Ibolya Zsoldos

Topological and energetic conditions for lithographic production of carbon nanotubes from graphene

Density Functional Based Tight-Binding (DFTB) molecular dynamics (MD) simulations were performed for producing carbon nanotubes from graphene nanoribbons. The constant temperature simulations were controlled with the help of Nose-Hoover thermostat. In our systematic study we obtained critical curvature energies and determined topological conditions for nanotube production from two parallel graphene nanoribbons. We obtained linear relationship between the curvature energy and the square of the curvature.

Molecular Dynamics Simulation of Carbon Nanostructures: The Nanotubes

Molecular dynamics calculations can reveal the physical and chemical properties of various carbon nanostructures or can help to devise the possible formation pathways. In our days the most well-known carbon nanostructures are the fullerenes, the nanotubes, and the graphene. The fullerenes and nanotubes can be thought of as being formed from graphene sheets, i.e., single layers of carbon atoms arranged in a honeycomb lattice. Usually the nature does not follow the mathematical constructions. Although the first time the C60 and the C70 were produced by laser-irradiated graphite, the fullerene formation theories are based on various fragments of carbon chains and networks of pentagonal and hexagonal rings. In the present article, using initial structures cut out from graphene will be presented in various formation pathways for the armchair (5,5) and zigzag (9,0) nanotubes. The interatomic forces in our molecular dynamics simulations will be calculated using tight-binding Hamiltonian.

Self-organised formation of nanotubes from graphene ribbons. A molecular dynamics study

The conditions for self-organised formations of carbon nanotubes from two parallel graphene ribbons were studied in a density functional adjusted tight binding molecular dynamics simulation. We have found that the seemingly trivial process is significantly limited by the thermal motion of the carbon atoms. There are further difficulties as well, primarily the unfavourable position of the atoms at the edges of the zigzag graphene ribbons. In repeated molecular dynamics runs we analysed the conditions of perfect coalescences, the influence of the substrate and the impact of the zigzag graphene ribbon positions. We have obtained that contrary to the abovementioned unfavourable conditions perfect nanotube production can be obtained using substrates. As the positioning of the substrate can be made with piezoelectric devices, this can significantly help the experimental realisation of the nanotube formation as well.

Origami: Self Organizing Polyhexagonal Carbon Structures for Formation of Fullerenes, Nanotubes and Other Carbon Structures

The selective production of fullerenes and nanotubes is a challenging problem. Molecular dynamics calculations can reveal the physical and chemical properties of various carbon nanostructures and can help to devise the possible formation pathways. In our previous publications we have presented various graphene patterns which could transform in a self organising way into the desired structure. The processes were realized in molecular dynamics simulations. In the present publication we review the molecular dynamics method used in our previous calculations and give further graphene patterns for Cn fullerenes from C60 to C100. Also the possibility of experimental realizations will be discussed.

A Review on the Effect of Alternative Fuels on the Friction and Wear of Internal Combustion Engines

The climate policy of the EU specifies strict limits for harmful exhaust gases of passenger cars and commercial vehicles. Electric Mobility plays a significant role in reaching the fleet targets, but internal combustion engines (ICEs) will still be necessary in the next 30 years in medium to long distance transportation. Within the scope of this review article, research activities concerning engine performance, exhaust emissions, friction, wear and corrosion of components in relation to drop-in fuel alternatives, as well as the impact of such fuels on the degradation of the lubricant will be presented. Production pathways and properties of alternative fuels will be briefly introduced.

Position Sensitivity Study in Molecular Dynamics Simulations of Self-Organized Development of 3D Nanostructures

The sensitivity of defect free fusion of straight carbon nanotubes from graphene nanoribbons to the position of the nanoribbon edge positions has been investigated. A basic difference between the behavior of armchair and zigzag type nanoribbons was observed. When placing armchair type graphene nanoribbons above each other identical, fitting positions are obtained automatically. Zigzag type graphene nanoribbons, however, must not be placed above each other in identical positions. From the viewpoint of defect-free fusion, according to the MD simulations symmetric on nearly symmetric positions of the ribbon edges are favorable.

Failure Analysis of Aluminum – Ceramic Composites

The increasingly widespread use of syntactic metal foams is due to their excellent energy absorbing characteristics. Several research groups deal with developing methods that can further improve this characteristic. Several literature analyses have been devoted to the effects of materials selection, cell size and wall thickness of the reinforcing element on the compression strength. In this work an in situ test necessary for the modeling of the failure process introduced. The aluminum-ceramic composite foams were cyclically upset. The geometry of the test specimen was reconstructed at a certain point of the compression test by μCT technology and digital image analysis. The failure process was characterized by volume change, by the number of broken shells and by the formation of shear plane as a function of the deformation.

Self-organizing Behavior of Y-junctions of Graphene Nanoribbons

With the help of our molecular dynamics simulation we want to motivate emerging and development of technological methods for building of carbon nanostructure networks. We shall study self-organizing behaviors of graphene nanoribbons in Y-junctions. We determine the conditions for perfect formation of nanotube Yjunctions from parallel nanoribbons. The role of graphene nanolithography in nanoribbon network and nanotube network production is studied. Our simulations show the possibility of nanotube network realization as well.