基于混合自组装单分子层的可控分子整流

doi:10.6023/A19050192

摘要/Abstract

基于自组装单分子层(SAM)的分子器件的性能取决于分子层的超分子结构. 而混合自组装单分子层是一种简便易行的调控单分子层组成和结构的方法. 将具有整流特性的11-二茂铁基-1-十一烷基硫醇(FUT)和惰性1-十一烷硫醇(C11-SH)通过溶液共混制备了混合单分子层, 并用液态EGaIn作为顶电极研究了SAM器件的性质. C11-SH与FUT分子的比例可以调节器件的整流性能: 随着惰性C11-SH分子比例增高, SAM器件的整流比逐渐降低. 有趣的是, 当惰性C11-SH的比例小于20%时, 器件的整流性能反而随C11-SH的加入而得到了提升. 这是由于少量C11-SH分子减弱了由二茂铁分子的排列缺陷引起的漏电流, 改善了分子器件的稳定性和重现性, 为单分子层器件的性能调控提供了一种简便有效的方法.

关键词: 分子电子学, 自组装单分子层, 稀释法, 整流特性, 混合单分子层

We demonstrate in this work that the performance of self-assembled monolayer (SAM) molecular devices can be modulated by the composition and supramolecular structure of the molecular layer using mixed self-assembled monolayer strategy. We prepared the mixed monolayer on gold surface (with ca. 1 nm roughness) by co-adsorption of 11-(ferrocenyl)- undecanethiol (FUT, rectifier) and 1-undecanethiol (C11-SH, diluent). Micrometer scale molecular junctions were formed by using indium gallium eutectic alloy (EGaIn) as the top electrode. Electrical characterization of the junction found that the ratio of FUT and C11-SH molecules can tune the rectifying performance of the monolayer device: the higher the proportion of ferrocene is, the better the rectifying performance is. To our surprise, mixed monolayer prepared by 20% C11-SH and 80% FUT mixed solution exhibited higher rectification ratio than pure FUT monolayer, due to reduced leaking current. Surface reflective IR spectroscopy and the monolayer thickness characterization by the ellipsometer revealed loosely packed molecules on the surface in the pure FUT monolayer due to the bulky head group of the FUT and the rough gold substrate. FUT that partially lied down on the surface, or buried in the layer therefore created defects, which in turn become the origin of the leakage current. Upon insertion of C11-SH molecules in between the ferrocene molecules, the molecules in the monolayer become more ordered with the support of the C11-SH, as evidenced by decreased wave number of the C—H stretching mode of methylene group by reflective IR spectroscopy. Meanwhile, an increase in thickness for 80% FUT monolayer relative to pure FUT monolayer implied a better orientation of the FUT molecule in mixed monolayer. The ordered structure and better orientation largely improved the stability and reproducibility of the molecular device, reduced the leaking current and afforded higher rectification ratio. Our approach therefore provides a facile and effective strategy for regulating the performance of monolayer devices by molecule aggregation state.

Key words: molecular electronics, self-assembled monolayer, dilution effect, rectification property, mixed monolayer

引用此文

王紫嫣, Khalid,Hira, 李柏力, 李瑶, 于曦, 胡文平. 基于混合自组装单分子层的可控分子整流[J]. 化学学报, 2019, 77(10): 1031-1035.

Wang, Ziyan, Khalid, Hira, Li, Baili, Li, Yao, Yu, Xi, Hu, Wenping. Tuning Rectification Properties of Molecular Electronic Devices by Mixed Monolayer[J]. Acta Chimica Sinica, 2019, 77(10): 1031-1035.

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图/表 6

图1. 原子力显微镜下蒸镀金电极表面. (a) 截面图, (b) 2D图

Figure 1. The surface of evaporated gold electrode by atomic force microscope. (a) cross section image, (b) 2D image

图2. (a) 形成SAMs的两种分子. FUT为有机整流器. C11-HS是一种没有整流性能的稀释剂. (b) 混合SAM的厚度

Figure 2. (a) The molecules that form SAMs. FUT is the organic rectifier. C11-HS is the diluent with no rectifier performance. (b) The thickness of mixed SAM

图3. 混合SAMs(100% FUT, 80% FUT, 60%FUT, 40% FUT, 20%FUT)的红外光谱

Figure 3. Infrared spectra of mixed SAMs (100% FUT, 80% FUT, 60% FUT, 40% FUT and 20% FUT)

图4. (a) 混合SAMs的CV曲线. 其中扫速为50 mV/s. 曲线从上到下, FUT含量依次为100%, 80%, 60%, 40%, 20%. (b)混合SAM中二茂铁硫醇的表面覆盖度

Figure 4. (a) Cyclic voltammograms of mixed SAMs. The scan rate is 50 mV/s. As the curve goes from top to bottom, the ratios of FUT is 100%, 80%, 60%, 40% and 20% respectively. (b) Surface concentration of FUT in mixed SAMs

图5. (a), (b), (c), (d), (e)为EGaIn/Ga2O3//SAM//Au分子结的半对数I-V曲线热点统计图. 从(a)到(e)FUT在溶液中的比例为100%, 80%, 60%, 40%, 20%. (f) 所有分子结的平均I-V曲线

Figure 5. (a), (b), (c), (d), (e) is heat maps of semi-log10|I|-V curves of EGaIn/Ga2O3//SAM//Au molecular junctions. From (a) to (e) the ratios of FUT in solution is 100%, 80%, 60%, 40%, 20%. (f) The averaged I-V curves of all the molecular junctions

图6. 单组分二茂铁硫醇SAM (a)和混合SAM (b)的结构示意图

Figure 6. Schematic diagram of the structure of single-component FUT SAM (a) and mixed SAM (b)

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