Contrasting Transport and Electrostatic Properties of Selectively Fluorinated Alkanethiol Monolayers with Embedded Dipoles
Contrasting Transport and Electrostatic Properties of Selectively Fluorinated Alkanethiol Monolayers with Embedded Dipoles
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DOI：
10.1021/acs.jpcc.7b11892
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发表时间：
2018-03-08
影响因子：
3.7
通讯作者：
Hacker, Christina A.
中科院分区：
文献类型：
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作者：
Bruce, Robert C.;You, Lin;Hacker, Christina A.
表面偶极子是界面改性的有力工具，通过能级匹配来提高器件的输出。氟化烷基硫醇在这些应用中显示出很好的前景，因为它们可以基于氟位置和链长产生大的可调谐偶极子。此外，这些链可以被设计成仅沿着主链具有碳氟化合物，从而实现“嵌入”构型，该构型从氟产生显著的偶极效应，同时保持表面化学以防止来自改变的表面相互作用的有害副作用。然而，氟取代可以改变其他分子的电子性质，重要的是要考虑这些界面改性剂的传输性能，以便可以使用知识来定制最佳的器件性能。在本文中，我们报告的输运性质的自组装单分子膜衍生自一系列的氟化烷基硫醇，无论是有和没有嵌入偶极结构。光电子能谱和开尔文探针力显微镜显示显着的功函数修改从所有含氟分子相比，纯烃硫醇。然而，虽然嵌入式碳氟化合物产生比终端碳氟化合物更小的静电效应，它们产生更高的隧道电流跨越Au/单层/共晶镓-铟结相比，终端碳氟化合物和纯烃烷硫醇。计算研究表明，氟组分的位置不仅改变了偶极子和能级，而且还改变了分子轨道，使得在烷硫醇主链内存在离域的最低未占据分子轨道能级，从而与其他烷硫醇相比出现更大的隧穿电流。最终，我们表明，氟化烷硫醇和嵌入式偶极子架构都是强大的工具，但它们必须进行彻底的分析，以正确利用在设备设置。
Surface dipoles are a powerful tool in interfacial modification for improving device output via energy level matching. Fluorinated alkanethiols show a strong promise for these applications as they can generate large and tunable dipoles based on fluorine location and chain length. Furthermore, these chains can be designed to possess fluorocarbons solely along the backbone, enabling an "embedded" configuration that generates a significant dipole effect from the fluorines while maintaining surface chemistry to prevent deleterious side effects from altered surface interactions. However, fluorine substitution can modify other molecular electronic properties, and it is important to consider the transport properties of these interfacial modifiers so that knowledge can be used to tailor the optimal device performance. In this paper, we report the transport properties of self-assembled monolayers derived from a series of fluorinated alkanethiols, both with and without the embedded dipole structure. Photoelectron spectroscopy and Kelvin probe force microscopy show significant work function modification from all fluorine-containing molecules compared to purely hydrocarbon thiols. However, although embedded fluorocarbons generate a smaller electrostatic effect than terminal fluorocarbons, they yield higher tunneling currents across Au/monolayer/eutectic gallium-indium junctions compared to both terminal fluorocarbon and purely hydrocarbon alkanethiols. Computational studies show that the location of the fluorine constituents modifies not only dipoles and energy levels but also molecular orbitals, enabling the presence of delocalized lowest unoccupied molecular orbital levels within the alkanethiol backbone and, thereby, the appearance of larger tunneling currents compared to other alkanethiols. Ultimately, we show that fluorinated alkanethiols and the embedded dipole architecture are both powerful tools, but they must be thoroughly analyzed for proper utilization in a device setting.