Rosalba Gerbasi

Influence of substrate on structural properties of TiO2 thin films obtained via MOCVD

Abstract Among the techniques developed for depositing thin films, metal-organic chemical vapor deposition is one of the most promising. In the present work, the deposition of TiO2 thin films on stainless steel, titanium, barium borosilicate glass and alumina substrates, using titanium tetraisopropoxide as a precursor, was investigated. The films were deposited at 420 °C. The resulting film phase, checked by X-ray powder diffraction, was found to be polycrystalline anatase and was oriented with the a axis perpendicular to the substrate surface, except for alumina substrates where titania films were randomly oriented. Some considerations on texture and crystallite size as a function of film thickness are reported. Annealing up to 1100 °C induced the complete anatase-rutile transformation on alumina substrates.

PECVD of amorphous TiO2 thin films : effect of growth temperature and plasma gas composition

Abstract Amorphous TiO 2 thin films are grown using a r.f. plasma-enhanced chemical vapour deposition process at substrate temperatures between 393 and 523 K using titanium tetraisopropoxide as a precursor, and Ar or N 2 , pure or mixed with O 2 , as the plasma gas. All films are smooth and adherent, their roughness slightly increases by increasing the substrate temperature or if oxygen is added to the plasma gas. Films grown in the presence of oxygen result transparent in the visible region and highly resistive, as expected for pure titanium dioxide. Films grown in an oxygen-free plasma appear grey–blue and fairly conductive suggesting the presence of Ti(III) species. The operating conditions provide high deposition rates, up to 37 nm/min in the presence of oxygen.

Chemical vapour deposition and characterization of gallium oxide thin films

Abstract Gallium oxide thin films were deposited on alumina and TiO2 substrates by metal organic chemical vapour deposition using gallium trishexafluoroacetylacetonate (Ga(hfac)3) as precursor in the presence of oxygen. The depositions were carried out at 470°C and 2.6 kPa leading to a growth rate of 0.7 μm h−1. As-grown films appeared black, smooth and well adherent to the substrates. X-Ray photoelectron spectroscopy (XPS) analysis revealed stoichiometric Ga2O3 with a low carbon content (less than 5%) and almost undetectable fluorine. As-deposited Ga2O3 films were X-ray amorphous, but the onset of a crystallization process was evident after annealing in dry air at 700 °C. Moreover, after thermal treatment, the films became carbon free and transparent in the visible range. The effect of annealing at different temperatures on the film structure was investigated by X-ray diffraction. A phase modification from amorphous to polycrystalline Ga2O3 was observed after thermal treatment at temperatures from 600 to 1000 °C. As shown by secondary ion mass spectrometry (SIMS) studies, Al diffusion into Ga2O3 films was detected after annealing at 1000 °C when pure Al2O3 was used as substrate; this diffusion was completely inhibited using a TiO2 film as buffer layer with a thickness of at least 4 μm.

High conductivity and chemical stability of BaCe1−x−yZrxYyO3−δ proton conductors prepared by a sol–gel method

High-temperature proton conductors are promising as electrolytes for intermediate-temperature solid oxide fuel cells. Among them, BaCeO3-based materials have high proton conductivity but rather poor chemical stability. In contrast, barium zirconates are rather stable, but have poorly reproducible densities and conductivities. In this study, the investigation of BaCe1−x−yZrxYyO3−δ solid solutions (x = 0, 0.10, 0.20, 0.30, 0.40; y = 0.15, 0.20) was undertaken, with the final aim of finding a composition having both high conductivity and good stability. The influence of the modified sol–gel Pechini synthetic approach on the powder morphology, and of a barium excess on the densification were demonstrated. Single-phase perovskite powders were prepared and high density pellets were obtained at temperatures lower than those commonly employed. Stability tests demonstrated that the Zr introduction into doped barium cerate greatly enhanced the chemical stability, particularly for Zr ≥ 20%. The proton conductivities, measured in a humidified H2/Ar atmosphere by impedance spectroscopy, were only slightly influenced by the Zr amount. Overall, BaCe1−x−yZrxYyO3−δ solid solutions having Zr ≈ 20–40% and Y ≈ 15–20% showed good chemical stability and high conductivity.

Zirconium Dioxide Thin Films Characterized by XPS

In this work we use x-ray photoelectron spectroscopy (XPS) to analyze the principal core levels of a ZrO2 thin film deposited on glass using Zr(OPri)3(dpm) (OPri=isopropoxy; hdpm=2,2,6,6-tetramethyl-3,5-heptanedione) as precursor. Besides the general survey, charge corrected binding energies for the Zr 3d5/2, Zr 3d3/2, O 1s, and C 1s photoelectrons are reported. Deconvolution of the O 1s signal reveals the presence of –OH groups and adsorbed water, whose presence can be related to the air exposure of the film between its preparation and XPS analysis.

