分析奈米結構缺陷與穿透式電子顯微鏡檢驗和電性之關聯性

Abstract

此博士論文，針對奈米結構缺陷的電子顯微鏡成像與電性特徵之關聯性，發展了二種技術，一個是全新地偵測缺陷工具，一個是特別精心設計的晶片。這兩種技術的實驗細節都完整地呈現於內文中。前者，即是可移動奈米碳管懸臂閘極，選擇在一條懸浮的奈米線，以偵測出電荷缺陷做為成果表現。奈米碳管閘極是由一根奈米金針依續接著粗細兩根奈米碳管所組成，實驗結果裡，它不僅能偵測懸浮奈米線中的埋入鎵離子和捕捉電子，又可以分別地判斷離子的極性和測量捕捉電子的數量。這個技術更可以延伸應用在其他的懸浮奈米線。後者，是精心設計結構為局部中空沒有基板，卻有懸浮電極橫跨中空區域的晶片，成為一片晶片即可完成穿透式電子顯微鏡審視和電性特徵之物理關聯性連結的晶片平台。實驗結果展現，即是透過奈米操控技術放置一條聚集多根的單壁奈米碳管在這種特製晶片的懸浮電極上面，報導關於氧氣分子摻雜在缺乏碳的金屬性和半導體性奈米碳管的電子性質影響。缺乏碳的奈米碳管可利用電子束撞擊奈米碳管上的碳原子程序產生碳空缺，其結果可以透過穿透式電子顯微鏡清楚地檢驗。碳空缺上的垂懸鍵非常具有活性且很容易吸附氧氣分子，就半導體性碳管而言，氧氣分子鍵結可降低能帶差距，使原本p型碳管修飾變為雙極性。就金屬性碳管而言，由於外加電場可控制這些吸附在碳管上面的氧氣分子偶極場，因此在來回閘極電壓的電流反應上，可以觀測到雙重穩定狀態的滯後現象。

In this doctoral dissertation, we have developed a set of novel tool and a specific chip for a correlated study of defect based on electrical measurements and electron microscope imaging. Both of experimental details addressing these techniques are meticulously presented. In the former, a moveable carbon nanotube (CNT) cantilever gate is developed for the detection of embedded charge defects in suspended nanowires. The CNT gate is composed of a gold probe welded to a thick carbon nanotube which is in turn attached to a thinner carbon nanotube. It can not only detect embedded Ga ions in the suspended nanowires as well as trapped electrons, but also determine the polarity of the embedded ions and measure the amount of trapped electrons, respectively. The technique can be extended to other types of suspended nanowires. In the latter, a through-hole chip with suspended electrodes is fabricated to be a platform. This allows a physical correlation to be established for transmission electron microscopy inspection and electrical characterization. For demonstration purpose, the single-walled carbon nanotube bundles are placed on top of suspended electrodes by manipulators and we report the effects of oxygen doping on the electrical properties of defective metallic and semiconducting carbon nanotube bundles on the through-hole chip. Carbon vacancies are generated by electron beam knock-out process, which can be clearly examined by transmission electron microscopy. The dangling carbon bonds of the vacancies are very active and can easily adsorb oxygen molecules. In terms of the semiconducting bundles, oxygen bonding lowers the bandgap and the original p-type bundles thereby modifying them to become bi-polar. For the metallic bundles, a hysteretic bi-stable state in gate-voltage cycling is observed; this is attributed to the electrically controlled dipole field of the oxygen molecules.