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  • 1
    Electronic Resource
    Electronic Resource
    XPS and TRP/TPO Study of the behaviour of rhodium particles supported on TiO2 (1988)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 12 (1988), S. 247-252 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Oxidation/reduction processes occurring in rhodium particles supported on TiO2 have been studied by a combination of XPS and TPR/TPO. Rh(I) and Rh(III) are formed by calcination in excess of O2 at 773k, Rh(III) being favoured for samples with very small metal particles. For samples with particles in the range 2.0-10.0 nm, oxidation up to Rh2O of the whole particles occurs followed by a kinetically controlled growth of a thin Rh2O3 layer at their surface together with the formation of Rh(III) species at the particle/support interface. H2 adsorption at 300 K on the highly oxidized particles (up to Rh2O3) is an activated process which implies reduction of Rh(III) into Rh(I). Further reduction at 373 K leads to Rh(O) formation although some Rh(I) and Rh(III) species still remain unreduced up to T 〉 473 K. A model is proposed to decribe the evolution of these rhodium oxide particles as well as to explain their different behaviour against H2 adsorption at 300 K.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740120404
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  • 2
    Electronic Resource
    Electronic Resource
    Interpretation of surface textural changes in SrTiO3 ex-oxalate samples using XPS and IR spectroscopies (1990)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 15 (1990), S. 693-697 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: XPS, IR and x-ray diffraction (XRD) have been used to study high-surface-area ‘ex-oxalate’ polycrystalline SrTiO3 materials. Changes of surface area and pore size distribution are induced during lixiviation with a 0.1 M HCl solution, which removes carbonate impurities. The study shows the presence in the original sample of a microcrystalline SrCO3 phase at its surface and isolated CO32- species, these latter remaining even after outgassing at 773 K for 15 h. However, a complete elimination of the SrCO3 and other carbonate species at the surface is achieved by heating the acid-lixiviated sample at 773 K, although carbonate species still remain in the bulk of the SrTiO3 material after this treatment. The usefulness of the combined use of XPS and IR for the characterization of surface and bulk species in this type of powdered material is pointed out during this study.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740151109
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  • 3
    Electronic Resource
    Electronic Resource
    Size and support effects in the photoelectron spectra of small TiO2 particles (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 18 (1992), S. 392-396 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Three different TiO2 samples in the form of bulk material, colloidal particles and small clusters supported on SiO2 have been studied by extended x-ray adsorption fine structure (EXAFS), UV-visible, transmission electron microscopy (TEM) and XPS. The different values of the Ti 2p binding energies and the Auger parameter of Ti found for each sample show that the photoemission processes in these oxide materials are influenced by size and support effects. A difference in the relaxation energy of -1.1 eV is found for the TiO2/SiO2 sample with respect to TiO2, which is attributed to an effect of the silica support.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740180604
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  • 4
    Electronic Resource
    Electronic Resource
    Charging and mixing effects during the XPS analysis of mixtures of oxides (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 22 (1994), S. 111-114 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: In this article we present an XPS analysis of mixtures of Al2O3 and TiO2 powders of different relative size in order to study differential charging effects. To illustrate some of the possible situations we have studied the behaviour of three different samples: (1) very large (microns) and porous particles of Al2O3 supporting TiO2 particles of relatively small size (300 Å); (2) Al2O3 and TiO2 particles of similar size (300 Å); and (3) very small particles (20-30 Å) of TiO2 dispersed in Al2O3 particles of 300 Å. The observed effects are then analysed by using Auger parameters and relative binding energies and discussed in terms of the different morphologies of the samples, as determined by TEM. The influence on charging of an electron flood gun and of Ar+ sputtering is also presented. In addition, ion-induced mixing effects have been clearly observed in the case of very small particles of TiO2 dispersed on alumina.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740220127
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  • 5
    Electronic Resource
    Electronic Resource
    Control of the stoichiometry in the deposition of cobalt oxides on SiO2 (1998)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 62-71 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; ISS ; CoO ; Co3O4 ; interface effects ; cobalt oxide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Both CoO and Co3O4 overlayers have been deposited on SiO2 by evaporation from metallic Co and subsequent oxidation with oxygen and a plasma of oxygen. The combined use of ion scattering spectroscopy and XPS shows that both oxides grow in the form of small particles on the surface of SiO2. Ion scattering spectroscopy also shows that the surface of cobalt oxide exposed to a plasma of oxygen is enriched in oxygen ions with respect to the surface of the cobalt oxide formed by exposure to oxygen. The Co 2p spectra corresponding to the deposits obtained by oxidation with O2 are characteristic of CoO, while those corresponding to the deposits obtained after oxidation with a plasma are typical of Co3O4. Moreover, the OCo/Co ratios determined by XPS and factor analysis indicate the formation of CoO stoichiometry in the former case and Co3O4 stoichiometry in the latter. It has also been observed that no shift in either binding energy or modified Auger parameter α′ appears as a function of coverage. This absence of shifts is interpreted as a consequence of the type of screening mechanism that dominates the relaxation of the photoholes in these oxides. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    XPS characterization of coal surfaces: Study of aerial oxidation of brown coals (1988)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 12 (1988), S. 565-571 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: XPS was used to determine the surface concentrations of diferent elements present in two Spanish brown coals. Sputtering with Ar+ ions followed by XPS analysis permitted depth concentration profiles in both, fresh and oxidized coals, to be obtained, and show that aerial oxidation brought about a redispersion of the organic matter onto the mineral phase. Analysis of C 1s band shape together with Fourier transform infrared (FTIR) study of organic functional groups show that loss of hydroxyl groups from the organic phase occurs by thermal decomposition during the first stages of oxidation, leading to an increase of the hydroxyl groups in the mineral phase by proton transfer. At higher temperatures, oxidation gives rise to formation of new carboxyl groups. The usefulness of XPS and some bulk characterization techniques used for studying coal oxidation is compared.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740121203
