Letteratura scientifica selezionata sul tema "Single precursor synthesis"
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Articoli di riviste sul tema "Single precursor synthesis":
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Gianvittorio, Stefano, Domenica Tonelli e Andreas Lesch. "Print-Light-Synthesis for Single-Step Metal Nanoparticle Synthesis and Patterned Electrode Production". Nanomaterials 13, n. 13 (23 giugno 2023): 1915. http://dx.doi.org/10.3390/nano13131915.
Abstract (sommario):
The fabrication of thin-film electrodes, which contain metal nanoparticles and nanostructures for applications in electrochemical sensing as well as energy conversion and storage, is often based on multi-step procedures that include two main passages: (i) the synthesis and purification of nanomaterials and (ii) the fabrication of thin films by coating electrode supports with these nanomaterials. The patterning and miniaturization of thin film electrodes generally require masks or advanced patterning instrumentation. In recent years, various approaches have been presented to integrate the spatially resolved deposition of metal precursor solutions and the rapid conversion of the precursors into metal nanoparticles. To achieve the latter, high intensity light irradiation has, in particular, become suitable as it enables the photochemical, photocatalytical, and photothermal conversion of the precursors during or slightly after the precursor deposition. The conversion of the metal precursors directly on the target substrates can make the use of capping and stabilizing agents obsolete. This review focuses on hybrid platforms that comprise digital metal precursor ink printing and high intensity light irradiation for inducing metal precursor conversions into patterned metal and alloy nanoparticles. The combination of the two methods has recently been named Print-Light-Synthesis by a group of collaborators and is characterized by its sustainability in terms of low material consumption, low material waste, and reduced synthesis steps. It provides high control of precursor loading and light irradiation, both affecting and improving the fabrication of thin film electrodes.
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Hase, Takashi, Ryusuke Kita, Kenichi Kawaguchi, Takeshi Koga e Tadataka Morishita. "Synthesis of single phase YBa2Cu3O7−x thin films from a Y-Ba-Cu metallic precursor by a low-temperature annealing". Journal of Materials Research 9, n. 6 (giugno 1994): 1337–42. http://dx.doi.org/10.1557/jmr.1994.1337.
Abstract (sommario):
YBa2Cu3O7−x (YBCO) superconducting thin films that show no x-ray diffraction peaks due to any other non-superconducting phases have been synthesized by annealing Y-Ba-Cu-O amorphous precursors at 750 °C. The Y-Ba-Cu-O precursors have been fabricated by oxidizing Y-Ba-Cu metallic precursors coevaporated from Y, Ba, and Cu metallic sources under ultrahigh vacuum conditions. Crystallization behavior from the Y-Ba-Cu-O precursor to YBCO films drastically depends on an oxidation temperature for the Y-Ba-Cu metallic precursor. YBCO thin film synthesized from the precursor oxidized at an optimum temperature shows a zero resistance temperature of over 80 K and a very smooth surface.
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Guerette, Michael, Timothy A. Strobel, Haidong Zhang, Stephen Juhl, Nasim Alem, Konstantin Lokshin, Lakshmi Krishna e P. Craig Taylor. "Advanced Synthesis of Na4Si24". MRS Advances 3, n. 25 (2018): 1427–33. http://dx.doi.org/10.1557/adv.2018.44.
Abstract (sommario):
ABSTRACTThe recently discovered orthorhombic allotrope of silicon, Si24, is an exciting prospective material for the future of solar energy due to a quasi-direct bandgap near 1.3 eV, coupled with the abundance and environmental stability of silicon. Synthesized via precursor Na4Si24at high temperature and pressure (∼850 °C, 9 GPa), typical synthesis results have yielded polycrystalline samples with crystallites on the order of 20 μm. Several approaches to increase the crystal size have yielded success, including in-situ thermal spikes and refined selection of the starting materials. Microstructural analysis suggests that coherency exists between diamond silicon (d-Si) and Na4Si24. This hypothesis has led to the successful attempts at single crystal synthesis by selecting large crystals of d-Si along with metallic Na as the precursors rather than powdered and mixed precursor material. The new synthesis approach has yielded single crystals of Na4Si24greater than 100 μm. These results represent a breakthrough in synthesis that enables further characterization and utility. The promise of Si24for the future of solar energy generation and efficient electronics is strengthened through these advances in synthesis.
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Malik, M. A., M. Afzaal, P. O'Brien, U. Bangert e B. Hamilton. "Single molecular precursor for synthesis of GaAs nanoparticles". Materials Science and Technology 20, n. 8 (agosto 2004): 959–63. http://dx.doi.org/10.1179/026708304225019786.
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Bocharova, Irina V., e Galina B. Kunshina. "Study of ceramic and glass-ceramic solid electrolyte Li1,5Al0,5Ge1,5(PO4)3 properties obtained from oxalate and citrate precursors". Transactions of the Kоla Science Centre of RAS. Series: Engineering Sciences 13, n. 1/2022 (27 dicembre 2022): 26–32. http://dx.doi.org/10.37614/2949-1215.2022.13.1.004.
Abstract (sommario):
The synthesis of lithium conducting solid electrolyte Li1.5Al0.5Ge1.5(PO4)3 (LAGP) by liquid-phase method from oxalate and citrate precursors is investigated. The samples were characterized by XRD, DSC / TG, IR, impedance spectroscopy and potentiostatic chronoamperometry. It was found that the formation of a single - phase LAGP from an oxalate precursor occurs at a lower temperature (600–650 °C) and is preferable compared to the synthesis of LAGP from a citrate precursor. The ionic conductivity of the electrolyte was 4,2 · 10-4 S / cm, the electronic conductivity did not exceed 2 · 10-10 S / cm, the decomposition potential was 3.8 V.
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Liang, Li, Meihua Zhu, Le Chen, Caijun Zhong, Yiming Yang, Ting Wu, Heli Wang, Izumi Kumakiri, Xiangshu Chen e Hidetoshi Kita. "Single Gas Permeance Performance of High Silica SSZ-13 Zeolite Membranes". Membranes 8, n. 3 (13 luglio 2018): 43. http://dx.doi.org/10.3390/membranes8030043.
Abstract (sommario):
Continuous and high silica SSZ-13 zeolite membranes were prepared on porous mullite supports from high SiO2/Al2O3 ratio or aluminum-free precursor synthesis gel. Single gas permeance (CO2 and CH4) of the high silica SSZ-13 zeolite membrane was decreased with the SiO2/Al2O3 ratio in the precursor synthesis gel, while the ideal CO2/CH4 selectivity of the membrane was gradually increased. Moreover, effects of synthesis conditions (such as H2O/SiO2 and RNOH/SiO2 ratios of precursor synthesis gel, crystallization time) on the single gas permeance performance of high silica SSZ-13 zeolite membranes were studied in detail. Medium H2O/SiO2 and RNOH/SiO2 ratios in the initial synthesis gel were crucial to prepare the good CO2 perm-selective SSZ-13 zeolite membrane. When the molar composition of precursor synthesis gel, crystallization temperature and time were 1.0 SiO2: 0.1 Na2O: 0.1 TMAdaOH: 80 H2O, 160 °C and 48 h, CO2 permeance and ideal CO2/CH4 selectivity of the SSZ-13 zeolite membrane were 0.98 × 10−7 mol/(m2·s·Pa) and 47 at 25 °C and 0.4 MPa. In addition, the SiO2/Al2O3 ratio of the corresponding SSZ-13 zeolite was 410 by X-ray fluorescence spectroscopy.
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Cha, Sang Ho. "Synthesis of Single-Crystalline Gold Nanosheet Having Multilayer Structure under the Polymeric Bulk Condition". Applied Mechanics and Materials 548-549 (aprile 2014): 301–4. http://dx.doi.org/10.4028/www.scientific.net/amm.548-549.301.
