Gilberto Rossetto

MOCVD growth and characterization of ZrO2 thin films obtained from unusual organo-zirconium precursors

ZrO2 thin films were deposited on polycrystalline alumina, glass, 〈100〉 silicon, and stainless steel substrates by metal-organic chemical vapor deposition (MOCVD). Depositions were carried out in a hot wall reactor at reduced pressure (0.6 torr) in the temperature range 400–550 °C, using zirconium cyclopentadienyl derivatives as precursors, both in a flux of oxygen and of an oxygen/water vapor mixture. High quality zirconia films with high growth rates were obtained by employing (C5H5)2Zr(CH3)2. Scanning electron microscopy (SEM) images display, in both cases, a tapered polycrystalline columnar structure of the deposits. Films grown under O2 flux show a cracked surface with a variable carbon contamination depending on the experimental conditions, while those prepared in a O2/H2O mixture are smooth and well adherent to the substrate with 5 % carbon presence according to X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction shows that samples grown in O2 flux consist of the tetragonal phase with a small amount of the monoclinic polymorph, whose percentage increases with the growth temperature. The presence of water vapor led to larger crystalline domains predominantly composed of monoclinic phase.

Tri(η-cyclopentadienyl)uranium(IV) silyl and siloxide compounds. Crystal structure of [U(η5-C5H5)3(OSiPh3)]. Insertion of lsocyanide into a uranium–silicon bond

The complex [U(η5-C5H5)3(SiPh3)](1) has been synthesized from [U(η5-C5H5)3Cl] and Li(SiPh3) and fully characterized. The direct U–Si bond in (1) is quite reactive towards proton acidicmolecules, moreover it reacts with 2,6-dimethylphenyl isocyanide to give the insertion product [U(η5-C5H5)3{C(NC6H3Me2-2,6)SiPh3}](3), the 1H n.m.r. and i.r. data for which show that the isocyanide ligand is η2-co-ordinated to the uranium atom. The synthesis of [U(η5-C5H5)3(OSiPh3)](2) by reaction of [U(η5-C5H5)3(NEt2)] with SiPh3(OH) and its X-ray structural determination are also reported. Compound (2) crystallizes from diethyl ether in the monoclinic space group P21/n with a= 15.368(5), b= 17.333(5), c= 10.778(5)A and β= 106.27(3)° for Z= 4. The main features are the almost linear U–O–Si bond angle of 172.6(6)° and the short U–O distance of 2.135(8)A.

Facile insertion of carbon monoxide into the UC and UN bonds of some tris(cyclopentadienyl)uranium(IV)-alkyl and -dialkylamide derivatives

Abstract In contrast to some earlier indications, various organo-uranium(IV) complexes of the general type Cp 3 UX (Cp = η 5 -C 5 H 5 ; X = CH 3 , C 2 H 5 , i-C 3 H 7 , n-C 4 H 9 , t-C 4 H 9 , N(C 2 H 5 ) 2 , and even P(C 6 H 5 ) 2 and NCBH 3 , but not BH 4 or NCS) react in solution with CO under mild conditions, (viz. room temperature and atmospheric pressure of CO). The (IR, 1 H NMR and NIR/VIS) spectroscopic properties of the (1:1) insertion products in case of X = alkyl or dialkylamide are in full accord with their formulation as dihapto-acyl and dihapto-carbamoyl complexes, respectively. While the carbenoid η 2 -OCX ligands are reluctant to undergo consecutive reactions typical of other oxy-carbene systems, reversible equilibria between monomers and dimers in solution (for R = CH 3 and C 2 H 5 ) cannot be ruled out. On the other hand, the dihapto-acyl complexes show a clean reversibility of the CO-uptake at temperatures above 60°C.

Synthesis and crystal structure of triscyclopentadienyl(triphenyltin)uranium. The first example of a uranium–tin bond

The uranium–tin complex (cp)3U–SnPh3(cp =η5-C5H5) has been prepared from (cp)3UNEt2 and HSnPh3, and its crystal structure determined; it provides the first example of a compound with a uranium–tin bond.

A Study of Nanophase Tungsten Oxides Thin Films by XPS

Nanophasic tungsten oxides thin films have been deposited at 500 °C on quartz and glass substrates starting from W(CO)6 using the metal organic chemical vapor deposition technique (MOCVD). Two series of deposition experiments were carried out to make a comparison between the results obtained employing, as reactant gases, O2 mixed with water vapor and a dry mixture of N2 with 25% H2, respectively. The obtained tungsten oxides were analyzed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) in order to investigate their microstructure, chemical composition, and surface morphology. In this work, XPS analyses of two tungsten oxides thin films deposited in different atmospheres are presented. Besides the wide scan spectra, charge corrected binding energies for the W 4f7/2, W 4f5/2, O ls, and C 1s surface photoelectron signals are reported. In particular, the film obtained in H2 atmosphere shows the presence of W in an oxidation state lower than VI.

