Paolo Volpe

Gas phase ion/molecule reactions in monogermane-hydrocarbon mixtures: a comparative Fourier transform mass spectrometry and chemical ionization mass spectrometry study

Abstract The gas phase ion/molecule reactions of GeH 4 with some simple saturated (CH 4 , C 2 H 6 ) and unsaturated hydrocarbons (C 2 H 2 , C 3 H 4 , C 3 H 6 ) have been studied by high pressure mass spectrometry and Fourier transform mass spectrometry. The effects of the nature of the hydrocarbon and of the total pressure and the relative concentrations of the reagent gases on the formation of GeC containing ions are reported. Saturated hydrocarbons give only limited amounts of such species, whereas a variety of GeC containing products are efficiently produced when alkenes or alkynes are added to germane. In these latter cases, GeCH + 3 and GeCH + 5 are among the most abundant products, invariably accompanied by ions containing germanium, carbon and hydrogen in relative yields increasing with the hydrocarbon partial pressure. For all systems, the reaction pattern is presented and discussed in relation to the preparation of amorphous GeC containing materials for photovoltaic applications.

Gas phase ion-molecule reactions of monogermane with oxygen and ammonia☆

High pressure and Fourier transform mass spectrometry have been used to study the ion-molecule reactions of germanium-containing ions with oxygen, ammonia, and GeH4 itself. The effects of the total pressure and of the ratio between GeH4 and oxygen or ammonia are reported. In self-condensation reactions the most reactive species are Ge+ and GeH2P+, which give dimer ions containing an even number of hydrogen atoms. Formation of GeHnO2+ (n = 0, 1) and GeHnO+ (n = 0−3) ions is observed in GeH4/O2 mixture. The most abundant species is GeHO+, which originates in the reaction of Ge2H2+ with one O2 molecule, as demonstrated by FTMS. High pressure experiments suggest that oxygen-containing ions are also formed by pathways involving monogermanium ions. Analogous behaviour is observed in the GeH4/NH3 mixtures, where GeNHn+ (n = 2, 3, 4, 6) ions are formed in higher abundances than GeHO+ (n = 1−3) ions under similar conditions.

γ-Radiolysis of monogermane and the formation of solid germanium hydride polymers

H2, Ge2H6 and a solid material (GeHx)n (x = 0.55–1.81) are produced by γ-radiolysis of GeH4. The relative amount of all the products and the composition of the solid are reported vs the pressure of GeH4 in the sample and the radiation dose. The composition of the solid approaches the formula GenH2n as the pressure increases while the production of H2 and Ge2H6 decreases.

Gas phase ion-molecule reactions of monogermane with carbon oxides and ethylene: Formation of germanium-carbon bonds

Abstract The gas phase ion-molecule reactions of GeH 4 with some carbon-containing compounds (CO, CO 2 , and C 2 H 4 ) have been studied by high pressure mass spectrometry and Fourier transform mass spectrometry. The effects of the total pressure and of the relative concentrations of the reagent gases on the ion pattern are reported. In the presence of CO and CO 2 , GeH n CO + or GeH n CO 2 + , GeH n O + , and GeH n C + ions are observed, all of which show very low abundances. In contrast, condensation processes of GeH 4 with C 2 H 4 give GeC n H m + ( n = 1–4) species, in very high yield for n = 1, 2 but lower for n = 3, 4. For all three systems, reaction mechanisms are suggested and are discussed in relation to the preparation of amorphous materials containing germanium carbides for photovoltaic applications.

Thermolysis and mass spectra of polymeric germanium hydride produced by γ-radiolysis

Abstract TGA, MS and DSC of a solid polymeric Ge hydride, obtained by γ-radiolysis of GeH 4 , are reported. Upon heating, it undergoes two successive weight losses at 463 and 1173 K. At 948 K two crystal phases are formed, one of them is pure germanium. Some comparisons with a-Ge: H produced via RF sputtering or glow discharge are reported.

