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The nanoscale magnetic configuration of self-assembled groups of magnetite 40 nm cubic nanoparticles has been investigated by means of electron holography in the transmission electron microscope (TEM). The arrangement of the cubes in the form of chains driven by the alignment of their dipoles of single nanocubes is assessed by the measured in-plane magnetic induction maps, in good agreement with theoretical calculations This research received funding from the Xunta de Galicia, Program for Development of a Strategic Grouping in Materials (AeMAT, Grant No. ED431E2018/08), the Agencia Estatal de Investigación (project PID2019-109514RJ-100), the Spanish Ministry of Economy and Competitiveness, grant number MAT2010-16407, and from the European Union Seventh Framework Programme under Grant Agreement 312483-ESTEEM2 (Integrated Infrastructure Initiative–I3) SI

The physicochemical properties used in numerous advanced nanostructured devices are directly controlled by the oxidation states of their constituents. In this work we combine electron energy-loss spectroscopy, blind source separation, and computed tomography to reconstruct in three dimensions the distribution of Fe and Fe ions in a FeO/FeO core/shell cube-shaped nanoparticle with nanometric resolution. The results highlight the sharpness of the interface between both oxides and provide an average shell thickness, core volume, and average cube edge length measurements in agreement with the magnetic characterization of the sample., This work has been carried out in the frame of the Spanish research projects MAT2013-41506, MAT2013-48628-R, FIS2013-46159-C3-3-P, and CSD2009-00013, and Catalan Government support from the SGR2014-672 and 2014-SGR1015 projects is acknowledged. We also acknowledge the support received from the European Union Seventh Framework Program under Grant Agreement 312483 - ESTEEM2 (Integrated Infrastructure Initiative-I3). G.S.A. was partially supported by the Knut and Alice Wallenberg Foundation (Project: 3DEMNATUR). M.E. acknowledges the Spanish Ministry of Science and Innovation through the Juan de la Cierva Program. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295). F.d.l.P. and C.D. acknowledge funding from the ERC under grant no. 259619 PHOTO EM. C.D. acknowledges the Royal Society for funding

Tuning oxygen mass transport properties at the nanoscale offers a promising approach for developing high performing energy materials. A number of strategies for engineering interfaces with enhanced oxygen diffusivity and surface exchange has recently been proposed. However, the origin and the local magnitude of such local effects remain largely undisclosed to date. This is ascribed to the lack of direct measurement tools with sufficient resolution. In this work, we use atom probe tomography with sub-nanometric resolution to study oxygen mass transport on oxygen-isotope exchanged thin films of lanthanum chromite. We present a direct visualization of nanoscaled highly conducting oxygen incorporation pathways along grain boundaries, with reliable quantification of fast oxygen diffusion at grain boundaries and correlative link to local chemistries. Combined with finite element simulations of the precise 3D nanostructure, we quantify an enhancement in the grain boundary oxygen diffusivity and in the surface exchange coefficient of lanthanum chromite of about 4 and 3 orders of magnitude, respectively, compared to the bulk. This remarkable increase of the oxygen diffusivity in an interface-dominated material is unambiguously attributed to grain boundary conduction highways thanks to the use of a powerful technique that can be straightforwardly extended to the study of currently inaccessible multiple nanoscale mass transport phenomena.

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.

The atomic structure of nanoparticles can be easily determined by transmission electron microscopy. However, obtaining atomic-resolution chemical information about the individual atomic columns is a rather challenging endeavor. Here, crystalline monodispersed spinel Fe3O4/Mn3O4 core–shell nanoparticles have been thoroughly characterized in a high-resolution scanning transmission electron microscope. Electron energy-loss spectroscopy (EELS) measurements performed with atomic resolution allow the direct mapping of the Mn2+/Mn3+ ions in the shell and the Fe2+/Fe3+ in the core structure. This enables a precise understanding of the core–shell interface and of the cation distribution in the crystalline lattice of the nanoparticles. Considering how the different oxidation states of transition metals are reflected in EELS, two methods of performing a local evaluation of the cation inversion in spinel lattices are introduced. Both methods allow the determination of the inversion parameter in the iron oxide core and manganese oxide shell, as well as detecting spatial variations in this parameter, with atomic resolution. X-ray absorption measurements on the whole sample confirm the presence of cation inversion. These results present a significant advance toward a better correlation of the structural and functional properties of nanostructured spinel oxides., The authors acknowledge funding from the Spanish Ministerio de Economía y Competitividad (MINECO) through the projects MAT2016-77391-R and MAT2016-79455-P/FEDER (UE). This work has also been carried out in the framework of the projects 2017-SGR-292 and 2017-SGR-776 from the Generalitat de Catalunya. A.L.O. acknowledges the MINECO through the Juan de la Cierva Program (IJCI-2014-21530). M.W. acknowledges the European Union Seventh Framework Programme under grant agreement no. 312483-ESTEEM2. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Program (MINECO, grant SEV-2013-0295).

