Abstract: The effect of electron-impurity and electron-electron interactions on the energy spectrum of electrons moving in graphene is investigated in the presence of a high magnetic field. We find that the width of the broadened Landau levels exhibits an approximate 1/B dependence near half filling for charged impurity scattering. The Landau-level width, the density of states, and the Fermi energy exhibit an oscillatory behavior as a function of magnetic field. Comparison with experiment shows that scattering with charged impurities cannot be the main scattering mechanism that determines the width of the Landau levels.

Abstract: One of the main objectives of implementing a circular economy system is the reuse and recycling of resources. Closing material cycles and renewable-based electricity and fuel production are essential to such systems. To achieve a high degree of circularity, waste streams have to be rethought and integrated from a cradle-to-grave to a cradle-to-cradle approach. However, today’s circular economy strategies mostly focus on current waste streams, while past waste streams, buried in landfills, could play an important role when recovering resources and energy. Hence, a well-thought-out circular economy strategy should include the re-integration of past waste streams. A grave-to-cradle approach is needed. Landfill mining (LFM), i.e. the excavation and processing of formerly buried waste to energy and materials, aims at utilizing these past waste streams. Doing so could bear potential economic, environmental, and societal burdens and benefits. Originating from landfill remediation projects, landfill mining has been further developed towards resource recovery. Today, using up-to-date technologies and following the most stringent environmental and social criteria, the concept is also known as enhanced landfill mining (ELFM). Throughout the relevant scientific literature, most attention is given to advances in technological development for (E)LFM, as well as its techno-economic and environmental assessment. Societal assessments of LFM projects are rare and treat societal impacts only selectively or from unilateral societal perspectives. If stakeholders are included in societal (E)LFM assessments, only industrial actors, like landfill operators, and governmental actors are asked to participate. A holistic stakeholder assessment for (E)LFM is missing. Moreover, the diverse societal impacts – ranging from socio-environmental benefits through the mitigation of health risks, over socio-economic benefits through land reclamation, and social benefits through community engagement, for example – are either only studied selectively or evaluated as one, entangling various societal effects. A holistic and specific assessment of societal factors affecting (E)LFM implementation is also missing. This thesis uses an anticipatory approach to tackle these challenges. This approach aims to integrate stakeholder values and include uncertainty through the use of multiple social perspectives and prospective modeling tools. In-depth interviews were conducted to develop a typology of (E)LFM stakeholders and to elicit the most important stakeholder needs. Stakeholders were selected along an extended quadruple helix framework, including industrial, institutional, scientific, and community actors. Furthermore, using system dynamics tools, namely causal loop diagrams, societal systems of (E)LFM could be visualized and analyzed. Finally, a discrete choice experiment was conducted to evaluate a set of societal factors representing the conversion of a landfill into a public park for recreational use. The in-depth interviews included landfill operators, technology providers and incubators, local governments and governmental institutions, as well as researchers and community members. To structure the diverse perspectives of stakeholders on (E)LFM, five stakeholder archetypes were developed: The Entrepreneur, the Engaged Citizen, the Visionary, the Technology Enthusiast, and the Skeptic. The archetypes capture important characteristics and opinions approaching (E)LFM implementation. They differ in risk perceptions, knowledge base, influence on (E)LFM’s systemic and project implementation, and their main concerns and motivations. Furthermore, 18 stakeholder needs were derived from the interviews. This includes societal, environmental, regulatory, and techno-economic needs. The needs are put in relation to the affected stakeholders and sustainability dimensions. Uncertainties that could potentially be reduced through the fulfillment of each need are qualitatively assessed. Quantitatively, stakeholders were focusing on societal, regulatory, and techno-economic needs, whereas qualitative emphasis was given to environmental needs, especially the avoidance of impacts from primary resource production. When meeting stakeholder needs fairly, intra- and inter-dimensional trade-offs have to be considered as different perspectives can lead to different and sometimes contradicting implications for (E)LFM implementation. To conceptualize societal systems of (E)LFM, causal loop diagrams were developed following system dynamics methodology. The visualizations show how (E)LFM is embedded in its societal context. Variables comprising the societal impact were analyzed, and mechanisms affecting the public project acceptance and the market acceptance of (E)LFM products worked out. Leverage points were identified, helping (E)LFM practitioners and policymakers to minimize potential risks and maximize potential benefits. To these count technological choices, stakeholder involvement, the after-use, quality standards, and LFM regulation in general, amongst others. To disentangle and evaluate societal impacts of (E)LFM, a discrete choice experiment was conducted deriving the utility of five distinct attributes: the size of a landfill, the project duration, job creation, disamenities, and climate impacts. To determine the willingness to pay, perform scenario analysis, and model policy simulations, a sixth attribute was added representing a cost factor for project implementation. Environmental considerations are most important to the sample, while project duration and disamenities also play a significant role. The scenario analysis and policy simulations show that taxing households for (E)LFM implementation is a viable option, especially for environmentally beneficial projects. Nonetheless, a favorable combination of the remaining attributes can compensate utility losses for environmentally questionable projects. As risks of classical landfill management practices are likely to grow with an updated evaluation of after-care periods lasting up to 100 years and more, positive effects of (E)LFM become even more noteworthy. Nonetheless, (E)LFM projects also pose potential risks like groundwater contamination or the reintroduction of hazardous materials. If executed poorly, (E)LFM projects could potentially do more harm than good. A mix of policy measures is recommended to push a major part of potential (E)LFM projects from being environmentally beneficial and economically inefficient to being societally, environmentally, and economically favorable. Overall, more research is necessary to integrate (E)LFM into circular economy strategies and build a sensible grave-to-cradle approach.

