The effect of porosity on the vibrational and low temperature equilibrium thermodynamic properties of amorphous silicon via computer simulation

We have studied the effect of pores on the vibrational and thermodynamic behavior of amorphous silicon (a-Si) by separating the normal modes of vibration according to their spatial localization, as well as according to which atoms they are more localized or biased on, depending on their coordination, which differs on average at the surface and in the interior of the atomic skeletons. This latter classification has been done using a new quantity which we call the weighted average coordination. The presence of pores suppresses the boson peak found in nonporous a-Si and introduces a new peak in the specific heat curves arising principally from internal surface related modes. The effect of porosity on the internal energy of a-Si at low temperatures is also discussed.