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  • 7
    Electronic Resource
    Electronic Resource
    Use of XPS and Ar+ depth profiling to determine the dispersion degree of Ni in Ni/TiO2 and Ni/SiO2 catalysts (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 19 (1992), S. 508-512 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Two series of Ni/TiO2 and Ni/SiO2 catalysts prepared by different methods have been characterized by XPS and Ar+ sputtering. Depth profiles have been obtained from the intensity of the Ni 2p photoelectron peaks as a function of the sputtering time. The analysis has been carried out for samples in their precursor, calcined and reduced states, in order to obtain information on the changes in dispersion of the active phase through the whole activation process. In the case of reduced Ni/SiO2 catalysts, comparison with results by other techniques (i.e. H2 chemisorption, x-ray diffraction and transmission electron microscopy) has shown that the sputtering method may give a semi-quantitative assessment on the dispersion degree of nickel. However, for Ni/TiO2 catalysts in the SMSI state after reduction in H2 at 773 K only the Ar+ sputtering method was able to provide information on the distribution of nickel. In this case the depth profiles were consistent with partial solution of the nickel in the TiO2 matrix.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740190194
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  • 8
    Electronic Resource
    Electronic Resource
    XPS and ISS study of NiTiO3 and PbTiO3 subjected to low-energy ion bombardment. I. Influence of the type of ion (Ar+ and O2+) (1993)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 20 (1993), S. 941-948 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Compositional and chemical changes in PbTiO3 and NiTiO3 induced by 3.5 keV Ar+ and O2+ ion bombardment have been studied quantitatively by XPS and ISS. Whereas in NiTiO3 the Ti/Ni ratio determined by XPS remained practically constant, a preferential loss of lead was observed in PbTiO3 during ion bombardment. In that case, Ar+ removed lead more effectively than O2+ ions. Argon ion bombardment induced strong chemical changes in both titanates: Ni2+ and Pb2+ species were nearly totally reduced to the metallic state, while Ti4+ species were partially reduced to Ti3+ and Ti2+ oxidation states. This reduction is more efficient in PbTiO3 than in NiTiO3. The preferential loss of lead in PbTiO3 and the removal at equivalent rates of Ti and Ni in NiTiO3 are discussed within the context of the chemical stability and physical constants of the compounds by assuming a chemically guided lattice relaxation of the bombarded targets. The possibility that solid-state reactions play a role in the control of some of the results is stressed. Other possible effects, such as agglomeration or surface enrichment, are discussed by using the ISS results.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740201203
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  • 9
    Electronic Resource
    Electronic Resource
    Use of XAS and chemical probes to study the structural damage induced in oxide ceramics by bombardment with low-energy ionsPaper presented at ECASIA 93, Catania, Sicily, 4-8 October 1993. (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 21 (1994), S. 418-424 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A preliminary study by x-ray absorption spectroscopy (XAS) of the structural modifications induced in mixed oxides by low-energy (1-5 keV) Ar+ bombardment is presented in this paper. The analysis of the extended x-ray adsorption fine structure (EXAFS) and x-ray adsorption near-edge structure (XANES) spectra recorded for bombarded Al2TiO5 and BaTiO3 has shown the randomization of the atomic network and the formation of TiO2 in the outermost layers of these materials. On the other hand, SO2 is proposed as a probe molecule to asess semiquantitatively the extent of structural damage in the surface layers of bombarded oxides. The incorporation of sulphur into this zone has been proved by depth profiling with XPS and Ar+ ions of 0.5 keV. In BaTiO3 the incorporation of sulphur increases with the energy of the primary ions. This fact suggests that the concentration of defects increases with the energy of the Ar+ beam and that the most disordered surface layers are more reactive towards SO2. A similar effect is not observed with TiO2 and Al2TiO5 because in these materials, where a considerable reduction of titanium to Tin+ (n 〈 4) species is produced by the preferential removal of oxygen, an overlay of elemental sulphur is formed by the reaction of SO2 with these species. This overlay prevents the diffusion of SO2 and therefore the incorporation of sulphur into the damaged layer of those samples.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740210617
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  • 10
    Electronic Resource
    Electronic Resource
    Substrate Effects and Chemical State Plots for the XPS Analysis of Supported TiO2 Catalysts (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 292-294 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; Auger parameter ; TiO2 ; catalyst ; chemical state plot ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The analysis by XPS of TiO2 deposited on different substrates (SiO2, MgO, Ag, SnO) shows the existence of shifts in the Ti 2p binding energy and Auger parameter values. The magnitude of these shifts is a function of the support and of the coverage. A systematic representation of these shifts is possible with a chemical state plot. The implications of the existence of such shifts for the characterization of catalysts are discussed. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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