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This study focuses on H2-O2 operando AEMFC performance based on several platinum group metal (PGM) and PGM-free catalysts. Specifically, we evaluate the AEMFC performance of commercial PtRu/C, as-synthesized PtRu/C, and Pd-CeO2/C catalysts as anodes and commercial Pt/C and as-synthesized N-doped carbon catalysts as cathodes. The evolution of cell performance with varying cathode catalyst layer compositions, back pressure, and dew points is underscored. The as-synthesized PtRu/C catalyst is characterized by advanced transmission electron microscopy and showed significantly high performance reaching a peak power density of 1900 mW cm−2 at 80 °C with remarkably promising initial stability. We further showed the cell performances using Pd-CeO2/C anodes paired with both standard Pt/C and metal-free N-doped carbon as a cathodes, which resulted in peak power densities of 890 and 537 mW cm‒2, respectively. Data reported in this study sheds light on the development of AEMFCs using PGM and PGM-free catalysts.

In this study, we use differential phase contrast images obtained by scanning transmission electron microscopy combined with computer simulations to map the atomic electrostatic fields of MoS2 monolayers and investigate the effect of sulfur monovacancies and divancancies on the atomic electric field and total charge distribution. A significant redistribution of the electric field in the regions containing defects is observed, with a progressive decrease in the strength of the projected electric field for each sulfur atom removed from its position. The electric field strength at the sulfur monovacancy sites is reduced by approximately 50% and nearly vanishes at the divacancy sites, where it drops to around 15% of the original value, demonstrating the tendency of these defects to attract positively charged ions or particles. In addition, the absence of the sulfur atoms leads to an inversion in the polarity of the total charge distribution in these regions.

Ru attracted considerable attention as a candidate to replace TaN as a diffusion barrier layer for Cu interconnect metallisation. The addition of W improves the diffusion barrier properties of Ru but appears to weaken the adhesion strength between the barrier and Cu and the direct (seedless) electroplatability behaviour. Although Cu can be directly electroplated on near equimolar Ru-W thin films, no complete substrate coverage is obtained. The understanding of Cu electrocrystallisation on Ru–W is essential to develop methods of fabricating thin, continuous, and well adherent films for advanced interconnect metallisation, where Ru–W thin films could be used as diffusion barriers. This work studies the effect of ultrasonic agitation on the growth of Cu films electroplated on Ru–W, namely on the impact on substrate coverage. Film structure, morphology and chemical composition were evaluated by digital and scanning and transmission electron microscopies, and X-ray diffraction. The results show that Cu particles decrease with increasing current density, but when no electrolyte agitation is applied, substrate coverage is incomplete in the central region, with openings around larger Cu particles, regardless of current density. Under ultrasonic agitation, substrate coverage is remarkably improved. An active particle detachment mechanism is proposed as responsible for attaining improved substrate coverage, only possible at intermediate current density. Lower current densities promote growth over nucleation, whereas higher currents result in extensive hydrogen reduction/formation. Ultrasonic agitation also enhances a preferential Cu growth along direction.

Pt–Ni nanoparticles (NPs) are used as electrocatalysts toward the oxygen reduction reaction due to their high mass activity. However, degradation processes at high potential under the acidic conditions of proton exchange membrane fuel cells delay their massive implementation. The model presented here facilitates understanding of the corrosion by clearing variables related to the electrochemical measurement (non-equilibrium conditions and complex system) and focusing on the gradual etching of Ni via two-phase Ni(II) transfer treatment promoted by chelating agents (CAs). We synthesized Pt–Ni/C octahedral NPs and then used six chemically different CAs as corrosion agents for Ni. The corrosion yielded concave octahedral and hexapod NPs. Amine-rich CA treatment results in particle detachment from the carbon substrates, while carboxylic-rich CA treatment preserves the carbon–particle bond. We correlate the detachment to the type of chemical group in the CAs and the Ni etching is correlated to the pH. The ORR of the best catalyst is reported.

Background: Other tools for weed management should be considered in addition to the use of herbicides. In this context, the identification and use of allelopathic compounds deserves attention. Question: To quantify phenolic compounds and evaluate the allelopathic potential of extracts of Conyza sumatrensis on the germination of Bidens pilosa . Studied species: Conyza sumatrensis (Retz.) E.Walker, Bidens pilosa L. (Asteraceae) Study site: Palotina, state of Paraná, Brazil. Methods: The aqueous extracts were prepared with shoot and root portions of C. sumatrensis in concentrations: 0, 1, 5 and 10 %. Germination and germination speed index were evaluated. The total flavonoids and phenols of the tested extracts were also quantified. Results: With increasing concentrations of the extracts there was an increased inhibition of germination of B. pilosa and delays in the germination process. The extracts from the shoot of C. sumatrensis had a more expressive effect on seed germination when compared to the extracts obtained from the root. At concentration of 10 %, the extract from the shoot reduced in 83 % the percentage of germination. This may be related to the higher concentration of total flavonoids and phenols found. Conclusion: The allelopathic potential of C. sumatrensis plants can be considered since both shoot and root extracts inhibited and/or reduced the germination of B. pilosa .

