Search

Over the past few decades, telluride-based chalcogenide multilayers, such as PbSeTe/PbTe, Bi2Te3/Sb2Te3, and Bi2Te3/Bi2Se3, were shown to be promising high-performance thermoelectric films. However, the stability of performance in operating environments, in particular, influenced by intermixing of the sublayers, has been studied rarely. In the present work, the nanostructure, thermal stability, and thermoelectric power factor of Sb2Te3/Ge1+xTe multilayers prepared by pulsed laser deposition are investigated by transmission electron microscopy and Seebeck coefficient/electrical conductivity measurements performed during thermal cycling. Highly textured Sb2Te3 films show p-type semiconducting behavior with superior power factor, while Ge1+xTe films exhibit n-type semiconducting behavior. The elemental mappings indicate that the as-deposited multilayers have well-defined layered structures. Upon heating to 210 °C, these layer structures are unstable against intermixing of sublayers; nanostructural changes occur on initial heating, even though the highest temperature is close to the deposition temperature. Furthermore, the diffusion is more extensive at domain boundaries leading to locally inclined structures there. The Sb2Te3 sublayers gradually dissolve into Ge1+xTe. This dissolution depends markedly on the relative Ge1+xTe film thickness. Rather, full dissolution occurs rapidly at 210 °C when the Ge1+xTe sublayer is substantially thicker than that of Sb2Te3, whereas the dissolution is very limited when the Ge1+xTe sublayer is substantially thinner. The resulting variations of the nanostructure influence the Seebeck coefficient and electrical conductivity and thus the power factor in a systematic manner. Our results shed light on a previously unreported correlation of the power factor with the nanostructural evolution of unstable telluride multilayers.

Metal borides, a class of materials intensively used in industry as superconductors, magnetic materials, or hot cathodes, remain largely unexplored at the nanoscale mainly due to the difficulty in synthesizing single-phase nanocrystals. Recent works have shown that synthetic methods at lower temperatures (xB) could be a potential catalyst for a broad range of applications (hydrogenations, electrochemical hydrogen, and oxygen evolution reactions) under challenging conditions (such as high pH or high temperatures). Here, we report a novel solid-state method to synthesize NixB nanopowders (with a diameter of approximately 45 nm) and their conversion into colloidal suspensions (inks) through treatment of the nanocrystal surface. For the solid-state synthesis, we used commercially available salts and explored the reaction between the Ni and B sources while varying the synthetic parameters under mild and solvent-free reaction conditions. We show that pure phase Ni3B and Ni2B NCs can be obtained with high yield in the pure phase using as precursors NiCl2 and Ni, respectively. Through extensive mechanistic studies, we show that Ni nanoclusters (1-2 nm) are an intermediate in the boriding process, while the metal co-reactant lowers the decomposition temperature of NaBH4 (used as a reducing agent and B source). Size control can instead be exerted through reaction mediators, as seen from the differential nucleation and growth of Ni (clusters) or NixB NCs when employing L- (amine, phosphine) and X-type (carboxylate) mediators. Applying surface engineering methods to our NixB NCs, we stabilized them with inorganic (NOBF4) or organic (borane tert-butyl amine, oleylamine) ligands in the appropriate solvent (DMSO, hexane). With this method, we produce stable inks for further solution processing applications. Our results provide tools for further development of catalysts based on NixB NCs and pave the way for synthesizing other metal boride colloidal nanostructures.

The current lack of insight into nanoparticle-cell membrane interactions hampers smart design strategies and thereby the development of effective nanodrugs. Quantitative and methodical approaches utilizing cell membrane models offer an opportunity to unravel particle-membrane interactions in a detailed manner under well controlled conditions. Here we use total internal reflection microscopy for real-time studies of the non-specific interactions between nanoparticles and a model cell membrane at 50 ms temporal resolution over a time course of several minutes. Maintaining a simple lipid bilayer system across conditions, adsorption and desorption were quantified as a function of biomolecular corona, particle size and fluid flow. The presence of a biomolecular corona reduced both the particle adsorption rate onto the membrane and the duration of adhesion, compared to pristine particle conditions. Particle size, on the other hand, was only observed to affect the adsorption rate. The introduction of flow reduced the number of adsorption events, but increased the residence time. Lastly, altering the composition of the membrane itself resulted in a decreased number of adsorption events onto negatively charged bilayers compared to neutral bilayers. Overall, a model membrane system offers a facile platform for real-time imaging of individual adsorption-desorption processes, revealing complex adsorption kinetics, governed by particle surface energy, size dependent interaction forces, flow and membrane composition.

