DCOR / ASCOR – Cs correctors for STEM with optimized aberration correction for large aperture angles
The CEOS Cs corrector for STEM "CESCOR" was a huge success. However, new applications with demand for larger aperture angles require a reduction of the intrinsic six-fold astigmatism. This can be achieved with the DCOR/ASCOR STEM corrector, which is the advanced development of our proven CESCOR. The optimized hexapole design the DCOR/ASCOR corrector combines the benefits of the CESCOR (simultanious improvement of resolution and increased beam current) with an almost complete suppression of the six-fold astigmatism A5. New degrees of freedom allow for a complete correction of all axial aberrations up to including 4th order. This enables highest resolution STEM images with semi-convergence angles beyond 40 mrad in the high-voltage range between 30kV and 300kV.The enlargement of the aberration-free probe aperture angle additionally improves the depth-resolution, i.e. the STEM image's sensitivity along the z-axis, and therefore enables a certain 3D resolution in STEM focus series.The DCOR/ASCOR performance, especially the suppression of the intrinsic six-fold astigmatism A5, is independent of the microscope's high-tension. Consequently, the advantages of this corrector are fully available at all accelerating voltages in the same way. You can find more information about DCOR and ASCOR in our publications