Abstract (sommario):
A novel synthetic approach to ultrathin (< 5 nm) multilayered single crystalline gold nanosheets using amphiphilic comb-like polymer as template was presented. The poly (oxyethylene) containing decyl-tri (oxyethylene) amphiphile as well as the thioether linking group in the side chain was synthesized via polymer analogous reaction. The polymer and the gold precursor, LiAuCl4, were mixed and dried to afford a homogeneous complex. The gold precursors were reduced to gold crystals by photoreduction using long wave UV light (> 350 nm). The gold nanosheets with multilayered structure, where the layer spacing is about 3.6 nm, were obtained after 24 h. The formation of the multilayered nanosheets is due to the layered structure of the gold complex of the polymer and precursor.
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Devi, P. Sujatha, Yongjae Lee, Joshua Margolis, John B. Parise, Sanjay Sampath, Herbert Herman e Jonathan C. Hanson. "Comparison of citrate–nitrate gel combustion and precursor plasma spray processes for the synthesis of yttrium aluminum garnet". Journal of Materials Research 17, n. 11 (novembre 2002): 2846–51. http://dx.doi.org/10.1557/jmr.2002.0413.
Abstract (sommario):
The influence of synthesis conditions on the formation of yttrium aluminum garnet (YAG) powders starting from the same solution precursors was investigated by employing a citrate–nitrate gel combustion process and a precursor plasma spraying technique. YAG powders were formed at ≥500 °C, through the citrate–nitrate gel combustion process, without any intermediate phase formation. Time-resolved x-ray experiments were performed for the first time on these citrate–nitrate precursor materials to understand their mode of decomposition. The in situ data confirmed a single-step conversion to YAG from the precursor powder without any intermediate phase formation. Ex situ experiments also produced similar results. However, the use of the same citrate–nitrate precursor solution as a liquid feedstock material in the precursor plasma spraying technique revealed an entirely different transformation mechanism to YAG through intermediate phases like H–YalO3 and O–YalO3.
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Brune, Veronika, Nidal Raydan, Anja Sutorius, Fabian Hartl, Bhagyesh Purohit, Sweta Gahlot, Pascal Bargiela et al. "Single source precursor route to nanometric tin chalcogenides". Dalton Transactions 50, n. 46 (2021): 17346–60. http://dx.doi.org/10.1039/d1dt02964a.
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Stanton, C., e R. Wallin. "Processing and trafficking of clotting factor X in the secretory pathway. Effects of warfarin". Biochemical Journal 284, n. 1 (15 maggio 1992): 25–31. http://dx.doi.org/10.1042/bj2840025.
Abstract (sommario):
Clotting factor X undergoes several post-translational processing steps in the liver before the protein appears in blood as the mature two-chain zymogen. In this study we have followed the factor X precursor through the secretory pathway in rat liver in order to identify the site for proteolytic processing of the precursor into a two-chain form and the site for warfarin inhibition of precursor trafficking within the pathway. Isolated rat liver Golgi apparatus was shown to harbour two single-chains of factor X precursors of 70 and 74 kDa and the heavy (50 kDa) and light chains of factor X. It was demonstrated that the two-chain factor X form was produced from a late processing form of the factor X precursor, which indicated that the site for proteolytic conversion to a two-chain form was in the trans-Golgi compartment. The 70 and 74 kDa single-chain precursors and also the light chain of the two-chain form were shown to contain the factor X propeptide which is normally removed before the coagulation factor appears in blood. The data demonstrate that intra-chain cleavage of a single chain factor X precursor in the trans-Golgi compartment can precede release of the propeptide. Warfarin was shown to affect trafficking of the factor X precursor between the endoplasmic reticulum (ER) and the Golgi apparatus. The data suggest a link between vitamin K-dependent gamma-carboxylation of the precursor and its exit from the ER. Warfarin administration resulted in accumulation of factor X precursors associated with the ER membrane. These precursors appear to be stabilized from intracellular degradation while in the ER. In contrast to the large increase in the factor X precursor concentration in the ER membrane, there was no change in the prothrombin precursor concentration as a result of warfarin action on the liver. However, intracellular turnover of the microsomal prothrombin precursor pool in warfarin-treated rats resulted in a pool of less negatively charged proteins, indicating ongoing protein synthesis but inhibition of gamma-carboxylation. The data are consistent with previous findings [Wallin & Martin (1988) J. Biol. Chem. 263, 9994-10001] suggesting that prothrombin and factor X are processed differently by the vitamin K-dependent carboxylase in the ER membrane.
Tesi sul tema "Single precursor synthesis":
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Choujaa, Hamid. "Synthesis of novel single-source precursors for CVD of mixed-metal tungsten oxide". Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.478944.
Abstract (sommario):
There is a considerable interest in the use of tungsten oxide in the research and development of new materials and devices, such as gas sensors and as photocatalysts. In order to improve the photocatalytic properties of WO3, its combination with metals which allows the preparation of WMxOy materials are believed to be promising photocatalysts under visible light. The present work deals with the synthesis of homo- and hetero-metallic tungsten alkoxide and amide compounds using the single source precursor approach for potential chemical vapour deposition precursors of mixed-metal oxide films.
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Bera, A. "Scalable Synthesis of dispersible semiconducting metal chalcogenides nanocrystals and their application". Thesis(Ph.D.), CSIR-NCL, 2021. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/6030.
Abstract (sommario):
Abhijit Bera_Ph.D thesisThe work incorporated in this thesis is mainly focused on various single source metal precursors like metal thiolates and metal dithiocarbamate complexes. Herein, several simple and general methods have been developed for the synthesis of various such single source metal precursors, which comprising the main two constituents of metal chalcogenide nanocrystals (NCs), namely, the tiny inorganic metal chalcogenide complex as core and an organic molecule as shell. Specially, both binary metal thiolates and bimetallic (ternary) thiolates have been prepared and both of them turned out to be excellent precursors for the synthesis of metal sulfide/selenide NCs. The methods used to prepare metal chalcogenide NCs included a direct-heating (solvo-thermal decomposition) method or solid state grinding method. First, the large scale synthesis of various 2D molecular precursors like metal thiolates and metal dithiocarbamate complexes (M-C8DTCA) have been developed and studied their thermal decomposition to metal sulfide NCs via solution based methods. We observed that some of the metal thiolates like Pb-thiolate requires very high temperature to decompose into PbS resulting in particles bigger than their Bohr exciton radius and hence displayed poor optical properties. In the next, to reduce the decomposition temperature an active sulfur precursor called octyl ammonium octyldithiocarbamate (C8DTCA) has been utilized for the synthesis of various metal sulfide NCs (including most challenging PbS NCs, with tunable optical properties) by solution based method (hot injection) or solid state grinding method. We also show that the size of the nanocrystals could be controlled by changing the reaction temperature or metal: chalcogenide precursor ratio. Interestingly, we have also been successful in establishing that these newly developed solid state grinding methods are scalable without compromising their structural and optical properties. The binary or ternary materials synthesized by these solid state routes could be re-dispersed as desired in non-polar organic solvents allowing them to be solution processible. The optical properties of the metal chalcogenide nanocrystals could further be improved by post synthetic surface passivation.
CSIR-NCL
AcSIR
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Abdelhady, Ahmed Mohammed Said lutfi. "Developing novel processes in chemistry for several types of nanoparticles". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/developing-novel-processes-in-chemistry-for-several-types-of-nanoparticles(0712d3c6-e2d5-415a-b787-c9ce457e1355).html.
