National Institute Of Materials Physics - Romania

Publications

5781 articles found

311. Understanding the Photocatalytic Activity of Sodium Hexatitanate Nanoparticles for Pollutants Degradation: A Spectroscopic Insight

Authors: Teixeira, ARFA; de Oliveira, ALM; Neatu, F; Kuncser, AC; Galca, AC; Rostas, AM; dos Santos, IMG

Published: MAR 2023, ACS APPLIED NANO MATERIALS, DOI: 10.1021/acsanm.2c05577

Sodium hexatitanate (Na2Ti6O13) nanoparticles have been synthesized by the hydrothermal method with microwave and conven-tional heating, after which their photocatalytic properties toward an azo dye pollutant degradation have been investigated. Insights into the dynamics and reactivity of the species involved in the photocatalytic mechanism of the (Na2Ti6O13) samples were precisely investigated, for the first time, by X-band electron paramagnetic resonance (EPR) spectroscopy under different experimental conditions. X-ray diffraction structural analysis revealed that all samples crystallized in a monoclinic C2/m structure, with different short-range structural order according to the employed heating, as indicated by Raman. Field-emission scanning electron microscopy and transmission electron microscopy results revealed the formation of rod-and fiber-like nanoparticles with different diameters and lengths. EPR measurements indicated the presence of different Ti3+ point defects and F centers in the samples. X-ray photoelectron spectroscopy analysis proved the presence of oxygen-related defects, but no Ti3+ was detected on the surface. Spin trapping experiments monitored the generation of hydroxyl (OH center dot) radicals over UV-irradiation time. Various parameters contribute to the photocatalytic activity of the samples; however, the type of defect and particle morphology appeared as key factors for enhanced efficiency. Our study provides significant information about paramagnetic defects in Na2Ti6O13 materials and their role in photocatalysis to design other Ti-based photocatalysts.

312. Fermiology of Chiral Cadmium Diarsenide CdAs2, a Candidate for Hosting Kramers-Weyl Fermions

Authors: Mazzola, F; Zhang, YX; Olszowska, N; Rosmus, M; D'Olimpio, G; Istrate, MC; Politano, GG; Vobornik, I; Sankar, R; Ghica, C; Gao, JF; Politano, A

Published: 2023 MAR 23 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, DOI: 10.1021/acs.jpclett.3c00005

Nonmagnetic chiral crystals are a new class of systems hosting Kramers-Weyl Fermions, arising from the combination of structural chirality, spin- orbit coupling (SOC), and time-reversal symmetry. These materials exhibit nontrivial Fermi surfaces with SOC-induced Chern gaps over a wide energy range, leading to exotic transport and optical properties. In this study, we investigate the electronic structure and transport properties of CdAs2, a newly reported chiral material. We use synchrotron-based angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT) to determine the Fermiology of the (110)-terminated CdAs2 crystal. Our results, together with complementary magnetotransport measurements, suggest that CdAs2 is a promising candidate for novel topological properties protected by the structural chirality of the system. Our work sheds light on the details of the Fermi surface and topology for this chiral quantum material, providing useful information for engineering novel spintronic and optical devices based on quantized chiral charges, negative longitudinal magnetoresistance, and nontrivial Chern numbers.

313. Control of spectral, topological and charge transport properties of graphene via circularly polarized light and magnetic field

Authors: Pena, A

Published: MAR 2023, RESULTS IN PHYSICS, 46, 106257, DOI: 10.1016/j.rinp.2023.106257

In this paper, we present a theoretical perspective regarding the interaction of graphene with circularly polarized light and magnetic field, from the topological insulators point of view. We analyze how these two external fields affect the spectral, topological and transport properties of graphene and correlate the findings in order to explain in a fundamental and unified way the emerging topological phase transitions. In this respect, in the first step we introduce a model for interaction and charge transport. Then, based on the derived theory, we present numerical results aimed to explain the underlying processes which give graphene topological properties. The central point is represented by the time-reversal symmetry breaking which generates chiral edge states, namely electronic states localized at the edges of the system, having opposite velocity directions. We find that the light frequency, intensity and polarization state drastically influence the formation of the chiral edge states and their number. We correlate this effect with quantum Hall transport, analyzing the resulting transversal (Hall) resistance plateaus and their values. Moreover, if a supplementary magnetic field driving is applied, there emerge intricate topological phase transitions, characterized by introducing or removing specific Hall resistance plateaus.

