Search

The surface chemical properties of Y, Ti, Zr and Hf relevant to exoelectron and ion emission have been characterised by a range of techniques (XPS, UPS, AES, LEED, TDS, area-average and threshold φ). The chemisorptive properties of chlorine, bromine, sodium and rubidium are described, and (alkali + halogen) coadsorption has been studied also. Evolution of the trihalide corrosion layer is examined as are its decomposition properties; these features are rationalised in thermochemical and kinetic terms. In certain cases (Y/Na, Y/Rb, Hf/Rb) alkali adsorption results in a system work function equal to that of the bulk alkali at one-half monolayer coverage. Coadsorption of alkali and halogen leads to some particularly interesting observations. Substantial discrepancies (~ 1 eV) are found between the area-average work function \gf and the photoelectric threshold work function (φ∗); over certain coverage regimes, φ∗ actually decreases as \gf increases. This implies the formation of very low work function (< 2 eV) “exopatches”. Desorption from such systems does not occur via the alkali halide — in marked contrast with the behaviour of less electropositive substrates; this can be accounted for. The presence of halogens substantially increases the adsorption strength of the alkali. Models for the various surface phases are advanced and discussed.

Graphitic nanofibers have been synthesized on Ni(1 0 0) substrates via DC plasma chemical vapor deposition using a gas mixture of hydrogen and methane. The diameter of the fibers is in the range 50–200 nm, controlled by the size of the nickel tip of each fiber. The substrate temperature during deposition was 350–400°C. No special treatment of the substrate was employed to promote the nucleation of nanofibers, though scratches on the substrate surface were found to be favorable for the nucleation of the fibers. Scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and Raman spectroscopy were used to characterize the fibers obtained. The effect of the plasma on the growth of the fibers low temperature is discussed.

Using a modulated beam technique, the scattering of Cl 2 from tungsten is shown to be consistent with a model in which dissociative adsorption is accompanied by strong bulk diffusion effects. The (W Cl) bond strength is found to be ≈470 kJ/mole, confirmed by reactive scattering with adsorbed hydrogen and direct HCl adsorption.

Exoelectron and ion emission during chemisorption has been studied under UHV conditions for a variety of halogens (X = chlorine, bromine) and group IIIA (Y) and group IVA (Ti, Zr, Hf) surfaces, both clean and with alkali (M = Na, Rb) predosing. The experimental data include absolute yields and energy distribution functions, as well as the kinetics of the emission processes. The variation in electron yield over four orders of magnitude is acceptably described by a previous model invoking Auger relaxation, as are certain aspects of the energy distributions. Ionic species ejected during the reaction include M + , X − and MX 2 − , the latter exhibiting a kinetic behaviour strongly correlated to the formation of low work function “exopatches”, believed to consist of a polar halide overlayer.

The chemisorption of chlorine and sodium and their co-adsorption on polycrystalline foils of yttrium and scandium has been characterised by Auger electron spectroscopy, thermal desorption spectroscopy and work function measurements, preparatory to an investigation of exo-electron and ion emission during halogen chemisorption. Both monohalide and trihalide evolution is observed. An analysis of the thermochemistry indicates that a revised value of the bond strength of gaseous ScCl is warranted, to a value of at least 502 kJ mol −1 .

Chloride growth on zirconium is investigated by means of the novel thermal desorption spectroscopy of both neutral and negatively ionized products, and interpreted in terms of a single ionic adsorption model. The monohalide desorption energy decreases from a low-coverage value of 320 kJ to 255 kJ mol −1 at the monolayer level, at which point trihalide growth continues indefinitely, indicative of a corrosion layer. In contrast, the desorption energy for the chloride ion remains essentially independent of coverage, at 293 kJ mol −1

The preparation is reported of a series of metal(II) complexes of a quinquidentate ligand produced in situ or by complexation with the Schiff-base condensation-product of two moles of 2-acetylpyridine with 3,3′-iminobispropylamine. From the in situ synthesis of the Ni(II) compound only a quadridentate, mono-Schiff-base complex with coordinated acetyl-pyridine is isolable. The effect of varying the triamine used in this preparation is described and rationalised by consideration of ligand-strain, the effect of stability-constants on ligand-dissociation, and the influence of the acetyl(as opposed to a formyl-) group. Analytical data, infra-red studies, magnetic moments and solution-spectra of the complexes are described, and the interconversion of the two types of Ni(II) complex investigated.

We have used a titrimetric to study the rates of hydrolysis of a series of acetates R 3 MOAc (M = S or Ge; R = Ph, iPr, nPr, c-hex) in dioxane. The effects of the concentration of water, temperature and catalysis by potassium acetate have been studied and are discussed in terms of the proposed mechanism for the hydrolysis, in which bond-breaking processes appear to be important. High orders in the water concentration are observed and the germanium acetates are much more reactive than the silicon acetates.

The preparation and physical properties of a number of complexes formed between divalent nickel and aromatic diazo compounds of type (substituted phenyl)-azo-2-naphthol are described. The abnormal magnetic moment of these complexes in the solid state is explained in terms of incorporation of water to give six-coordinated molecules. Experimental evidence in support of this hypothesis has been obtained by the use of X-ray, magnetic, and infrared spectroscopic methods.

Trisacetylacetonato-germanium (IV) tetrachloroferrate (III) was prepared by the reaction of Ge(aca) 2 Cl 2 and anhydrous FeCl 3 : Ge(aca) 3 FeCl 4 can be prepared from GeCl 4 and acetylacetone in the presence of ferric chloride and Ge(aca) 2 Cl 2 is shown to be possible intermediate in this reaction. Conductance experiments indicate that Ge(aca) 3 FeCl 4 is a 1:1 electrolyte in acetonitrile, nitromethane and nitrobenzene. The ultra-violet and the visible spectra indicate the presence of the FeCl 4 − anion and the infra-red spectra confirm the presence of FeCl 4 − . The trisacetylacetonato-germanium compound may be formulated as [Ge(aca) 3 + ][FeCl 4 − ].

The series of compounds (n−Pr) 3 MO.CO.CH (3−n) Me n M = Si and Ge = O to 3) were prepared and the rates of hydrolysis measured in aqueous dioxane. The entropy of activation is shown to be the main factor determining the rate differences. pK a Values of the substituted acetic acids correlate well with log(k 1 ). A transition state similar to a solvated proton and a solvated carboxylate ion is proposed.

Previous work on exoelectron and ion emission during chemisorption under UHV conditions has been extended to include halogen (chlorine, bromine) adsorption on group IIIA (Y, Sc) and group IA (Zr) surfaces, both clean and with Na predosing. Ionic species observed include Na + Cl − and NaCl − 2 . By means of double dosing experiments, it is shown conclusively that the latter dichloride ion is formed by direct titration of Na by Cl − 2 , and that halogen dissociation is not a precursor step.