National Institute Of Materials Physics - Romania

Abstract: The growth of electrical transportation is crucially important to mitigate rising climate change concerns regarding materials supply. Supercapacitors are high-power devices, particularly suitable for public transportation since they can easily store breaking energy due to their high-rate charging ability. Additionally, they can function with two carbon electrodes, which is an advantage due to the abundance of carbon in biomass and other waste materials (i.e., plastic waste). Newly developed supercapacitive nanocarbons display extremely narrow micropores (0.8 nm), as it increases drastically the capacitance in aqueous electrolytes. Here, we present a strategy to produce low-cost flexible microporous electrodes with extremely high power density (100 kW kg(-1)), using fourty times less activating agent than traditionnal chemically activated carbons. We also demonstrate that the affinity between the carbon and the electrolyte is of paramount importance to maintain rapid ionic diffusion in narrow micropores. Finally, this facile synthesis method shows that low-cost and bio-based free-standing electrode materials with reliable supercapacitive performances can be used in electrochemistry. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: The present work reports the production and key properties of the CuCrFeTiV high entropy alloy synthetized mechanical alloying and spark plasma sintering. The milled powders and the as-sintered samples were analysed through scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy and particle induced X-ray emission. Magnetic properties together with electrical resistivity, thermal conductivity, specific heat differential thermal analysis were also evaluated on the consolidated samples. The powders reveal an increasing content in iron as the millings are prolonged up to 20 h. The elemental composition of the sintered alloy, determined through particle induced X-ray emission, confirms the final composition after mechanical alloying with an increase of iron and a decrease in the remaining elements. Furthermore, although the alloy presents electrical resistivity typical of a high entropy alloy, a ferromagnetic behaviour was found, consistently with major Fe content as detected in prior observations. Finally, thermal measurements show that this CuCrFeTiV entropy alloy possesses thermal properties suitable for its potential use as thermal barriers.

Abstract: Two core-double-shell pH-sensitive nanocarriers were fabricated using Fe3O4 as magnetic core, poly(glycidyl methacrylate-PEG) and salep dialdehyde as the first and the second shell, and doxorubicin as the hydrophobic anticancer drug. Two nanocarriers were different in the drug loading steps. The interaction between the first and the second shell assumed to be pH-sensitive via acetal cross linkages. The structure of nanocarriers, organic shell loading, magnetic responsibility, morphology, size, dispersibility, and drug loading content were investigated by IR, NMR, TG, VSM, XRD, DLS, HRTEM and UV-Vis analyses. The long-term drug release profiles of both nanocarriers showed that the drug loading before cross-linking between the first and second shell led to a more pH-sensitive nanocarrier exhibiting higher control on DOX release. Cellular toxicity assay (MTT) showed that DOX-free nanocarrier is biocompatible having cell viability greater than 80% for HEK-293 and MCF-7 cell lines. Besides, high cytotoxic effect observed for drug-loaded nanocarrier on MCF-7 cancer cells. Cellular uptake analysis showed that the nanocarrier is able to transport DOX into the cytoplasm and perinuclear regions of MCF-7 cells. In vitro hemolysis and coagulation assays demonstrated high blood compatibility of nanocarrier. The results also suggested that low concentration of nanocarrier have a great potential as a contrast agent in magnetic resonance imaging (MRI).

Abstract: The effect of potential tetragonal and triclinic distortions of the energetic favorable cubic crystalline structure in CoFeZrSi Heusler compound, was investigated, using semiclassic Boltzmann theory on the thermoelectric functionalities. Chemical potential dependence of the conductivity integral sigma/tau for relaxed cubic and tetragonal structures confirms p-type thermoelectric characteristics. When triclinic deformation is investigated, the electrical conductivity response indicates that the material's ability to conduct electric current decreases. The calculated Seebeck coefficients exhibit positive values for the crystalline structures whose angles are equal to 90 degrees (cubic and tetragonal), over the 300-1200K temperature range. The figures of merit ZT, for relaxed cubic and tetragonal structures, at optimum unit cell volume or higher, present around room temperature, promising features as a potential thermoelectric material (i.e. ZT = 0.94 for 350K in optimum cubic structure). (C) 2019 Elsevier B.V. All rights reserved.