The Effects of Structure on the Formation of Schottky Barriers at Nanoparticle-Oxide Interfaces
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The Effects of Structure on the Formation of Schottky Barriers at Nanoparticle-Oxide Interfaces Ramsey Kraya1 and Laura Y. Kraya1 1 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, 19104 U.S.A. ABSTRACT The surface structure of oxide materials may be the limiting factor in controlling switching properties at interfaces. Here we investigate and correlate the surface structure and electronic properties of BaTiO3 substrates. By using low energy electron diffraction and scanning tunneling microscopy we are able to identify surface reconstructions based on annealing treatments. We then investigate the effect of contact size on the transport properties on oxide surfaces utilizing atomic force microscopy. Our results show the critical importance of controlling surface structure to optimize electronic properties at oxide interfaces. INTRODUCTION Understanding atomic mechanisms of surface reactivity in ferroelectric oxides has garnered much interest in recent years because of the potential impact to nanolithography, device memory, and catalysis.[1] The physical properties (elastic, dielectric, piezoelectric, optical, etc) of many ferroelectric oxides are already well documented. However, the structure and electronic properties of defects is not understood. Due to the trend towards miniaturization of devices, an understanding of these relationships is crucial because ferroelectric oxides display a high sensitivity to structural variations and defects. As the surface science of metal oxides has developed over the past two decades, contributions have been made to the understanding of nanoparticle-oxide interfaces. The number of studies connecting atomic resolution SPM with interface studies on oxides is still quite limited and on ferroelectric oxides is nearly non-existent. Low Energy Electron Diffraction (LEED) and scanning tunneling microscopy (STM) are used to investigate the surface and electronic structures of BaTiO3 (001) of various reconstructed surfaces. The coexistence of the (¥5x¥5)R26.6o and (3x1) reconstructions have been observed using LEED, and corresponding STM images of the surface reveal the presence of these reconstructions in addition to defects, including Ba adatoms, oxygen vacancies, undercoordinated atoms, and other impurities. The presence of defects influences both the surface and electronic structure of the reconstructions, and it is important to understand the effect of these defects on the electronic structure of highly oriented surfaces. EXPERIMENT Polished BaTiO3 (001) (Princeton Scientific Co.) with sample dimensions 2.5 mm x 2.5 mm x 0.6 mm are used, and experiments were carried out in an ultrahigh vacuum STM Omicron chamber. The sample was annealed at 1000oC for 45 minutes and was characterized by LEED to
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determine the structure at the surface. After cooling, the sample was transferred to the STM stage. The STM measurements were obtained with etched tungsten tips at a bias voltage of 2.0 V and 0.2 nA. The (¥5x¥5)R26.6o and (3x1) surface structu
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