Chiara Demaria

Amorphous nonstoichiometric Ge1−x–Cx:H compounds obtained by radiolysis-chemical vapor deposition of germane/ethyne or germane/allene systems: A bonding and microstructure investigation performed by x-ray photoelectron spectroscopy and Raman spectroscopy

Hydrogenated germanium carbides have been produced by x-ray activated–chemical vapor deposition from germane/ethyne or germane/allene systems. The chemical composition and structure of the reaction products as a function of the hydrocarbon percentage in the irradiated mixture and of the solid annealing temperature have been studied and discussed. Bonding and microstructure of these alloys have been investigated by x-ray photoelectron spectroscopy and Raman spectroscopy. The results indicate that the solids are formed by a randomly bound network of carbon, germanium and hydrogen atoms with composition, and characteristics and properties variable with the radiolysis experimental conditions. The spectra show the presence of Ge–C bonds and a partial polymerlike character of the films with hydrogen atoms bonded both to germanium and carbon. Clustered-germanium zones dispersed in the material matrix are also evidenced. The results suggest that the conductive properties of the materials are related to the densit...

Correlations among hydrogen bonding configuration, structural order and optical coefficients in hydrogenated amorphous germanium obtained by x-ray-activated chemical vapour deposition

Hydrogenated nonstoichiometric germanium materials have been produced by x-ray-activated chemical vapour deposition from germane, GeH4. The optical gap, Tauc slope and Urbach energy have been obtained from UV?Vis spectra and correlated with structural parameters, considered as a measure of short and intermediate order, calculated by Raman spectra.The results show that the structural disorder increases with the irradiation time. Investigation of the hydrogen local bonding configuration demonstrates a correlation between the variation of the relative abundances of GeH, GeH2 and GeH3 groups and both structural parameters and Eopt value. Moreover, evidence of the crucial role played by the increase in the GeH3 group abundance in the determination of the Eopt value was revealed.

Characterization of hydrogenated amorphous germanium compounds obtained by x-ray chemical vapor deposition of germane: Effect of the irradiation dose on optical parameters and structural order

Hydrogenated nonstoichiometric germanium materials have been produced by x-ray activated-chemical vapor deposition from germane. The reactions pattern leading to the solid products has been investigated. The dose effect on the composition, the local bonding configuration, and structural characteristics of the deposited solids has been studied using infrared absorption and Raman spectroscopy and has been discussed. Optical parameters have been also determined from ultraviolet-visible spectrophotometry data. The results show that the solids are formed by a random bound network of germanium and hydrogen atoms with a-Ge zones dispersed in the matrix. The Raman results and optical parameters indicate that the structural order, both short-range and intermediate-range, decreases with increasing irradiation time. This behavior suggests that the solid is involved in the reactions leading to the final product and indicates that the formation of amorphous germanium zones is stimulated by postdeposition irradiation, ...

Bimolecular Homolytic Substitutions at Nitrogen: An Experimental and Theoretical Study on the Gas‐Phase Reactions of Alkyl Radicals with NF3

The X-ray irradiation of binary mixtures of alkyl iodides R-I (R=CH3 , C2 H5 , or i-C3 H7 radicals) and NF3 produces R-NF2 and R-F. Based on calculations performed at the CCSD(T), MRCI(SD+Q), G3B3, and G3 levels of theory, the former product arises from a bimolecular homolytic substitution reaction (SH 2) by the alkyl radicals R, which attack the N atom of NF3 . This mechanism is consistent with the suppression of R-NF2 by addition of O2 (an efficient alkyl radical scavenger) to the reaction mixture. The R-F product arises from the attack of R to the F atom of NF3 , but additional contributing channels are conceivably involved. The F-atom abstraction is, indeed, considerably more exothermic than the SH 2 reaction, but the involved energy barriers are comparable, and the two processes are comparably fast.

A catalyst-free synthesis of germanium nanowires obtained by combined X-ray chemical vapour deposition of GeH4 and low-temperature thermal treatment techniques

A catalyst-free innovative synthesis, by combined X-ray chemical vapour deposition and low-temperature thermal treatments, which has not been applied since so far to the growth of germanium nanowires (Ge-NWs), produced high yields of the nanoproducts with the GeH4 reactant gas. Nanowires were grown on both surfaces of a conventional deposition quartz substrate. They were featured with high purity and very large aspect ratios (ranging from 100 to 500). Products were characterized by scanning electron microscopy with energy-dispersive atomic X-ray fluorescence and transmission electron microscopies, X-ray powder diffraction diffractometry, thermogravimetric analysis with differential scanning calorimetry, vibrational infrared and Raman and ultraviolet–visible–near infrared spectroscopies. A quantitative nanowire bundles formation was observed in the lower surface of the quartz substrate positioned over a heating support, whilst spots of nanoflowers constituted by Ge-NWs emerged from a bulk amorphous germanium film matter, deposited on the upper surface of the substrate. The nanoproducts were characterized by crystalline core morphology, providing semiconductive features and optical band gap of about 0.67 eV. The possible interpretative base-growth mechanisms of the nanowires, stimulated by the concomitant application of radiant and thermal conditions with no specific added metal catalyst, are hereafter investigated and presented.