National Institute Of Materials Physics - Romania

Publications

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887 articles found

1. Surface properties, chemical reactivity, and ambient stability of cadmium diarsenide CdAs2, a topological chiral material hosting Kramers-Weyl fermions

Authors: Zhang, YX; D'Olimpio, G; Bondino, F; Nappini, S; Istrate, MC; Sankar, R; Ghica, C; Ottaviano, L; Gao, JF; Politano, A

Published: JUL 15 2023, APPLIED SURFACE SCIENCE, 625, 157132, DOI: 10.1016/j.apsusc.2023.157132

Chiral materials showing Kramers-Weyl fermions represent a suitable platform for quantum technology, i.e., for engineering quantum solenoids, spin-torque devices, polarization-sensitive photodetectors based on quantized circular photogalvanic effect, etc. Accordingly, the stability of this class of materials in oxidative environments, such as the ambient atmosphere, should be carefully investigated to succeed in technology transfer. Here, taking as case-study example the well-recognized topological chiral system cadmium diarsenide (CdAs2), we assess its chemical reactivity towards ambient gases (oxygen and water) and air by density functional theory and experiments. The surface of CdAs2 evolves into an oxide skin, but its thickness remains nanometric even after one year in air, as directly imaged by high-resolution transmission electron microscopy. Accordingly, it is evident that future quantum devices based on Kramers-Weyl fermions could be stable in air, as the oxide layer formed on chiral quantum materials only represents a native oxide, which actually protects bulk features, including Kramers-Weyl fermions (correlated to bulk band structure), from degradation in air.

2. A comparative overview of MXenes and metal oxides as cocatalysts in clean energy production through photocatalysis

Authors: Nair, MM; Iacoban, AC; Neatu, F; Florea, M; Neatu, S

Published: JUN 20 2023, JOURNAL OF MATERIALS CHEMISTRY A, 11, DOI: 10.1039/d2ta08983a

Photocatalytic conversion of H2O, CO2 and N-2 represents one promising approach to harvest and store solar energy, for which efficient visible light responsive semiconductors are inevitable. Often, the presence of a small amount of an additional component called a "cocatalyst", is required to synergistically enhance the performance of the photocatalyst. Tremendous efforts were made in the past to identify inexpensive materials to be used as cocatalysts, for which metal oxides (MOs) are one of the traditional choices. Among alternative categories of materials investigated, the recently discovered MXenes display enormous potential owing to their unique 2D layered structure, tuneable composition, abundant surface functionalities and superior electronic conductivity. Specifically, MOs and MXenes encompass a variety of distinct as well as analogous characteristics that allows them to be tailored to different extents. Unfortunately, a comprehensive overview covering the synthetic, structural and photocatalytic aspects of MOs and MXenes is not available as of now. Herein, we intend to summarize the progress achieved so far in these two families of materials to be used as cocatalysts for the photoconversion of H2O, CO2 and N-2. Followed by a general introduction, we briefly outline the fundamental principles and the role of cocatalysts in photocatalytic reactions. A discussion regarding the use of MOs and MXenes as cocatalysts for the conversion of H2O, CO2 and N-2 is then provided in separate sections. Critical assessment regarding structure and morphology control, surface properties and stability concerns can not only help to recognize the challenges that limit further advancement, but can also highlight the future research directions of these materials for the effective transformation of H2O, CO2 and N-2.

3. Solution-processed In2Se3 nanosheets for ultrasensitive and highly selective NO2 gas sensors

Authors: D'Olimpio, G; Galstyan, V; Ghica, C; Vorokhta, M; Istrate, MC; Kuo, CN; Lue, CS; Boukhvalov, DW; Comini, E; Politano, A

Published: JUN 13 2023, JOURNAL OF MATERIALS CHEMISTRY A, 11, DOI: 10.1039/d3ta01390a

In this work, we demonstrate that solution-processed In2Se3 nanosheets exhibit exceptional selectivity and sensitivity to NO2 gas, making them a promising candidate for gas detection systems. Theoretical simulations and surface-science experiments reveal the unique surface properties of In2Se3 nanosheets, which prevent physisorption of oxygen, carbon monoxide, and carbon dioxide, making them remarkably stable towards oxidation and CO-poisoning. Moreover, we show that NO2 molecules adsorb stably on In2Se3 nanosheets, particularly on Se vacancies, even at high temperatures. The coadsorption of water further enhances NO2 sticking on the In2Se3 surface, making it an ideal material for gas sensing applications in humid and harsh environments. The fabricated In2Se3 gas sensors exhibit excellent and reversible sensing response to NO2 gas, with a limit of detection of 5 ppb at 300 degrees C, and a highly selective response to NO2 compared to other gases and volatile organic compounds. Our sensors outperform other two-dimensional (2D) semiconductors, metal oxides, and their heterostructures, thanks to the unique surface properties of In2Se3 nanosheets. Importantly, the number of layers and termination of the surface almost have no impact on the sensing performance of In2Se3, which is advantageous for practical applications. The high sensitivity, selectivity, and stability of In2Se3 nanosheets make them an exciting platform for the fabrication of high-performance gas sensors, particularly in harsh environments, such as industrial settings or outdoor monitoring. Moreover, our solution processing approach enables scalable production of the sensors. Additionally, their unique surface properties make them an attractive candidate for developing complex composite nanostructures with tailored gas sensing characteristics for various applications.

