Browsing by Subject "Superconductors"
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item Direct measurement of dissipative forces in superconducting BSCCO(2001-08) Judge, Elizabeth Eileen; Markert, John T.Item Low temperature scanning tunneling microscope study of metallic thin films and nanostructures on the semiconductor substrates(2008-12) Qin, Shengyong, 1980-; Shih, Chih-kangMany properties of the thin films are different from the bulk value and in many cases, depend dramatically on the film thickness. In the metallic ultra-thin films epitaxially grown on the semiconductor substrate, the conduction electrons are confined by the vacuum and metal-semiconductor interface. When the film thickness is comparable to the electron Fermi wavelength, this confinement will produce discrete energy levels known as quantum well states (QWS), which dramatically modify the electronic structures of the thin film and this is called quantum size effect (QSE). QSE will have a profound effect on a lot of physical properties of the thin films. Among various systems exhibiting QSE, Pb/Si (111) is the most widely studied one and exhibits the richest phenomena in QSE. In this study, a home made low temperature Scanning Tunneling Microscopy/Spectroscopy (LT-STM/S) was used to study the superconductivities of the Pb thin films. Quantum oscillations of the superconductivity have been observed for the films down to 4 monolayer and the oscillation amplitude increases as the film gets thinner. To resolve the discrepancies between the superconductivities measured with ex-situ transport and in-situ STS. We also studied the influence of Au overlay on the Pb thin films with LT-STM/S, and found out the deposition of Au on Pb dramatically roughened the Pb films. Finally, we successfully grew large scale near perfect 2ML Pb films. There are two types of films which exhibit different Moiré patterns. LT-STS studies revealed there is big difference in the superconductivity Tc of these two films, both of which decreased dramatically from that of the 4ML film.Item A UHV variable temperature STM and its application to the study of high-T(C) superconductors and carbon nanotubes(2002) Lee, Jinho, 1969-; de Lozanne, Alejandro L.The first part of this dissertation describes brief theoretical background for scanning tunneling microscopy(STM), single electron tunneling, and Coulomb blockade phenomena. The second part addresses issues on the design and construction of Ultra High Vacuum Low Temperature Scanning Tunneling Microscope (UHV LTSTM)and also it’s operation, the third part describes topographic, spectroscopic data obtained on high-TC superconductors and HOPG with carbon nanotube(CNT) tips with hitherto made UHV LTSTM system. The fourth part discusses on the possibility of new microscopy using CNT tip’s remarkable I-V characteristic. Our UHV LTSTM can reach from room temperature down to ∼8K. To control the STM head, we used W.A.Technology’s TOPS °r system and it’s software. STM experiments were carried out using double etched W wire tips, and also carbon nanotubes grown on sharpened W wires. SEM images of these nanotube tips show bundles of SWNT or MWNT structures. Atomic-scale STM images on HOPG and 3 nm structural modulations on Bi2Sr2CaCu2O8+x crystals were observed with these nanotube tips. Rectifying I-V characteristics with a threshold voltage of ∼0.7 V were observed with a nanotube tip and a Bi2Sr2CaCu2O8+x sample at 84K. This unexpected characteristics were explained in terms of double barrier tunneling. Quantized differential conductance peaks were also observed reproducibly with different carbon nanotube tips and different sample at different temperature from 13K to 84K, with peak to peak ∆V as large as few 100 mV, which suggests coulomb blockade phenomena. Performing constant imaging tunneling spectroscopy(CITS) with these CNT tips with single electron box behavior, a new possibility of microscopy was discussed in virtue of Fourier transform.