Papers by Author: Hui Min Xie

Abstract: The thermo-creep deformation of interconnects related to the residual stress, directly affects their performance and lifetime. In this paper, we proposed an optical method to measure the residual thermo-creep deformation of copper interconnects. This method takes advantages of grating fabrication and the phase-shifting scanning electron microscope (SEM) moiré method. The residual thermo-creep deformation can be acquired through deformation transformation. A one-way grating with frequency of 5000 lines/mm is fabricated on the surface of the copper line in a focused ion-beam (FIB) system. The principal direction of the grating is along the axis of the copper line. The sample is heated in a high temperature furnace under 90 °C for 70 min. The SEM moiré patterns before and after heating are recorded by a field emission SEM in low vacuum. Through the random phase-shifting algorithm, the residual thermo-creep deformation of the copper interconnect line is found to be 500 με. The cause of the tensile strain is analyzed. This work offers an effective technique for measuring the creep deformation of the film lines.

Abstract: Moiré grating is a basic optical component, and can be used in various moiré methods. The conventional grating fabrication technology is based on photolithography and holographic interferometry, however, it requires complex optical components and is very difficult to put into practice. In this study, nanoimprint lithography (NIL), or rather, hot embossing lithography (HEL), is proposed for producing high frequency grating. Compared with silicon mold, holographic moiré grating mold costs less and is not easy to break, thus is chosen to be the mold in HEL. Using this mold and the hot embossing system, the grating structure can be transferred to the polymer after HEL process. Through a number of experiments, the process parameters were optimized and gratings were successfully fabricated. The multi-scale morphology of the fabricated gratings was then characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and moiré interferometry. The microscale images observed by AFM and SEM show the regulate dots with equal spacing and the macroscale moiré patterns illuminate the excellent qualities of fabricated grating in a large area. The successful experimental results demonstrate the feasibility of the grating fabricated by HEL for the moiré measurement.

Abstract: TiNi/Al-12%Si alloy is a kind of prospective material used as special energy absorbers for eliminating undesirable noise and mechanical vibration. The investigation on the mechanical properties of this composite alloy is of great importance. In this study, the surface deformation of TiNi/Al-12%Si composite alloy under external loading was measured experimentally by means of DSCM method. Some deformation characteristics of TiNi/AlSi composite alloy under the effect of the tensile load and the interaction between TiNi and AlSi are discussed. In addition, the elastic modulus and the poisson ' s ratio of this alloy were measured as well. The results agrees well with the theory predicts.

Abstract: In this study, focused gallium ion (Ga+) beam is utilised to fabricate micro/submicron spacing gratings on specimen surface. The grating types include: parallel, cross, and hybrid (grating with double-frequency). Several hybrid gratings with double frequency were produced in combination mode or superposition mode, which have a good potential to measure deformation within different range. Techniques for producing different type of gratings are discussed in detail. As an application, a 5000 lines/mm grating was fabricated on an amorphous SIC MEMS cantilever and was successfully used to measure its virtual strain with aid of digital moiré. The experimental results verify the feasibility of fabricating high frequency grating on metal or non-metal surface using the FIB milling and the resultant grating can be used to measure micro-deformation.

Abstract: The spider silk is considered as a new type of biomaterials with its excellent mechanical properties. The mechanical properties of the spider silk are crucial to their applications. In this study the mechanical properties of spider silk were studied with a micro-tensile system driven by magnet-coil force actuator, which is very effective to measure the properties of low dimensional materials. The Young’s modulus of the spider silk is obtained, the relationship between the mechanical properties of spider silk and time is also acquired.

Abstract: In this paper, scanning electron moiré method is used to measure the mechanical behavior of Ferro-based shape memory alloys(SMA). The moiré patterns are formed by the interference between a 1000 lines/mm cross-type specimen grating (which is fabricated using electron beam lithography) and the scanning lines of Scanning Electron Microscope (SEM). When the specimen is subjected to uniform tension load at the room temperature, the unloading residual strain values in the different regions under the same tensile load and the values in the same region under different tensile loads are compared respectively. The shape memory effect is also studied. From the experimental results, it can be concluded that the proposed moiré method is highly accurate to measure the mechanical behavior of microscopic field.

Abstract: Creep properties of polymer bonded explosives (PBXs), a particulate composite, was studied by using the method of moiré interferometry in this paper. The specimens fabricated by different heat pressing technology were used. Extensive creep deformation of PBXs material was indirectly measured by the aid of compressive circular disk test. The obtained results shown that creep properties are greatly influenced by pressing pressures and temperature of heat pressing technology. The results indicated that the higher the temperature and the pressing pressure are in the heat pressing technology to some degree, the better the PBXs material creep resistance is. The creep fracture surfaces of PBXs were also observed using Scanning Electronic Microscopy (SEM). It was shown that most of the fracture crack was initiated and propagated along the explosives crystal surface during creep.

Abstract: 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.

Abstract: In this study, the digital image correlation method(with Newton-Raphson iteration method) is used to measure the in-plane deformation of poly-crystal aluminum. When the specimen is exerted a tensile load, the strain distribution of the specimen surface will be inhomogeneous. The micro-deformation of the poly-crystal aluminum is studied under a SEM(scanning electron microscope), a series of images of the micro crystal are captured during the loading process. By using digital image correlation to analyze the images, the displacement and strain of a micro-crystal are obtained, which provide important data for further analysis of the inhomogeneous properties of the poly-crystal aluminum.

Abstract: Recently, many research works were concentrated on how to improve the accuracy of displacement fields in digital image correlation (DIC). However, the original displacement fields calculated at discrete locations using DIC are unavoidably contaminated by noises. If the strain fields are directly computed by differentiating the original displacement fields, the noises will be amplified even at a higher level and the resulting strain fields are untrustworthy. To acquire reliably estimation of strain fields, in this paper, Savitaky-Golay (SG) filters are introduced to obtain smoothed displacement fields and reasonable strain estimation. The principle of two-dimensional SG filters is described in detail first. Then images of uniaxial tensile and three-point bending experiments were used to verify the proposed approach. The resulting smoothed displacement fields and strain fields clearly show that the proposed method is simple and effective.