Bonnell, Dawn A

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Author: Shao, Rui ×

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Now showing 1 - 6 of 6
  • Publication
    Local Phenomena in Oxides by Advanced Scanning Probe Microscopy
    (2005-05-01) Kalinin, Sergei V.; Shao, Rui; Bonnell, Dawn A
    In the last two decades, scanning probe microscopies (SPMs) have become the primary tool for addressing structure and electronic, mechanical, optical, and transport phenomena on the nanometer and atomic scales. Here, we summarize basic principles of SPM as applied for oxide materials characterization and present recent advances in high-resolution imaging and local property measurements. The use of advanced SPM techniques for solutions of material related problems is illustrated on the examples of grain boundary transport in polycrystalline oxides and ferroelectric domain imaging and manipulation. Future prospects for SPM applications in materials science are discussed.
  • Publication
    Photo-induced Charge Dynamics on BaTIO3 (001) Surface Characterized by Surface Probe Microscopy
    (2006-09-11) Shao, Rui; Nikiforov, Maxim P; Bonnell, Dawn A
    The surface potential of a multidomain BaTiO3 (001) surface was imaged in the presence and absence of ultraviolet (UV) illumination. The UV radiation induces a decrease in the surface potential contrast between c+ and c− domains with a time constant of a few seconds due to redistribution of photocarriers and screening. A slower process of recovery was observed after illumination. In addition, scanning a conducting atomic force microscopy tip in contact under UV illumination destabilizes some ferroelectric domains.
  • Publication
    Evolution of the Structure and Thermodynamic Stability of the BaTiO3(001) Surface
    (2008-07-18) Kolpak, Alexie M; Li, Dongbo; Rappe, Andrew M; Shao, Rui; Bonnell, Dawn A
    We report a series of new surface reconstructions on BaTiO3(001) as a function of environmental conditions, determined via scanning tunneling microscopy and low energy electron diffraction. Using density functional theory calculations and thermodynamic modeling, we construct a surface phase diagram and determine the atomic structures of the thermodynamically stable phases. Excellent agreement is found between the predicted phase diagram and experiment. The results enable prediction of surface structures and properties under the entire range of accessible environmental conditions.
  • Publication
    Nanoimpedance Microscopy and Spectroscopy
    (2002-12-02) Shao, Rui; Bonnell, Dawn A; Kalinin, Sergei V
    One of the key limiting factors in current-based scanning probe microscopies (SPM) is the quality of tip-sample contact and stray capacitance in the probe-surface junction. We conduct impedance spectroscopy over a broad frequency range (40Hz~110MHz) through an AFM tip to quantify local electrical properties. Equivalent circuit for the tip-surface contact is constructed based on the impedance data and is used to study the mechanisms of relaxation in the near-tip region. Relative contributions of tip-surface contact and materials properties to the signal are discussed. This technique, referred to as Nanoimpedance Microscopy/Spectroscopy, is demonstrated in the imaging of an electronic ceramic: a ZnO varistor. Analysis of impedance spectra allows separation of tip-surface interactions and grain boundary behavior.
  • Publication
    Low-Temperature Resistance Anomaly at SrTiO3 Grain Boundaries: Evidence for an Interface-Induced Phase Transition
    (2005-11-04) Shao, Rui; Chisholm, Matthew F; Duscher, Gerd; Bonnell, Dawn A
    Variable temperature transport between 1.4 and 300 K, structural imaging, and theoretical calculations were used to characterize the properties of electrically active 24º and 36.8º [001] tilt SrTiO3 grain boundaries with 0.1 at.% niobium doping. An anomaly in boundary resistance and capacitance characteristics typical of a positive temperature coefficient effect is observed. This behavior is indicative of interface-induced dipole ordering. The detailed atomic structures of these grain boundaries were determined from a comparison of ab initio calculations and Z-contrast TEM images. The number of excess electrons at the boundaries determined experimentally and theoretically agrees and is associated with the boundary structural units.
  • Publication
    In situ deposition/positioning of magnetic nanoparticles with ferroelectric nanolithography
    (2005-03-01) Lei, Xiaojun; Li, Dongbo; Shao, Rui; Bonnell, Dawn A
    Ferroelectric nanolithography is a new approach to processing nanostructures, which can position multiple components made of various materials into predefined configurations. Local polarization in ferroelectric compounds is manipulated to control the surface electronic structure and direct attachment of molecules and particles. Here, the presence of optically excited electron-hole pairs on ferroelectric domains is confirmed, and reaction paths for photo reduction of several reactive metal particles are determined. Subsequent and simultaneous deposition of multiple metals is demonstrated, and the magnetic properties of Co based particles are confirmed.