The achievement of an efficient all-Si electrically-pumped light emitter is a major milestone in present optoelectronics still to be fulfilled. Silicon nanocrystals (Si NCs) are an attractive material which, by means of the quantum confinement effect, allow attaining engineered bandgap visible emission from Si by controlling the NC size. In this work, SiO2-embedded Si NCs are employed as an active layer within a light-emitting device structure. It is demonstrated that the use of an additional thin Si3N4 interlayer within the metal-insulator-semiconductor device design induces an enhanced minority carrier injection from the substrate, which in turn increases the efficiency of sequential carrier injection under pulsed electrical excitation. This results in a substantial increase in the electroluminescence efficiency of the device. Here, the effect of this Si3N4 interlayer on the structural, optical, electrical, and electro-optical properties of a Si NC-based light emitter is reported, and the physics underlying these results is discussed.

Interface-dominated materials such as nanocrystalline thin films have emerged as an enthralling class of materials able to engineer functional properties of transition metal oxides widely used in energy and information technologies. In particular, it has been proven that strain-induced defects in grain boundaries of manganites deeply impact their functional properties by boosting their oxygen mass transport while abating their electronic and magnetic order. In this work, the origin of these dramatic changes is correlated for the first time with strong modifications of the anionic and cationic composition in the vicinity of strained grain boundary regions. We are also able to alter the grain boundary composition by tuning the overall cationic content in the films, which represents a new and powerful tool, beyond the classical space charge layer effect, for engineering electronic and mass transport properties of metal oxide thin films useful for a collection of relevant solid-state devices.

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.-- et al., The intimate relationship between stoichiometry and physicochemical properties in transition-metal oxides makes them appealing as tunable materials. These features become exacerbated when dealing with nanostructures. However, due to the complexity of nanoscale materials, establishing a distinct relationship between structure-morphology and functionalities is often complicated. In this regard, in the FexO/Fe3O4 system a largely unexplained broad dispersion of magnetic properties has been observed. Here we show, thanks to a comprehensive multi-technique approach, a clear correlation between the magneto-structural properties in large (45 nm) and small (9 nm) FexO/Fe3O4 core/shell nanoparticles that can explain the spread of magnetic behaviors. The results reveal that while the FexO core in the large nanoparticles is antiferromagnetic and has bulk-like stoichiometry and unit-cell parameters, the FexO core in the small particles is highly non-stoichiometric and strained, displaying no significant antiferromagnetism. These results highlight the importance of ample characterization to fully understand the properties of nanostructured metal oxides., This work was supported by the 2014-SGR-1015 and 2009-SGR-35 projects of the Generalitat de Catalunya, by the MAT2010-20616-C02, MAT2011-27380-C02-01, MAT2010-16407, MAT2013-48628-R and CSD2009-00013 projects of the Spanish Ministerio de Economía y Competitividad (MINECO), the ONDA and COEFNANO projects (no. FP7-PEOPLE-2009-IRSES-247518 and no. FP7-PEOPLE-2012-IRSES-318901) of the European Union, the Russian grants RFBR 13-02-00121, 13-02-12429 and RG 14.B25.31.0025, the Brazilian grants CNPq-304368/2010-5 and FAPEMIG-PPM 00319-11, the Argentine grants PIP 1333 (CONICET) and SECTyP 06/C404 (Univ. Nac. de Cuyo) and the Swedish Research Council (VR). Research at NCSR “D” was supported by the HSF-EU program ARISTEIA, grant COMANA/22. GSA was partially supported by the Knut and Alice Wallenberg Foundation (Project: 3DEM-NATUR). I.V.G. thanks the Generalitat de Catalunya for his sabbatical fellowship (2010 PIV 00096). M.D.B. was partially supported by an ICREA Academia award. M.E. acknowledges the Spanish Ministry of Science and Innovation through the Juan de la Cierva Program. A. G. Roca would like to thank Generalitat de Catalunya for financial support under the Beatriu de Pinós fellowship program (2011 BP_B 00209). ICN2 acknowledges support from the Severo Ochoa Program (MINECO, grant SEV-2013-0295).

