Browsing by Author "Fuhrer, Michael S."
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Item Measuring the Complex Optical Conductivity of Graphene by Fabry-Pérot Reflectance Spectroscopy(Nature Publishing Group, 2016-09-29) Ghamsari, Behnood G.; Tosado, Jacob; Yamamoto, Mahito; Fuhrer, Michael S.; Anlage, Steven M.We have experimentally studied the dispersion of optical conductivity in few-layer graphene through reflection spectroscopy at visible wavelengths. A laser scanning microscope (LSM) with a supercontinuum laser source measured the frequency dependence of the reflectance of exfoliated graphene flakes, including monolayer, bilayer and trilayer graphene, loaded on a Si/SiO2 Fabry-Pérot resonator in the 545–700 nm range. The complex refractive index of few-layer graphene, n − ik, was extracted from the reflectance contrast to the bare substrate. It was found that each few-layer graphene possesses a unique dispersionless optical index. This feature indicates that the optical conductivity does not simply scale with the number of layers, and that inter-layer electrodynamics are significant at visible energies.Item "The Princess and the Pea" at the Nanoscale: Wrinkling and Delamination of Graphene on Nanoparticles(American Physical Society, 2012) Yamamoto, Mahito; Pierre-Louis, O.; Huang, Jia; Fuhrer, Michael S.; Einstein, Theodore L.; Cullen, William G.Thin membranes exhibit complex responses to external forces or geometrical constraints. A familiar example is the wrinkling, exhibited by human skin, plant leaves, and fabrics, that results from the relative ease of bending versus stretching. Here, we study the wrinkling of graphene, the thinnest and stiffest known membrane, deposited on a silica substrate decorated with silica nanoparticles. At small nanoparticle density, monolayer graphene adheres to the substrate, detached only in small regions around the nanoparticles. With increasing nanoparticle density, we observe the formation of wrinkles which connect nanoparticles. Above a critical nanoparticle density, the wrinkles form a percolating network through the sample. As the graphene membrane is made thicker, global delamination from the substrate is observed. The observations can be well understood within a continuum-elastic model and have important implications for strain-engineering the electronic properties of graphene.