National Institute Of Materials Physics - Romania

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924 articles found

21. Ferroelectric properties of ZrO2 films deposited on ITO-coated glass

Authors: Silva, JPB; Sekhar, KC; Negrea, RF; Ghica, C; Dastan, D; Gomes, MJM

Published: MAR 1 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2021.11.152

In this work, the ferroelectric characteristics of ZrO2 thin films grown on ITO-coated glass have been investigated. The ferroelectric nature of the ZrO2 films has been studied by polarization-electric field (P-E) hysteresis loops and found to be optimum for the films processed by rapid thermal annealing at 600 degrees C. The increase in the annealing temperature improves the ferroelectric properties through the increase of the in-plane strain that causes the formation of the ferroelectric orthorhombic phase. The formation of the orthorhombic phase was confirmed through high-resolution transmission electron microscopy. The effect of the electric field on the polarization switching kinetics of ZrO2 films has been investigated revealing that the switching kinetics follows the nucleation limited switching (NLS) model. The activation fields estimated from the peak values of the polarization currents (im) and the time (tm) at which im occurs are in good agreement with the values obtained from the switching characteristic time of the NLS model. This work paves the way towards the integration of (pseudo)binary oxide thin films on cheap substrates like glass for the next-generation of non-volatile memories.

22. The effect of noble metal addition on the properties of oxide semiconductors nanoparticles

Authors: Goncearenco, E; Morjan, IP; Dutu, E; Scarisoreanu, M; Fleaca, C; Gavrila-Florescu, L; Dumitrache, F; Banici, AM; Teodorescu, VS; Anastasescu, C; Sandulescu, A; Balint, I

Published: MAR 2022, JOURNAL OF SOLID STATE CHEMISTRY, 307, DOI: 10.1016/j.jssc.2021.122817

This work presents the preparation of W and V co-doped TiO2 nanoparticles (W:TiO2 and W:V:TiO2) using laser pyrolysis technique subsequently modified with noble metals Pt or Pd using chemical impregnation method. By using well defined TiO2 nanoparticles, the enhancement of catalytic activity is expected mainly due to their higher surface area and density defects relative to bulk material. Structural, morphological and optical properties of the as-obtained nanopowders have been characterized by transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV-VIS diffuse reflectance spectroscopy and photoluminescence techniques. The phase composition analysis reveals the preponderance of anatase (95%) in addition to ruffle phase, its particle average size ranging from 25 to 30 nm. The TiO 2 based nanomaterials were supplementary modified by noble metals deposition (Pt particles with dimensions of 3-4 nm and spherical Pd crystallites with a diameter between 3 and 9 nm) and their photocatalytic activity was tested in oxidative photo degradation of CH3OH, under simulated solar light. The metal modified samples displayed higher specific surface areas (3-6 times) and improved photocatalytic properties, the W:V:TiO2@Pt material showing better conversion efficiency of CH3OH to CH2O than the reference Degussa P25 sample (1.54 versus 0.90%).

23. Could Iron-Nitrogen Doping Modulate the Cytotoxicity of TiO2 Nanoparticles?

Authors: Nica, IC; Miu, BA; Stan, MS; Diamandescu, L; Dinischiotu, A

Published: MAR 2022, NANOMATERIALS, 12, 770, DOI: 10.3390/nano12050770

Titanium dioxide nanoparticles (TiO2 NPs) are found in several products on the market that include paints, smart textiles, cosmetics and food products. Besides these, TiO2 NPs are intensively researched for their use in biomedicine, agriculture or installations to produce energy. Taking into account that several risks have been associated with the use of TiO2 NPs, our aim was to provide TiO2 NPs with improved qualities and lower toxicity to humans and the environment. Pure TiO2 P25 NPs and the same NPs co-doped with iron (1%) and nitrogen atoms (P25-Fe(1%)-N NPs) by hydrothermal treatment to increase the photocatalytic activity in the visible light spectrum were in vitro evaluated in the presence of human lung cells. After 24 and 72 h of incubation, the oxidative stress was initiated in a time- and dose-dependent manner with major differences between pure P25 and P25-Fe(1%)-N NPs as revealed by malondialdehyde and reactive oxygen species levels. Additionally, a lower dynamic of autophagic vacuoles formation was observed in cells exposed to Fe-N-doped P25 NPs compared to the pure ones. Therefore, our results suggest that Fe-N doping of TiO2 NPs can represent a valuable alternative to the conventional P25 Degussa particles in industrial and medical applications.

