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

Theory of Multifrequency Method in FM-AFM
Zongmin Ma, Yoshitaka Naitoh, Yanjun Li, Masami Kageshima
and Yasuhiro Sugawara
Department of Applied Physics, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka,
Suita, Osaka 565-0871, Japan
P.I-29
FM-AFM has been succeeded in measuring topography and energy dissipation
with atomic resolution on the surface. Furthermore, force spectroscopy is
demonstrated to identify the atomic species. The elasticity information of the surface
is important physical information of the sample materials. Actually, it has been
measured by using multifrequency method in AM-AFM recently, which was proposed
by Rodriguez and Garcia and successfully demonstrated its usefulness theoretically
and experimentally [1-2].
In this paper, for the first time, we
proposed usage of the multifrequency
f 2
BPF PLL Δf 2
method in FM-AFM to measure the
AGC
sample properties such as elasticity.
Figure 1 shows the block diagram of
×
multifrequency method in FM-AFM.
f 1
BPF PLL
The cantilever is excited simultaneously
at the first and the second resonances.
Band pass filters (BPFs) are used to
separate the vibration signals of the
Optical
interferometer
+
+
AGC
×
cantilever. For each signal, the cantilever
Cantilever
Δf 1
is vibrated by self-oscillation at the first
Feedback
and the second resonances. Topography
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Topography
of the sample is obtained by the
feedback signal to keep the frequency
Figure 1. Block diagram of multifrequency
shift (△ f1) constant. The elasticity information of the sample surface is measured by
frequency shift (△ f2) of the second resonance, which is proportional to the
conservative force between tip and sample. Here, we show the theory for the
multifrequency method in FM-AFM.
[1] Rodriguez and R. Garcia, Appl. Phys. Lett. 84, 449 (2004).
[2] Jose R. Lozano and Ricardo Garcia. Phy Rev B 79, 014110 (2009).
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