Gas phase ion/molecule reactions in phosphine/germane mixtures studied by ion trapping

Abstract Gaseous mixtures of phosphine and germane have been investigated by ion trap mass spectrometry. Reaction pathways together with rate constants of the main reactions are reported. The mechanisms of ion/molecule reactions have been elucidated by single and multiple isolation steps. The GeHn+ (n = 1–3) ions react with phosphine to give GePHn+ (n = 2–4) ions. The GePH4+ ion further reacts with GeH4 to yield Ge2PH6+. The GePHn+ (n = 2–4) mixed ionic family also originates from the P+ phosphine primary ion, as well as from the P2Hn+ (n = 0–3) secondary ions of phosphine reacting with neutral germane and from Ge2H2+ reacting with phosphine. The main reaction pathways of the PHn+ (n = 0–2) ions with GeH4 lead to the formation of the GeH2+ and GeH3+ ionic species. Protonation of phosphine from different ionic precursors is a very common process and yields the stable phosphonium ion, PH4+. Trends in total abundances of secondary GePHn+ (n = 2–4) ions as function of reaction time for different PH3/GeH4 pressure ratios show that excess of germane slightly affects the nucleation of mixed Ge-P ions.

Fourier transform-ion cyclotron resonance study of the gas-phase acidities of germane and methylgermane; bond dissociation energy of germane

An accurate gas-phase acidity for germane (enthalpy scale, equivalent to the proton affinity of GeH3−), ΔHacido(GeH4) = 1502.0 ± 5.1 kJ mol−1, is obtained by constructing a consistent acidity ladder between GeH4, and H2S by using Fourier transform-ion cyclotron resonance spectrometry, and 0 and 298.15 K values for the first bond dissociation energy of GeH4 are proposed: D0o(H3Ge-H) = 352 ± 9 kJ mol−1; Do(H3Ge-H) = 358 ± 9 kJ mol−1, respectively. These results are compared with experimental and theoretical data reported in the literature. Methylgermane was found to be a weaker acid than germane by approximately 35 kJ mol−1: ΔHacido = 1536.6 kJ mol−1.

On the reliability of a rapid method for the determination of90Sr in natural samples

A method for the rapid evaluation of90Sr in environmental matrices has been developed. It is a one-day time-consuming procedure compared with 20–25 d of the traditional methods. It is based on a partial measurement of the sample activity and on data extrapolation. This work reports the methodology and its reliability.

Gas phase ion-molecule reactions in methylgermane/oxygen, /ammonia, and /unsaturated hydrocarbon systems

Abstract Gas phase ion-molecule reactions in systems containing CH 3 GeH 3 and oxygen, or ammonia, or unsaturated hydrocarbons (C 2 H 4 , C 3 H 6 , C 3 H 4 ) have been studied by Fourier-transform mass spectrometry and high-pressure mass spectrometry. The self-condensation processes of CH 3 GeH 3 as well as the effects of the nature and the concentration of the reagent, and of the total pressure of the system on the formation of new GeO, GeN and GeC bonds are investigated. For each system the reaction pattern is presented and the gas phase reactivity of CH 3 GeH 3 compared with that of GeH 4 towards the same reagents. The formation of ionic species containing new GeC bonds observed in the CH 3 GeH 3 /unsaturated hydrocarbons systems is discussed in relation to the preparation of amorphous germanium carbides, which are promising materials for photovoltaic applications.

Gas phase ion chemistry in silane/propane and silane/propene mixtures

Abstract The silane/propane and silane/propene gaseous mixtures have been investigated by ion trap mass spectrometry. The variations of ion abundances observed under different partial and total pressures are reported. The mechanisms of ion/molecule reactions have been elucidated by successive isolation steps. Moreover, the rate constants for the main processes have been experimentally measured and compared with the collisional rate constants to determine the reaction efficiencies. A great number of processes have been observed in SiH 4 /C 3 H 6 leading to the formation of silicon and carbon containing ions with high efficiency, whereas propane and silane give very few ion products with low efficiencies. Chain propagation in the SiH 4 /C 3 H 6 system gives clusters of increasing size, such as Si 2 C 2 H 7 + and Si 3 CH 7 + , with rather high efficiencies starting from silicon containing ions and neutral propene.