National Institute Of Materials Physics - Romania

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.

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.

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.

The synthesis and characterization of novel ionic liquid crystals based on pyridinium salts with Br- and PF6- counterions are described in this work. These pyridinium salts were derived from 4-hydroxypyridine, both by N- and O-alkylation. The 3,4,5-tri(alkyloxy)-benzyl mesogenic unit was attached to the nitrogen atom of the pyridinium ring. Alkyl chains with a different number of carbon atoms (6, 8, 10, 12 and 14) were employed in order to show the effect on the stability of mesophase. The POM (polarizing optical microscopy) and XRD (powder X-ray diffraction) studies indicated that bromide salts with shorter chains C-6, C-8 and C-10 do not show mesomorphic properties, while longer chain analogues with C-12 and C-14 exhibit two enantiotropic columnar phases. Surprisingly, the pyridinium salts with the larger size PF6- counterion do not exhibit liquid crystal properties.

The use of resorbable magnesium alloys in the design of implants represents a new direction in the healthcare domain. Two main research avenues are currently explored for developing or improving metallic biomaterials: (i) increase of their corrosion resistance by designed compositional and structural modifications, and (ii) functionalization of their surfaces by coating with ceramic or polymeric layers. The main objective of this work was to comparatively assess bio-functional coatings (i.e., highly-crystallized hydroxyapatite and silica-rich glass) deposited by radio-frequency magnetron sputtering (RF-MS) on a biodegradable Mg-0.8Ca alloy (0.8 wt.% of Ca). After probing their morphology (by scanning electron microscopy) and structure (by Fourier transform infrared spectroscopy and grazing incidence X-ray diffraction), the corrosion resistance of the RF-MS coated Mg-0.8Ca substrates was electrochemically tested (in synthetic biological media with different degrees of biomimicry), and their cytocompatibility was assessed in osteoblast and fibroblast cell cultures. By collective assessment, the most promising performances, in terms of mass loss (similar to 7% after 12 days), hydrogen release rate (similar to 6 mL/cm(2) after 12 days), electrochemical corrosion parameters and cytocompatibility, were obtained for the crystalline HA coating.

In this work, the influence of the preparation route on the structural, morphological, and thermoelectric properties of the Mg2Si0.4Sn0.6 solid solutions is investigated. The synthesis based on melting the constituent elements in a closed graphite crucible followed by spark plasma sintering allows mixing elements with a large difference of their melting temperatures and a good control of sample stoichiometry. The optimized synthesis route is validated by the doped V and Sb samples, which yield good thermoelectric performance. The n-type doping leads to two orders of magnitude increase of the carrier concentration, and thus a subsequent increase of the electrical conductivity, which, in turn, augments greatly the power factor of the Mg1.98V0.02Si0.385Sn0.6Sb0.015 to 42.61 x10(-4) Wm(-1)K 2 at 650K. Although doping slightly enlarges the thermal conductivity, a peak value of the figure of merit ZT similar to 1.15 is obtained at 723K, which is 20 times higher than the ZT of un-doped material.

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.

Complex ferroelectric structures with dielectric interlayers may become possible alternatives for neuromorphic computing and low-power field-effect transistors since they exhibit multiple polarization states and negative capacitance. However, the effects on the switching characteristics due to the electric properties of the nonferroelectric circuit element have not been clearly evaluated so far. A high-resistance or low-capacitance element is usually associated with an increased depolarization field and eventually with suppression of polarization but without further consideration of the electrostatic differences. Therefore, we show that switching behavior is dramatically changed if the non-FE element is a resistive component or a capacitive one. This is reflected by either an increased apparent coercive field or imprint, respectively. A negative capacitance regime was observed at different moments but strongly depends on the nature of the nonferroelectric element. The voltage on the ferroelectric component remains constant during switching, which is a fingerprint of the system passing through non-equilibrium states. Therefore, we propose an algorithm to recover the S-shape of polarization dependence on the ferroelectric internal voltage during the slowed transition between the two stable states of polarization.

In this work, the thermally stimulated current (TSC) technique has been used to investigate the properties of the radiation-induced interstitial boron and interstitial oxygen defect complex by 23-GeV (E-kin) protons, including activation energy, defect concentration, as well as the annealing behavior. At first isothermal annealing (at 80 degrees C for 0-180 min) followed by isochronal annealing (for 15 min between 100 degrees C and 190 degrees C in steps of 10 degrees C), studies had been performed in order to get information about the thermal stability of the interstitial boron and interstitial oxygen defect in 50-Omega cm material after irradiation with 23-GeV protons to a fluence of 6.91 x 10(13) p/cm(2). The results are presented and discussed. Furthermore, the extracted data from TSC measurements are compared with the macroscopic properties derived from current-voltage and capacitance-voltage characteristics. In addition, the introduction rate of interstitial boron and interstitial oxygen defect as a function of the initial doping concentration was determined by exposing diodes with different resistivities (10, 50, 250, and 2 k Omega cm) to 23-GeV protons. These results are compared with data from TSC and deep-level transient spectroscopy measurements achieved by the team of the CERN-RD50 "Acceptor removal project."