Formation of Ge nanocrystals from ion-irradiated GeO2 nanocrystals by swift Ni ion beam

GeO2 nanocrystal (NC) thin films were deposited on Si substrate using a magnetron sputtering method and irradiated with swift heavy ions of 80 MeV Ni at various fluences ranging from 5 × 1012 to 1 × 1014 ions/cm2. Grazing incidence X-ray diffraction measurements indicate the decrease in average size of NCs with increase in fluence of ion irradiation. Micro-Raman spectroscopy studies show clearly the formation of Ge NCs with the increase of irradiation fluence. Field emission scanning electron microscopy was employed to study the morphology and modifications in NCs due to ion irradiation. Transmission electron microscopy measurement of the ion-irradiated sample at 1 × 1014 ions/cm2 confirmed the presence of few nm-sized Ge NCs, which were not observed in as-deposited sample. The overall results suggest that GeO2 NCs are reduced in size and few of them are converted into Ge NCs due to the effects of electronic energy deposition by the irradiating ions. This formation of Ge NCs in the ion-irradiated GeO2 NC thin films has been understood on the basis of irradiation-induced separation of oxygen from GeO2 NCs.