National Institute Of Materials Physics - Romania

Biodegradable templates are sought for targeted antibiotic administration/delivery in bone infections to avoid detrimental reactions during bone regeneration. We investigated two key-aspects in this direction: 1) the optimal antibiotic delineation, with thermal stability equivalent to the temperature involved for templates preparation and 2) the antibacterial templates development by a two-step homogenization process. The selected antibiotic - ampicillin (AMP) was mechanically and then thermally mixed with the prime materials: poly(lactic acid) (PLA) - the polymeric matrix, biogenic bovine bone-derived hydroxyapatite (HA, particles <40 mu m), and graphene nanoplatelets (GnP, micrometric range). For the first time, all materials were used in simultaneous modulated ratios for the synthesis of PLA/AMP (1-5 wt.%)/HA (0-30 wt.%)/GnP (0-3 wt.%) composites. The influence of the concomitant materials modulation was surveyed through several assays. The FTIR-ATR spectroscopy depicted a three-level model of overlapping structures asserting the solid molecular cross-linking between all materials, without structural alterations induced to any material (XRD analysis). The addition of AMP to the PLA matrix caused a slight particle conglomeration, alleviated through GnP addition. The microporous HA particles supported the adhesion to the PLA matrix and promoted the AMP particles' entrapment/attachment. Linked to the enhanced wettability of the composite materials, the phosphate buffered saline solution (PBS) degradation profiles revealed a pronounced burst during the first 14-28 days of incubation and a long-term, low-level process hereafter. Thus, the formation of pores and cavities were signalled along with the HA particles' fragmentation. The released AMP (percentage) pictured an ascending trendline during the 24 h of analysis, at all targeted ratios. The preservation of AMP features at 200 degrees C was endorsed by the strong antibacterial activity of composite materials against Staphylococcus aureus (S. Aureus) growth and the medium response against Escherichia coli (E. Coli) - the higher the drug release, the higher the inhibitory effect on bacteria evolution.

Herein we present a comparative study among different spray-coated nanometric mesoporous electron transporting layers (ETLs) in perovskite solar cells (PSC), namely m-TiO2, 2 , m-SnO2 2 and m-SnO2 2 quantum dots (mSnO2QDs). 2 QDs). The solutions used for deposition were prepared from commercial pastes and colloidal suspensions for m-TiO2 2 and m-SnO2. 2 . For m-SnO2QDs 2 QDs in-house QDs solutions were prepared. The formamidiniummethylamonium-potassium (FAMA@10 K) has been used as light absorber material in the fabricated PSCs. The structural, compositional and morphological studies, correlated with the photovoltaic performance of PSCs, indicate that the m-SnO2 2 QDs layer is the best candidate among the three investigated mesoporous ETLs. Compared with the suspensions used for the other two ETLs, the in-house prepared SnO2 2 QDs solution presents smaller agglomerates of nanoparticles and results in the formation of a thinner, more uniform and compact mesoporous ETL. The FAMA@10 K perovskite deposited on m-SnO2 2 QDs ETL presents a lower roughness, better uniformity and a higher amount of PbI2. 2 . Our work unveils that the SnO2 2 QDs solution can be easily produced in laboratory and when is deposited as mesoporous scaffold in a PSC with FAMA@10 K perovskite, the power conversion efficiency increases up to 14.90 %, being with up to 27 % larger than in the PSCs with m-TiO2 2 and mSnO2 2 ETLs prepared from commercial solutions. By modeling the J-V dynamic hysteresis with more than 90 % match between the calculated and experimental J-V data, for all three types of mesoporous ETLs, the relevant parameters that explain the hysteresis magnitude and account for ionic-induced recombination processes in PSCs were determined.

