National Institute Of Materials Physics - Romania

In the present paper is presented an efficient strategy for synthesis of mesoporous TiO2 modified with different Ce concentrations through a sol-gel process in the presence of triblock Pluronic P123 as structure directing agent, integrated with evaporation-induced self- assembly (EISA) approach. The nanocomposite consisted mostly of small crystallite of anatase. The presence of a new crystal phase corresponding to cerium titanate was evidenced in Ce-modified powder samples. All materials were characterized by SEM and TEM microscopies, UV-vis, XPS and N-2 adsorption-desorption isotherms in order to examine the textural and structural characteristics and the chemical nature of their surface. Furthermore, the photoelectrochemical characterization evidenced the effect of the TiO2 mesoporous structure, the amount of cerium and the oxidation state of Ti and Ce in the new photocatalysts on the enhanced photovoltaic performance. The photocatalytic activity of the as-synthesized materials was evaluated for phenol photodegradation in aqueous media and the reactive species involved in photocatalytic process were established by using some radical scavengers in the photodegradation experiments. Based on the obtained results, these new Ce-modified mesoporous TiO2 photocatalysts could be considered for degradation of organic compounds from wastewaters by advanced oxidation processes or for photoanodes construction for efficient photoelectrochemical fuel cell (PFC) systems.

Gold is deposited on atomically clean, inwards polarized, ferroelectric lead zirco-titanate deposited by pulsed laser deposition on strontium titanate (001) single crystal, then carbon monoxide adsorption and desorption experiments are investigated by in situ fast photoelectron spectroscopy using synchrotron radiation. Atomic force microscopy and high resolution photoelectron spectroscopy are consistent with the formation of 50?100 nm nanoparticles, and their Au 4f core levels point to a negative charge state of gold. As compared with a similar experiment performed on ferroelectric lead zirco-titanate with similar polarization state and without gold, the saturation coverage after exposure to carbon monoxide increases by about 68 %, and also most of the additional carbon is found in oxidized state. Desorption experiments with in situ follow-up by photoelectron spectroscopy are performed as function of temperature, and the neutral carbon intensity decreases when the ferroelectric polarization decreases, while the components corresponding to oxidized carbon remain unchanged. It looks that neutral carbon adsorption is strictly related to the polarization of the ferroelectric film, while carbon still found in molecular form is related to its carbonyl bonding on metal nanoparticles, independent of the polarization state of the substrate. Desorbed carbon at higher temperature uptakes oxygen from the substrate.

Properties of epitaxial PbZr0.2Ti0.8O3 (PZT) films deposited on Si substrates were investigated for integration in the present CMOS technology. Polarization is downward oriented, in association with the presence of an internal electric field, and has a lower value compared to the PZT films deposited on single crystal perovskite SrTiO3 (STO) substrates (40 mu C/cm(2) versus 80 mu C/cm(2)), while the dielectric constant is larger (180 versus 120). Large value for the pyroelectric coefficient was also found, 1.22 x 10(-3)C/m(2)K, as for PZT grown on single crystal STO. The macroscopic ferroelectric and pyroelectric properties appear to be affected by the structural quality and stoichiometry of the PZT film. The changes in the electric properties are an effect of the strain gradients induced by the large difference between the thermal expansion coefficients of PZT and Si substrate, leading in turn to Pb oxidation and antisite defect formation compared to PZT films deposited on STO substrates.

The rich functionalities of transition-metal oxides and their interfaces bear an enormous technological potential. Its realization in practical devices requires, however, a significant improvement of yet relatively low electron mobility in oxide materials. Recently, a mobility boost of about 2 orders of magnitude has been demonstrated at the spinel-perovskite gamma-Al2O3/SrTiO3 interface compared to the paradigm perovskite-perovskite LaAlO3/SrTiO3 interface. We explore the fundamental physics behind this phenomenon from direct measurements of the momentum-resolved electronic structure of this interface using resonant soft-X-ray angle-resolved photoemission. We find an anomaly in orbital ordering of the mobile electrons in gamma-Al2O3/SrTiO3 which depopulates electron states in the top SrTiO3 layer. This rearrangement of the mobile electron system pushes the electron density away from the interface, which reduces its overlap with the interfacial defects and weakens the electron-phonon interaction, both effects contributing to the mobility boost. A crystal-field analysis shows that the band order alters owing to the symmetry breaking between the spinel gamma-Al2O3 and perovskite SrTiO3. Band-order engineering, exploiting the fundamental symmetry properties, emerges as another route to boost the performance of oxide devices.

Cu-Fe-Sn-S films were obtained on indium tin oxide / glass substrates by a low-cost electrodeposition using an aqueous solution of CuSO4, FeSO4, SnSO4, and Na2S2O3 at room temperature followed by high-temperature sulfurization (500 degrees C) in argon flow. A range of cathodic potentials have been used for electrodeposition, those being chosen after a preliminary cyclic voltammetry study. The coatings were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray Photoelectron Spectroscopy and conventional spectroscopy (diffuse reflectance and specular transmission). The results are discussed with respect to the used applied potential.

