Piezoresponse Measurements Research Articles

HYDROTHERMAL SYNTHESIS OF THIN FILMS OF BARIUM TITANATE NANOTUBE ARRAYS

ABSTRACT Recently, there has been great demand for patterned perovskite Barium titanate (BT, BaTiO3) in electroceramic device applications. Well ordered BaTiO3 nanotube arrays could be fabricated on the anodized Ti substrates at the hydrothermal condition of 200°C 0.05 M Ba(OH)2, and 2 hr ∼ 7 hr. XRD patterns of as-prepared BaTiO3 nanotube arrays reveal a perovskite structure. Meanwhile, piezoresponse measurements confirm the existence of ferroelectricity of the BaTiO3 nanotube arrays. Moreover, SAED result indicates the high-oriented nature of a single BaTiO3 nanotube.

Phase transition and high dielectric constant of bulk dense nanograin barium titanate ceramics

Barium titanate (BTO) ceramics with an average grain size of 8nm were fabricated and studied. The temperature dependent Raman spectra revealed successive transitions from rhombohedral to orthorhombic, tetragonal, and cubic as the temperature increased from 87to673K. Local piezoresponse force measurements indicated that the ceramics had switchable polarization at room temperature. Dielectric measurements showed a broad ferroelectric-to-paraelectric phase transition with a maximum permittivity of 1800 at 390K. All these results suggest that ferroelectricity could remain in BTO ceramics with grain size as small as 8nm in diameter.

Nanoscopic observation of bistable piezoresponse, polarization retention, and domain imaging of sub-50 nm-thick (Pb,La)(Zr,Ti)O 3 thin films

Nanoscopic characterization of the local ferroelectricity by piezoresponse measurements with scanning probe microscope is performed on a 40 nm-thick (Pb,La)(Zr,Ti)O 3 (PLZT) (8/65/35) thin film prepared on a Nb-SrTiO(001) substrate. The microscopic piezoresponse showed a nearly linear dependence on the DC bias voltage with a slight bistability. The poled structure showed rapid retention. We attribute the bistability observed in the piezoresponse and the vanishing of the poled structure to a phase transition between the relaxor phase and the field-induced ferroelectric phase. The control and imaging of the local domain structure are also performed.

Investigation of Ferroelectric Properties of Vinylidene Fluoride Oligomer Evaporated Films

ABSTRACTStructures and electrical properties of newly synthesized vinylidene fluoride (VDF) oligomer [CF3(CH2CF2)17I] films evaporated onto various substrates around liquid nitrogen temperature were investigated. As a result, the VDF oligomer films were mainly formed with ferroelectric phase (form I) crystals and the molecular chains were oriented parallel to the substrate surfaces regardless of both the kind of the substrates and the thickness of the VDF oligomer films. In addition to these properties, the VDF oligomer films showed polarization reversal due to 180° rotation of the polar VDF oligomer molecules according to the applied voltages. This ferroelectric behavior was verified by local poling and piezoresponse measurements with an atomic force microscope, and by measurements of D-E hysteresis curves.

Investigation of Polarization Switching Processes in Pb(Zr,Ti)O 3 Capacitors Using Piezoresponse Imaging

Polarization switching processes in ferroelectric capacitors with epitaxial Pb(Zr,Ti)O 3 (PZT) thin films grown on SrRuO 3 /SrTiO 3 (100) were investigated using piezoresponse imaging technique with and on the top electrodes using atomic force microscopy. PZT thin films had only 180° domains because of a tetragonal structure and completely (001)-orientations. Piezoresponse measurements revealed that the polarization switching process changed as the switching pulse voltage increased. At lower switching pulse voltage regions (∼1.4 V c ), the polarization switching occurred from only the latent nuclei. On the other hand, at higher switching pulse voltage (>2 V c ), the new nucleations during switching period were observed. Activation field can be also estimated 310-370 kV/cm.

