Tafila Technical University, Tafila, Jordan.
Langmuir. 2012 Jul 10;28(27):10192-208. doi: 10.1021/la301601c. Epub 2012 Jun 27.
Self-assembled monolayers (SAMs) of pentafluorobenzenethiol (PFBT) on Au(111) substrates, prepared with different immersion times (ITs) at room temperature, were studied using scanning tunneling microscopy (STM) and infrared reflection-absorption spectroscopy (IRRAS). In the present study, the focus was on several important points of interest in the field of SAMs. First, the gold islands formed upon adsorption of PFBT molecules on the gold surface were monitored at different ITs in terms of their size, density, and shape. After short ITs (5 to 30 min), small gold islands with rounded shape were formed. These gold islands were arranged in a rather regular fashion and found to be quite mobile under the influence of the STM-tip during the scanning. When the IT was increased to 16 h, the results revealed the formation of highly ordered and orientated gold islands with very unusual shapes with straight edges meeting at 60° or 120° running preferentially along the [11(-)0] substrate directions. The density of the gold islands was found to decrease with increasing IT until they almost disappeared from the SAMs prepared after 190 h of IT. On top of the gold islands, the PFBT molecules were found to adopt the closely packed (10√3 × 2) structure. Second, a number of structural defects such as disordered regions at the domain boundaries and dark row(s) of molecules within the ordered domains of the PFBT SAMs were observed at different ITs. The SAMs prepared after 190 h of IT were found to be free of these defects. Third, at low and moderate ITs, a variation in the PFBT molecular contrast was observed. This contrast variation was found to depend mainly on the tunneling parameters. Finally, our results revealed that the organization process of PFBT SAMs is IT-dependent. Consequently, a series of structural phases, namely, α, β, γ, δ, and ε were found. The α-, β-, γ-, and δ-phases were typically accompanied by the ε-phase that appeared on top of gold islands. With increasing IT, the α→β→ γ→δ→ε phase transitions took place. The resulting ε-phase, which covered the entire gold surface after 190 h of IT, yielded well-ordered self-assembled monolayers with large domains having a (10√3 × 2) superlattice structure.
在室温下，通过不同的浸泡时间（IT）制备了五氟苯硫醇（PFBT）在 Au（111）衬底上的自组装单分子层（SAM），并用扫描隧道显微镜（STM）和红外反射吸收光谱（IRRAS）进行了研究。在本研究中，重点关注了 SAM 领域的几个重要问题。首先，在不同的 IT 下，监测了吸附在金表面上的 PFBT 分子形成的金岛的大小、密度和形状。在短的 IT（5 至 30 分钟）后，形成了具有圆形的小金岛。这些金岛以相当规则的方式排列，并发现它们在扫描过程中受到 STM 针尖的影响而非常移动。当 IT 增加到 16 小时时，结果显示形成了具有非常不寻常形状的高度有序和取向的金岛，其边缘呈 60°或 120°的直线相交，沿[11（-）0]衬底方向优先延伸。金岛的密度随着 IT 的增加而降低，直到在 IT 后 190 小时制备的 SAM 中几乎消失。在金岛的顶部，PFBT 分子被发现采用紧密堆积（10√3×2）结构。其次，在不同的 IT 下观察到了一些结构缺陷，例如畴边界处的无序区域和 PFBT SAM 中有序域内的暗行分子。在 IT 后 190 小时制备的 SAM 中未发现这些缺陷。第三，在低和中等 IT 下，观察到 PFBT 分子对比度的变化。发现这种对比度变化主要取决于隧道参数。最后，我们的结果表明，PFBT SAM 的组织过程取决于 IT。因此，发现了一系列结构相，即α、β、γ、δ和ε。α-、β-、γ-和δ-相通常伴随着出现在金岛顶部的ε-相。随着 IT 的增加，发生了α→β→γ→δ→ε 相转变。在 IT 后 190 小时，覆盖整个金表面的所得的ε 相产生了具有大畴的有序自组装单层，具有（10√3×2）超晶格结构。
