nearly pure Pt outermostsurface layer can be achieved in those nanoparticles. (2) EquilibriumPt75Re25 nanoparticles adopt a core-shell structure: a nearly pure Ptshell surrounding a more uniform Pt-Re core. (3) In Pt80Mo20nanoparticles, the facets are fully occupied by Pt atoms, the Mo atomsonly appear at the edges and vertices, and the Pt and Mo atoms arrangethemselves in an alternating sequence along the edges and vertices. Oursimulations quantitatively agree with previous experimental andtheoretical results for the extended surfaces of Pt-Ni, Pt-Re, and Pt-Moalloys. We further discuss the reasons for the different types of surfacesegregation found in the different alloys, and some of theirimplications.

  10. Synthesis of Pt-Mo-N Thin Film and Catalytic Activity for Fuel Cells

    SciTech Connect

    Miura, Akira; Tague, Michele E.; Gregoire, John M.; Wen, Xiao-Dong; van Dover, R. Bruce; Abruña, Héctor D.; DiSalvo, Francis J.

    2010-05-13

    Pt-Mo-N composition gradient film was synthesized by combining thin-film deposition techniques and subsequent thermal nitridation. A ternary platinum-based nitride, Pt2Mo3N, showed catalytic activities for fuel cell applications and higher electrochemical stability when it was compared with a PtMo alloy with the same Pt:Mo ratio.

  11. Effects of carbon supports on Pt distribution, ionomer coverage and cathode performance for polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Park, Young-Chul; Tokiwa, Haruki; Kakinuma, Katsuyoshi; Watanabe, Masahiro; Uchida, Makoto

    2016-05-01

    We investigate the effects of the carbon supports on the Pt distribution, ionomer coverage and cathode performance of carbon-supported Pt catalysts, by using STEM observation, N2 adsorption analysis and electrochemical characterization. According to the STEM observation, the effective Pt surface area (S(e)Pt), which is determined by the location and size of the Pt particles on the supports, increases in the following order: c-Pt/CB < c-Pt/GCB < n-Pt/AB800 < n-Pt/AB250. The N2 adsorption analyses show that the Pt particles observed in the interior of the CB and AB800-supported Pt catalysts during the STEM observation could be ascribed to the hollow structures inside the carbon supports, which decrease their effective Pt surface areas. The S(e)Pt values are in good agreement with the cell performance in the high current density region. In spite of the highest Pt utilization (UPt) value (>90%) and uniform ionomer coverage, the c-Pt/CB catalyst shows the lowest cell performance due to the lower S(e)Pt value. On the other hand, the n-Pt/AB250 catalyst, for which all of the Pt particles exist only on the exterior surface, is found to be the most attractive in order to generate the large current densities required by actual fuel cell operation.

  12. Component, Microstructure and Simulation Calculation Study of Bimetallic Pt-Cu Alloys Towards Catalyzing Methanol Oxidation Reaction

    NASA Astrophysics Data System (ADS)

    Wei, Shenying; Gao, Huaizhi; Li, Haibo; Li, Rui; Liu, Jifeng

    2014-12-01

    Three Pt-Cu alloys (Pt0.3Cu0.7, Pt0.5Cu0.5, and Pt0.7Cu0.3) with different Cu contents were synthesized by adjusting the Pt/Cu precursor ratio, and their electrocatalytic activities for methanol oxidation reaction (MOR) were systematically studied. Component and microstructure study revealed that the relationship between the lattice parameters and Cu content followed the Vegard's law. Electrochemistry measurement showed that the MOR catalytic activity for Pt-Cu alloys displayed a dependency on the Cu content, and it decreased following: Pt0.3Cu0.7 > Pt0.5Cu0.5 > Pt0.7Cu0.3. Among the three Pt-Cu alloys, the Pt0.3Cu0.7 alloy exhibited the highest oxidation current density and best CO tolerance activity. Density functional theory simulation calculation, taking into account the shrinking of Pt-Cu alloy's lattice after Cu incorporation, confirmed that the adsorption energy of CO also displayed a dependency on the Cu content in Pt-Cu alloys, and it increased following: Pt0.3Cu0.7 < Pt0.5Cu0.5 < Pt0.7Cu0.3 < Pt, which could rationally explain the best CO tolerance ability for the Pt0.3Cu0.7.

  13. Microbial fuel cell cathode with dendrimer encapsulated Pt nanoparticles as catalyst

    NASA Astrophysics Data System (ADS)

    Yang, Xiaoling; Lu, Jindan; Zhu, Yihua; Shen, Jianhua; Zhang, Zhen; Zhang, Jianmei; Chen, Cheng; Li, Chunzhong

    In this paper, we investigated the use of polyamidoamine (PAMAM) dendrimer-encapsulated platinum nanoparticles (Pt-DENs) as a promising type of cathode catalyst for air-cathode single chamber microbial fuel cells (SCMFCs). The Pt-DENs, prepared via template synthesis method, have uniform diameter distribution with size range of 3-5 nm. The Pt-DENs then loaded on to a carbon substrate. For comparison, we also electrodeposited Pt on carbon substrate. The calculation shows that the loading amount of Pt-DENs on carbon substrate is about 0.1 mg cm -2, which is three times lower than that of the electrodeposited Pt (0.3 mg cm -2). By measuring batch experiments, the results show that Pt-DENs in air-cathode SCMFCs have a power density of 630 ± 5 mW m -2 and a current density of 5200 ± 10 mA m -2 (based on the projected anodic surface area), which is significantly better than electrodeposited Pt cathodes (power density: 275 ± 5 mW m -2 and current density: 2050 ± 10 mA m -2). Additionally, Pt-DENs-based cathodes resulted in a higher power production with 129.1% as compared to cathode with electrodeposited Pt. This finding suggests that Pt-DENs in MFC cathodes is a better catalyst and has a lower loading amount than electrodeposited Pt, and may serve as a novel and alternative catalyst to previously used noble metals in MFC applications.

  14. Simultaneous tunable structure and composition of PtAg alloyed nanocrystals as superior catalysts.

    PubMed

    Fang, Caihong; Zhao, Jun; Zhao, Guili; Kuai, Long; Geng, Baoyou

    2016-08-11

    PtAg alloyed nanostructural catalysts were firstly prepared by co-reduction of AgNO3 and H2PtCl6 precursors in growth solution using a seed-mediated method. By simply changing the molar ratio of the metal precursors, the morphologies of the porous alloyed nanocrystals can be tuned from multipetals to multioctahedra. Simultaneously, the alloy composition can be varied from Pt76Ag24 to Pt66Ag34. The catalytic properties of the prepared PtAg alloyed nanocrystals with a tunable structure and composition were tentatively examined by choosing the reduction of 4-nitrophenol with NaBH4. The reaction rate normalized to the concentration of catalysts was calculated to be 318.9 s(-1) mol(-1) L and 277.4 s(-1) mol(-1) L for Pt70Ag30 and Pt66Ag34 porous catalysts, which is much higher than the pure Pt catalysts. Moreover, PtAg nanostructures can also serve as efficient electrocatalysts toward the methanol oxidation reaction, especially for Pt70Ag30 and Pt66Ag34 porous nanocrystals. The electrocatalytic activity and the durability were both highly enhanced compared to the commercial Pt/C catalyst. In addition, we also investigated the enhancement mechanism.

  15. Carbon-supported Pt nanowire as novel cathode catalysts for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Li, Bing; Yan, Zeyu; Higgins, Drew C.; Yang, Daijun; Chen, Zhongwei; Ma, Jianxin

    2014-09-01

    Carbon-supported platinum nanowires (PtNW/C) are successfully synthesized by a simple and inexpensive template-free methodology and demonstrated as novel, suitable cathode electrode materials for proton exchange membrane fuel cell (PEMFC) applications. The synthesis conditions, such as the amount of reducing agent and reaction time, were investigated to investigate the effect on the nanostructures and activities of the PtNW/C catalysts. High-resolution transmission electron microscopy (TEM) results show that the formic acid facilitated reduction is capable of producing uniformly distributed 1-dimensional PtNW with an average cross-sectional diameter of 4.0 ± 0.2 nm and length of 20-40 nm. Investigation of the electrocatalytic activity by half-cell electrochemical testing reveals that PtNW/C catalyst demonstrates significant oxygen reduction reaction (ORR) activity, superior to that of commercially available Pt/C. Using a loading of 0.4 mgPt cm-2 PtNW/C as the cathode catalyst, a maximum power density of 748.8 mW cm-2 in a 50 cm2 single cell of commercial Pt/C. In addition, accelerated degradation testing (ADT) showed that the PtNW/C catalyst exhibits better durability than commercial Pt/C, rendering PtNW/C as a promising replacement to conventional Pt/C as cathode electrocatalysts for PEMFCs applications.

  16. Localized Pd Overgrowth on Cubic Pt Nanocrystals for Enhanced Electrocatalytic Oxidation of Formic Acid

    SciTech Connect

    Lee, H.; Habas, S.E.; Somorjai, G.A.; Yang, P.

    2008-03-20

    Binary Pt/Pd nanoparticles were synthesized by localized overgrowth of Pd on cubic Pt seeds for the investigation of electrocatalytic formic acid oxidation. The binary particles exhibited much less self-poisoning and a lower activation energy relative to Pt nanocubes, consistent with the single crystal study.

  17. Epitaxial growth of intermetallic MnPt films on oxides and large exchange bias

    DOE PAGESBeta

    Liu, Zhiqi; Biegalski, Michael D.; Hsu, Shang-Lin; Shang, Shunli; Marker, Cassie; Liu, Jian; Li, Li; Fan, Lisha S.; Meyer, Tricia L.; Wong, Anthony T.; et al

    2015-11-05

    High-quality epitaxial growth of intermetallic MnPt films on oxides is achieved, with potential for multiferroic heterostructure applications. Antisite-stabilized spin-flipping induces ferromagnetism in MnPt films, although it is robustly antiferromagnetic in bulk. Thus, highly ordered antiferromagnetic MnPt films exhibit superiorly large exchange coupling with a ferromagnetic layer.

  18. Surface topographical changes on Pt(100) and Pt(111) in the NO + CO reaction: a reflection electron microscopy study

    NASA Astrophysics Data System (ADS)

    Uchida, Y.; Imbihl, R.; Lehmpfuhl, G.

    1992-09-01

    The structural modifications which are induced by the NO + CO reaction on Pt surfaces were studied using reflection electron microscopy (REM) to image atomic steps. Small single crystal spheres of Pt (diameter ≈ 0.3 mm) were prepared and then exposed in a UHV chamber to a flow of CO and NO at 10 -6 Torr. The sample temperature was cycled between 300 and 700 K over an exposure time of typically ˜ 1 h. On the (100) orientations, the reaction led to a strong roughening of the substrate and to the development of a domain structure. As was demonstrated in adsorption experiments with CO (NO) alone, the major contribution to the roughening originated from the 1 × 1 ⇄ hex phase transition of Pt(100). On the (111) facets the flat terraces were only weakly affected by the reaction, but the step edges were quite strongly attacked leading to a meandering of the initially straight step edges. The observations made on Pt(111) are consistent with a mechanistic picture in which the NO + CO reaction takes entirely place at step and kink sites.

  19. Effect of stoichiometry on the magnetocrystalline anisotropy of Fe-Pt and Co-Pt from first-principles calculation.

    PubMed

    Luo, H B; Xia, W X; Ruban, A V; Du, J; Zhang, J; Liu, J P; Yan, A

    2014-09-24

    The effect of stoichiometry on magnetocrystalline anisotropy energy (MAE) of Fe1+xPt1-x and Co1+xPt1-x (-0.5 < x < 0.5) is studied by use of first-principles method. The calculated MAEs show maxima at x = 0 for both fully L10-ordered systems. Compared with that, the MAEs of partially L10-ordered systems reduce but their composition dependences do not change, without shift of the maximum MAE to Fe/Co-rich alloy as found in experiment at room temperature. In the off-stoichiometric alloys, the misoccupied Fe/Co and Pt show large MAEs, which is explained by the enhanced in-plane hybridization between Fe/Co and Pt. The composition dependence of the atom-resolved MAE is governed by the varying number of heterogeneous ligands around the atom. The MAE(T)/MAE(0) is discussed based on spontaneous magnetization and Curie temperature, which suggests that the temperature effect may contribute to the discrepancy between calculation and experiment in the composition dependence of MAE. PMID:25181285

  20. Thermoelectric and Magnetic Properties of Pt-Substituted {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} Compounds

    NASA Astrophysics Data System (ADS)

    Sertkol, Murat; Ballıkaya, Sedat; Aydoğdu, Fatih; Güler, Adil; Özdemir, Mustafa; Öner, Yıldırhan

    2016-08-01

    {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} (x = 0, 0.1, 0.2) compounds were prepared by melting and annealing, followed by a spark plasma sintering method. Low-temperature thermoelectric and magnetic properties were investigated based on Seebeck coefficient, electrical and thermal conductivity and magnetization measurements. The structural properties of {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} (x = 0, 0.1, 0.2) compounds were ascertained by powder x-ray diffraction analysis, confirming that all samples have a main phase of a skutterudite structure with the space group Im{bar{3}} . The lattice parameters obtained, 9.202(5), 9.199(5) and 9.202(1) Å for x = 0, 0.1 and 0.2, respectively, were found consistent with literature. The Seebeck coefficient sign shows that holes are dominant carriers in all compounds. The local maximum Seebeck coefficient was observed around 50 K which may be a trace of paramagnon-drag effect of charge carriers. Thermal conductivity and electrical resistivity measurements were carried out between 4.2 and 300 K. Temperature dependence of electrical resistivity reflects that all samples show semi-metallic behavior in our temperature range of 4.2-300 K. Samples for x = 0.1 and x = 0.2 show Kondo-like behavior. In magnetization measurement, we observe that there are two successive magnetic transitions in Pt-substituted compounds; however, there is only one (transition from a paramagnetic state to long-range magnetic ordering) in Pt-free compounds. In Pt-substituted compounds, the first transition appears at T _{ c} = 48 K. In addition, the second transition is observed at T _{ irr} = 30 K where an intermediate state is observed before the magnetic ordering transforms to an irreversible ferromagnetic state. We concluded that Pt substitution on the Fe side effectual on the thermoelectric and magnetic properties of {BaFe_{4-{x}}Pt_{{x}}Sb_{12}} (x = 0, 0.1, 0.2) compounds.

  1. Ultra-thin L1{sub 0}-FePt for perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves

    SciTech Connect

    Ho, Pin; Chow, Gan Moog; Chen, Jing-Sheng; Han, Guchang; He, Kaihua

    2014-05-07

    Perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves (PSVs) with ultra-thin L1{sub 0}-FePt alloy free layer possessing high anisotropy and thermal stability have been fabricated and studied. The thickness of the L1{sub 0}-FePt layer was varied between 2 and 4 nm. The PSV became increasingly decoupled with reduced L1{sub 0}-FePt thickness due to the larger difference between the coercivity of the L1{sub 0}-FePt and [Co/Pd]{sub 30} films. The PSV with an ultra-thin L1{sub 0}-FePt free layer of 2 nm displayed a high K{sub u} of 2.21 × 10{sup 7} ergs/cm{sup 3}, high thermal stability of 84 and a largest giant magnetoresistance of 0.54%.

  2. Prevalence of antibodies to prothrombin in solid phase (aPT) and to phosphatidylserine-prothrombin complex (aPS/PT) in patients with and without lupus anticoagulant.

    PubMed

    Bertolaccini, Maria Laura; Sciascia, Savino; Murru, Veronica; Garcia-Fernandez, Cesar; Sanna, Giovanni; Khamashta, Munther A

    2013-02-01

    Antibodies to prothrombin in solid phase (aPT) and those to phosphatidiyserine-prothrombin complex (aPS/PT) have been suggested to strongly correlate with the presence of lupus anticoagulant (LA). As their clinical diagnostic value and true relationship with the LA remains elusive, we designed this study to evaluate the prevalence and significance of aPT and aPS/PT in a large cohort of patients with and without LA. Samples from 257 patients were included. aPT and aPS/PT were tested by ELISA. LA was tested as per the current criteria from the ISTH Subcommittee on LA-Phospholipid-dependent antibodies. aPS/PT and aPT were found in 51% and 32% of LA-positive (LA+ve) patients and in 22% and 28% of LA-negative (LA-ve) patients, respectively. Thrombosis, particularly venous thrombosis was associated with IgG aPT in the LA+ve group (p=0.0006) and in the LA-ve group (p=0.017). Antibodies to phosphatidylserine-prothrombin, either IgG and IgM were associated with thrombosis in general (p=0.0003) in particularly with venous thrombosis in the LA+ve group (p<0.0001 for IgG and p=0.025 for IgM; respectively) and the LA-ve group (p=0.028, 0.02 and 0.001, respectively). Further multivariate logistic regression analysis showed that LA and of IgG and/or IgM aPS/PT were independent risk factors for thrombosis and pregnancy loss. In conclusion, aPS/PT, but not aPT, are more frequently found in patients with LA. Their association with thrombosis seems to be independent of the presence of LA. PMID:23254928

  3. Elucidation of the mechanism for sulfur oxidation on Pt and Pt3Co electrocatalysts using in situ X-ray absorption spectroscopy

    SciTech Connect

    Ramaker, D.; Gatewood, D; Garsany, Y; Korovina, A; Swider-Lyons, K

    2009-01-01

    Adsorbed sulfur is a poison to the Pt catalysts used in proton exchange membrane fuel cells, but it can be removed by potential cycling. This process is studied for S{sub x}-poisoned nanoscale Pt- and Pt{sub 3}Co- on Vulcan carbon (Pt/VC and Pt{sub 3}Co/VC) in perchloric acid electrolyte using the {Delta}{mu} adsorbate isolation technique for in situ X-ray absorption spectroscopy. The {Delta}{mu} technique is modified to better distinguish the {Delta}{mu} signatures for H, O, and Sx on Pt. The resulting {Delta}{mu} analysis suggests that SO{sub 2} on nanoscale Pt is oxidized to bisulfate or sulfate species in two regions, near 1.05 V on the cluster edges of the Pt nanoparticle, and at higher potentials from the Pt(111) faces where oxygen is less strongly bound. The bisulfate or sulfate species desorb from the Pt surface at high potentials due to O(OH) adsorption/replacement and at low potentials due to loss of the Coulomb attraction between the bisulfate anion and the Pt. A similar oxidation process occurs for S{sub x}-poisoned Pt{sub 3}Co/VC, but at lower potentials because a ligand effect coming from Co shifts the oxidization potential of adsorbed SO{sub 2} to lower potentials while pushing OH adsorption to higher potentials. The spectroscopic results give insights into cyclic voltammetry data and are consistent with electrochemical cycling procedures for removing the sulfur.

