STEREOSCOPY BY TILTED ILLUMINATION IN TRANSMISSION ELECTRON-MICROSCOPY

We describe a new technique for stereoscopic observation in transmissi on electron microscopy, employing tilted illumination. A triple-hole o bjective aperture is used so that the bright beam can pass through wit h or without tilt. Stereo views can be acquired by tilting the illumin ation such that the bright beam passes through a pair of symmetrically arranged apertures alternately. The advantages of this technique as c ompared to the commonly used method of single-axis tilt are: (i) great er speed, potentially at or close to video rate so that live 3D observ ation is possible; (ii) elimination of specimen movement associated wi th stage tilt; and (iii) perspective views corresponding to multiple t ilting axes which can be realized by installing more aperture-holes an d choosing their positions properly. The main limitation is that the a ngle of tilt is limited by the extent to which the astigmatism, introd uced by beam tilt, can be compensated by the objective lens stigmators .