A UHV variable temperature STM and its application to the study of high-T(C) superconductors and carbon nanotubes

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Lee, Jinho, 1969-

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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.