Korrosionsuntersuchungen an mittels PVD mit Zn und Zn/Mn beschichteten Stählen

Corrosion Studies of Steels Coated by means of PVD with Zn and Zn/Mn Alternative methods for hot dip‐ or electrogalvanic deposition of zinc coatings on steel are gas phase depositions (PVD). They posess high flexibility with respect to alloy composition, and are environmentally harmless. However, a PVD‐coated steel must have at least the same corrosion resistance than steels with “classical” surface finishing. Therefore, the corrosion behaviour of Zn‐coatings and Zn/Mn/system‐coatings deposited by electron beam evaporation without and with ion beam assistance (IBAD) on low alloy steel, was determined by means of salt spray test and electrochemical potential/time measurements. At first the influence of chemical and irradiation pre‐treatment and ion bombardment during deposition on the corrosion resistance of the coatings was investigated. Than the effect of the Zn‐layer thickness was determined in comparison with an 8μm thick electrogalvanized reference coating. Finally Zn/Mn‐alloys, Zn/Mn‐multilayers and Zn‐coatings with Mn‐ or Zn/Mn‐surface layers (top layers) were investigated. By means of optimised pre‐treatment and ion bombardment conditions one obtains, considering the layer thickness, PVD‐Zn coatings with corrosion resistance comparable with the reference layer. The best Mn‐containing coatings are Zn‐coatings with Mn‐toplayer. They surpass the corrosion resistance of the reference layer considerably. Additionally it could be shown that in tendency the potential/time measurements agree very well with the results of the salt spray test.     

Dual Growth Factor Delivery Using Biocompatible Core–Shell Microcapsules for Angiogenesis

An optimized electrodropping system produces homogeneous core–shell microcapsules (C‐S MCs) by using poly(L ‐lactic‐co‐glycolic acid) (PLGA) and alginate. Fluorescence imaging clearly shows the C‐S domain in the MC. For release control, the use of high‐molecular‐weight PLGA (HMW 270 000) restrains the initial burst release of protein compared to that of low‐MW PLGA (LMW 40 000). Layer‐by‐layer (LBL) assembly of chitosan and alginate on MCs is also useful in controlling the release profile of biomolecules. LBL (7‐layer) treatment is effective in suppressing the initial burst release of protein compared to no LBL (0‐layer). The difference of cumulative albumin release between HMW (7‐layer LBL) and LMW (0‐layer LBL) PLGA is determined to be more than 40% on day 5. When dual angiogenic growth factors (GFs), such as platelet‐derived GF (PDGF) and vascular endothelial GF (VEGF), are encapsulated separately in the core and shell domains, respectively, the VEGF release rate is much greater than that of PDGF, and the difference of the cumulative release percentage between the two GFs is about 30% on day 7 with LMW core PLGA and more than 45% with HMW core PLGA. As for the angiogenic potential of MC GFs with human umbilical vein endothelial cells (HUVECs), the fluorescence signal of CD31+ suggests that the angiogenic sprout of ECs is more active in MC‐mediated GF delivery than conventional GF delivery, and this difference is significant, based on the number of capillary branches in the unit area. This study demonstrates that the fabrication of biocompatible C‐S MCs is possible, and that the release control of biomolecules is adjustable. Furthermore, MC‐mediated GFs remain in an active form and can upregulate the angiogenic activity of ECs.     

Atomic‐Scale Fabrication of In‐Plane Heterojunctions of Few‐Layer MoS2 via In Situ Scanning Transmission Electron Microscopy

Layered MoS₂ is a prospective candidate for use in energy harvesting, valleytronics, and nanoelectronics. Its properties strongly related to its stacking configuration and the number of layers. Due to its atomically thin nature, understanding the atomic‐level and structural modifications of 2D transition metal dichalcogenides is still underdeveloped, particularly the spatial control and selective precision. Therefore, the development of nanofabrication techniques is essential. Here, an atomic‐scale approach used to sculpt 2D few‐layer MoS₂ into lateral heterojunctions via in situ scanning/transmission electron microscopy (STEM/TEM) is developed. The dynamic evolution is tracked using ultrafast and high‐resolution filming equipment. The assembly behaviors inherent to few‐layer 2D‐materials are observed during the process and included the following: scrolling, folding, etching, and restructuring. Atomic resolution STEM is employed to identify the layer variation and stacking sequence for this new 2D‐architecture. Subsequent energy‐dispersive X‐ray spectroscopy and electron energy loss spectroscopy analyses are performed to corroborate the elemental distribution. This sculpting technique that is established allows for the formation of sub‐10 nm features, produces diverse nanostructures, and preserves the crystallinity of the material. The lateral heterointerfaces created in this study also pave the way for the design of quantum‐relevant geometries, flexible optoelectronics, and energy storage devices.     

