[Show abstract][Hide abstract]ABSTRACT: A generic method to determine the aberration center is established, which can be utilized for aberration calculation and axis alignment for aberration corrected electron microscopes. In this method, decentering induced secondary aberrations from inherent primary aberrations are minimized to find the appropriate axis center. The fitness function to find the optimal decentering vector for the axis was defined as a sum of decentering induced secondary aberrations with properly distributed weight values according to the aberration order. Since the appropriate decentering vector is determined from the aberration values calculated at an arbitrary center axis, only one aberration measurement is in principle required to find the center, resulting in /very fast center search. This approach was tested for the Ronchigram based aberration calculation method for aberration corrected scanning transmission electron microscopy. Both in simulation and in experiments, the center search was confirmed to work well although the convergence to find the best axis becomes slower with larger primary aberrations. Such aberration center determination is expected to fully automatize the aberration correction procedures, which used to require pre-alignment of experienced users. This approach is also applicable to automated aperture positioning.
[Show abstract][Hide abstract]ABSTRACT: We developed a new electron optical system with three dodecapoles to compensate for spherical aberration and six-fold astigmatism, which generally remains in a two-hexapole type corrector. In this study, we applied the corrector for image-forming system in transmission electron microscope. Compensation for higher-order aberration was demonstrated through a diffractogram tableau using a triple three-fold astigmatism field system, which was then compared with a double hexapole field system. Using this electron optical system, six-fold astigmatism was measured to be less than 0.1mm at an acceleration voltage of 60kV, showing that the system successfully compensated for six-fold astigmatism.
[Show abstract][Hide abstract]ABSTRACT: A new concept of a spherical aberration correction system using three dodecapoles is proposed. The system compensates for
higher order aberration of 6-fold astigmatism, which generally limits a uniform phase area for image forming and probe forming
in an electron microscope with a conventional two-hexapole corrector. Triple 3-fold astigmatism field is used to correct the
spherical aberration of the objective lens, and the total 3-fold astigmatism is eliminated by their combination. The optimum
azimuth relationship among three dodecapoles is calculated to eliminate the 6-fold astigmatism. The principle of the method
was verified using a mathematically complex representation. This new concept was experimentally tested with a scanning transmission
electron microscope at 60 kV acceleration. The 6-fold astigmatism was certainly compensated and the coherent convergent angle
became almost twice compared to a conventional double hexapole system.
No preview · Article · Aug 2009 · Journal of electron microscopy
[Show abstract][Hide abstract]ABSTRACT: Aberrations up to the fifth-order were successfully measured using an autocorrelation function of the segmental areas of a Ronchigram. The method applied to aberration measurement in a newly developed 300kV microscope that is equipped with a spherical aberration corrector for probe-forming systems. The experimental Ronchigram agreed well with the simulated Ronchigram that was calculated by using the measured aberrations. The Ronchigram had an infinite magnification area with a half-angle of 50mrad, corresponding to the convergence angle of a uniform phase.