In the book we have discussed the synthesis of Ge NCs in SiO2 matrix by RF co-sputtering, followed by RTA. It has been observed that the crystallite size increases with the increase in annealing temperature. We have used these annealed samples to study the effects of heavy ion irradiation (120 MeV Ag and 80 MeV Ni at different fluences) on the Ge NCs. We have observed from XRD, Raman and TEM measurements that the size of the Ge NCs decreases with the increase in fluence. The main reason for this is the interaction of tracks formed in SiO2 during irradiation with the embedded Ge NCs. Due to this interaction some of the Ge atoms might have diffused from the larger Ge NCs and dissolved into SiO2. We have also studied the synthesis of Ge NCs embedded in HfO2 by using RF sputtering and subsequent RTA or ion irradiation. The size of NCs was observed to increase with the increase in temperature. GeO2 NC thin films were deposited on Si substrate using the RF sputtering and irradiated with 80 MeV Ni ions at various fluences. The results show that GeO2 NCs are reduced in size and few of them are converted into Ge NCs. Finally we have studied the effects of ion irradiation on the Si NCs.