Lehrstuhl für Physikalische Chemie II and Interdisciplinary Center for Molecular Materials, Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen, Germany.
Langmuir. 2010 Jun 15;26(12):9632-9. doi: 10.1021/la100209v.
The adsorption of Ca on electron-irradiated poly(3-hexylthiophene) (P3HT) surfaces at 300 K (E(kin) = 100 eV) has been studied by adsorption microcalorimetry, atomic beam/surface scattering, X-ray photoelectron spectroscopy (XPS), and low-energy He(+) ion scattering spectroscopy (LEIS). The results are compared to previous studies of Ca adsorption on pristine P3HT. The major structural effect of electron irradiation is a substantial increase in the fraction of unsaturated carbon atoms, probably a result of electron-induced hydrogen abstraction from the hexyl chains and formation of new C=C double bonds. No loss of sulfur was observed. The combined XPS, LEIS, and calorimetry data indicate that the reaction and growth behavior of Ca on P3HT surfaces is not significantly affected by this electron damage, apart from an increased sticking probability at low coverages. The sticking probability of Ca on the irradiated P3HT is initially 0.63, compared to 0.36 on the pristine surface. It increases with coverage, approaching unity between 4 and 5 ML. The heat of adsorption stays nearly constant at 405 kJ/mol up to a coverage of 0.6 ML, which is ascribed to Ca diffusing below the surface and forming CaS clusters by abstraction of sulfur from the thiophene rings, based on XPS and LEIS data. The heat of adsorption then decreases gradually until it reaches the heat of sublimation of bulk Ca, 178 kJ/mol, by 4 ML; this is attributed to the formation of 3D Ca islands on top of the polymer, which eventually coalesce into a continuous Ca film by 11 ML. The heat of reaction versus coverage and the ultimate depth up to which the Ca atoms react with the polymer thiophene groups (approximately 3 nm) are nearly independent of electron damage, except for a difference in the heat of adsorption below 0.1 ML associated with defects or impurities. The increase in initial sticking probability caused by electron damage is attributed to stronger bonding of Ca adatoms to unsaturated versus saturated hydrocarbons. These very weakly held Ca adatoms are transient precursors to the two reactions which dominate the measured heat of adsorption (reaction with thiophene units and Ca cluster formation), but they can also desorb in this three-path kinetic competition. Mass spectrometer data show that these precursors have longer surface residence times on the electron-damaged surface.
在 300 K（E(kin) = 100 eV）下，通过吸附量热法、原子束/表面散射、X 射线光电子能谱（XPS）和低能氦（+）离子散射光谱（LEIS）研究了 Ca 在电子辐照聚（3-己基噻吩）（P3HT）表面上的吸附。将结果与之前对原始 P3HT 上 Ca 吸附的研究进行了比较。电子辐照的主要结构效应是不饱和碳原子的分数大幅增加，可能是电子诱导从己基链中提取氢并形成新的 C=C 双键的结果。未观察到硫的损失。XPS、LEIS 和量热法数据的综合结果表明，除了在低覆盖率下的吸附增加外，Ca 在 P3HT 表面上的反应和生长行为不受这种电子损伤的显著影响。在电子辐照的 P3HT 上，Ca 的吸附初始时的吸附几率为 0.63，而在原始表面上为 0.36。它随着覆盖度的增加而增加，在 4 到 5 ML 之间接近 1。吸附热在 0.6 ML 之前几乎保持在 405 kJ/mol 不变，这归因于 Ca 扩散到表面以下并通过从噻吩环中提取硫形成 CaS 团簇，这是基于 XPS 和 LEIS 数据。然后，吸附热逐渐降低，直到在 4 ML 时达到块状 Ca 的升华热，178 kJ/mol；这归因于聚合物顶部形成 3D Ca 岛，这些岛最终在 11 ML 时合并成连续的 Ca 膜。反应热与覆盖率以及 Ca 原子与聚合物噻吩基团反应的最终深度（约 3nm）几乎与电子损伤无关，除了与缺陷或杂质相关的 0.1 ML 以下的吸附热的差异。电子损伤引起的初始吸附几率增加归因于 Ca adatoms 与不饱和烃与饱和烃的键合更强。这些非常弱的 Ca adatoms是两种主导测量吸附热的反应（与噻吩单元的反应和 Ca 团簇的形成）的瞬态前体，但它们也可以在这种三路径动力学竞争中解吸。质谱数据表明，这些前体在电子损伤表面上的表面停留时间更长。
