tip characterization sin in japan 2011 1 teemu hynninen m. bieletzki, t. soini, c. barth, c. henry,...
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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
Tip characterization
SIN in Japan 2011 2
AFM reversed: can the surface “image” the tip? Of course, but can we say something quantitative?
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 O2 atmosphere at 300 oC
frequency modulated nc-AFM and KPFM
• constant detuning mode• room temperature• 10-10 mbar UHV
EXPERIMENTS CALCULATIONS density functional theory
• VASP code• plane wave basis• PAW potentials• PBE functional
Tip characterization
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Topography: experimental
Ag surface
MgO islands
Relative height of islands (2 Å):
supported
embedded
MgO
Ag
MgO
Mg OAg
Mg OAg
images in constant df mode 0.3 ML MgO coverage
Bieletzki et al., Phys. Chem. Chem. Phys. 12 (2010) 3203
Tip characterization
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+-
+
–
+
–
+
–
+
–
+
–
+
–
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
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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
Tip characterization
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Kelvin: experimentalTopography Kelvin voltage
neutral
+- negative
+- positive
Contrast Tip
Tip characterization
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Kelvin: simple model
+-
+-
-
--
-
+
+++
Tip characterization
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Kelvin: simple model
= + +
energy polarization charge-capacitor capacitor
dipole charge
L. Kantorovich et al. Surf Sci 445, 283–299 (2000).
Tip characterization
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Kelvin: simple model
-80 -60 -40 -20 0 20 40 60 800
200
400
600
800Equal charges 5 nm apart
Lateral distance (Å)
Ke
lvin
vo
lta
ge
(m
V)
-80 -60 -40 -20 0 20 40 60 80-800
-400
0
400
800Opposite charges 5 nm apart
R = 5 nm, z = 1 nm
R = 20 nm, z = 1 nm
R = 5 nm, z = 3 nm
R = 20 nm, z = 3 nm
Lateral distance (Å)
+ -+ +
T. Hynninen et al. E-J. Surf. Sci. Nanotech. 9 6 (2011)
Tip characterization
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Kelvin: beyond the simple model
bias potentialin a realisticgeometry (FEM)
10 cm 1 nm
field fed toatomisticmodels (DFT?)
Tip characterization
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Tip characterization: SummaryTopography 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
neutralMgO = Ag no shift
Thank you!