Energy gap and surface structure of superconducting diamond films probed by scanning tunneling microscopy

We have performed scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond at T = 0.47 K. The STM topography shows two kinds of atomic structures: a hydrogenated 1 × 1 structure, C(1 1 1)1 × 1:H, and an amorphous structure. On the C(1 1 1)1 × 1:H region, the tunneling spectra show superconducting property with the energy gap Δ = 0.83 meV. The obtained gap ratio 2 Δ / k B T c = 3.57 is consistent with the weak-coupling BCS theory.