Chengdong Wu

Global Shape Reconstruction of the Bended AFM Cantilever

Principle of atomic force microscope (AFM) is on the basis of cantilevers deflection. However, up to now, there are still no effective methods to model the cantilevers deflection with high precision, which will usually result in a poor measurement accuracy of AFM and has greatly limited further applications of AFM in more different fields. Thus, a global shape from defocus method, which is only based on a single vision sensor, is introduced in this paper to reconstruct the bended shape of AFM cantilever. First, the model of the defocus imaging is given using the concepts of relative blurring and diffusion equation. Second, the relationship between the relative blurring and the interested depth information is built with basic imaging formulas. Subsequently, the depth measurement problem is transformed into an optimization issue and an algorithm is designed to compute the deflection of cantilever. Finally, extensive experiments are conducted and results are analyzed to show the feasibility and the effectiveness of the proposed method.

Efficient Shape Reconstruction of Microlens Using Optical Microscopy

The imaging properties of a microlens are highly related to its 3-D profile; therefore, it is of fundamental importance to measure its 3-D geometrical characteristics with high accuracy after industrial fabrication. However, common 3-D measurement tools are difficult to use for fast, noninvasive, and precise 3-D measurement of a microlens. Depth acquisition is a direct way to understand the 3-D properties of objects in computer vision, and shape from defocus (SFD) has been demonstrated to be effective for 3-D reconstruction. In this paper, a depth reconstruction method from blurring using optical microscopy and optical diffraction is proposed to reconstruct the global shape of a microlens. First, the relationship between the intensity distribution and the depth information is introduced. Second, a blurring imaging model with optical diffraction is formulated through curve fitting, accounting for relative blurring and heat diffusion, and a new SFD method with optical diffraction and defocused images is proposed. Finally, a polydimethylsiloxane (PDMS) microlens is used to validate the proposed SFD method, and the results show that its global shape can be reconstructed with high precision. The average estimation error is 77 nm, and the cost time is reduced by 92.5% compared with atomic force microscopy scanning.

Global depth from defocus with fixed camera parameters

Reconstruction depth from 2D images is an important research issue in computer vision, and depth from defocus (DFD) is an effective way which takes the blurred degree of the region images whose depth of field is limit as the tool of computing depth. Now though there are many DFD methods, they all need to change camera parameters in order to attain blurred images, such as the focal length of the lens, the radius of the lens. If cameras with high level of amplification are used, it is inhibitory to change camera parameters. Therefore, in this paper a novel DFD method is proposed. First, two different blurred images are captured through changing depth. Second, the blurred imaging model is constructed with the relative blurring and the diffusion equation, and the relation between depth and blurring is discussed from two aspects. Finally, the problem of computing depth is transformed into an optimization issue. The method proposed in this paper does not need to change camera parameters, so the process is very simple and can be used in some special applications. The simulation results show that this method can attain depth with high precision.

A study on the influence of surface active agent molecules on the AFM scanning and imaging of SWCNTs

The paper proposed a preprocessing method for scanning samples based on rinsing technology, and solved the effective fabrication problem of AFM scanning samples based on facilitated dispersing SWCNTs with SDS surface active agents. First, the ultrasonication oscillation method was applied, and the uniform alignment of SWCNTs in SDS was realized. Then, SDS solution of different concentrations was scanned and imaged with AFM, the influence of SDS solution on the imaging quality of SWCNTs was analyzed, and the method to effectively fabricate scanning samples after dispersing SWCNTs was found. The results of the experiments showed that the preprocessing of the SWCNTs solution scanning samples was the decisive factor to influence SWCNTs imaging quality, that the result of rinsing SWCNTs scanning samples for 5s at 0.1ml/s with di-ionized water was the best, and that with the same rinsing rate and angle, the rinsing di-ionized water quantity would influence the alignment degree of SWCNTs on the substrates and SDS macromolecules residual quantity on SWCNTs scanning samples.

