where A is a constant, D is the mass fractal dimension, Γ(D − 1) is the
gamma function of D−1, and ξ is the characteristic length ξ of a fractal
structure. The fractal structure diminishes at a length scale larger than ξ
and becomes homogeneous. The corresponding values of D and ξ
calculated using Eq. (5) were 2.4 and 88.4 nm. In the linear regime,
the surface fractal dimension (DS) can be calculated using the following
equation [48]: