Magnetic and luminescent coordination networks based on imidazolium salts and lanthanides for sensitive ratiometric thermometry

The synthesis and characterization of six new lanthanide networks [Ln(L)(ox)(H2O)] with Ln = Eu3+, Gd3+, Tb3+ , Dy3+ , Ho3+ and Yb3+ is reported. They were synthesized by solvo-ionothermal reaction of lanthanide nitrate Ln(NO3)(3)center dot xH(2)O with the 1,3-bis(carboxymethyl)imidazolium [HE] ligand and oxalic acid (H(2)ox) in a water/ethanol solution. The crystal structure of these compounds has been solved on single crystals and the magnetic and luminescent properties have been investigated relying on intrinsic properties of the lanthanide ions. The synthetic strategy has been extended to mixed lanthanide networks leading to four isostructural networks of formula [Tb1-xEux(L)(ox)(H2O)] with x = 0.01, 0.03, 0.05 and 0.10. These materials were assessed as luminescent ratiometric thermometers based on the emission intensities of ligand, Tb3+ and Eu3+ . The best sensitivities were obtained using the ratio between the emission intensities of Eu3+ (D-5(0) -> F-7(2) transition) and of the ligand as the thermometric parameter. [Tb0.97Eu0.03 (L)(ox)(H2O)] was found to be one of the best thermometers among lanthanide-bearing coordination polymers and metal-organic frameworks, operative in the physiological range with a maximum sensitivity of 1.38%.K-1 at 340 K

Two dimensional dipolar coupling in monolayers of silver and gold nanoparticles on a dielectric substrate

The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices

Films of Tunable ZnO Nanostructures Prepared by a Surfactant-Mediated Soft Synthesis Route

Films of ZnO nanostructures were prepared by a soft chemical synthesis route from ZnO crystal seeds in aqueous medium, in the presence of alkylsulfates of different chain length acting as structure-directing agents. Films of arrayed single crystal ZnO nanorods were formed with short alkyl sulfates, from C6 to C8 alkylene chains, while hybrid lamellar ZnO with a platelike morphology were obtained with C10 to C18 alkyl sulfates. In the case of the short alkyl sulfates, due to the interaction between the sulfate groups and the Zn2+ planes of the ZnO structure, the growth along the c axis is partially inhibited and smaller aspect ratios of the nanorods are obtained than in alkylsulfate-free conditions. In the case of the hybrid lamellar ZnO structures which consist in ZnO layers intercalated with alkylsulfate bilayers, the structural characteristics depend on the alkylene chain length. Basal spacings increase linearly with the chain length, while the plate size decreases dramatically when the chain length exceeds C14. The different characteristics of these ZnO nanostructured films allow modifying their optical properties

Salts and Solvents Effect on the Crystal Structure of Imidazolium Dicarboxylate Salt Based Coordination Networks

The solvothermal synthesis of novel metal–organic networks from the 1,3-bis(carboxymethyl)-imidazolium chloride ([H2L][Cl]) and cobalt or nickel salts (acetate or nitrate) in different solvents (water or ethanol and water/ethanol or water/ethylene glycol mixture) has been explored leading to four isotypic compounds of general formula [M(L)(H2O)4][Cl]·Solv with M = Ni or Co and Solv = H2O for 1 and 2, respectively, and M = Ni or Co and Solv = (EG)0.5 for 3 and 4, respectively, and two other isostructural compounds, namely, [Ni(L)(ox)0.5(μ2-H2O)0.5] (5) and [Co(L)(ox)0.5(μ2-H2O)0.5] (6) where the in situ formation of oxalate (ox) was observed. The structural characterizations evidence a significant influence of the solvent as well as of the metal salt on the structure and crystallinity of the final compounds, the former leading to observation of different magnetic behaviors. A one-dimensional antiferromagnetic behavior is thus observed in compounds 5 and 6 containing oxalate ligand while compounds 1–4 exhibited typical behavior of quasi-isolated magnetic species

Magnetic Properties of Mono- and Multilayer Assemblies of Iron Oxide Nanoparticles Promoted by SAMs

Owing to the wide scope of applications of magnetic nanoparticle assembling, the aim of this study is to evaluate the influence of nanoparticle aggregates on the magnetic properties of 2D assemblies. Magnetic iron oxide nanoparticles (NPs) have been synthesized by the coprecipitation (NPcop) and thermal decomposition (NPdec@OA) methods, and were assembled on self-assembled monolayers of organic molecules decorated by a phosphonic acid terminal group at their surface (SAM-PO3H2). The nanostructure and magnetic properties of assemblies depend directly on the aggregation of NP suspensions. NPcop, result in an unstable suspension and were assembled into a non-homogeneous monolayer of aggregates. The post-functionalization of NPcop with oleic acid after synthesis (NPcop@OA) favors a better stability of the suspension and enhances the nanostructure of the assembly, although smaller NP aggregates remain. In contrast, NPdec@OA which are functionalized in situ by oleic acid during the synthesis step were assembled as individual nanomagnets and result in a dense monolayer. Multi layer assemblies were also prepared from NPcop@OA and NPdec@OA by performing the alternative deposition of these NPs with (1,4-phenylene)bisphosphonic acid. The nanostructure of assemblies has been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The magnetic properties of monolayer and multilayer assemblies have been studied by using a SQUID magnetometer. While assemblies of individual NPs enhance dipolar interactions in-plane as a result of shape anisotropy, assemblies of NP aggregates favor stronger dipolar interactions with random orientation. The magnetic properties of monolayer and multilayer assemblies have also been compared. The dimensionality (2D vs 3D) has a strong effect on the dipolar interactions when individual NPs are considered in contrast to aggregated nanoparticles