Abstract (sommario):
The work presented in this thesis reports the use of a series of novel thiobiuret metal complexes [M(SON(CNiPr2)2)n] (M = Cu, Ni, Fe, Zn, Cd or In; n = 2 or 3) for the first time as single source precursors for the colloidal synthesis of metal sulfide nanoparticles. Other single source precursor(s) were also used for the synthesis of CdSe, CdS, CdSe/CdS core/shell, CdSeS alloys and Cu2-xS nanoparticles in microfluidic reactors. Thermolysis experiments of [Cu(SON(CNiPr2)2)2] using only oleylamine produced Cu7S4 nanoparticles as a mixture of monoclinic and orthorhombic phases. Pure orthorhombic Cu7S4 nanoparticles were obtained when a solution of precursor in octadecene was injected into hot oleylamine whereas, Cu1.94S nanoparticles were obtained when a solution of the precursor in oleylamine was injected into hot dodecanethiol. The thermolysis of [Ni(SON(CNiPr2)2)2] gave Ni3S4 in all cases except when precursor solution in oleylamine was injected into hot octadecene which produced NiS nanoparticles. The thermolysis of [Fe(SON(CNiPr2)2)3] in oleylamine/oleylamine produced Fe7S8 nanoparticles but other combinations, in most cases, gave amorphous material. Thermolysis of [Zn(SON(CNiPr2)2)2] in oleylamine produced spherical ZnS nanoparticles. Particles with size smaller than 4.3 nm had a cubic phase, whereas the particles with size larger than 4.3 nm had a hexagonal crystal structure as suggested by the selected area electron diffraction. Powder X-Ray diffraction showed that the CdS nanoparticles obtained from the thermolysis of [Cd(SON(CNiPr2)2)2] in oleylamine were cubic under all reaction conditions except when dodecanethiol was used as an injection solvent which produced hexagonal CdS. β-In2S3 were synthesized from the thermolysis of [In(SON(CNiPr2)2)3]. Transmission electron microscopy showed that the copper, nickel and iron sulfide nanoparticles had various morphologies such as spherical, hexagonal disks, trigonal disks, rods or wires; depending on the reaction temperature, concentration of the precursor, the growth time and the solvent/capping agent combination. The zinc and cadmium sulfide nanoparticles were mostly spherical whereas the indium sulfide nanoparticles were produced in the form of ultra-thin (< 1.0 nm) nanorods or nanowires. ZnxCd1-xS and CuInS2 nanoparticles were synthesised from the 1,1,5,5-tetra-iso-propyl-4-thiobiureto complexes of Zn, Cd and Cu, In, respectively. Powder X-Ray diffraction showed that the obtained ZnxCd1-xS nanoparticles are cubic under all reaction conditions. The ZnxCd1-xS nanoparticles had an average diameter between 3.5 to 6.4 nm as shown by transmission electron microscopy. The optical properties of the ZnxCd1-xS nanoparticles were highly dependent on the ZnS to CdS precursor ratio and the solvents/capping agents. Chalcopyrite (tetragonal), wurtzite (hexagonal) or a mixture of both CuInS2 nanoparticles were obtained depending on the reaction conditions. TEM showed that the CuInS2 nanoparticles could be synthesised with different morphologies (spherical, hexagonal, trigonal or cone). Luminescent CuInS2 nanoparticles were obtained only in the absence of oleylamine. [Cd(S2CNMenHex)2], [Cd(Se2P(iPr)2)2] and [Cu(SON(CNiPr2)2)2] were used as single source precursor(s) for the synthesis of CdS, CdSe, CdSe/CdS core/shell, CdSeS alloys and Cu2-xS in microfludic reactor. The CdS nanoparticles were in size range of 5.0 to 8.0 nm whereas the CdSe nanoparticles were ultra small (ca. 2 nm) with blue luminescence. The CdSe/CdS core/shell and the CdSeS alloys were bluish green or green luminescent depending on their size. The copper sulfide nanoparticles were found to be monoclinic Cu7S4 or monoclinic Cu7S4 with minor impurities of rhombohedral Cu9S5 depending on the reaction conditions.
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Zhou, Cong [Verfasser], Ralf [Akademischer Betreuer] Riedel e Zhaoju [Akademischer Betreuer] Yu. "Ternary Si-Metal-N Ceramics: Single-Source-Precursor Synthesis, Nanostructure and Properties Characterization / Cong Zhou ; Ralf Riedel, Zhaoju Yu". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1130323242/34.
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Kaur, Sarabjeet [Verfasser], Ralf [Akademischer Betreuer] Riedel e Sanjay [Akademischer Betreuer] Mathur. "Single-Source-Precursor Synthesis of SiC-Based Ceramic Nanocomposites for Energy-Related Applications / Sarabjeet Kaur. Betreuer: Ralf Riedel ; Sanjay Mathur". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1112269851/34.
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Wen, Qingbo [Verfasser], Ralf [Akademischer Betreuer] Riedel e Zhaoju [Akademischer Betreuer] Yu. "Single-Source-Precursor Synthesis and Properties of SiMC(N) Ceramic Nanocomposites (M = Hf, Ta, HfTa) / Qingbo Wen ; Ralf Riedel, Zhaoju Yu". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1130323250/34.
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Yuan, Jia [Verfasser], Ralf [Akademischer Betreuer] Riedel e Zhaoju [Akademischer Betreuer] Yu. "SiHf(B)CN-based ultra-high temperature ceramic nanocomposites: Single-source precursor synthesis and behavior in hostile environments / Jia Yuan. Betreuer: Ralf Riedel ; Zhaoju Yu". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2015. http://d-nb.info/111191138X/34.
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Liu, Xingmin [Verfasser], Ralf [Akademischer Betreuer] Riedel e Nahum [Akademischer Betreuer] Travitzky. "Single-Source-Precursor Synthesis and Electromagnetic Properties of SiCN-Based Ceramic Nanocomposites Modified with Carbon Nanofillers from 1D CNTs to 3D RGO/CNTs / Xingmin Liu ; Ralf Riedel, Nahum Travitzky". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/116930530X/34.
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Trindade, Tito Da Silva. "The synthesis of metal chalcogenide nanocrystallites using single molecule precursors". Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363125.
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Pearce, Amber Marie. "Synthesis and characterisation of metal chalcogenide thin films". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/synthesis-and-characterisation-of-metal-chalcogenide-thin-films(7a22c662-639c-4aaf-a4cc-f2ae655115c0).html.
Abstract (sommario):
There is much interest in the electronic potential of ‘nano’-semiconductors. The avenue of research pursued in this project was in inorganic analogues of graphene, namely metal chalcogenides MxEy (M = metal, E = S, Se, Te, x ≠ y = integer value). Thin films of these materials have been used in solar cells, ambient thermoelectric generators and IR detectors, due to their interesting properties, such as: optoelectronics, magnetooptic, piezoelectric, thermoelectric and photovoltaic, as well as electrical conductivity. The key issues with the use of these materials are the formation of controlled films, especially in terms of stoichiometry, crystallinity and uniformity, and also the precursor system used. The aim of this research was to synthesise and isolate novel precursor compounds for use in the deposition of metal sulfide thin films (for use with molybdenum and tungsten). The potential viability of the compounds as single source precursors (ssp) was judged following ThermoGravimetric Analysis (TGA). The compounds were also subjected to analysis using NMR (1H, 13C and 31P where applicable), infrared and UV-Vis spectroscopy, as well as elemental analysis. Cadmium sulfide (CdS) is one of the key direct band gap II-VI semiconductors, having vital optoelectronic applications for laser light-emitting diodes, and optical devices based on non-linear properties. The ratio of these films should ideally be 1:1, however, during the formation of cadmium sulfide films, particularly at elevated temperatures, a common problem encountered is the production of sulfur deficient films. These films have a formula consistent with 〖Cd〗_x S_y, where x is an integer value greater than y, but the sulfur deficiency is generally no greater than 10 %. In order to correct this sulfur deficiency, it was decided to investigate deposition making use of both a ssp and an additional sulfur source, with the aim of producing uniform films with 1:1 Cd:S.Molybdenum disulfide films have been deposited previously from multi source precursors and more recently using ssp. In this project MoS2 was deposited using novel ssps in both LP and AACVD on a variety of substrates with the aim of producing uniform thin films and assessing any differences in the morphology of the deposition. This work was continued with the deposition of WS2 and MoxW1-xS2 from ssps which had not been reported previously. The films deposited were analysed using XRD, SEM, EDX (when available) and Raman spectroscopy.
Libri sul tema "Single precursor synthesis":
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Barron, Andrew, Allen Apblett e Aloysius Hepp. Nanomaterials Via Single-Source Precursors: Synthesis, Processing and Applications. Elsevier, 2021.
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Barron, Andrew, Aloysius F. Hepp e Allen Apblett. Nanomaterials via Single-Source Precursors: Synthesis, Processing and Applications. Elsevier, 2021.
