Low frequency band pass Fourier filtering for irradiation damage analysis in the transmission electron microscope

We demonstrate a simple technique for improved imaging of non-crystallographic, irradiation-induced defects in the transmission electron microscope (TEM). By Fourier filtering bright-field TEM images to isolate relatively low-frequency fluctuations in intensity, it is possible to better resolve defects such as cavities caused by He-ion irradiation of iron. This analysis can be done with basic TEM imaging and most image processing software. This technique requires minimal defocus and can eliminate contrast mechanisms on both longer and short length scales. The resulting images are sensitive to filtering parameters, but clearly reveal the size, density, and distribution of cavities when compared with standard imaging techniques.