National Institute Of Materials Physics - Romania

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51. Pinning Potential of the Self-Assembled Artificial Pinning Centers in Nanostructured YBa2Cu3O7-x Superconducting Films
Authors: Ivan, I; Ionescu, AM; Crisan, DN; Andrei, A; Galluzzi, A; Polichetti, M; Mosqueira, J; Crisan, A

Published: MAY 2022, NANOMATERIALS, 12, 1713, DOI: 10.3390/nano12101713

For high-field power applications of high-temperature superconductors, it became obvious in recent years that nano-engineered artificial pinning centers are needed for increasing the critical current and pinning potential. As opposed to the artificial pinning centers obtained by irradiation with various particles, which is a quite expensive approach, we have studied superconducting samples having self-assembled defects, created during the sample fabrication, that act as effective pinning centers. We introduced a simple, straight-forward method of estimating the frequency-dependent critical current density by using frequency-dependent AC susceptibility measurements, in fixed temperatures and DC magnetic fields, from the positions of the maxima in the dependence of the out-of-phase susceptibility on the amplitude of AC excitation magnetic field. The results are compatible with a model that stipulates a logarithmic dependence of the pinning potential on the probing current. A mathematical derivation allowed us to estimate from the experimental data the pinning potentials in various samples, and in various DC magnetic fields. The resulted values indicate large pinning potentials, leading to very small probability of magnetic flux escaping the pinning wells, hence, leading to very high critical currents in high magnetic fields.
52. Physicochemical and Biological Evaluation of Chitosan-Coated Magnesium-Doped Hydroxyapatite Composite Layers Obtained by Vacuum Deposition
Authors: Predoi, D; Ciobanu, CS; Iconaru, SL; Raaen, S; Badea, ML; Rokosz, K

Published: MAY 2022, COATINGS, 12, 702, DOI: 10.3390/coatings12050702

In the present work, the effectiveness of vacuum deposition technique for obtaining composite thin films based on chitosan-coated magnesium-doped hydroxyapatite Ca10-xMgx(PO4)(6) (OH)(2) with x(Mg) = 0.025 (MgHApCh) was proved for the first time. The prepared samples were exposed to three doses (0, 3, and 6 Gy) of gamma irradiation. The MgHApCh composite thin films nonirradiated and irradiated were evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) studies. The biological evaluation of the samples was also presented. All the results obtained from this study showed that the vacuum deposition method allowed for obtaining uniform and homogeneous layers. Fine cracks were observed on the MgHApCh composite thin films' surface after exposure to a 6 Gy irradiation dose. Additionally, after gamma irradiation, a decrease in Ca, P, and Mg content was noticed. The MgHApCh composite thin films with doses of 0 and 3 Gy of gamma irradiation showed a cellular viability similar to that of the control. Samples with 6 Gy doses of gamma irradiation did not cause significantly higher fibroblast cell death than the control (p > 0.05). On the other hand, the homogeneous distribution of pores that appeared on the surface of coatings after 6 Gy doses of gamma irradiation did not prevent the adhesion of fibroblast cells and their spread on the coatings. In conclusion, we could say that the thin films could be suitable both for use in bone implants and for other orthopedic and dentistry applications.
53. Iron-Oxide-Nanoparticles-Doped Polyaniline Composite Thin Films
Authors: Butoi, B; Ciobanu, CS; Iconaru, SL; Negrila, CC; Badea, MA; Balas, M; Dinischiotu, A; Predoi, G; Bita, B; Groza, A; Predoi, D

