• PDF / 1,500,901 Bytes
• 8 Pages / 612 x 792 pts (letter) Page_size
• 66 Downloads / 215 Views

DOWNLOAD

REPORT

---

H. Hao and X.X. Xi Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 12 March 2001; accepted 12 September 2001)

We studied the microstructure of SrTiO3/SrRuO3 bilayer films on (001) LaAlO3 substrates by high-resolution transmission electron microscopy. At the SrRuO3/LaAlO3 interface a defect configuration of stacking faults and nanotwins bounding either Frank partial dislocations or Shockley partial dislocations and complex interaction between these planar defects were found to be the dominant means of misfit accommodation. The misfit in the SrTiO3/SrRuO3 system, however, is mainly accommodated by elastic strain. Most of the observed defects in the SrTiO3 layer can be related to the {111} planar defects in the SrRuO3 layer propagating and reaching the SrTiO3/SrRuO3 interface. Furthermore, a {110} planar defect can also be introduced in the SrTiO3 layer due to the structure change of the SrTiO3/SrRuO3 interface.

I. INTRODUCTION

The deposition of high-quality perovskite ceramic thin films for various applications is one of the most active areas in materials research. SrRuO3 has attracted considerable interest in recent years due to its good conductivity, high chemical and thermal stability, and excellent lattice match with many other electroceramic materials such as SrTiO3 and YBa2Cu3O7.1–6 In superconducting devices, SrRuO3 films have been used as buffer layers for the growth of high-temperature superconducting YBa2Cu3O7−x films and also as a barrier layer in Josephson junctions.3,4 In ferroelectric nonvolatile memory applications, they have been employed as electrodes.5,6 The microstructure and defects in the SrRuO3 layer are important since they can have a considerable effect on the device layers which directly connect to the SrRuO3 layer. It is known that SrTiO3 is an interesting dielectric material and suitable for various applications such as voltage tunable filters, oscillators, and phase shifters for microwave circuits.8,9 However, the properties of SrTiO3 thin films which are necessary for device applications are not as good as those of bulk single crystals. Their tunability is lower and the dielectric losses are high.10,11 Recently, with employment of SrRuO3 as the buffer layer, high-quality SrTiO3 films with near single-crystal level dielectric loss were successfully prepared on LaAlO3 substrates.12 Besides perfect dislocations, partial

a)

Present address: Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287. J. Mater. Res., Vol. 16, No. 12, Dec 2001

http://journals.cambridge.org

Downloaded: 11 Mar 2015

dislocations including both Shockley-type with Burgers vectors inclined to the interfaces and Frank-type in the interfaces were proposed as effective means of misfit relaxation in the heterostructure system.13 The dissociation of 60° dislocations in epitaxial semiconductor films and the role of the resulting partials in misfit relaxation have been well established. Partial dislocations of a/2〈101〉 type accompanied by stack