Elucidating the influence of the monolayer interface versus bulk on the macroscopic properties (e.g., surface hydrophobicity, charge transport, and electron transfer) of organic self-assembled monolayers (SAMs) chemically anchored to metal surfaces is a challenge. This article reports the characterization of prototypical SAMs of n-alkanethiolates on gold (CH3(CH2)nSAu, n = 6-19) at the macroscopic scale by electrochemical impedance spectroscopy and contact angle goniometry, and at the molecular level, by infrared reflection absorption spectroscopy. The SAM capacitance, dielectric constant, and surface hydrophobicity exhibit dependencies on both the length (n) and parity (nodd or neven) of the polymethylene chain. The peak positions of the CH2 stretching modes indicate a progressive increase in the chain conformational order with increasing n between n = 6 and 16. SAMs of nodd have a greater degree of structural gauche defects than SAMs of neven. The peak intensities and positions of the CH3 stretching modes are chain length independent but show an odd-even alternation of the spatial orientation of the terminal CH3. The correlations between the different data trends establish that the chain length dependencies of the dielectric constant and surface hydrophobicity originate from changes in the polymethylene chain conformation (bulk), while the odd-even variation arises primarily from a difference in the chemical com-position of the interface related to the terminal group orientation. These findings provide new physical insights into the structure-property relation of SAMs for the design of ultrathin film dielectrics as well as the understanding of stereostructural effects on the electrical characteristics of tunnel junctions.

中文翻译：

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正链烷硫醇自组装单层的宏观特性奇偶效应的分子起源：本体还是界面？

阐明单层界面与体积对化学锚定到金属表面的有机自组装单层 (SAM) 的宏观特性（例如，表面疏水性、电荷传输和电子转移）的影响是一个挑战。本文报道了通过电化学阻抗谱和接触角测角法在宏观尺度上和通过红外反射吸收在分子水平上表征金 (CH3(CH2)nSAu，n = 6-19) 上的正链烷硫醇的原型 SAM光谱学。SAM 电容、介电常数和表面疏水性取决于聚亚甲基链的长度 (n) 和奇偶校验（nodd 或 neven）。CH2 拉伸模式的峰值位置表明随着 n = 6 和 16 之间的 n 增加，链构象顺序逐渐增加。 nodd 的 SAM 比 neven 的 SAM 具有更大程度的结构 gauche 缺陷。CH3 拉伸模式的峰值强度和位置与链长无关，但显示出 CH3 末端空间取向的奇偶交替。不同数据趋势之间的相关性表明，介电常数和表面疏水性的链长依赖性源于聚亚甲基链构象（本体）的变化，而奇偶变化主要源于化学成分的差异。与终端组方向相关的接口。