四炔聯苯基苯之單層膜結構與其穿隧能譜：炔基與聯苯之旋轉對分子自組裝的影響

Abstract

電子平行於表面傳遞對於發展奈米級有機分子元件而言是一項重要的議題。自組裝分子可被廣泛用來製備分子元件中的圖案，分子排列後堆疊的位向則決定了電子傳遞的路徑，如何依據元件的需求而設計自組裝分子堆疊的位向來達到有效的電子傳遞則是現今熱門的研究方向。本論文所使用的分子結構主要是以苯環為核心、四組炔基聯苯所構成的1,2,4,5-四炔聯苯基苯(1,2,4,5-tetrakis-(4-dodecyl- 4'-ethynylbiphenyl)benzene, TBPB)雙軸分子，報導新穎的自組裝排列。利用乙炔基連接可旋轉的特徵，使聯苯的旋轉達到face-on與edge-on的位向，透過掃描穿隧顯微術(Scanning Tunneling Microscopy)及掃描穿隧能譜(Scanning Tunneling Spectroscopy)討論分子於表面排列的情形與其電性。

This thesis reports the electronic communications between edge-on biphenyl moieties of biaxial TBPB (1,2,4,5-tetrakis-(4-dodecyl-4'- ethynyl-biphenyl)-benzene) by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Assemblies were realized by taking the advantages of the rotatable ethynyl linkers of the TBPB. Rotatable ethynyl linkers allowed the biphenyl moieties of the TBPB to adopt both face-on and edge-on orientations. We compared the difference of arrangements and electronic properties of TBPB under two concentrations, 0.32 mM and 3.2 microM. Topographic images revealed two kinds of concentrations, 0.32 mM and 3.2 microM., respectively, linear and mesh. Linear motif showed face-on and edge-on orientations because of different heights between biphenyls of TBPB in section profiles. Mesh motif showed only face-on orientation because of the same height of biphenyls of TBPB in section profiles. I–V curves of both motifs are asymmetric with respect to current at zero bias. The asymmetric feature was more significant for the linear motif than the mesh one, resulting in a larger tunneling current and a smaller turn-on voltage for the former. Linear motif were more conductive since edge-on orientations produce an effective electronic coupling between π-stacked biphenyls. Thereby, edge-on biphenyl moieties of biaxial molecule TBPB is the key to the successful assembly of conjugated 1D nanowires.