National Institute Of Materials Physics - Romania

Cu2ZnSnS4 (CZTS) is regarded as one of the emerging materials for next-generation thin film solar cells. However, its synthesis is complex, and obtaining a single-phase CZTS thin film is difficult. This work reports the elaboration of Cu2ZnSnS4 thin films by a sequential magnetron sputtering deposition of Cu2SnS3 (CTS) and ZnS as stacked films. Initially, the CTS films were prepared on a soda lime glass substrate by annealing Cu and SnS2 stacked layers. Second, ZnS was deposited by magnetron sputtering on the CTS films. The CTS\ZnS stacks were then annealed in Sn + S or S atmospheres. The tetragonal CZTS structure was obtained and confirmed by grazing incidence X-ray diffraction and Raman spectroscopy. The morphological and compositional characteristics, measured by scanning electron microscopy and energy-dispersive spectroscopy, revealed large grains and dense surfaces with the elemental composition close to the intended stoichiometry. Additional X-ray photoemission spectroscopy measurements were performed to determine the surface chemistry and particularities of the obtained films. The optical properties, determined using conventional spectroscopy, showed optimal absorber layer band gap values ranging between 1.38 and 1.50 eV. The electrical measurements showed that all the films are p-type with high carrier concentrations in the range of 10(15) to 10(20) cm(-3). This new synthesis route for CZTS opens the way to obtain high-quality films by an industry-compatible method.

The aim of this experimental work was to investigate the influence of the ion beam charge state on damage production in nanomaterials. To achieve this, we employed Raman spectroscopy, atomic force microscopy, and transmission electron microscopy to investigate nanomaterials irradiated by a 23 MeV I beam. We found a significant influence of the ion charge state on damage production in monolayer graphene, but found no evidence of this effect in bilayer and trilayer graphene, nor in graphite. Furthermore, we found no evidence of this effect in CaF2 and SiO2 nanocrystals irradiated with the same ion beam.

Cu2SnS3 (CTS) is emerging as a promising absorber for the next generation thin film solar cells (TFSC) due to its excellent optical and electronic properties, earth-abundance and eco-friendly elemental composition. In addition, CTS can be used as precursor films for the Cu2ZnSnS4 (CZTS) synthesis. The optical properties of CTS are influenced by stoichiometry, crystalline structure, secondary phases and crystallite size. Routes for obtaining CTS films with optimized properties for TFSC are still being sought. Here, the CTS thin films synthesized by magnetron sputtering on soda lime glass (SLG) using Cu and SnS2 targets in two different stacks, were studied. The SLG\Cu\SnS2 and SLG\SnS2\Cu stacks were annealed in S and Sn + S atmospheres, at various temperatures. Both stacks show a polymorphic structure, and higher annealing temperatures favor the monoclinic CTS phase formation. Morphology is influenced by the stacking order since a SnS2 top layer generates several voids on the surface due to the evaporation of SnS, while a Cu top layer provides uniform and void-free surfaces. The films in the copper-capped stack annealed under Sn + S atmosphere have the best structural, morphological, compositional and optical properties, with tunable band gaps between 1.18 and 1.37 eV. Remarkably, secondary phases are present only in a very low percent (< 3.5%) in samples annealed at higher temperatures. This new synthesis strategy opens the way for obtaining CTS thin films for solar cell applications, that can be used also as intermediary stage for CZTS synthesis.

A novel and disposable biosensor based on superoxide dismutase (SOD) immobilized on gold metallized polycaprolactone electrospun polymeric fibers (PCl/Au) has been developed for the determination of superoxide (O-2(center dot-)) in cell culture media. SOD biosensors were constructed employing three immobilization methods: crosslinking with EDC/NHS at a cysteine self-assembled monolayer (PCl/Au/SODCYS), biopolymer encapsulation with chitosan (PCl/Au/SODCHI) and cross-linking with glutaraldehyde (PCl/Au/SODGA). Scanning electron microscopy was performed at the three different biosensors to evaluate their surface morphologies. Biosensors were employed for the electrochemical detection of superoxide by fixed potential amperometry at different applied potentials, with two distinct enzymatic mechanisms being proposed: i) the reduction of the enzymatically generated peroxide, at -0.3 V, for which the PCl/Au/SODCHI biosensor presented the highest value of sensitivity of 40.1 mu A mM(-1) cm(-2), and ii) the regeneration of the enzyme catalytic copper centre, at +0.3 V, for which the PCl/Au/SODCYS biosensor had the highest sensitivity value of 16.1 mu A mM(-1) cm(-2). The proposed recognition mechanisms were further confirmed by cyclic voltammetric measurements, which enabled also to determine the amount of immobilized electroactive SOD, with highest value corresponding to the PCl/Au/SODCYS biosensor. The biosensors with best analytical performance, PCl/Au/SODCYS and PCl/Au/SODCHI, were further investigated for stability and selectivity, with best results for the PCl/Au/SODCYS, chosen for superoxide monitoring in cell culture media. The study is promising for future application of PCl/Au/SODCYS for the on-line superoxide monitoring of superoxide in cell cultures, grown directly on the biosensor itself.

