Flucto-Order Functions Research Team, RIKEN-HYU Collaboration Research Center, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
J Colloid Interface Sci. 2013 Mar 15;394:522-9. doi: 10.1016/j.jcis.2012.12.035. Epub 2012 Dec 28.
Scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) were used to examine the surface structure and adsorption conditions of hexanethiol (HT) and cyclohexanethiol (CHT) self-assembled monolayers (SAMs) on Au(111) as a function of storage period in ultrahigh vacuum (UHV) conditions of 3×10(-7) Pa at room temperature (RT). STM imaging revealed that after storage for 7 days, HT SAMs underwent phase transitions from c(4×2) phase to low coverage 4×√3 phase. This transition is due to a structural rearrangement of hexanethiolates that results from the spontaneous desorption of chemisorbed HT molecules on Au(111) surface. XPS measurements showed approximately 28% reduction in sulfur coverage, which indicates desorption of hexanethiolates from the surfaces. Contrary to HT SAMs, the structural order of CHT SAMs with (5×2√3)R35° phase completely disappeared after storage for 3 or 7 days. XPS results show desorption of more than 80% of the cyclohexanethiolates, even after storage for 3 days. We found that spontaneous desorption of CHT molecules on Au(111) in UHV at RT occurred quickly, whereas spontaneous desorption of HT molecules was much slower. Thermal desorption spectroscopy (TDS) results suggest CHT SAMs in UHV at RT can desorb more efficiently than HT SAMs due to formation of thiol desorption fragments that result from chemical reactions between surface hydrogen atoms and thiolates on Au(111) surfaces. This study clearly demonstrated that organic thiols chemisorbed on gold surfaces are desorbed spontaneously in UHV at RT and van der Waals interactions play an important role in determining the structural stability of thiolate SAMs in UHV.
扫描隧道显微镜（STM）和 X 射线光电子能谱（XPS）被用于研究十六硫醇（HT）和环己硫醇（CHT）自组装单层（SAM）在 Au(111)表面的吸附状态和表面结构，实验是在室温（RT）和超高真空（UHV）条件下（3×10(-7) Pa）进行的，存储时间为 7 天。STM 成像表明，在储存 7 天后，HT SAM 经历了从 c(4×2)相到低覆盖度 4×√3 相的相变。这种转变是由于十六硫醇盐的结构重排引起的，它是由 Au(111)表面上化学吸附的 HT 分子的自发脱附引起的。XPS 测量表明硫覆盖率约减少了 28%，这表明硫醇盐从表面上脱附。与 HT SAM 相反，具有（5×2√3）R35°相的 CHT SAM 的结构有序性在储存 3 或 7 天后完全消失。XPS 结果表明，即使在储存 3 天后，也有超过 80%的环己硫醇盐脱附。我们发现，在 RT 的 UHV 中，CHT 分子在 Au(111)表面上的自发脱附很快发生，而 HT 分子的自发脱附要慢得多。热脱附光谱（TDS）结果表明，由于表面氢原子和 Au(111)表面上的硫醇盐之间的化学反应形成了硫脱附碎片，因此在 RT 的 UHV 中，CHT SAM 可以比 HT SAM 更有效地脱附。这项研究清楚地表明，在 RT 的 UHV 中，化学吸附在金表面上的有机硫醇会自发脱附，范德华相互作用在确定硫醇 SAM 在 UHV 中的结构稳定性方面起着重要作用。
