1,721,070 research outputs found
Electrospray ionization in the study of sol-gel processes: the polycondensation of Ti(O-n-Bu)4 in the presence of Si(OEt)4
No full textThe polycondensation of Ti(O‐n‐Bu)4 in presence of Si(OEt)4 (Et = C2H5, Bu = C4H9) has been studied by electrospray ionization of their mixtures in methanol. Series of oligomers due to Ti(OMe)4 (Me = CH3) polycondensation have been detected and represent the most abundant species. This result can be explained by the ready alcoholysis of Ti(O‐n‐Bu)4 and by its fast kinetics of oligomerization. However a series of Ti,Si‐containing oligomers, with molecular weights in the range 400–1300 Da, has also been detected. Their structures have been characterized by isotopic cluster analysis and MS/MS experiments, proving that they originate by reaction of Ti‐OH and Si‐OEt moieties. Copyright © 2001 John Wiley & Sons, Ltd
UV photoelectron and theoretical studies of organometal carbonyl clusters of ruthenium and osmium. μ-hydrido-μ3-alkynyl triangulo cluster compounds
No full textHfO2-doped Silica Thin Films by XPS
No full textThe development of molecularly homogeneous multicomponent oxide based glasses is a key concern in many fields of materials chemistry. Oxide nanoparticles covalently embedded in dielectric matrices represent a class of nanocomposite systems endowed with outstanding optical, mechanical, electronic, and thermal properties. In this study, silica thin films embedding HfO2 were prepared by dip-coating on silica glass via a modified sol-gel processing. This powerful synthetic method, mainly based on the hydrolysis and condensation of metal alkoxides, provides a reliable route to oxide materials which can be processed into a variety of different forms (thin films, powders, monoliths, etc.). The novel synthetic route here presented is based on the copolymerization of the organically modified oxohafnium clusters (Hf4O2(OMc)12 with OMc = OC(O)–C(CH3)=CH2)) with (methacryloxymethyl)triethoxysilane (MAMTES). The crystalline clusters, which are the precursors for the corresponding metal oxide (MO2) were prepared via the sol-gel route by reaction of hafnium butoxide with methacrylic acid. The copolymerization of the cluster with previously prehydrolysed methacrylate-functionalized siloxane, allows the anchoring of the oxocluster to the forming silica network. Thin films were prepared starting from a THF (tetrahydrofurane) solution with molar ratios Hf4O2(OMc)12:MAMTES of 1:44 and a MAMTES:THF molar ratio of 1:5, which was stirred at room temperature for 8 h. After deposition, the film was annealed 3 h at 800 °C in air to promote the decomposition of the hafnium oxocluster to give the corresponding HfO2. The obtained HfO2-SiO2 film resulted transparent and homogeneous. The composition of the film was investigated by secondary ionization mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS), which were used also to investigate the in-depth distribution. The depth profiles evidenced a very homogenous distribution of hafnium within the whole silica film and a sharp film-substrate interface. TEM micrographs revealed the formation of isolated nanocrystalline particles, thus ruling out the formation of a HfO2–SiO2 mixture. Concerning the herewith reported XPS analyses, the main XPS core-levels were analyzed for the sample annealed 3 h at 800 °C. The formation of hafnium oxide was evidenced. Furthermore, a very homogeneous distribution of the guest oxide in the host matrix was evidenced, in agreement with SIMS data
Electrospray ionization in the study of the polycondensation of Ti(O-i-C3H7)4 and Ti(O-n-C4H9)4
No full textThe polycondensation of Ti(O‐i‐C3H7)4 (1) and Ti(O‐n‐C4H9)4 (2), precursors widely employed in sol‐gel processes, has been investigated by electrospray ionization mass spectrometry. By analysis of 10−6 M methanol solutions of compounds 1 and 2, the same ionic species are detected, proving that the first step in the polycondensation reaction is the i‐propyl (or n‐butyl) alcohol‐methanol complete exchange. This reaction leads to the Ti(OCH3)4 (3) species, representing the synthon of the polycondensation. Various oligomers of 3 have been detected and characterized by MS/MS experiments, and the related mechanisms have been discussed. A minor oligomeric series due to hydroxyl‐containing polycondensation products has also been characterized. Copyright © 2000 John Wiley & Sons, Ltd
HfO2-ZrO2 doped silica thin films by XPS
