National Institute Of Materials Physics - Romania

Publications

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873 articles found

1. Up-Conversion Luminescence and Magnetic Properties of Multifunctional Er3+/Yb3+-Doped SiO2-GdF3/LiGdF4 Glass Ceramics

Authors: Secu, C; Bartha, C; Radu, C; Secu, M

Published: JAN 2023, MAGNETOCHEMISTRY, 9, 11, DOI: 10.3390/magnetochemistry9010011

Glassy nanocomposites containing Yb3+/Er3+-doped GdF3 and LiGdF4 nanocrystals have been prepared by controlled crystallization of the xerogel and the structural, up-conversion luminescence, and magnetic properties were analyzed and discussed. Structural and morphological analysis showed uniform distribution of both GdF3 and LiGdF4 nanocrystals (tens of nm size), embedded in silica glass matrix as the result of thermal decomposition of the trifluoracetates, revealed as a strong exothermic peak at about 300 degrees C; the Li-ions co-doping showed a strong influence on the GdF3 and LiGdF4 nanocrystalline fraction. The energy dispersive spectrometry mapping showed Gd, F and Yb, Er within the nanocrystals but not in the silica glass matrix. X-ray diffraction pattern analysis indicated the crystalline lattice distortion consistent with the Yb/Er incorporation in both fluoride nanocrystals. The "green" ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and "red" (F-4(9/2)-> I-4(15/2)) up-conversion luminescences at 525, 545, and 660 nm observed under 980 nm laser light pumping were assigned to the Er3+ ions deexcitation through a two-photon process. The magnetic properties of the nanocomposite are strongly temperature dependent. The magnetization hysteresis loops show a ferromagnetic behavior at low temperatures (5K) related to the rare-earth ions contribution and the saturation magnetization of 39 emu/g. At 300 K a paramagnetic behavior was observed that was ascribed to the non-interacting localized nature of the magnetic moment of the rare-earth ions. Hence, such novel, multifunctional magnetic and optical materials can allow the intertwining between magnetism and photonics and might offer new opportunities for new magneto-optical device development.

2. Characterization of defect structures in nanoscaled W-doped TiO2 tested as supercapacitor electrode materials

Authors: Ammar, AU; Stefan, M; Macavei, SG; Tripon, S; Pana, O; Leostean, C; Vlaicu, ID; Rostas, AM; Erdem, E

Published: JAN 2023, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 34, 8, DOI: 10.1007/s10854-022-09540-8

In this work, Tungsten(W)-doped TiO2 nanoparticles were synthesized using the sol-gel method and were used as electrode materials in supercapacitor applications. The structural and morphological properties of the prepared samples were analyzed by means of XRD, STEM, TEM, and XPS. The analysis of the defect centers was carried out using EPR spectroscopy. The electrochemical analysis of the assembled supercapacitor was done using cyclic voltammetry, galvanostatic cycling with potential limitation technique, potentiostatic electrochemical impedance spectroscopy, and voltage-holding experiments. All the presented samples showed paramagnetic defects in the EPR analysis, while 0.5% W-doped TiO2 showed a maximum signal intensity. The supercapacitor performance from the synthesized electrode material showed highly encouraging results. The equivalent series resistance (R-s) value for all the designs showed values under "1 omega,' which reflects high conductivity. As the maximum EPR intensity comes from TiO2 doped with 0.5% W, the supercapacitor performance of this sample was tested with a newly designed five-electrode system. This design showed superior performance compared to any other used designs with a specific capacitance of 25.5 F g(-1), with an energy density of 14.16 Wh kg (-1 )at 302 kW kg (-1).

