Thin Film Textures
Pronounced textures occur in thin films. Modern technological devices to a large extent rely on polycrystalline thin films with thickness in the nanometer and micrometer range. This holds, for instance, for all microelectronic and most optoelectronic systems or sensoric and superconducting layers. Most thin film textures may be categorized into two different types: (1) for so-called fiber textures the orientation of a certain lattice plane is preferentially parallel to the substrate plane. (2) In contrast, in biaxial textures also the in-plane orientation of crystallites becomes locked with respect to the sample. The latter phenomenon is accordingly observed in nearly epitaxial growth processes, where the crystallographic axes of the layer tend to align along those of the substrate.
Tailoring the texture on demand became an important task in thin film technology. In the case of oxide compounds intended for transparent conducting films or surface acoustic wave (SAW) devices, for instance, the polar axis should be aligned along the substrate normal. Another example is given by cables from high-temperature superconductors that are being developed as oxide multilayer systems deposited on metallic ribbons. The adjustment of the biaxial texture in YBa2Cu3O7 layers turned out as the decisive prerequisite for achieving sufficiently large critical currents.
The degree of texture is often subjected to an evolution during thin film growth and the most pronounced textures are only obtained after the layer has achieved a certain thickness. Thin film growers thus require information about the texture profile or the texture gradient in order to optimize the deposition process. The determination of texture gradients by x-ray scattering, however, is not straightforward, because different depths of a specimen contribute to the signal. Techniques that allow for the adequate deconvolution of diffraction intensity were developed only recently.
Read more about this topic: Texture (crystalline)
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