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- ItemFabrication of metal nanoparticle arrays by controlled decomposition of polymer particles(Bristol : IOP Publishing, 2013) Brodoceanu, Daniel; Fang, Cheng; Voelcker, Nicolas Hans; Bauer, Christina T.; Wonn, Anne; Kroner, Elmar; Arzt, Eduard; Kraus, TobiasWe report a novel fabrication method for ordered arrays of metal nanoparticles that exploits the uniform arrangement of polymer beads deposited as close-packed monolayers. In contrast to colloidal lithography that applies particles as masks, we used thermal decomposition of the metal-covered particles to precisely define metal structures. Large arrays of noble metal (Au, Ag, Pt) nanoparticles were produced in a three-step process on silicon, fused silica and sapphire substrates, demonstrating the generality of this approach. Polystyrene spheres with diameters ranging between 110 nm and 1 µm were convectively assembled into crystalline monolayers, coated with metal and annealed in a resistive furnace or using an ethanol flame. The thermal decomposition of the polymer microspheres converted the metal layer into particles arranged in hexagonal arrays that preserved the order of the original monolayer. Both the particle size and the interparticle distance were adjusted via the thickness of the metal coating and the sphere diameter, respectively.
- ItemMicrostructure evolution during annealing of an SPD- processed supersaturated Cu – 3 at.% Ag alloy(Bristol : IOP Publishing, 2014) Gubicza, J.; Hegedűs, Z.; Lábár, J.L.; Sarma, V.S.; Kauffmann, A.; Freudenberger, J.Supersaturated Cu-3 at.% Ag alloy was processed by rolling at liquid nitrogen temperature and subsequent annealing at 623 K up to 20 min. It was found that after annealing, an inhomogeneous solute atom distribution developed, since the Ag particles with small size and/or large specific interfacial energy were dissolved due to the Gibbs-Thomson effect. In the region where the solute concentration increased, a high dislocation density was retained in the Cu matrix even after annealing, while in the region where the Ag solute content did not increase, the dislocation density decreased by more than one order of magnitude. Therefore, in the cryorolled and annealed samples, heterogeneous microstructures were developed where both the dislocation density and the solute concentration varied considerably.
- ItemThe 2018 correlative microscopy techniques roadmap(Bristol : IOP Publishing, 2018) Ando, Toshio; Bhamidimarri, Satya Prathyusha; Brending, Niklas; Colin-York, H; Collinson, Lucy; De Jonge, Niels; de Pablo, P J; Debroye, Elke; Eggeling, Christian; Franck, Christian; Fritzsche, Marco; Gerritsen, Hans; Giepmans, Ben N G; Grunewald, Kay; Hofkens, Johan; Hoogenboom, Jacob P; Janssen, Kris P F; Kaufmann, Rainer; Klumpermann, Judith; Kurniawan, Nyoman; Kusch, Jana; Liv, Nalan; Parekh, Viha; Peckys, Diana B; Rehfeldt, Florian; Reutens, David C; Roeffaers, Maarten B J; Salditt, Tim; Schaap, Iwan A T; Schwarz, Ulrich S; Verkade, Paul; Vogel, Michael W; Wagner, Richard; Winterhalter, Mathias; Yuan, Haifeng; Zifarelli, GiovanniDevelopments in microscopy have been instrumental to progress in the life sciences, and many new techniques have been introduced and led to new discoveries throughout the last century. A wide and diverse range of methodologies is now available, including electron microscopy, atomic force microscopy, magnetic resonance imaging, small-angle x-ray scattering and multiple super-resolution fluorescence techniques, and each of these methods provides valuable read-outs to meet the demands set by the samples under study. Yet, the investigation of cell development requires a multi-parametric approach to address both the structure and spatio-temporal organization of organelles, and also the transduction of chemical signals and forces involved in cell–cell interactions. Although the microscopy technologies for observing each of these characteristics are well developed, none of them can offer read-out of all characteristics simultaneously, which limits the information content of a measurement. For example, while electron microscopy is able to disclose the structural layout of cells and the macromolecular arrangement of proteins, it cannot directly follow dynamics in living cells. The latter can be achieved with fluorescence microscopy which, however, requires labelling and lacks spatial resolution. A remedy is to combine and correlate different readouts from the same specimen, which opens new avenues to understand structure–function relations in biomedical research. At the same time, such correlative approaches pose new challenges concerning sample preparation, instrument stability, region of interest retrieval, and data analysis. Because the field of correlative microscopy is relatively young, the capabilities of the various approaches have yet to be fully explored, and uncertainties remain when considering the best choice of strategy and workflow for the correlative experiment. With this in mind, the Journal of Physics D: Applied Physics presents a special roadmap on the correlative microscopy techniques, giving a comprehensive overview from various leading scientists in this field, via a collection of multiple short viewpoints.