This paper reports the synthesis and characterization of Cu2ZnSnS4 (CZTS) absorber films, prepared by a two-step electrodeposition of a ZnS (zinc sulfide) binary and a CZT (copper, zinc and tin) ternary precursors on Mo/Ti/Si substrates. The as-electrodeposited ZnS/CZT and CZT/ZnS stacks were thermally treated in a tubular furnace in sulfur environment at 550 degrees C. The role of the ZnS buffer layer is to provide a zinc and sulfur reservoir, needed to complete the formation of kesterite phase. X-ray diffraction and Raman analyses revealed the formation of the CZTS phase. The surface morphology and chemical composition of the films were studied using a scanning electron microscope. The bandgap values inferred from diffuse reflectance data, are discussed with respect to the stoichiometry which is considerably affected by the order of the stacks. Room-temperature photoluminescence of the CZT/ZnS sample showed a board PL band of 1.51 eV. It was found that the film with a ZnS layer on top is preferred for the formation of a Zn-rich single CZTS phase.

Dextran coated cerium doped hydroxyapatite (Ca(10-x)Cex(PO4)(6)(OH)(2)), with x = 0.05 (5CeHAp-D) and x = 0.1 (10CeHAp-D) were deposited on Si substrates by radio frequency magnetron sputtering technique for the first time. The morphology, composition, and structure of the resulting coatings were examined by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), atomic force microscopy (AFM), metallographic microscopy (MM), Fourier transform infrared spectroscopy (FTIR), and glow discharge optical emission spectroscopy (GDOES), respectively. The obtained information on the surface morphologies, composition and structure was discussed. The surface morphologies of the CeHAp-D composite thin films are smooth with no granular structures. The constituent elements of the CeHAp-D target were identified. The results of the FTIR measurements highlighted the presence of peaks related to the presence of nu(1), nu(3), and nu(4) vibration modes of (PO43-) groups from the hydroxyapatite (HAp) structure, together with those specific to the dextran structure. The biocompatibility assessment of 5CeHAp-D and 10CeHAp-D composite coatings was also discussed. The human cells maintained their specific elongated morphology after 24 h of incubation, which confirmed that the behavior of gingival fibroblasts and their proliferative capacity were not disturbed in the presence of 5CeHAp-D and 10CeHAp-D composite coatings. The 5CeHAp-D and 10CeHAp-D coatings' surfaces were harmless to the human gingival fibroblasts, proving good biocompatibility.

Li-ion batteries, widely used in portable electronics, electric vehicles, and energy storage systems, are an integral element of our daily life. However, the limitation of lithium sources, which leads to high prices, prompts the search for alternatives. Recently there has been noticed a rapid interest in Na-ion batteries technology. Especially, suitable cathode structures are investigated to accumulate larger sodium ions. In this paper, the high entropy layered oxide NaMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 is presented which achieves superior electrochemical properties with a stable capacity of ca. 180 mAh g(-1). The understanding of its high performance is based on a complex study of the multiphase intercalation mechanism. The combination of advanced structural analysis by XAS, in situ XRD, TEM, and computational DFT modelling gives a new concept on the nature of O3-P3 structure reorganization. The presented experimental and theoretical evidence indicates that the P3 phase of layered oxides is energetically favourable for a lower sodium content for specific transition metal-oxide pair distance. Fundamental understanding of the nature of phase transformation is crucial for tailoring structural composition, where the desirable O3-P3 reorganization will occur, resulting in achieving high-performance cathodes.

A recent theory of band ferromagnetism in 3d metals predicts 're-entrant' ferromagnetism at temperatures far above the boiling point of these metals in normal conditions (Teodorescu, C.M., 2021. Spin asymmetry originating from densities of states: Criterion for ferromagnetism, structures and magnetic properties of 3d metals from crystal field based DOSs. Results in Physics 25, 104,241). Metals, and in particular iron rich alloys, are still solid at such extremal temperatures in the Earth's inner solid core. It follows that this piece of the Earth may become ferromagnetic. This hypothesis is investigated in this work in more details, by using densities of states derived by ab initio density functional theory calculations for hexagonal close-packed iron and applying the basic theory of band ferromagnetism derived in the above Reference. The temperature for 're-entrant' ferromagnetism increases with the pressure, ranging between about 6530 and 6640 K for pressures between 330 and 360 GPa; these temperatures are in the range of most estimates for the temperature of the inner solid core of our planet. The dimension of the ferromagnetic "innermost inner core" (IMIC) derived from the estimated Fe magnetic moment are within the dimensions of a IMIC with different anisotropy in the propagation of seismic waves. For body centered cubic Fe no 're-entrant' ferromagnetism is predicted based on the actual model. It follows that the Earth's inner solid core with hexagonal close-packed structure is the main responsible for the geomagnetic field, and also most probably the reversal of this field proceeds by simple rotation of the magnetization of this core, while keeping a non-vanishing magnetic field during the reversal. This might prevent the Earth's surface bombardment with energetic charged particles during the reversals, with beneficial effects for complex lifeforms and for mankind civilization.

Photoelectron spectromicroscopy data cubes with sub-micrometer spatial resolution from a lead zirconate titanate thin film are fitted in each spatial point for several areas investigated, and correlations between the results of the fitting parameters are established, enabling one to suggest that surface band bending manifests also in the case of samples with multiple polarization states. These surface band bendings may be used for preliminary assessment of polarization states by using the contrast in binding energy. However, the individual curve fitting of each spectrum and the analysis of correlations between the derived parameters (binding energies and amplitudes) yields results of deeper significance in deriving the distribution of band bending. This allows in some cases discriminating between the origin of the individual components, assessing charging effects and compensation mechanisms, also enabling one to establish correlations between areas with different polarization. It is found that the major part of the investigated areas consist in regions with outwards polarization and without out-of-plane polarization, with the presence of some isolated metal Pb clusters. On a single area, components attributed to inwards polarization are detected, and their formation occurs at the expense of areas without out-of-plane polarization, mostly for a given proportion of the outwards polarization.