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91. Hierarchical composites of B4C-TiB2 eutectic particles reinforced with Ti
Authors: Solodkyi, I; Bogomol, I; Bolbut, V; Loboda, P; Kuncser, A; Vasylkiv, O; Badica, P

Published: DEC 15 2020, CERAMICS INTERNATIONAL, 46, 28144, DOI: 10.1016/j.ceramint.2020.07.312

Eutectic particles of B4C-TiB2 were reinforced with Ti by spark plasma sintering (SPS) or infiltration. The SPSed samples with 20, 30 and 40 wt. % Ti consisted of ceramic phases, and had a bicontinuous macrostructure formed by the Ti-rich region and the eutectic particles region, while the infiltrated sample was a complex composite comprised of a 3D Ti-rich continuous network, composite in nature, that contained Ti-metal and in which are embedded isolated ceramic (eutectic) particles. The SPSed samples are brittle with the maximum bending strength of 300 MPa for the 30 wt. % Ti, higher than for a reference sample produced by SPS from directionally solidified eutectic particles. A higher amount of added Ti results in a higher displacement in the bending test suggesting a higher fracture toughness. Simultaneous strengthening and toughening of the composite was realized. The infiltrated sample was ductile, while its bending strength (220 MPa) was comparable to the values measured for the brittle as-introduced reference sample and the sample with 20 wt. % Ti, both produced by SPS. In the SPSed and infiltrated samples at the interface between the Ti-rich region and B4C-TiB2 eutectic particles, a local 'pull-out' intergranular fracturing mechanism mainly involving Ti-B 1D-grains was observed. This local micromechanism together with a 'pull out' macromechanism of the eutectic grains from the Ti-rich component are considered important for the bridging/anchoring behavior responsible for the strengthening and toughening processes in our novel hierarchical composites.
92. Wafer-scale graphene-ferroelectric HfO2/Ge-HfO2/HfO(2)transistors acting as three-terminal memristors
Authors: Dragoman, M; Dinescu, A; Dragoman, D; Palade, C; Moldovan, A; Dinescu, M; Teodorescu, VS; Ciurea, ML

Published: DEC 4 2020, NANOTECHNOLOGY, 31, DOI: 10.1088/1361-6528/abb2bf

In this paper we report a set of experiments at the wafer level regarding field-effect transistors with a graphene monolayer channel transferred on the ferroelectric HfO2/Ge-HfO2/HfO(2)three-layer structure. This kind of transistor has a switching ratio of 10(3)between on and off states due to the bandgap in graphene induced by the ferroelectric structure. Both top and back gates effectively control the carriers' charge flow in graphene. The transistor acts as a three-terminal memristor, termed a memtransistor, with applications in neuromorphic computation.
93. Functionalization of eggshell membranes with CuO-ZnO based p-n junctions for visible light induced antibacterial activity against Escherichia coli
Authors: Preda, N; Costas, A; Beregoi, M; Apostol, N; Kuncser, A; Curutiu, C; Iordache, F; Enculescu, I

Published: DEC 1 2020, SCIENTIFIC REPORTS, 10, DOI: 10.1038/s41598-020-78005-x

Biopolymers provide versatile platforms for designing naturally-derived wound care dressings through eco-friendly pathways. Eggshell membrane (ESM), a widely available, biocompatible biopolymer based structure features a unique 3D porous interwoven fibrous protein network. The ESM was functionalized with inorganic compounds (Ag, ZnO, CuO used either separately or combined) using a straightforward deposition technique namely radio frequency magnetron sputtering. The functionalized ESMs were characterized from morphological, structural, compositional, surface chemistry, optical, cytotoxicity and antibacterial point of view. It was emphasized that functionalization with a combination of metal oxides and exposure to visible light results in a highly efficient antibacterial activity against Escherichia coli when compared to the activity of individual metal oxide components. It is assumed that this is possible due to the fact that an axial p-n junction is created by joining the two metal oxides. This structure separates into components the charge carrier pairs promoted by visible light irradiation that further can influence the generation of reactive oxygen species which ultimately are responsible for the bactericide effect. This study proves that, by employing inexpensive and environmentally friendly materials (ESM and metal oxides) and fabrication techniques (radio frequency magnetron sputtering), affordable antibacterial materials can be developed for potential applications in chronic wound healing device area.
94. Unidirectional Magnetic Anisotropy in Dense Vertically-Standing Arrays of Passivated Nickel Nanotubes
Authors: Locovei, C; Filipoiu, N; Kuncser, A; Stanciu, AE; Antohe, S; Florica, CF; Costas, A; Enculescu, I; Piraux, L; Kuncser, V; Antohe, VA

Published: DEC 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10122444

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures' electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis.
95. SnSe2-Zn-Porphyrin Nanocomposite Thin Films for Threshold Methane Concentration Detection at Room Temperature
Authors: Lorinczi, A; Fagadar-Cosma, E; Socol, G; Mihailescu, A; Matei, E; Sava, F; Stefan, M

Published: DEC 2020, CHEMOSENSORS, 8, DOI: 10.3390/chemosensors8040134

Nanocomposite thin films, sensitive to methane at the room temperature (25-30 degrees C), have been prepared, starting from SnSe2 powder and Zn(II)-5,10,15,20-tetrakis-(4-aminophenyl)- -porphyrin (ZnTAPP) powder, that were fully characterized by XRD, UV-VIS, FT-IR, Nuclear Magnetic Resonance (H-1-NMR and C-13-NMR), Atomic Force Microscopy (AFM), SEM and Electron Paramagnetic Resonance (EPR) techniques. Film deposition was made by drop casting from a suitable solvent for the two starting materials, after mixing them in an ultrasonic bath. The thickness of these films were estimated from SEM images, and found to be around 1.3 mu m. These thin films proved to be sensitive to a threshold methane (CH4) concentration as low as 1000 ppm, at a room temperature of about 25 degrees C, without the need for heating the sensing element. The nanocomposite material has a prompt and reproducible response to methane in the case of air, with 50% relative humidity (RH) as well. A comparison of the methane sensing performances of our new nanocomposite film with that of other recently reported methane sensitive materials is provided. It is suitable for signaling gas presence before reaching the critical lower explosion limit concentration of methane at 50,000 ppm.
96. The enhancement mechanism of dielectric properties of Pb(Zr,Ti)O-3 via (Mg2+,Sb3+) incorporation for supercapacitors
Authors: Craciun, F; Dimitriu, E; Vasile, BS; Negrila, CC; Trusca, R; Birjega, R; Cernea, M

Published: DEC 2020, MATERIALS TODAY CHEMISTRY, 18, DOI: 10.1016/j.mtchem.2020.100350

Due to the extraordinary versatility of the perovskite structure in accommodating different dopant ions in its structure, in recent years a huge number of multifunctional perovskite materials have been developed. In this work we aim to obtain high temperature-stable and huge dielectric constant materials for supercapacitors by doping divalent Mg2+ and trivalent Sb3+ ions into the octahedral sites, and divalent Sr2+ ions into the dodecahedral sites of lead zirconate-titanate perovskite. The resulting (Pb0.95Sr0.05)(Zr0.425Ti0.45Mg0.042Sb0.083)O3-delta is examined by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), dielectric spectroscopy (DS) and resonance dielectric spectroscopy (RDS) in order to correlate composition, local structure, ion valence and chemical environment of the doped material with the dielectric properties. HRTEM evidences that a composite structure, with co-existent ferroelectric domains and relaxor nanodomains, is formed by doping. XPS shows that Sb3+ and Mg2+ substitute for the Ti4+/Zr4+ ions, pointing to these strong defects as the main cause for the appearance of the relaxor phase. DS and RDS found that the ferroelectric lead zirconate-titanate transforms into a re-entrant relaxorferroelectric composite with a huge dielectric constant of about 10(4) which remains stable (within +/- 10%) in the high temperature range up to 250 degrees C, pointing to this mechanism of relaxor phase re-entrance below the normal ferroelectric phase transition, as being responsible for the enhancement. (C) 2020 Elsevier Ltd. All rights reserved.
97. Temperature dependence and defect related structure, photoluminescence, (ferro)magnetism and ammonia sensitivity of un-doped nanocrystalline ZnO
Authors: Mihalache, V; Secu, M; Negrila, C; Bercu, V; Mercioniu, I; Leca, A

Published: DEC 2020, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 262, DOI: 10.1016/j.mseb.2020.114748

ZnO nanostructures with intrinsic and extended defects were prepared by rapid decomposition of zinc-propio-nate and annealing at 400 degrees C-970 degrees C. The correlation between the structure/morphology, type of native defects (photoluminescence (PL), EPR) and ferromagnetism was investigated, together with ammonia adsorption capacity. All the samples show room temperature ferromagnetism (RTFM). Crystallite size increases while the unit cell volume, c-axis constant, microstrain and saturation magnetization relax with increasing temperature; morphology varies from aggregated nanoparticles to frameworks of well-welded crystals. 400 degrees C-800 degrees C annealed samples show a broad visible and/or a prominent violet-blue PL emission and, two narrow g = 2.0065 and g = 1.9632 EPR signals. 800 degrees C-970 degrees C annealed samples exhibit very intense green-yellow photoluminescence. The intrinsic defects in conjunction with a deformed lattice and/or pinned by grain-boundaries appear responsible for RTFM and Curie temperature exceeding 700 degrees C. Tuning the morphology, PL intensity and ferromagnetic signal by choice of annealing temperature can find applications in (gas) sensing, photonic/optoelectronic and spintronic devices.
98. Structure of K alpha(1,2)- and K beta(1,3)-emission x-ray spectra for Se, Y, and Zr
Authors: Ito, Y; Tochio, T; Yamashita, M; Fukushima, S; Vlaicu, AM; Marques, JP; Sampaio, JM; Guerra, M; Santos, JP; Syrocki, L; Slabkowska, K; Weder, E; Polasik, M; Rzadkiewicz, J; Indelicato, P; Menesguen, Y; Lepy, MC; Parente, F

