Surface Conductivity of Hydrogenated Diamond Films

The experimentally observed high surface conductivity of hydrogenated diamond films is explained through ab initio results as well as model calculations based on the tight-binding molecular dynamics method. Our results support the previously reported experimental results indicating that the surface conductivity of the hydrogenated diamond surfaces is due to the surface adsorption of a ${\mathrm{H}}_3{\mathrm{O}}^{+}$ monolayer. Specifically, it is shown that the presence of the ${\mathrm{H}}_3{\mathrm{O}}^{+}$ adlayer results in the formation of an electrostatic surface dipole moment which makes the potential of the surface H layer effectively more attractive. This, in turn, ignites charge transfer from the diamond lattice to the surface layer creating, thus, the necessary charge carriers (holes) for the observed high conductivity.

Figure 1

Transmission function and $I\mathrm{\text{−}}V$ characteristics under symmetric bias for a hydrogenated diamond-(111) film with and without carbon vacancies. The Fermi level is taken to be the HOMO level and set to zero.

Figure 2

Model calculations for the transmission function and the $I\mathrm{\text{−}}V$ characteristics under asymmetric bias for a hydrogenated diamond-(111) film with positively and negatively charged H adlayer. The Fermi level is taken to be the HOMO level and is set to zero.

Figure 3

As in Fig. 2, for a reconstructed hydrogenated diamond-(001)-($2\times 1$) film with an H adlayer at various charge states.

Figure 4

Comparison of transmission function and $I\mathrm{\text{−}}V$ characteristics (under symmetric bias) of a hydrogen-free and a hydrogenated diamond (111) film. The Fermi level is taken to be the HOMO level and is set to zero.

Figure 5

Side (left) and top (right) view of an ${\mathrm{H}}_2\mathrm{O}$ molecule above the HD surface at a distance for which the interaction energy is found to be the optimum.