Band gap engineering in armchair-edged graphene nanoribbons by edge dihydrogenation

We report our first principles study of dihydrogenation effects on the electronic structures of armchair-edged graphene nanoribbons (AGNRs). It is found that dihydrogenation brings completely different effects from mono-hydrogenation. For AGNRs, when the edge hydrogenation scheme varies from H:H to H:H2 and then to H2:H2, the band gap of the ribbon will change in a “V” style, “⧹” style or “Λ” style, depending on whether the ribbon width n = 3p or 3p + 1 or 3p + 2. Further analysis shows that this interesting change arises from the decrease of the effective ribbon width induced by dihydrogenation. In addition, the band structures of H2:H2 (n − 2)-AGNRs, H:H2 (n − 1)-AGNRs and H:H n-AGNRs around the Fermi level are very similar and their gaps are slightly different. Like in the band gap, the family behaviors are also observed in the formation energy. The trend in band gap change is consistent with the trend in the formation energy in reflecting the relative stability of the AGNRs with different hydrogenations. These findings provide a basis for band gap engineering with different edge hydrogenations in AGNRs and may find applications in the design of graphene based devices.