We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity.

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We report on the micro-Raman spectroscopy of monolayer, bilayer, trilayer, and many layers of graphene ͑graphite͒ bombarded by low-energy argon ions with different doses. The evolution of peak frequencies, intensities, linewidths, and areas of the main Raman bands of graphene is analyzed as function of the distance between defects and number of layers. We describe the disorder-induced frequency shifts and the increase in the linewidth of the Raman bands by means of a spatial-correlation model. Also, the evolution of the relative areas A

The ability of Mo (Cr) impurities in a CaO (MgO) matrix to act as charge donors to adsorbed gold has been investigated by means of scanning tunneling microscopy and density functional theory. Whereas CaO(Mo) features a robust donor characteristic, as deduced from a charge-transfer-driven crossover in the Au particles' geometry in the presence of dopants, MgO(Cr) is electrically inactive. The superior performance of the CaO(Mo) system is explained by the ability of the Mo ions to evolve from a +2 oxidation state in ideal CaO to a +5 state by transferring up to three electrons to the Au adislands. Cr ions in MgO, on the other hand, are stable only in the +2 and +3 charge states and can provide a single electron at best. Since this electron is likely to be captured by cationic vacancies or morphological defects in the real oxide, no charge transfer to Au particles takes place in this case. On the basis of our findings, we have developed general rules on how to optimize the electron donor characteristics of doped oxide materials.

Here we analyse the evolution of the disorder induced D-band ($1350 cm À1 ) and of the first-order allowed G-band ($1584 cm À1 ) in the Raman spectra of ion bombarded graphene. By increasing the bombardment time, we increase the disorder and, consequently, decrease the average distance (L D ) between defects. We describe how the intensity, full width at half maximum (FWHM) and integrated area vary for the D and G bands as a function of L D . Finally, we compare the evolution of the intensity ratio I D /I G and of the integrated area ratio A D /A G between the D and G bands as a method for quantifying disorder in graphene. For practical use and interlaboratorial comparison, the authors advise using the intensity ratio for a more suitable measure for analysing defect density.