3. Effects of Solvent Additive and Micro-Patterned Substrate on the Properties of Thin Films Based on P3HT:PC70BM Blends Deposited by MAPLE

Authors: Socol, M; Preda, N; Breazu, C; Petre, G; Stanculescu, A; Stavarache, I; Popescu-Pelin, G; Stochioiu, A; Socol, G; Iftimie, S; Thanner, C; Rasoga, O

Published: JAN 2023, MATERIALS, 16, 144, DOI: 10.3390/ma16010144

Lately, there is a growing interest in organic photovoltaic (OPV) cells due to the organic materials' properties and compatibility with various types of substrates. However, their efficiencies are low relative to the silicon ones; therefore, other ways (i.e., electrode micron/nanostructuring, synthesis of new organic materials, use of additives) to improve their performances are still being sought. In this context, we studied the behavior of the common organic bulk heterojunction (P3HT:PC70BM) deposited by matrix-assisted pulsed laser evaporation (MAPLE) with/without 0.3% of 1,8-diiodooctane (DIO) additive on flat and micro-patterned ITO substrates. The obtained results showed that in the MAPLE process, a small quantity of additive can modify the morphology of the organic films and decrease their roughness. Besides the use of the additive, the micro-patterning of the electrode leads to a greater increase in the absorption of the studied photovoltaic structures. The inferred values of the filling factors for the measured cells in ambient conditions range from 19% for the photovoltaic structures with no additive and without substrate patterning to 27% for the counterpart structures with patterning and a small quantity of additive.

4. Magnetite-Based Nanostructured Coatings Functionalized with Nigella sativa and Dicloxacillin for Improved Wound Dressings

Authors: Dorcioman, G; Hudita, A; Galateanu, B; Craciun, D; Mercioniu, I; Oprea, OC; Negut, I; Grumezescu, V; Grumezescu, AM; Ditu, LM; Holban, AM

Published: JAN 2023, ANTIBIOTICS-BASEL, 12, 59, DOI: 10.3390/antibiotics12010059

In this study, we report the performance improvement of wound dressings by covering them with magnetite-based nanostructured coatings. The magnetite nanoparticles (Fe3O4 NPs) were functionalized with Nigella sativa (N. sativa) powder/essential oil and dicloxacillin and were synthesized as coatings by matrix assisted pulsed laser evaporation (MAPLE). The expected effects of this combination of materials are: (i) to reduce microbial contamination, and (ii) to promote rapid wound healing. The crystalline nature of core/shell Fe3O4 NPs and coatings was determined by X-ray diffraction (XRD). Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) have been coupled to investigate the stability and thermal degradation of core/shell nanoparticle components. The coatings' morphology was examined by scanning electron microscopy (SEM). The distribution of chemical elements and functional groups in the resulting coatings was evidenced by Fourier transform infrared (FTIR) spectrometry. In order to simulate the interaction between wound dressings and epithelial tissues and to evaluate the drug release in time, the samples were immersed in simulated body fluid (SBF) and investigated after different durations of time. The antimicrobial effect was evaluated in planktonic (free-floating) and attached (biofilms) bacteria models. The biocompatibility and regenerative properties of the nanostructured coatings were evaluated in vitro, at cellular, biochemical, and the molecular level. The obtained results show that magnetite-based nanostructured coatings functionalized with N. sativa and dicloxacillin are biocompatible and show an enhanced antimicrobial effect against Gram positive and Gram negative opportunistic bacteria.

5. Silver Nanoparticle Synthesis via Photochemical Reduction with Sodium Citrate

Authors: Pascu, B; Negrea, A; Ciopec, M; Duteanu, N; Negrea, P; Bumm, LA; Grad, O; Nemes, NS; Mihalcea, C; Duda-Seiman, DM

Published: JAN 2023, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 24, 255, DOI: 10.3390/ijms24010255

The aim of this paper is to provide a simple and efficient photoassisted approach to synthesize silver nanoparticles, and to elucidate the role of the key factors (synthesis parameters, such as the concentration of TSC, irradiation time, and UV intensity) that play a major role in the photochemical synthesis of silver nanoparticles using TSC, both as a reducing and stabilizing agent. Concomitantly, we aim to provide an easy way to evaluate the particle size based on Mie theory. One of the key advantages of this method is that the synthesis can be "activated" whenever or wherever silver nanoparticles are needed, by premixing the reactants and irradiating the final solution with UV radiation. UV irradiance was determined by using Keitz's theory. This argument has been verified by premixing the reagents and deposited them in an enclosed space (away from sunlight) at 25 degrees C, then checking them for three days. Nothing happened, unless the sample was directly irradiated by UV light. Further, obtained materials were monitored for 390 days and characterized using scanning electron microscopy, UV-VIS, and transmission electron microscopy.

