Research - under construction

Computational Material Science:
  • Ab initio calculations: Atomic and electronic structure of metals and theirs alloys, nanosized objects, biological molecules, metal/(graphene or CNT) hybrids based on the Augmented Plane Wave (APW) theory, the Density Functional theory (DFT) and the NRL-Tight Binding (NRL-TB) scheme.
  • Classical Molecular Dynamics (MD) simulations: Study of structural, vibrational, mechanical and diffusion properties of metals and their alloys (emphasis on metallic glasses, surface properties and nanosized objects)

  • Current research topics

    A. Biocompatible Titanium-based Structures for Orthopaedics:
    PhD student: J.J. Gutierrez-Moreno, Collaborations, Publications

    B. Graphene or Carbon nanotubes' interactions with metals or metal oxides

    C. Bulk metallic glasses

    D. Biological molecules (Flavonoids) and metallic ions (Fe, Cu, Zn) complexes

    Other research topics

    E. Metal nitrides
    F. Metallic surfaces


    A. Biocompatible Titanium-based Structures for Orthopaedics

    Project : FP7-PEOPLE-2010-ITN (# 264635), Academic-Industrial Initial Training Network on Innovative Biocompatible Titanium-based Structures for Orthopaedics (BioTiNet) 2011-2014 http://www.biotinet.eu/

    Theory-guided bottom-up design of low-rigidity Ti-based alloys

    BioTiNet

    The project objective is to develop a computational procedure (from ab-initio towards large scale molecular dynamics simulations) for the investigation and design of low rigidity Ti-based alloys. This project aims in studying and understanding the relations between the mechanical properties and the structure and chemistry of existing and/or proposed β-type Ti-based alloys, goal being the design of new β-type Ti-based alloys. Tasks: a) physical and chemical insight of existing and/or proposed Ti-based systems by means of the prediction of the basic thermodynamic, mechanical and chemical properties based on ab-initio calculations for the crystalline alloys, b) Design of new Ti-based crystalline systems from ab-initio, c) Scale-up to nanocrystalline via modeling of suitable semi-empirical approaches: from total energy and ab-initio computations to interatomic model interactions and large scale parallel Computations and Simulations and d) Simulation into real cases (e.g. β-type and nano-structured Ti-based, as well as glassy alloys) and comparison with the other experimental data.



    BioTiNet







    Collaboration:

    Coordinator BioTiNet group: Prof. Mariana Calin, Dr. Annett Gebert and Prof. Jurgen Eckert, Institude of Complex Materials, IFW Dresden, Germany http://www.ifw-dresden.de/institutes/ikm/
    Other BioTiNet partners: Prof. Reza Yavary, Grenoble, France and Prof. Nicole Grobert, Oxford, UK
    UoI BioTiNet group: Assist. Prof. Ch.E. Lekka, Accos. Prof. D.G. Papageorgiou and Prof. G.A.Evangelakis


    PhD student

    Jose Julio Guttierrez Moreno
    Thesis: Theory-guided bottom-up design of low-rigidity Ti-based alloys (ab initio and molecular dynamics calculations)
    http://cmsl.materials.uoi.gr/people.php/



    Undergraduate student

    Alexis Papaioannou
    Thesis: Structural and electronic properties of Ti-xNb-Y (x=14:40, Y=Si,In, Sn) biocompatible alloys
    http://cmsl.materials.uoi.gr/people.php/



    Publications

  • The role of Sn doping in the β-type Ti-25at%Nb alloys: experiment and ab initio calculations, J.J. Gutiérrez-Moreno, Y. Guo, K. Georgarakis, A.R. Yavari, G.A. Evangelakis, Ch.E. Lekka, Journal of Alloys and Compounds , DOI: 10.1016/j.jallcom.2014.05.024
  • Elastic softening of β-type Ti-Nb alloys by indium (In) additions, Mariana Calina, Arne Helth, Julio J. Gutierrez Moreno, Matthias Bönisch, Varvara Brackmann, Lars Giebelera, Thomas Gemming, Christina E. Lekka, Annett Gebert, Reinhard Schnettler, Jürgen Eckert (under review in Journal of the Mechanical Behavior of Biomedical Materials)
  • Structural and electronic properties of TiNb, J.J. Gutierrez Moreno et al, to be submitted


  • B. Graphene or Carbon nanotube interactions with metals or metal oxides

    B.1. Graphene growth on Cu substrates

    Controlling the Orientation, Edge Geometry and Thickness of Chemical Vapor Depostion Graphene

    A new way of growing graphene without the defects that weaken it and prevent electrons from flowing freely within it could open the way to large-scale manufacturing of graphene-based devices with applications in fields such as electronics, energy, and healthcare. A team led by Nicole Grobert has overcome a key problem of growing graphene by chemical vapour deposition. by using copper substrate to control the orientation of growing graphene flakes. Where these flakes, called ‘domains’, are well-aligned, which will create a neater, stronger, and more ‘electron-friendly’ material. The Oxford-led team, which includes researchers from Forschungszentrum Juelich Germany, the University of Ioannina Greece, and Renishaw plc, has also shown that it is also possible using the new technique to selectively grow bilayer domains of graphene – a double layer of closely packed carbon atoms – which are of particular interest for their unusual electrical properties. http://www.materials.ox.ac.uk/blog/148/544/Controlling-the-Orientation-Edge-Geometry-and-Thickness-of-Chemical-Vapor-Depostion-Graphene.html

    The UoI contribution: The orientation of the graphene flakes along e.g. the Cu(110) surface <101> direction were supported by Density Functional Theory calculations revealing that the zig-zag edge is preferentially aligned along the surface channel due to Cu3d- C2p hybridizations, thus reducing the lattice mismatch.



