The use of a Ga+ focused ion beam to modify graphene for device applications.

In this work, we clarify the features of the lateral damage of line defects in single layer graphene. The line defects were produced through well-controlled etching of graphene using a Ga(+) focused ion beam. The lateral damage length was obtained from both the integrated intensity of the disorder induced Raman D band and the minimum ion fluence. Also, the line defects were characterized by polarized Raman spectroscopy. It was found that graphene is resilient under the etching conditions since the intensity of the defect induced Raman D peak exhibits a dependence on the direction of the lines relative to the crystalline lattice and also on the direction of the laser polarization relative to the lines. In addition, electrical measurements of the modified graphene were performed. Different ion fluences were used in order to obtain a completely insulating defect line in graphene, which was determined experimentally by means of charge injection and electric force microscopy measurements. These studies demonstrate that a Ga+ ion column combined with Raman spectroscopy is a powerful technique to produce and understand well-defined periodic arrays of defects in graphene, opening possibilities for better control of nanocarbon devices.

Thermal enhancement of chemical doping in graphene: a Raman spectroscopy study.

The Raman spectrum of monolayer graphene deposited on the top of a silicon oxide/silicon substrate was investigated as a function of temperature up to 515 K. An anomalous temperature dependence of the Raman features was observed, including an important frequency upshift for the Raman G band at room temperature, after the heating process. On the other hand, the frequency of the Raman G(') band is only slightly affected by the thermal treatment. We discuss our experimental results in terms of doping and strain effects associated with the interaction of graphene with the substrate and with the presence of water in the sample. We conclude that the doping effect gives the most important contribution to the spectral changes observed after the thermal cycle.

Observation of distinct electron-phonon couplings in gated bilayer graphene.

A Raman study of a back gated bilayer graphene sample is presented. The changes in the Fermi level induced by charge transfer splits the Raman G band, hardening its higher component and softening the lower one. These two components are associated with the symmetric (S) and antisymmetric vibration (AS) of the atoms in the two layers, the later one becoming Raman active due to inversion symmetry breaking. The phonon hardening and softening are explained by considering the selective coupling of the S and AS phonons with interband and intraband electron-hole pairs.