[Show abstract][Hide abstract] ABSTRACT: A specific feature of the Mössbauer spectra of 119Sn in Y1–xCaxCrO3 samples containing 0.3 at % Sn4+ in the bulk of crystallites is an extra sextet component corresponding to hyperfine field H(119Sn) = 65 kOe at 4.2 K. This effect is explained by the formation of Sn4+ impurity associates in the chromium sublattice. A drastic weakening in spin polarization is observed for the Sn4+ ions in surface sites, but is found not to be related to the presence of heterovalent Ca2+ ions.
Bulletin of the Russian Academy of Sciences Physics 08/2015; 79(8). DOI:10.3103/S1062873815080055
[Show abstract][Hide abstract] ABSTRACT: A detailed study of the structure-composition-properties correlation is reported for the as-prepared (AP) and two oxygenated (oxygenation carried out at ambient pressure and under high pressure) Mo0.3Cu0.7Sr2ErCu2Oy samples. Their crystal structures were characterized by combining the x-ray/neutron powder diffraction (NPD) and electron diffraction techniques. All the samples show tetragonal symmetry, crystallizing in the P4/mmm space group. The influence of oxygenation in the electronic states for the Mo0.3Cu0.7Sr2ErCu2Oy system associated with an oxidation reaction leading from a non-superconducting to a superconducting state has also been investigated by means of x-ray photoelectron spectroscopy (XPS). XPS measurements show the predominance of the MoV oxidation state over the MoVI one in the AP sample; annealing under flowing oxygen enhances both the MoVI and CuII amounts. The AP sample shows the existence of ferromagnetic clusters originated from the short-range magnetic correlations of the paramagnetic MoV cations. On the other hand, all the oxygenated samples are not magnetic but superconducting. The high-pressure oxygenated sample shows the highest superconducting transition temperature of T C = 84 K. A partial oxygen ordering in the (Mo/Cu)O1+δ chain and a decrease in the charge transfer energy after oxygenation induces superconductivity in the oxygenated samples.
[Show abstract][Hide abstract] ABSTRACT: Detailed studies of the electronic states for Mo0.3Cu0.7Sr2ErCu2Oy samples with different oxygen contents are presented here. The influence of oxygenation in the electronic states for the Mo0.3Cu0.7Sr2ErCu2Oy system from a semiconducting to a superconducting state has been investigated by means of X-ray photoelectron spectroscopy (XPS). The XPS studies show that Mo is in a mixed MoV and MoVI oxidation state and MoV is predominant over the MoVI in the as-prepared (AP) sample. Yet annealing under an oxygen atmosphere enhances the MoVI state. At the same time, a reduction in the copper species is observed. In the Cu 2p spectra, a larger energy separation between the satellite and main peaks (ES-EM) and a lower intensity ratio (IS/IM) are found to correlate with higher values of the superconducting transition temperature (TC). Analysis of these spectra within the Con?guration Interaction (CI) model suggests that higher values of TC are related to lower values of the O 2p?Cu 3d charge transfer energy. The change in the Sr 3d and O 1s core level spectra correlates with the oxygen insertion in the (Mo/Cu)O1+[small delta] chain site, after oxygenation. The hole concentration (Ph) in the copper plane has been obtained using the room temperature thermoelectric power (TEP) value; this shows an increasing tendency in parallel with increasing TC, after oxygenation. From these experimental results, one observes that TC increases with decreasing charge transfer energy. This is, indeed, opposite to accepted views and occurs in parallel with the shortening of the apical Copper-Oxygen distance (Cu2?O2) and the increasing of the CuO2 plane buckling angle.
[Show abstract][Hide abstract] ABSTRACT: Posterior Capsular Opacification (PCO) is the capsule fibrosis developed on implanted IntraOcular Lens (IOL) by the de-differentiation of Lens Epithelial Cells (LECs) undergoing Epithelial Mesenchymal Transition (EMT). Literature has shown that the incidence of PCO is multifactorial including the patient's age or disease, surgical technique, and IOL design and material. Reports comparing hydrophilic and hydrophobic acrylic IOLs have shown that the former has more severe PCO. On the other hand, we have previously demonstrated that the adhesion of LECs is favored on hydrophobic compared to hydrophilic materials. By combining these two facts and contemporary knowledge in PCO development via the EMT pathway, we propose a biomimetically inspired strategy to promote LEC adhesion without de-differentiation to reduce the risk of PCO development. By surface grafting of a cell adhesion molecule (RGD peptide) onto the conventional hydrophilic acrylic IOL material, the surface-functionalized IOL can be used to reconstitute a capsule-LEC-IOL sandwich structure, which has been considered to prevent PCO formation in literature. Our results show that the innovative biomaterial improves LEC adhesion, while also exhibiting similar optical (light transmittance, optical bench) and mechanical (haptic compression force, IOL injection force) properties compared to the starting material. In addition, compared to the hydrophobic IOL material, our bioactive biomaterial exhibits similar abilities in LEC adhesion, morphology maintenance, and EMT biomarker expression, which is the crucial pathway to induce PCO. The in vitro assays suggest that this biomaterial has the potential to reduce the risk factor of PCO development.
