Jim-Wei Wu

Design and Control of Phase-Detection Mode Atomic Force Microscopy for Reconstruction of Cell Contours in Three Dimensions

Atomic force microscopy (AFM) is capable of producing accurate 3-D images at nanometer resolution. As a result, AFM is widely used in applications related to cell biology, such as the diagnosis and observation of tumor cells. This paper proposes phase-detection mode atomic force microscopy (PM-AFM) for the 3-D reconstruction of cell contours. The proposed three-axis scanning system employs two piezoelectric stages with one and two degrees of freedom, respectively. Accurately rendering the contours of delicate cells required a multi-input multi-output (MIMO) adaptive double integral sliding mode controller (ADISMC) in the xy-plane to overcome uncertainties within the system as well as cross-coupling, hysteresis effect, and external disturbance. An adaptive complementary sliding-mode controller (ACSMC) was installed along the z axis to improve scanning accuracy and overcome the inconvenience of conventional controllers. Phase feedback signals were also used to increase the sensitivity of scanning, while providing faster response times and superior image quality. A comprehensive series of experiments was performed to validate the performance of the proposed system.

Lissajous Hierarchical Local Scanning to Increase the Speed of Atomic Force Microscopy

Atomic force microscopy (AFM) is a highly useful instrument for material inspection, capable of scanning conductive and nonconductive samples without any restrictions as to the environment in which it is applied. This technique has, therefore, become an indispensable tool for measurement at the micro-/nanoscale. However, raster scanning in conventional AFM may induce undesirable mechanical resonance within the scanner and cannot skip the portions outside the actual area of interest within the sample. Furthermore, expanding the range and resolution of traditional AFM images may require excessive scan time. In an attempt to overcome these limitations, in this paper, we design a tapping mode AFM system using a smooth Lissajous scanning trajectory for the desired scan pattern. Based on the path characteristics of the smooth Lissajous trajectory, we develop a scanning algorithm using information related to the height of the sample from which subareas of interest are extracted for the following phase of scanning. Dividing the scanning process in two phases, actually reduces scanning times. To deal with more significant variations in the topography of some parts of the sample, we increase the resolution of scanning in those critical areas. The effectiveness of the proposed scan methodology is demonstrated in a number of conducted experiments.

Design and control of long travel range electromagnetically actuated positioning stage with application to precise machining

This paper proposes a long travel range electromagnetically actuated positioning stage with application to micro machining. Specially, a probe with titanium coating is integrated with an electromagnetically actuated and damped positioning stage to perform millimeter range movement. Here, the developed stage replaces traditional piezoelectric actuators for the purpose of lengthening the motion range while minimizing the complexity of the electrical system. Besides that, a laser interferometer is installed and high precision metrology is implemented to improve precision of machining. Next, a robust adaptive sliding-mode controller is proposed to enhance system robustness and to reject environmental disturbance. The controller architecture consists of two major components: 1) sliding mode controller, and 2) robust adaptive law. With the proposed controller, the high precision machining, with the horizontal positioning error (in root-mean-square level) kept within 52nm, can be successfully achieved.

Effective Tilting Angles for a Dual Probes AFM System to Achieve High-Precision Scanning

Because of the everlasting promotion of micro/nanofabrication techniques, the measurement of the feature contour of micro/nanofabricated structures becomes an important issue. Atomic force microscopy (AFM) is a high accuracy measurement instrument that has been frequently used in measuring of micro/nanofabricated structures. However, most conventional AFM systems use a single probe with a monotonic tilting angle to scan all kinds of sample profiles. This type of AFM design easily suffers from the so-called side wall effect, and the scanning result will induce a distortion phenomenon at the corner part. To solve this problem, a novel dual probe AFM system is proposed in this paper. A highly flexible system structure is adopted in this work to create different tilting angle of each probe. With the method developed for obtaining the appropriate tilting angle, we set up the so-called effective tilting angles under different scanning scenarios. In addition, a useful merging method has been developed to stitch together the scanning results from two different probes out of two different scanning units. For scanning a standard grating, the error of sidewall angle from the scan image decreases from 27.3% to 4.5% when our method is compared with a traditional scan. Finally, by integrating the proposed scan method with a new raster-based local scan strategy, we can achieve a high-throughput precision scan. In the scan of human blood cells, we not only can remove unnecessary scan area up to 61.04%, but also can improve sidewall distortion. A comprehensive series of experiments have been conducted to validate the scanning capability of the proposed methods on our self-developed AFM system.

