Browsing by Subject "sapphire"
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Item Density functional study of graphene on insulating substrates(2009-08) Jadaun, Priyamvada; Banerjee, Sanjay; Sahu, Bhagawan R.; Fiete, GregoryThis is a study of the structural and electronic behavior and properties of graphene on α-quartz and α-sapphire using Density Functional Theory. We construct initial structures using the above 2 substrates, place a layer of graphene on them and subsequently allow the atoms to relax. After relaxation we study any structural changes, band structures, density of states, charge density to determine the electronic properties of the entire structure. Eventually this study will help in the search for good substrates for graphene based transistors.Item Dielectric-Loaded Microwave Cavity for High-Gradient Testing of Superconducting Materials(2011-08-08) Pogue, Nathaniel JohnstonA superconducting microwave cavity has been designed to test advanced materials for use in the accelerating structures contained within linear colliders. The electromagnetic design of this cavity produces surface magnetic fields on the sample wafer exceeding the critical limit of Niobium. The ability of this cavity to push up to 4 times the critical field provides, for the first time, a short sample method to reproducibly test these thin films to their ultimate limit. In order for this Wafer Test cavity to function appropriately, the large sapphire at the heart of the cavity must have specific inherent qualities. A second cavity was constructed to test these parameters: dielectric constant, loss tangent, and heat capacity. Several tests were performed and consistent values were obtained. The consequences of these measurements were then applied to the Wafer Cavity, and its performance was evaluated for different power inputs. The Q_0 of the cavity could be as low as 10^7 because of the sapphire heating, therefore removing the ability to measure nano-resistances. However, with additional measurements in a less complex environment, such as the Wafer Test Cavity, the Q_0 could be higher than 10^9.