| 摘要: | 噻吩及其衍生物可廣泛用於製作光電材料及元件，這些分子在金電極上的空
間結構和吸附位向會影響兩者之間的電荷傳輸，進而影響到發光二極體、有機
薄膜電晶體(OTFTs)的性能。同時，有機相或水相中通過陽極氧化可製備聚噻
吩，此材料已被廣泛的應用於光電的研究，我們利用循環伏安法和掃描式電子
穿隧顯微鏡，來研究噻吩衍生物在金(111)電極上的吸附結構與氧化聚合。
金（111）電極上吸附的三噻吩（TT）的結果，顯示 TT 分子與金載體之間
的相互作用、電位、陰離子對 TT 吸附結構和氧化的影響。在硫酸中，電位往
正移動後， TT 分子和硫酸氫根陰離子的覆蓋率增加。STM 顯示在 0.5 V 時產
生(19 6) - TT 的結構，但其二維結構及其吸附位向會隨著電位而改變。相比
之下，在過氯酸中，STM 顯示無序的 TT 結構，這種對比也顯現於 CV 結果，
由此推論 TT 與硫酸氫根有吸引的作用力。STM 也顯示 TT 單體在金(111)電極
上的氧化聚合，電解液的 pH 值對 TT 氧化聚合反應有重要的影響。在 pH5 硫
酸鹽中，可以產生較長(~200 Å)的聚噻吩分子鍊，呈現直線或曲線狀，這和分
子鏈中噻吩的反式和順式構型有關。在 pH 1 的硫酸中，聚噻吩只有幾十埃。
在 0.1 M 過氯酸和硫酸中，DNT-Ph 分子形成有序的吸附分子膜。電位對
DNT-Ph 的吸附結構有極大影響。有序 DNT-Ph 結構僅在-0.1 和 0.4 V(Ag/AgCl)
之間，在金的重排相上觀察到。在-0.15 V， DNT-Ph 從金電極上脫附。在正電
位，金表面逐漸變成 1 1，有序的 DNT-Ph 結構被破壞，分子變得更加緊密並
重新排列。DNT-Ph 主要以其分子平面平行於金電極表面的方式吸附，STM 圖
像中揭示了 DNT-Ph 分子結構的細節，連接噻吩的單鍵，因旋轉產生了 DNT Ph 吸附分子的兩種幾何異構物。
為更進一步了解分子結構對吸附的影響，STM 也用來研究 Ph(DTP)2 分子，
發現在過氯酸和硫酸中，重排以及 1X1 相都有整齊的吸附結構，在重排線上的
吸附比在 1X1 上快速且緊密，在硫酸中發現 Ph(DTP)2 在負電位，會於重排線上
產生二層分子結構。
;Thiophene and its derivatives have been important constituents in the study of
organic semiconductors and solar cell research. Their spatial structures and adsorption
configuration can affect the charge transport between molecules and gold electrode,
which is an important process in the operation of light-emitting diodes, organic thin film transistors (OTFTs), etc. Polythiophenes have been prepared by anodization in
organic or aqueous phases containing thiophenes or oligothiophenes. Cyclic
voltammetry (CV) and scanning tunneling microscopy (STM) were used to study the
adsorption and polymerization of thiophene and its derivatives on gold (111)
electrode.
First, the adsorption of terthiophene (TT) on the Au (111) electrode was
investigated as a function of potential and anion coadsorption. In H2SO4, we obtained
molecular resolution STM images to show that the pre-deposited TT layer became
more compact with more positive potential. Judged from the STM appearance of TT
admolecule and intermolecular spacing, TT molecule lay horizontally. In contrast, in
perchloric acid, TT admolecules were poorly ordered. This contrast also manifested in
the CV results, showing multiple sharp peaks in H2SO4, but featureless in HClO4.
STM also showed the oxidative polymerization of TT monomers on Au(111)
electrodes, producing ribbon-like oligothiophenes with molecular sizes varying
between 1 and 20 nm in pH 1 and 5 sulfate media. The oligothiophenes could be
linear or curved, which suggests the possible trans and cis configurations of
thiophenes in the molecular chains. High pH value appeared to benefit the formation
of oligothiophenes.
In 0.1 M H2SO4 and HClO4, DNT-Ph molecule was adsorbed in highly ordered
arrays on the reconstructed Au(111). Potential control affected greatly the adsorption
structure of DNT-Ph, as ordered DNT-Ph structures were only observed between −0.1
and 0.4 V. DNT-Ph was desorbed at -0.15 V, whereas the ordered DNT-Ph structures
were destroyed, as Au(111) surface became (1 1) at positive potential. DNT-Ph was
mainly adsorbed with its molecular plane parallel to the surface of the gold electrode.
High resolution STM imaging revealed details in the molecular conformations of
DNT-Ph, as two geometric isomers resulting from rotating the single bond connecting
the thiophene were distinguished by the STM.
In 0.1 M perchloric acid and sulfuric acid, the adsorption of Ph(DTP)2 molecule on
Au(111) electrode was also examined by using in situ STM. Ordered molecular
adlayers were found on the reconstructed and (1 1) phases of the Au(111) electrode
in a wide potential region. The spatial structure of Ph(DTP)2 was formed faster and
more compact on the reconstructed Au(111) than (1 1) phase in sulfuric acid at
negative potential. Local bilayer structure of was observed on the reconstructed lines. |
