Noncontact Atomic Force Microscopy - Yale School of Engineering ...

Short and medium range electrostatic forces analyzed by
Kelvin probe force microscopy
Th. Glatzel, S. Kawai, S. Koch, A. Baratoff, and E. Meyer
Department of Physics, University of Basel, 4056 Basel, Switzerland.
Tu-1510
We discuss the influences of short and medium range electrostatic forces on the local
contact potential difference (LCPD) by means of amplitude modulated Kelvin probe
force microscopy (AM-KPFM) measured on single crystal KBr(100) surfaces. Bias- and
z-spectroscopic curves at atomic scale showing clear features related to the influence of
the short range electrostatic interaction [1].
In Fig.1 a typical nc-AFM /KPFM measurement of a KBr(100) in UHV is shown. While
the topography (a) was measured at the first resonance frequency of the cantilever
(approx 160kHz), the LCPD image (b) was measured by compensating the inphase signal
detected at he second resonance (approx 1MHz). A clear contrast between the different
ionic sides is observed. To clarify the origin of this contrast we performed bias- and zspectroscopy
measurements. c) shows a bias-spectroscopy measurement illustrating the
amplitude R, the inphase signal X, and the frequency shift at a maxima of the topography.
Comparing these measurements with the ones at the minimas of the topography (not
presented here) clearly shows the expected CPD difference.
Figure 1: Typical topography (3x3nm 2 , �z=100pm) and
local contact potential image (�LCPD=300mV) of a
KBr(100) surface. In c) the lockin signals amplitude R,
inphase X (second resonance of the cantilever) as well as
the frequency shift of the first resonance �f are plotted
over the bias voltage applied to the sample. The
measurement was done at a maxima of the topography.
[1] F. Bocquet et al., Phys. Rev. B 78, (2008), 035410.
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