Bandgap engineering and quantum confinement in semiconductor heterostructures provide the means to fine-tune material response to electromagnetic fields and light in a wide range of the spectrum. Nonetheless, forming semiconductor heterostructures on lattice-mismatched substrates has been a challenge for several decades, leading to restrictions for device integration and the lack of efficient devices in important wavelength bands. Here, we show that the van der Waals epitaxy of two-dimensional (2D) GaSe and InSe heterostructures occur on substrates with substantially different lattice parameters, namely silicon and sapphire. The GaSe/InSe heterostructures were applied in the growth of quantum wells and superlattices presenting photoluminescence and absorption related to interband transitions. Moreover, we demonstrate a self-powered photodetector based on this heterostructure on Si that works in the visible-NIR wavelength range. Fabricated at wafer-scale, these results pave the way for an easy integration of optoelectronics based on these layered 2D materials in current Si technology., 16 Pages, 5 figures. Supplementary Information included in the end (+10 pages, +10 Figures, + 2 Tables). Partially presented at 21st ICMBE - September 2021

For decades, Ta/TaN has been the industry standard for a diffusion barrier against Cu in interconnect metallisation. The continuous miniaturisation of transistors and interconnects into the nanoscale are pushing conventional materials to their physical limits and creating the need to replace them. Binary metallic systems, such as Ru-W, have attracted considerable attention as possible replacements due to a combination of electrical and diffusion barrier properties and the capability of direct Cu electroplating. The process of Cu electrodeposition on Ru-W is of fundamental importance in order to create thin, continuous, and adherent films for advanced interconnect metallisation. This work investigates the effects of the current density and application method on the electro-crystallisation behaviour of Cu. The film structure, morphology, and chemical composition were assessed by digital microscopy, atomic force microscopy, scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The results show that it was possible to form a thin Cu film on Ru-W with interfacial continuity for current densities higher than 5 mA·cm−2; however, the substrate regions around large Cu particles remained uncovered. Pulse-reverse current application appears to be more beneficial than direct current as it decreased the average Cu particle size.

In this study, we use differential phase contrast images obtained by scanning transmission electron microscopy combined with computer simulations to map the atomic electrostatic fields of MoS

Water oxidation catalysts (WOCs) are essential to electrochemical hydrogen production, but (electro)chemical instability remains a critical issue for WOCs especially under acidic conditions. Here we present a hybrid organic-inorganic polymeric dual network gel (DN gel) electrocatalyst based on earth-abundant elements via in situ oxidative polymerization of polypyrrole and simultaneous cyano-polymerization for efficient acidic water oxidation. X-ray absorption and X-ray photoelectron spectra reveal a synergistic interplay between the inorganic polymer and the organic conductive polymer in producing a favorable local coordination environment, further supported by the DFT calculation. The DN gel electrocatalyst exhibits highly active and stable catalytic activity for oxygen evolution in the pH = 0 electrolyte, with no noticeable degradation after more than 3000 cycles. This work presents an alternative insight into developing highly active and robust WOCs as promising alternatives to noble metal catalysts in strong acids.

Solvents play an essential role in many areas of chemistry and is the cornerstone of understanding reactivity in solution-phase reactions. Solvent effects have been widely observed in intercalation reactions; however, understanding of the influence of solvents on the thermodynamics and kinetics remains largely elusive in intercalation chemistry. Now, the solvent-dependent kinetics of ferrocene intercalation into a layered vanadyl phosphate (VOPO4 ⋅2 H2 O) host is presented, with a special focus on primary alcohols. From methanol to 1-hexnaol, the intercalation rate peaks in 1-propanol (80 times faster than the slowest case in methanol). Similar kinetics of exfoliation are also found in these solvents without ferrocene. The correlation between intercalation and exfoliation is understood at atomic level by DFT calculations, which reveal the role of pre-intercalated solvent molecules play in intralayer interactions, interlayer expansion, and layer sliding.

Super duplex stainless steels are prone to the formation of undesirable secondary phases, particularly when exposed to slow cooling rates. In the current study, the mechanisms of formation of secondary phases have been characterized using a combination of optical microscopy, scanning electron microscopy, and transmission electron microscopy, on samples aged at temperatures ranging between 700 °C and 1000 °C. Among the possible secondary phases, χ-phase and σ-phase were detected and identified as the main phases responsible for the destabilization of the duplex microstructure. The kinetics of both phases were assessed. In particular, the χ-phase forms prior to σ-phase, until it starts to convert into σ-phase. Finally, the TTT curves for the stable σ-phase were calculated. We found that the precipitation of the σ-phase starts as early as 30 seconds at 950 °C.

Our previous work demonstrated that the decorated Pt nano particles (PNP) distributed uniformly over the surface of the PBI-functionalized graphene. Considering the excellent chemical stability and conductivity, graphene are the promising catalyst supports for PEMFCs. However, the mass transfer issue is a huge challenge for the application of graphene as catalyst supports. In this paper, a method to overcome such an issue was proposed, in which the highly stable spacers were introduced during catalyst ink preparation to create channels/pores which facilitates the mass transfer, consequently, increase the high current density performance while maintain the excellent stability.

