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

P.I-13
Deconvolution and Tip Geometry Effects in Atomic- and Nanoscale Kelvin probe
Force Microscopy
George Elias 1 , Yossi Rosenwaks 1 , Amir Boag 1 , Ernst Meyer 2 , and Thilo Glatzel 2
1 Dept. of Physical Electronics, Tel-Aviv University, Tel Aviv 69978, Israel
2 Dept. of Physics, University of Basel, Klingelbergstr. 82, 4056 Basel, Switzerland
In Kelvin probe force microscopy (KPFM) the long range electrostatic forces between the
tip and the surface prevents quantitative measurement of nanostructures; however this
can become feasible by developing appropriate deconvolution algorithms that restore the
actual sample work function. We present such novel algorithms and methods that enable
us to restore measurements conducted at tip-sample distances below 1 nm, while taking
into account also the measured topography. Fitting the restored images with KPFM
measurements of samples with well defined work function values has allowed us to
extract the measuring tip geometry and validate our deconvolution methods.
The three dimensional potential of the tip-sample system is calculated using an
integral equation based boundary element method, combined with modeling the sample
by an equivalent dipole-layer and image-charge model. The tip is modeled using MSC
Patran finite element mesh, to create a high density mesh on the tip apex and a lower
density mesh far from the sample as shown in Figure 1 (left). The middle figure shows a
measured UHV-KPFM image of NaCl thin film grown on Cu (111) and a comparison
with convolutions performed with 3 different tip apex radii (right). The excellent
agreement obtained for a tip apex of 10nm allows to estimate the tip apex geometry, and
helps to validate our convolution algorithms. Implications for real tip shapes (nanotips)
and atomic resolution imaging is demonstrated and discussed
Figure 1: (left) Full tip geometry mesh and tip apex mesh ; (middle) a KPFM measurement of
NaCl thin films grown on Cu(111); (right) a comparison between the measured KPFM line in the
middle image and convolutions performed for 3 tip apex radii (half opening angle of 17.5º) of 3,
6, and 10 nm.
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