Controlled hot-stage experiments in the HREM with active drift compensation and 2Å lattice resolution

Abstract

An electronic system has been developed to compensate electronically, with <2Å lattice resolution, for the image shift due to specimen and/or stage drift in the HREM. A simple system has been highly effective in compensating for the drift which has long limited many scientifically important but technically demanding applications of TEM in both the physical and biological sciences. It has facilitated controlled hot stage experiments with full HREM resolution.Over an extended period of time (>15s) which is fully adequate to record a high resolution image photographically or electronically, most drift of either the stage or the specimen can be approximated to a constant and relatively slow rate along a straight line path segment. With the new system the drift characteristic is video analyzed and an inverse correction ramp derived from a 12-bit DAC or external analog function generator is applied to existing post-specimen electrical image shift coils to stabilize the image position at the TEM camera. Image stabilization is also necessary for high quality data recording by digital processing of multiple (e.g. 256 or more) TV frames for an equivalent exposure time of several (8.5) seconds. This is the main data recording method for the dynamic experiments and with it low dose techniques can be used to minimize the beam damage effects which otherwise can be a serious problem in many HREM applications.