Silicon/Electrolyte Interface - Electrochemistry of Silicon and Its Oxide - page 71

is terminated by Si-O-Si, Si-H, and groups. 427,906 Also, the oxide film grown
in air on HF cleaned surface has a larger contact angle than that formed in pure water,
indicating that the oxide formed in air is terminated by hydrogen whereas that formed
in water is terminated by O or OH. 554 According to Morita et al ., 554 in air the oxygen
species break Si-Si bonds to produce Si-O bonds. The Si-Si bonds underneath are
broken after all of the Si atoms in the overlayer are oxidized, resulting in layer-by-layer
growth. The Si-H bonds, which remain on the surface, are responsible for the
hydrophobic behavior as shown in Fig. 2.24. The degree of hydrophobicity of a silicon
surface can be modified by anodization. 1081
2.6. SURFACE STATES
It can be expected from the nature of silicon/electrolyte interfaces described in
the previous sections that the surface states on silicon electrodes may have different
physical and chemical characteristics such as type, quantity, distribution, transfer kinet-
ics, and so on, depending on the surface condition. Table 2.12 shows examples of mea-
surements of surface states reported in the literature. Thus, while the energy levels in
bulk silicon and electrolyte can be described by a general theory, those of surface states
can only be dealt with by specific theories applicable to the specific situations.