24. Unidirectional Magnetic Anisotropy in Molybdenum Dioxide-Hematite Mixed-Oxide Nanostructures

Authors: Tolea, F; Sorescu, M; Diamandescu, L; Iacob, N; Tolea, M; Kuncser, V

Published: MAR 2022, NANOMATERIALS, 12, 938, DOI: 10.3390/nano12060938

MoO2-Fe2O3 nanoparticle systems were successfully synthesized by mechanochemical activation of MoO2 and alpha-Fe2O3 equimolar mixtures throughout 0-12 h of ball-milling. The role of the long-range ferromagnetism of MoO2 on a fraction of more defect hematite nanoparticles supporting a defect antiferromagnetic phase down to the lowest temperatures was investigated in this work. The structure and the size evolution of the nanoparticles were investigated by X-ray diffraction, whereas the magnetic properties were investigated by SQUID magnetometry. The local electronic structure and the specific phase evolution in the analyzed system versus the milling time were investigated by temperature-dependent Mossbauer spectroscopy. The substantially shifted magnetic hysteresis loops were interpreted in terms of the unidirectional anisotropy induced by pinning the long-range ferromagnetic order of the local net magnetic moments in the defect antiferromagnetic phase, as mediated by the diluted magnetic oxide phase of MoO2, to those less defect hematite nanoparticles supporting Morin transition. The specific evolutions of the exchange bias and of the coercive field versus temperature in the samples were interpreted in the frame of the specific phase evolution pointed out by Mossbauer spectroscopy. Depending on the milling time, a different fraction of defect hematite nanoparticles is formed. Less nanoparticles supporting the Morin transition are formed for samples exposed to a longer milling time, with a direct influence on the induced unidirectional anisotropy and related effects.

25. SiGeSn Quantum Dots in HfO2 for Floating Gate Memory Capacitors

Authors: Palade, C; Slav, A; Cojocaru, O; Teodorescu, VS; Stoica, T; Ciurea, ML; Lepadatu, AM

Published: MAR 2022, COATINGS, 12, 348, DOI: 10.3390/coatings12030348

Group IV quantum dots (QDs) in HfO2 are attractive for non-volatile memories (NVMs) due to complementary metal-oxide semiconductor (CMOS) compatibility. Besides the role of charge storage centers, SiGeSn QDs have the advantage of a low thermal budget for formation, because Sn presence decreases crystallization temperature, while Si ensures higher thermal stability. In this paper, we prepare MOS capacitors based on 3-layer stacks of gate HfO2/floating gate of SiGeSn QDs in HfO2/tunnel HfO2/p-Si obtained by magnetron sputtering deposition followed by rapid thermal annealing (RTA) for nanocrystallization. Crystalline structure, morphology, and composition studies by cross-section transmission electron microscopy and X-ray diffraction correlated with Raman spectroscopy and C-V measurements are carried out for understanding RTA temperature effects on charge storage behavior. 3-layer morphology and Sn content trends with RTA temperature are explained by the strongly temperature-dependent Sn segregation and diffusion processes. We show that the memory properties measured on Al/3-layer stack/p-Si/Al capacitors are controlled by SiGeSn-related trapping states (deep electronic levels) and low-ordering clusters for RTA at 325-450 degrees C, and by crystalline SiGeSn QDs for 520 and 530 degrees C RTA. Specific to the structures annealed at 520 and 530 degrees C is the formation of two kinds of crystalline SiGeSn QDs, i.e., QDs with low Sn content (2 at.%) that are positioned inside the floating gate, and QDs with high Sn content (up to 12.5 at.%) located at the interface of floating gate with adjacent HfO2 layers. The presence of Sn in the SiGe intermediate layer decreases the SiGe crystallization temperature and induces the easier crystallization of the diamond structure in comparison with 3-layer stacks with Ge-HfO2 intermediate layer. High frequency-independent memory windows of 3-4 V and stored electron densities of 1-2 x 10(13) electrons/cm(2) are achieved.

