多通道單分子導線的量子輸送現象

Quantum Transport Through Individual Molecular Wires With Multiple Pathways

許良彥(Liang-Yan Hsu)

指導教授 ： 金必耀

國立臺灣大學/理學院/化學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.03115

摘要

近十年來，由於分子自我組裝和顯微技術的進步，單分子電子學在理論跟實驗上獲得許多進展。本篇論文主要是探討多通道分子導線的量子輸送現象，內容主要包含兩部份，第一部分是利用自由電子網路模型(free electron network model)，探討benzenedithiol分子在不同連結方式下的量子輸送現象，包含著名的共振(resonance)與干涉(interference)效應；再利用非平衡格林函數法(non-equilibrium Green's function)和緊束縛近似法 (tight-binding approximation)，比較兩種模型的相似之處。第二部份則是利用非平衡格林函數法和拓展的休克爾模型(extended Hückel model)探討三核線型金屬串(M3(μ3-dpa)4(NCS)2 (dpa=2,2'-dipyridylamide), M = Co, Ni, and Cr. )的穿透函數，導電度以及電壓電流特徵圖；從理論計算，半定量分析法，以及假想分子實驗三種不同的方法，我們發現三核線型金屬串分子中間的金屬原子以及他們的dz2軌域是單分子導電中最主要的機制。

關鍵字

量子輸送 ； 分子電子學 ； 導電度 ； 非平衡格林函數法

並列摘要

During last decade, the investigations of single molecular electronics receive much attention both experimentally and theoretically because of its potential applications to nanoelectronic devices. Many interesting behaviors such as non-linear I-V characteristics and negative differential resistance (NDR) have been observed experimentally for electron transport in a single molecular wire. More complicated manifestation of many-body effects such as the coulomb blockade and the Kondo effect in the molecular wires provides a new impetus to study the role of electron correlations in the quantum transport. In our study, we utilize two different methods including the free-electron network model and the non equilibrium Green's function with the extended Hückel theory to discuss the behavior of electron transport in a single molecular wire.

In chapter one, quantum coherent transport through a multiply-connected network is investigated by the free electron network model (FENM). Within this model, we study π-conjugated molecules such as benzenedithiol (BDT) in order to understand the influence of nontrivial topological structures on the transport behavior. The analytical solutions for transmission functions and I-V characteristics of simplest networked conjugated molecules are derived. Moreover, novel quantum effects such as resonance and interference are clearly revealed in this approach. We have also compared our FENM approach with the non-equilibrium Green's function (NEGF) method within tight-binding calculation.

In chapter two, the Non-Equilibrium Green's Function (NEGF) method and the extended Hückel theory (the NEGF EHT) are employed to study transmission functions and conductance of linear trimetal complexes, M3(μ3-dpa)4(NCS 2 (dpa=2,2'-dipyridylamide), M = Co, Ni, and Cr. The trend and order of magnitudes of the resulting conductance based on the independent electron approach are in good agreement with the experimental observations. Moreover, the effects of ligands on the conduction pathways of molecular wires are investigated comparatively by studying a family of hypothetical complexes coordinated with different ligands. We have found the molecular orbital consisted of the out of-phase combination of central dz2 orbitals in metal strings plays a major role in electron transport of linear trimetal complexes.

並列關鍵字

quantum transport ； molecular electronics ； conductance

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