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- ItemRevealing all states of dewetting of a thin gold layer on a silicon surface by nanosecond laser conditioning(Amsterdam : Elsevier, 2021) Ernst, Owen C.; Uebel, David; Kayser, Stefan; Lange, Felix; Teubner, Thomas; Boeck, TorstenDewetting is a ubiquitous phenomenon which can be applied to the laser synthesis of nanoparticles. A classical spinodal dewetting process takes place in four successive states, which differ from each other in their morphology. In this study all states are revealed by interaction of pulsed nanosecond UV laser light with thin gold layers with thicknesses between 1 nm and 10 nm on (100) silicon wafers. The specific morphologies of the dewetting states are discussed with particular emphasis on the state boundaries. The main parameter determining which state is formed is not the duration for which the gold remains liquid, but rather the input energy provided by the laser. This shows that each state transition has a separate measurable activation energy. The temperature during the nanosecond pulses and the duration during which the gold remains liquid was determined by simulation using the COMSOL Multiphysics® software package. Using these calculations, an accurate local temperature profile and its development over time was simulated. An analytical study of the morphologies and formed structures was performed using Minkowski measures. With aid of this tool, the laser induced structures were compared with thermally annealed samples, with perfectly ordered structures and with perfectly random structures. The results show that both, structures of the laser induced and the annealed samples, strongly resemble the perfectly ordered structures. This reveals a close relationship between these structures and suggests that the phenomenon under investigation is indeed a spinodal dewetting generated by an internal material wave function. The purposeful generation of these structures and the elucidation of the underlying mechanism of dewetting by short pulse lasers may assist the realisation of various technical elements such as nanowires in science and industry. © 2020
- ItemDevelopment and characterization of a metastable Al-Mn-Ce alloy produced by laser powder bed fusion(Amsterdam : Elsevier, 2021) Gabrysiak, Katharina; Gustmann, Tobias; Freudenberger, Jens; Neufeld, Kai; Giebeler, Lars; Leyens, Christoph; Kühn, UtaLaser powder bed fusion (LPBF) can help to overcome two challenges occurring by casting of metastable Al alloys: (1) the high amount of casting defects and (2) the limited part size while maintaining rapid solidification of the whole cross-section. In this study, an Al92Mn6Ce2 alloy was processed crack-free without baseplate heating by LPBF. The high cooling rate during fabrication has a significant impact on the microstructure, which was characterized by SEM, TEM and XRD. The processing through LPBF causes a high amount and a strong refinement of the intermetallic Al20Mn2Ce precipitates. This leads, compared to suction-cast specimens, to a higher hardness (180 HV 5) and a higher tolerable compressive stress (>1200 MPa) associated with a pronounced plasticity without failure up to a strain of 40%. The extraordinary mechanical properties of additively manufactured Al92Mn6Ce2 can extend the possibilities of producing novel LPBF lightweight structures for potential applications under harsh conditions.
- ItemIn situ grown palladium nanoparticles on polyester fabric as easy-separable and recyclable catalyst for Suzuki-Miyaura reaction(Amsterdam : Elsevier, 2021) Xu, Tiefeng; Lu, Panting; Wohlrab, Sebastian; Chen, Wenxing; Springer, Armin; Wu, Xiao-Feng; Lu, WangyangPalladium nanoparticles supported on low-melting polyester (Pd/LMPET) fabric were prepared through a microwave irradiation assisted method. In this way, in situ growth of Pd nanoparticles onto an easy to handle material was initiated and proceeded. The results of the characterization revealed that the palladium nanoparticles were well-dispersed on the surfaces of the polyester fibers. The Pd/LMPET fabrics were then employed in the Suzuki-Miyaura coupling. They exhibited excellent catalytic activity in ethanol/water under air atmosphere at 50 °C. Importantly, the Pd/LMPET fabrics could be separated from reaction mixture conveniently and they can still maintain good activity after 8 cycles without Pd leaching. © 2021 The Authors
- ItemAerobic iron-catalyzed site-selective C(sp3)–C(sp3) bond cleavage in N-heterocycles(Amsterdam : Elsevier, 2021) Leonard, David K.; Li, Wu; Rockstroh, Nils; Junge, Kathrin; Beller, MatthiasThe kinetic and thermodynamic stability of C(sp3)–C(sp3) bonds makes the site-selective activation of these motifs a real synthetic challenge. In view of this, herein a site-selective method of C(sp3)–C(sp3) bond scission of amines, specifically morpholine and piperazine derivatives, using a cheap iron catalyst and air as a sustainable oxidant is reported. Furthermore, a statistical design of experiments (DoE) is used to evaluate multiple reaction parameters thereby allowing for the rapid development of a catalytic process. © 2021
- ItemNickel-catalyzed carbonylative synthesis of dihydrobenzofurans(Amsterdam : Elsevier, 2021) Geng, H.-Q.; Wang, W.; Wu, X.-F.A nickel-catalyzed carbonylative synthesis of dihydrobenzofurans has been developed. With Mo(CO)6 as the CO source and manganese metal as the reductant, alkyl halides were reacted with aryl iodides to give the desired products in moderate to good yields. © 2020 Elsevier B.V.
