A new type of texture in thin films : axiotaxy for tetragonal $\alpha$-FeSi$_2$ films on Si(001) (title in journal: Texture of Tetragonal alpha-FeSi2 Films on Si(001)

Synchrotron radiation was used to measure pole figures of a-FeSi 2 films on Si(001) substrates. Complex, though symmetrical patterns of lines were observed on the pole figures. The texture could not be categorized within the standard classification of random, fiber and in-plane texture for thin films. The lines on the pole figures are created by grains for which the a-FeSi 2 (110) or (102) plane is parallel to Si(110)-type planes in the substrate. As a direct consequence of the constraint that a plane in the film is preferentially parallel to a plane in the substrate, the texture manifests itself as though it were a fiber texture, with the fiber axis normal to the Si(110)-type planes (i.e. at 45=and 90=from the surface normal). The spacing between a-FeSi 2 (110) planes is similar to the spacingof 1:9201 A between Si(220) planes. Hence, if the a-FeSi 2 (110) are parallel to Si(110) planes, the resulting interface with the Si(001) substrate will be periodic along the direction perpendicular to the Si(110) plane. Intensity variations along the lines on the pole figure are explained by modeling the interface structure, and checking for periodic arrangements of lattice planes in the film that are parallel to other low-index planes in the Si substrate. The brightest spots on the lines are interface structures for which in-plane texture is achieved.