Nanoscale depth reconstruction from defocus: within an optical diffraction model

Depth from defocus (DFD) based on optical methods is an effective method for depth reconstruction from 2D optical images. However, due to optical diffraction, optical path deviation occurs, which results in blurring imaging. Blurring, in turn, results in inaccurate depth reconstructions using DFD. In this paper, a nanoscale depth reconstruction method using defocus with optical diffraction is proposed. A blurring model is proposed by considering optical diffraction, leading to a much higher accuracy in depth reconstruction. Firstly, Fresnel diffraction in an optical system is analyzed, and a relationship between intensity distribution and depth information is developed. Secondly, a blurring imaging model with relative blurring and heat diffusion is developed through curving fitting of a numerical model. In this way, a new DFD method with optical diffraction is proposed. Finally, experimental results show that this new algorithm is more effective for depth reconstruction on the nanoscale.

An Automatic Surface Elasticity Measurement and Error Compensation Method Based on Contact Mode AFM

Force aroused from the contact of atomic force microscope (AFM) tip to a sample surface can induce compression of the sample due to its elasticity, thus causing the scanned height image of AFM to be lower than expected. A theoretical investigation of surface elasticity measurement and error compensation method is proposed in this paper. The error source of the height image is systematically demonstrated by analyzing the force curve of different materials in contact mode. Furthermore, an automatic surface elasticity measurement and error compensation method based on information fusion and parameter identification are proposed. In addition, Kalman filter is utilized to filter the compensated height image in order to eliminate system noise. Experimental results show the validity of the proposed compensation method and Kalman filter.

Analysis, comparison and improvement of block matching based sub-pixel motion measurement methods for image sequences

In this paper, the sub-pixel motion measurement for image sequences is researched, and an improved two-dimensional distance-similarity measurement based on block matching algorithm is proposed to decrease the huge computational burden of existing strategies by reducing the searching region. Then, the normal sub-pixel motion estimation based on quadratic curve fitting is analyzed and several other fitting functions are proposed to be used in sub-pixel motion estimation. Finally, the extensively comparison experiments are conducted with respect to the motion measurement for image sequences, and the detailed analysis about influence of the objective functions, the block size, and the fitting function on the estimation precision is given.

A height error compensation method based on contact mode AFM

Nowadays, atomic force microscope(AFM) has become an important tool in micro/nano research, and its height image even has been taken as an indispensable approach to understand characters of micro/nano samples. However, some preceding researches have shown that the height image scanned by AFM appears to be lower than expected sometime because of the compression force of the tip, and some arguments have also been proposed to try to explain this phenomenon. But until now, there is not a method analyzing it systematically and quantificationally, let alone compensate this error in the height image. Therefore, in this paper, a new error compensation method is proposed. First, since the force curve of AFM has become an effective method to research the elasticity, through analysis on the force curve of different kinds of materials, the error source of the height image is proved in theory based on contact mode AFM. Subsequently an error compensation method based on information fusion and parameters identification is proposed. Finally, extensively experiments are conducted with respect to the height measurement of nano carbon tube. This method not only has an integrated foundation in theory analysis, but also has calculated the error firstly in the height image of AFM numerically, and the results of experiments show its validity and correctness.

High Yield Assembly of Cu/CuO Nanowires Device

The high yield assembly and fabrication method for Cu/CuO nanowires for nanoelectronic devices was implemented. Assembly of Cu/CuO nanowires nano-electronic devices were realized by floating potential and dielectrophoresis approach. The simulation of floating potential distribution of the chip was performed by comsol multiphysics coupling software. Six hundred devices were assembled on the area of less than one square centimeter. The assembled devices were characterized by scanning electron microscopy. The experimental results showed that high yield assembly had been realized, and the success rate of Cu/CuO nanowires ideal assembly for nanoelectronic devices had been assessed.

Applications of Computer Vision in Micro/Nano Observation

Nowadays, micro/nano science and technology has been one of the most attractive research fields. However, real time and accurate observation in micro/nano manipulation is a top important enabling technique. Most recently, with the great development of microscopes and computer vision techniques, real time visualization, including 2D motion measurement and 3D reconstruction, on micro/nano scale is becoming possible.