Energetics of the dihydride phases on the diamond (100) surface

Abstract

It was previously claimed that the herringbone and lean-to dihydride structures possessing a $(2\ifmmode\times\else\texttimes\fi{}1)$ symmetry are more stable than other suggested dihydride structures on the C(100) surface, so that the $(2\ifmmode\times\else\texttimes\fi{}1)$ patterns frequently observed in low-energy electron diffraction (LEED) experiments at low temperatures are not sufficient to distinguish between the monohydride and dihydride phases on C(100). To clarify this situation, we investigate the herringbone and lean-to structures using the pseudopotential plane-wave method. Contrary to the claim, we find that these two $(2\ifmmode\times\else\texttimes\fi{}1):2\mathrm{H}$ structures on C(100) are higher in energy than the canted $\mathrm{C}(100)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1):2\mathrm{H}$ structure. For completeness, these two structures are also considered for the Si(100) case. Our calculations show that for both the C and Si cases, the canted $(100)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1)$ dihydride phase is the lowest in energy among the dihydride structures considered so far. Therefore, the $(2\ifmmode\times\else\texttimes\fi{}1)$ LEED patterns can be assigned to the bare (100) surface or the monohydride (100) surface, while the $(1\ifmmode\times\else\texttimes\fi{}1)$ symmetry can be associated with the dihydride (100) surface.