  4. Prevalence of antibodies to prothrombin in solid phase (aPT) and to phosphatidylserine-prothrombin complex (aPS/PT) in patients with and without lupus anticoagulant.

    PubMed

    Bertolaccini, Maria Laura; Sciascia, Savino; Murru, Veronica; Garcia-Fernandez, Cesar; Sanna, Giovanni; Khamashta, Munther A

    2013-02-01

    Antibodies to prothrombin in solid phase (aPT) and those to phosphatidiyserine-prothrombin complex (aPS/PT) have been suggested to strongly correlate with the presence of lupus anticoagulant (LA). As their clinical diagnostic value and true relationship with the LA remains elusive, we designed this study to evaluate the prevalence and significance of aPT and aPS/PT in a large cohort of patients with and without LA. Samples from 257 patients were included. aPT and aPS/PT were tested by ELISA. LA was tested as per the current criteria from the ISTH Subcommittee on LA-Phospholipid-dependent antibodies. aPS/PT and aPT were found in 51% and 32% of LA-positive (LA+ve) patients and in 22% and 28% of LA-negative (LA-ve) patients, respectively. Thrombosis, particularly venous thrombosis was associated with IgG aPT in the LA+ve group (p=0.0006) and in the LA-ve group (p=0.017). Antibodies to phosphatidylserine-prothrombin, either IgG and IgM were associated with thrombosis in general (p=0.0003) in particularly with venous thrombosis in the LA+ve group (p<0.0001 for IgG and p=0.025 for IgM; respectively) and the LA-ve group (p=0.028, 0.02 and 0.001, respectively). Further multivariate logistic regression analysis showed that LA and of IgG and/or IgM aPS/PT were independent risk factors for thrombosis and pregnancy loss. In conclusion, aPS/PT, but not aPT, are more frequently found in patients with LA. Their association with thrombosis seems to be independent of the presence of LA.

  5. Sr{sub 4}PbPt{sub 4}O{sub 11}, the first platinum oxide containing Pt{sub 2}{sup 6+} ions

    SciTech Connect

    Renard, Catherine . E-mail: catherine.renard@ensc-lille.fr; Roussel, Pascal; Rubbens, Annick; Daviero-Minaud, Sylvie; Abraham, Francis

    2006-07-15

    We report the synthesis and crystal structure of the new compound Sr{sub 4}PbPt{sub 4}O{sub 11}, containing platinum in highly unusual square pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction techniques on a twinned sample, the final R factors are R=0.0260 and wR=0.0262. The symmetry is triclinic, space group P1-bar , with a=5.6705(6)A, b=9.9852(5)A, c=10.0889(5)A, {alpha}=90.421(3){sup o}, {beta}=89.773(8){sup o}, {gamma}=90.140(9){sup o} and Z=2. The structure is built from dumbell-shaped Pt{sub 2}O{sub 9} entities formed by a dinuclear metal-metal bonded Pt{sub 2}{sup 6+} ion with asymmetric environments of the two Pt atoms, classical PtO{sub 4} square plane and unusual PtO{sub 5} square pyramid. Successive Pt{sub 2}O{sub 9} entities deduced from 90{sup o} rotations are connected through the oxygens of the PtO{sub 4} basal squares to form [Pt{sub 4}O{sub 10}{sup 8-}]{sub {approx}} columns further connected through Pb{sup 2+} and Sr{sup 2+} ions. Raman spectroscopy confirmed the peculiar platinum coordination environment.

  6. Reforming of oxygenates for H2 production: correlating reactivity of ethylene glycol and ethanol on Pt(111) and Ni/Pt(111) with surface d-band center.

    PubMed

    Skoplyak, Orest; Barteau, Mark A; Chen, Jingguang G

    2006-02-01

    The dehydrogenation and decarbonylation of ethylene glycol and ethanol were studied using temperature programmed desorption (TPD) on Pt(111) and Ni/Pt(111) bimetallic surfaces, as probe reactions for the reforming of oxygenates for the production of H2 for fuel cells. Ethylene glycol reacted via dehydrogenation to form CO and H2, corresponding to the desired reforming reaction, and via total decomposition to produce C(ad), O(ad), and H2. Ethanol reacted by three reaction pathways, dehydrogenation, decarbonylation, and total decomposition, producing CO, H2, CH4, C(ad), and O(ad). Surfaces prepared by deposition of a monolayer of Ni on Pt(111) at 300 K, designated Ni-Pt-Pt(111), displayed increased reforming activity compared to Pt(111), subsurface monolayer Pt-Ni-Pt(111), and thick Ni/Pt(111). Reforming activity was correlated with the d-band center of the surfaces and displayed a linear trend for both ethylene glycol and ethanol, with activity increasing as the surface d-band center moved closer to the Fermi level. This trend was opposite to that previously observed for hydrogenation reactions, where increased activity occurred on subsurface monolayers as the d-band center shifted away from the Fermi level. Extrapolation of the correlation between activity and the surface d-band center of bimetallic systems may provide useful predictions for the selection and rational design of bimetallic catalysts for the reforming of oxygenates. PMID:16471734

  7. Mechanistic aspects of the ethanol steam reforming reaction for hydrogen production on Pt, Ni, and PtNi catalysts supported on gamma-Al2O3.

    PubMed

    Sanchez-Sanchez, Maria Cruz; Navarro Yerga, Rufino M; Kondarides, Dimitris I; Verykios, Xenophon E; Fierro, Jose Luis G

    2010-03-25

    Mechanistic aspects of ethanol steam reforming on Pt, Ni, and PtNi catalysts supported on gamma-Al(2)O(3) are investigated from the analysis of adsorbed species and gas phase products formed on catalysts during temperature-programmed desorption of ethanol and during ethanol steam reforming reaction. DRIFTS-MS analyses of ethanol decomposition and ethanol steam reforming reactions show that PtNi and Ni catalysts are more stable than the Pt monometallic counterpart. Ethanol TPD results on Ni, Pt, and NiPt catalysts point to ethanol dehydrogenation and acetaldehyde decomposition as the first reaction pathways of ethanol steam reforming over the studied catalysts. The active sites responsible for the acetaldehyde decomposition are easily deactivated in the first minutes on-stream by carbon deposits. For Ni and PtNi catalysts, a second reaction pathway, consisting in the decomposition of acetate intermediates formed over the surface of alumina support, becomes the main reaction pathway operating in steam reforming of ethanol once the acetaldehyde decomposition pathway is deactivated. Taking into account the differences observed in the mechanism of ethanol decomposition, the better stability observed for PtNi catalyst is proposed to be related with a cooperative effect between Pt and Ni activities together with the enhanced ability of Ni to gasify the methyl groups formed by decomposition of acetate species. On the contrary, monometallic catalysts are believed to dehydrogenate these methyl groups forming coke that leads to deactivation of metal particles. PMID:19824680

  8. Controlled FCC/on-top binding of H/Pt(111) using surface stress

    NASA Astrophysics Data System (ADS)

    Shuttleworth, I. G.

    2016-08-01

    The preferred binding site of H/Pt(111) has been shown to be change from the on-top to FCC as the Pt(111) surface goes approximately from a state of compressive to tensile strain. A chemical analysis of the system has shown that for both FCC and on-top bound cases the H ssbnd Pt s and H ssbnd Pt d interactions have a similar importance in determining the preferred binding position. It has been seen that FCC-bound H forms a distinct state below the Pt d-band, whereas the on-top bound H does not.

  9. Low-Pt-Content Anode Catalyst for Direct Methanol Fuel Cells

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram; Whitacre, Jay

    2008-01-01

    Combinatorial experiments have led to the discovery that a nanophase alloy of Pt, Ru, Ni, and Zr is effective as an anode catalyst material for direct methanol fuel cells. This discovery has practical significance in that the electronic current densities achievable by use of this alloy are comparable or larger than those obtained by use of prior Pt/Ru catalyst alloys containing greater amounts of Pt. Heretofore, the high cost of Pt has impeded the commercialization of direct methanol fuel cells. By making it possible to obtain a given level of performance at reduced Pt content (and, hence, lower cost), the discovery may lead to reduction of the economic impediment to commercialization.

  10. Observation and elimination of broken symmetry in L1{sub 0} FePt nanostructures

    SciTech Connect

    Quarterman, P.; Wang, Hao; Qiu, Jiao-Ming; Ma, Bin; Liu, Xiaoqi; Wang, Jian-Ping; Guo, Honghua

    2015-12-07

    An unexplained surface anisotropy effect was observed and confirmed in the magnetization reversal process of both L1{sub 0} phase FePt nanoparticles with octahedral shape and (001) textured L1{sub 0} FePt thin films with island nanostructures. We suggest that the nature of the observed surface effect is caused by broken symmetry on the FePt surface, which results in weakened exchange coupling for surface atoms. Furthermore, we propose, and experimentally demonstrate, a method to repair the broken symmetry by capping the FePt islands with a Pt layer, which could prove invaluable in understanding fundamental limitations of magnetic nanostructures.

  11. The effect of composition and structural ordering on the magnetism of FePt nanoparticles.

    PubMed

    Kalogirou, O; Angelakeris, M; Dendrinou-Samara, C; Mourdikoudis, S; Simeonidis, K; Gloystein, K; Vilalta-Clemente, A; Tsiaoussis, I

    2010-09-01

    Spherical 4 nm FePt nanoparticles were synthesized by the simultaneous decomposition of Fe(CO)5 and the polyol reduction of Pt(acac)2. The final Fe-to-Pt composition was tuned between 15-55 at.% by varying the ingredient precursor ratios. The effect of composition and structural ordering on the macroscopic magnetic features of final FePt nanoparticles was examined via post-synthetic annealing stages at different conditions. Structural ordering is promoted in all cases, though samples approximating equiatomic Fe/Pt ratios eventually transform to fct-FePt phase while the FePt3-phase is favored for the Pt-richer samples. Consequently, the magnetic features of the annealed nanoparticles may be categorized; the hard magnetic FePt region dominating for Fe content between 40-55 at.% and the soft magnetic FePt3 region dominating in the region 20-30 at.% while Fe content less than 20 at.% results in Pt-richer phases with diminishing ferromagnetic behavior. PMID:21133141

  12. Hybrid magnetoresistance in Pt-based multilayers: Effect originated from strong interfacial spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Meng, Kangkang; Xiao, Jiaxing; Wu, Yong; Miao, Jun; Xu, Xiaoguang; Zhao, Jianhua; Jiang, Yong

    2016-02-01

    The hybrid magnetoresistance (MR) behaviors in Pt/Co90Fe10/Pt, Mn1.5Ga/Pt and Mn1.5Ga/Pt/Co90Fe10/Pt multilayers have been investigated. Both planer Hall effect (PHE) and angle-dependent MR in Pt/Co90Fe10/Pt revealed the combination of spin Hall MR (SMR) and normal anisotropic MR (AMR), indicating the large contribution of strong spin-orbit coupling (SOC) at the interfaces. When Pt contacted with perpendicular magnetic anisotropy (PMA) metal Mn1.5Ga, the strong interfacial SOC modified the effective anomalous Hall effect. The MR in Mn1.5Ga/Pt/Co90Fe10/Pt is not a simple combination of SMR and AMR, but ascribed to the complicated domain wall scattering and strong interfacial SOC when Pt is sandwiched by the in-plane magnetized Co90Fe10 and the PMA Mn1.5Ga.

  13. Hybrid magnetoresistance in Pt-based multilayers: Effect originated from strong interfacial spin-orbit coupling

    PubMed Central

    Meng, Kangkang; Xiao, Jiaxing; Wu, Yong; Miao, Jun; Xu, Xiaoguang; Zhao, Jianhua; Jiang, Yong

    2016-01-01

    The hybrid magnetoresistance (MR) behaviors in Pt/Co90Fe10/Pt, Mn1.5Ga/Pt and Mn1.5Ga/Pt/Co90Fe10/Pt multilayers have been investigated. Both planer Hall effect (PHE) and angle-dependent MR in Pt/Co90Fe10/Pt revealed the combination of spin Hall MR (SMR) and normal anisotropic MR (AMR), indicating the large contribution of strong spin-orbit coupling (SOC) at the interfaces. When Pt contacted with perpendicular magnetic anisotropy (PMA) metal Mn1.5Ga, the strong interfacial SOC modified the effective anomalous Hall effect. The MR in Mn1.5Ga/Pt/Co90Fe10/Pt is not a simple combination of SMR and AMR, but ascribed to the complicated domain wall scattering and strong interfacial SOC when Pt is sandwiched by the in-plane magnetized Co90Fe10 and the PMA Mn1.5Ga. PMID:26843035

  14. Directly patternable SnO{sub 2} thin films incorporating Pt nanoparticles

    SciTech Connect

    Kim, Hyuncheol; Choi, Yong-June; Kang, Kyung-Mun; Park, Hyung-Ho

    2014-04-01

    Highlights: • Direct-patterning of SnO{sub 2} films incorporated with Pt nanoparticles. • Pt incorporated SnO{sub 2} thin films by using photochemical solution deposition. • Reduction catalytic behavior of Pt nanoparticles. • Progress reduction of SnO{sub 2} with increasing amount of Pt nanoparticles. • Enhanced electrical conductivity of SnO{sub 2} films with Pt nanoparticles incorporation. - Abstract: Direct-patterning of SnO{sub 2} films incorporating Pt nanoparticles was performed by using a photochemical solution deposition without a photoresist or dry etching. Incorporating Pt nanoparticles into these films had a slight effect on their crystallinity and almost no effect on their transmittance. The inclusion of Pt nanoparticles enhanced the electrical conductivity of the SnO{sub 2} thin films compared to their pristine forms. The chemical bonding state of the films was analyzed by X-ray photoelectron spectroscopy to investigate the effect of the Pt nanoparticles on the carrier concentration in the film. It was concluded that the reduction of SnO{sub 2} thin films by Pt nanoparticles progressed as a result of the presence of the Pt nanoparticles, causing an oxygen deficiency to develop in SnO{sub 2} and thereby influencing the carrier concentration of the film.

  15. Mesoporous graphene-like nanobowls as Pt electrocatalyst support for highly active and stable methanol oxidation

    NASA Astrophysics Data System (ADS)

    Yan, Zaoxue; He, Guoqiang; Jiang, Zhifeng; Wei, Wei; Gao, Lina; Xie, Jimin

    2015-06-01

    Mesoporous graphene-like nanobowls (GLBs) with high surface area of 1091 m2 g-1, high pore volume of 2.7 cm3 g-1 and average pore diameter of 9.8 nm are synthesized through template method. The GLBs with inherent excellent electrical conductivity and chemical inertia show the properties of well mass transfer, poison resistance and stable loading of smaller Pt particles. Therefore, the Pt/GLB catalyst shows much higher activity and stability than that of commercial Pt/C (TKK) for methanol oxidation reaction (MOR). Therein, the peak current density on Pt/GLB (2075 mA mgPt-1) for MOR is 2.87 times that of commercial Pt/C (723 mA mgPt-1); and the onset potential for the MOR on the former is negatively shifted about 160 mV compared with that on the latter. The catalytic performances of the Pt/GLB are also better than those of the Pt loading on mesoporous amorphous carbon nanobowls (Pt/BLC), indicating promotion effect of graphite on Pt catalytic performance.

  16. Kinetic limitations in surface alloy formation: PtCu/Ru(0001)

    NASA Astrophysics Data System (ADS)

    Engstfeld, A. K.; Jung, C. K.; Behm, R. J.

    2016-01-01

    We have systematically investigated the structure and structure formation of two-dimensional PtCu monolayer surface alloys on Ru(0001) as model systems for bimetallic PtCu catalysts and surfaces by scanning tunneling microscopy (STM). The surface alloys were prepared by deposition of Pt and Cu on Ru(0001) and thermal intermixing; different procedures were developed and tested to produce bimetallic surfaces with homogeneous structure, including also a homogeneous distribution of the different surface species, while at the same time intermixing with the Ru(0001) substrate should be inhibited. STM imaging revealed that for Pt concentrations below 65% surface alloys with homogeneous distribution could be formed, while at higher concentrations in the mixed phase, up to 82%, pure Pt or Pt-rich surface areas were formed as well. At Pt contents of 0.20 < xPt < 0.65, the PtxCu1 -x/Ru(0001) surface alloys were pseudomorphic, while lower Pt contents resulted in triangular dislocation line patterns. Also at xPt > 0.65 line structures were observed, but of different nature. The distribution of surface atoms in the mixed phase was evaluated from STM images with chemical contrast, the related short-range order parameters were determined. The resulting structures and their energetics, the influence of different deposition and annealing procedures and the suitability of these surfaces as model systems for studies of the surface chemistry of bimetallic PtCu surfaces are discussed.

  17. Phase investigation in Pt supported off-stoichiometric iron-platinum thin films

    SciTech Connect

    Gupta, Rekha; Medwal, Rohit; Annapoorni, S.

