掃描穿隧顯微術之電場效應：液晶單層膜組裝及富勒烯寡聚反應

Abstract

本論文是討論以電場驅動富勒烯寡聚化與液晶分子單層組裝，在富勒烯寡聚化的研究是以新穎的合成策略進行表面合成，透過苯三甲酸(trimesic acid, TMA)在高定向熱解石墨(highly oriented pyrolytic graphite, HOPG)表面自組裝形成多孔洞結構，以提供孔洞容納客體分子富勒烯(C84)，透過主客作用力捕捉客體分子。利用纖維紙以毛細現象吸取HOPG表面含有主客體分子的溶液，強迫富勒烯分子進入主體模板孔洞形成單層膜。藉由掃描穿隧顯微鏡(scanning tunneling microscope, STM)在HOPG表面與探針之間施加電場脈衝，誘導富勒烯單層膜進行[2+2]環化反應使富勒烯寡聚化。透過去除溶劑增加富勒烯分子在孔洞模板的密度形成富勒烯單層膜，富勒烯的排列方式與下層TMA模板的孔洞排列方式相同。單層膜寡聚化後富勒烯分子間距從1.7 nm縮短為1.4 nm。在掃描穿隧能譜觀察到寡聚化後LUMO半高寬由0.5增至0.6 eV，推測為寡聚化後增加分子間作用力，相鄰分子的分子能態重疊使能階變寬。在質譜量測中增加富勒烯二聚體及三聚體的訊號。富勒烯透過模板輔助形成單層膜進行反應的概念類似酵素催化反應，此研究證明模板孔洞可作為奈米尺度的化學反應槽概念，這是以往的文獻中沒有相關的例子。 關於電場驅動液晶分子單層組裝的研究，我們利用盤狀液晶分子dibenzo[a,c]phenazine的衍生物，是具有永久性平面方向分子內偶極的分子，在液固界面環境下可透過電場控制單層分子組裝並且改變電子傳遞效率。我們對於單層分子級的盤狀液晶分子提出控制晶相與電性量測的方法。未來有助於分析有機電子元件的缺陷。

The formation of covalent bonds between elementary units transforms the dimensions of building blocks and is envisaged an important bottom-up approach for the fabrication of nanomaterials and nanodevices. To facilitate bond formation, close proximity between reactants is required. In this research presentation, we present a template-assisted method in conjunction with a concentration-enrichment skill to obtain a fullerene monolayer for the subsequent fullerene oligomerization. The template was a two-dimensional porous framework, comprised of 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA), in which the void space was able to accommodate fullerenes. Fullerene monolayers were subjected to a 10-μsec pulse of 4 volts or higher via an STM (scanning tunneling microscope) tip. STM images showed that the apparent nearest neighboring spacing was reduced from 1.7 nm to 1.4 nm. STS (scanning tunneling spectroscopy) revealed an increased LUMO FWHM from 0.5 eV to 0.6 eV, suggesting that the oligomerization took place and the fullerene of molecular states overlaped with those of neighboring molecules. MS spectra exhibited signals of oligomer dimer and trimer in m/z 2000 to 4000. The mechanism is ascribed to a [2+2] cycloaddition reaction. The other part, we studied a discotic liquid crystalline (DLC) of dibenzo[a,c]phenazine at the liquid-solid interface using scanning tunneling microscopy/spectroscopy, by which we show how to tailor the DLC assemblies and in turn their electron-transfer efficiency. We presents an alternative method for phase control and electronic measurements for DLCs, especially at the microscopic level.