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This Week at Physics

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Events on Thursday, March 15th, 2012

R. G. Herb Condensed Matter Seminar
Graphene: it’s all about the surface
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Kirill Bolotin, Vanderbilt University
Abstract: Every atom of graphene, a monolayer of graphite, belongs to the surface. Therefore, the environment of graphene -- the substrate onto which graphene is deposited and the coating on top of graphene -- intimately affects the properties of graphene. In this talk, we demonstrate that both mechanical and electrical properties of graphene can be greatly tuned by varying its environment.

First, we discuss ultraclean graphene devices suspended in vacuum. We achieve a carrier mobility in excess of 200,000 cm2/Vs in these devices and demonstrate previously inaccessible transport regimes, including ballistic transport and the fractional quantum Hall effect.

Second, we explore the electrical properties of graphene surrounded by liquid dielectrics. We find that the ions in liquids can cause strong scattering in graphene and demonstrate very large values for room temperature mobility (>60,000 cm2/Vs) in ion-free liquids with high dielectric permittivity.

Finally, we demonstrate that the environment of graphene affects its mechanical properties. We develop a novel technique to study the mechanical properties of graphene films attached to substrates by measuring the temperature-dependent deflection of a "bimetallic" cantilever composed of graphene and silicon nitride or gold layers. We demonstrate that the built-in strain, the substrate adhesion force and even the thermal expansion coefficient of graphene depend on the substrate under it.
Host: Vavilov
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Astronomy Colloquium
"New Results on Gas Flows In and Out of Galaxies"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Alice Shapley, UCLA
Abstract: Over the last several years, there has been growing consensus in the theoretical literature about the process of galaxy growth through cold gas accretion. Both analytic calculations and numerical simulations suggest that high-redshift galaxies primarily grow by smoothly accreting cold gas from the surrounding intergalactic medium (IGM). Furthermore, simulations indicate that gas is accreted in collimated cool streams containing both smooth gas and small galaxies. While recent theoretical work has identified the importance of cold accretion, spectroscopic observations have much more consistently indicated the existence of large-scale outflows from star-forming galaxies at high redshift. Resolving the apparent disconnect between simulations and observations and identifying observational signatures of infalling gas are crucial for testing the theoretical paradigm of cold accretion. Here we present new evidence for the smoking gun of cool gas accreting onto star-forming galaxies at high redshift (z~1-3), using spectroscopy of both HI and heavy elements. We also describe new insights into the properties of outflowing gas around galaxies, which will provide important constraints on models for star-formation feedback.
Host: Prof Snezana Stanirmirovic
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