Search results for "Chemical state"
showing 10 items of 19 documents
Nanostructured Pt–TiO2 composite thin films obtained by direct liquid injection metal organic chemical vapor deposition: Control of chemical state by…
2015
Abstract Nanostructured Pt–TiO 2 composite thin films were synthesized by direct liquid injection metal organic chemical vapor deposition process, using trimethyl(methylcyclopentadienyl)platinum and titanium isopropoxide as precursors. Surface and cross-sectional morphologies obtained by scanning electron microscopy and transmission electron microscopy evidenced the uniform distribution of platinum nanoparticles in the TiO 2 matrix. At higher Pt content, the X-ray diffraction analysis showed that the face-centered cubic phase of platinum appeared together with an anatase TiO 2 structure. In addition, as far as the platinum chemical state is concerned, the co-deposition of TiO 2 and Pt allow…
Superficial defects induced by argon and oxygen bombardments on (110) TiO2 surfaces
1998
Abstract Compositional and chemical changes of titanium dioxide monocrystalline surfaces induced by bombardment with 4 keV argon and oxygen ions have been studied by AES, XPS and AFM. Argon ion bombardment induced strong changes in the composition and chemical state of the surface: loss of oxygen due to preferential sputtering occurred, and, related to this, Ti4+ species were reduced to Ti3+ and Ti2+. During oxygen bombardment, competition between preferential sputtering of oxygen ions of the oxide surface and oxygen implantation was observed. This phenomenon was found to be strongly dependent upon the incidence angle of the oxygen ions. Moreover, an oxygen bombardment with normal incidence…
Growth and composition of nanostructured and nanoporous cerium oxide thin films on a graphite foil.
2015
The morphology and composition of CeOx films prepared by r.f. magnetron sputtering on a graphite foil have been investigated mainly by using microscopy methods. This study presents the formation of nanocrystalline layers with porous structure due to the modification of a carbon support and the formation of cerium carbide crystallites as a result of the deposition process. Chemical analyses of the layers with different thicknesses performed by energy dispersive X-ray spectroscopy, electron energy loss spectroscopy and X-ray photoelectron spectroscopy have pointed to the reduction of the cerium oxide layers. In the deposited layers, cerium was present in mixed Ce(3+) and Ce(4+) valence. Ce(3+…
MOCVD growth of porous cerium oxide thin films on silicon substrate
2015
Abstract Porous cerium oxide thin films were grown by pulsed direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD) on silicon substrate, using cerium tetrakis (1-methoxy-2-methyl-2-propanolate) dissolved in cyclohexane as precursor as well as oxygen as oxidant agent. The chemical and morphological characteristics of the films were investigated by XPS, SEM and TEM. The influence of the growth conditions on the morphological features of the thin films and the cerium chemical states are reported and discussed. The decrease of the oxygen and/or alkoxide flow rate induces the decrease of both the film thickness and the porosity of the layer. Moreover, the growth of silicate…
ChemInform Abstract: Coupled Semiconductor Systems for Photocatalysis. Preparation and Characterization of Polycrystalline Mixed WO3/WS2 Powders.
2010
Mixed WO3/WS2 powders were prepared by oxidation of WS2. The physical properties of the samples were characterized by X-ray diffraction, diffuse reflectance spectroscopy, and scanning electron microscopy; they were strongly dependent upon the time and temperature of oxidation. The chemical state and the elemental distribution of the sample surface were investigated by X-ray photoelectron spectroscopy. The photocatalytic results have showed that the aqueous suspensions of the mixed WO3/WS2 systems have significantly higher activities than pure WS2 and WO3 for the photodegradation of phenol. The enhanced performance can be related to the presence of heterojunctions WO3/WS2 on the single parti…
Characterization of Pumice-Supported Ag–Pd and Cu–Pd Bimetallic Catalysts by X-Ray Photoelectron Spectroscopy and X-Ray Diffraction
1999
Bimetallic Ag–Pd and Cu–Pd catalysts supported on pumice have been prepared in order to be used in the selective hydrogenation of dienes. The catalysts were obtained by the classical impregnation method and in the case of the Cu–Pd system also by organometallic precursors. They were analysed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). XPS allowed us to determine the surface distribution and chemical state of the two elements; XRD yielded the lattice parameters and allowed us to establish the possible formation of alloys. The two bimetallic systems behave differently. In the case of the Ag-Pd catalysts, Pd particles covered by silver atoms along with highly dispers…
Chemical-state analyses of Ni, Zn, and W ions in NiWO$_4$-ZnWO$_4$ solid solutions by X-ray photoelectron spectroscopy
2022
The chemical states of Ni, Zn, and W in microcrystalline NiWO$_4$-ZnWO$_4$ solid solutions were studied by X-ray photoelectron spectroscopy. The recorded spectra of the Ni 2p, Zn 2p, and W 4f photoelectron lines and Ni L$_2$M$_{23}$M$_{45}$, Zn L$_3$M$_{45}$M$_{45}$, and W N$_4$N$_{67}$N$_{7}$ Auger-transition lines show pronounced changes with increasing Zn concentration. The positions of the resolved photoelectron and Auger-transition lines were combined to construct so-called chemical-state plots (Wagner or Auger-parameter plots) for metal ions in solid solutions. With increasing Zn concentration, the Auger parameter increases for Ni and decreases for W, thus evidencing a lowering and an…
Coupled Semiconductor Systems for Photocatalysis. Preparation and Characterization of Polycrystalline Mixed WO3/WS2 Powders
1999
Mixed WO3/WS2 powders were prepared by oxidation of WS2. The physical properties of the samples were characterized by X-ray diffraction, diffuse reflectance spectroscopy, and scanning electron microscopy; they were strongly dependent upon the time and temperature of oxidation. The chemical state and the elemental distribution of the sample surface were investigated by X-ray photoelectron spectroscopy. The photocatalytic results have showed that the aqueous suspensions of the mixed WO3/WS2 systems have significantly higher activities than pure WS2 and WO3 for the photodegradation of phenol. The enhanced performance can be related to the presence of heterojunctions WO3/WS2 on the single parti…
The fate of silver ions in the photochemical synthesis of gold nanorods: an Extended X-ray Absorption Fine Structure analysis
2009
Water-soluble gold nanorods (Au NRs) were synthesized using a silver-ion mediated photochemical route under UV irradiation. Extended X-ray Absorption Fine Structure (EXAFS) measurements on the Ag K-edge were performed on samples obtained at different Ag/Au ratios and at increasing irradiation times in order to investigate the fate of silver ions during the growth of Au NRs. EXAFS measurements allowed to probe the chemical state and the local environment of silver in the final product. Experimental data suggest that Ag atoms are placed on top of the Au particles as metallic Ag(0), while no significant contribution to the EXAFS spectra comes from AgBr or other Ag(+) based species. The reporte…
Photochemical Synthesis of Water-Soluble Gold Nanorods: The Role of Silver Ions in Assisting Anisotropic Growth
2009
The role of Ag+ ions in the ultraviolet-driven photochemical synthesis of Au nanorods (NRs) in aqueous surfactant mixtures has been investigated in order to elucidate the mechanism that drives anisotropic nanoparticle growth. The samples, grown in the presence of varying amounts of Ag+ ions for scheduled irradiation times, have been characterized by ultraviolet−visible−near infrared (UV−vis−NIR) absorption spectroscopy, analytical transmission electron microscopy (ATEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and extended X-ray absorption fine structure (EXAFS) measurements. Moreover, the time evolution of size and shape distribution has been investigated by stat…