Growth and structure of heteroepitaxial lead titanate thin films constrained by miscut strontium titanate substrates
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Toshiyuki Matsunaga Matsushita Techno-Research, Moriguchi, Osaka 570-0005, Japan
Mohsen Hassan,a) Isaku Kanno, and Takaaki Suzuki Department of Mechanical Engineering, Kyoto University, Kyoto 606-8501, Japan
Kiyotaka Wasab) Faculty of Science, Yokohama City University, Yokohama 236-0027, Japan (Received 16 August 2005; accepted 6 February 2006)
Single-crystal lead titanate [(001)PbTiO3 (PT)] thin films were heteroepitaxially grown on a miscut strontium titanate [(001)SrTiO3 (ST)] substrate by radio frequency magnetron sputtering. The PT thin films were grown via a step-flow growth. The step-flow growth enhanced the layer growth resulting in the continuous (001) single-crystal structure without a dislocated interface for the film thickness below 200 to 250 nm. The PT thin films show a small temperature variation of the lattice parameters unlikely to the bulk PT crystals due to the substrate clamping. The temperature variation of the lattice constants is discussed in terms of the thermo-elastic deformation analysis for the PT/ST heterostructure.
I. INTRODUCTION
The deposition of perovskite lead titanate [PbTiO3 (PT)] thin films with the controlled microstructure has been extensively investigated for the application of ferroelectric properties. A single-crystal film without microstructure is essential for the understanding of the ferroelectricty in thin films. The heteroepitaxial growth is useful for the deposition of perovskite PT thin films. Several deposition processes were used for the heteroepitaxial growth including sputtering, chemical vapor deposition (CVD), and pulsed laser deposition (PLD).1 However, these heteroepitaxial PT thin films were still composed of complicated microstructures, including a multidomain structure originating from the lattice mismatch to the substrate crystal.2,3 The origin of the microstructure is related to the lattice mismatch and/or the growth conditions.4 The formation of microstructure will be essentially governed by an initial stage of the film growth. The initial stage of the film growth is composed of an island growth and a lateral growth. The former is known as
Volmer–Weber mode, and the latter is known as Frank– van der Merwe mode. The lateral growth under the Frank–van der Merwe mode is useful for the deposition of the uniform single-crystal films. The lateral growth is possibly achieved by a deposition of perovskite on a miscut substrate under a step-flow growth mode.5 We have previously reported that the lateral growth of PT thin films has been achieved by the sputtering deposition on a miscut strontium titanate [(001) SrTiO3 (ST)] substrate. Systematic study on the lateral growth of the PT thin films has been done in relation to the growth conditions. The heteroepitaxial sputtered PT thin films via lateral growth showed a single-crystal structure of (001) orientation.6 However, the PT thin films were clamped by rigid substrates, and their structural and dielectric properties were modified by the substrate clamping. This paper describes the structure and growth mode
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