- ItemDeciphering the imprint of topology on nonlinear dynamical network stability(Bristol : IOP Publishing, 2017) Nitzbon, J.; Schultz, P.; Heitzig, J.; Hellmann, F.Coupled oscillator networks show complex interrelations between topological characteristics of the network and the nonlinear stability of single nodes with respect to large but realistic perturbations. We extend previous results on these relations by incorporating sampling-based measures of the transient behaviour of the system, its survivability, as well as its asymptotic behaviour, its basin stability. By combining basin stability and survivability we uncover novel, previously unknown asymptotic states with solitary, desynchronized oscillators which are rotating with a frequency different from their natural one. They occur almost exclusively after perturbations at nodes with specific topological properties. More generally we confirm and significantly refine the results on the distinguished role tree-shaped appendices play for nonlinear stability. We find a topological classification scheme for nodes located in such appendices, that exactly separates them according to their stability properties, thus establishing a strong link between topology and dynamics. Hence, the results can be used for the identification of vulnerable nodes in power grids or other coupled oscillator networks. From this classification we can derive general design principles for resilient power grids. We find that striving for homogeneous network topologies facilitates a better performance in terms of nonlinear dynamical network stability. While the employed second-order Kuramoto-like model is parametrised to be representative for power grids, we expect these insights to transfer to other critical infrastructure systems or complex network dynamics appearing in various other fields.
- ItemFabrication of silicon nanowire arrays by near-field laser ablation and metal-assisted chemical etching(Bristol : IOP Publishing, 2016) Brodoceanu, Daniel; Alhmoud, Hashim Z.; Elnathan, Roey; Delalat, Bahman; Voelcker, Nicolas H.; Kraus, TobiasWe present an elegant route for the fabrication of ordered arrays of vertically-aligned silicon nanowires with tunable geometry at controlled locations on a silicon wafer. A monolayer of transparent microspheres convectively assembled onto a gold-coated silicon wafer acts as a microlens array. Irradiation with a single nanosecond laser pulse removes the gold beneath each focusing microsphere, leaving behind a hexagonal pattern of holes in the gold layer. Owing to the near-field effects, the diameter of the holes can be at least five times smaller than the laser wavelength. The patterned gold layer is used as catalyst in a metal-assisted chemical etching to produce an array of vertically-aligned silicon nanowires. This approach combines the advantages of direct laser writing with the benefits of parallel laser processing, yielding nanowire arrays with controlled geometry at predefined locations on the silicon surface. The fabricated VA-SiNW arrays can effectively transfect human cells with a plasmid encoding for green fluorescent protein.
- ItemGrowth and applications of GeSn-related group-IV semiconductor materials(Bristol : IOP Publishing, 2015) Zaima, Shigeaki; Nakatsuka, Osamu; Taoka, Noriyuki; Kurosawa, Masashi; Takeuchi, Wakana; Sakashita, MitsuoWe review the technology of Ge1−xSnx-related group-IV semiconductor materials for developing Si-based nanoelectronics. Ge1−xSnx-related materials provide novel engineering of the crystal growth, strain structure, and energy band alignment for realising various applications not only in electronics, but also in optoelectronics. We introduce our recent achievements in the crystal growth of Ge1−xSnx-related material thin films and the studies of the electronic properties of thin films, metals/Ge1−xSnx, and insulators/Ge1−xSnx interfaces. We also review recent studies related to the crystal growth, energy band engineering, and device applications of Ge1−xSnx-related materials, as well as the reported performances of electronic devices using Ge1−xSnx related materials.
