Nano-Moiré Technique And Its Application

A nano-moire method, making use of crystal lattice as grating, is presented in this paper. The specimens are made of crystal materials. High-resolution electron microscopy (HREM) is used to record the changes in the crystals. The lattice image, which acts as a specimen grating, is superposed onto a standard grating to produce moire fringes. Optical filtering technique is used to increase the fringe contrast. The moire pattern measures displacement and strain, dislocations, stacking faults and atom slip in nanometer-order range. The sensitivity of this method can reach 0.1 nm. The high spatial resolution of fringes allows measuring high-gradient strain in very tiny area. It provides an effective experimental technique for nanomechanics. The model test of Au proves the validity of this method. Dislocations, stacking faults and bond failure are observed. The strain field around a non-crystal inclusion is measured. Based on this novel technique, we perform following researches. Firstly, we investigate the mechanical behaviors ahead of nanometer-order crack tip in silicon single crystal, a brittle material. Dislocations of Peierls type are detected and they extend from the crack tip over a length of hundreds of Burgers. We measure the near tip nanoscopic strain distribution ahead of the crack tip. It agrees with the linear elastic fracture mechanics prediction up to 10nm from the crack tip. The process of failure mechanism can be described as cleavage propagation of crack after a few dislocation emissions. The crack propagates in step by step manner. Secondly, we try to look into a dislocation configuration, measure the displacement field around a single dislocation in Si and Au single crystals and make a comparison between experimental results and Peierls-Nabarro model. Experimental results show that displacement fields for some dislocations coincide well with Peierls-Nabarro model. But the others may cause larger-range deformation but less strain concentration than the theoretical prediction. The widths of dislocations in same material can be different. Thirdly, under nanometer dimension we investigate the mechanical behaviors of the interface between GaAs and Sisubstrate in GaAs/Si, an important material used in making electronic elements. Several dislocations caused by the mismatch of thermal properties between GaAs and Si are detected. The strain distribution across the interface is measured. It also proves that nano-moire method provides a technique for nano-interface study. Finally, the failure mechanism of laminates with internally-dropped plies is studied by means of moire interferometry. Three failure modes are found.