DFT analysis of combined 3D NC-AFM and STM imaging of Cu(100)-O oxide surface
CFM Seminars
- Speaker
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Milica Todorovic, Universidad Autónoma de Madrid
- When
-
2012/07/16
18:00 - Place
- Auditorium of the Centro de Fisica de Materiales, Paseo Manuel de Lardizabal 5, Donostia-San Sebastián
- Add to calendar
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Investigation of novel catalytically active surfaces requires a comprehensive
experimental method for the identification and rapid characterization of
prospective catalytically active sites. The powerful method of three-
dimensional atomic force microscopy (3D-AFM) in non-contact mode [1] has been
combined with scanning tunnelling microscopy (STM) to study the oxygen-
terminated copper (100) surface. Complex 3D data sets, obtained by
simultaneously recording the tunnelling current and the AFM frequency shift,
allow for site specific quantification of forces and tunneling currents. The
wealth of information obtained is promising for future applications, but the
interpretation of the wide range of contrast modes requires a thorough
characterisation of the sources of contrast in AFM and STM imaging.
We combine DFT total-energy calculations with Non-equilibrium Green’s
Function (NEGF) methods for electronic transport to determine the tip-surface
interaction and tunnelling current [2, 3, 4] for a large set of tip models in
order to clarify the different contrast modes obtained in the experiments. At
the outset, we obtained a stable Cu(100)(2√2x√2)R45◦ -O surface
reconstruction model. Surface features were found to be in good agreement with
experimental data, and the analysis of surface electronic properties enabled
us to identify prospective reactive sites. The effect of tip changes on
contrast modes was explored by considering tips of different reactivity. Our
simulations, in comparison with AFM experimental images, identified a
contaminated tip with a Cu-terminated experimental conï¬guration. Charge
density and current calculations further helped to investigate the STM imaging
mode and explain the lateral shift between surface features identified
separately in AFM and STM images. Additionally, simulations of different
surface defect models led us to understand detailed STM image features and
enabled us to explore domain formation on the Cu(100)-O surface. The
combination of conductance calculations with total energy methods provides
insight into (1) the fundamentals of contrast formation in this novel
experimental technique and (2) into the correlation between tip-sample forces
and local chemical reactivity, factors that are essential for the further
development and application of this approach to characterise catalytic
activity.
[1] B. J. Albers, T. C. Schwendemann, M. Z. Baykara, et al., Nature Nanotech.
4, 307, (2009).
[2] Y. Sugimoto, P. Pou, M. Abe, et al., Nature 446, 64, (2007).
[3] P. Jelinek, M. Svec, P. Pou, et al., Phys. Rev. Lett. 101, 176101, (2008).
[4] J. M. Blanco, F. Flores and R. Perez, Prog. Surf. Sci. 81, 403, (2006).