Low dose electron tomography of novel nanocomposites for additive manufacturing

This is an open access article under the CC BY-NC-ND licenseThe development of new nanocomposites with added functionalities for Additive Manufacturing (AM) requires of a deep understanding of the 3D distribution of the selected nano-additives within the polymeric matrix, in order to optimize their performance. For this, electron tomography (ET) is an outstanding analysis technique that requires the material to withstand the electron exposure needed for the acquisition of several tens of images, becoming challenging for beam-sensitive materials. In this work, we analyse the parameters involved in the successful analysis by low dose ET of nanocomposites based in acrylic resins for stereolithography (SLA). Needleshape electron-transparent specimens have been fabricated by focused ion beam (FIB), minimizing surface damage due to the high energy Ga+ ions. Microscope settings for tuning the electron dose applied during the ET analysis of these nanoneedles are discussed. A phenomenological study of the effect of increasing the electron dose in the scanning transmission electron microscopy (STEM) analysis of the material has been carried out, showing that ET can be effectively performed at low electron doses. Two case studies are presented, to illustrate the relevance of these analyses in the development of nanocomposites with added functionalities. Our results have revealed the crucial role of the dose rate and of inaccuracies in the calculation of critical electron doses for the design of ET experiments.Junta de Andalucía 00955Universidad de Cádiz PR2022-00

Room-temperature Operation of Low-voltage, Non-volatile, Compound-semiconductor Memory Cells

Whilst the different forms of conventional (charge-based) memories are well suited to their individual roles in computers and other electronic devices, flaws in their properties mean that intensive research into alternative, or emerging, memories continues. In particular, the goal of simultaneously achieving the contradictory requirements of non-volatility and fast, low-voltage (low-energy) switching has proved challenging. Here, we report an oxide-free, floating-gate memory cell based on III-V semiconductor heterostructures with a junctionless channel and non-destructive read of the stored data. Non-volatile data retention of at least 104 s in combination with switching at ≤2.6 V is achieved by use of the extraordinary 2.1 eV conduction band offsets of InAs/AlSb and a triple-barrier resonant tunnelling structure. The combination of low-voltage operation and small capacitance implies intrinsic switching energy per unit area that is 100 and 1000 times smaller than dynamic random access memory and Flash respectively. The device may thus be considered as a new emerging memory with considerable potential

Structural changes during the natural aging process of InN quantum dots

The natural aging process of InN nanostructures by the formation of indium oxides is examined by transmission electron microscopy related techniques. Uncapped and GaN-capped InN quantum dots (QDs) on GaN/sapphire substrates were grown under the same conditions and kept at room temperature/pressure conditions. The GaN capping layer is found to preserve the InN QDs in the wurtzite phase, avoiding the formation of group-III oxides, while in the uncapped sample, a thin layer of cubic phases are formed that envelops the nucleus of wurtzite InN. These cubic phases are shown to be mainly bcc- In 2 O3 for long aged samples where the nitrogen atoms in the InN surface layers have been substituted by atmospheric oxygen. This process implies the gradual transformation of the In sublattice from hcp to a quasi-fcc structure. Metastable zinc-blende InN phases rich in oxygen atoms are proposed to act as intermediate phases and they are evinced in samples less aged. The large concurrence of interplanar spaces, the twin formation, and the existence of a free surface that facilitates the transformation support this mechanism and would explain the high instability of the InN nanostructures at ambient conditions.Comisión Interministerial de Ciencia y Tecnología (CICYT) MAT2007-60643Junta de Andalucía TEP383 EspañaUnión Europea NMP4-CT-2004- 50010

Induced damage during STEM-EELS analyses on acrylic-based materials for Stereolithography

(Scanning) transmission electron microscopy, (S)TEM, offers a powerful characterization tool based on electron-matter interactions, highly valuable in materials science. However, the possible electron beam induced damage during (S)TEM measurements hinders the analysis of soft materials, such as acrylic resins. Importantly, acrylic resins offer an appealing playground for the development of novel composites with customized properties and convenient processing capabilities for 3D-printing technologies, including Stereolithography (SLA). There are several factors preventing the optimal performance of TEM measurements applied to acrylic resins, among which we focus on the quality of the analyzed specimen (i.e., compromise between thickness and robustness, to achieve electron transparency while keeping the material integrity), particularly challenging when working with soft materials; the electrostatic charging/discharging effects, resulting in sample drift and related noise/artefacts; and the radiolysis and knock-on electron-induced damage, which directly degrade the material under study. We explore and compare different methodologies to obtain resin specimens suitable for (S)TEM analysis, employed for the subsequent study of the electron–beam damage induced during STEM-EELS measurements. Furthermore, we propose likely underlying mechanisms explaining the acrylic resin degradation based on the different EELS monitored signals. On one hand, we assess the evolution of the carbon and oxygen content, as well as the material thinning as a function of the accumulated electron dose. On the other hand, we extract meaningful information from the spectral shape of carbon and oxygen K-edges upon increasing electron doses, unraveling likely degradation pathways. The earned understanding on the electron-beam induced damage and the determination of critical doses provide a useful framework for the implementation of (S)TEM techniques as useful tools to help in the smart engineering of acrylic-based composites for SLA.DME-SC-ICyT-ELECMI-UCAUnión Europea - Junta de Andalucía - INNANOMAT TEP94

