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An analytical study is presented of the double resonant Raman scattering process in graphene, responsible for the D and D′ features in the Raman spectra. This work yields analytical expressions for the D and D′ integrated Raman intensities that explicitly show the dependencies on laser energy, defect concentration, and electronic lifetime. Good agreement is obtained between the analytical results and experimental measurements on samples with increasing defect concentrations and at various laser excitation energies. The use of Raman spectroscopy to identify the nature of defects is discussed. Comparison between the models for the edge-induced and the disorder-induced D-band intensity suggests that edges or grain boundaries can be distinguished from disorder by the different dependence of their Raman intensity on laser excitation energy. Similarly, the type of disorder can potentially be identified not only by the intensity ratio [ [I subscript D] over [I subscript D′]], but also by its laser energy dependence. Also discussed is a quantitative analysis of quantum interference effects of the graphene wave functions, which determine the most important phonon wave vectors and scattering processes responsible for the D and D′ bands., National Science Foundation (U.S.) (Grant DMR1004147), Conselho Nacional de Pesquisas (Brazil) (Grant 245640/2012-6), Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico

Porous materials are ubiquitous in the universe and weathering of porous surfaces plays an important role in the evolution of planetary and interstellar materials. Sputtering of porous solids in particular can influence atmosphere formation, surface reflectivity, and the production of the ambient gas around materials in space. Several previous studies and models have shown a large reduction in the sputtering of a porous solid compared to the sputtering of the non-porous solid. Using molecular dynamics simulations we study the sputtering of a nanoporous solid with 55% of the solid density. We calculate the electronic sputtering induced by a fast, penetrating ion, using a thermal spike representation of the deposited energy. We find that sputtering for this porous solid is, surprisingly, the same as that for a full-density solid, even though the sticking coefficient is high.