© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Phys. Status Solidi RRL 5, No. 8, 289– 291 (2011) / DOI 10.1002/pssr.201105243 www.pss-rapid.com pss Nanoscale retention-loss dynamics of polycrystalline PbTiO 3 nanotubes Hyunwoo Choi 1, 2 , Yunseok Kim **, 1 , Seungbum Hong *, 2 , Tae-Hyun Sung 3 , Hyunjung Shin 4 , and Kwangsoo No *, 1 1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea 2 Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA 3 Department of Electrical Engineering, Hanyang University, Seoul 133-791, Korea 4 School of Advanced Materials Engineering, Kookmin University, Seoul 136-732, Korea Received 15 May 2011, revised 4 July 2011, accepted 4 July 2011 Published online 6 July 2011 Keywords retention, ferroelectrics, nanotubes, piezoresponse force microscopy, PbTiO 3 ** Corresponding authors: e-mails hong@anl.gov and ksno@kaist.ac.kr ** Present address: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Ferroelectric materials have attracted much attention because of their excellent ferroelectric characteristics such as high spontaneous polarizations and large piezoelectric displacement. Retention, which is defined as the capability of ferroelectric materials to maintain their polarization in the absence of an external field, is one of the most impor- tant properties of ferroelectric materials. In addition, there are currently considerable technological interests in reten- tion properties, for a large number of applications [1]. Up to now, many authors have reported micro- and nanoscale retention-loss dynamics of various ferroelectric materials. However, most of the literature on the polarization reten- tion have covered thin films, so there is scant information on the retention properties of one-dimensional (1D) ferro- electric materials – e.g. nanotubes (NTs), nanorods and na- nowires. 1D ferroelectric materials are of interest because of their intriguing properties such as enhanced polarization or piezoelectric coefficient compared to their bulk or thin- film counterparts [2–7]. Since the NTs have solid geometry with internal pores, in contrast to flat thin films, it is pos- sible to fabricate highly integrated 1D ferroelectric memo- ry devices with enhanced surface area. Therefore, it is es- sential that the retention-loss dynamics of 1D ferroelectric materials are studied for the advanced application to highly integrated 3D nonvolatile memory devices. In this Letter we investigated the local retention-loss dynamics of ferro- electric PbTiO 3 (PTO) NTs using piezoresponse force mi- croscopy (PFM). Detailed procedures of fabrication of PTO NTs are well described elsewhere [8]. In this experiment, we used the PTO NTs fabricated at 400 °C (our PTO NTs have a diameter around 200 nm, a tube-wall thickness of 25–30 nm, and a length of 5–10 μm). The polarizations of the PTO NTs were aligned from top to bottom by applying a +6 V dc voltage to the conductive probe for background poling (see Supporting Information for background poling in detail at www.pss-rapid.com). After the background pol- ing, nanodot domains were written by applying a –6 V dc voltage to the probe on two arbitrary points of the underly- ing NTs (hereafter, we call them dot A and B). Evolutions of the domain structures of both dot domains with the lapsed time were analyzed using PFM, which is a powerful tool for analyzing ferroelectric domain structures due to its high spatial resolution, easy implementation and effective manipulation [9–11]. For the dot-domain imaging, we used a commercial atomic force microscopy (XE-100, Park Systems) connected to a lock-in amplifier (SR830, Stan- ford Research Systems) under ambient conditions. An ac We observed the nanoscale retention dynamics of poly- crystalline PbTiO 3 nanotubes using piezoresponse force mi- croscopy. We found that the retention loss of the nanodot domains on the nanotubes showed the stretched exponential relaxation behaviors with stretched exponential factor n being less than 1 (0.523 and 0.692), which are similar to the thin films. In addition, the nanodot domains showed a diverse re- laxation time constant τ due to different remnant polarization of each dot domains.