Simulation of hydrogenated graphene Field-Effect Transistors through a multiscale approach

In this work, we present a performance analysis of Field Effect Transistors based on recently fabricated 100% hydrogenated graphene (the so-called graphane) and theoretically predicted semi-hydrogenated graphene (i.e. graphone). The approach is based on accurate calculations of the energy bands by means of GW approximation, subsequently fitted with a three-nearest neighbor (3NN) sp3 tight-binding Hamiltonian, and finally used to compute ballistic transport in transistors based on functionalized graphene. Due to the large energy gap, the proposed devices have many of the advantages provided by one-dimensional graphene nanoribbon FETs, such as large Ion and Ion/Ioff ratios, reduced band-to-band tunneling, without the corresponding disadvantages in terms of prohibitive lithography and patterning requirements for circuit integration

Carbon release by selective alloying of transition metal carbides

We have performed first principles density functional theory calculations on TiC alloyed on the Ti sublattice with 3d transition metals ranging from Sc to Zn. The theory is accompanied with experimental investigations, both as regards materials synthesis as well as characterization. Our results show that by dissolving a metal with a weak ability to form carbides, the stability of the alloy is lowered and a driving force for the release of carbon from the carbide is created. During thin film growth of a metal carbide this effect will favor the formation of a nanocomposite with carbide grains in a carbon matrix. The choice of alloying elements as well as their concentrations will affect the relative amount of carbon in the carbide and in the carbon matrix. This can be used to design the structure of nanocomposites and their physical and chemical properties. One example of applications is as low-friction coatings. Of the materials studied, we suggest the late 3d transition metals as the most promising elements for this phenomenon, at least when alloying with TiC.Comment: 9 pages, 6 figure

Evolving properties of two dimensional materials, from graphene to graphite

We have studied theoretically, using density functional theory, several materials properties when going from one C layer in graphene to two and three g raphene layers and on to graphite. The properties we have focused on are the elastic constants, electronic structure (energy bands and density of state s), and the dielectric properties. For any of the properties we have investigated the modification due to an increase in the number of graphene layers is within a few percent. Our results are in agreement with the analysis presented recently by Kopelevich and Esquinazi (unpublished)

Database-driven High-Throughput Calculations and Machine Learning Models for Materials Design

This paper reviews past and ongoing efforts in using high-throughput ab-inito calculations in combination with machine learning models for materials design. The primary focus is on bulk materials, i.e., materials with fixed, ordered, crystal structures, although the methods naturally extend into more complicated configurations. Efficient and robust computational methods, computational power, and reliable methods for automated database-driven high-throughput computation are combined to produce high-quality data sets. This data can be used to train machine learning models for predicting the stability of bulk materials and their properties. The underlying computational methods and the tools for automated calculations are discussed in some detail. Various machine learning models and, in particular, descriptors for general use in materials design are also covered.Comment: 19 pages, 2 figure

GreenPilot, lotsbåt med minimal miljöpåverkan

The GreenPilot project was carried out to demonstrate the emissions reductions and environmental performance improvements that could be achieved by converting a small vessel to run on methanol fuel. Reducing emissions is a priority for all vessel sizes, as emissions regulations are becoming stricter and concern about greenhouse gases and global warming continues to grow. Within Sweden, the government has announced its ambition to convert all state-owned vessels to fossil-free operation and is investigating 2030 and 2045 as possible deadlines. Methanol produced from renewable feedstock is a possible solution for some of the vessels. By physically converting a Swedish pilot boat to run on methanol, the project demonstrated he feasibility of methanol as a fuel solution for small vessels. Work included converting and testing three different engines to run on methanol, two of which were installed and operated on the converted pilot boat. Emissions measurements showed good reductions as compared to conventional fuel oil. Fossil-free methanol produced from pulp mill black liquor in a Swedish pilot plant was used in some of the laboratory and on board tests. The project also investigated other solutions for reducing environmental impacts of the pilot boats, including the use of solar cells, batteries, and fuel cells.GreenPilot-projektet genomfördes för att demonstrera utsläppsminskningar ochmiljöprestanda förbättringar som kan uppnås genom att konvertera en litenkärl att köra på metanolbränsle. Att minska utsläppen är en prioritet för alla fartygsstorlekar, somUtsläppsreglerna blir hårdare och oroa sig för växthusgaser och globalauppvärmning fortsätter att växa. Inom Sverige har regeringen meddelat sin ambition attkonvertera alla statligt ägda fartyg till fossilfri drift och undersöker 2030 och 2045 sommöjliga tidsfrister. Metanol framställd av förnybart råmaterial är en möjlig lösning förnågra av fartygen.Genom att fysiskt konvertera en svensk pilotbåt för att köra på metanol visade projektethan genomförbarhet av metanol som en bränsle lösning för små fartyg. Arbetet inkluderade konvertering ochtesta tre olika motorer för att köra på metanol, varav två installerades och drivsGreenPilot, lotsbåt med minimal miljöpåverka

An open-source optimization tool for solar home systems: A case study in Namibia

Solar home systems (SHSs) represent a viable technical solution for providing electricity to households and improving standard of living conditions in areas not reached by the national grid or local grids. For this reason, several rural electrification programmes in developing countries, including Namibia, have been relying on SHSs to electrify rural off-grid communities. However, the limited technical know-how of service providers, often resulting in over- or under-sized SHSs, is an issue that has to be solved to avoid dissatisfaction of SHSs’ users. The solution presented here is to develop an open-source software that service providers can use to optimally design SHSs components based on the specific electricity requirements of the end-user. The aim of this study is to develop and validate an optimization model written in MS Excel-VBA which calculates the optimal SHSs components capacities guaranteeing the minimum costs and the maximum system reliability. The results obtained with the developed tool showed good agreement with a commercial software and a computational code used in research activities. When applying the developed optimization tool to existing systems, the results identified that several components were incorrectly sized. The tool has thus the potentials of improving future SHSs installations, contributing to increasing satisfaction of end-users