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National Aeronautics and Space Administration (NASA) Staff. Synthesis and Characterization of the First Liquid Single Source Precursors for the Deposition of Ternary Chalcopyrite (Cuins2) Thin Film Materials. Independently Published, 2018.
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Deegan, Patrick. Porphyria. A cura di Patrick Davey e David Sprigings. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780199568741.003.0179.
Abstract (sommario):
This chapter discusses six diseases caused by inborn errors of metabolism affecting the biosynthesis of haem. Haem is a tetracyclic metal-binding compound involved in oxygen transport (in haemoglobin and myoglobin) and redox reactions (e.g. in the cytochrome P450 system). Each of these conditions is caused by a single gene defect in one of the enzymes involved in the biosynthesis of haem. Inheritance is usually autosomal dominant with incomplete penetrance. The enzyme defect results in disease, not as a result of deficiency of the reaction product, but as a result of accumulation of precursors. Early, soluble precursors, 5-aminolaevulinic acid, and porphobilinogen (not porphyrins as such) are neurotoxic and, when present in great excess, as occurs when flux through the haem synthetic pathway is increased in response to particular medications or hormones, lead to acute neurovisceral crises. Later cyclical precursors (porphyrins) in the pathway are also water soluble and excreted in urine, but are susceptible to activation by electromagnetic radiation in the visible spectrum and are converted to free-radical metabolites that cause pain, inflammation, and tissue damage in the skin. The final haem precursors (also porphyrins) are hydrophobic and excreted in the bile and faeces and are also activated by light to toxic metabolites.
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Feldman, Seymour. Gersonides. Liverpool University Press, 2010. http://dx.doi.org/10.3828/liverpool/9781904113447.001.0001.
Abstract (sommario):
Gersonides (1288–1344) was a philosopher as well as an astronomer and biblical exegete. This book is a comprehensive picture of Gersonides' philosophy that is both descriptive and evaluative. Unusually for a Jewish scholar, Gersonides had contacts with several Christian notables and scholars. It is known that these related to mathematical and astronomical matters; the extent to which these contacts also influenced his philosophical thought is a matter of some controversy. Unquestionably, he wrote a library of philosophical, scientific, and exegetical works that testify not only to the range of his intellectual concerns but also to his attempt to forge a philosophical–scientific synthesis between these secular sciences and Judaism. He did not see any fundamental discrepancy between the pursuit of truth via reason and its attainment through divine revelation. As a philosopher-scientist and biblical exegete, Gersonides sought to make this agreement robustly evident. While philosophical and scientific ideas have progressed since Gersonides' time, his work is still relevant today because his attempt to make prophecy and miracles understandable in terms of some commonly held philosophical or scientific theory is paradigmatic of a religion that is not afraid of reason. His general principle that reason should function as a “control” of what we believe has interesting and important implications for the modern reader. He was not afraid to make religious beliefs philosophically and scientifically credible. In this respect he was a precursor of Kant and Hermann Cohen: Judaism is or should be a religion of reason.
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Mark, James E., Harry R. Allcock e Robert West. Inorganic Polymers. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780195131192.001.0001.
Abstract (sommario):
Polymer chemistry and technology form one of the major areas of molecular and materials science. This field impinges on nearly every aspect of modern life, from electronics technology, to medicine, to the wide range of fibers, films, elastomers, and structural materials on which everyone depends. Although most of these polymers are organic materials, attention is being focused increasingly toward polymers that contain inorganic elements as well as organic components. The goal of Inorganic Polymers is to provide a broad overview of inorganic polymers in a way that will be useful to both the uninitiated and those already working in this field. There are numerous reasons for being interested in inorganic polymers. One is the simple need to know how structure affects the properties of a polymer, particularly outside the well-plowed area of organic materials. Another is the bridge that inorganic polymers provide between polymer science and ceramics. More and more chemistry is being used in the preparation of ceramics of carefully controlled structure, and inorganic polymers are increasingly important precursor materials in such approaches. This new edition begins with a brief introductory chapter. That is followed with a discussion of the characteristics and characterization of polymers, with examples taken from the field. Other chapters in the book detail the synthesis, reaction chemistry, molecular structure, and uses of polyphosphazenes, polysiloxanes, and polysilanes. The coverage in the second edition has been updated and expanded significantly to cover advances and interesting trends since the first edition appeared. Three new chapters have been added, focusing on ferrocene-based polymers, other phosphorous-containing polymers, and boron-containing polymers; inorganic-organic hybrid composites; and preceramic inorganic polymers.
Capitoli di libri sul tema "Single precursor synthesis":
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Sugimoto, Masaki, Akira Idesaki, Masahito Yoshikawa, Shogo Watanabe e Shu Seki. "Synthesis of Ceramic Nano Fiber from Precursor Polymer by Single Particle Nano-Fabrication Technique". In Ceramic Transactions Series, 105–10. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2010. http://dx.doi.org/10.1002/9780470880630.ch13.
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Pentyala, Nagaswetha, Ramesh K. Guduru, Elizabeth M. Shnerpunas e Pravansu S. Mohanty. "Synthesis of Ultrafine Single Crystals and Nanostructured Coatings of Indium Oxide from Solution Precursor". In Supplemental Proceedings, 51–58. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2011. http://dx.doi.org/10.1002/9781118062173.ch8.
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Camargo, P. H. C., G. G. Nunes, D. J. Evans, G. J. Leigh, G. Tremiliosi-Filho, E. L. Sá, A. J. G. Zarbin e J. F. Soares. "Single-source precursor and homometal approaches to the sol–gel synthesis of iron and titanium oxides". In Surface and Colloid Science, 221–26. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/b97089.
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Mathur, Sanjay, Michael Veith, Nicolas Lecerf, Nicole Donia, Volker Huch, Hao Shen e Stefan Hüfner. "Molecular Routes to Advanced Materials: Synthesis of NdAlO3 Ceramic and NdAlO3 /Al2 O3 Composite From Single Source Precursors". In Ceramics - Processing, Reliability, Tribology and Wear, 282–88. Weinheim, FRG: Wiley-VCH Verlag GmbH & Co. KGaA, 2006. http://dx.doi.org/10.1002/3527607293.ch48.
5
Jones, M. Thomas, Megh Singh, James H. Roble e Toshio Maruo. "Single Crystal ESR Studies of Transition metal (o-Benzene-Diselenolate) 2 - [BDS] and (o-Benzenedithiolate) 2 - [BDT] Complexes: Potential Synthetic Metal Precursors". In 25th Congress Ampere on Magnetic Resonance and Related Phenomena, 531–32. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-76072-3_278.
6
Jain, Vimal K., e Rohit Singh Chauhan. "Metal–Chalcogenolates: Synthesis and Applications in Material Chemistry". In Chalcogen Chemistry: Fundamentals and Applications, 58–82. The Royal Society of Chemistry, 2023. http://dx.doi.org/10.1039/bk9781839167386-00058.
Abstract (sommario):
Metal chalcogenolate complexes have been known for a long time. These complexes exhibit rich and diverse structural chemistry and find numerous applications in widely different areas. Their utility as a single source molecular precursor for the design and synthesis of metal chalcogenides was quickly realized with the emergence of nano-science and nanotechnology in the 1990s. This chapter intends to cover synthetic approaches for the preparation of metal chalcogenolates and their applications in materials chemistry. Metal chalcogenolate precursor chemistry for both binary and ternary metal chalcogenides is discussed.
7
Taber, Douglass F. "Diels-Alder Cycloaddition: (+)-Armillarivin (Banwell), Gelsemiol (Gademann), (+)-Frullanolide (Liao), Myceliothermophin A (Uchiro), Peribysin E (Reddy), Caribenol A (Li/Yang)". In Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0081.
