以不同製程製備氧化鈦薄膜作為釔鋇銅氧高溫超導薄膜緩衝層的特性研究

Abstract

本論文探討以不同製程製備氧化鈦薄膜，作為釔鋇銅氧高溫超導薄膜緩衝層的特性研究。當氮化鈦作為緩衝層製備釔鋇銅氧，氮化鈦在釔鋇銅氧成長過程中，會氧化為金紅石結構的氧化鈦。反之，若以脈衝雷射直接在鈦酸鍶(100)基板上蒸鍍氧化鈦薄膜，則可得到銳鈦礦結構的氧化鈦薄膜。我們利用晶格匹配性與氮化鈦氧化前後的結構，解釋不同氧化鈦結構在鈦酸鍶基板上的成因，與氮化鈦薄膜氧化時，晶格結構的變化。利用上述兩種結構的薄膜，當作釔鋇銅氧的緩衝層時，可以得到超導性質良好的結果。反之，利用直流濺鍍成長氧化鈦薄膜，隨後經過熱處理，仍可得到銳鈦礦與金紅石結構的氧化鈦，但鍍在其上的釔鋇銅氧卻發現不超導的行為。我們分別利用原子力顯微鏡、X-ray繞射儀、與X-ray吸收光譜等探討釔鋇銅氧成長在這些不同氧化鈦薄膜上呈現不同超導性行為的成因。

YBa2Cu3O7(YBCO)/TiN and YBCO/TiO2 bilayer structures have been prepared on SrTiO3(STO)(100) substrates by in-situ pulsed laser deposition (PLD). The TiN films were originally intended to serve as the lower contact electrode for studying the c-axis transport properties of YBCO thin films. It was found that, under the optimum conditions of depositing YBCO thin films, the TiN(100) layer was oxidized and transformed into rutile TiO2(110) film. On the other hand, pure anatase TiO2(001) films were prepared by PLD using a rutile TiO2(110) substrate as the target. We explained why the different structure of TiO2 could be grown on STO. After preparing buffer layers of TiO2, YBCO films grown on both phases of TiO2 films show virtually the same transport properties of typical good quality single-layer YBCO films. Comparative studies of depositing YBCO films directly onto a dc-sputtered TiO2 template commonly used in the selective epitaxial growth (SEG) process have, however, resulted in formation of a nonsuperconducting YBCO top layer. Experiments including interfacial X-ray absorption spectroscopy (XAS) for determining the possible interactions occurring at the YBCO and TiO2 interface are reported.