Exploring the Capability of HAADF-STEM Techniques to Characterize Graphene Distribution in Nanocomposites by Simulations

This paper explores the capability of scanning transmission electron microscopy (STEM) techniques in determining the dispersion degree of graphene layers within the carbon matrix by using simulated high-angle annular dark-field (HAADF) images. Results ensure that unmarked graphene layers are only detectable if their orientation is parallel to the microscope beam. Additionally, gold-marked graphene layers allow evaluating the dispersion degree in structural composites. Moreover, electron tomography has been demonstrated to provide truthfully 3D distribution of the graphene sheets inside the matrix when an appropriate reconstruction algorithm and 2D projections including channelling effect are use

Active and Stable Embedded Au@CeO2 Catalysts for Preferential Oxidation of CO

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Solution-Processed Ni-Based Nanocomposite Electrocatalysts: An Approach to Highly Efficient Electrochemical Water Splitting

In this study, we report an up-scalable and low-cost solution-processed method to in situ synthesize an earth-abundant non-stoichiometric NiOx-based electrocatalytic film for water oxidation. The catalytic activity was found to be inversely proportional to the baking temperature, which varied from 50 to 500 °C. We found the formation of a hybrid nanocomposite thin film of NiOx nanocrystals (<2 nm size) inside an acetate-based organic matrix at low temperatures (<200 °C). The defective and short-range structural order of the NiOx-based nanocomposite electrocatalysts, compatible with lattice stress, low electrical conductivity, and high density of catalytically active surface species, and higher Fe incorporation were responsible for the enhanced electrocatalytic activity. Our champion NiOx catalyst features a 358 mV overpotential at 10 mA cm–2 and more than 60 h of continuous operation without significant losses, which is a remarkable milestone for undoped NiOx electrocatalysts synthesized at nearly room temperature by a solution-processed up-scalable method.Funding for open access charge: CRUE-Universitat Jaume IThe authors acknowledge the financial support from the Ministerio de Ciencia, Innovación y Universidades of Spain through funded projects ENE2017-85087-C3-1-R, RYC-2015-18349, and TEC2017-86102-C2-1-R and Agencia Valenciana de la Innovacion (AVI) INNVAL10/18/032. The authors thank the Central Support Service for Experimental Research (SCSIE) (XRD and SEM facilities) and the Institute of Materials Science (TGA and DTA equipment) of the University of Valencia and the Central Service of Scientific Instrumentation (SCIC) at University Jaume I. The authors also thank Prof. Juan P. Martinez-Pastor for his constructive suggestions and scientific discussions

Polymer nanocomposites for plasmonics: In situ synthesis of gold nanoparticles after additive manufacturing

A series of nanocomposites containing gold nanoparticles (AuNPs) are prepared by stereolithography (SL) by simply adding a precursor (KAuCl4) to a photoresist. A thermal treatment is performed after manufacturing the nanocomposites, triggering the reduction of KAuCl4 into AuNPs in solid state. In this approach, the photopolymerization of the resin and the formation of the AuNPs occur independently, allowing the optimization of these two processes separately. Advanced electron microscopy analyses reveal the distribution, size and morphology of the AuNPs synthesized within the resin, showing the influence of the gold precursor concentration and different thermal treatments. The localized surface plasmon resonance (LSPR) of the AuNPs modifies the optical properties of the 3D-printed nanocomposites, yielding transparent yet colored materials even for concentrations as low as 0.1 wt% KAuCl4. This behavior can be modelled by the Mie theory, correlating the macroscopic properties of the nanocomposites with the individual AuNPs embedded in the resin. The possibility of tuning the LSPR of the AuNPs together with the ability of manufacturing 3D-structures with sub-millimeter precision by SL, paves the way for the design of advanced platforms for plasmonics, such as sensors for surface enhanced Raman spectroscopy9 página

Effect of an in-situ thermal annealing on the structural properties of self-assembled GaSb/GaAs quantum dots

