DEVELOPMENT OF REAL-TIME DEFOCUS-MODULATION-TYPE ACTIVE IMAGE-PROCESSING (DMAIP) FOR SPHERICAL-ABERRATION-FREE TEM OBSERVATION

A new technique for spherical-aberration-free observations under Transmission Electron Microscope (TEM) by real-time defocus-modulation-type active image processing (DMAIP) has been developed. This technique is based on a sophisticated accelerating-voltage modulation which enables both rapid through-focusing and functionized irradiation-time control to be performed. The functionized irradiation-time control which we have newly developed for the present DMAIP, is as follows: The through-focusing, Delta f(t), is controlled so that the irradiation time of the primary beam per unit defocus value, dt/d Delta f, is proportional to the weighting function, W(Delta f), at each defocus value, bf. The simple accumulation of the image signal per unit time, i(Delta f(t)), expressed by the integral, li(Delta f(t)) dt, is proved to lead to the real-time DMAIP. The driving signal for the accelerating-voltage modulation was simply supplied to the feedback circuit of the high-voltage stabilizing unit of the TEM, and the processed images were successively displayed on a cathode ray tube (CRT) in real time at the video-frame rate (4/30 s). The experimental confirmation has been made through the Then-diagramming technique with a commercial type TEM, the JEM-200CX. The Then diagram constructed from these real-time processed images have clearly revealed that the spherical aberration of the objective lens has been successfully corrected in the range of intermediate spatial frequency (< 3.0 nm(-1)).