    2013-10-15

    Graphical abstract: - Highlights: • Low temperature FePt L1{sub 0} phase transformation using Pt/Fe{sub 3}Pt/Pt structure. • Temperature dependent FCC to FCT phase investigation using Rietveld refinement. • Estimation of soft and hard ferromagnetic contribution from demagnetization curve. • Interlayer diffusion and stoichiometry conformation of L1{sub 0} phase using RBS. • Correlation of structural, magnetic and RBS studies were successfully understood. - Abstract: The structural and magnetic phase transformation of Pt/Fe{sub 3}Pt/Pt films on Si <1 0 0> substrates prepared by DC magnetron sputtering is investigated as a function of annealing temperature. Pt diffusion driven low temperature phase transformation from A1 to L1{sub 0} phase is achieved at 300 °C, attaining a very high coercivity of 9 kOe. At 300 °C, 85% L1{sub 0} phase transformation is observed using the X-ray diffraction profile fitting. The estimated phase content is also further verified by fitting the demagnetization curve. The underlayer promotes the ordering at lower temperature while overlayer induces growth along (0 0 1) preferred orientation. Rutherford back scattering study reveals interlayer diffusion and confirms the desired stoichiometry for L1{sub 0} phase. The presence of Pt under-overlayer provides the Pt source and further facilitates the Pt diffusion, which makes it effective in promoting the phase ordering at a lower temperature.

  18. Improved oxygen reduction reaction catalyzed by Pt/Clay/Nafion nanocomposite for PEM fuel cells.

    PubMed

    Narayanamoorthy, B; Datta, K K R; Eswaramoorthy, M; Balaji, S

    2012-07-25

    A novel Pt nanoparticle (Pt NP) embedded aminoclay/Nafion (Pt/AC/N) nanocomposite catalyst film was prepared for oxygen reduction reaction by sol-gel method. The prepared nanocomposite films were surface characterized using XRD and TEM and thermal stability was studied by TGA. The prepared film has firmly bound Pt NP and could exhibit an improved electro-reduction activity compared to vulcan carbon/Nafion supported Pt NP (Pt/VC/N). Moreover, the Pt/AC/N film possessed good stability in the acidic environment. The limiting current density of the Pt/AC/N film with 35.4 μg/cm(2) of Pt loading was found to be 4.2 mA/cm(2), which is 30% higher than that of the Pt/VC/N. The maximum H2O2 intermediate formation was found to be ∼1.6% and the reaction found to follow a four electron transfer mechanism. Accelerated durability test for 2000 potential cycles showed that ca. 78% of initial limiting current was retained. The results are encouraging for possible use of the Pt/AC/N as the free-standing electrocatalyst layer for polymer electrolyte membrane fuel cells.

  19. Roles of Pt and BaO in the Sulfation of Pt/BaO/Al2O3 Lean NOx Trap Materials: Sulfur K-edge XANES and Pt LIII XAFS Studies

    SciTech Connect

    Kim, Do Heui; Kwak, Ja Hun; Szanyi, Janos; Cho, Sung June; Peden, Charles HF

    2008-02-28

    The roles of barium oxide and platinum during the sulfation of Pt-BaO/Al2O3 lean NOx trap catalysts were investigated by S K edge XANES (X-ray absorption near-edge spectroscopy) and Pt LIII XAFS (X-ray absorption fine structure). All of the samples studied (Al2O3, BaO/Al2O3, Pt/Al2O3 and Pt-BaO/Al2O3) were pre-sulfated prior to the X-ray absorption measurements. It was found that barium oxide itself has the ability to directly form barium sulfate even in the absence of Pt and gas phase oxygen. In the platinum-containing samples, the presence of Pt-O species plays an important role in the formation of sulfate species. Even if barium and aluminum sites are available for SO2 to form sulfate, for the case of the BaO(8)/Al2O3 sample, where the barium coverage is about 0.26 ML, S XANES spectroscopy results show that barium sulfates are preferentially produced over aluminum sulfates . When oxygen is absent from the gas phase, the sulfation route that involves Pt-O is eliminated after the initially present Pt-O species are completely consumed. In this case, formation of sulfates is suppressed unless barium oxide is also present. Pt LIII XAFS results show that the first coordination sphere around the Pt atoms in the Pt particles is dependent upon the redox nature of the gas mixture used during the sulfation process. Sulfation under reducing environments (e.g. SO2+H2) leads to formation of Pt-S bonds, while oxidizing conditions (e.g. SO2+O2) continue to show the presence of Pt-O bonds. In addition, the former condition was found to give rise to a higher degree of Pt sintering than the latter one. This result explains why samples sulfated under reducing conditions had lower NOx uptakes than those sulfated under oxidizing conditions. Therefore, our results provide needed information for the development of optimum practical operation conditions (e.g. sulfation or desulfation) for lean NOx trap catalysts that minimize deactivation by sulfur.

  20. Growth-induced perpendicular magnetic anisotropy and clustering in Ni xPt 1- x alloys

    NASA Astrophysics Data System (ADS)

    Vasumathi, D.; Shapiro, A. L.; Maranville, B. B.; Hellman, F.

    2001-02-01

    Polycrystalline and epitaxial (1 0 0), (1 1 0), and (1 1 1)-oriented Ni 3Pt, NiPt, and NiPt 3 films were deposited over a range of growth temperatures from 80°C to 700°C. Films grown at moderate temperatures (200-400°C) exhibit growth-induced properties similar to Co-Pt alloys: enhanced and broadened Curie temperature, perpendicular magnetic anisotropy and large coercivity. As in Co-Pt, the magnetic properties suggest a clustering of Ni into platelets on the growth surface, as the films are being grown. Unlike Co-Pt, however, NiPt films exhibit a strong orientational dependence of anisotropy and enhanced Curie temperature, possibly resulting from different types of surface reconstructions which affect the growth surface.

  1. Microwave-assisted synthesis of Pt/CNT nanocomposite electrocatalysts for PEM fuel cells.

    PubMed

    Zhang, Weimin; Chen, Jun; Swiegers, Gerhard F; Ma, Zi-Feng; Wallace, Gordon G

    2010-02-01

    Microwave-assisted heating of functionalized, single-wall carbon nanotubes (FCNTs) in ethylene glycol solution containing H(2)PtCl(6), led to the reductive deposition of Pt nanoparticles (2.5-4 nm) over the FCNTs, yielding an active catalyst for proton-exchange membrane fuel cells (PEMFCs). In single-cell testing, the Pt/FCNT composites displayed a catalytic performance that was superior to Pt nanoparticles supported by raw (unfunctionalized) CNTs (RCNTs) or by carbon black (C), prepared under identical conditions. The supporting single-wall carbon nanotubes (SWNTs), functionalized with carboxyl groups, were studied by thermogravimetric analysis (TGA), cyclic voltammetry (CV), and Raman spectroscopy. The loading level, morphology, and crystallinity of the Pt/SWNT catalysts were determined using TGA, SEM, and XRD. The electrochemically active catalytic surface area of the Pt/FCNT catalysts was 72.9 m(2)/g-Pt. PMID:20644806

  2. Fabrication of Pt nanoparticle incorporated polymer nanowires by high energy ion and electron beam irradiation

    NASA Astrophysics Data System (ADS)

    Tsukuda, Satoshi; Takahasi, Ryouta; Seki, Shu; Sugimoto, Masaki; Idesaki, Akira; Yoshikawa, Masahito; Tanaka, Shun-Ichiro

    2016-01-01

    Polyvinylpyrrolidone (PVP)-Pt nanoparticles (NPs) hybrid nanowires were fabricated by high energy ion beam irradiation to PVP thin films including H2PtCl6. Single ion hitting caused crosslinking reactions of PVP and reduction of Pt ions within local cylindrical area along an ion trajectory (ion track); therefore, the PVP nanowires including Pt NPs were formed and isolated on Si substrate after wet-development procedure. The number of Pt NPs was easily controlled by the mixed ratio of PVP and H2PtCl6. However, increasing the amount of H2PtCl6 led to decreasing the radial size and separation of the hybrid nanowires during the wet-development. Additional electron beam irradiation after ion beam improved separation of the nanowires and controlled radial sizes due to an increase in the density of crosslinking points inner the nanowires.

  3. A Kinetic and DRIFTS Study of Supported Pt Catalysts for NO Oxidation

    SciTech Connect

    Toops, Todd J; Ji, Yaying; Graham, Uschi; Jacobs, Gary; Crocker, Mark

    2006-01-01

    NO oxidation was studied over Pt/CeO2 and Pt/SiO2 catalysts. Apparent activation energies (Ea) of 31.4 and 40.6 kJ/mole were determined for Pt/CeO2 and Pt/SiO2, respectively, while reaction orders for NO and O2 were fractional and positive for both catalysts. Pre-treatment of the catalysts with SO2 caused a decrease in the Ea values, while the reaction orders were only slightly changed. In situ DRIFTS measurements indicated that high concentrations of nitrate species were formed on the surface of Pt/CeO2 during NO oxidation, while almost no surface species could be detected on Pt/SiO2. The addition of SO2 resulted in the formation of a highly stable sulfate at the expense of nitrate species and caused an irreversible loss of catalytic activity for Pt/CeO2.

  4. Photocatalytic and thermal catalytic oxidation of acetaldehyde on Pt/TiO{sub 2}

    SciTech Connect

    Falconer, J.L.; Magrini-Bair, K.A.

    1998-10-01

    Low concentrations of acetaldehyde in air (60 ppm) were oxidized over TiO{sub 2} (Degussa P25) and 0.5% Pt/TiO{sub 2} catalysts from 24 to 200 C by photocatalytic and thermal catalytic reactions. On Pt/TiO{sub 2}, the contribution by photocatalytic oxidation (PCO) is a maximum at 140 C, where conversion is 2.8 times that at 24 C. Titania without Pt deactivates rapidly during PCO at elevated temperature due to a thermal catalytic reaction that takes place in parallel with PCO, but the addition of Pt dramatically slows deactivation. Apparently, Pt supplies spillover oxygen onto the TiO{sub 2}, and the oxygen oxidizes the acetaldehyde decomposition products in a dark reaction. Deactivated TiO{sub 2} without Pt was regenerated by PCO at room temperature. Seven distinct reactions (photocatalytic and thermal catalytic) are identified on Pt/TiO{sub 2}.

  5. Evaluation of bimetallic catalyst PtAg/C as a glucose-tolerant oxygen reduction cathode

    NASA Astrophysics Data System (ADS)

    Guerra-Balcázar, M.; Cuevas-Muñiz, F. M.; Álvarez-Contreras, L.; Arriaga, L. G.; Ledesma-García, J.

    2012-01-01

    PtAg/C nanoparticles were synthesized by chemical reduction and evaluated for the oxygen reduction reaction (ORR) in the absence and presence of glucose. PtAg/C catalyst formed onion-like layered structures, which are uniformly distributed on the support. PtAg/C showed activity comparable to that of Pt/C ETEK for ORR. Further, the catalyst exhibited high selectivity for ORR in the presence of glucose. PtAg/C was evaluated as cathode in a microfluidic fuel cell operated with high concentration of glucose (100 mM) as fuel. The results demonstrated that the use of PtAg/C as cathode electrode achieved higher selectivity and better performance compared with Pt/C catalyst.

  6. New data on the mobility of Pt emitted from catalytic converters.

    PubMed

    Fliegel, Daniel; Berner, Zsolt; Eckhardt, Detlef; Stüben, Doris

    2004-05-01

    The mobility and speciation of Pt was investigated in dust deposited in highway tunnels and in gully sediments. For this, a sequential extraction technique was used in combination with a microwave digestion procedure, followed by detection of Pt with high resolution ICP-MS. A digestion procedure using HNO(3)/HCl/H(2)O(2) was developed and its efficiency tested for environmental materials. Total Pt contents ranged from approximately 100 to 300 microg/kg. The high share of chemically mobile Pt in the tunnel dust (up to about 40%) indicates that Pt is predominantly emitted in a mobile form from the converter. The absence of a mobile fraction in the gully sediment is explained by the elution of Pt by run-off. Except for the mobile and easily mobilised fractions none of the other fractions of the sequential extraction contains Pt, neither in the dust samples nor in the gully sediment.

  7. Graphene supported nano particles of Pt-Ni for CO oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Lv, Wei; Yang, Quanhong; Liu, Yuan

    2012-08-01

    In this study, a series of graphene supported Pt, Ni and Pt-Ni nano particles were successfully synthesized by a simple impregnation method. The resultant composites were characterized using SEM, XRD, HRTEM, XPS and TPR techniques and their catalytic performance for the oxidation of carbon monoxide was tested. It was shown that in the prepared metal/graphene composite, metal particles were highly dispersed on the graphene sheets (GS) with an average particle size of 1-3 nm. The results of catalytic performance tests indicate that the activity decreases in the order of Pt-Ni/GS, Pt/GS and Ni/GS. In the sample of Pt-Ni/GS, Pt-Ni alloy was formed, which contributed to the high activity of Pt-Ni/GS for CO oxidation.

  8. Perpendicular coercivity enhancement of CoPt/TiN films by nitrogen incorporation during deposition

    NASA Astrophysics Data System (ADS)

    An, Hongyu; Wang, Jian; Szivos, Janos; Harumoto, Takashi; Sannomiya, Takumi; Muraishi, Shinji; Safran, Gyorgy; Nakamura, Yoshio; Shi, Ji

    2015-11-01

    The effect of N incorporation on the structure and magnetic properties of CoPt thin films deposited on glass substrates with TiN seed layers has been investigated. During the deposition of CoPt, introducing 20% N2 into Ar atmosphere promotes the (001) texture and enhances the perpendicular coercivity of CoPt film compared with the film deposited in pure Ar and post-annealed under the same conditions. From the in situ x-ray diffraction results, it is confirmed that N incorporation expands the lattice parameter of CoPt, which favors the epitaxial growth of CoPt on TiN. During the post-annealing process, N releases from CoPt film and promotes the L10 ordering transformation of CoPt.

  9. Perpendicular coercivity enhancement of CoPt/TiN films by nitrogen incorporation during deposition

    SciTech Connect

    An, Hongyu; Harumoto, Takashi; Sannomiya, Takumi; Muraishi, Shinji; Nakamura, Yoshio; Shi, Ji; Wang, Jian; Szivos, Janos; Safran, Gyorgy

    2015-11-28

    The effect of N incorporation on the structure and magnetic properties of CoPt thin films deposited on glass substrates with TiN seed layers has been investigated. During the deposition of CoPt, introducing 20% N{sub 2} into Ar atmosphere promotes the (001) texture and enhances the perpendicular coercivity of CoPt film compared with the film deposited in pure Ar and post-annealed under the same conditions. From the in situ x-ray diffraction results, it is confirmed that N incorporation expands the lattice parameter of CoPt, which favors the epitaxial growth of CoPt on TiN. During the post-annealing process, N releases from CoPt film and promotes the L1{sub 0} ordering transformation of CoPt.

  10. Pt nanoparticles embedded on reduced graphite oxide with excellent electrocatalytic properties

    NASA Astrophysics Data System (ADS)

    Saravanan, Gengan; Mohan, Subramanian

    2016-11-01

    Economically viable electrochemical approach has been developed for the synthesis of Pt nanoparticles through electrodeposition technique on the surface of Reduced Graphite Oxide (RGO). Pt nanoparticles embedded Reduced Graphite Oxide on Glassy Carbon Electrode are employed (Pt-rGO/GCE) for electrooxidation of formic acid. Scanning Electron Microscopy (SEM) image and Transmission Electron Microscopy (TEM) image shows that reduced graphite oxide act as an excellent support to anchor the Pt nanoparticles. Cyclic voltammetry results confirmed that Pt-rGO/GCE enhanced current density as many folds than that of bare platinum electrode for electrooxidation of formic acid. X-ray diffraction (XRD) patterns for Pt-graphene composites illustrate that peaks at 69.15 and 23° for Pt (220) and graphene carbon (002) respectively. 13C NMR spectrum of the electrochemically reduced graphite oxide resonance contains only one peak at 133 ppm which retains graphitic sp2 carbon and does not contain any oxygenated carbon and the carbonyl carbons.

  11. XAFS Study of HY Zeolite Supported Pt Nanoparticle Catalysts Prepared With Different Methods

    SciTech Connect

    Li Zhongrui; Yan Wensheng; Wei Shiqiang

    2007-02-02

    The electronic and geometric effects induced by preparation methods on small platinum particles supported on high surface-area zeolite HY were studied by X-ray absorption fine structure (XAFS) spectroscopy. Pt/HY catalysts were prepared by a variety of techniques, including incipient wetness impregnation (IWI) and vapor-phase impregnation (VPI). Results of EXAFS for series of equal loadings of Pt prepared by IWI and VPI showed that the Pt clusters resulting from the VPI preparation had lower Pt--Pt coordination and higher coordination to the zeolite lattice oxygen. The electronic properties and structures of Pt/HY catalysts prepared with IWI approach can be altered by using different Pt precursor solutions.

  12. Tailoring the morphology of Pt3Cu1 nanocrystals supported on graphene nanoplates for ethanol oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, Genlei; Yang, Zhenzhen; Zhang, Wen; Hu, Hongwei; Wang, Chunzhen; Huang, Chengde; Wang, Yuxin

    2016-01-01

    In the search for alternatives to conventional Pt electrocatalysts, we synthesized a series of graphene nanoplate (GNP)-supported Pt3Cu1 nanocrystals (NCs), possessing almost the same composition but different morphologies to probe their electrochemical properties as a function of morphology for the ethanol oxidation reaction. The morphology of the Pt3Cu1 catalysts could be systematically evolved from dendritic (D-Pt3Cu1/GNPs) to wire-like (W-Pt3Cu1/GNPs) and spherical (Pt3Cu1/GNPs) by only varying pH of the reaction solution. The as-prepared Pt3Cu1 catalysts were subsequently characterized using a suite of techniques including transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS) and X-ray photoelectron spectroscopy (XPS) to verify not only their morphologies and chemical compositions but also the incorporation of Cu into the Pt lattice, as well as physical structure and integrity. Gratifyingly, the three Pt3Cu1 catalysts exhibited superior electrocatalytic properties for the ethanol oxidation compared to the monometallic Pt/GNPs and Pt/C-JM (Johnson Matthey), with the activities, durabilities and anti-poisonous abilities following the order Pt3Cu1/GNPs < W-Pt3Cu1/GNPs < D-Pt3Cu1/GNPs.In the search for alternatives to conventional Pt electrocatalysts, we synthesized a series of graphene nanoplate (GNP)-supported Pt3Cu1 nanocrystals (NCs), possessing almost the same composition but different morphologies to probe their electrochemical properties as a function of morphology for the ethanol oxidation reaction. The morphology of the Pt3Cu1 catalysts could be systematically evolved from dendritic (D-Pt3Cu1/GNPs) to wire-like (W-Pt3Cu1/GNPs) and spherical (Pt3Cu1/GNPs) by only varying pH of the reaction solution. The as-prepared Pt3Cu1 catalysts were subsequently characterized using a suite of techniques including transmission electron microscopy (TEM), selected

  13. Surface restructuring of Pt films on Au stepped surfaces: effects on catalytic behaviour.

    PubMed

    Prieto, Mauricio J; Tremiliosi-Filho, Germano

    2013-08-21

    In this paper, the reconstruction of Pt films deposited on stepped Au(hkl) surfaces belonging to the [n(111) × (110)] family of planes has been studied. Pt films were deposited using the galvanic displacement procedure of a pre-deposited Cu monolayer. We experimentally found that the Pt film deposition onto Au(hkl) surfaces is not fully epitaxial suggesting an atomic arrangement different from the underlying substrate. Additionally, we found that even though voltammetric profiles are not much different from those reported in the literature for Pt single crystals having the same crystallographic orientation, there is a reconstruction of the Pt layers on all Pt/Au(hkl) surfaces upon CO adsorption/oxidation as indicated by comparing the active areas of the Pt films before and after stripping. Additional FTIR in situ experiments on ethanol oxidation confirm that film reconstruction affects the reaction by product yield modification.