Featured Application Optoelectronic devices in space missions.Abstract Transparent conductive oxides are essential materials for many optoelectronic applications. For new devices for aerospace and space applications, it is crucial to know how they respond to the space environment. The most important issue in commonly used low-Earth orbits is proton radiation. This study examines the effects of high-energy proton irradiation (226.5 MeV) on thin films of aluminium-doped zinc oxide (AZO) and indium tin oxide (ITO). We use X-ray diffraction and electron microscopy observations to see the changes in the structure and microstructure of the films. The optical properties and homogeneity of the materials are determined by spectrophotometry and spectroscopic ellipsometry (SE). Analysis of the chemical states of the elements with X-ray photoelectron spectroscopy (XPS) gives insight into what proton irradiation changes at the surface of the oxides. All measurements show that ITO is less influenced than AZO. The proton energy and fluence used in this study simulate about a hundred years in low Earth orbit. This research demonstrates that both transparent conductive oxide thin films can function under simulated space conditions, with ITO showing superior resilience. The ITO film was more homogenous in terms of the total thickness measured with SE, had fewer defects and adsorbates present on the surface, as XPS analysis proved, and did not show a difference after irradiation regarding its optical properties, transmission, refractive index, or extinction coefficient.

The present study is focused on describing the influence of the sintering method (fast field-assisted Spark Plasma Sintering vs. conventional sintering) on the functional properties of BaTi0.90Hf0.10O3 ceramics with polymorph superposition around room temperature. Dense ceramics, derived from nanopowders synthesized via Pechini method, with grain size downscaled from 3.7 to 0.07 mu m were prepared using different sintering strategies. XRD data at room temperature revealed the presence of mixtures of dissimilar structural modifications either for the starting nanopowder, as well as for the related ceramics. The Landau-based calculations indicated that different amounts of polymorphs are stable in these ceramics, by considering the grain size reduction and the strain-stress fields produced by the fast sintering method, thus confirming the experimental results of the structural and Raman analyses. By decreasing the average grain size from micro-to nanoscale, a slight decrease of the Curie temperature, accompanied by the increase of the diffuseness of the ferroelectric-to-paraelectric phase transition and the decrease of both the permittivity maxima and the dielectric losses was detected. Both the dielectric response and the ferroelectric P(E) loops indicated a ferroelectric-relaxor crossover as the grain size decreased in the nanometre range. The beneficial effect of the nanostructuring on the energy storage efficiency was also revealed.

Capitalizing on invasive plant species and stopping their aggressive spread might be achieved by using them as a renewable source of useful products such as cellulose. The study aimed to develop new cellulose-based food packaging materials with antioxidant and antimicrobial activity. The cellulose was extracted from the invasive plant species Robinia pseudoacacia pods, crosslinked with citric acid, used as reinforcement for polyvinyl alcohol (PVA) and functionalized with ferulic acid (FA). The obtained materials were characterized by XRD, ATR-FTIR, contact angle and SEM. The materials exhibited low solubility in water and the swelling degree was proportional to the FA content. The FA release from the matrix was assessed by HPLC and the antioxidant profile by CUPRAC, FRAP, and TEAC methods. The obtained materials inhibited the growth of bacteria, yeasts and molds, being especially active on Gram-positive bacteria and yeasts. Overall, the most promising formulation for further developing new packaging materials for products with water activity less than 0.95 was the one with the highest FA content.

Cu2ZnSnSe4 (CZTSe) is a promising material for thin-film solar cells due to its suitable band gap, high absorption coefficient, and composition of earth-abundant and nontoxic elements. In this study, we prepared CZTSe thin films from Cu/SnSe2 and ZnSe stacks using a two-step annealing process. Initially, Cu-Sn-Se (CTSe) films were synthesized by sequential deposition and annealing of Cu and SnSe2 precursors in either a selenium (Se) or tin-selenium (Sn+Se) atmosphere. After the deposition of a ZnSe layer on top of CTSe films, the stack underwent a second annealing process, again in either a Se or Sn+Se atmosphere, resulting in four distinct annealing combinations: Se -> Se, Sn+Se -> Se, Se -> Sn+Se, and Sn+Se -> Sn+Se. The first annealing step enabled the formation of CTSe, while the second annealing step, performed after ZnSe deposition, led to the formation of the CZTSe phase. Comprehensive characterization including grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrical measurements was conducted. GIXRD and Raman analysis revealed kesterite CZTSe phase peaks, with some samples showing a split in the main peak at similar to 27 degrees (2 theta), indicating the presence of Cu x Se and ZnSe secondary phases. SEM analysis showed the impact of Sn and Se annealing on grain size, with larger grains observed in films annealed in Sn+Se atmospheres, particularly in the second heat treatment process. EDS results displayed consistent elemental composition across samples, with varying Cu/(Zn+Sn), Zn/Sn and Se/metal ratios influencing the band gap values from 1.09 to 1.63 eV. Hall measurements indicated p-type conductivity with carrier concentrations between 1016 and 1023 cm-3. These results highlight the effectiveness of our two-step annealing process, particularly the Sn+Se atmosphere, in optimizing CZTSe thin films for potential use in high-efficiency thin-film solar cells.

