RuO $_2$（110）表面摩擦聚合物的形成机理
Tribopolymer Formation Mechanism on the RuO$_2$(110) Surface
摘要：
微机电和纳机电系统（MEMS/NEMS）器件的接触面上形成的摩擦聚合物是阻碍其在信息技术中实际应用的主要问题。导电金属氧化物，例如RuO $_2$和ReO $_3$，由于其导电性、硬度和相对化学惰性的表面，已被认为是用于MEMS/NEMS接触的有希望的候选材料。然而，最近的实验工作表明，痕量的聚合物仍然可以形成在RuO $_2$表面。在这项研究中，我们证明了这类意外的摩擦聚合物形成的机制进行密度泛函理论为基础的计算压缩实验与苯作为污染气体。首先，压缩过程中的机械力改变了苯分子从轻微的物理吸附到强烈的化学吸附。进一步的压缩导致苯分子的变形和化学键。最后，两个触点分离，其中一个具有连接的复杂有机分子，另一个具有更具反应性的表面。具有氧杂双环链段的复杂有机分子可以被视为摩擦聚合物的雏形，并且更具反应性的表面可以触发下一个吸附-反应-摩擦聚合物形成循环。在此基础上，利用过渡态理论和二级速率定律预测了摩擦聚合物的生成速率。这项研究加深了我们对摩擦聚合物形成（特别是金属氧化物）的理解，并提供了抑制摩擦聚合的策略。
英文摘要：
Tribopolymer formed on the contacts of microelectromechanical and nanoelectromechanical system (MEMS/NEMS) devices is a major concern hampering their practical use in information technology. Conductive metal oxides, such as RuO$_2$ and ReO$_3$, have been regarded as promising candidate materials for MEMS/NEMS contacts due to their conductivity, hardness, and relatively chemically inert surfaces. However, recent experimental works demonstrate that trace amounts of polymer could still form on RuO$_2$ surfaces. In this study, we demonstrate the mechanism of this class of unexpected tribopolymer formation by conducting density functional theory based computational compression experiments with benzene as the contamination gas. First, mechanical force during compression changes the benzene molecules from slightly physisorbed to strongly chemisorbed. Further compression causes deformation and chemical linkage of the benzene molecules. Finally, the two contacts detach, with one having a complex organic molecule attached and the other with a more reactive surface. The complex organic molecule, which has an oxabicyclic segment, can be viewed as the rudiment of tribopolymer, and the more reactive surface can trigger the next adsorption--reaction--tribopolymer formation cycle. Based on these results, we also predict tribopolymer formation rates by using transition--state theory and the second--order rate law. This study deepens our understanding of tribopolymer formation (especially on metal oxides) and provides strategies for suppressing tribopolymerization.
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