  14. Microwave-assisted synthesis of Pt/CNT nanocomposite electrocatalysts for PEM fuel cells.

    PubMed

    Zhang, Weimin; Chen, Jun; Swiegers, Gerhard F; Ma, Zi-Feng; Wallace, Gordon G

    2010-02-01

    Microwave-assisted heating of functionalized, single-wall carbon nanotubes (FCNTs) in ethylene glycol solution containing H(2)PtCl(6), led to the reductive deposition of Pt nanoparticles (2.5-4 nm) over the FCNTs, yielding an active catalyst for proton-exchange membrane fuel cells (PEMFCs). In single-cell testing, the Pt/FCNT composites displayed a catalytic performance that was superior to Pt nanoparticles supported by raw (unfunctionalized) CNTs (RCNTs) or by carbon black (C), prepared under identical conditions. The supporting single-wall carbon nanotubes (SWNTs), functionalized with carboxyl groups, were studied by thermogravimetric analysis (TGA), cyclic voltammetry (CV), and Raman spectroscopy. The loading level, morphology, and crystallinity of the Pt/SWNT catalysts were determined using TGA, SEM, and XRD. The electrochemically active catalytic surface area of the Pt/FCNT catalysts was 72.9 m(2)/g-Pt.

  15. Tip-bias-induced domain evolution in PMN-PT transparent ceramics via piezoresponse force microscopy

    NASA Astrophysics Data System (ADS)

    Zhao, K. Y.; Zhao, W.; Zeng, H. R.; Yu, H. Z.; Ruan, W.; Xu, K. Q.; Li, G. R.

    2015-05-01

    Piezoresponse force microscopy (PFM) was employed to investigate ferroelectric domain structures and their dynamic behavior of lead magnesium niobate-lead titanate [Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT)] transparent ceramics under an tip-bias-induced electric field. A remarkable effect of fluctuation of PT content on the domain configurations and domain dynamic response in PMN-PT transparent ferroelectric ceramics were found by PFM. Comparing with PMN-10%PT and PMN-20%PT, the reversed polarization of macrodomain area in PMN-35%PT and PMN-25%PT exhibits a relatively higher response behavior and better polarization retention performance under the PFM tip-bias-induced electric field, which correspond to their unique macroscopic electro-optic properties.

  16. Adsorption and desorption of NO and CO on a Pt(111)Ge surface alloy

    NASA Astrophysics Data System (ADS)

    Fukutani, K.; Magkoev, T. T.; Murata, Y.; Terakura, K.

    1996-08-01

    Adsorption of NO and CO on Pt(111) alloyed with a few per cent of Ge is investigated by reflection—absorption infrared spectroscopy and thermal desorption spectroscopy. Both molecules exclusively occupy the on-top site in contrast to bridge and on-top adsorption on clean Pt(111). The adsorption energy of NO is dramatically reduced compared with that on clean Pt(111). Photodesorption of CO observed on the clean Pt(111) is noticeably suppressed on the Pt(111)Ge surface alloy, while NO desorption is induced by photon irradiation. The rotational and translational temperatures of photodesorbed No are similar to those on clean Pt(111). The change in chemical properties of Pt(111) for molecular adsorption is discussed in terms of d-band filling of the substrate.

  17. Synthesis, characterization and antibacterial activity of polyaniline/Pt-Pd nanocomposite.

    PubMed

    Boomi, Pandi; Prabu, Halliah Gurumallesh; Mathiyarasu, Jayaraman

    2014-01-24

    Pt colloid and Pt-Pd colloid, pristine polyaniline, polyaniline/Pt nanocomposite and polyaniline/Pt-Pd nanocomposite were synthesized by simple chemical method. They were characterized by UV-Vis, FT-IR, XRD, TGA, SEM, HR-SEM and HR-TEM with EDAX techniques. The results proved that there is a strong interaction between metal nanoparticles (Pt-Pd) and polyaniline chains. This interaction creates changes in the backbone chain of polyaniline/Pt-Pd nanocomposite when compared to pristine polyaniline. The synthesized materials were evaluated for antibacterial activity, minimal inhibitory concentration and minimal bactericidal concentration. The results indicated that the nanocomposites exhibited improved antibacterial activity when compared to pristine polyaniline and individual metal colloids. This is the first report on the chemical synthesis of polyaniline/Pt-Pd nanocomposite, which exhibits antibacterial activity at micro molar concentration levels.

  18. Thermodynamic modeling of Pt-Al and Pd-Al

    NASA Astrophysics Data System (ADS)

    Carr, Derek

    2011-03-01

    Pure platinum and pure palladium are too soft for typical jewelry applications. Adding small amounts of other metals can significantly increase their performance. However, international hallmarking standards require the alloys to be 95% pure by weight. How does one achieve significant improvements in performance adding only small amounts (5 wt-%) of other metals? Significant improvements are possible even with small additions if precipitate hardening can be induced. Using a combination of first-principles, cluster expansion, and Monte Carlo modeling, we have identified new Pt-rich/Pd-rich phases in Pt-Al and Pd-Al that should be useful in precipitate hardening. Thermodynamical modeling indicates that the phases are experimentally feasible (not kinetically inhibited).

  19. Synthesis and magnetic properties of CoPt nanoparticles

    NASA Astrophysics Data System (ADS)

    Sun, Xiangcheng; Jia, Z. Y.; Huang, Y. H.; Harrell, J. W.; Nikles, D. E.; Sun, K.; Wang, L. M.

    2004-06-01

    High magnetocrystalline anisotropy CoPt particles with an average size of 8 nm were synthesized by the superhydride reduction of CoCl2 and Pt(acac)2 at a high temperature. As-made particles showed a disordered face-centered cubic lattice and were superparamagnetic. Upon heat treatment at temperatures above 600 °C, the particles transformed to the L10 phase, as indicated by the appearance of the superlattice peaks in the x-ray diffraction and high magnetocrystalline anisotropy. The temperature dependence of the coercivity of nanoparticles annealed at 650 °C was measured from 10 to 300 K and analyzed using a Sharrock formula. After annealing at 650 °C, the anisotropy of the nanoparticles was K˜1.7×107 erg/cm3.

  20. Ru, Re, Os, Pt and Au in iron meteorites

    NASA Technical Reports Server (NTRS)

    Pernicka, Ernst; Wasson, John T.

    1987-01-01

    Neutron activation analysis is used to ascertain the proportions of Ru, Re, Os, and Pt refractory siderophiles, and moderately volatile Au, in 41 iron meteorites. The Ni-element trends defined for groups IID and IIIF support a magmatic origin; in addition, the results obtained for groups IAB and IIICD contrast with trends observed in magmatic groups, where the Ru and Pt slopes are substantially less steep. In group IIIAB, at Ni concentrations above 90 mg/g, the steep decrease of Re, Os, and Ir with Ni levels off, and the interelement ratios exhibit considerable scatter. These observations may be explained in terms of the contamination of the residual molten core with small amounts of late primitive melts draining from the mantle.

  1. PT-symmetric phase in kagome-based photonic lattices.

    PubMed

    Chern, Gia-Wei; Saxena, Avadh

    2015-12-15

    The kagome lattice is a two-dimensional network of corner-sharing triangles and is often associated with geometrical frustration. In particular, the frustrated coupling between waveguide modes in a kagome array leads to a dispersionless flat band consisting of spatially localized modes. Here we propose a complex photonic lattice by placing PT-symmetric dimers at the kagome lattice points. Each dimer corresponds to a pair of strongly coupled waveguides. With balanced arrangement of gain and loss on individual dimers, the system exhibits a PT-symmetric phase for finite gain/loss parameter up to a critical value. The beam evolution in this complex kagome waveguide array exhibits a novel oscillatory rotation of optical power along the propagation distance. Long-lived local chiral structures originating from the nearly flat bands of the kagome structure are observed when the lattice is subject to a narrow beam excitation.

  2. Facile synthesis of complex shaped Pt-Cu alloy architectures

    NASA Astrophysics Data System (ADS)

    Nosheen, Farhat; Ni, Bing; Xu, Xiaobin; Yang, Haozhou; Zhang, Zhicheng; Wang, Xun

    2016-07-01

    Several intricate Pt-Cu alloy architectures have been synthesized including hexapod backbones with stretchers and caved octahedron like hexapods, as well as some other intermediates with complex structures. The mechanistic study indicates that the shape is realized via a competitive effect between etching and growth induced by different chemicals.Several intricate Pt-Cu alloy architectures have been synthesized including hexapod backbones with stretchers and caved octahedron like hexapods, as well as some other intermediates with complex structures. The mechanistic study indicates that the shape is realized via a competitive effect between etching and growth induced by different chemicals. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03511f

  3. Adsorption and Coupling of 4-aminophenol on Pt(111) surfaces

    PubMed Central

    Otero-Irurueta, G.; Martínez, J. I.; Bueno, R.A.; Palomares, F. J.; Salavagione, H. J.; Singh, M. K.; Méndez, J.; Ellis, G. J.; López, M. F.; Martín-Gago, J. A.

    2016-01-01

    We have deposited 4-aminophenol on Pt(111) surfaces in ultra-high vacuum and studied the strength of its adsorption through a combination of STM, LEED, XPS and ab initio calculations. Although an ordered (2√3×2√3)R30° phase appears, we have observed that molecule-substrate interaction dominates the adsorption geometry and properties of the system. At RT the high catalytic activity of Pt induces aminophenol to lose the H atom from the hydroxyl group, and a proportion of the molecules lose the complete hydroxyl group. After annealing above 420K, all deposited aminophenol molecules have lost the OH moiety and some hydrogen atoms from the amino groups. At this temperature, short single-molecule oligomer chains can be observed. These chains are the product of a new reaction that proceeds via the coupling of radical species that is favoured by surface diffusion. PMID:27279673

  4. PT Symmetry, Conformal Symmetry, and the Metrication of Electromagnetism

    NASA Astrophysics Data System (ADS)

    Mannheim, Philip D.

    2016-05-01

    We present some interesting connections between PT symmetry and conformal symmetry. We use them to develop a metricated theory of electromagnetism in which the electromagnetic field is present in the geometric connection. However, unlike Weyl who first advanced this possibility, we do not take the connection to be real but to instead be PT symmetric, with it being iA_{μ } rather than A_{μ } itself that then appears in the connection. With this modification the standard minimal coupling of electromagnetism to fermions is obtained. Through the use of torsion we obtain a metricated theory of electromagnetism that treats its electric and magnetic sectors symmetrically, with a conformal invariant theory of gravity being found to emerge. An extension to the non-Abelian case is provided.

  5. In-plane anisotropic effect of magnetoelectric coupled PMN-PT/FePt multiferroic heterostructure: Static and microwave properties

    NASA Astrophysics Data System (ADS)

    Vargas, Jose M.; Gómez, Javier

    2014-10-01

    The effects of the electric and magnetic field variation on multiferroic heterostructure were studied in this work. Thin films of polycrystalline Fe50Pt50 (FePt) were grown by dc-sputtering on top of the commercial slabs of lead magnesium niobate-lead titanate (PMN-PT). The sample was a (011)-cut single crystal and had one side polished. In this condition, the PMN-PT/FePt operates in the L-T (longitudinal magnetized-transverse polarized) mode. A FePt thin film of 20 nm was used in this study to avoid the characteristic broad microwave absorption line associated with these films above thicknesses of 40 nm. For the in-plane easy magnetization axis (01-1), a microwave magnetoelectric (ME) coupling of 28 Oe cm kV -1 was estimated, whereas a value of 42 Oe cm kV -1 was obtained through the hard magnetization axis (100). Insight into the effects of the in-plane strain anisotropy on the ME coupling is obtained from the dc-magnetization loops. It was observed that the trend was opposite along the easy and hard magnetic directions. In particular, along the easy-magnetic axis (01-1), a square and narrow loop with a factor of Mr/MS of 0.96 was measured at 10 kV/cm. Along the hard-magnetic axis, a factor of 0.16 at 10 kV/cm was obtained. Using electric tuning via microwave absorption at X-band (9.78 GHz), we observe completely different trends along the easy and hard magnetic directions; Multiple absorption lines along the latter axis compared to a single and narrower absorption line along the former. In spite of its intrinsic complexity, we propose a model which gives good agreement both for static and microwave properties. These observations are of fundamental interest for future ME microwave components, such as filters, phase-shifters, and resonators.

  6. DFT analysis of CO behaviour on Pt(111)

    NASA Astrophysics Data System (ADS)

    Sivaramakrishna, J.

    2010-10-01

    Adsorption of reactants on the surface of a catalyst is an important elementary step in surface catalyzed reactions. Adsorption on transition metal catalyst involves complex interactions between reactant molecular orbitals and metal d-bands. We study the adsorption of CO on Pt(111). At low surface coverage of CO on Pt(111), experiments show an atop site preference while density functional theory (DFT) predicts an fcc hollow site. Further, vibrational analysis predicts a combination of bridge and atop sites. In light of these contrasting reports, we undertake a systematic study of the adsorption process. We perform plane wave pseudo potential based DFT calculations within the Generalized Gradient Approximation (GGA). The system is relaxed from an unbiased initial configuration. We find that the projected density of states (PDOS) and Löwdin charge population analysis provide significant insights into the choice of adsorption site of CO on Pt(111). We validate our simulation setup and parameter set by comparing the bulk modulus (238.2 GPa) and the lattice parameter (3.99 Å) for fcc Platinum using Murnaghan equation of state with experiments (230 GPa and 3.92 Å). From a detailed study of orbital resolved bonding patterns, we attribute the discrepancy in the preferred adsorption site between DFT calculations and experiments to two competing effects: (a) destabilization of atop preferred CO due to back donation of electron density to C by Pt (b) destabilization of fcc preferred CO due to the shift in density distribution peak to higher energies. An interesting hint is the non-involvement of certain d-orbitals of metal when CO is fcc bonded. The effect of initial configuration and the exchange-correlation functional on site preference of CO is explored and discussed in detail.

  7. XMCD studies of antiferromagnetically coupled Co/Pt Multilayers

    NASA Astrophysics Data System (ADS)

    Baruth, A.; Keavney, D. J.

    2005-03-01

    Previous results on multilayered structures of [Pt(5å)/Co(4å)]3/NiO(tNiOå) /[Co(4å)/Pt(5å)]3 show exchange coupling between the two Co/Pt layers as well as exchange bias between the Co and NiO below 200K [1]. The exchange coupling is explained through the canting of AFM NiO spins which were theoretically predicted [2] and seen using X-ray Magnetic Circular Dichroism [3]. Using XMCD we have studied the element specific magnetization of Co and NiO as functions of field and temperature (above and below the blocking temperature, 200K) in two samples with 11å and 12å NiO. At these thicknesses of NiO, both sets of Co/Pt multilayers couple antiferromagnetically, but the coupling strength for the 12å NiO sample is approximately half that of the 11å. Element specific hysteresis loops showed identical behavior for both Co and Ni implying that the AFM NiO spins at the interface cant in the direction of the Co magnetization. Photoemission electron microscope images on a virgin sample at room temperature revealed the exact correlation between FM domains in the Co and NiO layers in the strongest antiferromagnetically coupled sample. We plan to measure the AFM domain structure of NiO using Magnetic Linear Dichroism. [1] Phys. Rev. Lett. 91, 037207 (2003) [2] Phys. Rev. Lett. 92, 219703 (2004) [3] Z.Y. Liu et. al. Phys Rev B (accepted) Funded by NSF MRSEC

  8. Synthesis of Pt/PEI-MWCNT composite materials on polyethyleneimine-functionalized MWNTs as supports

    SciTech Connect

    Yi, Sung-Chul; Jung, Chi Young; Kim, Wha Jung

    2011-12-15

    Graphical abstract: Schematic diagram for (a) the preparation of Pt/MWCNT functionalized with PEI and (b) TEM of Pt/PEI-MWCNT. Highlights: Black-Right-Pointing-Pointer We prepared Pt/PEI/MWCNT where MWCNT was first functionalized by PEI (polyethyleneimine) followed by Pt deposit onto it. Black-Right-Pointing-Pointer PEI functionalization provided high density homogeneous functional groups on MWCNT's sidewall. Black-Right-Pointing-Pointer Cationic PEI leads to homogeneous dispersion in solutions such as water and organic solvents. Black-Right-Pointing-Pointer Pt/PEI/MWCNT catalyst exhibits excellent electrocatalytic activity compared to that of Pt/MWCNT catalyst obtained with polyvinylpyrrolidine (PVP). -- Abstract: Composite materials with highly dispersed platinum (Pt) nanoparticles on multiwalled carbon nanotubes (MWCNTs), functionalized with polyethyleneimine (PEI) by a noncovalent method were prepared. The PEI-functionalization provided high density homogeneous functional groups on the MWCNTs' sidewalls for binding Pt nanoparticles. Cationic PEI leads to homogeneous dispersion in solutions such as water and organic solvents. The effects of a reducing agent on the Pt nanoparticles that form on the surfaces of the MWCNT were studied by varying the molar ratio of NaOH to H{sub 2}PtCl{sub 6}. These composite materials were characterized with transmission electron micrograph (TEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The Pt/PEI-MWCNT catalyst exhibits excellent electrocatalytic activity and compared with Pt/PVP-MWCNT catalysts obtained with polyvinylpyrrolidone (PVP). Finally, the cyclic voltammogram of methanol electrooxidation for Pt/PEI-MWCNT shows better tolerance to CO and methanol oxidation to CO{sub 2} than of Pt/PVP-MWCNT.

