National Institute Of Materials Physics - Romania

The source of collective magnetism in II-VI semiconductor quantum dots (QDs) doped with Mn2+ ions at high nominal impurity levels is still under debate. In the particular case of mesoporous, self-assembled cubic ZnS:Mn QDs, quantitative electron paramagnetic resonance (EPR) studies have shown that the Mn2+ ions incorporated in the core and on the surface of the QDs cannot be responsible for the observed collective magnetism because they remain in a diluted paramagnetic state up to the 50 000 ppm nominal concentration. Here we investigate the composition, localization, structure, and magnetic properties of the aggregates of Mn2+ ions incorporated in the mesoporous cZnS:Mn as a possible source of the observed collective magnetism. Samples of mesoporous cubic ZnS:Mn prepared by coprecipitation at several nominal impurity levels from 200 to 50 000 ppm are investigated by EPR, magnetometry, and analytical high resolution (scanning) transmission electron microscopy. The low temperature magnetic properties of the Mn2+ aggregates change from paramagnetic-like, for samples with nominal impurity levels up to 2000 ppm, to ones specific to larger clusters with distributed antiferromagnetic coupling at higher concentrations, behaving superparamagnetically above a certain temperature. There is also strong evidence that the Mn2+ aggregates responsible for the observed low temperature collective magnetism are incorporated as an amorphous phase of mainly Mn-Zn-O composition, localized in the interstices and pores of the mesoporous structure of the cubic ZnS:Mn QDs.

Background: We evaluated the Bovine hydroxyapatite (BHA) structure. BHA powder was admixed with 5 and 10 wt% natural pumice (NP). Compression strength, Vickers micro hardness, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction studies were performed on the final NP-BHA composite products. The cells proliferation was investigated by MTT assay and SEM. Furthermore, the antimicrobial activity of NP-BHA samples was interrogated. Results: Variances in the sintering temperature (for 5 wt% NP composites) between 1000 and 1300 degrees C, reveal about 700 % increase in the microhardness (similar to 100 and 775 HV, respectively). Composites prepared at 1300 degrees C demonstrate the greatest compression strength with comparable result for 5 wt% NP content (87 MPa), which are significantly better than those for 10 wt% and those that do not include any NP (below 60 MPa, respectively). Conclusion: The results suggested the optimal parameters for the preparation of NP-BHA composites with increased mechanical properties and biocompatibility. Changes in micro-hardness and compression strength can be tailored by the tuning the NP concentration and sintering temperature. NP-BHA composites have demonstrated a remarkable potential for biomedical engineering applications such as bone graft and implant.

We report the high-frequency electrical characterization of Ba2/3Sr1/3 TiO3 (BST) thin films exhibiting a very high dielectric tunability with low losses at 2.45 GHz under very low applied electrical fields. BST layers were integrated in out-of-plane Metal-Insulator-Metal (MIM) devices with optimized Ir/MgO(100) bottom electrodes. The high frequency properties of BST films with thicknesses of 200 nm, 450 nm and 1450 nm were thoroughly investigated in the 100 MHz-10 GHz domain and exhibit extremely high capacitance tuning abilities of 82%, 81% and 70% respectively, under applied voltages as low as 10 V. MIM devices responses show the onset of acoustic resonances associated with the BST electrostrictive behavior under an electric field. By combining high tunability with low resistive losses under low applied voltages, these devices are opening promising avenues for their integration in high-performance tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used ISM (industrial, scientific and medical) frequency band.

Superparamagnetic iron oxide nanoparticles (SPION) have attracted a lot of interest due to their widespread biomedical and diagnostic applications. Coating the SPIONs with various surface layers can provide an interface between the core and the surrounding environment. The aim of this study was to examine the in vivo behaviour of dextran-coated iron oxide nanoparticles (D-IONPs) in aqueous suspensions. The SPIONs stabilized with dextran (D-IONPs) were synthesized in aqueous solutions by co-precipitation method. The average grain size deduced from transmission electron microscopy is 7.5 nm. The hematological parameters registered for the rats exposed to D-IONPs at 1 ml/kg have had values approximately equal to those examined for the control specimen. The architecture of liver and kidneys was not affected after one day of intraperitoneal injection of D-IONPs compared to the reference group. After 21 and 28 days respectively from the administration of the D-IONPs solution, the liver and kidneys from the injected rats showed a normal aspect without abnormalities compared to the rats uninjected. Our findings suggest that the administration of 1 ml/kg D-IONPs did not cause any toxicological effect since the parameters of renal and liver function were in the normal range as reported to the control group.