PLoS ONE 12/2014; 9(12):e114973. DOI:10.1371/journal.pone.0114973 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The engineering of novel catalytic nanomaterials that are highly active for crucial carbon–carbon bond formations, easily recoverable many times, and biocompatible is highly desirable in terms of sustainable and green chemistry. To this end, catalysts comprising dendritic “click” ligands that are immobilized on a magnetic nanoparticle (MNP) core, terminated by triethylene glycol (TEG) groups, and incorporate Pd nanoparticles (PdNPs) have been prepared. These nanomaterials are characterized by transmission electron microscopy (TEM), high-resolution TEM, inductively coupled plasma analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectra and energy-dispersive X-ray spectroscopy. They are shown to be highly active, dispersible, and magnetically recoverable many times in Suzuki, Sonogashira, and Heck reactions. In addition, a series of pharmacologically relevant or natural products were successfully synthesized using these magnetic PdNPs as catalyst. For comparison, related PdNP catalysts deposited on MNPs bearing linear “click” PEGylated ligands are also prepared. Strong positive dendritic effects concerning ligand loading, catalyst loading, catalytic activity, and recyclability are observed, that is, the dendritic catalysts are much more efficient than non-dendritic analogues.
Chemistry - A European Journal 11/2014; 21(4). DOI:10.1002/chem.201404590 · 5.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The simple impregnation of γ-Fe2O3(core)/SiO2(shell) magnetic nanoparticles with a dendrimer that contains stabilized Pd nanoparticles is presented as a new method to produce highly efficient heterogeneous catalysts. This technique provides much better stability, recyclability, and activity in CC cross-coupling reactions and selective oxidation of benzyl alcohol to benzaldehyde in water than unsupported Pd nanoparticles.
[Show abstract][Hide abstract] ABSTRACT: Information provided by 119Sn2+ Mössbauer probe ions, located on surface sites of anatase-type TiO2 microcrystals exposed, at room temperature, to a H2S/H2 mixture, has permitted to conclude that the interaction of H2S molecules with the substrate surface leads to the dissociation of a fraction of the absorbate molecules. This gives rise to the formation of elemental sulfur which oxidizes the neighboring Sn2+ ions, the produced Sn4+ ions being found coordinated only by S2− anions. Subsequent exposure to ambient air is shown to result in the oxidation of S2− ions, yielding both S0 and SO42−-like species, with concomitant stabilization of Sn4+ ions in coordination polyhedra where they are surrounded by only oxygen anions.
[Show abstract][Hide abstract] ABSTRACT: The surface of ultrahigh molecular weight polyethylene and high density polyethylene was modified using two different fluorination routes: radio-frequency plasma-enhanced fluorination using O-2/CF4 mixtures or c-C4F8 and the direct fluorination with 10%F-2+ 90%He mixtures. The modification of the surface layers was characterized by FTIR and visible spectroscopy, AFM, XRD, XPS and surface energy measurement. A diffusion-controlled mechanism of the growth of fluorinated layer was confirmed. The dependence of the surface energy values on storage duration was studied. The chemical composition, texture and roughness of the polymer surface strongly depend on the treatment method and conditions. Fluorine concentration varies within the depth from the polymer surface.
[Show abstract][Hide abstract] ABSTRACT: For optimal performance, the intermediate window layer in multijunction photovoltaics should transmit as much light as possible to guarantee maximum device efficiency. In this work, we demonstrate that indium molybdenum oxide (IMO) is a more suitable intermediate layer, compared to indium tin oxide (ITO), as it would absorb significantly less infrared light with comparable electrical conductivity once integrated into a multijunction solar cell. In fact, we show that IMO optoelectronic properties are virtually unchanged by the typical thermal budgets used in solar absorber deposition processes used in low-cost high-performance multijunction photovoltaics (e.g. CuInGaSe2). Specifically, IMO and ITO thin films were reactively sputtered onto glass substrates at 150 degrees C, then subjected to a vacuum annealing process (550 degrees C, 2 h) identical to that of co-evaporated copper gallium diselenide (CGSe), a candidate material for the top absorber in multijunction cells. We found that annealing substantially reduces the infrared transmittance of ITO starting at 900 nm, reducing by 2.5% per 100 nm, while IMO only started experiencing a reduction at 1400 nm and decaying more slowly at 1.6% per 100 nm. Furthermore, the resistivity of IMO was comparable to that of ITO after annealing. The resilience of IMO to such high temperature processes show that it has potential to enhance the performance of multijunction devices.