Abstract (sommario):
Martin G. Banwell of the Australian National University prepared (Org. Lett. 2013, 15, 1934) the enantiomerically pure diol 1 by fermentation of the aromatic precursor. Diels-Alder addition of cyclopentenone 2 proceeded well at elevated pressure to give 3, the precursor to (+)-armillarivin 4. Karl Gademann of the University of Basel found (Chem. Eur. J. 2013, 19, 2589) that the Diels-Alder addition of 6 to 5 proceeded best without solvent and with Cu catalysis to give 7. Reduction under free radical conditions led to gelsemiol 8. Chun-Chen Liao of the National TsingHua University carried out (Org. Lett. 2013, 15, 1584) the diastereoselective addition of 10 to 9. A later oxy-Cope rearrangement established the octalin skeleton of (+)-frullanolide 12. D. Srinivasa Reddy of CSIR-National Chemical Laboratory devised (Org. Lett. 2013, 15, 1894) a strategy for the construction of the angularly substituted cis-fused aldehyde 15 based on Diels-Alder cycloaddition of 14 to the diene 13. Further transformation led to racemic peribysin-E 16. An effective enantioselective catalyst for dienophiles such as 14 has not yet been developed. Hiromi Uchiro of the Tokyo University of Science prepared (Tetrahedron Lett. 2012, 53, 5167) the bicyclic core of myceliothermophin A 19 by BF3•Et2O-promoted cyclization of the tetraene 17. The single ternary center of 17 mediated the formation of the three new stereogenic centers of 18, including the angular substitution. En route to caribenol A 22, Chuang-Chuang Li and Zhen Yang of the Peking University Shenzen Graduate School assembled (J. Org. Chem. 2013, 78, 5492) the triene 20 from two enantiomerically pure precursors. Inclusion of the radical inhibitor BHT sufficed to suppress competing polymerization, allowing clean cyclization to 21. Methylene blue has also been used (J. Am. Chem. Soc. 1980, 102, 5088) for this purpose.
8
Ko, Jeong-Rae, Ju-Won Min, Byung-Don You e Wha-Seung Ahn. "Synthesis of β-SiC nanofiber using PMOs as a single precursor". In Recent Progress in Mesostructured Materials - Proceedings of the 5th International Mesostructured Materials Symposium (IMMS2006), Shanghai, P.R. China, August 5-7, 2006, 279–82. Elsevier, 2007. http://dx.doi.org/10.1016/s0167-2991(07)80317-x.
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Dhadda, Surbhi, Prakash Giri Goswami e Himanshu Sharma. "Green Synthesis of Chalcone Derivatives Using Chalcones as Precursor". In Green Chemistry - New Perspectives [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.103959.
Abstract (sommario):
Recently, the use of green methodologies like sonication, use of ionic liquids, etc. attracted the attention of researchers in the field of organic synthesis as they have advantages such as mild reaction conditions, environmentally benign procedures, etc. Herein, this chapter highlights some recyclable ionic liquids (ILs) catalyzed ring closure reactions of chalcones to obtain several heterocyclic rings viz.; pyrazoles, pyrans, pyrimidines under ultrasonification. These reactions have very important features i.e., short routine, high yields, being environmentally friendly, high functional group tolerance, formation of a single product, high atom economy, high yielding, no need for column purification, etc. The various synthesized compounds were prepared in optimized reaction conditions in good to efficient yields. Analytical and spectral (FTIR, 1H, and 13C NMR) techniques were employed for the structural elucidation of the synthesized compounds. The ionic liquids used in the synthesis are recycled and reused several times.
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Weller, Mark T. "The synthesis of inorganic materials". In Inorganic Materials Chemistry. Oxford University Press, 1995. http://dx.doi.org/10.1093/hesc/9780198557982.003.0003.
Abstract (sommario):
This chapter examines the synthesis of inorganic materials. The synthesis methods used in the preparation of inorganic materials, many of which have extended lattices rather than discrete molecules, are quite different from those used by organic, organometallic, and coordination chemists. Rather than altering a single functional group or ligand attached to a molecule, the materials chemist works with complete lattices, either building or modifying them. The chapter begins by looking at high temperature reactions. The most widely used method for the synthesis of inorganic materials follows an almost universal route that involves heating the components together at high temperature over an extended period. The chapter then details the process of the reaction between solids, before studying the precursor, solution, and gel methods. It also assesses hydrothermal methods, phase diagrams, and low temperature methods.
Atti di convegni sul tema "Single precursor synthesis":
1
Disale, Sujit D., Shivram S. Garje, P. K. Giri, D. K. Goswami, A. Perumal e A. Chattopadhyay. "Synthesis of single phase magnetite, Fe[sub 3]O[sub 4] nanocrystallites using single source precursor". In INTERNATIONAL CONFERENCE ON ADVANCED NANOMATERIALS AND NANOTECHNOLOGY (ICANN-2009). AIP, 2010. http://dx.doi.org/10.1063/1.3504326.
2
Wank, A., e B. Wielage. "Synthesis of BCN Coatings in Thermal Plasma Jets". In ITSC2003, a cura di Basil R. Marple e Christian Moreau. ASM International, 2003. http://dx.doi.org/10.31399/asm.cp.itsc2003p0913.
Abstract (sommario):
Abstract The system B-C-N contains the hardest known materials like diamond, cubic boron nitride and boron carbide, which also show excellent chemical resistance. The oxidation resistance is shifted to higher temperatures in comparison to pure diamond. But pure BCN coatings cannot be produced by conventional thermal spray processes, as the materials lack both a liquid phase and sufficient ductility to permit deposition. Conventional VPS equipment is successfully applied in Thermal Plasmajet CVD processes for high deposition rate synthesis of diamond coatings. The feasibility of SiCN or boron carbide synthesis by this method has also been proven. The use of liquid precursors results in outstanding deposition rates and improved operational safety. Methylized borazine is applied for synthesis of BCN coatings in thermal plasma jets. The use of single source precursors is advantageous with concern to the homogeneity of the coating forming species stoichiometry. For long-term storage cooling is necessary, but also under ambient conditions the precursor shows sufficient stability. Plasma gun nozzles with different diameter and design are applied and evaluated with concern to the resulting coating properties. Deposition rates of up to 1,500 µm/h have been achieved with homogeneous coating thickness and morphology on areas with 50 mm diameter. No porosity is detected in SEM investigations on cross sections and fracture surfaces show a fine columnar coating morphology. XRD investigations point at an amorphous structure. Only for very high substrate temperatures the formation of crystalline boron carbide B8C and h-BN or graphite phases is detected. Oxygen contamination results in boric acid formation and therefore has to be avoided carefully. During coating deposition on mild steel substrates the formation of boride and nitride reaction zones is observed. VPS sprayed nickel or molybdenum interlayers permit to inhibit the evolution of reaction zones. Thereby BCN coatings with thicknesses of up to 10 µm are deposited without local delamination. Space resolved emission spectroscopic analyses are carried out in order to detect coating forming and intermediate species. As Thermal Plasmajet CVD is a pure gas phase deposition process, the control of the space resolved emission permits easy process control.
3
Rajput, H. "Exploiting Reducing Ability of DMF For Assembled Gold Nanostructures". In Functional Materials and Applied Physics. Materials Research Forum LLC, 2022. http://dx.doi.org/10.21741/9781644901878-14.
Abstract (sommario):
Abstract. We explore stable assembly of gold NPs in single step process by introducing a simple chemical synthesis in which pH changed gold precursor is added to dimethylformamide solution at RT. The redox chemistry of N, N-dimethylformamide (DMF) has been effectively utilized in the formation of surfactant free, small chain metal NPs networks (plasmonic oligomers) via molecular dipolar coupling. Kinetic absorption / TEM images illustrate gold nanocrystals formation, their inter-particle coupling as a function of pH as well as with DMF-Water ratio. Sub-nano gap inter-particle coupling b/w spherical/anisotropic Au NPs is seen through arising of new LSPR hump in NIR region. 1-D organized gold nanocrystals are formed when pH modified metal precursor is added to refluxed (80 0C) DMF: Water mixture. The inter-particle coupling provides unique strategy can promote complex sub-wavelength optical waveguides and nanophotonic devices.
