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Micron
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Real-time scan speed control of the atomic force microscopy for reducing
imaging time based on sample topography
Yingxu Zhang
a,c
, Yingzi Li
b,c,
⁎
, Guanqiao Shan
b,c
, Yifu Chen
b,c
, Zhenyu Wang
b,c
,
Jianqiang Qian
b,c,
⁎
a
School of Instrumentation Science and Opto-Electronics Engineering, Beihang University, Beijing 100191, China
b
School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China
c
Key Laboratory of Micro-nano Measurement-Manipulation and Physics, Beihang University, Beijing 100191, China
ARTICLE INFO
Keywords:
Atomic force microscopy
Amplitude modulation
Real-time control
Fast imaging
ABSTRACT
Here, a novel method, real-time scan speed control for raster scan amplitude modulation atomic force micro-
scopes (AM-AFMs), is proposed. In general, the imaging rate is set to a fixed value before the experiment, which
is determined by the feedback control calculations on each imaging point. Many efforts have been made to
increase the AFM imaging rate, including using the cantilever with high eigenfrequency, employing new scan
methods, and optimizing other mechanical components. The proposed real-time control method adjusts the scan
speed linearly according to the error of every imaging point, which is mainly determined by the sample topo-
graphy. Through setting residence time on each imaging point reasonably, the performance of AM-AFMs can be
fully exploited while the scanner vibration is avoided when scan speed changes. Experiments and simulations are
performed to demonstrate this control algorithm. This method would increase the imaging rate for samples with
strongly fluctuant topography up to about 3 times without sacrificing any image quality, especially in large-scale
and high-resolution imaging, in the meanwhile, it reduces the professional requirements for AM-AFM operators.
Since the control strategy employs a linear algorithm to calculate the scanning speed based on the error signal,
the proposed method avoids the frequent switching of the scanning speed between the high speed and the low
speed. And it is easier to implement because there is no need to modify the original hardware of the AFM for its
application.
1. Introduction
The atomic force microscope (AFM) has been a powerful tool for
obtaining the nano-characteristics of materials and cell biology since it
was invented in 1986 (Binnig et al., 1986). However, the normal AFM
needs several minutes to acquire the topographic information of sam-
ples (Fleming et al., 2010). The slow imaging rate limits its application
in dynamical observation of living cells (Schitter et al., 2004), chemical
reaction (Ichii et al., 2014), physical process (Fantner et al., 2006), and
large-range surface inspection (Borionetti et al., 2004) within desired
time.
The working principle of the AFM is based on the interaction force
between the probe and the sample surface, and it is a kind of me-
chanical scan (Picco et al., 2007). That is to say, fast imaging rate re-
quires fast motion of the sample or the probe. In recent years, many
attempts have been developed to increase the imaging rate. They can be
roughly divided into two types: optimization of components and new
scan methods. In the first approach, the hardware including the canti-
lever, the scanner and the electronic system is improved to meet the
demands for the fast imaging (Fantner et al., 2006; Herfst et al., 2015;
Bozchalooi and Youcef-Toumi, 2014). Fantner et al. (2006) improved
the performance of AFM components to record 30 frames per second at
150 × 150 pixels as early as 2006. However, due to its complexity
implementation and the current industrial level, there is almost no
breakthrough in fast-speed AFMs until now.
In the second approach, which is more generally adopted recently,
new scan methods including optimized control methods are proposed to
increase the scan speed. Yong et al. (2010) introduced a cycloid scan
method to promote the scan rate to 156.25 Hz. Schitter et al. (2007)
designed a scanner for a fast-speed AFM whose scan rate is up to
20 kHz. However there are special requirements for the controllers and
the scanners, which limit wide-spread applications of these methods.
Practically, the closed-loop feedback control (e.g. PID control) is uti-
lized for maintaining the distance between the probe and the sample
https://doi.org/10.1016/j.micron.2017.12.004
Received 17 October 2017; Received in revised form 13 December 2017; Accepted 13 December 2017
⁎
Corresponding authors at: School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China.
E-mail addresses: liyingzi@buaa.edu.cn (Y. Li), qianjq@buaa.edu.cn (J. Qian).
Micron 106 (2018) 1–6
Available online 15 December 2017
0968-4328/ © 2017 Elsevier Ltd. All rights reserved.
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