4. Phytochemical Synthesis of Silver Nanoparticles and Their Antimicrobial Investigation on Cotton and Wool Textiles

Authors: Lite, MC; Constantinescu, R; Tanasescu, EC; Kuncser, A; Romanitan, C; Mihaiescu, DE; Lacatusu, I; Badea, N

Published: MAY 24 2023, MATERIALS, 16, 3924, DOI: 10.3390/ma16113924

The use of bio-based reagents for silver nanoparticle (AgNP) production has gained much attention among researchers as it has paved the way for environmentally friendly approaches at low cost for synthesizing nanomaterials while maintaining their properties. In this study, Stellaria media aqueous extract was used for silver nanoparticle phyto-synthesis, and the resulting treatment was applied to textile fabrics to test its antimicrobial properties against bacteria and fungi strains. The chromatic effect was also established by determining the L*a*b* parameters. For optimizing the synthesis, different ratios of extract to silver precursor were tested using UV-Vis spectroscopy to observe the SPR-specific band. Moreover, the AgNP dispersions were tested for their antioxidant properties using chemiluminescence and TEAC methods, and the phenolic content was evaluated by the Folin-Ciocalteu method. For the optimal ratio, values of average size, 50.11 +/- 3.25 nm, zeta potential, 27.10 +/- 2.16 mV, and polydispersity index, 0.209, were obtained via the DLS technique and zeta potential measurements. AgNPs were further characterized by EDX and XRD techniques to confirm their formation and by microscopic techniques to evaluate their morphology. TEM measurements revealed cvasi-spherical particles with sizes in the range of 10-30 nm, while SEM images confirmed their uniform distribution on the textile fiber surface.

5. Titania nanoparticles for photocatalytic degradation of ethanol under simulated solar light

Authors: Goncearenco, E; Morjan, IP; Fleaca, CT; Dumitrache, F; Dutu, E; Scarisoreanu, M; Teodorescu, VS; Sandulescu, A; Anastasescu, C; Balint, I

Published: MAY 22 2023, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 14, DOI: 10.3762/bjnano.14.51

TiO2 nanoparticles were synthesized by laser pyrolysis from TiCl4 vapor in air in the presence of ethylene as sensitizer at different working pressures (250-850 mbar) with and without further calcination at 450 degrees C. The obtained powders were analyzed by energydispersive X-ray spectroscopy, X- ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy. Also, specific surface area and photoluminescence with optical absorbance were evaluated. By varying the synthesis parameters (especially the working pressure), different TiO2 nanopowders were obtained, whose photodegradation properties were tested compared to a commercial Degussa P25 sample. Two series of samples were obtained. Series "a" includes thermally treated TiO2 nanoparticles (to remove impurities) that have different proportions of the anatase phase (41.12-90.74%) mixed with rutile and small crystallite sizes of 11-22 nm. Series "b" series represents nanoparticles with high purity, which did not require thermal treatment after synthesis (ca. 1 atom % of impurities). These nanoparticles show an increased anatase phase content (77.33-87.42%) and crystallite sizes of 23-45 nm. The TEM images showed that in both series small crystallites form spheroidal nanoparticles with dimensions of 40-80 nm, whose number increases with increasing the working pressure. The photocatalytic properties have been investigated regarding the photodegradation of ethanol vapors in Ar with 0.3% O2 using P25 powder as reference under simulated solar light. During the irradiation H-2 gas production has been detected for the samples from series "b", whereas the CO2 evolution was observed for all samples from series "a".