Gold–iron oxide nano-heterostructures with a clear and well-defined morphology were prepared via a seed-assisted method. The synthesis process and the events of heterogeneous nucleation during the decomposition of the iron precursor were carefully studied in order to understand the mechanism of the reaction and to tailor the architecture of the fabricated heterostructures. When employing Au seeds of 3 and 5 nm, nanoparticles with a dimer-like morphology were produced due to the occurrence of a single iron oxide nucleation event. Otherwise, multi-nucleation events could be favored by two mechanisms: (i) by the incorporation of a reducing agent and the slowing down of the heating protocol, leading to a core–shell system; (ii) by the increase of the Au seed size to 8 nm, leading to a flower-like system. Further increase of the Au seed size to 12 nm using similar synthesis conditions promotes the homogeneous nucleation and growth of the iron oxide phase, without formation of heterostructures. An in-depth study was performed on the gold–iron oxide heterostructures to confirm the epitaxial growth of the oxide domain over the Au seed and to analyze the elemental distribution of the components within the heterostructures. Finally, it was found that the modification of the plasmonic properties of the Au nanoparticles are strongly influenced by the architecture of the heterostructure, with a more pronounced damping effect for the systems produced after multi-nucleation events.

Uncorrected proof, Graphene-based materials have attracted significant attention in many technological fields, but scaling up graphene-based technologies still faces substantial challenges. High-throughput top-down methods generally require hazardous, toxic, and high-boiling-point solvents. Here, an efficient and inexpensive strategy is proposed to produce graphene dispersions by liquid-phase exfoliation (LPE) through a combination of shear-mixing (SM) and tip sonication (TS) techniques, yielding highly concentrated graphene inks compatible with spray coating. The quality of graphene flakes (e.g., lateral size and thickness) and their concentration in the dispersions are compared using different spectroscopic and microscopy techniques. Several approaches (individual SM and TS, and their combination) are tested in three solvents (N-methyl-2-pyrrolidone, dimethylformamide, and cyrene). Interestingly, the combination of SM and TS in cyrene yields high-quality graphene dispersions, overcoming the environmental issues linked to the other two solvents. Starting from the cyrene dispersion, a graphene-based ink is prepared to spray-coat flexible electrodes and assemble a touch screen prototype. The electrodes feature a low sheet resistance (290 Ω □−1) and high optical transmittance (78%), which provide the prototype with a high signal-to-noise ratio (14 dB) and multi-touch functionality (up to four simultaneous touches). These results illustrate a potential pathway toward the integration of LPE-graphene in commercial flexible electronics, Prof. F. Arciprete (University of Rome Tor Vergata) for assistance with AFM measurements, Dr. Yury Kolen'ko for technical assistance and fruitful discussions. The authors acknowledge the financial support of the projects GNESIS with the reference POCI-01-0247-FEDER-033566 and “GEMIS – Graphene-enhanced Electro-Magnetic Interference Shielding,” with the reference POCI-01-0247-FEDER-045939, co-funded by COMPETE 2020 – Operational Programme for Competitiveness and Internationalization and FCT – Science and Technology Foundation, under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). FCT partially supported UMinho's research in the framework of the Strategic Funding UIDB/04650/2020. This work was partially supported by FCT, through IDMEC, under LAETA, project UIDB/50022/2020

2D GaSe is a semiconductor belonging to the group of post-transition metal chalcogenides with great potential for advanced optoelectronic applications. The weak interlayer interaction in multilayer 2D materials allows the formation of several polymorphs. Here, the first structural observation of a new GaSe polymorph is reported, characterized by a distinct atomic configuration with a centrosymmetric monolayer (D-3d point group). The atomic structure of this new GaSe polymorph is determined by aberration-corrected scanning transmission electron microscopy. Density-functional theory calculations verify the structural stability of this polymorph. Furthermore, the band structure and Raman intensities are calculated, predicting slight differences to the currently known polymorphs. In addition, the occurrence of layer rotations, interlayer relative orientations, as well as translation shear faults is discussed. The experimental confirmation of the new GaSe polymorph indicates the importance of investigating changes in the crystal structure, which can further impact the properties of this family of compounds, This article has received support from the project Nanotechnology Based Functional Solutions (NORTE-01-0145-FEDER-000019), supported by Norte Portugal Regional Operational Programme (NORTE2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). Additional support by National Funds through the Portuguese Foundation for Science and Technology (FCT) in the framework of the project "LA2D" -PTDC/FIS-NAN/3668/2014 is acknowledged. This work was supported by FCT, through IDMEC, under LAETA, project UIDB/50022/2020. A. M.-S. thanks the Marie-Curie-COFUND program Nano TRAIN for Growth II (Grant Agreement 713640) and the Ramon y Cajal programme (grant RYC2018-024024-I, MINECO, Spain). This work was carried out in part through the use of the INL Advanced Electron Microscopy, Imaging, and Spectroscopy Facility. The computations were performed on the Tirant III cluster of the Servei d'Informatica of the University of Valencia (project vlc82) and on Mare Nostrum cluster of the Barcelona Supercomputing Center (project FI-2020-2-033 and FI-2020-3-0021).