- ItemVerification of impurity-related photocatalytic activity of insulating oxide supports(Amsterdam : Elsevier, 2021) Kortewille, Bianca; Springer, Armin; Strunk, JenniferPhotocatalysts composed of vanadium oxide species supported on commercial MgO and ZrO2 are investigated in selective methanol oxidation. Both support oxides are insulators, so the vanadium oxide species are expected as sole active component in photocatalysis. However, the pure supports showed considerable activity: Bare MgO was more active than MgO-supported vanadia catalysts, and ZrO2 showed intermediate activity. By various characterization methods, the presence of TiO2 (anatase) in the MgO support, and the presence of Zn, possibly as ZnO, in ZrO2 is demonstrated. The present study highlights that photocatalysts containing commercial supports must be carefully checked for impurity-related photocatalytic performance. © 2021 The Authors
- ItemEnhancement and limits of the selective oxidation of methane to formaldehyde over V-SBA-15: Influence of water cofeed and product decomposition(Amsterdam : Elsevier, 2021) Kunkel, Benny; Wohlrab, SebastianThe possibility of a selective catalytic oxidation of methane to formaldehyde has been known for decades, and positive influences of water added to the reaction mixture and ultra-short contact times have been reported. In the present work, the complexity of interdependencies has been revealed. Specific parameter variations can increase conversion and selectivity of the target product. Surprisingly, formaldehyde formation over VOx species and its decomposition in gas phase were equally dependent on the partial pressure of the added water, so that the sweet spot can only be found by varying the residence time. © 2021 The Author(s)
- ItemLow-power emerging memristive designs towards secure hardware systems for applications in internet of things(Amsterdam : Elsevier, 2021) Du, Nan; Schmidt, Heidemarie; Polian, IliaEmerging memristive devices offer enormous advantages for applications such as non-volatile memories and in-memory computing (IMC), but there is a rising interest in using memristive technologies for security applications in the era of internet of things (IoT). In this review article, for achieving secure hardware systems in IoT, low-power design techniques based on emerging memristive technology for hardware security primitives/systems are presented. By reviewing the state-of-the-art in three highlighted memristive application areas, i.e. memristive non-volatile memory, memristive reconfigurable logic computing and memristive artificial intelligent computing, their application-level impacts on the novel implementations of secret key generation, crypto functions and machine learning attacks are explored, respectively. For the low-power security applications in IoT, it is essential to understand how to best realize cryptographic circuitry using memristive circuitries, and to assess the implications of memristive crypto implementations on security and to develop novel computing paradigms that will enhance their security. This review article aims to help researchers to explore security solutions, to analyze new possible threats and to develop corresponding protections for the secure hardware systems based on low-cost memristive circuit designs.
- ItemRecent developments of stamped planar micro-supercapacitors: Materials, fabrication and perspectives(Amsterdam : Elsevier, 2021) Li, Fei; Li, Yang; Qu, Jiang; Wang, Jinhui; Bandari, Vineeth Kumar; Zhu, Feng; Schmidt, Oliver G.The rapid development of wearable and portable electronics has dramatically increased the application for miniaturized energy storage components. Stamping micro-supercapacitors (MSCs) with planar interdigital configurations are considered as a promising candidate to meet the requirements. In this review, recent progress of the different stamping materials and various stamping technologies are first discussed. The merits of each material, manufacturing process of each stamping method and the properties of stamping MSCs are scrutinized, respectively. Further insights on technical difficulties and scientific challenges are finally demonstrated, including the limited thickness of printed electrodes, poor overlay accuracy and printing resolution.
- ItemDevelopment of bioactive catechol functionalized nanoparticles applicable for 3D bioprinting(Amsterdam : Elsevier, 2021) Puertas-Bartolomé, MarÃa; WÅ‚odarczyk-Biegun, MaÅ‚gorzata K.; del Campo, Aránzazu; Vázquez-Lasa, Blanca; San Román, JulioEfficient wound treatments to target specific events in the healing process of chronic wounds constitute a significant aim in regenerative medicine. In this sense, nanomedicine can offer new opportunities to improve the effectiveness of existing wound therapies. The aim of this study was to develop catechol bearing polymeric nanoparticles (NPs) and to evaluate their potential in the field of wound healing. Thus, NPs wound healing promoting activities, potential for drug encapsulation and controlled release, and further incorporation in a hydrogel bioink formulation to fabricate cell-laden 3D scaffolds are studied. NPs with 2 and 29 M % catechol contents (named NP2 and NP29) were obtained by nanoprecipitation and presented hydrodynamic diameters of 100 and 75 nm respectively. These nanocarriers encapsulated the hydrophobic compound coumarin-6 with 70% encapsulation efficiency values. In cell culture studies, the NPs had a protective effect in RAW 264.7 macrophages against oxidative stress damage induced by radical oxygen species (ROS). They also presented a regulatory effect on the inflammatory response of stimulated macrophages and promoted upregulation of the vascular endothelial growth factor (VEGF) in fibroblasts and endothelial cells. In particular, NP29 were used in a hydrogel bioink formulation using carboxymethyl chitosan and hyaluronic acid as polymeric matrices. Using a reactive mixing bioprinting approach, NP-loaded hydrogel scaffolds with good structural integrity, shape fidelity and homogeneous NPs dispersion, were obtained. The in vitro catechol NPs release profile of the printed scaffolds revealed a sustained delivery. The bioprinted scaffolds supported viability and proliferation of encapsulated L929 fibroblasts over 14 days. We envision that the catechol functionalized NPs and resulting bioactive bioink presented in this work offer promising advantages for wound healing applications, as they: 1) support controlled release of bioactive catechol NPs to the wound site; 2) can incorporate additional therapeutic functions by co-encapsulating drugs; 3) can be printed into 3D scaffolds with tailored geometries based on patient requirements.