1. Tip characterization SIN in Japan 2011 1 Teemu Hynninen M. Bieletzki, T. Soini, C. Barth, C. Henry, F. Esch, A. S. Foster, U. Heiz Tip characterization in nc-AFM and KPFM imaging of thinfilms

2. Tip characterization SIN in Japan 2011 2 AFM reversed: can the surface image the tip? Of course, but can we say something quantitative?

3. Tip characterization SIN in Japan 2011 3 Methodology MgO(001) grown on Ag(001) Ag sputtered and annealed Mg evaporation (0.1 ML/min) in O 2 atmosphere at 300 o C frequency modulated nc-AFM and KPFM constant detuning mode room temperature 10 -10 mbar UHV E XPERIMENTS C ALCULATIONS density functional theory VASP code plane wave basis PAW potentials PBE functional

4. Tip characterization SIN in Japan 2011 4 Topography: experimental Ag surface MgO islands Relative height of islands (2 Å): supported embedded MgO Ag MgO Mg O Ag Mg O Ag images in constant df mode 0.3 ML MgO coverage Bieletzki et al., Phys. Chem. Chem. Phys. 12 (2010) 3203

5. Tip characterization SIN in Japan 2011 5 + - + – + – + – + – + – + – Topography: simple model Polar/charged tip: attractive interaction with metal Bieletzki et al., Phys. Chem. Chem. Phys. 12 (2010) 3203 Dipole layer on the MgO island breaks charge symmetry + - positive + - negative + - + - positive + - negative + - + – + – + – + – + – + – + - relative height: Ag > MgO relative height: Ag < MgO

6. Tip characterization SIN in Japan 2011 6 Topography: calculations non-stoichiometric tips (polar) stoichiometric tips Bieletzki et al., Phys. Chem. Chem. Phys. 12 (2010) 3203 + - positive + - negative neutral Long-range electrostatic interaction for polar tip and MgO film Relative height differences of several Ångströms

7. Tip characterization SIN in Japan 2011 7 Kelvin: experimental TopographyKelvin voltage neutral + - negative + - positive ContrastTip

8. Tip characterization SIN in Japan 2011 8 Kelvin: simple model + - + - ----++++

9. Tip characterization SIN in Japan 2011 9 Kelvin: simple model =++ energypolarizationcharge-capacitorcapacitor dipole charge L. Kantorovich et al. Surf Sci 445, 283–299 (2000).

10. Tip characterization SIN in Japan 2011 10 Kelvin: simple model +-++ T. Hynninen et al. E-J. Surf. Sci. Nanotech. 9 6 (2011)

11. Tip characterization SIN in Japan 2011 11 Kelvin: beyond the simple model bias potential in a realistic geometry (FEM) 10 cm1 nm field fed to atomistic models (DFT?)

12. Tip characterization SIN in Japan 2011 12 Tip characterization: Summary Topography contrast (neutral vs. positive surface) Tip charge/polarization Average Kelvin voltage (w.r.t contact potential) + - negative MgO > Ag negative shift + - positive MgO < Ag positive shift neutral MgO = Ag no shift Thank you!