4
Yu, Zexin, Meimei Liu, Michel Moliere, Hanlin Liao, Hatem Moussa, Raphaël Schneider e Weize Wang. "Spinel Copper Ferrite and Zinc Ferrite Films Synthesized via Solution Precursor Plasma Spray Process for Functional Applications". In ITSC2018, a cura di F. Azarmi, K. Balani, H. Li, T. Eden, K. Shinoda, T. Hussain, F. L. Toma, Y. C. Lau e J. Veilleux. ASM International, 2018. http://dx.doi.org/10.31399/asm.cp.itsc2018p0627.
Abstract (sommario):
Abstract Binary spinel-type metal oxides (AB2O4) semiconductors, including ferrites (AFe2O4), are attractive photocatalysts thanks to their excellent visible light response and good photochemical activity and stability for the photodegradation of organic pollutants. Currently, their synthesis proceeds via conventional chemical routes that follow rather tedious protocols and the final preparations consist in nano-powders, a form that is not exempt of EHS (Environment, health and safety) risks along their handling. From an industry perspective, it is desirable to dispose of an efficient and preferably simple synthesis route capable to produce photocatalytic preparations in a non-dispersible form, for instance in the form of robust films attached on solid substrates. We report herein a single-step method based on the Solution Precursor Plasma Spray (SPPS) process that enables the preparation of promisingly active ferrite-based photocatalytic films, namely CuFe2O4 and ZnFe2O4. We have investigated various types of precursor solutions, including the atomic A/Fe ratios, solvent type and solute concentration, and studied the evolution of the phase composition of the resultant CuFe2O4 and ZnFe2O4 films by XRD. The corresponding surface morphologies and energy bandgaps were also studied by SEM and UV-Vis spectroscopy, respectively. Then the photocatalytic activities of the selective ferrite films were evaluated through the degradation of aqueous solutions of the Orange II dye under different light irradiations. The results of the overall work also revealed that SPPS process represents a fast, one-step, versatile alternative compared to conventional multi-step processes, which is suitable for preparing complex composition metal oxide film-formed photocatalyst.
5
Custodio, Aisa Grace, Gobinda C. Saha e Clodualdo Aranas. "Development of a Synthesis Route for High-Entropy Alloy Feedstock Particles for Cold Spray Following Conventional and Sequential Mechanical Milling Regimes". In ITSC 2023. ASM International, 2023. http://dx.doi.org/10.31399/asm.cp.itsc2023p0567.
Abstract (sommario):
Abstract Material’s tensile strength can be improved by the presence of a body-centered cubic (BCC) phase, which is essential in highstrength applications and highly corrosive environments. Thus, synthesizing a BCC single-phase, equiatomic AlCoCrFeNi high-entropy alloy (HEA) feedstock particle using a highenergy mechanical alloying (HE-MA) method was investigated. The transient alloy particles were developed using a planetary mill at a constant rotational speed of 580 rpm employing milling times in the range of 4 to 24 hours. During the process, stearic acid of 3 wt.% of the precursor composition was used as a process-controlling agent (PCA). Two HE-MA manufacturing regimes were utilized: i) conventional (milling constituent elements simultaneously), and ii) sequential (progressive milling while adding elements in a certain order). In addition to the conventional method, a sequential regime was employed to develop FeNiCoCrAl, wherein individual elements were added every 4 hours to the starting/milled Fe + Ni mixture. Based on the results, the HE-MA FeNiCoCrAl showed a BCC single-phase formation after 24 hours, with no intermetallic or contamination traceability. Finally, a nanoindentation hardness measurement was carried out to support the observed phase transformation before and after the HE-MA process.
6
Ravi, B. G., S. Sampath, R. Gambino, P. S. Devi e J. B. Parise. "Plasma Spray Synthesis from Precursors: Progress, Issues and Considerations". In ITSC2006, a cura di B. R. Marple, M. M. Hyland, Y. C. Lau, R. S. Lima e J. Voyer. ASM International, 2006. http://dx.doi.org/10.31399/asm.cp.itsc2006p0871.
Abstract (sommario):
Abstract Precursor plasma spray synthesis is an innovative and rapid method to make functional oxide ceramic coatings by starting from solution precursors and directly producing inorganic films. This emerging method, utilizes molecularly mixed precursor liquids, which essentially avoids the handling and selection of powders, opening up new avenues for developing compositionally complex functional oxide coatings. Precursor plasma spray also offers excellent opportunities in exploring the non-equilibrium phase evolution during plasma spraying of multi-component oxides from inorganic precursors. Although there have been efforts in this area since the 1980s and early 1990s with the goal of synthesizing nanoparticles, only recently has the work progressed in the area of functional systems. At the Center for Thermal Spray Research an integrated investigative strategy has been conducted to explore the benefits and limits of this synthesis strategy. Water and alcohol based sol/solution precursors derived from various chemical synthesis methods were used as feedstocks to deposit thin/thick films of spherical and nanostructured coatings of yttrium aluminum garnet (YAG), yttrium iron garnet (YIG), lanthanum strontium manganite (LSM) and Zr-substituted yttrium titanates, compositions of Y2O3-Al2O3 and their microstructural space centered around stochiometric YAG. A detailed discussion of the salient features of RF induction plasma spraying (RFPPS) approach, results obtained in the investigations to develop various functional oxide coatings and process issues and challenges are presented.
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Samuel, B. A., C. M. Lentz e M. A. Haque. "Experimental Study of Structure-Electrical Transport Correlation in Single Disordered Carbon Nanowires". In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11739.
Abstract (sommario):
We present experimental results characterizing the changes in electrical transport of single disordered carbon nanowires (diameter 150–250 nm) to the changes in microstructure within the nanowires induced by synthesis temperature. The material system studied is a nanoporous, semiconducting disordered carbon nanowire obtained from the pyrolysis of a polymeric precursor (polyfurfuryl alcohol). Unlike the other allotropes of carbon such as diamond, graphite (graphenes) and fullerenes (CNT, buckyballs), disordered carbons lack crystalline order and hence can exhibit a range of electronic properties, dependent on the degree of disorder and the local microstructure. Such disordered carbon nanowires are therefore materials whose electronic properties can be engineered to specifications if we understand the structure-property correlations. Using dark DC conductivity tests, measurements were performed from 300K to 450K. The charge transport behavior in the nanowires is found to follow an activation-energy based conduction at high temperatures. The conductivity for nanowires synthesized from 600°C to 2000°C is calculated and is linked to changes in the microstructure using data obtained from SEM, TEM and Raman spectroscopy. The electrical properties of the nanowire are shown to be linked intrinsically to the microstructure and the degree of disorder, which in turn can be controlled to a great extent just by controlling the pyrolysis temperature. This ability to tune the electrical property, specifically conductivity, and map it to the structural changes within the disordered material makes it a candidate material for use in active/passive electronic components, and as versatile transducers for sensors.
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Gerna, M., e M. B. Donati. "HYPERCOAGULABILITY AND REDUCED SENSITIVITY TO WARFARIN IN RATS FOLLOWING CAFFEINE INTAKE". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643399.
Abstract (sommario):
The effect(s) of caffeine Intake on cardiovascular functions are still a matter of debate. We have considered here the level of the prothrombin complex activity as a parameter of blood coagulability following caffeine Intake. The activity of the four vitamin K-dependent clotting factors (II, VII, IX and X) was tested after acute and chronic administration of high doses of caffeine. With a single administration of 50 mg/kg caffeine a statistically significant increase in the activity of factors VII, IX and X was observed. The increase lasted for 4, 3 and 2 days respectively. Factor II was not affected by caffeine administration. The same effect was observed during chronic administration (50 mg/kg/day). With a lower dose of caffeine during chronic administration (5 mg/kg/day) only factor X showed a significant increase. A single dose of caffeine (50 mg/kg) given to animals 24h before-a dose of warfarin (0.4 mg/kg i.v.) markedly reduced the anticoagulant effect of warfarin, as measured by the thrombotest. During the latter experiment we measured also the rate of synthesis (Rsyn) of the prothrombin complex activity. Rsyn, during warfarin treatment, was significantly higher in the rats pretreated with caffeine than In controls. γ-Carboxylase activity in rat liver mlcrosomes was measured after administration of 50 mg/kg of caffeine as a single dose. The Incorporation of 14CO2 in the endogenous precursor was higher in the rats pretreated with caffeine than In controls (84,905 cpm/mg of protein versus 59,826 cpm/mg of proteins); this difference, however, was not statistically significant. In conclusion, caffeine jntake may affect the clotting system mainly by stimulating the synthesis of factors of the prothrombin complex and, as a consequence, their response to coumarin anticoagulation.