Biomedical Applications of Layer‐by‐Layer Assembly: From Biomimetics to Tissue Engineering

The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer‐by‐layer assembly method introduced by Decher and co‐workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials' structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer‐by‐layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer‐by‐layer assembly are introduced. The applications of layer‐by‐layer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer‐by‐layer assembly are also discussed.     

Flexible Nonvolatile Transistor Memory with Solution‐Processed Transition Metal Dichalcogenides

Nonvolatile field‐effect transistor (FET) memories containing transition metal dichalcogenide (TMD) nanosheets have been recently developed with great interest by utilizing some of the intriguing photoelectronic properties of TMDs. The TMD nanosheets are, however, employed as semiconducting channels in most of the memories, and only a few works address their function as floating gates. Here, a floating‐gate organic‐FET memory with an all‐in‐one floating‐gate/tunneling layer of the solution‐processed TMD nanosheets is demonstrated. Molybdenum disulfide (MoS₂) is efficiently liquid‐exfoliated by amine‐terminated polystyrene with a controlled amount of MoS₂ nanosheets in an all‐in‐one floating‐gate/tunneling layer, allowing for systematic investigation of concentration‐dependent charge‐trapping and detrapping properties of MoS₂ nanosheets. At an optimized condition, the nonvolatile memory exhibits memory performances with an ON/OFF ratio greater than 10⁴, a program/erase endurance cycle over 400 times, and data retention longer than 7 × 10³ s. All‐in‐one floating‐gate/tunneling layers containing molybdenum diselenide and tungsten disulfide are also developed. Furthermore, a mechanically‐flexible TMD memory on a plastic substrate shows a performance comparable with that on a hard substrate, and the memory properties are rarely altered after outer‐bending events over 500 times at the bending radius of 4.0 mm.     

Role of Thick‐Lithium Fluoride Layer in Energy Level Alignment at Organic/Metal Interface: Unifying Effect on High Metallic Work Functions

The function of ≈3‐nm thick lithium fluoride (LiF) buffer layers in combination with high work function metal contacts such as coinage metals and ferromagnetic metals for use in organic electronics and spintronics is investigated. The energy level alignment at the organic/LiF/metal interface is systematically studied using photoelectron spectroscopy and the integer charge transfer model. The thick‐LiF buffer layer is found to pin the Fermi level to ≈3.8 eV, regardless of the work function of the initial metal due to energy level bending in the LiF layer caused by depletion of defect states. At 3‐nm thickness, the LiF buffer layer provides full coverage, and the organic semiconductor adlayers are found to physisorb with the consequence that the energy level alignment at the organic/LiF interface follows the integer charge transfer model's predictions.     

Identifying the Intrinsic Relationship between the Restructured Oxide Layer and Oxygen Evolution Reaction Performance on the Cobalt Pnictide Catalyst

Cobalt pnictides show good catalytic activity and stability on oxygen evolution reaction (OER) behaviors in a strong alkaline solution. Identifying the intrinsic composition/structure‐property relationship of the oxide layer on the cobalt pnictides is critical to design better and cheaper electrocatalysts for the commercial viability of OER technologies. In this work, the restructured oxide layer on the cobalt pnictides and its effect on the activity and mechanism for OER is systematically analyzed. In‐situ electrochemical impedance spectroscopy (EIS) and near edge x‐ray absorption fine structure (NEXAFS) spectra indicate that a higher OER performance of cobalt pnictides than Co₃O₄ is attributed to the more structural disorder and oxygen defect sites in the cobalt oxide layer evolved from cobalt pnictides. Using angle resolved x‐ray photoelectron spectroscopy (AR‐XPS) further demonstrates that the oxygen defect sites mainly concentrate on the subsurface of cobalt oxide layer. The current study demonstrated promising opportunities for further enhancing the OER performance of cobalt‐based electrocatalysts by controlling the subsurface defects of the restructured active layer.     

