Modification of the crystalline structure of ZnO nanoparticles embedded within a SiO2 matrix due to thermal stress effects

Abstract

Self-assembled nanocrystals of ZnO were embedded within a SiO2 matrix by a sequential deposit using reactive R.F. sputtering. The ZnO nanoparticles (NP's) were obtained by depositing a very thin layer (∼20 nm) of Zn on the bottom of the valleys of a first SiO2 rough surface and then covered by another SiO2 layer at 500 °C. The stress produced, due to the cooling process, by the SiO2 matrix on the ZnO NP's generates an unusual crystalline phase of ZnO. The crystal structure was determined by means of X ray diffraction patterns. The ZnO + SiO2 composite shows a transmittance higher than 80 % for wavelengths > 450 nm. Optical absorption allows to reveal the character and value of the optical band gap. Vibrational modes of the material were determined by Raman spectroscopy.