A non-equiatomic interstitial-strengthened high entropy alloy (iHEA), Fe49.5Mn30Co10Cr10C0.5 (at.%), is manufactured by laser powder-bed fusion (LPBF) with stripe and chessboard scanning strategies. The present study highlights the correlation between the laser scanning strategies with resulting microstructure, textures, and anisotropic mechanical properties in as-built iHEA. The results show that the LPBF processed iHEA exhibits an excellent strength-ductility synergy due to the combined deformation mechanisms of dislocation slip, martensite phase transformation- and nano twinning-induced plasticity. The samples printed by the stripe scanning strategy show more evident mechanical anisotropy than that of the chessboard-scanned samples. The difference in the degree of mechanical anisotropy is mainly attributed to the heterogeneous grain morphology and crystallographic texture resulted from different scanning strategies.

3D superlattices made of colloidal quantum dots are a promising candidate for the next generation of optoelectronic devices as they are expected to exhibit a unique combination of tunable optical properties and coherent electrical transport through minibands. While most of the previous work was performed on 2D arrays, the control over the formation of these systems is lacking, where limited long-range order and energetical disorder have so far hindered the potential of these metamaterials, giving rise to disappointing transport properties. Here, it is reported that nanoscale-level controlled ordering of colloidal quantum dots in 3D and over large areas allows the achievement of outstanding transport properties. The measured electron mobilities are the highest ever reported for a self-assembled solid of fully quantum-confined objects. This ultimately demonstrates that optoelectronic metamaterials with highly tunable optical properties (in this case in the short-wavelength infrared spectral range) and charge mobilities approaching that of bulk semiconductor can be obtained. This finding paves the way toward a new generation of optoelectronic devices.

Hydrogenation of biomass using bimetallic catalysts.

Scanning transmission electron microscopy (STEM) is the most widespread adopted tool for atomic scale characterization of two-dimensional (2D) materials. However, damage free imaging of 2D materials with electrons has remained problematic even with powerful low-voltage 60 kV-microscopes. An additional challenge is the observation of light elements in combination with heavy elements, particularly when recording fast dynamical phenomena. Here, we demonstrate that 2D WS2 suffers from electron radiation damage during 30 kV-STEM imaging, and we capture beam-induced defect dynamics in real-time by atomic electrostatic potential imaging using integrated differential phase contrast (iDPC)-STEM. The fast imaging of atomic electrostatic potentials with iDPC-STEM reveals the presence and motion of single sulfur atoms near defects and edges in WS2 that are otherwise invisible at the same imaging dose at 30 kV with conventional annular dark-field STEM, and has a vast speed and data processing advantage over electron detector camera based STEM techniques like electron ptychography.

Bi2Te3-based alloys are known to have outstanding thermoelectric properties. Although structure-property relations have been studied, still, detailed analysis of the atomic and nano-scale structure of Bi2Te3 thin film in relation to their thermoelectric properties remains poorly explored. Herein, highly-textured (HT) and single-crystal-like (SCL) Bi2Te3 films have been grown using pulsed laser deposition (PLD) on Si wafer covered with (native or thermal) SiOx and mica substrates. All films are highly textured with c-axis out-of-plane, but the in-plane orientation is random for the films grown on oxide and single-crystal-like for the ones grown on mica. The power factor of the film on thermal oxide is about four times higher (56.8 mu W.cm(-1).K-2) than that of the film on mica (12.8 mu W.cm(-1).K-2), which is comparable to the one of the polycrystalline ingot at room temperature (RT). Reduced electron scattering in the textured thin films results in high electrical conductivity, where the SCL film shows the highest conductivity. However, its Seebeck coefficient shows a low value. The measured properties are correlated with the atomic structure details unveiled by scanning transmission electron microscopy. For instance, the high concentration of stacking defects observed in the HT film is considered responsible for the increase of Seebeck coefficient compared to the SCL film. This study demonstrates the influence of nanoscale structural effects on thermoelectric properties, which sheds light on tailoring thermoelectric thin films towards high performance.

Understanding the size-dependent electronic properties of germanium nanocrystals (Ge NCs) is of fundamental importance for improving the efficiency of optoelectronic devices based on such NCs. Here, Ge NCs with a tunable size were synthesized by magnetron-sputtering cluster-beam deposition, where the size of the as-deposited Ge NCs can be finely controlled between 6 and 36 nm by helium gas flow rates and variable magnetic field configurations above the target surface. Because the size of the as-deposited Ge NCs highly depends on the nucleation process inside the plasma region, a detailed comparison between these two process parameters on the size control was formulated from the perspective of the growth kinetic mechanism. Furthermore, the local surface potential of different-sized Ge NCs deposited on n-type silicon substrates was measured by Kelvin probe force microscopy. The surface potential fluctuation of n-type Si covered by Ge NCs shows a strong size-dependent relationship with the size of the Ge NCs, whereas the surface potential fluctuation increases when their size reduced. Because the surface potential fluctuation between the intrinsic Ge NCs and the n-type silicon substrate tends to get smaller as the NCs' size decreases due to the quantum confinement effect, the number of charges transferred between the electronic bands will reduce as the size of Ge NCs decreases. The latter exactly explains the observed experimental results. Therefore, this work offers a perspective to understand the behavior of charge transfer, which plays an important role in the performance of optoelectronic devices.

Germanane (GeH), a germanium analogue of graphane, has recently attracted considerable interest because its remarkable combination of properties makes it an extremely suitable candidate to be used as 2D material for field effect devices, photovoltaics, and photocatalysis. Up to now, the synthesis of GeH has been conducted by substituting Ca by H in a β‐CaGe2 layered Zintl phase through topochemical deintercalation in aqueous HCl. This reaction is generally slow and takes place over 6 to 14 days. The new and facile protocol presented here allows to synthesize GeH at room temperature in a significantly shorter time (a few minutes), which renders this method highly attractive for technological applications. The GeH produced with this method is highly pure and has a band gap (E g) close to 1.4 eV, a lower value than that reported for germanane synthesized using HCl, which is promising for incorporation of GeH in solar cells., Germanane was synthesized by topotatic deintercalation of β‐CaGe2 in aqueous HF solution at room temperature under stirring for 2‐3 minutes. In order to remove the residual CaF2 the material was treated with a saturated aqueous solution of EDTA.

Intensive studies have been carried out over the past decade to identify nanostructured thermoelectric materials that allow the efficient conversion of waste heat to electrical power. However, less attention has been paid to the stability of such materials under operating temperatures, typically 400 degrees C or higher. Conventionally nanostructured ceramics tend to undergo grain growth at high temperature, lowering the density of interfaces and raising the thermal conductivity, which is detrimental to device performance. Therefore it is preferable to identify materials with stable nanostructures, for example systems that undergo spontaneous phase separation. Here we investigate PbTe-GeTe alloys, in which spinodal decomposition occurs on initial cooling from above 580 degrees C, forming complex nanostructures consisting of Ge-rich and Pb-rich domains on different size scales. The resulting dense arrangement of interfaces, combined with mass fluctuation associated with Pb-Ge mixing, enhances phonon scattering and strongly reduces the thermal conductivity. Here we focus on the nominal composition Pb0.49Ge0.51Te and show that by tuning the synthesis procedure, we are able to control the pattern of compositional domains and the density of interfaces between them. This allows low lattice thermal conductivities to be maintained even after thermal cycling over the operating temperature range.

