Tip characterization SIN in Japan 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

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

Tip characterization SIN in Japan 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 mbar UHV E XPERIMENTS C ALCULATIONS density functional theory VASP code plane wave basis PAW potentials PBE functional

Tip characterization SIN in Japan 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

Tip characterization SIN in Japan – + – + – + – + – + – 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

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

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

Tip characterization SIN in Japan Kelvin: simple model

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

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

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

Tip characterization SIN in Japan 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!