走到世紀交會之處，科技的發展已獲得空前的成就，其中又以半導體科技的發展最為顯著。而今，半導體科技已經接近熱力學極限，似乎是在催促我們找尋新的次世代電晶體，以取代現有的金氧半電晶體，猶如金氧半電晶體取代當年的真空管電晶體一般。自1995年C. Joachim等人利用STM探針量測碳六十分子電性之後[1]，1997年M. A. Reed等人更成功製造直接跨過金屬接點的分子元件 [2]。隔年，第一個奈米碳管電晶體也被製作出來[3][4]，自此分子電晶體與奈米碳管電晶體似乎成為取代半導體的熱門候選之一。在經過無數實驗過程而不斷有所進展之際，其相關理論的分析也進行的如火如荼，但是那些理論結果卻與實驗結果有所出入，並且引發許多對於傳輸機制的爭議。故此，倘若要更進一步改進奈米級電晶體，對其機制必須充分瞭解是相當重要的。筆者藉此以第一原理(First Principle)與非平衡格林函數(Nonequilibrium Green’s Function)試對分子電晶體與奈米碳管電晶體進行理論分析與模擬，並且試圖尋找當中更基本、更直觀的傳輸機制，希望能對分子電晶體與奈米碳館電晶體的研究有所貢獻。

In the beginning of the New Age, the development of technology was more rapid than the other ages, specifically the semiconductor technology. Today, nonstop scale-down devices are approaching the limit of thermodynamics. It implies that researchers need to search new transistors which have innovative structure. These innovative transistors could replace MOS-transistors, like MOS replaced vacuum tubes. The study of electron transport through single molecules has evolved thanks to C. Joachim et al, who measured the current through C60[1], and M. A. Reed et al who fabricated molecule that are suspended on metal contacts[2]. In the following year, first carbon nanotube field-effect transistors (CNTFETs) had been fabricated [3][4]. Therefore, the molecular transistor is one among several of the next generation transistors. At the same time theoretical efforts have been made to describe and understand the experiments. Actually, theoretical and experimental results had showed errors. Furthermore, some theories which talk about transport have provoked a great deal of controversy. Consequently, if researchers want to improve nanotransistors, they would need to understand the transport theory. In this thesis, I have simulated the properties of hydrogen molecular junction and CNTFETs ab initio. In addition to this, I attempt to understood their transport mechanism.

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