In this work, the fabrication and the structural, optical and electrical properties of Al-Tb/SiO2 nanomultilayers have been studied. The nanomultilayers were deposited by means of electron beam evaporation on top of p-type Si substrates. Optical characterization shows a narrow and strong emission in the green spectral range, indicating the optical activation of Tb3+ ions. The electrical characterization revealed conduction limited by the electrode, although trapped-assisted mechanisms can also contribute to transport. The electroluminescence analysis revealed also emission from Tb3+ ions, a promising result to include this material in future optoelectronics applications as integrated light-emitting devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., This work was financially supported by the Spanish Ministry of Economy and Competitiveness (TEC2016-76849-C2-1-R and MAT2015-71035-R). O.B. also acknowledges the subprogram “Ayudas para Contratos Predoctorales para la Formaci on de Doctores” from the Spanish Ministry of Economy and Competitiveness for economical support.

Nanostructured metal oxide semiconductors are ideally suited for their integration in different devices due to their high thermal and mechanical stability, unique electronic characteristics, and low-cost fabrication. The modification of their surface allows the design of heterostructures with novel properties. In this work, we have synthesized single-crystalline niobium pentoxide (Nb2O5) nanorods and niobium-pentoxide-coated tin oxide (Nb2O5/SnO2) heterostructures by chemical vapor deposition. HR-TEM analysis and computer simulation studies showed the low density of defects and high crystallinity of the Nb2O5 nanorods, which exhibited high sensitivity toward humidity at low temperatures (60 °C). The fabrication of SnO2/Nb2O5 core–shell heterostructures combines the high sensitivity of Nb2O5 shell toward moisture with the good electrical conductivity of SnO2. The growth of the nanoscopic Nb2O5 overlayer on SnO2 nanowires introduces defects in the structure, which influence the electronic properties of the ...

Recently, colored H-doped TiO2 (H-TiO2) has demonstrated enhanced photoelectrochemical (PEC) performance due to its unique crystalline core—disordered shell nanostructures and consequent enhanced conduction behaviors between the core-shell homo-interfaces. Although various hydrogenation approaches to obtain H-TiO2 have been developed, such as high temperature hydrogen furnace tube annealing, high pressure hydrogen annealing, hydrogen-plasma assisted reaction, aluminum reduction and electrochemical reduction etc., there is still a lack of a hydrogenation approach in a controlled manner where all processing parameters (temperature, time and hydrogen flux) were precisely controlled in order to improve the PEC performance of H-TiO2 and understand the physical insight of enhanced PEC performance. Here, we report for the first time a controlled and local rapid thermal annealing (RTA) approach to prepare hydrogenated core-shell H-TiO2 nanorods grown on F:SnO2 (FTO) substrate in order to address the degradation issue of FTO in the typical TiO2 nanorods/FTO system observed in the conventional non-RTA treated approaches. Without the FTO degradation in the RTA approach, we systematically studied the intrinsic relationship between the annealing temperature, structural, optical, and photoelectrochemical properties in order to understand the role of the disordered shell on the improved photoelectrochemical behavior of H-TiO2 nanorods. Our investigation shows that the improvement of PEC performance could be attributed to (i) band gap narrowing from 3.0 to 2.9 eV; (ii) improved optical absorption in the visible range induced by the three-dimensional (3D) morphology and rough surface of the disordered shell; (iii) increased proper donor density; (iv) enhanced electron–hole separation and injection efficiency due to the formation of disordered shell after hydrogenation. The RTA approach developed here can be used as a suitable hydrogenation process for TiO2 nanorods/FTO system for important applications such as photocatalysis, hydrogen generation from water splitting and solar energy conversion. Electronic supplementary material The online version of this article (doi:10.1186/s11671-017-2105-x) contains supplementary material, which is available to authorized users.

Structural properties of rare earth niobates (RE3NbO7, RE = Y, Er, Yb, Lu) have been studied using selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). SAED patterns show diffuse scattering features along the [111] direction of the pure fluorite (Fm–3m) structure due to a short-range ordering of anion vacancies in the fluorite structure or the change of coordination number around some cations. The latter is related to the presence of small domains of pyrochlore phase (Fd-3m), which are observed in the HRTEM images.

