Grain BoundariesPerovskite manganites with general formula RE 1−x B x MnO 3±δ (where RE stands for a trivalent rare-earth element and B for a divalent alkaline ion) have been extensively investigated for their wide variety of intriguing properties, such as oxygen electrocatalysis in solid oxide fuel cell (SOFC), [1,2] The ORCID identification number(s) for the author(s) of this article can be found under https://doi.

(001)-Epitaxial La2WO6 (LWO) thin films are grown by pulsed laser deposition on (001)-oriented SrTiO3 (STO) substrates. The α-phase (high-temperature phase in bulk) is successfully stabilized with an orthorhombic structure (a = 16.585(1) Å, b = 5.717(2) Å, c = 8.865(5) Å). X-ray-diffraction pole-figure measurements suggest that crystallographic relationships between the film and substrate are [100]LWO ∥ [110]STO, [010]LWO ∥ [11̅0]STO and [001]LWO ∥ [001]STO. From optical properties, investigated by spectroscopic ellipsometry, we extract a refractive-index value around 2 (at 500 nm) along with the presence of two absorption bands situated, respectively at 3.07 and 6.32 eV. Ferroelectricity is evidenced as well on macroscale (standard polarization measurements) as on nanoscale, calling for experiments based on piezo-response force-microscopy, and confirmed with in situ scanning-and-tunneling measurements performed with a transmission electron microscope. This work highlights the ferroelectric behavior, at room temperature, in high-temperature LWO phase when stabilized in thin film and opens the way to new functional oxide thin films dedicated to advanced electronic devices.

The long-term stability of InGaN photoanodes in liquid environments is an essential requirement for their use in photoelectrochemistry. In this paper, we investigate the relationships between the compositional changes at the surface of n-type In(x)Ga(1-x)N (x ∼ 0.10) and its photoelectrochemical stability in phosphate buffer solutions with pH 7.4 and 11.3. Surface analyses reveal that InGaN undergoes oxidation under photoelectrochemical operation conditions (i.e., under solar light illumination and constant bias of 0.5 VRHE), forming a thin amorphous oxide layer having a pH-dependent chemical composition. We found that the formed oxide is mainly composed of Ga-O bonds at pH 7.4, whereas at pH 11.3 the In-O bonds are dominant. The photoelectrical properties of InGaN photoanodes are intimately related to the chemical composition of their surface oxides. For instance, after the formation of the oxide layer (mainly Ga-O bonds) at pH 7.4, no photocurrent flow was observed, whereas the oxide layer (mainly In-O bonds) at pH 11.3 contributes to enhance the photocurrent, possibly because of its reported high photocatalytic activity. Once a critical oxide thickness was reached, especially at pH 7.4, no significant changes in the photoelectrical properties were observed for the rest of the test duration. This study provides new insights into the oxidation processes occurring at the InGaN/liquid interface, which can be exploited to improve InGaN stability and enhance photoanode performance for biosensing and water-splitting applications.

Pioneering electron energy loss spectroscopy (EELS) measurements of α-Bi2O3 are performed on three samples obtained through different synthesis methods. Experimental low-loss and core-loss EELS spectra are acquired. By combining them with detailed structural characterization and Density Functional Theory (DFT) simulations, we are able to detect and evaluate the presence of oxygen vacancies in the samples. This type of information has not been accessed previously from EELS data in bismuth oxide, because high-resolution EELS spectra or how vacancies reflect in Bi2O3 spectra were unreported. This novel measurement is further validated through comparison with photoluminescence data. Therefore, the technique has the ability to probe oxygen vacancies in Bi2O3 at an unprecedented resolution, which might allow solving material science and technological issues related to this material.

No abstract

Abstract. Density functional theory is used to study the atomic and electronic structure of NanK m clusters with up to seventy atoms. The simplifying approximation has been made of replacing the external potential of the ionic background by its spherical average about the cluster centre in the iterative process of solving the Kohn-Sham equations for each geometry tested. The search for the equilibrium geometry is performed by employing steepest descent and simulated annealing techniques. We have found segregation of K to the surface and when the cluster is large enough, a neat stratification of K and Na shells. Those effects (segregation and stratification) do not perturb the electronic magic numbers well known for pure alkali metal clusters. Our results for the atomic structure are rather similar to those reported earlier for NanCsn clusters. We have also studied in a selected case, Naz0Cs20 , the dependence of the collective electronic excitation spectrum on the segregation and other geometric characteristics of the cluster.

The resistive switching properties of silicon-aluminium oxynitride (SiAlON) based devices have been studied. Electrical transport mechanisms in both resistance states were determined, exhibiting an ohmic behaviour at low resistance and a defect-related Poole-Frenkel mechanism at high resistance. Nevertheless, some features of the Al top-electrode are generated during the initial electroforming, suggesting some material modifications. An in-depth microscopic study at the nanoscale has been performed after the electroforming process, by acquiring scanning electron microscopy and transmission electron microscopy images. The direct observation of the devices confirmed features on the top electrode with bubble-like appearance, as well as some precipitates within the SiAlON. Chemical analysis by electron energy loss spectroscopy has demonstrated that there is an out-diffusion of oxygen and nitrogen ions from the SiAlON layer towards the electrode, thus forming silicon-rich paths within the dielectric layer and indicating vacancy change to be the main mechanism in the resistive switching.

Resistive random-access memory (ReRAM) devices are currently the object of extensive research to replace flash non-volatile memory. However, elucidation of the conductive-filament formation mechanisms in ReRAM devices at nanoscale is mandatory. In this study, the different states created under real operation conditions of HfO 2 -based ReRAM devices are characterized through transmission electron microscopy and electron energy-loss spectroscopy. The physical mechanism behind the conductive-filament formation in Ni/HfO 2 /Si ReRAM devices based on the diffusion of Ni from the electrode to the Si substrate and of Si from the substrate to the electrode through the HfO 2 layer is demonstrated.