Recoverable catalysts for lignin fragmentation were prepared as Xwt%Co@Nb2O5@Fe3O4 composites having magnetite as an inner core. A shell of niobia covering the magnetic nanoparticles (leading to intermediate Nb2O5@Fe3O4 composite) was deposed from a solution of ammonium niobate (V) oxalate complex by precipitation with NH3. Finally, the deposition of cobalt following the deposition-precipitation method generated the Xwt%Co3O4@Nb2O5@Fe3O4 composites that were reduced with hydrogen to Xwt %Co@Nb2O5@Fe3O4. Catalysts with loading of cobalt in the range X = 1-20 were prepared using this procedure. The different steps of the preparation were followed using various techniques such as surface area measurements, XRD, Raman and NH3-DRIFT spectroscopy, XPS, Mossbauer and TEM. On this basis it was concluded that the synthesized composites exhibit both Lewis and Bronsted acid sites associated with the niobia shell and contain finely dispersed cobalt nanoparticles. The fragmentation of lignin occurred on the constituent parts of this composite, i.e. Fe3O4, Nb2O5, Nb2O5@Fe3O4 but with lower performances. The addition of cobalt (Co@Nb2O5@Fe3O4 catalysts) led to a complete fragmentation of lignin where the dominant fragments were those containing C20-C28 molecules. This catalytic behavior is explained on the capability of niobia to catalyze the acidic hydrolysis of the beta-O-4' bounds and of Co to break the C-C bonds via hydrogenolysis. The optimization of the catalyst composition indicated a loading of 4 wt% as optimal. Working at 180 degrees C and 10 atm H-2 this catalyst allowed a conversion of 53% leading to a mixture containing over 96% in C20-C28 and C29-C37 fragments. The investigated catalysts were completely recyclable as it was showed in six successive cycles. No leaching of the elements included in the composition was determined by ICP-OES. (C) 2016 Elsevier Inc. All rights reserved.

The strong correlation between advancing the performance of Si microelectronics and their demand of low power consumption requires new ways of data communication. Photonic circuits on Si are already highly developed except for an eligible on-chip laser source integrated monolithically. The recent demonstration of an optically pumped waveguide laser made from the Si-congruent GeSn alloy, monolithical laser integration has taken a big step forward on the way to an all-inclusive nanophotonic platform in CMOS. We present group IV microdisk lasers with significant improvements in lasing temperature and lasing threshold compared to the previously reported nonundercut Fabry Perot type lasers. Lasing is observed up to 130 K with optical excitation density threshold of 220 kW/cm(2) at 50 K. Additionally the influence of strain relaxation on the band structure of undercut resonators is discussed and allows the proof of laser emission for a just direct Ge0.915Sn0.085 alloy where Gamma and L valleys have the same energies. Moreover, the observed cavity modes are identified and modeled.

Carbon nanowalls (CNW) are two-dimensional interconnected graphitic nanostructures that have a few mu m in length and height, reaching typical thicknesses of a few tens of nm. We present results on such layers synthesized in a low pressure argon plasma jet, injected with acetylene and hydrogen, on transparent substrates (quartz) heated at 600 degrees C, without catalyst. Thermogravimetric analysis reveals that the CNW are stable up to 420 degrees C in air, and Raman spectroscopy investigations highlight their graphene-like structure. Finally, using a pulsed Nd:YAG laser device (355 nm, 50 ps), we show that 2D-arrays of CNW (pixels and lines) can be printed by laser-induced forward transfer (LIFT), preserving their architecture and structure. Electrical measurements on 1 mu m thick CNW demonstrate typical values in the range of 357.5-358.4 Omega for the samples grown on Au/Cr electrodes, and in the range of 450.1-474.7 Omega for the LIFT printed lines (under positive, negative, and neutral polarization; 1 kHz-5 MHz frequency range; 500 mV and 1 V, respectively). Their morphology is highlighted by means of optical and electronic microscopy. Such structures have potential applications as soft conductive lines, in sensor development and/or embedding purposes. (C) 2015 Elsevier B.V. All rights reserved.

The effects of 800 keV Ar ion irradiation on thin nanocrystalline SiC films grown on (100) Si substrates using the pulsed laser deposition (PLD) technique were investigated. On such PLD grown films, which were very dense, flat and smooth, X-ray reflectivity, glancing incidence X-ray diffraction and nanoindentation investigations were easily performed to evaluate changes induced by irradiation on the density, surface roughness, crystalline structure, and mechanical properties. Results indicated that the SiC films retained their crystalline nature, the cubic phase partially transforming into the hexagonal phase, which had a slightly higher lattice parameter then the as-deposited films. Simulations of X-ray reflectivity curves indicated a 3% decrease of the films density after irradiation. Nanoindentation results showed a significant decrease of the hardness and Young's modulus values with respect to those measured on as-deposited films. Raman and X-ray photoelectron spectroscopy investigations found an increase of the C-C bonds and a corresponding decrease of the Si-C bonds in the irradiated area, which could explain the degradation of mechanical properties. (C) 2015 Elsevier B.V. All rights reserved.

This paper presents some studies about the preparation by matrix-assisted pulsed laser evaporation (MAPLE) of mixed layers based on two arylenevinylene oligomers, 1,4-bis [4-(N,N'-diphenylamino)phenylvinyl] benzene (L78) and 3,3'-bis(N-hexylcarbazole)vinylbenzene (L13) as donor and buckminsterfullerene (C-60) as acceptor, blended in three different weight ratios: 1:1, 1:2 and 1:3. The optical, morphological, structural and electrical properties of these mixed layers have been investigated emphasizing the effect of the layer composition and of the significant degree of disorder. I-V characteristics have revealed typically solar cell behaviour for the heterostructures prepared with mixed layers containing L78 (L13) and fullerene blended in a weight ratio of 1:2. The solar cell structure glass/ITO/L13:C-60/Al has shown the best parameters. (C) 2015 Elsevier B.V. All rights reserved.