Berg Iris, Mondal Rajarshi, Sims Joshua M, Ben-Tzvi Tzipora, Lahav Linoy, Friedman Barak, Michel Carine, Nairoukh Zackaria, Gross Elad
Institute of Chemistry, The Hebrew University, Jerusalem 91904, Israel.
The Center for Nanoscience and Nanotechnology, The Hebrew University, Jerusalem 91904, Israel.
ACS Appl Mater Interfaces. 2024 Nov 27;16(47):65469-65479. doi: 10.1021/acsami.4c12514. Epub 2024 Nov 18.
Fluorinated self-assembled monolayers (SAMs) have been utilized in a variety of applications such as transistors and optoelectronic devices. However, in most SAMs the fluorinated groups could not be positioned in high proximity to the surface due to steric effects. This limitation hinders the direct analysis of the impact of the fluorination level on surface properties. Herein, fluorinated aromatic N-heterocyclic carbenes (NHCs), with 1-5 fluorine atoms, were self-assembled on a gold substrate. These NHCs enabled the positioning of fluorinated groups in high proximity to the metal surface to identify the influence of the fluorination level on surface properties. Experimental measurements and theoretical calculations identified that all fluorinated NHCs formed SAMs and adopted a flat-lying adsorption configuration while anchored to the metal surface via Au adatom. A higher fluorination level induced a stronger interaction of the fluorinated side groups with the Au surface. The stronger interaction and surface proximity of the fluorinated side groups deteriorated the overall binding energy of the NHC due to the less-optimized adsorption geometry of the carbene carbon. Ultraviolet photoelectron spectroscopy measurements revealed that fluorinated NHC monolayers lowered the surface work function by up to 1 eV and induced an increase of 15-20° in the water contact angle. The impact on surface properties did not vary according to the fluorination level of NHCs, and similar values were measured for NHC with 1-5 fluorine atoms. It is therefore identified that dominant adsorbate-substrate interactions between the fluorinated side groups and the Au surface quenched the distinct impact of the fluorination level on surface functionality.
氟化自组装单分子层（SAMs）已被应用于各种领域，如晶体管和光电器件。然而，在大多数SAMs中，由于空间效应，氟化基团无法紧密靠近表面。这一限制阻碍了对氟化水平对表面性质影响的直接分析。在此，含有1 - 5个氟原子的氟化芳香族氮杂环卡宾（NHCs）在金基底上进行了自组装。这些NHCs能够使氟化基团紧密靠近金属表面，以确定氟化水平对表面性质的影响。实验测量和理论计算表明，所有氟化NHCs均形成了SAMs，并通过金吸附原子锚定在金属表面时采用平躺吸附构型。较高的氟化水平导致氟化侧基与金表面的相互作用更强。由于卡宾碳的吸附几何结构不太优化，氟化侧基更强的相互作用和表面接近度降低了NHC的整体结合能。紫外光电子能谱测量表明，氟化NHC单分子层使表面功函数降低了高达1 eV，并使水接触角增加了15 - 20°。对表面性质的影响并不随NHCs的氟化水平而变化，对于含有1 - 5个氟原子的NHC测量得到了相似的值。因此可以确定，氟化侧基与金表面之间主要的吸附质 - 底物相互作用消除了氟化水平对表面功能的明显影响。
