Complex edge effects in zigzag graphene nanoribbons due to hydrogen loading

TL;DR

This study investigates how hydrogen passivation affects the electronic and magnetic properties of zigzag graphene nanoribbons, revealing complex edge effects, re-entrant magnetism, and phase stability considerations.

Contribution

It combines density functional theory and tight-binding models to analyze hydrogen's impact on ZGNRs, highlighting re-entrant magnetism and stability of sp$^3$ bonded edges.

Findings

Hydrogen passivation opens a gap and suppresses magnetism in narrow ZGNRs.

Re-entrant magnetism and metallic states occur in wider ZGNRs (8 rows and above).

sp$^3$ bonded edge atoms are stable under laboratory conditions.

Abstract

We have performed density functional calculations as well as employed a tight-binding theory, to study the effect of passivation of zigzag graphene nanoribbons (ZGNR) by Hydrogen. We show that each edge C atom bonded with 2 H atoms open up a gap and destroys magnetism for small widths of the nanoribbon. However, a re-entrant magnetism accompanied by a metallic electronic structure is observed from 8 rows and thicker nanoribbons. The electronic structure and magnetic state are quite complex for this type of termination, with sp$^3$ bonded edge atoms being non-magnetic, whereas the nearest neighboring atoms are metallic and magnetic. We have also evaluated the phase stability of several thicknesses of ZGNR, and demonstrate that sp$^3$ bonded edge atoms, with 2 H atoms at the edge, should be stable at temperatures and pressures which are reachable in a laboratory environment.