有機半導體的非線性光學效應及電子性質

Abstract

本論文主要在探討導電聚合物的三個主題，分別為：雙極子誘發的非線 性光學效應、新的鍵結序參數的影響、以及具有高直流導電性的梯狀共軛 聚合物等。在第一個主題中，我們提出一種可引起強烈非線性光學效應的 新機制，其成因乃由於雙極子受光激發下產生明顯的能階飄移所致。在第 二個主題中，我們發現共軛聚合物的結構除了要考慮眾所周知的二元化序 參數之外，用來描述平均鍵長的序參數則是另一個不可或缺的條件。在最 後的主題中，前面提到的新的序參數也可應用在梯狀共軛聚合物(如結構 最簡單的polyacene )，然後我們計算出在室溫下其直流導電性可高達銅 的十分之一，並且發現其為一沒有能隙的半導體結構。 This thesis focuses on three topics on the basic physics ofconjugated conducting polymers, which are: bipolaron- inducedoptical nonlinearity, a new bond order parameter, and conjugatedladder polymer with high dc conductivity. In the first topic, wepropose a new mechanism for optical nonlinearity taking advantageof the peculiar energy levels shift of bipolarons under optical pumping.In the second topic, we find that the configuration of a conjugated polymer chain is characterized by a new bond-length orderparameter, in addition to the well-known dimerization orderparameter. Based on this new order parameter, we predict, in the last topic, that the simplestladder polymer, polyacene, is a gapless semiconductor, with room temperature dc conductivity as high as one tenth of the conductivity of copper.