186 research outputs found
The effect of thermal annealing on the properties of Al-AlOx-Al single electron tunneling transistors
The effect of thermal annealing on the properties of Al-AlOx-Al single
electron tunneling transistors is reported. After treatment of the devices by
annealing processes in forming gas atmosphere at different temperatures and for
different times, distinct and reproducible changes of their resistance and
capacitance values were found. According to the temperature regime, we observed
different behaviors as regards the resistance changes, namely the tendency to
decrease the resistance by annealing at T = 200 degree C, but to increase the
resistance by annealing at T = 400 degree C. We attribute this behavior to
changes in the aluminum oxide barriers of the tunnel junctions. The good
reproducibility of these effects with respect to the changes observed allows
the proper annealing treatment to be used for post-process tuning of tunnel
junction parameters. Also, the influence of the annealing treatment on the
noise properties of the transistors at low frequency was investigated. In no
case did the noise figures in the 1/f-regime show significant changes.Comment: 6 pages, 7 eps-figure
Assessing biorefineries
Biomass, a product of the solar energy influx and the synthesis of carbon dioxide and water, has been used since the dawn of humanity, always as a source of food and as a source of energy and materials since the invention of controlled fire and simple tools some hundred thousand years ago. The transition from hunting and gathering to agriculture has over the last five millennia led to a rapid increase of world population and a human dominance over the Earth’s land surface and biota
Mapping the content and fates of scarce metals in discarded cars
A great variety of current products make use of components or materials (e.g. electronics, steel and aluminium alloys) that utilise increasing amounts of ‘critical’ or scarce metals (SM). For example, design trends for cars point at increasing SM utilisation in order for regulatory, business and consumer requirements on environmental performance, safety, costs, comfort and infotainment to be met. Modern cars now hold SM in substantial amounts, i.e. the circa one billion cars in use worldwide today, constitute a significant near-term secondary SM resource. However, current end-of-life vehicle (ELV) recycling is mainly aimed at isolating hazardous contents, dismantling spare parts and recycling bulk metals. There is thus a clear risk that ELV SM are not functionally recycled and thus lost for further use. Assessments of the opportunities for increased functional recycling require estimates of SM content of discarded cars and individual waste flows in ELV recycling. However, information on both is limited. Data related to cars is sparse, and challenged by the large range and age span of discarded car brands and models. Measurements of SM in waste flows are few and cover a limited range of SM. Consequently, available data does not allow us to quantify with precision the SM contents of discarded cars reaching the ELV recycling system, or map individual metal flows within it. Instead, our approach relies on mapping 25 ELV SM to main types of applications within three newly produced car models using automotive industry data (International Material Data System, IMDS), and letting these models represent the ELV fleet so that the annual input magnitudes of SM to ELV management can be estimated. Subsequently, we employ material flow analysis of ELV waste streams as basis for identifying potential pathways of these main applications, and the extent to which contained metals may reach processes capable of functional recycling. The approach allows us to qualitatively distinguish subsets of systems flows holding groups of SM, and discuss the potential for functional recycling. Using Swedish ELV management as a case, we conclude that only platinum may be functionally recycled in its main application. Cobalt, gold, manganese, molybdenum, palladium, rhodium and silver may be functionally recycled depending on application and pathways taken. For remaining 17 metals, functional recycling is lacking. Consequently, there is considerable risk of losing SM with current ELV procedures. Given differences in the application of metals and identified pathways, strategies for improving recycling and resource security are considered. Moreover, our case illustrates the considerable challenge, posed by the complexity and range of car configurations and the sparsity of information on SM, to closer assess recycling strategies and advance secondary SM resource utilisation
Green Nanotechnology in Nordic Construction - Eco-innovation strategies and Dynamics in nordic Window Chains
This project analyzes Nordic trends in the development and industrial uptake of green nanotechno-logy in construction. The project applies an evolutionary economic perspective in analyzing the innovation dynamics and firm strategies in the window value chains in three Nordic countries, Denmark, Finland and Sweden. Hence the project investigates two pervasive parallel market trends: The emergence of the green market and the emergence of nanotechnology. The analysis investigates how a traditional economic sector such as the construction sector reacts to such major trends.Conclusions are multiple, but among the most important are: Eco-innovation has become the perhaps most important driver for innovation in the construction sector. Search into eco-innovative business opportunities is intense among all companies along the three analyzed Nordic window chains. While we generally find a low uptake of nanotechnology in the construction sector in the Nordic countries we do find quite a high number of nanotech applications in the Nordic window chains. Eco-innovation is influencing strongly on the nanotech development. We see several examples of nano-enabled smart, multifunctional green solutions in the Nordic window chains already or about to having a commercial impact. Currently, it seems the greening of markets is beginning to affect the roles different companies play in the chain. We see a marked shift towards more sys-temic, smart eco-innovative solutions which fit well with nanotech opportunities. Overall, the recent greening of the market seems to be opening a window of opportunity for nanotechnology in the Nordic countries but the widespread discreet firm strategizing towards nanotechnology may reduce the exploitation of these
Prospective Life Cycle Assessment of Graphene Production by Ultrasonication and Chemical Reduction
One promising future bulk application of graphene is as
composite additive. Therefore, we compare two production routes for insolution
graphene using a cradle-to-gate lifecycle assessment focusing on
potential differences in energy use, blue water footprint, human toxicity,
and ecotoxicity. The data used for the assessment is based on information
in scientific papers and patents. Considering the prospective nature of this
study, environmental impacts from background systems such as energy
production were not included. The production routes are either based on
ultrasonication or chemical reduction. The results show that the
ultrasonication route has lower energy and water use, but higher human
and ecotoxicity impacts, compared to the chemical reduction route.