Multilayers consisting of silicon nanocrystals (Si NCs) and SiO2 are successfully fabricated by electron beam evaporation, using pure Si and SiO2 targets in an oxygen-rich atmosphere for alternately depositing silicon-rich oxide (SRO) layers and SiO2 barriers, respectively. A post-deposition annealing process is carried out at different temperatures in order to achieve the Si precipitation in the form of nanocrystals. The stoichiometry of the layers is determined by X-ray photoelectron spectroscopy, which confirms the controlled silicon oxidation in order to attain SRO layers. Transmission electron microscopy and Raman-scattering measurements confirm the presence of crystalline Si-nanoprecipitates. Photoluminescence spectra from the Si NC samples can be deconvolved into two contributions, whose dynamics suggest that two different luminescent centers are responsible for the optical emission of the samples. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, This work was financially supported by the Spanish Ministry of Economy and Competitiveness (TEC2016‐76849‐C2‐1‐R and MAT2015‐71035‐R). O.B. also acknowledges the subprogram “Ayudas para Contratos Predoctorales para la Formación de Doctores” from the Spanish Ministry of Economy and Competitiveness for economical support. J.L.F. also acknowledges the subprogram “Ayudas para la Formación de Profesorado Universitario” from the Spanish Ministry of Education, Culture and Sports for economical support.

We offer a complete structural and optical study of samples containing silicon nanocrystals (Si-NCs) embedded in SiO2/SiON multilayers, varying the oxynitride layer thickness from 2.5 to 7 nm. Using energy-filtered transmission electron microscopy we have determined the size distribution of the precipitated Si-nanoaggregates. Raman scattering measurements were used to investigate the Si-NC size and crystalline quality. By combining both techniques, the nanoaggregate crystalline degree has been evaluated, with values around 50% for all the samples. Photoluminescence spectroscopy has shown a blueshift of the emission at smaller NC sizes, presenting the sample with Si-NCs of 3.9 nm the best emission properties.

Charge transport in nanocrystalline SiC with and without embedded Si nanocrystals (Si NCs) prepared by annealing of $a\ensuremath{-}\mathrm{S}{\mathrm{i}}_{1\ensuremath{-}x}{\mathrm{C}}_{x}:\mathrm{H}$ precursors is studied using temperature-dependent current-voltage measurements supported by electron spin resonance and mass spectrometry data. Transport is Ohmic in all films at all temperatures and the temperature dependence of conductivity shows that the materials behave as disordered semiconductors, exhibiting extended-state transport at high temperature and variable-range hopping transport at low temperature. Grain-boundary-, surface-, and interface-dominated transport is systematically ruled out. Films are $n$ type, and films with Si NCs exhibit up to ${10}^{3}$ times higher conductivity (up to $0.1\phantom{\rule{0.16em}{0ex}}\mathrm{S}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$) after exposure to a hydrogen plasma which passivates dangling bonds, particularly on Si NCs. A forming gas anneal does not have such an effect, indicating that atomic rather than molecular hydrogen is required. The conductivity of SiC films without Si NCs is largely unchanged by passivation and the Fermi level is not raised nearly as closely to the conduction band. This is attributed to a type I band offset between Si NCs and SiC that leads to extended-state conduction in films with Si NCs taking place in a Si network. This is confirmed by the dependence of the extended-state mobility on the volume fraction of excess Si. Variable-range hopping is relatively insensitive to the presence of excess Si and is hence considered to take place via shallow defect states throughout the volume of the films. The high conductivities are found to be a consequence of background doping by oxygen and nitrogen.

In this work we apply low-loss electron energy loss spectroscopy (EELS) to probe the structural and electronic properties of single silicon nanocrystals (NCs) embedded in three different dielectric matrices (SiO2, SiC and Si(3)N(4)). A monochromated and aberration corrected transmission electron microscope has been operated at 80 kV to avoid sample damage and to reduce the impact of radiative losses. We present a novel approach to disentangle the electronic features corresponding to pure Si-NCs from the surrounding dielectric material contribution through an appropriate computational treatment of hyperspectral datasets. First, the different material phases have been identified by measuring the plasmon energy. Due to the overlapping of Si-NCs and dielectric matrix information, the variable shape and position of mixed plasmonic features increases the difficulty of non-linear fitting methods to identify and separate the components in the EELS signal. We have managed to solve this problem for silicon oxide and nitride systems by applying multivariate analysis methods that can factorize the hyperspectral datacubes in selected regions. By doing so, the EELS spectra are re-expressed as a function of abundance of Si-NC-like and dielectric-like factors. EELS contributions from the embedded nanoparticles as well as their dielectric surroundings are thus studied in a new light, and compared with the dielectric material and crystalline silicon from the substrate. Electronic properties such as band gaps and plasmon shifts can be obtained by a straightforward examination. Finally, we have calculated the complex dielectric functions and the related electron effective mass and density of valence electrons.

