Au nanoparticles ͑NPs͒ have been formed by ion beam synthesis in 600 nm thin SiO 2. Subsequently the NPs were irradiated with 2.3 MeV Sn ions at liquid nitrogen temperature. Samples were analyzed using extended x-ray absorption fine structure ͑EXAFS͒ spectroscopy and small angle x-ray scattering ͑SAXS͒ as a function of Sn irradiation dose. Transmission electron microscopy shows that the NPs largely retain their spherical shape upon irradiation. However, we observe a reduction in average NP size and a concomitant significant narrowing of the size distribution with increasing irradiation dose as consistent with inverse Ostwald ripening. At lower irradiation doses, significant structural disorder is apparent with an effective bond length expansion as consistent with amorphous material. At higher irradiation doses, EXAFS measurements indicate dissolution of a significant fraction of Au from the NPs into the SiO 2 matrix ͑as monomers͒ and the formation of small Au clusters ͑dimers, trimers, etc.͒. We estimate the volume fraction of such monomers/clusters. Ion irradiation thus yields disordering then dissolution of Au NPs.

Porosity in GaSb induced by 69 Ga ion irradiation has been investigated as a function of implant dose and temperature. Initially pores form in the implanted material which become elongated as they increase in size. With increasing implant dose, the structure continues to evolve into plates and finally a network of nanoscale rods. Swelling to 25 times the original implanted layer thickness has been observed. The temperature dependence of the minimum feature size has been established. The crystalline-to-amorphous and continuous-to-porous transformations proceed simultaneously. We suggest the latter results from the precipitation of interstitials at extended crystalline defects in preference to Frenkel pair recombination as potentially related to anomalous diffusion in GaSb.

No abstract

No abstract

No abstract