Published: MAY 2022, POLYMERS, 14, 1821, DOI: 10.3390/polym14091821

Iron-oxide-doped polyaniline (PANI-IO) thin films were obtained by the polymerization of aniline monomers and iron oxide solutions in direct current glow discharge plasma in the absence of a buffer gas for the first time. The PANI-IO thin films were deposited on optical polished Si wafers in order to study surface morphology and evaluate their in vitro biocompatibility. The characterization of the coatings was accomplished using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), metallographic microscopy (MM), and X-ray photoelectron spectroscopy (XPS). In vitro biocompatibility assessments were also conducted on the PANI-IO thin films. It was observed that a uniform distribution of iron oxide particles inside the PANI layers was obtained. The constituent elements of the coatings were uniformly distributed. The Fe-O bonds were associated with magnetite in the XPS studies. The surface morphology of the PANI-IO thin films was assessed by atomic force microscopy (AFM). The AFM topographies revealed that PANI-IO exhibited the morphology of a uniformly distributed and continuous layer. The viability of Caco-2 cells cultured on the Si substrate and PANI-IO coating was not significantly modified compared to control cells. Moreover, after 24 h of incubation, we observed no increase in LDH activity in media in comparison to the control. In addition, our results revealed that the NO levels for the Si substrate and PANI-IO coating were similar to those found in the control sample.
54. Self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on interdigitated electrodes for visible-light photodetectors
Authors: Costas, A; Florica, C; Preda, N; Besleaga, C; Kuncser, A; Enculescu, I

Published: APR 27 2022, SCIENTIFIC REPORTS, 12, 6834, DOI: 10.1038/s41598-022-10879-5

An original photodetector system based on self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on metallic interdigitated electrodes, operating as visible-light photodetector was developed by combining simple preparation approaches. Metallic interdigitated electrodes were fabricated on Si/SiO2 substrates using a conventional photolithography process. Subsequently, a Cu layer was electrodeposited on top of the metallic interdigitated electrodes. The CuO nanowire arrays (core) were obtained by thermal oxidation in air of the Cu layer. Afterwards, a ZnO thin film (shell) was deposited by RF magnetron sputtering covering the surface of the CuO nanowires. The morphological, structural, compositional, optical, electrical and photoelectrical properties of the CuO nanowire arrays and CuO-ZnO core-shell nanowire arrays grown on metallic interdigitated electrodes were investigated. The performances of the devices were evaluated by assessing the figures of merit of the photodetectors based on self-connected CuO-ZnO core-shell heterojunction nanowire arrays grown on the metallic interdigitated electrodes. The radial p-n heterojunction formed between CuO and ZnO generates a type II band alignment that favors an efficient charge separation of photogenerated electron-hole pairs at the CuO-ZnO interface, suppressing their recombination and consequently enhancing the photoresponse and the photoresponsivity of the photodetectors. The electrical connections in the fabricated photodetector devices are made without any additional complex and time-consuming lithographic step through a self-connecting approach for CuO-ZnO core-shell heterojunction nanowire arrays grown directly onto the Ti/Pt metallic interdigitated electrodes. Therefore, the present study provides an accessible path for employing low dimensional complex structures in functional optoelectronic devices such as photodetectors.
55. Electrochemical quantification of levothyroxine at disposable screen-printed electrodes
Authors: David, M; Serban, A; Enache, TA; Florescu, M

Published: APR 15 2022, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 911, 116240, DOI: 10.1016/j.jelechem.2022.116240

The concentration of thyroxine hormone is linked to a large variety of medical conditions, where the best therapy is hormone substitution, through administration of levothyroxine (LT4) medication. Herewith, the detection of these biomolecules still lacks a simple, reliable tool, such as label-free sensors.In this work, the performances of commercial screen-printed carbon electrodes, containing different nanostructured materials (carbon nanotubes, graphene, and gold nanoparticles), used as sensors for LT4 detection, were described and compared. Electrochemical methods were used for the characterization of the nanostructure-based sensors. Several optimization steps were undertaken to achieve optimum performances for selective LT4 quantification. The redox behaviour of LT4 at sensors surface together with the interfacial changes, which occur due to the interaction between nanostructures and LT4, were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Differential pulse voltammetry (DPV) was used for LT4 detection, where best performances were obtained in the presence of carbon nanotubes, with a detection limit of 30 nM.
56. Effect of dopants on the optical properties of benzil crystals
Authors: Stanculescu, F; Socol, M; Rasoga, O; Preda, N; Ionita, I; Petre, G; Breazu, C; Stanculescu, A

