WhatEELS. A python-based interactive software solution for ELNES analysis combining clustering and NLLS.

The analysis of energy loss near edge structures in EELS is a powerful method for a precise characterization of elemental oxidation states and local atomic coordination with an outstanding lateral resolution, down to the atomic scale. Given the complexity and sizes of the EELS spectrum images datasets acquired by the state-of-the-art instrumentation, methods with low convergence times are usually preferred for spectral unmixing in quantitative analysis, such as multiple linear least squares fittings. Nevertheless, non-linear least squares fitting may be a superior choice for analysis in some cases, as it eliminates the need of calibrated reference spectra and provides information for each of the individual components included in the fitted model. To avoid some of the problems that the non-linear least squares algorithms may suffer dealing with mixed-composition samples and, thus, a model comprised by a large number of individual curves we proposed the combination of clustering analysis for segmentation and non-linear least squares fitting for spectral analysis. Clustering analysis is capable of a fast classification of pixels in smaller subsets divided by their spectral characteristics, and thus increases the control over the model parameters in separated regions of the samples, classified by their specific compositions. Furthermore, along with this manuscript we provide access to a self-contained and expandable modular software solution called WhatEELS. It was specifically designed to facilitate the combined use of clustering and NLLS, and includes a set of tools for white-lines analysis and elemental quantification. We successfully demonstrated its capabilities with a control sample of mesoporous cerium oxide doped with praseodymium and gadolinium, which posed challenging case-study given its spectral characteristics.

A high-entropy manganite in an ordered nanocomposite for long-term application in solid oxide cells.

The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of functional materials with enhanced electrochemical properties. Here we report on the realization of vertically aligned nanocomposites of lanthanum strontium manganite and doped ceria with straight applicability as functional layers in high-temperature energy conversion devices. By a detailed analysis using complementary state-of-the-art techniques, which include atom-probe tomography combined with oxygen isotopic exchange, we assess the local structural and electrochemical functionalities and we allow direct observation of local fast oxygen diffusion pathways. The resulting ordered mesostructure, which is characterized by a coherent, dense array of vertical interfaces, shows high electrochemically activity and suppressed dopant segregation. The latter is ascribed to spontaneous cationic intermixing enabling lattice stabilization, according to density functional theory calculations. This work highlights the relevance of local disorder and long-range arrangements for functional oxides nano-engineering and introduces an advanced method for the local analysis of mass transport phenomena.

High-temperature superconductivity at the lanthanum cuprate/lanthanum-strontium nickelate interface.

The utilization of interface effects in epitaxial systems at the nanoscale has emerged as a very powerful approach for engineering functional properties of oxides. Here we present a novel structure fabricated by a state-of-the-art oxide molecular beam epitaxy method and consisting of lanthanum cuprate and strontium (Sr)-doped lanthanum nickelate, in which interfacial high-temperature superconductivity (Tc up to 40 K) occurs at the contact between the two phases. In such a system, we are able to tune the superconducting properties simply by changing the structural parameters. By employing electron spectroscopy and microscopy combined with dedicated conductivity measurements, we show that decoupling occurs between the electronic charge carrier and the cation (Sr) concentration profiles at the interface and that a hole accumulation layer forms, which dictates the resulting superconducting properties. Such effects are rationalized in the light of a generalized space-charge theory for oxide systems that takes account of both ionic and electronic redistribution effects.

High-temperature superconductivity in space-charge regions of lanthanum cuprate induced by two-dimensional doping.

The exploitation of interface effects turned out to be a powerful tool for generating exciting material properties. Such properties include magnetism, electronic and ionic transport and even superconductivity. Here, instead of using conventional homogeneous doping to enhance the hole concentration in lanthanum cuprate and achieve superconductivity, we replace single LaO planes with SrO dopant planes using atomic-layer-by-layer molecular beam epitaxy (two-dimensional doping). Electron spectroscopy and microscopy, conductivity measurements and zinc tomography reveal such negatively charged interfaces to induce layer-dependent superconductivity (Tc up to 35 K) in the space-charge zone at the side of the planes facing the substrate, where the strontium (Sr) profile is abrupt. Owing to the growth conditions, the other side exhibits instead a Sr redistribution resulting in superconductivity due to conventional doping. The present study represents a successful example of two-dimensional doping of superconducting oxide systems and demonstrates its power in this field.