Fulong Dai

A study on the digital nano-moire method and its phase shifting technique

A novel digital nano-moire method is proposed to measure the in-plane nanoscopic deformation of an object. In the measurement, the periodic lattice of a single-crystal material acts as a specimen grating while a digital reference grating (DRG) is prepared by computer software. These two gratings overlap to generate a moire fringe pattern. The preparation of the grating, the formation principle of digital nano-moire fringes and its relative phase shifting technique are described in detail. A typical experiment was conducted with a highly oriented pyrolytic graphite (HOPG) sample. The residual deformation of the irradiated HOPG sample was measured using this method. The experiment result verifies the feasibility of this method, and demonstrates the potential for further applications.

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...

Residual strain around a step edge of artificial Al∕Si(111)-7×7 nanocluster

During artificial Al∕Si(111)-7×7 nanocluster fabrication by using surface-mediated clustering, original step with an atomically straight edge becomes curved and irregular because of stronger attractive interaction between Al atoms and Si atoms. Surface residual strain around step edges has been studied by using digital geometric phase technique. The results show that the residual strain is compressive and there is larger compressive stress near both of the up and down step edges.

Geometric micron-moiré

A high spatial resolution and high-sensitivity geometric micron-moire method is presented. The method is based upon classical geometric moire method and microscopic principle, the frequency of the specimen and reference gratings used in this method can be higher than 1000 lines/mm. By a microscopic moire system, the high-frequency gratings could be magnified to a low-frequency level, so geometric moire patterns can be formed. Experiments show that both the spatial resolution and the sensitivity can reach or exceed micron-level.

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.

Phase shifting nano-moiré method with scanning tunneling microscope

In this paper, a new nano-moire method using scanning tunneling microscope (STM) is proposed. This method is capable of measuring nanoscopic deformation of matter. The formation mechanism of the STM moire fringe and the phase shifting technique used in STM moire fringes are explained in details. Typical experiments are conducted with the crystal lattices of freshly cleaved highly oriented pyrolytic graphite, are used as specimen grating, to generate STM moire fringe patterns. Phase shifting is realized in four steps from 0 to 2π by controlling the PZT in the STM system to shift the specimen in the vertical direction. This method provides a new way for disposal of moire fringes pattern in the nano-moire measurement.

A 2D mark shearing technique for characterizing the mechanical properties of material

The digital image correlation (DIC) method has been widely used in mechanical experiments due to their non-contact, full-field feature and high accuracy in displacement measurement. Yet the precision in strain determination is not so desirable. In this paper, a 2D mark shearing technique was proposed to improve the accuracy of the strain measurement in both vertical direction and horizontal direction. A four-prism system was designed and used to introduce a shearing distance of the marks, which were made on the specimen to calculate the two strain components. The measurement principle of the mark shearing technique is described in detail. A tensile experiment using an aluminum sample was conducted, and the Youngs modulus and Poisson ratio were measured. The successful experimental results demonstrated the feasibility of this method.

A new mark shearing technique for strain measurement using digital image correlation method

The digital image correlation (DIC) method is a noncontact, full-field surface deformation measuring method, which is widely used in experimental mechanics. Although the DIC method has a high precision in displacement measurement, its precision in strain determination is a bit low. In this paper, a new mark shearing technique is proposed to improve the accuracy of the strain measurement of the DIC method. A wedge mirror is used to introduce a shearing distance of the marks, which are made on the specimen to calculate the strain. The measurement principle of the mark shearing technique is described in detail. From the analysis, it can be concluded that this method is suitable for both large-scaled and small-scaled specimens, and thus has a wider adaptability than the common DIC method. Using this method, the maximum gauge length is 80 mm, and the accuracy of strain measurement can reach 4 microm strains. A tensile experiment with aluminum sample was conducted, and the successful results demonstrated the feasibility of this method.

Development and instrumentation of an integrated three–dimensional optical testing system for application in integrated circuit packaging

Measurement of hygrothermomechanical deformation is critical for the failure analysis and reliability evaluation of integrated circuit (IC) packages. Conventional methods, however, provide one– or two–dimensional measurements, and these measurements are not enough for accurate analysis and evaluation in many cases. In this paper, the development of a compact three-dimensional (3D) optical testing system based on moire interferometry and Twyman-Green interferometry is described. Furthermore, a novel technique to simultaneously record the fringe patterns of three deformation fields with a single CCD camera is developed based on this 3D testing system. Some well-established measurement methods like thermal-mechanical-analyzer (TMA) and Taylor-Hobson stylus profilometer are used to verify the system performance. The results show good comparisons. In general, hygrothermomechanical deformation of IC packages during their fabrication and service can be measured comprehensively and dynamically using our 3D optica...

Experimental investigation of micromechanical behavior of advanced materials by moiré interferometry

Several typical instances show that moire interferometry is an effective experimental method for micromechanics study of advanced materials. By using moire interferometry, stress-induced martensitic transformation plastic zone in ceria-stabilized tetragonal zirconia polycrystalline ceramics (Ce-TZP) is studied. The experimental results show that the stress-induced transformation at room temperature is not uniform within the transformation zone and the phenomenon of microscopic plastic flow localization for transformation is revealed. Meanwhile, the experimental investigation of the pseudoelasticity behavior of Cu-Zn-Al polycrystalline shape memory alloy and bending behavior of carbon-fiber aluminium laminates (CALL) are reported. The experiments reveal some important features of the deformation processes of the materials. Finally, the measuring ability of moire interferometry for micromechanics study is discussed.