Browsing by Author "F. Canova, Filippo"

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Measuring Electric Field Induced Subpicometer Displacement of Step Edge Ions
(2012) Kawai, Shigeki; F. Canova, Filippo; Glatzel, Thilo; Hynninen, Teemu; Meyer, Ernst; Foster, Adam S.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We provide unambiguous evidence that the applied electrostatic field displaces step atoms of ionic crystal surfaces by subpicometers in different directions via the measurement of the lateral force interactions by bimodal dynamic force microscopy combined with multiscale theoretical simulations. Such a small imbalance in the electrostatic interaction of the shifted anion-cation ions leads to an extraordinary long-range feature potential variation and is now detectable with the extreme sensitivity of the bimodal detection.
Noncontact atomic force microscopy imaging of the atomic structure and cation defects of the polar MgAl2O4 (100) surface
(2011) Rasmussen, Morten K.; Foster, Adam S.; F. Canova, Filippo; Hinnemann, Berit; Helveg, Stig; Meinander, Kristoffer; Besenbacher, Flemming; Lauritsen, Jeppe V.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Atom-resolved noncontact atomic force microscopy (NC-AFM) was recently used to reveal that the insulating spinel MgAl2O4(100) surface, when prepared under vacuum conditions, adopts a structurally well-defined Al and O-rich structure (Al4-O4-Al4 termination) consisting of alternating Al and double-O rows, which are, however, interrupted by defects identified as interchanged Mg in the surface layers (so-called antisite defects). From an interplay of futher NC-AFM experiments and first-principles NC-AFM image simulations, we present here a detailed analysis of the NC-AFM contrast on the MgAl2O4(100) surface. Experiments show that the contrast on MgAl2O4(100) in atom-resolved NC-AFM is dominated by two distinctly different types of contrast modes, reflecting two oppositely charged tip-apex terminations. In this paper, we analyze the contrast associated with these imaging modes and show that a positively charged tip-apex (presumably Mg2+) interacts most strongly with the oxygen atoms, thus imaging the oxygen lattice, whereas a negatively charged tip-apex (O2−) will reveal the cation sublattice on MgAl2O4. The analysis of force-vs-distance calculations for the two tips shows that this qualitative picture, developed in our previous study, holds for all realistic tip-surface imaging parameters, but the detailed resolution on the O double rows and Al rows changes as a function of tip-surface distance, which is also observed experimentally. We also provide an analysis of the tip dependency and tip-surface distance dependency for the NC-AFM contrast associated with single Al vacancies and Mg-Al antisite defects on the MgAl2O4(100) surface and show that it is possible on the basis of NC-AFM image simulations to discriminate between the Al3+ and Mg2+ species in antisite defects and hypothetical Al vacancies.