Structure, optical absorption and electronic states of Zn+ ion implanted and subsequently annealed sol-gel anatase TiO2 films

Zn+ or both Zn+ and Of ions were implanted in porous anatase TiO2 films pre pared by sol-gel method and subsequently annealed in N-2 or O-2 atmosphere. The results were compared with that obtained after Ar+ ion implantation an d subsequent annealing, The samples were evaluated by scanning electron mic roscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED) and X-ray diffraction (XRD). Optical absorption and electronic states were characterized by photothermal deflection spectrometry (PDS) and elect ron energy loss spectrometry (EELS). The porous film was densified by Zn+ i on implantation up to the ion penetration depth. After the subsequent annea ling at 800 degrees C the phase transformation from anatase to rutile accom panied with grain growth up to the film thickness was observed. In addition , the phase transformation was not induced by the annealing up to 800 degre es C with or without preceding Ar+ ion implantation. Thus, the implanted im purity Zn assisted the phase transformation. Annealing in O-2 tends to redu ce the rate of phase transformation and create ZnTiO3. Optical absorption a bove the photon energy of 2.9 eV was increased remarkably by the Zn+ or Zn and O+ ion implantation and subsequent annealing. EELS spectra of the Znimplanted and annealed sample is consistent with the results of PDS, The ch ange in the optical absorption above 2.9 eV is due to the phase transformat ion. (C) 2000 Elsevier Science B.V. All rights reserved.