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- ItemAmyloids: From molecular structure to mechanical properties(Amsterdam [u.a.] : Elsevier, 2013) Schleeger, M.; Vandenakker, C.C.; Deckert-Gaudig, T.; Deckert, V.; Velikov, K.P.; Koenderink, G.; Bonn, M.Many proteins of diverse sequence, structure and function self-assemble into morphologically similar fibrillar aggregates known as amyloids. Amyloids are remarkable polymers in several respects. First of all, amyloids can be formed from proteins with very different amino acid sequences; the common denominator is that the individual proteins constituting the amyloid fold predominantly into a β-sheet structure. Secondly, the formation of the fibril occurs through non-covalent interactions between primarily the β-sheets, causing the monomers to stack into fibrils. The fibrils are remarkably robust, considering that the monomers are bound non-covalently. Finally, a common characteristic of fibrils is their unbranched, straight, fiber-like structure arising from the intertwining of the multiple β-sheet filaments. These remarkably ordered and stable nanofibrils can be useful as building blocks for protein-based functional materials, but they are also implicated in severe neurodegenerative diseases. The overall aim of this article is to highlight recent efforts aimed at obtaining insights into amyloid proteins on different length scales. Starting from molecular information on amyloids, single fibril properties and mechanical properties of networks of fibrils are described. Specifically, we focus on the self-assembly of amyloid protein fibrils composed of peptides and denatured model proteins, as well as the influence of inhibitors of fibril formation. Additionally, we will demonstrate how the application of recently developed vibrational spectroscopic techniques has emerged as a powerful approach to gain spatially resolved information on the structure-function relation of amyloids. While spectroscopy provides information on local molecular conformations and protein secondary structure, information on the single fibril level has been developed by diverse microscopic techniques. The approaches to reveal basic mechanical properties of single fibrils like bending rigidity, shear modulus, ultimate tensile strength and fracture behavior are illustrated. Lastly, mechanics of networks of amyloid fibrils, typically forming viscoelastic gels are outlined, with a focus on (micro-) rheological properties. The resulting fundamental insights are essential for the rational design of novel edible and biodegradable protein-based polymers, but also to devise therapeutic strategies to combat amyloid assembly and accumulation during pathogenic disorders.
- ItemUltrathin structures derived from interfacially modified polymeric nanocomposites to curb electromagnetic pollution(Cambridge : Royal Society of Chemistry, 2021) Sushmita, Kumari; Formanek, Petr; Fischer, Dieter; Pötschke, Petra; Madras, Giridhar; Bose, SuryasarathiThe use of electronic devices and wireless networks is increasing rapidly, and electromagnetic (EM) pollution remediation remains a challenge. We employed a unique approach to fabricate two ultrathin (approx. 53 μm) multilayered assemblies to address this. By sequentially stacking thin films of polyvinylidene difluoride (PVDF) and polycarbonate (PC) nanocomposites and interfacially locking them with a mutually miscible polymer (PMMA, polymethyl methacrylate), materials with enhanced structural properties and electromagnetic interference (EMI) shielding performance can be designed. Utilizing reduced graphene oxide (rGO) and molybdenum disulfide (MoS2) as a template, ferrite was grown on the surface to design two different nanohybrid structures (rGO–Fe3O4 and MoS2–Fe3O4). PVDF was composited with either rGO–Fe3O4 or MoS2–Fe3O4, and multiwall carbon nanotubes (CNTs) were dispersed in the PC component. As PC and PVDF are immiscible, their poor interface would result in inferior structural properties, which can be challenging in designing EMI shielding materials due to cyclic thermal fatigue. Hence, PMMA is sandwiched to interfacially stitch the components (PC and PVDF) and improve interfacial adhesion. This was confirmed using SEM/EDS and Raman mapping/imaging. The mechanical stability of the multilayered assemblies was characterized using a dynamic mechanical analyzer (DMA), and the storage modulus was found to be as high as 2767 MPa at 40 °C (@constant frequency and strain amplitude), for the multilayered film with rGO–Fe3O4 in PVDF, PMMA as a sandwich layer and CNTs in PC. A typical assembly of 9 multilayers (∼480 μm) with rGO–Fe3O4 in PVDF, and CNTs in PC, and interfacially stitched with PMMA gave rise to a high EMI shield effectiveness (SET) of −26.3 dB @ 26.5 GHz. This unique arrangement of a multilayered assembly suppressed EMI primarily by absorption.
- ItemUnderstanding the catalyst-free transformation of amorphous carbon into graphene by current-induced annealing(London : Nature Publishing Group, 2013) Barreiro, Amelia; Börrnert, Felix; Avdoshenko, Stanislav M.; Rellinghaus, Bernd; Cuniberti, Gianaurelio; Rümmeli, Mark H.; Vandersypen, Lieven M.K.We shed light on the catalyst-free growth of graphene from amorphous carbon (a–C) by current-induced annealing by witnessing the mechanism both with in-situ transmission electron microscopy and with molecular dynamics simulations. Both in experiment and in simulation, we observe that small a–C clusters on top of a graphene substrate rearrange and crystallize into graphene patches. The process is aided by the high temperatures involved and by the van der Waals interactions with the substrate. Furthermore, in the presence of a–C, graphene can grow from the borders of holes and form a seamless graphene sheet, a novel finding that has not been reported before and that is reproduced by the simulations as well. These findings open up new avenues for bottom-up engineering of graphene-based devices.