Structure and volatility of copper complexes containing pyrazolyl-based ligands

Abstract Volatility studies, electrospray mass spectra and IR in vapour phase were carried out for a series of Cu(I) and Cu(II) complexes containing anionic pyrazole-based ligands such as 4-acyl-5-pyrazolonates and poly(pyrazolyl)borates. The volatility has been related to structural features and molecular parameters of the copper complexes. The crystal structures of [Cu(Q′)2(bipy)]·(acetone)1.5 (Q′=1-phenyl-3-methyl-4-benzoyl-pyrazolon-5-ato, bipy=2,2′-bipyridyl) and [Cu(QF)2(phen)]·EtOH (QF=1-phenyl-3-methyl-4-trifluoroacetyl-pyrazolon-5-ato, phen=1,10-phenanthroline), have been also determined. In these complexes the copper atom is in a tetragonally distorted octahedral arrangement of the four O-atoms of pyrazolones with N2-donor ligand in equatorial position. Two sets of CuO distances, the longer being in axial positions, have been found. XRD data of films obtained from metal organic chemical vapour deposition MOCVD experiments on [Cu(poly(pyrazolyl)borate)(PR3)] complexes have also been reported.

The use of 210Pb and 137Cs in the study of sediment pollution in the Lagoon of Venice

The activity of 137Cs per unit area in sediments of the central part of the Lagoon of Venice was determined with the aim of identifying boundaries of homogeneous depositional zones. The 210Pb dating technique was used to date vertical profiles of cores from the same area. A comparison of the total amounts of 137Cs and non-supported 210Pb present in each core and the atmospheric input allows us to identify different depositional areas inside the basin and to outline the possible drainage effect of industrial solid wastes used in past reclaiming operations.

MOCVD of Al2O3 Films Using New Dialkylaluminum Acetylacetonate Precursors: Growth Kinetics and Process Yields

Dimethyl, diethyl, and di-iso-butyl aluminum acetylacetonate compounds were synthesized to deposit Al 2 O 3 thin films by low-pressure metal-organic (LP-MO)CVD. Alumina films were grown in the temperature range 400-520°C under an oxygen or water vapor atmosphere. A kinetic model was applied to analyze the experimental data and to compare the properties of the three precursors. The model, supported by in-line Fourier transform infrared (FTIR) measurements, clearly distinguished the rate-determining steps of the heterogeneous process, with kinetic constants correlated to the molecular structure of the precursors. A method of optimizing deposition conditions, on the basis of the uniformity of the obtained thin films, is discussed.

Fallout distribution in Padua and Northeast Italy after the chernobyl nuclear reactor accident

Abstract The radioactive cloud from the Chernobyl nuclear reactor accident arrived in northeast Italy on 30 April 1986. Ground-level air activities detected in Padua reached maximum values of 28·6, 19·2, 3·3, 1·7 and 7·5 Bq m −3 for 131 I, 132 Te( 132 I), 137 Cs and 103 Ru, respectively, on 1 May; about 10 days later, the activities had fallen to less than 1% of peak values. Considerations of cloud homogeneity are reported. The distribution of fallout radionuclides in Padua was evaluated on the basis of radioactivity detected on natural surfaces. The average committed dose equivalent to the thyroid for adult people in Padua through 131 I inhalation was estimated at 0·37 mSv. Soil activity was monitored daily in samples collected in Padua during the first weeks of May 1986. Fallout deposition over northeast Italy was measured on 75 surface soil samples collected during June 1986 and long-lived radionuclide distribution maps were derived.

Chemical Vapor Deposited Fe2O3 Thin Films Analyzed by XPS

In the present study, x-ray photoelectron spectroscopy (XPS) was employed to investigate the principal core levels of a Fe2O3 thin film. The sample was deposited on glass in a N2+O2 atmosphere by chemical vapor deposition (CVD), using Fe(acac)3 (Hacac = 2,4-pentanedione) as the source compound. XPS surface data for the Fe 2p3/2, O 1s, and C 1s photoelectrons, obtained by an Al Kα monochromatized excitation source, are reported. Deconvolution of the O 1s signal revealed the presence of –OH groups along with the major component ascribed to lattice oxygen. The relatively high carbon content in the film indicated an incomplete decomposition of the used precursor.