  9. Chiral selectivity of amino acid adsorption on chiral surfaces—The case of alanine on Pt

    SciTech Connect

    Franke, J.-H.; Kosov, D. S.

    2015-02-07

    We study the binding pattern of the amino acid alanine on the naturally chiral Pt surfaces Pt(531), Pt(321), and Pt(643). These surfaces are all vicinal to the (111) direction but have different local environments of their kink sites and are thus a model for realistic roughened Pt surfaces. Alanine has only a single methyl group attached to its chiral center, which makes the number of possible binding conformations computationally tractable. Additionally, only the amine and carboxyl group are expected to interact strongly with the Pt substrate. On Pt(531), we study the molecule in its pristine as well as its deprotonated form and find that the deprotonated one is more stable by 0.47 eV. Therefore, we study the molecule in its deprotonated form on Pt(321) and Pt(643). As expected, the oxygen and nitrogen atoms of the deprotonated molecule provide a local binding “tripod” and the most stable adsorption configurations optimize the interaction of this “tripod” with undercoordinated surface atoms. However, the interaction of the methyl group plays an important role: it induces significant chiral selectivity of about 60 meV on all surfaces. Hereby, the L-enantiomer adsorbs preferentially to the Pt(321){sup S} and Pt(643){sup S} surfaces, while the D-enantiomer is more stable on Pt(531){sup S}. The binding energies increase with increasing surface density of kink sites, i.e., they are largest for Pt(531){sup S} and smallest for Pt(643){sup S}.

  10. Dilute NiPt alloy interactions with Si

    NASA Astrophysics Data System (ADS)

    Corni, F.; Grignaffini Gregorio, B.; Ottaviani, G.; Queirolo, G.; Follegot, J. P.

    1993-11-01

    The reaction between a dilute Ni 95Pt 5 alloy and <111>Si has been investigated as a function of the annealing temperature and time, and the film thickness. Contrary to the concentrate alloys the first phase formed is Ni 2Si and the growth kinetics in the initial steps are similar to the case of pure Ni. Pt segregates in the alloy and its presence slows down the silicide growth rate suggesting that a new mechanism, namely the release of Ni from the alloy, is competing with the diffusion process in the silicide. In all the cases here considered NiSi starts to form only when all the Ni is reacted, indicating that the Pt never reaches high enough concentrations to inhibit the Ni 2Si growth. The further evolution of the system is similar to the ones reported for bilayers and non-dilute alloys. The I-V characteristics measured after annealing give a barrier height of 0.70 ± 0.01 eV.

  11. Non-local magnetoresistance in YIG/Pt nanostructures

    SciTech Connect

    Goennenwein, Sebastian T. B. Pernpeintner, Matthias; Gross, Rudolf; Huebl, Hans; Schlitz, Richard; Ganzhorn, Kathrin; Althammer, Matthias

    2015-10-26

    We study the local and non-local magnetoresistance of thin Pt strips deposited onto yttrium iron garnet. The local magnetoresistive response, inferred from the voltage drop measured along one given Pt strip upon current-biasing it, shows the characteristic magnetization orientation dependence of the spin Hall magnetoresistance. We simultaneously also record the non-local voltage appearing along a second, electrically isolated, Pt strip, separated from the current carrying one by a gap of a few 100 nm. The corresponding non-local magnetoresistance exhibits the symmetry expected for a magnon spin accumulation-driven process, confirming the results recently put forward by Cornelissen et al. [“Long-distance transport of magnon spin information in a magnetic insulator at room temperature,” Nat. Phys. (published online 14 September 2015)]. Our magnetotransport data, taken at a series of different temperatures as a function of magnetic field orientation, rotating the externally applied field in three mutually orthogonal planes, show that the mechanisms behind the spin Hall and the non-local magnetoresistance are qualitatively different. In particular, the non-local magnetoresistance vanishes at liquid Helium temperatures, while the spin Hall magnetoresistance prevails.

  12. Transforming AdaPT to Ada9x

    NASA Technical Reports Server (NTRS)

    Goldsack, Stephen J.; Holzbach-Valero, A. A.; Volz, Richard A.; Waldrop, Raymond S.

    1993-01-01

    How the concepts of AdaPT can be transformed into programs using the object oriented features proposed in the preliminary mapping for Ada9x are described. Emphasizing, as they do, the importance of data types as units of program, these features match well with the development of partitions as translations into Abstract Data Types which was exploited in the Ada83 translation covered in report R3. By providing a form of polymorphic type, the Ada83 version also gives support for the conformant partition idea which could be achieved in Ada83 only by using UNCHECKED CONVERSIONS. It is assumed that the reader understands AdaPT itself, but the translation into Ada83 is briefly reviewed, by applying it to a small example. This is then used to show how the same translation would be achieved in the 9x version. It is important to appreciate that the distribution features which are proposed in current mapping are not used or discussed in any detail, as those are not well matched to the AdaPT approach. Critical evaluation and comparison of these approaches is given in a separate report.

  13. Deactivation Mechanisms of Pt/Pd-based Diesel Oxidation Catalysts

    SciTech Connect

    Wiebenga, Michelle H.; Kim, Chang H.; Schmieg, Steven J.; Oh, Se H.; Brown, David B.; Kim, Do Heui; Lee, Jong H.; Peden, Charles HF

    2012-04-30

    Currently precious metal-based diesel oxidation catalysts (DOC) containing platinum (Pt) and palladium (Pd) are most commonly used for the oxidation of hydrocarbon and NO in diesel exhaust hydrocarbon oxidation. The present work has been carried out to investigate the deactivation mechanisms of the DOC from its real-world vehicle operation by coupling its catalytic activity measurements with surface characterization including x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. A production Pt-Pd DOC was obtained after being aged on a vehicle driven for 135,000 miles in order to study its deactivation behavior. The performance of the vehicle-aged part was correlated with that of the simulated hydrothermal lab aged sample assuming that Pt-Pd sintering plays a major role in irreversible catalyst deactivation. In addition to the hydrothermal sintering, the deterioration of hydrocarbon and NO oxidation performance was caused by surface poisoning. The role of the various aging factors in determining long-term performance in mobile applications will be discussed.

  14. Hydrogen reduction of Ga-Pt loaded HZSM-5

    SciTech Connect

    Price, G.L. )

    1991-08-01

    Catalysts containing 1.2, 3.1, 6.1, and 10.0 g Ga as Ga(NO{sub 3}) per 100 g HZSM-5 prepared by incipient wetness impregnation have been subjected to hydrogen reduction at 848 K in a microbalance and the reduction rates and capacities compared with identical materials further impregnated with 0.5 g Pt as Pt(NH{sub 3}){sub 4} (NO{sub 3}){sub 2} per 100 g HZSM-5. Weight loss stoichiometry suggests that supported Ga(NO{sub 3}){sub 3} is converted to Ga{sub 2}O{sub 3} upon calcination in 3% O{sub 2} in He while weight loss stoichiometry upon hydrogen reduction at 848 K in all cases can be correlated (within certain bounds which are discussed) as Ga{sub 2}O{sub 3} + 2H{sup +}Z{sup {minus}} {yields} 2Ga{sup +}Z{sup {minus}} + 3H{sub 2}O, where Z{sup {minus}} is the anionic zeolitic framework. The addition of Pt does not increase the total amount of Ga{sub 2}O{sub 3} which can be reduced even in cases where the cation capacity of the zeolite limits the reduction reaction but does increase the maximum rate of Ga{sub 2}O{sub 3} reduction.

  15. Adsorption, Desorption, and Clustering H20 on Pt (111)

    SciTech Connect

    Daschbach, John L.; Peden, Brandon M.; Smith, R. Scott; Kay, Bruce D.

    2004-01-15

    The adsorption, desorption, and clustering behavior of H20 on Pt(111) has been investigated by specular He scattering. The data show that water adsorbed on a clean Pt(111) surface undergoes a transition from a random to a clustered structure near 60 K. The initial helium scattering cross sections as a function of temperature are found to be insensitive to H20 flux over a range of 0.005 ML/s to 0.55 ML/s indicating the clustering process is more complex than simple surface diffusion. The coarsening process of an initially random distribution of water deposited at 25 K is found to occur over a broad temperature range, 60 K< T <140 K, during thermal annealing. The desorption kinetics for submonolayer water are determined to be zero-order for surface coverages greater than 0.05 ML and temperatures between 150 K and 174 K. The zero-order desorption kinetics are consistent with a two-dimensional two-phase coexistence between H2O condensed phase and a 2-gas phase on the Pt surface

  16. Heterobimetallic coordination polymers based on the [Pt(SCN)4]2- and [Pt(SeCN)4]2- building blocks.

    PubMed

    Kobayashi, Masayuki; Savard, Didier; Geisheimer, Andrew R; Sakai, Ken; Leznoff, Daniel B

    2013-05-01

    New complexes and the first coordination polymers containing [Pt(SCN)4](2-) of the type [M(L)x][Pt(SCN)4] (where L = 2,2'-bipyridine (bipy), x = 2, M = Co(II), Ni(II), Cu(II); L = ethylenediamine (en), x = 2, M = Ni(II), Cu(II); L = N,N,N',N'-tetramethylethylenediamine (tmeda), x = 1, M = Cu(II); L = 2,2';6',2″-terpyridine (terpy), x = 1, M = Mn(II), Co(II); L = 1,10-phenanthroline (phen), x = 2, M = Pb(II)) were prepared by reacting the appropriate metal-ligand cations with K2[Pt(SCN)4] and structurally characterized. [M(bipy)2Pt(SCN)4]2·2MeOH (M = Co (1), Cu (4)) consist of supramolecular tetranuclear distorted squares containing two [M(bipy)2](2+) and two [Pt(SCN)4](2+) units. [Cu(bipy)2(NCS)]2[Pt(SCN)4] (6) is a double salt of the [Pt(SCN)4](2-) anion and two [Cu(bipy)(NCS)](+) cations. [Cu(en)2Pt(SCN)4] (7, 8) are 1-D coordination polymers that are coordinated in either cis or trans fashion at the [Pt(SCN)4](2-) unit, for 7 and 8, respectively. Complexes [Cu(en)2Pt(SeCN)4] (9) and [Ni(en)2Pt(SCN)4] (10) are similar to 8 and 7, respectively, but complex 9 (prepared using ((n)Bu4N)2[Pt(SeCN)4]) also presents intermolecular Se-Se interactions which resulted in an increased dimensionality. Compounds [M(terpy)Pt(SCN)4] (M = Mn (11), Co (13)) involve 2-D sheets of [M(terpy)](2+) and [Pt(SCN)4](2-) units, whereas [Mn(terpy)2][Pt(SCN)4] (12) is a double salt of one [Mn(terpy)2](2+) unit and one [Pt(SCN)4](2-). [Cu(tmeda)Pt(SCN)4] (14) contains a five-coordinate Cu(2+) metal center coordinated to one tmeda ligand and three different [Pt(SCN)4](2-) units, resulting in 2-D sheets. [Pb(phen)2Pt(SCN)4] (15) contains an 8-coordinate Pb(2+) metal center coordinated to two phen ligands and four [Pt(SCN)4](2-), generating a 3-D network in the solid state. Structural correlations were established between the ancillary ligand, the choice of metal, the structure of the [Pt(SCN)4](2-) building block, and the resulting dimensionality of the coordination polymers. PMID:23574270

  17. Halogen poisoning effect of Pt-TiO2 for formaldehyde catalytic oxidation performance at room temperature

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaofeng; Cheng, Bei; Yu, Jiaguo; Ho, Wingkei

    2016-02-01

    Catalytic decomposition of formaldehyde (HCHO) at room temperature is an important method for HCHO removal. Pt-based catalysts are the optimal catalyst for HCHO decomposition at room temperature. However, the stability of this catalyst remains unexplored. In this study, Pt-TiO2 (Pt-P25) catalysts with and without adsorbed halogen ions (including F-, Cl-, Br-, and I-) were prepared through impregnation and ion modification. Pt-TiO2 samples with adsorbed halogen ions exhibited reduced catalytic activity for formaldehyde decomposition at room temperature compared with the Pt-TiO2 sample; the catalytic activity followed the order of F-Pt-P25, Cl-Pt-P25, Br-Pt-P25, and I-Pt-P25. Characterization results (including XRD, TEM, HRTEM, BET, XPS, and metal dispersion) showed that the adsorbed halogen ions can poison Pt nanoparticles (NPs), thereby reducing the HCHO oxidation activity of Pt-TiO2. The poison mechanism is due to the strong adsorption of halogen ions on the surface of Pt NPs. The adsorbed ions form coordination bonds with surface Pt atoms by transferring surplus electrons into the unoccupied 5d orbit of the Pt atom, thereby inhibiting oxygen adsorption and activation of the Pt NP surface. Moreover, deactivation rate increases with increasing diameter of halogen ions. This study provides new insights into the fabrication of high-performance Pt-based catalysts for indoor air purification.

  18. Large and robust resistive switching in co-sputtered Pt-(NiO-Al2O3)-Pt devices

    NASA Astrophysics Data System (ADS)

    Rebello, A.; Adeyeye, A. O.

    2016-02-01

    We have systematically investigated the resistive switching and electroresistance behavior in Pt-[NiO-Al2O3]-Pt (PNAP) capacitor-like structures. The PNAP devices show a large ON-OFF ratio (˜107), which is strongly dependent on the rate of the voltage sweep. Interestingly, the devices exhibit a robust electroresistance behavior in the high resistance OFF state and show an intriguing change of sign of rectification with increasing end voltage. Our direct measurement of the surface temperature of the sample during resistive switching indicates that RESET process is assisted by Joule heating effects. The results are explained on the basis of plausible interplay between Schottky barrier modification due to the trapped charge carriers at the metal-oxide interface and percolation effects of conducting nanofilaments.

  19. Ferroelectricity-modulated resistive switching in Pt/Si:HfO2/HfO2-x /Pt memory

    NASA Astrophysics Data System (ADS)

    Ran, Jiang; Xianghao, Du; Zuyin, Han

    2016-08-01

    It is investigated for the effect of a ferroelectric Si:HfO2 thin film on the resistive switching in a stacked Pt/Si:HfO2/highly-oxygen-deficient HfO2-x /Pt structure. Improved resistance performance was observed. It was concluded that the observed resistive switching behavior was related to the modulation of the width and height of a depletion barrier in the HfO2-x layer, which was caused by the Si:HfO2 ferroelectric polarization field effect. Reliable switching reproducibility and long data retention were observed in these memory cells, suggesting their great potential in non-volatile memories applications with full compatibility and simplicity. Project supported by the National Natural Science Foundation of China (No. 11374182), the Natural Science Foundation of Shandong Province (No. ZR2012FQ012), and the Jinan Independent Innovation Projects of Universities (No. 201303019).

  20. FT-Raman spectroscopy of structural isomers of Pt(II) complex PtCl2(PEt3)2

    NASA Astrophysics Data System (ADS)

    Bhatt, Himal; Deo, M. N.; Vishwakarma, S. R.; Bajaj, Naini; Sharma, Surinder M.

    2015-06-01

    We report here the detailed spectroscopic aspects of the structural isomers of Pt(II) complex PtCl2(P(C2H5)3)2 using FT-Raman spectroscopy. A comparison of the structural contraction instigated by lowering the temperature up to liquid nitrogen temperature in the cis and trans isomers has been presented. The lattice region lying in the far infrared region upto 50cm-1 has been analyzed in detail to probe the structural modifications. It was found that the ambient temperature lower symmetry structure of the cis isomer is preserved at low temperatures. The trans isomer, stabilizing in a high symmetry structure at room temperature, transforms to a low symmetry structure on lowering the temperature, which can be attributed to a loss of inversion symmetry of the trans isomer.

  1. Effect of NiO crystallinity on forming characteristics in Pt/NiO/Pt cells as resistive switching memories

    NASA Astrophysics Data System (ADS)

    Nishi, Yusuke; Kimoto, Tsunenobu

    2016-09-01

    Resistive switching (RS) in metal/oxide/metal stack structures plays a key role in resistive RAM. The formation and rupture of conductive filaments have been widely accepted as an origin of RS mechanism especially in binary transition metal oxides. Forming exhibits some analogies with a dielectric breakdown of SiO2 thin films. In this study, Time-Dependent Forming (TDF) characteristics of Pt/NiO/Pt stack structures have been investigated. The results revealed that the formation of conductive filaments at the forming process by applying constant voltage followed a weakest-link theory and that the weakest spots were almost randomly distributed in NiO thin films according to the Poisson statistics. Furthermore, the distribution of TDF characteristics depends on NiO crystallinity. A small variation of initial resistance tends to result in a large variation of time to forming and vice versa.

