Publications

In this work, new films containing composite materials based on blends of thermoplastic polymers of the polyurethane (TPU) and polyolefin (TPO) type, in the absence and presence of BaTiO3 nanoparticles (NPs) with the size smaller 100 nm, were prepared. The vibrational properties of the free films depending on the weight ratio of the two thermoplastic polymers were studied. Our results demonstrate that these films are optically active, with strong, broad, and adjustable photoluminescence by varying the amount of TPU. The crystalline structure of BaTiO3 and the influence of thermoplastic polymers on the crystallization process of these inorganic NPs were determined by X-ray diffraction (XRD) studies. The vibrational changes induced in the thermoplastic polymer's matrix of the BaTiO3 NPs were showcased by Raman scattering and FTIR spectroscopy. The incorporation of BaTiO3 NPs in the matrix of thermoplastic elastomers revealed the shift dependence of the photoluminescence (PL) band depending on the BaTiO3 NP concentration, which was capable of covering a wide visible spectral range. The dependencies of the dielectric relaxation phenomena with the weight of BaTiO3 NPs in thermoplastic polymers blends were also demonstrated.

Partially-oriented MgB2 bulk discs (13 and 9 %) with the starting compositions of (MgB2)(0.99)(B4C)(0.01) and (MgB2)(0.99)(c-BN)om were fabricated by slip casting under an H-0 = 12 T magnetic field (perpendicular to the disc surface) and subsequent spark plasma sintering. The maximum critical current density and irreversibility field are for H//H-0 (H=applied field). These values are higher or similar to the randomly-oriented samples with the same composition. The maximum volume pinning force (F-p) is lower in the partially-oriented ones than in the randomly-oriented samples. The pinning-force-related parameters depend on the additive and orientation. Assessment of the major pinning mechanism within the scaling and percolation models considering these parameters shows significant limitations. A method to scale F-p is proposed; for the randomly and partially-oriented samples (that show an extra peak in F-p), the single and double Gaussian functions fit well. The results suggest an anisotropic influence of carbon substituting for boron in the MgB2.

A composite material with applications in optoelectronics has been investigated. Pulsed laser deposition CdSe-doped glass film was prepared by the combinatorial deposition from two targets, namely pure CdSe and glass belonging to the 20Li(2)O-10Al(2)O(3)-7BaO-2La(2)O(3)-2ZnO-59P(2)O(5)system. Exciton peaks in the Vis domain, related to electron-hole pairs transitions from the valence band to the conduction band, were revealed in the optical absorption spectra of the CdSe-doped film. CdSe quantum dots (QDs) band gap energy depends on the CdSe quantum confinement effect. CdSe-doped film photoluminescence exhibits peaks in the red domain assigned to CdSe transitions from the excited state to the ground state. The size of CdSe nanoclusters, determined from x-ray diffraction is correlated with scanning electron microscopy-energy dispersive x-ray spectroscopy and atomic force microscopy results. Vibration modes specific both to CdSe QDs and to the vitreous network have been evidenced by Fourier transform infrared and Raman spectroscopy.

The investigation of the effect of carbon nanomaterials and lipids on the aggregation particularities of the amyloid beta/A beta(1-42) layers is important for understanding the generation mechanism of neuronal disorder and how it can be inhibited. Additionally, amyloids are nanomaterials with a wide area of potential applications from nanotechnology to biotechnology. This paper presents a study about the preparation of A beta(1-42) layer by two different methods, Langmuir-Blodgett (L-B) and drop cast (DC), on Si and Si covered by a layer of Buckminster fullerene, C-60, and on the effect of fullerene layer or/and cholesterol (Ch) on the generation of A beta(1-42) secondary structure forms, relevant for specific applications. AFM, SEM FTIR and Raman analysis offered details about the layer surface topography, morphology and particularities of the secondary structure generated in the process of A beta(1-42) molecules aggregation. This study showed that the presence of Ch inhibited the formation of fibrils in A beta(1-42) film deposited by L-B on Si covered by C-60 The structures developed during aggregation were correlated with the topography and roughness of the films. The presence of Ch determined a decrease in roughness for L-B film and increase in roughness for DC film deposited on Si covered by C-60 layer.

