Characterization of TiO nanocrystalline thin film by scanning 2 tunneling microscopy and scanning tunneling spectroscopy

TiO2 nanocrystalline semiconductor films have been studied by scanning tunneling microscopy STM.and scanning tunneling spectroscopy STS.. The presence of interconnected TiO2 nanocrystallites with mean diameters of 30 nm and different size of pores were indicated in the STM images. Surface structural features were characterized by fractal dimension analysis in terms of surface roughness. Tunneling current vs. bias and differential conductance spectra were measured for as prepared and air-stored nanocrystalline thin films. The results obtained by statistical analysis show that surface bandgap energy of TiO2 nanocrystallites of as prepared thin film was 3.10"0.08 eV and quite different surface bandgap energy of 1.76"0.19 eV was observed for TiO2 nanocrystallites in air-stored thin film. Negative shifts of onset potential of differential conductance in both negative and positive bias and the presence of surface states at 1.59"0.16 V for TiO2 nanocrystallites of air-stored thin films revealed a difference in surface electronic properties for both TiO2 nanocrystalline thin films. q1999 Elsevier Science B.V. All rights reserved.