| AVS 58th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing Division | Wednesday Sessions |
| Session EM-WeA |
| Session: | Defects in Electronic Materials |
| Presenter: | Enxia Zhang, Vanderbilt University |
| Authors: | E.X. Zhang, Vanderbilt University A.K.M. Newaz, Vanderbilt University S. Bhandaru, Vanderbilt University M.L. Alles, Vanderbilt University D.M. Fleetwood, Vanderbilt University R.D. Schrimpf, Vanderbilt University K. Bolotin, Vanderbilt University R.A. Reed, Vanderbilt University R.A. Weller, Vanderbilt University S.M. Weiss, Vanderbilt University S.T. Pantelides, Vanderbilt University |
| Correspondent: | Click to Email |
Graphene is a truly two-dimensional material that consists of carbon atoms connected by sp2 bonding and arranged in a honeycomb lattice. Due to its unique properties and potential applications in future electronic devices, graphene has received much attention recently from the scientific community. Initial studies of the effects of electron-beam and proton irradiation have been performed on graphene materials, but there remain significant questions about the nature of the conductivity and of the defects.
In this work, the responses of graphene materials to 10-keV x-ray radiation are evaluated with Raman spectroscopy. A defect related peak (D-peak) appears (~1345 cm-1) after x-ray irradiation in air; the intensity of the D-peak increases with increasing total dose, and decreases with post-irradiation vacuum annealing at 350 °C. (See supplemental figures.) These results suggest that new defects can be created and/or that weak bonds at defect precursor sites can be scissioned and decorated with impurities (e.g., H, O) during x-ray exposure. The charge neutral point of graphene transistors made from similar material shifts positively with increasing x-ray dose, suggesting that similar defects may contribute to shifts in the Dirac point and degradation in the conductivity.
It has been shown previously that ozone can react with C-C bonds to degrade graphene layers. We have measured significant ozone generation during x-ray irradiation, suggesting that the x-rays may not directly create the defects sensed by Raman, but that x-ray generated ozone may lead to at least some of the observed defects. However, it is likely that there is an additional source of degradation, since in previous work the ozone reaction typically has been shown to lead to irreversible degradation, but we find that vacuum annealing at elevated temperature leads to partial recovery. Hydrogen annealing treatments of graphene have shown reversible degradation. Thus, it seems likely that hydrogen released by x-ray exposure in the SiO2 substrate reacts with defect precursors (e.g., weak bond sites) in the graphene. Hydrogen reactions with C-C bonds can enhance the intervalley scattering, thereby increasing the D line intensity. Much of the hydrogen may be driven out by annealing in vacuum at 350 °C, leading to recovery of the degradation, consistent with our experimental results.
This work was supported by the DTRA Basic Research Program through Grants HDTRA1-10-1-0016 and HDTRA1-10-1-0041.