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Quasi-Freestanding multilayer graphene films on the carbon face of SiC

Description: The electronic band structure of as-grown and doped graphene grown on the carbon face of SiC is studied by high-resolution angle-resolved photoemission spectroscopy, where we observe both rotations between adjacent layers and AB-stacking. The band structure of quasi-freestanding AB-bilayers is directly compared with bilayer graphene grown on the Si-face of SiC to study the impact of the substrate on the electronic properties of epitaxial graphene. Our results show that the C-face films are nearly freestanding from an electronic point of view, due to the rotations between graphene layers.
Date: June 30, 2010
Creator: Siegel, D. A.; Hwang, C. G.; Fedorov, A. V. & Lanzara, A.
Partner: UNT Libraries Government Documents Department

Three-fold diffraction symmetry in epitaxial graphene and the SiC substrate

Description: The crystallographic symmetries and spatial distribution of stacking domains in graphene films on 6H-SiC(0001) have been studied by low energy electron diffraction (LEED) and dark field imaging in a low energy electron microscope (LEEM). We find that the graphene diffraction spots from 2 and 3 atomic layers of graphene have 3-fold symmetry consistent with AB (Bernal or rhombohedral) stacking of the layers. On the contrary, graphene diffraction spots from the buffer layer and monolayer graphene have apparent 6-fold symmetry, although the 3-fold nature of the satellite spots indicates a more complex periodicity in the graphene sheets.
Date: December 10, 2009
Creator: Siegel, D A; Zhou, S Y; El Gabaly, F; Schmid, A K; McCarty, K F & Lanzara, A
Partner: UNT Libraries Government Documents Department

VERTIGO (VERtical Transport In the Global Ocean): A study of particle sources and flux attenuation in the North Pacific

Description: The VERtical Transport In the Global Ocean (VERTIGO) study examined particle sources and fluxes through the ocean's 'twilight zone' (defined here as depths below the euphotic zone to 1000 m). Interdisciplinary process studies were conducted at contrasting sites off Hawaii (ALOHA) and in the NW Pacific (K2) during 3 week occupations in 2004 and 2005, respectively. We examine in this overview paper the contrasting physical, chemical and biological settings and how these conditions impact the source characteristics of the sinking material and the transport efficiency through the twilight zone. A major finding in VERTIGO is the considerably lower transfer efficiency (T{sub eff}) of particulate organic carbon (POC), POC flux 500/150 m, at ALOHA (20%) vs. K2 (50%). This efficiency is higher in the diatom-dominated setting at K2 where silica-rich particles dominate the flux at the end of a diatom bloom, and where zooplankton and their pellets are larger. At K2, the drawdown of macronutrients is used to assess export and suggests that shallow remineralization above our 150 m trap is significant, especially for N relative to Si. We explore here also surface export ratios (POC flux/primary production) and possible reasons why this ratio is higher at K2, especially during the first trap deployment. When we compare the 500 m fluxes to deep moored traps, both sites lose about half of the sinking POC by >4000 m, but this comparison is limited in that fluxes at depth may have both a local and distant component. Certainly, the greatest difference in particle flux attenuation is in the mesopelagic, and we highlight other VERTIGO papers that provide a more detailed examination of the particle sources, flux and processes that attenuate the flux of sinking particles. Ultimately, we contend that at least three types of processes need to be considered: heterotrophic degradation of sinking ...
Date: June 10, 2008
Creator: Buesseler, K.O.; Trull, T.W.; Steinberg, D.K.; Silver, M.W.; Siegel, D.A.; Saitoh, S.-I. et al.
Partner: UNT Libraries Government Documents Department