1,721,180 research outputs found
Homodinuclear Lanthanide Complexes with the Divergent Heterotopic 4, 4′‐Bipyridine N‐Oxide (bipyMO) Ligand
No full textThe synthesis of dinuclear molecular complexes [Eu-2(dbm)(6)(bipyMO)(2)], 1, [Tb-2(dbm)(6)(bipyMO)(2)], 2, [Eu-2(tta) 6( bipyMO)(2)], 3 [Eu-2(hfac)(6)(bipyMO)(3)], 4, [Tb-2(hfac)(6)(bipyMO)(3)], 5 is here reported (bipyMO = 4,4'-bipyridine N-oxide, Hdbm = dibenzoylmethane, Htta = thenoyltrifluoroacetone, Hhfac = hexafluoroacetylacetone). The products were obtained in mild conditions and with high yields reacting anhydrous lanthanide beta-diketonates and bipyMO in 1:1 or 1.5 molar ratio in toluene. X-ray single crystal studies on 2, 3, 4 showed that the heterotopic ligands are hypodentate, bridging the two lanthanide centres exclusively through the oxygen atom. Photoluminescence studies show bright red emissions from europium derivatives with absolute quantum yields up to 44 %
XPS as a powerful tool to investigate the surface properties of simple and mixed metal oxides
No full textXPS is a well established surface sensitive method for the analysis of solid materials,
allowing the determination of surface composition and the assessment of oxidation state
and chemical environment of the different species. In fact, core level XPS is highly
sensitive to the chemical environment, i.e. the binding energy may be strongly dependent
on the oxidation state of the investigated ion, as well as on the neighbouring atoms.
Oxide-based materials (simple, multicomponent and composites), are a fascinating
and technologically appealing class of materials, exhibiting a huge variety of chemical,
structural, optical, magnetic, electric and electronic properties. Since in oxides the
functional properties are mainly related to the complex interplay among composition,
microstructure, shape, characteristic size, charge density, chemical environment, presence
of defects etc., the understanding of their actual chemical nature and electronic structure
is a primary concern to fully exploit their functionalities in different fields.
In this chapter, after a general overview on metal oxides and on their electronic
structure and peculiarities, the application of XPS to their investigation will be introduced
and discussed and some selected application fields will be considered.
The effect of ion sputtering in oxides will be moreover shortly examined.
Furthermore, in this contribution, the issues related to the determination of the actual
chemical state of metal species in mixed oxides will be also extensively addressed and
discussed. The possibility of XPS to evidence the presence of M-O-M’ mixed bonds will
be highlighted.
In the second part of the chapter, several different selected case studies will be
analysed in detail, which deal with different oxide systems: simple oxides, also in mixedvalence
state, (ZnO, WO3, CuxOy, VxOy), mixed oxides (e.g. SiO2-HfO2, SiO2-ZrO2, SiO2-TiO2, ZrO2-TiO2), doped oxides (FexOy:TiO2, M(Pt, Ag):TiO2, M (Au, Pt, Pd,
Rh):SiO2).
In particular, the use of this method for the investigation of the chemical composition
of different typologies of surfaces (thin films, powders) will be discussed.
