PRACTICAL AUTOALIGNMENT OF TRANSMISSION ELECTRON-MICROSCOPES

We present a working method for automatic correction of beam misalignment, defocus and objective lens astigmatism based upon computer-induced beam tilts which result in image shifts that are measured and used to adjust the microscope. The performance of the method has been tested on 100 and 400 keV microscopes, and it proves to work reliably over a wide range of magnifications for both weak phase and amplitude contrast specimens. The performance of the alignment procedure is instrumentation, specimen and magnification dependent. The reproducibility for alignment on the coma-free axis was measured to be less then 0.1 mrad at magnification M = 500 000 and less then 2 mrad at M = 10 000. The reproducibility for focusing and stigmation was measured to be less then 3 nm at M = 500 000 and less then 50 nm at M = 10 000.