In this work we present a structural, optical and electrical characterization of Si x C 1− x /SiC multilayer systems with different silicon content. After the deposition process, an annealing treatment was carried out in order to induce the silicon nanocrystals formation. By means of energy-filtered transmission electron microscopy (EFTEM) we observed the structural morphology of the multilayers and the presence of crystallized silicon nanoprecipitates for samples annealed up to 1100 °C. We discuss the suitability of optical techniques such as Raman scattering and reflectance and transmittance ( R&T ) for the evaluation of the crystalline fraction of our samples at different silicon excess ranges. In addition, the combination of R&T measurements with simulation has proved to be a useful instrument to confirm the structural properties observed by EFTEM. Finally, we explore the origin of the extremely high current density revealed by electrical measurements, probably due to the presence of an undesired defective SiC y O z ternary compound layer, already supported by the structural and optical results. Nevertheless, the variation of the electrical measurements with the silicon amount indicates a small but significant contribution from the multilayers.

We present a detailed examination of a multiple InxGa1−xN quantum well (QW) structure for optoelectronic applications. The characterization is carried out using scanning transmission electron microscopy (STEM), combining high-angle annular dark field (HAADF) imaging and electron energy loss spectroscopy (EELS). Fluctuations in the QW thickness and composition are observed in atomic resolution images. The impact of these small changes on the electronic properties of the semiconductor material is measured through spatially localized low-loss EELS, obtaining band gap and plasmon energy values. Because of the small size of the InGaN QW layers additional effects hinder the analysis. Hence, additional parameters were explored, which can be assessed using the same EELS data and give further information. For instance, plasmon width was studied using a model-based fit approach to the plasmon peak; observing a broadening of this peak can be related to the chemical and structural inhomogeneity in the InGaN QW layers. Additionally, Kramers-Kronig analysis (KKA) was used to calculate the complex dielectric function (CDF) from the EELS spectrum images (SIs). After this analysis, the electron effective mass and the sample absolute thickness were obtained, and an alternative method for the assessment of plasmon energy was demonstrated. Also after KKA, the normalization of the energy-loss spectrum allows us to analyze the Ga 3d transition, which provides additional chemical information at great spatial resolution. Each one of these methods is presented in this work together with a critical discussion of their advantages and drawbacks.

The optimization of a material functionality requires both the rational design and precise engineering of its structural and chemical parameters. In this work, we show how colloidal chemistry is an excellent synthetic choice for the synthesis of novel ternary nanostructured chalcogenides, containing exclusively noble metals, with tailored morphology and composition and with potential application in the energy conversion field. Specifically, the Ag–Au–Se system has been explored from a synthetic point of view, which leads to a set of Ag2Se-based hybrid and ternary nanoparticles including the room temperature synthesis of the rare ternary Ag3AuSe2 fischesserite phase. An in-depth structural and chemical characterization of all nanomaterials has been performed, which proofed especially useful for unravelling the reaction mechanism behind the formation of the ternary phase in solution. The work is complemented with the thermal and electric characterization of a ternary Ag–Au–Se nanocomposite with promising results: we found that the use of the ternary nanocomposite represents a clear improvement in terms of thermoelectric energy conversion as compared to a binary Ag–Se nanocomposite analogue.

Light emitting Al-Tb/SiO2 nanomultilayers (NMLs) for optoelectronic applications have been produced and characterized. The active layers were deposited by electron beam evaporation onto crystalline silicon substrates, by alternatively evaporating nanometric layers of Al, Tb, and SiO2. After deposition, all samples were submitted to an annealing treatment for 1 h in N2 atmosphere at different temperatures, ranging from 700 to 1100 °C. Transmission electron microscopy confirmed the NML structure quality, and by complementing the measurements with electron energy-loss spectroscopy, the chemical composition of the multilayers was determined at the nanoscopic level. The average composition was also measured by X-ray photoelectron spectroscopy (XPS), revealing that samples containing Al are highly oxidized. Photoluminescence experiments exhibit narrow emission lines ascribed to Tb3+ ions in all samples (both as-deposited and annealed ones), together with a broadband related to SiO2 defects. The Tb-related emission intensity in the sample annealed at 1100 °C is more than one order of magnitude higher than identical samples without Al. These effects have been ascribed to the higher matrix quality, less SiO2 defects emitting, and a better Tb3+ configuration in the SiO2 matrix thanks to the higher oxygen content favored by the incorporation of Al atoms, as revealed by XPS experiments.