Metal Sources

The delta lactone can be obtained in very high yields when triisopropylphosphine or tricyclohexylphosphine is the ligand along with Pd(acac)2 as the metal source (171). 

Fig. 11. Composition dependence of the resistivity p x) for thick films of Cbo doped with Na, K, Rb, and Cs. Points indicate where exposure to the alkali-metal source was stopped and x-ray and ultraviolet photoemission spectra were acquired to determine the concentration x. The labels indicate the known fulleride phases at 300 K. The minima in p x) occur for stoichiometries corresponding to NaQCeo, K.iCeo and Cs,.,.Cfio[ll3].

Whether these advances come from the study of zinc carbenoids, other organo-metallic sources, diazo precursors or as yet unrecognized sources of methylene transfer, it is our hope that this chapter will serve as a helpful starting point to guide future explorers of this fascinating landscape. 

Tungsten carbonyl is also used as a metal source at 350 00°C but carbon tends to remain incorporated in the stmcture.P l The reaction is as follows ... 

A common CVD reaction uses the bromide as a metal source at a temperature range of 1350-1550°C in an atmosphere of hydrogen and argon 1 2]... 

AIN is produced by CVD in the form of coatings and powder both experimentally and on a production basis by the following high temperature reactions in a hydrogen atmosphere at low pressure (1 Torr) with ammonia and either the chloride or the bromide as metal sources 1 1... 

Reduction Reactions. Titanium nitride coatings are produced by CVD with titanium tetrachloride as the metal source and either nitrogen gas or ammonia as a source of nitrogen ... 

Tin oxide is deposited with tin chloride as a metal source at 600-800°C, usually at low pressure ... 

An older process to form silicides is siliconizing which is a relatively simple CVD process used to provide oxidation and chemical resistance to refractory metals. The siliconizing reaction uses the substrate itself, (such as Mo or Ti), as the metal source. Silicon diffuses readily in... 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

Palladium NHC systems for the hydrodehalogenation of aryl chlorides and bromides and polyhalogenated aromatic substrates originate from about the same time as the first reports on Ni chemistry, and show many similarities. Initial efforts showed that the combination of PdCdba) (2 mol%), one equivalent of imidazolium chloride and KOMe produced an effective system for the reduction of 4-chlorotolu-ene, especially upon use of SIMes HCl 2 (96% yield of toluene after 1 h at 100°C) [7]. Interestingly, higher ligand to metal ratios severely inhibited the catalysis with only 7% yield of toluene achieved in the same time in the presence of two equivalents of SIMes HCl 2. Variation of the metal source (Pd(OAc)2, Pd(CjHjCN)jClj), alkoxide (NaOMe, KO Bu, NaOH/ ec-BuOH) or imidazolium salt (IMes HCl 1, IPr HCl 3, lAd HCl, ICy HCl) all failed to give a more active catalyst. 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

In 2007, Fernandez et al. demonstrated that transition-metal complexes with heterobidentate S/C ligands based on imidazopyridin-3-ylidene and thioether functionalities could be readily prepared from the corresponding azolium salts by reaction with Ag20 and transmetalation of the resulting silver carbenes with appropriate metal sources. The cationic Pd(allyl)(carbene-S) complexes have proven to be active catalysts in the test reaction, reaching enantioselectivities of... 

Fig. 7.34 Mossbauer spectrum of C02RUO4 at 4.2 K with respect to the Ru metal source...

Nuclear resonance absorption for the 136 keV transition has been established by Steiner et al. [174]. The authors used a metal source and an absorber of metallic tantalum to determine the mean lifetime of the 136 keV level from the experimental line width ( 52.5 mm s for zero effective absorber thickness) and found a value of 55 ps. This has been the only report so far on the use of the 136 keV excited state of Ta for Mossbauer experiments. 

The broadened single-line spectrum of the early measurements by Cohen et al. [176], obtained with a TaC absorber and an annealed W/W metal source at room temperature, was assigned by the authors to the 3/2 <-> 3/2 transition with an estimated QJQg ratio between 0.8 and 0.95. 

Sauer et al. [185] determined the gyromagnetic ratio g(9/2)/g(7/2) and the magnetic moment of the 6.2 keV level in Ta in two ways, (1) from the Zeeman split velocity spectrum of a metal source in a longitudinal field versus a Ta... 

Each of the eight hyperfine resonances is an unresolved quadmpole doublet, due to the quadmpole interaction of Os in the hexagonal Os metal source. The authors have interpreted the hyperfine fields in terms of core polarization, orbital and spin-dipolar contributions. 

Fig. 7.67 Conversion electron Mossbauer spectra of the 73 keV y-rays in Ir recored at 4.2 K using a metal source, (a, b) metallic iridium, 5 mg cm, (c, d) iridium dioxide, 5 and 1 mg cm , respectively. Measuring time about 10 h for spectra a-c and 20 h for spectrum d (from [308])...

Liquid Metal Sources. The source feed is a metal of low melting point - Ga and In are commonly employed. It is introduced as a liquid film flowing over a needle towards the tip whose radius is relatively blunt (10 pm). The electrostatic and surface tension forces form the liquid into a sharp point known as the Taylor cone. Here the high electric field is sufficient to allow an electron to tunnel from the atom to the surface, leaving the atom ionized. 

Evaporation from an alloy source largely avoids the problems of source geometry which may be encountered in simultaneous evaporation from separate pure metal sources. The success of the method depends on the relative vapor pressures of the component metals in the alloy source because one component metal with a substantially higher vapor pressure will evaporate preferentially. The alloy film will then be rich in the more volatile component compared with the composition of the source and may also be stratified into layers of different composition. Evaporation from alloy sources is discussed in detail by Dushman (43) and Holland (44) on the basis of Raoult s law, and it is possible to predict which metal pairs... 

Zinc chalcogenide thin hlms have been grown by ECALE using zinc sulphate as metal source and sodium sulphide and sodium selenite as chalcogenide precursors.145-148 The formation of the hrst layers of ZnS on (lll)Au has been analyzed by STM and XPS.145 HRSEM images showed that the him surface was very hat, even at an atomic level. On the other hand, thicker ZnS hlms were formed of well-separated crystal nuclei. The stoichiometry of a thicker ZnS him showed a slight excess of sulphur, with a Zn S ratio of 1 1.2. The band gap of a thicker him (deposition time 12 h) was 3.60eV.147... 

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