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

P.I-12
Resolution enhanced multifrequency electrostatic force microscopy
under ambient conditions
X. D. Ding 1 , J. B. Xu 2 , and J. X. Zhang 1
1 State Key Laboratory of Optoelectronic Materials and Technologies, and School of Physics Science &
Engineering, Sun Yat-sen University, Guangzhou 510275, China
2 Department of Electronic Engineering, and Materials Science and Technology Research Center, The
Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
Electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM)
are widely used to study the electrical and electrochemical characteristics of a variety of
material. The lateral resolution for EFM ia better than 10~20nm under vacuum conditions
In contrast, the lateral resolution reported in literature is only 100 nm or so under ambient
conditions. Though suffering from strong mechanical non-linearity of repulsive tip–
sample contact, multifrequency method has been introduced to EFM recently[1].
Here, we report an extension of multifrequency AFM with enhanced resolution to
measure electrostatic force under ambient conditions[2]. The first eigenmode of a
cantilever is used for topography imaging, while the third eigenmode is resonantly
excitated with a sinusoidal modulation voltage applied on tip to measure electrostatic
force in lift mode. Figure 1 shows the images for a thermally evaporated aluminum (Al)
film on Si(111). Due to the surface potential variation of the sample, the EFM image in
figure 1(b) shows a well reproduced contrast different from its corresponding topographic
image in figure 1(a). The lateral resolution is better than 15nm determined from the line
profile in figure 1(c). The enhancement of resolution is ascribed to the suppress of the
cantilever-sample interactions and the increase of the tip-sample interactions due to the
use of the third eigenmode of the probe.
80nm
30 50 70
Position, nm
(a) (b) (c)
Figure 1: Experimental results of the multifrequency EFM for Al film on Si(111) under ambient
conditions. (a) Topography image. (b) EFM Image, and (c) The line profile along the arrow in (b)
[1] R. W. Stark, N. Naujoks, and A. Stemmer, Nanotechnology 18, 065502 (2007).
[2] X. D. Ding, C. Li, R. Y. Zeng, J. An, and J. B. Xu, Appl. Phys. Lett. (To be published)
(X. D. Ding, Category 7-Kelvin probe microscopy is fitted and an Oral presentation is preferred)
103
Electrostatic Force, a.u.
1.5
1.0
0.5
10-15nm