Noncontact atomic force microscopy imaging of the atomic structure and cation defects of the polar MgAl2O4 (100) surface : Experiments and first-principles simulations
Loading...
Access rights
openAccess
publishedVersion
URL
Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This publication is imported from Aalto University research portal.
View publication in the Research portal (opens in new window)
View/Open full text file from the Research portal (opens in new window)
View publication in the Research portal (opens in new window)
View/Open full text file from the Research portal (opens in new window)
Date
Department
Major/Subject
Mcode
Degree programme
Language
en
Pages
Series
Physical Review B, Volume 84, issue 23, pp. 1-14
Abstract
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.Description
Keywords
Other note
Citation
Rasmussen, M K, Foster, A S, F. Canova, F, Hinnemann, B, Helveg, S, Meinander, K, Besenbacher, F & Lauritsen, J V 2011, 'Noncontact atomic force microscopy imaging of the atomic structure and cation defects of the polar MgAl2O4 (100) surface : Experiments and first-principles simulations', Physical Review B, vol. 84, no. 23, 235419, pp. 1-14. https://doi.org/10.1103/PhysRevB.84.235419