Ab Initio Molecular Dynamics Simulations of Nitrogen/VN(001) Surface Reactions: Vacancy-Catalyzed N2 Dissociative Chemisorption, N Adatom Migration, and N2 Desorption

详细信息    查看全文

• 作者：D. G. Sangiovanni ; A. B. Mei ; L. Hultman ; V. Chirita ; I. Petrov ; J. E. Greene
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 16, 2016
• 年：2016
• 卷：120
• 期：23
• 页码：12503-12516
• 全文大小：877K
• 年卷期：0
• ISSN：1932-7455

文摘

We use density-functional ab initio molecular dynamics to investigate the kinetics of N/VN(001) surface reactions at temperatures ranging from 1600 to 2300 K. N adatoms (N_ad) on VN(001) favor epitaxial atop-V positions and diffuse among them by transiting through 4-fold hollow (FFH) sites, at which they are surrounded by two V and two N surface atoms. After several atop-V → FFH → atop-V jumps, isolated N adatoms bond strongly with an underlying N surface (N_surf) atom. Frequent N_ad/N_surf pair exchange reactions lead to N₂ desorption, which results in the formation of an anion surface vacancy. N vacancies rapidly migrate via in-plane ⟨110⟩ jumps and act as efficient catalysts for the dissociative chemisorption of incident N₂ molecules. During exposure of VN(001) to incident atomic N gas atoms, N_ad/N_ad recombination and desorption is never observed, despite a continuously high N monomer surface coverage. Instead, N₂ desorption is always initiated by a N adatom removing a N surface atom or by energetic N gas atoms colliding with N_ad or N_surf atoms. Similarities and differences between N/VN(001) vs. previous N/TiN(001) results, discussed on the basis of temperature-dependent ab initio electronic structures and chemical bonding, provide insights for controlling the reactivity of NaCl-structure transition-metal nitride (001) surfaces via electron-concentration tuning.