Published: APR 15 2022, JOURNAL OF CRYSTAL GROWTH, 584, 126577, DOI: 10.1016/j.jcrysgro.2022.126577

Single-doped [Ag, Na, iodine, naphthalene (Naph), meta-dintrobenzene (m-DNB)] and double-doped, organic-inorganic (Naph + iodine; m-DNB + iodine) benzil (Bz) crystals have been grown from melt in a Bridgman-Stockbarger configuration. All crystals have been grown in the same experimental conditions, temperature variation at the growth interface = 30 K and moving speed of the growth ampoule = 1 mm/h. These conditions have been estimated from the theoretical analysis involving the solution of the classical (conventional) Stefan problem for flat solid-liquid interface in the boundary conditions imposed by our growth system. The effect of doping on the disorder degree, photoluminescence and dielectric constant of the Bz matrix has been investigated. The disorder in the crystals increased with the increase of dopant concentration. The highest disorder was induced by the organic dopant m-DNB, whose molecules does not show an adequate geometrical similarity with Bz molecules. The position of the photoluminescence peak, both at excitation with 335 nm and 435 nm, has not been affected by the presence of dopant(s). All doped samples show Second Harmonic Generation, even those with a significant degree of disorder. The effect of the single and double-doping on the second-order ONL co-efficient was analyzed by comparison with the second-order ONL coefficient of pure Bz crystals. In the case of the double-doping, the highest second-order optical nonlinear coefficient has been evidenced in the Bz crystals simultaneously doped with m-DNB and iodine in the same concentration (1%).
57. 'Put variety in White': Multi-analytical investigation of the white pigments inlaid on Early Chalcolithic pottery from Southern Romania
Authors: Opris, V; Velea, A; Secu, M; Rostas, AM; Buruiana, AT; Simion, CA; Mirea, DA; Matei, E; Bartha, C; Dimache, M; Lazar, C

Published: APR 2022, JOURNAL OF ARCHAEOLOGICAL SCIENCE-REPORTS, 42, 103402, DOI: 10.1016/j.jasrep.2022.103402

The current study aims to present and discuss the results obtained by complementary archaeometric methods applied for the first time on white pigments inlaid on excised pottery of the Boian-Vidra tradition (Early Chalcolithic, c. 4900-4600 BCE). The samples came from three settlements located in Southern Romania (Sultana-Ghetarie, Vidra, and Vladiceasca). They were selected considering that the pottery was produced in approximately contemporary sites, located relatively close to each other in the same geographical region, namely the Romanian Plain. The experimental part included the analysis of local samples of carbonate concretions and prehistoric animal bone ash as reference materials. Archaeometric investigations consisted in applying "in-air" PIXE and EDX methods for the chemical composition, XRD and FTIR for mineralogical data, SEM for microstructure observation, and EPR for the characterisation of the paramagnetic centres. Calcite, bone ash, and silica rich sediments were identified as the primary decorating pigments. The mixtures of calcite and bone-ash observed in 13 samples were specific to the sites at Vidra and Vladiceasca. Silica-rich sediments from distant sources were the main whitening materials in two samples from Vladiceasca, while for the samples from Sultana-Ghetarie, calcite was the only whitening mineral. The results show with a high degree of confidence the use of both local (i.e., carbonate neo-formations and bone ash) and exotic (silica-rich sediments) raw materials to obtain the white pigment applied to Boian-Vidra pottery. Thus, the current data show the adaptability of the potters with respect to the surrounding resources and also provide new evidence for a vast trade network of raw materials and/or finished products in the Lower Danube area during the Early Chalcolithic. The deliberate mixing of two whitening materials from different sources could be a technological choice and may highlight complex symbolic behaviours.
58. Ferromagnetism and Superconductivity in CaRuO3/YBa2Cu3O7-delta Heterostructures
Authors: Ionescu, AM; Ivan, I; Locovei, C; Onea, M; Crisan, A; Soltan, S; Schutz, G; Albrecht, J

