Formation of Biaxially Textured MgO Buffer Layers using Ion-Beam Assisted Pulsed Laser Deposition
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Formation of Biaxially Textured MgO Buffer Layers using Ion-Beam Assisted Pulsed Laser Deposition Ruben Hühne1, Christoph Beyer1, Bernhard Holzapfel2, Carl-Georg Oertel1, Ludwig Schultz2 and Werner Skrotzki1 1 Institut für Kristallographie und Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany 2 Institut für Metallische Werkstoffe, IFW Dresden, D-01171 Dresden, Germany
ABSTRACT MgO thin films were deposited on amorphous substrates using ion-beam assisted pulsed laser deposition. The texture formation was investigated in-situ with RHEED. The microstructure of the films was observed by AFM. Using an ion beam at an angle of 55° with respect to the substrate normal, strong nucleation textures develop. Above 250°C a cube texture is observed in films thinner than 10 nm. During further growth this nucleation texture changes in a way that the 〈200〉 direction becomes parallel to the ion beam. This change can be explained by the anisotropic sputter rate of MgO found in sputter experiments on single crystals. Moreover, MgO films were deposited homoepitaxially on MgO single crystals above 250°C with internal stresses decreasing with increasing deposition temperature. This result gives rise to hope that homoepitaxial growth of MgO on the nucleation layer without ion-beam assistance should be possible in future PLD-experiments keeping the desired cube texture in thicker films.
INTRODUCTION In the last ten years, much basic research work has been directed towards the growth of biaxially textured buffer layers on polycrystalline substrates using ion-beam assisted deposition (IBAD) [1]. These buffers are then used as a basis for YBa2Cu3O7-x (YBCO) thin films with high critical current densities jc as desired for applications such as transmission cables or high field magnets. IBAD has been successfully applied in the deposition of cube textured YSZ [2-6], Pr6O11 [7] and CeO2 [6,8] films, and has allowed the preparation of high jc tapes on metallic tapes [9]. There is strong evidence that the ion beam affects the film growth and in this way texture formation in these materials. To obtain layers with good in-plane texture the films must be grown to a sufficient thickness using a low deposition rate, which makes this method timeconsuming and therefore expensive for technical applications. In contrast, Wang et al. [10] reported on the deposition of MgO films using IBAD in an electron-beam evaporation system where an in-plane texture of 7° full width at half maximum (FWHM) was obtained after the deposition of only 10 nm MgO films on amorphous Si3N4. It was assumed that in this material the ion beam already influences the nucleation. Based on these results a jc of more than 3Â6 A/cm² was measured in YBCO deposited on such an IBAD-MgO substrate [11]. So far it is not clear in which way the ion beam influences the nucleation and further growth of these films. Therefore, it is the aim of the present work to study thoroughly the mechanisms of texture and microstructure evolution in MgO films grown by ion-beam assist
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