National Institute Of Materials Physics - Romania

Lowering the temperature of crystallization by deposition of thin films on a heated substrate represents the easiest way to find new means to develop and improve new working devices based on nanocrystals embedded in thin films. The improvements are strongly related with the increasing of operation speed, substantially decreasing the energy consumption and reducing unit fabrication costs of the respective semiconductor devices. This approach avoids major problems, such as those related to diffusion or difficulties in controlling nanocrystallites size, which appear during thermal treatments at high temperatures after deposition. This article reports on a significant progress given by structuring Ge nanocrystals (Ge-NCs) embedded in silicon dioxide (SiO2) thin films by heating the substrate at 400 degrees C during co-deposition of Ge and SiO2 by magnetron sputtering. As a proof-of-concept, a Si/Ge-NCs:SiO2 photo-sensitive structure was fabricated thereof and characterized. The structure shows superior performance on broad operation bandwidth from visible to near-infrared, as strong rectification properties in dark, significant current rise in the inversion mode when illuminated, high responsivity, high photo-detectivity of 10(14) Jones, quick response and significant conversion efficiency with peak value reaching 850% at -1 V and about 1000 nm. This simple preparation approach brings an important contribution to the effort of structuring Ge nanocrystallites in SiO2 thin films at a lower temperature for the purpose of using these materials for devices in optoelectronics, solar cells and electronics on flexible substrates.

Hydroxyapatite is a calcium phosphate intensively proposed as a bone substitution material because of its resemblance to the constituents of minerals present in natural bone. Since hydroxyapatite's properties are mainly adequate for nonload bearing applications, different solutions are being tested for improving these properties and upgrading them near the target values of natural bone. On the other hand, starch (a natural and biodegradable polymer) and its blends with other polymers have been proposed as constituents in hydroxyapatite mixtures due to the adhesive, gelling, and swelling abilities of starch particles, useful in preparing well dispersed suspensions and consolidated ceramic bodies. This article presents the perspectives of incorporating starch and starch blends in hydroxyapatite materials. Based on the role of starch within the materials, the review covers its use as (i) a polymeric matrix in hydroxyapatite composites used as adhesives, bone cements, bone waxes, drug-delivery devices or scaffolds and (ii) a sacrificial binder for fabrication of porous hydroxyapatite scaffolds. The suitability of these materials for bone reconstruction has becomes a reachable aim considering the recent advancements in ceramic fabrication and the current possibilities of controlling the processing parameters.

A new family of cyclometalated palladium(II) complexes with the non-symmetric dimeric liquid crystal Schiff base alpha-(4-cyanobipheny1-4'-yloxy)-omega-(4-n-decyloxyanilinebenzylidene-4'-oxy) hexane and alkoxysubstituted N-benzoyl thiourea (BTU) derivatives as auxiliary ligands was designed and prepared with the aim to study the influence of increasing the number of aliphatic chains on the molecular organization in the liquid crystal phase. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction. A transition from the lamellar (complex 3a with two aliphatic chains on BTU ligand) to columnar organization (complexes 3b and 3c having three and four chains on BTU ligand, respectively) was evidenced for these palladium(II) complexes, which was correlated with the increase of the number of terminal chains at molecular periphery. (C) 2017 Elsevier B.V. All rights reserved.

A new composite material based on poly (para-phenylenevinylene) (PPV), pyrene (Py) and reduced graphene oxide (RGO) is synthesized using thermal conversion route. The properties of this material are investigated by Raman scattering, photoluminescence (PL), infrared (IR) and ultraviolet visible (UV-Vis) spectroscopy. Adding Py at PPV precursor solution (PPV PS) containing RGO, yields to important modifications in both vibrational and electronic properties of these composites. The presence of Py into PPV matrix determines a blue shift of PPV PL. According to Raman and IR studies, PPV is non-covalently functionalized with Py which interacts forward with RGO through pi-pi interactions causing an important modification into the polymer chains conjugation length. (C) 2017 Elsevier B.V. All rights reserved.

Thin films of TiN, ZrC, and ZrN were deposited at room temperature on highly polished Ti and Si samples using the pulsed laser deposition technique. Grazing incidence X-ray diffraction investigations showed that films were nanocrystalline, with grain sizes from 5 to 12 nm and under compression. Simulations of X-ray reflectivity curves acquired from the samples indicated that the deposited layers were dense and smooth. Electrochemical tests performed in simulated body fluid showed that the deposited coatings significantly improved the corrosion resistance of Ti samples. The comparative study found out that the best sample was ZrN/Ti, its corrosion current after 32 days immersion in simulated body fluids being half of that measured for the bare Ti sample and in the same time almost unchanged from the initial value. (C) 2017 Elsevier B.V. All rights reserved.

