Electron Speckle Photography - some recent advances

摘要

When the speckle pattern is displaced, the displacement vector can be obtained by performing a correlation comparison between the two patterns, either optically or numerically. The so-called speckle photography technique has become an important metrological, strain analysis and fluid mechanics tool. The resolution of speckle technique depends on the size of the speckles employed. For an optical recording system, it is essentially limited to the wavelength of the light used and is about 0.5μm within the visible spectrum. In 1982 Chiang introduced the electron speckle photography concept whereby sub-micron and nanometer speckles were created via a process of physical vapor deposition and recording was made by an electron microscope, either a SEM or a TEM. As a result the resolution of speckle photography was increased by several orders of magnitude. With the advancement of digital speckle techniques the method is now fully automated. This paper discusses the current state art of this technique, and its application to the determination of differential thermal strains in electronic packaging, shear band formation in the lamellar interfaces of TiAl and prediction of the crack growth, the size effect of MEMS material SU-8, the micro-mechanical properties of artificial tissues, and the mechanical properties of metal oxide nanofibers. Also discussed in the paper are potential applications of this technique to nanotechnology and bio mechanics.