AVS 60th International Symposium and Exhibition
    Graphene and Other 2D Materials Focus Topic Monday Sessions
       Session GR+EM+NS+PS+SS+TF-MoM

Paper GR+EM+NS+PS+SS+TF-MoM1
Using Nitrogenated SiC to Produce Wide-gap Semiconducting Graphene

Monday, October 28, 2013, 8:20 am, Room 104 B

Session: Growth of 2D Materials
Presenter: P.I. Cohen, University of Minnesota
Authors: P.I. Cohen, University of Minnesota
S. Rothwell, University of Minnesota
L.C. Feldman, Rutgers University
G. Liu, Rutgers University
E.H. Conrad, Georgia Institute of Technology
F. Wang, Georgia Institute of Technology
Correspondent: Click to Email
All carbon electronics based on graphene has been an elusive goal. For more than a decade, the inability to produce significant band gaps in this material has prevented the development of semiconducting graphene. While chemical functionalization was thought to be a route to semiconducting graphene, disorder in the chemical adsorbates leads to low mobilities that have proved to be a hurdle in its production. In this work we demonstrate a new approach to produce semiconducting graphene that uses a small concentration of covalently bonded nitrogen, not as a means to functionalize graphene, but instead as a way to constrain and bend graphene. First, about half a monolayer of nitrogen was adsorbed onto a carbon-polar SiC(000-1) surface by annealing in NO. X-ray photoelectron spectroscopy (XPS) indicates that the layer of N that is introduced forms both C=N and C-N bonds that are stable up to 1550C. Then graphene is grown using a controlled silicon sublimation technique, producing, in this case, 3 or 8 layers of graphene. The N coverage and bonding during this process is determined from the XPS signal. After graphene growth the N coverage is about 7 at. % with its bonding unchanged. Examination of the peak intensity in variable energy XPS suggests that the N remains at the interface and there are no other peaks normally associated with either intercalated or substitutional N in graphene. Scanning tunneling microscopy (STM) confirmed that for the case of either 3 layer or 8 layer graphene, N was not present in the top layer. STM, however, showed that the graphene sheet is buckled with 2-4 nm wide folds. The folds can meander and are 5-25 nm long. In addition, atomic resolution images show that the folds are part of a continuous graphene sheet. The implication is that sp3 bonded N at the interface produces this buckling. Finally, angle resolved photoelectron spectroscopy from the buckled, 3-layer graphene is dramatically different than that from pristine 3-layer graphene. With N at the interface, a bandgap of at least 0.7 eV is resolved, presumably due to a finite size effect. For both 3-layer and 8-layer graphene the Fermi velocity is 0.8 x 106 m/s.