In this work, the effect of the application of a thermal annealing on the structural properties of GaSb/GaAs quantum dots (QDs)1 is analyzed by aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM)2 and electron energy loss spectroscopy (EELS)3 Our results show that the GaSb/GaAs QDs are more elongated after the annealing, and that the interfaces are less abrupt due to the Sb diffusion. We have also found a strong reduction in the misfit dislocation density with the annealing. The analysis by EELS of a threading dislocation has shown that the dislocation core is rich in Sb. In addition, the region of the GaAs substrate delimited by the threading dislocation is shown to be Sb-rich as well. An enhanced diffusion of Sb due to a mechanism assisted by the dislocation movement is discussed

Global, regional, and national disability-adjusted life-years (DALYs) for 359 diseases and injuries and healthy life expectancy (HALE) for 195 countries and territories, 1990-2017: a systematic analysis for the Global Burden of Disease Study 2017.

How long one lives, how many years of life are spent in good and poor health, and how the population's state of health and leading causes of disability change over time all have implications for policy, planning, and provision of services. We comparatively assessed the patterns and trends of healthy life expectancy (HALE), which quantifies the number of years of life expected to be lived in good health, and the complementary measure of disability-adjusted life-years (DALYs), a composite measure of disease burden capturing both premature mortality and prevalence and severity of ill health, for 359 diseases and injuries for 195 countries and territories over the past 28 years. Methods We used data for age-specific mortality rates, years of life lost (YLLs) due to premature mortality, and years lived with disability (YLDs) from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 to calculate HALE and DALYs from 1990 to 2017. We calculated HALE using age-specific mortality rates and YLDs per capita for each location, age, sex, and year. We calculated DALYs for 359 causes as the sum of YLLs and YLDs. We assessed how observed HALE and DALYs differed by country and sex from expected trends based on Socio-demographic Index (SDI). We also analysed HALE by decomposing years of life gained into years spent in good health and in poor health, between 1990 and 2017, and extra years lived by females compared with males. Findings Globally, from 1990 to 2017, life expectancy at birth increased by 7·4 years (95% uncertainty interval 7·1-7·8), from 65·6 years (65·3-65·8) in 1990 to 73·0 years (72·7-73·3) in 2017. The increase in years of life varied from 5·1 years (5·0-5·3) in high SDI countries to 12·0 years (11·3-12·8) in low SDI countries. Of the additional years of life expected at birth, 26·3% (20·1-33·1) were expected to be spent in poor health in high SDI countries compared with 11·7% (8·8-15·1) in low-middle SDI countries. HALE at birth increased by 6·3 years (5·9-6·7), from 57·0 years (54·6-59·1) in 1990 to 63·3 years (60·5-65·7) in 2017. The increase varied from 3·8 years (3·4-4·1) in high SDI countries to 10·5 years (9·8-11·2) in low SDI countries. Even larger variations in HALE than these were observed between countries, ranging from 1·0 year (0·4-1·7) in Saint Vincent and the Grenadines (62·4 years [59·9-64·7] in 1990 to 63·5 years [60·9-65·8] in 2017) to 23·7 years (21·9-25·6) in Eritrea (30·7 years [28·9-32·2] in 1990 to 54·4 years [51·5-57·1] in 2017). In most countries, the increase in HALE was smaller than the increase in overall life expectancy, indicating more years lived in poor health. In 180 of 195 countries and territories, females were expected to live longer than males in 2017, with extra years lived varying from 1·4 years (0·6-2·3) in Algeria to 11·9 years (10·9-12·9) in Ukraine. Of the extra years gained, the proportion spent in poor health varied largely across countries, with less than 20% of additional years spent in poor health in Bosnia and Herzegovina, Burundi, and Slovakia, whereas in Bahrain all the extra years were spent in poor health. In 2017, the highest estimate of HALE at birth was in Singapore for both females (75·8 years [72·4-78·7]) and males (72·6 years [69·8-75·0]) and the lowest estimates were in Central African Republic (47·0 years [43·7-50·2] for females and 42·8 years [40·1-45·6] for males). Globally, in 2017, the five leading causes of DALYs were neonatal disorders, ischaemic heart disease, stroke, lower respiratory infections, and chronic obstructive pulmonary disease. Between 1990 and 2017, age-standardised DALY rates decreased by 41·3% (38·8-43·5) for communicable diseases and by 49·8% (47·9-51·6) for neonatal disorders. For non-communicable diseases, global DALYs increased by 40·1% (36·8-43·0), although age-standardised DALY rates decreased by 18·1% (16·0-20·2)