6. Layered SnSe nanoflakes with anharmonic phonon properties and memristive characteristics

Authors: Buruiana, AT; Bocirnea, AE; Kuncser, AC; Tite, T; Matei, E; Mihai, C; Zawadzka, N; Olkowska-Pucko, K; Kipczak, L; Babinski, A; Molas, MR; Velea, A; Galca, AC

Published: OCT 15 2022, APPLIED SURFACE SCIENCE, 599, 153983, DOI: 10.1016/j.apsusc.2022.153983

Understanding the phonon anharmonicity and temperature-dependent behavior of phonons that affect the thermal transport properties in 2D materials is crucial for developing efficient thermoelectric and memristor devices. SnSe has attracted significant interest because of its potential applications for developing such novel devices. Here, orthorhombic SnSe nanoflakes with a thickness of less than 100 nm and oriented along the [100] crystal axis were obtained using physical vapor transport at atmospheric pressure. Polarization-resolved Raman spectroscopy of SnSe nanoflakes was performed at a temperature of 5 K. Temperature-dependent frequencies and linewidths of Raman modes in tin selenide were fitted according to the anharmonic phonon coupling theory. The results indicate that both two and three order processes are responsible for the phonon decay in tin selenide. The memristive property was confirmed by electrical measurements of SnSe devices. SnSe memristors have an operating current of 10-4 A, similar to other transition-metal dichalcogenide memristors, but are more energy efficient than memristors based on defect migration, with a threshold voltage of 3 V.

7. New superdielectric materials: (1-x) SrFe12O19 - x BNT-BT nanocomposites

Authors: Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A; Smaranda, I; Amarande, L; Cioangher, M; Burdusel, M; Teodorescu, V

Published: OCT 1 2022, PHYSICA B-CONDENSED MATTER, 642, 414139, DOI: 10.1016/j.physb.2022.414139

Novel (1-x) SrFe12O19 - x BNT-BT0.08 (x = 0; 0.5; 0.8; 1) nanocomposites were explored in this study. The samples were produced by sol-gel method and compacted by conventional sintering. The composition, morphology, local structure, dielectric and magnetic properties were investigated by X-ray diffraction, Transmission Electron Microscopy, Impedance Analysis, Mossbauer spectroscopy, and SQUID magnetometry. The desired composition and the presence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. Irregular morphology and large size distributions are evidenced in the electron microscopy micrographs. The reported room temperature dielectric constants in this study are the highest values obtained in multiferroic composites at room temperature: giant dielectric constants (similar to 1.3 x 10(6)) were obtained, relative to 0.13 x 10(4) in BNT-BT. The hyperfine parameters allowed the identification of the Wyckoff positions of the Fe ions corresponding closely to the theoretical case. The hard magnetic character of the SrFe12O19 phase is evidenced from the magnetic measurements. For the first time in multifermic composites, superdielectric characteristics are evidenced at room temperature.

8. Influence of relative humidity on CO2 interaction mechanism for Gd-doped SnO2 with respect to pure SnO2 and Gd2O3

Authors: Ghica, C; Mihalcea, CG; Simion, CE; Vlaicu, ID; Ghica, D; Dinu, IV; Florea, OG; Stanoiu, A

Published: OCT 1 2022, SENSORS AND ACTUATORS B-CHEMICAL, 368, 132130, DOI: 10.1016/j.snb.2022.132130