26. Fracture peculiarities and high-temperature strength of bulk polycrystalline boron

Authors: Demirskyi, D; Badica, P; Kuncser, A; Vasylkiv, O

Published: MAR 2022, MATERIALIA, 21, 101346, DOI: 10.1016/j.mtla.2022.101346

We report the mechanical behavior of a bulk boron ceramic prepared by spark plasma sintering of commercially available beta-boron powder. In order to fabricate polycrystalline boron ceramic, we used a protective tantalum foil reacted with carbon from the graphite die or graphite foil forming a thin layer of TaB2 and TaC covering the boron specimen. This is the first study to show the high-temperature flexural strength, toughness, and Young's moduli of boron up to 1400 degrees C. At 1600 degrees C and above, boron will react with testing environment forming an outer shell. The flexural strength and fracture toughness at room temperature reached an average of 340 MPa and 4.1 MPa m (1/2) , respectively. Despite showing clear signs of plastic deformation on the strain-stress curves, the yield strength of the monolithic boron ceramic exceed 1 GPa at 1200 degrees C. It was determined that fracture at elevated temperatures follows a quasi-transgranular mechanism, where the sub-grains of the boron fracture as plate-like structures. An interpretation for the observed fracture behavior was proposed.

27. Progress and perspective on different strategies to achieve wake-up-free ferroelectric hafnia and zirconia-based thin films

Authors: Silva, JPB; Sekhar, KC; Negrea, RF; MacManus-Driscoll, JL; Pintilie, L

Published: MAR 2022, APPLIED MATERIALS TODAY, 26, 101394, DOI: 10.1016/j.apmt.2022.101394

In the last decade orthorhombic hafnia and zirconia films have attracted tremendous attention arising from the discovery of ferroelectricity at the nanoscale. However, an initial wake-up pre-cycling is usually needed to achieve a ferroelectric behaviour in these films. Recently, different strategies, such as microstructure tailoring, defect, bulk and interface engineering, doping, NH3 plasma treatment and epitaxial growth, have been employed to obtain wake-up free orthorhombic ferroelectric hafnia and zirconia films. In this work we review recent developments in obtaining polar hafnia and zirconia-based thin films without the need of any wake-up cycling. In particular, we discuss the rhombohedral phase of hafnia/ zirconia, which under a constrained environment exhibits wake-up-free ferroelectric behaviour. This phase could have a strong impact on the current investigations of ferroelectric binary oxide materials and pave the way toward exploiting ferroelectric behaviour for next-generation memory and logic gate applications. Crown Copyright (c) 2022 Published by Elsevier Ltd. All rights reserved.

28. Increasing Permittivity and Mechanical Harvesting Response of PVDF-Based Flexible Composites by Using Ag Nanoparticles onto BaTiO3 Nanofillers

Authors: Horchidan, N; Ciomaga, CE; Curecheriu, LP; Stoian, G; Botea, M; Florea, M; Maraloiu, VA; Pintilie, L; Tufescu, FM; Tiron, V; Rotaru, A; Mitoseriu, L