A hybrid direct current magnetron sputtering/high-power impulse magnetron sputtering (DCMS/HiPIMS) technique was used to improve the structural and electrical properties of single-crystal titanium carbide (TiC) thin films. The hetero-epitaxial TiC films, similar to 60 nm thick, were grown on MgO (001) substrates at temperatures ranging from 200 degrees C to 800 degrees C, by co-sputtering of Ti and C targets powered by DCMS and HiPIMS, respectively. Films' composition and the structural, morphological, and electrical properties were comparatively investigated to those of a set of samples deposited at same temperatures by reactive-DCMS (R-DCMS) in Ar/CH4 atmosphere. The composition and the FWHM of rocking curves of the films deposited by R-DCMS varied from TiC0.84 to TiC0.94 and from 1.38 degrees to 0.64 degrees, respectively, as the growth temperature increased. TiC0.94 - TiC0.96 layers were deposited by hybrid DCMS/HiPIMS method at temperatures higher than 400 degrees C, fully strained over their full thickness, with FWHM of rocking curves of about 0.13 degrees. Electrical resistivity values measured for these films were of about 155 mu Omega cm, significantly close to those corresponding to bulk TiC0.95 single crystals. The resistivity of R-DCMS films is higher by 6% to 23% in comparison with that of the DCMS/HiPIMS grown samples, depending on the growth temperature.

We investigate topological and disorder effects in non-Hermitian systems with chiral symmetry. The system under consideration consists in a finite Su-Schrieffer-Heeger chain to which two semi-infinite leads are attached. The system lacks the parity-time and time-reversal symmetries and is appropriate for the study of quantum transport properties. The complex energy spectrum is analyzed in terms of the chain-lead coupling and chiral disorder strength, and shows substantial differences between chains with even and odd number of sites. The mid-gap edge states acquire a finite lifetime and are both of topological origin or generated by a strong coupling to the leads. The disorder induces coalescence of the topological eigenvalues, associated with exceptional points and vanishing of the eigenfunction rigidity. The electron transmission coefficient is approached in the Landauer formalism, and an analytical expression for the transmission in the range of topological states is obtained. Notably, the chiral disorder in this non-Hermitian system induces unitary conductance enhancement in the topological phase. (C) 2020 Elsevier B.V. All rights reserved.

Despite extensive studies on lanthanide (Ln) doped TiO2 nanoparticles, there is still considerable uncertainty as to whether Ln reside in the bulk (either as substitutional or interstitial dopant) or on the surface. Herein, new Ln (Eu, Sm, Nd and Er) discrete substitutional centers are identified in the anatase phase using low temperature, site selective time-gated luminescence spectroscopy. The excitation wavelength spanned UV (TiO2 host absorption) to visible excitation range into Ln f-f absorption transitions. The Ln multisite distribution is described in terms of fingerprint emission/excitation spectra and emission decays. The emission of Ln centers cover the visible (Eu, Sm) to near-infrared range (Nd, Er) and display narrow emission with full width at half maximum (FWHM) as small as 0.2 nm. The role of TiO2 host in sensitization of Ln emission is emphasized for each center. We have also found that besides discrete distribution, Ln distribute continuously on closely related anatase lattice sites. In this case, the Ln emission is significantly broader, with FWHM around 20 nm and change continuously in spectral shape and intensity with the excitation wavelength. The challenges encountered while identifying the Ln centers in TiO2 and comparison with case of CeO2 and SnO2 are also discussed. (C) 2020 Elsevier B.V. All rights reserved.

