Graphite surface reconstruction

For reactions of H with H-covered graphite surfaces, the energetics and dynamics are quite different. The H-graphite chemisorption is comparatively weak, and requires significant surface reconstruction. The attraction of the incident H to the chemisorbed H is very strong, leading to steering of the incident... 

For Sb and A1 on HOPG, and for Si and Ge on crystalline SiNx/Si(lll), most grown-up crystallites have definite polar (also azimuthal for some) orientation alignment with the substrate. In contrast, for Ge on graphite, and Si and Ge on amorphous SiNx/Si(001), the orientation of the nanocrystals seems completely random, and high-index facets are observed quite often. Surface reconstructions not formed on bulk crystals are observed on some facets. These observations reflect the unique capacity of nanoscale facets to accommodate certain surface superstructures that are not observable on a macroscopic scale. 

From a theoretical point of view, the stability of nanocrystalline diamond was discussed by several authors. Badziag et al. [25] pointed out that, according to semi-empirical quantum chemistry calculations, sufficiently small nanocrystalline diamond (3-5 nm in diameter) may be more stable than graphite by forming C-H bonds at the growing surface. Barnard et al. [26] performed the ab initio calculations on nanocrystalline diamond up to approximately 1 nm in diameter. The results revealed that the surfaces of cubic crystals exhibit reconstruction and relaxations comparable to those of bulk diamond, and the surfaces of the octahedral and cubooctahedral crystals show the transition from sp to sp bonding. 

The chemisorption case is exemplified by oxygen and sulfur on metals, the physisorption case by krypton and xenon on metals and graphite. Intermediate cases do exist for example, undissociated CO on metals is not physisorbed but chemisorbed and nevertheless it seems in many cases to be able to produce close-packed hexagonal overlayers. Also, some metal surfaces [for example, Pt(lOO), Ir(lOO), Au(100)] reconstruct into different lattices, exhibiting the effect of adsorbate-adsorbate interactions (here the adsorbate is just another metal atom of the same species as in the substrate). 

---