High-resolution surface-sensitive C1score-level spectra of clean and hydrogen-terminated diamond (100) and (111) surfaces

The carbon $1s$ core levels of diamond (100) and (111) surfaces were investigated using high-resolution photoelectron spectroscopy. The surfaces were prepared in a hydrogen plasma, which is known to result in atomically flat surfaces. From the signature of the C $1s$ core-level spectra, four different surface terminations can be distinguished. The as-prepared surfaces exhibit a surface component shifted by $+0.5$ to $+0.8\mathrm{eV}$ toward higher binding energy, which we assign to multiple termination of carbon atoms by hydrogen. Annealing these surfaces first results in the development of the surfaces terminated monoatomically by hydrogen. A small chemical shift of $\ensuremath{-}0.15\mathrm{eV}$ was deduced for the hydrogen-terminated surface atoms of the (111):H surface with respect to the bulk carbon atoms. Further annealing leads to spectra characteristic for hydrogen-free, reconstructed diamond surfaces. This process is shown to be thermally activated with an activation energy of $3.4\ifmmode\pm\else\textpm\fi{}0.4\mathrm{eV}.$ The corresponding chemical shifts between surface and bulk components vary between $\ensuremath{-}0.78$ and $\ensuremath{-}1.15\mathrm{eV}$ depending on surface orientation and surface treatment. Finally, annealing at $T\ensuremath{\approx}1250\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ leads to a partially graphitized surface for diamond (111) while on the diamond (100) surface a $4\ifmmode\times\else\texttimes\fi{}1$ reconstruction is observed. The sign and magnitudes of the chemical shifts are discussed.