• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.204-204
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• 2012

Peierls instability and spin ordering of zigzag graphene nanoribbons (GNR) created on a fully hydrogenated graphene (graphane) are investigated as a function of their width using first-principles density-functional calculations within the generalized-gradient approximation. For the width containing a single zigzag C chain (N=1), we find the presence of a Peierls instability with a bond alternated structure. However, for width greater than N=1, the Peierls distortion is weakened or disappears because of the incommensurate feature of Fermi surface nesting due to the interaction of C chains. Instead, there exists the antiferromagnetic (AFM) spin ordering in which the edge states are ferromagnetically ordered but the two ferromagnetic (FM) edges are antiferromagnetically coupled with each other, showing that electron-lattice coupling and spin ordering in GNR are delicately competing at an extremely thin width of N=2. It is found that, as the width of GNR increases, the energy gain arising from spin ordering is enhanced, but the energy difference between the AFM and FM (where two edge states are ferromagnetically coupled with each other) orderings decreases.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.211-211
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• 2012

Using spin-polarized density-functional theory calculations, we find that the existence of either Peierls instability or antiferromagnetic spin ordering is sensitive to hydrogen passivation near the step. As hydrogens are covered on the terrace, the dangling bond electrons are localized at the step, leading to step-induced states. We investigate the competition between charge and spin orderings in dangling-bond (DB) wires of increasing lengths fabricated on an H-terminated vicinal Si(001) surface. We find antiferromagnetic (AF) ordering to be energetically much more favorable than charge ordering. The energy preference of AF ordering shrinks in an oscillatory way as the wire length increases. This oscillatory behavior can be interpreted in terms of quantum size effects as the DB electrons fill discrete quantum levels.