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Geometrical and orientation investigations on the electronic structures of elements adsorption on graphene via density functional theory

Widjaja, Hantarto (2016) Geometrical and orientation investigations on the electronic structures of elements adsorption on graphene via density functional theory. PhD thesis, Murdoch University.

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Nano-sized materials have promising contemporary and novel technological applications as they possess favourable properties due to quantum effects. The nano-sized graphene material exhibits remarkable electrical, optical, thermal and mechanical characteristics. Adding impurities or doping constitutes an effective way in fine-tuning properties of graphene for specific applications. This study aims to investigate the geometrical aspects of elements adsorption on graphene to produce more accurate models of the electronic structure of graphene as a result of the doping.

Previous models investigated mainly the adsorption sites (bridge, hollow, top); however, they could not systematically explain certain phenomena, e.g. nonlinearity of band gaps to atomic ratios in oxygen-adsorbed graphene. We hypothesise that this is attributed to the positions and orientation of the adatoms (adsorbed elements) relative to one another, which is, in essence, a geometrical phenomenon.

In the present study, geometrical investigations of elemental adsorption on graphene focused on side (single-, double-sided), site (bridge, hollow, top) and orientation (the position of adatom relative to one another and graphene). The computational simulations were conducted by using the generalized gradient approximation (GGA) functional within the density functional theory (DFT) framework. The VASP (Vienna Ab initio Simulation Package) software was utilised for all simulations.

Trends in the elemental adsorption on graphene in terms of sides/sites/orientations are presented in terms of: binding energy (stability); migration (barrier) energy; adatom height; graphene distortion; Fermi energy; magnetization; charge transfer and energy band gap. The calculated results of 10 elements (Na, Mg, Al, Si, P, S, F, Cl, Br and I) adsorbed on pristine graphene indicate that the geometrical combination of side, site and orientation is vital in determining the most stable configuration of the adsorbed systems. This study reinforces the notion that the involvement of site/orientation of element (or functional group) is essential in future models of adsorption on graphene.

Item Type: Thesis (PhD)
Supervisor(s): Jiang, Zhong-Tao, Altarawneh, Mohammednoor and Jennings, Philip
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