Fluorine-doped titanium dioxide was prepared via sol−gel synthesis and subsequent calcination in air. The presence of fluorine in the lattice induces the formation of reduced Ti3+ centers that ...localize the extra electron needed for charge compensation and are observed by electron paramagnetic resonance. Density functional theory calculations using hybrid functionals are in full agreement with such description. The extra electron is highly localized in a 3d orbital of titanium and lies a few tenths of an electron volt below the bottom of the conduction band. The preparation via sol−gel synthesis using aqueous solutions of fluorides also causes the formation of surface F− ions that substitute surface hydroxyl groups (OH−) without generating reduced centers.
We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional ...theory. The loss spectrum of indium selenide shows the direct free exciton at ~1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed.
A series of perovskite-type manganites AMnO
3
(A = Sr, La, Ca and Y) particles were investigated as electrocatalysts for the oxygen reduction reaction. AMnO
3
materials were synthesized by means of ...an ionic-liquid method, yielding phase pure particles at different temperatures. Depending on the calcination temperature, particles with mean diameter between 20 and 150 nm were obtained. Bulk versus surface composition and structure are probed by X-ray photoelectron spectroscopy and extended X-ray absorption fine structure. Electrochemical studies were performed on composite carbon-oxide electrodes in alkaline environment. The electrocatalytic activity is discussed in terms of the effective Mn oxidation state, A:Mn particle surface ratio and the Mn–O distances.
Transparent conductive oxides are emerging materials in several fields, such as photovoltaics, photoelectrochemistry, and optical biosensing. Their high chemical inertia, which ensured long-term ...stability on one side, makes challenging the surface modification of transparent conductive oxides; long-term robust modification, high yields, and selective surface modifications are essential prerequisite for any further developments. In this work, we aim at inducing chemical functionality on fluorine-doped tin oxide surfaces (one of the most inexpensive transparent conductive oxide) by means of electrochemical grafting of aryl diazonium cations. The grafted layers are fully characterized by photoemission spectroscopy, cyclic voltammetry, and atomic force microscopy showing linear correlation between surface coverage and degree of modification. The electrochemical barrier effect of modified surfaces was studied at different pH to characterize the chemical nature of the coating. We showed immuno recognition of biotin complex built onto grafted fluorine-doped tin oxides, which opens the perspective of integrating FTO samples with biological-based devices.
The ability to control the three-dimensional architecture of graphene-based materials following a rational design is essential for technological applications. Here we demonstrate that the ...electrochemical etching can be used as a surgical tool to tailor the morphology of graphene electrodes and to impart special features, like micrometric channels and controlled mesoporosity (foams). The final materials, thanks to the high surface area, can represent a promising class of carbon-based supercapacitors. Otherwise, new materials can be prepared using a bottom-up strategy that exploits the self-assembly of the graphene oxide quantum dots produced during the electrochemical erosion. The advantages of this second approach reside not only in the possibility to downscale the control over the spatial organization as compared to the use of conventional micrometric graphene sheets, but also in the introduction of the intrinsic luminescent properties of the quantum dots in the final material. As a proof of concept we report the preparation of luminescent nanospheres by exploiting the self-organization of the graphene oxide quantum dots around frozen water nuclei.
Zinc oxide nanocrystals, pure and doped with transition metal ions, have been synthesized using colloidal techniques; after purification and concentration protocols, the ZnO solutions are mixed with ...monodisperse Au colloidal suspensions and used for thin film depositions. The effect of the dopant ions on the structural, morphological and optical properties of the as-synthesized colloids as well as the nanocomposite thin films has been analyzed and discussed. The dopant presence has been found to affect the CO optical sensing properties of the nanocomposite ZnO–Au films: compared to pure ZnO, an increase in sensitivity up to 80% and 55% has been detected for Co-doped and Mn-doped ZnO respectively, while Ni-doped ZnO films show only minor improvements. This observation has been ascribed to the multiple oxidation states of cobalt and manganese ions that can facilitate electron transfer between the target gas and semiconductive oxide matrix, and also to the lower surface concentration of Ni ions inside ZnO crystals, as compared to Co and Mn. A fast and reversible response after repeated CO exposures has been detected for all tested samples, and a linear response intensity with the order of magnitude of CO concentration has been observed in the 10–10,000
ppm range, with a lower detection limit of 1–2
ppm.
Zirconium tetra-tert-butoxide was used as precursor for the growth of ZrO2 films on TiO2(110) in ultrahigh vacuum conditions. The composition of the film was characterized by X-ray photoelectron ...spectroscopy (XPS), while its thickness and growth mode were characterized by angle-resolved photoelectron spectroscopy (AR-XPS). The structure of the interface was studied in detail by angle-scanned X-ray photoelectron diffraction (AS-XPD). These data, compared with multiple-scattering spherical wave (MSSW) simulations suggest the growth, at the interface, of Zr2O3 nanostripes aligned along the 001 direction. The structure and composition of the interface are responsible for the lower acidity of the ZrO2/TiO2(110) surface if compared with that of the bare substrate.
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