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Tsakalakos, Loucas, Lauraine Denault, Michael Larsen, Mohamed Rahmane, Yan Gao, Joleyn Balch e Paul Wilson. "Mo2C Nanowires and Ribbons on Si via Two-Step Vapor Phase Growth". In ASME 2004 3rd Integrated Nanosystems Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/nano2004-46098.
Abstract (sommario):
Transition metal carbides are an interesting class of electronic materials owing to their high electrical conductivity at room temperature, which is only slightly lower than that of their constituent transition metal elements. For example, the room temperature electrical resistivity of bulk Mo2C is ∼70 μΩ-cm compared to that of Mo (4.85 μΩ-cm), whereas that of NbC is ∼50 μΩ-cm as compared to 15.2 μΩ-cm for Nb. Indeed, the temperature dependent resistivity of many transition metal carbides suggests metallic-like conduction. Furthermore, certain transition metal carbides are known to become superconducting, with transition temperatures ranging from 1.15 °K for TiC1−x to 14 °K for NbC. [1] They are also able to withstand high temperatures and are chemically stable. Initial synthesis of metal carbide nanorods was demonstrated using the carbon nanotube (CNT) confined reaction mechanism by Lieber and co-workers [2] and subsequent superconducting behavior was shown by Fukunaga et al. [3]. Vapor-liquid-solid growth was employed by Johnson et al. [4] to synthesize micron-sized carbide whiskers. Here, we have successfully synthesized Mo2C nanorods and ribbons on Si substrates using a novel two-step catalytic approach, which allows for synthesis of such high temperature nanostructures at manufacturable temperatures (≤ 1000 °C) and time scales (≤ 60 min). In the first step we utilize a catalytic vapor phase process to grow Mo and/or molybdenum oxide nanostructures, which are subsequently carburized in situ to form the desired Mo2C nanostructures. Unlike true VLS growth of carbides, in which high temperature (≤ 1100–1200 °C) is required to adequately dissolve carbon into the catalyst particles, our strategy is to react the nanostructures along their entire length with a carbon vapor source after creating the oxide/metal nanostructures, which for Mo2C can be achieved at relatively low temperatures. (≤ 1000 °C). The nanorods and ribbons are polycrystalline, with a mean grain size of 20–50 nm and 50–150 nm, respectively. We hypothesize that the growth mechanism is a complex mixture of VLS, VSS, and auto-catalytic growth, in which molten catalyst nanoparticles enter a three phase region once the metal precursor is supplied. The growth then presumably continues via a vapor-solid-solid process and is possible assisted by the presence of various molybdenum oxide species on the surface. Initial single nanowire electrical measurements yield a higher resistivity than in the bulk, which is attributed to the fine grain sizes and/or the presence of an oxide layer. A discussion of the growth mechanism will be presented along with issues relating to single nanowire device fabrication and control of nanowire orientation.
10
Wilden, J., e A. Wank. "Process Features During the Plasmajet CVD Synthesis of Si-C-N Coatings". In ITSC2001, a cura di Christopher C. Berndt, Khiam A. Khor e Erich F. Lugscheider. ASM International, 2001. http://dx.doi.org/10.31399/asm.cp.itsc2001p0487.
Abstract (sommario):
Abstract Materials in the system Si-C-N feature excellent properties for wear and corrosion protection applications even at elevated temperatures and an excellent thermal shock resistance among the ceramics. As these materials have no melting point, they cannot be processed purely by conventional spraying techinques, but need to be synthesized. Plasmajet CVD processes with single and triple DC torches and HF torches with supersonic nozzles have successfully been applied to produce Si-C(-N) coatings on different steel, aluminum, titanium and copper alloys as well as on graphite. Various liquid single precursors with suitable structure have been tested and evaluated with regard to the morphology and structure of the produced coatings. The processes are compared taking into account their characteristics concerning the injection modes, gas temperature and velocity profiles. Emission spectroscopy is used to determine the mechanisms of the coating formation. Guidelines for the optimum production of Si-C(-N) coatings by Plasmajet CVD are deducted.
Rapporti di organizzazioni sul tema "Single precursor synthesis":
1
Gantt, Elisabeth, Avigad Vonshak, Sammy Boussiba, Zvi Cohen e Amos Richmond. Carotenoid-Rich Algal Biomass for Aquaculture: Astaxanthin Production by Haematococcus Pluvialis. United States Department of Agriculture, agosto 1996. http://dx.doi.org/10.32747/1996.7613036.bard.
Abstract (sommario):
The synthesis of carotenoids has been studied toward enhancing the production of ketocarotenoids, since fish and crustaceans raised by aquaculture require astaxanthin and other ketocaroteinoids in their feed for desirable pigmentation. Notable progress has been made in attaining the goals of determining improved conditions for ketocarotenoid production in Haematococcus pluvialis and in elucidating the carotenoid biosynthetic pathway. For production of astaxanthin a number of strains of the green alga Haematococcus were evaluated, a strain CCAG was found to be optimal for photoautotrophic growth. Of four mutants, selected for enhanced carotenoid production, two hold considerable promise because caroteinoid accumulation occurs without encystment. The biosynthetic pathway of carotenoids was elucidated in photosynthetic organisms by characterizing novel genes encoding carotenoid enzymes and by examining the function of these enzymes in a bacterial complementation system. Two cyclases (b- and e-) were cloned that are at a critical branch point in the pathway. One branch leads to the formation of b-carotene and zeaxanthin and astaxanthin, and the other to the production of a-carotene and lutein. Cyclization of both endgroups of lycopene to yield b-carotene was shown to be catalyzed by a single gene product, b-lycopene cyclase in cyanobacteria and plants. The formation of a-carotene was found to require the e-cyclase gene product in addition to the b-cyclase. By cloning a b-hydroxylase gene we showed that a single gene product forms zeaxanthin by hydroxylatin of both b-carotene rings. It is expected that a second hydroxylase is required in the synthesis of astaxanthin, since canthaxanthin rather than zeaxanthin is the precursor. Evidence, from inhibitor studies, suggests that astaxanthin is formed from canthaxanthin and that b-carotene is a major precursor. Feasibility studies with the photobioreactors have shown that a two-stage system is the most practical, where Haematococcus cultures are first grown to high cell density and are then switched to high light for maximal astaxanthin production. The basic knowledge and molecular tools generated from this study will significantly enhance Haematococcus as a viable model for enhanced astaxanthin production.
2
Ohad, Itzhak, e Himadri Pakrasi. Role of Cytochrome B559 in Photoinhibition. United States Department of Agriculture, dicembre 1995. http://dx.doi.org/10.32747/1995.7613031.bard.