Monolithic and Flexible ZnS/SnO2 Ultraviolet Photodetectors with Lateral Graphene Electrodes

A continuing trend of miniaturized and flexible electronics/optoelectronic calls for novel device architectures made by compatible fabrication techniques. However, traditional layer‐to‐layer structures cannot satisfy such a need. Herein, a novel monolithic optoelectronic device fabricated by a mask‐free laser direct writing method is demonstrated in which in situ laser induced graphene‐like materials are employed as lateral electrodes for flexible ZnS/SnO₂ ultraviolet photodetectors. Specifically, a ZnS/SnO₂ thin film comprised of heterogeneous ZnS/SnO₂ nanoparticles is first coated on polyimide (PI) sheets by a solution process. Then, CO₂ laser irradiation ablates designed areas of the ZnS/SnO₂ thin film and converts the underneath PI into highly conductive graphene as the lateral electrodes for the monolithic photodetectors. This in situ growth method provides good interfaces between the graphene electrodes and the semiconducting ZnS/SnO₂ resulting in high optoelectronic performance. The lateral electrode structure reduces total thickness of the devices, thus minimizing the strain and improving flexibility of the photodetectors. The demonstrated lithography‐free monolithic fabrication is a simple and cost‐effective method, showing a great potential for developement into roll‐to‐roll manufacturing of flexible electronics.     

Tuning Surface Wettability and Adhesivity of a Nitrogen‐Doped Graphene Foam after Water Vapor Treatment for Efficient Oil Removal

An environment‐friendly water vapor treatment for realizing a highly hydrophobic (contact angle ≈147.5°) and oleophilic N‐doped graphene foam (NGF) for efficiently removing oil from oil/water emulsions is presented. 3D porous networks of NGF with high N content are prepared by subjecting a mixture of graphene oxide and 5 vol% pyrrole to a hydrothermal process; the mixture is then freeze‐dried and annealed under a N₂ atmosphere. The surface wettability and adhesivity are tuned through water vapor treatment by forming a low‐surface‐energy hydrocarbon layer, with no chemical modification. The effectiveness of the hydrophobic/oleophilic NGF in removing oil from an oil/water emulsion is demonstrated.     

Dual‐Locking Nanoparticles Disrupt the PD‐1/PD‐L1 Pathway for Efficient Cancer Immunotherapy

The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR‐associated (Cas) enzyme, Cas13a, holds great promise in cancer treatment due to its potential for selective destruction of tumor cells via collateral effects after target recognition. However, these collateral effects do not specifically target tumor cells and may cause safety issues when administered systemically. Herein, a dual‐locking nanoparticle (DLNP) that can restrict CRISPR/Cas13a activation to tumor tissues is described. DLNP has a core–shell structure, in which the CRISPR/Cas13a system (plasmid DNA, pDNA) is encapsulated inside the core with a dual‐responsive polymer layer. This polymer layer endows the DLNP with enhanced stability during blood circulation or in normal tissues and facilitates cellular internalization of the CRISPR/Cas13a system and activation of gene editing upon entry into tumor tissue. After carefully screening and optimizing the CRISPR RNA (crRNA) sequence that targets programmed death‐ligand 1 (PD‐L1), DLNP demonstrates the effective activation of T‐cell‐mediated antitumor immunity and the reshaping of immunosuppressive tumor microenvironment (TME) in B16F10‐bearing mice, resulting in significantly enhanced antitumor effect and improved survival rate. Further development by replacing the specific crRNA of target genes can potentially make DLNP a universal platform for the rapid development of safe and efficient cancer immunotherapies.     

Gallium Complexes in Three‐Layer Organic Electroluminescent Devices

Organic light‐emitting diodes fabricated by subsequently spin‐coating two layers—a hole‐transporting followed by a metal chelate emissive layer—onto poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonate) are presented for the first time. The electron–hole recombination occurs in a layer consisting of Ga complexes (see Figure), which exhibit high fluorescence quantum yields, and their emission spectra are blue‐shifted relative to that of tris(8‐hydroxyquinoline) aluminum. By doping this spin‐coated emission layer with fluorescent emitters the emission band can be shifted within the visible spectral range.     

Liquefied Capsules Coated with Multilayered Polyelectrolyte Films for Cell Immobilization

Natural‐derived polymers are used to coat liquid‐core capsules layer by layer to encapsulate cells. Human osteoblast‐like cells (SaOs‐2) are encapsulated in such spherical devices using a three‐step methodology: i) ionotropic gelation to produce alginate beads encapsulating the cells; ii) layer‐by‐layer coating using water‐soluble chitosan and alginate; and iii) core liquefaction. Cells remain viable for 3 d after the encapsulation procedure, suggesting that the developed capsules possess a semipermeable, nanostructured coating. All of the capsules exhibit a spherical shape, smooth surface and liquid‐core characteristics. All of the processes are conducted under mild conditions and physiological pH. We consider that the methodology employed in the development of the capsules obtained from natural‐based biomaterials has potential to find applicability in the development of scaffolds or cell carriers in tissue engineering and regenerative medicine.     

