Oxygen-induced stress-modified reconstructions of the Ta(1 1 0)/Al2O3(1 1 −2 0) surface: a surface X-ray diffraction study

The knowledge of the surface structure of thick metallic buffer layers is important to understand subsequent growth. We present here a surface X-ray diffraction study of an oxygen-induced surface reconstruction observed on thick Ta(1 1 0) layers grown on sapphire (1 1 −2 0). The solving of the atomic structure was performed using both Ta crystal truncation rods and superstructure rods. The model found for the reconstruction can be described as a misfit defect network at the interface between one plane of TaO(1 1 1) in Kurdjumov–Sachs epitaxy and the Ta. The reconstruction is not always commensurate. This probably arises from the coexistence of several commensurate supercells of slightly different periods. A small anisotropy (0.1–0.2%) of the in-plane lattice parameter of the Ta has been measured in all the samples. This anisotropy, which is due to the epitaxy on the sapphire, induces on the surface a selection of one of the two domains of the reconstruction.