Abstract: A large number of materials have a highly degenerate ground state and therefore a complex microstructure. Because of this degenerate state, phase transitions between the different phases play an important role. High resolution techniques in electron microscopy and nano-scale chemical analysis allow to study not only the microstructure but also the interfaces down to an atomic scale. We focus particularly on the ambiguity of alloys oil approaching the phase transition. The short range order (SRO) in ''1 1/20'' type alloys and the microstructure of ''tweed'' and needle formation in martensite like alloys with composition Ni5Al3 are considered in more detail.

Abstract: We predict enhanced electron-hole superfluidity in two coupled electron-hole armchair-edge terminated graphene nanoribbons separated by a thin insulating barrier. In contrast to graphene monolayers, the multiple subbands of the nanoribbons are parabolic at low energy with a gap between the conduction and valence bands, and with lifted valley degeneracy. These properties make screening of the electron-hole interaction much weaker than for coupled electron-hole monolayers, thus boosting the pairing strength and enhancing the superfluid properties. The pairing strength is further boosted by the quasi one-dimensional quantum confinement of the carriers, as well as by the large density of states near the bottom of each subband. The latter magnifies superfluid shape resonances caused by the quantum confinement. Several superfluid partial condensates are present for finite-width nanoribbons with multiple subbands. We find that superfluidity is predominately in the strongly-coupled BEC and BCS-BEC crossover regimes, with large superfluid gaps up to 100 meV and beyond. When the gaps exceed the subband spacing, there is significant mixing of the subbands, a rounding of the shape resonances, and a resulting reduction in the one-dimensional nature of the system.

Abstract: The addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O7−δ (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m3 at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.

Abstract: The observation of a significant temperature-dependent variation in the ${I}$ – ${V}$ characteristics of tunneling devices is often interpreted as a signature of a trap-assisted-tunneling dominated current. In this letter, we use a ballistic 2D quantum-mechanical simulator, calibrated using the measured temperature-dependent ${I}$ – ${V}$ characteristics of Esaki diodes, to demonstrate that the temperature dependence of band-to-band tunneling (BTBT) current can vary significantly in both Esaki diodes and tunnel FETs. The variation of BTBT current with temperature is impacted by doping concentration, gate voltage, possible presence of a highly-doped pocket at the tunnel junction, and material.

Abstract: The large-scale production of single-wall carbon nanotubes (SWNTs) is reported. Large quantities of SWNTs can be synthesised by catalytic decomposition of methane over well-dispersed metal particles supported on MgO at 1000 degrees C. The thus produced SWNTs can be separated easily from the support by a simple acidic treatment to obtain a product with high yields (70-80%) of SWNTs. Because the typical synthesis time is 10 min, 1 g of SWNTs can be synthesised per day by this method. The SWNTs are characterized by high-resolution transmission electron microscopy and by Raman spectroscopy, showing the quality and the quantity of products. (C) 2000 Elsevier Science B.V. All rights reserved.