Qinghua Wang

Characterization of planar periodic structure using inverse laser scanning confocal microscopy moiré method and its application in the structure of butterfly wing

An effective measuring method for characterizing the planar periodic structure on specimen surface, i.e., inverse laser scanning confocal microscopy moire method, is presented and verified by experiments in this paper. The planar character of the periodic surface structure in a large region of several hundreds of millimeters, as well as the dimension at micro- and nanoscales, can be obtained through seeking the specimen grating equation as well as the virtual strain distribution. Verification experiment is carried out using a 1200lines∕mm holography grating as the specimen. The calculated results are in good coincidence with the actual character, demonstrating the validity, feasibility, and high accuracy of this method. Applying this method into identifying the structure of butterfly wing, gratings composed of a cluster of curves with pitches of a little less than 438nm are found on multiscales of butterfly wing, which provides the possibility for further explaining its attractive iridescence. Furthermore...

In situ remineralizaiton of partially demineralized human dentine mediated by a biomimetic non-collagen peptide

Biomineralization is a well-regulated process mediated by many extracellular matrix proteins. Some collagenous proteins act as frameworks for depositing minerals in a preferred orientation while non-collagenous proteins (BSP, BPP, OC, etc.) function as regulators of the mineralization process, either as nuclei or inhibitors of hydroxyapatite. Biomimetic remineralization strategies should reproduce the dimension and structural hierarchy of apatite within a collagen matrix. Here we synthesized a peptide with sequence (EEEEEEEEDSpESpSpEEDR) mimicking the function of BSP and DMP1 as calcium phosphate- and collagen-binding matrix protein analogues. More metastable calcium phosphate nanoprecursors were combined with the collagen matrix in acid-demineralized dentine pre-incubated with peptides during the process of remineralization in the phosphate-containing fluid. With the presence of our synthetic peptides, these nanoprecursors were transformed into polyelectrolyte-stabilized apatite nanocrystals that assembled at the “hole zones” (gap remineralization) and along the surface of the dentine collagen fibrils (surface remineralization). The transition from nanocrystals to larger apatite platelets was promoted by synthetic peptidesvia the formation of mesocrystal intermediates. It was concluded that deliberately designed peptide (EEEEEEEEDSpESpSpEEDR) improved in situ remineralization of acid-etched dentine.

Study of the surface structure of butterfly wings using the scanning electron microscopic moiré method

Scanning electron microscopic (SEM) moiré method was used to study the surface structure of three kinds of butterfly wings: Papilio maackii Menetries, Euploea midamus (Linnaeus), and Stichophthalma howqua (Westwood). Gratings composed of curves with different orientations were found on scales. The planar characteristics of gratings and some other planar features of the surface structure of these wings were revealed, respectively, in terms of virtual strain. Experimental results demonstrate that SEM moiré method is a simple, nonlocal, economical, effective technique for determining which grating exists on one whole scale, measuring the dimension and the whole planar structural character of the grating on each scale, as well as characterizing the relationship between gratings on different scales of each butterfly wing. Thus, the SEM moiré method is a useful tool to assist with characterizing the structure of butterfly wings and explaining their excellent properties.

Three-directional structural characterization of hexagonal packed nanoparticles by hexagonal digital moiré method

We present the hexagonal digital moiré method for three-directional structural characterization of hexagonal packed nanostructures. A mismatch between a three-way grating and a nanoparticle assembly is shown to produce hexagonal moiré fringes due to the interference between three groups of parallel moiré patterns. The measuring principles of the pitches and the orientations of the three 1D arrays of the nanoparticles are presented. The structural information on a silica nanoparticle assembly is analyzed.

Simultaneous analysis of residual stress and stress intensity factor in a resist after UV-nanoimprint lithography based on electron moiré fringes

In this study, the residual stress in a resist (PAK01) film and the stress intensity factor (SIF) of an induced crack are simultaneously estimated during ultraviolet nanoimprint lithography (UV-NIL) based on electron moir? fringes. A micro grid in a triangular arrangement on the resist film fabricated by UV-NIL is directly used as the model grid. Electron moir? fringes formed by the interference between the fabricated grid and the electron scan beam are used to measure the displacement distribution around the tip of a crack induced by the residual stress in the resist. The SIF of the crack is estimated using a displacement extrapolation method. The residual strain fields and the corresponding residual stress in the resist film far from the crack are determined and analyzed. This method is effective for evaluating the grid quality fabricated by the UV-NIL technique.