- ItemImproved Capacitive Deionization Performance of Mixed Hydrophobic / Hydrophilic Activated Carbon Electrodes(Bristol : IOP Publishing, 2016) Aslan, Mesut; Zeiger, Marco; Jäckel, Nicolas; Grobelsek, Ingrid; Weingarth, Daniel; Presser, VolkerCapacitive deionization (CDI) is a promising salt removal technology with high energy efficiency when applied to low molar concentration aqueous electrolytes. As an interfacial process, ion electrosorption during CDI operation is sensitive to the pore structure and the total pore volume of carbon electrodes limit the maximum salt adsorption capacity (SAC). Thus, activation of carbons as a widely used method to enhance the porosity of a material should also be highly attractive for improving SAC values. In our study, we use easy-to-scale and facile-to-apply CO2 activation at temperatures between 950 °C and 1020 °C to increase the porosity of commercially available activated carbon. While the pore volume and surface area can be significantly increased up to 1.51 cm3/g and 2113 m2/g, this comes at the expense of making the carbon more hydrophobic. We present a novel strategy to still capitalize the improved pore structure by admixing as received (more hydrophilic) carbon with CO2 treated (more hydrophobic) carbon for CDI electrodes without using membranes. This translates in an enhanced charge storage ability in high and low molar concentrations (1 M and 5 mM NaCl) and significantly improved CDI performance (at 5 mM NaCl). In particular, we obtain stable CDI performance at 0.86 charge efficiency with 13.1 mg/g SAC for an optimized 2:1 mixture (by mass).
- ItemComment on 'Oxygen vacancy-induced magnetic moment in edge-sharing CuO2 chains of Li2CuO2'(Bristol : IOP Publishing, 2018) Kuzian, R.O.; Klingeler, R.; Lorenz, W.E.A.; Wizent, N.; Nishimoto, S.; Nitzsche, U.; Rosner, H.; Milosavljevic, D.; Hozoi, L.; Yadav, R.; Richter, J.; Hauser, A.; Geck, J.; Hayn, R.; Yushankhai, V.; Siurakshina, L.; Monney, C.; Schmitt, T.; Schmitt, T.; Roth, G.; Ito, T.; Yamaguchi, H.; Matsuda, M.; Johnston, S.; Málek, J.; Drechsler, S.-L.In a recent work devoted to the magnetism of Li2CuO2, Shu et al (2017 New J. Phys. 19, 023026) have proposed a 'simplified' unfrustrated microscopic model that differs considerably from the models refined through decades of prior work. We show that the proposed model is at odds with known experimental data, including the reported magnetic susceptibility χ(T) data up to 550 K. Using an 8th order high-temperature expansion for χ(T), we show that the experimental data for Li2CuO2 are consistent with the prior model derived from inelastic neutron scattering studies. We also establish the T-range of validity for a Curie–Weiss law for the real frustrated magnetic system. We argue that the knowledge of the long-range ordered magnetic structure for T < T N and of χ(T) in a restricted T-range provides insufficient information to extract all of the relevant couplings in frustrated magnets; the saturation field and INS data must also be used to determine several exchange couplings, including the weak but decisive frustrating antiferromagnetic interchain couplings.
- ItemDeformation at ambient and high temperature of in situ Laves phases-ferrite composites(Bristol : IOP Publishing, 2014) Donnadieu, Patricia; Pohlmann, Carsten; Scudino, Sergio; Blandin, Jean-Jacques; Surreddi, Kumar Babu; Eckert, JürgenThe mechanical behavior of a Fe80Zr10Cr10 alloy has been studied at ambient and high temperature. This Fe80Zr10Cr10 alloy, whoose microstructure is formed by alternate lamellae of Laves phase and ferrite, constitutes a very simple example of an in situ CMA phase composite. The role of the Laves phase type was investigated in a previous study while the present work focuses on the influence of the microstructure length scale owing to a series of alloys cast at different cooling rates that display microstructures with Laves phase lamellae width ranging from ∼50 nm to ∼150 nm. Room temperature compression tests have revealed a very high strength (up to 2 GPa) combined with a very high ductility (up to 35%). Both strength and ductility increase with reduction of the lamella width. High temperature compression tests have shown that a high strength (900 MPa) is maintained up to 873 K. Microstructural study of the deformed samples suggests that the confinement of dislocations in the ferrite lamellae is responsible for strengthening at both ambient and high temperature. The microstructure scale in addition to CMA phase structural features stands then as a key parameter for optimization of mechanical properties of CMA in situ composites.
- ItemBa termination of Ge(001) studied with STM(Bristol : IOP Publishing, 2015) Koczorowski, W.; Grzela, T.; Radny, M.W.; Schofield, S.R.; Capellini, G.; Czajka, R.; Schroeder, T.; Curson, N.J.We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (~0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology.