第一性原理研究C在Fe(111)表面和次表面的积炭机理

使用密度泛函方法对C原子在Fe(111)表面吸附团聚和次表层的吸附扩散进行了研究。在炭覆盖度θ_C <1 ML时,C主要以孤立的原子态存在并导致表面重构;1 ML≤θ_C ≤2 ML,"mC₂+nC"为主要的吸附形式;θ_C≥2 ML时,复杂的吸附形态比如碳链和岛状碳团簇开始生成。这些复杂岛状碳团簇是Fe(111)表面石墨沉积或碳纳米管生长的成核中心。在次表层,C原子在八面体位稳定存在。C在表面的迁移能垒为0.45 eV,由表面迁移到次表面的的能垒为0.73 eV。虽然C₂团簇的生成是热力学有利的,但是C向次表层的迁移动力学上占优。

First-principles study of the mechanism of carbon deposition on Fe(111) surface and subsurface

A theoretical study of the carbon atoms adsorption and diffusion on the surface and into the subsurface of Fe(111) is performed using DFT calculations.Before the carbon coverages up to 1 ML,the adsorbed carbons tend to exist in an isolated atomic state and cause a reconstruction of Fe(111) surface.The configurations of "mC2+nC" are energetically favorable on the Fe(111) surface at 1 ML ≤ θC ≤ 2 ML.At a higher coverage,complicated adsorbed patterns such as chains and islands are found,and we predict that these carbon islands can function as the nucleation center of the precipitation of graphite or carbon nanotubes on the Fe(111) surface.In the subsurface region,the carbon atom prefers the octahedral site.The barriers for diffusion on and into the Fe(111) surface and subsurface are 0.45 eV and 0.73 eV,respectively.Actually,C2 formation is thermodynamically favored,whereas C migration into the subsurface region is kinetically feasible.