Integration of the prototypical GeSbTe (GST) ternary alloys, especially on the GeTe-Sb2Te3 tie-line, into non-volatile memory and nanophotonic devices is a relatively mature field of study. Nevertheless, the search for the next best active material with outstanding properties is still ongoing. This search is relatively crucial for embedded memory applications where the crystallization temperature of the active material has to be higher to surpass the soldering threshold. Increasing the Ge content in the GST alloys seems promising due to the associated higher crystallization temperatures. However, homogeneous Ge-rich GST in the as-deposited condition is thermodynamically unstable, and phase separation upon annealing is unavoidable. This phase separation reduces endurance and is detrimental in fully integrating the alloys into active memory devices. This work investigated the phase separation of Ge-rich GST alloys, specifically Ge5Sb2Te3 or GST523, into multiple (meta)stable phases at different length scales in melt-quenched bulk and annealed thin film. Electron microscopy-based techniques were used in our work for chemical mapping and elemental composition analysis to show the formation of multiple phases. Our results show the formation of alloys such as GST213 and GST324 in all length scales. Furthermore, the alloy compositions and the observed phase separation pathways agree to a large extent with theoretical results from density functional theory calculations.

Lead halide perovskite nanocrystals are highly attractive for next-generation optoelectronics because they are easy to synthesize and offer great compositional and morphological tunability. However, the replacement of lead by tin for sustainability reasons is hampered by the unstable nature of Sn2+ oxidation state and by an insufficient understanding of the chemical processes involved in the synthesis. Here we demonstrate an optimized synthetic route to obtain stable, tunable, and monodisperse CsSnI3 nanocrystals, exhibiting well defined excitonic peaks. Similar to lead halide perovskites, we prepare these nanocrystals by combining a precursor mixture of SnI2 , oleylamine and oleic acid, with a Cs-oleate precursor. Among the products, nanocrystals with 10 nm lateral size in the γ-orthorhombic phase prove to be the most stable. To achieve such stability, an excess of precursor SnI2 as well as sub-stoichiometric Sn:ligand ratios are key. Structural, compositional and optical investigations complemented by first-principle DFT calculations confirm that nanocrystal nucleation and growth follow the formation of (R-NH3 + )2 SnI4 nanosheets with R = C18 H35 . Under specific synthetic conditions, stable mixtures of 3D nanocrystals CsSnI3 and 2D nanosheets (Ruddlesden-Popper (R-NH3 + )2 Csn-1 Snn I3n+1 with n>1) are obtained. These results set a path to exploiting the high potential of Sn halide perovskite nanocrystals for opto-electronic applications. This article is protected by copyright. All rights reserved.

The present study is dedicated to explore the effect of grain refinement on cracking resistance of hot-dip galvanized Zn–Al–Mg coatings on steel substrate. In this work, we demonstrate the enhancement of plastic deformation and cracking resistance by refining the microstructure (primary zinc grains) of the Zn–Al–Mg coatings. For this purpose, two types of Zn–Al–Mg coatings namely, fine grained and coarse grained microstructures are investigated utilizing in-situ scanning electron microscopy tensile tests. Electron backscatter diffraction technique is used to illuminate the deformation behavior at the scale of grains (and/or within grains). The results reveal that the coating with fine grained microstructure possesses higher ductility and cracking resistance, whereas the coating with coarse grain microstructure induces more transgranular cracking during deformation. Moreover, primary zinc grain refinement has been shown to decrease the fraction of coarse deformation twins that serve as undesirable sites of micro-cracking. In particular, both deformation mechanisms and cracking behavior are found to be grain size-dependent in these coatings.

Microscopy and diffraction measurements are presented of ultrathin binary alloy films of ruthenium and molybdenum that are obtained by standard sputter deposition. For compositions close to Ru50Mo50, we find the films to be amorphous. The amorphicity of the films is accompanied by a significant reduction of the roughness with respect to the roughness of equally thick films of either ruthenium or molybdenum. We ascribe this to the absence of the grain structure that is characteristic of the polycrystalline films of the separate elements.