Solar Energy Materials and Solar Cells 08/2014; 127:174–178. DOI:10.1016/j.solmat.2014.04.029 · 5.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Well crystallized VO2 (A) microrods were grown via a single step hydrothermal reaction in
the presence of V2O5 and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO2 (A) micro rods. The structural and electronic transitions in VO2 (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter-
(HTP-A to VO2 (M1)) structural phase transformations were studied by in-situ powder X-ray
diffraction. Attempts to increase the size of the VO2 (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO2 (M1) are described.
Journal of Solid State Chemistry 01/2014; 213. DOI:10.1016/j.jssc.2014.01.037 · 2.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract Ageing effect phenomenon is artificially stimulated on room temperature magnetocaloric material Gd6Co1.67Si3 by using constant flux of water up to time interval of 3 months. A core–shell model of oxide layer formation (SiOx–Gd2O3) on surface of Gd6Co1.67Si3 due to corrosion is justified using spontaneous single metal electrochemical reactions. The model is first proposed by a detailed microstructure study using Electron Probe Micro-Analysis, X-ray diffraction experiments on the aged slab revealing Gd2O3 phase and elemental depth profile analysis against time by Auger spectroscopy. It is further supported by surface chemical bonding study using X-ray Photoelectron Spectroscopy (XPS) concentrated on Si2p and O1s spectra. It is finally demonstrated that the room temperature bulk magnetocaloric performances of the material are not affected even under formation of corroded layer at the micron level scale. The Gd2O3 shell certainly acts as a passivation layer.
Journal of Alloys and Compounds 01/2014; 584:34-40. DOI:10.1016/j.jallcom.2013.08.211 · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ba2LnFeNb4O15 (Ln = Pr, Nd, Sm, and Eu) single crystals were grown from high-temperature solution under controlled atmosphere. Chemical, structural, and dielectric characterizations were performed on four crystals with tetragonal tungsten bronze (TTB) structure. The main difference between the four crystals’ compositions is the proportion of rare-earth, as well as vacancies, located in the square site. All crystals displayed an incommensurately modulated structure at room temperature in the paraelectric state. The corresponding basic structures were refined using the P4/mbm space group (R = 0.0274; 0.0416; 0.0328; 0.0357 for Ln = Pr, Nd, Sm, and Eu, respectively). Examination of the structural parameters confirmed the central role played by square-shaped channels in the crystal chemistry of these materials. All crystals display a relaxor behavior with Tm (1 MHz) ranging from 110 to 270 K. The chemical, structural, and physical properties of the crystals are discussed and compared, for the latter, with those of corresponding ceramics.
[Show abstract][Hide abstract] ABSTRACT: The present study provides the first experimental evidence for the stabilization of tin dopant cations immediately on the surface of an oxide having a tetragonal structure. Sn-119 Mossbauer spectra of the dopant, introduced by air annealing into the bulk of anatase microcrystals, showed that it was located, in the tetravalent state, in somewhat distorted octahedral sites of a unique type. On the contrary, the reduced tin species, formed upon subsequent hydrogen annealing the Sn4+-doped samples, are found to occupy different sites being characterized by two sets of the isomer shift delta and quadrupole splitting Delta E-Q values (delta(I) = 3.25 mm s(-1), Delta E-QI = 1.75 mm s(-1); and delta(Pi) = 2.85 mm s(-1), Delta E-QII = 1.71 mm s(-1)). Either of them implies both the divalent state of tin atoms and their presence at low-coordination sites that can be assigned to the surface of crystallites. Mossbauer spectra of Sn4+<- 2+ daughter ions, formed upon contact with air of Sn2+, consist of a symmetrically broadened peak characterized by only slightly different average values of both the isomer shift ( = 0.07 mm s(-1)) and quadrupole splitting ( = 0.50 mm s-1), as compared to the 0 and Delta E-Q. values for the bulk-located Sna-E. However, considerable broadening of Sn4+<- 2+ doublet components (Gamma = 0.97 mm s(-1)) allows one to suggest that these secondary formed ions remain distributed over the non equivalent sites inherited from their Sn2+ precursors. The occurrence of Sn4+<- 2+ at surface sites is independently proven by XPS measurements that revealed a greater than 10-fold enrichment with tin of 3-5 nm thick surface layers.
