The CdS nanotubes are ordered structures with
an average length, inner diameter, and wall thickness
of approximately 200, 35, and 20 nm, respectively.
From an examination of the SEM images, the average
center-to-center distance between the CdS nanotubes
is 110 nm and thus the average intertube spacing is
35 nm. Based on the CdS nanotube feature parameters,
the porosity and CdS nanotube density are determined
to be 36.5% and 2.26 × 1010 nanotubes/cm2, respectively.