Natural polarization phenomenon of superstructure film composed of metal-doped silica layers

The piezoelectricity and its related characteristics of a superstructure of silica-based thin films were investigated. Thin films with a periodic structure of nanometer-ordered silica layers containing metal dopants performed like c-axis oriented piezoelectric thin films. Piezoelectricity, pyroelectricity, and an anomalous photovoltaic effect were observed in poled superstructure silica films. The polarization was stabilized by this structure to prevent aging. We found that under some deposition conditions, piezoelectricity was observed in as-deposited films that were not poled.