Si (111) samples have been irradiated with Ar ions to produce disordered and amorphous states in the near-surface regions, respectively. Depth resolved positron Doppler S-parameter and lifetime measurements have been carried out on these samples. The variation of S-parameter indicates the presence of divacancies in the disordered sample and higher order vacancy clusters in the amorphous sample. Pulsed positron beam lifetime results on the disordered Si sample indicates lifetime values ascribable mostly to divacancies. In the case of amorphous sample, the lifetime distribution is indicative of nano-voids in the size range of four to eight vacancy clusters, with V-6 and V-5 being the dominant defects species.