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

3D Scanning Force Microscopy at Solid/Liquid Interface
Takeshi Fukuma 1,2 and Yasumasa Ueda 1
1 Frontier Science Organization, Kanazawa University, Kanazawa, Japan
2 PRESTO, Japan Science and Technology Agency, Kawaguchi, Japan.
Tu-0920
The solid/liquid interface inherently has a three-dimensional (3D) extent in XYZ
directions. This is particularly evident when solvation layers exist at the interface [1]. In
frequency modulation atomic force microscopy (FM-AFM), a tip is scanned in XY
directions to produce a 2D height (or Δf ) image having no vertical extent in Z direction.
Therefore, the information contained in a 2D FM-AFM image is insufficient for
understanding 3D distribution of solvent molecules interacting with the atoms or
molecules constituting the solid surface. In an effort to resolve this issue, 3D force
mapping technique has been proposed, where a number of force curves are measured at
arrayed XY positions. This, however, results in a considerable increase of imaging time
and hence has been used mainly in vacuum at low temperatures.
In this study, we propose a method referred to as “3D scanning force microscopy (3D-
SFM)”, where a tip is scanned in Z as well as XY directions. While 3D force mapping is
based on 1D force spectroscopy, 3D-SFM is based on 2D imaging technique. This
methodological advancement, together with our recent development of high-speed
scanner and frequency detector, has enabled us to obtain 3D-SFM image of mica/water
interface in 53 sec (Fig. 1). The atomically-resolved XY and XZ cross-sectional images
obtained from the 3D-SFM image allow us to correlate the lateral positions of the surface
atoms with the vertical distribution of the force field. The site-specific Δf vs distance
curves are obtained from the Z profiles of the 3D-SFM image, revealing the remarkable
variation of the force profiles depending on the tip positions. The results demonstrate that
3D-SFM provides diverse information that has not been accessible with conventional 2D
imaging techniques.
Figure 1: (a) XY and XZ cross-sectional images and (b) Δf vs distance curves obtained from a
3D-SFM image of mica/water interface (53 sec / 3D image, 0.82 sec / XZ image, Raw data).
[1] T. Fukuma, M. J. Higgins and S. P. Jarvis, Biophys. J. 92 (2007) 3603-3609.
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