Ideal structure of strained anatase TiO2 (001) film on TiO2-terminated SrTiO3 single crystal (Sr ions are green spheres, Ti are cyan, and oxygen ions are in red). (b) In situ non-contact AFM surface topography of our Ti-terminated STO substrates. (c) LEED pattern of single terminated samples.
Typical (a) RHEED pattern during the early stage of deposition on Ti-terminated STO. (b) Exponential decay of the specular RHEED spot intensity vs. nominal thickness for TiO2 films deposited on Ti-terminated STO (black squares), on non-etched STO (red circles), on SLAO (green down triangles), and on LAO (up blue triangles) substrates (c) LEED pattern, and (d) and (e) STM surface topography of 3 nm pseudomorphic film. RHEED and LEED patterns are unchanged with respect to the previous Ti-terminated STO surface. The terrace structure also persists, showing faceted edges along the in-plane principal directions, absent in the case of STO surfaces (e). The step profile (f) shows a vertical lattice parameter that is close to the STO c axis.
(a) 3d 5/2-3d 3/2 Sr peaks collected at grazing incidence for a series of samples: non-etched STO single crystal (reference sample) before (black circles), and after deposition of a nominally 3 nm thick TiO2 film (green circles); 3nm TiO2 film grown on TiO2-terminated STO (red circles), 3 nm thick TiO2 film grown at room temperature (blue circles). The intensities of all the 3d 5/2-3d 3/2 Sr peaks were normalized to the 2p 3/2-2p 1/2 Ti emissions. All data have been rescaled by setting the maximum of the Sr emission intensity to 1.
RHEED patterns of a TiO2 film during (a) the pseudomorphic growth of the STO-like phase and (b) during the intermediate phase where 3D anatase islands appear. In (c) the RHEED intensity of different diffraction spots as function of time is shown (the colors correspond to the circles in (a) and (b). The arrow indicates the starting of nucleation of 3D islands.
(a) LEED pattern at the transition between phase B and phase C. The in-plane lattice parameter, as deduced by the dimension of the BZ, shows a ≈2%–3% reduction in real space, compatible with a partial relaxation towards the TiO2 in-plane lattice parameter values. Furthermore, a cross-like structure compatible with a sixfold reconstructions is visible around the diffractions spots. (b) AFM image showing the nucleation of islands on a background surface where the presence of steps is still visible. Islands have lateral dimensions on the order of 100 nm and an average height of 3–4 nm. (c) A zoom of a region not containing the 3D islands, showing the step structure and the presence of a sixfold superstructure.
(a) RHEED and (b) LEED data from 10 nm thick TiO2 film deposited on SrTiO3 surface. (a) The RHEED pattern is indicative of the coalescence of the islands into a uniform anatase film and shows an evident (4 × 1) reconstruction. (b) LEED pattern showing a square in-plane lattice and the presence of two perpendicular (4 × 1) reconstructed domains. The spot width demonstrates an inferior crystal quality with respect to samples grown on LAO and SLAO (not shown). (c) STM images (It = 1 nA Vbias = 1.0 V, 200 × 200 nm2) showing a continuous anatase film formed by the coalescence of faceted islands. (d) High resolution STM image of a single domain area of the anatase film proves the existence of the surface reconstruction. The “row-like” structure has a periodicity of four unit cells.
Calculated mismatch between anatase (001) TiO2 (the plane lattice parameter is 0.3785 nm) and (001) STO, SLAO, and LAO substrates; The values of t0 are found by fitting according to Eq. (1) for films deposited on different substrates.
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