科研之友
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摘要
Several in situ studies of carbon nanotube and carbon nanofiber growth on transition-metal nanoparticles have observed the growth of graphitic material from specific nanoparticle facets. In many of the studies these facets have been associated with rough nanoparticle surfaces with atomic size steps. Taking as a reference case a recent in situ study [G. E. Begtrup et al., Phys. Rev. B 79 205409 (2009)] where the facet producing graphitic material in situ was associated with the alpha-iron (111) surface, we demonstrate, using density-functional theory calculations, that the diffusion barrier for carbon entering and leaving the nanoparticle and migrating in the vicinity of the nanoparticle surface is smaller on the undercoordinated (111) facet than on the more closely packed (110) and (100) facets. We explain this behavior by the flexibility of the atomic steps on the (111) surface. This idea is general and can be used to explain similar behavior in other transition-metal nanoparticles as observed in the in situ studies.
- 出版日期2011-6-17
