Mosaic nanostructure of TiO2 with rutile short-range atomic order

A nanolaminate film of six 36nm TiO2–7nm Al2O3 bilayers is sputter deposited at room temperature and examined by high resolution transmission electron microscopy (HRTEM). Neither the TiO2 nor the Al2O3 layers have long-range crystallographic order. Previous Raman spectroscopy of the nanolaminate showed that short-range atomic order in the TiO2 component is characteristic of bulk rutile. The HRTEM images of the Al2O3 layers consist entirely of random contrast speckle characteristic of a material with no atomic ordering beyond the nearest-neighbor level. However, the predominant feature in the images of the TiO2 layers is a mosaic structure, with fewer regions of random contrast speckle. The mosaic consists of four repetitive elements: (1) domains of {110} planes terminating along ⟨100⟩ directions, (2) planar faults along ⟨100⟩ directions, (3) {110} facets in steps along the [001] direction, and (4) a herringbone structure of short strands of (110) and (−110) planes on either side of a ⟨100⟩ midrib. We show...