  2. CO-Induced Embedding of Pt Adatoms in a Partially Reduced FeOx Film on Pt(111)

    SciTech Connect

    Merte, L. R.; Knudsen, Jan; Eichhorn, Falk M.; Porsgaard, Soeren; Zeuthen, Helene; Grabow, Lars C.; Laegsgaard, E.; Bluhm, Hendrik; Salmeron, Miquel B.; Mavrikakis, Manos; Besenbacher, Fleming

    2011-07-20

    The reduction of a single-layer FeOfilmgrown on Pt(111) by CO at elevated pressures and temperatures has been studied through an interplay of scanning tunneling microscopy, ambient-pressure X-ray photoelectron spectroscopy, and density functional theory calculations. Exposure of the FeO thin film to CO at pressures between 1 and 30 Torr and temperatures between 500 and 530 K leads to formation of a honeycomb-structured Fe3O2 film with hollow sites occupied by single Pt atoms extracted from the substrate surface. The formation of these adatoms is driven by an increase in CO adsorption energy. In addition, the structure incorporates undercoordinated Fe centers, which are proposed to have substantial effects on the catalytic properties of the surface.

  3. Modeling of diffusion mechanism of conductive channel oxidation in a Pt/NiO/Pt memory switching structure

    NASA Astrophysics Data System (ADS)

    Sysun, V. I.; Bute, I. V.; Boriskov, P. P.

    2016-09-01

    The transition process from the low resistance state into the high resistance state in a Pt/NiO/Pt memory switching structure has been studied by numerical modeling. Detailed analysis shows, that thermally induced diffusion oxidation by nickel vacancies is the key factor for distortion of the channel metallic conductivity. Spatial dynamics of the process of oxidation defines channel narrowing mainly in its central part, and also sets the critical current through the structure sufficient for final rupture of the channel and the transition to high resistance state. The increase in critical current above the limit even by 10% reduces the switching time by an order of magnitude, which is in agreement with experiments. The developed radial diffusion model of conductive channel (or filaments) oxidation may be suitable for the analysis of switching effect a number of other ReRAM oxide structures.

  4. Efficient C–C bond splitting on Pt monolayer and sub-monolayer catalysts during ethanol electro-oxidation: Pt layer strain and morphology effects

    SciTech Connect

    Loukrakpam, Rameshwori; Yuan, Qiuyi; Petkov, Valeri; Gan, Lin; Rudi, Stefan; Yang, Ruizhi; Huang, Yunhui; Brankovic, Stanko R.; Strasser, Peter

    2014-07-23

    Efficient catalytic C–C bond splitting coupled with complete 12-electron oxidation of the ethanol molecule to CO2 is reported on nanoscale electrocatalysts comprised of a Pt monolayer (ML) and sub-monolayer (sML) deposited on Au nanoparticles (Au@Pt ML/sML). The Au@Pt electrocatalysts were synthesized using surface limited redox replacement (SLRR) of an underpotentially deposited (UPD) Cu monolayer in an electrochemical cell reactor. Au@Pt ML showed improved catalytic activity for ethanol oxidation reaction (EOR) and, unlike their Pt bulk and Pt sML counterparts, was able to generate CO2 at very low electrode potentials owing to efficient C–C bond splitting. To explain this, we explore the hypothesis that competing strain effects due to the Pt layer coverage/morphology (compressive) and the Pt–Au lattice mismatch (tensile) control surface chemisorption and overall activity. Control experiments on well-defined model Pt monolayer systems are carried out involving a wide array of methods such as high-energy X-ray diffraction, pair-distribution function (PDF) analysis, in situ electrochemical FTIR spectroscopy, and in situ scanning tunneling microscopy. The vibrational fingerprints of adsorbed CO provide compelling evidence on the relation between surface bond strength, layer strain and morphology, and catalytic activity.

  5. Enhancement of ethanol oxidation at Pt and PtRu nanoparticles dispersed over hybrid zirconia-rhodium supports

    NASA Astrophysics Data System (ADS)

    Rutkowska, Iwona A.; Koster, Margaretta D.; Blanchard, Gary J.; Kulesza, Pawel J.

    2014-12-01

    A catalytic material for electrooxidation of ethanol that utilizes PtRu nanoparticles dispersed over thin films of rhodium-free and rhodium-containing zirconia (ZrO2) supports is described here. The enhancement of electrocatalytic activity (particularly in the potential range as low as 0.25-0.5 V vs. RHE), that has been achieved by dispersing PtRu nanoparticles (loading, 100 μg cm-2) over the hybrid Rh-ZrO2 support composed of nanostructured zirconia and metallic rhodium particles, is clearly evident from comparison of the respective voltammetric and chronoamperometric current densities recorded at room temperature (22 °C) in 0.5 mol dm-3 H2SO4 containing 0.5 mol dm-3 ethanol. Porous ZrO2 nanostructures, that provide a large population of hydroxyl groups in acidic medium in the vicinity of PtRu sites, are expected to facilitate the ruthenium-induced removal of passivating CO adsorbates from platinum, as is apparent from the diagnostic experiments with a small organic molecule such as methanol. Although Rh itself does not show directly any activity toward ethanol oxidation, the metal is expected to facilitate C-C bond splitting in C2H5OH. It has also been found during parallel voltammetric and chronoamperometric measurements that the hybrid Rh-ZrO2 support increases activity of the platinum component itself toward ethanol oxidation in the low potential range.

  6. Pt/Ceria-based Catalysts for Small Alcohol Electrooxidation

    NASA Astrophysics Data System (ADS)

    Menendez-Mora, Christian L.

    High emissions of fossil-based energy sources have led to scientists around the world to develop new alternatives for the future. In this sense, fuel cells are a remarkable and promising energy option with less environmental impact. The most used fuels for this technology are hydrogen and small chain alcohols, which can be oxidized to transform their chemical energy into electrical power. To do this, fuel cells need catalysts that will act as an active surface where the oxidation can take place. The problem with platinum catalysts is its possible CO poisoning with intermediates that are produced before the complete oxidation of alcohol to CO2. Different approaches have been taken to try to resolve this issue. In this case, cerium oxide (ceria) was selected as a co-catalyst to mitigate the effect of CO poisoning of platinum. Ceria is a compound that has the ability to work as an "oxygen tank" and can donate oxygen to carbon monoxide that is strongly adsorbed at platinum surface to produce CO2 (carbon dioxide), regenerating the Pt surface for further alcohol oxidation. Therefore, enhancing the current density as well as the power output of a fuel cell. First, an occlusion deposition technique was used to prepare platinum/ceria composite electrodes and tested them towards small chain alcohol oxidation such as methanol oxidation reaction in acidic and alkaline media. The preliminary results demonstrated that the Pt/ceria electrodes were more efficient towards methanol electrooxidation when compared to Pt electrodes. This enhancement was attributed to the presence of ceria. A second preparation method was selected for the synthesis of ceria/Pt catalysts. In this case, a hydrothermal method was used and the catalysis were studied for the effect of MeOH, EtOH and n-BuOH oxidation. The observed effect was that electrodes made of Pt/Pt:CeO2-x showed better catalytic effect than Pt/ceria and platinum electrodes. Moreover, a comparison between ceria nanorods versus

  7. Pt-B System Revisited: Pt2B, a New Structure Type of Binary Borides. Ternary WAl12-Type Derivative Borides.

    PubMed

    Sologub, Oksana; Salamakha, Leonid; Rogl, Peter; Stöger, Berthold; Bauer, Ernst; Bernardi, Johannes; Giester, Gerald; Waas, Monika; Svagera, Robert

    2015-11-16

    On the basis of a detailed study applying X-ray single-crystal and powder diffraction, differential scanning calorimetry, and scanning electron microscopy analysis, it was possible to resolve existing uncertainties in the Pt-rich section (≥65 atom % Pt) of the binary Pt-B phase diagram above 600 °C. The formation of a unique structure has been observed for Pt2B [X-ray single-crystal data: space group C2/m, a = 1.62717(11) nm, b = 0.32788(2) nm, c = 0.44200(3) nm, β = 104.401(4)°, RF2 = 0.030]. Within the homogeneity range of "Pt3B", X-ray powder diffraction phase analysis prompted two structural modifications as a function of temperature. The crystal structure of "hT-Pt3B" complies with the hitherto reported structure of anti-MoS2 [space group P63/mmc, a = 0.279377(2) nm, c = 1.04895(1) nm, RF = 0.075, RI = 0.090]. The structure of the new "[Formula: see text]T-Pt3B" is still unknown. The formation of previously reported Pt∼4B has not been confirmed from binary samples. Exploration of the Pt-rich section of the Pt-Cu-B system at 600 °C revealed a new ternary compound, Pt12CuB6-y [X-ray single-crystal data: space group Im3̅, a = 0.75790(2) nm, y = 3, RF2 = 0.0129], which exhibits the filled WAl12-type structure accommodating boron in the interstitial trigonal-prismatic site 12e. The isotypic platinum-aluminum-boride was synthesized and studied. The solubility of copper in binary platinum borides has been found to attain ∼7 atom % Cu for Pt2B but to be insignificant for "[Formula: see text]T-Pt3B". The architecture of the new Pt2B structure combines puckered layers of boron-filled and empty [Pt6] octahedra (anti-CaCl2-type fragment) alternating along the x axis with a double layer of boron-semifilled [Pt6] trigonal prisms interbedded with a layer of empty tetrahedra and tetragonal pyramids (B-deficient α-T[Formula: see text]I fragment). Assuming boron vacancies ordering (space group R3), the Pt12CuB6-y structure exhibits serpentine-like columns of edge

  8. Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions

    SciTech Connect

    Yang, G.; Li, D. L.; Wang, S. G. Ma, Q. L.; Liang, S. H.; Wei, H. X.; Han, X. F.; Hesjedal, T.; Ward, R. C. C.; Kohn, A.; Elkayam, A.; Tal, N.; Zhang, X.-G.

    2015-02-28

    Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1{sub 0}-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.

  9. Pt-B System Revisited: Pt2B, a New Structure Type of Binary Borides. Ternary WAl12-Type Derivative Borides.

    PubMed

    Sologub, Oksana; Salamakha, Leonid; Rogl, Peter; Stöger, Berthold; Bauer, Ernst; Bernardi, Johannes; Giester, Gerald; Waas, Monika; Svagera, Robert

    2015-11-16

    On the basis of a detailed study applying X-ray single-crystal and powder diffraction, differential scanning calorimetry, and scanning electron microscopy analysis, it was possible to resolve existing uncertainties in the Pt-rich section (≥65 atom % Pt) of the binary Pt-B phase diagram above 600 °C. The formation of a unique structure has been observed for Pt2B [X-ray single-crystal data: space group C2/m, a = 1.62717(11) nm, b = 0.32788(2) nm, c = 0.44200(3) nm, β = 104.401(4)°, RF2 = 0.030]. Within the homogeneity range of "Pt3B", X-ray powder diffraction phase analysis prompted two structural modifications as a function of temperature. The crystal structure of "hT-Pt3B" complies with the hitherto reported structure of anti-MoS2 [space group P63/mmc, a = 0.279377(2) nm, c = 1.04895(1) nm, RF = 0.075, RI = 0.090]. The structure of the new "[Formula: see text]T-Pt3B" is still unknown. The formation of previously reported Pt∼4B has not been confirmed from binary samples. Exploration of the Pt-rich section of the Pt-Cu-B system at 600 °C revealed a new ternary compound, Pt12CuB6-y [X-ray single-crystal data: space group Im3̅, a = 0.75790(2) nm, y = 3, RF2 = 0.0129], which exhibits the filled WAl12-type structure accommodating boron in the interstitial trigonal-prismatic site 12e. The isotypic platinum-aluminum-boride was synthesized and studied. The solubility of copper in binary platinum borides has been found to attain ∼7 atom % Cu for Pt2B but to be insignificant for "[Formula: see text]T-Pt3B". The architecture of the new Pt2B structure combines puckered layers of boron-filled and empty [Pt6] octahedra (anti-CaCl2-type fragment) alternating along the x axis with a double layer of boron-semifilled [Pt6] trigonal prisms interbedded with a layer of empty tetrahedra and tetragonal pyramids (B-deficient α-T[Formula: see text]I fragment). Assuming boron vacancies ordering (space group R3), the Pt12CuB6-y structure exhibits serpentine-like columns of edge

  10. Large faceted Pd nanocrystals supported small Pt nanoparticles as highly durable electrocatalysts for oxygen reduction

    NASA Astrophysics Data System (ADS)

    Zhang, Geng; Lu, Wangting; Cao, Longsheng; Qin, Xiaoping; Ding, Fei; Tang, Shun; Shao, Zhi-Gang; Yi, Baolian

    2016-09-01

    The reduction of Pt content together with the improvement of the durability of the catalyst for oxygen reduction reaction (ORR) is required to the large-scale commercialization of proton exchange membrane fuel cells. In this work, a novel ORR catalyst consisting of large Pd nanocrystal as the core with small Pt nanoparticles supported on the Pd core is prepared by a facile one-step synthesis method. The Pd substrate is presented in the form of well-defined cuboctahedrons and icosahedrons. The type of metal precursors and Pt/Pd molar ratio are important factors to obtain this Pd-supporting-Pt structure. The Pd2-s-Pt1 catalyst with a nominal Pt/Pd atomic ratio at 1/2 shows improved ORR activity: its mass specific activity and area specific activity is 2.5 and 3.5 times that of commercial Pt/C, respectively. More importantly, the Pd2-s-Pt1 catalyst demonstrates outstanding durability against potential cycling which can be ascribed to the slow dissolution of Pd core and the structure transformation from Pd@Pt to hollow PdPt alloyed nanocages. This exciting result provides a new pathway to the design of ORR catalyst with excellent durability.

  11. Preparation and characterization of Pt supported on graphene with enhanced electrocatalytic activity in fuel cell

    NASA Astrophysics Data System (ADS)

    Xin, Yuchen; Liu, Jian-guo; Zhou, Yong; Liu, Wenming; Gao, Jian; Xie, Yun; Yin, Ying; Zou, Zhigang

    Pt nanoparticles are deposited onto graphene sheets via synchronous reduction of H 2PtCl 6 and graphene oxide (GO) suspension using NaBH 4. Lyophilization is introduced to avoid irreversible aggregation of graphene (G) sheets, which happens during conventional drying process. Pt/G catalysts reveal a high catalytic activity for both methanol oxidation and oxygen reduction reaction compared to Pt supported on carbon black (Pt/C). The performance of Pt/G catalysts is further improved after heat treatment in N 2 atmosphere at 300 °C for 2 h, and the peak current density of methanol oxidation for Pt/G after heat treatment is almost 3.5 times higher than Pt/C. Transmission electron microscope (TEM) images show that the Pt particles are uniformly distributed on graphene sheets. X-ray photoelectron spectroscopy (XPS) results demonstrate that the interaction between Pt and graphene is enhanced during annealing. It suggests that graphene has provided a new way to improve electrocatalytic activity of catalyst for fuel cell.

  12. The effect of the surface composition of Ru-Pt bimetallic catalysts for methanol oxidation

    DOE PAGESBeta

    Garrick, Taylor R.; Diao, Weijian; Tengco, John M.; Stach, Eric A.; Senanayake, Sanjaya D.; Chen, Donna A.; Monnier, John R.; Weidner, John W.

    2016-02-23

    Here, a series of Ru-Pt bimetallic catalysts prepared by the electroless deposition of controlled and variable amounts of Ru on the Pt surface of a commercially-available 20 wt% Pt/C catalyst has been characterized and evaluated for the oxidation of methanol. The activity of each Ru-Pt catalyst was determined as a function of surface composition via cyclic voltammetry. For the Ru-Pt bimetallic catalysts, activity passed through a maximum at approximately 50% monodisperse Ru surface coverage. However, due to the monolayer coverage of Ru on Pt, the amount of metal in the catalyst is minimized compared to a bulk 1:1 atomic ratiomore » of Ru:Pt seen in commercial bimetallic catalysts. Chemisorption and temperature programmed reduction experiments confirmed that the surface had characteristics of a true bimetallic catalyst. On a mass of Pt basis, the activity of this composition for methanol oxidation was 7 times higher than pure Pt and 3.5 times higher than a commercial catalyst with a 1:1 Pt:Ru bulk atomic ratio.« less

  13. Facile assembly of tetragonal Pt clusters on graphene oxide for enhanced nonlinear optical properties

    NASA Astrophysics Data System (ADS)

    Zheng, Chan; Li, Yubing; Huang, Li; Li, Wei; Chen, Wenzhe

    2015-11-01

    A facile method to assemble tetragonal Pt clusters on the surface of graphene oxide (Pt-cluster/GO) using anatase TiO2 as a template is proposed. The morphology and structure of Pt-cluster/GO were investigated, revealing that tetragonal Pt clusters with a diameter of 20-50 nm composed of 2-3 nm Pt nanoparticles (NPs) were homogenously decorated on the surface of GO. The nonlinear optical properties were characterized by the open-aperture Z-scan technique in the nanosecond regime using a laser with wavelength of 532 nm. The as-prepared Pt-cluster/GO hybrid was found to show strong optical limiting (OL) effects for nanosecond laser pulses at 532 nm, and the OL performance is superior to that of carbon nanotubes, a benchmark optical limiter. Furthermore, the Z-scan results showed that the OL performance of the Pt-cluster/GO hybrid is superior to that of GO and the Pt-NP/GO hybrid. The OL behavior of the metal/GO composite nanostructure can be effectively tailored by altering the aggregation means of metal NPs. Scattering measurements suggested that nonlinear scattering (NLS) played an important role in the observed OL behavior in the Pt-cluster/GO hybrid. The OL properties of the Pt-cluster/GO hybrid are attributed to the reverse saturable absorption in the GO sheet and NLS in the metal NPs.

  14. Injection of synthesized FePt nanoparticles in hole-patterns for bit patterned media

    NASA Astrophysics Data System (ADS)

    Hachisu, Takuma; Sato, Wataru; Ishizuka, Shugo; Sugiyama, Atsushi; Mizuno, Jun; Osaka, Tetsuya

    2012-02-01

    FePt nanoparticles of uniform sizes, compositions, and crystal structures can be obtained by chemical synthesis. Additionally, the nanoparticles can be well dispersed by the adsorption of a surfactant on the nanoparticle surface. Previously, the immobilization of FePt nanoparticles on a thermal oxide Si substrate was carried out by chemical synthesis, utilizing the Pt-S bonding between the -SH functional group in (3-mercaptopropyl)trimethoxysilane, MPTMS and Pt in FePt nanoparticles. However, controlling FePt nanoparticle arrays by this synthesis method was very difficult. In the present study, we attempted to control the distortion of the arrangement of FePt nanoparticles using an MPTMS layer modified with a silane coupling reaction and a geometrical structure prepared by ultraviolet nanoimprint lithography (UV-NIL). In this study, the hole-patterns used for the geometrical structure on Si(1 0 0) were 200 nm wide, 40 nm deep, and had a 500 nm pitch. The 5.6 nm FePt nanoparticles were used to coat the hole-patterns by using a picoliter pipette. An XHR-SEM image clearly revealed that the FePt nanoparticles were successfully arranged as a single layer with an average pitch of 10.0 nm by Pt-S bonding in the hole-patterns on Si(1 0 0).

