Vortex properties of the high-temperature superconductor bismuth strontium calcium copper oxide, and controlled deposition of carbon nanotubes.

摘要

This thesis contains two sections. The first section discusses vortex matter behavior in a high temperature superconductor, Bi2Sr 2CaCu2O8+delta (BSCCO), studied using transport and local magnetization measurements. Vortex matter phase transitions in micron-sized BSCCO are investigated using GaAs/AlGaAs Hall sensors. We observe that the vortex solid 3D-2D phase transition disappears below a temperature-dependent critical sample size. Vortex penetration field measurements in micron-sized BSCCO show that the Bean-Livingston surface barrier effect dictates the vortex penetration field at high temperatures, and the bulk pinning effect dictates the vortex penetration field at low temperatures. When measuring the c-axis magneto-resistance of BSCCO in tilted magnetic fields, we observe that the in-plane pancake vortices arrange in a zigzag structure along the c-axis of the sample at low tilt angles and high magnetic fields. This zigzag arrangement lowers the interaction energy of pancakes with Josephson vortices. Finally, in order to avoid the Bean-Livingston surface barrier effect, we measured vortex dissipation in BSCCO using a Corbino disk contact geometry. We found that, the vortex matter transport properties in BSCCO are determined by sample bulk properties, and not the Bean-Livingston surface barrier effect.;The second section of this thesis discusses the controlled deposition and manipulation of single carbon nanotubes using MEMS (Microelectromechanical systems) devices. Large-scale controlled deposition of individual nanotubes is a crucial requirement for realistic applications of nanotube-based electronic devices. Using novel substrate designs, we deposit single aligned nanotubes with complete control utilizing capillary forces and dielectrophoresis. We can also pull and bend the deposited single nanotubes in situ in a Transmission Electron Microscope.;The majority of the measurements on BSCCO and carbon nanotubes discussed here are made possible by the development of novel micro-fabrication techniques using the Micro-fabrication Laboratory facilities at UC Berkeley.