A systematic study on adatom interaction with graphyne polymorphs


Thesis Type: Post Graduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Physics, Turkey

Approval Date: 2016

Student: YILDIZ GÖZDE SAĞLAM

Consultant: ALPAN BEK

Abstract:

Carbon never stops surprising the world with its enormous number of allotropes and their excellent properties. In this study, recently discovered carbon allotropes, which are called α, β, γ and 6612 – graphyne, are studied by ab-initio modeling. It is revealed that these polymorphs can exhibit varying types of hybridization sp3, sp2, still they are relatively uncharacterized compared to other planar materials. At first, lowest-energy stable forms of each polymorph and their electronic, structural and magnetic properties were obtained. Furthermore, the changes that occur in these properties in response to adsorption of atmospheric single atoms (H, O, N and S) and their molecular forms were studied. Atomic configurations, binding energies and variations of material properties were studied systematically. Subsequent to adsorption phenomena, diffusion of the same atoms on γ - polymorph was considered and it was revealed that atoms do not diffuse on the surface but prefer to bind to the underlying C atoms. In the light of our findings, it is concluded that the adsorption of single hydrogen atoms creates a magnetized system for all four graphyne isoforms. Afterwards, it was discovered that all four foreign atoms are able to convert the planar structures from semimetallic to semiconducting or from semimetallic to metallic systems, or further open up the band gap. In particular; H, O and S convert semimetallic systems into semiconductors, while N converts semimetallic systems into metals. In addition, graphyne exhibits symmetry-breaking in the presence of atmospheric foreign atoms. As for the structural effects; O, N and S atoms commonly prefer to remain in in-plane sites, while H atom typically stays out of the graphyne planes.