Tetlow Holly, Posthuma de Boer Joel, Ford Ian J, Vvedensky Dimitri D, Curcio Davide, Omiciuolo Luca, Lizzit Silvano, Baraldi Alessandro, Kantorovich Lev
Physics Department, King's College London, London, WC2R 2LS, UK.
The Blackett Laboratory, Imperial College London, London SW7 2AZ, UK.
Phys Chem Chem Phys. 2016 Oct 12;18(40):27897-27909. doi: 10.1039/c6cp03638d.
The complete mechanism behind the thermal decomposition of ethylene (CH) on Ir(111), which is the first step of graphene growth, is established for the first time employing a combination of experimental and theoretical methods. High-resolution X-ray photoelectron spectroscopy was employed, along with calculations of core level binding-energies, to identify the surface species and their evolution as the surface temperature is increased. To understand the experimental results, we have developed a reaction sequence between the various CH species, from ethylene to C monomers and dimers, based on ab initio density functional calculations of all the energy barriers and the Arrhenius prefactors for the most important processes. The resulting temperature evolution of all species obtained from the simulated kinetics of ethylene decomposition agrees with photoemission measurements. The molecular dissociation mechanism begins with the dehydrogenation of ethylene to vinylidene (CHC), which is then converted to acetylene (CHCH) by the removal and addition of an H atom. The C-C bond is then broken to form methylidyne (CH), and in the same temperature range a small amount of ethylidyne (CHC) is produced. Finally methylidyne dehydrogenates to produce C monomers that are available for the early stage nucleation of the graphene islands.
乙烯（CH）在Ir(111)上的热分解是石墨烯生长的第一步，首次采用实验和理论方法相结合的方式确定了其完整机制。利用高分辨率X射线光电子能谱以及核心能级结合能的计算，来识别表面物种及其随表面温度升高的演变。为了理解实验结果，我们基于对所有能量势垒和最重要过程的阿仑尼乌斯指前因子的从头算密度泛函计算，建立了从乙烯到C单体和二聚体的各种CH物种之间的反应序列。从乙烯分解的模拟动力学得到的所有物种的温度演变结果与光发射测量结果一致。分子解离机制始于乙烯脱氢生成亚乙烯基（CHC），然后通过去除和添加一个H原子将其转化为乙炔（CHCH）。接着C-C键断裂形成次甲基（CH），并且在相同温度范围内会产生少量的乙叉基（CHC）。最后，次甲基脱氢生成可用于石墨烯岛早期成核的C单体。
