6533b7dcfe1ef96bd12728a5

RESEARCH PRODUCT

First-principles calculations of the initial incorporation of carbon into flat and stepped Pd surfaces

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description

We employ density-functional-theory calculations to examine carbon adsorption and diffusion in Pd bulk, and on Pd(111) and Pd(211) surfaces. Different possible subsurface and on-surface structures are explored and the most stable structures are analyzed. We calculate various diffusion paths: lateral diffusion on a surface, migration to a subsurface region, and within the first interlayer. Our calculations show in accordance with the earlier theoretical results that on Pd(111) carbon prefers to adsorb on octahedral interstitial sites. On Pd(211) the fourfold hollow site under the step is energetically the most favorable one and the second best sites are the octahedral sites. The calculations indicate that migration into the first interlayer is more favorable than diffusion on the Pd(111) surface and migration into the second interlayer is already highly activated with barrier height close to those obtained in bulk. Nearly nonactivated diffusion paths into the first interlayer are found at the step edge of bare Pd(211) but carbon is found to diffuse easily from the first interlayer to the fourfold hollow site on Pd(211) thus leading to the decoration of step edges with carbon. Preadsorbed carbon increases the surface-subsurface diffusion barrier but it remains smaller than the corresponding value on bare Pd(111). At higher carbon concentration the mixed surface-subsurface structures are the most stable ones and carbon atoms tend to sit as far away from each other as possible.