- ItemNanoscale distribution of Bi atoms in InP1-xBix(London : Nature Publishing Group, 2017) Zhang, Liyao; Wu, Mingjian; Chen, Xiren; Wu, Xiaoyan; Spiecker, Erdmann; Song, Yuxin; Pan, Wenwu; Li, Yaoyao; Yue, Li; Shao, Jun; Wang, ShuminThe nanoscale distribution of Bi in InPBi is determined by atom probe tomography and transmission electron microscopy. The distribution of Bi atoms is not uniform both along the growth direction and within the film plane. A statistically high Bi-content region is observed at the bottom of the InPBi layer close to the InPBi/InP interface. Bi-rich V-shaped walls on the (−111) and (1–11) planes close to the InPBi/InP interface and quasi-periodic Bi-rich nanowalls in the (1–10) plane with a periodicity of about 100 nm are observed. A growth model is proposed to explain the formation of these unique Bi-related nanoscale features. These features can significantly affect the deep levels of the InPBi epilayer. The regions in the InPBi layer with or without these Bi-related nanostructures exhibit different optical properties.
- ItemDislocation-free Ge nano-crystals via pattern independent selective Ge heteroepitaxy on Si nano-tip wafers(London : Nature Publishing Group, 2016) Niu, Gang; Capellini, Giovanni; Schubert, Markus Andreas; Niermann, Tore; Zaumseil, Peter; Katzer, Jens; Krause, Hans-Michael; Skibitzki, Oliver; Lehmann, Michael; Xie, Ya-Hong; von Känel, Hans; Schroeder, ThomasThe integration of dislocation-free Ge nano-islands was realized via selective molecular beam epitaxy on Si nano-tip patterned substrates. The Si-tip wafers feature a rectangular array of nanometer sized Si tips with (001) facet exposed among a SiO2 matrix. These wafers were fabricated by complementary metal-oxide-semiconductor (CMOS) compatible nanotechnology. Calculations based on nucleation theory predict that the selective growth occurs close to thermodynamic equilibrium, where condensation of Ge adatoms on SiO2 is disfavored due to the extremely short re-evaporation time and diffusion length. The growth selectivity is ensured by the desorption-limited growth regime leading to the observed pattern independence, i.e. the absence of loading effect commonly encountered in chemical vapor deposition. The growth condition of high temperature and low deposition rate is responsible for the observed high crystalline quality of the Ge islands which is also associated with negligible Si-Ge intermixing owing to geometric hindrance by the Si nano-tip approach. Single island as well as area-averaged characterization methods demonstrate that Ge islands are dislocation-free and heteroepitaxial strain is fully relaxed. Such well-ordered high quality Ge islands present a step towards the achievement of materials suitable for optical applications.
- ItemChemical and electrochemical synthesis of platinum black(London : Nature Publishing Group, 2017) Stanca, S.E.; Hänschke, F.; Ihring, A.; Zieger, G.; Dellith, J.; Kessler, E.; Meyer, H.-G.We present electrochemical and chemical synthesis of platinum black at room temperature in aqueous and non-aqueous media. X-ray analysis established the purity and crystalline nature. The electron micrographs indicate that the nanostructures consist of platinum crystals that interconnect to form porous assemblies. Additionally, the electron micrographs of the platinum black thin layer, which was electrochemically deposited on different metallic and semiconductive substrates (aluminium, platinum, silver, gold, tin-cooper alloy, indium-tin-oxide, stainless steel, and copper), indicate that the substrate influences its porous features but not its absorbance characteristics. The platinum black exhibited a broad absorbance and low reflectance in the ultraviolet, visible, and infrared regions. These characteristics make this material suitable for use as a high-temperature resistant absorber layer for the fabrication of microelectronics.
- ItemTowards the better: Intrinsic property amelioration in bulk metallic glasses(London : Nature Publishing Group, 2016) Sarac, Baran; Zhang, Long; Kosiba, Konrad; Pauly, Simon; Stoica, Mihai; Eckert, JürgenTailoring the intrinsic length-scale effects in bulk metallic glasses (BMGs) via post-heat treatment necessitates a systematic analyzing strategy. Although various achievements were made in the past years to structurally enhance the properties of different BMG alloys, the influence of short-term sub-glass transition annealing on the relaxation kinetics is still not fully covered. Here, we aim for unraveling the connection between the physical, (thermo)mechanical and structural changes as a function of selected pre-annealing temperatures and time scales with an in-house developed Cu46Zr44Al8Hf2 based BMG alloy. The controlled formation of nanocrystals below 50 nm with homogenous distribution inside the matrix phase via thermal treatment increase the material’s resistance to strain softening by almost an order of magnitude. The present work determines the design aspects of metallic glasses with enhanced mechanical properties via nanostructural modifications, while postulating a counter-argument to the intrinsic property degradation accounted for long-term annealing.
- ItemFormation of metallic magnetic clusters in a Kondo-lattice metal: Evidence from an optical study(London : Nature Publishing Group, 2012) Kovaleva, N.N.; Kugel, K.I.; Bazhenov, A.V.; Fursova, T.N.; Löser, W.; Xu, Y.; Behr, G.; Kusmartsev, F.V.Magnetic materials are usually divided into two classes: those with localised magnetic moments, and those with itinerant charge carriers. We present a comprehensive experimental (spectroscopic ellipsomerty) and theoretical study to demonstrate that these two types of magnetism do not only coexist but complement each other in the Kondo-lattice metal, Tb2PdSi3. In this material the itinerant charge carriers interact with large localised magnetic moments of Tb(4f) states, forming complex magnetic lattices at low temperatures, which we associate with self-organisation of magnetic clusters. The formation of magnetic clusters results in low-energy optical spectral weight shifts, which correspond to opening of the pseudogap in the conduction band of the itinerant charge carriers and development of the low- and high-spin intersite electronic transitions. This phenomenon, driven by self-trapping of electrons by magnetic fluctuations, could be common in correlated metals, including besides Kondo-lattice metals, Fe-based and cuprate superconductors.