Doping ions, ionization potential

The performance of many metal-ion catalysts can be enhanced by doping with cesium compounds. This is a result both of the low ionization potential of cesium and its abiUty to stabilize high oxidation states of transition-metal oxo anions (50). Catalyst doping is one of the principal commercial uses of cesium. Cesium is a more powerflil oxidant than potassium, which it can replace. The amount of replacement is often a matter of economic benefit. Cesium-doped catalysts are used for the production of styrene monomer from ethyl benzene at metal oxide contacts or from toluene and methanol as Cs-exchanged zeofltes ethylene oxide ammonoxidation, acrolein (methacrolein) acryflc acid (methacrylic acid) methyl methacrylate monomer methanol phthahc anhydride anthraquinone various olefins chlorinations in low pressure ammonia synthesis and in the conversion of SO2 to SO in sulfuric acid production. 

The ionization potential of PTH has been estimated to be above 5.0 eV [347] whereas that of (CH), and undoped PPY are 4.7 eV and 4.0 eV respectively [348], The undoped PPY and (CH) readily reacts with oxygen, whereas PTH should be resistant to oxygen since its Fermi energy is sufficiently low that there is no tendency for electron transfer from the polymer to oxygen [348]. The doped polymer would also be stable to oxygen but vulnerable to degradative reactions with the counter-ions. The conductivities of PTH-BF and PTH/CIO4 decreased markedly when heated in air to above 70°C [348], while electrochemically syntehsized... 

Material Charge transfer equation Ionization potential of the doping ions (eV) Electronic conductivity (S cm- )... 

The ion microprobe was early recognized [2-4] to be a potential chemical microscope for many elements, and qualitative analyses rapidly became routine, especially in the study of metals and doped semiconductors. The ion microprobe uses a focused primary ion beam (O , 02, Cs ) to sputter a small volume of material from a target (usually a solid sample). A fraction of the sputtered atoms, characteristic of the surface composition of the sample, are ionized these secondary ions are the source of information in secondary ion mass spectrometry (SIMS) (Figure 43.1). 

Ion implantation has become the dominant doping technique, particularly in the fabrication of bipolar-CMOS devices and in the formation of shallow junctions. Laser ablation sampling coupled with ICP-MS was applied recently to the determination of total dopant dose. Since this technique spatially and temporally separates the sampling and ionization steps, it has the potential to produce more quantitative results than SIMS for trace elements in a given matrix. Wafer surface analysis can also be used to monitor the contamination induced hy different process steps. The importance, in terms of contamination contrihution, of the chamber components used for film deposition and ion implantation was demonstrated, as was the effect of cleaning bath solution purity. ... 

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