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

Fr-1000
Visualization of Anisotropic Conductance in Polydiacetylene Crystal
by Two-probe FM-AFM/KFM
Eika Tsunemi 1 , Kei Kobayashi 2 , Kazumi Matsushige 1 , and Hirofumi Yamada 1
1 Department of Electronic Science & Engineering, Kyoto University, Katsura Nishikyo, Kyoto, Japan
2 Innovative Collaboration Center, Kyoto University, Katsura Nishikyo, Kyoto, Japan
Atomic force microscopy probe tips serve as a wide variety of roles such as
nanometer-scale electrical probes or atom manipulation tools in addition to imaging tools.
However, their simultaneous, multiple use is often limited because only a single probe is
available in AFM. Implementation of two or more probe tips can tremendously expand
the capability of AFM. We recently developed a high-resolution two-probe AFM system
using the optical beam deflection method [1]. It allows us to make a multi-probe
electrical measurement or to conduct stimulus-response experiments for various materials.
In this presentation, anisotropic conduction in a polydiacetylene (PDA) single
crystal was studied by the two-probe FM-AFM/KFM. A PDA single crystal shows an
anisotropic conductance due to the quasi-one-dimentional electronic band structure along
the diacetylene main chain. In this experiment, we used a poly-PTS (polydiacetylene
para-toluene sulfonate) single crystal (inset of the right of Fig. 1). The left of Fig. 1
shows an experimental setup. While a bias voltage was locally applied to the surface with
Probe-1, the surface potential was mapped with Probe-2 as a FM-KFM probe to visualize
the injected carrier distribution. An obtained KFM image (the right of Fig. 1) shows that
the higher potential region extends linearly along the PDA main chain from the Probe-1
contact point, which means that the carriers injected from Probe-1 travel mainly through
the diacetylene chain. In addition, the effect of a defect on the carrier transport was
investigated. We positioned Probe-1 at a point on a line parallel to the main chain through
a line defect which we had found. The right image of Fig. 2 shows that the potential
sharply drops near the edge of the defect, which indicates a resistance increase at this
point.
Figure 1: AFM (Left) and KFM (Right) images
of a poly-PTS single crystal obtained by twoprobe
FM-AFM/KFM. Schematic of two-probe
measurement is also shown (Left).
[1] E. Tsunemi et al, Jpn. J. Appl. Phys. 46, 5636 (2007).
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Figure 2: AFM (Left) and KFM (Right)
images of a poly-PTS single crystal surface
with a line defect.