Jean-Charles Dupin

Systematic XPS studies of metal oxides, hydroxides and peroxides

The results of a systematic XPS study, under high controlled conditions, of different basic oxides of transition metals, alkali and alkaline-earth metals are presented; the XPS data of some hydroxides and peroxides are also reported. Variations of the O 1s binding energies are analysed and one point of interest is the large binding energy scale obtained for O 1s peaks all associated with a ‘‘2− ’’ formal charge. Through extended Huckel theory-tight binding (EHT-TB) calculations, attempts are made to rationalize the observed variations. The results illustrate the significant differences between real charges on oxygen atoms in transition metal and alkaline-earth oxides.

XPS analysis of new lithium cobalt oxide thin-films before and after lithium deintercalation

Lithium cobalt oxides thin-films, prepared by radio frequency magnetron sputtering and which could be used as positive electrode materials in microbatteries, were studied by X-ray photoelectron spectroscopy. The results have shown two formal oxidation numbers (+III and +IV) for cobalt ions and two environments, octahedral and tetrahedral for lithium ions. A systematic overcontent of oxygen compared to crystalline LiCoO2 has been evidenced for the thin-films, this excess, attributed to unusual co-ordinations with metal and more covalent Co–O bonds, could be localised in the boundaries of the randomly oriented nanodomains observed by transmission electron microscopy. The evolution of these LixCoO2+y thin-films at different stages of their cycle in experimental microbatteries has also been studied by an analysis of both core peaks and valence bands. The deintercalation of lithium has led to an increase of the proportion of ‘Co4+’ ions; in parallel an implication of the anions has been observed.

Characterisation of r.f. sputtered tungsten disulfide and oxysulfide thin films

Abstract Tungsten disulfide (WS2) and tungsten oxysulfide (WOySz) thin films were prepared by reactive radio frequency magnetron sputtering using a WS2 target and argon or a mixture of argon and oxygen as a discharge gas. For a total pressure of 1 Pa, a large range of composition, determined by Rutherford backscattering spectroscopy, can be obtained from WS2.05 when no oxygen gas is introduced in the sputtering chamber to WO3.04S0.09 when the oxygen partial pressure is 10−2 Pa. Scanning electron microscopy studies have shown that the film morphology depends on the sputtering conditions (oxygen partial pressure, total pressure and sputtering time). A structural analysis (X-ray diffraction and transmission electron microscopy) has highlighted that the tungsten oxysulfide thin films such as WO1.05S2.01, WO1.35S2.20 and WO3.04S0.09 are amorphous. Only the WS2 and the WO0.4S1.96 films are made of small crystallites (length ≤80 nm and width ≤10 nm) which grow with their c-axis parallel to the substrate. An X-ray photoelectron spectroscopy study on both the core levels (W4f and S2p peaks) and the valence bands has shown that three different environments of the tungsten atoms exist inside the tungsten oxysulfide thin films: an oxygen and a sulfur environment, respectively as in WO3 and WS2, and a mixed oxygen–sulfur environment constituted of O2−, S2− and S22−.

Amorphous oxysulfide thin films MOySz (M = W, Mo, Ti) XPS characterization: structural and electronic pecularities

Abstract The present paper reports the XPS study of different amorphous oxysulfides thin films MOySz (M=W, Ti, Mo), prepared by radio frequency magnetron sputtering. It has been shown the coexistence of various environments and formal oxidation numbers for metal atoms. In addition, the observation of several types of sulfur ions has revealed the specific character of such amorphous layers. In order to precise the common features and the differences as a function of the nature of the metal atom, a comparison of the data for the three kinds of thin films has been done.

Biosorption of chromium by alginate extraction products from Sargassum filipendula: investigation of adsorption mechanisms using X-ray photoelectron spectroscopy analysis.

The alginate extraction products from Brazilian brown seaweed Sargassum filipendula were studied for chromium biosorption. Batch experiments were conducted at pH 2 and 3 and 20°C to determine the sorption capacity of this biosorbents for chromium (VI) and (III). The biomass was characterized before and after metal binding by X-ray photoelectron spectroscopy (XPS) in order to determine the mechanisms of chromium biosorption. The residue has a high adsorption capacity, close the value obtained with seaweed and higher than that of alginate for both Cr(III) and Cr(VI). XPS analysis of the biosorbents revealed that carboxyl, amino and sulfonate groups are responsible for the binding of the metal ions. The analysis also indicated that the Cr(VI) bound to the biomass was reduced to Cr(III).