314. Defect characterization studies on irradiated boron-doped silicon pad diodes and Low Gain Avalanche Detectors

Authors: Himmerlich, A; Castello-Mor, N; Rivera, EC; Gurimskaya, Y; Maulerova-Subert, V; Moll, M; Pintilie, I; Fretwurst, E; Liao, C; Schwandt, J

Published: MAR 2023, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 1048, 167977, DOI: 10.1016/j.nima.2022.167977

High-energy physics detectors with internal charge multiplication, like Low Gain Avalanche Detectors (LGADs), that will be used for fast timing in the High Luminosity LHC experiments, have to exhibit a significant radiation tolerance. In this context, the impact of radiation on the highly boron-doped gain layer is of particular interest, since due to the so-called Acceptor Removal Effect (ARE) a radiation-induced deactivation of active boron dopants takes place, that is causing a progressive loss in the gain with increasing irradiation level. In this paper we present defect-spectroscopy measurements (Deep-Level Transient Spectroscopy and Thermally Stimulated Current technique) on neutron, proton and electron irradiated p-type silicon pad diodes of different resistivity as well as LGADs neutron irradiated at fluences up to 1 x 1015 neq/cm2. We show that compared to silicon pad diodes the determination of LGAD defect introduction rates is less straightforward as they are strongly influenced by the impact of the gain layer. The measured gain layer capacitance has a strong frequency and temperature dependence which makes DLTS measurements challenging to perform with results difficult to interpret. With the TSC technique the defects formed in the LGADs are nicely observed and can be compared to the defects formed in the silicon pad diodes. However, the exact assignment of defects to the gain layer or bulk region remains challenging and the charge amplification effect of the LGADs impacts the exact determination of defect concentrations. We also demonstrate that, depending on the TSC measurement conditions, defect induced internal electric fields are built up in the irradiated LGADs which impact the signal current.

315. Macrocyclic Compounds: Metal Oxide Particles Nanocomposite Thin Films Deposited by MAPLE

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

Published: MAR 2023, MATERIALS, 16, 2480, DOI: 10.3390/ma16062480

Nanocomposite films based on macrocyclic compounds (zinc phthalocyanine (ZnPc) and 5,10,15,20-tetra(4-pyridyl) 21H,23H-porphyrin (TPyP)) and metal oxide nanoparticles (ZnO or CuO) were deposited by matrix-assisted pulsed laser evaporation (MAPLE). 1,4-dioxane was used as a solvent in the preparation of MAPLE targets that favor the deposition of films with a low roughness, which is a key feature for their integration in structures for optoelectronic applications. The influence of the addition of ZnO nanoparticles (similar to 20 nm in size) or CuO nanoparticles (similar to 5 nm in size) in the ZnPc:TPyP mixture and the impact of the added metal oxide amount on the properties of the obtained composite films were evaluated in comparison to a reference layer based only on an organic blend. Thus, in the case of nanocomposite films, the vibrational fingerprints of both organic compounds were identified in the infrared spectra, their specific strong absorption bands were observed in the UV-Vis spectra, and a quenching of the TPyP emission band was visible in the photoluminescence spectra. The morphological analysis evidenced agglomerated particles on the composite film surface, but their presence has no significant impact on the roughness of the MAPLE deposited layers. The current density-voltage (J-V) characteristics of the structures based on the nanocomposite films deposited by MAPLE revealed the critical role played by the layer composition and component ratio, an improvement in the electrical parameters values being achieved only for the films with a certain type and optimum amount of metal oxide nanoparticles.

316. Unravelling the role of nickel incorporation on the physical properties of CuO thin films deposited by spray pyrolysis and theoretical analysis of nanostructured ZnO/Ni:CuO-based heterojunction solar cells

Authors: Daoudi, O; Jellal, I; Haddout, A; Zimou, J; EL Khouja, O; Nouneh, K; Lharch, M; Fahoume, M; Bendoumou, A

Published: MAR 2023, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 34, 819, DOI: 10.1007/s10854-023-10167-6

Whereas solar photovoltaic cells are promising for proper power production, their wide deployment is hampered by production costs, material availability and toxicity. One of these materials is CuO, which has great chemical stability as well as interesting physical properties, including a direct band gap, a high absorption coefficient, and p-type conductivity. These properties indicate CuO as an exciting semiconducting material to use an absorber layer in thin films solar cells. For this specific reason, this paper focuses on the synthesis of pristine and Ni-incorporated CuO thin films by spray pyrolysis process. Several techniques such as; X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDX) and UV-Visible spectroscopy have been employed to characterize the synthesized samples. The XRD analysis indicated the formation of polycrystalline CuO thin films and the average crystallite size was decreased from 35 to 20 nm for the samples with x = 0-8 at%, respectively. Furthermore, Raman spectroscopy also confirms the single-phase formation of CuO films. The SEM images demonstrated that the incorporation of Ni in the CuO matrix improved the films surface. The EDX analysis and the elemental mapping belay the homogeneous distribution of the elements. Moreover, UV-Visible spectroscopy has shown a significant expansion in optical energy band gap from 1.45 to 1.53 eV with an increase of Ni concentration. On the other hand, to investigate the impact of Ni-incorporated CuO on nanostructure Ni:CuO/ZnO-NRs heterojunction solar cell performance, SCAPS-1D software is used. It has been found that, 8% Ni:CuO layer has been revealed as better for nanostructured solar cells. The results of this contribution will provide some vital guidelines for fabricating higher-efficiency solar cells.

317. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO2 Thin Films

Authors: Lenzi, V; Silva, JPB; Smid, B; Matolin, V; Istrate, CM; Ghica, C; MacManus-Driscoll, JL; Marques, L

Published: MAR 2023, ENERGY & ENVIRONMENTAL MATERIALS, DOI: 10.1002/eem2.12500

Rhombohedral phase HfxZr1-xO2 (HZO, x from 0 to 1) films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling, as is normally the case for the more commonly studied orthorhombic phase. However, a large spontaneous polarization observed in rhombohedral films is not fully understood, and there are also large discrepancies between experimental and theoretical predictions. In this work, in rhombohedral ZrO2 thin films, we show that oxygen vacancies are not only a key factor for stabilizing the phase, but they are also a source of ferroelectric polarization in the films. This is shown experimentally through the investigation of the structural properties, chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature (400 degrees C) in an oxygen environment to reduce the V-O concentration compared. The experimental work is supported by density functional theory (DFT) calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO2 films. The DFT calculations also show that V-O contribute to the ferroelectric polarization. Our findings reveal the importance of V-O for stabilizing rhombohedral ZrO2 thin films with superior ferroelectric properties.

318. Surface species of nematic mixture E7 in hard confinement: spectroscopic investigations cannot distinguish among the E7 components interacting with the support surface

Authors: Frunza, L; Zgura, I; Ganea, CP; Loiko, VA; Manaila-Maximean, D

Published: MAR 2023, LIQUID CRYSTALS, DOI: 10.1080/02678292.2023.2182379

Properties of surface species of the nematic mixture E7 in contact with inorganic oxides (especially those containing more or less aluminium ions) are in detail investigated by infrared spectroscopy and thermogravimetry. The absorption infrared peaks were decomposed into Gaussian components, the procedure allowing an easier comparison with the behaviour of related composites. We worked at enough small concentrations of the E7 relatively to support this ratio permitting the (partial) elimination of the species belonging to the bulk. Species put here in evidence are species that are hydrogen bonded to the surface of OH groups, molecules randomly oriented on the surface, some species bonded by involvement of pi electrons of the CN group to the aluminium ions, thus implying a strong interaction to the support. Supramolecular assemblies of E7 molecules are thus followed up.

319. Surface species of nematic mixture E7 in hard confinement: spectroscopic investigations cannot distinguish among the E7 components interacting with the support surface

Authors: Frunza, L; Zgura, I; Ganea, CP; Loiko, VA; Manaila-Maximean, D

Published: 2023 MAR 1 2023, LIQUID CRYSTALS, DOI: 10.1080/02678292.2023.2182379

320. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing

Authors: Crema, APS; Istrate, MC; Silva, A; Lenzi, V; Domingues, L; Hill, MO; Teodorescu, VS; Ghica, C; Gomes, MJM; Pereira, M; Marques, L; MacManus-Driscoll, JL; Silva, JPB

Published: MAR 2023, ADVANCED SCIENCE, DOI: 10.1002/advs.202207390

A new approach for the stabilization of the ferroelectric orthorhombic ZrO2 films is demonstrated through nanosecond laser annealing (NLA) of as-deposited Si/SiOx/W(14 nm)/ZrO2(8 nm)/W(22 nm), grown by ion beam sputtering at low temperatures. The NLA process optimization is guided by COMSOL multiphysics simulations. The films annealed under the optimized conditions reveal the presence of the orthorhombic phase, as confirmed by X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of 12.8 mu C cm(-2), remnant polarization of 12.7 mu C cm(-2) and coercive field of 1.2 MV cm(-1). The films exhibit a wake-up effect that is attributed to the migration of point defects, such as oxygen vacancies, and/or a transition from nonferroelectric (monoclinic and tetragonal phase) to the ferroelectric orthorhombic phase. The capacitors demonstrate a stable polarization with an endurance of 6.0 x 10(5) cycles, demonstrating the potential of the NLA process for the fabrication of ferroelectric memory devices with high polarization, low coercive field, and high cycling stability.