Molybdenum disulfide (MoS2 ) is a multifunctional material that can be used for various applications. In the single-crystalline form, MoS2 shows superior electronic properties. It is also an exceptionally useful nanomaterial in its polycrystalline form with applications in catalysis, energy storage, water treatment, and gas sensing. Here, the scalable fabrication of longitudinal MoS2 nanostructures, i.e., nanoribbons, and their oxide hybrids with tunable dimensions in a rational and well-reproducible fashion, is reported. The nanoribbons, obtained at different reaction stages, that is, MoO3 , MoS2 /MoO2 hybrid, and MoS2 , are fully characterized. The growth method presented herein has a high yield and is particularly robust. The MoS2 nanoribbons can readily be removed from its substrate and dispersed in solution. It is shown that functionalized MoS2 nanoribbons can be manipulated in solution and assembled in controlled patterns and directly on microelectrodes with UV-click-chemistry. Owing to the high chemical purity and polycrystalline nature, the MoS2 nanostructures demonstrate rapid optoelectronic response to wavelengths from 450 to 750 nm, and successfully remove mercury contaminants from water. The scalable fabrication and manipulation followed by light-directed assembly of MoS2 nanoribbons, and their unique properties, will be inspiring for device fabrication and applications of the transition metal dichalcogenides.

Tantalum oxide (Ta2O5) nanostructures exhibit outstanding electrical and optical properties, as well as, high chemical resistance and stability. These materials have great potential for biomedical, catalysis, semiconductors and energy applications due to their large surface area and high specific charge, when arranged in nanoporous or nanotubular morphologies. In order to obtain these structures, an anodization process, which is inexpensive, reproducible and easy to scale up, is used. Yet, depending on the anodization conditions, the formation of a nanoporous or nanotubular layer is difficult to stabilize during the anodization process. In this regard, anodized tantalum oxide nanostructures were produced to understand the effect of the anodization conditions, including electrolyte concentration, potential and time. The nanopores or nanotubes morphologies, their chemical composition and structure were investigated by FIB-SEM, double-corrected TEM-STEM and EDS. We found that it is necessary to have high acid concentrations (mixture of H2SO4 with HF) to be able to form nanoporous or nanotubular structures. Despite the capacity of HF to dissolve and create anodic oxide nanostructures, the amount of H2SO4 concentration in the mixture is very important, leading to a dimple morphology. Furthermore, the increase of the anodization potential/electrical field clearly leads to an increase in the dimples diameter., This research is sponsored by FEDER funds through the program COMPETE -Programa Operacional Factores de Competitividade and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020, and UID/EMS/00285/2020 and with a PhD fellowship SFRH/BD/98199/2013.The authors thank the financial support in the framework of HEALTHYDENT -POCI-01-0145-FEDER-030708 and PTDC/CTM-NAN/4242/2014 projects.This work was supported by FCT, through IDMEC, under LAETA, project UIDB/50022/2020.The authors would like to acknowledge that this project has received funding from the EU Framework Programme for Research and Innovation H2020, scheme COFUND -Co-funding of Regional, National and International Programmes, under Grant Agreement 713640.

The purpose of this work is the development of Ag/a:C and Ag-Au/a:C coatings for ureteral stents, to provide them with antimicrobial characteristics. Silver was selected due to the well-known antibacterial properties, while gold was included to assess its capacity to accelerate the silver ion release forming a galvanic couple between Au and Ag. Thus, the metallic (Ag) and bimetallic clusters (Ag/Au) were produced by three different configurations: i) unbalanced magnetron sputtering (conventional sputtering), (ii) plasma gas condensation process and by (iii) a combination between both previous approaches. Coatings with Ag/Au bimetallic clusters were characterized by transmission electrons microscopy (TEM) in order to study the arrangement (alloy, core-shell and galvanic couple) of these particles in the carbon matrix. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to quantify the Ag ions released through artificial urine from the different coatings deposited on thermoplastic polyurethane (TPU) tape (one of the materials used in the ureteral stent manufacture). Then, the antibacterial and cytotoxicity properties of Ag and Ag-Au/a:C coatings were evaluated. TEM shows that a biphasic structure was not detected, thus not allowing to anticipate the establishment of a galvanic couple. The ICP-OES results demonstrate that the silver ionization is mainly a function of the amount of silver incorporated in the amorphous carbon (a:C) matrix, and the formation of bimetallic alloy has a detrimental effect on release of the silver ions. The antibacterial activity was regulated by the silver ionization mechanisms since the coatings with higher Ag release had a higher antibacterial activity., This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the projects: PTDC/CTM-NAN/4242/2014, under the framework of the Strategic Funding; UIDB/04650/2019 and UIDB/04469/2020; BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020; CEMMPRE - UID/EMS/00285/2019 [co-financed via FEDER and FCT (COMPETE)]; ATRITO-0 (co-financed via FEDER (PT2020) POCI 01-0145-FEDER-030446 and FCT (PIDDAC)); On-SURF (co-financed via FEDER (PT2020) POCI-01-0247-FEDER-024521); IDMEC, under LAETA, project UID/EMS/50022/2019., info:eu-repo/semantics/publishedVersion

