Epitaxial growth of iridium on strontium-titanate (0 0 1) studied by in situ scanning tunneling microscopy

The growth of iridium on top of TiO2 terminated SrTiO3(0 0 1) surfaces at a temperature of 920 °C has been investigated by in situ scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) as well as ex situ X-ray diffraction. Under these conditions, an epitaxial growth is obtained with the following orientation: SrTiO3(0 0 1)∥Ir(0 0 1), SrTiO3[1 0 0]∥Ir[1 0 0]. Up to a film thickness of 2 nm, the Ir shows a pronounced Volmer–Weber growth resulting in three dimensional needle-like columns, while the SrTiO3 surface in between is preserved including its reconstruction. For a film thickness between 2 and 10 nm, the observed coalescence of the Ir columns is accompanied by a significant change of the I/V characteristics as determined by STS. At a thickness of 20 nm the final morphology of the metal film develops characterized by a surprisingly flat Ir(0 0 1) surface with predominantly rectangular holes of a maximum depth of approximately the film thickness and a width of ∼25 nm covering about 8% of the surface.