Scientific interests (Still under construction)

My scientific interest include electronic, mechanical, thermodynamic and transport properties of structures at the nanoscale.

Graphene: One of the strongest materials

Energetics of graphene flakes

Our results show that the cohesive energy U_coh of graphene flakes depend on the local enviroment of the bonds. It can be written as
U_coh=(n₃/N)V₃+(n_zz/N)V_zz+(n_ac/N)V_ac
where V₃, V_zz and V_ac are the contributions of the 3-fold coordinated atoms, the atoms at the zig-zag edges and the atoms at the arm chair edges and n₃, n_zz and n_ac the corresponding number of atoms, respectively and N=n₃+n_zz+n_ac is the total number of atoms in the flake.
(See: Zacharias G. Fthenakis, Energetics of graphene flakes , Mol. Phys. 111 , 3289 (2013))

Haeckelites

According to Terrones et al , haeckelites are planar Carbon structures that are ordered arrangements of pentagons, hexagons and heptagons. They are graphene allotropes and can be derived from graphene upon extensive periodically arranged Stone - Walles transformations. They have not been synthesized yet, although it has been predicted theoretically that they are stable structures.
The simplest haeckelites are Pentaheptites, which are built entirely out of pentagonal and heptagonal Carbon rings. Octagraphene is another haeckelite built entirely of octagons and squares. The conversion of graphene to Pentaheptites and their further conversion to Octagraphene through Stone - Walles transformations are shown in the figure bellow. Apparently, there is a whole world of haeckelites.

My interests on haeckelites include the study of their electronic, mechanical and transport properties.
(See:
* Zacharias G. Fthenakis, Zhen Zhu and David Tomanek, Effect of structural defects on the thermal conductivity of graphene: From point to line defects to haeckelites Phys. Rev. B 89 , 125421 (2014)
* Zhen Zhu, Zacharias G. Fthenakis and David Tomanek, Electronic Structure and Transport in Graphene/Haeckelite Hybrids: An Ab Initio Study
* Zacharias G. Fthenakis and Nektarios N. Lathiotakis, Graphene allotropes under extreme uniaxial strain: An ab-initio study , submmited for publication in Nanoscale
* Zacharias G. Fthenakis and Nektarios N. Lathiotakis, Unisotropic behaviour of 2D structures with octagraphene topology under uniaxial strain, in preparation

Carbon foam

Carbon foams are 3D periodic structures composed of sp² and sp³ C atoms. They can be seen as graphitic walls connected with each other with sp³ atoms. The simplest foams can be seen in the figure bellow and their surfaces can be either sp² or sp³ terminated.

According to our findings, sp³ terminated slabs (as well as the bulk carbon foam) is semiconductor, while sp² terminated slabs are metalic. This can be explained in terms of first and second nearest neighbour interactions between p-orbitals, which are directed perpendicular to the graphtic walls and consequently parallel to the foam surface, unlike graphene, where conductivity is owed to the p-orbitals, which are perpendicular to the surface.
(See: Zhen Zhu, Zacharias G. Fthenakis, Jie Guan and David Tomanek, Topologically protected conduction state at carbon foam surfaces: An ab-initio study Phys. Rev. Lett. 112 , 026803 (2014) )

Nanotube deformations under compression

T8 Carbon

T8 Carbon is a new stable form of Carbon made of vertically arranged zig-zag graphene nanoribbons of one hexagonal ring width. They are sp² bonded 3D materials, they are metallic and anisotropic, with very high Young's modulus, comparable to the Young's modulus of graphene.
See preliminary results here Stress along x direction Stress along y direction