Spontaneous polarization in nanosized ferroelectrics and its size dependence

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In order to investigate physical properties of nanosized ferroelectrics, we developed a measurement system based on scanning probe microscopy (SPM), which was capable of detecting electrical charges smaller than 10 fC. By using the SPM system developed, switching charges of lead titanate nanoislands with lateral dimensions of several tens nanometers and heights of several nanometers were successfully measured. The SPM revealed that the switching charge of lead titanate nanoislands was as large as those of thin films. From the size dependence and relationship between spontaneous polarization and piezoelectric coefficient, it was found that the decrease in the spontaneous polarization with the island height was responsible for the decrease in the piezoelectric coefficient.