Lens-field axis alignment: a new objective lens alignment for high-resolution Electron Microscopy

Accurate alignment of an electron microscope is important when the highest achievable resolution is demanded. In a conventional alignment for high-resolution electron microscopy, the incident beam direction is aligned for the object point imaged at a viewing-screen center. It should be noted however that the object point corresponding to the viewing-screen center does not usually located on the magnetic-field axis of an objective lens due to lens misorientation and/or beam deflection caused by a leakage field around the objective lens. Then, the voltage-center and coma-free conditions cannot be satisfied simultaneously, even if a magnetic-field is rotationally symmetric. We implemented last year a proposed scheme to satisfy both coma-free and voltage-center conditions. This alignment scheme however requires a suitable deflector at the objective image plane.In this report, we summarize ordinary alignment procedures for high resolution electron microscopy and propose a new alignment procedure, which we call a lens-field axis alignment. Using this alignment we can satisfy the coma-free and voltage-center conditions simultaneously.