Ion-beam Texturing at Nucleation -Manipulation of Crystallographic Orientation in Cubic Materials at the Nanometer Scale

The use of an ion beam assist during the concurrent deposition of cubic materials can result in the growth of crystallographically oriented thin films. A model system, magnesium oxide (MgO), has been successfully used as a biaxially textured template film and develops texture in a different manner from that of other well-studied materials, like yttria-stablized zirconia. Here, we present data on the initial nucleation of biaxial texture in this model system using a novel in-situ quartz crystal microbalance (QCM) substrate combined with in-situ reflected high-energy electron diffraction (RHEED). Temporal correlation of mass uptake with the RHEED images of the growing surface can be used to elucidate the mechanism of texture development in these films. Experimental data shows that the initially polycrystalline MgO film develops biaxial crystallographic texture at a thickness of ~2 nm, regardless of the ion-to-molecule ratio. RHEED images show the onset of texture occurs quickly and is somewhat analogous to a solid phase re-crystallization process with crystallite sizes of ~3 to 4 nm. Imaging with transmission electron microscopy has corroborated these observations. Changes in the ion-to-molecule ratio can influence the crystallite size and affect the nucleation density of these films. Growth of these films on various substrates changes the sticking coefficient of the MgO and influences the nucleation density and film growth mode as well. This opens the possibility of using MgO and other materials to develop biaxially textured crystallites with a narrow, specified size distribution for nanoscale applications.