    Graphene_on_Cu_surfaces

    Collaboration:

    Prof. Nicole Grobert, Department of Materials, University of Oxford
    http://www.materials.ox.ac.uk/peoplepages/grobert.html


    Publications

  • Controlling the Orientation, Edge Geometry and Thickness of Chemical Vapor Depostion Graphene
    Murdock, A.T., Koos, A., Britton, T.B., Houben, L., Batten, T., Zhang, T., Wilkinson, A.J., Dunin-Borkowski, R.E., Lekka, C.E., Grobert, N.
    ACS Nano 7 (2) (2013) pp. 1351-1359
    DOI: 10.1021/nn3049297


  • MsD student

    Athanasia-Kiriaki Mpalermpa
    Thesis: "Structural and transport properties of Graphene flakes on Cu(110) surface"
    http://cmsl.materials.uoi.gr/people.php/



    Undergraduate student

    Alexis Kotanidis
    Thesis: "Structural properties of Graphene flakes on Cu(001) surface"
    http://cmsl.materials.uoi.gr/people.php/









    B.2. TiN and Ti-O decoration of Single Wall Carbon Nanotubes and Graphene by Density Functional Theory computations

    Ti_n decoration

    Ti nanostructures on Single Wall Carbon Nanotubes (SWCNTs) attracted considerable attention due to their potential applications in electronic nanodevices and molecular adsorption. We report on Density Functional Theory results referring to TiN (N=1,2,3,7,13) supported on SWCNTs and graphene. Two new equivalent positions emerged that trisect the line joining the hexagon along the tube’s axis sides (TSH). These sites accommodate dimmers and trimmers in compact linear and 2D triangular forms, respectively, and 3D Ti7 and Ti13 conformations. Ti adsorbates introduce new electronic states close and at the Fermi level. Despite the significant charge transfer from adsorbates to substrates, these otherwise reduced TiN induce substantial charge screening in their surrounding substrate’s ldlstoms and appear eventually as charged locations. These findings enlighten the early stages of Ti deposition, predict possible active sites and may be of use for the design of metal-carbon coatings for applications in catalysis and nano-electronics.

    PhD student

    Martha Gialampouki
    Thesis: "Organic-inorganic hybrid nanomaterials with predetermined properties "
    http://cmsl.materials.uoi.gr/people.php/

    Publications

  • TiN decoration of single-wall carbon nanotubes and graphene by density functional theory computations
    M.A. Gialampouki, Ch.E. Lekka
    Journal of Physical Chemistry C 115 (2011) 15172-15181.
    DOI: 10.1021/jp202130g
  • Structural and electronic properties of Ti-nanowires/C-single wall nanotubes composites by density functional theory calculations
    M.A. Gialampouki, M.A. Balerba, Ch.E. Lekka
    Materials Chemistry and Physics 134 (2012) 214
    DOI: journal_link
  • Early stage of Ti-O clusters' growth on SWNTs by ab initio calculations
    M.A. Gialampouki, Ch.E. Lekka
    submitted
    DOI: journal_link




  • B.3. Growth of Carbon Nanotubes on Ti-based alloys

    2

    Clustering and mechanical properties in Cu/Zr-based glassy models

    CuZr glass

    It is now accepted that Cu-Zr Metallic Glasses (MG) are mainly composed by small Icosahedral-like (ICO) clusters that may be interconnected and/or interpenetrating. Using Molecular Dynamics and Reverse Monte Carlo simulations we show that the interpenetrating ICOs carrying the compositional signature of the system form SuperClusters (SC) which obey particular sequences of magic numbers. It comes out that these SCs are reproducing very well the structural features of the experimental Radial Distribution Functions (RDF). Interestingly, we found that the atomic pair distances do not depend on the respective compositions of the systems, suggesting that the experimental shift of the RDFs when changing the stoichiometry is due only to the alterations of the relative heights of the peaks. Upon deformation, the ICO clusters are destructed and recreated while similar behavior follow the SCs explaining the way the Cu-Zr MGs accommodate the stress upon deformation. In addition, we addressed the issue of Microalloying in CuxZr12-xY (Y=Mg,Be,Al,Si,P,Nb,Ag) ICO cases and in selective CuZrAl and CuZrNb SCs by means of Density Functional Theory calculations. We found significant alterations in the electronic structures of the CuZr clusters and SCs manifested by new low-energy states and charge transfer near the Fermi level. In the CuZrAl ICO and SC cases these new states are due to covalent-like bonding between Al core and Cu shell atoms and Cu-Al core-core atoms, respectively. In the case of Nb substitution the effects in the electronic structure are similar, but the interactions between Nb core and Cu/Zr shell atoms are characterized by directional π-like bonds. In addition, we found that a p-electron type dopant, as central atom, results in the creation of a plane with free of core–shell atomic bonds, at certain energies and weak interactions at the Fermi level, which could be viewed as a slip plane. s or d-electron type dopants may behave similarly due to significant charge transfer towards unoccupied p-electrons occurring upon alloying. These results could explain the experimental findings referring to the short range order, the elucidation of the micro-alloying effect and the modifications induced in the mechanical properties of these MGs by small Al or Nb additions.

    Collaboration: Ch.E. Lekka and D.G. Papageorgiou