National Institute Of Materials Physics - Romania

When used as the active layers-either as a light absorber in photovoltaic devices or as an electroluminescent material in light-emitting devices-lead-free perovskites significantly impact the performance of optoelectronic devices. This study focuses on antimony-based perovskites, which are promising for lighting applications. These types of perovskites enable the formation of self-trapped excitons (STEs) with higher dissociation energy than lead-based perovskites, which generate excitons with lower dissociation energy. The (CH3NH3)3Sb2I9 crystals are synthesized using two methods, resulting in distinct spatial configurations - dimer and dimer/layered mixtures, each exhibiting unique structural and spectroscopic properties, as revealed by comprehensive multi-parametric complementary analyses. Their emissive properties underscore the efficiency of the STE photoluminescence, driven by electron-phonon interactions and influenced by Sb-Sb distances in (CH3NH3)3Sb2I9 powder, whether dispersed in polymethyl-methacrylate or solution. The phase transition from monoclinic to hexagonal (dimer) and trigonal (layered) structures enabled the tuning of the optical properties in direct correlation with the structural and electrical features. The photoluminescence behavior of the STEs, analyzed in conjunction with the Raman spectroscopy, elucidates the dynamic process of the electron-phonon coupling effects in the dimer (face-capping Sb-I octahedra) and layered (corner-sharing Sb-I octahedra) crystallographic structures.

By experiment we evaluated the longitudinal magnetostriction on cylindrical samples of MnZn ferrite. Starting from the idea that the magnetostriction phenomenon is closely related to the magnetization phenomenon of the ferromagnetic sample, by plotting the magnetostriction curve it is possible to extract the magnetization curve of the ferromagnetic material and to evaluate the saturation magnetization of the material and the demagnetizing factor of the sample. At the same time, the paper suggests a way to study the dynamics of the movement of the magnetic domain walls in the sample, by examining the resonance curve at each point on the magnetization curve.

Laser thin layer deposition technologies were applied to develop organic heterostructures on flexible transparent conductive electrode (TCE). Flexible substrates such as flexible glass (FG), polyethersulfone (PES), amorphous polyethylene terephthalate (PET-A) and biaxially-oriented polyethylene terephthalate (PET-B) were employed to assess the influence of the substrate type on the optical and electrical characteristics of the organic devices. For comparison reason, the organic heterostructures were fabricated on rigid glass substrate and commercially available indium tin oxide (ITO)-coated PET. Hence, flexible and rigid glass substrates were coated with ITO film by pulsed laser deposition (PLD) at low fluence, subsequently a blend layer based on zinc phthalocyanine (ZnPc) and N, N '-bis-(1-dodecyl)perylene-3,4,9,10 tetracarboxylic diimide (AMC14) being deposited by matrix assisted pulsed laser evaporation (MAPLE) on the TCE film. The investigations evidenced that the roughness and the substrate type can strongly influence the properties of the ITO layer deposited by PLD as well as the optical and electrical characteristics of the organic heterostructures based on the blend layer deposited by MAPLE. Thus, the lowest roughness (0.8 nm) and the best Hall mobility (41.9 cm2/V center dot s) were achieved for ITO coatings deposited on flexible glass substrate. Also, the highest current density value (9.3 x 10- 4 A/cm2 at 0.5 V) was reached for the organic heterostructures fabricated on this type of flexible substrate.

In this work, three methods for the synthesis of composites based on poly(ortho-toluidine) (POT) and WS2 are reported: (a) the solid-state interaction (SSI) of POT with WS2 nanoparticles (NPs); (b) the in situ chemical polymerization (ICP) of ortho-toluidine (OT); and (c) the electrochemical polymerization (ECP) of OT. The preparation of WS2 sheets was performed by the ball milling of the WS2 NPs followed by ultrasonication in the solvent N,N'-dimethyl formamide. During the synthesis of the POT/WS2 composites by SSI and ICP, an additional exfoliation of the WS2 NPs was reported. In this work, we demonstrated the following: (a) the ICP method leads to POT/WS2 composites, which contain repeating units of POT in the leucoemeraldine salt (LS) state, while (b) the ECP method leads to POT/WS2 composites, which contain repeating units of POT in the emeraldine salt (ES) state. Capacitances equal to 123.5, 465.76, and 751.6 mF cm-2 in the cases of POT-ES/WS2 composites, synthesized by SSI, ICP, and ECP, respectively, were reported.

