碳六十分子於銅金屬表面經表面重構之量子傳輸特性

Abstract

本篇論文主要分為兩個部分，第一個部分我們探討單分子層吸附在金屬表面上時，其介面重構(reconstruct)與無重構(unreconstruct)對分子/金屬介面之導電行為造成的影響。當一個單層的分子層(如C60)吸附在金屬(如Cu)表面時，由於分子軌域與表面原子間存在交互作用，使得電子結構發生變化，所以在分子/金屬介面上，其電荷轉移現象非常複雜，而細微的介面結構足以影響分子電子元件的傳輸性質，進而造成龐大的宏觀現象。 本篇論文主要是研究當單層C60分子吸附於Cu(111)金屬表面上時，其介面重構與無重構對於分子/金屬介面電導性所造成的影響。 而在理論架構的部份，我們以密度泛函理論(Density Function Theory)結合非平衡格林函數(Non-Equilibrium Green's Function)的NANODCAL模擬軟體為主，透過第一原理運算方法計算分子金屬介面的傳輸性質。 計算結果顯示，當C60/ Cu(111)介面有重構時，其傳輸性相較於無重構介面將會大幅提升。而第二個部分我們計算磁性雜質於尖端電極之間的Wannier函數，我們磁性雜質選擇Co原子，電極選擇Cu(111)。這樣的系統被預期具有Kondo效應，此論文中所計算的Wannier函數，將可被用於日後此Kondo系統的量子傳輸計算。

This thesis contains two parts. In the first part, we explore how the conducting behavior depends on the molecule-metal interface, where the interfacial metal surface can undergo reconstruction in the presence of the molecules. The interaction between the molecular orbitals and surface atoms alters the electronic structures, and consequently the charge transfer of the molecule-metal interface is very complex. The details of the microscopic interface structures can affect the transport properties of molecular-electronics devices, which may cause an enormous macroscopic consquence. This thesis is focused on the effect of surface-reconstruction on the conducting behavior of the molecule-electrode contact, where the molecules and the electrodes studied here are C60 and Cu(111), respectively. We perform the first-principles quantum transport calculations by the computer code NANODCAL, which combines density function theory (DFT) and the Keldysh non-equilibrium Green's function (NEGF). Our calculations show that the conductance is enhance significantly when the molecule-metal interface undergoes a reconstruction. In the second part, we calculate the Wannier functions of a magnetic impureity in between two atomic-scale electrodes, where the impurity and electrodes are chosen to be Co and Cu(111). Such an impureity-electron complex is expected to exhibit a Kondo effect. The calculated Wannier functions are key quantities of future quantum transport calculations of such Kondo systems.