Ws Ahn

Switchable single c-domain formation in a heteroepitaxial PbTiO3 thin film on a (001) Nb-SrTiO3 substrate fabricated by means of hydrothermal epitaxy

We used hydrothermal epitaxy to fabricate a heteroepitaxial PbTiO3 (PTO) thin film on a Nb-doped (001) cubic SrTiO3 (NSTO) substrate while avoiding the phase transition. By means of transmission electron microscopy and piezoresponse force microscopy analyses, it was confirmed that no a domain formed in the heteroepitaxial PTO film; the film had a single +c-domain structure at an as-synthesized state. From the measurement of the polarization-voltage hysteresis curve, large remanent polarization (2Pr:144μC∕cm2) resulting from the single +c-domain structure and an imprint induced by an asymmetric electrode configuration were observed. It is suggested that the single +c-domain structure was caused by the interface of the PTO film and solution rather than the interface of the PTO film and NSTO electrode under the hydrothermal conditions. This hydrothermally synthesized PTO film is anticipated to be very suitable for high-performance engineering applications.

Ferroelectric properties and fatigue behavior of heteroepitaxial PbZr1−xTixO3 thin film fabricated by hydrothermal epitaxy below Curie temperature

A heteroepitaxial PbZr1−xTixO3 (PZT) thin film was fabricated by means of hydrothermal epitaxy at 210 °C below Curie temperature without undergoing the paraelectric to ferroelectric phase transition. From transmission electron microscope and piezoresponse force microscope observations, it was confirmed that the fabricated PZT thin films had only a −c monodomain without an a domain in the as-synthesized state. The polarization-electric-field hysteresis curve and the fatigue behavior of the heteroepitaxial PZT capacitor with a Pt top and n-type semiconductor bottom electrode was observed. The remanent polarization 2Pr of the PZT capacitor was about 63μC∕cm2. This value was much lower compared to that of the PbTiO3 capacitor, which was also fabricated by means of hydrothermal epitaxy at 160 °C below Curie temperature. It was suggested that a lower polarization of the PZT capacitor was due to the nonswitchable interfacial layer grown in the initial growth stage. However, this layer did not exert an influence ...

Retention loss phenomena in hydrothermally fabricated heteroepitaxial PbTiO3 films studied by scanning probe microscopy

We observed the retention loss phenomena of the nanodomains with an average diameter of 36nm and that of the square domains with a size of 1 and 25μm2 that were reversed by an applying electric field at an atomic force microscopy conductive tip in a heteroepitaxial PbTiO3 thin film, which was fabricated via hydrothermal epitaxy below Curie temperature, TC. While the nanodomains did not undergo significant retention loss until 5.3×106s, the square domains revealed some retention loss for a fixed period after long latent periods. The observed phenomena were explained in terms of the instability of the curved c∕c domain wall and the compressive strain energy. Analyses showed that the nanodomains composed a cylinder extending to the bottom electrode; however, the square domains had a curved c∕c domain wall, including the compressive strain energy, and these factors caused the retention loss.

Two-dimensional self-patterning of PbTiO3 on a Nb–SrTiO3 (001) surface using atomic force microscope lithography and hydrothermal epitaxy

Atomic force microscope (AFM) lithography and hydrothermal epitaxy processes were used to resolve issues related to aligning ferroelectric micro- and nanosized cell arrays through a bottom-up approach. A Nb-doped SrTiO3 (100) surface was transformed in two dimensions by applying bias using a conductive AFM tip. The locally transformed areas were etched out with an acidic solution. It was found that the PbTiO3 crystal nucleated and grew on the artificially aligned grooves preferentially during a hydrothermal epitaxial process. The self-patterned PbTiO3 cell had excellent piezoresponse hysteresis with ferroelectric properties suitable for the fabrication of micro- and nanosized ferroelectric devices.

Retention loss behaviors in heteroepitaxial ferroelectric film with a +c monodomain fabricated by hydrothermal epitaxy below Tc

We observed the retention loss of dot domains (36nm diameter) and square domains with sizes of 1 and 25μm2 that were reversed by applying an electric field at an atomic force microscopy (AFM) conductive tip on a heteroepitaxial PbTiO3 thin film with + polarization in the virgin state, which was fabricated via hydrothermal epitaxy below Tc. Through theoretical calculations, it was discussed that the retention loss phenomena of a domain reversed by using an AFM tip were derived from the summation of the depolarization field energy and the strain-polarization coupling energy. Since the retention loss of the reversed domain with a straight c∕c domain wall by applying a homogeneous electric field did not occur, we suggest that a cylindrical domain, which has a nearly straight c∕c domain wall that extends to the bottom electrode on the given thin film, would be free from the retention loss.