| AVS 58th Annual International Symposium and Exhibition | |
| Graphene and Related Materials Focus Topic | Monday Sessions |
| Session GR+TF+ET-MoA |
| Session: | Graphene: Electronic Properties and Charge Transport |
| Presenter: | Srivats Rajasekaran, Stanford University |
| Authors: | S. Rajasekaran, Stanford University S. Kaya, Stanford Synchrotron Light Source T. Anniyev, Stanford Synchrotron Light Source F. Yang, Brookhaven National Laboratory D. Stacchiola, Brookhaven National Laboratory H. Ogasawara, Stanford Synchrotron Light Source A. Nilsson, Stanford Synchrotron Light Source |
| Correspondent: | Click to Email |
Graphene has received tremendous interest due to its unique electronic structure. Manipulating its electronic structure has received considerable interest. Hydrogenating graphene to open a band gap has been proposed and certain groups have demonstrated hydrogenation induced band opening for graphene on metal substrates.
We employed carbon specific soft x-ray spectroscopy (X-ray photoelectron (XPS), X-ray absorption (XAS) and X-ray emission spectroscopy (XES)) and scanning tunneling microscopy (STM) to investigate how hydrogenation changes the geometric and electronic structure of graphene on Pt(111). Graphene growth on Pt(111) is accompanied with Moiré structure due to periodic rippling in the graphene overlayer due to lattice mismatch and weak interaction between graphene and Pt. Hydrogenation leads to complete disappearance of long range order, although STM indicates that ripple periodicity survives even after hydrogenation. We show that hydrogenation of the unit cell of Moiré nano-patterns is accompanied by pinning of the graphene layer to underneath metal substrate. Structural changes involved in the process of hydrogenation induce covalent graphene-metal interaction. Angle resolved XES and XAS make it possible to probe symmetry resolved states in σ and π bond geometry. XES-XAS indicates that the density of states (DOS) of graphene is very similar to that of graphite. Hydrogenation induces significant changes in the electronic DOS, most of which reflect the formation of C-H σ bonds. For disordered hydrogenated graphene, contrary to band opening, we observe states at the Fermi level after hydrogenation which we reason to arise due to graphene metal interaction and localized C-H bonds. This effect is proposed to be a way to tailor its electronic properties as a possible method to form better graphene-metal contact.