The thermal behavior of Cu-doped TiO2 gels obtained by the sol-gel method was investigated by thermogravimetric and differential thermal analysis (TG/DTG/DTA) and differential scanning calorimetry (DSC) measurements. The comparative investigation of the structure and morphology of the as-prepared gels and of the nanopowders obtained by annealing them was realized by transmission electron microscopy (TEM), Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Significant differences were noticed depending on the amount of dopant (0.5 or 2.0 mol % CuO). A higher dopant concentration resulted in a more complex decomposition of the sample. This behavior was associated with the formation of various molecular species in the sol-gel solutions before gelation, determined by the different amount of the dopant used.

A simple view of ferroelectricity is proposed for a thin film with uniform polarization oriented perpendicular to its surface, starting from the assumption that this situation is always accompanied by charge accumulation in the outer metal electrodes, in the contamination layers or near the surface, in the ferroelectric film itself. Starting with the formula derived for an "elemental" dipole moment in the film, simple statistical mechanics allows one to derive hysteresis cycles, and their dependence on temperature starting with only two parameters: the dielectric constant of the material and the maximum value of the dipole moment of a unit cell. Values obtained for Curie temperatures and coercive fields agree well with experiments. "Exact" energy dependencies on the asymmetry parameter are derived, and their connection with the Landau-Ginsburg-Devonshire is proven. By considering also the dipolar interaction in a continuous model, in addition to the ordering energy in the presence of surface charge accumulation, one may estimate the distribution of the polarization inside the film and the validity of the hypothesis of uniform polarization.

Hydroxyapatite Ca-10(PO4)(6)(OH)(2) (HAp) is an important bioactive material for bone tissue reconstruction, due to its highly thermodynamic stability at a physiological pH without bio-resorption. In the present study, the Ag:HAp and the corresponding Ag:HAp + D-3 thin films (similar to 200 nm) coating were obtained by vacuum deposition method on Ti substrate. The obtained samples were exposed to different UV irradiation times, in order to investigate the UV light action upon thin films, before considering this method for the thin film's decontamination. The effects of UV irradiation upon Ag:Hap + D-3 are presented for the first time in the literature, marking a turning point for understanding the effect of UV light on composite biomaterial thin films. The UV irradiation induced an increase in the initial stages of surface roughness of Ag:HAp thin film, correlated with the modifications of XPS and FTIR signals. The characteristics of thin films measured by AFM (RMS) analysis corroborated with XPS and FTIR investigation highlighted a process of recovery of the thin film's properties (e.g., RMS), suggesting a possible adaptation to UV irradiation. This process has been a stage to a more complicated UVA rapid degradation process. The antifungal assays demonstrated that all the investigated samples exhibited antifungal properties. Moreover, the cytotoxicity assays revealed that the HeLa cells morphology did not show any alterations after 24 h of incubation with the Ag:HAp and Ag:HAp + D-3 thin films.

The growth of electrical transportation is crucially important to mitigate rising climate change concerns regarding materials supply. Supercapacitors are high-power devices, particularly suitable for public transportation since they can easily store breaking energy due to their high-rate charging ability. Additionally, they can function with two carbon electrodes, which is an advantage due to the abundance of carbon in biomass and other waste materials (i.e., plastic waste). Newly developed supercapacitive nanocarbons display extremely narrow micropores (0.8 nm), as it increases drastically the capacitance in aqueous electrolytes. Here, we present a strategy to produce low-cost flexible microporous electrodes with extremely high power density (100 kW kg(-1)), using fourty times less activating agent than traditionnal chemically activated carbons. We also demonstrate that the affinity between the carbon and the electrolyte is of paramount importance to maintain rapid ionic diffusion in narrow micropores. Finally, this facile synthesis method shows that low-cost and bio-based free-standing electrode materials with reliable supercapacitive performances can be used in electrochemistry. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

A new method to obtain poly(vinyl chloride) (PVC) spheres, which consists of an interaction between commercial PVC grains and hexyl ethyl cellulose and lauroyl peroxide at a temperature of 60 degrees C, is reported. The addition of the graphene oxide (GO) sheets dispersed in dimethylformamide to the reaction mixture leads to the generation of composites made of PVC spheres coated with GO sheets. Scanning electron microscopy studies have demonstrated that this method allows for the transformation of PVC grains with sizes between 75 and 227 mu m into spheres with sizes varying from 0.7 to 3.5 mu m when the GO concentration in the PVC/GO composite mass increases from 0.5 to 5 wt.%. Our studies of Raman scattering and FTIR spectroscopy highlight a series of changes that indicate the appearance of ClCH=CH-, CH2=CCl-, and/or -CH=CCl- units as a result of PVC partial dehydrogenation. New -COO- and C-OH bonds on the GO sheet surfaces are induced during the preparation of PVC spheres coated with GO sheets. A photoluminescence (PL) band with a maximum at 325 nm is reported to characterize the PVC spheres. A PVC PL quenching process is demonstrated to be induced by the increase in the concentration of the GO sheets in the PVC/GO composite mass. The perspectives regarding the use of this composite as a flame-retardant material are also reported.