No full textSilica thin films embedding ZrO2 and HfO2 were prepared by spin-coating on silica glass via a modified sol-gel processing. The novel synthetic route is based on the co-polymerization of two organically modified oxozirconium and oxohafnium clusters (M4O2(OMc)12 with M = Zr, Hf and OMc = OC(O)–C(CH3)=CH2)) with (methacryloxypropyl)trimethoxysilane (MAPTMS). The crystalline clusters, which are the precursors for the corresponding metal oxides (MO2) were prepared via the sol-gel route by reacting zirconium or hafnium butoxide with methacrylic acid. The copolymerization of the cluster with previously prehydrolyzed methacrylate-functionalized siloxane, allows the anchoring of the oxoclusters to the forming silica network. Thin films were prepared starting from a THF (tetrahydrofurane) solution with molar ratios Hf4O2(OMc)12: Zr4O2(OMc)12:MAPTMS of 1:1:88. After deposition, the films were annealed 3 h at 800 °C in air to promote the decomposition of the hafnium and zirconium oxoclusters to give the corresponding HfO2 and ZrO2 oxides. The obtained HfO2–ZrO2–SiO2 films resulted transparent, homogeneous and displayed a very good adhesion to the substrate. The composition of the films was investigated by secondary ionization mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). The depth profiles evidenced a very homogenous distribution of both zirconium or hafnium species within the whole silica films and sharp film-substrate interfaces. As far as XPS analyses are concerned, the main XPS core-levels were analyzed for the annealed sample and the formation of hafnium and zirconium oxides was evidenced
Embedding of electroluminescent ZnS : Cu phosphors in PMMA matrix by polymerisation of particle suspension in MMA monomer
No full textAlternating current powder electroluminescent lamps (ACPELs) were produced by UV initiated polymerization of liquid methylmethacrylate (MMA) monomer containing a ZnS:Cu phosphor powder dispersion. This method is suitable for the formation of a compact and void-free polymer matrix that limits water diffusion thus preventing the consequent corrosion of particles and luminescence quenching. A lamp was built up by sticking aluminum and indium–tin oxide (ITO) electrodes by using the pre-polymerized MMA/ZnS:Cu dispersion as a UV-curable glue. Dispersions were prepared by mixing the dry powder with MMA monomer activated with 2% weight of the photoinitiator Ciba Irgacure 184 UV and by pre-polymerization under stirring with a 125 W mercury lamp. Due to the high content of powder necessary to produce a bright lamp (1:1 weight of ZnS:Cu in MMA), a high viscosity slurry obtained with a 30 min pre-polymerization was required to maintain suspended the large size (tenths of μm) commercial phosphors. The polymerization process as a function of the irradiation time was investigated by FT-IR on films prepared by sticking two NaCl windows. The intensity decrease of the CC band at 1640 cm−1 indicates that polymerization is complete after 10 min irradiation. Electrical and spectroscopic characterization of the lamp was performed by analysis of luminescence spectra and determination of the current flowing in the circuit at different feeding voltages and frequencies. This preliminary investigation shows that UV polymerization of phosphor/monomer dispersions is a promising route for an easy and cheap production of ACPELs
Sol-gel and CVD Co3O4 thin films characterized by XPS
No full textThe present investigation is focused on x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XE-AES) analysis of the main core levels (O 1s, Co 2p, and Co LVV) of nanocrystalline Co3O4 coatings. The samples were obtained by CVD and sol-gel routes. Co(dpm)2 (Hdpm = 2,2-6,6-tetramethyl-3,5-heptanedione) was chosen as CVD precursor thanks to its appreciable volatility, the absence of direct Co–C bonds and the presence of thermally labile Co–O moieties. The preparation of the sol-gel films was accomplished starting from methanolic solutions of Co(OCOCH3)2⋅4H2O due to the clean conversion of cobalt acetate into cobalt oxides. The obtained Co3O4 films were bluish-brown, homogenous, crack-free, and adhered well to the substrates. The microstructural analyses revealed the formation of single-phase nanostructured layers with average crystallite dimensions ranging between 15 and 26 nm
UV PHOTOELECTRON AND THEORETICAL-STUDIES OF ORGANOMETAL CARBONYL CLUSTERS OF RUTHENIUM AND OSMIUM. μ-HYDRIDO-μ3-ALLYL AND μ-HYDRIDO-μ3-ALLENYL TRIANGULO CLUSTER COMPOUNDS
No full textBismuth oxychloride nanoflakes: Interplay between composition-structure and optical properties
No full textStrongly (001) oriented BiOCl nanoflakes have been prepared at room temperature by the controlled hydrolysis of bismuth chloride in the presence of acetylacetone. The nanoflakes thermally treated in air up to 600 °C have been studied by X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Composition, structure and morphology of the nanoflakes have been correlated to their electronic absorption and luminescence properties. Irrespective of the thermal treatments, the samples are characterized by transmittance higher than 98% in the near-infrared region. In the mildly annealed specimen (≤ 200 °C), the absorption bands in the ultraviolet can be effectively exploited for the selective excitation of the blue (394 nm) and green (520 nm) photoluminescence, the latter being visible only for λexc > 310 nm. Conversely, at higher temperature only the blue emission is observed which, on the basis of the observed trend, can be assigned to emitting centres located in the oxide sheet of the Bi–O–Cl stacks
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