Seo Dongjin, Han Jin Wook, Kim Hongki, Kim Yeon O, Sung Hyun Sun, Kaizu Riko, Latag Glenn Villena, Hayashi Tomohiro, Lee Nam-Suk, Noh Jaegeun
Department of Chemistry, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea.
Department of Materials Science and Engineering, School of Materials and Chemical Technology, Institute of Science Tokyo, Yokohama 226-8502, Kanagawa, Japan.
Int J Mol Sci. 2024 Dec 27;26(1):160. doi: 10.3390/ijms26010160.
The effect of solution pH on the formation and surface structure of 2-pyrazinethiolate (2-PyzS) self-assembled monolayers (SAMs) formed by the adsorption of 2-mercaptopyrazine (2-PyzSH) on Au(111) was investigated using scanning tunneling microscopy (STM) and X-ray photoelectron microscopy (XPS). Molecular-scale STM observations clearly revealed that 2-PyzS SAMs at pH 2 had a short-range ordered phase of (2√3 × √21)R30° structure with a standing-up adsorption structure. However, 2-PyzS SAMs at pH 8 had a very unique long-range ordered phase, showing a "ladder-like molecular arrangement" with bright repeating rows. This ordered phase was assigned to the (3 × √37)R43° structure, consisting of two different adsorption structures: standing-up and tilted adsorption structures. The average arial density of 2-PyzS SAMs on Au(111) at pH 8 was calculated to be 49.47 Å/molecule, which is 1.52 times more loosely packed compared to the SAMs at pH 2 with 32.55 Å/molecule. XPS measurements showed that 2-PyzS SAMs at pH 2 and pH 8 were mainly formed through chemical interactions between the sulfur anchoring group and the Au(111) substrates. The proposed structural models of packing structures for 2-PyzS SAMs on Au(111) at different pHs are well supported by the XPS results. The results of this study will provide new insights into the formation, surface structure, and molecular orientation of SAMs by N-heteroaromatic thiols with pyrazine molecular backbone on Au(111) at the molecular level.
利用扫描隧道显微镜（STM）和X射线光电子显微镜（XPS）研究了溶液pH值对2-巯基吡嗪（2-PyzSH）吸附在Au(111)上形成的2-吡嗪硫醇盐（2-PyzS）自组装单分子层（SAMs）的形成及表面结构的影响。分子尺度的STM观察清楚地表明，pH值为2时的2-PyzS SAMs具有(2√3 × √21)R30°结构的短程有序相，吸附结构为直立式。然而，pH值为8时的2-PyzS SAMs具有非常独特的长程有序相，呈现出带有明亮重复行的“梯状分子排列”。该有序相被确定为(3 × √37)R43°结构，由两种不同的吸附结构组成：直立式和倾斜式吸附结构。计算得出pH值为8时Au(111)上2-PyzS SAMs的平均面密度为49.47 Å/分子，与pH值为2时面密度为32.55 Å/分子的SAMs相比，堆积更松散，是其1.52倍。XPS测量表明，pH值为2和8时的2-PyzS SAMs主要通过硫锚定基团与Au(111)基底之间的化学相互作用形成。XPS结果很好地支持了在不同pH值下Au(111)上2-PyzS SAMs堆积结构的 proposed 结构模型。本研究结果将在分子水平上为具有吡嗪分子骨架的N-杂芳族硫醇在Au(111)上形成SAMs的形成、表面结构和分子取向提供新的见解。
