Phase separation of alkanethiol self-assembled monolayers during the replacement of adsorbed thiolates on Au(111) with thiols in solution
Phase separation of alkanethiol self-assembled monolayers during the replacement of adsorbed thiolates on Au(111) with thiols in solution
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DOI：
10.1021/la991590l
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发表时间：
2000-09-05
期刊：
影响因子：
3.9
通讯作者：
Niki, K
中科院分区：
文献类型：
--
作者：
Kakiuchi, T;Sato, K;Niki, K
用还原脱附伏安法和扫描隧道显微镜（STM）研究了乙醇溶液中12-巯基十二烷酸（MDDA）对Au（111）表面十六烷基硫醇（HDT）自组装单分子膜（SAM）的置换作用。吸附的HDT分子与溶解在乙醇中的MDDA的交换按域进行，也就是说，不是以随机的方式进行。在置换过程的伏安图中出现了两个分离良好的峰，分别对应于MDDA富集区和HDT富集区的解吸。与富含NDT的结构域的脱附相关的峰值电位在替换过程中保持不变，表明MDDA在富含HDT的结构域中的溶解度非常小。衬底的STM成像显示，尺寸大于15 nm（2）的畴占主导地位，并占据富含HDT畴面积的85%。整个交换过程为准一级反应，在31 ℃下，1 mmol dm（-3）MDDA的乙醇溶液中的速率常数为9.1 × 10（-3）h（-1）。相反的过程，即，用溶解在乙醇中的HDT替换吸附的MDDA要慢得多，这表明MDDA单分子膜通过横向氢键稳定。在置换过程中MDDA富集域的峰电位的显著偏移表明HDT在MDDA域中的相当大的溶解。
Replacement of self-assembled monolayers (SAM) of hexadecanethiol (HDT) on the Au( 111) surface with 12-mercaptododecanoic acid (MDDA) in ethanol solution has been studied using voltammetry of the reductive desorption and scanning tunneling microscopy (STM). The exchange of adsorbed HDT molecules with MDDA dissolved in ethanol proceeds domainwise, that is, not in a random fashion. Two well-separated peaks, corresponding to the desorption of MDDA-rich domains and HDT-rich domains, appear in a voltammogram over the replacement process. The peak potential associated with the desorption of NDT-rich domains remains unchanged in the course of the replacement, indicating that the solubility of MDDA in HDT-rich domains is very small. STM imaging of the substrate shows that domains whose sizes are greater than 15 nm(2) are predominant and occupy 85% of the area of HDT-rich domains. The entire exchange process is pseudo-first-order with the rate constant being 9.1 x 10(-3) h(-1) in 1 mmol dm(-3) MDDA in ethanol at 31 degrees C. The reverse process, i.e., the replacement of adsorbed MDDA with dissolved HDT in ethanol, is much slower, suggesting the stabilization of MDDA monolayers by lateral hydrogen bonding. A significant shift in the peak potential of MDDA-rich domains during the replacement indicates the considerable dissolution of HDT in MDDA domains.