The aim of our research was to synthesize and investigate the physico-chemical and biological features of composite coatings based on poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) and commercial calcium phosphates (CaPs), hydroxyapatite and beta-tricalcium phosphate, obtained by means of matrix assisted pulsed laser evaporation (MAPLE) technique. In this respect, laser fluence and dropcast studies were performed for pristine polymer and PHBV-CaPs composites. The microstructure of the synthesized coatings was investigated by scanning electron microscopy, while for the chemical structure and functional integrity we performed Fourier transform infrared spectroscopy comparative analysis. By using the X-ray diffraction measurements we experimentally evaluated the crystalline nature of the obtained composite materials, while relevant data regarding the hydrophilic/hydrophobic behavior of the synthesized coatings were obtained by performing static CA measurements. The biocompatibility of PHBV/CaPs coatings was evaluated by performing cellular adhesion and differentiation in vitro assays on mesenchymal stem cells. (C) 2017 Elsevier B.V. All rights reserved.

In this study, coatings based on lysozyme embedded into a matrix of polyethylene glycol (PEG) and polycaprolactone (PCL) were fabricated by two different methods (Matrix Assisted Pulsed Laser Evaporation -MAPLE and Dip Coating) for obtaining antimicrobial coatings envisaged for long term medical applications. Coatings with different PEG: PCL compositions (3: 1; 1: 1; 1: 3) were synthesized in order to evaluate the antimicrobial activity of lysozyme embedded into the polymeric matrix. The main surface features, such as roughness and wettability, with impact on the microbial adhesion as well as on the eukaryote cell function were measured. The obtained composite coatings exhibited a significant antibacterial activity against Escherichia coli, Bacillus subtilis, Enterococcus faecalis and Staphylococcus aureus strains. As well, specific blended coatings showed appropriate viability, good spreading and normal cell morphology of SaOs2 human osteoblasts and mesenchymal stem cells (MSCs). These investigations highlight the suitability of biodegradable composites as implant coatings for decreasing the risk of bacterial contamination associated with prosthetic procedures. (C) 2016 Elsevier B.V. All rights reserved.

Mixed layers of azomethine oligomers containing 2,5-diamino-3,4-dicyanothiophene as central unit and triphenylamine (LV5) or carbazol (LV4) at both ends as donor and fullerene derivative, [6,6]-phenylC61 butyric acid butyl ester ([C60] PCB-C4) as acceptor, have been prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) on glass/ITO and Si substrates. The effect of weight ratio between donor and acceptor (1: 1; 1: 2) and solvent type (chloroform, dimethylsulphoxide) on the optical (UV-vis transmission/absorption, photoluminescence) and morphological properties of LV4 (LV5): [C60] PCB-C4 mixed layers has been evidenced. Dark and under illumination I-V characteristics of the heterostructures realized with these mixed layers sandwiched between ITO and Al electrodes have revealed a solar cell behavior for the heterostructures prepared with both LV4 and LV5 using chloroform as matrix solvent. The solar cell structure realized with oligomer LV5, glass/ITO/LV5: [C60] PCB-C4 (1: 1) has shown the best parameters. (C) 2017 Elsevier B.V. All rights reserved.

Tungsten trioxide (WO3) thin films were grown by pulsed laser deposition (PLD) with the aim to be applied in gas sensors. The films were studied by atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and profilometry. To study the gas sensing behavior of these WO3 films, they were deposited on quartz resonators and the quartz crystal microbalance (QCM) method was applied to analyze their gas sensitivity. Synthesis of tetragonal-WO3 films starting from a target with predominantly monoclinic WO3 phase was observed. The films deposited at 300 degrees C presented a surface topology favorable for the sorption properties, consisting of a film matrix with protruding craters/cavities. QCM prototype sensors with such films were tested for NO2 sensing. The PLD grown WO3 thin films show good sensitivity and fast reaction at room temperature, even in as-deposited state. With the presented technology, the manufacturing of QCM gas sensors is simple, fast and cost-effective, and it is also suitable for energy-effective portable equipment for on-line monitoring of environmental changes. (C) 2017 Elsevier B.V. All rights reserved.

Organic heterostructures based on poly(3-hexylthiophene) (P3HT) and fullerene (C60) as blends or multilayer were deposited on Al:ZnO (AZO) by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The AZO layers were obtained by Pulsed Laser Deposition (PLD) on glass substrate, the high quality of the films being reflected by the calculated figure of merit. The organic heterostructures were investigated from morphological, optical and electrical point of view by atomic force microscopy (AFM), UV-vis spectroscopy, photoluminescence (PL) and current-voltage (I-V) measurements, respectively. The increase of the C60 content in the blend heterostructure has as result a high roughness. Compared with the multilayer heterostructure, those based on blends present an improvement in the electrical properties. Under illumination, the highest current value was recorded for the heterostructure based on the blend with the higher C60 amount. The obtained results showed that MAPLE is a useful technique for the deposition of the organic heterostructures on AZO as transparent conductor electrode. (C) 2017 Elsevier B.V. All rights reserved.