Solid State Sciences 11/2013; 25:143-148. DOI:10.1016/j.solidstatesciences.2013.09.006 · 1.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fluorination processes of polymer surfaces are able to lead to drastic modifications of the surface properties without changing the bulk characteristics of the virgin material. In this paper, two types of polymers, i.e. ultrahigh molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE), are considered. The surface of these materials have been modified using two different fluorination routes, both carried out at room temperature: the direct fluorination with 10% F2 + 90% He gaseous mixtures and the radio-frequency plasma-enhanced fluorination (PEF) using either O2/CF4 mixtures or c-C4F8. The effect of these processes on the surface of the polymer samples are compared using mostly XPS results. The different components of the C1s spectra are assigned in term of CFx bonding, giving valuable information on the surface fluorination rate.
[Show abstract][Hide abstract] ABSTRACT: Oh my Gold! Gold atoms stabilise catalytically active palladium nanoparticles when engaged in an alloy heterogenised on carbon. The increased durability makes the Pd-Au/C catalyst more recyclable than the gold-free Pd/C catalyst for the Sonogashira reaction.
Chemistry - A European Journal 10/2013; 19(42):14024-14029. DOI:10.1002/chem.201300347 · 5.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Original core/corona nanoparticles composed of a maghemite core and a stimuli-responsive polymer coating made of poly(acrylic acid)-block-poly(vinyl alcohol) macromolecules were fabricated for drug delivery system (DDS) application. This kind of DDS aims to combine the advantage of stimuli-responsive polymer coating, in order to regulate the drug release behaviours under different conditions and furthermore, improve the biocompatibility and in vivo circulation half-time of the maghemite nanoparticles. Drug loading capacity was evaluated with methylene blue (MB), a cationic model drug. The triggered release of MB was studied under various stimuli such as pH, ionic strength and temperature. Local heating generated under alternating magnetic field (AMF) application was studied, and remotely AMF-triggered release was also confirmed, while a mild heating-up of the release medium was observed. Furthermore, their potential application as magnetic resonance imaging (MRI) contrast agents was explored via relaxivity measurements and acquisition of T2-weighted images. Preliminary studies on the cytotoxicity against mouse fibroblast-like L929 cell line and also their cellular uptake within human melanoma MEL-5 cell line were carried out. In conclusion, this kind of stimuli-responsive nanoparticles appears to be promising carriers for delivering drugs to some tumour sites or into cellular compartments with an acidic environment.
[Show abstract][Hide abstract] ABSTRACT: Strain-dependent microstructural modifications were observed in epitaxial BiCrO3 (BCO) thin films fabricated on single crystalline substrates, utilizing pulsed laser deposition. The following conditions were employed to modify the epitaxial-strain: (i) in-plane tensile strain, BCOSTO [BCO grown on buffered SrTiO3 (001)] and in-plane compressive strain, BCONGO [BCO grown on buffered NdGaO3 (110)] and (ii) varying BCO film thickness. A combination of techniques like X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (TEM) was used to analyse the epitaxial growth quality and the microstructure of BCO. Our studies revealed that in the case of BCOSTO, a coherent interface with homogeneous orthorhombic phase is obtained only for BCO film with thicknesses, d < 50 nm. All the BCOSTO films with d >= 50 nm were found to be strain-relaxed with an orthorhombic phase showing 1/2 < 100 > and 1/4 < 101 > satellite reflections, the latter oriented at 45 degrees from orthorhombic diffraction spots. High angle annular dark field scanning TEM of these films strongly suggested that the satellite reflections, 1/2 < 100 > and 1/4 < 101 >, originate from the atomic stacking sequence changes (or "modulated structure") as reported for polytypes, without altering the chemical composition. The unaltered stoichiometry was confirmed by estimating both valency of Bi and Cr cations by surface and in-depth XPS analysis as well as the stoichiometric ratio (1 Bi: 1 Cr) using scanning TEM-energy dispersive X-ray analysis. In contrast, compressively strained BCONGO films exhibited monoclinic symmetry without any structural modulations or interfacial defects, up to d similar to 200 nm. Our results indicate that both the substrate-induced in-plane epitaxial strain and the BCO film thickness are the crucial parameters to stabilise a homogeneous BCO phase in an epitaxially grown film. c 2013 Elsevier B. V. All rights reserved.
Thin Solid Films 10/2013; 545:130-139. DOI:10.1016/j.tsf.2013.07.053 · 1.76 Impact Factor