STM observation of metal-nonmetal granular thin films

Abstract

We have observed scanning tunneling microscopy (STM) topographic images for structural characterization and measured current-voltage (I-V) spectra (scanning tunneling spectroscopy: STS) for the investigation of local transport properties of Co-Al-O granular thin films exhibiting tunnel-type giant magnetoresistance (GMR). STM topographic images indicated round-shaped bright regions and dark channels, which are associated with Co granules and Al-oxide, respectively. From the I-V characteristics the electronic charging effect, i. e., the effect of Coulomb blockade, was confirmed. In addition, the tunneling current varied stepwise as a function of the voltage, suggesting the appearance of a Coulomb staircase.