The proposed work aims to functionalize leathers for footwear industry with antimicrobial properties based on AgTiO2 nanoparticles. The synthesis of nanoparticles was carried out by the hydrothermal method with significant advantages in terms of time, energy savings and low cost. Anatase TiO2 nanoparticles with dimensions below 10nm were obtained as observed by X-ray diffraction and transmission electron microscopy. Fourier transform infrared spectroscopy showed that the based structure of leather was not modified by the addition of the nanoparticles. The antimicrobial activity was evaluated and it was observed that Ag containing leathers gained antimicrobial activity. In addition, the nanoparticles were found to be non-cytotoxic. This achievement, by itself, should be quite appealing to the footwear industry as it could consist in a solid value-preposition given the commonness of fungal infections promoted by humidity, poor breathability and temperature that promote the expansion of the microflora of the skin., This research is sponsored by FEDER funds through theprogram COMPETE – Programa Operacional Factores de Competitividade and by the Portuguese Foundation for Science andTechnology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013, and UID/EMS/00285/2013 and in the framework of ERA-SIINN/0004/2013 project., info:eu-repo/semantics/publishedVersion

A novel organized di-urethane crossed-linked dodecyl/siloxane (di-alkyl-urethanesil) was synthesized by the sol–gel process and self-directed assembly, from the organosilane precursor (CH3CH2O)3-Si-(CH2)3-NHC( = O)O-(CH2)12-O(O = C)NH-(CH2)3-Si-(OCH2CH3)3, through a fine control of the reaction conditions (hyper-stoichiometric amount of water, minor amount of tetrahydrofuran, and acid catalysis; molar ratio Si:H2O:HCl:THF = 1:300:0.1:12.5). The new bridged silsesquioxane was identified by the notation d-Ut(CY)AC, where Y = 12 is the number of carbon atoms C of the bridging alkyl chains and AC represents acid catalysis. The d-Ut(C12)AC material exhibits a structured lamellar organization with medium long-range order, a texture composed of homogeneous lamellae immersed in a sponge-like matrix made of randomly distributed thin plates, and is thermally stable up to ca. 350 °C. Despite the hydrophobic nature of the dodecane chains, the weakness of the urethane–urethane hydrogen-bonded array formed led to the growth of moderately ordered assemblies of amphiphilic organo(bis-silanetriol) substructures comprising mainly all-trans conformers.

Pastes of calcium silicate binders with low CaO/SiO2 (C/S) ratio with an overall C/S molar ratio of 1.1 were produced by mixing these materials with water or with an aqueous solution of Na2SiO3. Both types of pastes (non-activated and Na2SiO3 activated) were analysed using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The observations show that the hydration process of this novel type of cements results in the formation of tobermorite nanocrystals embedded in the amorphous calcium-silicate-hydrate (C-S-H) matrix, both in the case of water and of water + Na2SiO3 hydration. Selected area electron diffraction (SAED) patterns obtained in the HR-TEM observations enabled a full characterization of the tobermorite crystalline structure (type, unit cell, space group, lattice angles and parameters). Molecular dynamics (MD) simulations of the identified tobermorite structure were performed at various temperatures, showing its viability and thereby supporting the experimental results. To the best of the authors' knowledge, this report is the first to describe the spontaneous formation of crystalline tobermorite in the form of nanodomains dispersed in the C-S-H phase upon the hydration of calcium-silicate binders.

In order to make bio-based packaging materials competitive in comparison to petroleum-based one, some of their properties need to be improved, among which gas permeability is of crucial importance. Thus, in this work, carbon-based coatings were applied on chitosan-based films by radiofrequency reactive magnetron sputtering aiming to improve their barrier properties. Chemical and morphological properties were evaluated in order to determine the effect of the coatings on the chemical structure, surface hydrophobicity and barrier properties of the system. Chemical analysis, performed by electron energy loss spectroscopy and Fourier transform infrared spectroscopy, suggests similar chemical characteristics among all coatings although higher incorporation of hydrogen as the acetylene flux increases was observed. On the other hand, scanning transmission electron microscopy revealed thatthe porosity ofthe carbon layer can be tailored by the acetylene flux. More importantly, the chitosan oxygen permeability showed a monotonic reduction as a function of the acetylene flux. This study opens up new opportunities to apply nanostructured coatings on bio-based polymer for enhanced oxygen barrier properties., This research is sponsored by FEDER funds through the program COMPETE – Programa Operacional Factores de Competitividade and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013, and UID/EMS/00285/2013 and in the framework of ERA-SIINN/0004/2013 and PTDC/CTM-NAN/4242/2014 projects. This research was supported by Norte Regional Operational Program 2014–2020 (Norte2020) through the European Regional Development Fund (ERDF) Nanotechnology based functional solutions (NORTE-01-0145-FEDER-000019)., info:eu-repo/semantics/publishedVersion

The performance characteristics of lithium-ion battery cathode materials are governed by the surface structure and chemistry. Synthesis is known to affect the structure of these materials; however, a full understanding of the effects of the surface structure is not well understood. Here, we explore the atomic scale structure of lithium-layered oxides prepared with two different thermal treatments. We show that, under certain thermal treatments, the surface perpendicular to the transition-metal layers is enriched in nickel, which results in Ni occupying the lithium layer of the layered oxide structure. Under both thermal treatments, this surface also shows a reduction of Mn, with some of the reduced Mn occupying sites in the lithium layer. The surface parallel to the transition-metal layers under both treatments shows significant Mn reduction, oxygen loss, and reduced Mn in the lithium layer. The Mn reduction and surface reconstruction are the result of unstable surface terminations and are intrinsic to la...

