Departamento de Química Inorgánica, Analítica y Química Física, INQUIMAE-CONICET, Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria , Pabellón 2, Buenos Aires C1428EHA, Argentina.
Área de Química Física, Departamento de Química, Facultad de Ciencias, Universidad de La Laguna, Instituto de Materiales y Nanotecnología , Avenida Francisco Sánchez, s/n 38200-La Laguna, Tenerife, Spain.
Langmuir. 2017 Sep 26;33(38):9565-9572. doi: 10.1021/acs.langmuir.7b01627. Epub 2017 Sep 13.
4-Mercaptopyridine (4MPy) self-assembled on Au(111) has been studied by in situ electrochemical scanning tunneling microscopy (EC-STM) in HClO, cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). Samples prepared by varying the immersion time at constant concentration named short time (30 s) and long time (3 min) adsorption have been studied. Cyclic voltammetry and XPS showed that the chemistry of the adsorbed molecules does not depend on the adsorption time resulting in a well established chemisorbed thiol self-assembled monolayer on Au(111). EC-STM study of the short time adsorption sample revealed a new self-assembled structure after a cathodic desorption/readsorption sweep, which remains stable only if the potential is kept negative to the Au(111) zero charge potential (E). DFT calculations have shown a correlation between the observed structure and a dense weakly adsorbed phase with a surface coverage of θ = 0.4 and a (5 × √3) lattice configuration. At potentials positive to the E, the weakly adsorbed state becomes unstable, and a different structure is formed due to the chemisorption driven by the electrostatic interaction. Long time adsorption experiments, on the other hand, have shown the typical (5 × √3) structure with θ = 0.2 surface coverage (chemisorbed phase) and are stable over the whole potential range. The difference observed in long time and short time immersion can be explained by the optimization of molecular interactions during the self-assembly process.
4-巯基吡啶（4MPy）在 Au(111)上自组装，通过原位电化学扫描隧道显微镜（EC-STM）、循环伏安法、X 射线光电子能谱（XPS）和密度泛函理论（DFT）进行了研究。通过在恒定浓度下改变浸泡时间制备的样品，分别命名为短时间（30 s）和长时间（3 min）吸附。循环伏安法和 XPS 表明，吸附分子的化学性质不依赖于吸附时间，导致在 Au(111)上形成了稳定的化学吸附硫醇自组装单层。对短时间吸附样品的 EC-STM 研究表明，在阴极去吸附/再吸附扫掠后出现了一种新的自组装结构，如果电势保持在 Au(111)零电荷电势（E）以下，这种结构是稳定的。DFT 计算表明，观察到的结构与一种密集的弱吸附相之间存在相关性，该相的表面覆盖率为θ=0.4，具有（5×√3）晶格构型。在电势正于 E 的情况下，弱吸附态变得不稳定，由于静电相互作用驱动的化学吸附，形成了不同的结构。另一方面，长时间吸附实验显示出典型的（5×√3）结构，表面覆盖率为θ=0.2（化学吸附相），在整个电势范围内都是稳定的。长时间和短时间浸泡观察到的差异可以通过自组装过程中分子相互作用的优化来解释。
