Chain-Length-Dependent Reactivity of Alkanethiolate Self-Assembled Monolayers with Atomic Hydrogen
Chain-Length-Dependent Reactivity of Alkanethiolate Self-Assembled Monolayers with Atomic Hydrogen
复制标题
烷硫醇自组装单分子层与原子氢的链长依赖性反应性
DOI：
10.1021/acs.jpcc.9b06809
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Sibener, S. J.
中科院分区：
文献类型：
--
作者：
Sayler, Jeffrey D.;Brown, Sarah;Sibener, S. J.
气体-表面相互作用是最重要但最复杂的化学过程之一，因为它们本质上涉及广泛的能量和长度尺度的多体现象。为了理解这些复杂的界面相互作用，我们经常使用模型系统，如硫醇盐自组装单分子膜（SAMs）来研究反应性和钝化等现象，因为这些系统提供了对控制所讨论事件的表面参数的精细控制。在这项研究中，我们研究链长的反应性的烷硫醇自组装膜与原子氢通过监测整个反应的表面形态演变的影响。这些时空数据是使用直接原位原子氢剂量的超高真空扫描隧道显微镜（UHV-STM）获得的。对于一系列的烷硫醇SAMs 8- 11-碳长，我们发现，链长的小增加导致不成比例的反应性大幅度下降。这些反应趋势使我们开发了一个动力学模型，其特征在于两个速率常数：一个缓慢的速度与紧密堆积的域，这是链长依赖的氢反应性，和一个快速的反应性与低密度区域，这是相同的所有样品检查。除了反应速率之外，我们还跟踪了表面形态的链长依赖性变化，特别是在氢暴露后SAM蚀刻坑的大小和形状如何演变。在10 C和11 C样品中观察到很少的差异，而8 C和9 C SAM的平均蚀刻坑面积显著增加。总的来说，这项研究提供了重要的定量见解如何表面包装和动态无序的有机薄膜可以影响其钝化能力。
Gas–surface interactions are some of the most important yet complex chemical processes to occur, as they intrinsically involve many-body phenomena across a wide spectrum of energies and length scales. To understand these complicated interfacial interactions, we often use model systems such as thiolate self-assembled monolayers (SAMs) to study phenomena like reactivity and passivation, as these systems afford fine control over the surface parameters governing the events in question. In this study, we examine the effect of chain length on the reactivity of alkanethiolate SAMs with atomic hydrogen by monitoring morphological surface evolution throughout the reaction. These spatiotemporal data were obtained using ultrahigh vacuum scanning tunneling microscopy (UHV-STM) with directed in situ atomic hydrogen dosing. For a series of alkanethiolate SAMs 8- to 11-carbons long, we find that small increases in chain length cause disproportionately large decreases in reactivity. These reaction trends led us to develop a kinetic model characterized by two rate constants: a slow rate for hydrogen reactivity with close-packed domains, which is chain-length dependent, and a fast rate for reactivity with low-density regions, which is the same for all samples examined. In addition to reaction rates, we also tracked chain-length-dependent changes in surface morphology, notably how the size and shape of the SAMs’ etch pits evolved following hydrogen exposure. Few differences were observed in the 10C and 11C samples, while there was a significant increase in the mean etch pit area of the 8C and 9C SAMs. Overall, this study provides important quantitative insights into how surface packing and dynamic disorder of organic thin films can influence their passivation capabilities.
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