Free-standing layers of nanoscale thickness are essential in numerous applications but challenging to fabricate for all but a small selection of materials. We report a versatile, chemical-free pathway of exfoliating centimeter-sized free-standing nanolayers from Si(100) with native oxide based on the spontaneous delamination of thin Ru and Ru-based films upon annealing at temperatures as low as 400 °C. Combining results from X-ray photoelectron spectroscopy (XPS), and transmission and scanning electron microscopy (TEM, SEM), we identify that the element Ru, a thin SiO2 layer, and the Si(100) substrate are essential ingredients for the delamination and propose a stress-based mechanism to explain the effect. The diffusion of Si into the layer upon annealing leads to the formation of a Ru-Si compound at the thin-film side of the Ru/Si(100) interface and pyramidal cavities in the Si(100) substrate. Moreover, the uptake of Si results in an increase in layer thickness and the buildup of in-plane compressive stress, which is reduced by local buckling and finally by the separation of the full layer from the substrate at the SiO2-Si(100) interface. The use of a thin Ru-buffer layer allows us to apply this delamination process to produce free-standing nanolayers of Mo and HfMoNbTiZr in this simple, chemical-free, and vacuum-compatible manner. These results indicate the potential of the reported effect for the fabrication of free-standing layers using a wide range of compositions, deposition techniques, and growth conditions below the onset temperature of delamination.

High quality Van der Waals chalcogenides are important for phase change data storage, thermoelectrics, and spintronics. Using a combination of statistical design of experiments and density functional theory, we clarify how the out-of-equilibrium van der Waals epitaxial deposition methods can improve the crystal quality of Sb2Te3 films. We compare films grown by radio frequency sputtering and pulsed laser deposition (PLD). The growth factors that influence the crystal quality for each method are different. For PLD grown films a thin amorphous Sb2Te3 seed layer most significantly influences the crystal quality. In contrast, the crystalline quality of films grown by sputtering is rather sensitive to the deposition temperature and less affected by the presence of a seed layer. This difference is somewhat surprising as both methods are out-of-thermal-equilibrium plasma-based methods. Non-adiabatic quantum molecular dynamics simulations show that this difference originates from the density of excited atoms in the plasma. The PLD plasma is more intense and with higher energy than that used in sputtering, and this increases the electronic temperature of the deposited atoms, which concomitantly increases the adatom diffusion lengths in PLD. In contrast, the adatom diffusivity is dominated by the thermal temperature for sputter grown films. These results explain the wide range of Sb2Te3 and superlattice crystal qualities observed in the literature. These results indicate that, contrary to popular belief, plasma-based deposition methods are suitable for growing high quality crystalline chalcogenides., Comment: 24 pages, 8 figs

A series of monometallic and bimetallic metal catalysts (Pd, Cu, Fe, PdCu, PdFe) supported on ZrO2 (6-8 nm) were synthesized and tested for the hydrogenation of bio-oil model compounds (furfural, vanillin, glucose) under 50 bar H2 at 100 °C. The catalysts were fully characterized and their properties related to their catalytic activity. The bimetallic PdFe and PdCu displayed enhanced catalytic performance compared to the monometallic catalysts for aldehyde hydrogenation (furfural, vanillin, glucose). For the best catalyst, 98% vanillin alcohol (VA) and 65.5% furfuryl alcohol (FA) conversion was obtained for 80 min batch-time. PdFe showed high selectivity toward sorbitol (74%) from glucose, though at low conversion (20%). Overall, we have demonstrated that bimetallic Fe- A nd Cu-based catalysts promoted by Pd show significantly better performance for the partial hydrogenation of bio-oil model compounds than the corresponding monometallic ones. The better performance of the Pd-doped Fe/Cu catalysts is linked to the presence of smaller and better dispersed Pd nanoparticles (STEM) and their lower acidity (∼90 μmol/g cat) than corresponding monometallic ones (∼167 μmol/g cat).