The paper aims to identify the CO2 interaction mechanism for chemical sensors based on Gd-doped SnO2, SnO2 and Gd2O3 powders deposited as thick sensitive layers. The low reactivity of CO2 conferred by the thermodynamic stability and chemical inertia can be offset by the presence of relative humidity. The sensitive powders were prepared by wet chemical co-precipitation method. The Gd concentration was varied from 1% to 20 at% in order to determine the limit for Gd integration as a doping ion prior to chemical segregation as a secondary phase. Analytical transmission electron microscopy points to a homogeneous Gd doping of the nanostructured SnO2 powders for low doping concentrations and the formation of a nanocomposite based on SnO2 as main phase and cubic Gd2O3 as secondary phase for the highly doped samples. The electrical resistance is either influenced by the density of oxygen vacancies, or is the result of compensation for two opposite behaviours into the SnO2- Gd2O3 nanocomposite structures. The CO2 exposure to humid atmosphere determines distinct behaviours cor-responding to SnO2 and Gd2O3 as constitutive elements. The associated CO2 interaction mechanism is based on simultaneous DC electrical resistance and Contact Potential Difference measurements, which allow decoupling the ionosorption from the dipolar processes, thus highlighting specific chemical interactions on the SnO2 and Gd2O3 surfaces.

9. Tuning the acidity by addition of transition metal to Mn modified hollow silica spheres and their catalytic activity in ethanol dehydration to ethylene

Authors: Florea, M; Bocirnea, A; Neatu, S; Kuncser, AM; Trandafir, MM; Neatu, F

Published: SEP 25 2022, APPLIED CATALYSIS A-GENERAL, 646, 118860, DOI: 10.1016/j.apcata.2022.118860

Due to the currently worldwide petrochemical feedstock shortage, the ethylene synthesis from renewable non-oil sources becomes of high interest. The catalysts were prepared in two steps: (i) formation of spheres containing the carbon-coated Mn core by hydrothermal method, (ii) formation of the Si-Zr oxide shell by sol-gel method. The prepared catalysts were characterized by N2 physisorption, SEM-EDX, XRD, XPS, and NH3-TPD. The catalytic results have shown that Fe, Zn or Ni modified Mn core exhibited superior activity compared to the catalysts containing only Mn in the core. With 75% yield and 98% ethanol conversion at 350 degrees C and WHSV of 1.4 h-1, MnNi@SiZr was the best catalyst. These results are due to an increased number of acid sites compared to the other materials and an optimal ratio of weak/medium acid sites. Our findings suggest new lines for developing active and stable catalysts for ethylene synthesis from ethanol.

10. Multifunctional Zn-Doped ITO Sol-Gel Films Deposited on Different Substrates: Application as CO2-Sensing Material

Authors: Gartner, M; Anastasescu, M; Calderon-Moreno, JM; Nicolescu, M; Stroescu, H; Hornoiu, C; Preda, S; Predoana, L; Mitrea, D; Covei, M; Maraloiu, VA; Teodorescu, VS; Moldovan, C; Petrik, P; Zaharescu, M

Published: SEP 2022, NANOMATERIALS, 12, 3244, DOI: 10.3390/nano12183244

Undoped and Zn-doped ITO (ITO:Zn) multifunctional thin films were successfully synthesized using the sol-gel and dipping method on three different types of substrates (glass, SiO2/glass, and Si). The effect of Zn doping on the optoelectronic, microstructural, and gas-sensing properties of the films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE), Raman spectroscopy, Hall effect measurements (HE), and gas testing. The results showed that the optical constants, the transmission, and the carrier numbers were correlated with the substrate type and with the microstructure and the thickness of the films. The Raman study showed the formation of ITO films and the incorporation of Zn in the doped film (ITO:Zn), which was confirmed by EDX analysis. The potential use of the multifunctional sol-gel ITO and ITO:Zn thin films was proven for TCO applications or gas-sensing experiments toward CO2. The Nyquist plots and equivalent circuit for fitting the experimental data were provided. The best electrical response of the sensor in CO2 atmosphere was found at 150 degrees C, with activation energy of around 0.31 eV.