  15. Thermally stable Pt/mesoporous silica core-shell nanocatalysts for high-temperature reactions.

    PubMed

    Joo, Sang Hoon; Park, Jeong Young; Tsung, Chia-Kuang; Yamada, Yusuke; Yang, Peidong; Somorjai, Gabor A

    2009-02-01

    Recent advances in colloidal synthesis enabled the precise control of the size, shape and composition of catalytic metal nanoparticles, enabling their use as model catalysts for systematic investigations of the atomic-scale properties affecting catalytic activity and selectivity. The organic capping agents stabilizing colloidal nanoparticles, however, often limit their application in high-temperature catalytic reactions. Here, we report the design of a high-temperature-stable model catalytic system that consists of a Pt metal core coated with a mesoporous silica shell (Pt@mSiO(2)). Inorganic silica shells encaged the Pt cores up to 750 degrees C in air and the mesopores providing direct access to the Pt core made the Pt@mSiO(2) nanoparticles as catalytically active as bare Pt metal for ethylene hydrogenation and CO oxidation. The high thermal stability of Pt@mSiO(2) nanoparticles enabled high-temperature CO oxidation studies, including ignition behaviour, which was not possible for bare Pt nanoparticles because of their deformation or aggregation. The results suggest that the Pt@mSiO(2) nanoparticles are excellent nanocatalytic systems for high-temperature catalytic reactions or surface chemical processes, and the design concept used in the Pt@mSiO(2) core-shell catalyst can be extended to other metal/metal oxide compositions. PMID:19029893

  16. Noncovalently functionalized graphitic mesoporous carbon as a stable support of Pt nanoparticles for oxygen reduction

    SciTech Connect

    Shao, Yuyan; Zhang, Sheng; Kou, Rong; Wang, Xiqing; Wang, Chong M.; Dai, Sheng; Viswanathan, Vilayanur V.; Liu, Jun; Wang, Yong; Lin, Yuehe

    2010-01-01

    We report the facile synthesis of an extremely durable electrocatalyst for oxygen reduction with highly graphitized mesoporous carbon (GMPC) as support (Pt/GMPC). GMPC is prepared through graphitizing the self-assembled soft-template mesoporous carbon (MPC) under high temperature. Most of the mesoporous structures and the specific surface area of MPC are retained even after 2800 °C heat-treatment, and the graphitization degree is greatly improved. GMPC is then noncovalently functionalized with poly(diallyldimethylammonium chloride) (PDDA) and then coated with Pt nanoparticles with ethylene glycol reduction method. Pt nanoparticles of ~3.0 nm in diameter are uniformly dispersed on GMPC. Pt/GMPC exhibits a higher activity towards oxygen reduction reaction (ORR) than Pt nanoparticles supported on Vulcan XC-72 carbon (Pt/XC-72). The durability of Pt/GMPC is improved by a factor of ~2 compared with Pt/XC-72. The enhanced activity and durability of Pt/GMPC are attributed to the graphitic structure of GMPC which makes GMPC more resistant to corrosion and the interaction between Pt nanoparticles and GMPC stronger. GMPC is promising as catalyst support. This provides a facile, eco-friendly promising strategy, avoiding the usually used chemical functionalization of carbon support with oxidizing strong acid, to synthesize electrocatalysts with high durability and activity for polymer electrolyte membrane fuel cells. This strategy can be widely applied in synthesizing metal nanoparticles on hydrophobic support materials.

  17. Activity and selectivity control by niobium for the preferential oxidation of co on pt supported catalysts

    SciTech Connect

    Guerrero, S.; Miller, J.T.; Wolf, E.E.

    2010-10-22

    The promotional effect of Nb on Pt supported on alumina or on niobia, was studied for the preferential oxidation of CO (PROX) in hydrogen. The results show a unique effect of Nb as a promoter to Pt. At low Nb loadings on Pt/alumina, the CO oxidation activity and selectivity are significantly increased. The CO selectivity is 100% at conversions up to about 60%. For Pt supported on Nb{sub 2}O{sub 5}, however, the CO oxidation activity is strongly suppressed with low CO conversion but high H{sub 2} oxidation activity. Pt on niobia, therefore, is poorly selective for the PROX reaction, but is an active hydrogen oxidation catalyst, resistant to CO poisoning. For Pt supported on highly loaded Nb-alumina or Nb{sub 2}O{sub 5}, XPS indicate an increase in the Pt and Nb oxidation states. These surface changes also correlate with changes in the DRIFTS spectra suggesting that CO is more weakly adsorbed on Pt/Nb{sub 2}O{sub 5} compared to Pt/Al{sub 2}O{sub 3}, or Pt/Nb-Al{sub 2}O{sub 3}.

  18. Easy control of the size and composition of FePt nanoparticles with Improved synthesis

    NASA Astrophysics Data System (ADS)

    Kang, S.; Shi, S.; Nikles, D. E.; Harrell, J. W.

    2008-04-01

    A new synthesis of FePt nanoparticles with tunable size and composition has been developed. Unlike conventional synthesis methods with which it is difficult to simultaneously control the size and chemical composition of FePt nanoparticles, the new synthesis offers a convenient way to tune FePt nanoparticles with different sizes and compositions. The synthesis involves the simultaneous decomposition of Fe3(CO)12 and reduction of Pt(acac)2 in diethylene glycol. Fe3(CO)12 is a powder (nonvolatile) which is critical in governing the FePt particle size and composition. By varying the amount of surfactants and precursors ratio [Fe3(CO)12/Pt(acac)2], FePt particles with tunable composition and particle size (2-8nm) can be obtained. After high temperature annealing (˜600°C), Fe50Pt50 nanoparticles are partially transformed to the L10 phase as indicated by the soft and hard components in the hysteresis loops. The coercivity ranges from a few kilo-Oersted to more than 15kOe, depending on the particle size. Dynamic coercivity measurements reveal that the large FePt particles are easier to chemically order than the small FePt particles under the same annealing condition.

  19. [Catalytic ozonation of oxalic acid in water with Pt/graphite catalyst].

    PubMed

    Liu, Zheng-Qian; Ma, Jun; Zhao, Lei

    2007-06-01

    Pt/graphite catalyst was prepared by incipient wetness impregnation using H2PtCl6 x 6H2O as precursor substance. The removal efficiencies of oxalic acid by Pt/graphite, graphite catalyzed ozonation and ozonation alone were compared. It was found that the removal efficiency of oxalic acid in ozonation alone, graphite and Pt/graphite catalyzed ozonation was 3.0%, 47.6% and 99.3% respectively under the present experimental conditions. Results showed that loading of Pt could significantly increase the catalytic activity of graphite. Taking oxalic acid degradation efficiency as indication, the preparation conditions of Pt/graphite were optimized. The pretreatment of graphite had no favor to improve the activity of Pt/graphite catalyst. The optimal preparation conditions of Pt/graphite catalyst are as follow: impregnant, distilled water; impregnation time, 24 h; the loading amount of Pt, 1.0%; reduction temperature, 35 degrees C. The Pt/graphite catalyst was used for five times with no significant decrease of its activity and more than 90% oxalic acid removal was obtained. PMID:17674732

  20. Thermally Stable Nanocatalyst for High Temperature Reactions: Pt-Mesoporous Silica Core-Shell Nanoparticles

    SciTech Connect

    Joo, Sang Hoon; Park, J.Y.; Tsung, C.-K.; Yamada, Y.; Yang, P.; Somorjai, G.A.

    2008-10-25

    Recent advances in colloidal synthesis enabled the precise control of size, shape and composition of catalytic metal nanoparticles, allowing their use as model catalysts for systematic investigations of the atomic-scale properties affecting catalytic activity and selectivity. The organic capping agents stabilizing colloidal nanoparticles, however, often limit their application in high-temperature catalytic reactions. Here we report the design of a high-temperature stable model catalytic system that consists of Pt metal core coated with a mesoporous silica shell (Pt{at}mSiO{sub 2}). While inorganic silica shells encaged the Pt cores up to 750 C in air, the mesopores directly accessible to Pt cores made the Pt{at}mSiO{sub 2} nanoparticles as catalytically active as bare Pt metal for ethylene hydrogenation and CO oxidation. The high thermal stability of Pt{at}mSiO{sub 2} nanoparticles permitted high-temperature CO oxidation studies, including ignition behavior, which was not possible for bare Pt nanoparticles because of their deformation or aggregation. The results suggest that the Pt{at}mSiO{sub 2} nanoparticles are excellent nanocatalytic systems for high-temperature catalytic reactions or surface chemical processes, and the design concept employed in the Pt{at}mSiO{sub 2} core-shell catalyst can be extended to other metal-metal oxide compositions.

  1. Study of Pt catalyst on graphene and its application to fuel cell

    NASA Astrophysics Data System (ADS)

    Hsieh, S. H.; Hsu, M. C.; Liu, W. L.; Chen, W. J.

    2013-07-01

    In this work Pt nanoparticles on graphene (PtNPs/GN) were formed from graphite oxide by two routes (one-step and two-step routes). For one-step route, a fixed weight of graphene oxide (GO) and a variable weight of H2PtCl6·6H2O were put in ethylene glycol for a reflux at 120 and 150 °C for 3, 6, 12 and 24 h, respectively. For the two-step route, the first step is reduction of GO films by sodium tetrahydridoborate to obtain graphene. Then, the graphene deposited with Pt particles was put in ethylene glycol for a reflux at 120, 150 and 180 °C for 3, 6, 12 and 24 h. The results show that the electrode catalyst Pt particles have a smaller size and a better distribution on the surface of graphene under the following reducing condition: two-step reduction, reaction time of 12 h, reaction temperature of 150 °C and the 1 g/L of H2PtCl6. These PtNPs/GN composites exhibit superior electrochemically active surface area and high poison tolerance toward methanol oxidation compared to Vulcan XC-72-Pt with the same Pt content. This revealed that the PtNPs/GN can be used as promising electrocatalyst support for direct methanol fuel cells.

  2. Particle swarm optimization of the stable structure of tetrahexahedral Pt-based bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Tun-Dong; Fan, Tian-E.; Shao, Gui-Fang; Zheng, Ji-Wen; Wen, Yu-Hua

    2014-08-01

    Bimetallic nanoparticles, enclosed by high-index facets, have great catalytic activity and selectivity owing to the synergy effects of high-index facets and the electronic structures of alloy. In this paper, a discrete particle swarm optimization algorithm was employed to systematically investigate the structural stability and features of tetrahexahedral Pt-based bimetallic nanoparticles with high-index facets. Different Pt/Ag, Pt/Cu, Pt/Pd atom ratios and particle sizes were considered in this work. The simulation results reveal that these alloy nanoparticles exhibit considerably different structural characteristics. Pt-Ag nanoparticles tend to form Pt-Ag core-shell structure. Pt-Cu nanoparticles are preferred to take multi-shell structure with Cu on the outer surface while Pt-Pd nanoparticles present a mixing structure in the interior and Pd-dominated surface. Atomic distribution and bonding characteristics were applied to further characterize the structural features of Pt-based nanoparticles. This study provides an important insight into the structural stability and features of Pt-based nanoparticles with different alloys.

  3. Segregated Pt on Pd nanotubes for enhanced oxygen reduction activity in alkaline electrolyte.

    PubMed

    St John, Samuel; Atkinson, Robert W; Dyck, Ondrej; Sun, Cheng-Jun; Zawodzinski, Thomas A; Papandrew, Alexander B

    2015-12-01

    Nanoscaled Pt domains were integrated with Pd nanotubes via vapor deposition to yield a highly active electrocatalyst for the oxygen reduction reaction (ORR) in alkaline media. The surface-area-normalized ORR activity of these bi-metallic Pt-on-Pd nanotubes (PtPdNTs) was nearly 6× the corresponding carbon-supported Pt nanoparticle (Pt/C) activity at 0.9 V vs. RHE (1.5 vs. 0.24 mA cmmetal(-2), respectively). Furthermore, the high specific activity of the PtPdNTs was achieved without sacrificing mass-normalized activity, which is more than twice that of Pt/C (0.333 A mgPtPdNT(-1)vs. 0.141 A mgPt/C(-1)) and also greater than that of Pd/C (0.221 A mgPd/C(-1)). We attribute the enhancements in specific and mass activity to modifications of the segregated Pt electronic structure and to nanoscale porosity, respectively. PMID:26553367

  4. Microstructural characterization of bimetallic Ni-Pt catalysts supported on SiO 2

    NASA Astrophysics Data System (ADS)

    Arenas-Alatorre, J.; Avalos-Borja, M.; Díaz, G.

    2002-04-01

    A set of Pt, Ni and a bimetallic Ni50Pt50 catalysts supported on SiO2 of low and high surface area (S=50 and 200 m2/g) with a total metal loading of 2 wt.% was characterized by high-resolution electron microscopy (HREM), conventional transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and computational techniques such as digital processing and image simulation. Special attention was placed to the identification of intermetallic phases in the Ni50Pt50/SiO2 sample. Catalysts were prepared by impregnation and submitted to calcination-reduction activation treatments. For all the set, the increase in support's surface area led to an improvement of the metal dispersion. TEM and HREM images showed significant differences in the shape and crystalline lattice of the Pt and Ni particles in the monometallic samples taken as reference. While in Pt/SiO2 catalyst we identified only reduced Pt particles, in Ni/SiO2 some NiO particles were detected. HREM characterization of the Ni50Pt50 catalysts showed that many particles have defects such as twinning and dislocations. Cubo-octahedral shapes were predominant in the bimetallic catalyst. Crystal lattice and angles measurements were consistent with the identification of NiPt and/or Ni3Pt intermetallic phases. Superlattice structures were also identified and confirmed by image simulation. EDS analysis on a particle by particle basis confirmed that in bimetallic catalysts supported in SiO2 of low and high surface area, particles were present consisting of Ni-rich, nominal and Pt-rich metal compositions. Pt-only particles were found but no Ni-only particles were detected. Among the possibilities, NiPt and Ni3Pt compositions were identified.

  5. Pt-Ni bilayers on n-type silicon: Metallurgical and electrical behavior

    NASA Astrophysics Data System (ADS)

    Mantovani, S.; Nava, F.; Nobili, C.; Queirolo, G.; Celotti, G.

    1984-02-01

    Silicide formation in the Ni-Pt-Si system has been investigated mainly by megaelectronvolt backscattering spectrometry, glancing-angle x-ray diffraction, and Auger electron spectroscopy as a function of heat treatment (200-850 °C). Schottky-barrier values have been used to identify the kinds of metals present at the silicide/silicon interface. Pt/Ni/Si and Ni/Pt/Si structures have been prepared by e-gun deposition of thin Pt and Ni films on <100> n-type silicon single crystals. The reaction starts by forming the silicide, Ni2Si or Pt2Si, of the metal in contact with silicon and proceeds until all the inner-metal film has reacted. At about 300 °C for 30 min the outer metal starts to diffuse through the already formed silicide and builds up at the silicon surface. Further annealing enhances the reaction and there is evidence also of silicon diffusion towards the outside layer. At 400 °C for 30 min and in both structures, NiSi starts to form and pushes out the Pt from the silicon surface. The conversion of Ni2Si into NiSi provides the driving force for mass transport. The structures become laterally nonuniform and the changes are difficult to follow. The transformation of Pt2Si into PtSi, at about 500 °C, is accompanied by the transport of Pt through NiSi towards the silicon surface. Most Pt remains in the outside layer and both structures assume the configuration PtSi/NiSi/Si. At higher temperatures PtSi and NiSi intermix and there is no evidence of contribution from the silicon underneath. At 750 °C an almost uniform layer is formed with a Si1(NiPt)1 composition. The barrier height measurements reflect the mass transport in the silicides at the silicide/silicon interface.

  6. Novel Pt/Mg(In)(Al)O catalysts for ethane and propane dehydrogenation

    SciTech Connect

    Sun, Pingping; Siddiqi, Georges; Vining, William C.; Chi, Miaofang; Bell, Alexis T.

    2011-10-28

    Catalysts for the dehydrogenation of light alkanes were prepared by dispersing Pt on the surface of a calcined hydrotalcite-like support containing indium, Mg(In)(Al)O. Upon reduction in H{sub 2} at temperatures above 673 K, bimetallic particles of PtIn are observed by TEM, which have an average diameter of 1 nm. Analysis of Pt LIII-edge extended X-ray absorption fine structure (EXAFS) data shows that the In content of the bimetallic particles increases with increasing bulk In/Pt ratio and reduction temperature. Pt LIII-edge X-ray absorption near edge structure (XANES) indicates that an increasing donation of electronic charge from In to Pt occurs with increasing In content in the PtIn particles. The activity and selectivity of the Pt/Mg(In)(Al)O catalysts for ethane and propane dehydrogenation reactions are strongly dependent on the bulk In/Pt ratio. For both reactants, maximum activity was achieved for a bulk In/Pt ratio of 0.48, and at this In/Pt ratio, the selectivity to alkene was nearly 100%. Coke deposition was observed after catalyst use for either ethane or propane dehydrogenation, and it was observed that the alloying of Pt with In greatly reduced the amount of coke deposited. Characterization of the deposit by Raman spectroscopy indicates that the coke is present as highly disordered graphite particles <30 nm in diameter. While the amount of coke deposited during ethane and propane dehydrogenation are comparable, the effects on activity are dependent on reactant composition. Coke deposition had no effect on ethane dehydrogenation activity, but caused a loss in propane dehydrogenation activity. This difference is attributed to the greater ease with which coke produced on the surface of PtIn nanoparticles migrates to the support during ethane dehydrogenation versus propane dehydrogenation.