Texturising and structurising mechanisms of carbon nanofilaments during growth

The question of how the texture and structure of carbon nanofilaments (CNTs) are determined during growth is addressed via their preparation using the vapour phase method over Ni–Cu–Mg–Al catalysts. The CNTs formed and the related catalyst particles were investigated by high resolution transmission electron microscopy, electron diffraction, and X-ray energy dispersive spectroscopy. The nanofilament features were found to directly relate to the catalyst particle size and morphologies, which in turn depend on both the Ni/Cu ratio in the Ni–Cu alloy that forms the catalyst particles and the route by which they were prepared. The extent and orientation of graphenes within the carbon nanofilaments were found to be controlled by the extent of the related catalyst crystal faces and the angle value between the latter. It is proposed that energetics of graphenes, basically involving the ratio of the edge over the core carbon atoms, the energetic cost of heterocycles (pentagon), and that of the stress induced by the strain at graphene bending sites, determine whether the carbon nanofilaments would actually grow as nanotubes (i.e., hollow) with the dual “herringbone–bamboo” texture, or as nanofibres (i.e., not hollow) with either the “herringbone” texture or the platelet texture. Only the latter allowed the genuine graphite (3D periodicity) structure to develop, while the other nanofilament types could merely adopt the turbostratic structure. Meanwhile, it was demonstrated that the herringbone nanotubes and nanofibres here prepared are of “cup-stack” rather than “single helix” type.

A new route for local probing of inner interactions within a layered double hydroxide/benzene derivative hybrid material.

This paper presents the preparation and characterization of hybrid hydrotalcite-type layered double hydroxides (Zn1-xAlx(OH)2HBSx.nH2O, with x=0.33) where HBS is the 4-phenol sulfonate, with a detailed analysis of the grafting process of this organic entity onto the host lattice. As a set of the usual techniques (XRD, TG-DT/MS, FTIR and 27Al MAS NMR) was used to characterize the hybrid materials, this work focuses on a joint study by X-ray photoelectron spectroscopy and some quantum-calculation modeling in order to highlight the nature of the interactions between the organic and the mineral sub-systems. For the as-prepared hybrid material, the main results lead to a quasi-vertical orientation of the organic molecules within the mineral sheets via H-bond stabilization. By heating the hybrid material up to 200 degrees C, the structure shrinks with the condensation of the organics; the different theoretical modeling done gives an energy-stable situation when a direct attachment of the HBS sulfonate group sets up with the mineral layers, in agreement with the recorded XPS experimental data.

New insights into micro/nanoscale combined probes (nanoAuger, μXPS) to characterize Ag/Au@SiO2 core–shell assemblies

This work has examined the elemental distribution and local morphology at the nanoscale of core@shell Ag/Au@SiO2 particles. The characterization of such complex metal/insulator materials becomes more efficient when using an initial cross-section method of preparation of the core@shell nanoparticles (ion milling cross polisher). The originality of this route of preparation allows one to obtain undamaged, well-defined and planar layers of cross-cut nano-objects. Once combined with high-resolution techniques of characterization (XPS, Auger and SEM), the process appears as a powerful way to minimize charging effects and enhance the outcoming electron signal (potentially affected by the topography of the material) during analysis. SEM experiments have unambiguously revealed the hollow-morphology of the metal core, while Auger spectroscopy observations showed chemical heterogeneity within the particles (as silver and gold are randomly found in the core ring). To our knowledge, this is the first time that Auger nano probe spectroscopy has been used and successfully optimized for the study of some complex metal/inorganic interfaces at such a high degree of resolution (≈12 nm). Complementarily, XPS Au 4f and Ag 3d peaks were finally detected attesting the possibility of access to the whole chemistry of such nanostructured assemblies.

Thermoresponsive gold nanoshell@mesoporous silica nano-assemblies: an XPS/NMR survey

This work provides a detailed study on the physico-chemical characterization of a mechanized silver-gold alloy@mesoporous silica shell/pseudorotaxane nano-assembly using two main complementary techniques: XPS and NMR (liquid- and solid-state). The pseudorotaxane nanovalve is composed of a stalk (N-(6-aminohexyl)-aminomethyltriethoxysilane)/macrocycle (cucurbit[6]uril (CB6)) complex anchored to the silica shell leading to a silica/nanovalve hybrid organic-inorganic interface that has been fully characterized. The stalk introduction in the silica network was clearly demonstrated by XPS measurements, with the Si 2p peak shifting to lower energy after grafting, and through the analysis of the C 1s and N 1s core peaks, which indicated the presence of CB6 on the nanoparticle surface. For the first time, the complex formation on nanoparticles was proved by high speed (1)H MAS NMR experiments. However, these solid state NMR analyses have shown that the majority of the stalk does not interact with the CB6 macrocycle when formulated in powder after removing the solvent. This can be related to the large number of possible organizations and interactions between the stalk, the CB6 and the silica surface. These results highlight the importance of using a combination of adapted and complementary highly sensitive surface and volume characterization techniques to design tailor-made hybrid hierarchical structured nano-assemblies with controlled and efficient properties for potential biological purposes.

Design of gold nanoshells via a gelatin-mediated self-assembly of gold nanoparticles on silica cores

A gelatin-mediated self-assembly of gold nanoparticles on silica particles has been performed during gold ion reduction using ascorbic acid as reductant and PVP as stabilizer. Gold nanoshells with near infrared photothermal properties have been successfully designed.