Abstract (sommario):
The aim of this research project was to obtain information on the role of the cytochrome b559 in the function of Photosystem-II (PSII) with special emphasis on the light induced photo inactivation of PSII and turnover of the photochemical reaction center II protein subunit RCII-D1. The major goals of this project were: 1) Isolation and sequencing of the Chlamydomonas chloroplast psbE and psbF genes encoding the cytochrome b559 a and b subunits respectively; 2) Generation of site directed mutants and testing the effect of such mutation on the function of PSII under various light conditions; 3) To obtain further information on the mechanism of the light induced degradation and replacement of the PSII core proteins. This information shall serve as a basis for the understanding of the role of the cytochrome b559 in the process of photoinhibition and recovery of photosynthetic activity as well as during low light induced turnover of the D1 protein. Unlike in other organisms in which the psbE and psbF genes encoding the a and b subunits of cytochrome b559, are part of an operon which also includes the psbL and psbJ genes, in Chlamydomonas these genes are transcribed from different regions of the chloroplast chromosome. The charge distribution of the derived amino-acid sequences of psbE and psbF gene products differs from that of the corresponding genes in other organisms as far as the rule of "positive charge in" is concerned relative to the process of the polypeptide insertion in the thylakoid membrane. However, the sum of the charges of both subunits corresponds to the above rule possibly indicating co-insertion of both subunits in the process of cytochrome b559 assembly. A plasmid designed for the introduction of site-specific mutations into the psbF gene of C. reinhardtii. was constructed. The vector consists of a DNA fragment from the chromosome of C. reinhardtii which spans the region of the psbF gene, upstream of which the spectinomycin-resistance-conferring aadA cassette was inserted. This vector was successfully used to transform wild type C. reinhardtii cells. The spectinomycin resistant strain thus obtained can grow autotrophically and does not show significant changes as compared to the wild-type strain in PSII activity. The following mutations have been introduced in the psbF gene: H23M; H23Y; W19L and W19. The replacement of H23 involved in the heme binding to M and Y was meant to permit heme binding but eventually alter some or all of the electron transport properties of the mutated cytochrome. Tryptophane W19, a strictly conserved residue, is proximal to the heme and may interact with the tetrapyrole ring. Therefore its replacement may effect the heme properties. A change to tyrosine may have a lesser affect on the potential or electron transfer rate while a replacement of W19 by leucine is meant to introduce a more prominent disturbance in these parameters. Two of the mutants, FW19L and FH23M have segregated already and are homoplasmic. The rest are still grown under selection conditions until complete segregation will be obtained. All mutants contain assembled and functional PSII exhibiting an increased sensitivity of PSII to the light. Work is still in progress for the detailed characterization of the mutants PSII properties. A tobacco mutant, S6, obtained by Maliga and coworkers harboring the F26S mutation in the b subunit was made available to us and was characterized. Measurements of PSII charge separation and recombination, polypeptide content and electron flow indicates that this mutation indeed results in light sensitivity. Presently further work is in progress in the detailed characterization of the properties of all the above mutants. Information was obtained demonstrating that photoinactivation of PSII in vivo initiates a series of progressive changes in the properties of RCII which result in an irreversible modification of the RCII-D1 protein leading to its degradation and replacement. The cleavage process of the modified RCII-D1 protein is regulated by the occupancy of the QB site of RCII by plastoquinone. Newly synthesized D1 protein is not accumulated in a stable form unless integrated in reassembled RCII. Thus the degradation of the irreversibly modified RCII-D1 protein is essential for the recovery process. The light induced degradation of the RCII-D1 protein is rapid in mutants lacking the pD1 processing protease such as in the LF-1 mutant of the unicellular alga Scenedesmus obliquus. In this case the Mn binding site of PSII is abolished, the water oxidation process is inhibited and harmful cation radicals are formed following light induced electron flow in PSII. In such mutants photo-inactivation of PSII is rapid, it is not protected by ligands binding at the QB site and the degradation of the inactivated RCII-D1 occurs rapidly also in the dark. Furthermore the degraded D1 protein can be replaced in the dark in absence of light driven redox controlled reactions. The replacement of the RCII-D1 protein involves the de novo synthesis of the precursor protein, pD1, and its processing at the C-terminus end by an unknown processing protease. In the frame of this work, a gene previously isolated and sequenced by Dr. Pakrasi's group has been identified as encoding the RCII-pD1 C-terminus processing protease in the cyanobacterium Synechocystis sp. PCC 6803. The deduced sequence of the ctpA protein shows significant similarity to the bovine, human and insect interphotoreceptor retinoid-binding proteins. Results obtained using C. reinhardtii cells exposes to low light or series of single turnover light flashes have been also obtained indicating that the process of RCII-D1 protein turnover under non-photoinactivating conditions (low light) may be related to charge recombination in RCII due to back electron flow from the semiquinone QB- to the oxidised S2,3 states of the Mn cluster involved in the water oxidation process.
3
Meidan, Rina, e Robert Milvae. Regulation of Bovine Corpus Luteum Function. United States Department of Agriculture, marzo 1995. http://dx.doi.org/10.32747/1995.7604935.bard.
Abstract (sommario):
The main goal of this research plan was to elucidate regulatory mechanisms controlling the development, function of the bovine corpus luteum (CL). The CL contains two different sterodigenic cell types and therefore it was necessary to obtain pure cell population. A system was developed in which granulosa and theca interna cells, isolated from a preovulatory follicle, acquired characteristics typical of large (LL) and small (SL) luteal cells, respectively, as judged by several biochemical and morphological criteria. Experiments were conducted to determine the effects of granulosa cells removal on subsequent CL function, the results obtained support the concept that granulosa cells make a substaintial contribution to the output of progesterone by the cyclic CL but may have a limited role in determining the functional lifespan of the CL. This experimental model was also used to better understand the contribution of follicular granulosa cells to subsequent luteal SCC mRNA expression. The mitochondrial cytochrome side-chain cleavage enzyme (SCC), which converts cholesterol to pregnenolone, is the first and rate-limiting enzyme of the steroidogenic pathway. Experiments were conducted to characterize the gene expression of P450scc in bovine CL. Levels of P450scc mRNA were higher during mid-luteal phase than in either the early or late luteal phases. PGF 2a injection decreased luteal P450scc mRNA in a time-dependent manner; levels were significantly reduced by 2h after treatment. CLs obtained from heifers on day 8 of the estrous cycle which had granulosa cells removed had a 45% reduction in the levels of mRNA for SCC enzymes as well as a 78% reduction in the numbers of LL cells. To characterize SCC expression in each steroidogenic cell type we utilized pure cell populations. Upon luteinization, LL expressed 2-3 fold higher amounts of both SCC enzymes mRNAs than SL. Moreover, eight days after stimulant removal, LL retained their P4 production capacity, expressed P450scc mRNA and contained this protein. In our attempts to establish the in vitro luteinization model, we had to select the prevulatory and pre-gonadotropin surge follicles. The ratio of estradiol:P4 which is often used was unreliable since P4 levels are high in atretic follicles and also in preovulatory post-gonadotropin follicles. We have therefore examined whether oxytocin (OT) levels in follicular fluids could enhance our ability to correctly and easily define follicular status. Based on E2 and OT concentrations in follicular fluids we could more accurately identify follicles that are preovulatory and post gonadotropin surge. Next we studied OT biosynthesis in granulosa cells, cells which were incubated with forskolin contained stores of the precursor indicating that forskolin (which mimics gonadotropin action) is an effective stimulator of OT biosynthesis and release. While studying in vitro luteinization, we noticed that IGF-I induced effects were not identical to those induced by insulin despite the fact that megadoses of insulin were used. This was the first indication that the cells may secrete IGF binding protein(s) which regonize IGFs and not insulin. In a detailed study involving several techniques, we characterized the species of IGF binding proteins secreted by luteal cells. The effects of exogenous polyunsaturated fatty acids and arachidonic acid on the production of P4 and prostanoids by dispersed bovine luteal cells was examined. The addition of eicosapentaenoic acid and arachidonic acid resulted in a dose-dependent reduction in basal and LH-stimulated biosynthesis of P4 and PGI2 and an increase in production of PGF 2a and 5-HETE production. Indomethacin, an inhibitor of arachidonic acid metabolism via the production of 5-HETE was unaffected. Results of these experiments suggest that the inhibitory effect of arachidonic acid on the biosynthesis of luteal P4 is due to either a direct action of arachidonic acid, or its conversion to 5-HETE via the lipoxgenase pathway of metabolism. The detailed and important information gained by the two labs elucidated the mode of action of factors crucially important to the function of the bovine CL. The data indicate that follicular granulosa cells make a major contribution to numbers of large luteal cells, OT and basal P4 production, as well as the content of cytochrome P450 scc. Granulosa-derived large luteal cells have distinct features: when luteinized, the cell no longer possesses LH receptors, its cAMP response is diminished yet P4 synthesis is sustained. This may imply that maintenance of P4 (even in the absence of a Luteotropic signal) during critical periods such as pregnancy recognition, is dependent on the proper luteinization and function of the large luteal cell.