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S.V. Kalinin, H.N. Lee, and H.M. Christen Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831

R.G. Moore and E.W. Plummer Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831; and Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996

A.P. Baddorf Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (Received 14 June 2004; accepted 28 September 2004)

Surface stability of nearly defect-free epitaxial SrRuO3 thin films grown by pulsed laser deposition was studied using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and electron spectroscopies. Even after exposure to atmosphere, surfaces exhibited distinct LEED patterns providing evidence of unusual chemical stability. Surface order disappeared after heating to 200 °C in vacuum. To investigate, SrRuO3 thin films were annealed up to 800 °C in high vacuum and examined for chemical state and topography. Formation of unit-cell deep pits and the Ru-rich particles begins at low temperatures. Hydrocarbon contamination on the surface contributes to this process.

Strontium ruthenates have recently attracted significant attention due to their outstanding electrical transport properties.1,2 The perovskite SrRuO3 is a promising electrode material for oxide-based electronic devices such as nonvolatile ferroelectric random access memories or ferroelectric gate transistors.3 Understanding the thermodynamic stability and the physical and chemical properties of SrRuO3 thin films is crucial for the device fabrication process. Deviation in the stoichiometry of SrRuO3 surfaces can result in poorer quality of subsequent growth and in the formation of weakly conductive dead-layers that degrade device performance through retention loss, fatigue, and reduced device capacitance. Here we analyze surface properties and the thermal stability of epitaxial SrRuO3 thin films using scanning probe microscopies, electron diffraction, and electron spectroscopies. Epitaxial SrRuO3 thin films (thickness 4–10 nm) were grown on SrTiO3 (001) substrates by pulsed laser deposition (PLD) as reported elsewhere.4 Ambient atomic force microscopy (AFM) images of SrRuO3 films after deposition [Fig. 1(a)] illustrate a stepped topography— similar to that of the TiO2-teminated SrTiO3 substrate

a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0480 J. Mater. Res., Vol. 19, No. 12, Dec 2004

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prior to deposition—with a low step density and flat terraces. These growth conditions have been shown to produce SrO terminated SrRuO3 films as confirmed by Z-contrast scanning transmission microscopy5 and by reflection high-energy electron diffraction (RHEED).6 After reinsertion into high vacuum (∼10−9 Torr), a (1 × 1) low-energy electron diffraction (LEED) pattern (SPECS ErLEED 1000) has been observed as illustrated in Fig. 1(b), confirming