This work investigates the gelation behavior and phase stability of E7 liquid crystals using a series of mesogenic benzoylthiourea (BTU) gelators with different alkyl chain lengths (6, 10, 12) at concentrations as low as 2.5 wt.%. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) confirm that the BTU gelators effectively stabilize the E7/gel composites through hydrogen bonding and pi-pi interactions. DSC studies reveal a concentration-dependent shift in transition temperatures, with evidence of distinct LC-isotropic and isotropic-gel transitions. Rheological and dielectric studies further demonstrate a reversible gel-sol transition and enhanced dipolar relaxation times (37.7 ns), indicating strong interactions between E7 and the BTU network.

Background . Algeria has long sought to exploit its uranium deposits in the Hoggar region, whose objective is to market the ore, and use part of the production exclusively in the civil field, especially in electricity generation. The exploitation and valorisation of this ore; require a very specific process of exploitation, characterization and treatment. The main objective of this work is to establish a detailed and complete technical data sheet for the Tahaggart deposit, enabling the implementation of a uranium ore mining and beneficiation technique to obtain a marketable product known as "yellow cake". Methods . To achieve this objective, samples were taken from the site understudy, followed by microscopic and macroscopic analyses non-thin sections to obtain petrographic, mineralogical and geochemical identifications. Results . The analyses confirmed the sandstone character of the ore and the predominance of quartz, clays, oxides and iron hydroxides as well as uranium and rutile minerals. The uranium contents in the mineralized altered levels varied from 0.90 to 1.32 and from 0.34 to 0.74 % in the mineralized conglomeratic sandstones. Uranium occurred either in the high-grade uranium minerals or low-grade apatite, zircon, rutile, and in traces in monazite. & Scy; o n c l u s ions . Different studies carried out on the Tahaggart region have proven the presence of Uranium ores with remarkable quantities, varying between 0.90 to 1.32 % in the mineralized altered levels and 0.34 to 0.74 % in the mineralized conglomeratic sandstones, however, despite this, and in view of the strategic value that uranium enjoys at the international level; to date, there is no exploitation this mine by the state. The best treatment method in this case is heap leaching; the recovery rate by this method can reach 70 % in uranium as "yellow cake".

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.

Nanocomposites based on Fe3O4 and carbonaceous nanoparticles (CNPs), including carbon nanotubes (CNTs) and graphene derivatives (graphene oxide (GO) and reduced graphene oxide (RGO)), such as Fe3O4@GO, Fe3O4@RGO, and Fe3O4@CNT, have demonstrated considerable potential in a number of health applications, including tissue regeneration and innovative cancer treatments such as hyperthermia (HT). This is due to their ability to transport drugs and generate localized heat under the influence of an alternating magnetic field on Fe3O4. Despite the promising potential of CNTs and graphene derivatives as drug delivery systems, their use in biological applications is hindered by challenges related to dispersion in physiological media and particle agglomeration. Hence, a solid foundation has been established for the integration of various synthesis techniques for these nanocomposites, with the wet co-precipitation method being the most prevalent. Moreover, the dimensions and morphology of the composite nanoparticles are directly correlated with the value of magnetic saturation, thus influencing the efficiency of the composite in drug delivery and other significant biomedical applications. The current demand for this type of material is related to the loading of a larger quantity of drugs within the hybrid structure of the carrier, with the objective of releasing this amount into the tumor cells. A second demand refers to the biocompatibility of the drug carrier and its capacity to permeate cell membranes, as well as the processes occurring within the drug carriers. The main objective of this paper is to review the synthesis methods used to prepare hybrids based on Fe3O4 and CNPs, such as GO, RGO, and CNTs, and to examinate their role in the formation of hybrid nanoparticles and the correlation between their morphology, the dimensions, and optical/magnetic properties.