Delamination and Electromigration of Film Lines on Polymer Substrate Under Electrical Loading

As the main influencing factors for instability of film lines are widely used in microelectromechanical systems, buckle-driven delamination and electromigration of film lines on polymer substrate under electrical loading are reported in this letter. The critical buckling condition is obtained through Euler formula. In addition, postbuckling analysis for the film is derived to calculate the residual stress distribution. Both electromigration and buckling stress control the film fracture. Film buckling depends not only on the thermal mismatch between the film line and the substrate but also on the applied electrical loading.

Buckling modes of polymer membranes restricted by metal wires

Using field emission SEM, the thermal deformation of metal-wire/polymer-membrane/glass structures was observed. The thermal mismatch between the metal wire and the polymer membrane can trigger new instability modes of the polymer membrane. In the direction parallel to the axis of the wire, the orthogonal wave, oblique wave, or crumpled wave buckling mode with micro wavelength arises, while in the perpendicular direction, harmonic nano wrinkles appear on the polymer membrane. These two kinds of mutually orthogonal multi-scale instability modes can form a novel micro/nano buckling pattern. This paper discusses the formation mechanisms of these buckling patterns. The research results can provide insights into the optimization design and manufacturing process control of metal-wire/polymer-membrane structures.

A new method for the reconstruction of micro- and nanoscale planar periodic structures

In recent years, the micro- and nanoscale structures and materials are observed and characterized under microscopes with large magnification at the cost of small view field. In this paper, a new phase-shifting inverse geometry moiré method for the full-field reconstruction of micro- and nanoscale planar periodic structures is proposed. The random phase shift techniques are realized under the scanning types of microscopes. A simulation test and a practical verification experiment were performed, which demonstrate this method is feasible. As an application, the method was used to reconstruct the structure of a butterfly wing and a holographic grating. The results verify the reconstruction process is convenient. When being compared with the direct measurement method using point-by-point way, the method is very effective with a large view field. This method can be extended to reconstruct other planar periodic microstructures and to locate the defects in material possessing the regular lattice structure. Furthermore, it can be applied to evaluate the quality of micro- and nanoscale planar periodic structures under various high-power scanning microscopes.

Phase-shifting laser scanning confocal microscopy moiré method and its applications

The laser scanning confocal microscopy (LSCM) moire method is an effective method for full-field displacement and strain measurement in the micrometer scale. In this study, the phase-shifting LSCM moire method is proposed for automatic processing of the moire fringe. A combined phase-shifting and loading system for LSCM was developed, which could offer a tensile load on the plate type sample with a maximum load range of up to 500 N. Using the PZT (piezoelectric ceramic) phase shifter in the loading system, the moire fringe phase was shifted and measured. Full field deformation was calculated according to the phase data. With the combination of LSCM and the self-developed loading system, tensile deformation of the aluminum sample was measured by the phase-shifting LSCM moire technique. Full-field deformations under the different loads and elastic modulus of the sample were obtained. Experimental results demonstrated the feasibility of this technique, and the accuracy for deformation measurement is clearly improved.

Investigation on the Deformation of TiNi Shape Memory Alloy with a Crack Using Moiré Interferometry

Martensitic phase transformation can greatly affect the mechanical behaviors and the stress-strain response of shape memory alloys (SMAs). In this study, the effect of martensitic phase transformation on the deformation of a single-crystal TiNi SMA specimen with a triangle crack was investigated experimentally by means of moiré interferometry method. A typical displacement field and the corresponding strain field in areas both around and far from the tip of the crack were measured in a certain time during the loading process in which the tensile load is coupled with the stress-induced martensitic phase transformation. Some characteristics of the deformation and the martensitic phase transformation of the specimen are revealed. These results may provide a reliable support for revealing the fracture mechanism of single crystal TiNi SMAs, and may enable further development in putting forward the failure criterion of SMAs.