6. Cost-effective, high-performance Ni3Sn4 electrocatalysts for methanol oxidation reaction in acidic environments

Authors: Boukhvalov, DW; D'Olimpio, G; Liu, JZ; Ghica, C; Istrate, MC; Kuo, CN; Politano, GG; Lue, CS; Torelli, P; Zhang, LX; Politano, A

Published: MAY 16 2023, CHEMICAL COMMUNICATIONS, 59, DOI: 10.1039/d3cc01623d

Methanol (CH3OH) oxidation offers a promising avenue for transitioning to clean energy, particularly in the field of direct methanol fuel cells (DMFCs). However, the development of efficient and cost-effective catalysts for the methanol oxidation reaction (MOR) remains a critical challenge. Herein, we report the exceptional electrocatalytic activity and stability of Ni3Sn4 toward MOR in acidic media, achieving a performance comparable to that of commercial Pt/C catalysts. Our catalyst design incorporates Earth-abundant Ni and Sn elements, resulting in a material that is 1800 times more cost-effective than Pt/C. Density functional theory (DFT) modeling substantiates our experimental findings, shedding light on the favorable reaction mechanisms and kinetics on the Ni3Sn4 surface. Additionally, the as-synthesized Ni3Sn4 electrocatalyst demonstrates commendable durability, maintaining its electrocatalytic activity even after prolonged exposure to harsh acidic conditions.

7. Solution-processed In2Se3 nanosheets for ultrasensitive and highly selective NO2 gas sensors

Authors: D'Olimpio, G; Galstyan, V; Ghica, C; Vorokhta, M; Istrate, MC; Kuo, CN; Lue, CS; Boukhvalov, DW; Comini, E; Politano, A

Published: 2023 MAY 31 2023, JOURNAL OF MATERIALS CHEMISTRY A, DOI: 10.1039/d3ta01390a

8. 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: MAY 2023, ADVANCED SCIENCE, 10, 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.

9. High bending strength at 1800 degrees C exceeding 1 GPa in TiB2-B4C composite

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

Published: APR 27 2023, SCIENTIFIC REPORTS, 13, DOI: 10.1038/s41598-023-33135-w

High density (99.5%) ceramic composite composed of titanium boride and boron carbide (70/30 vol%) was obtained by spark plasma sintering and was tested by 3-point bending test in Ar atmosphere at 1800 degrees C. Bending strength was high, around 1.1 GPa. The strength-strain curve presents a peculiar shape composed of three regions where elastic and plastic deformations are active with a different weight. Based on transmission electron microscopy observations we propose a process of mechanical energy absorption driven by shear stress in the boron carbide crystals: stacking faults with (1-11) and (011) stacking planes and twins with (1-11) twinning plane rearrange into nano-twins with (10-1) twinning planes, orthogonal but equivalent to the initial ones. This rearrangement mechanism provides in the first instance a plastic signature, but further contributes strengthening.

10. Atomic scale insight into the decomposition of nanocrystalline zinc hydroxynitrate toward ZnO using Mn2+ paramagnetic probes

Authors: Vlaicu, ID; Stefan, M; Radu, C; Culita, DC; Radu, D; Ghica, D

Published: APR 6 2023, FRONTIERS IN CHEMISTRY, 11, 1154219, DOI: 10.3389/fchem.2023.1154219

Layered zinc hydroxynitrate (ZHN), with the chemical formula Zn-5 (OH)(8) (NO3)(2)center dot 2H(2)O, exhibits a range of special properties such as anion-exchange and intercalation capacity, as well as biocompatibility, making it attractive for a large variety of applications in fields from nanotechnology to healthcare and agriculture. In this study nanocrystalline ZHN doped with 1,000 ppm Mn2+ was prepared by two synthesis methods (coprecipitation and solid state reaction) using similar environment-friendly precursors. The complex morpho-structural [X-ray diffraction, scanning and transmission electron microscopy, textural analysis] and spectroscopic [Fourier transform infrared and electron paramagnetic resonance (EPR)] characterization of the two ZHN nanopowders showed similar crystalline structures with Mn2+ ions localized in the nanocrystals volume, but with differences in their morphological and textural characteristics, as well as in the doping efficiency. ZHN obtained by coprecipitation consists of larger nanoplatelets with more than two times larger specific surface area and pore volume, as well as a dopant concentration than in the ZHN sample obtained by solid state reaction. The thermal stability and the on-set of the structural phase transformation have been investigated at atomic scale with high accuracy by EPR, using Mn2+ as paramagnetic probes. The on-set of the ZHN structural phase transformation toward ZnO was observed by EPR to take place at 110 degrees C and 130 degrees C for the samples prepared by coprecipitation and solid state reaction, respectively, evidencing a manganese induced local decrease of the transformation temperature. Our results contribute to the selection of the most appropriate ZHN synthesis method for specific applications and in the development of new green, cost-effective synthesis routes for Mn2+ doped nano-ZnO.