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Featured Application: Optoelectronic devices in space missions. 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. [ABSTRACT FROM AUTHOR]

In the present work, we report the synthesis and investigations of La0.9K0.1MnO3 and La0.8K0.1Pb0.1MnO3 bulk samples which could be potential magnetocaloric materials for magnetic refrigeration close to room temperature. A flash combustion reaction and sintering at 1200 °C for 10 h are used to prepare the bulk materials. Both compounds crystallized into a rhombohedral structure with R 3 ¯ c space group confirmed by X-ray powder diffraction results. Scanning electron microscopy analysis, combined with XRD peak profiles is performed to estimate the particle/crystallite size of the samples. Moreover, the Curie temperature, TC, is found to be higher in lead-rich sample due to the enhancement of the grain size and the Mn3+–O–Mn4+ double exchange (DE) interaction. Therefore, the bulk sample La0.8K0.1Pb0.1MnO3 shows a room temperature phase transition of 289 K as well as a higher saturation magnetization. The La0.8K0.1Pb0.1MnO3 bulk compound exhibits a high and sharp peak in magnetic entropy change up to 5.5 Jkg−1 K−1 under 5 T at the magnetic transition temperature TC. To compare the magnetocaloric performances of the studied compounds, relative cooling power (RCP) was employed. The obtained experimental results revealed that the increase in particle size influences severely the magnetocaloric properties. [ABSTRACT FROM AUTHOR]

Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI2.6Cl0.4 hybrid perovskite (MA—methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1−xZnxI2.6Cl0.4 based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion efficiency) range, compared to pristine MAPbI2.6Cl0.4 based devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

GeTe and GaSb thin films obtained by pulsed laser deposition were investigated by spectroscopic ellipsometry at controlled temperatures. The GeTe films were fully amorphous, while the GaSb films were partially crystalized in the as-deposited state. The Tauc-Lorentz model was employed to fit the experimental data. From the temperature study of the optical constants, it was observed the crystallization in the 150–160 °C range of GeTe amorphous films and between 230 and 240 °C of GaSb amorphous phase. A second transition in the resonance energy and the broadening parameter of the Lorentz oscillator was observed due to the crystallization of Sb after 250 °C. The temperatures of 85 °C and 130 °C are noticed as the start of the relaxation of the amorphous GeTe phase and as-deposited GaSb. The peaks of the imaginary part of the dielectric function red shifted after the phase change, while the variation with temperature of the crystalline phase follows the Varshni law. The electron-phonon coupling constants are 2.88 and 1.64 for c-GeTe and c-GaSb, respectively. An optical contrast up to 60% was obtained for GeTe films and a maximum value of 7.5% is revealed in the case GaSb, which is altered by the partial crystallinity of the as-deposited films. [ABSTRACT FROM AUTHOR]

Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 °C and 198 °C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 °C. Furthermore, at 210 °C, the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples. [ABSTRACT FROM AUTHOR]

In this paper, we report on the structural, optical, and electrical properties of a wide compositional range of AlxIn1-xN thin layers deposited on glass and polyethylene terephthalate substrates. AlxIn1-xN layers of controlled composition were obtained by a simple reactive magnetron co-sputtering protocol, using a single aluminium target with indium insets, by varying the Al/In target surface area ratio, and the composition of the deposition atmosphere. The relevant physical properties were investigated and discussed. It is shown that the texture of the thin films is dependent on the cation ratio, while the bowing parameters of lattice constants and band gap values are larger than those of epitaxial layers. [ABSTRACT FROM AUTHOR]

The porous aluminum oxide obtained by anodization of thin aluminum films, is characterized by using spectroscopic ellipsometry and scanning electron microscopy (SEM) experiments. A nearly complete transformation from aluminum to aluminum oxide, is showed by the comparison of x-ray diffraction spectra obtained before and after anodization.