Diethylindium(III) derivatives: Synthesis and characterization of diethylindium(III) dialkylamides and diethylindium(III) pyrrolide. X-Ray crystal structures of diethylindium(III) pyrrolide and diethylindium(III) bromide

Abstract The compounds Et2InNR2 (R  Me, Et, or SiMe3) and Et2InPyrr (HPyrr  pyrrole) have been prepared by reaction of Et2InCl with the corresponding lithium amide or pyrrolide in diethylether. Their 1H NMR, IR and mass spectra are reported and discussed. The amides are dimers in the vapour phase. Diethylindium bromide is a layer polymer. The octahedral coordination geometry of indium is characterized by four distinct InBr distances ranging from 2.777(2) to 3.848(2) A. Diethylindium pyrrolide has a chain structure as shown by the relatively short intermolecular interactions between each indium atom and the double bonds of two adjacent different pyrrole units (3.063(5) and 2.950(5) A, respectively). The indium coordination geometry is then trigonal bipyramidal, with the shortest bonds in the equatorial plane (InC(5) 2.143(5) A, InC(7) 2.141(5) A, InN 2.166(4) A).

Reactivity of dicyclopentadienyluranium(IV) derivatives: formation and structural characterization of an oxygen bridged cluster containing both inorganic and organometallic uranium atoms

Abstract Reactions of [U(Cp) 2 (NEt 2 ) 2 ] (Cp = η 5 -cyclopentadienyl) and [U(Cp) 2 (BH 4 ) 2 ] with LiAlH 4 in diethyl ether give [U(Cp) 2 (AlH 4 ) 2 NEt 2 ]Li ( 1 ) and [U(Cp) 2 (AlH 4 ) 2 ]· n Et 2 O ( 2 ), respectively. Reaction of 2 with CH 3 COOH gives a low yield of the cluster [Cp(CH 3 COO) 5 U 2 O] 2 ( 3 ), whose crystal structure is reported. Complex 3 is a centrosymmetric tetranuclear dimer in which two Cp(CH 3 COO) 5 U 2 O moieties are connected by chelating carboxylato and oxide bridges. A peculiarity of 3 is the presence of two oxygens each of them bridging three uranium atoms.

Cyclopentadienyluranium(IV) complexes containing phosphido and/or amido ligands: Access to the new complex (C5H5)3UP(C6H5)2☆

Abstract The first organoactinide complex involving a phosphido ligand, Cp3UPPh2 (Cp = η5-C5H5, Ph = C6H5), has been prepared by several routes, the best of which involves the reaction of equimolar quantities of Cp2U(NEt2)2 and HPPh2. The complex Cp3UPPh2 is also formed on treatment of the new compounds (NEt2)3UPPh2 and CpU(NEt2)3 with HCp and PPh2 respectively. The by-products containing both amido and phosphido ligands, e.g. (NEt2)2U(PPh2)2, CpU(NEt2)2PPh2 and Cp2U(NEt2)(PPh2), are very unstable. The direct UP bond in Cp3UPPh2 is very reactive towards all types of chemically unsaturated or (proton) acidic molecules. The MS-, NIR/VIS- and 1H NMR-spectroscopic data show that the virtually free electron pair of the P atom is notably less involved in the UP bonding than, e.g., the corresponding electron pair of the related amido complexes Cp3UNEt2 and Cp3UNPh2.

Nanocrystalline Pt thin films obtained via metal organic chemical vapor deposition on quartz and CaF2 substrates: an investigation of their chemico-physical properties

Abstract Nanocrystalline platinum thin films were deposited on quartz and CaF2 substrates using platinum(II)acetylacetonate as a precursor. The depositions were carried out at 420 °C in N2+O2, N2+O2+H2O and N2+H2 atmospheres in order to examine the effect of synthesis conditions on the chemico-physical properties of the layers. Their microstructure, chemical composition and morphology were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and atomic force microscopy. The obtained results revealed the formation of metallic platinum thin films with no preferential orientation. The presence of C and O contamination, as indicated by XPS and SIMS analyses, is discussed in terms of the precursor decomposition pathway.

Bond length variation in In0.25Ga0.75As/InP epitaxial layers thicker than the critical thickness

We address the issue of the local structure in an epitaxial semiconductor thin film undergoing strain relaxation due to extended defects when the critical thickness for their introduction is exceeded. The nearest neighbor environment is probed by x-ray absorption fine structure spectroscopy. The particular system studied is a set of In0.25Ga0.75As films grown on InP(001) of increasing thickness; the thicknesses were chosen so as to obtain a varying degree of relaxation, ranging from pseudomorphic growth to completely relaxed state. The samples have been thoroughly characterized with complementary structural techniques and the residual strain is measured by x-ray diffraction. We find that the Ga–As bond length exhibits a linear decrease with decreasing residual strain. By comparing these results with previous studies on bond lengths in pseudomorphic InxGa1−xAs films as a function of concentration we conclude that the bond lengths have an identical behavior as a function of the mean residual strain independ...