Effects of Embedded Dipole Layers on Electrostatic Properties of Alkanethiolate Self-Assembled Monolayers
Effects of Embedded Dipole Layers on Electrostatic Properties of Alkanethiolate Self-Assembled Monolayers
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DOI：
10.1021/acs.jpcc.7b04694
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发表时间：
2017-07-27
影响因子：
3.7
通讯作者：
Allara, David L.
中科院分区：
文献类型：
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作者：
Cabarcos, Orlando M.;Schuster, Swen;Allara, David L.
硫醇烷酯（AT）在钴金属和半导体基底上形成自组装单分子膜（SAMs）已经成功地用于定制这些表面的性质数十年。在这里，我们提供了一个非常有前途的一类AT为基础的系统，这是由一个或多个偶极羧酸酯基团嵌入到烷基主链的修改的详细分析。为了获得全面的了解，我们研究了九种不同的嵌入偶极单分子膜和五个参考非取代自组装膜。我们系统地改变了烷基链段的长度，酯基的方向，和链中所含的酯基的数量。为了了解自组装膜的结构和电子性质，我们采用了各种互补的实验技术，即红外反射吸收光谱（IRS），高分辨率X射线光电子能谱（XPS），紫外光电子能谱（UPS），原子力显微镜（AFM），开尔文探针（KP）AFM。这些实验与国家的最先进的电子能带结构计算的补充。我们发现有趣的电子特性，如大和可变SAM诱导的功函数修改和偶极子诱导的层内的静电势的位移。这些观察结果进行了详细分析，加入不同的实验技术的结果与量子力学模拟提供的原子的洞察力。
Alkanethiolates (ATs) forming self-assembled monolayers (SAMs) on coinage metal and semiconductor substrates have been used successfully for decades for tailoring the properties of these surfaces. Here, we provide a detailed analysis of a highly promising class of AT-based systems, which are modified by one or more dipolar carboxylic acid ester groups embedded into the alkyl backbone. To obtain comprehensive insight, we study nine different embedded-dipole monolayers and five reference nonsubstituted SAMs. We systematically varied lengths of the alkyl segments, ester group orientations, and number of ester groups contained in the chain. To understand the structural and electronic properties of the SAMs, we employ a variety of complementary experimental techniques, namely, infrared reflection absorption spectroscopy (IRS), high-resolution X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), atomic force microscopy (AFM), and Kelvin probe (KP) AFM. These experiments are complemented with state-of-the-art electronic band-structure calculations. We find intriguing electronic properties such as large and variable SAM-induced work function modifications and dipole-induced shifts of the electrostatic potential within the layers. These observations are analyzed in detail by joining the results of the different experimental techniques with the atomistic insight provided by the quantum-mechanical simulations.