Spectroscopy of Covalently Functionalized Graphene

We have focused on the application of chemistry to engineer a band gap into graphene;11,12 covalent carbon‐carbon bond formation reactions can be used to change the hybridization of the graphitic atoms from sp2 to sp3 to modify the conjugation length of the delocalized carbon lattice

Sandip Niyogi; Elena Bekyarova; Mikhail E. Itkis; Hang Zhang; Kristin Shepperd; Jeremy Hicks; Michael Sprinkle; Claire Berger; Chun Ning Lau; Walt A. deHeer; Edward H. Conrad; Robert C. Haddon

2010

Scholarcy highlights

  • Graphene band gap engineering efforts are mainly focused on the use of lithographic methods to dice the graphene lattice into nanoribbons which physically confine the carriers.4­6 the lithography process involves high‐energy electron beams that has been shown to alter the intrinsic chemical structure of graphene. The demonstration that physical methods can open a band gap in graphene has led to efforts in synthesizing graphene nanoribbons.8­10
  • We have focused on the application of chemistry to engineer a band gap into graphene; covalent carbon‐carbon bond formation reactions can be used to change the hybridization of the graphitic atoms from sp to sp to modify the conjugation length of the delocalized carbon lattice
  • Such chemistry has been shown to be effective in modifying the electronic structure of single‐walled carbon nanotubes, and these side‐wall reactions serve to introduce a band gap in metallic SWNTs
  • The observations are interpreted as a demonstration of the application of covalent bond forming chemistry to affect the conjugation length and periodicity in graphene that results in the ∼0.4 eV band gap measured using angle‐ resolved photoelectron spectroscopy
  • We begin by discussing the functionalization of exfoliated graphene because it gives rise to the simplest spectra; we found that the same functionalization scheme that we employed with epitaxial graphene wafers is effective in derivatizing exfoliated graphene on silicon substrates
  • Transport measurements and theoretical calculations imply the presence of an energy band gap in sp functionalized graphene, and we investigated the effect of nitrophenyl functionalization on epitaxial graphene using angle‐resolved photoemission spectroscopy; Figure 3a shows the band structure at the graphene K‐point
  • The widths of the spectral peaks do not broaden as is characteristic of disordered graphitic materials. Taking 1347 cm­1 as the mean D‐band frequency of a structural defect in pristine graphene and graphitic materials with long‐range crystalline order and 1620 cm­1 as that for the D* band, the product of the nitrophenyl radical functionalization on thin epitaxial graphene indicates that the introduction of the nitrophenyl groups leads to saturated sites in the graphene lattice that may be viewed as internal edges to the conjugated regions

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