Covalent and Hydrogen Bonding in Adsorption of Alanine Molecules on Si(111)7 × 7.
Covalent and Hydrogen Bonding in Adsorption of Alanine Molecules on Si(111)7 × 7.
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Si(111)7 × 7 上丙氨酸分子吸附中的共价键和氢键。
DOI：
10.1021/acs.langmuir.1c00283
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
K. Leung
中科院分区：
文献类型：
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作者：
L. Zhang;H. Farkhondeh;F. Rahsepar;A. Chatterjee;K. Leung
结合扫描隧道显微镜(STM)和X射线光电子能谱(XPS)的计算结果，结合密度泛函理论(DFT)的从头计算方法，确定了丙氨酸在Si(111)7×7表面的分子吸附组态和特定的界面化学。N-1S区的XPS谱表明丙氨酸分子以N-Si共价键结合在7×7表面，而STM成像显示丙氨酸的这种N-H解离吸附发生在相邻的Si吸附原子-重原子对上，脱氢的丙氨酸部分和解离的H原子分别占据了硅吸附原子和重原子位置。在+2V以上的样品偏压下，脱氢丙氨酸呈现为明亮的圆形突起，略偏离硅吸附原子中心，并在二聚体壁上向相反的硅吸附原子倾斜。这种偏心特性可以归因于脱氢丙氨酸的富电子的羰基O与最近的贫电子的Si吸附原子之间穿过二聚体的静电吸引。我们的密度泛函计算还表明，O-H解离吸附形成的单齿O-Si成键构型比实验观察到的N-Si成键构型在热力学上更有利，这表明界面解离吸附反应是一个动力学控制的过程，而不是热力学驱动的过程。第二层(过渡层)中的丙氨酸分子通过N···HO氢键与第一层(界面层)中的丙氨酸分子结合，这与401.0 eV下N-1S特征的存在是一致的。在STM中也观察到第一层脱氢丙氨酸上有一个与脱氢丙氨酸氢键相连的丙氨酸分子，这是一个更明亮和更大的突起，接近脱氢第一层丙氨酸中自由羟基的预期位置。在室温下不能得到厚实的两性丙氨酸薄膜，这可能是由于甲基引起的空间位阻。
Molecular adsorption bonding configurations and specific interfacial chemistry of alanine on Si(111)7 × 7 have been determined by combining the results from scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) with ab initio calculations based on the density functional theory (DFT). XPS spectra of the N 1s region show that alanine molecules bind to the 7 × 7 surface by N-Si covalent bonding, while STM imaging reveals that such N-H dissociative adsorption of alanine occurs on an adjacent Si adatom-restatom pair, with the dehydrogenated alanine moiety and dissociated H atom occupying the Si adatom and restatom sites, respectively. At a sample bias above +2 V, the dehydrogenated alanine appears as a bright round protrusion, slightly off-center from a Si adatom site and leaning toward the opposite Si adatom across the dimer wall. The off-center character can be attributed to an electrostatic attraction between the electron-rich carbonyl O of the dehydrogenated alanine and electron-deficient nearest Si adatom across the dimer wall. Our DFT calculation also shows that the monodentate O-Si bonding configuration resulting from O-H dissociative adsorption is more thermodynamically favorable than the experimentally observed N-Si bonding configuration, suggesting that the interfacial dissociative adsorption reaction is a kinetically controlled rather than a thermodynamically driven process. Alanine molecules in the second adlayer (transitional layer) are found to attach to those in the first adlayer (interfacial layer) by N···HO hydrogen bonding, as supported by the presence of the N 1s feature at 401.0 eV. An alanine molecule H-bonded to a dehydrogenated alanine in the first adlayer has also been observed in STM as a brighter and larger protrusion close to the expected location of the free OH group in the dehydrogenated first-adlayer alanine. No thick zwitterionic alanine film can be obtained at room temperature possibly due to steric constraint caused by the methyl group.