A dual probes AFM system with effective tilting angles to achieve high-precision scanning

With the constant improvement of micro-fabrication techniques, the measurement of feature size of micro-fabricated structures becomes an important issue. Atomic force microscopy (AFM) is a high accuracy measurement instrument which has been widely used in micro-fabricated structures measurement recently. However, due to the monotonic tilting angle of the probe in traditional AFM system, the scanning results of sample with high steep wall feature usually have distortion phenomenon at the corner part of the sample. To solve this problem, a novel dual probe AFM system is proposed in this paper. A system structure with high flexibility is used in this work to create different tilting angle of each probe. With the tilting angle deciding method developed in this paper, we can estimate the effective tilting angles for scanning under different scenarios. In addition, a useful merging method is also designed in this work, which can stich result from different scanning unit together and produce high-precision scanning results. Experimental results are shown to validate the outstanding capability of the proposed system and methods.

Sinusoidal trajectory for atomic force microscopy precision local scanning with auxiliary optical microscopy

Atomic force microscopy (AFM) is a useful measurement instrument which can build three-dimensional topography image of conductive and nonconductive samples at high resolution. However, due to the scanning trajectory of conventional AFM, the induced mechanical resonance of the scanner and uninteresting area scanning would limit the scanning speed. In this paper, we improve these problems with our designed AFM system from three aspects. First, the sinusoidal trajectory is applied to AFM lateral scanning rather than the traditional raster trajectory, so the scanning rate can be increased without inducing vibration of the lateral scanner. Second, with this well-known trajectory, the neural network complementary sliding mode controller (NNCSMC) based on internal model principle (IMP) is proposed to achieve high precision scanning and to cope with the system parameter uncertainties and external disturbance. Finally, with the aid of an auxiliary optical microscopy which is usually used for calibration, a simple path planning method can be adopted to focus the scanning on the samples for the purpose of removing the redundant background scanning for shortening the total scanning time. Experimental results are provided to demonstrate the effectiveness of the proposed method.

Apply tapping mode Atomic Force Microscope with CD/DVD pickup head in fluid

This paper proposes a tapping mode scanning sample type Atomic Force Microscope (AFM) equipped with a CD/DVD pick-up-head (PUH) used to measure the deflection of the cantilever beam of the probe in the liquid. To start with, we build an adaptive Quality-Factor-controller (Q-controller) to modulate the interaction force between the tip and the sample. To implement the above systems, we have designed a novel AFM mechanism and proposed an adaptive sliding-mode controller for it. For testing the system capability and analyzing the biomorphic change of the sample in liquid, we have conducted a series of experiments, and the results can help us to understand more about the mechanism of the sample in liquid.

Precision sinusoidal tracking for galvanometer scanner with smith predictor-based adaptive sliding mode control

Galvanometer scanner (GVS) is a versatile instrument in the modern engineering fields. One of the important applications is to realize the laser scanning confocal microscope. Such inspection tool usually needs an affine signal to be its scanning trajectory like triangular waveform or sinusoidal signal. However, there still exists some problems such as temperature variation and time delay in GVS system, and thus the tracking performance of GVS will be jeopardized. In this paper, we design a smith predictor-based adaptive sliding mode control combined with an internal model principle (IMP) to address those limitations. With the proposed control method, it can simultaneously handle the mismatch model problem, which often occurs in Smith predictor control, as well as the issue of tracking the sinusoidal reference signals. A series of comprehensive experiments have been conducted, which demonstrate a better tracking accuracy as compared to the performances of those which only apply a traditional PD controller.

Adaptive tilting angles for a dual-probe AFM system to increase image accuracy

While the feature size of micro-fabricated structures is continuously diminishing, the issue of high accuracy measurement becomes increasingly significant. In recent years, Atomic Force Microscopy (AFM) has become a powerful measurement tool which has been widely used in micro- and nano-fabricated structure inspection. However, owing to the fixed tilting angle of the scanning probe in traditional AFM, there generally exists a distorted scanning result at the corner and sidewall of the scanned sample. To mitigate the mentioned problem, this paper presents a self-designed dual-probe AFM system with an on-line adaptive tilting angle algorithm which can estimate the most effective tilting angle for each scanning probe. Above all, a novel probe-tilting mechanism is designed to change the tilting angle after one-line scanning process is accomplished. As a result, a complete and high-precision scanning image can be obtained in a single scan through such dual-probe structure.

Lissajous scan trajectory with internal model principle controller for fast AFM image scanning

Atomic force microscopy (AFM) is a very useful measurement instrument. It can scan the conductive and nonconductive samples and without any restriction in the environments of application. Therefore, it has become an indispensable micro-/nano-scale measurement tool. However, controller of the conventional AFMs do not consider the dynamic characteristics of the scan trajectory and mostly use raster scanning easily to induce the mechanical resonance of the scanner. In an attempt to improve these problems for increasing the scan speed and accuracy, we designed an internal model principle (IMP) based neural network complementary sliding mode control (NNCSMC) for tracking a smooth Lissajous trajectory, which can allow an effectively increasing in the scan speed without obviously sacrificing in the scan accuracy. To validate the effectiveness of the proposed scan methodology, we have conducted extensive experiments and promising results have been acquired.