We investigate the morphology and crystalline structure of Au/Ge films in a wide range of temperatures by in situ TEM heating. Au/Ge films with Au mass thickness of 0.2–0.3 nm and Ge thickness of 5 nm were produced in vacuum by the sequential deposition of components on a carbon substrate at room temperature. It has been shown that particles with an average size of 4 nm, formed by Au film de-wetting, melt on the germanium substrate at temperatures 110–160 °C, which are below the eutectic temperature for the bulk. The effect of crystallization-induced capillary motion of liquid eutectic particles over Ge surface has been found in this work. Formation of metastable fcc phase of Ge has been observed at the liquid–germanium interface and behind the moving particle. Formation of a liquid phase with its subsequent crystallization at the metal–semiconductor interface seems to play a key role in the metal-induced crystallization effect.

Nanocomposite Ti-Si-N thin films have been extensively studied for more than two decades mainly for the production of super hard materials. However, recently, several authors have shown that the use of HiPIMS in Ti-Si-N deposition bring about new opportunities for optimization of the films properties. HiPIMS allows for markedly different film growth pathways depending on the deposition conditions. In a previous work, regarding the deposition of Ti-Si-N films by DOMS (Deep Oscillation Magnetron Sputtering), authors also showed that, at low peak power, a unique optimal compromise of ionization fraction and energy of the sputtered species can be achieved. The main objective of the present work is to further investigate the low peak power regime in the deposition of Ti-Si-N films by DOMS. For this purpose, Ti-Si-N films with a Si content of 7 at.% were deposited by DOMS using a similar configuration as in our previous work but with fewer Si pellets placed on the Ti target in order to achieve a lower Si content. The Ti-Si-N films deposited in the low peak power regime have a fine compact columnar morphology with V-shaped columns with sharp and thin column boundaries (1 nm wide) with Si preferentially segregated to the column boundaries. These films have a high crystalline quality with a mosaic-like structure with sub-grains (diffraction domains) only slightly misoriented with respect to each other. Increasing the peak power (high peak power regime) results in the deposition of Ti-Si-N films with brother columns and higher compressive stresses characteristic of deposition under energetic bombardment. These results show that dense and hard Ti-Si-N films with a high degree of crystallinity can be deposited by DOMS without the need of energetic bombardments, i.e., without the need of high peak powers and/or substrate biasing.

Mesoporous silica nanoparticles (MSNs) feature ideal structural properties and surface chemistry for use as nanocarriers of molecules, polymers and biomolecules in cutting-edge applications. One important challenge remaining in their preparation is the ability to tune their diameter in the range of a few tens of nanometers, with narrow size dispersity, preferably using a simple, sustainable and scalable synthetic process. This work presents a fully controllable low-temperature and purely aqueous sol-gel method to prepare MSNs with user-defined diameters from 15 nm to 80 nm and narrow size dispersity. The method also allows modification of the pore structure and offers the possibility of incorporating a luminescent species in the silica network for optical traceability. Control was achieved by tuning the colloidal stability of the assembly of cylindrical micelles that template the MSN synthesis. Using CTAB cylindrical micelles as template and sodium hydroxide (NaOH) as catalyst, precise diameter control was achieved either by changing the pH (that controls micelle surface charge) or by adding salt at constant pH (to tune the ionic strength and charge screening). This new sustainable MSN synthesis method provides full control over the nanoparticles diameters and can be used as platform for the application of these user-defined nanoparticles in different fields.

The production of Ta1-xOx coatings has attracted a lot of attention due to their wide variety of industrial applications. Nonetheless, to properly control the functional properties of these coatings, a good understanding of their structural properties must be achieved. Ta1-xOx phases have structural similarities since they are formed by the distortion of the body centered cubic (bcc) Ta structure and, therefore, a clear and unequivocal identification of the crystalline phases is not trivial. In this regard, this work proposes a theoretical and experimental study to understand the evolution of the structural and the elastic properties of Ta-based coatings. The coatings were deposited by magnetron sputtering as a function of oxygen content and characterized by EPMA (electron probe microanalysis), XRD (X-ray diffraction), STEM (scanning transmission electron microscopy) and SAW (surface acoustic waves). The results demonstrate the formation of a bcc alpha-Ta phase in the non-reactive Ta coating, which transitions to a mixture of crystalline tantalum and tantalum oxide phases for low oxygen concentrations while amorphous phases are observed for high oxygen levels. Ab-initio calculations of different Ta-O phases are in good agreement with the experimental results and reveal that the oxygen addition to the metallic Ta phase, leads to a distortion of the Ta crystal structure, causing a decrease in density and an increase of the elastic constants., This research is sponsored by FEDER funds through the program COMPETE -Programa Operacional Factores de Competitividade and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013, and UID/EMS/00285/2013 and with a PhD fellowship SFRH/BD/98199/2013. The authors also thank the financial support in the framework of ERA-SIINN/0004/2013 and PTDC/CTM-NAN/4242/2014 projects.