Published: MAR 2022, NANOMATERIALS, 12, 934, DOI: 10.3390/nano12060934

The role of Ag addition on the structural, dielectric, and mechanical harvesting response of 20%(xAg - (1 - x)BaTiO3) - 80%PVDF (x = 0, 2, 5, 7 and 27 vol.%) flexible composites is investigated. The inorganic fillers were realized by precipitating fine (similar to 3 nm) silver nanoparticles onto BaTiO3 nanoparticles (similar to 60 nm average size). The hybrid admixtures with a total filling factor of 20 vol.% were embedded into the PVDF matrix. The presence of filler enhances the amount of beta-PVDF polar phase and the BaTiO3 filler induces an increase of the permittivity from 11 to 18 (1 kHz) in the flexible composites. The addition of increasing amounts of Ag is further beneficial for permittivity increase; with the maximum amount (x = 27 vol.%), permittivity is three times larger than in pure PVDF (epsilon(r) similar to 33 at 1 kHz) with a similar level of tangent losses. This result is due to the local field enhancement in the regions close to the filler-PVDF interfaces which are additionally intensified by the presence of silver nanoparticles. The metallic addition is also beneficial for the mechanical harvesting ability of such composites: the amplitude of the maximum piezoelectric-triboelectric combined output collected in open circuit conditions increases from 0.2 V/cm(2) (PVDF) to 30 V/cm(2) for x = 27 vol.% Ag in a capacitive configuration. The role of ferroelectric and metallic nanoparticles on the increasing mechanical-electric conversion response is also been explained.

29. Mechanochemical synthesis and Mossbauer characterization of neodymium oxide-hematite magnetic ceramic nanoparticles: Phase sequence and recoilless fraction

Authors: Sorescu, M; Diamandescu, L; Sofronie, M; Pratt, C; Jubeck, J

Published: FEB 1 2022, MATERIALS CHEMISTRY AND PHYSICS, 277, 125511, DOI: 10.1016/j.matchemphys.2021.125511

Magnetic ceramic nanoparticles system xNd(2)O(3)-(1-x)alpha-Fe2O3 (x = 0.1, 0.3 and 0.5) was synthesized by mechanochemical activation starting from hematite and neodymium oxide precursors and characterized by X-ray diffraction (XRD) and Mossbauer spectroscopy. Rietveld refinement of XRD data evidenced the formation of neodymium orthoferrite NdFeO3 as an end-product with a particle size of about 22 nm, determined using the Scherrer method for x = 0.5. The Mossbauer spectra were typically analyzed considering 2 sextets, corresponding to hematite and neodymium orthoferrite and a doublet, representing superparamagnetic particles (SPM). The recoilless fractions were determined using our dual absorber method and were found consistent with a decrease in particle size as consequence of the ball milling process performed.

30. Soft Chemistry Synthesis and Characterization of CoFe1.8RE0.2O4 (RE3+ = Tb3+, Er3+) Ferrite

Authors: Gingasu, D; Mindru, I; Ianculescu, AC; Diamandescu, L; Surdu, VA; Marinescu, G; Bartha, C; Preda, S; Popa, M; Chifiriuc, MC

Published: FEB 2022, MAGNETOCHEMISTRY, 8, 12, DOI: 10.3390/magnetochemistry8020012

Nanosized CoFe1.8RE0.2O4 (RE3+ = Tb3+, Er3+) ferrites were obtained through wet ferritization method. These ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM/HR-TEM), Fourier transform infrared spectroscopy (FTIR), Mossbauer spectroscopy and magnetic measurements. The XRD results revealed that the average crystallite size is 5.77 nm for CoFe1.8Tb0.2O4 and 6.42 nm for CoFe1.8Er0.2O4. Distribution of metal cations in the spinel structure estimated from X-ray diffraction data showed that the Tb3+ and Er3+ ions occupy the octahedral sites. TEM images indicated the presence of polyhedral particles with average size 5.91 nm for CoFe1.8Tb0.2O4 and 6.80 nm for CoFe1.8Er0.2O4. Room temperature Mossbauer spectra exhibit typical nanoscaled cobalt ferrite spectra in good agreement with XRD and TEM data. The saturation magnetization value (M-s) is 60 emu/g for CoFe1.8Tb0.2O4 and 80 emu/g for CoFe1.8Er0.2O4. CoFe1.8RE0.2O4 nanoparticles showed similar antimicrobial efficacy against the five tested microbial strains, both in planktonic and biofilm state. The results highlight the promising potential of these types of nanoparticles for the development of novel anti-biofilm agents and materials.

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