Operation of a magnetron sputtering gas aggregation cluster source in a plasma jet regime is presented. In specific experimental conditions, the plasma extends from the inside of the cluster source in the deposition chamber as a plasma jet, transporting also the nanoparticles (NPs) produced in the cluster source. The chemistry of the NP surface is modified in-flight by injecting a chemical precursor in the plasma jet, resulting in core-shell NPs. Also, the plasma jet presents a low gas temperature, safely interacting with materials sensitive to thermal degradation (like polymers). These findings prove the potential of the presented plasma jet for applications in nanotechnology.

Novel composite materials are being investigated for improving the energy storage performance of electrochemical capacitors. For this goal, synergistic effects via the combination of diverse types of materials are crucial. In this work, electrodes composed of reduced graphene oxide, multiwall carbon nanotubes, as well as cerium and manganese oxides were fabricated through reactive inverse matrix-assisted pulsed laser evaporation (RIMAPLE). UV-pulsed laser irradiation of frozen aqueous dispersions containing graphene oxide sheets, carbon nanotubes, and ceria nanoentities, besides manganese acetate precursor, led to the simultaneous chemical transformation and co-deposition of hybrid electrodes onto flexible metallic substrates via photothermal and photochemical processes. Thorough morphological and compositional studies of the electrodes demonstrated the laser-induced reduction of graphene oxide, besides the crystallization of a mixture of cerium and manganese oxide nanostructures decorating the carbon nanoentities during the deposition process. Electrochemical analyses revealed a remarkable improvement of performance with the combination of electrochemical double layer in the porous nanocarbon framework with pseudocapacitance from the oxide nanostructures, obtaining excellent volumetric capacitances of up to 140 F cm(-3) at 10 mV s(-1) with the combination of all four materials. The attained results are the best ones yet published regarding RIMAPLE of hybrid nanocarbon-based electrodes with micrometric thickness. Finally, symmetric electrochemical capacitors were fabricated using aqueous electrolyte, revealing excellent stability upon tens of thousands of charge-discharge cycles.

The 17th-19th century wooden and stone churches are an iconic symbol for the Romanian national heritage, raising urgent needs for the development of efficient and ecofriendly restoration and preservation solutions. Nanotechnology has a great but largely unexplored potential in this field, providing new tools and methods to achieve higher consolidation and protection efficiency, mainly due to the ability of nanoparticles to inhibit the growth and metabolic activity of different biodeteriorating agents, including fungi. The purpose of the present study was to report for the first time on the efficiency of MgB2 materials, mainly prized for their practical superconducting properties, against a large collection of filamentous fungal strains recently isolated from biodeteriorated wooden and stone heritage objects. Four types of MgB2 powders, with a crystallite size of 42-113 nm, were tested by qualitative (on 149 strains) and quantitative (on 87 strains) assays. The cytotoxicity was evaluated by the microscopic analysis of SiHa cells morphology and Hep2 cell cycle analysis and the ecotoxicity by the Allium test. The tested filamentous fungal strains belonged to 11 different genera, and those isolated from mural paintings and wooden objects exhibited the best capacity to colonize the inert substratum. All MgB2 powders exhibited similar and relatively low minimal inhibitory concentrations (MIC) values against the Aspergillus and Penicillium isolates, which were predominated among isolates. From the tested powders, PVZ and CERAC proved to be more efficient against the strains isolated from stone and wood materials, while LTS was active against the fungal strains colonizing the mural paintings and museum objects. The cytotoxicity results indicated that the tested powders are toxic for the human cells at concentrations higher than 50 mu g/ml, but, however, the very short lifetime of these NPs prevents their accumulation in the natural environment and, thus, the occurrence of toxic effects. The tested powders proved to be ecofriendly at the active antifungal concentrations, as suggested by the phytotoxicity test results. Taken together, our results suggest the potential of the MgB2 materials for the development of environmentally safe antifungal substances, which can be used in the control of the material cultural heritage biodeterioration process.