Size-dependent optical properties of germanium (Ge) nanocrystals (NCs) make them a desirable material for optoelectronic applications. So far, the synthesis of ligand-free and tunable-size Ge NCs by inert gas condensation has been scarcely reported. In this work, we introduce a gas-phase approach to synthesize quantum-confined Ge NCs by inert gas condensation, where the size of the Ge NCs can be readily tuned by controlling the thickness of a Cu plate supporting the Ge target. As explained by simulations using the finite element method, the magnetic field configuration above the target can be manipulated by varying the thickness of the Cu backing plate. In-depth analysis based on transmission electron microscopy (TEM) results reveals the morphology and crystalline structure of Ge NCs. X-ray photoelectron spectroscopy has proven the formation of a substoichiometric Ge oxide shell for the as-deposited Ge NCs. In addition, Raman spectroscopy indicated peak shifts according to the phonon confinement model that yielded nanoparticle sizes in a good agreement with the TEM results. Furthermore, the quantum confinement effect for Ge NCs was demonstrated by analysis of the absorption (UV-vis-NIR) spectrum, which indicated that the band gap of the Ge NCs was increased from ∼0.8 to 1.1 eV with decreasing size of Ge NCs. Comparison with theory shows that the quantum confinement effect on the band gap energy for different-sized Ge NCs follows the tight-binding model rather well.

Phase change materials, with more than one reflectance and resistance states, have been a subject of interest in the fields of phase change memories and nanophotonics. Although most current research focuses on rather complex phase change alloys, e.g., Ge2Sb2Te5, recently, monatomic antimony thin films have aroused a lot of interest. One prominent attractive feature is its simplicity, giving fewer reliability issues like segregation and phase separation. However, phase transformation and crystallization properties of ultrathin Sb thin films must be understood to fully incorporate them into future memory and nanophotonics devices. Here, we studied the thickness-dependent crystallization behavior of pulsed laser-deposited ultrathin Sb thin films by employing dynamic ellipsometry. We show that the crystallization temperature and phase transformation speed of as-deposited amorphous Sb thin films are thickness-dependent and can be precisely tuned by controlling the film thickness. Thus, crystallization temperature tuning by thickness can be applied to future memory and nanophotonic devices. As a proof of principle, we designed a heterostructure device with three Sb layers of varying thicknesses with distinct crystallization temperatures. Measurements and simulation results show that it is possible to address these layers individually and produce distinct and multiple reflectance profiles in a single device. In addition, we show that the immiscible nature of Sb and GaSb could open up possible heterostructure device designs with high stability after melt-quench and increased crystallization temperature. Our results demonstrate that the thickness-dependent phase transformation and crystallization dynamics of ultrathin Sb thin films have attractive features for future memory and nanophotonic devices.

Zn-Al-Mg coatings are important materials for the corrosion protection of steel sheets. However, susceptibility towards cracking limits the formability performance of these coatings. In this study, we focus on the effect of the underlying steel substrate on cracking behavior in these coatings. In order to elucidate this, a high-strength low-alloy (HSLA) steel substrate and an interstitial-free (IF) steel substrate are coated with two different ZnAlMg coatings with and without binary eutectic microstructures. Meticulous in-situ tensile and bending tests are conducted in a scanning electron microscope. To quantify the strain distribution and damage incidents, micro and macro digital image correlation techniques are utilized in order to illuminate the associated cracking causes across length scales. Furthermore, electron backscatter diffraction method is applied to study the role of crystallographic orientation on the cracking tendency. Crack opening and crack area fractions are correlated with the applied strain and bending angles. The findings denote that the discontinuous yielding (Luders banding) of the HSLA steel substrate generates substantial surface roughening and heterogeneous deformation in the coatings that facilitates cracking. In contrast, the IF steel induces a more uniform deformation within the coatings leading to much reduced crack size and crack area fraction. This study has resulted in a key element of a guideline towards crack-resistant and formable Mg-alloyed zinc coatings.

The wetting state of surfaces can be rendered to a highly hydrophobic state by the deposition of hydrophilic gas phase synthesized Ag nanoparticles (NPs). The aging of Ag NPs leads to an increase in their size, which is also associated with the presence of Ag adatoms on the surface between the NPs that have a strong effect on the wetting processes. Furthermore, surface airborne hydrocarbons were removed by UV-ozone treatment, providing deeper insight into the apparent mobility of the NPs on different surfaces and their subsequent ripening and aging. In addition, the UV-ozone treatment revealed the presence of adatoms during the magnetron sputtering process. This surface treatment lowers the initial contact angle of the substrates and facilitates the mobility of Ag NPs and adatoms on the surface of substrates. Adatoms co-deposited on clean high surface energy substrates will nucleate on Ag NPs that will remain closely spherical and preserve the pinning effect due to the water nanomeniscus. If the adatoms are co-deposited on a UV-ozone cleaned low surface energy substrate, their mobility is restricted, and they will nucleate in two-dimensional islands and/or nanoclusters on the surface instead of connecting to existing Ag NPs. This growth results in a rough surface without overhangs, where the wetting state is reversed from hydrophobic to hydrophilic. Finally, different material surfaces of transmission electron microscopy grids revealed strong differences in the sticking coefficient for the Ag NPs, suggesting another factor that can strongly affect their wetting properties.

OBJECTIVES The liquid–solid interactions have attracted broad interest since solid surfaces can either repel or attract fluids, configuring a wide spectrum of wetting states (from superhydrophilicity to superhydrophobicity). Since the blood–artificial surface interaction of bileaflet mechanical heart valves essentially represents a liquid–solid interaction, we analysed the thrombogenicity of mechanical heart valve prostheses from innovative perspectives. The aim of the present study was to modify the surface wettability of standard St. Jude Medical Regent™ occluders. METHODS Four pyrolytic carbon occluders were irradiated by means of ultra-short pulse laser, to create 4 different nanotextures (A–D), the essential prerequisite to achieve superhydrophobicity. The static surface wettability of the occluders was qualified by the contact angle (θ) of 2 µl of purified water, using the sessile drop technique. The angle formed between the liquid–solid and the liquid–vapour interface was the contact angle and was obtained by analysing the droplet images captured by a camera. The morphology of the occluders was characterized and analysed by a scanning electron microscope at different magnifications. RESULTS The scanning electron microscope analysis of the textures revealed 2 different configurations of the pillars since A and B showed well-rounded shaped tops and C and D flat tops. The measured highest contact angles were comprised between 108.1° and 112.7°, reflecting an improved hydrophobicity of the occluders. All the textures exhibited, to different extents, an orientation (horizontal or vertical), which was strictly related to the observed anisotropy. CONCLUSIONS In this very early phase of our research, we were able to demonstrate that the intrinsic wettability of pyrolytic carbon occluders can be permanently modified, increasing the water repellency.

Mg-alloyed zinc coatings suffer from early cracking during deformation due to the combined influences of detrimental constituents (e.g., Zn/MgZn2 binary eutectic), unfavorable crystal orientations and incompatible local plastic deformation. This study addresses the crack resistance and deformation mechanisms of a ZnAlMg coating, in the absence of binary eutectic, by using correlative in-situ scanning electron microscopy tensile tests, electron backscatter diffraction, scanning transmission electron microscopy and micro digital image correlation methods. The plasticity and strengthening mechanisms of the binary eutectic-free ZnAlMg coating are thoroughly unravelled via theoretical and experimental approaches including dislocation slip trace analysis, Taylor factor calculations, quantitative dislocation density determination and slip/strain transfer across the grain boundaries. It has been found that the microstructure of the coating, comprising of primary zinc and ternary eutectic, effectively accommodates the applied strain without cracking till fracture of steel substrate. The absence of binary eutectic and the activation of abundant deformation mechanisms in the coating microstructure, promote local compatible plastic deformation and inhibit early damage. Effective slip transfer is unveiled by activation of pyramidal slip in addition to primary dislocation slip systems. The present findings deliver significant insights and solution for improvement in the formability of Mg-alloyed zinc coatings on steel sheets by tailoring the microstructure.