Annealing treatment for restoring and controlling the interface morphology of organic photovoltaic cells with interfacial sputtered ZnO films on P3HT: PCBM active layers:

In this paper, we report on the photovoltaic properties of conventional organic photovoltaic solar cells integrating a sputtered ZnO interfacial film deposited on the absorber P3HT:PCBM layer. An emphasis has been put on the influence of the annealing temperature and time for restoring and controlling the P3HT:PCBM/ZnO interface morphology, which can be damaged by the sputtering process. We show a significant improvement in the current-voltage (J-V) characteristics upon annealing up to 160 degrees C. This is evidenced by the reduction of the S-shape of these curves systematically observed for the cells integrating thick (100 nm) sputtered ZnO films. This approach was also highlighted on cells containing thinner (20 nm) ZnO films using a longer annealing process at 140 degrees C, which led to a significant improvement of the power conversion efficiency compared with the value recorded in as-prepared cells or in cells with no interfacial ZnO layer. These photovoltaic performances have been related to the change of the morphology of the absorber layer and to the vertical phase segregation of P3HT:PCBM at the interface with ZnO. Optical microscopy, scanning electron microscopy and atomic force microscopy have been performed in order to confirm this approach

Stabilization of scandium rich spinel ferrite CoFe(2-x)Sc(x)O4 (x <= 1) in thin films

Scandium rich cobalt ferrites CoyFe3-x-yScxO4 with y-1 never obtained in bulk could be stabilized in pulsed laser deposited thin films. Scandium contents of up to x=1 are reached. The cell parameter increases versus x as awaited when considering the size of scandium. It is equal to 0.8620 nm for x=1, significantly higher than that of CoFe2O4 (0.8396 nm). The lattice mismatch between the MgO (100) substrate and the scandium-containing spinel leads to an increased roughness. Cobalt is displaced from the octahedral site by Sc and mainly occupies the tetrahedral sites for high x values

Influence of the Carbo-Chromization Process on the Microstructural, Hardness, and Corrosion Properties of 316L Sintered Stainless Steel

We report on the changes on the microstructural, hardness, and corrosion properties induced by carbo-chromization of 316L stainless steel prepared by Spark Plasma Sintering technique. The thermo-chemical treatments have been performed using pack cementation. The carburizing and chromization were carried out between 1153 K (880 A degrees C)/4 h to 1253 K (980 A degrees C)/12 h and 1223 K (950 A degrees C)/6 h to 1273 K (1000 A degrees C)/12 h in a solid powder mixture of charcoal/BaCO3 and ferrochromium/alumina/NH4Cl, respectively. The obtained layers were investigated using X-ray and electron diffraction, optical and scanning electron microscopies, Vickers micro-hardness, and potentiodynamic measurements. The thickness of the carbo-chromized layer ranges between 300 and 500 mu m. Besides the host gamma-phase, the layers are mainly constituted of carbides (Fe7C3, Cr23C6, Cr7C3, and Fe3C) and traces of alpha'-martensite. The average hardness values decrease smoothly from 650 HV at the sample surface down to 200 HV at the center of the sample. The potentiodynamic tests revealed that the carbo-chromized samples have smaller corrosion resistance with respect to the untreated material. For strong chromization regimes, the corrosion rate is increased by a factor of four with respect to that of the untreated material, while the micro-hardness of the layer is three times larger. Such materials are suited to be used in environments where good corrosion resistance and wear properties are required

Structural, optical, spectroscopic and electrical properties of Mo-doped ZnO thin films grown by radio frequency magnetron sputtering

Undoped and Mo-doped ZnO (2% Mo) films about 1 mu m thick were deposited by radio-frequency magnetron sputtering on Si(100) and glass substrates at 30 and 300 degrees C. X-ray diffraction patterns show that all films exhibit the hexagonal wurtzite crystal structure with a preferred orientation of the crystallites along the [002] direction. Plane view and cross-section transmission electron microscopy observations showed that the films present a columnar growth. Rutherford backscattering spectrometry indicates that Mo is homogeneously distributed inside the films. Scanning electron microscopy and atomic force microscopy show that Mo doping leads to a reduction of the grain size and surface roughness. According to X-ray photoelectron spectroscopy measurements, the valence of the Mo ions in the ZnO matrix is +5 and +6. Optical measurements in the UV-Visible range show a transmittance increasing from about 60 to 80% when increasing the wavelength from 400 to 800 nm. A sharp absorption onset is observed at about 375 nm corresponding to the fundamental absorption edge of ZnO at 3.26 eV. This gap value remains unchanged upon Mo doping. The Hall effect measurements carried out at room temperature show that both undoped and Mo-doped ZnO films present an n-type conduction. The 2% Mo doping increases the carrier concentration and decreases the resistivity measured in pure ZnO by about three orders of magnitude. A comparison with 2% Al-doped ZnO films grown in the same conditions underlines the important role of the preparation conditions on the transport properties of ZnO based transparent conductive oxides. (C) 2014 Elsevier B.V. All rights reserved