掃描式穿隧顯微術的十一核鎳金屬串錯合物電性結構與電子傳遞機制之研究

本論文使用超高真空掃描穿隧顯微術(ultrahigh-vacuum scanning tunneling microscopy, UHV-STM)，研究Au(111)單晶表面上的長鏈狀十ㄧ核鎳金屬串錯合物[Ni11(bnatpya)4(NCS)2](PF6)4分子結構與單分子電性表現。Au(111)在真空腔體內退火處理產生表面重排結構(reconstruction)。十一核鎳金屬串分子則溶於甲醇中滴至Au(111)表面上。在78 K的UHV-STM的實驗環境中，觀察金屬串分子在表面上的STM影像結構，可發現分子呈現橢圓狀電子雲結構，由縱寬分析得到單分子長寬尺寸與高度資訊。使用掃描穿隧能譜(scanning tunneling spectroscopy, STS)分析金屬串分子的dI/dV能譜，顯示分子在Au(111)上的能態密度(density of state)隨能量呈現特徵峰分佈，除了金表面態(surface state)因分子耦合產生位移以外，在-1.20 eV、+0.82 eV處較高的能態密度，對照紫外線-可見光吸收光譜(UV-visible spectroscopy)，可指認此能量差為分子在能態密度波峰的HOMO-LUMO能階間隔。利用STM探針與分子末端硫氰基接觸，可使分子抬離表面，形成頭基接合電極的單分子電路。執行分子抬升同時記錄導電值對距離的關係(G-Z圖)，推算金屬串單分子導電值。量測十一核金屬串錯合物的單分子導電值相較於室溫量測結果稍高，對於分子導電值在變溫環境下的熱活化傳遞機制預測有差異，其中設定偏壓與末端硫氰基與電極的耦合作用力等效應，對於解釋量測導電值是重要參考。

關鍵字

掃描穿隧顯微術；掃描穿隧能譜； Au(111) ；多核金屬串錯合物；能態密度；單分子導電值

並列摘要

This thesis presents the molecular structures and the single-molecular conductivity of a long-chain-shaped polynuclear metal string complex [Ni11(bnatpya)4(NCS)2]4+ (Ni11) on the single crystal surface of Au(111) by ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). The Au(111) surface was prepared by annealing to generate the reconstruction. Ni11 was dissolved in methanol and deposited on Au(111). At 78 K UHV-STM, the STM images showed oblate-shaped structures of Ni11 on Au(111). From the height profiles, single-molecular size of Ni11 could be obtained from the images of topography. Scanning tunneling spectroscopy (STS) indicated density of states (DOS) of Ni11 by dI/dV spectra exhibiting the distributions of peaks at -1.20 eV and +0.82 eV, excluding the shifting peak of gold surface state. Compared with ultraviolet-visible spectroscopy, the energy difference acquired from dI/dV spectra could be identified with aligned energy of HOMO-LUMO gap. The STM probe was able to contact the ending thiocyanate group of Ni11, which would contribute to the single-molecular circuit while the Ni11 molecules were lifted from the surface. Conductance-to-distance graph was measured in the process of lifting to calculate the single-molecular conductance. The measured conductance at 78 K was slightly higher than the previous results at room temperature. Despite the discrepancy from heat-dependent mechanism of electron tunneling, this is an important reference to further discuss on molecular conductance if considering the effects of setpoint bias as well as coupling interactions between ending thiocyanate group and the electrodes.

並列關鍵字

Scanning Tunneling Microscopy ； Scanning Tunneling Spectroscopy ； Au(111) ； Polynuclear Metallic String Complex ； Density of State ； Single-molecular Conductance