LiMn2O4 has been considered one of the most promising cathode materials for Li-ion batteries due to its thermal stability, abundance, environmental affinity, and the possibility to exchange Li-ions in three-dimensions. However, it still suffers from major problems, such as capacity fading and voltage decay, which has been associated to phase transformations and dissolution of transition metals. In this report, we use scanning transmission electron microscopy, coupled with differential phase contrast (DPC), to better understand the mechanisms behind the structural transformations occurring in LiMn2O4. We use the fact that DPC has the ability to observe simultaneously light and heavy elements, as well as measure projected electric fields and charge distribution at the atomic level. This approach allows us to monitor the migration of very low amounts of Mn to the Li atomic positions, at the surface and subsurface regions, which otherwise is very challenging to observe using other techniques such as HAADF and ABF. These observations not only provide a fundamental understanding of the structure of LiMn2O4 but also reveal DPC as a novel technique to determine local structural changes in materials consisting of heavy and light elements, as well as identify the location of light elements, monitor low concentrations of substitutional species and identify phase transformations.

The cost and performance of proton exchange membrane fuel cells strongly depend on the cathode electrode due to usage of expensive platinum (Pt) group metal catalyst and sluggish reaction kinetics. Development of low Pt content high performance cathodes requires comprehensive understanding of the electrode microstructure. In this study, a new approach is presented to characterize the detailed cathode electrode microstructure from nm to μm length scales by combining information from different experimental techniques. In this context, nano-scale X-ray computed tomography (nano-CT) is performed to extract the secondary pore space of the electrode. Transmission electron microscopy (TEM) is employed to determine primary C particle and Pt particle size distributions. X-ray scattering, with its ability to provide size distributions of orders of magnitude more particles than TEM, is used to confirm the TEM-determined size distributions. The number of primary pores that cannot be resolved by nano-CT is approximated using mercury intrusion porosimetry. An algorithm is developed to incorporate all these experimental data in one geometric representation. Upon validation of pore size distribution against gas adsorption and mercury intrusion porosimetry data, reconstructed ionomer size distribution is reported. In addition, transport related characteristics and effective properties are computed by performing simulations on the hybrid microstructure.

Pt 3 Co catalyst nanoparticles of 4.9 nm size present on the cathode side of a PEMFC membrane-electrode assembly (MEA) were analyzed by transmission electron microscopy after 10 K voltage cycles under different operating conditions. The operating conditions include baseline (0.4–0.95 V, 80° C, 100% Relative Humidity (RH)), high potential (0.4–1.05 V, 80° C, 100% RH), high temperature (0.4–0.95 V, 90° C, 100% RH), and low humidity (0.4–0.95 V, 80° C, 30% RH). Particle growth and particle loss to the membrane is more severe in the high potential sample than in the high temperature and baseline MEAs, while no significant particle growth and particle precipitation in the membrane can be observed in the low humidity sample. Particles with different morphologies were seen in the cathode including: 1-Spherical individual particles resulting from modified electro-chemical Ostwald ripening and 2-aggregated and coalesced particles resulting from either necking of two or more particles or preferential deposition of Pt between particles with consequent bridging. The difference in the composition of these morphologies results in composition variations through the cathode from cathode/diffusion media (DM) to the cathode/membrane interface.

We show that in layered oxides that are employed as cathodes in lithium-ion batteries, the cation layers can order on different {111}NaCl planes within a single particle, which makes the lithium layer discontinuous across a particle. The findings challenge previous assertions that lithium undergoes 2-D diffusion in layered oxides and the data provide new insights into the decrease in rate capabilities for some layered oxides. Therefore, it is critically important to understand how these discontinuities form and how the loss of 2-D diffusion impacts the overall performance of the layered oxide cathode materials. Employing X-ray diffraction (XRD) and aberration-corrected scanning transmission electron microscopy (STEM), we find that as the material transitions from a disordered to an ordered state, it forms four orientation variants corresponding to the four {111}NaCl planes. This transition is not intrinsic to all layered oxides and appears to be more strongly affected by nickel. Furthermore, with energy dispersive spectroscopy (EDS), we show that there is an increase in the nickel concentration at the interface between each orientation variant. This reduces the rate of lithium diffusion, negatively affects the rate capability, and could be contributing to the overall capacity fade.

The durability of carbon supported PtCo-alloy based nanoparticle catalysts play a key role in the longevity of proton-exchange membrane fuel cells (PEMFC) in electric vehicle applications. To improve its durability, it is important to understand and mitigate the various factors that cause PtCo-based cathode catalyst layers (CCL) to lose performance over time. These factors include i) electrochemical surface area (ECSA) loss, ii) specific activity loss, iii) H+/O2-transport changes and iv) Co2+ contamination effects. We use a catalyst-specific accelerated stress test (AST) voltage cycling protocol to compare the durability of Pt and PtCo catalysts at similar average nanoparticle size and distribution. Our studies indicate that while Pt and PtCo nanoparticle catalysts suffer from similar magnitudes of electrochemical surface area (ECSA) losses, PtCo catalyst shows a significantly larger cell voltage loss at high current densities upon durability testing. The distinctive factor causing the large cell voltage loss of PtCo catalyst appears to be the secondary effects of the leached Co2+ cations that contaminate the electrode ionomer. A 1D performance model has been used to quantify the cell voltage losses arising from various factors causing degradation of the membrane electrode assembly (MEA).