Potassium ions are important for developing electrode materials because they have similar properties to lithium and sodium ions. Mixed chromium phosphates (KMIICr(PO4)2) II Cr (PO 4 ) 2 ) with substituted M II sites using divalent elements (M = Ni, Co, Cu) were synthesized using a solid-state reaction method. The samples were analyzed using various techniques such as powder X-ray diffraction, Fourier transform infrared, Raman, and electron paramagnetic resonance spectroscopy. The proposed phosphates had a monoclinic phase structure with a P21/n 1 /n space group, and they contained large tunnels occupied by K+ + cations. The dielectric properties showed that the Ni-based phosphates had slower dielectric relaxation, while the Co and Cu-based phosphates had quicker polarization and depolarization processes. Additionally, the resistance of the grains decreased from Ni to Co to Cu-based phosphates, indicating easier charge movement in each material, consistent with the increase in conductive losses and a.c. conductivity when changing the M II ions.

Interest in self-cleaning coatings is rising due to their potential to enhance comfort and quality of life in polluted urban environments, driving the search for materials with optimal physical properties. Convergent with this goal, this study investigates the wetting properties and photo-catalytic efficiency of reticulated TiO2 layers. It shows that these properties are significantly influenced by the topographical characteristics of the TiO2 surface, which can be precisely controlled through variations in pulverization pressure and low-temperature post-annealing treatments. Post-deposition annealing of the TiO2 layers achieves 100 % self-cleaning efficiency for both thick and thin films, with optical transmission ranging from approximately 60 %-80 % in the visible spectrum. Additionally, the TiO2 layers exhibited promising capabilities for eliminating pathogenic microorganisms and disinfecting surfaces. The underlying causal factors of these remarkable and technologically promising surface features are explored and discussed.

In this study, the Cu2Zn1-xCoxSnS4 (CZn1-xCoxTS) films with partial cation substitution of cobalt are synthetized by sol gel spin coating, followed by sulfurization treatment. The incorporation of cobalt cation in the CZTS crystalline lattice as well as the phase transition from kesterite to stannite were confirmed by the X-ray diffraction (XRD) and Raman spectroscopy data. The XRD pattern shows peak-shifting toward higher 2 theta by increasing the Co concentration, indicating a decrease in lattice parameters. The red shift of Raman peaks by increasing x from 0 to 0.6, confirms the phase transition. The CZn1-xCoxTS morphology was observed by scanning electron microscopy, showing large grain size as x increases and a good distribution of elements for all films. Xray photoelectron spectroscopy was employed to study the valence of cations/anions and to probe the chemical bonds. The optical band gap showed a parabolic behavior versus the molar ratio Co/(Co + Zn), this deviation from Vegard's law being induced by the difference in electronegativity between cobalt and zinc. The pure CZTS has a band gap of 1.47 eV, while for CZn0.6Co0.4TS the gap is 1.17 eV, which indicates that the incorporation of cobalt cation produces a red-shift of the band to band transition energy.

Random sampling provides several benefits for multi-band signals compared to uniform sampling case. These benefits include greater sample frequency flexibility, fewer restrictions on signal filtering, and, in the case of stationary sampling sequences, a decrease or suppression of spectrum aliases. This makes random sampling a preferred option in Software Defined Radio (SDR) systems, which face the challenge of supporting different standards with different sampling frequencies. However, the task of reconstruction becomes more complex with random sampling. In the literature, various reconstruction techniques are provided. In this paper, we focus on employing the ADPW-CG iterative method to address the reconstruction issue with randomly sampled signals within an SDR system context. The effectiveness of the proposed algorithm is evaluated in terms of complexity, reconstructed signal quality, and robustness, and robustness and the findings is compared with the performance of the SVD direct algorithm and other iterative methods. Based on the obtained results, we observed that the proposed approach demonstrates promising performance in comparison to other algorithms.