We have investigated the effect of thermal annealing on the structure of single and stacked phase change memory films based on SnSe and GaSb. Samples were prepared by pulsed laser deposition and investigated by X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) methods. Electrical resistance versus temperature investigations showed crystallisation temperatures of 292°C and 198°C for SnSe and GaSb single films, respectively. Above the transition temperature, GaSb crystallises into a face-centered cubic structure, whereas SnSe has an orthorhombic arrangement. Annealing at three temperatures (160°C, 250°C and 350°C) of the SnSe\GaSb stacked films promotes bond breaking, atom diffusion between the two layers and formation of new phases. At 160°C, GaSb films crystallise partially and no effect is observed on the crystallinity of SnSe films. After 250°C, rhombohedral SnSb emerges in addition to GaSb complete crystallisation. A major, completely new, body-centered orthorhombic unindexed quaternary Ga-Sn-Sb-Se phase formation was observed in the samples annealed at 350°C. The GaSb crystallites are fully dissolved and we have observed the formation of a minor hexagonal SnSe2 phase. The analysis of EXAFS data, measured at Se and Ga K-edges, revealed changes in the local atomic environment as a function of the annealing temperature. A tetrahedral configuration is obtained for the Ga atoms in both as-deposited and annealed samples, whereas Se is mostly bivalent in the amorphous samples and has an octahedral arrangement in crystalline SnSe. Our results show that inter-layer diffusion should always be considered and evaluated when designing memory cells composed of stacked phase change chalcogenide films. [ABSTRACT FROM AUTHOR]

The thermal stress effect on the structure of phase change memory materials, namely single films and double stacked films of GeTe and SnSe, is evaluated. The crystallization temperatures of GeTe and SnSe single films are 138 °C and 292 °C, respectively. The films are amorphous before annealing and crystallize in rhombohedral and orthorhombic structures afterwards. Ge is tetrahedrally bonded and Se is bivalent after deposition. Both Ge and Se have an octahedral configuration after annealing. The double stacked structure is studied in the as‐deposited state and after annealing at temperatures of 100, 210, and 350 °C. Pulsed laser deposition produces the crystallization of both as‐deposited layers when stacked, mostly of SnSe, but also some crystalline GeTe is present. GeTe fully crystallizes after annealing at 210 °C, in the face‐centred cubic structure. Annealing at 350 °C leads to the evaporation of a significant quantity of Se and to the formation of a cubic Ge0.75Sn0.25Te solid solution. Ge has an octahedral coordination, while Se is tetrahedrally bonded as a result of a combination of bivalent amorphous Se and octahedral Se from crystalline SnSe. The study shows that diffusion between layers at high annealing temperatures might suppress the memory property and determines the formation of irreversible solid solutions. [ABSTRACT FROM AUTHOR]

In this paper, we report the realization and characterization of a condensation sensor based on indium nitride (InN) layers deposited by magnetron sputtering on glass and flexible plastic substrates, having fast response and using potentially low cost fabrication technology. The InN devices work as open gate thin film sensitive transistors. Condensed water droplets, formed on the open gate region of the sensors, deplete the electron accumulation layer on the surface of InN film, thus decreasing the current of the sensor. The current increases back to its initial value when water droplets evaporate from the exposed InN film surface. The response time is as low as 2 s. [ABSTRACT FROM AUTHOR]

Indium Zinc Oxide compositional libraries were fabricated by combinatorial pulsed laser deposition technique on glass substrate at room temperature. Two pairs of targets with In atomic concentrations, In/(In+Zn), of 28 at.% and 56 at.% or 42 at.% and 70 at.% were employed. A high transparency was observed for all the coatings with transmittance values better than 95%. The maximum thicknesses of the samples, inferred by spectroscopic ellipsometry, were within the 174-310 nm range for the simple PLD films, whereas in case of combinatorial PLD coatings were 341 or 467 nm. Energy dispersive X-ray spectroscopy revealed that In content in the combinatorial films was in the 27-52 at. % range. From atomic force microscopy histograms we evidenced a decrease of the RMS roughness down to 1 nm with the increase of the In content. As a result of the compositional library studies two minimum values of the electrical resistivity were identified at 2.3×10-3 Ω·cm and 8.6 ×10-4 Ω·cm, which correspond to 28.8-29.5 at.% and 44-49 at% range of Indium content. [ABSTRACT FROM AUTHOR]