Bio-Inspired Micro- and Nano-Scale Surface Features Produced by Femtosecond Laser-Texturing Enhance TiZr-Implant Osseointegration.

Surface design plays a critical role in determining the integration of dental implants with bone tissue. Femtosecond laser-texturing has emerged as a breakthrough technology offering excellent uniformity and reproducibility in implant surface features. However, when compared to state-of-the-art sandblasted and acid-etched surfaces, laser-textured surface designs typically underperform in terms of osseointegration. This study investigated the capacity of a bio-inspired femtosecond laser-textured surface design to enhance osseointegration compared to state-of-the-art sandblasted & acid-etched surfaces. Laser-texturing facilitates the production of an organized trabeculae-like microarchitecture with superimposed nano-scale laser-induced periodic surface structures on both 2D and 3D samples of titanium-zirconium-alloy. Following a boiling treatment to modify the surface chemistry, improving wettability to a contact angle of 10°, laser-textured surfaces enhance fibrin network formation when in contact with human whole blood, comparable to state-of-the-art surfaces. In vitro experiments demonstrate that laser-textured surfaces significantly outperform state-of-the-art surfaces with a 2.5-fold higher level of mineralization by bone progenitor cells after 28 days of culture. Furthermore, in vivo evaluations reveal superior biomechanical integration of laser-textured surfaces after 28 days of implantation. Notably, during abiological pull-out tests, laser-textured surfaces exhibit comparable performance, suggesting that the observed enhanced osseointegration is primarily driven by the biological response to the surface. This article is protected by copyright. All rights reserved.

Atomic scale volume and grain boundary diffusion elucidated by in situ STEM.

Diffusion is one of the most important phenomena studied in science ranging from physics to biology and, in abstract form, even in social sciences. In the field of materials science, diffusion in crystalline solids is of particular interest as it plays a pivotal role in materials synthesis, processing and applications. While this subject has been studied extensively for a long time there are still some fundamental knowledge gaps to be filled. In particular, atomic scale observations of thermally stimulated volume diffusion and its mechanisms are still lacking. In addition, the mechanisms and kinetics of diffusion along defects such as grain boundaries are not yet fully understood. In this work we show volume diffusion processes of tungsten atoms in a metal matrix on the atomic scale. Using in situ high resolution scanning transmission electron microscopy we are able to follow the random movement of single atoms within a lattice at elevated temperatures. The direct observation allows us to confirm random walk processes, quantify diffusion kinetics and distinctly separate diffusion in the volume from diffusion along defects. This work solidifies and refines our knowledge of the broadly essential mechanism of volume diffusion.

From metal nanowires to ultrathin crystalline ALD nanotubes: process development and mechanism revealed by in situ TEM heating experiments.

The creation of hollow nanomaterials based on metal oxides has become an important research topic, as they show potential in a broad range of technical applications. However, the controlled synthesis of long and at the same time thin nanotubes is still challenging. Here we present a universal approach to create ultrathin aluminum oxide nanotubes with a length/diameter ratio of >1200 and minimum wall thickness of ≤4 nm. We use a facile process based on defined heat treatment of specific core-shell nanowires. The metal nanowires act as a template, which is thermally removed during heat treatment until an empty tube is created. The core-shell nanowires are produced by Physical Vapour Deposition (PVD) with a subsequent coating via Atomic Layer Deposition (ALD). The custom-built PVD-ALD system enables a direct sample transfer without breaking the vacuum, which allows determining the effect of a native oxide layer on the metal-ALD bonding. In combination with correlative ex situ observations, in situ Transmission Electron Microscopy (TEM) heating experiments unravel the dynamical processes going on at small scales. Based on the microscopic analysis, the energetics of the core material is analyzed, giving insights about heat induced effects as well as the phase transition from the amorphous to the crystalline state.

Influence of tin oxide decoration on the junction conductivity of silver nanowires.

Flexible electrodes using nanowires (NWs) suffer from challenges of long-term stability and high junction resistance which limit their fields of applications. Welding via thermal annealing is a common strategy to enhance the conductivity of percolated NW networks, however, it affects the structural and mechanical integrity of the NWs. In this study we show that the decoration of NWs with an ultrathin metal oxide is a potential alternative procedure which not only enhances the thermal and chemical stability but, moreover, provides a totally different mechanism to reduce the junction resistance upon heat treatment. Here, we analyze the effect of SnOxdecoration on the conductance of silver NWs and NW junctions by using a four-probe measurement setup inside a scanning electron microscope. Dedicated transmission electron microscopy analysis in plan-view and cross-section geometry are carried out to characterize the nanowires and the microstructure of the junctions. Upon heat treatment the junction resistance of both plain silver NWs and SnOx-decorated NWs is reduced by around 80%. While plain silver NWs show characteristic junction welding during annealing, the SnOx-decoration reduces junction resistance by a solder-like process which does not affect the mechanical integrity of the NW junction and is therefore expected to be superior for applications.

Sensing Capabilities of Single Nanowires Studied with Correlative In Situ Light and Electron Microscopy.

Modern devices based on modular designs require versatile and universal sensor components which provide an efficient, sensitive, and compact measurement unit. To improve the space capacity of devices, miniaturized building elements are needed, which implies a turning away from conventional microcantilevers toward nanoscale cantilevers. Nanowires can be seen as high-quality resonators and offer the opportunity to create sensing devices on small scales. To use such a one-dimensional nanostructure as a resonant cantilever, a precise characterization based on the fundamental properties is needed. We present a correlative electron and light microscopy approach to characterize the pressure and environment sensing capabilities of single nanowires by analyzing their resonance behavior in situ. The high vacuum in electron microscopes enables the characterization of the intrinsic vibrational properties and the maximum quality factor. To analyze the damping effect caused by the interaction of the gas molecules with the excited nanowire, the in situ resonance measurements have been performed under non-high-vacuum conditions. For this purpose, single nanowires are mounted in a specifically designed compact gas chamber underneath the light microscope, which enables direct observation of the resonance behavior and evaluation of the quality factor with dependence of the applied gas atmosphere (He, N2, Ar, Air) and pressure level. By using the resonance vibration, we demonstrate the pressure sensing capability of a single nanowire and examine the molar mass of the surrounding atmosphere. Together this shows that even single nanowires can be utilized as versatile nanoscale gas sensors.

Composition Dependent Electrical Transport in Si1-x Gex Nanosheets with Monolithic Single-Elementary Al Contacts.

Si1-x Gex is a key material in modern complementary metal-oxide-semiconductor and bipolar devices. However, despite considerable efforts in metal-silicide and -germanide compound material systems, reliability concerns have so far hindered the implementation of metal-Si1-x Gex junctions that are vital for diverse emerging "More than Moore" and quantum computing paradigms. In this respect, the systematic structural and electronic properties of Al-Si1-x Gex heterostructures, obtained from a thermally induced exchange between ultra-thin Si1-x Gex nanosheets and Al layers are reported. Remarkably, no intermetallic phases are found after the exchange process. Instead, abrupt, flat, and void-free junctions of high structural quality can be obtained. Interestingly, ultra-thin interfacial Si layers are formed between the metal and Si1-x Gex segments, explaining the morphologic stability. Integrated into omega-gated Schottky barrier transistors with the channel length being defined by the selective transformation of Si1-x Gex into single-elementary Al leads, a detailed analysis of the transport is conducted. In this respect, a report on a highly versatile platform with Si1-x Gex composition-dependent properties ranging from highly transparent contacts to distinct Schottky barriers is provided. Most notably, the presented abrupt, robust, and reliable metal-Si1-x Gex junctions can open up new device implementations for different types of emerging nanoelectronic, optoelectronic, and quantum devices.

The response of soft tissue cells to Ti implants is modulated by blood-implant interactions.

Titanium-based dental implants have been highly optimized to enhance osseointegration, but little attention has been given to the soft tissue-implant interface, despite being a major contributor to long term implant stability. This is strongly linked to a lack of model systems that enable the reliable evaluation of soft tissue-implant interactions. Current in vitro platforms to assess these interactions are very simplistic, thus suffering from limited biological relevance and sensitivity to varying implant surface properties. The aim of this study was to investigate how blood-implant interactions affect downstream responses of different soft tissue cells to implants in vitro, thus taking into account not only the early events of blood coagulation upon implantation, but also the multicellular nature of soft tissue. For this, three surfaces (smooth and hydrophobic; rough and hydrophobic; rough and hydrophilic with nanostructures), which reflect a wide range of implant surface properties, were used to study blood-material interactions as well as cell-material interactions in the presence and absence of blood. Rough surfaces stimulated denser fibrin network formation compared to smooth surfaces and hydrophilicity accelerated the rate of blood coagulation compared to hydrophobic surfaces. In the absence of blood, smooth surfaces supported enhanced attachment of human gingival fibroblasts and keratinocytes, but limited changes in gene expression and cytokine production were observed between surfaces. In the presence of blood, rough surfaces supported enhanced fibroblast attachment and stimulated a stronger anti-inflammatory response from macrophage-like cells than smooth surfaces, but only smooth surfaces were capable of supporting long-term keratinocyte attachment and formation of a layer of epithelial cells. These findings indicate that surface properties not only govern blood-implant interactions, but that this can in turn also significantly modulate subsequent soft tissue cell-implant interactions.

Monolithic and Single-Crystalline Aluminum-Silicon Heterostructures.

Overcoming the difficulty in the precise definition of the metal phase of metal-Si heterostructures is among the key prerequisites to enable reproducible next-generation nanoelectronic, optoelectronic, and quantum devices. Here, we report on the formation of monolithic Al-Si heterostructures obtained from both bottom-up and top-down fabricated Si nanostructures and Al contacts. This is enabled by a thermally induced Al-Si exchange reaction, which forms abrupt and void-free metal-semiconductor interfaces in contrast to their bulk counterparts. The selective and controllable transformation of Si NWs into Al provides a nanodevice fabrication platform with high-quality monolithic and single-crystalline Al contacts, revealing resistivities as low as ρ = (6.31 ± 1.17) × 10-8 Ω m and breakdown current densities of Jmax = (1 ± 0.13) × 1012 Ω m-2. Combining transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the composition as well as the crystalline nature of the presented Al-Si-Al heterostructures, with no intermetallic phases formed during the exchange process in contrast to state-of-the-art metal silicides. The thereof formed single-element Al contacts explain the robustness and reproducibility of the junctions. Detailed and systematic electrical characterizations carried out on back- and top-gated heterostructure devices revealed symmetric effective Schottky barriers for electrons and holes. Most importantly, fulfilling compatibility with modern complementary metal-oxide semiconductor fabrication, the proposed thermally induced Al-Si exchange reaction may give rise to the development of next-generation reconfigurable electronics relying on reproducible nanojunctions.

Microscopic Deformation Modes and Impact of Network Anisotropy on the Mechanical and Electrical Performance of Five-fold Twinned Silver Nanowire Electrodes.

Silver nanowire (AgNW) networks show excellent optical, electrical, and mechanical properties, which make them ideal candidates for transparent electrodes in flexible and stretchable devices. Various coating strategies and testing setups have been developed to further improve their stretchability and to evaluate their performance. Still, a comprehensive microscopic understanding of the relationship between mechanical and electrical failure is missing. In this work, the fundamental deformation modes of five-fold twinned AgNWs in anisotropic networks are studied by large-scale SEM straining tests that are directly correlated with corresponding changes in the resistance. A pronounced effect of the network anisotropy on the electrical performance is observed, which manifests itself in a one order of magnitude lower increase in resistance for networks strained perpendicular to the preferred wire orientation. Using a scale-bridging microscopy approach spanning from NW networks to single NWs to atomic-scale defects, we were able to identify three fundamental deformation modes of NWs, which together can explain this behavior: (i) correlated tensile fracture of NWs, (ii) kink formation due to compression of NWs in transverse direction, and (iii) NW bending caused by the interaction of NWs in the strained network. A key observation is the extreme deformability of AgNWs in compression. Considering HRTEM and MD simulations, this behavior can be attributed to specific defect processes in the five-fold twinned NW structure leading to the formation of NW kinks with grain boundaries combined with V-shaped surface reconstructions, both counteracting NW fracture. The detailed insights from this microscopic study can further improve fabrication and design strategies for transparent NW network electrodes.

Low energy nano diffraction (LEND) - A versatile diffraction technique in SEM.

Electron diffraction is a powerful characterization method that is used across different fields and in different instruments. In particular, the power of transmission electron microscopy (TEM) largely relies on the capability to switch between imaging and diffraction mode enabling identification of crystalline phases and in-depth studies of crystal defects, to name only examples. In contrast, while diffraction techniques have found their way into the realm of scanning electron microscopy (SEM) in the form of electron backscatter diffraction and related techniques, on-axis transmission diffraction is still in its infancy. Here we present a simple but versatile setup that enables a 'diffraction mode' in SEM using a fluorescent screen and a dedicated in vacuo camera. With this setup spot-like nano-beam diffraction patterns of thin samples can be acquired with electron energies as low as 500 eV. We therefore coin the name Low Energy Nano Diffraction (LEND). Diffraction patterns can be recorded from single positions on the sample or integrated over selected areas by adjustable scan patterns. Besides showing the principal application of the technique to standard materials such as gold and silicon we also explore the application to graphene and other 2D materials. Besides single pattern measurements, also full 4D-STEM diffraction mappings are demonstrated. Finally, we show how the integration of a versatile diffraction mode in SEM enables a thorough analysis performed with a single instrument.

Mechanical cleaning of graphene using in situ electron microscopy.

Avoiding and removing surface contamination is a crucial task when handling specimens in any scientific experiment. This is especially true for two-dimensional materials such as graphene, which are extraordinarily affected by contamination due to their large surface area. While many efforts have been made to reduce and remove contamination from such surfaces, the issue is far from resolved. Here we report on an in situ mechanical cleaning method that enables the site-specific removal of contamination from both sides of two dimensional membranes down to atomic-scale cleanliness. Further, mechanisms of re-contamination are discussed, finding surface-diffusion to be the major factor for contamination in electron microscopy. Finally the targeted, electron-beam assisted synthesis of a nanocrystalline graphene layer by supplying a precursor molecule to cleaned areas is demonstrated.

Transforming layered MoS2 into functional MoO2 nanowires.

A new in situ synthesis method for the growth of MoO2 nanowires via controlled thermal oxidation of MoS2 flakes is presented, going from a 2D transition metal chalcogenide to a transition metal oxide nanostructure. The wire growth is performed under an optical microscope using a heating stage with adjustable atmospheric conditions. In contrast to prevalent syntheses, this templated growth leads to highly directional wires along defined MoS2 crystallographic directions. We examine the growth kinetics of the wires in dependence of the process temperature. In the temperature regime from 650 °C to 710 °C high quality MoO2 nanowires are formed in a reaction-limited growth process with an activation energy of 596 kJ mol-1. The functional properties of the nanowires are studied by a combination of in situ electron microscopy techniques. Four point measurements in an SEM reveal outstanding metal-like behavior of the nanowires with resistivity values as low as 3.5 × 10-6 Ω m. Surprisingly, junctions between intergrown nanowires show hardly any increase in resistivity which can be attributed to the well-defined orientational relationship of the nanowires resulting from their templated growth on MoS2. Elastic properties of the nanowires are studied by complementary in situ bending and resonance measurements in SEM yielding consistent values of 383 GPa for the Young's modulus. Finally, field emission of single MoO2 nanowires is studied in situ inside the TEM, and an emission current of 500 nA is achieved. The combination of simple synthesis route with outstanding functional properties make the MoO2 nanowires promising candidates for functional devices in the field of novel 1D-oxide/2D-chalcogenide hybrids. The presented synthesis can be generalized and applied to other metal chalcogenides such as WS2, as well.

In Vitro Endothelialization of Surface-Integrated Nanofiber Networks for Stretchable Blood Interfaces.

