Computational Studies On Metallic Glasses And Metal-Graphene Hybrids

Although bulk metallic glasses (MGs) reveal excellent mechanical strength, soft magnetic properties, and high resistance to wear and corrosion,  they lack in  tensile ductility. Large-scale molecular dynamics (MD) simulations showed that MGs exhibit short range order consisting of icosahedral (ICO) clusters as well as of superclusters (SCs) thus accounting for the system’s stochiometry. These SCs can be considered as the MG’s fundamental structural units while  the macroscopic deformation is achieved through their destruction and recreation. Density Functional Theory (DFT) - calculations exhibit Free-of-Bond areas (FoB), which may act as slip planes like in crystals thus enhancing the ductility of MGs. The presence of p-type dopants  can create  FoBs  at new well localized eigenstates whereas  FoB slip planes could develop  even in d/s-type impurities, via charge transfer in the p-bands. The amorphous-like bulk systems indeed show electronic features similar to the corresponding ICO-and SC-clusters. These presented calculations may shed more light on the microalloying effect occurring in many MGs, and thus allow for the targeted design of new MGs with desirable properties.

Metallic nanostructures on graphene and Carbon Nanotubes (CNTs) are of high interest  due to their high application potential in electronic nanodevices, sensors and catalyses. This lecture reports on DFT calculations of  Ti (or Cu) nanoclusters’ /nanowires’ decoration on graphene or CNT, and of graphene flakes on Cu substrates. First calculations  aimed at the electronic origin of the grown nanostructures which are – according to experiment - uniform for Ti, but clustered for Cu.  More calculations exhibited  the shapes, orientations and edge geometries of CVD-grown graphene flakes to be governed by the crystallographic directions of the Cu substrate. In experiments  in case of the Cu(101) face, rectangular four-lobed, parallel-sided flakes oriented along [101] directions were found. These results are well reflected by DFT calculations which revealed that because of  C2p-Cu3d hybridizations the zig-zag edge observed is preferentially aligned along the surface channel [101], thus reducing the lattice mismatch.

Institution: 

University of Ioannina, Greece

Department of Materials Science and Engineering

 

Date: 
Friday, June 16, 2017 - 10:00
Speaker: 
Prof. Christina E. Lekka