  ALETHEIA is a newly established dark matter direct detection project that
aims at hunting for low-mass WIMPs. TPB is widely implemented in liquid helium
and argon experiments to shift VUV photons to visible light. We first report
that we have successfully coated $\sim 3 ~\mu$m TPB on the inner walls of a
10-cm cylindrical PTFE detector; we split the coating process into two steps to
have all of the surfaces being coated with the same thickness; three
independent methods were applied to figure out the thickness of the TPB coating
layers, and consistent results were obtained. Second, with an SEM machine, we
scanned the surface of TPB coating sample films exposed to different cryogenic
temperatures. The first group of sample layers were immersed into a liquid
nitrogen dewar for forty hours, the second group samples were cooled to 4.5 K
for three hours, and the third group stayed at room temperature after coating.
The SEM-scanned images of the sample films barely show any noticeable
difference.