Despite major technological advances within the field of cardiovascular engineering, the risk of thromboembolic events on artificial surfaces in contact with blood remains a major challenge and limits the functionality of ventricular assist devices (VADs) during mid- or long-term therapy. Here, a biomimetic blood-material interface is created via a nanofiber-based approach that promotes the endothelialization capability of elastic silicone surfaces for next-generation VADs under elevated hemodynamic loads. A blend fiber membrane made of elastic polyurethane and low-thrombogenic poly(vinylidene fluoride- co-hexafluoropropylene) was partially embedded into the surface of silicone films. These blend membranes resist fundamental irreversible deformation of the internal structure and are stably attached to the surface, while also exhibiting enhanced antithrombotic properties when compared to bare silicone. The composite material supports the formation of a stable monolayer of endothelial cells within a pulsatile flow bioreactor, resembling the physiological in vivo situation in a VAD. The nanofiber surface modification concept thus presents a promising approach for the future design of advanced elastic composite materials that are particularly interesting for applications in contact with blood.

In situ manipulation and switching of dislocations in bilayer graphene.

Topological defects in crystalline solids are of fundamental interest in physics and materials science because they can radically alter the properties of virtually any material. Of particular importance are line defects, known as dislocations, which are the main carriers of plasticity and have a tremendous effect on electronic and optical properties. Understanding and controlling the occurrence and behavior of those defects have been of major and ongoing interest since their discovery in the 1930s. This interest was renewed with the advent of two-dimensional materials in which a single topological defect can alter the functionality of the whole system and even create new physical phenomena. We present an experimental approach to directly manipulate dislocations in situ on the nanometer scale by using a dedicated scanning electron microscope setup. With this approach, key fundamental characteristics such as line tension, defect interaction, and node formation have been studied. A novel switching reaction, based on the recombination of dislocation lines, was found, which paves the way for the concept of switches made of a bimodal topological defect configuration.

Ligand-assisted thickness tailoring of highly luminescent colloidal CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets.

Quantum size-confined CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

Overcoming the Interface Losses in Planar Heterojunction Perovskite-Based Solar Cells.

A scalable, hysteresis-free and planar architecture perovskite solar cell is presented, employing a flame spray synthesized low-temperature processed NiO (LT-NiO) as hole-transporting layer yielding efficiencies close to 18%. Importantly, it is found that LT-NiO boosts the limits of open-circuit voltages toward an impressive non-radiative voltage loss of 0.226 V only, whereas PEDOT: PSS suffers from significant large non-radiative recombination losses.

Solar spectral conversion for improving the photosynthetic activity in algae reactors.

Sustainable biomass production is expected to be one of the major supporting pillars for future energy supply, as well as for renewable material provision. Algal beds represent an exciting resource for biomass/biofuel, fine chemicals and CO2 storage. Similar to other solar energy harvesting techniques, the efficiency of algal photosynthesis depends on the spectral overlap between solar irradiation and chloroplast absorption. Here we demonstrate that spectral conversion can be employed to significantly improve biomass growth and oxygen production rate in closed-cycle algae reactors. For this purpose, we adapt a photoluminescent phosphor of the type Ca0.59Sr0.40Eu0.01S, which enables efficient conversion of the green part of the incoming spectrum into red light to better match the Qy peak of chlorophyll b. Integration of a Ca0.59Sr0.40Eu0.01S backlight converter into a flat panel algae reactor filled with Haematococcus pluvialis as a model species results in significantly increased photosynthetic activity and algae reproduction rate.

Environmental indicators of biofuel sustainability: what about context?

Indicators of the environmental sustainability of biofuel production, distribution, and use should be selected, measured, and interpreted with respect to the context in which they are used. The context of a sustainability assessment includes the purpose, the particular biofuel production and distribution system, policy conditions, stakeholder values, location, temporal influences, spatial scale, baselines, and reference scenarios. We recommend that biofuel sustainability questions be formulated with respect to the context, that appropriate indicators of environmental sustainability be developed or selected from more generic suites, and that decision makers consider context in ascribing meaning to indicators. In addition, considerations such as technical objectives, varying values and perspectives of stakeholder groups, indicator cost, and availability and reliability of data need to be understood and considered. Sustainability indicators for biofuels are most useful if adequate historical data are available, information can be collected at appropriate spatial and temporal scales, organizations are committed to use indicator information in the decision-making process, and indicators can effectively guide behavior toward more sustainable practices.

Casa, moradia, habitaçäo / House, home, habitation

Procura provocar reflexöes diversas sobre a questäo habitacional brasileira a partir do exame da nossa realidade atual e recente.