Published: APR 2022, MATERIALS, 15, 2345, DOI: 10.3390/ma15072345

The deposition of a ferromagnetic layer can affect the properties of high-temperature superconductors underneath. We investigated the influence of ferromagnetic CaRuO3 on the properties of YBa2Cu3O7-x (YBCO) superconducting thin films when the layers are either in direct contact or separated by a barrier layer of 5 nm SrTiO3. Detailed measurements of the magnetic moment of the superconductor and ferromagnet as a function of temperature and magnetic field have been performed using SQUID magnetometry. Magnetometry and relaxation measurements show that the modification of the superconducting properties of YBCO strongly depends on the interaction with the ferromagnetic layer on top. The barrier layer has a significant impact on both the supercon-ducting properties of the YBCO film and the ferromagnetic ordering of CaRuO3. The physical properties mentioned above were discussed in correlation with the materials' structure determined by XRD analysis.
59. Influence of the synthesis parameters on the transport properties of Mg2Si0.4Sn0.6 solid solutions produced by melting and spark plasma sintering
Authors: Assahsahi, I; Popescu, B; Enculescu, M; Galatanu, M; Galca, AC; El Bouayadi, R; Zejli, D; Galatanu, A

Published: APR 2022, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 163, DOI: 10.1016/j.jpcs.2021.110561

In this work, the influence of the preparation route on the structural, morphological, and thermoelectric properties of the Mg2Si0.4Sn0.6 solid solutions is investigated. The synthesis based on melting the constituent elements in a closed graphite crucible followed by spark plasma sintering allows mixing elements with a large difference of their melting temperatures and a good control of sample stoichiometry. The optimized synthesis route is validated by the doped V and Sb samples, which yield good thermoelectric performance. The n-type doping leads to two orders of magnitude increase of the carrier concentration, and thus a subsequent increase of the electrical conductivity, which, in turn, augments greatly the power factor of the Mg1.98V0.02Si0.385Sn0.6Sb0.015 to 42.61 x10(-4) Wm(-1)K 2 at 650K. Although doping slightly enlarges the thermal conductivity, a peak value of the figure of merit ZT similar to 1.15 is obtained at 723K, which is 20 times higher than the ZT of un-doped material.
60. ZnS stacking order influence on the formation of Zn-poor and Zn-rich Cu2ZnSnS4 phase
Authors: Zaki, MY; El Khouja, O; Nouneh, K; Touhami, ME; Matei, E; Azmi, S; Rusu, MI; Grigorescu, CEA; Briche, S; Boutamart, M; Badica, P; Burdusel, M; Secu, M; Pintilie, L; Galca, AC

Published: APR 2022, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, DOI: 10.1007/s10854-022-08160-6

This paper reports the synthesis and characterization of Cu2ZnSnS4 (CZTS) absorber films, prepared by a two-step electrodeposition of a ZnS (zinc sulfide) binary and a CZT (copper, zinc and tin) ternary precursors on Mo/Ti/Si substrates. The as-electrodeposited ZnS/CZT and CZT/ZnS stacks were thermally treated in a tubular furnace in sulfur environment at 550 degrees C. The role of the ZnS buffer layer is to provide a zinc and sulfur reservoir, needed to complete the formation of kesterite phase. X-ray diffraction and Raman analyses revealed the formation of the CZTS phase. The surface morphology and chemical composition of the films were studied using a scanning electron microscope. The bandgap values inferred from diffuse reflectance data, are discussed with respect to the stoichiometry which is considerably affected by the order of the stacks. Room-temperature photoluminescence of the CZT/ZnS sample showed a board PL band of 1.51 eV. It was found that the film with a ZnS layer on top is preferred for the formation of a Zn-rich single CZTS phase.

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