A further aspect to be dealt with is the perspective combination of XPS, also at
variable pressure, with other site-specific spectroscopic methods (XAS, XEOL) and
theoretical tools (e.g. DFT), which represents a valuable tool to unravel and predict issues
related to the reactivity and to other functional properties of these materials
Construction and Characterization of Ru(II)Tris(bipyridine)-Based Silica Thin Film Electrochemiluminescent Sensors. L. Armelao, R. Bertoncello, S. Gross, D. Badocco and P. Pastore,
No full textRu(II) tris-bipyridine based ECL sensors were produced by embeddingthe complex inside silica glass thin films
deposited via a sol-gel dipping procedure on K-glass conducing substrates. Films were prepared starting from a prehydrolyzed
ethanolic solution of Si(OC2H5)4 and Ru(bpy)3Cl2. Transparent, crack-free and homogeneous reddish
silica layers, havinga thickness of 20020 nm, were obtained. The films, either deposited at room temperature or
thermally annealed at 100, 200 and 300 C for 30 h, were structurally and chemically characterized. Ru(bpy)3Cl2
thermal stability was previously checked by thermogravimetric analysis (TGA). The films were investigated by X-Ray
photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and UV-vis spectroscopy. XPS in-depth
profiles revealed a homogeneous distribution of the ruthenium complex inside the silica thin layers. SIMS data
suggested that the embedded Ru(bpy)3Cl2 did not react with oxygen inside the oxygen-rich silica matrix to give Ru-O
bonds. Electrochemical and ECL characterization of the thin film electrodes were made by means of cyclic
voltammetry (CV) and controlled potential step experiments. The ECL sensor showed a diffusive redox behavior of
the Ru(bpy)3
2+/Ru(bpy)3 3+ system. Light emission produced from the reaction between oxalic acid and the
electrogenerated Ru(bpy)3
3+ was larger and stable when thermally treated electrodes were used after a suitable
hydration period. The 300°C treated sample was the best performingsensor both in terms of low complex leakage and
sensitivity. Calibration plots relative to oxalic acid were obtained both in stationary and in flowingsolutions in the
concentration range 2uM - 300 uM. A linear behavior appeared in the former case, while in the latter a slight
curvature was evident as a consequence of a finite diffusion time of the analyte inside the thin film. The signal
repeatability, obtained by multiple 100 uL of 10 uM oxalic acid injections in flowingsolutions , was better than 4%.
The obtained detection limit (computed as three times the standard deviation of the base-line noise) was 10-6M as
oxalic acid
Low temperature synthesis of MgxAl2(1−x)Ti(1+x)O5 films by sol-gel processing
No full textAluminium titanate films thicker than 0.5 microns have been synthesized by sol–gel methods. The films have been deposited via repetitive dip-coating on silicon wafers and their thermal stability has been tested as a function of the annealing time and temperature. The sol–gel approach has allowed the formation of the aluminium titanate phase at temperatures (∼700 °C) much lower than those necessary for solid-state reactions (∼1450 °C). Magnesium oxide has been used to improve the thermal stability of the films at high temperatures. The behavior of
samples prepared with two different Mg content, i.e. Mg0.2Al1.6Ti0.8O5 and Mg0.6Al0.8Ti1.6O5, has been studied. The films have proven to be stable at 1150 °C, for up to 90 h. X-ray photoelectron spectroscopy has shown that after firing at 500 °C the surface chemical composition of
the films is in accordance with the nominal one, whilst at higher annealing temperatures some differences, attributed to diffusion effects, have been observed
Wetting properties of flat and porous silicon surfaces coated with a spiropyran
No full textWe report the immobilization and characterization of a spiropyran (SP) derivative (1) on smooth Si(I 00) and porous H-terminated silicon surfaces through a thermal hydrosilylation protocol. Under visible light exposure the SP is in a closed, hydrophobic form, whereas under UV irradiation it converts to a polar, hydrophilic open form named merocyanine (MC). The SP-MC photoinduced isomerization gives a small contact angle (CA) change of 9 degrees for smooth Si(100) samples under sequential irradiation cycles with white and UV light. Irradiation of porous silicon (PS) surfaces, under the same conditions, gave a CA change of 11 degrees. Treatment of PS surfaces, bearing the MC form of chromophore 1, with cobalt(11) ions enhances the wettability switching of the PS surface to a much larger extent, giving rise to a CA variation as high as 32 degrees
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
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
Implementing sustainability in laboratory activities: A case study on aluminum titanium nitride based thin film magnetron sputtering deposition onto commercial laminated steel
No full textThe goal of the study was to identify the environmental hotspots of an experimental research work at lab scale consisting in the physical vapor deposition magnetron sputtering of aluminum titanium nitride based thin coatings onto commercial laminated steel. The findings can provide useful insights for supporting the design of future experimental research campaigns, or instrumentation set-ups, with lower environmental impacts. Results highlighted that the main driver of impacts in the analyzed laboratory activities was the electricity used for instruments operations, in particular for the vacuum keeping. Thus, several optimization strategies were evaluated to reduce the overall electricity consumption, and to improve the environmental profile of experimental activities
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