In this work, suspended 4-mm-wide graphene membranes are obtained through a sublimation-assisted transfer process, using few-layer films grown by microwave plasma chemical vapor deposition. This result is achieved by a new approach involving the removal of the graphene-transfer supporting layer in vacuum. The membranes produced by this procedure show the largest area-to-thickness ratio described in the literature with a 2-fold improvement when compared to the best results using the conventional PMMA-assisted transfer, and a five orders of magnitude increase when compared to previous sublimation-assisted processes. This breakthrough allows the implementation of a wide variety of technological applications where 2D materials with atomic thickness and large areas are required. As large-area free-standing membranes are difficult to obtain, a new figure of merit is defined to benchmark the various methods of suspending graphene. A high transfer yield is achieved, and the mechanical and optical properties of the 3.7 nm thick membranes are evaluated. Finally, a prototype condenser microphone is built and tested, and found to exhibit an enhanced specific response.

The epitaxial growth of two-dimensional (2D) $\beta-In_2Se_3$ material was obtained over 2-inches c-sapphire wafers using molecular beam epitaxy (MBE). Excellent quality of thick (90 nm) and very thin films, down to two quintuple layers (2 nm), was confirmed by x-ray diffraction (XRD), Raman spectroscopy, and aberration-corrected scanning transmission electron microscopy (ac-STEM). Wafer-scale fabrication of photodetectors based on five quintuple layers was produced using photolithography and other standard semiconductor processing methods. The photodetectors exhibit responsivity of 3 mA/W, peak specific detectivity (D*) of $10^9$ Jones, external quantum efficiency (EQE) of 0.67 % at 550 nm, and response-time of ~7 ms, which is faster than any result previously reported for $\beta-In_2Se_3$ photodetectors. From the photocurrent measurements, an optical bandgap of 1.38 eV was observed. These results on wafer-scale deposition of 2D $In_2Se_3$, as well as its fabrication into optoelectronic devices provide the missing link that will enable the commercialization of 2D materials.

This work aims to study the electrochemical and the corrosion resistance of amorphous carbon coatings with metallic (Ag) and bimetallic (Ag Au) nanoparticles deposited on stainless steel 316L by dc magnetron sputtering technique. These coatings were designed to coat ureteral stents and, accordingly, the Ag release measurement, morphological and electrochemical investigations were performed on the coatings immersed into artificial urine solution during 14 days to imitate the ureter electrolyte (urine) where the stents are inserted. These coatings are intended for insertion into the human body; then, in addition to the biocompatibility, they should not corrode since the resulting products can cause different adverse reactions. The Ag release study showed that the concentration of Ag+ release from the Ag-doped coating is much higher than the Ag Au one over the measured time. Moreover, scanning electron microscopy analysis on the immersed and non-immersed coatings supported the Ag ion release assessment. From STEM analysis, the formation of Ag Au nanoalloys in a wide size distribution was confirmed. Additionally, the electrochemical characteristics and corrosion resistance behavior of the coatings were investigated in artificial urine solution over immersion time by electrochemical impedance spectroscopy. The Nyquist plots were successfully fitted with a proper equivalent circuit based on a two-layer model representing a porous outer layer and a barrier inner layer for the coatings. The electrochemical measurements revealed that the coating doped with Ag Au nanoparticles has improved corrosion resistance and less porosity compared to the Ag-doped one. The enhanced protective feature of the Ag-Au/a:C coatings can be attributed to the formation of Ag Au nanoalloys that helps to block the solution penetration into the substrate.

Transmission electron microscopy (TEM) provides information about Inorganic nanoparticles that no other method is able to deliver. Yet, a major task when studying Inorganic nanoparticles using TEM is the automated analysis of the images, i.e. segmentation of individual nanoparticles. The current state-of-the-art methods generally rely on binarization routines that require parameterization, and on methods to segment the overlapping nanoparticles (NPs) using highly idealized nanoparticle shape models. It is unclear, however, that there is any way to determine the best set of parameters providing an optimal segmentation, given the great diversity of NPs characteristics, such as shape and size, that may be encountered. Towards remedying these barriers, this paper introduces a method for segmentation of NPs in Bright Field (BF) TEM images. The proposed method involves three main steps: binarization, contour evidence extraction, and contour estimation. For the binarization, a model based on the U-Net architecture is trained to convert an input image into its binarized version. The contour evidence extraction starts by recovering contour segments from a binarized image using concave contour points detection. The contour segments which belong to the same nanoparticle are grouped in the segment grouping step. The grouping is formulated as a combinatorial optimization problem and solved using the well-known branch and bound algorithm. Finally, the full contours of the NPs are estimated by an ellipse. The experiments on a real-world dataset consisting of 150 BF TEM images containing approximately 2,700 NPs show that the proposed method outperforms five current state-of-art approaches in the overlapping NPs segmentation. Post-print / Final draft

In sand casting of metallic alloys, the cooling rate is a key parameter that affects the microstructure and the appearance of defects and residual stresses in the end cast components. In this work, a numerical model was developed to simulate the cooling of a duplex stainless steel casting on a furan-bonded sand mold. The heat transfer coefficient (HTC) as a function of temperature was determined by an inverse method. A good agreement between experimental and numerical cooling curves was achieved, showing the importance of estimating HTC as a function of temperature. On the basis of these results, it is possible to calculate thermal residual stresses and model the microstructure of duplex stainless steel castings with complex geometries.