Investigation of Polarization Switching Processes in Pb(Zr,Ti)O 3 Capacitors Using Piezoresponse Imaging

Polarization switching processes in ferroelectric capacitors with epitaxial Pb(Zr,Ti)O 3 (PZT) thin films grown on SrRuO 3 /SrTiO 3 (100) were investigated using piezoresponse imaging technique with and on the top electrodes using atomic force microscopy. PZT thin films had only 180° domains because of a tetragonal structure and completely (001)-orientations. Piezoresponse measurements revealed that the polarization switching process changed as the switching pulse voltage increased. At lower switching pulse voltage regions (∼1.4 V c ), the polarization switching occurred from only the latent nuclei. On the other hand, at higher switching pulse voltage (>2 V c ), the new nucleations during switching period were observed. Activation field can be also estimated 310-370 kV/cm.

Growth of ferroelectric PbZr xTi 1− xO 3 thin films by metalorganic chemical vapor deposition (MOCVD)

Growth mechanism of PbTiO 3 and PbZr x Ti 1− x O 3 (PZT) films grown by metalorganic chemical vapor deposition on Pt(1 1 1)/SiO 2/Si(1 0 0), SrTiO 3(1 0 0) and SrRuO 3(1 0 0)/SrTiO 3(1 0 0) substrates was investigated using scanning electron microscopy, scanning probe microscopy and transmission electron microscopy. The Volmer–Weber growth mode was observed for PbTiO 3 and/or PZT on both Pt/SiO 2/Si and SrTiO 3 with the SrO-terminated plane. PZT on both SrTiO 3 with TiO 2-terminated plane and SrRuO 3/SrTiO 3 showed the Stranski–Krastanov growth mode. From piezoresponse measurements using SPM, it was found that nano-size PbTiO 3 and PZT islands on Pt/SiO 2/Si observed at the initial growth stage showed ferroelectricity. Using PbTiO 3 islands as a seed, low temperature growth at 395°C of PZT thin films was demonstrated.

Piezoresponse scanning force microscopy: What quantitative information can we really get out of piezoresponse measurements on ferroelectric thin films

Voltage modulated scanning force microscopy in contact mode or piezoresponse scanning force microscopy is now turning into an established technique for imaging ferroelectric domains in ferroelectric thin films. The quantities measured, however, are the amplitude and phase of a locally induced piezoelectric strain, and not the ferroelectric polarization itself. As all ferroelectrics possess piezoelectric properties, the domain structure visualized does correspond to that of the ferroelectric domains whose polarization is partly normal to the film surface, but the amplitude of the signal is actually not proportional to the magnitude of the normal component of the polarization. Likewise, the shear mode of scanning force microscopy allows the imaging of domains with a polarization component in the plane of the film. Methods to relate the amplitude of the piezoresponse signal to the magnitude of the ferroelectric polarization taking into account the anisotropic nature of the piezoelectric coefficients are described and discussed for the most common ferroelectric materials.

Observations of Island Structures at the Initial Growth Stage of PbZrxTi1-xO3 Thin Films Prepared by Metalorganic Chemical Vapor Deposition

Island structures of PbZrxTi1-xO3(PZT) (x=0.26 and 0.74) were observed prior to formation of a continuous film at the initial growth stage on a Pt(111)/SiO2/Si substrate by metalorganic chemical vapor deposition (MOCVD). Triangular-shaped (111)-oriented PZT islands were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Transmission electron microscopy (TEM) observations revealed that PZT islands 80 to 100 nm wide and 20 to 30 nm high had a twin structure due to the presence of tetragonal or rhombohedral structures. Hence, small PZT islands could have spontaneous polarization. In piezoresponse measurements using scanning probe microscopy (SPM), the phase difference between the vibrational signal of the SPM cantilever and the applied ac voltage changed from 0 to 180°, resulting in a hysteresis loop due to polarization reversal by a dc bias voltage. From this piezoresponse result, it was found that PZT islands had ferroelectricity.