Microstructural investigation of BaTiO 3 thin films deposited on (001) MgO
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M. Siegert and J. Schubert Institut fu¨ r Schicht und Ionontechnik, Ju¨lich Research Centre, D-52425, Ju¨lich, Germany (Received 17 December 2001; accepted 29 April 2002)
The microstructure of BaTiO3 thin films, epitaxially deposited on (001) MgO by pulsed laser ablation, has been investigated by transmission electron microscopy. The films are always c-axis-orientated, but dislocations, {111} stacking faults, and antiphase boundaries are frequently observed. Conventional TEM and high-resolution microscopy allow one to deduce the Burgers vectors of dislocations as b1 ⳱ 〈 100〉 or b2 ⳱ 〈 110〉 , both being perfect dislocations. Most extrinsic stacking faults are ending at 1/3〈 112〉 or 1/3〈 111〉 partial dislocations; the displacement vector of the antiphase boundaries is 1/2〈 101〉 . Studying the interfacial structure by means of zone images taken along [100] and [110] shows that the misfit is mainly released by dislocations with Burgers vectors of 1/2〈 110〉 and 1/2〈 101〉 . I. INTRODUCTION
The modern microelectronics industry requires the integration of several thin-film materials with different properties. The growth of oxide films such as hightemperature superconductors, ferroelectric materials, and colossal-magnetoresistance (CMR) materials is one of the main trends of such an exploration.1 Monocrystalline films usually have better performances and applications than the polycrystalline films. To obtain epitaxial monocrystalline films, the oxide thin films are usually grown on monocrystalline substrates such as SrTiO3, LaAlO3, and MgO. The (001) MgO qualifies as a good substrate for growing cube-oriented oxide films; oxide films of high quality for example superconductors, PbTiO3 and BaTiO3, have been successfully grown on the (001) MgO substrate.2–6 BaTiO3 is a typical oxide of the perovskite family. Thin films of this material are extensively investigated since BaTiO3 is a transparent oxide with a high dielectric constant.7 It has promising applications in microelectronic devices used as various device components; for instance, it is used as a waveguide. The optical properties of BaTiO3 wave guides deposited on (001) MgO substrates have been investigated.6 Compared with BaTiO3 films grown on oxide substrates such as SrTiO 3 , 8 epitaxial BaTiO3 films grown on (001) MgO have a wide range of applications since MgO is a transparent oxide exhibiting good microwave properties. Although the epitaxial BaTiO3 films grown on (001) MgO have been reported,4 –6 a detailed investigation of the film a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 8, Aug 2002
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microstructure is still missing. In this contribution, BaTiO3 film has been deposited on (001) MgO using the pulsed laser deposition (PLD) technique. Transmission electron microscopy (TEM) allows the characterization of the defects in the films and the misfit dislocations at the interface. Perovskite BaTiO3 (BTO) exhibits a tetragonal ferroelectric to cubic parae
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