However, a sensitivity analysis showed that solvent recovery in the ultrasonication process gives lower impacts for all included
impact categories. The sensitivity analysis also showed that solvent recovery is important to lower the blue water footprint of the
chemical reduction route as well. The results demonstrate the possibility to conduct a life cycle assessment study based mainly on
information from patents and scientific articles, enabling prospective life cycle assessment studies of products at early stages of
technological development
How to make policy-relevant life cycle assessments of future products? Lessons learned from nanomaterials
Many new nanomaterials are currently being developed, and there is a great demand from policy-makers such as governments and agencies to understand the future environmental impact of nanomaterials. However, assessing the life cycle environmental impacts, e.g. in terms of emissions and energy use, related to these materials and products that contain them constitutes a great challenge, which makes it difficult to meet such needs from policy-makers. The challenge is much due to the many uncertainties that surround new nanomaterials at an early point of technological development, which makes environmental assessment methods such as life cycle assessment difficult to apply. These uncertainties include the future areas of application of the nanomaterial, future designs of products within those areas, and future production processes. When one or more of these uncertainties are present, we say that the life cycle or product chain is embryonic. This embryonic nature of nanomaterial life cycles differentiates them from the life cycles of more established products, such as cups and cucumbers. Assessing the environmental impacts of embryonic nanomaterial life cycles requires the assessor to understand the future, or rather some aspects of a number of possible futures. Hence, we need to make use of methods belonging to the field of future studies, including monitoring of trends in technology development (e.g. via patent analysis) and application areas as well as predicting and exploring by trend analysis, expert judgement, and sometimes even fantasizing. We illustrate the theoretical concept of embryonic life cycles with a number of examples of embryonic nanomaterial life cycles, including carbon nanotubes in composites, titanium dioxide nanoparticles in self-cleaning cement and graphene in electronic devices and composites. We show that a range of future study approaches may enrich, or even be essential to, policy-relevant life cycle assessments. We also show that environmental assessments such as life cycle assessment can be misused or used in questionable ways when applied to embryonic life cycles with the purpose of obtaining policy-relevant results
Challenges in Exposure Modeling of Nanoparticles in Aquatic Environments
Managing the potential environmental risks of nanoparticles requires methods to link nanoparticle properties with macro-scale risks. This study outlines challenges in exposure modeling of nanoparticles in aquatic environments, such as the role of natural organic matter, natural colloids, fractal dimensions of agglomerates, coatings and doping of particles, and uncertainties regarding nanoparticle emissions to aquatic environments. The pros and cons of the exposure indicators mass concentration, particle number concentration, and surface area are discussed. By applying colloid chemistry kinetic equations describing particle agglomeration and sedimentation for the case of titanium dioxide nanoparticles, a limited exposure assessment including some of the factors mentioned is conducted with particle number concentration as the exposure indicator. The results of the modeling indicate that sedimentation, shear flows, and settling are of less importance with regard to particle number based predicted environmental concentrations. The inflow of nanoparticles to the water compartment had a significant impact in the model, and the collision efficiency (which is affected by natural organic matter) was shown to greatly affect model output. Implications for exposure modeling, regulation and science are discussed. A broad spectrum of scientific disciplines must be engaged in the development of exposure models where nano-level properties are linked to macro-scale risk
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