A Combined Analytic,Numeric, and Experimental Investigation Performed on NiTi/NiTiCu Bi‐Layer Composites under Tensile Loading

Adjusting mechanical behavior and controlling deformation parameters are significant tasks in designing shape memory components. In this paper, an analytical model describes the deformation behavior of NiTi/NiTiCu bi‐layer composites under tensile loading. Different deformation stages are considered based on single mechanical behavior at each stage. Closed‐form equations are derived for stress–strain variations of bi‐layer composites under uniaxial loading–unloading. Bi‐layer composites made via the diffusion bonding method from single layers of NiTi alloy with a composition of Ti‐50.7 at.% Ni, as an austenitic layer, and Ti‐45 at% Ni‐5 at% Cu, as a martensitic layer, are produced by the vacuum arc remelting technique. The tensile behavior of single‐ and bi‐layers is investigated by using loading–unloading experiments to find the nominal stress–strain curves. Numerical simulations are also done by employing Lagoudas constitutive model to simulate stress–strain diagrams. The solutions of the analytical method presented are validated by using the numerical simulations as well as the experimental results. With regard to the results obtained from the analytical modeling, the numerical simulations, and the experiments, it is evident that the bi‐layer composites with different thickness ratios provide adjustable mechanical behavior that can be considered in different application designs, for example, actuators equipped with shape memory components.

     

Development of Polymeric Nanoprobes with Improved Lifetime Dynamic Range and Stability for Intracellular Oxygen Sensing

A class of core‐shell nanoparticles possessing a layer of biocompatible shell and hydrophobic core with embedded oxygen‐sensitive platinum‐porphyrin (PtTFPP) dyes is developed via a radical‐initiated microemulsion co‐polymerization strategy. The influences of host matrices and the PtTFPP incorporation manner on the photophysical properties and the oxygen‐sensing performance of the nanoparticles are investigated. Self‐loading capability with cells and intracellular‐oxygen‐sensing ability of the as‐prepared nanoparticle probes in the range 0%–20% oxygen concentration are confirmed. Polymeric nanoparticles with optimized formats are characterized by their relatively small diameter (<50 nm), core‐shell structures with biocompatible shells, covalent‐attachment‐imparted leak‐free construction, improved lifetime dynamic range (up to 44 μs), excellent storage stability and photostability, and facile cell uptake. The nanoparticles’ small sensor diameter and core‐shell structure with biocompatible shell make them suitable for intracellular detection applications. For intracellular detection applications, the leak‐free feature of the as‐prepared nanoparticle sensor effectively minimizes potential chemical interferences and cytotoxicity. As a salient feature, improved lifetime dynamic range of the sensor is expected to enable precise oxygen detection and control in specific practical applications in stem‐cell biology and medical research. Such a feature‐packed nanoparticle oxygen sensor may find applications in precise oxygen‐level mapping of living cells and tissue.     

Analysis of multiple cracks in laminate composites under anti-plane static loads

This paper investigates multiple cracking of a laminate composite subjected to anti‐plane loads. The laminate composite is made up of a central layer sandwiched between two layers of different properties. There is a periodic array of cracks in the central layer along the central axis of the medium. A singular integral equation is formulated in terms of the crack‐face displacement. The model developed is applied to the analysis of fibre multiple cracking in fibre‐matrix laminate composites. It is also applied to the analysis of matrix cracking in fibre‐matrix laminate composites. Numerical results have been given for the effects of crack spacing and constituent volume fraction on the crack tip field intensity factor and stress.     

Investigation of the Effects of Different Types of Investments on the Alpha‐Case Layer of Ti6Al7Nb Castings

The effects of four different types of investment on the alpha‐case layer of Ti6Al7Nb (Ti67) castings are summarized. The formation mechanism of the alpha‐case layer is investigated. Four different investment materials are compared. The alpha‐case layers on castings produced with Invest‐Ti? T? , Al₂O₃? , and ZrSiO₄‐based investments comprise an oxide layer, an alloy layer, and a hardening layer, and are not only formed by interstitial oxygen but also by substitutional elements dissolved from mould materials. The Y₂O₃‐based investment material provides the most‐reliable choice for the production of titanium castings and is beneficial for the casting of Ti67 because of no alpha‐case formation.     