Published: NOV 20 2020, PHYSICAL REVIEW A, 102, DOI: 10.1103/PhysRevA.102.052820

The K alpha and K beta x-ray spectra of Se, Y, and Zr were studied experimentally and theoretically in order to obtain information on the K alpha(1) line asymmetry and the spin doublet in K beta(1,3) diagram lines. Using a high-resolution antiparallel double-crystal x-ray spectrometer, we obtained the line shapes, that is, asymmetry index and natural linewidths. We found that the corrected full width at half maximum of the K alpha(1) and K alpha(2) lines as a function of Z is in good agreement with the data in the literature. Furthermore, satellite lines arising from shake-off appear in the low-energy side of the K alpha(1) and K alpha(2) lines in Se but, in Y and Zr, it was very difficult to identify the contribution of the shake process to the overall lines. The K beta(1,3) natural linewidth of these elements was also corrected using the appropriate instrumental function for this type of x-ray spectrometer, and the spin doublet energies were obtained from the peak positions. The corrected full width at half maximum (FWHM) of the K alpha(1) x-ray lines increases linearly with Z, but this tendency was found to be, in general, not linear for K alpha(3) x-ray lines. This behavior may be due to the existence of satellite lines originated from shake processes. Simulated line profiles, obtained using the multiconfiguration Dirac-Fock formalism, accounting for radiative and radiationless transitions and shake-off processes, show a very good agreement with the high-resolution experimental spectra.
99. Influence of SiGe Nanocrystallization on Short-Wave Infrared Sensitivity of SiGe-TiO2 Films and Multilayers
Authors: Lepadatu, AM; Palade, C; Slav, A; Cojocaru, O; Maraloiu, VA; Iftimie, S; Comanescu, F; Dinescu, A; Teodorescu, VS; Stoica, T; Ciurea, ML

Published: NOV 12 2020, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 25053, DOI: 10.1021/acs.jpcc.0c06290

Continuous development of Si photonics requires ecological and cost-effective materials. In this work, SiGe nanocrystals (NCs) embedded in TiO2 are investigated as a photosensitive material for visible (VIS) to short-wave infrared (SWIR) broad-range detection. The TiO2 matrix has the advantage of a lower band gap than SiO2, facilitating transport of photogenerated carriers in NCs. The advantage of SiGe NCs over Ge NCs is emphasized by elucidating the mechanisms involved in rapid thermal annealing (RTA)-induced nanocrystallization. An efficiently increased NC stabilization is achieved by avoiding the detrimental fast Ge diffusion. For this, the structure, morphology, and composition were carefully characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy. Two types of structures were investigated, a film of SiGe-TiO2 alloy and a multilayer of a stack of six SiGe/TiO2 pairs. The layers have been deposited on Si wafers using magnetron sputtering of Si, Ge, and TiO2 followed by RTA in an inert atmosphere. The stabilization of SiGe NCs is achieved by the formation during RTA of protective SiO2 thin layers through Si oxidation at the SiGe NC surface, acting as a barrier for Ge diffusion. Thus, embedded Ge-rich SiGe NCs are obtained, resulting in the SWIR extension of the spectral photocurrent up to 1700 nm for films and 1600 nm for multilayers. This study has shown that in multilayers, the local anisotropy of crystallization is compensated by the stress field developed in the SiGe lattice, highly visible in the bottom part. Also, SiGe crystallizes faster than TiO2 in the rutile phase, and therefore, TiO2 remains mainly amorphous.
100. Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of alpha-Lipoic Acid in the Presence of Ag and Au Nanoparticles
Authors: Toulbe, N; Stroe, MS; Daescu, M; Cercel, R; Mogos, A; Dragoman, D; Socol, M; Mercioniu, I; Baibarac, M

Published: NOV 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10112238

The influence of Ag and Au nanoparticles and reduced graphene oxide (RGO) sheets on the photodegradation of alpha-lipoic acid (ALA) was determined by UV-VIS spectroscopy. The ALA photodegradation was explained by considering the affinity of thiol groups for the metallic nanoparticles synthesized in the presence of trisodium citrate. The presence of excipients did not induce further changes when ALA interacts with Ag and Au nanoparticles with sizes of 5 and 10 nm by exposure to UV light. Compared to the Raman spectrum of ALA powder, changes in Raman lines' position and relative intensities when ALA has interacted with films obtained from Au nanoparticles with sizes between 5 and 50 nm were significant. These changes were explained by considering the chemical mechanism of surface-enhanced Raman scattering (SERS) spectroscopy. The photodegradation of ALA that had interacted with metallic nanoparticles was inhibited in the presence of RGO sheets.

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