Phase-change memory (PCM) holds great potential in realizing the combination of DRAM-like speeds with non-volatility and large storage capacity for future electronic devices including in-memory computing. However, various (reliability) issues related to e.g. too high programming current (power consumption), resistance drift, data retention (low crystallization temperature), phase separation and density change upon switching stand in the way to make PCM really attractive. GaSb thin films have interesting optical and electrical properties which are attractive for optoelectronic and PCM applications but so far reported stoichiometric GaSb compositions are Sb-rich which produced reliability issues in PCM devices. In this study, we managed to deposit stoichiometric GaSb thin films using pulsed laser deposition (PLD) by varying deposition parameters and conditions. Using electron microscopy, the morphology of deposited films and target surface and the compositional deviation from exact stoichiometry have been investigated. We show that the directional nature of laser-target interaction is directly responsible for film quality in PLD in which particulates with high number density are generated due to directional pillar formation. Suppressing this pillar formation, by a simple 180° target rotation, showed an increase in deposition yield by 60%, exact stoichiometric transfer from target to substrate, and large reduction in particulate density. Moreover, from XRD analysis, we show that exact stoichiometric transfer from target to substrate is crucial for structural integrity of the produced films. Temperature induced structural transformation from resistivity vs. temperature measurements show a high crystallization temperature of 250 °C for stoichiometric GaSb thin film. We believe the exact stoichiometric GaSb thin films with reduced particulate densities and favorable structural and (opto)electronic properties are attractive for future PCM devices.

We explore here the decisive role of film thickness on Casimir and electrostatic forces from topological insulating ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ films. The forces were measured for the Au-${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ system under ambient conditions to simulate realistic applications. It is shown that the electrostatic forces associated with a nonzero contact potential of ${V}_{\mathrm{o}}\ensuremath{\sim}200\phantom{\rule{0.28em}{0ex}}\mathrm{mV}$ played a dominant role, and could not be compensated for thinner films ($\ensuremath{\le}20\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ thick). However, for thicker films the measured force, after voltage compensation, started to approach the genuine Casimir force in very good agreement with Lifshitz theory. Our results point out that any gradual deviation from theory for thinner films underlies the presence of strong electrostatic effects.

Strain engineering as a method to control functional properties has seen in the last decades a surge of interest. Heterostructures comprising 2D-materials and containing van der Waals(-like) gaps were considered unsuitable for strain engineering. However, recent work on heterostructures based on Bi2Te3, Sb2Te3, and GeTe showed the potential of a different type of strain engineering due to long-range mutual straining. Still, a comprehensive understanding of the strain relaxation mechanism in these telluride heterostructures is lacking due to limitations of the earlier analyses performed. Here, we present a detailed study of strain in two-dimensional (2D/2D) and mixed dimensional (2D/3D) systems derived from mica/Bi2Te3, Sb2Te3/Bi2Te3, and Bi2Te3/GeTe heterostructures, respectively. We first clearly show the fast relaxation process in the mica/Bi2Te3 system where the strain was generally transferred and confined up to the second or third van der Waals block and then abruptly relaxed. Then we show, using three independent techniques, that the long-range exponentially decaying strain in GeTe and Sb2Te3 grown on the relaxed Bi2Te3 and Bi2Te3 on relaxed Sb2Te3 as directly observed at the growth surface is still present within these three different top layers a long time after growth. The observed behavior points at immediate strain relaxation by plastic deformation without any later relaxation and rules out an elastic (energy minimization) model as was proposed recently. Our work advances the understanding of strain tuning in textured heterostructures or superlattices governed by anisotropic bonding.

In-situ Neutron Diffraction and Small-Angle Neutron Scattering (SANS) are employed for the first time simultaneously in order to reveal the interaction between the austenite to ferrite phase transformation and the precipitation kinetics during isothermal annealing at 650 and at 700 °C in three steels with different vanadium (V) and carbon (C) concentrations. Austenite-to-ferrite phase transformation is observed in all three steels at both temperatures. The phase transformation is completed during a 10 h annealing treatment in all cases. The phase transformation is faster at 650 than at 700 °C for all alloys. Additions of vanadium and carbon to the steel composition cause a retardation of the phase transformation. The effect of each element is explained through its contribution to the Gibbs free energy dissipation. The austenite-to-ferrite phase transformation is found to initiate the vanadium carbide precipitation. Larger and fewer precipitates are detected at 700 than at 650 °C in all three steels, and a larger number density of precipitates is detected in the steel with higher concentrations of vanadium and carbon. After 10 h of annealing, the precipitated phase does not reach the equilibrium fraction as calculated by ThermoCalc. The external magnetic field applied during the experiments, necessary for the SANS measurements, causes a delay in the onset and time evolution of the austenite-to-ferrite phase transformation and consequently on the precipitation kinetics.