Mesh‐free models for static analysis of smart laminated composite beams

This paper is concerned with the development of mesh‐free models for the static analysis of smart laminated composite beams. The overall smart composite beam is composed of a laminated substrate composite beam and a piezoelectric layer attached partially or fully at the top surface of the substrate beam. The piezoelectric layer acts as the distributed actuator layer of the smart beam. A layer‐wise displacement theory and an equivalent single‐layer theory have been used to derive the models. Several cross‐ply substrate beams are considered for presenting the numerical results. The responses of the smart composite beams computed by the present new mesh‐free model based on the layer‐wise displacement theory excellently match with those obtained by the exact solutions. The mesh‐free model based on the equivalent single‐layer theory cannot accurately compute the responses due to transverse actuation by the piezoelectric actuator. The models derived here suggest that the mesh‐free method can be efficiently used for the numerical analysis of smart structures. Copyright © 2016 John Wiley & Sons, Ltd.     

Rapid and Low‐Cost Prototyping of 3D Nanostructures with Multi‐Layer Hydrogen Silsesquioxane Scaffolds

A layer‐by‐layer (LBL) method can generate or approximate any three‐dimensional (3D) structure, and has been the approach for the manufacturing of complementary metal‐oxide‐semiconductor (CMOS) devices. However, its high cost precludes the fabrication of anything other than CMOS‐compatible devices, and general 3D nanostructures have been difficult to prototype in academia and small businesses, due to the lack of expensive facility and state‐of‐the‐art tools. It is proposed and demonstrated that a novel process that can rapidly fabricate high‐resolution three‐dimensional (3D) nanostructures at low cost, without requiring specialized equipment. An individual layer is realized through electron‐beam lithography patterning of hydrogen silsesquioxane (HSQ) resist, followed by planarization via spinning SU‐8 resist and etch‐back. A 4‐layer silicon inverse woodpile photonic crystal with a period of 650 nm and a 7‐layer HSQ scaffold with a period of 300 nm are demonstrated. This process provides a versatile and accessible solution to the fabrication of highly complex 3D nanostructures.     

Phoretic Liquid Metal Micro/Nanomotors as Intelligent Filler for Targeted Microwelding

Micro/nanomotors (MNMs) have emerged as active micro/nanoplatforms that can move and perform functions at small scales. Much of their success, however, hinges on the use of functional properties of new materials. Liquid metals (LMs), due to their good electrical conductivity, biocompatibility, and flexibility, have attracted considerable attentions in the fields of flexible electronics, biomedicine, and soft robotics. The design and construction of LM‐based motors is therefore a research topic with tremendous prospects, however current approaches are mostly limited to macroscales. Here, the fabrication of an LM‐MNM (made of Galinstan, a gallium–indium–tin alloy) is reported and its potential application as an on‐demand, self‐targeting welding filler is demonstrated. These LM‐MNMs (as small as a few hundred nanometers) are half‐coated with a thin layer of platinum (Pt) and move in H₂O₂ via self‐electrophoresis. In addition, the LM‐MNMs roaming in a silver nanowire network can move along the nanowires and accumulate at the contact junctions where they become fluidic and achieve junction microwelding at room temperature by reacting with acid vapor. This work presents an intelligent and soft nanorobot capable of repairing circuits by welding at small scales, thus extending the pool of available self‐propelled MNMs and introducing new applications.     

An Optically Flat Conductive Outcoupler Using Core/Shell Ag/ZnO Nanochurros

Transparent conductive electrodes (TCEs) featuring a smooth surface are indispensable for preserving pristine electrical characteristics in optoelectronic and transparent electronic devices. For high‐efficiency organic light emitting diodes (OLEDs), a high outcoupling efficiency, which is crucial, is only achieved by incorporating a wavelength‐scale undulating surface into a TCE layer, but this inevitably degrades device performance. Here, an optically flat, high‐conductivity TCE composed of core/shell Ag/ZnO nanochurros (NCs) is reported embedded within a resin film on a polyethylene terephthalate substrate, simultaneously serving as an efficient outcoupler and a flexible substrate. The ZnO NCs are epitaxially grown on the {100} planes of a pentagonal Ag core and the length of ZnO shells is precisely controlled by the exposure time of Xe lamp. Unlike Ag nanowires films, the Ag/ZnO NCs films markedly boost the optical tunneling of light. Green‐emitting OLEDs (2.78 × 3.5 mm²) fabricated with the Ag/ZnO TCE exhibit an 86% higher power efficiency at 1000 cd m^?2 than ones with an Sn‐doped indium oxide TCE. A full‐vectorial electromagnetic simulation suggests the suppression of plasmonic absorption losses within their Ag cores. These results provide a feasibility of multifunctional TCEs with synthetically controlled core/shell nanomaterials toward the development of high‐efficiency LED and solar cell devices.