Self-assembled monolayers (SAMs) of perfluoroalkanethiols [CF3(CF2)xCH2CH2SH (x = 3, 5, 7, and 9)] on gold were characterized by x-ray photoelectron spectroscopy (XPS), near edge x-ray absorption fine structure (NEXAFS), and static time-of-flight secondary ion mass spectrometry (ToF-SIMS). Perfluoroalkanethiols of several chain lengths were synthesized using a known hydride reduction method for transforming commercially available perfluoroalkyliodides to corresponding perfluoroalkanethiols. This strategy provides improved product yields compared to other known routes based on hydrolysis from the common thioacetyl perfluoroalkyl intermediate. Angle-dependent XPS analysis revealed that CF3(CF2)xCH2CH2SH (x = 5, 7, and 9; F6, F8, and F10, respectively) SAMs on gold exhibited significant enrichment of the terminal CF3 group at the outer monolayer surface with the sulfur present as a metal-bound thiolate located at the monolayer-gold interface. XPS of the CF3(CF2)3CH2CH2SH (F4) monolayer revealed a thin film with a significant (>50%) amount of hydrocarbon contamination consistent with poorly organized monolayers, while the longest thiol (F10) showed XPS signals attributed to substantial ordering and anisotropy. ToF-SIMS spectra from all four SAMs contained molecular ions representative of the particular perfluorinated thiol used to prepare the monolayer. NEXAFS methods were used to determine degrees of ordering and average tilt for molecules comprising monolayers. The SAMs prepared from the longest (F10) thiols exhibited the highest degree of ordering with the molecular axis nearly perpendicular to the gold surface. The degree of ordering decreased significantly with decreasing length of the perfluorocarbon tail.

中文翻译：

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金表面全氟烷硫醇分子顺序的定量评价。

通过 X 射线光电子能谱 (XPS)、近边 X 射线吸收精细结构表征金上全氟烷硫醇 [CF3(CF2)xCH2CH2SH（x = 3、5、7 和 9）] 的自组装单分子层（SAM） (NEXAFS) 和静态飞行时间二次离子质谱 (ToF-SIMS)。使用已知的氢化物还原方法合成了几种链长的全氟烷硫醇，用于将市售的全氟烷基碘化物转化为相应的全氟烷硫醇。与基于普通硫代乙酰基全氟烷基中间体水解的其他已知路线相比，该策略提供了更高的产品收率。角度依赖性 XPS 分析显示 CF3(CF2)xCH2CH2SH（x = 5、7 和 9；F6、F8 和 F10，分别）金上的 SAM 在外单层表面表现出末端 CF3 基团的显着富集，硫作为金属结合的硫醇盐存在于单层-金界面。CF3(CF2)3CH2CH2SH (F4) 单层的 XPS 显示薄膜具有大量 (>50%) 的碳氢化合物污染，与组织不良的单层一致，而最长的硫醇 (F10) 显示 XPS 信号归因于大量有序和各向异性. 所有四个 SAM 的 ToF-SIMS 光谱都包含代表用于制备单层的特定全氟化硫醇的分子离子。NEXAFS 方法用于确定包含单层的分子的有序度和平均倾斜度。由最长 (F10) 硫醇制备的 SAM 表现出最高程度的有序性，分子轴几乎垂直于金表面。随着全氟化碳尾部长度的减少，有序度显着降低。