William Jo

Properties of Iron Oxide Films Grown by Pulsed Laser Deposition

Epitaxial magnetite (Fe 3 O 4 ) thin films have been grown on MgO(001) substrates by pulsed laser deposition. The films have characteristics of the “Verwey transition”: the electric conductivity decreases by about one order of magnitude and the magnetization curve shows anomaly at the transition temperature, i.e. about 125 K. Effects of annealing the Fe 3 O 4 thin films at various oxygen partial pressures have also been investigated. Phase identification was made using XRD techniques and infrared reflectivity measurements. The surface morphologies were studied by SEM and AFM. Under an oxidizing atmosphere, the Fe 3 O 4 phase is transformed mainly into α-Fe 2 O 3 , and this transformation is accompanied by development of needle-like structures along directions of MgO substrate. It is also found that electrical and magnetic properties of the iron oxide films are changed significantly by the annealing process.

Pulsed Laser Deposition of Bi 4 Ti 3 O 12 Thin Films on Indium Tin Oxide Coated Glass

Bi 4 Ti 3 O 12 thin films have been grown on indium tin oxide coated glass by pulsed laser deposition. The films are rapidly thermal annealed at 650 °C in various kinds of ambients. X-ray diffraction and scanning electron microscopy are used to investigate crystallization and microstructures, respectively. Using Auger electron microscopy, chemical compositions and depth profiles are examined. Optical and current-voltage characteristics measurements of the films show that their transmittance and leakage current behaviors are strongly dependent upon the microstructures. O 2 partial pressure in the rapid thermal annealing process is found to be an important parameter which determines crystallization, microstructures, and leakage current behaviors of the Bi 4 Ti 3 O 12 thin films.

Domain Images and Retention Properties of Pb(Zr,Ti)O3 Thin Films Observed by Electrostatic Force Microscopy

We report results on domain retention in preferentially oriented Pb(Zr,Ti)O 3 (PZT) thin films on Pt and on LaNiO 3 (LNO) electrodes. Effects of bottom electrodes on domain images and retention properties have been explored by detecting an electrostatic force exerted on the biased conductive probe. It was demonstrated that polarization loss of PZT crystallites on LNO appears to be less than that of PZT grains on Pt. Moreover, charge retention was controlled by a reverse-poling protocol during electrostatic force microscopy (EFM) measurements. The surface charge density of the PZT films was observed as a function of time in a selected area where a region is single-poled and another region is reverse-poled. The retention behavior of the regions is very different; the single-poled region shows a declined response and the reverse-poled region reveals a retained characteristic. Decay and retention mechanisms are explained by space-charge redistribution and trapping of defects in the films.