  7. RhPt/graphite catalysts for CO electrooxidation: Performance of mixed metal and alloyed surfaces

    NASA Astrophysics Data System (ADS)

    Fang, L.; Vidal-Iglesias, F. J.; Huxter, S. E.; Attard, G. A.; Wells, P. B.

    2015-01-01

    Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) have been used to characterise novel PtRh mixed metal and surface alloyed active phases supported on 5% Pt/graphite catalysts (5% Pt/G). The active phases could be prepared using forced deposition or a combination of forced deposition and thermal annealing in a flowing 5% hydrogen in argon gas mixture at 700 K. The protocols employed originate directly from previous single crystal studies of Rh on Pt{100} whereby Rh overlayers (either singly adsorbed or as a 'sandwich structure' of alternate Pt/Rh/Pt layers) could be transformed into surface PtRh alloys by careful thermal annealing. We demonstrate that this method is also successful for the preparation of active supported catalysts for CO electrooxidation whereby a peak potential as low as 0.60 V (Pd/H) for the CO oxidation is reported (0.12 V lower than that on 5% Pt/G). Moreover, the onset potential for CO stripping is lowered to 0.33 V (Pd/H). The presence of alloyed PtRh phases gives rise to a small but reproducible 0.1-0.2 eV shift to higher binding energy of the Pt 4f7/2 XPS peak together with strongly modified Pt and Rh electrosorption features in the CV which correlate with changes in surface composition. Unusual kinetic behaviour in the CO stripping peaks from the PtRh catalyst as a function of CO coverage is ascribed to competition between electrochemical oxide on Rh and CO-induced blocking of electrochemical oxide formation sites at the highest CO coverage. For PtRh alloys, the onset of electrochemical oxide formation shifts to more positive potentials relative to Rh overlayers and so a different behaviour towards CO electrooxidation is observed.

  8. Monte Carlo Simulations of Segregation in Pt-Ni Catalyst Nanoparticles

    SciTech Connect

    Wang, Guofeng; Van Hove, Michel A.; Ross, Philip N.; Baskes, M.I.

    2004-04-01

    We have investigated the segregation of Pt atoms in the surfaces of Pt-Ni nanoparticles, using Modified Embedded Atom Model potentials and the Monte Carlo method. The nanoparticles are assumed to have disordered fcc configurations at two fixed overall concentrations (50 at. percent Pt and 75 at. percent Pt). We use four kinds of nanoparticle shapes [cube, tetrahedron, octahedron, and cubo-octahedron] terminated by {l_brace}111{r_brace} and {l_brace}100{r_brace} facets to examine the extent of the Pt segregation to the nanoparticle surfaces and determine the equilibrium structures of Pt-Ni nanoparticles at T=600 K. The model particles contain between 560 and 4631 atoms (particle size ranging from 2.5 to 5 nm). Our results imply that a complete (100)-facet reconstruction could make the cubo-octahendral Pt-Ni nanoparticles most energetically favorable, consistent with experimental observations. We predict that at 600 K due to segregation the equilibrium Pt50Ni50 nanoparticles with fewer than 2000 atoms and Pt75Ni25 nano particles with fewer than 4000 atoms would achieve a surface-sandwich structure, in which the Pt atoms are enriched in the outermost and third atomic shells while the Ni atoms are enriched in the second atomic shell. We also find that due to an order-disorder transition the Pt50Ni50 cubo-octahedral nanoparticles containing more than 2000 atoms would form a core-shell structure with a Pt-enriched surface and a Pt-deficient homogeneous core.

  9. Theoretical prediction of the fundamental properties for the ternary Li{sub 2}PtH{sub 6} and Na{sub 2}PtH{sub 6}

    SciTech Connect

    Ghebouli, M.A.; Choutri, H.; Bouarissa, N.; Ghebouli, B.; Bouhemadou, A.; Soyalp, F.; Ucgun, E.; Ocak, H.Y.

    2012-12-15

    Li{sub 2}PtH{sub 6} and Na{sub 2}PtH{sub 6} are good candidate for hydrogen storage. The structural, elastic, electronic and optical properties of Li{sub 2}PtH{sub 6} and Na{sub 2}PtH{sub 6} compounds have been investigated using pseudo-potential plane-wave method based on the density functional theory. Computed lattice constant and H atom positional parameter at equilibrium agree well with the available experimental data. A quadratic pressure dependence of the elastic stiffness is found. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young's modulus, Poisson's ratio, average sound velocity and Debye temperature are numerically estimated in the framework of the Voigt-Reuss-Hill approximation for Li{sub 2}PtH{sub 6} and Na{sub 2}PtH{sub 6} polycrystalline aggregate. The analyses of the band structure indicates that Li{sub 2}PtH{sub 6} and Na{sub 2}PtH{sub 6} are indirect gap semiconductors. The static dielectric constant and static refractive index are inversely proportional to the fundamental gap. Highlights: Black-Right-Pointing-Pointer We predict elastic moduli, energy gaps and optical parameters. Black-Right-Pointing-Pointer Electron effective mass is anisotropic. Black-Right-Pointing-Pointer Li{sub 2}PtH{sub 6} and Na{sub 2}PtH{sub 6} are indirect gap semiconductors. Black-Right-Pointing-Pointer The contribution to the optical spectra from main transitions are predicted.

  10. Certification of Pd and Pt single spikes and application to the quantification of Pt and Pd in automotive exhaust emissions

    NASA Astrophysics Data System (ADS)

    Vogl, Jochen; Meyer, Christian; Noordmann, Janine; Rienitz, Olaf; Geilert, Sonja

    2014-05-01

    Numerous epidemiological studies show the effect of increased ambient pollution. Therefore measurement networks for air quality have been installed worldwide and legislation requires the monitoring of air pollution. Besides monitoring it is also important to be able to identify, to quantify and finally to regulate the emission of distinct sources in order to improve the quality of life. Automotive vehicles are a major source of environmental pollution especially through contaminants such as CO, NOX, SOX and hydrocarbons which derive from petrol combustion, while for example Platinum Group Elements (PGE) can be present from catalytic converters. The release of PGE into the environment, however, may be damaging in terms of public health, ecological and economic interests. In order to reliably assess the risks from PGEs, traceable and thus comparable data on the release rates of PGE from automotive catalysers are needed. As no Certified Reference Materials (CRM) are available for such samples the development of analytical procedures enabling SI-traceable results will be challenging. Therefore reference procedures for Pd and Pt in automotive exhaust emissions based on isotope dilution mass spectrometry (IDMS) have been developed and applied to specifically sampled automotive exhaust emissions. Due to the commonly known advantages, IDMS often is applied for quantification PGEs, as is the case within this work. The main reasons here are the required accuracy and the low PGE mass fractions in the sample. In order to perform IDMS analysis the analyte element must be available in an isotopically enriched form as so-called spike material or solution thereof, which is mixed with the sample. Unfortunately, no certified PGE spike solutions are available yet. To fill this gap two single PGE spikes, one 106Pd and one 194Pt spike, have been produced and characterized. The selection of the isotopes, the production of the solutions and the ampoulation will be described in this

  11. PtRu nanofilm formation by electrochemical atomic layer deposition (E-ALD).

    PubMed

    Jayaraju, Nagarajan; Banga, Dhego; Thambidurai, Chandru; Liang, Xuehai; Kim, Youn-Guen; Stickney, John L

    2014-03-25

    The high CO tolerance of PtRu electrocatalysis, compared with pure Pt and other Pt-based alloys, makes it interesting as an anode material in proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC). This report describes the formation of bimetallic PtRu nanofilms using the electrochemical form of atomic layer deposition (E-ALD). Metal nanofilm formation using E-ALD is facilitated by use of surface-limited redox replacement (SLRR), where an atomic layer (AL) of a sacrificial metal is first formed by UPD. The AL is then spontaneously exchanged for a more noble metal at the open-circuit potential (OCP). In the present study, PtRu nanofilms were formed using SLRR for Pt and Ru, and Pb UPD was used to form the sacrificial layers. The PtRu E-ALD cycle consisted of Pb UPD at -0.19 V, followed by replacement using Pt(IV) ions at OCP, rinsing with blank, then Pb UPD at -0.19 V, followed by replacement using Ru(III) ions at OCP. PtRu nanofilm thickness was controlled by the number of times the cycle was repeated. PtRu nanofilms with atomic proportions of 70/30, 82/18, and 50/50 Pt/Ru were formed on Au on glass slides using related E-ALD cycles. The charge for Pb UPD and changes in the OCP during replacement were monitored during the deposition process. The PtRu films were then characterized by CO adsorption and electrooxidation to determine their overpotentials. The 50/50 PtRu nanofilms displayed the lowest CO electrooxidation overpotentials as well as the highest currents, compared with the other alloy compositions, pure Pt, and pure Ru. In addition, CO electrooxidation studies of the terminating AL on the 50/50 PtRu nanostructured alloy were investigated by deposition of one or two SLRR of Pt, Ru, or PtRu on top.

  12. Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction.

    PubMed

    Escudero-Escribano, María; Malacrida, Paolo; Hansen, Martin H; Vej-Hansen, Ulrik G; Velázquez-Palenzuela, Amado; Tripkovic, Vladimir; Schiøtz, Jakob; Rossmeisl, Jan; Stephens, Ifan E L; Chorkendorff, Ib

    2016-04-01

    The high platinum loadings required to compensate for the slow kinetics of the oxygen reduction reaction (ORR) impede the widespread uptake of low-temperature fuel cells in automotive vehicles. We have studied the ORR on eight platinum (Pt)-lanthanide and Pt-alkaline earth electrodes, Pt5M, where M is lanthanum, cerium, samarium, gadolinium, terbium, dysprosium, thulium, or calcium. The materials are among the most active polycrystalline Pt-based catalysts reported, presenting activity enhancement by a factor of 3 to 6 over Pt. The active phase consists of a Pt overlayer formed by acid leaching. The ORR activity versus the bulk lattice parameter follows a high peaked "volcano" relation. We demonstrate how the lanthanide contraction can be used to control strain effects and tune the activity, stability, and reactivity of these materials. PMID:27034369

  13. Antisite-defect induced surface segregation in ordered NiPt

    NASA Astrophysics Data System (ADS)

    Pourovskii, Leonid V.; Ruban, Andrei V.; Abrikosov, Igor A.; Johansson, Borje

    2003-03-01

    By means of bulk and surface Monte Carlo simulations using effective interatomic interactions obtained from first principles Green's function calculations, we demonstrate that tiny deviations from stoichiometry in the bulk composition of the NiPt-L10 ordered alloy have a great impact on the segregation behavior and atomic configuration of the (111) surface. We predict that at T = 600 K the (111) surface of the Ni_51Pt_49 and Ni_50Pt_50 alloys has the usual 2 × 1 structure which corresponds to the (111) truncation of the bulk L10 ordered structure. However, the (111) surface of the nickel deficient Ni_49Pt_51 alloy is strongly enriched by Pt and should exhibit the pattern of the 2 × 2 structure. Such a drastic change in the segregation behavior is due to the presence of different antisite defects in the Ni- and Pt-rich alloys, and is a manifestation of the so-called offstoichiometric effect.

  14. Antisite-Defect-Induced Surface Segregation in Ordered NiPt Alloy

    NASA Astrophysics Data System (ADS)

    Pourovskii, L. V.; Ruban, A. V.; Johansson, B.; Abrikosov, I. A.

    2003-01-01

    By means of first principles simulations we demonstrate that tiny deviations from stoichiometry in the bulk composition of the NiPt-L10 ordered alloy have a great impact on the atomic configuration of the (111) surface. We predict that at T=600 K the (111) surface of the Ni51Pt49 and Ni50Pt50 alloys corresponds to the (111) truncation of the bulk L10 ordered structure. However, the (111) surface of the nickel deficient Ni49Pt51 alloy is strongly enriched by Pt and should exhibit the pattern of the 2×2 structure. Such a drastic change in the segregation behavior is due to the presence of different antisite defects in the Ni- and Pt-rich alloys and is a manifestation of the so-called off-stoichiometric effect.

  15. Photoelectron spectroscopic and computational study of the PtMgH3,5(-) cluster anions.

    PubMed

    Zhang, Xinxing; Ganteför, Gerd; Alexandrova, Anastassia N; Bowen, Kit

    2016-07-28

    The two cluster anions, PtMgH3(-) and PtMgH5(-), were studied by photoelectron spectroscopy and theoretical calculations. Experimentally-determined electron affinity (EA) and vertical detachment energy (VDE) values were compared with those predicted by our computations; excellent agreement was found. The calculated structures of PtMgH3(-) and PtMgH3 both exhibit η2-bonded H2 moieties. Activation of these H2 moieties is implied by the elongation of their bond lengths relative to the bond length of free H2. The calculated structures of PtMgH5(-) and PtMgH5 both exhibit all-hydrogen, five-member, σ-aromatic rings. These attributes are responsible for this anion's special stability. PMID:27373793

  16. The mechanism of Ag top layer on the coercivity enhancement of FePt thin films

    SciTech Connect

    Zhao, Z.L.; Ding, J.; Yi, J.B.; Chen, J.S.; Zeng, J.H.; Wang, J.P.

    2005-05-15

    The magnetic properties of the FePt thin films with a Ag top layer prepared by magnetron sputtering have been studied. With 4 nm Ag layer deposited right after the deposition of FePt layer, the ordering temperature of the L1{sub 0} FePt phase decreased to 350 deg. C or below. X-ray photoelectron spectroscopy results indicate that Ag has diffused into the FePt layer when Ag was deposited at 350 deg. C, while Ag remains on the top of the FePt when Ag was deposited at room temperature. The Ag top layer deposited at 350 deg. C was also found to protect the FePt layer from oxidation.

  17. Stellated Ag-Pt bimetallic nanoparticles: An effective platform for catalytic activity tuning

    PubMed Central

    Liu, Hui; Ye, Feng; Yao, Qiaofeng; Cao, Hongbin; Xie, Jianping; Lee, Jim Yang; Yang, Jun

    2014-01-01

    The usefulness of Pt-based nanomaterials for catalysis can be greatly enhanced by coupling morphology engineering to the strategic presence of a second or even third metal. Here we demonstrate the design and preparation of stellated Ag-Pt bimetallic nanoparticles where significant activity difference between the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR) may be realized by relegating Ag to the core or by hollowing out the core. In particular the stellated Pt surface, with an abundance of steps, edges, corner atoms, and {111} facets, is highly effective for the ORR but is ineffective for MOR. MOR activity is only observed in the presence of a Ag core through electronic coupling to the stellated Pt shell. The bimetallic Ag-Pt stellates therefore demonstrate the feasibility of tuning a Pt surface for two very different structure sensitive catalytic reactions. Stellated bimetallics may therefore be an effective platform for highly tunable catalyst designs. PMID:24495979

  18. Shape-dependent electrocatalysis: methanol and formic acid electrooxidation on preferentially oriented Pt nanoparticles.

    PubMed

    Solla-Gullón, J; Vidal-Iglesias, F J; López-Cudero, A; Garnier, E; Feliu, J M; Aldaz, A

    2008-07-01

    Reactivity towards methanol and formic acid electrooxidation on Pt nanoparticles with well characterised surfaces were studied and compared with the behaviour of single crystal electrodes with basal orientations. Polyoriented and preferential (100), (111) and (100)-(111) Pt nanoparticles were synthesised, cleaned preserving its surface structure, characterised and employed to evaluate the influence of the surface structure/shape of the Pt nanoparticles on these two relevant electrochemical reactions. The results pointed out that, in agreement with fundamental studies with Pt single crystal electrodes, the surface structure of the electrodes plays an important role on the reactivity of both oxidation processes, and thus the electrocatalytic properties strongly depend on the surface structure/shape of the nanoparticles, in particular on the presence of sites with (111) symmetry. These findings open the possibility of designing new and better electrocatalytic materials using decorated shape-controlled Pt nanoparticles as previously described with Pt single crystal electrodes. PMID:18563230

  19. EFFECT OF PRETREATMENT ON PT-CO/C CATHODE CATALYSTS FOR THE OXYGEN-REDUCTION REACTION

    SciTech Connect

    Fox, E.; Colon-Mercado, H.

    2010-01-19

    Carbon supported Pt and Pt-Co electrocatalysts for the oxygen reduction reaction in low temperature fuel cells were prepared by the reduction of the metal salts with sodium borohydride and sodium formate. The effect of surface treatment with nitric acid on the carbon surface and Co on the surface of carbon prior to the deposition of Pt was studied. The catalysts where Pt was deposited on treated carbon the ORR reaction preceded more through the two electron pathway and favored peroxide production, while the fresh carbon catalysts proceeded more through the four electron pathway to complete the oxygen reduction reaction. NaCOOH reduced Pt/C catalysts showed higher activity that NaBH{sub 4} reduced Pt/C catalysts. It was determined that the Co addition has a higher impact on catalyst activity and active surface area when used with NaBH{sub 4} as reducing agent as compared to NaCOOH.

  20. XAFS Study of HY Zeolite Supported Pt Nanoparticle Catalysts Prepared With Different Methods

    NASA Astrophysics Data System (ADS)

    Li, Zhongrui; Yan, Wensheng; Wei, Shiqiang

    2007-02-01

    The electronic and geometric effects induced by preparation methods on small platinum particles supported on high surface-area zeolite HY were studied by X-ray absorption fine structure (XAFS) spectroscopy. Pt/HY catalysts were prepared by a variety of techniques, including incipient wetness impregnation (IWI) and vapor-phase impregnation (VPI). Results of EXAFS for series of equal loadings of Pt prepared by IWI and VPI showed that the Pt clusters resulting from the VPI preparation had lower Pt—Pt coordination and higher coordination to the zeolite lattice oxygen. The electronic properties and structures of Pt/HY catalysts prepared with IWI approach can be altered by using different Pt precursor solutions.