製造穩定的超導點接觸是實現超導量子彈道裝置的關鍵，本論文致力於開發一種利用聚焦離子束(FIB)制定超導體鋁(Al)奈米結的技術。我們對離子撞擊鋁薄膜和矽基板進行SRIM-2013/TRIM的蒙地卡羅模擬，建立模擬與實驗的關聯，使我們能夠估計實驗所需的銑削條件。通過利用鋁薄膜和矽基板銑削速率和濺射率的變化，我們能夠在鋁觸點下雕刻矽，使薄膜變薄並形成尺寸約為30奈米的三維懸橋。我們測量嵌入在SQUID結構之奈米觸點的電流與電壓特性，發現明顯的次諧波間隙特徵和超電流。在間隙狀態中觀察到的強非線性表明了耗散性質，並表明在奈米點接觸中發生了多重安德列夫反射。我們的工作可能為開發超導量子點接觸裝置開闢一條路徑，例如安德列夫量子位元，以及一種修復超導電路的方法。

Fabricating a stable superconducting point contact is key challenge to realize superconducting quantum ballistic device. This thesis is devoted to develop a technique to tailor a superconducting aluminum (Al) adjacent nano-point junctions by using focused ion beam (FIB). We perform the SRIM-2013/TRIM Monte Carlo simulation to Al thin film and Si-substrate under the impinging of ions, and subsequently correlate the estimated displacement depth to the milling rate as a function of ion dosages in experiments, thus establish an empirical rule to guide us the milling conditions. By utilizing variance of milling rate and sputter yield of Al thin film and Si-substrate, we are able engrave the Si underneath Al contacts, thinner the film and form a suspended three-dimensional nano-bridge with size about 30 nm. We measure the current vs. voltage I(V) characteristics of the nano-contacts embedded in a SQUID geometry, and find distinct subharmonic gap features and a super-current. The observed strong non-linearities in the gap regime indicates a dissipative nature and suggest the occurrence of multiple Andreev-reflection in the nano-point contacts.
Our work could potentially open a route for developing superconducting quantum point contact devices, e.g. Andreev qubits, and a way to repair superconducting circuits.

摘要…………………………………………………...………………………………..i
Abstract…………………………….…………………………………….……………ii
致謝………………...…………………………………………………………………iii
目錄……………………………………………………………………………...……iv
第一章 緒論
1.1 研究動機………….…………………………………………………………1
1.2 文獻回顧..………..……………………………………………….…………2
第二章 背景知識
2.1 約瑟芬結(Josephson junction)……………………………………………..10
2.1.1 約瑟芬方程式(Josephson equations)………………………….………10
2.2 電流-電壓特性(Current-voltage characteristics)…………………...…......12
2.3 直流超導量子干涉儀(DC-SQUID)……………………...……………..…13
2.4 超導量子點接觸(Superconducting quantum point contact)………………15
2.4.1 安德列夫反射(Andreev reflection)………………………………..….17
2.4.2 安德列夫束縛態(Andreev bound state)…………………………...….18
第三章 樣品製作儀器及原理
3.1 掃描式電子顯微鏡(Scanning Electron Microscope，SEM)……………….19
3.1.1 掃描式電子顯微鏡的基本原理………………………………...….…20
3.1.2 掃描式電子顯微鏡的基本構造…………………………..….….……21
3.2 聚焦離子束(Focused Ion Beam，FIB) ……………………………………22
3.2.1 聚焦離子束系統的基本原理……………………………….…….…..22
3.2.2 聚焦離子束系統的基本構造…………………………………………23
3.2.3 聚焦離子束系統的成像反應………………………….…………..….28
3.2.4 聚焦離子束系統的劑量影響…………………………………………40 3.3 原子力顯微鏡(Atomic Force Microscope，AFM) …………………..……46
3.3.1 原子力顯微鏡的基本原理……………………………...…………….46
3.3.2 原子力顯微鏡的基本構造…………..…………………..……………47
3.3.3 原子力顯微鏡的成像反應……………………………………………49
3.4 樣品的設計….……………………………………………………………..50
第四章 實驗量測
4.1 樣品參數…………………………………………………………………...51
4.2 電流-電壓特性…………………………………………………………….54
4.2.1改變溫度下，電流-電壓特性………………………………………….56
4.2.2 改變磁場下，電流-電壓特性…………………………………………58
第五章 總結與未來展望
附錄A 樣品備製……………………………………………………………….62
附錄B 樣品載台(Sample holder)與超導小線圈設計…………..……………63附錄C 磁場估計…….…………………………………………………………67
附錄D 電阻估計…………………………………………………….…………68
D.1 電阻的理論估計…………………………………………...…………...68
D.2 電阻的實際量測……………………………………………...…...……69
D.3 四點量測(Four-point measurement)……………………………………70
附錄E 臨界電流估計……………………………………………….…………72
附錄F 實驗架設…………………………………………………….…………74
附錄G 微波量測…………………………………………………….…………76
參考文獻……………………………………………………………………………..78

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