Development of a High-Imaging Speed SEM for Dynamically Loaded Materials

During this research effort, the concept of using a high-speed scanning electron microscope SEM observer real-time microstructural response of dynamically loaded structural materials was verified experimentally at a maximum framing rate of 381 Hz 256 horizontal pixels x 128 vertical pixels, about order of magnitude higher than previously possible with conventional SEMs. This experiment accomplishment proved the soundness of several key concepts 1 That a tungsten hairpin cathode is bright enough to obtain useful digital images at the framing rate listed above 2 that a secondary electronic detector can be built and operated at high enough count rates to obtain such images 3 that the scan can assembly standard on an ISI SX-40A SEM can be replaced to allow imaging at such rates with spat resolution approaching 100nm 4 that signal acquisition and scan generation can be synchronized obtain a succession of well-defined frames i n a movie format at pixel rates far in excess of convention TV-rate SEM video bandwidths and 5 that a magnetically-induced stress wave device can be used obtain dynamic fracture within the SEM chamber and field of view, with scanning timed to coincide with fracture. Also documented herein are unanticipated results which occurred during the research period. ttl